O X
F O
2 0 1 4
R
D
I B
D
I p l O
m
a
p
R
O
g R
a
m
m
e
E D I T I O N
BI O LO G Y
C O U R S E
C O M PA N I O N
Andrew Allott
David Mindor
PHOTO
Tony
3
Great
Clarendon
Street,
Oxford,
OX2
6DP,
United
University
Press
is
a
department
of
the
the
University’s
education
by
objective
publishing
of
University
excellence
worldwide.
in
Oxford
OLDFIELD/SCIENCE
p126a:
OUP;
of
Oxford.
Oxford
University
Press
in
the
UK
and
in
OUP;
Oxford
University
Press
is
research,
a
moral
rights
of
the
trade
p144:
certain
other
Eye
been
All
in
published
rights
a
the
prior
system,
permission
permitted
by
law,
reprographics
the
Oxford
No
by
scope
of
University
or
of
this
publication
transmitted,
in
writing
licence
rights
or
of
the
above
at
under
be
be
or
agreed
reproduced,
by
University
terms
address
may
form
Enquiries
should
the
any
Oxford
organization.
Press,
in
must
this
same
not
circulate
this
work
in
of
the
OUP;
any
Press,
with
concerning
sent
to
the
means,
or
the
as
without
on
any
Data
Library
p158a:
p164a,b,c,d:
expressly
OUP;
appropriate
Rights
Department,
7
9
10
8
form
and
you
must
used
made
from
conforms
in
of
in
MAURO
Virginia;
OUP;
L.
Image;
p130a:
p132a:
p143b:
OUP;
Jax.org;
p146a:
Eye
of
OUP;
p133:
p143c:
Science/SPL;
FERMARIELLO/SCIENCE
p155a:
CLINICAL
o
PHOTO
fBasel/SPL;
p152:
OUP;
Dr.
p155b:
p169:
p150b:
Oscar
Andrew
Lee
Allot;
OUP;
p171a:
p190a:
OUP;
OUP;
Allot;
OUP;
OUP;
OUP;
VOLKER
Andrew
p190c-196c:
p166a:
p172:
GENETICS
Andrew
OUP;
William
p186:
RIA
DAVID
WALLY
Allot;
p166b:
Allott;
NOVOSTI/
STEGER/SCIENCE
p190b:
p197:
p162a:
Allot;
p171b:
p184b:
p188:
Markowski/
REGIONAL
OUP;
Andrew
ADDENBROOKES
Tomasz
ANGLIAN
p160-161b:
p165a,b,c,d:
p177-184a:
p158b:
EAST
LIBRARY;
LIBRARY;
OUP;
CYTOGENETICS,
LIBRARY;
WILLAT T,
Allot;
Coen;
p189:
OF
PHOTO
PHOTO
LIBRARY;
in
Publication
Data
PHOTO
/SCIENCE
p203a:
PHOTO
PHOTO
LIBRARY;
LIBRARY;
p198c:
LIBRARY;
OUP;
LIBRARY;
p198b:
Author
p201:
p203b:
OUP;
the
production
the
grown
in
of
this
book
sustainable
environmental
is
a
natural,
forests.
regulations
of
The
the
recyclable
product
manufacturing
country
of
OUP;
process
OUP;
OUP;
p198a:
GERARD
Image;
p202:
p203c:
p204a,b,c,d:
origin.
p207b:
p212a:
OUP;
Andrew
p215e:
Printed
Author
PHOTO
PARKER/SCIENCE
EBERHART,
GERARD
VISUALS
PEAUCELLIER,
p199:
PHILIPPE
Parinya
ERIC
Andrew
PEAUCELLIER,
ISM
/SCIENCE
PLAILLY/SCIENCE
Hirunthitima/Shutterstock;
GRAVE/SCIENCE
Allot;
ISM
p205a:
PHOTO
Author
LIBRARY;
Image;
p205b:
2
wood
to
Allott;
Jax.org;
www.ncbi.nlm.nih.gov;
CreativeNature.nl/Shutterstock;
Paper
©
p124a:
impose
PHOTO
4
p122:
acquirer
Cataloguing
6
DEPT.
PHOTO
LIBRARY;
other
available
5
p151:
p159:
Enrico
SCIENCE
p203d:
3
Andrew
p143a:
.Wurtz/Biozentrum/University
Andrew
p166c:
p176:
reproduction
978-0-19-839211-8
1
p131c:
OUP;
p148:
University
SERVICE/SCIENCE
/SCIENCE
British
M
Kim/SPL;
UNLIMITED
condition
Allott;
p141:
Science/SPL;
Dreamstime;
stored
above.
any
p124b:
Andrey/Shutterstock;
www.ncbi.nlm.nih.gov/pubmed;
p150a:
Jr
PHOTO
You
OUP;
HOSPITAL/SCIENCE
part
LIBRARY;
Petrov
Image;
Tattersall;
asserted
2014
reserved.
retrieval
outside
in
Author
Glenn
countries
p156:
First
Andrew
p134:
of
Kwangshin
have
PHOTO
p126b:
p116:
p123b:
mark
2014
authors
SPL;
OUP;
scholarship,
registered
Miller,
The
OUP;
p130c:
Allott;
LIBRARY;
©
p110:
It
p146b:
of
OUP;
p123a:
p152:
Jax.org;
and
Alamy;
MAT THEW
William
furthers
p101-102:
/
Kingdom
p130b:
Oxford
LIBRARY;
Rusecki
Author
p212b:
Allott;
OUP;
Image;
Andrew
p215c:
p217a:
p205c:
p209:
Allott;
Andrew
OUP;
Author
Author
p214:
Image;
Andrew
Allott;
p217b:
Image;
Andrew
p210:
Allott;
p215d:
p206:
Rich
OUP;
OUP;
p215a:
p207:
p211:
OUP;
OUP;
p215b:
Lindie/Shutterstock;
Allott;
p217d:
OUP;
p221:
Malaysia
Giorgiogp2/Wikipedia;
p223a:
Andrew
Allott;
p223b:
Andrew
Allott;
p224:
Acknowledgements
OUP;
The
publishers
their
would
like
to
thank
the
following
for
permissions
to
use
p225a:
OUP;
photographs:
p243:
Wikipedia;
p248a:
Cover
image:
©
Paul
Souders/Corbis;
p1:
Sulston
&
Horvitz;
p2:
DR
PHOTO
LIBRARY;
p3a:
DR.JEREMY
Erik
p225b:
Daiju
Allott;
LIBRARY;
p3b:
Shutterstock;
p6:
Ferran
Garcia-Pichel,
Max
of
Marine
Biology,
Bermen
Germany;
OUP;
p251b:
p7a:
Prof.
P.Motta
&
SPL;
OUP;
p7b:
Andrew
Allot;
p7c:
Andrew
Allot;
p7d:
MICHAEL
PHOTO
LIBRARY;
p8a:
Carolina
p262a:
Biological
Supply
Inc.;
p8b:
ASTRID
&
HANNS-FRIEDER
OUP;
MICHLER/SCIENCE
p9:
MICHAEL
ABBEY/SCIENCE
PHOTO
LIBRARY;
p10a:
DR.
OUP;
VISUALS
UNLIMITED
/SCIENCE
PHOTO
LIBRARY;
p10b:
Sulston
p12:
JAMES
CAVALLINI/SCIENCE
UNLIMITED,
INC.
PHOTO
/SCIENCE
LIBRARY;
PHOTO
LIBRARY;
OF
HAEMATOLOGY,
RVI,
p14a:
LIBRARY;
p16a:
TEK
IMAGE/SCIENCE
A
B
BERKELEY
Dowsett/SPL;
NATIONAL
p20a:
Eye
of
LABORATORY/
Science/SPL;
p21a:
BIOPHOTO
PHOTO
SCIENCE
p20b:
ASSOCIATES/SCIENCE
LIBRARY;
PHOTO
LIBRARY;
p22a:
PHOTO
LIBRARY;
p22b:
DR
PHOTO
p22c:
DR
GOPAL
PHOTO
p283a:
Author
Andrew
OUP;
p305:
PHOTO
PHOTO
LIBRARY;
LIBRARY;
p22f:
PHOTO
p22e:

DON
W.
PHOTO
Allot;
p292a:
PHOTO
LIBRARY;
p23c:
Wikipedia;
PHOTO
DR
KARI
LIBRARY;
Andrew
LIBRARY;
PHOTO
LIBRARY;
p25b:
LIBRARY;
M.
p25a:
STEVE
DEERINCK,
LIBRARY;
p23b:
DR.
PHOTO
PHOTO
LIBRARY;
p29:
LIBRARY;
Author
p24b:
Allot;
p24a:
DR.JEREMY
PHOTO
p27:
LIBRARY;
Author
Image;
p339:
p43a:
OUP;
p43b:
Andrew
Allot;
Mayer,
p343:
Consultant
p46a:
and
THOMAS
CSL
Liver
p32:
p44:
Surgery,
DEERINCK,
The
VRoma
Project
Image;
Janaka
Herve
Queen
p48:
A.W.
p28:
PHOTO
LIBRARY;
p49:
DAVID
Conge/SPL;
);
OUP;
PHOTO
PHOTO
p51:
M.I.
LIBRARY;
Walker/SPL;
p54a,b:
p53a,b,c,d:
STEVE
PHOTO
Dharam
M
Ramnani;
GEORGET TE
with
p55c:
MANFRED
HEALTH
MANFRED
KAGE/SCIENCE
LTD/SCIENCE
PHOTO
PHOTO
LIBRARY;
OUP;
p306:
PHOTO
LIBRARY;
ST
p307:
OUP;
p317:
p318:
DU
OUP;
CANE
p320a:
MEDICAL
OUP;
PHOTO
LIBRARY;
p323:
p320b:
OUP;
LIBRARY;
p327:
PHOTO
OUP;
LIBRARY;
p328a:
p328b:
p325:
SCIENCE
OUP;
VU,
p330:
PHOTO
LIBRARY;
p331:
OUP;
p332:

J.
OAK
LABORATORY/US
OUP;
p334:
DEPARTMENT
POWER
AND
OF
ENERGY/SCIENCE
SYRED/SCIENCE
PHOTO
LIBRARY;
PHOTO
p340:
SIMON
FRASER/SCIENCE
PHOTO
LIBRARY;
p344:
Author

PHOTO
LIBRARY;
p346:
SPL;
p348:
Image
of
PDB
ID
LEE
D.
1aoi
(K.
the
R.K.
core
Richmond,
particle
at
D.F.
2.8
A
Sargent,
T.J.
resolution
Richmond
Nature
389:
(1997)
251-260)
Chimera
and
(UCSF
analysis.
Chimera--a
Pettersen
EF,
visualization
Goddard
TD,
system
Huang
for
exploratory
CC,
DM,
Meng
Public
EC,
Ferrin
TE.
J
Comput
Domain/Wikipedia;
Chem.
p351:
2004
SCIENCE
Couch
GS,
Oct;25(13):1605-
PHOTO
LIBRARY;
Andrew
Allot;
p358:
p353:
Charvosi/Wikipedia;
PNAS.Org;
p359:
DR
ELENA
p357:
Axel
Bueckert/
KISELEVA/SCIENCE
PHOTO
DOUWMA/
p363a:
Jmol;
p363b:
RCSB.org;
p367:
©
1970American
Association
PHOTO
PHOTO
the
Advancement
in
action.
of
Science.Miller,
KAGE/SCIENCE
PHOTO
LIBRARY;
LIBRARY;
p58:
p57:
OUP;
Science
169,392–395
O.
L.et
al.Visualization
(1970).
All
rights
of
bacterial
reserved;
p368a:
LIBRARY;
p368b:
POWER
AND
SYRED/SCIENCE
PHOTO
LIBRARY;
PHOTO
SINCLAIR
STAMMERS/SCIENCE
PHOTO
LIBRARY;
p370a:
Andrew
MOREDUN
Allot;
ANIMAL
Allot;
p304a:
Hospital,
p368c:
LIBRARY;
Andrew
Allot;
GSCHMEISSNER/SCIENCE
GSCHMEISSNER/SCIENCE
p55b:
p315:
CHASSENET/BSIP/SCIENCE
Nobelprize.org;
p55a:
p298:
Andrew
LIBRARY;
MCCARTHY/SCIENCE
STEVE
LIBRARY;
p303b:
LIBRARY;
/SCIENCE
p333:
Mader,
of
p349:
genes
PHOTO
PHOTO
OUP;
p45:
for
LIBRARY;
p290:
p294b:
NIBSC/
LIBRARY;
SCIENCE
OUP;
Dharmasena/
Elizabeth
NCMIR/SCIENCE
(www.vroma.org);
Image;
p294a:
STEVE
Shutterstock;
p46b:
Author
OUP;
PHOTO
p25c:
p352:
Birmingham;
p286:
BURGESS/
12.
David
OUP;
p292b:
STEVE
Greenblatt
Shutterstock;
BSIP
p282:
GOPAL
research
SCIENCE
p283b:
OUP;
NCMIR/SCIENCE
UNLIMITED
NATIONAL
created
GSCHMEISSNER/SCIENCE
OUP;
p279:
LIBRARY;
GSCHMEISSNER/SCIENCE
PHILLIPS/SCIENCE
p272:
LOUNATMAA/
PHOTO
structure
DAVID
Image;
LIBRARY;
Kunkel/Photolibrary;
p22d:
Luger,
SCIENCE
Author
PHOTO
SCHOOL/SCIENCE
p309:
LTD/SCIENCE
SIMON/SCIENCE
GSCHMEISSNER/SCIENCE
p270b:
Dennis
CAVALLINI/SCIENCE
MEDICAL
VEM/SCIENCE
Image;
MURTI/SCIENCE
Kipling
PHOTO
LIBRARY;
MICROSCAPE/SCIENCE
FAWCET T/SCIENCE
Image;
p265:
ASSOCIATES/
LIBRARY;
p23a:
Author
Allot;
p21b:
PHOTO
SCIENCE
Image;
p281:
p303a:
JAMES
HOSPITAL
p308:
RIDGE
MICROSCAPE/SCIENCE
p259:
PHOTO
LIBRARY;
MURTI/SCIENCE
MURTI/SCIENCE
OUP;
Andrew
GIBBONS/SCIENCE
LIBRARY;
ZBAEREN/EURELIOS/SCIENCE
LIBRARY;
p253:
p264:
LIBRARY;
CNRI/SCIENCE
BIOPHOTO
GOPAL
BOB
PHOTO
p302:
OUP;
VISUALS
SCIENCE
OUP;
PETER
p17:
BSIP
MICROSCAPE/SCIENCE
p250b:
p251e:
NEWCASTLE/SCIENCE
THOMAS
LIBRARY;
OUP;
ASSOCIATES/SCIENCE
OUP;
IMAGING
p19:
OUP;
OUP;
SIMON
OUP;
LAWRENCE
p251d:
CHRIS
p14b:
MARY’S
PHOTO
LIBRARY;
p262b:
p270a:
p276b:
Image;
p304b:
FRASER/DEPARTMENT
PHOTO
OUP;
Domain/Wikipedia;
p299:
BARRY/VISUALS
OUP;
&
BIOPHOTO
Horvitz;
p251c:
PETER
Public
SIVER,
p250a:
p246a:
Shutterstock;
PHOTO
Author
LIBRARY;
p246d:
Co/Visuals
VEM/SCIENCE
Unlimited,
Stammers/SPL;
Wikipedia;
Allott;
p228-242b:
ABBEY/
p276a:
SCIENCE
Andrew
Sinclair
Allott;
T.
Brock/Shutterstock;
Naguro/
p248b
p244:
p246c:
Andrew
Planck
p261:
Institute
AZUMA;
p225c:
BURGESS/SCIENCE
CHADWICK/SCIENCE
PHOTO
Allott;
Lam/Shutterstock;
p246b:
Andrew
Andrew
YORGOS
p251a:
NIKAS/SCIENCE
OUP;
p54:
p373:
Shutterstock;
p375:
RAMON
ANDRADE
3DCIENCIA/SCIENCE
Andrew
PHOTO
LIBRARY;
p387a:
CNRI/SCIENCE
PHOTO
LIBRARY;
p387b:
Petrov
Allot; p60: J Herve Conge, ISM/ SPL; p61: OUP; p62: Vasiliy Koval/Shutterstock;
Andrey/Shutterstock;
p66:
LAGUNA
DESIGN/SCIENCE
PHOTO
LIBRARY;
p69a-p69b:
OUP;
Allot;
CLAIRE
PAXTON
&
JACQUI
FARROW/SCIENCE
PHOTO
LIBRARY;
p71:
WHEELER/SCIENCE
PHOTO
LIBRARY;
p72:
OUP;
p73a:
Dr.
p73b:
Dr.
Gopal
Murti/SPL;
p73c:
Dr.
Elena
Kiseleva/SPL;
p387e:
p392:
DESIGN/SCIENCE
PHOTO
LIBRARY;
p75b:
LAGUNA
PHOTO
p79:
LIBRARY;
OUP;
p80a:
p75c:
Andrew
LAGUNA
Allot;
DESIGN/SCIENCE
p80b-81:
OUP;
p83a:
Bell;
p90a:
OUP;
p90b:
www.rcsb.org;
p91:
p92b:
OUP;
p95:
JAMES
p387d:
Andrew
State
Allot;
p388:
Department
Allot;
p398:
Dr.
of
Carmen
Health;
Andrew
p390:
Allot;
Manella,
Prof.
p399:
Wadsworth
Kenneth
Barrie
R
Miller/
Juniper;
SYRED/SCIENCE
PHOTO
LIBRARY;
p404:
SINCLAIR
p403:
STAMMERS/
PHOTO
www.rcsb.org;
p406a:
LIBRARY;
POWER
p405a:
AND
Smugmug.Com;
SYRED/SCIENCE
p405b:
PHOTO
SCIENCE
LIBRARY;
PHOTO
p406b:
DR
p83b:
WHEELER/SCIENCE
PHOTO
LIBRARY;
p410:
SIDNEY
MOULDS/
p92a:
SCIENCE
Yikrazuul/Wikipedia;
SPL;
PHOTO
OUP;
KEITH
Giles
Andrew
York
Andrew
AND
LIBRARY;
LIBRARY;
Miller/
DESIGN/
SCIENCE
SCIENCE
R
p75a:
POWER
LAGUNA
Kenneth
Elena
SPL;
Kiseleva/SPL;
Prof.
DR
Center,New
KEITH
p387c:
p70:
PHOTO
LIBRARY;
p411:
DR
KEITH
WHEELER/SCIENCE
PHOTO
KING-HOLMES/SCIENCE
Continued
on
back
page.
Contents
1
Cell Biology
Introduction
to
Ultrastructure
7
cells
of
1
cells
16
Membrane
structure
25
Membrane
transport
33
Nucleic acids (AHL)
DNA
structure
Environmental
and
replication
343
Transcription
and
Bioformatics
591
gene
expression
Ecology and conser vation
355
Species
origin
of
cells
45
Translation
and
communities
division
603
362
Communities
Cell
575
582
C
The
protection
Medicine
and
51
ecosystems
8
Impacts
2
613
Metabolism, cell
Molecular Biology
of
humans
on
respiration and
ecosystems
Molecules
to
metabolism
625
photosynthesis (AHL)
61
Conservation
Water
68
Metabolism
373
73
Cell
380
Population
Carbohydrates
and
lipids
respiration
The
Proteins
87
Enzymes
96
Photosynthesis
of
ecology
nitrogen
of
DNA
replication,
and
RNA
105
transcription
9
translation
111
cycles
649
Plant biology (AHL)
Transport
in
the
Human physiology
xylem
Human
and
642
389
D
DNA
of
plants
nutrition
659
403
Digestion
Cell
respiration
122
Transport
in
the
phloem
671
of
Functions
Photosynthesis
129
plants
of
in
plants
Genetics
liver
678
heart
684
422
Hormones
Reproduction
in
plants
and
metabolism
694
429
Transport
Genes
the
412
The
Growth
3
635
and
phosphorous
Structure
biodiversity
of
respiratory
141
gases
Chromosomes
149
Meiosis
159
Inheritance
168
10
699
Genetics and evolution
(AHL)
Internal Assessment
Meiosis
439
Inheritance
445
(with
Genetic
modication
and
his
biotechnology
187
Gene
pool
and
speciation
thanks
assistance
Ecology
Species,
11
communities
and
ecosystems
Energy
ow
Carbon
cycling
Climate
change
213
Movement
220
The
this
for
chapter)
708
713
and
465
476
kidney
and
osmoregulation
Sexual
5
production
vaccination
229
with
Headlee
Animal physiology (AHL)
Antibody
201
Mark
455
Index
4
to
485
reproduction
499
Evolution and biodiversity
Evidence
for
evolution
241
A
Natural
selection
Neurobiology and
249
behaviour
Classication
and
Neural
biodiversity
development
The
Cladistics
human
brain
518
263
Perception
Innate
6
513
258
and
of
stimuli
526
learned
Human physiology
behaviour
Digestion
The
blood
Defence
and
absorption
system
against
Neuropharmacology
541
Ethology
548
289
infectious
diseases
302
B
Gas
533
279
exchange
Biotechnology and
310
bioinformatics
Neurones
and
synapses
319
Microbiology:
Hormones,
homeostasis
organisms
in
and
industry
reproduction
557
329
Biotechnology
in
agriculture
565
iii
Course book denition
The
IB
Diploma
resource
throughout
course
help
is
Programme
materials
of
their
study
students
expected
designed
two-year
in
a
gain
from
course
to
an
books
support
Diploma
particular
the
The IB Learner Prole
of
subject.
an
IB
The
They
of
aim
of
all
a
will
better
and
what
learner
subject
while
that
illustrates
reect
the
presenting
the
purpose
philosophy
and
and
content
in
and
encourage
a
deep
aims
approach
of
the
of
by
providing
making
understanding
connections
opportunities
for
to
of
wider
critical
books
mirror
in
the
terms
IB
of
a
issues
use
of
a
wide
and
of
Diploma
of
the
range
of
resources,
learner
Programme
knowledge,
action,
IB
service
the
core
prole
essay,
issues
book
materials
required
a
variety
and
and
and
and
of
be
so
the
indeed,
and
reading
suggestions
for
conjunction
students
encouraged
resources.
further
in
to
of
draw
the
theory
creativity,
are
given
how
to
in
with
IB
for
each
extend
natural
to
curiosity.
conduct
research
and
actively
snow
enjoy
independence
learning
and
in
this
will
be
sustained
throughout
their
love
lives.
that
They
have
explore
local
and
concepts,
global
ideas,
signicance.
doing,
they
acquire
understanding
in-depth
across
a
knowledge
broad
and
and
balanced
of
disciplines.
Thinkers:
thinking
They
skills
exercise
critically
approach
complex
ethical
initiative
and
in
applying
creatively
problems,
to
and
recognize
make
decisions.
other
Communicators:
are
conclusions
Suggestions
their
necessary
IB
and
used
below.
international
and
(CAS).
can
ten
the
reasoned,
Each
the
through
approach;
requirements,
extended
skills
Knowledgeable:
viewing
whole-course
develop
the
They
learning
range
mindedness,
described
create
of
and
thinking.
philosophy
They
acquire
develop
the
person
to
aim
each
In
curriculum
as
this
work
The
IB.
and
The
develop
world.
the
of
subject
peaceful
develop
who
a
learning.
IB
to
attributes,
inquiry
They
is
to
people
Diploma
They
way
programmes
minded
more
programme
Inquirers:
Programme
IB
internationally
Programme
understanding
study
are
students
from
additional
ideas
more
of
book
research
are
and
They
information
than
one
language
communication.
willingly
in
understand
condently
and
They
in
work
collaboration
with
a
and
and
express
creatively
variety
of
effectively
in
modes
and
others.
provided.
Principled:
In
addition,
and
the
guidance
requirements
They
are
being
course
on
the
and
specic
on
distinctive
companions
course
academic
and
provide
advice
assessment
honesty
authoritative
protocol.
with
for
a
the
action
act
sense
dignity
communities.
own
without
They
strong
of
the
They
and
the
with
of
integrity
fairness,
individual,
take
and
justice
groups
responsibility
consequences
honesty,
and
for
that
respect
and
their
accompany
them.
prescriptive.
Open-minded:
They
understand
and
appreciate
IB mission statement
their
The
International
inquiring,
who
help
world
Baccalaureate
knowledgeable
to
create
through
a
and
better
caring
and
intercultural
aims
more
to
develop
young
people
peaceful
understanding
and
respect.
To
this
open
of
to
other
the
governments
organization
and
and
works
international
challenging
education
with
schools,
organizations
programmes
rigorous
These
programmes
world
to
their
the
points
of
to
individuals
of
international
assessment.
Caring:
respect
They
to
to
view,
personal
and
seeking
and
become
who
encourage
active,
understand
differences,
can
students
compassionate
also
that
be
other
right.
across
and
people,
They
show
towards
have
act
are
values
histories,
and
communities.
and
evaluating
willing
to
and
are
traditions
They
a
grow
are
range
from
of
the
to
a
empathy,
needs
personal
make
and
the
to
a
feelings
commitment
positive
the
compassion
and
of
and
others.
to
service,
to
the
difference
and
lives
of
environment.
the
lifelong
with
Risk-takers:
They
and
uncertainty
and
have
new
the
roles,
articulate
iv
and
perspectives,
accustomed
others
learners
cultures
experience.
end
develop
own
and
unfamiliar
courage
independence
ideas,
in
approach
with
and
of
spirit
strategies.
defending
their
situations
forethought,
to
They
beliefs.
explore
are
brave
and
Balanced:
They
intellectual,
achieve
understand
physical
personal
and
the
importance
emotional
well-being
for
of
ballance
themselves
What constitutes malpractice?
to
Malpractice
and
result
others.
in,
is
advantage
in
Malpractice
Reective:
to
their
able
to
They
own
assess
limitations
personal
give
learning
and
in
thoughtful
and
order
to
their
support
or
any
one
that
student
or
more
includes
results
in,
gaining
an
assessment
plagiarism
and
or
may
unfair
component.
collusion.
consideration
experience.
understand
behaviour
you
They
are
strengths
their
Plagiarism
and
learning
and
ideas
or
is
work
following
are
dened
of
as
the
another
some
of
representation
person
the
ways
as
to
your
of
own.
avoid
the
The
plagiarism:
development.
●
words
one’s
and
ideas
of
arguments
another
must
be
person
to
support
acknowledged
A note on academic honesty
●
It
is
of
vital
importance
appropriately
when
After
that
all,
credit
to
the
owners
information
owners
of
acknowledge
is
used
ideas
of
in
and
your
(intellectual
property
rights.
To
have
an
that
enclosed
work,
it
must
be
based
on
work.
authentic
your
original
ideas
with
the
work
verbatim
quotation
must
marks
and
CD-Roms,
email
messages,
web
sites
on
the
piece
and
any
other
electronic
media
must
individual
be
and
quoted
property)
Internet
of
are
within
acknowledged
●
have
passages
be
information
of
others
treated
in
the
same
way
as
books
and
fully
journals
acknowledged.
Therefore,
all
assignments,
written
●
or
oral,
own
completed
language
used
or
for
and
referred
assessment
expression.
to,
whether
must
Where
in
the
use
sources
form
of
the
sources
of
all
illustrations,
computer
or
paraphrase,
appropriately
such
sources
maps,
audio-visual
and
programs,
data,
graphs,
are
similar
material
must
be
direct
acknowledged
quotation
photographs,
your
must
if
they
are
not
your
own
work
be
acknowledged.
●
works
of
theatre
art,
arts
whether
or
visual
music,
arts
lm
and
dance,
where
the
How do I acknowledge the work of others?
creative
The
way
that
you
acknowledge
that
you
have
ideas
of
footnotes
other
and
people
is
through
the
use
endnotes
to
be
from
(placed
(placed
provided
another
at
at
the
the
Collusion
when
bottom
end
you
document,
of
a
quote
or
of
a
page)
document)
or
●
summarize
provided
in
another
artist
is
not
that
is
need
part
denitions
part
of
the
to
of
provide
a
do
‘body
not
a
of
document.
need
assumed
footnote
for
knowledge’.
to
be
allowing
for
footnoted
include
as
Other
is,
they
are
that
that
you
used
in
your
formal
list
of
work.
forms
of
that
accepted
involves
into
as
works
to
nd
how
the
should
of
a
compulsory
art)
of
(e.g.
or
the
viewer
of
A
supporting
malpractice
by
by
to
be
copied
another
or
submitted
student
work
for
and/or
different
diploma
assessment
requirements.
you
of
malpractice
an
unfair
another
student.
unauthorized
include
advantage
or
Examples
material
into
an
any
action
affects
the
include,
misconduct
during
an
examination
examination
and
‘Formal’
a
CAS
record.
several
you
use
magazines,
resources,
full
the
acknowledged.
usually
that
books,
providing
Extended
the
This
resources
information.
in
one
internet-based
and
reader
same
the
categories
articles,
of
use
presentation.
separating
different
newspaper
and
you
forms
place,
the
falsifying
means
takes
includes:
work
assessment
gives
room,
resources
be
as
This
your
duplicating
results
a
work
information
That
knowledge.
should
a
You
taking
Bibliographies
must
dened
student.
components
do
of
the
●
information
part
or
are
paraphrase
closely
a
of
bibliographies.
another
Footnotes
of
used
original
the
use
Cds
information
your
work
bibliography
can
is
Essay.
v
Online Resources
What is Kerboodle?
Kerboodle
is
subscription
to
access
guide
a
you
an
to
online
IB
huge
learning
Biology
bank
through
of
this
platform.
Kerboodle
resources,
If
your
Online
school
Resources
assessments,
and
has
you
a
will
be
presentations
able
to
course.
What is in your Kerboodle Online Resources?
There
are
three
planning,
main
resources,
areas
and
for
students
on
the
IB
Biology
Kerboodle:
assessment.
Resources
There
a
hundreds
Kerboodle
develop
your
Watch
of
Online.
skills
videos
science
in
Hundreds
extra
You
and
and
resources
can
use
available
these
knowledge
animations
at
as
of
home
you
on
or
the
in
progress
experiments,
IB
the
Biology
classroom
through
difcult
the
to
course.
concepts,
and
action.
of
simulations,
worksheets
practice
–
read
your
articles,
skills,
or
use
perform
your
experiments
knowledge
to
and
answer
questions.
Look
Find
at
galleries
out
answer
more
of
by
images
looking
questions,
or
do
from
at
the
book
and
recommended
more
see
sites
their
on
details
the
close
up.
Internet,
research.
Planning
Be
prepared
extra
Learn
Plan
and
about
and
Learn
vi
for
resources
the
on
the
practical
the
to
skills
data
and
your
Kerboodle
that
experiments
analyse
accurately.
work
Biology
different
prepare
how
IB
of
and
you
assessment
with
online.
need
your
draw
internal
to
perform
an
investigation.
own.
conclusions
successfully
Assessment
Click
on
the
assessment
examinations.
style
practice
Here
tests:
auto-marked
about
attempts
marks
how
a
at
are
you
as
if
it
each
one
mark.
The
These
an
of
knowledge
interactive
marks
where
and
these
until
are
you
to
quiz
you
or
revise
quizzes
for
and
–
go
your
exam-
can
be
the
back
to
printed
You
after
there’s
condent
will
every
markbook,
for
every
happy,
come
test.
how
so
have
one
you
two
question.
you
can
The
see
year.
more
these
will
the
practice
for
comprehension,
Evaluate
feedback
the
are
need
use
you
your
in
automatically
may
practice:
worksheets
get
reported
throughout
use
questions
check
complete
examination
about
Assessment
written
your
lots
sub-topic.
then
question
tests:
to
every
auto-marked
were
sure
see
check
nd
these
for
sub-topic,
progress
aren’t
can
use
quiz
automatically
Summative
there’s
to
will
questions.
Formative
feel
tab
you
your
topic.
and
exams
Work
change
then
any
submit
reported
in
or
the
as
revision,
through
the
the
test
questions
test
for
markbook,
a
you
nal
so
you
practice.
practice
across
out
answering
when
and
you
the
are
performed
longer
examined.
as
a
timed
test.
Don't forget!
You can also nd extra
resources on our free website
www.oxfordscondry.co.uk/ib-biooy
Here you can nd all of the answers
and even more practice questions.
vii
Introduction
Nature of science
This
book
is
a
companion
for
students
of
Biology
Here
in
the
International
Baccalaureate
you
can
explore
the
methods
of
science
and
Diploma
some
of
the
knowledge
issues
that
are
associated
Programme.
with
Biology
subject
is
as
biology
the
most
part
of
should
popular
the
lead
a
focus
on
diploma.
students
interconnectedness
With
IB
choice
of
life
to
science
The
study
appreciate
within
understanding
of
the
the
scientic
carefully
of
research
the
endeavour.
selected
that
led
understanding
of
This
examples,
to
done
including
paradigm
the
is
natural
shifts
in
using
biological
our
world.
biosphere.
nature
of
Thory of K nowd
science,
level
you
with
of
of
to
a
IB
Biology
scientic
act
on
full
will
allow
literacy
issues
of
that
local
understanding
you
to
will
better
and
of
the
develop
global
a
prepare
concern,
scientic
`knowledge questions´. The text that follows often
point
details one possible answer to the knowledge question.
view.
The
We encourage you draw on these examples of
structure
biology
These shor t sections have headings that are equivocal
of
this
programme
headings
restate
book
in
the
is
the
closely
Subject
specic
based
Guide.
assessment
on
the
knowledge issues in your TOK essays. Of course, much
of the material elsewhere in the book , par ticularly in the
Sub-
statements.
nature of science sections, can be used to prompt TOK
discussions.
Topics
1
that
common
7
–
is
11
–
6
explain
explain
to
in
detail
both
the
AHL
SL
the
and
Core
HL
material
courses.
(additional
higher
Topics
level
activity
material).
Topics
A,
B,
C
and
D
cover
the
content
A variety of shor t topics are included under this heading
of
the
options.
All
topics
include
the
following
with the focus in all cases on active learning. We
elements:
encourage you research these topics yourself, using
information available in textbooks or on the Internet. The
Understanding
aim is to promote an independent approach to learning.
The
specics
of
the
content
requirements
for
We believe that the optimal approach to learning is to
each
sub-topic
are
covered
in
detail.
Concepts
promote
enduring
are
be active – the more that you do for yourself, guided by
presented
in
ways
that
will
your teacher, the better you will learn.
understanding.
Applications
Data-based questions
These
sections
help
you
to
develop
your
These questions involve studying and analysing data
understanding
by
studying
a
specic
illustrative
from biological research – this type of question appears
example
or
learning
about
a
signicant
experiment
in both Paper 2 and Paper 3 for SL and HL IB Biology.
in
the
history
of
biology.
Answers to these questions can be found at
www.oxfordsecondary.co.uk/ib-biology
Skills topics
These
sections
encourage
you
to
apply
your
End -of-Topic Questions
understanding
through
practical
activities
At
and
analysis
of
results
from
classic
the
end
In
some
cases
this
involves
handling
data
from
experiments
and
of
ICT.
Some
experiments
promoting
seeing.”
work
valuable
assessed
viii
Others
the
the
skills
known
understanding
with
dene
of
with
involve
unknown
problem
IA
(see
ideas
for
outcomes,
and
opportunities
in
sections
outcomes,
through
the
to
page
708).
involve
aimed
“doing
at
and
experimental
where
methods.
build
the
topic
you
both
will
past
IB
nd
a
range
Biology
of
exam
you
These
skills
and
new
questions.
Answers
can
be
also
found
use
each
including
instructions
questions
for
of
biological
questions,
research.
can
are
that
a
are
at
www.oxfordsecondary.co.uk/ib-biology
1
C E L L
B I O L O G Y
Introduction
There
cells
alive
is
on
an
today.
complex
to
all
of
structure
is
and
essential
have
than
cell
but
of
life
found
multicellular
specialization
division
chain
cells
Eukaryotes
cell
evolution
cell
unbroken
Earth
is
a
in
from
the
much
more
prokaryotes.
organisms
out
The
allowed
replacement.
carried
rst
organisms
Cell
differently
in
prokaryotes
has
resulted
in
diversity,
the
there
also
the
are
uid
and
membranes
composition
and
a
eukaryotes.
biological
study
of
cells
universal
dynamic
allows
of
While
world
shows
features.
structure
them
of
to
us
For
of
evolution
enormous
that
example,
biological
control
the
cells.
1.1 Ii  
Understanding
Applications
➔
According to the cell theory, living organisms
➔
Questioning the cell theory using atypical
are composed of cells.
examples, including striated muscle, giant
➔
Organisms consisting of only one cell carry out
algae and aseptate fungal hyphae.
all functions of life in that cell.
➔
➔
Surface area to volume ratio is impor tant in the
Paramecium and one named photosynthetic
limitation of cell size.
➔
Multicellular organisms have proper ties
Investigation of functions of life in
unicellular organism.
➔
that emerge from the interaction of their
Use of stem cells to treat Stargardt ’s disease
and one other named condition.
cellular components.
➔
➔
Specialized tissues can develop by cell
specially created embryos, from the umbilical
dierentiation in multicellular organisms.
➔
Ethics of the therapeutic use of stem cells from
cord blood of a new-born baby and from an
adult ’s own tissues.
Dierentiation involves the expression of some
genes and not others in a cell’s genome.
➔
The capacity of stem cells to divide and
dierentiate along dierent pathways is
necessary in embryonic development. It also
makes stem cells suitable for therapeutic uses.
Skills
Nature of science
➔
Looking for trends and discrepancies: although
➔
are exceptions.
➔
➔
and raises ethical issues.
Drawing cell structures as seen with the
light microscope.
Ethical implications of research: research
involving stem cells is growing in impor tance
Use of a light microscope to investigate the
structure of cells and tissues.
most organisms conform to cell theory, there
➔
Calculation of the magnication of drawings
and the actual size of structures shown in
drawings or micrographs.
1
1
C E L L
B I O L O G Y
The cell theory
Living organisms are composed of cells.
The
up
internal
from
the
eye
organs
were
This
are
made
the
developed
states
cell.
many
Cells
a
Larger
they
and
of
nothing
century
animals
certain
are
the
the
smallest
are
organisms
can
tissues,
but
seen
features
are
the
we
about
microscopes.
were
as
biologists
fundamental
are
intricate
such
discovered
using
organisms
very
dissected
onwards
basic
is
Organs
different
was
features
explain
cells
The
If
organisms
parts.
number
or
17th
to
that
living
visible.
of
plants
of
individual
little
variation,
organisms.
one
easily
From
both
much
was
are
small
invented
tissues.
from
structure
very
again
of
that
until
the
they
large
–
there
A
the
cell
all
was
theory
of
–
consist
are
of
tissues
blocks
they
built
and
microscopes
again.
structure
is
structure
Although
and
unicellular
–
see
examined
building
multicellular
and
kidney
theory.
living
of
composed
just
of
cells.
vary
considerably
in
size
and
shape
but
they
share
certain
common
features:
Every
●
cell
Cells
●
living
contain
needed
Many
●
for
of
So,
cell’s
activities.
▲
2
can
can
cell’s
their
be
the
material
a
membrane,
which
separates
the
outside.
which
stores
all
of
the
instructions
are
chemical
reactions,
catalysed
by
enzymes
cell.
own
thought
by
else
activities.
activities
inside
have
cells
surrounded
everything
genetic
the
Cells
smaller
is
from
these
produced
●
cell
contents
energy
of
as
release
the
system
smallest
that
living
powers
structures
all
–
of
the
nothing
survive.
Figure 1 Coloured scanning electron micrograph (SEM) of a human embryo on the tip of a pin
1 . 1
I n t r o d u c t I o n
t o
c e l l s
Exceptions to the cell theory
Looking for trends and discrepancies: although most
organisms conform to cell theory, there are exceptions.
An
early
that
stage
appear
These
trends
theory
make
These
to
is
a
in
scientic
be
found
can
way
lead
of
are
called
unreliable
to
the
Sometimes
be
common
useful.
The
cell
and
discrepancies.
is
an
to
the
Scientists
theory
example
of
of
natural
serious
look
than
exceptions
or
The
is
rather
development
discrepancies.
are
theory
to
interpreting
predictions.
discrepancies
investigation
generally
a
a
have
then
where
trends
to
to
–
specic
A
allow
trend
judge
make
things
cases.
scientic
Theories
general
enough
is
in
theory.
world.
to
for
just
are
us
to
found.
whether
the
predictions
too
discarded.
scientists
have
looked
for
trends
▲
structures
in
and
parts
other
Nor
is
living
of
this
Elder
or
stems
of
kind
So
a
Hooke
tissue
–
Hooke’s
living
Teasels,
kind
of
day
at
organisms.
tree,
Fearn,
some
with
Many
of
in
as
to
of
kind
I
cork
of
these
at
only,
pith
Reeds
lately
at
just
discovered
looked
a
the
after
cork
for
of
have
wrote
pith
Cany
Carrets,
Figure 2 Rober t Hooke’s drawing of cork cells
for
cork
this:
Aiviy
the
much
that
type
of
hollow
Daucus,
have
shown
one
cell
examining
he
the
the
etc.
word
upon
that
general
tissues
tissues
in
Fennel,
have
use
1665
found
inner
as
to
cells
have
looking
and
have
rst
this
I
the
vegetables:
many
biologists
did
peculiar
Schematisme,
content
looked
the
describing
microscope
other
other
was
He
After
texture
my
any
several
wasn’t
he
of
with
almost
Bur-docks,
Hooke
organisms.
plants.
examination
such
Robert
of
of
cork.
plant
trend.
from
a
huge
been
found
Since
variety
to
of
consist
▲
of
cells,
so
the
cell
theory
has
not
been
discarded.
However,
Figure 3 What is the unit of life:
some
the boy or his cells?
discrepancies
that
do
not
discovered,
be
have
consist
but
discarded,
it
been
of
is
discovered
typical
cells.
extremely
because
so
–
organisms
More
unlikely
many
tissues
or
parts
discrepancies
that
do
the
cell
consist
of
of
may
theory
organisms
These two answers represent
be
will
the holistic and the reductionist
ever
approach in biology.
cells.
image viewed here
Using light microscopes
eyepiece lens
Use of a light microscope to investigate the
structure of cells and tissues.
coarse-focusing
Try
to
much
improve
as
you
your
skill
at
using
microscopes
as
knob
can.
ne-focusing
turret
knob
●
●
Learn
the
names
Understand
how
of
parts
to
focus
of
the
the
microscope.
microscope
to
objective lens
get
the
specimen
best
●
possible
Look
after
stage
image.
your
microscope
so
it
stays
in
perfect
light from mirror
working
●
Know
or light bulb
order.
how
to
troubleshoot
problems.
▲
Figure 4 Compound light microscope
3
1
C E L L
B I O L O G Y
Focusing
●
Put
Types of slide
the
slide
promising
hole
in
on
the
region
the
stage
stage,
exactly
that
with
in
the
the
the
light
most
middle
comes
The
of
the
be
slides
permanent
Always
focus
eventually
at
you
low
power
need
high
rst
even
power
if
a
magnication.
long
by
Focus
rst,
with
then
the
larger
when
you
coarse-focusing
have
nearly
in
focus
make
it
really
got
sharp
ne-focusing
a
microscope
can
so
slides
these
thin
is
slides
slices
very
are
slides
of
skilled
and
normally
of
tissues
takes
made
are
made
tissue.
knobs
the
using
temporary
slides
is
quicker
and
easier
so
the
we
smaller
with
temporary.
Permanent
very
Making
image
or
examine
permanent
time,
experts.
using
●
we
through.
Making
●
that
can
do
this
for
ourselves.
knobs.
Examining and drawing plant and
●
If
you
want
to
increase
the
magnication,
animal cells
move
the
slide
so
the
most
promising
region
is
Almost
exactly
in
the
middle
of
the
eld
of
view
all
cells
thenaked
then
change
to
a
higher
magnication
are
too
small
to
be
seen
with
and
eye,
so
a
microscope
is
needed
to
lens.
studythem.
Looking after your microscope
It
●
Always
focus
by
moving
the
lens
and
is
usually
plant
specimen
further
apart,
never
closer
to
each
or
an
Make
sure
before
that
putting
the
it
slide
on
the
is
clean
and
Never
your
●
touch
the
ngers
Carry
hand
the
or
under
it
anything
to
of
the
lenses
carefully
support
its
with
sure
by
lens,
weight
when
the
I
specimen
carefully
Add
is
easier
●
Carefully
try
to
to
nd
the
a
drop
avoid
Remove
is
in
both
the
plant
and
animal
on
the
slide
in
a
layer
not
specimen
if
of
water
lower
a
trapping
excess
inside
the
or
stain.
cover
a
any
slip
uid
folded
air
onto
the
drop.
circle
Solution: There
it
making
and
with
slides
when
I
is
try
so
Problem: There
an
to
a
thick
air
you
black
bubble
improve
that
are
focus
or
stain
piece
of
by
putting
paper
the
towel
lightly
on
the
cover
and
slip.
is
best
to
examine
focus
at
Move
the
the
slide
slide
to
get
rst
the
using
most
low
promising
low
in
the
rim
is
up
to
middle
there
are
blurred
it
as
on
your
of
the
as
air
of
power.
eld
Draw
of
a
view
few
and
cells,
visible.
their
structure.
slide.
technique
no
parts
well
the
high
cover
carefully lower the
slip
cover slip
for
bubbles.
the
image
Ican.
gently squeeze
Solution: Either
the
lenses
or
the
slide
have
dirt
to remove ex
them.
Ask
your
teacher
to
clean
it.
uid
Problem: The
image
is
very
dark.
cover slip
Solution: Increase
through
the
the
amount
specimen
by
of
light
adjusting
passing
the
diaphragm.
slide
folded
Problem: The
image
looks
rather
bleached.
r towel
▲
Solution: Decrease
through
4
Try
bubbles.
slide.
remember
on
more
thick.
then
rst.
Problem: A
even
a
many
actually
positioning
move
Ignore
from
are
focus.
areas
power
is
securely.
power.
It
cell
●
It
the
cells
one
pressing
under
cell
there
a
slide
Solution: Make
types
the
than
●
visible
a
though
else.
Troubleshooting
is
cell
Place
with
to
Problem: Nothing
whether
even
stage.
surfaces
microscope
see
kingdoms.
dry
●
●
to
animal,
other.
different
●
easy
the
the
the
specimen
amount
by
of
light
adjusting
the
passing
diaphragm.
Figure 5 Making a temporary mount
so
you
1 . 1
1
Moss
leaf
2
Banana
fruit
I n t r o d u c t I o n
cell
3
t o
c e l l s
Mammalian
liver
cell
10 μm
5 μm
20 µm
Use
a
thin
leaf
moss
in
a
Leaf
with
Mount
drop
methylene
4
plant
leaves.
of
blue
lower
a
very
Scrape
single
water
soft
or
drop
5
epidermis
small
tissue
place
stain.
a
on
of
amountof
from
a
a
slide.
iodine
Human
banana
Mount
the
Scrape
and
in
surface
a
of
frozen).
solution.
cheek
cells
add
cell
6
from
liver
Smear
methylene
White
a
freshly
(not
previously
onto
blue
blood
cut
a
slide
to
and
stain.
cell
20 μm
2 μm
10 μm
Peel
the
leaf.
The
lower
cell
epidermis
drawn
from
Valeriana.
or
methylene
▲
in
off
here
Mount
in
a
Scrape
was
your
water
Smear
blue.
cells
cheek
from
with
them
methylene
on
the
a
a
blue
inside
cotton
slide
to
A
of
and
thin
blood
bud.
slide
add
layer
can
and
mammalian
smeared
stained
Leishman’s
stain.
of
be
overa
with
stain.
Figure 6 Plant and animal cell drawings
Drawing cells
Drawing cell structures as seen with the light microscope.
Careful
drawings
Usually
the
detail
than
and
the
only
a)
same
Use
a
are
on
use
structures
calculating
the
lines
the
a
useful
the
faint
way
drawing
shading.
actually
are
magnication
of
of
recording
represent
–
Drawings
the
a
the
of
drawing
drawing
is
the
structure
edges
of
structures
shows
seen
them
explained.
of
cells
structures.
or
Do
using
a
biological
show
On
on
a
page
structures.
unnecessary
microscope
magnied.
Everything
other
not
6
drawing
will
the
be
larger
method
should
be
a
sharp
hard
lead
pencil
to
sharp
with
draw
lines.
b)
Join
to
up
form
lines
carefully
continuous
structures
such
as
cells
c)
Draw
but
lines
use
a
labelling
freehand,
ruler
for
lines.
cell
▲
to
magnication.
single
bad
for
shown
good
bad
good
bad
cell
good
Figure 7 Examples of drawing styles
5
1
C E L L
B I O L O G Y
Calculation of magnication and actual size
Calculation of the magnication of drawings and the actual size of structures shown
in drawings or micrographs.
When
that
are.
we
we
look
see
The
or
rotating
lens
to
three
allow
three
the
is
us
turret
of
to
A
microscope
than
magnify
factors.
switch
typical
the
they
magnifying
to
different
another.
levels
a
larger
microscope
microscopes
two
down
appear
structures
them.
from
school
is
done
one
is
important
sure
and
same.
by
or
objective
has
They
the
be
thousand.
millimetres
●
×
40
●
×
100
(low
(medium
400
we
take
(high
a
power)
photo
the
down
image
bars
straight
a
microscope,
we
are
microscope
even
is
called
micrographs
micrographs
When
we
drawing
of
the
wrong.
by
in
taken
draw
larger
drawing
magnication
a
more.
a
A
photo
micrograph.
using
book,
an
smaller,
isn’t
of
this
taken
There
including
electron
specimen,
or
sometimes
lines,
we
so
nd
the
drawing
necessarily
the
put
need
the
image
(in
the
actual
size
long
to
the
of
of
know
a
a
as
a
label
length
structure
Determine
the
or
things:
the
the
or
on
a
specimen.
30 mm
size
micrograph)
of
This
formula
of
×10,000
of
1
of
an
that
the
image
has
an
of
is
30
magnication
=
30
×
10
3 µm
=
3
×
10
m
m
3
=
6
10,000
size
of
the
10
Or:
specimen
30 mm
the
×
×
image
of
image
and
=
30,000 µm
the
30,000
_
we
can
calculate
the
actual
Magnication
size
=
3
of
a
specimen.
=
10,000
×
Data-based questions
1
a)
Determine
of
scale
b)
bar
magnication
cells.
cells
represents
Determine
of
the
Thiomargarita
the
width
in
0.2
of
of
gure
the
8,
mm
the
if
string
the
[3]
string
[2]
▲
6
if
These
that
there
scale
mm.
actual
and
=
size
size
the
6
=
size
magnication,
micrographs
the
was
are
scale
a
with
bar
a
would
µm.
is
calculation:
actual
know
converted
micrograph
3
a
___
we
can
by
EX AMPLE:
The
the
micrograph
two
drawing
the
magnication
If
be
them.
actual
example,
bar
3
the
Millimetres
are
make
same
the
30 × 10
_
for
or
different
electron
magnication
the
For
scale
Magnication
used
(mm)
be
thousand.
on
alongside
microscope.
magnication
we
the
multiplying
can
one
Either:
To
by
not
the
down
microscope.
can
the
just
with
represents.
mm
have
many
be
must
micrometres
dividing
or
magnication
a
millimetres
they
of
are
can
10
magnify
be
formula
size
specimen
Micrometres
by
drawings,
bar
If
will
the
this
the
power)
or
×
but
for
power)
Scale
●
of
both
calculation
using
units
size
( µm)
to
when
the
could
converted
one
magnication:
that
actual
micrometres
by
microscope
very
make
image
Most
specimens
This
It
to
actually
Figure 8 Thiomargarita
size
of
It
represents
of
the
3 µm.
image.
to
1 . 1
2
In
gure
9
the
actual
mitochondrion
a)
Determine
electron
b)
c)
is
8
the
length
of
b)
the
how
would
on
be
magnication
Determine
long
this
the
Determine
cheek
µm.
of
a
5
µm
of
scale
of
the
[2]
[2]
the
[1]
▲
4
Figure 10 Human cheek cell
a)
Using
the
guide,
ostrich
b)
width
estimate
egg
Estimate
the
of
(gure
the
the
the
hen’s
actual
egg
length
as
of
a
the
11).
[2]
magnication
of
image.
[2]
Figure 9 Mitochondrion
▲
The
magnication
from
is
length
cell.
bar
micrograph.
mitochondrion.
3
c e l l s
[2]
electron
width
the
t o
this
micrograph.
Calculate
I n t r o d u c t I o n
a
compound
2,000
a)
of
the
human
microscope
cheek
(gure
cell
10)
×.
Calculate
how
would
on
be
long
the
a
20
µm
scale
bar
image.
[2]
▲
Figure 11 Ostrich egg
Testing the cell theory
Questioning the cell theory using atypical examples, including striated muscle,
giant algae and aseptate fungal hyphae.
To
test
the
the
cell
structure
you
can,
using
microscope
case
you
Three
●
by
or
use
bres,
cells.
and
the
t
is
change
are
are
However
are
the
this
similar
by
have
own
worth
type
in
division
their
energy
muscle
much
own
of
are
than
of
some
a
of
for
mostly
of
each
in
humans
about
30
less
having
the
as
have
an
whereas
than
one
sometimes
the
they
mm,
0.03
mm
nucleus
many
average
other
as
in
they
length
human
length.
have
several
of
cells
are
Instead
many,
hundred.
cell
cells?”
tissue
by
In
as
considering:
tissue
that
our
are
body.
muscle
ways
to
membrane
pre-existing
genetic
release
bres
larger
In
“Does
stated
position
of
4.
more
surrounded
formed
They
page
or
are
at
Instructions
trend
one
the
blocks
on
look
organisms
question,
the
of
examples
which
their
They
given
ask
muscle
They
are
cells.
and
are
building
should
living
microscope.
tissue
to
you
many
consisting
Striated
The
a
use
atypical
we
as
should
organism
theory
theory
of
material
system.
far
from
most
typical.
animal
cells.
▲
Figure 12 Striated muscle bres
7
1
C E L L
●
B I O L O G Y
Fungi
consist
of
called
hyphae.
white
in
They
cell
colour
have
wall.
are
a
In
divided
cross
walls
fungi
narrow
These
and
cell
there
types
into
called
are
uninterrupted
have
a
of
small
septa.
no
are
and,
fungi
appearance.
outside
the
cell-like
septa.
Each
it,
in
by
aseptate
hypha
structure
a
hyphae
sections
However,
tube-like
structures
usually
uffy
membrane
some
up
thread-like
hyphae
is
with
an
many
Figure 13 Aseptate hypha
▲
nuclei
●
Algae
spread
are
along
organisms
photosynthesis
nuclei,
and
but
one
of
these
form
basis
They
If
are
a
mm,
new
It
organism
consist
of
many
that
to
cells,
to
a
a
not
algae
be
and
chains.
to
a
they
Less
much
single
length
length
one
of
cells.
of
as
is
much
nucleus.
100
certainly
just
consist
numbers
Acetabularia
having
would
structure
oceans
grow
by
inside
vast
food
algae.
grow
only
with
we
are
the
seem
giant
can
despite
discovered,
still
their
Many
marine
algae
as
in
genes
in
There
algae
most
themselves
their
plants.
cell.
they
known
feed
simpler
than
some
yet
example.
100
was
are
size,
of
that
store
are
unicellular
the
larger
as
they
microscopic
common
one
and
organization
of
it.
mm
expect
it
to
one.
Figure 14 Giant alga
▲
Unicellular organisms
Organisms consisting of only one cell carry out all
functions of life in that cell.
The
functions
Some
out
all
the
organisms
is
–
for
●
Response
●
Excretion
●
Homeostasis
an
–
a
complex
than
carry
out
food,
–
chemical
release
the
of
most
at
to
organisms
cell.
This
this
cells
least
the
in
seven
provide
must
cell
do
to
therefore
structure
stay
has
alive.
to
carry
of
unicellular
multicellular
organisms.
functions
energy
and
of
the
life:
materials
reactions
–
inside
the
cell,
including
cell
energy.
ability
getting
increase
to
rid
keeping
react
of
the
to
in
size.
changes
waste
conditions
in
the
products
inside
the
of
environment.
metabolism.
organism
within
limits.
unicellular
in
all
one
Because
irreversible
Reproduction
remain
8
–
to
Growth
tolerable
that
only
life.
obtaining
●
–
things
of
growth.
Metabolism
Many
of
organisms
respiration
●
are
consist
more
Nutrition
needed
●
life
functions
Unicellular
●
of
organisms
xed
–
producing
organisms
position
or
offspring
also
have
merely
a
either
sexually
method
drift
in
of
water
or
asexually.
movement,
or
air
but
currents.
some
1 . 1
I n t r o d u c t I o n
t o
c e l l s
Limitations on cell size
Surface area to volume ratio is impor tant in the limitation
of cell size.
In
the
cytoplasm
These
rate
reactions
of
these
volume
For
metabolism
move
of
its
into
the
the
numbers
collectively
(the
metabolic
continue,
cell
out
The
large
of
as
chemical
the
rate
of
reactions
metabolism
the
cell)
is
of
take
the
place.
cell.
proportional
The
to
cell.
to
the
and
cell.
surface
The
of
by
cells,
known
reactions
the
absorbed
of
are
and
of
rate
cells
at
substances
waste
through
which
used
products
the
in
must
plasma
substances
cross
the
be
reactions
removed.
membrane
this
must
be
Substances
at
the
membrane
surface
depends
on
area.
surface
area
to
volume
ratio
of
a
cell
is
therefore
very
important.
If
same cube
the
ratio
they
are
is
small
required
produced
Surface
too
more
area
to
then
and
substances
waste
rapidly
volume
than
ratio
will
products
will
they
be
is
can
also
not
enter
the
accumulate
cell
as
quickly
because
they
as
unfolded
are
excreted.
important
in
relation
to
heat
▲
production
and
loss.
If
the
ratio
is
too
small
then
cells
may
Figure 15 Volume and surface area
overheat
of a cube
because
the
metabolism
produces
heat
faster
than
it
is
lost
over
the
cell’ssurface.
Functions of life in unicellular organisms
Investigation of functions of life in Paramecium and one named photosynthetic
unicellular organism.
Paramecium
some
pond
Place
a
Add
a
is
a
unicellular
water
drop
cover
of
and
use
culture
slip
and
organism
a
that
centrifuge
solution
examine
to
can
containing
the
slide
be
cultured
concentrate
the
Paramecium
with
a
quite
easily
organisms
on
a
in
in
the
it
to
microscope
laboratory.
see
if
Alternatively
Paramecium
is
collect
present.
slide.
microscope.
The nucleus of the cell can divide to produce
The contractile vacuoles at each end of the cell ll up with water and
the ex tra nuclei that are needed when the cell
then expel it through the plasma membrane of the cell, to keep the
reproduces. Often the reproduction is asexual with
cell’s water content within tolerable limits.
the parent cell dividing to form two daughter cells.
Food vacuoles contain smaller
organisms that the Paramecium
has consumed.
These are gradually
digested and the nutrients are
absorbed into the cytoplasm where
they provide energy and materials
Metabolic reactions take place
in the cytoplasm, including the
reactions that release energy
by respiration. Enzymes in the
cytoplasm are the catalysts that
cause these reactions to happen.
needed for growth.
Beating of the cilia moves the
The cell membrane controls
Paramecium through the water
what chemicals enter and leave.
and this can be controlled by the
It allows the entry of oxygen for
cell so that it moves in a par ticular
respiration. Excretion happens
direction in response to changes
simply by waste products
in the environment.
diusing out through the
membrane.
▲
Figure 16 Paramecium
9
1
C E L L
B I O L O G Y
Chlamydomonas
research
not
a
into
true
is
cell
plant
a
unicellular
and
and
alga
molecular
its
cell
wall
that
lives
biology.
is
not
in
soil
Although
made
of
and
it
is
freshwater
green
in
habitats.
colour
and
It
has
been
carries
out
used
widely
for
photosynthesis
it
is
cellulose.
The nucleus of the cell
The contractile vacuoles
can divide to produce
at the base of the agella
genetically identical
ll up with water and then
nuclei for asexual
expel it through the plasma
reproduction. Nuclei can
membrane of the cell, to keep
also fuse and divide
the cell’s water content within
to carry out a sexual
tolerable limits.
form of reproduction.
In this image, the
nucleus is concealed by
chloroplasts in the cytoplasm.
Carbon dioxide can be conver ted
Metabolic reactions take
into the compounds needed
place in the cytoplasm,
for growth here, but in the dark
with enzymes present to
carbon compounds from other
speed them up.
organisms are sometimes
absorbed through the cell
membrane if they are available.
The cell wall is freely
permeable and it is the
Beating of the two agella
membrane inside it that
moves the Chlamydomonas
controls what chemicals
through the water. A light-
enter and leave. Oxygen
sensitive “eyespot” allows
is a waste product of
the cell to sense where the
photosynthesis and is
brightest light is and respond
excreted by diusing out
by swimming towards it.
through the membrane.
▲
Figure 1
7 Chlamydomonas
Multicellular organisms
Multicellular organisms have proper ties that emerge from
the interaction of their cellular components.
Some
type
a
unicellular
of
alga
protein
Figure
gel,
18
Figure 18 Volvox colonies
shows
Although
single
cell
mass
one
like
more
cells.
body
is
a
and
a
common
feeds
on
female
long
large
very
the
or
are
are
of
a
the
are
more
it
but
reproductive
to
of
organs.
of
It
are
cells,
fused
elegans.
exactly
such
million
as
oak
The
of
to
inside
form
a
adult
cells.
in
or
third
of
an
the
has
cells
is
about
might
have
adult
elegans
elegans
so
body
This
far
human
whales.
organic
C.
are
multicellular
Caenorhabditis
decomposing
a
a
made
surface.
fused
organisms
trees
hermaphrodite
Almost
its
together,
959
cells
decomposition.
is
to
ball
forming
not
researched
multicellular
million
in
colonies
example
a
organism.
biologists,
cause
anus.
up
most
ten
unseen
that
and
mass
for
of
attached
they
intensively
made
consists
daughter
single
organisms
lives
bacteria
a
colonies,
cells
Caenorhabditis
is
about
in
with
in
colony
identical
single
known
and
intestine
not
called
and
together
Each
cooperating,
most
number,
well
more
colonies,
so
of
live
aureus.
cells
and
There
name
pharynx,
two
worm
even
Although
500
the
One
millimetre
seem
Volvox
consisting
multicellular.
organisms
10
with
them.
Organisms
▲
organisms
called
has
matter.
has
both
are
a
no
It
mouth,
male
and
neurons,
or
1 . 1
nerve
cells.
Most
of
these
neurons
are
located
at
the
front
I n t r o d u c t I o n
end
of
t o
c e l l s
the
toK
worm
in
a
Although
structure
the
brain
environment,
in
this
and
it
that
in
does
other
can
C.
be
elegans
not
regarded
the
coordinates
control
multicellular
as
how
animal’s
responses
individual
organisms
can
cells
be
brain.
to
the
develop.
regarded
as
Hw a w i wh  m i
worm’s
The
cells
 ha ah?
cooperative
An emergent proper ty of a system is
groups,
without
any
cells
in
the
group
acting
as
a
leader
or
supervisor.
not a proper ty of any one component
It
is
remarkable
how
individual
cells
in
a
group
can
organize
themselves
of the system, but it is a proper ty of
and
interact
with
each
other
to
form
a
living
organism
with
distinctive
the system as a whole. Emergence
overall
properties.
The
characteristics
of
the
whole
organism,
including
refers to how complex systems and
the
fact
that
it
is
alive,
are
known
as
emergent
properties.
patterns arise from many small and
Emergent
of
a
complex
the
of
properties
whole
an
is
written
clay.
But
can
structure.
greater
emergent
text
it’s
carry
these
the
than
hollow
that
some
sum
was
interaction
of
years
makes
things
in
pot
of
this
parts.
ago:
the
studying
bigger
sum
its
described
2,500
by
the
sometimes
the
that
research
from
We
than
property
more
out
remember
arise
a
up
A
work.”
are
with
from
the
in
parts
phrase:
parts,
but
interactions
cannot therefore necessarily predict
approach known as reductionism).
from
Molecular biology is an example of the
we
we
We
each par t of a system separately (an
philosophical
biology
relatively simple interactions.
emergent proper ties by studying
example
fashioned
So,
component
component
simple
Chinese
“Pots
result
the
success that a reductionist approach
must
between
can have. Many processes occurring in
living organisms have been explained
components.
at a molecular level. However, many
argue that reductionism is less useful
Cell dierentiation in multicellular organisms
in the study of emergent proper ties
including intelligence, consciousness
Specialized tissues can develop by cell dierentiation in
and other aspects of psychology. The
multicellular organisms.
In
is
multicellular
sometimes
or
a
and
role.
the
organisms
called
For
division
example
function
of
a
the
rod
interconnectivity of the components
different
of
labour.
function
cell
cells
in
In
of
the
perform
a
simple
red
retina
different
terms,
blood
of
the
cell
eye
a
is
is
functions.
function
to
to
carry
is
This
a
job
oxygen,
absorb
light
in cases like these is at least as
impor tant as the functioning of each
individual component.
and
One approach that has been used to
then
transmit
impulses
to
the
brain.
Often
a
group
of
cells
specialize
in
the
study interconnectivity and emergent
same
way
to
perform
the
same
function.
They
are
called
a
tissue.
proper ties is computer modelling. In
By
becoming
more
the
efciently
ideal
cells
reactions
in
different
differentiation.
cell
than
structure,
chemical
of
specialized,
types
have
In
if
the
they
with
the
cells
had
to
humans,
been
a
with
carry
220
tissue
many
enzymes
associated
ways
in
different
needed
the
out
all
specic
of
to
function.
distinctively
recognized,
can
which
carry
roles.
carry
The
out
their
They
out
can
all
of
both animal behaviour and ecology,
role
develop
Life” has been used. It was devised
the
by John Conway and is available on
development
functions
different
develop
is
by
the Internet. Test the “Game of Life” by
called
highly
a programme known as the “Game of
specialized
differentiation.
creating initial congurations of cells and
seeing how they evolve.
Research ways
in which the model has been applied.
Gene expression and cell dierentiation
Dierentiation involves the expression of some genes and
not others in a cell’s genome.
There
all
are
have
have
and
the
same
able
a
to
pigments
different
same
activities.
produce
be
many
the
set
To
set
of
its
and
is
an
that
job
cell
of
types
genes.
genes,
take
pigment
do
of
The
despite
example,
absorbs
sensing
transparent.
If
in
multicellular
cell
large
rod
light.
light.
it
a
220
did
types
differences
cells
in
the
Without
A
in
lens
cell
contain
it,
in
organism
the
in
their
retina
the
the
of
rod
eye
pigments,
but
human
structure
the
cell
eye
would
produces
less
they
body
light
not
no
would
11
1
C E L L
B I O L O G Y
pass
through
developing,
but
these
This
is
genes
the
cell
and
types
When
a
in
it
of
a
not
is
is
used
cell
is
nose,
one
of
Cell
of
the
smells.
in
key
genes
This
work
in
a
or
on
is
have
in
other
particular
happens
cell
a
body
be
that
gene
they
the
are
pigment,
genes
The
with
cell.
on
a
or
gene
and
and
in
human
is
information
development
expressing
of
most
being
the
The
in
used.
different
control
in
the
However,
needed
the
the
specialize
genes
product.
because
types.
to
25,000
ever
say
genes
needed
switched
differentiation
only
so
how
cells.
makes
we
and
involves
for
making
expressed
receptor
this
we
gene
information
are
Axel
on
just
will
While
making
cell.
genes
present
worse.
for
them,
sequence
gene
but
of
expression
development.
of
and
is
not
have
cell,
the
different
the
genes
rod
genes
protein
to
olfactory
Richard
their
all
the
switching
do
be
genes
approximately
differentiation
carry
These
called
are
of
would
the
the
they
are
used
a
in
cells
terms,
example
that
odorant.
for
the
extreme
smells.
make
expressed
humans
genes
being
involves
–
need,
half
vision
contain
used
There
simple
to
therefore
An
is
In
others.
genes
than
gene
expressed.
they
way.
our
types
only
these
less
and
cell
situation
that
possible
genome,
lens
are
usual
instructions
every
the
both
one
can
in
Each
type
cells
of
of
distinguish
Linda
Buck
a
large
family
receptors
in
the
these
for
skin
cells
inside
receptor
to
detect
so
many
given
the
genes
Nobel
in
–
the
expresses
between
were
of
odorants
just
one
type
different
Prize
in
2004
system.
Stem cells
The capacity of stem cells to divide and dierentiate
along dierent pathways is necessary in embryonic
development. It also makes stem cells suitable for
therapeutic uses.
A
new
animal
zygote.
This
of
are
tissue.
different
In
cells
stem
Stem
cells
●
●
12
so
are
the
from
have
of
cells
different
of
At
a
sperm
when
again
these
dividing
any
of
century,
early
to
the
zygote
produce
early
stages
times
versatile
the
cell
name
embryo,
fertilizes
the
many
extremely
into
a
in
to
stem
meaning
egg
cell
to
can
cell
embryo,
then
development
large
that
given
the
a
cells.
amounts
differentiate
in
was
all
produce
two
embryonic
found
that
to
give
four-cell
produce
and
types
an
divides
along
particular
to
the
tissues
of
zygote
the
them.
two
can
key
are
to
biology
again
are
of
not
ways,
properties
in
divide
They
replacement
Stem
divides
on.
research
cells.
when
formed
also
19th
of
cells
new
the
Figure 19 Embryonic stem cells
the
areas
Stem
of
▲
They
and
active
and
pathways
adult
is
capable
animal.
the
starts
embryo
sixteen
cells
life
embryo
two-cell
eight,
the
An
and
therefore
cells
fully
that
that
and
have
again
different
the
lost
They
cell
them
one
of
the
most
today.
produce
for
been
differentiated.
produce
to
useful
have
made
medicine
or
of
quantities
tissues
damaged.
can
types.
copious
growth
differentiate
in
or
1 . 1
Embryonic
be
used
have
to
stem
suffered
such
as
cells
produce
type
burns.
1
are
called
health
There
are
is
to
for
use
also
human
is
the
might
–
stem
stage
The
whether
to
cell
in
including
the
may
of
still
same
cells
means
cell
in
for
useful.
skin
for
of
type
the
They
people
healing
has
to
therapies
for
could
who
lost
grow
These
c e l l s
diseases
been
future
example.
allow
to
way
of
cells
as
They
skin
one
to
limited
a
or
is
whole
types
of
diseases
repair
into
cells,
brain,
use
or
give
and
a
to
a
cell
Eventually
type.
cells
Once
will
cells.
and
some
be
cattle.
which
they
human
The
meat,
therefore
cell
stem
many
repair.
at
these
however,
or
versatile.
another.
of
possibility
themselves
specic
all
kidney
may
points
or
One
bres,
slaughter
most
longer
in
They
and
the
of
but
and
commit
one
no
present
liver.
–
are
cells
cells.
muscle
future
rear
series
are
stem
and
that
divide,
regeneration
the
to
pathway
they
are
of
the
stem
striated
need
develop
and
of
burgers
the
able
remain
marrow,
embryonic
involves
along
be
body.
powers
for
stem
This
develop
adult
bone
considerable
only
very
as
provide
development
committed
the
numbers
tissues
embryo
becomes
beef
without
embryonic
decides
a
large
cells,
differentiation.
in
they
uses
of
present
a
used
quantities
produce
pattern
Small
be
to
during
differentiate
provide
particular
kidneys,
because
consumption.
committed,
or
such
non-therapeutic
from
early
cell
a
even
hearts
Gradually
each
could
where
potentially
tissue,
t o
problems.
them
produced
It
They
organs
therapeutic,
other
therefore
They
diabetes
malfunctioning.
replacement
are
regenerated
I n t r o d u c t I o n
human
stem
cells
heart
are
still
tissues,
for
tissues
in
other
example.
Therapeutic uses of stem cells
Use of stem cells to treat Stargardt’s disease and one other named condition.
There
are
diseases,
many
of
few
and
a
cells
are
current
huge
which
examples
stem
a
are
one
range
being
given
and
uses
here:
using
of
of
stem
cells
possible
actively
one
treat
future
uses,
researched.
involving
adult
to
stem
Two
embryonic
Researchers
embryonic
This
were
a
cells.
was
stem
done
then
developed
cells
similar
cells
were
with
into
to
methods
develop
initially
injected
condition
injected
have
the
into
not
retina
mouse
eyes
of
Stargardt’s
rejected,
for
cells.
cells,
which
mice
that
disease.
did
not
making
had
The
develop
Stargardt’s disease
into
The
full
name
of
this
disease
is
Stargardt’s
It
is
a
genetic
disease
that
moved
children
between
the
ages
of
six
and
cases
are
due
to
a
recessive
mutation
gene
called
protein
used
ABCA4.
for
malfunction.
As
This
active
a
causes
transport
consequence,
a
in
in
the
detect
retina
light,
degenerate.
so
vision
an
retina
cells
got
in
50s
her
The
person
loss
to
of
be
These
becomes
vision
can
registered
be
as
retina
where
they
The
attached
and
remained.
improvement
Very
in
the
encouragingly,
vision
of
the
they
mice.
2010,
approval
researchers
for
trials
in
in
the
United
humans.
with
Stargardt’s
disease
was
A
woman
treated
by
photoreceptive
are
the
50,000
retina
cells
derived
from
embryonic
cells
cells
injected
into
her
eyes.
Again
the
cells
progressively
severe
enough
to
the
retina
and
remained
there
during
for
the
the
the
to
attached
worse.
to
November
States
stem
that
problems.
membrane
having
cells
other
of
In
a
any
twelve.
caused
Most
cause
develops
themselves
in
or
macular
cells
dystrophy.
tumours
four-month
trial.
There
was
an
improvement
blind.
in
her
vision,
and
no
harmful
side
effects.
13
1
C E L L
Further
are
we
B I O L O G Y
trials
needed,
can
be
larger
after
optimistic
treatments
stem
with
but
for
numbers
these
initial
about
Stargardt’s
the
of
at
using
be
done
chemicals
least,
development
disease
can
patients
trials
is
of
embryonic
known
healthy
able
cells.
to
to
by
in
needle
the
cells
by
and
blood
that
present,
The
patient
blood
cells
procedure
can
be
needed
produce
they
following
remain
must
cells
but
to
are
killed
procedure
is
is
inserted
pelvis,
and
into
uid
is
a
large
bone,
removed
from
marrow.
cells
stored
▲
be
with
The
However,
the
white
Stem
must
bone
Stem
patient
cells.
used:
large
the
term
the
disease.
usually
●
long
chemotherapy.
A
the
dividing
chemotherapy.
the
cells
therefore
●
as
treating
kill
produce
ght
blood
by
that
are
extracted
freezing
only
from
them.
have
the
this
They
uid
are
potential
and
adult
for
are
stem
producing
cells.
Figure 20 Stargardt’s disease
●
A
high
dose
of
chemotherapy
drugs
is
given
lkmia
to
This
disease
when
is
a
type
mutations
division.
For
a
of
occur
cancer
cancer.
in
to
All
genes
cancers
that
develop,
start
control
several
the
cell
must
occur
in
these
genes
in
patient,
bone
ability
is
one
very
unlikely
numbers
of
to
cells
happen,
in
the
but
body,
as
there
the
The
stem
of
a
becomes
million
year
globally
from
the
Once
form
with
of
a
or
leukemia.
bone
it
are
More
are
over
than
a
blood
cells
marrow
in
loses
of
into
when
leukemia.
In
most
tumour
White
a
such
200,000
cells
are
body.
then
They
returned
re-establish
to
the
themselves
are
the
bone
red
marrow,
and
multiply
white
blood
and
start
to
cells.
each
In
many
cases
this
procedure
cures
the
leukemia
completely.
deaths
the
blood,
normal
large
this
both
in
numbers
adult
in
the
are
the
femur.
white
of
cancer
not
cells
happen
produced
hollow
They
are
normal
are
involves
numbers
does
cells
tissue
the
repeatedly,
Leukemia
cancers,
but
have
divides
cells.
blood
soft
as
excessive
A
more
abnormally
marrow,
bones
and
in
centre
then
conditions
produced
blood
cell
with
count
is
3
between
person
4,000
with
and
11,000
leukemia
this
per
mm
number
of
blood.
rises
In
higher
a
and
3
higher.
a
Counts
person
may
above
have
30,000
per
leukemia.
If
mm
there
suggest
are
that
more
3
than
has
To
100,000
acute
cure
14
mm
white
it
is
likely
that
the
person
leukemia.
leukemia,
marrow
of
per
that
are
blood
the
cancer
producing
cells
must
cells
in
excessive
be
its
cells.
quarter
diagnosed
mutations
grows
and
cells.
lump
released
there
cell,
more
blood
large
and
a
production
white
the
and
larger.
leukemia
cancer-inducing
in
producing
the
of
bone
cancer
disease.
the
occurred
much
cases
The
the
overall
produce
chance
produce
all
cell.
in
huge
kill
marrow.
to
patient’s
This
to
specic
●
mutations
the
the
bone
numbers
destroyed.
This
▲
Figure 2
1 Removal of stem cells from bone marrow
1 . 1
I n t r o d u c t I o n
t o
c e l l s
The ethics of stem cell research
Ethical implications of research: research involving stem cells is growing in
impor tance and raises ethical issues.
Stem
cell
Many
research
ethical
Scientists
has
should
always
implications
of
Some
research
past
of
the
would
today,
not
such
patients
been
objections
as
their
be
that
the
was
out
ethically
research
in
out
the
stem
it.
the
acceptable
carried
informed
of
ethical
doing
carried
Decisions
about
acceptable
raised.
before
considered
their
controversial.
been
consider
research
medical
without
very
have
of
of
consent.
science
cell
whether
be
the
stem
cells
possible
research
research
based
involved.
research
misunderstanding
three
on
must
as
on
a
Some
the
being
sources
involving
but
different
used.
of
In
stem
them
ethically
understanding
people
unethical,
of
is
clear
the
next
and
all
shows
possible
cells
are
dismiss
this
a
sources
section,
the
ethics
discussed.
Sources of stem cells and the ethics of using them
Ethics of the therapeutic use of stem cells from specially created embryos, from
the umbilical cord blood of a new-born baby and from an adult’s own tissues.
Stem
●
cells
can
Embryos
obtained
can
fertilizing
the
be
be
egg
resulting
from
a
deliberately
cells
with
zygote
to
variety
of
created
sperm
and
develop
for
sources.
and
by
a
few
it
has
between
four
and
sixteen
cells.
the
cells
are
embryonic
stem
Stem
Blood
can
be
extracted
from
the
of
a
new-born
baby
and
stem
from
it.
The
cells
can
be
emyi m 
Almost unlimited growth potential.
●
Can dierentiate into any type in
cells
types
below
give
the
Easily obtained and stored.
●
Commercial collection and
as
be
obtained
bone
from
some
adult
marrow.
of
stem
their
cell
vary
potential
in
for
their
properties
therapeutic
use.
and
The
gives
some
properties
of
the
three
types,
scientic
basis
for
an
ethical
assessment.
A m 
●
Dicult to obtain as there are
very few of them and they are
buried deep in tissues.
storage services already
available.
●
Less growth potential than
embryonic stem cells.
●
including teratomas that contain
Fully compatible with the tissues of
the adult that grows from the baby,
dierent tissue types.
●
in
●
More risk of becoming tumour
cells than with adult stem cells,
can
such
c  m 
the body.
●
the
frozen
to
●
in
cells
table
obtained
later
umbilical
therefore
cord
use
cells.
These
●
possible
All
tissues
of
for
days
●
until
stored
baby’slife.
allowing
●
so no rejection problems occur.
Less chance of malignant
tumours developing than from
Less chance of genetic damage
embryonic stem cells.
●
Limited capacity to dierentiate
due to the accumulation of
into dierent cell types – only
●
Limited capacity to dierentiate
mutations than with adult
into dierent cell types.
naturally develop into blood
stem cells.
cells, but research may lead to
●
●
Likely to be genetically dierent
Fully compatible with the adult’s
production of other types.
tissues, so rejection problems do
from an adult patient receiving
●
Limited quantities of stem cells
not occur.
the tissue.
from one baby’s cord.
●
●
Removal of stem cells does not
Removal of cells from the
●
The umbilical cord is discarded
kill the adult from which the cells
whether or not stem cells are
are taken.
embryo kills it, unless only one
or two cells are taken.
taken from it.
15
1
C E L L
Stem
cell
Many
are
the
research
ethical
most
cells,
B I O L O G Y
objections
because
death
taken.
stage
of
The
been
to
current
the
is
undoubtedly
the
when
is
a
which
raised.
usually
the
stem
whether
human
case
stem
involve
cells
an
are
early
individual
killing
the
as
lived
However,
There
embryonic
techniques
much
in
of
have
controversial.
been
use
question
as
baby,
very
have
embryo
main
embryo
new-born
is
has
objections
a
embryo
to
create
has
a
human
obtaining
stem
cells.
of
well
invasive
of
as
an
eggs
from
supplying
denied
lives
treatment
its
the
of
solely
Also,
women,
eggs
exploitation
unethical.
been
counterargument
IVF
If
that
the
vulnerable
unethical
purpose
procedure
could
living.
is
are
lead
groups
of
hormone
associated
women
this
of
it
involves
some
surgical
ovary.
for
for
IVF
with
chance
is
risk,
as
forremoval
paid
to
such
for
the
as
college
students.
When
views
does
on
sperm
say
developed
of
so
stem
begins
brain
that
Some
that
they
when
Some
capable
There
that
human
stage
be
is
a
embryos
thought
that
of
stages
take
has
surviving
in
as
is
developed
groups
truly
tissue
a
that
into
the
yet
suffer
life
after
view
outside
not
cannot
bone
a
or
few
it
fetus
scientists
argue
that
if
embryos
by
in
vitro
fertilization
(IVF)
cells.
the
stem
cells,
no
human
that
would
the
They
potential
to
allow
of
treatment
methods
diseases
disabilities
they
and
that
are
incurable,
could
greatly
specially
in
order
the
suffering
▲
Figure 22 Har vesting umbilical
to
of
obtain
of
have
reduce
created
forget
embryonic
currently
uterus.
are
of
stem
for
is
not
arguments
favour
use
so
Some
must
ethical
simply
place
Another
We
begun.
have
human
or
different
the
has
and
a
are
when
life
heartbeat,
embryo
of
a
suggest
These
the
begin?
characteristics
development.
when
is
egg,
early
there
life
consider
should
cells.
of
the
human
activity.
weeks
only
human
fertilizes
Others
pain,
a
this.
some
individuals.
cord blood
otherwise
1.2 ua   
Understanding
Applications
➔
Prokaryotes have a simple cell structure
➔
The structure and function of organelles within
without compar tments.
exocrine gland cells of the pancreas.
➔
Eukaryotes have a compar tmentalized cell
➔
The structure and function of organelles within
structure.
palisade mesophyll cells of the leaf.
➔
Prokaryotes divide by binary ssion.
➔
Electron microscopes have a much higher
resolution than light microscopes.
Skills
Nature of science
➔
Developments in scientic research follow
➔
based on electron micrographs.
improvements in apparatus: the invention
of electron microscopes led to greater
Drawing the ultrastructure of prokaryotic cells
➔
understanding of cell structure.
Drawing the ultrastructure of eukaryotic cells
based on electron micrographs.
➔
Interpretation of electron micrographs to
identify organelles and deduce the function of
specialized cells.
16
1 . 2
u lt r A s t r u c t u r e
o f
c e l l s
th ivi  h  mip
Developments in scientic research follow improvements in apparatus: the
invention of electron microscopes led to greater understanding of cell structure.
Much
years
of
the
has
progress
followed
microscopes.
improved
of
In
light
bacteria
and
Chromosomes
processes
were
many
had
the
other
were
structures
of
the
the
the
19th
the
rst
time
William
such
discovered
0.001
of
found
had
to
as
be
to
the
Harvey
chloroplasts
and
be
was
made
than
a
limit
though.
explained
cannot
a
later
was
the
other
tiny
clear
images
structures
of
are
membranes
microscope
cells
than
are
until
invented
–
For
0.01
a
that
lysosomes
is
It
electron
of
is
microscopes
were
developed
these
in
the
and
the
1930s
and
came
into
use
microscope.
in
in
in
the
1940s
and
50s.
electron
the
and
The
ideas
green
the
electron
of
in
the
interpreted
attened
located
under
microscope
shown
microscope
mitochondria
spheres
was
light
areas
and
stacks
cells
biologists
were
1890s
chlorophyll
internal
in
appear
the
as
light
revealed
membrane
of
in
there
be
A
the
are
them
structure.
electron
what
cells,
reticulum
1950s,
but
for
example,
as
were
all
example.
signicant
improvements
microscopes
allows
is
including
Ribosomes,
structures
discovered,
recent
of
features.
improvement
made.
revealed
endoplasmic
named
that
to
design
new
continue
discoveries
described
in
to
sub-
Germany
8.2,
is
electron
tomography
–
a
method
of
research
producing
laboratories
or
light
most
grana
fact
Whereas
unknown
still
each
topic
during
the
ultrastructure
and
unlikely
as
be
Electron
in
as
with
than
darker
the
rods
in
small
eukaryotic
called
microscopes
the
discovered
thick.
type
called
previously
smaller
example,
μm
the
are
with
intricate
electron
now
biological
different
the
The
are
microscopes
structures
Many
grana
structureless
an
were
chlorophyll.
sacs,
of
previous
revealed
membranes.
have
many
as
than
intricate
example,
They
that
things
could
micrometre
this.
about
hampered
was
of
(A
millimetre.)
smaller
in
was
a
(μm).
light
and
had
of
smaller
structure
more
For
of
membrane
times
The
far
microscope,
that
reasons
sub-topic,
be
wrong.
showed
of
cells.
discoveries
technical
this
micrometres
thousandth
Progress
the
For
in
produce
0.2
to
to
droplets
to
There
produced
200
expected
be
as
embryos.
kidney
–
chloroplast.
and
fusion
of
be
microscope
formation
the
the
within
and
to
μm
microscopes.
century
reproduction,
development
organs
images
150
discovery
gamete
sexual
seen
last
design
organisms.
and
eluded
mitochondria,
were
of
the
of
was
in
allowed
for
basis
subsequent
and
half
meiosis
The
biologists,
complexity
over
unicellular
seen
previously
and
revealed
second
mitosis,
other
gametes
biology
microscopes
discovered.
which
The
of
in
improvements
They
3-D
images
by
electron
microscopy.
allowed
The resolution of electron microscopes
Electron microscopes have a much higher resolution
than light microscopes.
If
we
we
look
cannot
with
a
within
things
size
the
at
a
see
of
tree
the
0.1
leaf
with
a
cells
mm
we
size
with
within
as
need
of
become
individually
Making
the
unaided
its
separate
to
down
use
to
visible
separate
eyes
parts
a
leaves.
light
they
of
an
can
The
objects,
about
–
we
but
see
its
unaided
no
0.2
μm
be
object
as
eye
smaller.
microscope.
can
individual
This
can
To
see
see
allows
separate
leaves,
objects,
things
the
us
to
so
but
cells
see
cells
can
distinguished.
distinguishable
by
eye
is
called
resolution.
The
maximum
nanometres
are,
the
resolution
(nm).
resolution
of
However
cannot
a
light
microscope
powerful
be
higher
the
than
is
lenses
this
0.2
of
a
μm,
light
because
it
is
which
is
200
microscope
limited
by
the
▲
wavelength
of
light
(400–700
nm).
If
we
try
to
resolve
smaller
objects
Figure 1 An electron microscope
by
in use
17
1
C E L L
B I O L O G Y
making
focus
lenses
them
with
magnication
Beams
of
have
much
a
microscopes
is
could
size
not
of
be
It
1
a
blurred
microscopes
a
much
μm
or
times
the
1
nm.
structure
explains
why
until
electron
that
×
is
of
so
but
electron
with
microscopes
a
to
maximum
microscopes
therefore
This
is
have
why
microscopes
were
needed
diameter
had
impossible
the
electron
microscopes.
microscopes
is
electron
modern
microscopes
light
it
why
400.
wavelength,
cells,
viruses
nd
This
usually
resolution
than
light
but
is
Electron
of
we
image.
shorter
The
greater
micrometre,
seen
magnication,
get
resolution.
200
reveal
ultrastructure.
a
have
0.001
is
and
light
higher
that
microscopes
with
with
electrons
resolution
greater
properly
been
of
to
0.1
a
light
reveal
see
the
bacteria
micrometres
invented.
ri
Miim
Mim
nam
(mm)
(µm)
(m)
Unaided eyes
0.1
Light microscopes
Electron microscopes
100
100,000
0.0002
0.2
200
0.000001
0.001
1
Aiviy
cmm a i
Prokaryotic cell structure
While still a young student in
Berlin in the late 1920s Ernst
Ruska developed magnetic
Prokaryotes have a simple cell structure without
compar tments
coils that could focus beams
All
organisms
can
be
divided
into
two
groups
according
to
their
cell
of electrons. He worked on the
structure.
Eukaryotes
have
a
compartment
within
the
cell
that
contains
idea of using these lenses to
the
chromosomes.
It
is
called
the
nucleus
and
is
bounded
by
a
nuclear
obtain an image as in a light
envelope
consisting
of
a
double
layer
of
membrane.
Prokaryotes
do
not
microscope, but with electron
have
a
nucleus.
beams instead of light. During
the 1930s he developed and
Prokaryotes
rened this technology. By
have
1939 Ruska had designed
are
the rst commercial electron
intestines
the
were
the
simplest
found
almost
and
rst
cell
organisms
structure.
everywhere
even
in
pools
–
of
to
They
in
soil,
hot
evolve
are
on
mostly
in
water,
water
in
Earth
small
on
and
in
our
volcanic
they
size
skin,
still
and
in
our
areas.
microscope. In 1986 he was
All
cells
have
a
cell
membrane,
but
some
cells,
including
prokaryotes,
awarded the Nobel Prize in
also
have
a
cell
wall
outside
the
cell
membrane.
This
is
a
much
Physics for this pioneering
thicker
and
stronger
structure
than
the
membrane.
It
protects
the
cell,
work. Ruska worked with the
maintains
its
shape
and
prevents
it
from
bursting.
In
prokaryotes
as
being
the
cell
German rm Siemens. Other
wall
contains
peptidoglycan.
It
is
often
referred
to
extracellular.
companies in Britain, Canada
and the United States also
developed and manufactured
electron microscopes.
As
no
with
nucleus
membranes
simpler
●
is
cytoplasm.
–
than
it
in
present
The
is
in
a
prokaryotic
cytoplasm
one
is
not
uninterrupted
eukaryotic
cells,
cell
divided
its
chamber.
though
we
interior
into
The
must
is
entirely
compartments
structure
remember
is
lled
by
therefore
that
it
is
still
Scientists in dierent
very
complex
in
terms
of
the
biochemicals
present
in
the
cytoplasm
that
are
present,
including
countries usually
many
enzymes.
cooperate with each
other but commercial
Organelles
companies do not. What
analogous
are the reasons for this
distinct
dierence?
cytoplasmic
the
organs
structures
Svedberg
18
are
to
with
organelles
units
(S)
is
of
specialized
apart
70S,
of
multi-cellular
from
which
eukaryotic
organisms
functions.
ribosomes.
is
smaller
cells
in
that
Prokaryotes
Their
than
size,
those
of
that
are
they
do
not
are
have
measured
in
eukaryotes.
1 . 2
Part
of
the
cytoplasm
micrographs.
one
circular
explains
that
DNA
the
contain
nucleoid
–
This
appears
region
molecule.
lighter
lighter
contains
The
appearance
enzymes
meaning
and
than
the
DNA
is
ribosomes.
as
the
in
many
cell,
other
lighter
contains
area
DNA
with
parts
of
but
in
the
form
proteins,
of
the
is
o f
c e l l s
electron
usually
associated
with
This
it
rest
of
not
compared
nucleus-like
the
DNA
u lt r A s t r u c t u r e
the
cell
not
a
of
which
cytoplasm
is
called
true
the
nucleus.
Cell division in prokaryotes
Prokaryotes divide by binary ssion.
All
living
division
binary
organisms
of
ssion
chromosome
to
opposite
follows.
so
they
need
pre-existing
and
is
are
is
used
replicated
ends
Each
it
to
of
of
the
the
produce
cells.
Cell
for
and
cell.
genetically
asexual
the
two
Division
daughter
new
division
cells
cells.
in
They
can
prokaryotic
reproduction.
copies
of
the
of
the
The
one
do
is
copy
of
single
the
of
the
this
by
called
circular
chromosome
cytoplasm
contains
only
cells
cell
move
quickly
chromosome
identical.
dawig pkayi 
Draw the ultrastructure of prokaryotic cells based on
electron micrographs.
Because
cannot
prokaryotes
be
seen
magnication
using
in
are
a
Aiviy
mostly
light
electron
very
small,
microscope.
micrographs
It
their
is
that
internal
only
we
with
can
see
structure
much
the
higher
details
oh am 
pkay
of
Biologists sometimes use
the
structure,
called
the
ultrastructure.
Drawings
of
the
ultrastructure
the term “bacteria” instead
of
prokaryotes
are
therefore
based
on
electron
micrographs.
of “prokaryote”. This may
Shown
E.coli,
and
below
a
shows
also
you
the
learn
the
found
internal
technique
shown.
can
on
bacterium
different
is
and
By
next
in
our
and
shows
to
The
the
the
identify
are
two
intestines.
structure.
comparing
how
page
One
other
external
drawings
structures
electron
has
of
micrographs
them
been
structure.
with
within
the
is
a
thin
prepared
A
electron
prokaryotic
section
by
drawing
of
a
of
not always be appropriate
because the term
prokaryote encompasses
each
micrographs
cells.
a larger group of organisms
than true bacteria
(Eubacteria). It also includes
organisms in another group
Electron
micrograph
of
Escherichia
coli
(1–2μm
in
length)
called the Archaea.
There is a group of
photosynthetic organisms
that used to be called
blue-green algae, but their
cell structure is prokaryotic
and algae are eukaryotic.
This problem has been
Drawing
to
help
interpret
the
electron
micrograph
solved by renaming them as
nucleoid (region
Cyanobacteria.
containing naked DNA)
ribosomes
cell wall
plasma membrane
cytoplasm
●
What problems are
caused by scientists
using dierent words
for things than non-
scientists?
19
1
C E L L
B I O L O G Y
Electron
micrograph
of
Escherichia
coli
showing
surface
features
pili
agellum
Shown
below
practice
can
and
your
also
try
many
copies
another
at
other
drawing
indicate
and
nd
is
skill
of
their
annotate
electron
these.
a
micrograph
drawing
appearance
your
of
a
is
no
need
structure,
in
drawing
one
to
prokaryote.
ultrastructure
micrographs
There
particular
the
such
small
say
of
to
of
can
prokaryotic
cells
a
as
ribosomes.
the
long
they
are
time
part
found
use
of
it
cells.
on
spend
representative
that
You
prokaryotic
the
to
You
internet
drawing
You
the
can
cytoplasm
elsewhere.
Aiviy
Gai  a
mpa maizai
Garlic cells store a harmless
sulphur-containing
compound called alliin in
their vacuoles. They store
an enzyme called alliinase
in other parts of the cell.
Alliinase converts alliin into
a compound called allicin,
which has a very strong
smell and avour and is
toxic to some herbivores.
▲
Figure 2 Brucella abor tus (Bang’s bacillus), 2 μm in length
This reaction occurs when
herbivores bite into garlic
and damage cells, mixing the
Eukaryotic cell structure
enzyme and its substrate.
Perhaps surprisingly, many
Eukaryotes have a compar tmentalized cell structure.
humans like the avour, but to
Eukaryotic
cells
have
a
much
more
complicated
internal
structure
than
get it garlic must be crushed
prokaryotic
cells.
Whereas
the
cytoplasm
of
a
prokaryotic
cell
is
one
or cut, not used whole.
undivided
●
You can test this by
that
smelling a whole garlic
are
they
space,
are
single
or
eukaryotic
divided
double
up
by
cells
are
compartmentalized.
partitions
into
compartments.
This
The
means
partitions
membranes.
bulb, then cutting or
The
most
important
of
these
compartments
is
the
nucleus.
It
contains
crushing it and smelling
the
cell’s
chromosomes.
The
compartments
in
the
cytoplasm
are
known
it again.
as
20
organelles.
Just
as
each
organ
in
an
animal’s
body
is
specialized
1 . 2
to
perform
distinctive
There
●
are
a
particular
structure
several
Enzymes
●
●
that
membrane
of
a
could
lysosome
the
particular
other
if
such
Organelles
in
with
being
a
cause
digest
as
organelle
in
a
eukaryotic
cell
has
c e l l s
a
spread
damage
For
and
compartmentalized:
particular
were
organelle.
process,
processes
in
for
they
could
an
lysosome
Conditions
●
substrates
than
Substances
inside
each
o f
function.
advantages
and
concentrated
role,
and
u lt r A s t r u c t u r e
kill
process
to
the
example,
a
cell,
can
throughout
if
cell
the
they
be
much
the
can
be
kept
digestive
were
more
cytoplasm.
inside
enzymes
not
safely
the
of
stored
membrane.
pH
can
which
a
be
maintained
may
be
at
different
an
to
ideal
the
level
levels
for
a
needed
for
cell.
their
contents
can
be
moved
around
within
thecell.
dawig kayi 
Draw the ultrastructure of eukaryotic cells based on electron micrographs.
The
ultrastructure
complex
of
a
the
cell.
and
it
Your
structure,
structure
of
is
of
eukaryotic
often
drawing
so
the
you
best
is
an
need
organelles
n
to
cells
draw
is
very
only
part
interpretation
to
understand
that
might
be
of
the
present.
The
of
table
each
with
a
of
below
the
drawing
recognition
organelle
contains
of
the
features
are
an
commonly
electron
occurring
structure.
and
the
micrograph
organelles,
Brief
function
notes
of
on
each
included.
The nuclear membrane is double and has pores
through it. The nucleus contains the chromosomes,
double nuclear
membrane
consisting of DNA associated with histone proteins.
nuclear pores
Uncoiled chromosomes are spread through the
nucleus and are called chromatin. There are often
densely staining areas of chromatin around the edge
of the nucleus. The nucleus is where DNA is replicated
and transcribed to form mRNA , which is expor ted via
dense
chromatin
the nuclear pores to the cytoplasm.
chromatin
rgh pami
The rER consists of attened membrane sacs, called
im
cisternae. Attached to the outside of these cisternae
are ribosomes. They are larger than in prokaryotes and
ribosomes
are classied as 80S. The main function of the rER is to
synthesize protein for secretion from the cell. Protein
synthesized by the ribosomes of the rER passes into
its cisternae and is then carried by vesicles, which bud
o and are moved to the Golgi apparatus.
cisterna
21
1
C E L L
B I O L O G Y
Ggi appaa
This organelle consists of attened membrane sacs
called cisternae, like rER. However the cisternae are
cisterna
not as long, are often curved, do not have attached
ribosomes and have many vesicles nearby. The Golgi
apparatus processes proteins brought in vesicles
from the rER. Most of these proteins are then carried in
vesicles
vesicles to the plasma membrane for secretion.
These are approximately spherical with a single
lym
digestive enzymes
membrane. They are formed from Golgi vesicles. They
contain high concentrations of protein, which makes
them densely staining in electron micrographs. They
contain digestive enzymes, which can be used to
break down ingested food in vesicles or break down
organelles in the cell or even the whole cell.
lysosome membrane
Mihi
inner
outer
membrane
membrane
A double membrane surrounds mitochondria, with
the inner of these membranes invaginated to form
structures called cristae. The uid inside is called the
matrix. The shape of mitochondria is variable but is
usually spherical or ovoid. They produce ATP for the
cell by aerobic cell respiration. Fat is digested here if it
is being used as an energy source in the cell.
matrix
crista
f im
These appear as dark granules in the cytoplasm and
are not surrounded by a membrane. They have the
same size as ribosomes attached to the rER – about
20nm in diameter, and known as 80S. Free ribosomes
synthesize protein, releasing it to work in the
cytoplasm, as enzymes or in other ways. Ribosomes
are constructed in a region of the nucleus called
the nucleolus.
A double membrane surrounds the chloroplast. Inside
chpa
are stacks of thylakoids, which are attened sacs of
starch grain
membrane. The shape of chloroplasts is variable but
stroma
is usually spherical or ovoid. They produce glucose
and a wide variety of other organic compounds by
double
membrane
thylakoid
photosynthesis. Starch grains may be present inside
chloroplasts if they have been photosynthesizing
rapidly.
Va a
These are organelles that consist simply of a single
vi
membrane with uid inside. Many plant cells have
vacuole
containing food
large vacuoles that occupy more than half of the cell
volume. Some animals absorb foods from outside
and digest them inside vacuoles. Some unicellular
organisms use vacuoles to expel excess water.
large vacuole
Vesicles are very small vacuoles used to transpor t
vesicles
materials inside the cell.
22
1 . 2
u lt r A s t r u c t u r e
o f
c e l l s
Mi a
In the cytoplasm of cells there are small cylindrical
i
bres called microtubules that have a variety of roles,
including moving chromosomes during cell division.
triple
Animal cells have structures called centrioles, which
consist of two groups of nine triple microtubules.
Centrioles form an anchor point for microtubules
during cell division and also for microtubules inside
cilia and agella.
These are whip-like structures projecting from the
ciia a aga
cell surface. They contain a ring of nine double
microtubules plus two central ones. Flagella are larger
and usually only one is present, as in a sperm. Cilia are
smaller and many are present. Cilia and agella can be
used for locomotion. Cilia can be also be used to create
a current in the uid next to the cell.
microtubule
membrane
The
electron
with
are
labels
micrograph
to
identify
below
some
of
shows
the
a
liver
organelles
cell
that
●
Using
draw
your
the
understanding
whole
cell
to
of
show
these
its
organelles,
ultrastructure.
present.
free
mitochondrion
rough endoplasmic
reticulum
▲
nucleus
ribosomes
Golgi
lysosome
apparatus
Figure 3 Electron micrograph of par t of a liver cell
23
1
C E L L
B I O L O G Y
Exocrine gland cells of the pancreas
The structure and function of organelles within exocrine gland cells of
the pancreas.
Gland
cells
through
types
cells
of
digestive
small
Enzymes
have
in
cells
gland
ready
intestine
are
micrograph
plasma
in
proteins,
and
on
the
a
the
to
right
secrete
carries
digest
them
them.
cells
them
the
The
plasma
electron
organelles:
apparatus
mitochondrion
vesicles
nucleus
lysosomes
rough
to
proteins
to
these
Golgi
gland
make
them
shows
membrane
to
them
foods.
synthesize
release
them
two
Endocrine
exocrine
transport
are
bloodstream.
that
they
release
There
pancreas
process
the
the
duct
so
needed
then
they
pancreas.
into
where
secretion,
membrane
the
into
quantities,
for
in
cells
enzymes
–
membrane.
hormones
organelles
large
substances
plasma
gland
secrete
Exocrine
the
secrete
their
▲
ER
Figure 4 Electron micrograph of pancreas cell
Paia mphy 
The structure and function of organelles
within palisade mesophyll cells of the leaf.
The
function
producing
dioxide
using
out
and
light
most
of
other
cylindrical.
Like
surrounded
membrane
the
simple
The
shape
all
by
inside
right
mesophyll
cell
is
a
of
in
type
the
these
–
carbon
compounds,
that
carries
leaf
is
palisade
cells
is
roughly
plant
wall,
The
the
from
inorganic
living
cell
it.
shows
cell
photosynthesis
cell
photosynthesis
The
on
leaf
compounds
energy.
mesophyll.
is
the
organic
cells
with
electron
organelles
a
the
cell
plasma
micrograph
that
a
palisade
contains:
wall
plasma
membrane
chloroplasts
mitochondrion
vacuole
▲
nucleus
24
Figure 5 Electron micrograph of palisade mesophyll cell
1 . 3
M e M b r A n e
s t r u c t u r e
Ipig h   kayi 
Interpret electron micrographs to identify organelles and deduce the function
of specialized cells.
If
the
organelles
identied
possible
●
and
to
Study
in
deduce
the
and
8.
and
try
eukaryotic
function
the
electron
Identify
to
a
their
the
deduce
is
overall
cell
function
micrographs
organelles
the
can
known,
in
that
function
of
be
it
of
is
often
the
gures
are
cell.
6,
7
present
each
cell.
▲
▲
Figure 7
Figure 6
▲
Figure 8
1.3 Mma 
Understanding
Applications
➔
Phospholipids form bilayers in water due to the
➔
Cholesterol in mammalian membranes reduces
amphipathic properties of phospholipid molecules.
membrane uidity and permeability to some
➔
Membrane proteins are diverse in terms of
solutes.
structure, position in the membrane and function.
➔
Cholesterol is a component of animal cell
membranes.
Skills
Nature of science
➔
Using models as representations of the
real world: there are alternative models of
➔
Drawing the uid mosaic model.
➔
Analysis of evidence from electron microscopy that
membrane structure.
➔
Falsication of theories with one theory being
superseded by another: evidence falsied the
led to the proposal of the Davson–Danielli model.
➔
Analysis of the falsication of the Davson–Danielli
model that led to the Singer–Nicolson model
Davson–Danielli model.
25
1
C E L L
B I O L O G Y
OH
Phospholipid bilayers
hydrophilic
O
O
P
phosphate
Phospholipids form bilayers in water due to the
O
head
H
C
H
H
H
amphipathic proper ties of phospholipid molecules.
C
C
Some
O
substances
are
attracted
to
water
–
they
are
hydrophilic
O
H
C
O
C
O
C
H
C
H
C
H
C
H
Other
substances
Phospholipids
hydrophilic
C
H
C
H
C
H
C
H
C
H
C
H
described
The
H
C
H
C
H
C
H
hydrophilic
structure
C
H
H
C
H
C
H
H
C
H
of
not
attracted
unusual
part
is
to
because
water
part
hydrophobic.
of
–
a
they
are
hydrophobic.
phospholipid
Substances
with
molecule
this
property
is
are
amphipathic.
hydrophobic
C
are
and
as
are
part
part
of
a
phospholipid
consists
of
phospholipids
two
is
is
the
phosphate
hydrocarbon
shown
in
gure
chains.
group.
The
The
chemical
1.
hydrophobic
hydrocarbon
The
structure
can
be
represented
simply
using
a
circle
for
the
phosphate
tails
C
H
C
H
H
C
H
C
H
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
group
▲
and
two
two
parts
hydrocarbon
H
hydrocarbon
chains.
of
the
tails.
molecule
When
are
often
phospholipids
called
are
phosphate
mixed
with
heads
water
and
the
heads
are
attracted
to
the
water
but
the
hydrocarbon
H
tails
▲
the
H
C
phosphate
H
for
Figure 2 Simplied diagram of a phospholipid molecule
The
C
lines
are
attracted
Figure 1 The molecular structure
phospholipids
of a phospholipid.
hydrocarbon
The phosphate
often has other hydrophilic groups
heads
facing
to
each
become
tails
the
but
arranged
facing
water
other,
into
inwards
on
not
either
to
water.
double
towards
side.
layers,
each
These
Because
with
other
double
of
the
and
this
the
layers
the
hydrophobic
hydrophilic
are
called
attached to it, but these are not
phospholipid
bilayers.
They
are
stable
structures
and
they
form
the
basis
shown in this diagram
of
all
cell
membranes.
hydrophilic
phosphate
hydrophobic
head
hydrocarbon
tails
phospholipid
bilayer
▲
Figure 3 Simplied diagram of a phospholipid bilayer
M  mma 
Using models as representations of the real world: there are alternative models of
membrane structure.
In
the
1920s,
Gor te r
phospholipids
of
red
area
26
blood
that
fro m
cells
the
a nd
the
a nd
Gr e nde l
pla s ma
ca lcul ate d
pho s p ho l ip id s
e x t ra c t e d
me mbr an e
that
occupi ed
arranged
the
area
the
in
of
a
mono l a ye r
plasma
the
that
w h en
phospholipids.
wa s
twice
me mb ra ne .
membran e
co ntai ne d
The r e
w er e
as
The y
a
la rg e
bilayer
s e ve ra l
as
d ed u c ed
er r or s
of
in
1 . 3
their
methods
other
for
out
cell
and
but
l uck il y
the r e
membrane s
is
the s e
now
b e i ng
canc e l le d
ve ry
s tr ong
ba s ed
on
ea c h
e vid en c e
p ho sp h ol ipi d
Membranes
also
and
Grendel’s
this
is
to
the
proposed
because
very
some
the
1950s,
of
–
protein
on
this
and
appear
dark
phospholipids
appearance
thought
barrier
High
to
the
would
very
showed
dark
a
railroad
lines
with
a
the
tted
the
in
electron
appear
light,
Davson-Danielli
proteins
the
membrane.
the
inner
cases
tiles
move.
track
of
occupy
a
protruding
free
to
bilayer,
the
The
Integral
out
from
move
the
in
model
its
are
in
the
are
this
attached
are
some
bilayer
likened
to
phospholipid
each
proteins
In
positions
proteins
bilayer,
proteins
Because
the
of
proteins
phospholipid
was
Nicolson.
variety
surface.
sides.
gives
structure
and
Peripheral
mosaic.
are
the
This
mosaic
lighter
parts
a
Singer
outer
the
both
in
molecules
layers
in
or
or
in
with
one
membrane
by
to
the
of
of
1966
in
on
are
electron
made
in
embedded
explain
thin,
movement
were
of
sandwich
magnication
membranes
two
it
model
sides
model
proposed
adjacent
this
being
Another
Gorter
where
and
both
proposed
despite
which
appearance
of
and
explain
Davson
bilayer,
they
substances.
micrographs
1930s
They
effective
not
layers
membranes,
protein
did
the
phospholipid
model
a
In
membrane.
how
contain
model
located.
the
between.Proteins
micrographs
so
s t r u c t u r e
model.
bilayers.
Danielli
band
M e M b r A n e
of
are
name
the
also
–
two
able
the
to
uid
model.
Pm wih h dav–daii m
Falsication of theories with one theory being superseded by another: evidence
falsied the Davson–Danielli model.
The
Davson–Danielli
structure
for
about
tted
and
In
the
was
30
the
1950s
accumulated
Danielli
●
years.
model
electron
including
of
membrane
most
of
cell
biologists
many
X-ray
experiments
diffraction
studies
microscopy.
and
60s
that
some
did
not
experimental
t
with
the
evidence
Davson–
model:
This
technique
cells
and
then
occurs
along
centre
of
scattered
electron
involves
through
of
Structure
them.
of
The
fracture
the
structures
freeze-etched
were
of
including
Globular
membranes
images
of
interpreted
as
proteins.
membrane
Improvements
freezing
weakness,
membranes.
centre
allowed
of
micrographs.
rapid
fracturing
lines
transmembrane
●
by
Results
Freeze-etched
the
model
accepted
in
proteins
proteins.
biochemical
to
be
techniques
extracted
▲
from
Figure 4 Freeze-etched electron micrograph of nuclear
membranes, with nuclear pores visible and vesicles in the
membranes.
They
were
found
to
be
very
surrounding cytoplasm. The diagram on page 28 shows the line
varied
in
size
and
globular
in
shape
so
of fracture through the centre of the inner and outer nuclear
were
unlike
the
type
of
structural
protein
membranes. Transmembrane proteins are visible in both of the
that
would
form
continuous
layers
on
the
membranes
27
1
C E L L
B I O L O G Y
periphery
were
of
the
membrane.
hydrophobic
surface
so
they
on
at
would
tails
centre
membrane.
the
of
be
hydrocarbon
of
Also
least
the
the
part
of
attracted
proteins
to
the
the
phospholipids
in
replacement
and
their
the
it
Fluorescent
green
uorescent
antibodies
The
antibody
that
tagged
with
with
green
together.
green
markers
bind
membrane
to
red
of
markers
Within
40
were
and
The
other
cells
mixed
were
the
leading
be
model
unwise
superseded.
uid
to
There
of
An
maxim
in
important
that
science
dogma
fused
mosaic
for
over
assume
are
tted
widely
the
model.
fty
that
already
evidence
accepted
it
was
It
has
years
but
will
some
never
the
suggested
model.
you
happen
and
for
might
scientists
be
because
instead
search
is
“Think
mistaken.”
scientists
it
Advances
reject
continually
for
better
understanding.
and
throughout
modications
possible
were
cells
red
the
would
that
became
to
proteins.
cells
needed
that
or
attached
some
minutes
were
Red
membrane
proteins
markers.
markers
tagging.
was
model
Singer–Nicolson
been
be
●
the
the
cytoplasm
membrane
of
membrane
proteins
the
membrane
peripheral
Taken
the
the
are
rather
cell.
This
free
to
than
showed
move
being
that
within
xed
in
a
layer.
together,
falsied
fused
this
experimental
Davson–Danielli
evidence
model.
nucleus
A
inner membrane
outer membrane
Evidence for and against the Davson–Danielli model of
membrane structure
Analysis of evidence from electron microscopy that led to the proposal of the
Davson–Danielli model.
Figure
blood
edge
1.
5
shows
cell
of
and
the
the
plasma
some
of
the
membrane
cytoplasm
of
a
near
red
the
cell.
Describe
the
appearance
of
the
plasma
membrane.
2.
Explain
how
membrane
with
3.
of
4.
the
of
the
are
two
sets
used
to
on
for
of
on
either
the
dark
red
10
that
types
the
of
the
that
side.
[2]
appearance
cell.
the
[2]
electron
thickness
nanometres.
of
questions
data
that
the
phospholipid
grainy
Davson–Danielli
structure.
of
blood
magnication
is
suggested
region
the
data-based
the
falsify
membrane
28
of
central
assuming
membrane
based
appearance
protein
reasons
micrograph
The
a
cytoplasm
Calculate
the
this
had
layers
Suggest
[2]
of
[3]
that
follow
were
model
of
▲
Figure 5 TEM of plasma membrane of a red blood cell
1 . 3
M e M b r A n e
s t r u c t u r e
daa-a qi: Membranes in
Diusion of proteins in membranes
freeze-etched electron micrographs
Frye
to
Figure
6
shows
a
freeze-etched
and
Edidin
obtain
image
of
part
of
a
cell.
It
by
Professor
Horst
Robenek
uid
technique
nature
They
attached
of
uorescent
markers
membrane
proteins
–
green
markers
to
mouse
of
cells
Münster
elegant
the
was
to
prepared
an
for
electron
membranes.
micrograph
used
evidence
and
red
markers
to
human
cells.
In
both
University.
cases,
spherical
were
used.
were
then
had
but
one
the
green
were
minutes
completely
cell
membrane.
not
prevent
processes
tim a
mixing
in
the
culture
human
the
one
fusion,
merged,
of
cells
one,
the
red
until
the
ATP
(ATP
cells
fused
red
throughout
Blocking
this
rst,
following
mixed
tissue
and
and
gradually
did
active
At
hemisphere
markers
in
mouse
together.
the
for
growing
marked
fused
green
over
and
cells
The
they
whole
of
production
supplies
energy
cell).
c wih mak y mix/%
i /
r
r
r
r
1
2
3
4
5
0
0
–
–
10
3
0
–
–
25
40
54
–
–
40
87
88
93
100
120
100
–
–
–
Ma
mi
▲
1
Figure 6
In
all
of
the
fractured
micrograph
small
membranes
granules
are
in
the
visible.
1
a)
State
what
b)
Explain
these
granules
are.
Calculate
markers
[2]
the
fully
mean
percentage
mixed
for
each
of
cells
time
with
after
fusion.
the
granules
in
membrane
signicance
the
of
investigation
2
of
structure.
Plot
bars
[3]
in
2
One
the
of
the
membranes
nucleus
is
micrograph.
visible
Deduce
that
on
the
a
graph
for
the
or
outer
left
whether
nuclear
results.
it
of
is
and
lowest
your
reasons
membrane.
when
Identify
the
three
asked
describing
4
Explain
that
its
mitochondria
this
their
the
either
to
cell
visible
using
was
from
join
these
labels
the
in
or
4
Explain
at
this
with
with
plot
will
a
the
lie
micrograph
proteins
the
you
a
range
variation
plot
small
ruled
mean
on
trend
whether
Davson–Danielli
Singer–Nicolson
5
the
bar
highest
and
line.
You
the
result
range
with
a
bar.
[4]
Explain
the
shown
the
results
model
model
benet
by
of
or
the
t
graph.
in
[1]
the
the
more
closely.
plotting
range
[2]
bars
ongraphs.
[2]
[2]
6
questions
also
Describe
by
cytoplasm.
Extension
results
bars
This
3
[2]
processing
do
was
deduce
positions.
evidence
To
including
there
(Always
[2]
micrograph,
results,
the
something.)
3
the
where
the
cross.
give
of
times
surround
should
inner
[4]
these
on
this
topic
can
be
found
www.oxfordsecondary.co.uk/ib-biology
During
this
incubated
experiment
at
researchers
37
°C.
the
Suggest
choosing
this
cells
a
were
reason
for
temperature.
the
[1]
29
1
C E L L
7
B I O L O G Y
The
experiment
the
trends
temperatures
8
Explain
the
When
the
ATP
trends
of
the
15
15
the
in
results.
graph
35
the
for
°C.
[2]
graph
for
°C.
was
red
in
different
the
and
shown
below
at
shows
shown
synthesis
mixing
7
between
temperatures
9
repeated
[2]
blocked
and
srekram htiw sllec fo %
Explain
was
Figure
green
in
the
cells,
markers
setunim 04 retfa dexim ylluf
temperatures.
1
100
1
1
1
1
50
still
1
1
1
1
occurred.
drawn
Explain
from
what
conclusion
can
be
0
this.
Predict,
with
15
reasons,
the
results
of
25
35
incubation temperature (°C)
[1]
▲
10
5
Figure 7 Eect of temperature on the
the
rate of diusion of uorescent markers
experiment
if
it
was
repeated
using
cells
in membranes
from
or
arctic
sh
rather
than
from
mice
humans.
[1]
Membrane proteins
Membrane proteins are diverse in terms of structure,
position in the membrane and function.
Cell
is
to
membranes
form
cannot
all
a
barrier
easily
other
have
examples
are
wide
through
pass.
functions
a
This
are
listed
in
is
range
which
carried
carried
table
of
ions
out
out
functions.
and
by
by
The
primary
hydrophilic
the
molecules
phospholipid
proteins
in
the
function
bilayer.
membrane.
Almost
Six
1.
fi  mma pi
Hormone binding sites (also called hormone receptors), for example the insulin
receptor. Figure 8 shows an example.
Immobilized enzymes with the active site on the outside, for example in the small
intestine.
Cell adhesion to form tight junctions between groups of cells in tissues and organs.
Cell-to-cell communication, for example receptors for neurotransmitters at
synapses.
Channels for passive transpor t to allow hydrophilic par ticles across by facilitated
diusion.
Pumps for active transpor t which use ATP to move par ticles across the membrane.
▲
T
able 1
Because
in
▲
Figure 8 Hormone receptor (purple)
of
these
structure
into
two
and
varied
in
their
functions,
position
membrane
in
the
proteins
membrane.
are
They
very
can
diverse
be
divided
groups.
embedded in phospholipid bilayer (grey).
●
Integral
proteins
are
hydrophobic
on
at
least
part
of
their
surface
and
The hormone (blue/red) is thyroid
they
are
therefore
embedded
in
the
hydrocarbon
chains
in
the
centre
stimulating hormone. G-protein (brown)
of
the
membrane.
Many
integral
proteins
are
transmembrane
–
conveys the hormone's message to the
interior of the cell
extend
across
through
30
the
the
membrane,
regions
of
with
phosphate
hydrophilic
heads
on
parts
either
projecting
side.
they
1 . 3
●
Peripheral
proteins
embedded
in
of
a
integral
single
the
Figure
the
proteins
includes
all
orientated
example,
plants
are
pump
The
protein
of
have
pump
them
membranes
just
as
The
cell
content
about
50%.
chloroplasts
respiration.
that
the
of
and
and
of
face
most
have
which
is
the
of
membrane
up
face
out
to
surface
have
into
surface.
membrane
function
membranes
potassium
the
Some
protein.
and
their
not
inserted
membrane
outer
carry
are
reversible.
to
plasma
pick
so
attached
often
them
an
can
is
surface,
are
s t r u c t u r e
of
ions
root
from
correctly.
cells
the
in
soil
cell.
is
very
active
in
the
a
a
protein
sheath
content
contents
which
because
membrane,
membranes
protein
protein
variable,
myelin
plasma
mitochondria,
These
and
the
more
highest
to
types
they
they
have
their
them
protein
membranes
The
The
attached
in
root
of
attachment
both
that
Membranes
insulators
protein
is
so
varies.
content.
inner
so
on
Most
the
of
proteins
into
content
protein
act
an
orientated
and
chain
examples
proteins
For
this
anchoring
Membranes
are
hydrophilic
and
hydrocarbon
membrane,
9
are
membrane.
M e M b r A n e
are
contents
of
only
on
in
about
higher
around
are
active
of
the
the
in
the
function
is
nerve
its
bres
18 %.
outside
the
of
the
membranes
photosynthesis
of
and
75 %
dawig mma 
Draw the uid mosaic model of membrane structure.
The
for
but
structure
us
to
we
can
symbols
A
in
to
diagram
gure
of
show
membranes
all
show
of
it
our
represent
of
in
full
is
far
too
detail
in
understanding
the
membrane
molecules
structure
complicated
a
of
drawing,
it
The
diagram
shows
these
components
of
a
membrane:
using
●
phospholipids;
●
integral
●
peripheral
●
cholesterol.
present.
is
shown
proteins;
9.
▲
proteins;
Figure 9 Membrane structure
31
1
C E L L
Identify
Using
B I O L O G Y
which
similar
each
symbols
components
draw
according
the
these
to
proteins:
pumps
for
receptors
It
worth
is
of
you
membrane
interpret
in
a
science
merely
on
visual
with
are
A
we
diagram
which
is
but
is
a
a
a
book
and
draw.
to
to
their
are
and
as
it
all
For
paper
based
example,
the
cells
we
usually
author,
for
printing.
still
the
needed
biologists
skills.
of
software,
perhaps
drawing
our
not
theory.
by
is
and
group
suitable
ability
show
are
a
and
used
membranes,
computer
artistic
drawing,
improve
They
cell
paper
make
are
process
scientic
use
paper
No
the
been
model
simplify
plasma
on
or
or
tissue
the
enzymes
have
They
theories.
drawingon
up
you
mosaic
Drawings
or
contains
diffusion,
neurotransmitters.
uid
animal
drawing
possible
pencil
to
scientic
and
in
or
structure
represent
our
as
an
that
immobilized
Drawings
like.
diagramis.
membrane,
facilitated
process.
hypotheses
a
model,
explanations.
a
the
the
of
what
the
or
looks
tidied
now
way
it
to
basing
out
of
show
lines
starts
It
what
models,
when
about
draw
structure.
understanding
for
hormones
structure
as
mosaic
transport,
for
in
represent
structure
channels
thinking
when
to
the
uid
active
and
doing
component
can
Of
best
for
develop
course
some
▲
biologists
Some
produce
examples
particularly
are
shown
in
good
gure
Figure 10 Anatomical drawings by Leonardo da Vinci
drawings.
10.
Cholesterol in membranes
Cholesterol is a component of animal cell membranes.
The
two
main
proteins.
Cholesterol
CH
CH
3
CH
2
CH
CH
is
a
cell
type
of
cell
membranes
of
lipid,
but
membranes
also
it
is
contain
not
a
fat
are
phospholipids
and
cholesterol.
or
oil.
Instead
it
belongs
CH
2
3
to
cholesterol
components
Animal
a
group
of
substances
called
steroids.
Most
of
a
cholesterol
molecule
CH
2
is
hydrophobic
so
it
is
attracted
to
the
hydrophobic
hydrocarbon
CH
3
CH
tails
in
the
centre
of
the
membrane,
but
one
end
of
the
cholesterol
3
molecule
has
a
hydroxyl
(
OH)
group
which
is
hydrophilic.
This
is
CH
3
attracted
to
Cholesterol
in
the
the
phosphate
molecules
are
heads
on
therefore
the
periphery
positioned
of
the
between
membrane.
phospholipids
membrane.
HO
The
hydrophilic
amount
membranes
▲
of
cholesterol
in
animal
cell
membranes
of
vesicles
that
hold
neurotransmitters
Figure 11 The structure of cholesterol
of
32
varies.
In
the
hydrophobic
30%
of
the
lipid
in
the
membrane
is
cholesterol.
at
synapses
as
much
1 . 4
M e M b r A n e
t r A n s P o r t
The role of cholesterol in membranes
Cholesterol in mammalian membranes reduces
membrane uidity and permeability to some solutes.
Cell
of
membranes
matter.
liquid,
but
Overall
free
The
to
The
the
the
of
If
of
is
exactly
hydrocarbon
phosphate
uid
as
to
any
tails
heads
of
the
usually
act
components
as
a
permeability
hydrogen
curve
vesicles
the
to
into
a
during
uid
and
the
so
Ho wev er
of
hyd r o p hi l ic
to
i ts
conca v e
but
r eg ul a r
ui di ty
Due
they
if
needs
more
of
the
pa c ki n g
it
a ls o
s ha pe
s ha pe ,
it
three
behave
like
a
states
as
a
solid.
membrane
are
of
whi c h
he l ps
able
to
uid
be
hydr oc ar bon
al s o
ca n
h e lp
the
t a i ls
and
m o t io n
re duc e s
s odi u m
the
restricted.
m ol e c ul a r
in
control
enough
c r ys t a ll iz in g
It
as
ch ol e st e r ol
not
t he
r es t r ic t s
such
carefully
less
would
them
me m br a ne .
p ar ti cle s
be
be
were
within
p re ven t s
the
to
would
they
substances
mo l e cule s ,
soli d .
ions.
membranes
too
through,
cell
disrupts
therefore
cell
were
pass
the
phospholipid
behaving
to
animal
they
substances
Cholesterol
and
correspond
hydrophilic
membrane
uidity
movement
of
not
move.
controlled.
what
do
hydrophobic
io ns
the
and
m e m bra n e s
f or m a t i on
of
end o cy tos is .
1.4 Mma ap 
Understanding
Applications
➔
Par ticles move across membranes by simple
➔
Structure and function of sodium–potassium
diusion, facilitated diusion, osmosis and
pumps for active transpor t and potassium
active transpor t.
channels for facilitated diusion in axons.
➔
The uidity of membranes allows materials to
➔
Tissues or organs to be used in medical
be taken into cells by endocytosis or released
procedures must be bathed in a solution with
by exocytosis.
the same osmolarity as the cytoplasm to
➔
Vesicles move materials within cells.
prevent osmosis.
Nature of science
➔
Experimental design: accurate quantitative
measurements in osmosis experiments
Skills
➔
Estimation of osmolarity in tissues by bathing
samples in hypotonic and hyper tonic solutions.
are essential.
33
1
C E L L
B I O L O G Y
Endocytosis
outside of cell
endocytosis
The uidity of membranes allows materials to be taken
into cells by endocytosis or released by exocytosis.
cell interior
A
vesicle
Vesicles
They
are
around
of
a
a
small
To
very
and
this
a
Vesicles
method
Figure
of
1
Vesicles
outside
the
be
of
It
a
cell
from
in
of
uid
inside.
eukaryotic
are
happen
cells.
constructed,
because
surrounded
by
a
of
moved
the
uidity
membrane
to
by
is
into
a ls o
p as s
are
is
the
off
the
in
pulled
from
the
membrane
rest
carry
out
a
small
on
was
cell.
piece
the
outside
It
is
of
inside
the
called
the
of
plasma
the
cell,
so
plasma
this
is
a
endocytosis.
occurs.
e ndo cy tos i s
the y
membrane
Proteins
formed
that
process
large
a
off.
pinching
p l a ce nta ,
in
of
ATP
.
material
ca nno t
take
droplet
They
can
structures
vesicle
the
antibod i e s ,
cells
a
present
cells.
This
region
by
The
but
the
of
pinched
materials
in
that
in
including
is
energy
how
cell
feature
small
and
contains
taken
with
normally
allows
formed
taking
the
are
move.
cells.
shows
example,
Some
and
using
can
membrane.
by
which
vesicle,
membrane
membrane
deconstructed.
membrane
process,
of
and
dynamic
then
shape
form
the
sac
spherical
membranes,
change
of
is
are
co nta i n
ofte n
a cr os s
the
p ro te ins
wat e r
c on t a i n
p la sm a
fr om
a bs or be d
i nt o
undi g es ted
the
the
foo d
and
la r g er
so lu t e s
m e m bra n e .
mot h er ’s
fetus
f ro m
m ol e c ul e s
by
pa rti c l es
n e ed ed
For
bl ood ,
e nd oc yt os is .
by
e ndo c yt os is .
Th is
vesicle
happens
Some
and
▲
in
unicel l ul a r
types
of
viruses
whi te
by
o rg a ni sms
b l oo d
ce l ls
end o cy tos i s
a nd
i ncl u di ng
ta ke
in
then
Amoeba
pa t h og e n s
kil l
them,
as
and
Paramecium .
in c l u din g
p ar t
of
ba c t e r ia
the
b ody’s
Figure 1 Endocytosis
response
to
infect i o n.
Vesicle movement in cells
Vesicles move materials within cells.
Vesicles
can
be
cases
it
is
the
cases
it
is
proteins
vesicle
An
The
vesicles
a
into
Golgi
protein
In
of
is
the
the
a nd
bud
its
off
the
materials
vesicle
around
that
membrane
the
ve s icl e
the
na l
by
of
need
the
inside
to
be
vesicle
r ER
the
a nd
a nd
Gol g i
f o r m.
cells.
In
moved.
that
insi de
carr y
to
this
th e
occ u r s
on
th e
has
the
r E R.
th e m
ap pa r at u s ,
W he n
mo ve
c ont e n t s
ri bo s om e s
a ccumul ate s
wi th
apparatus
are
some
In
the
other
reason
for
to
p la sm a
s ec r e t or y
e n dop la s m i c
Ves i c le s
t he
wh i c h
bee n
in
r oug h
Golg i
c o nt a i ni n g
a pp ar a t u s.
p ro ces s es
don e ,
t he
ves i c le s
m em bra n e ,
bu d
where
off
th e
secreted .
growing
proteins
off
of
the
synthe s ize d
fuse
cell,
Phospholipids
into
in
move
mo v i ng
is
(rER)
proteins
protein
the
contents
Protein
reticulum
the
to
movement.
example
cells.
34
used
rER
are
area
and
of
the
synthesized
membrane.
which
rER
the
also
to
next
to
Ribosomes
become
move
plasma
the
plasma
the
on
inserted
membrane
rER
the
into
and
rER
the
needs
become
synthesize
membrane.
membrane.
They
to
increase.
inserted
membrane
Vesicles
fuse
with
it,
bud
each
1 . 4
increasing
This
the
method
area
can
of
also
the
be
plasma
used
to
membrane
increase
by
the
a
very
size
of
small
M e M b r A n e
t r A n s P o r t
outside of cell
amount.
organelles
in
the
exocytosis
cytoplasm
such
as
lysosomes
and
mitochondria.
Vesicles bud o from
Proteins are synthesized
Vesicles bud o from
The Golgi
the Golgi apparatus
by ribosomes and then enter
the rER and carry the
apparatus
and carry the modied
the rough endoplasmic
proteins to the Golgi
modies the
proteins to the plasma
reticulum
apparatus
proteins
membrane
vesicle
ENDOCYTOSIS
EXOCYTOSIS
Part of the plasma
Vesicles fuse
membrane is pulled inwards
with the plasma
A droplet of uid becomes
membrane
enclosed when a vesicle is
The contents of
pinched o
the vesicle are
expelled
Vesicles can then move
through the cytoplasm
The membrane
carrying their contents
then attens
out again
▲
Figure 2
Exocytosis
The uidity of membranes allows materials to be taken
into cells by endocytosis or released by exocytosis.
Vesicles
the
can
plasma
be
used
outside
Digestive
enzymes
polypeptides
Golgi
in
the
In
this
the
cell.
are
the
materials
contents
This
and
case
then
the
from
are
from
are
process
released
enzymes
apparatus
exocytosis.
release
membrane,
therefore
the
to
then
is
gland
release
is
to
a
vesicle
the
by
by
to
with
membrane
exocytosis.
the
rER,
membrane
referred
fuses
and
exocytosis.
cells
the
If
outside
called
synthesized
carried
cells.
as
The
processed
in
vesicles
secretion,
in
for
because
cell interior
a
▲
useful
substance
Exocytosis
materials.
unicellular
called
a
can
An
is
being
also
used
example
organisms.
contractile
membrane
be
for
released,
is
to
the
The
expel
by
is
which
a
waste
waste
removal
water
vacuole,
expulsion
not
of
is
then
exocytosis.
products
excess
loaded
into
or
water
a
can
unwanted
from
vesicle,
moved
This
Figure 3 Exocytosis
product.
to
be
the
the
cells
of
sometimes
plasma
seen
quite
easily
in
contractile
Paramecium,
showing
a
using
a
microscope.
contractile
vesicle
at
Figure
each
4
end
shows
of
the
a
drawing
of
Paramecium
vesicle
cell.
Simple diusion
mouth
Par ticles move across membranes by simple diusion,
facilitated diusion, osmosis and active transpor t.
Simple
across
diffusion
is
one
of
the
four
methods
of
moving
endoplastule
particles
membranes.
endoplast
Diffusion
happens
is
the
spreading
because
the
out
particles
of
particles
are
in
in
liquids
continuous
and
gases
random
that
motion.
contractile
vesicle
More
area
particles
of
There
lower
is
move
from
an
concentration
therefore
concentration
–
a
a
net
area
than
of
move
movement
movement
higher
down
in
from
the
concentration
the
the
opposite
higher
to
concentration
to
an
direction.
the
lower
gradient.
Living
▲
Figure 4 Drawing of Paramecium
35
1
C E L L
B I O L O G Y
organisms
do
not
have
to
use
energy
to
make
diffusion
occur
so
it
is
a
toK
passive
process.
ca h am aa jiy
Simple
may xiv
between
i?
if
the
diffusion
the
across
phospholipid
particles
membranes
phospholipids
such
as
bilayer
oxygen
in
is
can
the
involves
particles
membrane.
permeable
diffuse
to
It
the
through
can
passing
only
particles.
easily.
If
happen
Non-polar
the
oxygen
In an experiment to test
concentration
inside
a
cell
is
reduced
due
to
aerobic
respiration
and
whether NaCl can diuse
the
concentration
outside
is
higher,
oxygen
will
pass
into
the
cell
through dialysis tubing, a
through
the
plasma
membrane
by
passive
diffusion.
An
example
is
1% solution of NaCl was
shown
in
gure
6.
placed inside a dialysis tube
and the tube was clamped
shut. The tube containing
the solution was immersed
in a beaker containing
water.
A conductivity meter
was inser ted into the water
surrounding the tubing. If the
Figure 5 Model of diusion with dots representing par ticles
▲
conductivity of the solution
increases,
then the NaCl is
The
centre
of
membranes
is
hydrophobic,
so
ions
with
positive
or
negative
diusing out of the tubing.
charges
cannot
positive
tim / ± 1
and
easily
negative
pass
through.
charges
over
Polar
their
molecules,
surface,
can
which
have
diffuse
at
partial
low
rates
particles
such
civiy
between
1
the
phospholipids
of
the
membrane.
Small
polar
as
± 10 mg 
urea
0
81.442
30
84.803
60
88.681
90
95.403
120
99.799
or
ethanol
pass
through
more
easily
than
largeparticles.
the cornea has no blood supply so its cells obtain
oxygen by simple diusion from the air
high concentration
of oxygen in the air
air
high concentration
uid (tears)
of oxygen in the tears
Noting the uncer tainty of the
cell on outer
that coat the cornea
conductivity probe,
discuss
surface of the
cornea
whether the data suppor ts
the conclusion that NaCl is
diusing out of the dialysis
oxygen passes through
tubing.
lower concentration
the plasma membrane by
of oxygen in the cornea
simple diusion
cells due to aerobic respiration
Figure 6 Passive diusion
▲
daa-a qi:
Diusion of oxygen in the cornea
Oxygen
cornea
concentrations
of
anesthetized
were
1
measured
rabbits
at
in
different
the
outer
surface.
These
the
thickness
into
the
aqueous
the
The
rabbit’s
cornea
is
400
a)
behind
μm)
thick.
The
graph
Describe
the
trend
to
the
of
eye
The
20
36
structure
oxygen
You
may
before
7)
shows
look
answering
concentration
kilopascals
to
(20kPa).
in
in
the
oxygen
cornea
from
the
surface.
[2]
micrometres
(gure
need
in
inner
Suggest
reasons
the
normal
at
a
is
in
the
trend
in
oxygen
thecornea.
[2]
diagram
questions.
air
for
the
concentration
measurements.
in
the
b)
(400
cornea
were
outer
cornea.
rabbit
distances
measurements
humor
the
[1]
concentrations
continued
of
millimetres.
2
from
Calculate
3
a)
Compare
the
the
aqueous
oxygen
concentrations
humorwith
concentrations
in
the
in
the
cornea.
[2]
1 . 4
b)
Using
the
whether
cornea
Using
as
a
the
to
a)
Predict
lenses
the
b)
the
data
method
graph,
deduce
the
20
humor.
graph,
moving
effect
of
oxygen
[2]
evaluate
substances
diffusion
in
large
[2]
wearing
contact
concentrations
in
cornea.
Suggest
[1]
how
this
effect
could
t r A n s P o r t
the
organisms.
the
on
the
diffusesfrom
aqueous
in
of
multicellular
5
in
aPk/negyxo fo noitartnecnoC
4
data
oxygen
M e M b r A n e
be
15
10
5
minimized.
6
The
range
how
bars
much
the
[1]
for
each
data
point
measurements
indicate
varied.
0
Explain
the
reason
for
showing
range
0
barson
the
graph.
100
200
300
400
[2]
distance from outer surface of cornea/µm
▲
Figure 7
Facilitated diusion
Par ticles move across membranes by simple diusion,
facilitated diusion, osmosis and active transpor t.
Facilitated
across
Ions
can
the
and
pass
other
into
plasma
diameter.
and
diffusion
walls
passes
both.
Because
a
are
of
these
higher
the
four
cannot
if
channels
methods
of
the
for
and
of
moving
channel
a
Cells
in
are
to
can
the
for
particles
phospholipids
them
with
protein.
ensure
lower
that
ions,
pass
a
only
or
control
in
and
one
the
type
ions,
process
of
and
(a)
of
membrane,
the
types
membrane
diffuse
narrow
diameter
potassium
through
which
through
very
The
concentration,
plasma
substances
holes
of
sodium
particles
to
between
channels
consist
example
help
placed
which
diffuse
are
channels
channel
diffusion.
control
there
These
the
concentration
facilitated
can
of
that
cells
through,
synthesized
they
of
properties
but
not
out
membrane.
particle
called
one
particles
or
The
chemical
from
is
membranes.
is
channel
in
this
way
out.
(b)
Figure
8
viewed
shows
from
the
the
structure
side
and
of
from
a
channel
the
for
outside
of
magnesium
the
ions,
membrane.
The
Membrane
structure
of
magnesium
the
protein
ions
are
making
able
to
up
pass
the
channel
through
the
ensures
hole
in
that
the
only
centre.
Cytoplasm
Osmosis
Par ticles move across membranes by simple diusion,
facilitated diusion, osmosis and active transpor t.
Osmosis
is
one
membranes.
of
the
four
methods
of
moving
particles
across
▲
Figure 8 Magnesium channel
37
1
C E L L
B I O L O G Y
Water
is
able
Sometimes
in
and
but
at
out
is
other
direction
Osmosis
or
is
dissolve
Figure 9
water
of
the
water
therefore
than
is
a
to
have
regions
net
because
with
no
Osmosis
can
cells
increase
reabsorb
its
a
of
have
water
in
all
cells
hair
the
which
regions
of
pass
to
cells
channel
therefore
an
pass
in
is
of
with
movement
free
of
to
this
it
is
passive
occur.
despite
which
are
only
greatly
the
cells
that
soil.
slightly
le.
being
bilayer.
kidney
from
single
move
there
concentration
phospholipid
water
aquaporin
through
the
molecules,
Examples
absorb
osmosis.
concentration
make
the
one
is
Substances
bonds
solute
aquaporins,
water.
that
in
water
movement,
in
movement
to
freely.
moving
concentration
Because
lower
though
called
the
restrict
This
cells
net
molecules
directly
because
to
no
move
(solutes).
solute
water
most
movement
in
bonds
higher
of
expended
channels
root
point,
a
concentration.
enough
is
intermolecular
concentration.
from
be
net
water
These
with
permeability
and
molecules,
to
there
This
in
of
molecules
molecules
differences
forming
solute
solute
water
membrane
to
out
water
and
other.
molecules.
water
small
the
and
of
more
dissolved
by
in
same
concentration
has
happen
are
the
times
Regions
lower
higher
narrowest
water
lower
energy
hydrophilic,
At
a
with
movement
regions
Some
molecules.
move
number
due
substances
▲
to
the
wider
Positive
than
charges
+
at
this
point
in
the
channel
prevent
protons
(H
)
from
passing
through.
Active transport
Par ticles move across membranes by simple diusion,
facilitated diusion, osmosis and active transpor t.
Active
transport
is
one
of
the
four
methods
of
moving
particles
across
membranes.
Cells
sometimes
higher
against
pump
the
type
needed
transport
process.
Active
of
to
uses
10
enters
the
The
though
Less
The
commonly,
there
is
already
is
called
produces
is
carried
its
out
proteins.
proteins
membranes
therefore
ATP
own
by
as
allowing
not
is
cells
a
already
is
a
absorbed
sometimes
larger
the
cell
ATP
proteins
to
of
and
transport.
energy
of
membranes
the
diffusion
active
supply
globular
The
is
called
supply
by
in
cell
energy
Most
for
this
respiration.
contain
the
many
content
of
illustrates
pump
After
this,
pump
and
how
protein
change
the
the
protein
ion
a
pump
and
to
or
pump
shown
can
the
protein
reach
protein
molecule
protein
far
takes
can
as
The
a
place
pass
returns
transports
works.
as
to
to
its
Vitamin
molecule
central
using
the
its
B
intoE.
ion
chamber.
energy
opposite
original
or
A
from
side
of
the
conformation.
coli
is
active
membranes,
cells
control
12
38
there
substance
precisely.
membrane
Figure 10 Action of a pump protein
even
outside.
though
across
It
substance
pump
conformational
▲
than
gradient.
even
out.
cell
pump
Figure
ATP
.
it
a
Every
cytoplasm
out,
movement
carry
called
different
substances,
inside
outside.
transport
usually
in
concentration
substances
concentration
This
take
concentration
1 . 4
M e M b r A n e
t r A n s P o r t
o x yg
nig
Phpha
/%
/%
api/μm
daa-a qi: Phosphate absorption in barley roots
Roots
were
cut
off
from
barley
plants
and
were
used
to
investigate
1
g
phosphate
air
was
in
each
in
the
absorption.
bubbled
case,
air
1
but
Table
Describe
on
the
the
rate
the
Explain
21.0to
effect
the
0.1
of
the
on
of
of
phosphate
concentration
and
solutions
was
nitrogen
phosphate
the
was
the
oxygen
in
was
the
roots.Youshould
In
0.07
99.7
0.15
0.9
99.1
0.27
2.1
97.1
0.32
21.0
79.0
0.33
only
use
T
able 1
▲
0.4
[3]
oxygen
absorption.
99.9
0.3
below21.0 %
youranswer.
reducing
phosphate
by
0.1
same
varied
absorption
concentration
percentage
your
1
h
and
results.
absorption
table
in
oxygen
rate
reducing
phosphate
effect
of
The
the
placed
phosphate
percentage
shows
from
were
The
through.
1
of
information
2
through.
bubbled
measured.
Roots
0.3
from
answer
you
Phosphate
0.2
shoulduse
as
much
biological
understanding
as
possible
absorption
of
1
/µmol g
howcells
absorb
mineral
ions.
1
0.1
h
[3]
0
An
experiment
was
done
to
test
which
method
of
membrane
0
2
4
6
8
10
3
transport
placed
in
the
bubbling
DNP
was
were
added.
with
Discuss
DNP
the
thegraph
theroots
11
a
phosphateby
4
the
roots
blocks
shows
reason,
to
absorb
as
phosphate.
before,
the
the
with
of
a
production
results
of
the
the
transport.
that
can
method
of
be
roots
21.0 %
ATP
DNP concentration / mmol dm
were
oxygen
by
Figure 11 Eect of DNP concentration
▲
on phosphate absorption
called
aerobic
cell
experiment.
whether
active
Roots
substance
of
or
conclusions
the
absorb
concentrations
diffusion
about
to
solution
Varying
Figure
Deduce,
by
phosphate
through.
respiration.
3
used
absorbed
drawn
membrane
the
[2]
from
the
transport
data
in
used
by
phosphate.
[2]
Active transport of sodium and potassium in axons
Structure and function of sodium–potassium pumps for active transpor t.
An
axon
consists
inside.
in
is
of
part
a
Axons
diameter,
function
part
of
called
is
the
a
of
a
neuron
tubular
can
but
to
be
as
nerve
as
long
convey
body
to
(nerve
membrane
narrow
as
one
in
as
one
micrometre
from
electrical
one
form
nerve
sodium
and
involves
then
rapid
potassium
These
movements
being
through
ions
movements
across
occur
by
the
sodium
and
The
axon.
They
occur
by
between
The
active
because
the
inside
concentration
transport,
potassium
of
pumped
it
in
the
in.
axon
Each
uses
follows
three
one
and
time
ATP
.
a
repeating
sodium
two
the
The
ions
potassium
pump
cycle
goes
consists
steps:
interior
the
pump
axon
pump
of
carried
and
of
the
three
attach
pump
is
sodium
to
their
open
ions
to
the
enter
binding
inside
the
sites.
ATP
transfers
the
and
out
pump;
a
phosphate
this
causes
group
the
from
pump
to
itself
change
concentration
outside
gradients
protein.
axon;
potassium
shape
gradients
out
cycle
pump
result
facilitated
to
channels.
this
these
of
of
2
diffusion
that
pumped
round
of
steps
impulse.
impulse
membrane.
of
being
1
A
sodium–potassium
cycle
ions
Their
rapidly
an
The
and
cytoplasm
metre.
messages
another
cell)
with
by
are
a
of
built
and
the
interior
is
then
closed.
the
up
sodium–
3
The
interior
outside
ions
are
of
of
the
the
pump
axon
and
opens
the
to
three
the
sodium
released.
39
1
C E L L
4
Two
B I O L O G Y
potassium
enter
and
ions
attach
to
from
their
outside
binding
can
then
6
The
sites.
of
interior
the
axon
released;
5
Binding
of
potassium
causes
release
of
change
open
group;
shape
to
the
this
again
inside
causes
so
of
that
the
it
the
is
pump
again
the
pump
the
sodium
two
ions
opens
to
the
potassium
can
then
inside
ions
enter
are
and
bind
the
to
phosphate
of
and
the
pump
again
(stage
1).
to
only
axon.
1
2
3
p
p
ATP
ADP
4
5
6
p
p
Figure 12 Active transpor t in axons
▲
Facilitated diusion of potassium in axons
Structure and function of sodium–potassium pumps for active transpor t and
potassium channels for facilitated diusion in axons.
A
nerve
sodium
impulse
and
membrane.
diffusion
Each
as
a
subunits
allows
The
40
special
with
a
is
0.3
example
narrow
ions
nm
and
channels
channel
potassium
pore
sodium
of
wide
of
axon
facilitated
be
of
described
in
diffusion.
four
protein
them
either
that
direction.
narrowest.
Potassium
but
to
a
too
potassium
will
between
its
the
by
facilitated
pass
at
across
occur
consists
pore
to
movements
ions
movements
Potassium
potassium
rapid
potassium
These
through
channels.
here
involves
then
when
shell
large
through,
ion
and
ions
they
of
to
water
pass
the
the
ar e
thr o ug h
bonds
the
and
a
ion
ion
has
form
seri e s
part
passed
of
of
the
tha t
po re .
the
wa te r
a mino
thi s
0. 3
To
them
p a ss
p ot a ss i um
mo l ec ul e s
acid s
After
pa r t
nm,
bo n de d
m a ke s
te mpor a ri ly
p or e .
thr o ug h
th a n
be come
the
b e twe en
surro und i ng
and
s mal le r
the y
mo l e cule s
bond s
broken
narrowest
s l i g htly
dis s o l v e
in
the
of
a re
b e t wee n
the
pota s si u m
t he
por e ,
1 . 4
it
can
again
become
a s s ocia te d
wi th
a
sh e l l
of
positive
M e M b r A n e
charges
channels
watermolecules.
impulse
Other
positively
charged
ions
that
we
might
pass
through
the
pore
are
either
too
there
large
to
This
or
are
acids
in
too
small
the
narrowest
to
form
bonds
part
of
with
the
cannot
shed
explains
their
the
shell
specicity
of
of
water
the
Voltages
imbalance
the
channels
across
of
in
axons
membranes
positive
membrane.
If
an
and
are
are
has
a
positive
nerve
charges
causes
potassium
ions
to
channels
diffuse
to
open,
through.
to
the
be
channel
due
to
rapidly
an
extra
closes
again.
globular
This
protein
molecules.
voltage
due
negative
axon
more
or
ball,
attached
by
a
exible
chain
of
pump.
amino
Potassium
potassium
during
so
subunit
This
inside,
stage
the
pore,
seems
they
than
one
relatively
potassium
However,
amino
are
At
t
allowing
through
outside
closed.
expect
inside.
to
are
t r A n s P o r t
to
gated.
an
pore
charges
relatively
pore,
across
more
acids.
which
The
it
opening.
ball
does
The
channel
state.
is
t
within
ball
potassium
This
can
in
the
open
milliseconds
remains
returns
shown
inside
to
gure
in
its
of
place
the
until
original
the
closed
13.
net negative charge
1
channel closed
+
+
+
2
+
+
+
+
channel briey open
-
+
-
-
-
-
-
-
-
outside
+
+
+
+
+
+
+
+
+
+
+
+
+
++
-
-
-
+
-
-
-
-
-
inside of axon
-
chain
net negative charge inside
+
K
ball
net positive
ions
the axon and net positive
charge
charge outside
3
channel closed by ‘ball and chain’
+
+
+
+
+
+
+
▲
+
hydrophobic core
hydrophilic outer
of the membrane
parts of the membrane
Figure 13
eimai  maiy
Estimation of osmolarity in tissues by bathing samples in hypotonic and
hyper tonic solutions.
Osmosis
water.
is
Glucose,
ions
due
These
are
to
sodium
all
solutes
solutes
are
ions,
that
form
potassium
osmotically
bonds
osmotically
active
ions
and
with
and
chloride
solutions
units
is
about
are
often
used
in
osmosis
experiments.
many
different
osmotically
active
The
300
isotonic
a
tissue.
osmolarity
concentration
of
of
a
solution
osmotically
is
the
osmolarity.
total
active
are
osmoles
osmolarity
or
of
milliosmoles
human
tissue
mOsm.
solution
A
has
hypertonic
the
same
solution
osmolarity
has
a
higher
solutes.
osmolarity
The
it
normal
Cells
as
contain
measuring
of
An
them
for
(mOsm).
active.
solutes.
The
in
and
If
hypertonic
a
hypotonic
samples
and
of
a
solution
tissue
hypotonic
are
has
a
lower
bathed
solutions,
and
41
1
C E L L
B I O L O G Y
measurements
water
enters
deduce
are
or
what
taken
leaves
to
the
nd
out
tissue,
concentration
of
it
whether
is
isotonic
possible
solution
to
would
be
tissue.
the
results
4
daa-a qi: Osmosis in
plant tissues
If
samples
of
plant
tissue
are
bathed
in
salt
and
the
therefore
The
from
Explain
nd
data-based
the
an
out
the
experiment
reasons
mass
change
rather
mass
change
in
for
of
using
than
grams
osmolarity
questions
in
the
below
this
type.
percentage
actual
this
type
of
or
experiment.
sugar
or
solutions
decrease
in
for
a
mass
short
is
time,
due
any
almost
of
give
[2]
increase
entirely
to
40
water
entering
or
leaving
the
cells
by
osmosis.
+
+
+
+
+
Figure14
shows
the
percentage
mass
change
+
+
+
30
+
PINE
of
four
tissues,
when
they
were
bathed
in
salt
KERNEL
solutions
of
different
20
concentrations.
Sodium chloride
1
a)
State
whether
water
moved
into
or
out
10
concentration
3
of
the
tissues
at
0.0
mol
dm
sodium
%
3
/ mol dm
0
chloride
solution.
0.1
Mass
[1]
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
change
BUTTERNUT
10
b)
State
whether
water
moved
into
or
out
SQUASH
3
of
the
tissues
at
1.0
mol
dm
sodium
20
chloride
solution.
SWEET
[2]
POTATO
30
2
Deduce
which
concentration
how
you
tissue
in
its
reached
had
the
lowest
cytoplasm.
your
solute
Include
conclusion
40
in
CACTUS
50
your
3
answer.
Suggest
[2]
reasons
concentration
The
be
experiment
repeated
plant
tissue
from
homogeneous
without
in
using
for
the
between
the
tubers,
around
tough
the
in
solute
tissues.
data-based
potato
and
differences
the
question
or
world
enough
[3]
any
be
Figure 14 Mass changes in plant tissues bathed in
salt solutions
5
can
not
is
the
the
so
mass,
handled
tissue
to
get
long
such
a
in
that
as
the
solutions
signicant
another
mass
factor
for
affects
with
a
following
Dilute
a
solution
on
2
the
Obtain
are
partner
or
group
how
you
could
do
You
in
might
your
gives
things:
1
mol
to
dm
obtain
choose
to
be
experimental
one
idea
turgidity
of
could
used.
for
plant
more
inventive
approach.
measuring
tissue,
but
Figure
changes
other
sodium
the
chloride
concentrations
be
samples
similar
of
a
enough
plant
to
tissue
each
shown
that
other
to
°
give
angle gives
results.
measure
plant tissue
of turgidity
Ensure
dry
and
that
when
end
the
surface
nding
of
the
their
of
the
mass,
tissue
both
samples
at
the
is
start
experiment.
weight
4
Ensure
apart
from
bathing
42
that
all
salt
variables
are
kept
concentration
solution.
of
constant,
the
▲
Figure 15 Method of assessing turgidity
of plant tissue
15
to
the
methods
graph.
comparable
3
but
the
decomposition!
3
1
long
change,
disintegrating.
6
Discuss
Leave
enough
other
that
to
▲
1 . 4
M e M b r A n e
t r A n s P o r t
expima ig
Experimental design: accurate quantitative
measurements in osmosis experiments are essential.
An
ideal
experiment
interpretation.
doubts
and
can
or
or
be
This
●
uncertainties.
uncertainties,
a
can
be
if
than
used
have
drawn
only
from
experiments
design
should
Repeats
needed,
are
best
of
an
one
the
there
then
provides
reasonable
results
are
experiment
is
without
some
rigorous,
strong
any
doubts
these
evidence
for
All
might
that
with
and
all
be
taken
only
as
quantitative
accurate
meters
other
affect
the
experiment:
as
these
possible,
other
give
stronger
using
of
under
remaining
the
most
apparatus.
accurately
samples
results
factors
factors
as
or
however
biological
the
an
results.
because
are
factors
be
designing
quality
measurements
controlled,
when
possible
and
vary
most
the
that
be
experiment
appropriate
to
can
descriptive
Measurements
●
In
if
The
should
evidence
●
results
hypothesis.
checklist
Results
●
but
minimized.
against
gives
Conclusions
are
the
quantitative
variable.
experiment
investigation
must
being
be
allowed
▲
constant.
Figure 16 Replicates are needed for each
treatment in a rigorous experiment
After
doing
checklist.
that
If
you
can
The
would
tissue
an
were
made
done
bathed
evaluate
solution,
evaluation
have
have
are
experiment
and
its
an
in
probably
osmosis
If
lead
can
to
experiment
of
you
were
in
which
for
similar
to
using
to
the
this
design
rigorous.
solute
repeats
very
evaluated
improvements
varying
did
be
more
experiment
solutions
results
design
might
the
design.
the
the
samples
of
plant
concentration,
each
each
you
concentration
other,
your
of
results
reliable.
Designing osmosis experiments
Rigorous experimental design is needed to produce
reliable results: how can accurate quantitative
measurements be obtained in osmosis experiments?
The
osmolarity
Figure
17
sodium
of
shows
chloride
observe
the
1
Peel
off
2
Cut
3
Mount
slide,
tissues
red
solution.
a
The
the
with
of
sample
a
of
epidermis
sample
cover
it,
in
can
onion
consequences
some
out
plant
some
a
slip.
be
cells
investigated
that
following
osmosis
from
about
drop
the
5
of
×
in
had
method
red
scale
can
onion
of
a
in
been
red
many
placed
be
ways.
in
used
a
to
cells.
onion
bulb.
5mm.
distilled
water
on
a
microscope
▲
Figure 1
7 Micrograph of red onion cells placed
in salt solution
43
1
C E L L
B I O L O G Y
4
Observe
inside
5
using
the
Mount
cell
a
microscope.
wall,
another
with
sample
the
of
The
cytoplasm
plasma
should
membrane
epidermis
in
ll
the
pushed
sodium
space
up
chloride
against
it.
solutions
3
with
by
concentration
osmosis
membrane
Plant
are
This
cells
with
method
can
of
be
used
be
to
can
try
0.5mol
volume
away
their
onion
cytoplasm
can
the
pulls
plasmolysed
osmolarity
the
and
of
and
to
cell
process
help
or
be
seen.
that
3%.
pulled
is
The
water
leaves
reduced,
as
shown
away
the
in
from
the
cells
plasma
Figure17.
their
cell
walls
plasmolysis.
cells
the
If
is
wall,
design
other
ensure
or
cytoplasm
the
membranes
cells
easily
of
from
the
used
to
dm
an
in
experiment
which
checklist
design
is
the
in
to
area
the
nd
out
occupied
previous
the
by
section
rigorous.
Preventing osmosis in excised tissues and organs
Tissues or organs to be used in medical procedures must be bathed in a solution
with the same osmolarity as the cytoplasm to prevent osmosis.
Animal
Figure
cells
18
can
be
shows
damaged
blood
cells
by
that
osmosis.
bathed
have
(b)
been
in
solutions
higher
with
osmolarity
(a)
and
the
(c)
same
lower
osmolarity,
osmolarity.
a)
▲
In
a
Figure 18 Blood cells bathed in solutions of dierent solute concentration
solution
solution),
their
with
water
cytoplasm
higher
leaves
osmolarity
the
shrinks
in
cells
by
(a
hypertonic
osmosis
volume.
The
so
used,
which
osmolarity
plasma
membrane
does
not
change,
so
indentations,
which
are
sometimes
(hypotonic),
and
swell
ruptured
Both
In
a
the
up.
solution
cells
They
plasma
hypertonic
take
may
with
in
water
eventually
membranes
and
lower
by
hypotonic
osmolarity
saline
red
human
osmolarity
enter
and
remain
any
an
the
leave
healthy.
human
isotonic
Usually
44
as
an
cells,
but
cells
the
It
tissues
solution
at
the
therefore
and
solution
isotonic
a
(isotonic),
cells
is
in
organs
during
sodium
same
be
medical
chloride
an
used
in
many
medical
It
can
be:
to
intravenous
a
patient’s
blood
system
drip.
●
used
to
rinse
●
used
to
keep
areas
skin
grafts.
wounds
and
skin
abrasions.
of
damaged
skin
moistened
therefore
to
same
●
used
●
frozen
as
the
basis
for
eye
drops.
molecules
rate
important
to
has
ghosts.
with
water
is
introduced
an
prior
damage
It
(milliOsmoles).
leaving
cell
solutions
safely
via
osmosis
burst,
called
saline.
mOsm
called
●
crenellations.
normal
300
it
procedures.
develops
called
about
area
Normal
of
is
of
so
they
for
bathed
hearts,
in
procedures.
solution
is
have
the
to
the
consistency
kidneys
to
be
and
other
transported
transplant
to
operation
of
slush
donor
the
is
to
for
packing
organs
hospital
be
that
where
done.
1 . 5
▲
t H e
o r I G I n
o f
c e l l s
Figure 19 Donor liver packed in an isotonic medium, surrounded by isotonic slush. There is a worldwide shor tage of donor
organs – in most countries it is possible to register as a possible future donor
1.5 th igi  
Understanding
Applications
➔
Cells can only be formed by division of
Evidence from Pasteur ’s experiments that
➔
pre-existing cells.
spontaneous generation of cells and organisms
➔
The rst cells must have arisen from
does not now occur on Ear th.
non-living material.
➔
The origin of eukaryotic cells can be explained
Nature of science
by the endosymbiotic theory.
Testing the general principles that underlie the
➔
natural world: the principle that cells only come
from pre-existing cells needs to be veried.
Cell division and the origin of cells
Cells can only be formed by division of pre-existing cells.
Since
the
produced
is
very
The
1880s
by
there
division
strong
and
implications
trillions
of
cells
is
of
in
has
of
a
been
discussed
the
our
a
theory
pre-existing
in
the
hypothesis
bodies,
each
in
cell.
biology
The
nature
are
of
that
science
remarkable.
one
was
cells
evidence
panel
If
formed
for
we
can
this
only
below.
consider
when
be
hypothesis
a
the
previously
45
1
C E L L
B I O L O G Y
existing
cell
divided
in
two.
Before
that
all
of
the
genetic
material
in
toK
the
nucleus
nucleus
was
with
a
copied
full
so
that
both
complement
of
cells
formed
genes.
We
by
can
cell
trace
division
the
had
origin
of
a
cells
Wha  w gai, a wha  w ,
in
the
body
back
to
the
rst
cell
–
the
zygote
that
was
the
start
of
our
wh w am mhig?
lives,
produced
by
the
fusion
of
a
sperm
and
an
egg.
When Dr Craig Venter ’s team
Sperm
and
egg
cells
were
produced
by
cell
division
in
our
parents.
We
announced that they had succeeded
can
trace
the
origins
of
all
cells
in
our
parents’
bodies
back
to
the
zygote
in transplanting the synthetic genome
from
which
they
developed,
and
then
continue
this
process
over
the
from one bacterium into another
generations
of
our
human
ancestors.
If
we
accept
that
humans
evolved
bacterium in the journal Science some
from
pre-existing
ancestral
species,
we
can
trace
the
origins
of
cells
back
ethicists responded by questioning
through
hundreds
of
millions
of
years
to
the
earliest
cells
on
Earth.
the language of calling it the creation
There
is
therefore
a
continuity
of
life
from
its
origins
on
Earth
to
the
cells
of a “synthetic cell”:
in
our
bodies
In
2010
today.
The science is ying 30,000 feet over
the public’s understanding ... Scientists
can be their own worst enemy by using
words like “clone” or “synthetic life”.
cell,
of
but
a
there
this
were
cell
bacterium
few
deliberate
of
different
reports
was
not
(Mycoplasma
changes.
that
biologists
entirely
new.
mycoides)
This
DNA
was
was
had
The
created
base
the
sequence
synthesized
transferred
to
rst
of
articial
the
articially,
DNA
with
pre-existing
a
cells
G Mg,   Amia
a
type
of
bacterium
( Mycoplasma
capricolum),
which
was
Ja  bihi
effectively
Frankly, he’s describing it in a way
that’s drumming up controversy more
an
converted
extreme
new
cells
form
of
remains
into
Mycoplasma
genetic
an
mycoides.
modication
insuperable
and
challenge
This
the
at
process
creation
the
was
of
therefore
entirely
moment.
than characterising it accurately. His
claim that we’ve got the rst self-
replicating life form whose parent is a
Aiviy
computer, that’s just silly.
th   siphim
It misuses the word “parent”. The
The Greek coin in gure 2 depicts a Silphium plant, which grew in a small par t
advance here needs to be described
of what is now Libya and was highly prized for its medicinal uses, especially
in sane and accurate ways. What
as a bir th control agent. It seems to have been so widely collected that within a
he's managed to do is synthesise a
few hundred years of the ancient Greeks colonizing Nor th Africa it had become
genome much larger than any genome
extinct. Rather than arising again spontaneously, Silphium has remained extinct
that’s been synthesised from scratch
and we cannot now test its contraceptive proper ties scientically. How can we
before.
prevent the loss of other plants that could be of use to us?
Ggy Kaik , Haig Ii
rah sha
▲
▲
Figure 1 Synthetic Mycoplasma bacteria
46
Figure 2 An ancient Greek coin, showing Silphium
1 . 5
t H e
o r I G I n
o f
c e l l s
Spontaneous generation and the origin of cells
Verifying the general principles that underlie the natural world: the principle that
cells only come from pre-existing cells needs to be veried.
Spontaneous
organisms
philosopher
that
a
plant
where
this
it
as
an
the
dew
faeces
Swiss
not
of
had
In
and
the
or
16th
astrologer
living
was
reported
up
and
from
soil
described
formed
the
hair,
century
the
Paracelsus
Some
biologists
spontaneous
by
access
esh
or
German-
of
spontaneous
and
eels
from
water,
air
or
of
is
easy
to
see
generation
how
could
ideas
have
of
decaying
had
been
when
the
and
cells
discovered
biologists
come
from
of
sexual
the
17th
reproduction
century
was
onwards
not
experiments
arise
from
showed
meat
if
to
test
non-living
that
ies
maggots
were
the
only
allowed
that
come
it.
Lazzaro
Spallanzani
A
cell
No
could
is
a
highly
others
then
open
containers
to
left
sealed
the
air.
open
four
of
Organisms
but
not
in
tissue
rotting
in
and
grew
the
se c t i on
of
from
there
the
are
experiments
other
reasons
accepting
that
cells
only
cells:
complex
has
structure
been
and
suggested
no
for
from
simpler
subunits.
of
is
known
cells
without
in
a
cell
of
increases
population,
division
in
the
organism
or
occurring.
contact
soup
them
cells
example
Viruses
left
in
are
produced
from
simpler
subunits
eight
but
containers,
evidence
others,
mechanism
number
Redi
in
into
boiled
Pa ste u r ’s
ne xt
the
●
with
o ccur.
the
carried
life
Francesco
developed
to
in
understood.
biologists
theory
matter.
s pont a n e ou s
no w
d e s cr i b e d
e xp er i me n t s
e s t a bli sh e d
and
and
●
out
tha t
not
universally
producing
From
whi ch
d o ub t
does
pre-existing
natural
nature
are
d es i gned
a s k s ,
t h er e
re s pon d ed
matter.
spontaneous
persisted
not
from
Pasteur
●
microorganisms
life
Pa s te ur
if
mice,
for
It
ca r e ful l y
reasonabl e
of
L oui s
th a t
occur
quoted
generation
of
frogs
a i r.
convinced
coul d
sub-topic.
Apart
observations
out
experiments
this
the
swan-necked
generation
from
rema i ned
gene r a ti o n
to
carrying
with
beyond
generation.
being
from
of
Greek
sprung
present
insects
leaves
The
Theophrastus
spontaneous
about
on
formation
matter.
Silphium
animals.
botanist
the
previously
example
falling
of
botanist
called
wrote
is
non-living
and
was
Aristotle
generation
from
they
do
not
consist
of
cells,
and
they
can
the
only
be
produced
they
have
inside
the
host
cells
that
the
infected.
others.
Spontaneous generation and Pasteur ’s experiments
Evidence from Pasteur ’s experiments that spontaneous generation of cells and
organisms does not now occur on Ear th.
Louis
Pasteur
made
a
water
containing
if
broth
was
kept
unchanged,
and
no
this
nutrient
yeast
and
in
a
broth
sugar.
sealed
by
He
boiling
showed
ask,
it
that
then
a
melted
variety
or
other
He
then
passed
air
then
though
a
pad
wool
in
a
tube,
to
lter
out
from
the
air,
including
bacteria
and
of
placed
in
fungi.
If
broth
in
the
pad
of
cotton
wool
sealed
ask,
to
kill
were
large
number
of
as
broth
and
mould
grew
within
36
its
any
most
involved
samples
famous
the
of
of
Pasteur’s
use
of
swan-necked
in
asks
with
it
into
in
some
of
the
present
Fungi
and
but
other
left
others
organisms
the
unboiled
even
after
asks
long
but
periods
not
of
in
time.
broth
it
in
had
the
asks
been
was
in
suggested
contact
was
with
needed
air,
for
in
generation,
yet
no
spontaneous
surface.
some
experiments
broth
broth
organisms
in
ones,
generation
The
bent
3.
hours,
microorganisms
over
the
controls.
spontaneous
the
boiled
appeared
boiled
which
there
and
gure
was
The
a
necks
in
the
the
spores
the
microscopic
soon
particles
of
shown
of
unboiled
cotton
glass
organisms
asks
appeared.
the
shapes,
remained
Pasteur
fungi
of
asks.
long
He
necks
placed
and
of
occurred.
the
Organisms
asks
were
decomposed
the
to
Pasteur
leave
soon
a
snapped
shorter
apparent
in
the
necks
vertical
these
of
neck.
asks
and
broth.
47
1
C E L L
Pasteur
B I O L O G Y
published
subsequently
including
urine
concluded
his
results
repeated
that
and
the
them
milk,
swan
in
1860
with
with
necks
and
other
the
from
liquids
same
and
results.
prevented
He
the
that
air
getting
no
experiments
organisms
time
of
into
organisms
convinced
publication
the
broth
appeared
and
or
other
liquids
spontaneously.
most
biologists,
since
then.
both
at
His
the
Origin of the rst cells
The rst cells must have arisen from non-living material.
If
we
trace
eventually
living
else
all
for
have
It
the
is
a
over
to
long
they
been
there
periods
of
is
cells
it
how
argued
time.
could
that
this
cells
as
must
the
rst
somewhere
hardest
material.
question
complex
as
the
of
cell
material?
structures
can
may
from
non-living
the
structure
complex
we
were
happen
have
cannot
in
a
evolved
arise
series
over
of
by
stages
hundreds
Figure 3 Drawings of Pasteur ’s
of
swan-necked asks
millions
stages
of
could
years.
have
There
Miller
through
a
ammonia.
The
representative
Earth.
and
mixture
carbon
of
of
They
the
Urey
was
discharges
compounds
passed
that
needed
thought
were
of
to
life
simulate
and
were
A
possible
other
produced.
site
compounds
cracks
early
to
acids
and
be
the
used
amino
for
steam
hydrogen
atmosphere
found
for
in
gushing
the
hot
chemicals
represent
source
of
is
for
Earth’s
water
such
as
readily
energy
compounds
the
around
into
(NH
iron
for
the
)
electrode
4
(H
)
2
condenser
cold
water in
cooled water containing
organic compounds
▲
sample taken for
chemical analysis
Figure 4 Miller and Urey’s apparatus
Figure 5 Deep sea vents
the
of
the
rst
vents.
main
carbon
These
characterized
reduced
of
are
by
inorganic
These
supplies
assembly
polymers.
)
of
sulphide.
accessible
hydrogen
▲
some
deep-sea
carrying
3
methane (CH
origin
surface,
ammonia
water vapour
how
polymers
methane,
mixture
Electrical
lightning.
Harold
hypotheses
2. Assembly of carbon compounds into
sugars and amino acids
Stanley
are
occurred.
1. Production of carbon compounds such as
48
from
perhaps
a
years,
These
Earth
non-living
that
Living
on
arisen
gives
of
existed.
arrived
from
evidence
billions
have
have
but
means
over
to
cells
must
answer:
natural
of
cells
Unless
conclusion,
sometimes
but
earliest
Earth.
biologists
by
ancestry
the
universe,
evolution,
▲
on
logical
arisen
has
the
reach
things
in
This
back
of
chemicals
energy,
these
a
carbon
1 . 5
3. Formation of membranes
If
phospholipids
compounds
were
compounds,
into
plasma
the
would
the
form
membrane
different
of
a
to
carbon
shown
cell.
This
chemistry
Living
assembled
that
resembling
small
o f
c e l l s
inheritance
carbon
naturally
have
vesicles
internal
surroundings
rst
have
o r I G I n
4. Development of a mechanism for
amphipathic
Experiments
readily
allowed
other
among
they
bilayers.
bilayers
or
t H e
these
the
and
DNA
and
enzymes
would
from
organisms
DNA
have
that
be
of
use
be
able
are
made,
develop.
evolution
It
can
DNA
act
but
as
a
ar e
may
when
store
to
as
pass
need e d .
genes
conundrum
cur r e ntly
enzy me s
is
ne e d ed .
ha v e
R NA
both
g ene s
be en
wa s
ge n es
on
Ho we ve r,
informa ti o n
it
ha ve
ca tal ys ts .
an
the
in
to
for
The
To
sol ut ion
ea r l ie r
sa m e
s e l f- r ep li ca ting
of
o f fsp ri n g,
e n z ym e s
g e ne tic
the
ma de
r ep li c a t e
to
to
t hi s
p ha s e
in
m at e r ia l .
wa y
an d
as
can
i tse l f
catalyst.
Figure 6 Liposomes
▲
Endosymbiosis and eukaryotic cells
The origin of eukaryotic cells can be explained by the
endosymbiotic theory.
The
theory
eukaryotic
of
endosymbiosis
cells.
It
states
prokaryotic
organisms
respiration.
Larger
helps
that
that
to
explain
mitochondria
had
developed
prokaryotes
that
could
the
evolution
were
the
once
process
only
of
respire
of
free-living
aerobic
cell
anaerobically
Aiviy
took
them
smaller
in
by
endocytosis.
prokaryotes
cytoplasm.
As
long
they
as
Instead
allowed
the
smaller
of
them
killing
to
and
digesting
continue
prokaryotes
grew
to
live
and
the
in
Wh i i gi?
their
divided
as
fast
Erasmus Darwin was
as
the
larger
ones,
they
could
persist
indenitely
inside
the
larger
cells.
Charles Darwin’s
According
to
the
theory
of
endosymbiosis
they
have
persisted
over
grandfather. In a poem
hundreds
of
millions
of
years
of
evolution
to
become
the
mitochondria
entitled The Temple of
inside
eukaryotic
cells
today.
Nature, published in 1803,
The
larger
in
symbiotic
a
known
as
supplied
carried
cell.
prokaryotes
a
relationship
mutualistic
with
out
and
food
aerobic
Natural
by
in
smaller
which
the
larger
therefore
The
one.
to
aerobically
both
relationship.
respiration
selection
endosymbiotic
the
The
supply
of
them
smaller
favoured
cells
ones
beneted.
cell
smaller
energy
respiring
would
cell
that
This
had
is
have
would
efciently
were
been
have
to
the
he believed life to have
originated:
Organic Life began
larger
developed
he tells us how and where
this
relationship.
beneath the waves ...
Hence without parent by
spontaneous bir th
Rise the rst specks of
The
endosymbiotic
theory
also
explains
the
origin
of
chloroplasts.
animated ear th
If
a
a
prokaryote
larger
have
cell
that
and
developed
Again,
both
of
had
was
into
the
developed
allowed
the
to
photosynthesis
survive,
chloroplasts
organisms
in
the
of
grow
and
was
divide,
photosynthetic
endosymbiotic
taken
it
in
by
could
eukaryotes.
relationship
would
Has Erasmus Darwin’s
hypothesis that life began in
the sea been falsied?
havebeneted.
49
1
C E L L
B I O L O G Y
original ancestral
prokaryote
Aiviy
evolution of the
nucleus
Bangiomorpha a h
igi  x .
evolution of
The rst known eukaryote
evolution of
photosynthesis
evolution of
and rst known
linear chromosomes,
multicellular organism is
mitosis and meiosis
Bangiomorpha pubescens.
Fossils of this red alga
were discovered in 1,200
million year old rocks
from nor thern Canada. It is
the rst organism known
mitochondria
to produce two dierent
endocytosis
types of gamete –a larger
to produce
sessile female gamete
chloroplasts
and a smaller motile male
gamete. Bangiomorpha is
therefore the rst organism
known to reproduce
sexually. It seems unlikely
evolution of
evolution of
plant cells
animal cells
that eukaryote cell
structure, multicellularity
and sexual reproduction
evolved simultaneously.
What is the most likely
sequence for these
landmarks in evolution?
plant cell
animal cell
(eukaryotic)
▲
(eukaryotic)
Figure 7 Endosymbiosis
Although
and
no
independent
●
longer
mitochondria
They
capable
both
of
have
living
independently,
features
that
suggest
chloroplasts
they
evolved
from
prokaryotes:
have
their
own
genes,
own
70S
on
a
circular
DNA
molecule
like
that
of
prokaryotes.
●
They
some
●
They
their
●
They
and
50
have
their
ribosomes
of
a
size
and
shape
typical
of
prokaryotes.
transcribe
own
can
their
DNA
and
use
the
mRNA
to
synthesize
some
of
proteins.
only
be
chloroplasts.
produced
by
division
of
pre-existing
mitochondria
1 . 6
c e l l
d I V I s I o n
1.6 c  i vii
Understanding
Applications
➔
Mitosis is division of the nucleus into two
The correlation between smoking and incidence
➔
genetically identical daughter nuclei.
of cancers.
➔
Chromosomes condense by supercoiling
during mitosis.
➔
Skills
Cytokinesis occurs after mitosis and is dierent
in plant and animal cells.
➔
Identication of phases of mitosis in cells
➔
viewed with a microscope.
Interphase is a very active phase of the cell
cycle with many processes occurring in the
Determination of a mitotic index from a
➔
nucleus and cytoplasm.
➔
micrograph.
Cyclins are involved in the control of the
cell cycle.
➔
Nature of science
Mutagens, oncogenes and metastasis are
involved in the development of primary and
Serendipity and scientic discoveries: the
➔
secondary tumours.
discovery of cyclins was accidental.
The role of mitosis
Mitosis is division of the nucleus into two genetically
identical daughter nuclei.
The
nucleus
identical
divide
two
genetically
eukaryotic
by
a
can
This
DNA
chromatids
Mitosis
is
required
repair
and
Although
events
is
to
mitosis
four
The
events
that
this
sub-topic.
divide
to
mitosis.
each
with
form
Mitosis
one
of
two
genetically
allows
the
the
nuclei
cell
and
to
therefore
other.
all
of
the
during
each
can
called
converted
DNA
a
the
cells
nucleus
the
single
chromatids.
daughter
during
in
interphase,
from
called
whenever
eukaryotes:
asexual
into
the
molecules,
passes
cell
cells,
occur,
involved
in
to
happens
chromosome
identical
process
daughter
identical
mitosis
replicated.
Each
a
nuclei
into
Before
of
period
DNA
must
be
before
molecule
During
mitosis,
mitosis.
into
one
two
of
these
nucleus.
with
genetically
embryonic
identical
development,
nuclei
growth,
are
tissue
reproduction.
is
a
continuous
phases:
occur
in
process,
prophase,
these
cytologists
metaphase,
phases
are
have
anaphase
described
in
a
divided
and
later
the
telophase.
section
of
▲
Figure 1 Hydra viridissima with a small
new polyp attached, produced by asexual
reproduction involving mitosis
51
1
C E L L
B I O L O G Y
Interphase
Aiviy
Interphase is a very active phase of the cell cycle with
There is a limit to how many times
many processes occurring in the nucleus and cytoplasm.
most cells in an organism can undergo
mitosis. Cells taken from a human
The
cell
cycle
is
the
sequence
and
the
next.
It
has
two
of
events
between
one
cell
division
embryo will only divide between
main
phases:
interphase
and
cell
division.
40 and 60 times, but given that
Interphase
is
a
very
active
phase
in
the
life
of
a
cell
when
many
the number of cells doubles with
metabolic
reactions
o c c u r.
Some
of
these,
such
as
the
reactions
of
each division, it is easily enough to
cell
respiration,
also
occur
during
cell
division,
but
DNA
replication
produce an adult human body. There
in
the
nucleus
and
protein
synthesis
in
the
cytoplasm
only
happen
are exceptions where much greater
during
interphase.
numbers of divisions can occur, such
During
interphase
the
numbers
of
mitochondria
in
the
cytoplasm
increase.
as the germinal epithelium in the
This
is
due
to
the
growth
and
division
of
mitochondria.
In
plant
cells
and
testes. This is a layer of cells that
algae
the
numbers
of
chloroplasts
increase
in
the
same
way.
They
also
divides to provide cells used in sperm
synthesize
cellulose
and
use
vesicles
three
phases,
to
add
it
to
their
cell
walls.
production. Discuss how many times
the cells in this layer might need to
Interphase
consists
of
the
G
the
genetic
phase,
S
phase
and
G
1
divide during a man's life.
In
the
that
do
S
phase
after
not
the
mitosis
progress
cell
both
replicates
the
beyond
new
G
,
all
cells
have
because
they
phase.
2
a
material
complete
are
never
in
set
its
of
going
nucleus,
genes.
to
divide
so
Some
so
do
1
not
need
to
prepare
for
mitosis.
They
enter
a
phase
called
G
which
may
0
be
temporary
or
permanent.
Supercoiling of chromosomes
G2
Mitosis
Chromosomes condense by supercoiling during mitosis.
y
C
to
in
k
e
is
s
mitosis,
the
two
chromatids
that
make
up
each
chromosome
must
N
During
R
S
P
H
Each of the
be
separated
and
moved
to
opposite
poles
of
the
cell.
The
DNA
molecules
A
SE
G1
chromosomes
in
these
chromosomes
are
immensely
long.
Human
nuclei
are
on
average
Cellular contents,
is duplicated
apart from the
less
than
5
µm
in
diameter
but
DNA
molecules
in
them
are
more
than
chromosomes
are duplicated.
50,000
much
µm
long.
shorter
It
is
therefore
structures.
chromosomes
and
it
This
occurs
essential
process
during
is
the
to
package
known
rst
as
stage
chromosomes
condensation
of
into
of
mitosis.
G0
Condensation
make
the
Proteins
▲
by
chromosome
called
chromosomes
Figure 2 The cell cycle
occurs
shorter
histones
help
means
that
with
repeatedly
and
are
wider.
associated
supercoiling
and
coiling
This
the
DNA
process
with
DNA
enzymes
is
in
are
molecule
called
to
supercoiling.
eukaryote
also
involved.
Phases of mitosis
Identication of phases of mitosis in cells viewed with a microscope.
There
tips
are
of
large
growing
chemically
can
be
make
mitosis
52
allow
squashed
microscope
to
to
numbers
roots.
slide.
the
can
to
If
the
a
be
tips
to
are
be
single
that
chromosomes
then
dividing
cells
form
Stains
of
root
bind
in
separated,
to
of
it
a
they
cells
DNA
and
using
To
the
treated
layer
visible
observed
cells
are
stages
on
a
used
of
microscope.
be
is
in
able
to
identify
necessary
them.
section
cells
After
you
using
assign
to
a
them
the
studying
should
be
one
of
the
able
microscope
to
four
understand
or
the
stages
what
is
of
mitosis,
happening
information
to
observe
in
a
in
this
dividing
micrograph
phases.
and
1 . 6
c e l l
d I V I s I o n
Prophase
The chromosomes become
shor ter and fatter by coiling. To
become shor t enough they have
to coil repeatedly. This is called
supercoiling. The nucleolus breaks
down. Microtubules grow from
structures called microtubule
organizing centres (MTOC) to form
▲
Interphase – chromosomes are
▲
a spindle-shaped array that links
visible inside the nuclear membrane
Prophase – nucleoli visible
in the nucleus but no
the poles of the cell. At the end of
individual chromosomes
prophase the nuclear membrane
centromere
MTOC
breaks down
microtubules
nuclear envelope
disintegrates
chromosome
spindle
consisting of two
microtubules
sister chromatids
▲
Early prophase
▲
Late prophase
Metaphase
Microtubules continue to grow
and attach to the centromeres
Metaphase
on each chromosome. The two
plate equator
attachment points on opposite
sides of each centromere allow the
chromatids of a chromosome to
mitotic spindle
attach to microtubules from dierent
poles. The microtubules are all put
under tension to test whether the
▲
Metaphase – chromosomes
▲
Metaphase
attachment is correct. This happens
aligned on the equator and not
by shortening of the microtubules at
inside a nuclear membrane
the centromere. If the attachment is
correct, the chromosomes remain on
the equator of the cell.
Anaphase
At the star t of anaphase, each
centromere divides, allowing
the pairs of sister chromatids to
separate. The spindle microtubules
pull them rapidly towards the
poles of the cell. Mitosis produces
two genetically identical nuclei
Daughter
because sister chromatids are
chromosomes
pulled to opposite poles. This
separate
is ensured by the way that the
▲
Anaphase – two groups of V-shaped
▲
spindle microtubules were
Anaphase
chromatids pointing to the two poles
attached in metaphase.
53
1
C E L L
B I O L O G Y
Telophase
The chromatids have reached
the poles and are now called
chromosomes. At each pole the
chromosomes are pulled into a
tight group near the MTOC and
a nuclear membrane reforms
around them. The chromosomes
uncoil and a nucleolus is formed.
▲
Telophase – tight groups of
▲
Interphase – nucleoli visible
By this stage of mitosis the cell is
chromosomes at each pole, new
inside the nuclear membranes
cell wall forming at the equator
but not individual chromosomes
usually already dividing and the
two daughter cells enter interphase
again.
Cleavage furrow
Nuclear envelope
forming
▲
Telophase
daa-a qi: Centromeres and telomeres
Figure
cells
3
and
centromeres
ends
have
1
of
the
been
have
the
cell
has
State
b)
Explain
In
with
stage
a)
c)
been
In
of
gure
stained
a
with
there
are
green
mitosis
on
3,
the
preceeding
DNA
has
a
uorescent
red
structures
uorescent
that
the
been
pages
stained
called
dye.
show
blue.
At
The
the
telomeres.
These
dye.
cell
was
in,
giving
reasons
answer.
an
how
having
▲
micrographs
chromosomes
your
The
other
mitosis.
stained
Deduce
for
2
the
undergoing
the
even
number
many
the
an
[3]
chromosomes.
chromosomes
reason
even
of
for
body
number
micrograph
of
a
of
cell
there
cells
in
are
in
plants
this
and
cell.
[1]
animals
chromosomes.
in
interphase,
[2]
the
centromeres
Figure 3 Cell in mitosis
d)
are
on
the
other
An
one
is
produce
cycle
a
54
in
the
only
or
nucleus
repeating
in
the
When
cells,
the
of
the
for
germ
of
the
is
telomeres
the
shorter.
telomeres,
sequences
cells
that
telomere
Predict
shortening
on
[2]
replicated
the
are
this.
lengthens
base
DNA
end
becomes
animal
and
reasons
telomerase
active
gametes.
body
the
Suggest
short
telomere
plant
of
called
many
enzyme
so
side.
enzyme
adding
side
of
of
are
DNA.
used
during
the
to
the
cannot
by
This
be
cell
replicated,
consequences
telomeres.
for
[2]
1 . 6
c e l l
d I V I s I o n
The mitotic index
Determination of a mitotic index from a micrograph.
The
mitotic
in
tissue
a
using
this
index
and
is
the
the
total
ratio
between
number
of
the
number
observed
cells.
of
cells
in
mitosis
It
can
be
calculated
that
has
developed
equation:
number of cells in mitosis
___
Mitotic
index
=
total
Figure
from
be
4
a
is
a
micrograph
Leydig
calculated
and
To
also
nd
the
the
in
the
the
total
number
mitotic
proliferating
●
cell
if
a
of
testis.
cells
the
of
these
prepared
andexamine
number
cells
The
in
of
from
number
index
rapidly,
Obtain
of
cells
a
tumour
mitotic
of
cells
the
for
this
tumour
micrograph
is
can
counted
meiosis.
the
part
of
a
instructions
slide
index
in
of
an
meristematic
root
can
onion
region,
tip
be
or
i.e.
where
garlic
a
cells
are
used:
root
region
of
tip.
Find
rapid
celldivision.
Figure 4 Cells undergoing mitosis in a Leydig
●
●
Create
a
region
as
Use
tally
this
chart.
being
data
Classify
either
to
in
each
of
interphase
calculate
the
about
or
mitotic
in
a
hundred
any
of
the
cells
in
stages
this
of
cell tumour
mitosis.
index.
Cytokinesis
Cytokinesis occurs after mitosis and is dierent in plant
and animal cells.
Cells
can
present
usually
divide
in
a
In
different
animal
equator
ring
at
the
of
these
the
The
centre,
cells
of
the
of
next
cell
it
This
of
by
builds
in
are
and
forms
own
is
to
for
the
middle
cells
adjacent
wall
to
to
the
and
to
the
that
are
the
similar
they
of
fuse
more
to
cells.
to
form
vesicles
membrane
across
membranes
plasma
using
furrow
daughter
of
the
the
membranes
at
cytoplasm.
substances
between
will
link
cellulose
middle
the
of
existing
other
bring
the
adjacent
happens
membrane
cleavage
two
plasma
of
lamella
and
fusion
exocytosis
then
it
around
plasma
the
layers
the
division
by
and
are
It
accomplished
where
the
two
into
pectins
deposited
into
equator
form
the
When
apart
is
the
myosin
With
develop
inwards
This
inside
and
the
connected
daughter
cell
to
nuclei
cytokinesis.
completed
pulled
muscle.
equator.
completing
exocytosis
its
moved
the
actin
in
identical
called
been
furrow.
pinched
merge
plants
the
are
is
which
and
cell,
vesicles
Both
deposit
cells
the
membranes.
walls.
are
structures
stage
in
cell
is
cleavage
is
cells.
immediately
proteins
across
actually
animal
contraction
equator,
daughter
sides
a
genetically
division
membrane
form
the
two
cell
has
and
protein
vesicles
structures
brought
plasma
The
of
mitosis
plant
to
cause
tubular
whole
two
that
the
plant
tubular
the
cell
equator.
reaches
In
the
in
when
process
before
contractile
proteins
mitosis
The
way
cells
of
after
cell.
begins
in
a
a
to
lamella.
equator.
to
be
the
two
the
new
the
As
a
new
cell
equator
result,
and
each
▲
Figure 5 Cytokinesis in (a) fer tilized sea urchin
egg (b) cell from shoot tip of Coleus plant
55
1
C E L L
B I O L O G Y
Cyclins and the control of the cell cycle
Cyclins are involved in the control of the cell cycle.
Each
of
the
phases
group
of
at
correct
the
the
cycle
Cyclins
then
cell.
bind
The
There
are
four
cycle.
that
and
the
of
called
involves
used
cell
to
only
many
ensure
moves
important
that
on
tasks
of
cyclin-dependent
phosphate
phosphate
types
levels
specic
of
cyclin
these
tasks
to
the
tasks.
are
A
performed
next
cell
but
one
in
the
not
the
of
stage
at
not
cell
fall.
of
The
cycle
other
of
to
and
to
the
graph
the
cycle.
gure6
cyclins
next
ensure
in
become
cell
in
these
the
kinases
proteins
proteins
Unless
progress
These
other
phases
cells.
and
to
other
the
human
rise
does
control
needed,
to
kinases.
groups
triggers
cyclins
the
therefore
are
is
attach
concentration,
cells
cycle
appropriate.
out
Cyclins
new
cell
cyclins
enzymes
main
the
threshold
when
is
active
carry
how
the
and
attachment
and
shows
cell
to
it
of
called
time
when
become
active
a
proteins
stage
that
cells
reach
of
the
divide
times.
noitartnecnoc
G
phase
S phase
G
1
phase
mitosis
2
Cyclin D triggers cells to move from G
to G
0
and from G
1
into S phase.
1
Cyclin E prepares the cell for DNA replication in S phase.
Cyclin A activates DNA replication inside the nucleus in S phase.
Cyclin B promotes the assembly of the mitotic spindle and other tasks
in the cytoplasm to prepare for mitosis.
▲
Figure 6
Discovery of cyclins
Serendipity and scientic discoveries: the discovery of cyclins was accidental.
During
in
sea
that
research
urchin
increased
decreased
which
in
soon
over
after
experiments
repeated
that
56
to
a
period
was
being
with
Hunt
of
The
the
of
ten
named
30
was
minutes
being
and
Further
went
through
concentration
the
cell
minutes
the
then
proteins
down.
in
synthesis
protein
fertilization
other
protein
phases
a
protein
about
broken
about
protein
after
unlike
decreases
the
occurred
mitosis.
that
and
of
discovered
increase.
showed
coincided
of
control
Hunt
concentration
increases
breakdown
start
in
the
Tim
concentration,
continued
synthesized
then
into
eggs,
protein
cycle.
after
The
the
cyclin.
Further
research
conrmed
stage
of
Prize
in
be
In
–
the
that
cell
for
the
what
cyclins
cycle.
downloaded
it
he
how
discovery
is
in
an
the
the
cell
factor
was
2001
to
His
he
cycle
of
discovery
is
in
the
honour
Nobel
internet
had
and
from
awarded
importance
example
unexpected
key
cyclins.
because
the
a
cyclins
suspected
Hunt
from
mentions
times
discover
and
of
other
had
are
Tim
Physiology
discovery
several
revealed
Hunt
not
work
can
viewed.
serendipity
set
out
serendipity
by
Nobel
his
controlled.
made
early
control
a
Lecture
and
of
an
–
to
This
a
happy
accident.
1 . 6
c e l l
d I V I s I o n
tm mai a a
Aiviy
Mutagens, oncogenes and metastasis are involved in the
ca ah
development of primary and secondary tumours.
Tumours can form in any tissue at any
Tumours
any
do
part
not
are
of
abnormal
the
invade
tumours
In
other
in
the
are
body.
body
malignant
In
nearby
unlikely
tumours
and
and
groups
the
some
tissues
to
develop
are
or
very
that
the
move
much
can
into
cells
cases
cause
cells
of
cells
to
become
to
be
at
adhere
other
harm
and
are
stage
each
of
the
body.
move
These
of
other
classied
and
tumours.
any
to
parts
detached
secondary
likely
develop
as
life
in
and
(bowel), breast and prostate gland are
These
par ticularly vulnerable. Cancer is a
benign.
major cause of death in most human
elsewhere
tumours
age, but the skin, lung, large intestine
populations so there is a pressing
are
need to nd methods of prevention
life-threatening.
and treatment. This involves basic
research into the control of the cell
Diseases
due
to
malignant
tumours
are
commonly
known
as
cancer
cycle. Great progress has been made
and
have
diverse
causes.
Chemicals
and
agents
that
cause
cancer
are
but more is needed.
known
There
as
are
various
mutagens
energy
are
do
become
normal
are
not
division.
cell
division
are
so
on.
and
are
malignant
including
chemical
that
changes
cancer
is
a
some
mutagens
short-wave
cause
gene
of
tumour
occur
cells
from
the
in
cells
is
is
a
in
tumours.
viruses.
and
also
ultraviolet
mutations
light.
and
Who should pay for research into
All
cancer?
high
This
is
mutations
in
in
is
a
primary
of
genes.
genes
that
Most
can
are
known
as
oncogenes.
control
of
the
them
can
same
cell
result
for
extremely
the
form
called
few
the
body,
signicant.
to
sequence
The
cell
in
In
cycle
a
and
uncontrolled
formation.
the
happening
of
base
mutating
mutations
lifetime
of
the
mutate.
involved
repeatedly
cells
parts
this
to
they
after
why
numbers
group
of
if
are
must
of
divides
This
other
both
X-rays
therefore
during
movement
in
This
and
vast
it
carcinogens
agents
random
chance
formation
formed
are
cause
mutations
The
there
as
oncogenes
cell
cell.
such
cancer-causing
cell
Several
of
carcinomas
cancer.
Mutations
genes
types
mutagens
cause
because
carcinogenic,
radiation
because
can
carcinogens,
the
then
primary
tumour
to
total
When
two,
it
small,
a
four,
chance
then
set
up
a
tumour
because
tumour
tumour.
to
become
but
of
cell
tumour
has
eight
Metastasis
secondary
been
cells
is
and
the
tumours
body.
Smoking and cancer
The correlation between smoking and incidence of
cancers.
A
correlation
factors.
of
a
The
in
correlation.
correlation,
they
also
factor
one
decrease
is
death
rate
1
There
when
increases
There
table
science
a
is
relationship
due
shows
to
the
are
relationship
two
factor
together.
the
positive
a
between
other
results
of
increases
a
and
two
cancer
correlation.
the
other
negative
variable
is
an
With
one
a
also
correlation,
example
positive
increases;
when
one
decreases.
correlation
cancer.
types
With
between
smoking
This
of
between
has
one
of
been
the
cigarette
shown
largest
smoking
repeatedly
surveys,
and
in
and
the
surveys.
the
longest
57
1
C E L L
B I O L O G Y
continuous
day,
the
death
The
rate
is
of
rate
due
bladder,
table
1
in
of
smoking
is
not
than
cancer
contains
have
been
other
that
body,
and
there
cancers
cervix.
of
one
is
the
cigarettes
They
time
but
also
larynx
into
a
the
in
smokers
the
and
per
higher
death
lung.
This
with
each
correlation
rate
likely
a
stopped.
stomach,
death
timesmore
had
and
positive
smoked
show
contact
esophagus,
in
also
increases
comes
Although
different
are
at
huge
cigarettes
but
more
pharynx,
several
kidney,
due
to
other
non-smokers,
to
die
from
all
non-smokers.
in
the
science
that
there
not
in
animals
in
is
are
humans.
is
a
to
cause
There
of
causes
a
is
are
correlation
between
cancer.
established.
substances.
smoke
cause
between
correlation
smoking
well
chemical
cigarette
ca  ah  w 1951
positive
experiments
or
smoking
distinguish
a
that
links
different
shown
to
prove
causal
chemicals
doubt
from
and
show
mouth,
the
cancer.
smoked
also
the
to
smokers
many
laboratory
of
that
due
signicantly
does
case
shows
rate
who
survey
the
pancreas
Finding
this
those
smoke
important
cause.
and
as
shows
cancers
is
the
data
death
cancers
parts
between
It
of
to
expected
these
The
the
among
results
cancers
one.
higher
tumours
evidence
of
in
that
carcinogenic.
a
However,
Cigarette
Twenty
and
smoking
smoke
these
the
at
lungs
least
This
of
forty
leaves
little
cancer.
M aiy a p 10 0,0 0 0 m/ya
a 20 01
(samp iz: 34,439 ma
lig
fm
-mk
iga
c mk (iga/ay)
1–14
 i biai)
All cancers
Lung cancer
15–24
≥25
mk
360
466
588
747
1,061
17
68
131
233
417
9
26
36
47
106
334
372
421
467
538
Cancer of mouth, pharynx,
larynx and esophagus
All other cancers
▲
58
T
able 1 from British Medical Journal 328(7455) June 24 2004
1 . 6
c e l l
d I V I s I o n
daa-a qi: The eect of smoking on health
One
of
the
smoking
doctors.
they
largest
on
ever
health
Information
smoked
from
studies
involved
was
1951
of
the
34,439
collected
to
2001
effect
male
on
and
how
the
of
death
British
much
cause
was
during
of
of
the
recorded
this
period.
results.
deaths
per
The
for
each
of
The
table
below
gures
hundred
the
given
thousand
are
men
doctors
shows
the
who
number
per
died
some
of
year.
1–14
15–24
iga
iga
p ay
p ay
107
237
310
471
1,037
1,447
1,671
1,938
>25 iga
typ  ia
n-mk
p ay
Respiratory (diseases of the lungs
and airways)
Circulatory (diseases of the hear t and
blood vessels)
1
Stomach and duodenal ulcers
8
11
33
34
Cirrhosis of the liver
6
13
22
68
Parkinson’s disease
20
22
6
18
Deduce
whether
between
due
2
to
Using
threat
all
the
to
there
smoking
types
data
of
in
health
respiratory
or
and
a
positive
correlation
mortality
the
table,
4
rate
disease.
from
with
is
the
discuss
circulatory
is
whether
greater
diseases.
the
with
[4]
Discuss
whether
the
data
suggests
that
small
number
of
cigarettes
is
safe.
a
the
cause
data
of
proves
cirrhosis
of
that
the
5
The
[3]
table
cancer.
of
does
The
cancer
not
include
survey
are
cancers
linked
that
deaths
showed
with
you
that
due
seven
smoking.
would
to
types
Suggest
expect
smoking
smoking
a
is
liver.
three
3
whether
smoking
[2]
smoking
Discuss
to
cause.
[3]
[3]
59
1
C E L L
B I O L O G Y
Questions
1
Figure
7
represents
a
cell
from
a
c)
multicellular
Explain
and
organism.
d)
Using
the
3
In
the
chloride
the
with
a
reason,
whether
the
cell
of
health
(i)
prokaryotic
(ii)
part
(iii)
in
a
of
a
or
root
phase
of
eukaryotic;
tip
or
a
mitosis
in
cells.
The
magnication
of
the
Calculate
the
actual
tip;
a)
[1]
interphase.
drawing
size
positively
The
and
Calculate
how
long
a
5
State
(i)
[1]
the
should
be
if
it
was
is
2,500
of
the
cell.
placed
hour.
what
μm
added
in
a
happen
concentrated
Include
reasons
salt
for
to
to
the
b)
if
it
for
shows
the
area
of
move
Explain
by
chloride
move
the
cells
associated
the
positively
processes
charged
that:
ions
out
of
cells
[1]
chloride
ions
out
of
the
cells.
[1]
membranes
water
out
of
the
secretory
cells.
[1]
in
why
cystic
the
uid
brosis
is
secreted
thick
and
by
people
viscous.
[4]
[3]
The
amount
a
cells
of
was
DNA
present
measured
taken
from
two
in
a
in
each
large
different
cell
number
cultures
of
rat
human
liver
the
ions
one
answer.
of
2
of
secretory
move
nucleus
Table
from
was
4
2
moves
the
cell
solution
your
with
are
secreted.
brosis,
secreted
lung
passively
also
few
the
scale
[1]
would
of
[2]
with
Predict
in
ions
been
too
liquid
two
×
drawing.
c)
and
[3]
[2]
follow
has
viscous,
names
move
(iii)
bar
identify
charged
cystic
inner
cells.
Water
that
the
example
ions
channels.
secretory
(ii)
for
of
problems.
(ii)
(i)
liver
chloride
liquid
area
membranes.
table,
of
cells,
disease
thick
the
b)
in
[1]
nger
or
the
malfunction
the
becomes
is
the
genetic
channels
Identify,
and
into
out
a)
out,
the
cells
in
secretory
through
In
Figure 7
data
activities
pancreas,
pumped
▲
difference
mitochondrial
the
main
human
and
the
outer
bone
marrow
(gure
8).
cell.
a)
For
each
label
(I,
II
and
III)
in
the
Sample
B
2
Mma mp
Aa (μm
)
graph,
Plasma membrane
the
1,780
b)
Rough endoplasmic reticulum
cells
Estimate
Mitochondrial outer membrane
7,470
Mitochondrial inner membrane
39,600
Lysosomes
100
Other components
18,500
T
able 2
liver
b)
the
total
area
of
membranes
in
cell.
Calculate
the
[2]
the
area
of
percentage
in
60
the
cell.
of
the
Show
plasma
total
your
in;
i.e.
of
G1,
approximate
the
G2
membrane
area
of
working.
that
would
cell
or
amount
human
cell
S.
of
cycle
[3]
DNA
at
prophase
(ii)
bone
marrow
at
telophase.
(non-dividing cell culture)
2
1
10
DNA/pg per nucleus
membranes
▲
Figure 8
15
in
the
types:
marrow
as
[3]
expected
bone
Sample A
3
be
(i)
5
a
be
phase
)sdnasuoht ni( sllec fo rebmuN
280
Calculate
the
nucleus
following
)sdnasuoht ni( sllec fo rebmuN
Nucleus
a)
could
which
30,400
per
▲
deduce
[2]
Sample B
3
(rapidly dividing cell culture)
I
2
III
1
II
5
10
DNA/pg per nucleus
15
2
M o l e c u l a r
B I o l o G Y
Intdtin
Water
is
control
of
the
chemical
medium.
sunlight
for
life
when
medium
their
reactions
is
life.
supply
cell
by
that
Photosynthesis
to
and
it
for
composition
the
occur
uses
organisms
complex
within
the
chemical
respiration
needed.
Living
a
of
this
energy
energy
releases
Compounds
web
this
in
hydrogen
store
control
have
a
the
oxygen
Many
Genetic
energy
be
range
information
accurately
proteins
are
copied
needed
by
used
proteins
metabolism
diverse
needed
carbon,
and
energy.
of
is
of
the
cell
in
supply
as
biological
stored
and
the
to
act
and
enzymes
and
to
others
functions.
DNA
translated
to
and
can
make
the
cell.
2.1 M  mm
undstnding
appitins
➔
Molecular biology explains living processes in
➔
Urea as an example of a compound that is
terms of the chemical substances involved.
produced by living organisms but can also be
➔
Carbon atoms can form four bonds allowing a
ar ticially synthesized.
diversity of compounds to exist.
➔
Life is based on carbon compounds
Skis
including carbohydrates, lipids, proteins and
nucleic acids.
➔
Drawing molecular diagrams of glucose, ribose, a
saturated fatty acid and a generalized amino acid.
Metabolism is the web of all the enzyme
catalysed reactions in a cell or organism.
➔
➔
➔
Identication of biochemicals such as
carbohydrate, lipid or protein from
Anabolism is the synthesis of complex
molecular diagrams.
molecules from simpler molecules including
the formation of macromolecules from
monomers by condensation reactions.
Nt f sin
➔
Catabolism is the breakdown of complex
➔
Falsication of theories: the ar ticial synthesis
molecules into simpler molecules including the
of urea helped to falsify vitalism.
hydrolysis of macromolecules into monomers.
61
2
M O L E C U L A R
B I O L O G Y
M bigy
Molecular biology explains living processes in terms
of the chemical substances involved.
The
discovery
biology
raised
of
that
the
and
biology
▲
is
the
structure
transformed
possibility
molecules
diverse
of
has
and
the
of
how
than
DNA
they
50
years
1953
biological
interact
are
in
started
understanding
explaining
interactions
more
of
our
with
very
old,
it
each
still
a
a
other.
so
revolution
living
processes
complex,
is
of
from
The
the
It
structure
structures
although
relatively
in
organisms.
are
molecular
young
science.
Figure 1 A molecular biologist at work in the
laboratory
Many
molecules
apparently
are
nucleic
They
are
varied
cell,
The
The
and
organisms
that
the
make
out
a
organisms
most
Nucleic
to
carry
the
varied
acids
genes.
huge
chemical
of
of
and
DNA
are
tasks
the
one
complex
Proteins
range
genes
including
and
comprise
reactions
between
molecular
various
down
that
we
not
and
that
and
and
RNA.
astonishingly
by
proteins
as
molecules
within
cell
the
when
that
reductionist
parts.
has
otherwise
of
is
processes
component
biology
approach
properties
system
its
in
would
though,
biologist
biochemical
into
productive
emergent
whole
of
the
reductionist
everything
are
and
living
the
is
the
acting
at
the
as
heart
biology.
breaking
immensely
used
controlling
in
but
proteins.
relationship
approach
considering
water,
and
structure
molecular
important
as
chemicals
including
enzymes.
of
acids
the
in
are
simple
of
have.
be
insights
involves
has
into
biologists
biologist
parts
studied
it
organism
approach
us
Some
molecular
as
living
This
given
component
cannot
a
argue
cannot
are
without
been
whole
explain
combined
looking
at
there
the
together.
Synthsis f 
Urea as an example of a compound that is produced by
living organisms but can also be ar ticially synthesized.
Urea
is
a
nitrogen-containing
molecular
where
of
it
was
amino
from
used
the
to
structure
acids
can
by
out
also
are
different
the
urea
the
it
body,
be
A
blood
the
as
3).
body
those
a
in
is
is
produced
of
a
relatively
the
of
when
urine
there
excreting
happens
to
the
the
catalysed
in
the
kidneys
is
liver.
an
this
was
excess
nitrogen
by
where
simple
and
enzymes,
Urea
it
is
is
is
then
ltered
out
urine.
articially.
the
with
component
reactions,
This
in
a
means
of
stream
synthesized
from
It
It
cycle
(gure
the
of
compound
2).
discovered.
acids.
produce
passes
Urea
in
amino
transported
and
rst
(gure
liver
and
The
chemical
enzymes
are
reactions
not
used
involved,
but
O
that
is
produced
ammonia
+
carbon
is
identical.
dioxide
→
ammonium
carbamate
C
→
H
N
2
▲
62
urea
+
water
NH
2
Figure 2 Molecular diagram of urea
About
as
a
100
million
nitrogen
tonnes
fertilizer
on
are
produced
crops.
annually.
Most
of
this
is
used
2 . 1
M o l e c u l e s
t o
M e t a b o l i s M
CO
+ NH
2
3
enzyme 1
carbamoyl phosphate
ornithine
urea
enzyme 2
arginase
citrulline
arginine
aspartate
fumarate
enzyme 3
enzyme 4
argininosuccinate
▲
Figure 3 The cycle of reactions occurring in liver cells that is used to synthesize urea
u nd th fsitin f vitism
Falsication of theories: the ar ticial synthesis of urea helped to falsify vitalism.
Urea
was
assumed
time
in
it
was
plants
help
of
discovered
to
are
due
to
of
vital
psyche
and
for
the
be
was
is
forces.
vital
of
with
of
different
–
a
organic
compounds
achievement
the
vitalism
Aristotle
principle
was
that
compounds
made
part
and
At
phenomena
which
physical
1720s
organic
only
This
principle,
or
the
kidneys.
that
could
origin
in
the
believed
the
chemical
word
urine
principle”.
that
a
in
product
animals
“vital
theory
the
a
widely
and
a
the
purely
be
–
life
from
used
of
vitalism.
did
not
meaning
breath,
life
or
cause
evidence
accept
that
1828
the
synthesized
isocyanate
the
rst
vital
articially
was
a
principle
Swedish
a
that
I
of
using
make
animal,
to
be
Jacob
water.
it
be
Wöhler
step,
in
excitedly
was
because
obvious
deduction
I
can
man
no
must
without
was
to
the
or
the
that
still
as
without
a
vital
has
been
a
well.
to
the
for
theory
theory,
but
pieces
biologists
and
it
vitalism
several
most
falsied
theory
Wöhler’s
the
abandon
requires
theory
over
and
now
there
have
that
after
to
his
of
to
sometimes
continue
for
decades.
accept
that
had
principle,
some
make
for
as
by
in
processes
example,
same
compounds
articially.
proteins
without
components
of
the
non-living
organic
complex
synthesis
chemistry
mad.
urea,
into
nowadays
To
tropical
remarkable
urea
forces
synthesized
other
one
primeval
kidneys
to
governed
of
It
is
such
using
cells.
Wöhler
Four
wrote
Berzelius:
drives
dog.
if
been
and
Organic
you
remain
not
impossible
years
are
physical
hemoglobin,
this
longer
tell
chemical
it
forest
things;
which
me
a
almost
appears
full
of
the
dreadful
one
dare
not
like
a
most
endless
enter,
for
been
there
synthesized
a
biologists
jungle
An
falsify
biologists
usually
organisms
ribosomes
the
Berzelius:
I
living
matter,
This
synthesized
involved
this
urea
to
as
against
Greek
silver
chloride.
speaking,
chemical
can
any
wrote
Friedrich
signicant
been
Jöns
manner
my
very
had
Wöhler
chemist
hold
of
It
chemist
compound
all
It
be
soul.
ammonium
organic
synthesis.
In
urea
and
articially.
no
German
it
could
evidence
helped
against
controversies
in
In
It
immediately.
Although
word
was
seems
no
way
out.
other
63
2
M O L E C U L A R
B I O L O G Y
cbn mpnds
av
Carbon atoms can form four bonds allowing a diversity
c mp
of compounds to exist.
Can you nd an example
of a biological molecule
Carbon
is
in which a carbon atom is
used
make
bonded to atoms of three
organisms
other elements or even four
activities
other elements?
by
Titin is a giant protein that
Carbon
acts as a molecular spring
is
in muscle. The backbone of
electron
the titin molecule is a chain
bond
between
Each
carbon
most
other
to
the
only
the
a
almost
of
their
formed
limitless
of
form
when
most
range
cells.
properties
atoms
15th
huge
abundant
of
different
possibilities
The
diversity
element
for
of
on
molecules.
the
Earth,
This
chemical
carbon
but
has
it
can
given
composition
compounds
is
be
living
and
explained
carbon.
covalent
two
bonds
adjacent
contributed
by
atoms
each
so
with
atoms
atom.
stable
other
share
a
pair
Covalent
molecules
atoms.
of
on
covalent
electrons,
bonds
based
A
are
the
carbon
bond
with
one
strongest
can
be
type
of
produced.
of 100,000 atoms, linked by
atom
can
form
up
to
four
covalent
bonds
–
more
than
single covalent bonds.
Can you nd an example
structures.
of a molecule in your
or
body with a chain of over
chains
atoms
1,000,000,000 atoms?
for
covalent
for
can
they
found
bonds
example
in
can
length.
oxygen,
or
molecules
bonds
any
atoms
(alcohol
so
example.
methane,
H
The
of
hydrogen,
Carbon
atoms,
The
bond
and
there
the
can
or
with
also
one
wine).
carboxyl
carbon
contain
more
be
carbon
be
atoms
chains
with
can
of
have
to
up
other
complex
make
to
20
rings
carbon
elements
such
as
phosphorus.
just
to
can
other
acids
bonds
bond
beer
or
with
Fatty
nitrogen
can
in
be
containing
other
than
The
two
group
four
single
of
element,
one
other
bonds
and
ethanoic
such
can
one
acid
as
element
all
be
double
(the
hydrogen
as
in
in
ethanol
single
covalent
acid
in
bond,
vinegar).
methane
cssifying bn mpnds
H
H
H
Life is based on carbon compounds including
H
H
ethanol
carbohydrates, lipids, proteins and nucleic acids.
Living
H
organisms
different
use
properties
four
and
main
so
can
classes
be
used
of
carbon
for
compound.
different
They
have
purposes.
H
O
Carbohydrates
C
are
characterized
by
their
composition.
of
O
carbon,
hydrogen
and
oxygen,
with
hydrogen
two
hydrogen
atoms
to
one
oxygen,
hence
the
Lipids
H
H
and
oxygen
are
in
composed
the
ratio
of
H
H
H
They
ethanoic acid
H
H
H
H
H
H
H
H
H
H
H
H
H
H
name
are
molecules
a
carbo hydrate
broad
that
are
class
of
insoluble
in
O
water,
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
fatty
including
acids
and
steroids,
waxes,
triglycerides.
In
OH
H
H
H
H
common
are
linolenic acid – an omega-3 fatty acid
fats
language,
if
they
temperature
▲
are
or
triglycerides
solid
oils
if
at
they
room
are
Figure 4 Some common naturally-occurring carbon compounds
liquid
Proteins
amino
and
carbon,
64
composed
in
nitrogen,
Nucleic
of
are
acids
these
but
acids
two
are
hydrogen,
nucleic
acid:
of
one
chains
of
the
chains
of
oxygen,
ribonucleic
or
more
contain
the
twenty
subunits
acid
chains
of
acids
called
and
(RNA)
room
elements
amino
nitrogen
at
temperature.
amino
also
All
of
hydrogen,
the
oxygen
containsulphur.
nucleotides,
phosphorus.
and
acids.
carbon,
which
There
contain
are
deoxyribonucleic
two
types
acid(DNA).
2 . 1
M o l e c u l e s
t o
M e t a b o l i s M
Dwing ms
Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a
generalized amino acid.
There
is
many
different
be
able
no
to
need
draw
important
to
memorize
molecules
diagrams
but
of
the
a
a
structure
biologist
few
of
the
of
atom
should
with
most
line
is
of
with
covalent
double
bonds
C
and
bonds
with
an
are
two
oxygen
shown
atom
with
a
lines.
molecules.
atom
symbol
Single
and
Some
Each
represented
O.
in
a
the
molecule
element.
is
represented
For
Name of group
example
a
using
the
carbon
gives
Full structure
chemical
atoms
together
groups
and
are
shown
bonds
not
with
the
indicated.
Table
1
examples.
Simplied notation
hydroxyl
–OH
H
amine
–NH
N
2
H
O
carboxyl
–COOH
C
O
H
H
–CH
methyl
3
H
▲
T
able 1
Ribose
●
OH
The
formula
for
ribose
is
C
H
5
●
The
molecule
is
a
5
O
10
5
ve-membered
ring
with
a
side
O
chain.
OH
4
C
C
H
●
Four
carbon
atoms
are
in
the
ring
and
one
forms
the
side
chain.
H
H
3
●
The
●
The
carbon
atoms
hydroxyl
can
be
groups
numbered
(OH)
on
starting
carbon
with
atoms
number
1,
2
and
1
3
on
the
point
and
down
C
C
OH
OH
2
right.
up,
Ribose
▲
down
1
H
respectively.
CH
6
OH
2
Glucose
5
C
●
The
formula
for
glucose
is
C
H
6
H
6
4
●
The
●
Five
●
The
molecule
is
a
six-membered
ring
with
a
side
chain.
1
C
OH
H
atoms
are
in
the
ring
and
one
forms
the
C
C
side
atoms
can
be
numbered
starting
with
number
1
on
the
The
hydroxyl
down,
down,
glucose
carbon
used
atom
groups
(OH)
up
down
by
1
and
plants
points
to
on
carbon
atoms
respectively,
make
cellulose
1,
2,
3
although
the
and
in
a
hydroxyl
4
OH
right.
▲
●
OH
2
chain.
H
carbon
C
HO
3
carbon
C
O
H
O
12
Glucose
point
form
of
group
on
upwards.
65
2
M O L E C U L A R
B I O L O G Y
Saturated fatty acids
C
●
The
●
In
●
The
carbon
saturated
At
one
●
At
the
All
fatty
number
●
●
atoms
end
of
other
other
of
form
acids
end
carbon
are
atoms
chain
the
unbranched
they
carbon
the
an
the
carbon
atoms
bonded
is
most
carbon
atom
are
is
chain.
to
each
commonly
atom
is
bonded
bonded
other
to
two
single
between
part
to
by
of
three
a
14
hydrogen
hydrogen
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
C
H
bonds.
and
carboxyl
H
20.
group
atoms.
atoms.
Amino acids
●
A
carbon
different
■
an
■
a
atom
group,
carboxyl
a
■
the
the
centre
of
the
molecule
is
bonded
to
four
things:
amine
■
in
hence
group
hydrogen
the
which
term
makes
amino
the
acid;
molecule
an
acid;
atom;
H
R
group,
which
is
the
variable
part
of
amino
acids.
H
O
R
▲
R
Full molecular diagram of a
O
H
saturated fatty acid
CH
(CH
3
C
N
)
2
C
n
COOH
2
H
O
H
H
OH
H
simplied molecular diagram
full molecular diagram
▲
▲
Molecular diagrams of an amino acid
Simplied molecular diagram
of a saturated fatty acid
Idntifying ms
Identication of biochemicals as carbohydrate, lipid or protein from molecular
diagrams.
The
molecules
proteins
usually
●
are
so
quite
Proteins
of
carbohydrates,
different
easy
to
contain
carbohydrates
but
●
not
Many
is
C
in
H
6
a
O
12
in
O
contain
and
Carbohydrates
used
H,
Lipids
N
contain
ratio
and
of
2:1,
sucrose
sulphur
C,
H
and
O
(S)
but
donot.
hydrogen
for
is
C
and
example
(the
H
sugar
oxygen
glucose
commonly
unsaturated
O
22
relatively
carbohydrates,
for
fatty
11
less
example
acid)
is
oxygen
oleic
C
H
18
testosterone
is
C
H
19
66
is
6
baking)
contain
steroid
it
whereas
contain
lipids
12
●
that
them.
and
lipids
and
other
N.
proteins
atoms
C,
lipids
each
recognize
and
carbohydrates
●
from
O
34
O
28
than
acid
(an
and
the
2
▲
2
Figure 5 A commonly-occurring biological molecule
2 . 1
M o l e c u l e s
t o
M e t a b o l i s M
Mtbism
Metabolism is the web of all the enzyme catalysed
reactions in a cell or organism.
All
living
organisms
reactions.
happen
in
reactions
sum
of
These
the
Even
1,000
in
digest
consists
another,
reactions
to
reactions
Metabolism
into
cytoplasm
used
all
but
in
a
They
of
are
relatively
Encyclopedia
out
of
cells
in
pathways
of
small
also
simple
are
large
but
the
by
which
one
An
chemical
Most
of
extracellular,
type
of
pathways
example
cells,
maps
the
are
intestine.
These
cycles.
on
different
them
such
Metabolism
as
is
the
the
organism.
prokaryote
and
of
enzymes.
some
an
Global
by
small
in
steps.
some
available
Genes
numbers
catalysed
occur
reactions.
of
are
food
that
series
there
different
complex.
carry
reactions
is
molecule
are
shown
metabolism
showing
internet,
all
for
is
mostly
in
transformed
chains
gure
consists
reactions
example
in
of
are
the
of
3.
over
very
Kyoto
Genomes.
anbism
Anabolism is the synthesis of complex molecules from
simpler molecules including the formation of macromolecules
from monomers by condensation reactions.
Metabolism
Anabolism
is
is
An
easy
are
hormones
energy,
way
often
to
is
includes
Protein
●
DNA
●
Photosynthesis,
●
synthesis
two
up
is
body
parts,
larger
by
supplied
these
synthesis
into
build
this
promote
usually
●
and
that
remember
that
which
Anabolism
divided
reactions
anabolism
molecules
recalling
building.
in
the
that
of
catabolism.
anabolic
Anabolic
form
and
from
smaller
ones.
steroids
reactions
require
ATP
.
processes:
using
during
ribosomes.
replication.
including
production
of
glucose
from
carbon
dioxide
water.
Synthesis
of
complex
carbohydrates
including
starch,
cellulose
and
glycogen.
ctbism
Catabolism is the breakdown of complex molecules
into simpler molecules including the hydrolysis of
macromolecules into monomers.
Catabolism
broken
in
be
some
used
is
down
in
this
the
Digestion
●
Cell
part
into
cases
●
and
Digestion
of
metabolism
energy
cell.
of
of
smaller
ones.
is
in
in
the
in
includes
mouth,
which
in
which
Catabolic
captured
Catabolism
food
respiration
dioxide
●
the
the
form
these
stomach
glucose
or
larger
reactions
ATP
,
are
energy
which
and
can
then
processes:
and
lipids
of
molecules
release
are
small
intestine.
oxidized
to
carbon
water.
complex
carbon
compounds
in
dead
organic
matter
by
decomposers.
67
2
M O L E C U L A R
B I O L O G Y
2.2 W
undstnding
appitins
➔
Water molecules are polar and hydrogen bonds
Comparison of the thermal proper ties of water
➔
form between them.
with those of methane.
➔
Hydrogen bonding and dipolarity explain
➔
Use of water as a coolant in sweat.
➔
Methods of transpor t of glucose, amino acids,
the adhesive, cohesive, thermal and solvent
proper ties of water.
cholesterol, fats, oxygen and sodium chloride
➔
Substances can be hydrophilic or hydrophobic.
in blood in relation to their solubility in water.
Nt f sin
➔
Use theories to explain natural phenomena:
the theory that hydrogen bonds form between
water molecules explains water ’s proper ties.
H
Hydgn bnding in wt
H
Water molecules are polar and hydrogen bonds form
O
between them.
A
water
and
tends to
small
pull the
positive
molecule
two
involves
is
is
hydrogen
unequal
because
the
formed
atoms.
sharing
nucleus
of
by
The
of
covalent
bond
electrons
the
bonds
between
oxygen
–
it
is
atom
a
is
between
hydrogen
polar
more
an
oxygen
and
atom
oxygen
covalent
bond.
attractive
to
This
electrons
+
electrons
charge δ
slightly
on each
in this
hydrogen
direction
atom
than
the
Because
nuclei
of
hydrogen
the
of
the
hydrogen
unequal
atoms
have
sharing
a
partial
atoms
of
(gure
electrons
positive
1).
in
water
charge
and
molecules,
oxygen
has
the
a
partial
Corresponding negative charge
negative
2δ
Because
water
molecules
are
bent
rather
than
linear,
on oxygen atom
the
▲
charge.
two
hydrogen
atoms
are
on
the
same
side
of
the
molecule
and
form
Figure 1 Water molecules
one
pole
and
Positively
particles
Water
is
still
oxygen
charged
molecules
enough
is
rather
a
ions)
only
to
bond.
opposite
each
partial
signicant
“hydrogen
a
the
(positive
attract
have
have
than
forms
particles
(negative
molecules
force
the
bond”.
A
ions)
other
and
Strictly
hydrogen
negatively
and
charges,
effects.
pole.
so
The
form
the
is
the
charged
ionic
attraction
attraction
speaking
bond
an
it
is
is
less
between
an
force
bond.
but
it
water
intermolecular
that
forms
when
water molecule
a
hydrogen
atom
of
atom
another
in
one
polar
polar
molecule
covalent
is
attracted
to
a
slightly
negative
molecule.
hydrogen bond
Although
▲
a
hydrogen
bond
is
a
weak
intermolecular
force,
water
Figure 2 The dotted line
molecules
are
small,
so
there
are
many
of
them
per
unit
volume
of
water
indicates the presence of
an intermolecular force
between the molecules. This
is called a hydrogen bond
68
and
large
water
its
numbers
unique
importance
to
of
hydrogen
properties
living
things.
and
bonds
these
(gure
2).
properties
Collectively
are,
in
turn,
they
of
give
immense
2 . 2
W a t e r
Hydgn bnds nd th pptis f wt
Use theories to explain natural phenomena: the theory that hydrogen bonds form
between water molecules explains water ’s proper ties.
There
is
bonds,
strong
but
between
without
it
experimental
remains
water
doubt
that
However,
way
explaining
of
the
properties
that
of
make
they
the
water.
water
exist
as
properties
is
these
useful
to
for
they
are
are
of
a
not
water.
distinctive
the
been
that
directly
is
useful
proven
science
correct
ifit
solvent
seem
unwise
natural
predict
They
and
might
of
prove
very
thermal
living
It
hydrogen
form
cannot
they
bonds
adhesive,
It
so
that
Scientists
hydrogen
cohesive,
evidence
theory
molecules.
visible.
explain
a
if
world
to
exist.
works
there
behaviour,
helps
to
–
is
to
on
base
However
we
can
if
it
understanding
has
for
not
natural
this
that
is
assume
evidence
explain
our
something
it,
that
if
been
has
the
it
not
way
a
theory
helps
falsied
to
and
phenomena.
properties
organisms.
Pptis f wt
Hydrogen bonding and dipolarity explain the cohesive,
adhesive, thermal and solvent proper ties of water.
Cohesive proper ties
Cohesion
type,
for
Water
each
This
to
molecules
other,
due
property
through
the
refers
instance
are
to
is
xylem
water
the
for
vessels
bonding
top
tallest
at
are
this
trees
–
they
low
not
over
of
two
cohere,
bonding,
water
molecules
pressure.
happens
a
which
described
transport
separated
rarely
–
together
of
the
same
molecules.
cohesive
hydrogen
molecules
the
water
useful
hydrogen
of
binding
two
in
The
by
the
plants.
method
the
and
hundred
in
means
can
can
stick
previous
Water
suction
water
they
is
section.
sucked
only
forces.
be
to
work
Due
pulled
if
to
up
to
the
metres.
Adhesive proper ties
Hydrogen
causing
useful
If
water
in
water
to
leaves,
of
nearest
carbon
can
air
form
stick
to
where
evaporates
network
the
bonds
xylem
dioxide
them.
water
from
spaces,
between
the
needed
cell
This
for
This
is
adheres
adhesive
vessel.
water
walls
forces
keeps
and
called
to
and
polar
adhesion.
cellulose
is
cause
the
other
lost
This
property
molecules
from
water
walls
molecules,
to
the
be
in
leaf
drawn
moist
so
they
useful
to
living
cell
via
the
out
can
is
walls.
of
absorb
photosynthesis.
Thermal proper ties
Water
●
has
High
water
several
specic
bonds
amount
relatively
●
energy.
to
air
it
or
of
To
Water’s
land,
latent
separates
molecule.
to
so
broken.
needed
in
is
a
of
down,
to
is
stable
do
in
needed
the
remains
molecules
bonds
must
vaporization.
needed
are
restrict
temperature
raise
water
thermally
other
heat
the
Energy
to
temperature
heat
The
be
that
Hydrogen
increases
cool
it
from
properties
capacity.
and
energy
large.
of
High
heat
molecules
hydrogen
the
thermal
this
lose
motion
require
do
this.
liquid
a
for
stable
As
large
in
of
result,
is
amounts
comparison
organisms.
evaporates
becomes
the
a
water
aquatic
molecule
and
called
of
relatively
relatively
habitat
is
to
the
water
temperature
When
a
of
organisms:
latent
a
vapour
heat
of
69
2
M O L E C U L A R
B I O L O G Y
vaporization.
amounts
bonds
of
have
Sweating
High
●
to
is
boiling
water
has
Water
is
100
a
are
be
an
temperature
to
Evaporation
heat
point.
high
it
This
is
the
use
boiling
heat
in
of
over
has
a
cooling
evaporate
makes
the
reach
liquid
to
This
of
The
can
latent
therefore
°C.
broken.
example
that
therefore
needed
of
it
a
good
water
point
a
water,
of
liquid
a
broad
temperature
range
range
For
its
of
Considerable
hydrogen
evaporative
a
is
the
the
same
boiling
highest
reasons
point
temperatures
found
in
coolant.
coolant.
substance
state.
vaporization,
a
as
effect.
because
most
is
that
high.
–
from
habitats
on
0
°C
Earth.
Solvent proper ties
Water
has
molecule
important
means
preventing
Water
oxygen
from
is
chemical
is
shells
clumping
bonds
pole
Cytoplasm
the
properties.
forms
attracted
hydrogen
dissolve.
it
hydrogen
pole
positive
which
them
forms
solvent
that
to
is
a
together
with
polar
positively
attracted
complex
reactions
of
The
around
polar
and
ions
negatively
mixture
of
metabolism
and
keeping
molecules.
charged
to
nature
charged
them
Its
and
the
its
water
molecules,
in
solution.
partially
charged
dissolved
of
polar
negative
partially
ions,
so
both
substances
in
occurs.
toK
Hydphii nd hydphbi
How do scientic explanations dier
Substances can be hydrophilic or hydrophobic.
from pseudo-scientic explanations?
The
literal
meaning
of
the
word
hydrophilic
is
water-loving.
It
is
used
to
Homeopathy is a practice where
describe
substances
that
are
chemically
attracted
to
water.
All
substances
remedies are prepared by dissolving
that
dissolve
in
water
are
hydrophilic,
including
polar
molecules
such
things like charcoal, spider venom
as
glucose,
and
particles
with
positive
or
negative
charges
such
as
or deadly nightshade. This “mother
sodium
and
chloride
ions.
Substances
that
water
adheres
to,
cellulose
for
tincture” of harmful substance is diluted
example,
are
also
hydrophilic.
again and again to the point where a
Some
substances
are
insoluble
in
water
although
they
dissolve
in
other
sample from the solution is unlikely to
solvents
such
as
describe
them,
propanone
(acetone).
The
term
hydrophobic
is
used
to
contain a single molecule of the solute.
though
they
are
not
actually
water-fearing.
Molecules
It is this ultra-dilute solution that is
are
hydrophobic
if
they
do
not
have
negative
or
positive
charges
and
are
claimed to have medicinal proper ties.
nonpolar.
All
lipids
are
hydrophobic,
including
fats
and
oils
The proper ties are referred to as the
“memory of water ”. Despite the large
number of practitioners of this practice,
no homeopathic remedy has ever been
shown to work in a large randomized
placebo-controlled clinical trial.
▲
Figure 3 When two nonpolar molecules in water come into contact, weak interactions form
between them and more hydrogen bonds form between water molecules
70
2 . 2
If
a
nonpolar
form
and
the
water
as
water
though
This
each
is
a
and
are
result,
in
are
to
water
nonpolar
each
but
to
bonds
forces
tend
bring
that
known
form
it
is
are
is
a
if
to
nonpolar
they
are
in
water
because
water
molecules
contact
molecules.
water
nonpolar
in
by
behave
attraction
they
the
bonds
molecule
surrounded
together,
between
together
hydrophobic
hydrogen
nonpolar
slight
simply
than
join
cause
as
There
other
the
them
signicantly,
can
to
molecules,
between
molecules
other.
more
each
molecules
are
water
not
water-fearing:
attracted
The
by
but
movements
hydrogen
they
more
nonpolar
groups
two
attracted
more
groups.
If
random
molecules,
because
larger
into
and
other,
are
surrounded
molecules,
molecules.
they
not
is
water
nonpolar
molecules
As
the
molecules
between
with
molecule
between
W a t e r
molecules.
to
to
form
join
larger
together
interactions.
cmping wt nd mthn
Comparison of the thermal proper ties of water with
those of methane.
The
properties
waste
product
in
habitats
in
swamps
termites,
and
cattle
single
can
form
do
and
very
other
be
it
form
lacking.
wetlands
sheep.
used
methane
already
as
a
are
bonds.
and
They
to
bonds,
in
produce
fuel
to
but
the
both
described.
certain
the
live
guts
in
methane
if
allowed
a
prokaryotes
animals,
dumps
escape
with
live
live
are
digesters.
into
atoms
are
molecules
result
a
including
and
anaerobic
molecules
methane
As
to
is
that
the
effect.
molecules
water
of
in
Methane
prokaryotes
waste
greenhouse
small
whereas
bonds.
in
Methanogenic
also
However
hydrogen
been
respiration
is
contributes
hydrogen
their
linked
polar
are
physical
and
by
can
nonpolar
and
properties
are
different.
The
data
and
water.
methane
a
oxygen
and
covalent
not
have
encouraged
atmosphere
Water
water
anaerobic
where
deliberately
Methane
of
of
higher
higher
liquid
in
table
The
and
melting
a
shows
water
specic
over
1
density
in
heat
point
range
some
and
a
liquid
capacity,
and
of
of
22
data
latent
boiling
°C,
water
of
of
given
that
methane
for
water
over
methane
100
H
O
2
16
18
3
Specic heat capacity
0.46g per cm
2.2 J per g per °C
Latent heat of vaporization
Melting point
760 J/g
is
°C.
W
4
Density
has
vaporization,
Whereas
liquid
CH
Molecular mass
are
shows
heat
point.
is
M
Formula
properties
capacity
The
higher
Pp 
physical
heat
state.
higher
only
the
specic
3
1g per cm
4.2 J per g per °C
2,257 J/g
−182 °C
0 °C
−160 °C
100 °C
▲
Boiling point
Figure 4 Bubbles of methane gas, produced by
prokaryotes decomposing organic matter at
▲
T
able 1 Comparing methane and water
the bottom of a pond have been trapped in ice
when the pond froze
71
2
M O L E C U L A R
B I O L O G Y
cing th bdy with swt
Use of water as a coolant in sweat.
Sweat
is
is
secreted
carried
skin
along
where
it
evaporation
tissues
Blood
of
the
skin,
This
body
can
as
sodium,
brain.
in
It
are
be
is
left
temperature
receptors
glands
to
Usually
the
target
secreted
is
because
to
is
sweat
to
two
the
is
of
if
we
secreted
body
to
of
evaporation
an
of
of
example.
water
which
from
is
of
cooling
these
also
water.
useful
in
leaves;
hot
on
Panting
Transpiration
plant
other
rely
is
it
than
heat
in
sweating,
loss
dogs
evaporative
has
a
due
and
cooling
birds
loss
effect
environments.
of
ions
and
hypothalamus
If
of
methods
many
taste.
the
from
body
the
sweat
body
when
blood
inputs
stimulates
are
intense
surface
monitor
the
to
is
the
heat
salty
the
skin.
if
the
are
cooling
sensory
though
even
period
cause
by
for
from
latent
skin
that
though
especially
their
litres
secreted
adrenalin
a
the
the
of
high
by
There
the
therefore
a
receives
temperature,
we
anticipates
tend
up
sweat
is
sweat,
on
sweat
of
temperature.
the
in
needed
taken
has
hypothalamus
secrete
no
skin
receptors
also
is
The
surface
heat
their
controlled
and
skin.
the
method
detected
has
the
the
in
temperature
overheated
sweat
water
the
to
The
reducing
Solutes
secretion
the
out.
effective
because
sometimes
Sweat
of
an
in
ducts
through
is
vaporization.
such
water
owing
cooled.
glands
spreads
of
the
by
narrow
per
is
is
sweat
hour.
below
adrenalin
already
when
cold.
our
activity
is
This
brain
that
will
overheat.
Tnspt in bd psm
Methods of transpor t of glucose, amino acids, cholesterol, fats, oxygen and
sodium chloride in blood in relation to their solubility in water.
Blood
using
and
transports
several
ensure
a
wide
methods
that
each
variety
to
avoid
of
substance
is
Glucose
substances,
possible
problems
carried
in
water
is
and
quantities
for
the
body’s
freely
chloride
soluble
in
is
an
water,
ionic
molecule.
It
dissolved
is
in
freely
blood
soluble
in
plasma.
is
a
nonpolar
molecule.
Because
of
the
needs.
small
Sodium
polar
carried
large
Oxygen
enough
a
is
compound
dissolving
to
that
form
is
sodium
only
size
of
the
sparingly
oxygen
at
molecule
and
water
relatively
low
it
dissolves
becomes
in
water
saturated
concentrations.
but
with
Also,
as
+
ions
(Na
carried
)
in
and
chloride
blood
ions
(Cl
),
which
are
the
temperature
oxygen
plasma.
hold
Amino
acids
have
both
negative
and
but
Because
their
group,
of
solubility
some
of
this
they
varies
which
are
soluble
depending
are
on
hydrophilic
decreases,
much
in
the
°C
or
hydrophobic.
All
amino
acids
are
to
be
carried
dissolved
in
lower.
plasma
can
little
provide
while
to
plasma
oxygen
solubility
at
37
than
°C
of
can
water
The
amount
of
oxygen
that
at
blood
transport
for
around
aerobic
the
cell
body
is
far
respiration.
too
This
others
is
overcome
the
use
of
Hemoglobin
by
has
binding
hemoglobin
in
soluble
blood
blood
cells.
sites
for
plasma.
oxygen
blood
72
blood
dissolved
the
R
red
enough
so
rises,
water
problem
are
less
water
positive
20
charges.
of
and
for
greatly
oxygen
increases
transport.
the
capacity
of
the
2 . 3
Fats
molecules
than
oxygen
carried
These
in
are
are
and
blood
entirely
are
inside
groups
of
nonpolar,
insoluble
in
lipoprotein
molecules
are
water.
c a r b o h y d r a t e s
a n d
l i P i d s
larger
They
phospholipid
are
complexes.
with
a
single
protein
layer
cholesterol
of
phospholipid
hydrophilic
on
the
phosphate
outside
heads
and
of
fats
the
inside.
The
phospholipids
triglyceride
face
the
outwards
blood
plasma.
tails
face
fats.
There
inwards
are
monolayer,
is
a
not
water
small
and
also
to
hydrophilic
in
the
are
the
at
cholesterol
transported
one
of
the
with
This
in
fats
in
molecules
monolayers,
outwards
the
apart
end.
dissolve
cholesterol
facing
heads
with
phospholipid
hydrophobic,
region
The
in
lipoprotein.
phospholipid
region
phosphate
in
water
hydrocarbon
contact
name
complexes.
positioned
in
proteins
is
with
hydrophobic
the
it
contact
are
make
instead
the
the
The
molecules
are
with
in
hydrophilic
enough
lipoprotein
are
and
hence
Cholesterol
from
and
in
the
with
region
phospholipids.
▲
Figure 5 Arrangement of molecules in a lipoprotein complex
2.3 c  p
undstnding
appitins
➔
Monosaccharide monomers are linked
➔
Structure and function of cellulose and starch
together by condensation reactions to form
in plants and glycogen in humans.
disaccharides and polysaccharide polymers.
➔
➔
Scientic evidence for health risks of trans-fats
Fatty acids can be saturated, monounsaturated
and saturated fats.
or polyunsaturated.
➔
➔
Lipids are more suitable for long-term energy
Unsaturated fatty acids can be cis or trans
storage in humans than carbohydrates.
isomers.
➔
➔
Evaluation of evidence and the methods used
Triglycerides are formed by condensation from
to obtain evidence for health claims made
three fatty acids and one glycerol.
about lipids.
Nt f sin
➔
Evaluating claims: health claims made about
Skis
➔
lipids need to be assessed.
Use of molecular visualization software to
compare cellulose, starch and glycogen.
➔
Determination of body mass index by
calculation or use of a nomogram.
73
2
M O L E C U L A R
B I O L O G Y
cbhydts
toK
Monosaccharide monomers are linked together by
i w mpg pgm gv
 xp   pm,
condensation reactions to form disaccharides and
w  w  w  ?
polysaccharide polymers.
Thomas Kuhn, in his book The Structure of
Glucose,
fructose
and
ribose
are
all
examples
of
monosaccharides.
The
Scientic Revolutions adopted the word
structure
of
glucose
and
ribose
molecules
was
shown
in
sub-topic
2.1.
‘paradigm’ to refer to the frameworks that
Monosaccharides
can
be
linked
are
single
together
to
make
larger
molecules.
dominate the interpretation of information
●
Monosaccharides
●
Disaccharides
sugar
units.
in a scientic discipline at a particular
point in time. The paradigm impacts the
kinds of questions that are supposed to
example,
be asked.
Sucrose
consist
maltose
is
made
is
by
of
two
made
monosaccharides
by
linking
a
linked
linking
two
glucose
glucose
and
a
together.
molecules
For
together.
fructose.
Nutritionism is the reductionist paradigm
Polysaccharides
●
that the presence
consist
of
many
monosaccharides
linked
together.
of indicator nutrients
Starch,
glycogen
and
cellulose
are
polysaccharides.
They
are
all
made
are the key determinant of healthy
by
food.
linking
together
glucose
molecules.
The
differences
between
them
Even highly processed food may
are
described
later
in
this
sub-topic.
be advertised as healthy depending
When
monosaccha r i d e s
combi ne ,
t hey
do
so
by
a
pr oc e ss
c al l ed
on the degree to which it contains
condensation
(gur e
molecule
an
1).
This
i nvo lve s
the
l os s
of
an
OH
from
one
‘healthy’ nutrients. Words like ‘carbs’,
and
H
from
another
m o l e cul e ,
whi ch
to g e th er
fo rm
‘vitamins’ and ‘polyunsaturated fat’ have
H
entered the everyday lexicon. Some
O.
Thus,
condensa ti o n
i nvo lve s
the
c om bin a t io n
of
s u bun i t s
and
2
yields
water.
argue that this aligns consumer anxiety
with the commercial interests of food
manufacturers.
Linking
together
polysaccharides
ATP
supplies
monosaccharides
is
an
energy
anabolic
to
the
to
form
process
and
disaccharides
energy
monosaccharides
and
has
this
to
and
be
used
energy
is
to
do
then
An alternative paradigm for determining
when
the
condensation
reaction
occurs.
the ‘healthiness’ of food is argued for by
Michael Pollan in his book “In Defense of
H
Food”. It argues that food quality should
H
H
H
Monosaccharides, C
H
6
O
12
6
be determined by cultural tradition which
e.g. glucose, fructose, galactose
tended to look at food more holistically:
OH
The sheer novelty and glamor of
H
O
2
the Western diet, with its seventeen
Condensation
thousand new food products every year
and the marketing power – thirty-two
Hydrolysis
(water removed)
(water added)
billion dollars a year – used to sell us
those products, has overwhelmed the
Disaccharide, C
H
12
O
22
11
force of tradition and left us where we
e.g. maltose, sucrose, lactose
now nd ourselves: relying on science
HO
O
OH
Glycosidic
and journalism and government and
bond
marketing to help us decide what to eat
Michael Pollan, In Defense of Food: An
Condensation
Hydrolysis
Eater's Manifesto
H
H
Polysaccharide
e.g. starch, glycogen
HO
▲
O
O
OH
Figure 1 Condensation and hydrolysis reactions between monosaccharides and
disaccharides
74
O
it.
used
2 . 3
c a r b o h y d r a t e s
a n d
l i P i d s
Imging bhydt ms
Use of molecular visualization software to compare
cellulose, starch and glycogen.
The
most
widely
can
be
use
JMol,
available
When
which
with
JMol
changes
●
used
downloaded
Use
to
is
to
use.
a
There
used,
on
the
that
you
molecule
function
are
software
also
Suggestions
resources
being
of
visualization
charge.
electronic
image
scroll
of
easier
software
the
the
are
the
molecular
free
of
you
mouse
to
be
see
JMol,
able
on
make
the
that
websites
this
to
the
which
websites
suitable
accompany
should
that
is
many
are
book.
make
these
screen:
image
larger
orsmaller.
●
Left
●
Right
of
click
and
click
move
to
molecular
display
model,
continuously
Spend
then
the
some
try
or
time
these
structure
the
menu
label
change
to
to
that
the
the
developing
questions
of
a
mouse
rotate
allows
atoms,
your
skill
your
in
skill
image.
you
make
background
test
the
to
the
change
the
molecule
style
rotate
colour.
molecular
level
and
visualization
learn
more
and
about
polysaccharides.
Questions
1
Select
●
glucose
What
colours
oxygen
2
Select
●
is
Select
the
amylose,
amylose
●
What
●
How
only
4
Select
is
must
●
at
a
the
How
to
stick
show
is
is
style
glucose
the
to
is
between
the
a
and
overall
and
sucrose
and
style
with
carbon,
a
black
hydrogen
background.
and
a
blue
the
glucose
unbranched
shape
ring
and
the
molecule?
white
then
background.
a
form
background.
longer
of
[1]
an
molecules
starch,
possible
with
select
the
molecule?
chain
are
[1]
linked
to
with
the
branched
where
an
different
between
extra
about
[1]
styles
form
there
third
this
glucose
is
and
colours
of
starch.
a
branch.
glucose
linkage,
molecules
to
that
Zoom
A
to
glucose
make
the
compared
in
you
in
to
prefer.
look
molecule
branch.
the
unbranched
parts
molecule?
many
glucose
in
glucose
the
a
one.
amylose
in
of
If
glucose?
position
linkages
●
the
which
other
linked
What
of
in
chain
many
one
sticks
amylopectin,
be
used
and
[2]
style
the
Amylopectin
closely
ball
difference
ring
wireframe
short
are
with
the
fructose
3
the
atoms?
sucrose
What
with
[1]
molecules
amylopectin
are
linked
molecule?
to
only
one
other
▲
[1]
Figure 2 Images of sugars using molecular
visualization software – (a) fructose,
(b) maltose, (c) lactose
75
2
M O L E C U L A R
B I O L O G Y
5
Select
glycogen.
amylopectin
●
6
What
Select
●
7
at
is
it
the
glucose
●
the
is
similar
of
starch.
difference
but
not
between
identical
glycogen
to
the
and
amylopectin?
[1]
cellulose.
How
Look
is
It
form
different
oxygen
molecule
What
pattern
atoms
along
shape
atom
in
do
the
in
the
that
from
forms
the
other
part
of
polysaccharides?
the
ring
in
[1]
each
chain.
you
notice
in
the
position
of
these
oxygen
chain?
Pyshids
Structure and function of cellulose and starch in plants and glycogen in humans.
Starch,
glycogen
together
glucose
functions
in
the
type
type
of
could
hand
at
top
glucose
in
in
Cellulose
glucose
is
made
atom
group
or
4
has
1
of
to
in
the
but
link
(on
to
link
the
is
the
6
is
right
glucose)
on
atom
on
group
it
major
from
and
left
(shown
used
to
form
In
points
points
atom
Figure 3 Glucose molecule
▲
Figure 4 Cellulose
1
alpha
downwards
upwards.
consequences
together
reactions
the
carbon
▲
for
glucose.
linking
on
and
which
downwards.
OH
Condensation
carbon
and
polysaccharides.
the
by
linking
differences
common
(shown
carbon
OH
made
of
atom
(β-glucose)
difference
molecules.
to
the
to
them
used
diagrams)
upwards
(α-glucose)
small
on
4
by
reactions,
diagrams
atom
some
due
any
most
carbon
OH
have
either
beta
The
made
structure
molecules.
actually
molecular
polysaccharides
1
groups,
molecular
The
can
on
is
make
glucose
are
carbon
of
This
to
all
their
condensation
OH
branches
pointing
This
in
on
side).
Glucose
but
OH
in
them
the
side
the
side
between
ve
of
used
are
yet
different.
polysaccharides.
OH
hand
cellulose
glucose
used
three
between
the
of
has
be
make
very
linkage
Glucose
only
are
and
molecules,
next
β-glucose
link
carbon
β-glucose.
atom
The
OH
Cellulose
groups
on
carbon
atom
1
and
4
point
in
molecules
β-glucose,
directions:
up
on
carbon
1
and
down
on
bring
these
OH
groups
together
and
allow
reaction
to
occur,
each
the
are
to
the
chain
previous
oriented
one.
has
The
to
be
positioned
glucose
alternately
subunits
upwards
and
at
in
180°
consequence
of
this
is
that
the
76
is
a
straight
chain,
rather
bonds
bundles
the
have
chains
bundles
of
with
linking
are
the
called
cellulose
cellulose
molecules.
microbrils.
very
high
tensile
strength
and
are
used
as
the
of
cellulose
basis
of
plant
cell
walls.
The
tensile
strength
chain
prevents
plant
cells
from
bursting,
downwards.
when
very
high
pressures
have
developed
cellulose
inside
molecule
form
to
even
The
to
β-glucose
They
added
unbranched
them
a
These
condensation
allowing
carbon4.
hydrogen
To
are
opposite
than
curved.
the
cell
due
to
entry
of
water
by
osmosis.
2 . 3
Starch
is
made
molecules.
As
condensation
carbon
of
the
point
in
atom
linking
1
of
one
can
curved,
starch.
be
In
is
Starch
types
this
amylose
and
is
only
are
has
by
the
a
helix.
more
plant
are
two
In
The
amylopectin
they
of
the
shape.
Molecules
but
is
forms
molecules
globular
cells.
hydrophilic
way.
molecule
α-glucose
a
both
molecules
same
There
on
atom4
groups
starch
of
are
of
too
both
large
▲
to
be
soluble
in
cells
in
where
water.
large
They
are
amounts
of
therefore
glucose
Figure 5 Starch
useful
need
to
be
glycogen
stored,
but
a
concentrated
glucose
solution
too
Starch
is
energy
much
used
in
water
as
seeds
a
to
store
and
enter
of
a
cell
glucose
storage
by
and
organs
it
remove
Starch
is
made
as
a
therefore
as
of
an
in
a
unbranched
glucose
is
being
made
faster
store
by
it
can
Glycogen
starch,
animals
liver
the
a
and
store
cause
▲
exported
very
there
more
and
similar
is
of
energy
in
stores
osmotic
in
It
is
in
form
leaf
is
at
molecules
both
molecule
or
at
any
of
ends
the
branched
molecule.
Starch
and
ends
glycogen
do
not
have
a
xed
size
and
the
cells
form
made
of
glucose
molecules
that
they
it
in
increased
or
contain
decreased.
in
of
by
the
acts
glucose,
be
the
Glycogen
glucose
both
glucose
done
plant.
making
plants:
of
With
the
stored
humans.
dissolved
problems.
of
branched
Glycogen
starch
the
of
parts
the
be
photosynthesis
branching,
fungi.
muscles
as
other
to
more
some
function
large
to
compact.
also
some
same
where
is
but
molecule
be
extra
can
potato
in
can
than
add
of
number
when
to
This
osmosis.
such
temporary
easy
them.
molecules
cells.
is
would
or
cause
l i P i d s
by
groups
carbon
OH
the
chain
forms
so
made
starch
in
that
made
OH
glucose
straight.
the
branched,
of
the
are
the
and
a n d
α-glucose
links
These
all
is
than
unbranched
chain
glucose
orientated
of
rather
so
the
between
glucose.
downwards,
starch
together
cellulose,
reactions
adjacent
consequence
is
by
in
c a r b o h y d r a t e s
has
as
cells
would
starch
and
Figure 6 Glycogen
lipids
Triglycerides are formed by condensation from three fatty
acids and one glycerol.
Lipids
are
of
being
of
lipid.
a
diverse
group
of
carbon
insoluble
in
water.
Examples
of
triglycerides
compounds
Triglycerides
are
the
are
fat
one
in
that
of
share
the
adipose
the
property
principal
tissue
in
groups
humans
77
2
M O L E C U L A R
B I O L O G Y
and
the
(37°C)
both
A
oil
in
but
body
sunower
solid
gure
condensation
linkage
This
an
of
alcohol.
acid
In
and
well,
by
they
Arctic
is
this
an
are
used
marine
used
room
so
fatty
each
the
on
as
cell
as
fatty
is
body
temperature
whereas
fatty
linked
and
acid
is
acids
to
the
molecules
acid
an
reaction
oils
are
liquid
at
the
are
with
the
one
glycerol
by
produced.
glycerol
reacts
between
with
glycerol
is
the
an
ester
OH
COOH
a
The
bond.
group
group
in
on
a
glycerol.
energy
stores.
respiration.
heat
at
°C)
three
water
when
the
liquid
(20
temperature.
acids
three
formed
case
are
combining
the
OH
aerobic
are
and
between
Fats
temperature
by
of
reaction,
bond
Triglycerides
released
made
Each
formed
type
fatty
is
7).
seeds.
room
temperature
triglyceride
(see
at
The
energy
Because
insulators,
for
they
from
do
example
them
not
in
can
conduct
the
be
heat
blubber
of
mammals.
Glycerol
Fatty acids
Triglyceride (fat)
H
H
HO
C
(CH
)
2
CH
n
C
O
3
(CH
)
2
CH
n
3
H
O
O
Condensation
(water removed)
H
HO
C
(CH
)
2
CH
n
C
O
3
(CH
)
2
O
CH
n
3
O
H
HO
C
(CH
)
2
CH
n
C
O
3
(CH
)
2
CH
n
3
H
O
3H
O
H
O
2
Ester
▲
bond
Figure 7 Formation of a triglyceride from glycerol and three fatty acids
engy stg
Lipids are more suitable for long term energy storage in humans than carbohydrates.
Lipids
and
storage
for
carbohydrates
humans,
long-term
used
of
in
are
cells
fats.
called
but
energy
They
adipose
immediately
around
some
organs
both
are
storage.
are
located
are
lipids
The
stored
tissue.
in
used
lipids
the
including
that
tissue
skin
the
and
greater
energy
used
specialized
Adipose
beneath
for
normally
cells
are
gram
of
groups
grams
is
more
can
also
kidneys.
is
are
several
r e a s o ns
for
us ing
than
carbo hy d r a tes
f or
The
is
lipids
are
around
of
we
with
of
body
have
with
us
in
whereas
each
about
actually
amount
gram
because
and
more
bats
important
that
amount
of
energy
released
in
six
energy
mass.
to
two
times
that
This
carry
our
wherever
we
go.
for
animals
such
as
y.
Stored
per
gram
of
lipids
is
lipids
have
amount
released
could
not
be
The
from
same
a
gram
amount
as
lipid
rather
than
adds
the
half
mass
as
Be ca us e
of
hea t,
insulators.
l ip id s
ar e
by
po or
the y
Thi s
is
ca n
the
be
use d
r e a so n
f or
as
much
carbohydrate
much
to
body
our
stored
advantage
of
lipids
fat
b e i ng
in
s ub- cuta ne ous
mass.
adipose
fact
r ol e s
w el l
energy
of
therefore
as
of
of
heat
stored
se cond ar y
p e r f or me d
double
conductors
carbohydrates.
s o me
cell
carbohydrates.
78
droplets
storage:
respiration
In
pure
associated
the
per
stores
even
that
the
is
so
in
form
associated,
l ong - ter m
●
●
stored
important,
birds
energy
water,
efcient
be
fats
water
li pi ds
It
rather
no
glycogen
of
energy
There
because
with
is
even
tissue
next
to
the
s ki n.
B eca us e
fat
2 . 3
is
liquid
as
a
at
shock
adipose
other
body
te mp e r atur e,
absorb e r.
tissue
T hi s
aro und
is
the
it
the
can
a l so
re a son
ki dney s
act
can
s om e
it
is
in
is
the
car b o hy dr ate
tha t
is
energy
muscles.
term
storage ,
in
Although
storage
of
the
lipids
ene r g y,
l ive r
ar e
a nd
i de a l
g ly co ge n
in
fo r
is
storag e .
T hi s
is
as
in
gl ucos e
by
the
a d i pos e
rapidl y.
or
to
easily
l i P i d s
tis sue
Glucos e
ae r o b i c
ce ll
r ap id ly
b lo od
ca n
to
and
wh e re
can n ot
be
u se d
r e sp ir a ti on
be
e it h e r
wh er e a s
and
fatty
acid s
ca n
onl y
be
use d
in
a e ro bi c
so m e
respiration.
The
of
and
li v e r
s tor es
up
to
15 0
gr a m s
lo n g-
u s ed
be ca us e
dow n
Fats
anaerobic
glycogen
s o me
m us cl es
stor e
up
to
for
2%
short-term
needed.
a n d
u se d
fats
for
broken
transported
mobilized
organs.
Glycogen
be
then
for
a nd
c a r b o h y d r a t e s
glycogen
by
mass .
gl yc og e n
d- q: Emperor penguins
0.4
During
the
Antarcti c
w inte r
fe mal e
0.5
E m pe ro r
8.0
penguins
live
and
feed
at
s ea ,
but
m a le s
h a ve
6.8
to
stay
on
the
ice
to
i ncuba te
the
s in g le
egg
the
18.2
female
eat
no
and
has
laid.
food.
the
Thr o ug hout
After
females
16
w e ek s
r e tur n.
thi s
the
W hil e
time
e ggs
the
th e
14.3
m al e s
h at c h
m a l es
ar e
0.8
12.0
incubating
groups
of
the
eg g s
about
the y
3,000
s ta nd
b ir ds .
in
To
tig ht l y
p ac k e d
i nv e st i g at e
the
captive before
reasons
were
for
standi ng
taken
from
a
in
g ro ups ,
co l o ny
at
10
ma le
Po inte
captive after
b i r ds
G e ol og ie
in
0.4
0.4
Antarctica.
They
ha d
a l r e ad y
s ur vi ve d
4
we e ks
6.9
without
food.
The y
were
ke pt
fo r
14
m o re
7
.7
14.4
1
7
.3
weeks
without
where
they
conditions
fo o d
could
were
in
no t
kept
f ence d
for m
the
encl os u re s
gr oups .
s ame
as
Al l
in
ot h e r
the
w il d
11.8
colony.
The
mean
air
te mpe r atur e
was
16.4 ° C.
2.2
The
composition
birds’
bodies
14-week
of
was
period
the
ca ptiv e
me a s ur e d
of
the
a nd
be for e
the
a nd
ex pe ri me nt.
w il d
a f t er
Th e
the
wild before
wild after
re s u lt s
Key
in
kilograms
are
s ho w n
a)
Calculate
the
total
in
gure
8.
water
group
of
mass
loss
for
each
lipid
birds.
[2]
protein
other substances
i)
wild
▲
ii)
b)
captive
Compare
captive
free
c)
Figure 8
in
the
birds
the
Besides
another
changes
with
lipid
of
content
the
birds
of
the
living
colony.
being
used
function
important
in
those
for
[2]
as
of
an
lipid
penguin
energy
which
survival.
source,
might
state
be
[1]
79
2
M O L E C U L A R
B I O L O G Y
Bdy mss indx
Determination of body mass index by calculation or use
of a nomogram.
The
by
body
mass
aBelgian
needed
to
index,
calculate
height
in
BMI
calculated
is
usually
statistician,
it:
abbreviated
Adolphe
the
mass
to
Quetelet.
of
the
BMI,
Two
person
in
was
developed
measurements
kilograms
and
are
their
metres.
mass
using
in
this
formula:
kilograms
__
BMI
=
2
(height
in
metres)
2
Units
BMI
can
straight
on
the
for
also
line
based
BMI
is
is
kg
found
hand
to
too
using
a
page
on
81
whether
or
type
height
intersects
on
assess
high
m
the
scale
questions
used
or
be
are
between
right
data
level,
BMI
too
a
low.
of
chart
the
the
left
BMI
include
person’s
Table
bMi
1
a
called
hand
on
the
BMI
body
shows
a
nomogram.
scale
and
central
the
scale.
A
mass
The
nomogram.
mass
how
is
at
this
a
is
healthy
done:
s
av
below 18.5
underweight
18.5–24.9
normal weight
25.0–29.9
overweight
30.0 or more
obese
emg  
pg
To estimate body fat
percentage, measure the
thickness of a skinfold in
millimetres using calipers in
▲
T
able 1
In
some
these four places:
parts
of
the
world
food
supplies
are
insufcient
or
are
unevenly
Front of upper arm
distributed
and
many
people
as
a
result
are
underweight.
In
other
parts
Back of upper arm
of
the
world
a
likelier
cause
of
being
underweight
is
anorexia
nervosa.
Below scapula
This
is
a
psychological
condition
that
involves
voluntary
starvation
and
Side of waist
loss
of
body
mass.
The measurements are
Obesity
is
an
increasing
problem
added and then analysis
in
some
countries.
Excessive
food
tools available on the internet
intake
and
insufcient
exercise
can be used to calculate
cause
an
accumulation
of
fat
in
the estimate.
adipose
fat
can
tissue.
be
(gure
the
of
coronary
diabetes.
the
Figure 9 Measuring body fat
heart
It
with skinfold callipers
80
overall
countries
are
9).
such
disease
and
costs
is
of
life
of
body
skinfold
Obesity
reduces
where
rising.
using
conditions
signicantly
▲
amount
estimated
calipers
risk
The
increases
as
and
type
2
expectancy
increasing
health
rates
of
care
in
obesity
▲
Measuring body mass. What was this
person’s body mass index if their height
was 1.80 metres?
2 . 3
c a r b o h y d r a t e s
a n d
l i P i d s
d  q: Nomograms and BMI
Use
gure
11
to
answer
these
b)
questions.
Suggest
could
1
a)
State
who
the
has
body
a
mass
mass
of
index
75
kg
of
a
man
and
a
height
4.
of1.45metres.
b)
Deduce
a)
State
the
Outline
and
[1]
body
mass
status
of
this
man.
the
BMI
two
ways
reduce
her
in
relationship
for
a
xed
on
the
the
body
scales
mass
on
the
of
the
person
the
woman
mass.
between
bodymass.
[2]
height
[1]
[1]
body mass/kg
2
which
body
height/cm
standing
previouspage.
150
[1]
125
140
b)
The
person
has
a
height
of
1.8
metres.
130
Deduce
their
body
mass
status.
130
[1]
body mass index
120
3
a)
A
woman
has
a
height
of
150
cm
and
135
110
a
BMI
of
40.
Calculate
the
minimum
50
100
amount
of
body
mass
she
must
lose
140
to
95
reach
normal
body
mass
status.
Show
40
90
145
allof
your
working.
[3]
85
80
150
30
75
155
70
65
160
60
20
165
55
170
50
175
45
180
40
185
10
190
35
195
30
200
205
210
25
▲
Figure 10 Jogger
▲
Figure 11
Ftty ids
Fatty acids can be saturated, monounsaturated or
polyunsaturated.
The
a
basic
chain
covalent
chain
is
structure
of
bonds.
the
can
be
The
length
used
carbon
It
acid
is
variable
of
living
the
fatty
of
as
is
the
described
a
atoms
hydrocarbon
molecule.
hydrocarbon
the
was
hydrogen
This
is
in
sub-topic
linked
chain.
a
to
At
one
carboxyl
2.1.
them
end
group,
There
by
is
single
of
the
which
COOH.
organisms
feature
acids
with
therefore
part
represented
by
of
atoms,
have
bonding
chain
is
variable
between
between
14
and
the
but
20
most
carbon
carbon
of
the
fatty
atoms.
atoms.
In
acids
Another
some
fatty
81
2
M O L E C U L A R
B I O L O G Y
acids
C
but
C
H
H
C
C
a
carbon
it
C
H
C
H
C
H
C
H
C
C
H
C
H
C
C
H
C
H
hydrogen
C
C
H
H
C
H
Fatty
C
H
H
C
H
C
H
C
H
is
linked
it
can
bonds
H
C
C
H
C
H
is
are
linked
are
one
there
are
linked
linked
than
H
C
H
H
C
H
and
names
H
C
H
C
H
C
H
H
C
H
C
C
H
H
C
H
C
C
H
C
H
C
C
H
C
H
H
H
Figure
it
they
12
one
bond
double
to
all
to
to
by
or
by
single
more
double
adjacent
of
have
covalent
positions
covalent
carbons
one
could
one
or
less
in
specic
and
it
fatty
acids
is
is
saturated
fatty
is
more
bond
polyunsaturated
of
atom.
atoms
acid
in
atoms.
adjacent
bonds,
in
the
chain
bonds.
the
fatty
therefore
called
than
If
carbon
A
double
hydrogen
fatty
double
shows
an
carbon
one
the
to
hydrogen
hydrogen
its
contain
bond,
two
bond
one
possibly
that
double
C
C
a
bond
as
acids
H
H
also
between
because
one
by
only
more
C
atoms
atom
can
C
C
H
atoms
acids
chain
by
single
H
C
C
carbon
fatty
carbon
bonds,
H
the
C
C
If
H
of
other
OH
O
C
in
where
C
OH
O
all
OH
O
a
a
carbon
in
the
acid
chain,
with
contains
saturated
bonds
they
are
atom
single
as
much
fatty
acid.
unsaturated
could.
If
monounsaturated
there
and
is
if
it
has
polyunsaturated
fatty
acid,
acid.
IB
It
is
one
not
monounsaturated
necessary
to
remember
Biology.
unsttd ftty ids
H
Unsaturated fatty acids can be cis or trans isomers.
In
palmitic acid
linolenic acid
palmitoleic acid
• saturated
• polyunsaturated
• monounsaturated
• non-essential
• all cis
• cis
• essential
• non-essential
• omega 3
• omega 7
unsaturated
are
nearly
are
double
is
for
the
acids.
▲
fatty
always
acids
on
bonded
–
hydrogens
These
two
the
in
these
to
living
same
be
are
on
organisms,
side
of
called
the
cis-fatty
opposite
conformations
are
the
two
sides
shown
–
hydrogen
carbon
acids.
The
called
in
atoms
atoms
that
alternative
trans-fatty
gure
14.
Figure 12 Examples of fatty acids
In
cis-fatty
double
fatty
acids
saturated
with
acids,
bond.
less
fatty
H
C
C
C
at
acids,
they
acids
the
bond,
double
room
solid
H
good
Trans-fatty
partial
H
–
do
so
for
use
in
bend
in
the
triglycerides
it
fatty
not
hydrocarbon
containing
together
lowers
acids
the
are
in
regular
melting
therefore
have
a
have
bend
a
Trans-fatty
of
acids
vegetable
margarine
in
the
higher
the
than
liquid
and
or
hydrocarbon
melting
are
sh
some
point
produced
oils.
other
This
at
is
chain
and
are
room
articially
done
to
C
Figure 13 Double bonds
in fatty acids
Figure 1
4 Fatty acid stereochemistry – (a) trans (b) cis
at
solid
by
produce
processedfoods.
trans
82
at
Triglycerides
usually
H
▲
arrays
point.
cis
▲
chain
cis-unsaturated
oils.
they
temperature.
a
packing
so
are
hydrogenation
fats
is
makes
cis-unsaturated
temperature
at
there
This
2 . 3
c a r b o h y d r a t e s
a n d
l i P i d s
Hth isks f fts
Scientic evidence for health risks of trans-fats and
saturated fats.
There
on
In
have
human
this
disease
deposits,
A
rates
low
be
There
are
Kenya
of
does
amounts
of
blood
not
dietary
example
arteries
that
bre,
that
a
is
do
with
t
fat
by
fatty
the
fat
fatty
acid
nding
disease.
intake,
It
such
as
CHD.
correlation.
in
of
(CHD).
However,
cause
causes
rich
blocked
saturated
saturated
the
is
fats
types
disease
attacks.
programs.
actually
that
different
heart
heart
between
saturated
not
of
partially
and
research
that
diet
effects
coronary
become
found
many
correlated
have
the
formation
been
in
prove
factor
about
concern
clot
has
CHD
populations
for
main
coronary
to
another
claims
The
correlation
and
correlation
could
many
the
leading
positive
intake
a
been
health.
meat,
The
fat,
Maasai
blood
of
and
▲
milk.
They
therefore
have
a
high
consumption
of
saturated
Figure 15 Triglycerides in olive oil
fats,
contain cis-unsaturated fatty acids
yet
CHD
is
members
Diets
are
almost
of
rich
another
in
olive
traditionally
populations
has
been
fatty
of
explain
There
is
of
the
CHD
also
a
and
see
can
they
therefore
fatty
these
this
concentrations
rates
of
account
do
the
of
is
genetic
such
that
contains
countries
countries
positive
in
in
tribe
as
the
show
to
the
factors
use
of
Figure
this
17
shows
trend.
cis-monounsaturated
around
typically
due
the
Maasai.
in
the
have
low
intake
these
of
rates
of
CHD
in
acids,
The
and
it
cis-monounsaturated
populations,
tomatoes
fatty
Mediterranean.
many
or
other
dishes
could
rates.
probably
deposits
which
that
diet
consumed
if
oil,
However,
the
among
Kenyan
eaten
claimed
acids.
aspects
unknown
correlation
CHD.
for
the
cause
trans-fats,
risk
In
arteries
which
amounts
factors
correlation,
CHD.
diseased
between
Other
but
patients
have
gives
have
none
who
been
more
of
trans-fat
been
did.
had
found
tested,
died
to
evidence
to
Trans-fats
from
contain
of
a
CHD,
high
causal
narrowed
fatty plaque causing
lumen of ar tery
thickening of the ar tery lining
link.
layer of muscle
outer coat of ar tery
and elastic bres
▲
▲
Figure 16 Ar tery showing fatty plaque
Figure 1
7 Samburu people of Nor thern Kenya. Like the Maasai, the Samburu have
a diet rich in animal products but rates of hear t disease are ex tremely low
83
2
M O L E C U L A R
B I O L O G Y
evting th hth isks f fds
Evaluating claims: health claims made about lipids need to be assessed.
Many
some
health
cases
benet
and
harmful.
when
claims
the
in
other
Many
they
about
claim
are
is
cases
claims
tested
foods
that
the
it
is
have
are
made.
food
that
been
has
the
a
food
found
similar
In
health
to
controlled
be
false
health,
would
scientically.
but
be
almost
It
is
of
relatively
diet
on
numbers
easy
health
of
to
test
using
claims
about
laboratory
genetically
uniform
the
of
groups
health
Variables
amount
do
not
can
be
and
them
be
other
of
than
inuence
designed
of
with
selected
exercise,
strong
effect
of
can
diet,
can
the
so
factor
be
on
of
as
can
be
be
sex
and
that
as
exercise
to
eat
a
of
animal
Diets
varies
about
the
obtained
nding
food
are
by
a
of
used
what
in
the
the
but
they
health
diet.
It
do
effects
would
not
are
be
tell
on
very
into
a
control
humans
sex
were
It
and
used
would
other
they
also
variables
would
controlled
health
cohort
and
be
diet
risks
be
such
willing
for
nd
associated
of
a
long
out
their
factors
in
their
over
can
is
involve
measuring
health
increased
must
These
procedures
whether
an
food
Evidence
studies.
people,
Statistical
with
of
approach.
following
years.
to
the
different
epidemiological
large
a
then
the
diet
frequency
of
a
often
particular
interesting,
few
strictly
use
intake
period
be
animal.
experiments
twins
different.
to
age,
period.
therefore
are
Results
and
very
Researchers
they
factor
obtained
of
It
of
state
and
experiment.
dietary
terms
identical
genetically
humans.
groups
bred
experiments.
so
unless
in
with
matched
Large
temperature
the
one
thus
the
age,
in
controlled
only
can
same
use
such
results
that
evidence
this
the
for
select
subjects
impossible
enough
and
to
effects
animals.
animals
experiments
possible
experimental
is
be
might
us
with
humans
difcult
of
to
disease.
The
analysis
has
to
eliminate
certainty
a
the
effects
of
the
disease.
other
factors
that
could
be
causing
factor
carry
out
Nature of science question: using volunteers in experiments.
During
were
using
as
the
Second
conducted
conscientious
volunteers.
sacrice
their
knowledge.
20
a
The
A
eight
War,
to
For
six
70
help
C
to
weeks
mg
months,
of
and
were
in
the
they
US
service
willing
were
C.
all
given
volunteers
for
in
on
the
diet
with
70
mg,
seven
had
in
The
cross-linking
reduced
C.
to
All
10
of
mg
and
these
ten
ten
were
their
Three-centimetre
thighs,
with
ve
stitches.
was
also
gums.
These
bleeding
Some
serious
the
of
heart
wounds
wounds
from
the
cuts
hair
The
to
follicles
up
70mg
of
vitamin
C
fared
heal.
and
2
Is
it
vitamin
protein
killed
The
to
well
of
acceptable
perform
where
the
this
the
C
had
bres
and
for
doctors
experiments
or
on
there
is
a
risk
that
the
volunteers
will
be
harmed?
people
are
experiments,
more
or
less
paid
such
to
as
acceptable
participate
drug
than
trials.
using
mg
and
Is
it
better
to
use
animals
for
experiments
for
vitamin
C
ethical
objections
the
same
Is
it
acceptable
been
ironically
84
done
are
using
suitable
real
guinea-pigs,
because
which
guinea-pigs,
to
kill
animals,
have
experiment
also
or
are
did
4
requirements
in
Is
unpaid
as
with
humans?
notdevelopscurvy.
on
less
volunteers?
more
10
Sometimes
the
Experiments
and
collagen
strength.
ethically
medical
There
from
given
equally
then
tested.
C,
were
in
3
or
the
urine
no
with
developed
groups
restricted
between
and
were
was
During
developed
made
closed
failed
volunteers
problems.
were
skin
acid.
vitamin
were
health
scurvy.
plasma
of
their
given
volunteers
and
with
volunteers,
vitamin
blood
ascorbic
intakes
guinea-pigs
lower
scientists
dose
various
in
bone
guinea-pigs
therefore
synthesize
with
concentrations
1
kept
cannot
periods
collagen
involved
Then,
trial
monitored.
to
medical
England
vitamin
three
in
military
extend
trial
humans,
experiments
England
volunteers
vitamin
containing
next
in
objectors
health
volunteers.
diet
the
World
both
like
can
be
done?
so
that
an
2 . 3
c a r b o h y d r a t e s
a n d
l i P i d s
anysis f dt n hth isks f ipids
Evaluation of evidence and the methods used to obtain the evidence for health
claims made about lipids.
An
evaluation
implications
claims
two
1
is
comes
to
Implications
or
2
not
the
at
IB
scientic
ask
–
about
do
the
health
as
an
assessment
Evidence
research.
this
of
rigorous,
There
are
or
of
the
strongly,
or
–
were
are
the
there
research
rst
question
of
the
results
or
easiest
if
of
is
answered
of
a
results
–
survey.
are
by
●
methods
used
about
type
of
statistical
and
●
the
as
visual
Is
there
lipid
a
the
between
investigated
health
or
is
a
usually
graph
How
large
benet?
negative
is
slightly
the
rates
in
a
of
lipid
be
a
are
This
a
bar
data,
been
is
is
shown
scattergraph
chart.
the
less
The
likely
it
signicant.
done
on
the
data,
differences?
answered
points
below
questions
by
assessing
refer
to
should
the
surveys
be
asked
to
experiments.
was
the
necessary
survey
How
and
intake
rate
of
of
the
to
get
sample
to
have
reliable
size?
In
surveys
thousands
of
it
is
people
results.
even
was
the
the
This
might
be
and
less
the
sample
other
style?
factors
The
in
sex,
can
more
age,
affect
even
state
the
of
sample,
theresults.
either
If
the
sample
was
uneven,
were
the
results
a
to
eliminate
the
effects
of
other
factors?
correlation.
difference
of
life
disease
between
Were
the
the
disease
with
intake?
Small
measurements
of
lipid
intake
and
mean
rates
reliable?
Sometimes
people
in
a
different
differences
do
not
report
their
intake
accurately
may
and
not
have
different
large
survey
levels
The
controlled
disease
(average)
on
or
●
●
data?
on
the
signicant
question
adjusted
positive
bars
differences
tests
used.
usually
●
or
the
points
display.
correlation
being
error
show
second
health
●
is
data
spread
mean
they
How
●
other
If
methods
in
analysing
Analysis
of
widely
that
The
experimental
presented
size
of
research
weaknesses
either
spread
spread
is
assess
research
results
the
the
more
moderately
uncertainties
because
widely
the
do
conclusions
results
How
by
methodology?
The
●
health
research:
results
claim
for
all?
Limitations
the
in
limitations.
from
questions
support
dened
and
diseases
are
sometimes
misdiagnosed.
signicant.
d- q: Evaluating evidence from a health sur vey
The
Nurses’
survey
into
factors.
It
Health
the
Survey
health
began
in
is
a
highly
consequences
1976
with
Health
respected
of
121,700
161:672–679.
many
in
the
USA
and
Canada,
who
completed
questionnaire
about
their
lifestyle
assess
CHD,
medical
been
history.
Follow-up
completed
every
the
the
into
two
years
since
of
diagnose
by
the
reading
Journal
on
the
of
in
a
Intake
used
heart
research
MJ
and
and
Women:
Oh,
paper
20
K,
of
Years
assess
in
FB,
WC.
is
diet
be
5
was
effects
of
trans-fats
participants
five
intake.
the
average
American
was
freely
energy
(2005)
Heart
Follow-up
and
found
Manson,
Coronary
of
can
the
which
Hu,
Willett,
Risk
to
disease
Epidemiology,
internet:
Stampfer,
Fat
methods
coronary
doi:10.1093/aje/kwi085
in
the
on
rates
survey
groups
according
to
were
their
of
available
JE,
Dietary
Disease
the
Quintile
1
was
the
20 %
of
then.
participants
Details
Epidemiology,
questionnaires
trans-fat
have
of
factors
divided
and
Journal
a
of
lengthy
American
female
To
nurses
Study.
Nurses’
with
20 %
with
intake
of
calculated,
found
intake.
for
assigned
each
a
differences
mass
risk
the
the
as
a
The
1.
for
percentage
relative
quintile,
of
intake
highest
trans-fats
between
index,
lowest
The
the
smoking,
risk
with
risk
and
intake.
each
of
of
was
alcohol
The
quintile
dietary
CHD
Quintile
quintiles
quintile
was
1
adjusted
in
age,
intake,
for
body
parental
85
2
M O L E C U L A R
history
affect
of
18
energy
quintiles
CHD.
risk
of
is
a
and
graph
from
and
The
intake
rates
the
confidence
is
other
for
adjusted
of
level
of
the
1.6
that
factors.
1.4
percentage
each
of
relative
trans-fat
statistically
foods
other
showing
trans-fats
effect
CHD
of
various
the
risk
intake
on
significant
DHC fo ksir evitaler
of
CHD,
CHD
Figure
B I O L O G Y
five
of
relative
with
a
1.2
1.0
0.8
0.6
0.4
99 %
0.2
1
Suggest
reasons
for
using
only
female
nurses
0
in
this
survey.
[3]
1
2
State
the
trend
3
The
mean
was
not
age
shown
of
in
nurses
the
graph.
1.5
in
the
ve
Explain
the
reasons
2.0
2.5
3.0
percentage of energy from trans-fats
[1]
quintiles
Data for graph
the
same.
for
% of energy from
adjusting
the
results
to
compensate
for
the
1.3
1.6
1.9
2.2
2.8
1.0
1.08
1.29
1.19
1.33
trans-fat
effects
of
age
differences.
[2]
Relative risk of
CHD
4
Calculate
tests,
of
the
the
chance,
based
differences
in
on
the
CHD
statistical
risk
being
due
▲
to
factors
trans-fat
5
Discuss
factors
other
Figure 18
than
intake.
[2]
evidence
from
the
graph
that
other
were
having
some
effect
on
rates
ofCHD.
[2]
d- q: Saturated fats and coronary hear t disease
ainovalS
edargleB
roclaverC
ninajnerZ
18
14
12
10
10
9
9
9
9
8
7
3
3
992
351
420
574
214
288
248
152
86
9
150
80
290
144
66
88
1727
1318
1175
1088
1477
509
1241
1101
758
543
1080
1078
1027
764
1248
1006
emoR
eterC
akubihsU
ASU
19
saturated fat
ufroC
nehptuZ
19
by % calories as
akileV
dnalniF .W
22
ranked
aitamlaD
dnalniF .E
uramihsunaT
oigroigetnoM
Populations
% Calories as
saturated fat
Death
CHD
rate/
100,000
All
1
yr
▲
1
2
3
86
causes
T
able 2
a)
Plot
a
b)
Outline
Compare
a)
East
b)
Crete
scattergraph
the
the
and
Evaluate
results
West
and
the
trend
of
the
shown
data
by
in
the
table
2.
[5]
scattergraph.
[2]
for:
Finland;
[2]
Montegiorgio.
evidence
from
this
[2]
survey
for
saturated
fats
as
a
cause
of
coronary
heartdisease.
[4]
2 . 4
P r o t e i n s
2.4 P
undstnding
appitins
Amino acids are linked together by
➔
Rubisco, insulin, immunoglobulins, rhodopsin,
➔
condensation to form polypeptides.
collagen and spider silk as examples of the
There are twenty dierent amino acids in
➔
range of protein functions.
polypeptides synthesized on ribosomes.
Denaturation of proteins by heat or deviation of
➔
Amino acids can be linked together in any
➔
pH from the optimum.
sequence giving a huge range of possible
polypeptides.
The amino acid sequence of polypeptides is
➔
Skis
coded for by genes.
Draw molecular diagrams to show the formation
➔
A protein may consist of a single polypeptide or
➔
of a peptide bond.
more than one polypeptide linked together.
The amino acid sequence determines the three-
➔
dimensional conformation of a protein.
Nt f sin
Living organisms synthesize many dierent
➔
Patterns, trends and discrepancies: most but
➔
proteins with a wide range of functions.
not all organisms assemble polypeptides from
Every individual has a unique proteome.
➔
the same amino acids.
amin ids nd pypptids
Amino acids are linked together by condensation to form
polypeptides.
Polypeptides
amino
a
acids
process
are
the
chains
of
amino
condensation
called
Polypeptides
they
are
by
translation,
are
the
only
and
other
The
condensation
main
which
contain
reaction
that
will
component
component.
proteins
acids
reactions.
Some
two
or
are
This
be
of
made
happens
described
proteins
proteins
by
on
in
and
contain
linking
together
ribosomes
sub-topic
in
many
one
by
2.7.
proteins
polypeptide
more.
involves
the
amine
group
(
NH
)
of
one
amino
2
acid
and
the
carboxyl
group
(
COOH)
of
another.
Water
is
eliminated,
as
peptide bond
carboxyl
amino
group
group
H
H
N
C
H
1
C
OH
H
H
condensation
O
H
H
O
O
O
H
(water removed)
N
C
H
R
H
C
N
OH
R
H
C
C
N
C
C
OH
H
R
R
O
2
▲
Figure 1 Condensation joins two amino acids with a peptide bond
87
2
M O L E C U L A R
B I O L O G Y
in
all
condensation
amino
acids,
of
amino
two
consisting
called
of
fewer
rather
many
amino
acids
can
even
amino
one
with
any
humans
longer
with
so
titin
is
35,213
A
bond.
by
number
are
far
is
is
of
a
is
a
molecule
the
34,350
is
the
two
consisting
is
a
molecule
bonds.
acids,
to
protein
and
between
polypeptide
referred
which
of
A
formed
amino
small
acids
chain
is
peptide
usually
titin,
amino
bond
dipeptide
linked
amino
a
new
peptide
Insulin
21
discovered
a
acids
polypeptides.
polypeptide
In
contain
20
a
bond.
by
polypeptides,
muscle.
peptide
linked
than
than
a
and
acids
Polypeptides
of
reactions,
amino
contains
with
of
chains
oligopeptides
that
other
part
though
as
the
30.
two
The
largest
structure
acids,
but
in
of
mice
it
is
acids.
Dwing pptid bnds
Draw molecular diagrams to show the formation of a peptide bond.
To
a
form
a
dipeptide,
condensation
of
one
other.
amino
This
is
two
reaction
acid
and
shown
amino
between
the
in
acids
the
carboxyl
gure
are
linked
amine
group
●
by
There
group
of
the
with
peptide
group
at
the
showing
showing
bond
amino
how
the
is
the
acid
same,
carries.
peptide
formation
chain
of
forming
a
atoms
the
repeating
linked
backbone
sequence
by
of
of
single
the
N
covalent
oligopeptide,
C
C
1.
●
The
is
bonds
whatever
To
bonds
test
are
of
a
in
gure
R
your
bond
hydrogen
to
skill
formed,
peptide
A
each
an
try
atom
nitrogen
oxygen
one
of
the
The
amine
linked
atom
atom
two
is
is
in
the
linked
carbon
by
by
a
single
bond
backbone
a
double
and
bond
to
atoms.
between
●
(
NH
)
and
carboxyl
(
COOH)
2
two
of
the
amino
acids
2.
There
are
groups
sixteen
possible
dipeptides
that
can
be
these
four
amino
could
amino
also
acids,
try
to
linked
draw
by
an
three
oligopeptide
peptide
of
bonds.
four
and
this
correctly,
you
only
should
see
these
If
These
terminals
in
forming
the
peptide
remain
at
the
ends
of
the
of
are
called
the
the
amino
and
carboxyl
chain.
you
●
do
up
acids.
chain.
You
used
produced
bond
from
are
The
R
groups
of
each
amino
acid
remain
and
features:
project
outwards
from
the
backbone.
COOH
OH
H
H
N
H
C
H
C
COOH
H
H
2
N
H
C
H
C
COOH
H
N
H
C
COOH
H
N
C
glutamic acid
COOH
2
H
H
H
serine
H
C
2
2
H
▲
H
H
C
alanine
glycine
Figure 2 Some common amino acids
Th divsity f min ids
There are twenty dierent amino acids in polypeptides
synthesized on ribosomes.
The
amino
acids
polypeptides
in
the
group
centre
and
group,
88
all
a
of
that
have
the
are
is
atom.
different
in
together
identical
molecule
hydrogen
which
linked
some
is
bonded
The
each
by
ribosomes
structural
to
carbon
amino
an
amine
atom
acid.
to
features:
is
a
make
carbon
group,
also
a
bonded
atom
carboxyl
to
an
R
2 . 4
Twenty
different
polypeptides.
forming
give
a
the
the
these
of
peptide
to
the
Some
and
use
proteins
it
between
the
The
by
the
R
ribosomes
carboxyl
it
of
the
repertoire
of
R
table
is
their
1.
wide
It
is
groups,
to
make
groups
of
twenty
used
up
acids
to
try
that
amino
in
that
allows
proteins.
necessary
remember
the
are
amino
range
not
important
R
to
groups
groups
amazingly
in
but
used
and
is
an
shown
differences
very
so
character.
are
differences
chemically
are
groups
bond,
its
make
differences
specic
acids
amine
polypeptide
organisms
of
amino
The
P r o t e i n s
living
Some
to
learn
because
acids
are
diverse.
contain
amino
acids
that
are
not
in
the
basic
repertoire
av
of
twenty.
In
most
cases
this
is
due
to
one
of
the
twenty
being
modied
s v 
after
a
polypeptide
modication
provide
walls.
at
of
tensile
been
amino
acids
strength
Collagen
many
has
in
in
hydroxyproline,
but
at
which
collagen,
tendons,
polypeptides
positions,
synthesized.
made
some
makes
of
a
by
is
an
structural
ligaments,
skin
ribosomes
these
the
There
protein
and
more
it
is
of
used
blood
contain
positions
collagen
example
to
Ascorbic acid (vitamin C) is
vessel
needed to conver t proline
proline
converted
into hydroxyproline, so
to
ascorbic acid deciency
stable.
leads to abnormal collagen
production. From your
Eleven R groups are hydrophilic
Nine R groups are hydrophobic
knowledge of the role of
with between zero and nine
collagen, what eects do
Seven R groups can become charged
carbon atoms
Four
you expect this to have?
hydrophilic
Four R groups act as
Three R groups act as
an acid by giving up a
a base by accepting a
proton and becoming
proton and becoming
negatively charged
positively charged
Test your predictions by
Three R
Six R groups
R groups are
groups contain
do not contain
polar but never
rings
rings
charged
researching the symptoms
of ascorbic acid deciency
(scurvy).
▲
T
able 1 Classication of amino acids
amin ids nd igins
Patterns, trends and discrepancies: most but not all organisms assemble
polypeptides from the same amino acids.
It
is
a
remarkable
proteins
cases
using
amino
fact
the
acids
that
same
are
most
20
organisms
amino
modied
acids.
after
a
In
make
will
always
some
and
do
been
synthesized,
but
the
initial
process
together
amino
acids
on
All
life
has
ribosomes
bonds
usually
involves
the
same
of
for
to
it.
exclude
chance.
Several
the
possibility
There
must
hypotheses
be
that
one
have
this
or
been
trend
more
is
by
acids,
reasons
These
by
of
20
amino
chemical
life,
so
all
continued
have
They
been
acids
processes
were
on
organisms
to
use
used,
them.
if
they
the
Earth
used
produced
before
them
Other
had
ones
and
amino
been
the
origin
have
acids
might
available.
are
way
that
ribosomes,
are
the
ideal
20
amino
wide
range
of
proteins,
so
to
change
by
new
acids
for
natural
is
a
it
single
20
ancestral
amino
acids.
polypeptides
is
difcult
the
for
repertoire
removing
are
any
existing
of
amino
ones
or
ones.
complicated
commonly
been
found
normally
(stop
signal
acid.
code
for
science
encountered.
that
codons)
amino
use
the
to
For
one
end
encode
of
of
example,
the
discrepancies
species
three
extra
some
and
have
codons
polypeptide
an
selenocysteine
and
Some
that
synthesis
non-standard
species
some
use
use
UGA
UAG
to
making
code
a
a
these
proposed:
to
●
from
used
the
either
adding
Biology
●
acids.
acids.
can
due
them
20
organism
We
amino
use
with
made
amino
evolved
which
Because
peptide
other
that
of
species,
linking
use
organisms
polypeptide
●
has
not
favour
for
pyrrolysine.
selection
89
2
M O L E C U L A R
B I O L O G Y
d- q: Commonality of amino acids
1
a)
Discuss
20
which
amino
of
acids
the
by
three
most
hypotheses
organisms
is
for
use
of
supported
the
by
same
the
evidence.
b)
2
Suggest
Cell
walls
of
of
these
Also,
whereas
▲
of
testing
bacteria
that
Some
20.
ways
of
compound
[3]
contain
contains
amino
some
the
20
of
one
them
are
are
acids
the
hypotheses.
peptidoglycan,
sugars
acids
amino
of
and
short
different
into
complex
chains
from
right-handed
made
a
[2]
of
the
carbon
amino
usual
forms
of
polypeptides
acids.
repertoire
amino
are
acids,
always
the
Figure 3 Kohoutek Comet – 26 dierent
left-handed
forms.
Discuss
whether
this
is
a
signicant
discrepancy
amino acids were found in an articial comet
that
falsies
the
theory
that
living
organisms
all
make
polypeptides
produced by researchers at the Institut
using
the
same
20
amino
acids.
[5]
d’Astrophysique Spatiale (CNRS/France),
which suggests that amino acids used by the
rst living organisms on Earth may have come
from space
Pypptid divsity
Amino acids can be linked together in any sequence
av
giving a huge range of possible polypeptides.
cg ppp v
Ribosomes
fully
nm
nm  p
 m
m  q
amino
The
link
formed.
acids,
number
amino
The
so
of
acids
together
ribosome
any
can
sequence
possible
of
amino
one
make
amino
acid
at
a
time,
peptide
acids
until
bonds
is
sequences
a
polypeptide
between
any
pair
is
of
possible.
can
be
calculated
starting

with
dipeptides
(table
2).
Both
amino
acids
in
a
dipeptide
can
be
any
1
1
20
2
20
of
the
twenty
so
there
are
twenty
times
twenty
possible
sequences
2
(20
2
3
).
There
are
20
×
20
×
20
possible
tripeptide
sequences
(20
).
For
400
n
apolypeptide
3
of
n
amino
acids
there
are
20
possible
sequences.
8,000
The
number
of
amino
acids
in
a
polypeptide
can
be
anything
from
20
to
4
tens
of
thousands.
one
example,
if
a
polypeptide
has
400
amino
400
6
20
Taking
64 million
acids,
there
bogglingly
are
20
large
possible
number
and
amino
some
acid
sequences.
online
This
calculators
is
a
simply
mind-
express
it
as
10.24 trillion
innity.
▲
T
able 2 Calculate the missing values
acids,
If
the
we
add
all
number
is
the
possible
effectively
sequences
for
other
numbers
of
amino
innite.
Gns nd pypptids
The amino acid sequence of polypeptides is coded for
by genes.
The
number
immense,
these.
Even
different
The
in
Some
acid
▲
amino
living
so,
a
base
acid
genes
have
of
and
of
other
a
sequences
cell
a
of
only
that
store
each
could
actually
produces
must
sequence
sequence
sequence
acid
organisms
typical
sequences
amino
the
of
but
be
polypeptides
the
produced
produce
is
small
with
information
polypeptide
a
thousands
needed
stored
is
fraction
in
a
to
do
coded
of
of
this.
form
gene.
roles,
but
polypeptide.
most
They
genes
use
the
in
a
cell
genetic
store
code
the
to
amino
do
this.
Figure 4 Lysozyme with nitrogen of amine
groups shown blue, oxygen red and sulphur
yellow. The active site is the cleft upper left
Three
the
bases
the
polypeptide.
require
90
of
a
gene
gene
In
are
theory
with
a
needed
a
to
code
polypeptide
sequence
of
1,200
for
with
each
400
bases.
In
amino
amino
acid
acids
practice
in
should
genes
are
2 . 4
always
longer,
also
at
certain
The
base
sequence
molecular
extra
in
as
frames
base
the
that
biologists
openreading
ofa
with
points
sequences
only
both
ends
and
sometimes
middle.
actually
the
at
P r o t e i n s
codes
open
for
reading
occupy
a
a
polypeptide
frame.
small
One
is
known
puzzle
proportion
of
the
is
to
that
total
DNA
species.
Ptins nd pypptids
A protein may consist of a single polypeptide or more than
one polypeptide linked together.
Some
or
proteins
more
are
single
polypeptides
polypeptides,
linked
but
others
are
composed
of
two
together.
▲
Figure 5 Integrin embedded in a membrane
(grey) shown folded and inactive and open
Integrin
is
a
membrane
protein
with
two
polypeptides,
each
of
which
with binding sites inside and outside the cell
has
a
hydrophobic
portion
embedded
in
the
membrane.
Rather
like
the
indicated (red and purple)
blade
and
adjacent
to
Collagen
a
handle
three
a
folding
other
consists
rope-like
the
each
of
of
or
can
three
molecule.
the
unfold
long
This
polypeptides
knife
and
polypeptides
move
polypeptides
structure
would
two
if
has
they
apart
wound
greater
were
can
when
it
is
together
tensile
separate.
either
working.
to
strength
The
be
form
than
av
winding
Molecular biologists are
allows
a
small
amount
of
stretching,
reducing
the
chance
of
the
investigating the numbers of
molecule
breaking.
open reading frames in selected
Hemoglobin
structures.
more
consists
The
four
effectively
to
of
four
parts
of
tissues
polypeptides
hemoglobin
that
need
it
with
associated
interact
than
if
to
they
non-polypeptide
transport
were
oxygen
species for each of the major
groups of living organism. It is
still far from cer tain how many
separate.
genes in each species code for
a polypeptide that the organism
nm 
exmp
bkg
actually uses, but we can
ppp
compare current best estimates:
Enzyme in secretions such as nasal mucus and
1
lysozyme
tears; it kills some bacteria by digesting the
•
Drosophila melanogaster,
the fruit y, has base
peptidoglycan in their cell walls.
sequences for about 14,000
Membrane protein used to make connections
2
polypeptides.
integrin
between structures inside and outside a cell.
•
Caenorhabditis elegans, a
Structural protein in tendons, ligaments, skin
nematode worm with less
3
collagen
and blood vessel walls; it provides high tensile
than a thousand cells, has
strength, with limited stretching.
about 19,000.
Transpor t protein in red blood cells; it binds
•
4
hemoglobin
Homo sapiens has base
oxygen in the lungs and releases it in tissues with
sequences for about 23,000
a reduced oxygen concentration.
dierent polypeptides.
▲
T
able 3 Example of proteins with dierent numbers of polypeptides
•
Arabidopsis thaliana, a
small plant widely used in
research, has about 27,000.
Ptin nfmtins
Can you nd any species with
The amino acid sequence determines the three-dimensional
greater or lesser numbers of
conformation of a protein.
The
conformation
conformation
and
its
is
of
a
protein
determined
constituent
open reading frames than these?
is
by
its
the
polypeptides.
three-dimensional
amino
Fibrous
acid
structure.
sequence
proteins
such
of
as
a
The
protein
collagen
91
2
M O L E C U L A R
B I O L O G Y
are
elongated,
globular,
or
with
usually
an
with
intricate
a
repeating
shape
that
structure.
often
Many
includes
proteins
parts
that
are
are
helical
sheet-like.
Amino
acids
always
added
globular
to
R
added
in
the
proteins
develop
the
are
the
groups
the
nal
of
the
one
same
by
one,
to
sequence
polypeptides
acids
a
make
This
that
is
polypeptide.
a
gradually
conformation.
amino
form
to
particular
fold
up
stabilized
have
been
as
They
they
by
are
polypeptide.
are
bonds
brought
In
made,
between
together
by
thefolding.
In
globular
Rgroups
▲
proteins
on
the
that
outside
are
of
soluble
the
in
water,
molecule
and
there
there
are
are
hydrophilic
usually
Figure 6 Lysozyme, showing how a polypeptide
hydrophobic
groups
on
the
inside.
In
globular
membrane
proteins
there
can be folded up to form a globular protein.
are
regions
with
hydrophobic
R
groups
on
the
outside
of
the
molecule,
Three sections that are wound to form a helix
which
are
attracted
to
the
hydrophobic
centre
of
the
membrane.
are shown red and a section that forms a sheet
is shown yellow. Other parts of the polypeptide
In
brous
proteins
the
amino
acid
sequence
prevents
folding
up
and
including both of its ends are green
ensures
that
the
chain
of
amino
acids
remains
in
an
elongated
form.
Dnttin f ptins
Denaturation of proteins by heat or pH extremes.
The
is
three-dimensional
stabilized
groups
of
of
these
weak
bonds
in
protein,
bonds
amino
and
results
by
a
acids
and
they
which
is
interactions
within
the
interactions
can
change
conformation
or
be
to
the
called
proteins
molecule.
are
disrupted
of
between
or
Most
conformation
of
As
This
of
the
protein
the
denatured
protein
does
not
normally
its
former
structure–
the
denaturation
Soluble
the
form
hydrophobic
molecule
by
and
proteins
the
Heat
often
cause
vibrations
break
in
in
microorganisms
that
or
water
are
near
not
higher.
was
National
of
this
the
it
that
Park.
at
heat
live
are
is
due
centre
the
new
ionic
ionic
water
exceptions:
and
bonds
to
on
R
within
form.
structure
that
become
contents
normally
acidic,
with
a
pH
as
is
the
optimum
pH
for
the
of
have
insoluble.
the
low
as
stomach
1.5,
but
protein-digesting
of
water
pepsin
that
works
in
the
stomach.
to
the
around
best
It
in
used
causes
lower
it
interactions.
vents
Some
springs
have
example
aquaticus ,
springs
at
causes
can
volcanic
best
in
or
that
80
is
a
in
°C
or
in
proteins
temperatures
hot
works
heat
much
by
known
Thermus
widely
because
of
80
°C
DNA
prokaryote
Yellowstone
and
because
biotechnology.
denaturation
temperatures.
of
most
▲
Figure 7 When eggs are heated, proteins that were dissolved
in both the white and the yolk are denatured. They become
insoluble so both yolk and white solidify
92
bonds
proteins
often
the
can
charges
three-dimensional
altered
in
alkaline,
become
This
tolerance.
in
geothermal
from
Nevertheless,
proteins
bonds
their
discovered
is
to
molecule
denatured
The
polymerase
that
exposed
the
denaturation
within
vary
in
is
and
because
breaking
causing
the
is
conformation.
intermolecular
Proteins
hot
precipitate.
groups
becoming
change
can
R
a
or
protein
enzyme
insoluble
changed,
heat,
acidic
This
is
this
permanent.
both
return
are
to
pH,
dissolved
There
A
are
with
been
denaturation.
of
denaturation.
groups
the
relatively
broken.
Extremes
cause
R
2 . 4
P r o t e i n s
Ptin fntins
av
Living organisms synthesize many dierent proteins with
d xpm
a wide range of functions.
A solution of egg albumen
Other
none
to
groups
can
the
of
compare
worker
functions
carbon
bees
listed
compounds
with
the
that
here
versatility
perform
are
have
carried
of
almost
out
by
important
proteins.
all
the
roles
They
tasks
in
in
the
can
a
be
hive.
cell,
but
compared
All
of
the
proteins.
in a test tube can be heated
in a water bath to nd the
temperature at which it
denatures. The eects of pH
can be investigated by adding
●
Catalysis
–
there
are
thousands
of
different
enzymes
to
catalyse
acids and alkalis to test tubes
specic
chemical
reactions
within
the
cell
or
outside
it.
of egg albumen solution.
●
Muscle
contraction
musclecontractions
–
actin
used
in
and
myosin
locomotion
together
and
cause
transport
the
To quantify the extent of
around
denaturation, a colorimeter
thebody.
can be used as denatured
albumen absorbs more light
●
Cytoskeletons
–
tubulin
is
the
subunit
of
microtubules
than dissolved albumen.
that
giveanimals
cells
their
shape
and
pull
on
chromosomes
duringmitosis.
●
Tensile
needed
strengthening
in
skin,
–
tendons,
brous
proteins
ligaments
and
give
blood
tensile
vessel
strength
walls.
av
●
Blood
clotting
–
plasma
proteins
act
as
clotting
factors
that
cause
bx
blood
to
turn
from
a
liquid
to
a
gel
in
wounds.
Botox is a neurotoxin
●
Transport
of
nutrients
and
gases
–
proteins
in
blood
help
obtained from Clostridium
transport
oxygen,
carbon
dioxide,
iron
and
lipids.
botulinum bacteria.
●
Cell
adhesion
–
membrane
proteins
cause
adjacent
animal
cells
1
tostick
to
each
other
within
What are the reasons
tissues.
for injecting it into
●
Membrane
transport
facilitateddiffusion
and
–
membrane
active
proteins
transport,
and
are
also
used
for
humans?
for
electron
2
transport
during
cell
respiration
and
What is the reason for
photosynthesis.
Clostridium botulinum
●
Hormones
–
some
buthormones
are
such
as
insulin,
chemically
very
FSH
and
LH
are
producing it?
proteins,
diverse.
3
●
Receptors
hormones,
–
●
sites
light
and
chromosomes
make
There
are
huge
insulinfor
this
treating
as
Increasingly,
microscopic
it
is
eye
the
of
to
are
most
is
still
genetically
protein
for
not
and
during
uses
to
modied
and
injecting it rather than
for
taking it orally?
also
group
with
DNA
in
eukaryotes
mitosis.
of
proteins,
as
cells
can
antibodies.
for
proteins
antibodies
treating
cytoplasm
smells,
associated
for
Pharmaceutical
easy
and
plants.
diverse
different
diabetics.
in
condense
monoclonal
proteins
tastes
and
biotechnological
stains,
different
expensive,
membranes
histones
numbers
many
forremoving
many
–
–
the
of
Immunity
DNA
in
Packing
help
in
neurotransmitters,
receptorsfor
●
binding
What are the reasons for
diseases.
synthesize
organisms
including
pregnancy
companies
These
tend
proteins
are
enzymes
tests
now
to
or
produce
be
very
articially.
being
used
as
factories.
93
2
M O L E C U L A R
B I O L O G Y
exmps f ptins
Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as
examples of the range of protein functions.
Six
proteins
which
illustrate
some
of
the
functions
of
proteins
are
described
r
in
table
4.
i
This name is an abbreviation for ribulose bisphosphate
This hormone is produced as a signal to many cells in
carboxylase, which is arguably the most impor tant
the body to absorb glucose and help reduce the glucose
enzyme in the world. The shape and chemical proper ties
concentration of the blood. These cells have a receptor
of its active site allow it to catalyse the reaction that xes
for insulin in their cell membrane to which the hormone
carbon dioxide from the atmosphere, which provides
binds reversibly. The shape and chemical proper ties of
the source of carbon from which all carbon compounds
the insulin molecule correspond precisely to the binding
needed by living organisms can be produced. It is
site on the receptor, so insulin binds to it, but not other
present at high concentrations in leaves and so is
molecules. Insulin is secreted by β cells in the pancreas
probably the most abundant of all proteins on Ear th.
and is transpor ted by the blood.
immg
rp
These proteins are also known as antibodies. They have
Vision depends on pigments that absorb light. One of
sites at the tips of their two arms that bind to antigens
these pigments is rhodopsin, a membrane protein of rod
on bacteria or other pathogens. The other par ts of the
cells of the retina. Rhodopsin consists of a light sensitive
immunoglobulin cause a response, such as acting as a
retinal molecule, not made of amino acids, surrounded
marker to phagocytes that can engulf the pathogen. The
by an opsin polypeptide. When the retinal molecule
binding sites are hypervariable. The body can produce
absorbs a single photon of light, it changes shape. This
a huge range of immunoglobulins, each with a dierent
causes a change to the opsin, which leads to the rod cell
type of binding site. This is the basis of specic immunity
sending a nerve impulse to the brain. Even very low light
to disease.
intensities can be detected.
cg
sp k
There are a number of dierent forms of collagen but all
Dierent types of silk with dierent functions are
are rope-like proteins made of three polypeptides wound
produced by spiders. Dragline silk is stronger than steel
together. About a quar ter of all protein in the human body
and tougher than Kevlar™. It is used to make the spokes
is collagen – it is more abundant than any other protein.
of spiders’ webs and the lifelines on which spiders
It forms a mesh of bres in skin and in blood vessel
suspend themselves. When rst made it contains
walls that resists tearing. Bundles of parallel collagen
regions where the polypeptide forms parallel arrays.
molecules give ligaments and blood vessel walls their
Other regions seem like a disordered tangle, but when
immense strength. It forms par t of the structure of teeth
the silk is stretched they gradually extend, making the
and bones, helping to prevent cracks and fractures.
silk extensible and very resistant to breaking.
Ptms
Every individual has a unique proteome.
A
proteome
organism.
an
organism.
mixtures
94
is
By
of
all
of
the
contrast,
To
nd
proteins
proteins
the
out
are
produced
genome
how
is
many
extracted
all
of
by
different
from
a
a
the
cell,
a
genes
tissue
of
proteins
sample
and
a
are
are
or
cell,
an
a
being
then
tissue
or
produced,
separated
2 . 4
by
gel
electrophoresis.
present,
marker
antibodies
can
Whereas
because
in
a
on
the
cell’s
a
unique,
us
has
become
▲
but
partly
exception
of
an
in
of
a
identify
protein
the
of
cells
the
species
differences
If
cell
an
in
The
there
are
the
identical
different
of
amino
unique
not
what
strong
differences
acid
twins,
none
proteome.
with
of
Even
the
vary
in
us
the
activity
the
variable
Even
is
actually
happen.
of
all
individual
also
because
With
of
is
depending
proteome
identical
proteome
is
what
each
proteins.
have
time
but
protein
uorescent
present.
could
of
a
proteins.
reveals
proteome
of
is
to
proteome
over
potentially
sequence
particular
different
therefore
of
a
linked
protein
xed,
make
similarities
The
not
been
the
made
proteome
differences.
because
is
organism
are
or
have
uoresces,
that
organism,
also
whether
that
organism
an
proteins
activities.
in
individuals,
To
the
genome
cell
happening
Within
used.
different
single
the
be
to
P r o t e i n s
the
small
possible
proteins,
identical
is
of
so
each
twins
can
age.
Figure 8 Proteins from a nematode worm have been separated by gel
electrophoresis. Each spot on the gel is a dierent protein
av
av : gm  pm
We might expect the proteome of an organism to be smaller than its genome,
as some genes do not code for polypeptides. In fact the proteome is larger.
How could an organism produce more proteins than the number of genes that
its genome contains?
95
2
M O L E C U L A R
B I O L O G Y
2.5 e m
undstnding
appitins
➔
Enzymes have an active site to which specic
Methods of production of lactose-free milk and
➔
substrates bind.
its advantages.
➔
Enzyme catalysis involves molecular motion
and the collision of substrates with the
active site.
➔
Temperature, pH and substrate concentration
aect the rate of activity of enzymes.
➔
Enzymes can be denatured.
➔
Immobilized enzymes are widely used in
industry.
Nt f sin
➔
Skis
Experimental design: accurate quantitative
Design of experiments to test the eect of
➔
measurements in enzyme experiments require
temperature, pH and substrate concentration
replicates to ensure reliability.
on the activity of enzymes.
Experimental investigation of a factor aecting
➔
enzyme activity. (Practical 3)
ativ sits nd nzyms
Enzymes have an active site to which specic
substrates bind
Enzymes
are
chemical
reactions
called
up
biological
biochemical
products
an
globular
in
proteins
without
catalysts
because
reactions.
these
The
reactions
enzyme-catalysed
that
being
as
they
called
catalysts
–
themselves.
are
substances
are
reaction
work
altered
made
that
by
they
living
enzymes
substrates.
A
speed
Enzymes
cells
and
convert
general
up
are
often
speed
into
equation
for
is:
enzyme
______
→
substrate
Enzymes
to
work
literally
only
Figure 1 Computer-generated image of the
reactions
enzyme hexokinase, with a molecule of its
This
substrate glucose bound to the active site. The
difference
enzyme bonds a second substrate, phosphate,
found
take
property
metals
all
of
living
them.
one
place
cells,
is
are
in
called
Many
and
are
produce
different
biochemical
nearly
all
in
and
catalytic
also
and
need
are
of
some
to
needed,
be
It
catalysts
cells
enzymes
thousands
specicity .
non-biological
by
different
enzymes
which
converters
secreted
many
reaction
of
enzyme–substrate
enzymes
used
cells
organisms
catalyse
between
that
in
Living
thousands
enzymes
▲
are
outside.
product
–
as
of
catalysed.
is
a
signicant
such
as
the
vehicles.
to the glucose, to make glucose phosphate
To
be
able
to
mechanism
96
explain
by
enzyme–substrate
which
enzymes
speed
specicity,
up
reactions.
we
must
This
look
involves
at
the
the
2 . 5
substrate,
enzyme
or
properties
the
substrates
called
of
the
substrate
into
to
products
then
the
active
bind,
while
released,
binding
active
site
but
they
freeing
site
and
not
are
the
to
a
(see
special
gure
the
The
substrate
other
to
site
the
to
on
the
shape
match
substances.
bound
active
region
1).
surface
and
each
active
catalyse
site
and
another
the
chemical
other.
Substrates
of
e n z y M e s
are
the
This
allows
converted
products
are
reaction.
d- q: Biosynthesis of glycogen
The
Nobel
Gerty
two
Prize
Cori
and
enzymes
for
her
that
Medicine
husband
convert
was
won
Carl.
in
They
glucose
1947
by
glycogen.
isolated
phosphate
of
into
ways,
4
Glycogen
glucose
called
Curve
B
hadnot
Explain
why
neededfor
two
the
different
synthesis
enzymes
of
Describe
b)
Explain
are
and
was
a)
Figure 2 Bonding in glycogen
1
1,4
a
polysaccharide,
bonded
1,6
together
bonds
obtained
been
noisrevnoc %
▲
is
molecules
(see
using
composed
in
two
gure
enzymes
2).
that
heat-treated.
the
the
shape
shape
of
of
Curve
Curve
B.
[2]
B.
80
[2]
B
60
glycogen
40
fromglucose
2
phosphate.
The
formation
rate
at
which
glucose
of
canbe
linked
on
[2]
side-branches
to
a
increases
phosphate
growing
20
the
molecules
A
10
glycogen
20
30
40
50
min
molecule.
Explain
the
reason
for
this.
[2]
▲
3
Curve
A
was
enzymes.
obtained
Explain
the
using
shape
heat-treated
of
curve
Figure 3 shows the percentage conversion of glucose
phosphate to glycogen by the two enzymes, over a
A.
[2]
50-minute period
enzym tivity
Enzyme catalysis involves molecular motion and the
collision of substrates with the active site.
Enzyme
three
The
●
activity
substrate
have
two
While
●
The
site
to
is
it.
and
we
how
With
the
to
two
of
a
reaction
need
by
an
enzyme.
There
are
a
substrate–active
most
reactions
enzyme.
can
site
of
the
different
to
the
which
the
only
enzyme.
parts
active
are
active
bind
together
on
a
site
of
This
road,
about
the
Because
bound
from
collision.
think
to
the
site,
of
site
Some
the
they
products
leaving
it
enzymes
active
site.
change
of
the
vacant
into
reaction.
for
again.
vehicles
to
are
active
bind
substances,
coming
as
the
that
separate
bind
molecule
The
known
between
to
substrates
products
substrate
close
catalysis
binds
chemical
substrates
A
the
substrates
the
different
●
is
stages:
but
is
in
a
active
site
if
it
molecule
suggest
that
molecular
substrates
the
substrate
might
collisions
water
to
a
a
would
motion
high
be
in
a
moves
and
an
velocity
very
active
impact
misleading
liquids
to
image
understand
occur.
are
dissolved
liquid
state,
in
its
water
around
molecules
and
all
97
2
M O L E C U L A R
B I O L O G Y
the
particles
dissolved
in
it
are
in
contact
with
each
other
and
are
in
toK
continual
motion.
movement
Each
repeatedly
particle
changes
can
and
move
is
separately.
random,
The
which
is
direction
the
basis
of
of
W   k  k m
diffusion
in
liquids.
Both
substrates
and
enzymes
with
active
sites
are
   p  
able
to
move,
though
most
substrate
molecules
are
smaller
than
the
- m?
enzyme
so
their
movement
is
faster.
The lock and key model and the
So,
collisions
between
substrate
molecules
and
the
active
site
occur
induced-t model were both developed
because
of
random
movements
of
both
substrate
and
enzyme.
The
to help to explain enzyme activity.
substrate
may
be
at
any
angle
to
the
active
site
when
the
collision
Models like these are simplied
occurs.
Successful
site
correctly
collisions
are
ones
in
which
the
substrate
and
active
descriptions, which can be used to
are
aligned
to
allow
binding
to
take
place.
make predictions. Scientists test these
predictions, usually by performing
experiments. If the results agree
with the predictions, then the model
is retained; if not then the model is
water molecules
modied or replaced. The German
scientist Emil Fischer introduced the
lock and key model in 1890. Daniel
substrates
Koshland suggested the induced-t
model in 1959 in the United States. The
conformational changes predicted by
Koshland's model were subsequently
observed using high-resolution X-ray
analysis of enzymes and other newly
active site
developed techniques. Although
much experimental evidence has
part of enzyme
accumulated conrming predictions
▲
Figure 4 Enzyme-substrate collisions. If random movements bring any of the substrate
based on the induced-t model, it is
molecules close to the active site with the correct orientation, the substrate can bind to the
still just viewed as a model of enzyme
active site
activity.
Fts ting nzym tivity
Temperature, pH and substrate concentration aect the
av
rate of activity of enzymes.
Mkg  p
Enzyme activity is aected by temperature in two ways
Bacillus licheniformis lives
●
In
liquids,
the
particles
are
in
continual
random
motion.
When
a
liquid
is
in soil and on decomposing
heated,
the
particles
in
it
are
given
more
kinetic
energy
.
Both
enzyme
and
feathers. What is the reason
substrate
molecules
therefore
move
around
faster
at
higher
temperatures
for it producing a protease
and
the
chance
of
a
substrate
molecule
colliding
with
the
active
site
of
the
that works best at alkaline
enzyme
is
increased.
Enzyme
activity
therefore
increases.
pH? Make a hypothesis to
explain the observations.
●
When
enzymes
How could you test your
the
chance
hypothesis?
enzyme
active
to
an
enzyme
typical
98
As
rises
the
the
has
more
are
Figure
has
and
shows
changes,
is
called
enzyme
activity
been
for
the
vibrate
When
denatured,
more
reasons
5
enzyme
enzyme
been
and
the
increased.
enzyme
enzyme
there
activity.
of
in
is
permanent
denatured,
when
enzyme.
is
molecule
reactions.
temperature
bonds
breaking
structure
change
become
altogether,
in
the
This
heated,
bonds
enzyme
catalyse
solution
are
the
break,
site.
When
of
is
no
of
the
longer
in
Eventually
and
able
a
it
denatured.
increases
effects
the
including
molecules
falls.
and
in
denaturation.
it
completely
both
more
bonds
stops
So,
as
decreases
temperature
on
a
2 . 5
e n z y M e s
Enzymes are sensitive to pH
rate at which reaction decreases owing
to denaturation of enzyme molecules
The
pH
The
lower
is
due
the
the
reducing
solution
ten
times
than
pH
used
pH,
at
the
measure
more
of
the
acid
ion
concentration.
pH
pH
7
by
is
and
so
one
than
A
pH
acidity
the
so
pH
makes
pH
4
alkalinity
alkaline
the
scale
a
solution
6,
or
less
ions,
The
unit
neutral.
acidic
or
hydrogen
the
more
6,
to
presence
hydrogen
that
A
to
is
is
is
pH
one
a
solution.
solution
the
pH,
6
is
ten
hundred
Acidity
higher
This
times
slightly
is.
the
logarithmic.
solution
at
a
lower
of
acidic;
times
means
more
acidic.
pH
more
noitcaer fo etar
the
scale
5
is
acidic
on.
rate at which
optimum
reaction increases
temperature
owing to increased
kinetic energy of
substrate and
enzyme
molecules
Most
enzymes
ha v e
highest.
If
the
pH
enzyme
activity
an
is
op ti mum
i ncr ea s e d
or
pH
at
wh ic h
de c r e as e d
th ei r
fr om
a c t ivi t y
the
is
actual
rate of
o ptim u m ,
reaction
the
hydrogen
d e cr e a s e s
ion
and
ev en t ua ll y
co nce ntr a ti on
is
h ig h e r
s tops
or
al t og e t he r.
l ower
t ha n
When
t he
le v el
at
0
which
the
enzyme
na tura l ly
wor ks ,
the
s tru c t u r e
of
t he
enz ym e
10
20
30
40
50
60
is
temperature/°C
altered,
of
the
including
enzyme
is
the
a cti ve
s ite .
ir r e v e rs ib ly
Be y on d
a lte re d.
a
T h is
c e rt ai n
is
pH
a n ot h er
the
s tru c t u r e
ex am pl e
▲
of
Figure 5 Temperature and enzyme activity
denaturation.
Enzymes
a
wide
do
not
range.
all
This
have
the
reflects
same
the
pH
wide
optimum
range
of
pH
–
in
fact,
there
environments
is
Key
in
stomach
which
enzymes
work.
For
example,
the
protease
secreted
by
1
Bacillus
acidic hot springs
licheniformis
has
a
pH
optimum
between
9
and
10.
This
bacterium
2
is
cultured
to
produce
its
alkaline-tolerant
protease
for
use
decaying plant matter
in
large intestine
biological
laundry
detergents,
which
are
alkaline.
Figure
6
shows
3
small intestine
the
pH
range
of
some
of
the
places
where
enzymes
work.
Figure7
alkaline lakes
4
shows
the
neutral
effects
of
pH
on
an
enzyme
that
is
adapted
to
work
at
pH.
5
6
Enzyme activity is aected by substrate concentration
Enzymes
site.
This
cannot
catalyse
happens
reactions
because
of
the
until
the
random
substrate
movements
binds
of
to
the
7
active
molecules
in
8
liquids
that
result
concentration
will
take
place
of
in
collisions
substrates
more
is
between
substrates
increased,
frequently
and
the
and
active
substrate–active
rate
at
which
site
the
sites.
If
the
collisions
9
enzyme
10
catalyses
its
However,
reaction
there
is
increases.
another
trend
that
needs
to
substrate
to
be
▲
considered.
an
active
After
site,
the
the
binding
active
site
of
is
a
occupied
Figure 6
and
Optimum pH at which enzyme
unavailable
to
other
substrate
molecules
until
activity is fastest (pH 7 is
products
have
been
formed
and
released
from
the
optimum for most enzymes).
active
more
any
site.
and
As
the
more
moment.
A
substrate
of
the
concentration
active
greater
and
sites
are
greater
rises,
occupied
proportion
at
As pH increases or decreases from the
of
optimum, enzyme activity is reduced.
For
this
reason,
enzymes
as
If
and
increases
concentration
enzyme
but
is
is
in
therefore
the
rate
smaller
at
and
blocked.
which
smaller
rises.
substrate
plotted
seen
never
are
get
between
activity
curve
steeply,
collisions
reactions
relationship
distinctive
less
the
catalyse
substrate
the
site
ytivitca emyzne
substrate–active
on
(gure
quite
a
8),
site is altered so the substrate does not
t so well. Most enzymes are denatured
by very high or low pH, so the enzyme
no longer catalyses the reaction.
concentration
graph,
rising
reaching
This is because the shape of the active
a
a
less
pH
and
maximum.
▲
Figure 7 pH and enzyme activity
99
2
M O L E C U L A R
B I O L O G Y
Dnttin
Enzymes can be denatured.
Enzymes
are
ytivitca emyzne
irreversibly
and
both
When
high
an
can
normally
no
like
certain
has
been
longer
catalyses
that
and
by
temperatures
enzyme
substrate
enzymes
proteins,
altered
were
does
and
proteins
either
or
if
its
occur.
dissolved
in
the
In
to
or
low
the
many
structure
process
active
binds,
water
their
This
high
denatured,
bind,
not
other
conditions.
is
pH
site
can
is
cases
be
cause
altered
reaction
become
can
denaturation
that
so
the
denaturation
insoluble
it.
the
enzyme
causes
and
form
a
precipitate.
substrate concentration
▲
Figure 8 The eect of substrate
concentration on enzyme activity
Qntittiv xpimnts
Experimental design: accurate quantitative measurements in enzyme
experiments require replicates to ensure reliability.
Our
on
understanding
evidence
from
evidence
these
designed
and
of
enzyme
activity
experiments.
experiments
To
must
is
be
●
based
obtain
strong
science
●
the
results
of
quantitative,
some
the
basic
just
close
be
to
accurate,
the
true
which
value;
in
and
the
experiment
the
replicate
should
be
repeated,
so
that
principles:
experiment
not
should
means
carefully
●
follow
measurements
should
how
be
reliable
results
they
can
be
compared
to
assess
are.
descriptive;
d- q: Digesting jello cubes
Figure
9
shows
investigate
apparatus
that
can
be
used
to
a)
describing
proteindigestion.
cubes
b)
tube
is
taking
whether
colourless
a
sample
the
or
of
a
the
solution
shade
of
around
pink
solution
or
the
red
and
tight-tting lid
measuring
c)
nding
the
electronic
2
If
method
would
protease in a solution
be
its
(c)
absorbance
mass
of
the
in
a
cubes
colorimeter
using
an
balance.
was
[3]
chosen,
discuss
whether
it
better
gelatine cubes
to
nd
the
mass
of
all
of
the
cubes
of
jello
with known pH
▲
or
the
of
the
cubes
are
made
from
sugar-free
jello
If
mass
the
the
colouring
that
they
contain
will
jello
The
as
questions
avoured
100
the
jello
protein
below
with
whether
the
of
digested
assume
red
Explain
rate
is
gradually
colouring
these
protein
that
by
one
separately.
have
a
mass
of
[2]
it
is
accurate
0.5
enough
grams,
to
be
their
mass
to:
protease.
a)
the
nearest
gram
(g)
b)
the
nearest
milligram
c)
the
nearest
microgram
strawberry-
has
methods
digestion
the
cubes
whether
measure
released
each
(jelly),
state
1
nd
Figure 9 Tube used to investigate the rate of digestion of gelatine
3
If
together,
are
of
been
used!
assessing
acceptable:
(mg)
(µg).
[3]
2 . 5
4
To
obtain
thejello
accurate
cubes,
themfrom
the
it
mass
is
measurements
necessaryto
tube
and
dry
of
7
Draw
a
8
Describe
that
there
are
no
their
the
tube
adhering.
drying
the
surface
drips
of
Explain
of
the
1
gives
sugar-free
the
results
jellocubes
that
the
and
a
the
Discuss
the
5
from
Discuss
the
esh
whether
of
the
Most
of
extract
called
the
after
this
used
to
results
protease
ran
out,
obtain
results
were
in
table
obtained
one
second
more
1
Deduce
which
usingthe
using
pineapple,
pineapple
protease
b)
Suggest
results
second
how
the
extractcould
and
[3]
conclusions
that
can
abouttheprecise
be
drawn
optimum
papain.
[2]
M  (mg)
for
use
were
have
of
80
87
77
3
122
127
131
an
4
163
166
164
5
171
182
177
6
215
210
213
7
167
163
84
8
157
157
77
9
142
146
73
but
was
in
the
obtained
extract.
use
2
are
experiment.
a)
pH
freshpineapples.
from
a
between
papain,
[2]
of
[5]
using
reliable.
6
relationship
data
ph
extracted
table.
[2]
obtained
protease
the
reason
blocks.
were
in
solution
pHof
Table
results
activity.
fromthis
for
the
surface
9
from
of
remove
papain
toensure
graph
e n z y M e s
[1]
a
second
affectedthe
results.
[2]
▲
T
able 1
Dsigning nzym xpimnts
Design of experiments to test the eect of temperature, pH and substrate
concentration on the activity of enzymes.
1
The
factor
that
independent
●
you
you
with
substrate
a
going
variable.
how
obtain
are
are
going
You
to
investigate
need
vary
it,
with
and
the
dilute
to
is
clock
the
you
●
example
would
to
get
what
the
units
should
be
used
independentvariable,
temperature
is
for
for
lower
●
measuring
example
measuredindegrees
what
range
variable,
levels
2
The
fast
need
for
includingthe
and
variable
the
you
the
that
enzyme
number
you
the
and
iscatalysing
to
the
would
be
colour
change;
how
variable.
You
many
Other
how
the
you
are
choice
device,
for
of
going
to
meter
nd
example
an
other
be
used
variable,
than
for
for
for
example
minutes
or
measuring
repeats
you
measuring
need
a
hours
rapid
to
get
reliable
that
could
variables.
affect
You
need
the
to
dependent
are
decide:
●
what
●
how
●
what
all
the
out
each
control
of
them
variables
can
be
are;
kept
constant;
how
is
level
they
should
be
kept
at,
for
the
temperature
should
be
kept
at
todecide:
measure
or
time
results.
factors
control
the
●
the
levels.
reaction
need
used
measure
change;
should
rather
example
dependent
colour
to
lowest
ofintermediate
measure
used
Celsius;
independent
highest
a
be
dependent
enough
3
●
for
units
seconds
concentrations;
●
what
the
highest
it
could
taken
decide:
for
concentration
solution
concentration
to
it,
including
measuring
electronic
optimum
investigated,
enzymes
for
but
should
the
enzyme
factors
be
kept
that
at
a
if
pH
might
is
being
inhibit
minimum
level.
stop
101
2
M O L E C U L A R
B I O L O G Y
enzym xpimnts
Experimental investigation of a factor aecting enzyme activity.
There
The
are
many
method
investigate
worthwhile
that
the
follows
effect
of
enzyme
can
be
used
substrate
constant
experiments.
concentration
activity
of
investigating
the
effect
of
[2]
on
4
the
if
substrateconcentration.
to
Predict
whether
the
enzyme
activity
will
catalase.
change
more
if
substrateconcentration
is
3
Catalase
It
a
is
one
catalyses
toxic
the
of
the
most
conversion
by-product
of
widespread
of
hydrogen
metabolism,
into
increased
enzymes.
peroxide,
water
by
The
apparatus
shown
in
gure
10
same
can
to
investigate
the
activity
of
catalase
in
Explain
experiment
could
be
repeated
using
the
of
yeast,
but
different
concentrations.
Another
would
concentrations
in
be
to
other
assess
cell
isdecreased
[2]
tissues
such
as
liver
must
be
in
before
investigating
catalase
them.
[2]
goggles
must
Care
be
worn
should
be
if
this
taken
experiment
not
to
get
possible
the
types,
it
amount.
why
performed.
hydrogen
investigation
if
hydrogen
is
peroxide
or
same
Safety
concentration
dm
yeast.
activity
The
mol
be
macerated
used
0.2
and
5
oxygen.
the
by
peroxide
on
the
skin.
catalase
such
as
liver,
oxygen
kidney
have
at
to
the
or
germinating
be
macerated
same
seeds.
and
concentration
These
then
as
tissues
mixed
the
would
with
water
yeast.
measuring cylinder
yeast
1
Describe
how
the
activity
of
the
three-way tap
enzyme
water
catalase
could
apparatus
2
Explain
be
be
shown
why
a
thoroughly
measured
in
yeast
gure
using
10.
suspension
stirredbefore
the
a
[2]
must
sample
always
of
it
is
water
3
0.8 mol dm
taken
for
use
in
an
experiment.
[2]
hydrogen peroxide
3
State
two
factors,
concentration,
apart
that
from
should
enzyme
bekept
▲
▲
102
Figure 11 Enzyme experiment
Figure 10 Apparatus for measuring catalase activity
2 . 5
e n z y M e s
d- q: Designing an experiment to nd the eect of temperature on lipase.
Lipase
converts
therefore
can
be
fats
causes
used
to
a
into
fatty
decrease
measure
acids
in
the
pH.
and
This
activity
of
glycerol.
pH
2
It
a)
Explain
12
shows
suitable
you
would
variable
measure
the
accurately.
[2]
lipase.
b)
Figure
how
dependent
change
State
the
units
for
measuring
the
apparatus.
dependent
c)
tube contents mixed when both
Explain
variable.
the
need
[1]
for
at
least
three
have reached target temperature
replicate
in
this
results
for
eachtemperature
experiment.
[2]
thermometer
3
a)
List
the
kept
b)
Explain
be
c)
Suggest
controlled
sodium carbonate (an alkali)
water bath
and phenolphthalein
a
these
suitable
being
lipids
this
that
must
be
experiment.
control
[3]
factors
can
[2]
level
for
each
factor.
reasons
milk
milk mixed with
factors
in
constant.
Suggest
a)
lipase
thermostatically
how
kept
control
4
control
constant
in
for:
used
this
vegetable
[3]
to
provide
a
source
experimentrather
of
than
oil.
[1]
(a pH indicator)
b)
▲
the
thermometer
being
placed
in
the
Figure 12 Apparatus for investigating the activity of lipase
tube
Phenolphthalein
but
7.
becomes
The
used
time
to
is
pink
colourless
taken
measure
temperatures.
for
the
in
alkaline
when
this
the
colour
activity
Alternatively,
of
pH
drops
change
at
to
can
c)
be
followed
using
a
pH
probe
changes
and
smaller,
the
substrate
enzyme,
different
the
larger,
volume
of
rather
than
liquid
[1]
being
rather
added
than
the
to
the
enzyme
to
substrate.
[1]
could
5
be
the
the
conditions,
lipase
pH
containing
Sketch
the
shape
of
graph
that
you
would
data-logging
expect
from
this
experiment,
with
a
software.
temperature
1
a)
State
the
independent
experiment
b)
State
the
and
units
independent
variable
howyou
for
in
would
measuring
this
vary
the
it.
[2]
to
the
6
variable.
[1]
State
an
appropriate
range
for
and
time
colour
0
taken
on
the
for
whether
expected
to
have
from
the
to
80
the
°C
on
indicator
y-axis.
germinatingcastor
from
lipase
°C
or
[2]
human
oil
seeds
higher
pancreas
would
optimum
the
temperature.
independent
from
Explain
be
c)
x-axis
change
range
variable.
[2]
[2]
Immbiizd nzyms
Immobilized enzymes are widely used in industry.
In
1897
extract
the
of
alcohol.
The
processes
Louis
only
Buchner
yeast,
door
outside
Pasteur
occur
if
brothers,
containing
had
was
opened
living
cells
yeast
to
the
and
Eduard,
cells,
use
would
of
showed
convert
enzymes
to
that
an
sucrose
catalyse
into
chemical
cells.
claimed
living
Hans
no
that
were
fermentation
present.
This
of
was
sugars
part
of
to
alcohol
the
could
theory
of
103
2
M O L E C U L A R
B I O L O G Y
vitalism,
which
be
under
stated
that
substances
in
animals
and
plants
can
only
toK
made
articial
the
synthesis
inuence
of
urea,
of
a
“vital
described
in
spirit”
or
sub-topic
“vital
2.1,
force”.
had
The
provided
W     w
evidence
against
vitalism,
but
the
Buchners’
research
provided
a
clearer
gm  ?
falsication
of
the
theory.
After the discovery in the 19th century
More
than
500
enzymes
now
have
commercial
uses.
Figure
13
shows
a
of the conversion of sugar into alcohol
classication
of
commercially
useful
enzymes.
Some
enzymes
are
used
in
by yeast, a dispute developed between
more
than
one
type
of
industry.
two scientists, Justus von Liebig and
Louis Pasteur. In 1860 Pasteur argued
other industries 5%
miscellaneous 4%
that this process, called fermentation,
agriculture 11%
could not occur unless live yeast cells
were present. Liebig claimed that
the process was chemical and that
living cells were not needed. Pasteur ’s
medical 21%
view reected the vitalistic dogma –
that the substances in animals and
biosensor 16%
plants could only be made under the
inuence of a “vital spirit” or “vital
food & nutrition 23%
force”. These contrasting views were
as much inuenced by political and
religious factors as by scientic
biotechnology 46%
evidence. The dispute was only
resolved after the death of both men.
In 1897 the Buchner brothers, Hans
environment 13%
and Eduard, showed that an extract of
yeast, containing no yeast cells, did
energy 3%
indeed conver t sucrose into alcohol.
The vitalistic dogma was over thrown
▲
Figure 13
and the door was opened to the use
of enzymes to catalyse chemical
The
processes outside living cells.
attachment
so
enzymes
that
doing
them
the
movement
this,
in
an
aggregates
Enzyme
●
used
of
The
in
of
including
alginate
of
up
to
enzyme
After
being
recycled,
●
can
104
restricted.
enzymes
them
to
or
into
There
a
are
glass
together
This
to
is
aggregations,
many
surface,
form
ways
of
trapping
enzyme
several
be
advantages.
separated
reaction
at
from
the
the
ideal
products
time
and
of
the
preventing
products.
from
useful
the
cost
reaction
savings,
mixture
especially
as
the
enzyme
many
may
enzymes
be
are
expensive.
have
to
Substrates
with
the
immobilized.
material
diameter.
has
the
is
the
bonding
mm
retrieved
giving
temperature
●
or
usually
another
enzyme
easily
of
Immobilization
and
gel,
0.1
stopping
contamination
very
the
are
to
attaching
immobilization
reaction,
●
industry
enzymes
increases
and
be
can
dissolved
pH,
the
stability
reducing
the
of
rate
enzymes
at
which
to
changes
they
are
in
degraded
replaced.
be
exposed
enzymes,
to
higher
speeding
enzyme
up
concentrations
reaction
rates.
than
2 . 6
s t r u c t u r e
o f
d n a
a n d
r n a
lts-f mik
Methods of production of lactose-free milk and its advantages.
Lactose
It
can
is
be
enzyme
the
sugar
that
converted
lactase:
into
lactose
is
naturally
glucose
→
present
and
glucose
in
galactose
+
milk.
by
●
the
Lactose
galactose.
texture.
are
Lactase
is
obtained
from
Kluveromyces
tends
production
type
of
yeast
that
Biotechnology
extract
it
for
the
sale
There
lactase
to
are
grows
companies
food
from
naturally
culture
the
yeast
manufacturing
several
reasons
for
crystallize
ice
soluble
cream,
glucose
than
during
giving
and
lactose
a
the
gritty
galactose
they
remain
lactis,
in
the
and
giving
a
smoother
texture.
milk.
●
yeast,
purify
lactase
Bacteria
quickly
companies.
using
to
Because
more
dissolved,
a
of
ferment
than
yoghurt
and
glucose
lactose,
cottage
so
and
the
cheese
galactose
production
is
more
of
faster.
in
Thailand
food
processing:
South India
●
Some
people
are
lactose-intolerant
and
cannot
Crete
drink
more
than
about
250
ml
of
milk
per
day,
France
unless
it
is
lactose-reduced
(see
gure
14).
Finland
●
Galactose
lactose,
sweet
and
so
less
foods
shakes
or
glucose
sugar
are
containing
fruit
sweeter
needs
to
milk,
be
than
added
such
as
Sweden
to
0%
milk
50%
100%
lactose intolerance
yoghurt.
▲
Figure 14 Rates of lactose intolerance
2.6 s  dn a  rn a
undstnding
appitins
➔
The nucleic acids DNA and RNA are polymers of
➔
Crick and Watson’s elucidation of the structure
nucleotides.
of DNA using model-making.
➔
DNA diers from RNA in the number of strands
normally present, the base composition and
the type of pentose.
➔
DNA is a double helix made of two antiparallel
strands of nucleotides linked by hydrogen
bonding between complementary base pairs.
Nt f sin
➔
Using models as representation of the real
Skis
➔
Drawing simple diagrams of the structure of
world: Crick and Watson used model-making to
single nucleotides and of DNA and RNA , using
discover the structure of DNA .
circles, pentagons and rectangles to represent
phosphates, pentoses and bases.
105
2
M O L E C U L A R
B I O L O G Y
Ni ids nd ntids
The nucleic acids DNA and RNA are polymers of
nucleotides.
Nucleic
acids
of
hence
cells,
were
rst
their
discovered
name.
There
in
material
are
two
extracted
types
of
from
nucleic
the
acid:
nuclei
DNA
O
and
O
P
RNA.
linking
2
Nucleic
together
acids
are
very
nucleotides
to
large
form
molecules
a
that
are
constructed
by
polymer.
5
O
1
O
C
C
N
Nucleotides
consist
of
three
parts:
4
●
a
sugar,
●
a
phosphate
OH
OH
nucleic
▲
has
ve
carbon
atoms,
so
is
a
pentose
sugar;
group,
acids;
which
is
the
acidic,
negatively-charged
part
of
and
Figure 1 The par ts of a nucleotide
●
a
base
atoms
Figure
and
To
1
the
sugar.
of
link
the
that
in
shows
are
Figure 2 A simpler representation of a
together
nucleotide
them
is
shows
a
four
in
and
along
as
a
a
has
of
either
in
one
or
two
rings
groups,
of
the
base
and
This
–
phosphate
the
is
for
so
can
and
base
the
The
base
pentose
the
base
to
used
is
ensures
sugar.
four
to
link
therefore
nucleic
sequence
backbone
are
of
linked
sugar
key
each
there
be
are
sugar
molecule
to
sequence
the
bonds
pentose
linked
RNA,
phosphate
information
sugar
a
nucleotides
molecule.
the
covalent
and
backbone
Any
to
form.
polymer,
with
DNA
different
nucleotide.
RNA
or
together.
bonds
nucleotide
strong
both
linked
symbolic
chain
a
are
covalent
one
because
genetic
the
in
four
every
or
a
of
they
by
creates
bases
The
in
and
into
phosphate
DNA
store
and
This
sequence,
same
how
linked
phosphate
different
any
the
and
nucleotide
together
the
sugar
and
both
nucleotide.
information
stable
parts
are
nucleotides.
are
possible
of
2
between
different
acting
these
nucleotides
alternating
nitrogen
structure.
phosphate
next
There
contains
its
Figure
formed
▲
which
2
3
is
the
that
acids
store
the
store
secure.
Dins btwn DNa nd rNa
DNA diers from RNA in the number of strands normally
present, the base composition and the type of pentose.
HOH
C
OH
O
2
There
H
H
H
are
three
1
The
sugar
Figure
OH
sugar
C
2
H
H
H
two
types
of
nucleic
3
within
shows
DNA
that
is
deoxyribose
deoxyribose
has
and
one
the
sugar
fewer
in
RNA
is
oxygenatom
ribose.
than
The
in
full
them
names
–
of
DNA
and
deoxyribonucleic
RNA
acid
are
and
based
on
the
ribonucleic
type
of
acid.
There
are
RNA.
usually
The
two
polymers
polymers
double-stranded
and
are
RNA
often
of
nucleotides
is
referred
to
as
in
DNA
strands,
but
so
only
DNA
one
is
single-stranded.
OH
3
▲
the
H
in
OH
between
OH
O
2
differences
H
ribose.
HOH
important
acid:
H
The
four
bases
in
DNA
ar e
a de ni ne,
cyt o si n e,
gu a n in e
and
Figure 3 The sugar within DNA is
thymine.
The
four
bases
in
R NA
a re
ad eni n e,
c yt o si n e,
g ua ni n e
deoxyribose (top) and the sugar in
and
uracil,
so
the
RNA is ribose (bottom)
thymine
106
in
RNA.
d i ff e r ence
is
tha t
u r ac il
is
pr e se nt
i n st e a d
of
2 . 6
s t r u c t u r e
o f
d n a
a n d
r n a
d- q: Charga’s data
DNA
samples
analysed
in
by
Edwin
by
others.
from
terms
a
of
Chargaff,
The
data
range
their
an
is
of
species
Austrian
presented
3
were
nucleotide
biochemist,
in
Evaluate
table
the
eukaryotes
composition
of
and
adenine
and
theamounts
1.
claim
and
that
in
the
DNA
prokaryotesthe
thymine
of
guanine
are
and
of
amount
equal
and
cytosine
areequal.
1
Compare
the
base
Mycobacterium
withthe
shown
2
base
composition
tuberculosis
in
the
table.
Calculate
the
base
humans
Show
and
your
(a
composition
for
4
prokaryote)
of
the
Explain
ofbases
eukaryotes
terms
[2]
ratio
A+
G/T
Mycobacterium
+
C,
5
for
the
in
ratios
the
structure
reasons
thepolio
between
eukaryotes
for
basecomposition
[2]
Gp
of
Suggest
tuberculosis .
working.
s  dna
[2]
of
of
the
amounts
andprokaryotes
of
the
in
DNA.
difference
[2]
in
bacteriophage
the
T2
and
virus.
[2]
a
G
c
tm
Human
Mammal
31.0
19.1
18.4
31.5
Cattle
Mammal
28.7
22.2
22.0
27.2
Salmon
Fish
29.7
20.8
20.4
29.1
Sea urchin
Inver tebrate
32.8
17.7
17.4
32.1
Wheat
Plant
27.3
22.7
22.8
27.1
Yeast
Fungus
31.3
18.7
17.1
32.9
Mycobacterium tuberculosis
Bacterium
15.1
34.9
35.4
14.6
Bacteriophage T2
Virus
32.6
18.2
16.6
32.6
Polio virus
Virus
30.4
25.4
19.5
0.0
▲
T
able 1
Dwing DNa nd rNa ms
Drawing simple diagrams of the structure of single
nucleotides and of DNA and RNA , using circles,
pentagons and rectangles to represent phosphates,
pentoses and bases.
The
structure
using
simple
of
●
circles
●
pentagons
●
rectangles
Figure
base
2
linked
for
to
the
C
and
for
for
for
pentose
molecules
can
be
shown
in
diagrams
subunits:
the
the
sugar;
bases.
structure
phosphate
–
RNA
the
phosphates;
shows
and
DNA
symbols
are
carbon
of
a
nucleotide,
linked
atom
on
to
the
the
using
pentose
right
hand
these
sugar.
side
of
symbols.
The
the
base
The
is
pentose
1
sugar.
The
phosphate
is
linked
to
C
–
the
carbon
atom
on
the
side
5
▲
Figure 4 Simplied diagram of RNA
107
2
M O L E C U L A R
B I O L O G Y
covalent bond
P
P
chain
these
S
A
on
the
upper
carbon
left
atoms
side
are
of
the
shown
in
pentose
gure
sugar.
The
positions
of
1.
S
T
To
show
the
structure
of
RNA,
draw
a
polymer
of
nucleotides,
with
a
P
P
line
to
show
nucleotide
the
to
covalent
the
bond
pentose
in
linking
the
next
the
phosphate
nucleotide.
group
The
of
each
phosphate
is
S
C
S
G
linked
to
C
of
the
pentose
–
the
carbon
atom
that
is
on
the
lower
left.
3
P
P
If
you
the
have
drawn
polymer
will
the
be
structure
different.
of
RNA
They
are
correctly,
referred
the
to
as
two
the
ends
3´
and
of
the
5´
S
S
A
T
terminals.
●
P
P
The
phosphate
of
another
nucleotide
could
be
linked
to
the
C
3
atom
of
the
3´
terminal.
S
G
S
C
●
The
pentose
phosphate
P
of
of
another
the
5´
nucleotide
could
be
linked
to
the
terminal.
P
Hydrogen bonds are formed
To
show
the
structure
of
DNA,
draw
a
strand
of
nucleotides,
as
with
between two bases
RNA,
Key:
then
should
– sugar
S
be
a
second
run
in
strand
the
alongside
opposite
the
direction,
rst.
so
The
that
at
second
each
P
molecule,
one
strand
has
a
C
terminal
and
the
other
a
C
3
A
of
the
DNA
terminal.
The
5
C
two
– nitrogenous bases
T
G
or
strands
names
and
▲
strand
end
– phosphate
are
to
linked
indicate
cytosine
(C)
by
the
only
hydrogen
bases.
pairs
bonds
Adenine
with
between
(A)
guanine
only
the
pairs
bases.
with
Add
letters
thymine
(T)
(G).
Figure 5 Simplied diagram of DNA
5
´ end
Stt f DNa
3
´ end
DNA is a double helix made of two antiparallel strands
complementary
S
base pairs
P
S
of nucleotides linked by hydrogen bonding between
P
A
T
S
complementary base pairs.
hydrogen
P
C
S
bonds
Drawings
of
the
structure
of
DNA
on
paper
cannot
show
all
features
of
P
P
the
C
three-dimensional
structure
of
the
molecule.
Figure
6
represents
S
G
S
some
of
these
features.
P
S
A
T
S
●
Each
●
The
two
said
to
and
the
●
The
two
●
The
strands
strand
consists
of
a
chain
of
nucleotides
linked
by
covalent
bonds.
P
P
S
strands
are
parallel
but
run
in
opposite
directions
so
they
are
P
G
S
S
P
A
T
S
antiparallel.
other
oriented
strand
in
the
P
P
T
strands
direction
3´
in
to
the
direction
5´
to
3´
5´.
are
wound
together
to
form
a
double
helix
are
held
together
by
hydrogen
P
P
bases.
Adenine
(A)
is
always
paired
between
with
the
thymine
sugar–phosphate
(T)
S
and
guanine
(G)
with
cytosine
(C).
This
is
referred
to
as
backbone
P
P
C
G
complementary
base
pairing ,
meaning
G
that
A
and
T
complement
S
each
other
by
forming
base
pairs
each
other
by
forming
base
pairs.
and
P
S
bonds
S
nitrogenous
C
S
3
´ end
P
5
´ end
108
oriented
S
S
▲
is
C
S
S
is
One
S
P
G
be
Figure 6 The double helix
similarly
G
and
C
complement
2 . 6
s t r u c t u r e
o f
d n a
a n d
r n a
d- q: The bases in DNA
Look
at
answer
1
the
the
State
molecular
following
one
theother
2
Each
of
atom
left
in
this
in
gure
3
and
the
and
between
adenine
4
and
to
position,
case
nitrogen
is
in
a
DNA
has
hydrogen
which
in
7.
when
from
its
in
in
Deduce
a
5
Guanine
the
[3]
structure
function
how
the
is
the
bases
each
structure
lower
subunits.
adenine
of
cytosine
and
[4]
features,
nucleotide
between
guanine.
Although
a
the
similarities
thymine.
nitrogen
appears
gure
used
a
atom
three
Compare
[1]
bases
each
Identify
questions.
difference
beingassembled
▲
7
bases.
bonded
similar
models
one
have
has
andshape.
of
bases
DNA,
each
to
a
shared
Remembering
explain
be
some
distinctive
the
chemical
the
importance
distinctive.
for
[5]
[2]
Adenine
Cytosine
Thymine
Figure 7
M mds
Using models as representation of the real world:
Crick and Watson used model-making to discover the
structure of DNA.
The
word
meaning
plans,
model
showing
dimensional
impression
Molecular
but
Models
always
they
with
what
models
what
in
science
that
are
show
in
the
not
are
of
a
building
possible
are
a
always
They
or
a
DNA,
in
but
be
to
to
a
be
more
in
theoretical
which
part
took
are
in
are
three
Crick
two
made
attempts
a
help
and
do
concepts
to
building
us
to
not
and
feature
be
rejected
and
dimensions,
is.
common
often
Three-
realistic
whether
models
actually
The
modus,
architects’
like.
decide
molecular
be
word
constructed.
give
three-dimensional
can
science
it
Latin
structure
used
processes.
critical
the
originally
would
molecule
proposals,
models
might
future,
of
from
were
developed
models
systems
played
structure
building
proposed
structures.
architecture,
the
a
derived
Models
then
structure
they
Model-making
of
new
also
represent
is
a
were
reality
the
is
method.
architects’
propose
can
models
how
become
discover
English
or
models
of
whereas
should
in
manner
and
Watson’s
before
of
tested.
As
replaced.
discovery
they
were
successful.
109
2
M O L E C U L A R
B I O L O G Y
toK
cik nd Wtsn’s mds f DNa stt
W   v  
Crick and Watson’s discovery of the structure of DNA
mp  p 
 ?
using model-making.
Crick
and
Watson’s
success
in
discovering
the
structure
of
DNA
was
Three prominent research groups
based
on
using
the
evidence
to
develop
possible
structures
for
DNA
openly competed to elucidate the
and
testing
them
by
model-building.
Their
rst
model
consisted
of
a
structure of DNA : Watson and Crick
triple
helix,
with
bases
on
the
outside
of
the
molecule
and
magnesium
were working at Cambridge; Maurice
holding
the
two
strands
together
with
ionic
bonds
to
the
phosphate
Wilkins and Rosalind Franklin were
groups
on
each
strand.
The
helical
structure
and
the
spacing
between
working at Kings College of the
subunits
in
the
helix
tted
the
X-ray
diffraction
pattern
obtained
by
University of London; and Linus
Rosalind
Franklin.
Pauling's research group was operating
out of Caltech in the United States.
A stereotype of scientists is that they
take a dispassionate approach to
investigation. The truth is that science is
a social endeavour involving a number
of emotion-inuenced interactions
between science. In addition to the
It
was
and
be
difcult
it
was
enough
strands.
not
of
get
all
account
the
parts
when
magnesium
Another
take
equals
to
rejected
of
Chargaff’s
thymine
this
available
deciency
of
of
Franklin
and
the
model
pointed
to
this
form
rst
nding
amount
to
t
out
the
cross
model
that
of
together
that
links
was
the
there
that
equals
not
between
is
amount
cytosine
satisfactorily
would
that
of
it
the
did
adenine
the
amount
guanine.
joy of discovery, scientists seek the
To
investigate
the
relationship
between
the
bases
in
DNA
pieces
of
esteem of their community. Within
cardboard
were
cut
out
to
represent
their
shapes.
These
showed
that
research groups, collaboration is
A-T
and
C-G
base
pairs
could
be
formed,
with
hydrogen
bonds
linking
impor tant, but outside of their research
the
bases.
The
base
pairs
were
equal
in
length
so
would
t
between
group competition often restricts open
two
outer
sugar-phosphate
backbones.
communication that might accelerate
Another
ash
of
insight
was
needed
to
make
the
parts
of
the
to
run
the pace of scientic discovery. On the
molecule
t
together:
the
two
strands
in
the
helix
had
in
other hand, competition may motivate
opposite
directions
–
they
must
be
antiparallel.
Crick
and
Watson
ambitious scientists to work tirelessly.
were
then
DNA.
able
They
together
angles
with
constructed
model
just
looked
for
DNA
must
▲
Figure 8 Crick and Watson and their DNA model
110
right”.
DNA.
consist
that
8
second
and
Bond
shows
model
sheeting
lengths
Crick
and
of
cut
the
to
were
structure
shape
all
Watson
to
and
scale
with
the
of
held
and
bond
newly
model.
structure
effects
their
rods
clamps.
Figure
convinced
copying
code
build
metal
small
correct.
The
to
used
are
all
The
It
also
of
led
triplets
started
still
those
who
structure
the
quickly
of
saw
to
bases.
great
it.
A
immediately
the
In
in
comment
suggested
realization
many
molecular
reverberating
typical
ways
biology
science
and
in
a
that
the
was
“It
mechanism
the
genetic
discovery
revolution,
society.
of
with
2 . 7
d n a
r e P l i c a t i o n ,
t r a n s c r i P t i o n
a n d
t r a n s l a t i o n
2.7 dn a p, p 
 
undstnding
appitins
➔
The replication of DNA is semi-conser vative and
➔
Use of Taq DNA polymerase to produce multiple
depends on complementary base pairing.
copies of DNA rapidly by the polymerase chain
➔
Helicase unwinds the double helix and
reaction (PCR).
separates the two strands by breaking
➔
Production of human insulin in bacteria as an
hydrogen bonds.
example of the universality of the genetic code
➔
DNA polymerase links nucleotides together to
allowing gene transfer between species.
form a new strand, using the pre-existing strand
as a template.
Skis
➔
Transcription is the synthesis of mRNA
➔
copied from the DNA base sequences by RNA
codon(s) corresponds to which amino acid.
polymerase.
➔
Use a table of the genetic code to deduce which
➔
Translation is synthesis of polypeptides on
Analysis of Meselson and Stahl’s results
to obtain suppor t for the theory of semi-
ribosomes.
conser vative replication of DNA .
➔
The amino acid sequence of polypeptides is
➔
determined by mRNA according to the genetic
Use a table of mRNA codons and their
corresponding amino acids to deduce the
code.
sequence of amino acids coded by a shor t
➔
Codons of three bases on mRNA correspond to
mRNA strand of known base sequence.
one amino acid in a polypeptide.
➔
➔
Deducing the DNA base sequence for the
Translation depends on complementary
mRNA strand.
base pairing between codons on mRNA and
anticodons on tRNA .
Nt f sin
➔
Obtaining evidence for scientic theories:
Meselson and Stahl obtained evidence for the
semi-conser vative replication of DNA .
Smi-nsvtiv pitin f DNa
The replication of DNA is semi-conservative and depends
on complementary base pairing.
When
a
separate
or
cell
template,
formed
by
The
result
and
a
to
gure
for
the
adding
is
newly
referred
prepares
(see
two
to
2).
divide,
these
creation
of
a
nucleotides,
DNA
being
two
of
one
strand.
by
strand.
one,
both
For
strands
original
new
molecules,
synthesized
as
the
Each
of
The
and
double
serves
new
linking
composed
this
the
strands
reason,
of
an
DNA
helix
as
strands
them
a
guide,
are
together.
original
strand
replication
is
semi-conservative.
111
2
M O L E C U L A R
B I O L O G Y
The
adenine
base
sequence
the
new
strand.
the
next
base
on
Only
the
a
template
nucleotide
strand
determines
carrying
a
base
the
that
is
base
sequence
on
complementary
to
thymine
strand
This
is
other,
cytosine
guanine
to
be
that
in
guanine
the
because
inserted,
with
the
their
the
structure.
hydrogen
not
another
DNA
base
strand
complementary
would
two
template
can
successfully
be
added
to
the
new
1).
stabilizing
nucleotide
pairs
on
(gure
is
a
bonding
be
added
called
to
form
hydrogen
nucleotide
between
to
the
with
bases
chain.
that
the
result
parent
from
rule
base
DNA
molecule
bonds
the
with
wrong
would
The
complementary
molecules
sequences
bases
If
not
that
occur
one
pairing.
It
replication
that
was
each
base
started
and
base
the
always
ensures
are
identical
replicated.
cytosine
obtining vidn f th thy f smi-
nsvtiv pitin
thymine
adenine
Obtaining evidence for scientic theories: Meselson
▲
and Stahl obtained evidence for the semi-conservative
Figure 1
replication of DNA.
Semi-conservative
replication
seemed
right,
is
an
example
of
a
scientic
theory
that
Parental DNA
with
intuitively
evidence.
but
Laboratories
nonetheless
around
the
needed
world
to
be
backed
attempted
to
up
conrm
C
experimentally
C
C
A
convincing
replication
evidence
had
been
of
DNA
is
semi-conservative
and
soon
obtained.
T
In
G
that
G
G
1958
Matthew
Meselson
and
Franklin
Stahl
published
the
results
C
of
T
exceedingly
elegant
experiments
that
provided
very
strong
A
15
T
A
C
evidence
for
semi-conservative
replication.
They
used
N,
a
rare
G
isotope
of
nitrogen
that
has
one
more
neutron
than
the
normal
Replication fork
A
14
T
N
G
A
G
isotope,
so
methods
T
C
of
T
In
the
stable
C
A
T
A
T
C
denser.
purifying
1930s
C
isotopes
Harold
that
Urey
could
be
had
developed
used
as
tracers
in
15
biochemical
T
is
C
pathways.
N
was
one
of
these.
A
A
Meselson
G
and
C
Stahl
devised
a
new
method
15
containing
of
separating
DNA
14
N
in
its
bases
from
DNA
with
N.
The
technique
is
G
C
G
called
A
T
A
caesium
A
gradient
centrifugation.
A
solution
T
of
caesium
chloride
spun
in
an
ultracentrifuge
at
nearly
45,000
T
revolutions
G
is
T
A
per
minute
for
20
hours.
The
dense
caesium
ions
tend
sediment
fully
C
C
A
density
T
A
to
move
towards
the
bottom
of
the
tube
but
do
not
T
A
T
chloride
A
T
because
A
T
of
diffusion.
A
gradient
is
established,
with
the
greatest
A
G
G
Parental
strand
▲
New
strand
New
strand
C
caesium
Parental
strand
Figure 2 Semi-conser vative replication
concentration,
the
lowest
at
the
caesium
the
top
of
chloride
corresponding
with
Meselson
Stahl
and
and
the
therefore
tube.
solution
its
density,
Any
at
substance
becomes
the
bottom
centrifuged
concentrated
at
a
and
with
level
density.
cul tur ed
the
b act e r iu m
E.
coli
for
fourteen
15
generations
Almost
all
in
a
me d i um
nitrogen
whe r e
a to ms
in
the
the
o nl y
b ase s
of
n i t ro ge n
the
DN A
s ou r c e
in
the
was
N.
b a c t e ri a
15
were
therefore
N.
They
then
trans f e r r e d
the
b acte r ia
abr u pt ly
to
a
14
medium
to
divided
112
in
culture
which
them,
and
all
the
the
ni tr og e n
g e ne r atio n
there f o r e
r e pl ica te d
was
ti me
N.
wa s
th e ir
At
50
DN A
the
tempera tur e
m i nu t e s
on c e
–
e v e ry
the
50
us e d
b a c t e r ia
m i n u t es .
2 . 7
Meselson
culture
and
for
Stahl
severa l
co l l ected
ho ur s
d n a
r e P l i c a t i o n ,
s a mp l e s
fr om
the
of
tim e
DNA
t r a n s c r i P t i o n
fr om
whe n
it
the
wa s
a n d
t r a n s l a t i o n
b a c t e ri a l
t r an s fe r re d
av
to
nw xpm q
14
the
N
medium.
They
e x tr a cte d
the
DNA
and
m e a su r e d
i ts
de n s it y
Meselson and Stahl used three
by
caesium
chlori d e
d e nsi ty
g r ad ie n t
ce n t r ifu ga t i on .
Th e
DNA
techniques in their experiments
could
be
detected
b e ca use
it
a bs or bs
u lt ra viol e t
l ig ht ,
and
so
that that were relatively new.
created
a
dark
ban d
w he n
the
tub es
were
il lu m in a t e d
wi t h
Identify a technique used by
ultraviolet.
Figure
3
s hows
the
r e sul ts.
In
th e
ne xt
pa r t
of
t h is
them that was developed:
sub-topic
position
there
of
the
is
g ui d a nce
dar k
in
how
to
a n al yse
the
cha n g es
in
b a nd s.
a)
by Urey in the 1930s
b)
by Pickels in the 1940s
c)
by Meselson and Stahl
themselves in the 1950s.
av
0
0.3
0.7
1.0
1.5
2.0
2.5
3.0
4.0
Mg  v
generations
To model helicase activity you
▲
Figure 3
could use some two-stranded rope
or string and a split key ring. The
strands in the rope are helical and
represent the two strands in DNA.
Open the key ring and put one
Mssn nd Sth’s DNa pitin
strand of the rope inside it. Close
xpimnts
the ring so that the other strand
is outside. Slide the ring along the
Analysis of Meselson and Stahl’s results to obtain suppor t
string to separate the strands.
for the theory of semi-conservative replication of DNA.
What problems are revealed by this
The
data-based
Meselson
of
and
question
Stahl’s
below
results
will
and
guide
help
to
you
build
through
your
the
skills
analysis
in
this
model of the activity of helicase?
of
Use the internet to nd the solution
aspect
used by living organisms.
science.
d- q: The Meselson and Stahl experiment
14
In
order
for
duplicated
same
to
genetic
process
The
cell
of
division
ensurethat
duplicating
the
occur,
DNA
progeny
information
Meselson–Stahl
understand
to
as
DNA
is
termed
of
be
have
theparent
experiment
mechanism
cells
must
the
cells.
The
replication.
sought
to
replication.
to
in
a
conservative
fashion,
a
N
taken
which
medium.
over
density
a
Did
Samples
period
gradient
heavier
inacentrifuge
of
of
time
the
and
centrifugation,
molecules
tube
than
settle
bacteria
by
a
in
method
further
lighter
were
separated
down
ones.
it
1
occur
a
The
single
band
of
DNA
at
the
start
semi-conservative
-3
(0generations)
fashion
or
in
a
dispersive
fashion
(see
gure
had
a
density
of
1.724
g
cm
.
4)?
The
main
had
a
band
of
DNA
after
four
generations
-3
Meselson
and
Stahl
grew
E.
coli
in
a
medium
density
of
1.710
g
cm
.
Explain
how
15
containing
of
“heavy”
generations.
nitrogen
They
then
(
N)
for
transferred
a
number
the
bacteria
DNA
by
with
the
a
lower
bacteria.
density
had
been
produced
[2]
113
2
M O L E C U L A R
2
a)
Estimate
B I O L O G Y
the
density
of
the
DNA
after
one
generation.
6
Predict
[2]
the
results
mixtureofDNA
of
centrifuging
from
0
a
generations
and
2generations.
b)
Explain
one
whether
generation
possible
shown
3
a)
density
falsies
mechanisms
in
Describe
Explain
gure
the
including
b)
the
the
DNA
whether
twogenerations
three
replication
after
the
of
two
the
results
falsify
any
mechanisms
generations,
DNA.
[3]
after
of
the
for
DNA
replication.
4
Explain
the
[3]
results
after
three
and
four
generations.
5
Figure
(0
4
[2]
after
[3]
density
threepossible
of
DNA
4.
results
the
any
for
of
[2]
shows
generations)
DNA
and
from
after
E.
coli
one
at
the
start
generation,
15
with
strands
of
DNA
containing
N
shown
14
red
and
Redraw
strands
either
mechanism
containing
(a),
that
is
(b)
or
N
(c),
shown
green.
choosing
supported
by
the
Meselson
Dispersive
and
can
Stahl’s
be
than
be
a
red
more
experiment.
shown
helix
and
as
and
two
the
green.
generations
parallel
colours
Draw
of
Each
the
DNA
lines
do
have
for
in
Semi-conser vative
Newly synthesized strand
rather
not
DNA
replication
Conser vative
molecule
a
Original template strand
to
two
▲
medium
Figure 4 Three possible mechanisms for
DNA replication
14
containing
N.
[3]
His
Helicase unwinds the double helix and separates the two
strands by breaking hydrogen bonds.
Before
must
of
a
DNA
new
enzymes
in
a
that
The
use
bonds
donut
shape.
from
the
Double-stranded
Helicase
time
it
as
energy
from
helicase
The
is
DNA
separates
is
the
two
act
as
carried
ATP
.
The
consists
of
the
move
of
the
between
cannot
be
causes
strands.
split
the
by
for
molecule
the
required
formation
a
group
for
of
breaking
bases.
polypeptides
with
donut
helicase
bases
into
the
helicases,
is
globular
the
of
template
energy
assemble
centre
to
bonds
six
strands
a
out
complementary
used
therefore
the
each
polypeptides
through
ATP
occur,
can
separation
hydrogen
helical.
can
they
between
passing
Energy
breaking
114
that
well-studied
molecule
it.
so
strand.
hydrogen
One
replication
separate
along
and
two
one
and
strand
the
the
parting
strands
unwinding
of
the
arranged
of
other
DNA
the
the
molecule,
two
while
it
helix
at
DNA
outside
stands.
is
still
the
same
2 . 7
d n a
r e P l i c a t i o n ,
t r a n s c r i P t i o n
a n d
t r a n s l a t i o n
DNa pyms
DNA polymerase links nucleotides together to form a new
strand, using the pre-existing strand as a template.
Once
helicase
strands,
for
the
formation
carried
DNA
out
the
four
of
base
brings
but
Each
four
the
a
making
a
new
strand.
group
the
is
free
DNA
the
It
the
have
to
the
bond
does
this
during
the
of
the
DNA
acts
the
is
template
time.
in
Free
the
as
new
a
into
two
template
strands
added
has
to
the
the
base
template
where
strand
in
nucleotides
area
where
new
that
strand.
base
the
is
strand,
can
pair
is
each
being
only
with
the
polymerase
bonds
pair
same
with
DNA
DNA
hydrogen
complementary
so
the
base
a
the
new
the
is
the
been
is
could
form,
formed,
3´
at
polymerase
moves
of
along
sequence
high
the
the
and
adds
done
of
the
on
template
delity
into
the
the
position
bases,
existing
existing
of
is
group
complementary
degree
two
This
the
terminal
brought
the
strand.
phosphate
terminal
very
has
between
nucleotide
DNA
3´
base
formed
of
sugar
the
with
correct
end
gradually
a
a
the
been
of
pentose
with
at
between
sugar
to
a
split
strands
again.
5´terminal,
strand
along
position
and
with
nucleotide
made
the
and
two
assembly
available
on
helix
the
The
nucleotide
away
the
The
the
of
into
it
polymerase
new
strand.
are
and
are
of
polymerase.
moves
reached
bonds
links
strand.
DNA
nucleotide
happens
covalent
nucleotide
a
types
double
Each
nucleotide
bases
time
nucleotide
polymerase
new
always
one
breaks
hydrogen
a
the
begin.
enzyme
position
this
nucleotide
and
of
nucleotides
unless
Once
can
possible
the
at
unwound
the
adding
replicated.
one
by
polymerase
direction,
of
has
replication
DNA
by
the
free
end
of
the
phosphate
5´terminal
of
strand.
strand,
to
–
the
very
assembling
template
few
mistakes
DNAreplication.
Pcr – th pyms hin tin
Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the
polymerase chain reaction (PCR).
The
polymerase
technique
used
DNA
sequence.
DNA
is
into
a
needed
PCR
repeatedly
DNA.
This
separated
chain
to
Only
at
a
the
machine
doubles
two
many
very
start.
in
(PCR)
copies
small
The
which
the
involves
into
reaction
make
a
cycle
of
strands
is
a
selected
at
of
the
loaded
of
the
double-stranded
single
of
a
quantity
DNA
quantity
is
of
one
being
stage
high
is
cycle
and
single
strands
combining
to
DNA
at
another
two
strands
hydrogen
but
in
a
in
bonds.
DNA
DNA
These
molecule
are
are
held
weak
there
are
at
hold
the
by
the
cooled
pair
the
most
cells.
the
two
strands
strands
again.
If
DNA
is
This
is
heated
bonds
separate.
bonds
together
normally
hydrogen
hydrogen
up
two
temperatures
can
called
If
to
a
eventually
the
form,
DNA
so
the
re-annealing.
of
PCR
machine
separates
DNA
strands
by
heating
form
to
95
°C
for
fteen
seconds.
It
then
cools
stage.
the
The
and
strands
them
double-stranded
they
temperature,
then
The
the
so
encountered
break
steps
selected
DNA
them
successfully
together
by
interactions,
large
numbers
DNA
quickly
annealing
DNA.
of
to
parent
However,
single-stranded
a
54
°C.
This
strands
large
DNA
to
excess
called
would
form
of
allow
short
primers
re-
double-stranded
is
sections
present.
of
The
115
2
M O L E C U L A R
primers
large
bind
excess
B I O L O G Y
rapidly
of
re-annealing
of
single
strands
parent
to
primers
the
target
is
sequences
present,
parent
then
they
strands.
starts
and
Copying
from
as
prevent
the
of
strands.
a
of
the
54
its
the
mixture
primers.
next
stage
in
PCR
is
synthesis
of
DNA,
using
the
single
strands
as
templates.
polymerase
a
is
bacterium,
including
those
°C.
of
Enzymes
denature
at
of
do
aquaticus,
to
springs
most
high
adapted
It
Yellowstone
in
Thermus
enzyme
this.
aquaticus,
these
such
be
The
to
Thermus
temperatures
80
used
found
organisms
its
heat-stable
in
National
range
hot
this
the
DNA
brief
polymerase
period
at
95
is
used
°C
50
would
but
of
to
a
very
enough
DNA
it
lower
the
72
to
temperature
primers,
°C.
The
this
but
reaction
temperature
polymerase
adds
rapid
of
by
a
the
it
can
base
is
about
rate
of
the
of
a
help
base
be
is
1,000
DNA
elapsed
cycles,
Taq
of
by
which
DNA
sequence
be
heating
take
huge
for
to
completed
billion,
of
production
has
sequence
started
can
Thirty
factor
With
are
denaturation.
separate
cycle
PCR
minutes.
of
time
selected
next
cycle
to
rapidly
those
the
the
The
°C
polymerase,
resist
because
used
is
heated
Taq
temperature
selected
Taq
when
the
attach
temperature
therefore
minute,
When
from
springs,
Park.
from
DNA
to
at
to
for
working.
nucleotides
replication.
DNA
obtained
temperatures,
including
very
Taq
was
work
used
with
per
primers
is
period
is
doubleAt
stranded
would
that
optimum
the
The
It
°C
in
to
95
less
than
the
an
polymerase,
a
of
very
°C.
than
amplify
less
numbers
in
replication
complete,
DNA
hour.
PCR
copies
short
A
two
allows
of
a
time.
resist
the
DNA
Select the DNA
sequence to be copied
Twice as many DNA
Raise temperature
15 seconds
Lower temperature
80 seconds
25 seconds
Raise temperature to 72°C to
allow rapid DNA replication by
T
aq DNA polymerase
▲
Figure 5
▲
Figure 6
Tnsiptin
Transcription is the synthesis of mRNA copied from the
DNA base sequences by RNA polymerase.
This
sequence
characteristic
sequence
often
of
using
the
is
strands
●
116
or
Two
base
Transcription
RNA
in
is
acids
DNA.
enzyme
of
gene.
in
indirectly
processes
the
gene
a
What
RNA
not,
a
RNA,
transcription
follows
is
to
The
an
polymerase
give
most
produce
rst
of
using
to
DNA
of
a
It
is
is
as
observable
to
specify
proteins
is
a
the
that
characteristics
specic
these
occurs
outline
a
any
genes
observable
only
binds
itself,
of
polypeptide.
the
needed
gene.
of
in
function
particular
are
of
does
The
determine
synthesis
single-stranded,
of
a
organism.
sequence
The
a
bases
an
amino
directly
individual.
of
in
of
an
polypeptide,
transcription.
template.
along
one
of
Because
the
two
transcription:
site
on
the
DNA
at
the
start
2 . 7
RNA
●
polymerase
strands
and
on
strand
one
a
of
in
●
RNA
polymerase
●
The
●
Transcription
molecule
The
product
that
is
base
base
separates
is
stops
of
uracil
in
sense
strand
is
the
a
the
gene
is
fashion
no
bonds
of
the
with
DNA
into
in
RNA,
so
a n d
t r a n s l a t i o n
single
complementary
bases
uracil
adenine.
between
and
t r a n s c r i P t i o n
separating
thymine
with
DNA
end
to
the
of
DNA
the
gene
molecule
template
to
of
strand
strand.
the
a
the
thymine.
strand
complementary
called
is
identical
one
is
has
is
place
of
The
called
There
the
transcription
that
sequence
at
the
nucleotides
covalent
from
r e P l i c a t i o n ,
the
double
and
RNA
helix
the
nucleotides.
reforms.
completed
RNA
released.
transcribed.
and
DNA.
forms
complementary
is
along
RNA
complementary
sequence
there
up
the
pairs
RNA
moves
pairing
d n a
a
The
base
antisense
So,
the
other
RNA
strand
other
to
DNA
with
of
of
DNA.
strand,
make
same
strand
to
base
This
RNA
the
base
a
with
an
molecule,
sequence
with
that
acts
the
as
of
a
the
strand
as
the
RNA
has
exception–
copy
sequence
both
RNA
one
other
sequence
the
is
RNA
template
and
the
sense
strand
RNA polymerase
free RNA nucleotides
antisense strand of DNA
direction of
transcription
3
´
5
´
5
´
3
´
RNA molecule
sense strand of DNA
▲
Figure 7
Tnstin
NOITPIRCSNART
Translation is synthesis of polypeptides on ribosomes.
The
second
of
polypeptide
with
an
part
of
of
this
large
in
the
of
the
amino
acid
RNA.
is
to
is
by
a
of
by
RNA
gene
produce
the
determined
production
determined
takes
place
Ribosomes
with
translation.
of
large
sequence
The
needed
Translation
the
by
was
a
specic
synthesis
base
of
a
transcription
described
polypeptide,
sequence
in
and
the
of
a
how
its
previous
sub-topic.
subunit,
composed
processes
RNA
to
cell
9
(green)
them
sites
shows
molecules
link
structures
complex
binding
Figure
subunit
acids,
on
are
for
each
the
two
(pink
is
the
in
and
site
together
the
structures
the
a
consist
of
and
makes
known
of
molecules
subunits
yellow)
that
into
of
cytoplasm
that
a
a
peptide
and
take
ribosome.
proteins
as
small
that
part
Each
(purple).
bonds
NOITA LSNART
ribosomes.
two
translation.
sequence
Translation
a
the
amino
molecule
base
is
is
Part
between
polypeptide.
▲
Figure 8
117
2
M O L E C U L A R
B I O L O G Y
▲
Figure 9 Large and small subunits of the ribosome with proteins shown in purple, ribosomal
RNA in pink and yellow and the site that catalyses the formation of peptide bonds green
Mssng rNa nd th gnti d
The amino acid sequence of polypeptides is determined
by mRNA according to the genetic code.
RNA
is
that
called
mRNA
carries
molecules
polypeptide
In
the
to
time
certain
will
but
be
cell
genes
large
the
mRNA
the
pancreas
Although
transfer
amino
are
acid
structure
that
make
most
of
is
many
need
of
a
RNA
is
to
ribosome.
a
the
particular
For
of
there
are
number
genes
some
and
is
that
of
mRNA
the
other
base
and
usually
amino
length
acids
2,000
carry
acid
these
only
polypeptide
The
about
Cells
information
sequence.
types
of
many
needed
to
for
sequence
ribosomal
to
At
Only
mRNA
need
or
copies
insulin-secreting
referred
the
nucleotides.
the
that
make
types;
of
in
polypeptides.
certain
polypeptide
are
of
amino
example,
a
mRNA.
cytoplasm.
translation
They
to
specic
the
decoding
during
synthesize
mammals
make
in
copies
in
for
the
transcribed
mRNA,
involved
to
different
polypeptide.
many
on
with
translation
sequence
the
length
therefore
amounts
for
RNA
are
only
for
needed
abbreviated
depending
polypeptide
will
available
secrete
a
usually
average
there
make
a
information
RNA,
varies
an
genome
needed
any
the
messenger
make
cells
of
in
insulin.
example,
of
mRNA
RNA
as
is
into
part
tRNA
of
and
an
the
rRNA.
d- q: Interpreting electron micrographs
The
electron
micrographs
transcription,
1
Deduce,
with
occurring
2
The
in
colour
been
118
translation
in
added
reasons,
each
the
to
in
gure
and
DNA
which
10
show
process
micrograph.
electron
micrographs
the
different
up
more
clearly.
Identify
each
of
these
structures:
is
electron
make
show
replication.
a)
the
red
structure
b)
the
thin
in
the
central
micrograph
[5]
has
structures
edge
of
blue
the
molecule
right-hand
near
the
lower
micrograph
2 . 7
c)
the
blue
molecules
attached
d)
the
red
to
this
of
thin
molecule
in
d n a
r e P l i c a t i o n ,
variable
blue
the
t r a n s c r i P t i o n
length
e)
molecule
left-hand
the
a n d
green
t r a n s l a t i o n
molecules
in
the
left-hand
micrograph.
[5]
micrograph
Figure 10
▲
cdns
Codons of three bases on mRNA correspond
to one amino acid in a polypeptide.
The
“translation
dictionary”
that
enables
the
f
cellular
machinery
to
convert
the
base
sequence
s p
t
on
p
the
mRNA
the
genetic
into
an
amino
acid
sequence
is
called
(5’ )
twenty
amino
one
amino
two
bases,
twenty
use
a
A
a
code,
amino
codon.
all
to
of
the
of
one
are
still
different
base
cannot
sixteen
too
acids.
with
few
Living
groups
to
bases
code
for
organisms
of
three
U
for
combinations
code
all
bases
codon
to
codes
the
possible
on
the
for
a
codons.
is
specic
polypeptide.
of
The
three
codon
second
and
Note
that
amino
GUC
both
also
for
the
Amino
For
code
the
that
third
designated
three
end
of
acids
codons
example
for
code
in
the
1
lists
of
tRNA.
specic
is
the
can
the
to
are
be
code
for
codons
amino
said
codons
carried
Each
as
acid
the
Cys
U
Phe
Ser
Tyr
Cys
C
Leu
Ser
Stop
Stop
A
Leu
Ser
Stop
Trp
G
Leu
Pro
His
Arg
U
Leu
Pro
His
Arg
C
Leu
Pro
Gln
Arg
A
Leu
Pro
Gln
Arg
G
IIe
Thr
Asn
Ser
U
IIe
Thr
Asn
Ser
C
IIe
Thr
Lys
Arg
A
Met
Thr
Lys
Arg
G
rst,
GUU
valine.
same
and
For
“degenerate”.
“stop”
on
amino
which
complementary
particular
Tyr
codons
this
G
Note
that
Val
Ala
Asp
Gly
U
Val
Ala
Asp
Gly
C
Val
Ala
Glu
Gly
A
Val
Ala
Glu
Gly
G
code
translation.
are
tRNA,
Ser
an
another
kind
of
RNA,
▲
called
Phe
called
bases
table
(3’ )
positions.
different
acid.
reason,
are
G
coding
A
mRNA
a
of
amino
Table
c
therefore
bases
mRNA
u
and
C
three
added
64
four
acid.
Each
be
is
are
so
There
amino
sequence
acid
acids,
acid.
triplet
an
There
which
the
for
code.
p
to
amino
has
the
acid
a
is
carried
three-base
mRNA
codon
by
T
able 1
a
anticodon
for
that
acid.
119
2
M O L E C U L A R
B I O L O G Y
Dding bs sqns
Use of a table of the genetic code to deduce which codon(s) corresponds to which
amino acid; use of a table of mRNA codons and their corresponding amino acids to
deduce the sequence of amino acids coded by a shor t mRNA strand of known base
sequence; deducing the DNA base sequence for the mRNA strand.
There
code,
is
no
but
should
need
if
be
a
to
table
able
to
try
to
memorize
showing
make
it
is
the
various
base
genetic
available,
sequence
example,
you
from
deductions.
the
strand
1
Which
codons
correspond
to
an
amino
the
letters
table
acids
of
has
are
the
used
to
genetic
between
one
indicate
code.
and
each
Each
six
of
amino
the
codons.
20
acid
in
off
base
from
amino
Read
base
of
complementary
codon
the
AUG
sequence
DNA.
A
in
TAC
longer
to
the
mRNA
on
the
mRNA.
is
For
transcribed
antisense
example
is
that
acid?
the
Three
the
sequence
GUACGUACG
CATGCATGC.
thymine
in
DNA
Note
but
that
with
is
transcribed
adenine
uracil
in
pairs
with
RNA.
the
Questions
three
letters
of
each
codon
for
the
amino
acid.
For
1
example,
Met
2
on
the
the
What
amino
table,
has
amino
translated
strand
of
acid
methionine,
one
acid
from
codon
which
sequence
a
shown
is
of
rst
three
codons
a)
Tryptophan
in
b)
Tyrosine
c)
Arginine
are
for
the
down
the
codon
the
left
of
a
(Tyr)
(Arg)
[3]
mRNA?
bases
in
the
mRNA
sequence
are
Deduce
the
amino
rst
for
amino
the
hand
acid,
second
side
of
the
base
the
next
and
table
to
three
so
on.
nd
codon,
across
the
top
of
the
table
acid
sequences
that
the
to
these
mRNA
sequences:
[3]
bases
Look
the
a)
to
ACG
b)
CACGGG
c)
CGCGCGAGG
[3]
rst
3
base
(Trp)
a
correspond
codon
for
be
codons
2
The
the
AUG.
would
sequence
Deduce
as
nd
If
mRNA
contains
the
base
sequence
the
CUCAUCGAAUAACCC
second
third
acid
base
base.
and
For
alanine,
down
the
example,
which
is
right
GCA
hand
codes
abbreviated
side
for
to
to
the
Ala
in
nd
the
a)
amino
the
deduce
the
table.
the
amino
polypeptide
acid
sequence
translated
from
of
the
mRNA
3
What
base
sequence
transcribed
strand
of
to
give
in
the
DNA
base
would
sequence
of
b)
a
deduce
strand
of
anti-sense
mRNA
strand
is
of
produced
the
the
antisense
mRNA?
the
A
[2]
be
DNA.
by
transcribing
This
therefore
base
strand
sequence
of
transcribed
the
to
produce
mRNA.
[2]
the
has
a
cdns nd ntidns
Translation depends on complementary base pairing
between codons on mRNA and anticodons on tRNA.
Three
●
components
mRNA
has
sequence
●
tRNA
a
of
work
sequence
the
molecules
complementary
corresponding
●
ribosomes
catalyse
120
act
the
together
synthesize
codons
that
polypeptides
species
the
by
amino
translation:
acid
polypeptide;
have
an
codon
to
as
of
to
that
the
anticodon
on
mRNA
three
they
bases
carry
that
the
binds
amino
to
of
the
site
for
mRNA
polypeptide.
and
tRNAs
and
a
acid
codon;
binding
assembly
of
and
also
2 . 7
A
summary
1
An
2
A
A
to
The
The
the
6
The
to
peptide
Stages
added
along
4,
to
5
the
and
the
the
amino
binds.
the
t r a n s l a t i o n
follows:
the
ribosome.
complementary
binds
to
the
maximum
of
to
the
rst
ribosome.
complementary
A
amino
tRNA,
carrying
moves
to
two
the
second
tRNAs
can
be
along
the
binds
a
the
acid
by
carried
making
chain
of
mRNA
a
two
so
by
the
new
rst
tRNA
peptide
amino
the
rst
acids
tRNA
to
bond.
–
a
is
the
The
dipeptide.
released,
rst.
with
an
anticodon
complementary
to
the
next
the
rst
mRNA.
transfers
amino
6
mRNA
is
the
Mistakes
mRNA
anticodon
second
then
the
acid
chain
on
repeated
each
the
of
amino
second
acids
tRNA,
by
carried
by
making
a
new
until
a
time
stop
again
the
and
cycle
codon
is
again,
is
with
repeated.
reached,
one
The
when
amino
process
the
acid
continues
completed
released.
of
translation
anticodon
are
acids
are
chain
accuracy
between
anticodon
the
then
of
a n d
bond.
polypeptide
The
the
translation
t r a n s c r i P t i o n
time.
becomes
ribosome
tRNA
the
tRNA
on
an
r e P l i c a t i o n ,
subunit
an
on
transfers
is
of
small
with
with
same
ribosome
second
codon
tRNA
on
tRNA
Another
7
the
acid
second
the
mRNA
ribosome
amino
5
the
at
to
events
translated
tRNA
on
bound
of
be
second
main
binds
molecule
codon
4
the
mRNA
codon
3
of
d n a
very
are
rare,
on
so
regularly
depends
each
on
tRNA
polypeptides
made
with
complementary
and
the
with
every
a
codon
on
sequence
amino
acid
base
pairing
mRNA.
of
hundreds
of
correct.
amino acid
growing polypeptide chain
large sub unit of ribosome
tRNA
tRNA
mRNA
anticodon
▲
Figure 11
Pdtin f hmn insin in bti
Production of human insulin in bacteria as an example of the universality of the
genetic code allowing gene transfer between species.
Diabetes
of
cells
insulin.
the
in
in
It
blood.
from
the
some
the
can
individuals
pancreas
be
that
treated
Porcine
and
pancreases
of
by
is
to
hormone
insulin
insulin,
and
destruction
the
injecting
bovine
pigs
due
secrete
cattle,
into
been
widely
difference
insulin
and
extracted
Shark
have
diabetics
both
in
used.
bovine
insulin,
in
Porcine
amino
acid
insulin
which
Japan,
has
has
insulin
has
sequence
has
been
three
used
seventeen
only
from
one
human
differences.
for
treating
differences.
121
2
M O L E C U L A R
Despite
the
between
to
the
of
blood
so
it
is
human
glucose
modied
E.
production
more
coli
amino
an
to
allergy
use
was
and
have
to
been
cause
Since
then
developed
safower
bind
some
In
1982
available
for
genetically
methods
using
yeast
This
may
obvious,
depends
tRNA
of
these
of
cells
having
amino
to
it
yeast
(a
plants.
by
species
has
transferring
been
the
insulin
to
it.
This
is
and
the
gene
mRNA
quantities
exactly
is
is
transcribed
of
the
translated
insulin.
same
to
done
to
The
amino
for
in
use
such
a
was
and
the
being
insulin
transcribed
a
a
plant)
mRNA
(an
as
animal).
and
is
fortunate
for
▲
Figure 12
harvestable
produced
sequence
and
same
code
as
genetic
engineers
that
organisms,
has
if
translated
all
with
very
few
exceptions,
use
the
same
genetic
code
as
it
makes
gene
transfer
in
possible
human
safower
way
the
gene
In
coli,
making
produce
produce
acid
E.
genetically
gene
It
the
attached
humans.
prokaryote,
humans
that
same
words,
genetic
human
anticodon
acid
in
it
each
a
the
as
other
all
modied
on
with
fungus
Each
seem
but
particular
insulins,
insulin.
using
all
lowering
However,
commercially
produced
sequence
they
animal
human
bacteria.
recently
acid
insulin,
receptor
became
It
the
concentration.
develop
time.
in
human
insulin
insulin
rst
and
and
preferable
human
the
differences
animal
diabetics
B I O L O G Y
between
widely
differing
species.
cells.
2.8 c  p
undstnding
appitins
➔
Cell respiration is the controlled release of
➔
Use of anaerobic cell respiration in yeasts to
energy from organic compounds to produce
produce ethanol and carbon dioxide in baking.
ATP.
➔
➔
Lactate production in humans when anaerobic
ATP from cell respiration is immediately
respiration is used to maximize the power of
available as a source of energy in the cell.
muscle contractions.
➔
Anaerobic cell respiration gives a small yield of
ATP from glucose.
➔
Aerobic cell respiration requires oxygen and
gives a large yield of ATP from glucose.
Nt f sin
➔
122
Assessing the ethics of scientic research:
Skis
➔
Analysis of results from experiments involving
the use of inver tebrates in respirometer
measurement of respiration rates in germinating
experiments has ethical implications.
seeds or inver tebrates using a respirometer.
2 . 8
c e l l
r e s P i r a t i o n
rs f ngy by  spitin
Cell respiration is the controlled release of energy from
organic compounds to produce ATP
.
Cell
respiration
Organic
be
used
in
breaking
then
In
be
is
one
compounds
the
cell.
down
used
humans
for
is
For
the
into
muscle
source
the
food
functions
broken
down
example,
glucose
the
respiration
of
are
of
energy
carbon
life
to
that
release
is
all
released
dioxide
and
living
energy,
in
cells
which
muscle
water.
The
perform.
can
then
bres
energy
by
can
contraction.
of
the
that
organic
we
eat.
compounds
broken
Carbohydrates
and
down
lipids
in
are
cell
often
▲
used,
but
amino
acids
from
proteins
may
be
used
if
we
eat
more
Figure 1 Breaking down 8 grams of glucose
protein
in cell respiration provides enough energy to
than
needed.
Plants
use
carbohydrates
or
lipids
previously
made
by
sprint 100 metres
photosynthesis.
Cell
respiration
way,
in
a
so
that
usable
as
form.
triphosphate,
phosphate
is
required
is
not
supply.
of
life
is
carry
of
as
This
almost
to
all
is
out
using
is
always
linked
organic
the
out
possible
form
transferred
This
in
carried
group
breakdown
ATP
is
much
enzymes
the
chemical
adenosine
reaction.
in
energy
abbreviated
to
this
a
of
a
careful
released
substance
to
ATP
.
To
make
energy
or
comes
controlled
retained
called
diphosphate,
The
and
is
adenosine
ATP
,
ADP
.
from
a
Energy
the
compounds.
from
reason
cell
for
to
cell
cell
and
all
respiration
cells
being
require
an
a
continuous
essential
function
cells.
aTP is  s f ngy
cell respiration
ATP from cell respiration is immediately available as a
source of energy in the cell.
A DP 1
AT P
Cells
require
energy
●
Synthesizing
●
Pumping
●
Moving
for
large
three
main
molecules
types
like
of
DNA,
pho s pha te
activity.
RNA
and
proteins.
active cell processes
vesicles,
molecules
things
or
in
or
ions
around
muscle
across
inside
cells
the
the
membranes
cell,
such
protein
as
bres
by
active
transport.
▲
Figure 2
▲
Figure 3 Infra red photo of toucan
chromosomes,
that
cause
muscle
contraction.
The
energy
for
advantageof
immediately
and
ATP
all
When
cell
as
these
an
available.
phosphate.
by
of
ATP
The
processes
energy
It
is
ADP
released
and
is
supply
supplied
is
that
simply
phosphate
by
can
by
the
ATP
.
The
energy
splitting
then
be
is
ATP
into
ADP
reconverted
to
respiration.
energy
from
ATP
is
used
in
cells,
it
is
ultimately
all
converted
showing that it is warmer than its
to
heat.
warm,
Although
it
cannot
environment.
ATP
for
cell
heat
be
This
energy
reused
is
the
activities.
for
may
cell
reason
be
useful
activities
for
cells
to
and
keep
is
requiring
an
organism
eventually
a
lost
continual
to
surroundings due to heat generated
the
source
of
by respiration. Excess heat is
dissipated by sending warm blood
to the beak
123
2
M O L E C U L A R
B I O L O G Y
anbi spitin
Anaerobic cell respiration gives a small yield of
ATP from glucose.
Glucose
is
oxygen.
The
quickly.
broken
●
when
a
●
when
oxygen
●
in
The
of
Anaerobic
short
products
in
ATP
cell
but
anaerobic
is
rapid
that
cell
relatively
respiration
supplies
environments
waterlogged
▲
down
yield
burst
run
are
is
of
out
respiration
small,
but
therefore
ATP
in
production
in
without
ATP
useful
respiring
decient
the
in
is
can
using
be
three
any
produced
situations:
needed;
cells;
oxygen,
for
example
soils.
of
anaerobic
respiration
are
not
the
same
in
all
organisms.
Figure 4 The mud in mangrove swamps is
In
humans,
glucose
is
converted
to
lactic
acid,
which
is
usually
in
a
decient in oxygen. Mangrove trees have
evolved ver tical roots called pneumatophores
which they use to obtain oxygen from the air
dissolved
to
form
ethanol
excess,
so
d  v  mk m
and
carbon
must
produced
av
known
in
Summary
be
as
lactate.
dioxide.
removed
strictly
limited
In
yeast
Both
from
and
lactate
the
cells
plants
and
that
glucose
ethanol
produce
are
is
converted
toxic
them,
or
in
be
quantities.
equations
glucose
lactate
pm?
ADP
ATP
There has been much debate about
This
occurs
in
animals
including
humans.
bioethanol production. A renewable
fuel that cuts down on carbon
+
emissions is obviously desirable.
carbon
dioxide
What are the arguments against
ADP
ATP
bioethanol production?
This
occurs
in
yeasts
and
plants.
Yst nd its ss
Use of anaerobic cell respiration in yeasts to produce
ethanol and carbon dioxide in baking.
Yeast
is
glucose
It
can
a
unicellular
or
other
respire
respiration
renewable
Bread
is
dough
to
is
warm
soon
from
▲
Figure 5
124
yeast
made
to
by
then
this
the
adding
of
occurs
or
basis
for
water
to
up
so
gas,
it.
naturally
such
as
the
anaerobically.
production
the
the
so
produced
dough
that
yeast
yeast
and
our,
Usually
ingredient.
encourage
dioxide
the
that
available,
aerobically
is
baking
bubbles
often
used
carbon
either
are
of
in
habitats
surface
of
Anaerobic
foods,
where
fruits.
cell
drinks
and
energy.
and
create
Yeast
in
fungus
sugars
the
After
to
by
kneading
ingredient
baked
bread
kneading,
respire.
carries
forms
an
out
cell
The
a
cell
in
is
to
the
the
texture.
dough
cannot
the
make
dough
kept
respiration.
respiration
of
to
lighter
dough
oxygen
swelling
mixture
added
has
the
anaerobic
anaerobic
bubbles.
Any
the
is
is
The
escape
dough
due
to
2 . 8
the
is
production
also
of
produced
bubbles
by
of
carbon
anaerobic
cell
dioxide
is
respiration,
called
but
it
rising.
c e l l
r e s P i r a t i o n
Ethanol
evaporates
duringbaking.
Bioethanol
a
is
renewable
utilized
to
as
converts
feed
the
rst
The
ethanol
and
various
improve
vehicles,
its
a nd
ca ne
brok e n
i nto
and
ca n
d o wn
produce d
metho d s
by
a re
combus ti o n.
sometime s
in
a
l iv in g
Al tho ug h
e tha no l
s ug a r s
by
v ar io us
ma tte r
in to
Only
be
s o urce.
su g a r
sugars
p ro duce d
s to ck
plant
from
respiration.
must
energ y
a
convert
produced
ethano l
in
e tha nol ,
p ur e
puri  e d
to
re m o ve
is
be
by
is
Yea s t
a nd
c e l lu l os e
u s in g
enz ym e s .
d is til l at i on
wa t e r
u s ed
be
u s ed
a n ae r obic
don e
is
an d
by
as
c an
ca n
ye a st .
s t a rc h
is
use
b io et h a n ol
us in g
so
Th i s
bi oe th an ol
s ta te
m a t t er
fe rm e n t er s
suga rs .
us e d
Mos t
m o st
conv e r t ed ,
ye a sts
then
p la nt
for
or g an i sm s
( m a i z e ),
l ar g e
into
the
any
l i vi n g
cor n
be
o rg a nis m s ,
as
s om et i m e s
a
fr om
fu e l
m ix ed
it
to
in
wit h
gasoline(petrol).
▲
Figure 6
d- q: Monitoring anaerobic cell respiration in yeast
The
apparatus
mass
ask
changes
was
in
gure
during
placed
on
7
the
an
was
used
brewing
electronic
to
of
monitor
wine.
balance,
2
Explain
3
Suggest
connected
to
a
computer
for
data-logging.
mass
two
loss
are
shown
in
gure
Calculate
the
total
loss
of
mass
during
and
the
[3]
reasons
from
for
the
the
start
increasing
of
the
rate
experiment
6.
[2]
Suggest
two
mean
daily
reasons
for
the
mass
remaining
the
constant
experiment
mass.
8.
4
1
of
The
untilday
results
loss
which
of
was
the
The
loss.
from
day
11
onwards.
[2]
[3]
airlock to
560
prevent
electronic
entry
balance
of oxygen
connected
555
g / ssam
to a data-
logging
yeast in a
computer
550
solution of
sugar and
545
nutrients
555.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
time / days
▲
▲
Figure 7 Yeast data-logging apparatus
Figure 8 Monitoring anaerobic cell respiration in yeast
anbi spitin in hmns
Lactate production in humans when anaerobic respiration is used to maximize the
power of muscle contractions.
The
lungs
most
and
organs
aerobic
of
blood
the
respiration
system
supply
body
rapidly
to
used,
be
oxygen
enough
but
to
resort
for
sometimes
to
reason
we
ATP
anaerobic
is
very
that
cell
respiration
anaerobic
rapidly
for
a
in
respiration
short
period
muscles.
can
of
The
supply
time.
It
is
125
2
M O L E C U L A R
therefore
power
of
used
B I O L O G Y
when
muscle
we
need
to
maximize
the
contractions.
After
vigorous
must
be
oxygen.
In
our
ancestors
maximally
powerful
will
have
been
needed
for
allowing
escape
from
a
predator
or
during
catching
times
occur
in
of
our
food
respiration
is
training
sport.
or
lives
shortage.
more
weight
●
short-distance
lifters
likely
These
●
today.
to
are
These
during
used
several
minutes
lactate
the
for
use
of
enough
be
absorbed
demand
for
for
all
lactate
oxygen
that
to
be
broken
builds
a
period
of
anaerobic
respiration
is
up
called
events
oxygen
debt.
anaerobic
during
examples:
the
runners
Instead
be
take
the
involves
of
the
rarely
to
The
during
prey
can
This
survival
down.
by
It
contractions,
down.
muscle
oxygen
contractions
muscle
broken
lift;
in
races
up
to
400
metres;
●
long-distance
during
Anaerobic
of
lactate,
the
a
cell
so
can
is
a
respiration
limit
tolerate
respiration
short
can
timescale
contractions
a
short
to
and
it
of
the
be
distance
and
involves
being
in
a
how
This
which
is
the
to
rowers
not
more
production
supply
muscle
the
the
than
body
anaerobic
reason
We
ATP
,
increases.
that
much
power
maximized.
–
the
used
concentration
limits
done.
over
can
is
lactate
this
be
cyclists
nish.
when
concentration
There
for
runners,
sprint
of
can
for
the
muscle
only
▲
sprint
Figure 9 Shor t bursts of intense exercise are fuelled
by ATP from anaerobic cell respiration
400metres.
abi spitin
Aerobic cell respiration requires oxygen and gives a large
yield of ATP from glucose.
If
oxygen
to
release
Whereas
a
available
greater
the
anaerobic
cell
is
yield
cell
to
a
cell,
quantity
of
ATP
is
respiration,
glucose
of
energy
only
it
is
dioxide
waste
cell
respiration
and
water
product
humans
are
that
about
a
involves
to
litre
be
cell respiration supplies its water needs
126
In
eukaryotic
including
the
more
in
fully
anaerobic
molecules
than
is
all
cells
of
series
In
thirty
of
most
excreted,
produced
per
per
broken
cell
glucose
glucose
chemical
organisms
down
respiration.
with
with
but
per
the
reactions.
carbon
water
is
aerobic
most
the
of
the
reactions
mitochondrion.
often
+
to
useful.
is
a
In
water
ATP
reactions
that
Carbon
dioxide
day.
+
ADP
despite only eating dry foods, because aerobic
a
produced.
has
half
glucose
Figure 10 The deser t rat never needs to drink
be
than
respiration.
Aerobic
▲
two
more
can
of
produce
aerobic
carbon
cell
respiration,
dioxide,
happen
inside
2 . 8
c e l l
r e s P i r a t i o n
rspimts
Analysis of results from experiments involving measurement of respiration rates in
germinating seeds or inver tebrates using a respirometer.
A
respirometer
measure
designs.
●
A
Most
sealed
An
A
One
in
or
or
plastic
such
as
is
that
There
these
tissue
carbon
capillary
the
device
rate.
involve
alkali,
absorb
●
any
glass
organism
●
is
respiration
is
used
are
in
to
many
possible
volume.
the
container
in
which
the
Respirometers
potassium
hydroxide,
●
to
the
possible
versions
11,
uid,
connected
to
●
the
that
it
of
is
respirometer
possible
require
only
a
to
is
syringe
●
shown
design
tube
attached
to
with
and
the
respirometer
the
organisms
cell
respiration,
is
inside
working
are
will
correctly
carrying
volume
reduce
table
out
and
tube
will
move
of
air
the
and
organisms.
carbon
This
dioxide
is
absorbed
and
the
towards
is
uid
the
because
produced
by
analyse
in
if
the
position
several
uid
If
is
the
times.
the
If
the
in
rate
even,
temperature
increase
uid
the
relatively
uctuates,
an
of
the
results
air
of
different
organisms
temperature
on
respiration
rate
rates
could
be
compared
in
active
organisms.
shows
pea
of
the
will
be
aerobic
is
the
results
of
temperature
an
seeds
was
on
experiment
respiration
in
investigated.
these
repeats
results
at
you
each
should
rst
temperature
check
are
to
close
for
you
should
to
then
decide
that
calculate
the
mean
results
results
are
for
reliable.
each
used
The
next
stage
is
to
plot
a
graph
of
the
cell
results,
are
of
graph
the
reliable.
not
be
reliable
causes
an
each
line.
respirometer
temperature
and
vertical
recorded
movement
results
the
of
the
oxygen
by
effect
with
temperature
on
the
horizontal
alkali.
should
inside
rate
container
x-axis
The
various
the
mean
respiration
of
below
temperature.
up
perform
aerobic
inside
You
with
to
investigated;
the
germinating
enough
capillary
be
inactive
which
see
respirometer
used
a
bath.
a
To
the
be
water
inside
using
it.
in
If
can
controlled
compared;
respiration
simpler
The
capillary
be
effect
could
design
but
temperature
be
controlled
respiration
could
container.
gure
the
should
experiments:
placed.
containing
possible
thermostatically
parts:
dioxide.
tube
If
respirometer
because
increase
the
y-axis.
by
rate
plotting
the
temperature
The
graph
relationship
respiration
is
of
movement
Range
bars
lowest
and
will
allow
of
the
you
the
of
be
and
joining
between
rate
can
on
to
highest
them
to
uid
added
result
with
a
conclude
temperature
germinating
the
the
at
ruled
what
and
the
the
peas.
Mvm    pm
1
(mm m
tmp
3
graduated 1 cm
(°c)
)
1
2
3
g
g
g
5
2.0
1.5
2.0
10
2.5
2.5
3.0
15
3.5
4.0
4.0
20
5.5
5.0
6.0
25
6.5
8.0
7.5
30
11.5
11.0
9.5
syringe
wire basket containing
animal tissue
lter paper rolled
to form a wick
capillary tube
potassium
hydroxide
solution
▲
Figure 11 Diagram of a respirometer
127
2
M O L E C U L A R
B I O L O G Y
d- q: Oxygen consumption in tobacco hornworms
Tobacco
Adults
hornworms
of
this
from
the
are
series
a
are
species
eggs
laid
of
by
larval
the
are
larvae
moths.
the
adult
stages
of
Manduca
Larvae
female
called
b)
sexta.
trends
moths.
instars.
above
There
grows
and
then
changes
into
the
next
shedding
its
exoskeleton
and
developing
researchers
a
air
one.
The
exoskeleton
includes
the
that
supply
oxygen
to
the
graphs
below
(gure
12)
rate
using
of
3rd,
a
simple
4th
and
show
instar
in
below
the
and
weight.
[2]
reared
some
oxygen
tobacco
content.
hornworms
They
larvae
moulted
at
a
lower
found
body
larvae
reared
in
normal
air
with
20 %
mass
oxygen.
tissues.
respirometer
5th
critical
reduced
instar
Suggest
a
reason
for
earlier
moulting
in
larvae
measurements
reared
made
difference
tracheal
3
The
with
the
than
tubes
the
new
that
larger
the
for
theperiods
one
in
by
reasons
between
Each
The
instar
Suggest
emerge
of
the
larvae.
in
air
withreduced
oxygen
content.
[2]
respiration
Details
after critical weight
before critical weight
of
5th instar
the
methods
the
biologists
are
given
in
the
paper
published
by
0.12
0.16
who
carried
out
the
research.
The
0.10
0.14
reference
to
the
research
is
Callier
V
and
Nijhout
0.08
0.12
H
F
(2011)
“Control
of
body
size
by
oxygen
supply
0.06
0.10
reveals
size-dependent
and
size-independent
0.04
mechanisms
of
molting
and
0.08
metamorphosis.”
0.02
PNAS;108:14664–14669.
on
the
internet
at
paper
is
freely
1
http://www.pnas.org/
content/108/35/14664.full.pdf+html.
2
and
data
respiration
results
low
have
to
with
are
point
the
rate
been
of
intermediate
mass
on
is
graphs
one
divided
intermediate
plotted
body
on
body
to
referred
larva.
into
and
body
graphs.
to
as
the
For
the
body
each
younger
mass
high
separate
shows
mass.
The
instar
larvae
older
mass
the
with
larvae
The
results
O lm( etar noitaripser
Each
3
4
5
6
7
0.025
9
10 11 12 13
4th instar
0.030
0.020
0.028
0.026
0.015
0.024
0.022
0.010
0.020
0.005
0.018
0.20.30.40.50.60.70.80.9
1.0
intermediate
critical
8
0.032
2
)nim/
available
This
1.1
1.2
1.3
1.4
weight.
0.007
3rd instar
0.009
0.006
1
a)
Predict,
using
the
data
in
the
graphs,
how
0.008
0.005
the
respiration
rate
of
a
larva
will
change
0.007
0.004
as
it
grows
from
moulting
until
itreaches
0.006
0.003
the
critical
weight.
0.005
[1]
0.002
0.004
0.001
b)
Explain
the
change
in
respiration
rate
that
0.003
0.000
.
0
2
Figure 12 Respiration rates of tobacco hornworms (after
Callier and Nijhout, 2011)
e  m   pm
Assessing the ethics of scientic research: the use of inver tebrates in
respirometer experiments has ethical implications.
It
is
important
ethics
of
debate
their
about
experiments.
128
for
all
scientists
research.
the
ethics
When
There
of
to
using
discussing
assess
has
been
the
we
intense
to
animals
ethical
in
issues,
consider
students
consider
do
are
the
who
consequences
are
intentions?
harmed
learning
For
such
example,
unintentionally
as
science?
does
if
benets
Do
the
that
we
animals
change
6
.
0
2
4
▲
.
0
[2]
2
weight (g)
weight (g)
in
2
rate
weight.
.
0
respiration
1
.
0
2
in
critical
8
6
1
.
0
0
the
1
trends
4
the
above
.
0
larvae
.
0
Discuss
1
a)
.
0
2
0
.
0
0
0
.
2
6
4
0
.
1
[2]
0
described.
0
have
8
you
2 . 9
whether
there
the
example,
be
can
subject
they
experiment
absolute
to
would
principles
we
say
was
of
that
conditions
encounter
ethical
right
animals
that
in
are
their
or
and
not?
Are
wrong:
should
outside
natural
3
Can
the
never
carrying
involving
be
out
animals
answered
to
respirometer
these
help
are
to
decide
ethically
Is
the
Is
it
acceptable
natural
can
habitat
they
be
to
remove
for
safely
Will
the
animals
is
the
of
or
In
be
that
be
cause
pain
minimized
particular,
can
or
during
contact
prevented?
animals
is
using
particularly
use
in
animals
an
returned
from
their
experiment
to
their
and
habitat?
suffer
pain
or
any
other
use
in
International
a
there
in
an
the
experiment
alternative
method
that
animals?
important
to
directive
respirometer
consider
the
An
experiments
Baccalaureate
that
investigations
ethics
of
laboratory
need
important
to
be
or
eld
of
this
has
is
in
that
an
the
issued
experiments
undertaken
aspect
because
Organization
and
ethical
experiments
harm
should
during
animals
the
way.
2
accidents
acceptable:
animal
1
of
the
alkali
use
avoids
should
whether
the
essential
It
experiments
to
habitat?
experiments
questions
risk
experiment?
with
what
4
Before
the
suffering
for
P h o t o s y n t h e s i s
not
be
undertaken
in
schools
that
inict
experiment?
pain
or
harm
on
humans
or
other
living
animals.
2.9 P
undstnding
appitins
➔
Photosynthesis is the production of carbon
➔
Changes to the Ear th’s atmosphere, oceans and
compounds in cells using light energy.
rock deposition due to photosynthesis.
➔
Visible light has a range of wavelengths with
violet the shor test wavelength and red the
Skis
longest.
➔
Chlorophyll absorbs red and blue light most
➔
other colours.
➔
➔
➔
Separation of photosynthetic pigments by
chromatography.
Oxygen is produced in photosynthesis from
photolysis of water.
Design of experiments to investigate limiting
factors on photosynthesis.
eectively and reects green light more than
➔
Drawing an absorption spectrum for chlorophyll
and an action spectrum for photosynthesis.
Energy is needed to produce carbohydrates and
other carbon compounds from carbon dioxide.
➔
Temperature, light intensity and carbon dioxide
Nt f sin
concentration are possible limiting factors on
➔
Experimental design: controlling relevant
the rate of photosynthesis.
variables in photosynthesis experiments is
essential.
129
2
M O L E C U L A R
B I O L O G Y
Wht is phtsynthsis?
Photosynthesis is the production of carbon compounds in
cells using light energy.
Living
organisms
structure
are
able
light
of
to
The
converted
is
into
the
that
an
complex
and
simple
process
compounds
▲
all
and
Photosynthesis
is
require
cells
make
energy
water.
their
to
carbon
this
example
chemical
produced
compounds
life
processes.
of
that
substances
is
called
energy
energy
include
out
compounds
inorganic
does
carbon
carry
in
they
such
as
to
build
Some
need
the
organisms
using
carbon
only
dioxide
photosynthesis.
conversion,
carbon
as
light
compounds.
carbohydrates,
proteins
energy
The
and
carbon
lipids.
Figure 2 The trees in one hectare of redwood
forest in California can have a biomass of more
than 4,000 tonnes, mostly carbon compounds
produced by photosynthesis
▲
Figure 1 Leaves absorb carbon dioxide and light and use them in photosynthesis
Spting phtsynthti pigmnts by hmtgphy
Separation of photosynthetic pigments by chromatography. (Practical 4)
Chloroplasts
and
other
Because
these
wavelength
us.
may
thin
This
is
be
light,
can
be
done
with
with
A
containing
tissue
is
solvent
the
1
a
is
Tear
in
a
a
thin
placed
up
separated
a
with
plastic
layer
near
types
leaf
a
to
of
up
that
porous
the
of
colour
to
chromatography
gives
of
ranges
chromatography.
better
has
the
results.
been
material.
extracted
end
run
chlorophyll
pigments.
different
by
strip
of
one
of
different
a
paper
pigments
allowed
different
look
chromatography
coated
spot
types
accessory
absorb
they
familiar
layer
several
called
pigments
of
Pigments
You
but
contain
pigments
from
strip.
strip,
to
leaf
A
separate
pigment.
into
small
pieces
and
put
them
mortar.
▲
2
130
Add
a
small
amount
of
sand
for
grinding.
Figure 3 Thin layer chromatography
and
2 . 9
3
Add
a
small
volume
of
propanone
P h o t o s y n t h e s i s
(acetone).
Pgm
c 
r

4
Use
the
pestle
dissolve
5
If
6
the
allow
7
Use
the
the
the
a
in
the
all
you
to
and
has
other
off
tissue
just
glass,
turned
into
from
a
a
pgm
and
3–4
a
little
dark
to
the
all
of
orange
0.98
Chlorophyll a
blue green
0.59
Chlorophyll b
yellow green
0.42
Phaeophytin
olive green
0.81
Xanthophyll 1
yellow
0.28
Xanthophyll 2
yellow
0.15
then
glass.
the
cells’
dry
drops
Carotene
more.
green,
settle,
watch
off
smear
add
add
solids
evaporate
water
have
watch
leaf
evaporates,
and
drier
the
pigments.
propanone
hair
When
grind
propanone
sand
propanone
8
the
propanone
When
pour
out
to
cytoplasm.
pigments
of
propanone
12
9
and
use
a
paint
Use
the
paint
brush
brush
to
to
dissolve
transfer
the
a
very
of
the
pigment
solution
to
the
outside
of
the
tube
just
below
the
level
of
the
Take
the
spot
on
the
TLC
strip.
small
13
amount
Mark
pigments.
strip
and
cork
out
of
the
the
tube.
TLC
strip.
spot
of
Your
aim
pigment
in
is
to
the
make
middle
a
very
of
the
small
strip,
14
10
millimetres
from
one
end.
It
should
be
Pour
up
dark.
This
small
drop
is
achieved
by
repeatedly
putting
the
strip
and
thenallowing
to
the
dry
before
Place
the
adding
another
amount.
You
up
dryingby
using
the
blowing
on
the
spot
or
When
the
it
specime n
will
not
tub e
be
of
spot
the
the
TLC
so
that
is
dark
enough,
slide
the
stripis
strip
into
the
slot
in
a
cork
or
ts
into
The
a
slot
tube
that
should
is
hold
wider
the
than
strip
Insert
the
the
TLC
cork
strip
Leave
and
strip
into
a
specimen
str i p
a nd
of
cor k
into
th e
the
just
tub e
is
s e al e d
d i p p i ng
should
extend
nearly
the
tube,
but
not
quite
i nto
and
the
the
r unnin g
must
NOT
tou c h
th e
spot.
the
tube
to
minutes,
co mp l e tel y
to
allow
the
al one
for
s olv ent
to
a bou t
run
tube.
through
the
TL C
s tr i p.
You
can
wa t c h
the
the
bottom
be nc h
C ar e f u l ly
TLC
up
The
la b
rmly.
ve
11
a
bung
16
strip.
tube
other
pigment
that
on
d i s tur be d.
solvent.Thesolvent
end
specimen
drier.
TLC
10
the
marked.
by
tube,
hair
into
you
can
lower
speed
that
it
where
to
solvent
level
a
15
onto
running
very
pigments
sepa r a te ,
b ut
DO
NOT
T OU CH
touch.
THETUBE.
17
sp
c
d
r
When
the
solvent
has
nearly
reached
the
nm 

top
m
mv
of
the
strip,
remove
it
from
the
tube
and
pgm
separate
it
from
the
cork.
(mm)
18
Rule
two
pencil
lines
across
the
strip,
one
at
1
the
level
reached
by
the
solvent
and
one
at
the
2
level
of
the
initial
pigment
spot.
3
19
Draw
a
circle
pigment
4
the
around
spots
and
a
e a ch
cr o s s
of
in
the
the
s e pa ra t e d
ce nt re
of
circle.
5
6
7
8
▲
Table
of
standard
R
Figure 4 Chromatogram of leaf pigments
values
f
131
2
M O L E C U L A R
20
Using
a
ruler
B I O L O G Y
with
millimetre
markings,
21
Calculate
the
R
for
each
pigment,
where
R
f
measure
solvent
and
the
(the
the
distance
distance
distance
moved
by
between
moved
by
the
the
each
running
two
the
lines)
pigment
distance
between
the
lower
line
and
the
the
centre
of
the
by
by
the
the
pigment
divided
by
the
solvent.
Show
all
your
results
in
the
table
above,
starting
cross
with
in
run
is
f
run
(the
22
distance
distance
the
pigment
that
had
moved
least
far.
circle).
Wvngths f ight
Visible light has a range of wavelengths with violet the
shor test wavelength and red the longest.
Sunlight
or
radiation
simply
that
wavelengths
from
very
X-rays
as
our
are
short
and
infrared
light
eyes
invisible.
to
very
ultraviolet
radiation
wavelengths
longer
wavelengths
of
When
droplets
formed,
a
including
of
violet,
by
wavelengths
plants
the
sun
other
in
water
of
and
of
green
the
light
so
m W / ecaf rus s’ht raE
visible light are separated
sky
and
the
and
split
of
to
electromagnetic
us
and
electromagnetic
wavelengths
energy;
lower
longer
energy.
than
other
radiation
such
as
wavelengths
Visible
infrared.
light
The
such
has
range
of
nanometres.
sunlight
visible.
which
This
we
Violet
up
is
see
and
and
a
rainbow
because
as
sunlight
different
blue
are
is
the
is
colours,
shorter
wavelength.
detected
for
by
this
the
is
atmosphere
particularly
blue
visible
of
shorter
700
reason
Earth’s
wavelengths
Shorter
have
red.
are
A
high
are
longest
2
eht gnihcaer noitaidar ralos
Figure 5 In a rainbow the wavelengths of
to
light
1.5
▲
have
400
that
are
the
therefore
spectrum
wavelengths,
is
penetrate
a
waves
the
photosynthesis.
wavelengths,
is
all
is
wavelengths.
is
in
colours
red
of
It
ultraviolet
light
blue,
and
There
radio
than
up
detect.
radiation
different
wavelengths
The
of
made
long
and
visible
different
mixture
is
can
eye
that
in
are
also
they
larger
are
those
used
emitted
quantities
by
than
abundant.
5 450
500 nm
green 5 525
575 nm
red
700 nm
5 650
1.0
0.5
0
500
1000
1500
2000
2500
3000
wavelength /nm
▲
Figure 6 The spectrum of electromagnetic radiation reaching the Ear th’s surface
light bsptin by hphy
Chlorophyll absorbs red and blue light most eectively
and reects green light more than other colours.
The
rst
involves
stage
substance
132
in
photosynthesis
chemical
does
substances
not
absorb
is
the
called
visible
absorption
pigments.
light.
A
Pigments
of
sunlight.
white
are
or
This
transparent
substances
that
do
2 . 9
absorb
all
of
There
not
light
the
are
the
For
except
sunlight
therefore
appear
pigments
others.
colours
and
colours
is
absorb
reected
It
the
can
some
blue
pass
to
they
us.
Pigments
emit
no
wavelengths
pigment
appears
and
coloured
because
in
to
into
a
gentian
us,
because
our
eye,
to
of
visible
ower
this
be
that
absorb
light.
light
but
absorbs
part
of
detected
all
the
by
cells
in
retina.
Photosynthesizing
photosynthetic
chlorophyll
red
that
example,
blue.
appear
black,
P h o t o s y n t h e s i s
and
much
This
less
is
being
but
blue
organisms
pigment
they
light
all
very
effectively.
the
reason
for
is
use
a
appear
green
effectively,
main
of
of
pigments,
There
to
but
Wavelengths
the
range
chlorophyll.
us.
the
This
in
but
various
is
light
the
they
green
therefore
ecosystems
main
forms
because
intermediate
green
colour
are
of
absorb
light
are
reected.
dominated
by
▲
Figure 7 Gentian owers contain the
pigment delphinidin, which reects blue
plants
light and absorbs all other wavelengths.
green.
absptin nd tin spt
Drawing an absorption spectrum for chlorophyll and an action spectrum
forphotosynthesis.
An
of
action
spectrum
photosynthesis
An
absorption
percentage
by
a
of
pigment
at
is
a
graph
each
spectrum
light
or
a
is
a
graph
absorbed
group
showing
wavelength
of
at
the
of
rate
showing
each
It
is
not
spectra
light.
the
wavelength
difcult
are
very
to
explain
similar:
occur
in
wavelengths
other
photosynthetic
of
why
action
and
photosynthesis
light
that
pigments
When
drawing
can
legend
●
as
the
to
700
On
of
The
should
have
nanometres
should
chlorophyll a
chlorophyll b
absorption
extend
the
shown
from
400
carotenoids
nanometres.
action
for
a
spectrum
measure
photosynthesis.
percentage
from
and
x-axis
with
scale
the
pigments.
action
horizontal
wavelength,
units.
an
used
the
or
absorb.
noitprosba %
spectra,
both
only
chlorophyll
100
●
absorption
can
0
to
of
the
of
the
the
This
is
y-axis
relative
often
maximum
should
given
rate,
be
400
amount
as
with
500
a
scale
600
700
wavelength (nm)
a
▲
Figure 8 Absorption spectra of plant pigments
100%.
100
●
an
absorption
the
from
0
legend
to
data
should
be
not
be
y-axis
absorption”,
with
should
a
scale
100%.
Ideally
curve
“%
the
points
plotted
drawn
possible,
fo r
a nd
s p eci c
the n
thr o ug h
the
cur v e
a
wa vel e ng t h s
smo ot h
the m.
fr om
a
If
th is
)etar xam fo %(
have
spectrum
sisehtnysotohp
●
On
is
publ i sh e d
400
spectrum
could
be
500
600
700
co p i e d.
wavelength (nm)
▲
Figure 9 Action spectrum of a plant pigment
133
2
M O L E C U L A R
B I O L O G Y
d- q: Growth of tomato seedlings in red, green and blue light
Tomato
for
seeds
30days
green
and
different
of
photons
light
of
of
of
In
The
each
tested
every
the
peak
Plot
Four
two
is
table
below,
together
with
the
mean
you
can
put
graph
Do
and
height
of
the
seedlings.
Plants
tall,
when
with
they
are
weak
stems
receiving
and
small
insufcient
different
and
on
left
theother
of
height.
scales
the
attempt
relationship
and
to
on
on
hand
the
plot
the
if
y-axis
side
right
the
between
Hint:
of
hand
resultsfor
LEDs.
[6]
in
Using
your
graph,
deduce
the
relationship
leaf
the
leaf
area
of
the
seedlings
and
often
their
grow
the
area
one
not
between
area
show
leaf
combinations
of
2
the
to
needtwo
side.
intensity
shown
graph
you
the
treatment
wavelength
a
wavelength,
orange,
and
same
wavelength
1
grown
red,
diodes.
were
received
light.
by
LED
and
by
emitting
colours.
plants
emitted
produced
light
colours
tomato
germinated
light
blue
combinations
the
were
in
height.
[1]
leaves
light
3
for
Evaluate
of
photosynthesis.
the
tomato
considering
Pk wvg  g m
data
crops
in
in
the
table
for
greenhouses
usingLEDs
to
a
provide
l   g
grower
who
is
light.
[3]
hg  g
c  led
2
 led (m)
Red
(m
630
)
(mm)
5.26
192
Orange
600
4.87
172
Green
510
5.13
161
Blue
450
7.26
128
Red and Blue
–
5.62
99
Red, Green and Blue
–
5.92
85
Source: Xiaoying, Shirong, T
aotao, Zhigang and Tezuka (201
2). “Regulation of the growth and photosynthesis of cherry tomato
seedlings by dierent light irradiations of light emitting diodes (LED).” African Journal of Biotechnology Vol. 11(22), pp. 6
169-6
1
77
oxygn pdtin in phtsynthsis
Oxygen is produced in photosynthesis from photolysis
of water.
One
of
of
the
water
essential
to
release
steps
in
electrons
photosynthesis
needed
in
is
other
the
splitting
of
molecules
stages.
+
H
O
→
4e
+
4H
+
O
2
This
and
in
reaction
the
word
is
2
called
lysis
photosynthesis
product
and
photolysis
means
comes
diffuses
because
disintegration.
from
photolysis
it
only
All
of
of
happens
the
water.
in
oxygen
Oxygen
the
light
generated
is
a
waste
away.
e  p   e 
Changes to the Ear th’s atmosphere, oceans and rock
deposition due to photosynthesis.
▲
Figure 10 Photosynthesizing organisms seem
Prokaryotes
were
but over billions of years they have changed it
about
million
signicantly
algae
insignicant in relation to the size of the Ear th
134
3,500
and
plants,
the
rst
years
which
organisms
ago.
have
They
been
to
perform
were
joined
carrying
out
photosynthesis,
millions
of
starting
years
photosynthesis
later
ever
by
since.
2 . 9
One
of
consequence
the
2%
of
atmosphere.
by
volume
by
photosynthesis
This
began
2,200
mya.
is
about
This
the
rise
2,400
is
in
the
million
known
as
oxygen
years
the
concentration
ago
Great
P h o t o s y n t h e s i s
(mya),
Oxidation
rising
to
av
Event.
d mp
At
the
due
to
same
to
the
a
time
the
reduction
rise
in
Earth
in
the
experienced
greenhouse
oxygenation
causing
a
its
rst
effect.
glaciation,
This
decrease
in
could
the
presumably
have
been
concentration
P
cmp 
due
mp (%)
of
N
CO
methane
carbon
potent
in
the
dioxide
atmosphere
and
concentration.
greenhouse
photosynthesis
Both
methane
causing
and
a
carbon
decrease
dioxide
in
2
are
Venus
increase
in
it
to
mya
oxygen
caused
precipitate
H
2
O
2
98
1
1
0
0
concentrations
in
the
oceans
between
2,400
0.04
78
1
21
0.1
96
2.5
1.5
2.5
0.1
and
Mars
2,200
O
gases.
Ear th
The
Ar
2
the
onto
oxidation
the
sea
of
bed.
dissolved
A
iron
distinctive
in
rock
the
water,
formation
causing
was
What are the main dierences
produced
called
the
banded
iron
formation,
with
layers
of
iron
oxide
between the composition of the
alternating
with
other
minerals.
The
reasons
for
the
banding
are
not
yet
Ear th's atmospheres and the
fully
understood.
The
banded
iron
formations
are
the
most
important
atmosphere of the other planets.
iron
ores,
so
it
is
thanks
to
photosynthesis
in
bacteria
billions
of
years
What is the cause of these
ago
that
we
have
abundant
supplies
of
steel
today.
dierences?
The
oxygen
2,200
20%
mya
or
concentration
until
more.
multicellular
about
This
of
the
750-635
corresponds
organisms
were
atmosphere
mya.
with
There
the
remained
was
period
then
a
when
at
about
2%
signicant
many
from
rise
groups
to
of
evolving.
50
erehpsomta fo %/negyxo
40
av
30
g 
20
1500
10
1
h lomµ/ekatpu
0
4.0
3.0
2.0
1.0
0
Millions of years ago (×1,000)
500
2
Figure 11
OC
▲
1000
0
75
150
225
300
200
2
light intensity /J dm
1
s
Pdtin f bhydts
▲
Figure 1
2 The graph shows the results
of an experiment in which the rate
Energy is needed to produce carbohydrates and other
of photosynthesis was found by
carbon compounds from carbon dioxide.
measuring the uptake of carbon dioxide
Plants
convert
carbon
dioxide
and
water
into
carbohydrates
by
1
What is the reason for a CO
2
photosynthesis.
The
simple
equation
below
summarizes
the
process:
uptake rate of −200 in
carbon
To
carry
involves
out
this
putting
involving
systems.
dioxide
the
+
water
process,
in
Reactions
energy
energy
production
→
is
of
carbohydrate
is
required.
described
oxygen
involving
as
are
combining
A
+
chemical
endothermic.
usually
darkness?
oxygen
reaction
endothermic
smaller
that
Reactions
molecules
to
in
living
make
2
What can you predict about cell
respiration and photosynthesis
at the point where the net rate of
CO
uptake is zero?
2
larger
such
ones
as
are
glucose
also
often
are
much
endothermic
larger
than
and
molecules
carbon
dioxide
of
or
carbohydrate
water.
135
2
M O L E C U L A R
B I O L O G Y
The
av
co
energy
obtained
for
by
the
conversion
absorbing
occurring
in
disappear
–
the
light.
light.
The
of
carbon
This
is
energy
the
dioxide
reason
absorbed
into
for
from
carbohydrate
photosynthesis
light
does
is
only
not

2
is
converted
to
chemical
energy
in
the
carbohydrates.
30
limiting fts
1
h
20
1
ah gk/
ssarg fo ssamoib ni esaercni
40
Temperature, light intensity and carbon dioxide
10
concentration are possible limiting factors on the
0
100
200
300
3
CO
2
/cm
rate of photosynthesis.
400
3
m
air
210
▲
it
The
Figure 13 In this graph the rate of
rate
of
photosynthesis
in
a
plant
can
be
affected
by
three
externalfactors:
photosynthesis was measured
●
temperature;
●
light
●
carbon
indirectly by measuring the change in
plant biomass.
1
The maximum carbon
intensity;
dioxide
concentration.
dioxide concentration of the
Each
3
atmosphere is 380 cm
of
these
factors
can
limit
the
rate
if
they
are
below
the
optimal
–3
m
air.
level.
These
three
factors
are
therefore
called
limiting
factors.
Why is the concentration often
According
to
the
concept
of
limiting
factors,
under
any
combination
lower near leaves?
of
2
light
In what weather conditions is
one
carbon dioxide concentration
is
likely to be the limiting factor
to
for photosynthesis?
but
of
the
intensity,
the
it
this
take
the
the
is
no
is
the
other
carbon
limiting
from
its
optimum,
factors
rises
over
limiting
factors
longer
the
will
dioxide
rate
of
optimum.
the
rate
have
as
and
the
light
one
the
the
is
of
no
moved
a
that
limiting
limiting
intensity
limiting
carbon
factor
constant,
the
becomes
presumably
morning,
limiting
actually
furthest
to
other
factor
intensity
sun
is
the
as
the
factor
another
is
and
If
concentration,
photosynthesis.
the
factor
is
photosynthesis
effect,
as
they
only
This
changed
increases,
are
not
the
factor.
course,
keeping
the
that
closer
changing
limiting
Of
factors
factor
make
temperature
factor.
dioxide
closer
point
is
furthest
factor.
factor
increases,
As
will
the
its
optimum,
reached
from
For
for
to
be
its
optimum
example,
at
temperature
might
will
light
When
usually
increases
well
and
night,
photosynthesis.
temperature
concentration
while
where
during
become
the
factor.
cntd vibs in imiting ft
xpimnts
Experimental design: controlling relevant variables in
photosynthesis experiments is essential.
In
any
the
The
experiment,
independent
independent
experiment
136
variable
is
affected
by
with
what
the
it
and
is
important
dependent
variable
a
range
you
is
of
the
measure
control
variable
one
levels
independent
to
that
that
during
variable.
that
you
you
the
all
variables
you
are
The
experiment,
than
investigating.
deliberately
choose.
other
vary
in
the
dependent
to
see
if
it
is
2 . 9
It
is
essential
during
independent
the
dependent
independent
These
an
are
questions
Which
to
●
type
the
All
will
that
variables
need
a
be
to
be
that
sure
be
that
the
affecting
might
affect
the
controlled.
answer
limiting
you
to
could
when
factor
on
investigate?
you
are
designing
photosynthesis:
This
will
be
your
variable.
How
will
your
dependentvariable.
How
will
optimal
factor
therefore
you
factor
experiment
other
must
that
of
only
investigate
limiting
independent
●
is
variable.
variable
experiment
●
this
variable
P h o t o s y n t h e s i s
you
measure
you
keep
level?
the
the
rate
other
Thesewill
be
of
photosynthesis?
limiting
your
factorsata
controlled
This
will
constant
be
and
variables.
Invstigting imiting fts
Design of experiments to investigate limiting factors
on photosynthesis.
There
used
are
to
below.
factor
many
possible
investigate
You
or
could
you
the
effect
either
could
experimental
of
carbon
modify
develop
an
designs.
this
to
A
dioxide
that
concentration
investigate
entirely
method
different
a
different
can
is
be
given
limiting
design.
Investigating the eect of carbon dioxide on photosynthesis
If
a
stem
placed
of
gas
of
pondweed
upside-down
may
be
seen
such
in
to
as
water
Elodea,
and
escape.
If
the
these
Cabomba
end
are
of
or
the
Myriophyllum
stem
collected
is
and
cut,
av
is
bubbles
tested,
tmp
they
100
found
rate
of
be
oxygen
Factors
nd
to
that
out
mostly
production
might
what
concentration
oxygen,
affect
effect
is
can
the
this
produced
be
rate
has.
In
by
measured
of
photosynthesis.
by
counting
photosynthesis
the
method
below
can
the
be
carbon
etar mumixam fo %
are
The
bubbles.
varied
to
dioxide
varied.
50
0
1
Enough
water
to
ll
a
large
beaker
is
boiled
and
allowed
to
cool.
0
10
20
30
40
50
temperature / °C
This
removes
carbon
dioxide
and
other
dissolved
gases.
▲
2
The
water
is
poured
repeatedly
from
one
beaker
to
another,
Figure 14 In this graph the
to
rate of photosynthesis was
oxygenate
the
water.
Very
little
carbon
dioxide
will
dissolve.
measured indirectly by
3
A
stem
of
pondweed
is
placed
upside-down
in
the
water
and
measuring the change in
the
plant biomass
end
of
its
stem
is
water
contains
water
should
illuminated.
cut.
No
almost
be
about
Suitable
bubbles
no
25
are
carbon
°C
and
apparatus
is
expected
dioxide.
the
The
water
shown
in
to
emerge,
as
temperature
should
gure
be
very
the
of
the
1
brightly
What was the optimum
temperature for
16.
photosynthesis in this
plant?
4
Enough
sodium
hydrogen
carbonate
is
added
to
the
beaker
to
raise
3
the
carbon
emerge,
until
dioxide
they
two
or
are
concentration
counted
three
for
consistent
30
by
0.01
seconds,
results
are
mol
dm
repeating
obtained.
.
If
bubbles
the
counts
2
What was the maximum
temperature for
photosynthesis?
137
2
M O L E C U L A R
B I O L O G Y
5
Enough
sodium
hydrogen
carbonate
is
added
to
raise
the
–3
concentration
in
the
same
by
another
0.01
mol
dm
.
Bubble
counts
are
done
way.
sodium
6
hydrogen
The
procedure
increases
carbonate
in
above
carbon
is
repeated
dioxide
do
again
not
and
affect
again
the
rate
until
of
further
bubble
production.
Questions
1
Why
are
the
following
procedures
necessary?
pondweed
a)
Boiling
and
b)
Keeping
c)
Repeating
then
the
cooling
water
bubble
at
25
counts
the
°C
water
and
until
before
brightly
several
the
experiment.
illuminating
consistent
it.
counts
have
water at 25 °C
been
2
What
obtained.
other
pondweed
factor
and
could
how
be
would
investigated
you
design
using
the
bubble
counts
with
experiment?
light source
3
How
could
production
▲
Figure 15 Apparatus for measuring
photosynthesis rates in dierent
concentrations of carbon dioxide
138
you
make
more
the
measurement
accurate?
of
the
rate
of
oxygen
Q u e s t i o n s
Qstins
1
Lipase
the
is
a
digestive
breakdown
intestine.
In
of
the
enzyme
that
triglycerides
laboratory,
accelerates
in
the
the
rate
a)
(i)
State
small
of
in
lipase
can
be
detected
by
a
decline
in
what
causes
the
pH
to
units
that
are
shown
[1]
State
the
mass
units
that
are
shown
in
pH.
the
Explain
volume
equation.
activity
(ii)
of
the
the
decline.
equation.
[2]
[4]
b)
(i)
Calculate
the
mass
of
ATP
produced
per
3
dm
(ii)
2
Papain
is
a
protease
that
can
be
extracted
of
of
fruits.
temperature
experiment
in
water
quantity
of
on
was
and
Figure
the
17
shows
activity
performed
then
Calculate
that
with
had
papain
the
been
The
c)
Explain
it
to
a
solid
surface.
d)
During
dissolved
immobilized
The
large
percentage
mixture
that
of
the
was
protein
digested
in
in
results
a
the
how
masses
a
mass
of
ATP
produced
per
1.
it
is
[4]
of
possible
ATP
to
during
synthesize
such
100 m
race,
by
80 g
races.
of
ATP
[3]
is
needed
3
only
0.5 dm
of
oxygen
is
consumed.
show
Deduce
the
the
table
same
but
attaching
in
effect
papain.
using
repeated
papain
of
the
[2]
from
race
pineapple
oxygen.
how
ATP
is
being
produced.
[3]
reaction
xed
time.
lg 
Vm  x g m  
3
/m
100
p g  /m
immobilized
detsegid neitorp fo %
papain
1500
36
10,000
150
42,300
700
80
dissolved
60
papain
40
20
▲
T
able 1
0
20
30
40
50
60
70
80
temperature / °C
4
▲
Figure
by
a)
(i)
Outline
the
the
activity
effects
of
of
temperature
dissolved
on
papain.
Explain
the
the
effects
activity
of
of
leaves,
Deduce
on
papain.
(i)
Compare
the
effect
of
activity
of
temperature
immobilized
the
papain
W
(ii)
effect
on
dissolved
Suggest
a
reason
for
papain.
the
Explain
have
difference
In
some
described.
parts
Explain
Suggest
body
be
3
The
pathways
from
+
below
the
enzyme
it
+
and
would
in
a
be
used
(ADP
limiting
factor
for
X
at:
(iii)
Y
(iv)
Z.
[4]
why
1
curves
and
7
I
and
units
of
II
are
light
the
same
intensity.
[3]
the
negative
absorption
values
when
for
the
carbon
leaves
a
membranes.
part
the
produce
of
of
for
the
it
ATP
,
→
to
[2]
results
glucose.
Pi)
light
were
intensities.
in
[3]
body,
membrane.
to
+
in
useful
summarizes
oxidation
oxygen
human
of
using
Z
OC fo etar
glucose
where
the
IV 0.4%CO
at 30°C
2
13
12
11
10
9
III 0.4%CO
at 20°C
2
8
7
Y
X
6
5
II 0.13%CO
4
2
energy
one
of
immobilized
immobilized
equation
metabolic
are
dioxide
[2]
stinu yrartibra / noitprosba
enzymes
carbon
temperatures.
that
low
(iii)
xed
light
absorption
[2]
dioxide
you
varying
with
c)
(ii)
and
of
dioxide
on
between
the
effects
different,
photosynthesis
b)
the
the
carbon
[2]
(i)
b)
at
the
[2]
temperature
dissolved
shows
on
concentrations
a)
(ii)
18
intensity
Figure 1
7
at 30°C
2
3
I 0.13%CO
at 20°C
2
2
1
W
0
1
1
2
3
4
5
6
7
3
180 g
134.4 dm
18.25 kg
light intensity / arbitrary units
carbon
dioxide
+
water
+
ATP
▲
Figure 18
3
134.4 dm
108 g
18.25 kg
139
2
M O L E C U L A R
5
Figure
in
19
which
shows
the
Chlorella
wavelengths
(far
B I O L O G Y
red).
from
The
rate
results
cells
660
of
of
were
nm
an
experiment
given
(red)
oxygen
light
up
to
a)
of
700
production
nm
was
measured
and
the
the
relationship
wavelength
of
when
was
there
light
no
and
between
oxygen
yield,
supplementary
light.
Describe
the
effect
of
the
supplementary
yield
light.
of
oxygen
per
photon
of
light
was
gives
a
measure
of
the
[2]
calculated.
c)
This
Explain
how
photosynthesis
at
each
experiment
supplementary
was
light
then
with
repeated
nm
at
the
same
time
a
The
probable
was
0.125
wavelength
from
660
to
bars
help
in
drawing
experiment.
[2]
as
each
of
700
nm,
maximum
molecules
yield
per
of
oxygen
photon
of
light.
of
how
many
photons
are
needed
the
to
wavelengths
this
with
Calculate
650
error
from
wavelength.
d)
The
the
efciency
conclusions
of
but
with
produce
one
oxygen
molecule
in
the
photosynthesis.
same
overall
intensity
of
[2]
by
b)
photosynthesis
Describe
light
as
in
the
[2]
rst
e)
experiment.
Oxygen
this
production
by
photolysis
involves
reaction:
with supplementary light
+
without supplementary light
4H
O
→
O
2
thgil fo notohp rep selucelom negyxo fo dliey
Each
0.15
of
(raise
Calculate
how
produced
by
during
0.05
0
680
700
wavelength (nm)
Figure 19 Photon yield of photosynthesis in dierent light
intensities
140
2H
O
+
4H
+
4e
2
light
it
to
a
many
is
used
higher
times
photolysis
to
excite
energy
each
must
be
an
level).
electron
excited
0.10
660
▲
photon
electron
+
2
the
reactions
of
photosynthesis.
[2]
3
G E n E t I C s
Iroducio
Every
life
living
from
follows
a
linear
of
a
its
organism
parents.
patterns.
sequence
species.
inherits
The
a
blueprint
inheritance
Chromosomes
that
Alleles
is
shared
segregate
of
carry
by
for
genes
genes
in
members
during
allowing
fusion
of
new
techniques
cells
and
combinations
gametes.
for
to
Biologists
articial
be
have
formed
by
the
developed
manipulation
of
DNA,
organisms.
meiosis
3.1 Gene
Uderadig
Applicaio
➔
A gene is a heritable factor that consists of
➔
The causes of sickle cell anemia, including a
a length of DNA and inuences a specic
base substitution mutation, a change to the
characteristic.
base sequence of mRNA transcribed from it and
➔
A gene occupies a specic position on one type
a change to the sequence of a polypeptide in
of chromosome.
➔
The various specic forms of a gene are alleles.
➔
Alleles dier from each other by one or a few
hemoglobin.
➔
Comparison of the number of genes in humans
with other species.
bases only.
➔
New alleles are formed by mutation.
➔
The genome is the whole of the genetic
skill
➔
Use of a database to determine dierences in
information of an organism.
the base sequence of a gene in two species.
➔
The entire base sequence of human genes was
sequenced in the Human Genome Project.
naure of ciece
➔
Developments in scientic research follow
improvements in technology: gene sequencers,
essentially lasers and optical detectors, are
used for the sequencing of genes.
141
3
G e n e t i c s
Wha i a gee?
A gene is a heritable factor that consists of a length of DNA
and inuences a specic characteristic.
Genetics
is
the
information
from
parents
before
from
the
the
the
to
word
of
Something
living
plants,
fruit
obvious
middle
made
a
can
of
of
for
DNA.
therefore
than
a
19th
of
other
was
deduce
that
chromosome
understood.
eyes
were
and
and
It
passed
long
came
interested
much
be
be
biologists
in
more.
passed
on
to
that
there
were
indeed
characteristics
passed
on
There
to
offspring
was
onwards
and
by
intense
and
the
factors
that
these
pea
research
word
gene
factors.
chemical
there
was
each
–
gene
that
composition
strong
few
example
and
by
of
can
develop.
specic
century
relatively
for
was
features
showed
storage
used
Biologists
again
be
the
information
was
blue
organisms.
20th
the
century
are
these
would
heritable
cell
origins.
could
with
this
genetics
baldness,
century
early
how
storage
inuenced
They
all
the
There
human
cause
that
question
20th
word
as
features
the
concerned
and
meaning
the
and
from
the
typical
DNA
the
ies
invented
One
be
the
The
such
heritable.
genetics
was
in
in
biology
information
genesis,
organisms
were
into
of
features
must
factors
of
organisms
progeny.
where
Experiments
in
living
method
origins
offspring
branch
in
DNA
yet
are
of
a
genes.
that
molecules
there
consists
each
of
evidence
in
a
cell
thousands
much
chromosome
By
genes
shorter
carries
–
of
the
were
just
46
genes.
We
length
many
of
genes.
Comparig umber of gee
Comparison of the number of genes in humans with other species.
How
many
bacterium,
many
see
are
genes
a
needed
ourselves
physiology
Prokaryotes
to
it
take
plant
make
more
or
a
to
a
so
in
we
a
and
human?
complex
behaviour
make
bat,
how
We
expect
more
true.
It
They
structure,
might
have
these
to
Nae of pece
genes.
gives
are
as
The
range
based
species
numbers
a
on
but
these
table
of
evidence
are
not
are
shows
predicted
not
from
precise
yet
Bef decpton
whether
gene
the
this
is
numbers.
DNA
counts
of
of
gene
known.
Nube of gene
Haemophilus inuenzae
Pathogenic bacterium
1,700
scherichia coli
Gut bacterium
3,200
Protoctista
Trichomonas vaginalis
Unicellular parasite
Fungi
Saccharomyces cerevisiae (Yeast)
Unicellular fungus
Plants
Oryza sativa (Rice)
Crop grown for food
41,000
Arabidopsis thaliana (Thale cress)
Small annual weed
26,000
Populus trichocarpa (Black cottonwood)
Large tree
46,000
Drosophila melanogaster (Fruit y)
Larvae consume ripe fruit
14,000
Caenorhabditis elegans
Small soil roundworm
19,000
Homo sapiens (Humans)
Large omnivorous biped
23,000
Daphnia pulex (Water ea)
Small pond crustacean
31,000
Animals
142
as
and
Goup
does
banana
60,000
6,000
3 . 1
G E N E s
Where are gee locaed?
Actvt
A gene occupies a specic position on one type
Etatng te nube of
of chromosome.
Experiments
show
of
that
the
has
of
ten
of
are
the
different
linked
in
chromosome
linked
groups
humans
which
genes
types
groups
in
uan gene
genes
of
in
linked
number
of
in
fruit
genes
both
varieties
groups
a
species.
ies
and
is
of
and
and
ten
plant
each
For
or
animals
group
example,
four
types
types
of
of
are
crossed
corresponds
there
are
to
American published an estimate
four
chromosome.
chromosome
In October 1970 Scientic
one
and
that the human genome might
Maize
consist of as many as 10 million
in
genes. How many times greater
23.
than the current predicted
number is this? What reasons
Each
gene
occupies
a
specic
position
on
the
type
of
chromosome
where
can you give for such a huge
it
is
located.
This
position
is
called
the
locus
of
the
gene.
Maps
showing
the
overestimate in 1970?
sequence
were
can
of
genes
produced
now
be
by
along
crossing
produced
in
experiments,
when
the
fruit
but
genome
of
ies
much
a
and
other
more
species
is
organisms
detailed
maps
sequenced.
1.1
2q7
3.41q7
3.21q7
2.22q7
3.1
2q7
2.51q7
1.41q7
1.21q7
22.11q7
31.1
2q7
11.1
2q7
3.1
2q7
2.22q7
53q7
2.23q7
13.13q7
1.13q7
33.13q7
33q7
2.63q7
▲
chromosomes
Figure 1 Chromosome 7: an example of a human chromosome. It consists of a single DNA
molecule with approximately 1
70 million base pairs – about 5% of the human genome. The
pattern of banding, obtained by staining the chromosome, is dierent from other human
chromosomes. Several thousand genes are located on chromosome 7
, mostly in the light
bands, each of which has a unique identifying code. The locus of a few of the genes on
chromosome 7 is shown
Wha are allele?
The various specic forms of a gene are alleles.
Gregor
Mendel
varieties
of
is
pea
plants,
white-owered
the
to
differences
different
factors
are
two
forms
and
the
These
a
alleles,
of
the
there
gene
As
is
gene
are
alleles
One
mice.
the
are
are
of
A
humans
eye
of
occupy
plant
cells
same
locus
in
of
of
two
There
of
these
For
one
He
dwarf
crossed
peas
and
deduced
together
pairs
example
making
and
the
ABO
that
were
of
there
pea
due
heritable
are
plants
tall
the
more
a
than
alleles
colour
There
blood
of
has
are
for
to
two
be
three
three
groups.
gene,
gene,
they
gene
copies
be
In
alleles
some
example
cases
the
ies.
same
–
coat
black.
alleles
fruit
can
multiple
inuences
grey
different
have
that
gene.
examples
chromosome
the
with
Mendel
crossed
height,
determines
colour
he
genetics.
dwarf.
that
forms
of
plants
know
alleles.
rst
yellow,
that
pea
that
now
the
called
gene
alternative
type
We
plants
of
tall
father
purple-owered.
varieties
of
the
inuences
the
numbers
one
can
and
that
mice
inuences
on
allele
animal
in
large
that
forms
in
with
the
the
as
example
forms
gene
making
making
position
one
the
gene.
discovered
for
factors.
alternative
of
regarded
plants
heritable
other
of
pea
between
different
alleles
usually
of
have
on
each
a
they
the
occupy
same
chromosome.
type
of
the
locus.
same
Only
Most
chromosome,
so
▲
Figure 2 Dierent coat colours in mice
143
3
G e n e t i c s
we
the
can
expect
same
two
allele
of
copies
the
of
gene
a
gene
or
two
to
be
present.
different
These
could
be
two
of
alleles.
Dierece bewee allele
Alleles dier from each other by one or a few bases only.
A
gene
consists
hundreds
slight
of
of
position
in
Positions
in
bases
particular
the
are
another
in
a
gene
nucleotide
snips.
Several
gene
length
position
single
the
a
thousands
variations
number
a
or
of
DNA,
bases
base
the
for
by
a
The
sequence.
different,
in
with
long.
base
Usually
in
sequence
different
example
sequence
only
one
adenine
one
allele
that
alleles
or
might
and
of
a
a
can
very
be
be
gene
have
small
present
cytosine
at
present
are
at
that
allele.
where
more
than
polymorphisms,
snips
differ
of
can
only
be
a
present
few
one
base
may
abbreviated
in
a
gene,
to
but
be
SNPs
even
and
called
pronounced
then
the
alleles
of
bases.
Comparig gee
Use of a database to determine dierences in the base sequence of a gene
in two species
One
that
outcome
the
enabled
allows
of
the
techniques
the
gene
Human
that
sequencing
sequences
Genome
were
of
to
developed
other
be
Project
●
have
genomes.
compared.
is
This
this
comparison
can
be
used
to
The
‘Fast
appear.
Copy
a
.txt
relationships.
of
sequences
Also,
the
for
exploring
the
allows
function
of
species
that
Repeat
to
be
chosen
Go
to
the
website
called
Choose
‘gene’
from
the
To
have
Enter
the
as
name
of
a
cytochrome
run
In
search
●
Select
menu.
gene
plus
the
oxidase
1
(COX1)
for
pan
the
in
your
mouse
File
over
transcripts,
‘Nucleotide
Links’
and
your
Under
the
section
products’
number
compare
of
different
and
computer
the
save
align
into
species
the
the
software
appears.
le.
choose
Your
ClustalX
the
that
les.
sequence
called
for
ClustalX
‘Load
Sequences’.
sequences
should
show
window.
the
Alignment
▲
menu
Alignment.’
sequence
‘Genomic
until
Figure 3
144
a
menu,
organisms.
regions,
it
it.
the
shows
Move
the
Complete
(chimpanzee).
●
paste
le.
organism,
●
such
to
download
●
up
●
and
should
GenBank
(http://www.ncbi.nlm.nih.gov/pubmed/)
●
sequence
sequence
notepad
with
want
you,
sequence.
and
●
the
the
identication
●
conserved
or
and
determine
you
evolutionary
le
A
’
results
●
of
Choose
The
choose
example
alignment
of
9
‘Do
below
different
3 . 1
G E N E s
Data-baed queton: COX-2, smoking and stomach cancer
COX-2
is
a
gene
that
cyclooxygenase.
6,000
nucleotides.
polymorphisms
codes
The
gene
Three
have
for
the
single
been
2
enzyme
consists
of
a)
of
nucleotide
discovered
associated
with
gastric
cancer
occurs
of
at
can
survey
copies
stomach.
nucleotide
nucleotide
large
the
of
be
in
the
One
either
COX-2
of
The
these
base
adenine
involved
gene
developed
gastric
Explain
in
at
or
3
this
guanine.
sequencing
357
patients
Deduce,
at
A
people
who
did
adenocarcinoma
not
people
smoked
were
have
asked
the
conclusion
the
1
shows
the
357
they
were
whether
they
had
nucleotide
patients
categorized
whether
and
gene
results
they
or
copies
(GG)
or
with
that
the
with
a
reason,
1195
risk
of
is
whether
associated
gastric
did
not
A
at
shown
this
All
had
Discuss,
using
the
data,
adenocarcinoma
Predict,
all
this
of
at
COX-2
least
one
with
whether
is
the
increased
risk
of
equally
as
(AG
percentages.
AG or AA
9.8%
Non-smokers
9.5%
43.7%
or
Table
copy
of
AA).
The
2
40.0%
G
for
the
985
T
able 1 Patients with cancer
shows
people
alleles
the
data,
common
9.4%
at
which
of
bases
nucleotide
G
1195
are
or
if
12.6%
42.4%
in
[2]
formed
The
in
35.6%
T
able 2 Patients without cancer
Actvt
changes
out.
AG or AA
who
controls.
example,
[2]
cancer.
using
more
base
an
[2]
Smokers
New aee
New alleles are formed by mutation.
One
with
A
and
Muaio
carried
or
to
▲
random
G
smokers.
Non-smokers
New
[2]
of
Smokers
the
drawn
ever
non-smokers
position
categorization
have
is
be
adenocarcinoma.
GG
same
A
can
percentages.
gastric
according
smokers
two
1195
with
are
the
1
[2]
in
▲
the
patients
cigarettes.
adenocarcinoma
at
the
percentage
who
disease.
whether
in
GG
Table
of
total
weresmokers.
difference
nucleotide
in
these
the
the
increased
both
gastric
985
that
and
SNPs
4
had
percentage
adenocarcinoma,
1195.
China
total
smokers
controls
from
a
the
were
that
b)
are
Calculate
that
over
the
–
from
there
most
is
was
of
alleles
by
mechanism
signicant
sequence
adenine
other
no
a
type
gene
present
at
of
is
a
gene
for
a
mutation.
mutation
replaced
by
particular
Mutationsare
particularmutation
is
a
a
base
substitution.
different
point
in
the
being
base.
base
For
sequence
Recent research into mutation
involved nding the base
sequence of all genes in parents
and their ospring. It showed that
there was one base mutation per
8
it
could
be
substituted
by
cytosine,
guanine
or
1.2 × 10
thymine.
bases. Calculate how
many new alleles a child is likely
A
random
change
to
an
allele
that
has
developed
by
evolution
over
to have as a result of mutations
perhaps
millions
of
years
is
unlikely
to
be
benecial.
Almost
all
in their parents. Assume that
mutations
are
therefore
either
neutral
or
harmful.
Some
mutations
there are 25,000 human genes
are
lethal
–
they
cause
the
death
of
the
cell
in
which
the
mutation
when
the
individual
and these genes are 2,000 bases
occurs.
Mutations
in
body
cells
are
eliminated
dies,
long on average.
but
mutations
in
cells
that
develop
into
gametes
can
be
passed
on
to
Source: Campbell, CD, et al. (201
2)
offspring
and
cause
genetic
disease.
“Estimating the human mutation
rate using autozygosity in a founder
population.” Nature Genetics, 44:
1
277
1
281. doi: 10.1038/ng.24
18
145
3
G e n e t i c s
TOK
sickle cell aemia
Wat ctea can be ued to
The causes of sickle cell anemia, including a base
dtngu between coeaton and
substitution mutation, a change to the base sequence
caue and eect?
There is a correlation between high
frequencies of the sickle-cell allele
of mRNA transcribed from it and a change to the
sequence of a polypeptide in hemoglobin.
in human populations and high rates
Sickle-cell
anemia
is
the
commonest
genetic
disease
in
the
world.
of infection with Falciparum malaria.
It
Where a correlation exists,
is
due
to
a
mutation
of
the
gene
that
codes
for
the
alpha-globin
it may
polypeptide
in
hemoglobin.
The
symbol
for
this
gene
is
Hb.
Most
or may not be due to a causal link .
A
humans
have
the
allele
Hb
.
If
a
base
substitution
mutation
converts
Consider the information in gure 4
the
sixth
codon
of
the
gene
from
GAG
to
GTG,
a
new
allele
is
formed,
to decide whether sickle-cell anemia
S
called
Hb
.
The
mutation
is
only
inherited
by
offspring
if
it
occurs
in
a
causes infection with malaria.
cell
the
When
the
codon
sixth
amino
15–20
s
allele (%)
10–15
or
testis
5–10
allele
instead
acid
causes
is
that
develops
transcribed,
of
in
GAG,
the
concentrations.
formed
are
rigid
sickle
capillaries,
cells
the
into
an
cause
to
is
bundles
distort
damage
them
and
mRNA
when
to
this
egg
or
sperm.
to
of
the
produced
mRNA
valine
molecules
The
enough
blocking
and
polypeptide
hemoglobin
oxygen
These
Key
Hb
sixth
change
Frequency of Hb
ovary
S
b)
a)
of
is
instead
stick
red
tissues
reducing
blood
by
of
together
hemoglobin
tissues
molecules
cells
ow.
GUG
glutamic
in
into
becoming
blood
has
transcribed,
a
with
sickle
This
low
are
shape.
in
sickle
its
acid.
that
trapped
When
as
the
blood
cells
0–5
return
break
to
up
high
and
oxygen
the
conditions
cells
return
to
in
the
their
lung,
normal
the
hemoglobin
shape.
These
bundles
changes
occur
Figure 4 Map (a) shows the frequency of
time
after
time,
as
the
red
blood
cells
circulate.
Both
the
hemoglobin
red
blood
and
the sickle cell allele and map
the
plasma
membrane
are
damaged
and
the
life
of
a
cell
can
be
cells
at
(b) shows malaria aected areas in
shortened
to
as
little
as
4
days.
The
body
cannot
replace
red
blood
Africa and Western Asia
a
rapid
So,
for
a
enough
small
rate
change
individuals
that
and
to
a
anemia
gene
inherit
therefore
can
the
have
gene.
It
develops.
very
is
harmful
not
consequences
known
how
often
this
S
mutation
has
remarkably
occurred
common.
have
two
copies
have
one
copy
These
of
so
individuals
but
In
the
allele
make
only
in
some
parts
both
suffer
of
and
parts
East
of
Africa
develop
normal
mild
the
up
world
the
to
of
severe
5%
anemia.
hemoglobin
and
anemia.
Figure 5 Micrographs of sickle cells and normal red blood cells
146
Hb
allele
newborn
Another
the
mutant
is
babies
35 %
form.
3 . 1
G E N E s
Wha i a geome?
The genome is the whole of the genetic information of
an organism.
Among
genetic
DNA,
of
its
●
biologists
so
a
living
DNA
In
today
information
the
●
number
of
In
plant
species
in
the
means
Genetic
is
the
the
whole
information
entire
base
is
of
the
contained
sequence
of
in
each
in
consists
the
This
is
the
chromosomes
nucleus
the
plus
is
the
plus
pattern
in
usually
genome
the
of
nucleus
is
DNA
the
46
molecules
the
DNA
other
that
form
molecule
animals,
in
the
though
the
different.
DNA
molecules
molecules
in
the
of
chromosomes
mitochondrion
and
chloroplast.
The
in
genome
genome
genome
chromosomes
the
word
organism.
organism’s
mitochondrion.
●
the
an
molecules.
humans
the
of
genome
the
of
circular
prokaryotes
is
chromosome,
much
plus
smaller
any
and
plasmids
consists
that
are
of
the
DNA
present.
the Huma Geome Projec
The entire base sequence of human genes was
sequenced in the Human Genome Project.
The
Human
base
Genome
sequence
of
improvements
the
in
be
Project
entire
base
sequence
to
complete
sequence
sequencing
published
in
began
human
much
in
1990.
Its
genome.
techniques,
sooner
aim
This
than
was
to
project
which
nd
allowed
expected
in
the
drove
rapid
a
2000
draft
and
a
Actvt
2003.
Etc of genoe eeac
Although
knowledge
immediate
what
can
and
be
total
of
entire
base
understanding
regarded
many
as
researchers
for
which
sequences
base
the
a
rich
years
are
to
of
mine
human
of
come.
sequence
data,
For
has
genetics,
which
example,
protein-coding
not
genes.
will
it
is
it
given
has
be
are
an
given
worked
possible
There
us
to
Ethical questions about
us
genome research are wor th
by
predict
discussing.
approximately
Is it ethical to take a DNA
23,000
of
these
in
the
human
genome.
Originally,
estimates
for
the
sample from ethnic groups
number
of
genes
were
much
higher.
around the world and
sequence it without their
Another
discovery
was
that
most
of
the
genome
is
not
transcribed.
permission?
Originally
that
called
within
expression
“junk
these
as
DNA,”
“junk”
well
as
it
is
regions,
highly
being
there
repetitive
increasingly
are
elements
sequences,
recognized
that
called
affect
gene
satellite
Is it ethical for a biotech
DNA.
company to patent the
base sequence of a gene to
The
genome
that
was
sequenced
consists
of
one
set
of
chromosomes
–
it
prevent other companies
is
a
human
genome
rather
than
the
human
genome.
Work
continues
from using it to conduct
to
nd
variations
in
sequence
between
different
individuals.
The
vast
research freely?
majority
unity,
of
but
base
there
contribute
to
sequences
are
also
human
are
many
shared
single
by
all
humans
nucleotide
giving
us
genetic
polymorphisms
which
Who should have access to
this genetic information?
diversity.
Should employers,
Since
the
publication
other
species
of
the
human
genome,
the
base
sequence
of
many
insurance companies and
has
been
determined.
Comparisons
between
these
genomes
law enforcement agencies
reveal
aspects
of
the
evolutionary
history
of
living
organisms
that
were
know our genetic makeup?
previously
of
biology
unknown.
in
the
21st
Research
into
genomes
will
be
a
developing
theme
century.
147
3
G e n e t i c s
techique ued for geome equecig
Developments in scientic research follow improvements in technology: gene
sequencers, essentially lasers and optical detectors, are used for the sequencing
of genes.
The
idea
seemed
of
sequencing
impossibly
improvements
in
the
entire
difcult
at
technology
human
one
time
towards
uorescent
genome
ending
but
the
end
20th
century
made
it
possible,
though
still
These
improvements
continued
The
samples
once
copies
was
underway
and
draft
sequences
Further
species
completed
advances
to
be
much
are
sooner
allowing
sequenced
at
an
than
the
ever
expected.
genomes
of
sequence
small
separately.
of
DNA,
using
a
lengths
genome,
of
To
DNA.
nd
the
it
base
single-stranded
DNA
is
rst
Each
polymerase,
of
increasing
broken
these
is
sequence
copies
but
of
the
it
of
up
a
the
whole
base
sequence
has
An
putting
small
quantities
of
a
for
the
copies
bases.
together
in
and
one
all
lane
the
of
number
of
a
gel
nucleotides.
scans
along
the
markers
lane
to
make
the
uoresce.
optical
is
of
a
detector
is
used
uorescence
series
of
to
along
peaks
each
to
of
detect
the
the
lane.
uorescence,
number
of
nucleotides
stopped
been
A
computer
deduces
the
base
sequence
from
copied
the
by
mixed
separated
the
corresponding
●
before
laser
There
fragment
is
A
colours
into
made
process
four
rate.
sequenced
are
are
are
to
uorescent
other
●
To
used
were
●
therefore
is
the
the
according
project
of
very
DNA
ambitious.
marker
each
of
●
the
in
sequence
of
colours
of
uorescence
non-standard
detected.
nucleotide
separately
each
of
of
DNA
with
copy
of
varying
four
samples
of
the
sequence
the
are
copy
tracks
bases
in
advance
sequencing
by
in
the
in
the
is
gel,
DNA
technology
uorescent
mark
DNA
it
markers
copies.
A
end
a
samples
each
each
according
band
be
number
in
just
which
the
deduced.
that
is
of
each
from
can
done
produced,
For
there
the
is
carrying
Four
separated
automating
Coloured
the
at
are
electrophoresis.
in
four
of
major
gel
bases.
length
bases
This
nucleotides
DNA
These
nucleotides
●
possible
DNA
by
mixture.
non-standard
four
of
base
reaction
of
length
The
the
four
to
one
148
with
the
one
copy.
into
speeded
up
this:
are
different
used
to
colour
of
Figure 6 Sequencing read from the DNA of Pinor Noir variety
of grape
3 . 2
C h r O m O s O m E s
3.2 Coooe
Uderadig
Applicaio
Prokaryotes have one chromosome consisting
➔
Cairns’s technique for measuring the length
➔
of a circular DNA molecule.
of DNA molecules by autoradiography.
Some prokaryotes also have plasmids but
➔
Comparison of genome size in T2
➔
eukaryotes do not.
phage, Escherichia coli, Drosophila
Eukaryote chromosomes are linear
➔
melanogaster, Homo sapiens and
DNA molecules associated with histone
Paris japonica.
proteins.
Comparison of diploid chromosome numbers
➔
In a eukaryote species there are
➔
of Homo sapiens, Pan troglodytes, Canis
dierent chromosomes that carry dierent
familiaris, Oryza sativa, Parascaris equorum.
genes.
Use of karyotypes to deduce sex and diagnose
➔
Homologous chromosomes carry the same
➔
Down syndrome in humans.
sequence of genes but not necessarily the
same alleles of those genes.
skill
Diploid nuclei have pairs of homologous
➔
chromosomes.
Use of online databases to identify the locus of
➔
a human gene and its protein product.
Haploid nuclei have one chromosome of
➔
each pair.
The number of chromosomes is a characteristic
➔
naure of ciece
feature of members of a species.
Developments in scientic research follow
➔
A karyogram shows the chromosomes of
➔
improvements in techniques: autoradiography
an organism in homologous pairs of
was used to establish the length of DNA
decreasing length.
molecules in chromosomes.
Sex is determined by sex chromosomes and
➔
autosomes are chromosomes that do not
determine sex.
Bacerial chromoome
Prokaryotes have one chromosome consisting
of a circular DNA molecule.
The
structure
most
molecule
of
of
prokaryotic
prokaryotes
the
there
containing
cell.
sometimes
The
DNA
described
all
in
as
is
cells
one
the
was
described
chromosome,
genes
bacteria
is
needed
not
in
sub-topic
consisting
for
the
associated
basic
with
of
a
life
1.2.
In
circular
DNA
processes
proteins,
so
is
naked.
149
3
G e n e t i c s
Because
is
only
usually
present
a
briey
preparation
are
one
only
moved
after
for
to
chromosome
single
cell
copy
the
of
present
The
poles
and
in
gene.
chromosome
division.
opposite
is
each
has
two
the
a
prokaryotic
Two
identical
been
replicated,
genetically
cell
then
identical
splits
in
cell,
there
copies
but
are
this
is
a
chromosomes
two.
Plamid
Some
do
prokaryotes
are
small
extra
prokaryotes
but
circular
and
naked,
but
those
not
antibiotic
when
an
a
antibiotic
are
not
of
formed
plas mids
cell
bu t
eukaryot es
of
spread
through
natural
a
present
or
in
a
life
the
the
cell
same
and
a
are
commonly
that
processes.
in
They
may
For
plasmids.
environment
replicated
at
genes
located
in
that
eukaryotes.
few
basic
cell
be
This
dies
method
to
can
at
the
rate.
same
may
are
be
found
usually
useful
example,
These
but
as
there
not
be
not
the
may
to
in
small,
the
genes
genes
are
time
Hence
plasmid
transferred
population.
barrier.
biologists
is
its
often
always
plasmids
prokaryotic
for
are
a
in
are
at
cell
for
benecial
other
times.
chromosome
be
passed
multiple
to
both
cells
division.
Copies
species
molecules
unusual
containing
cell
plasmids
by
DNA
very
needed
prokaryotic
copies
by
are
resistance
Plasmids
the
have
not .
Plasmids
of
also
of
is
It
is
happens
absorbed
gene
transfer
transfer
genes
from
even
if
by
a
one
plasmid
a
cell
of
between
between
cell
possible
a
for
that
to
is
released
different
species.
species
another,
plasmids
to
cross
when
species.
Plasmids
allowing
are
It
is
also
a
a
used
articially.
Figure 1 (a) Circular DNA molecule from
a bacterium (b) Bacterium preparing
trimethoprim
to divide
genes to help the
resistance
plasmid spread
penicillin family
disinfectant resistance
resistance
streptomycin family
resistance
vancomycin
resistance
Figure 2 The pLW1043 plasmid
Uig auoradiography o meaure DnA molecule
Developments in scientic research follow improvements in techniques:
autoradiography was used to establish the length of DNA molecules in chromosomes.
Quantitative
the
hypothesis,
that
150
data
strongest
type
but
provide
in
the
is
usually
of
considered
evidence
biology
most
it
is
for
or
to
sometimes
convincing
be
against
Developments
a
images
evidence.
to
be
invisible.
but
in
produced
of
These
sometimes
microscopy
structures
sometimes
also
change
have
that
allowed
were
conrm
our
images
previously
existing
ideas
understanding.
3 . 2
Autoradiography
the
1940s
substances
John
way
DNA
time
were
Cairns
in
the
was
used
not
used
to
the
biologists
in
where
cells
or
technique
He
obtained
from
E.
clear
by
discover
located
1960s.
molecules
it
was
onwards
coli
in
a
of
At
than
Cairns
time.
whole
to
the
was
one,
a
but
answered
revealed
different
images
the
more
tissues.
bacteria.
whether
chromosome
from
specic
C h r O m O s O m E s
single
the
this
replication
Cairns’s
question.
forks
technique
investigate
the
DNA
molecule
images
in
structure
They
DNA
was
used
of
or
produced
by
also
for
the
by
rst
others
eukaryote
chromosomes.
bacterial
Meaurig he legh of DnA molecule
Cairns’s technique for measuring the length of DNA molecules by autoradiography.
John
from
Cairns
E.coli
produced
using
this
images
of
DNA
The
molecules
technique:
images
molecule
●
Cells
a
were
culture
grown
medium
thymidine.
linked
by
to
coli
DNA
make
a
replication
●
The
cells
Tritiated
the
were
membrane
E.
then
and
of
DNA
coli
that
of
was
cell
the
enzyme
long
cells
2
burst
surface
●
A
thin
of
lm
applied
left
in
time
to
of
some
of
and
react
At
end
the
was
surface
the
with
of
the
At
the
of
two
researchers
in
contains
hydrogen,
a
The
of
there
given
1,100
µm.
that
the
This
length
of
is
the
E
coli
µm.
to
chromosomes.
so
the
fruit
that
by
y
was
the
was
then
produce
An
image
Drosophila
12,000
total
µm
melanogaster
at
least
of
a
by
of
chromosome
of
This
DNA
chromosome,
other
eukaryotic
melanogaster
long.
amount
D.
used
images
was
from
produced
corresponded
known
so
for
to
this
be
in
a
species
a
chromosome
molecule.
In
contains
contrast
to
one
very
long
prokaryotes,
was
linear
rather
than
the
circular.
the
was
membrane
and
During
tritium
energy
in
that
the
DNA
electrons,
lm.
and
is
a
of
period
examined
point
position
of
the
DNA
were
onto
emulsion
two-month
each
that
circular
digested
cells
DNA
the
high
the
showed
single
dialysis
were
months.
atoms
emitted
atomdecayed
indicate
for
developed
microscope.
their
Cairns
a
membrane.
photographic
the
which
lm
release
dialysis
darkness
decayed
●
to
the
is
length
Autoradiography
used
uses
produced
onto
only
molecule
gently
by
coli
base
is
it
is
with
walls
lysozyme.
a
remarkably
DNA
using
with
E.
in
cells.
placed
their
the
and
thymidine
isotope
labelled
in
consists
nucleotides
in
tritiated
deoxyribose
radioactive
radioactively
generations
containing
to
replication.
tritium,
two
Thymidine
thymine
E.
for
produced
chromosome
where
dark
the
the
with
a
grain.
a
tritium
These
DNA.
Figure 3
Eukaryoe chromoome
Eukaryote chromosomes are linear DNA molecules
associated with histone proteins.
Chromosomes
DNA
with
is
a
in
single
histone
eukaryotes
immensely
proteins.
are
long
Histones
composed
linear
are
of
DNA
globular
DNA
and
molecule.
in
shape
protein.
It
is
and
The
associated
are
wider
151
3
G e n e t i c s
than
the
DNA.
with
the
DNA
chromosome
are
not
in
There
are
of
a
many
with
string
histone
wound
separated
contact
appearance
are
molecule
by
short
histones.
of
beads
molecules
around
them.
stretches
This
gives
during
a
in
a
chromosome,
Adjacent
of
the
histones
DNA
eukaryotic
in
molecule
the
that
chromosome
the
interphase.
Dierece bewee chromoome
In a eukaryote species there are dierent chromosomes
that carry dierent genes.
Eukaryote
chromosomes
microscope
during
chromosomes
Figure 4 In an electron micrograph the
visible
histones give a eukaryotic chromosome
of
the appearance of a string of beads during
if
become
stains
mitosis
the
chromatids,
are
that
much
bind
identical
narrow
During
shorter
either
chromosomes
with
too
interphase.
DNA
can
DNA
be
to
be
mitosis
and
or
visible
and
fatter
by
proteins
seen
to
molecules
be
with
meiosis
a
light
the
supercoiling,
are
used.
double.
produced
In
so
the
There
are
rststage
are
two
byreplication.
interphase
When
can
the
be
chromosomes
seen.
centromere
can
be
They
differ
where
positioned
the
are
examined
both
two
in
during
length
and
chromatids
anywhere
from
are
close
to
in
mitosis,
the
held
an
different
position
together.
end
to
the
of
types
the
The
centromere
centre
of
the
chromosome.
OH
PH
There
are
at
least
two
different
types
in
every
eukaryote
but
in
most
phe 16S
7S DNA
val
species
there
are
more
than
that.
In
humans
for
example
there
are
23S
thr
23
types
of
chromosome.
cyt b
leu
PL
pro
Every
gene
in
eukaryotes
occupies
a
specic
position
on
one
type
of
N1
ile
chromosome,
called
the
locus
of
the
gene.
Each
chromosome
type
glu
f-met
therefore
gln
N6
N2
DNA
carries
molecule.
a
In
specic
many
sequence
of
genes
chromosomes
this
arranged
sequence
along
the
contains
linear
over
a
ala
control loop
asn
ribosomal RNA
trp
N5
thousand
genes.
cys
transfer RNAs
OL
tyr
leu
protein coding gene
Crossing
experiments
were
done
in
the
past
to
discover
the
sequenceof
ser
his
genes
ser
on
chromosome
types
in
Drosophila
melanogasterand
other
species.
OX1
The
base
sequence
of
whole
chromosomes
can
now
be
found,
allowing
N4
asp
a
rg
more
accurate
and
complete
gene
sequences
to
be
deduced.
OX2
3
N
gly
lys
OX3
ATPase
Having
the
genes
chromosome
arranged
allows
parts
in
of
a
standard
sequence
chromosomes
to
be
along
a
swapped
type
of
during
meiosis.
Figure 5 Gene map of the human mitochondrial
chromosome. There are genes on both of the
two DNA strands. The chromosomes in the
Homologou chromoome
nucleus are much longer, carry far more genes
and are linear rather than circular
Homologous chromosomes carry the same sequence of
genes but not necessarily the same alleles of those genes.
If
two
chromosomes
homologous.
each
are
If
of
other
because,
for
at
the
same
sequence
chromosomes
least
some
of
are
the
of
not
genes
genes
usually
on
they
are
identical
them,
the
to
alleles
different.
two
the
eukaryotes
are
chromosomes
chromosome
152
have
Homologous
in
the
members
in
one
other.
of
of
the
them
This
same
to
allows
be
species,
we
homologous
members
of
a
can
with
species
expect
at
to
each
least
one
interbreed.
3 . 2
C h r O m O s O m E s
Data-baed queton: Comparing the chromosomes of mice
Actvt
and humans
mcocope nvetgaton of gac
Figure
6
shows
all
of
the
types
of
chromosome
in
mice
and
in
coooe
humans.
Numbers
and
colours
are
used
to
indicate
sections
of
mouse
1
chromosomes
that
are
homologous
to
sections
of
human
Garlic has large chromosomes so is an
chromosomes.
ideal choice for looking at chromosomes.
Mouse and human genetic similarities
Cells in mitosis are needed. Garlic bulbs
Mouse chromosomes
1
2
3
4
5
Human chromosomes
6
7
8
9
19
10
8
1
2
3
4
5
6
grow roots if they are kept for 3 or 4 days
7
8
9
with their bases in water, at about 25°C.
11
7
8
19
6
19
9
7
8
3
Root tips with cells in mitosis are yellow
11
9
2
2
4
11
4
19
11
18
15
4
15
2
3
in colour, not white.
19
6
3
15
11
10
1
16
7
1
16
3
1
12
20
4
polystyrene
10
garlic bulb
1
13
11
10
10
11
12
13
14
15
16
1
7
11
12
13
14
15
16
1
7
18
disc with
18
hole cut
3
22
6
10
16
2
5
6
18
7
10
7
2
5
2
1
8
14
3
6
5
22
through
16
16
10
22
7
6
water at 25 °C
8
2
1
beaker
19
22
14
18
19
18
2
1
1
7
13
5
2
12
12
19
20
2
1
22
X
Y
2
19
X
Root tips are put in a mixture of a stain
Y
that binds to the chromosomes and
11
Y
9
acid, which loosens the connections
X
10
between the cell walls. A length of about
Figure 6 Chromosomes
5 mm is suitable. Ten parts of aceto-
3
orcein to one part of 1.0 mol dm
1
Deduce
the
number
of
types
of
chromosomes
in
mice
and
hydrochloric acid gives good results.
in
humans.
[2]
stain–acid mix ture
5 mm long garlic
2
Identify
the
similarto
two
human
mouse
chromosome
types
that
are
root tip
most
chromosomes.
[2]
watch glass
3
Identify
mouse
chromosomes
nothomologous
to
human
which
contain
sections
that
are
chromosomes.
[2]
3
4
Suggest
reasons
andhuman
for
the
many
similarities
between
the
The roots are heated in the stain–acid
mixture on a hot plate, to 80°C for
mouse
genomes.
5 minutes. One of the root tips is put
[2]
on a microscope slide, cut in half and
5
Deduce
how
chromosomes
have
mutated
during
the
evolution
the 2.5 mm length fur thest from the
of
animals
such
as
mice
and
humans.
[2]
end of the root is discarded.
root tip
watch glass
hot plate
Comparig he geome ize
set at
80 °C
Comparison of genome size in T2 phage, Escherichia
4
coli, Drosophila melanogaster, Homo sapiens and
A drop of stain and a cover slip is added
and the root tip is squashed to spread
Paris japonica.
out the cells to form a layer one cell
The
genomes
of
living
organisms
vary
by
a
huge
amount.
The
smallest
thick. The chromosomes can then be
genomes
are
those
of
viruses,
though
they
are
not
usually
regarded
as
examined and counted and the various
living
organisms.
The
table
on
the
next
page
gives
the
genome
size
of
phases of mitosis should also be visible.
one
virus
and
four
living
organisms.
thumb pressing down to
squash root ti p
One
of
the
smallest
four
living
genome.
The
organisms
genome
is
size
a
prokaryote.
of
eukaryotes
It
has
much
depends
on
the
the
size
cover
and
number
of
chromosomes.
It
is
correlated
with
the
complexity
slip
of
the
organism,
reasons
genes
is
for
this.
very
but
The
is
not
directly
proportion
variable
and
also
of
the
proportional.
the
DNA
amount
that
of
There
acts
gene
as
are
microscope
slide
folded
lter paper
several
functional
duplication
varies.
153
3
G e n e t i c s
Ogan
Genoe ze
Decpton
(on bae pa)
T2 phage
0.18
Virus that attacks
Escherichia coli
Escherichia coli
5
Drosophila melanogaster
Gut bacterium
140
Fruit y
Homo sapiens
3,000
Humans
Paris japonica
150,000
Woodland plant
Fidig he loci of huma gee
Use of online databases to identify the locus of a human gene and its
protein product.
The
locus
of
homologous
be
used
to
a
gene
is
its
particular
chromosomes.
nd
the
locus
of
position
Online
human
on
databases
genes.
together
can
that
with
the
total
an
example
Mendelian
by
Johns
of
such
a
Inheritance
Hopkins
database
in
Man
in
the
of
gene
loci
on
There
Gene nae
is
number
chromosome.
Decpton of gene
Online
website,
maintained
DRD4
A gene that codes for a dopamine
University.
receptor that is implicated in a variety of
neurological and psychiatric conditions.
●
Search
home
for
the
abbreviation
OMIM
to
open
the
page.
CF TR
A gene that codes for a chloride channel
protein. An allele of this gene causes
●
Choose
●
Enter
Search
Gene
Map.
cystic brosis.
the
name
of
a
gene
into
the
Search
HBB
Gene
Map
box.
This
should
bring
up
a
gene,
including
The gene that codes for the beta-globin
table
subunit of hemoglobin. An allele of this
with
information
about
the
its
gene causes sickle cell anemia.
locus,
the
starting
gene
genes
is
are
with
located.
shown
the
chromosome
Suggestions
on
the
of
on
which
human
F8
The gene that codes for Factor VIII, one
right.
of the proteins needed for the clotting of
blood. The classic form of hemophilia is
●
An
alternative
to
entering
the
name
of
a
gene
caused by an allele of this gene.
is
of
to
select
the
sex
sequence
a
chromosome
chromosomes
of
gene
loci
from
X
will
or
be
Y.
1–22
A
or
one
complete
TDF
Testis determining factor – the gene that
displayed,
causes a fetus to develop as a male.
Haploid uclei
Haploid nuclei have one chromosome of each pair.
A
haploid
set
of
the
humans
contain
Gametes
are
Gametes
have
contain
154
nucleus
has
one
chromosomes
23
the
23
chromosome
that
are
found
chromosomes
sex
cells
haploid
that
nuclei,
chromosomes.
fuse
so
for
of
in
each
its
It
has
one
Haploid
full
nuclei
in
example.
together
in
type.
species.
humans
during
both
sexual
egg
and
reproduction.
sperm
cells
3 . 2
C h r O m O s O m E s
Diploid uclei
Diploid nuclei have pairs of homologous chromosomes.
A
diploid
sets
of
humans
When
contain
with
cells
consist
a
46
two
gametes
with
gametes
are
fuse
found
for
is
nuclei
diploid
of
in
each
its
during
sexual
When
produced.
apart
type.
species.
It
has
two
Diploid
full
nuclei
in
example.
produced.
are
cells,
sexual
for
together
nucleus
diploid
of
chromosomes
that
chromosomes
diploid
entirely
produce
has
chromosomes
haploid
zygote
more
nucleus
the
from
Many
the
reproduction,
this
divides
animals
cells
that
by
and
they
a
mitosis,
plants
are
using
to
reproduction.
Figure 7 Mosses coat the trunks of the laurel
Diploid
nuclei
have
two
copies
of
every
gene,
apart
from
genes
on
the
trees in this forest in the Canary Islands.
sex
chromosomes.
An
advantage
of
this
is
that
the
effects
of
harmful
Mosses are unusual because their cells are
recessive
mutations
can
be
avoided
if
a
dominant
allele
is
also
present.
haploid. In most eukaryotes the gametes are
Also,
organisms
are
often
more
vigorous
if
they
have
two
different
alleles
haploid but not the parent that produces them
of
genes
reason
instead
for
of
strong
just
one.
growth
of
This
F
is
known
hybrid
as
crop
hybrid
vigour
and
is
the
plants.
1
Chromoome umber
The number of chromosomes is a characteristic feature
of members of a species.
One
of
are
a
of
the
unlikely
species
The
to
need
number
species.
if
most
fundamental
chromosomes.
splits
It
can
occur.
number
to
numbers
be
to
of
Organisms
able
decrease
There
to
if
are
same
so
all
number
can
change
these
are
unchanged
the
of
a
over
of
is
the
number
chromosomes
interbreeding
members
of
chromosomes.
during
that
rare
species
number
become
mechanisms
However,
of
different
chromosomes
also
remain
a
interbreed
the
chromosomes
double.
tend
to
have
characteristics
with
the
evolution
fused
can
events
millions
together
cause
and
of
the
of
a
or
increase
chromosome
Figure 8 Trillium luteum cell with a diploid
chromosome
years
of
number of 12 chromosomes. Two of each
evolution.
type of chromosome are present
Comparig chromoome umber
Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes,
Canis familiaris, Oryza sativa, Parascaris equorum
The
Oxford
large
of
English
volumes,
information
Dictionary
each
consists
containing
about
the
a
origins
large
and
of
twenty
and
amount
meanings
eukaryotes.
This
information
could
have
been
have
a
smaller
number
of
larger
volumes
or
in
a
of
smaller
volumes.
There
is
a
eukaryotes
the
numbers
and
sizes
of
small
large
chromosomes
ones.
have
so
the
at
least
diploid
two
different
chromosome
types
of
number
at
least
four.
In
some
cases
it
is
over
a
hundred.
parallel
The
with
few
larger
is
number
many
a
published
chromosome,
in
have
of
All
words.
others
Some
chromosomes
table
on
the
next
page
shows
the
diploid
in
chromosome
number
of
selected
species.
155
3
G e n e t i c s
scentc nae
Eng
Dpod coooe
of pece
nae
nube
Parascaris
horse
equorum
threadworm
4
Oryza sativa
rice
24
Homo sapiens
humans
46
Pan troglodytes
chimpanzee
48
Canis familiaris
dog
78
Figure 9 Who has more chromosomes – a dog or its owner?
Data-baed queton: Dierences in chromosome number
Pant
Coooe nube
Ana
Haplopappus gracilis
4
Parascaris equorum (horse threadworm)
Luzula purpurea (woodrush)
6
Aedes aegypti (yellow fever mosquito)
Crepis capillaris
8
Drosophila melanogaster (fruity)
Vicia faba (eld bean)
12
Musca domestica (house y)
Brassica oleracea (cabbage)
18
Chor thippus parallelus (grasshopper)
Citrullus vulgaris (water melon)
22
Cricetulus griseus (Chinese hamster)
Lilium regale (royal lily)
24
Schistocerca gregaria (deser t locust)
Bromus texensis
28
Desmodus rotundus (vampire bat)
Camellia sinesis (Chinese tea)
30
Mustela vison (mink)
Magnolia virginiana (sweet bay)
38
Felis catus (domestic cat)
Arachis hypogaea (peanut)
40
Mus musculus (mouse)
Coea arabica (coee)
44
Mesocricetus auratus (golden hamster)
Stipa spar tea (porcupine grass)
46
Homo sapiens (modern humans)
Chrysoplenum alternifolium (saxifrage)
48
Pan troglodytes (chimpanzee)
Aster laevis (Michaelmas daisy)
54
Ovis aries (domestic sheep)
Glyceria canadensis (manna grass)
60
Capra hircus (goat)
Carya tomentosa (hickory)
64
Dasypus novemcinctus (armadillo)
Magnolia cordata
76
Ursus americanus (American black bear)
Rhododendron keysii
78
Canis familiaris (dog)
T
able 1
1
There
are
in
table,
the
for
of
many
example,
the
different
but
5,
species
some
7,
has
11,
13
chromosome
numbers
13.
are
Explain
numbers
3
missing,
why
species
none
chromosomes.
of
Discuss,
using
hypothesis
organism
156
the
that
is,
the
data
the
in
more
more
the
table,
complex
why
the
cannot
size
be
of
the
deduced
genome
from
the
of
a
number
chromosomes.
[1]
[3]
4
2
Explain
the
in
an
chromosomes
it
Suggest,
occurred
has.
[4]
using
the
chromosome
during
data
in
structure
human
table
that
1,
a
may
evolution.
change
have
[2]
3 . 2
C h r O m O s O m E s
sex deermiaio
Sex is determined by sex chromosomes and autosomes
female
male
XX
XY
are chromosomes that do not determine sex.
are
two
chromosomes
in
humans
that
determine
sex:
X
X
There
●
the
X
the
middle.
chromosome
the
Y
the
end.
is
relatively
large
and
has
its
centromere
near
X
●
Y
XX
chromosome
is
m uch
s ma ll e r
and
ha s
its
c e n t ro m e r e
XX
n e ar
XY
XY
Because
the
X
and
chromosomes.
All
affect
a
whether
Y
chromosomes
the
other
fetus
determine
chromosomes
develops
as
a
male
sex
are
or
they
are
autosomes
called
and
the
do
sex
not
female.
1 female : 1 male
The
X
chromosome
has
many
genes
that
are
essential
in
both
males
and
Figure 10 Determination of gender
females.
The
Y
Y
All
humans
chromosome
chromosome
has
chromosome,
but
are
on
not
found
must
only
the
the
the
therefore
has
a
same
small
on
at
least
number
sequence
genes
X
have
the
of
as
remainder
of
and
are
X
genes.
genes
chromosome
of
one
not
a
chromosome.
A
small
small
the
Y
part
part
of
of
the
the
X
chromosome
needed
for
female
development.
One
Y
male.
male
this
A
chromosome
This
called
features,
gene
fetus
have
a
the
Females
has
TDF
of
their
an
X
or
a
X
by
Y
particular
SRY
one
so
X
in
mother.
chromosome
X
two
fertilization
be
two
in
testes
X
ovaries
not
The
one
egg
chromosome
and
one
sons
Y
Y
fetus
the
no
Y
instead
to
develop
a
develops
testes
and
of
Because
chromosome
of
as
development
production.
chromosome
and
develop
cell,
gender
the
a
initiates
as
a
does
of
male.
not
female
sex
testosterone.
Females
so
of
a
chromosome
half
It
testosterone
chromosomes.
each
causes
TDF
.
and
and
chromosome.
and
or
chromosomes
produced,
chromosomes
from
with
gene
are
have
gene
either
including
fetus
that
hormones
X
is
When
all
human
is
carried
in
sperm
his
Y
on
one
inherit
of
an
determined
are
chromosome.
inherit
pass
offspring
the
sperm.
formed,
Daughters
their
X
at
the
This
half
two
chromosome
moment
can
either
contain
inherit
their
the
X
father’s
chromosome.
Karyogram
A karyogram shows the chromosomes of an organism
in homologous pairs of decreasing length.
The
chromosomes
with
to
make
type
If
cells
a
in
the
burst
spread.
cells
by
Often
can
usually
can
be
an
organism
giving
chromosomes
distinctive
dividing
then
of
metaphase
are
they
on
the
are
visible
clearest
up.
in
cells
view.
Some
that
Stains
stains
give
are
have
each
in
to
mitosis,
be
used
chromosome
pattern.
and
the
overlap
found
of
show
stained
pressing
be
taken
banding
the
with
placed
cover
each
no
stained
on
slip,
other,
a
microscope
the
but
overlapping
slide
chromosomes
with
careful
and
are
become
searching
chromosomes.
A
a
cell
micrograph
chromosomes.
157
3
G e n e t i c s
Originally
analysis
involved
cutting
out
all
the
chromosomes
and
TOK
arranging
them
chromosomes
manually
are
but
arranged
this
process
according
to
can
their
now
size
be
done
and
digitally.
structure.
The
The
To wat ex tent  detenng gende
position
of
the
centromere
and
the
pattern
of
banding
allow
chromosomes
fo po tng copetton a centc
that
are
of
a
different
type
but
similar
size
to
be
distinguished.
queton?
As
most
cells
are
diploid,
the
chromosomes
are
usually
in
homologous
Gender testing was introduced at
pairs.
They
are
arranged
by
size,
starting
with
the
longest
pair
and
the 1968 Olympic games to address
ending
with
the
smallest.
concerns that women with ambiguous
physiological genders would have
an unfair advantage. This has proven
to be problematic for a number of
reasons. The chromosomal standard
is problematic as non-disjunction can
lead to situations where an individual
might technically be male, but might
not dene herself in that way. People
with two X chromosomes can develop
hormonally as a male and people with
an X and a Y can develop hormonally
as a female.
The practice of gender testing was
discontinued in 1996 in par t because
of human rights issues including the
right to self-expression and the right to
identify one's own gender.
Rather than
being a scientic question, it is more
fairly a social question.
Figure 11 Karyogram of a human female, with uorescent staining
Karyoype ad Dow ydrome
Use of karyotypes to deduce sex and diagnose Down
syndrome in humans.
A
karyogram
arranged
property
that
at
1
Figure 12 Child with trisomy 2
1 or
the
in
of
is
an
organism
deduce
and
2
To
one
Y
is
pregnancy.
sometimes
158
there
called
a
be
chromosomes
of
is
number
nuclei.
used
the
of
two
is
an
length.
and
Karyotypes
in
individual
type
are
organism,
A
karyotype
of
is
a
chromosomes
studied
by
looking
ways:
male
individual
or
is
female.
female
If
two
XX
whereas
one
X
male.
using
are
of
decreasing
the
syndrome
two,
of
other
cells
copies
the
21.
the
Mental
and
fetal
three
trisomy
features
disorders.
it
its
an
done
instead
the
present
Down
If
component
vision
in
indicate
usually
karyotype
are
of
pairs
–
can
whether
diagnose
This
has
They
chromosomes
Down syndrome
image
organism
karyograms.
To
an
homologous
child
of
growth
from
the
Down
21
in
syndrome.
individuals
are
abnormalities.
uterus
chromosome
has
While
syndrome
and
chromosome
taken
vary,
hearing
retardation
This
some
loss,
are
during
the
of
heart
also
is
the
and
common.
3 . 3
m E i O s i s
Data-based questions: A human karyotype
The
1
2
karyogram
State
shows
which
longest
b)
shortest.
a)
human
b)
the
karyotype
chromosome
a)
Distinguish
the
type
of
a
fetus.
is
[2]
between
the
structure
chromosome
human
a
X
3
Deduce
with
4
Explain
whether
and
reason
the
Y
2
and
of
chromosome
12
chromosome.
the
sex
of
karyotype
the
[4]
fetus.
shows
any
[2]
abnormalities.
[2]
Figure 13
3.3 meo
Uderadig
Applicaio
➔
One diploid nucleus divides by meiosis to
➔
Non-disjunction can cause Down syndrome
produce four haploid nuclei.
and other chromosome abnormalities. Studies
➔
The halving of the chromosome number allows
showing age of parents inuences chances of
a sexual life cycle with fusion of gametes.
➔
DNA is replicated before meiosis so that all
non-disjunction.
➔
chromosomes consist of two sister chromatids.
➔
Methods used to obtain cells for karyotype
analysis e.g. chorionic villus sampling and
amniocentesis and the associated risks.
The early stages of meiosis involve pairing of
homologous chromosomes and crossing over
followed by condensation.
➔
chromosomes prior to separation is random.
➔
skill
Orientation of pairs of homologous
➔
Drawing diagrams to show the stages of
meiosis resulting in the formation of four
Separation of pairs of homologous
haploid cells.
chromosomes in the rst division of meiosis
halves the chromosome number.
➔
Crossing over and random orientation promotes
naure of ciece
genetic variation.
➔
➔
Making careful obser vations: meiosis was
Fusion of gametes from dierent parents
discovered by microscope examination of
promotes genetic variation.
dividing germ-line cells.
159
3
G e n e t i c s
the dicovery of meioi
Making careful observations: meiosis was discovered by microscope examination
of dividing germ-line cells.
When
in
the
cell
improved
19th
structures,
specically
revealed
microscopes
century
it
that
was
stained
been
detailed
discovered
the
thread-like
had
gave
nucleus
structures
that
of
in
some
the
chromosome
developed
images
cell.
observation
of
a
dyes
These
dividing
halves
dyes
nuclei
special
named
chromosomes.
From
the
1880s
the
group
of
German
biologists
carried
out
observations
how
mitosis
of
dividing
and
nuclei
meiosis
careful
that
can
these
that
biologists
they
slides
can
a
on
bud
or
the
we
The
must
the
be
microscope
or
the
images
of
the
process.
by
shapes
A
key
experts
as
during
the
the
observation
(Parascaris
in
it
was
egg
of
egg
animals
of
there
contains
The
must
generation
be
that
number.
unlike
during
mitosis
gamete
had
already
development
and
plants.
These
divisions
in
were
as
the
method
used
to
halve
the
Suitable
anthers
cells
in
enough
of
cells
from
begins
at
of
this
birth
out
the
between
advantage
of
by
0
and
were
of
28
is
occurs
in
careful
ovaries
species
and
they
events
named
meiosis
rabbits
days
that
of
( Oryctolagus
old.
in
slowly
was
observation
The
females
over
meiosis
many
days.
to
are
show
slides
understand
variety
worked
taken
and
squashed
meiosis
prepared
number
sequence
eventually
cuniculus)
tissue
inside
locust.
then
The
the
bizarre
meiosis.
in
are
the
two
sperm
four.
a
meiosis.
of
microscope
and
clear
to
every
there
gradually
observations
dissected
with
form
that
and
a
no
difcult
stages
equorum)
nuclei
fertilized
is
not
Even
chromosomes
of
stained
Often
are
the
developing
of
in
fertilization.
that
and
achievements
challenging.
testis
slide.
details
images
is
the
xed,
visible
made
repeat
preparation
from
from
to
by
occur.
considerable
try
meiosis
obtained
tissue
a
if
made.
showing
be
lily
The
appreciate
division
divisions
observed
chromosome
We
doubled
chromosome
identied
revealed
is
hypothesis
onwards
both
detailed
the
that
been
a
to
nuclear
Nuclear
were
number
led
horse
chromosomes
cells,
This
threadworm
whereas
indicated
the
that
the
Figure 1
▲
Meioi i oulie
one diploid cell
2n
One diploid nucleus divides by meiosis to produce four
meiosis I
haploid nuclei.
two haploid cells
n
n
Meiosis
is
cell
divide.
can
one
of
the
The
two
ways
other
in
which
method
is
the
nucleus
mitosis,
of
a
eukaryotic
which
was
described
twice.
The
rst
in
meiosis II
sub-topic
four haploid cells
n
n
produces
nuclei.
1.6.
two
The
In
meiosis
nuclei,
two
the
each
divisions
nucleus
of
are
which
divides
divides
known
as
again
meiosis
I
to
give
and
a
division
total
meiosis
of
four
II.
Figure 2 Over view of meiosis
The
has
nucleus
two
known
by
known
The
the
160
as
undergoes
has
just
involves
as
cells
of
homologous
meiosis
Meiosis
that
chromosomes
a
a
of
the
by
rst
type.
division
chromosome
of
the
of
meiosis
Chromosomes
chromosomes.
halving
reduction
produced
halving
one
the
each
Each
of
of
each
the
type
chromosome
of
four
–
is
the
diploid
same
nuclei
they
number.
are
It
is
–
it
type
are
produced
haploid.
therefore
division.
meiosis
I
chromosome
have
one
number
chromosome
happens
in
of
the
each
rst
type,
so
division,
3 . 3
not
the
second
haploid
two
division.
number
of
chromatids.
four
nuclei
that
chromosome
The
two
nuclei
chromosomes,
These
have
but
chromatids
the
consisting
haploid
of
a
produced
each
separate
number
single
by
meiosis
chromosome
during
of
I
still
meiosis
the
consists
II,
chromosomes,
have
m E i O s i s
of
producing
with
each
chromatid.
Meioi ad exual life cycle
The halving of the chromosome number allows a sexual
life cycle with fusion of gametes.
The
life
life
cycles
cycle
the
genetically
of
living
offspring
identical.
organisms
have
In
of
In
organisms,
eukaryotic
from
two
different
chromosome
halved
at
number
Meiosis
it
some
can
happens
therefore
Meiosis
stage
happen
diploid
is
a
in
at
the
and
complex
What
is
and
the
it
be
sexual
cycle
there
so
reproduction
of
Fertilization
It
sex
cycle.
This
as
the
is
involves
cells,
or
an
the
the
the
are
cause
the
diversity.
process
number
of
so
genetic
number
halving
asexual
between
gametes,
therefore
if
In
parent
differences
there
doubles
would
generation,
life
asexual.
are
parents,
union
every
or
chromosomes
the
occurs.
the
during
during
developed.
time
number
happens
is
parents.
each
life
sexual
Fertilization
chromosomes
of
offspring
can
same
sexual
chromosomes
fertilization.
the
a
the
of
usually
of
a
doubling
was
not
also
chromosome
meiosis.
any
stage
process
have
two
process
clear
of
is
during
copies
and
that
a
creating
it
its
is
sexual
the
of
most
not
at
cycle,
but
Body
in
cells
animals
are
genes.
the
evolution
life
gametes.
moment
was
a
clear
critical
how
step
in
it
the
Figure 4 Fledgling owls (bottom) produced by
origin
of
eukaryotes.
Without
meiosis
there
cannot
be
fusion
of
gametes
a sexual life cycle have diploid body cells but
and
the
sexual
life
cycle
of
eukaryotes
could
not
occur.
mosses (top) have haploid cells
Data-baed queton: Life cycles
Figure
3
mosses,
number
shows
with
of
n
the
life
being
cycle
used
chromosomes
of
to
humans
represent
and
2n
to
and
the
1
haploid
represent
the
number.
main
moss
Sporophytes
plant
and
of
mosses
consist
of
a
grow
stalk
ve
cycle
a
of
similarities
moss
and
of
a
between
in
which
spores
are
life
[5]
Distinguish
between
a
a
the
life
cycles
of
on
and
moss
and
human
by
giving
ve
a
differences.
capsule
the
human.
the
2
diploid
Outline
[5]
produced.
egg
n
sperm
sperm
egg
n
n
n
moss
human male
zygote
human female
2n
2n
2n
plant
zygote
n
Key
mitosis
2n
spore
sporophyte
n
2n
meiosis
fer tilization
Figure 3
161
3
G e n e t i c s
Replicaio of DnA before meioi
DNA is replicated before meiosis so that all chromosomes
2n
interphase
consist of two sister chromatids.
During
by
the
early
supercoiling.
chromosome
stages
As
of
soon
consists
meiosis
as
of
they
two
the
chromosomes
become
visible
chromatids.
This
it
is
is
gradually
clear
because
that
all
shorten
each
DNA
in
2n
homologous
the
nucleus
is
replicated
during
the
interphase
before
meiosis,
so
each
chromosomes
chromosome
Initially
the
genetically
2n
n
n
two
of
two
chromatids
identical.
This
sister
that
is
chromatids.
make
because
up
DNA
each
chromosome
replication
is
very
are
accurate
and
meiosis I
the
n
consists
n
number
of
mistakes
We
might
the
second
expect
the
chromosome
the
division
in
the
DNA
of
to
copying
be
meiosis,
of
the
replicated
but
it
does
DNA
again
not
is
extremely
between
happen.
the
This
small.
rst
and
explains
how
meiosis II
n
n
in
which
to
produce
one
each
number
is
halved
chromosome
four
haploid
during
consists
nuclei
in
of
meiosis.
two
which
One
diploid
chromatids,
nucleus,
divides
eachchromosome
twice
consists
of
chromatid.
Figure 5 Outline of meiosis
Bivale formaio ad croig over
The early stages of meiosis involve pairing of homologous
chromosomes and crossing over followed by condensation.
Some
I
of
while
a
most
of
two
pair
of
DNA
and
of
the
junction
is
at
Because
a
and
in
each
As
the
is
us
one
occurred,
A
bivalent
there
at
is
pair
with
and
a
there
mutual
are
each
at
the
called
the
in
up
the
can
the
be
with
each
with
other.
consists
associated
in
each
chromosomes
place.
of
the
is
is
The
very
molecular
important.
homologous
chromatid.
Crossing
chromosomes.
At
over
least
one
several.
same
exchange
homologous
meiosis
synapsis.
takes
be
of
seen
chromosome
outcome
each
start
cannot
molecules
other
along
pair
over
but
the
and
homologous
crossing
here,
precisely
chromatids
of
sometimes
anywhere
occurs
DNA
chromatid
rejoins
happen
elongated
four
called
concern
meiosis
chromosomes
are
process
where
of
very
already
there
process
involved,
chromatids.
has
positions
crossover
chromatids
Figure 6 A pair of homologous
a
not
breaks
occurs
still
chromosomes.
created
random
crossover
so
pairing
need
chromosomes
occurs
and
synapsis,
this
events
are
homologous
replication
homologous
after
details
Firstly
chromatids
bivalent
Soon
important
chromosomes
microscope.
Because
A
the
the
position
of
but
on
genes
not
the
two
between
identical,
the
some
chromosomes contains four
alleles
of
the
exchanged
genes
are
likely
to
be
different.
Chromatids
with
chromatids and is sometimes called
new
combinations
of
alleles
are
therefore
produced.
a tetrad. Five chiasmata are visible
in this tetrad, showing that crossing
over can occur more than once
Radom orieaio of bivale
Orientation of pairs of homologous chromosomes prior to
separation is random.
While
pairs
nucleus
growing
162
of
of
a
homologous
cell
from
in
the
the
chromosomes
early
poles
of
stages
the
cell.
of
are
condensing
meiosis,
After
the
spindle
nuclear
inside
the
microtubules
membrane
has
are
3 . 3
broken
the
down,
these
attachment
The
principles
●
Each
●
The
two
The
The
the
The
to
the
centromeres
of
spindle
microtubules
is
not
the
same
as
in
mitosis.
is
attached
to
one
chromosomes
pole
in
a
only,
not
bivalent
to
are
both.
attached
to
poles.
to
which
pair
of
of
each
of
orientation
section
bivalents
of
of
on
chromosome
chromosomes
attaching
consequences
the
the
orientation
chance
●
attach
these:
homologous
pole
way
of
are
chromosome
different
●
microtubules
chromosomes.
The
●
spindle
m E i O s i s
to
each
one
the
is
and
bivalent
is
attached
facing.
random,
pole,
random
genetic
is
This
so
each
not
orientation
later
in
of
affect
of
depends
called
the
being
other
which
has
pulled
an
to
are
equal
it.
bivalents.
bivalents
this
on
orientation.
chromosome
eventually
does
diversity
is
The
discussed
MITOSIS
in
topic.
Halvig he chromoome umber
Separation of pairs of homologous chromosomes in the
rst division of meiosis halves the chromosome number.
either
The
movement
of
chromosomes
is
not
the
same
in
the
rst
division
or
of
MEIOSIS
meiosis
as
in
chromatids
mitosis.
that
Whereas
make
up
a
in
mitosis
the
chromosome
centromere
move
to
divides
opposite
and
poles,
in
the
two
Figure 7 Comparison of attachment
meiosis
of chromosomes to spindle
the
centromere
does
not
divide
and
whole
chromosomes
move
to
the
poles.
microtubules in mitosis and meiosis
Initially
by
the
two
chiasmata,
then
the
The
of
one
is
cell
rst
the
of
halves
division
chromosome
formed
these
called
of
separation
the
the
to
but
chromosomes
chromosomes
moves
chromosomes
in
of
the
chromosome,
pairs
so
the
of
the
homologous
type
moves
division
they
are
is
of
the
the
to
are
held
separation
of
chromosomes
the
reduction
each
pole,
contain
to
to
cell.
both
of
of
each
the
bivalent
other
opposite
It
is
division.
one
and
homologous
from
chromosome
of
together
chromosomes
chromosome
number
meiosis
both
of
This
One
other
chromosome
that
bivalent
end
separate.
and
meiosis
each
rst
can
to
each
disjunction.
poles
the
of
slide
in
poles
therefore
Because
the
each
pole.
two
one
nuclei
type
of
haploid.
Obaiig cell from a feu
Methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling
and amniocentesis and the associated risks.
Tw o
procedures
containing
producing
passing
wall,
The
a
the
a
needle
used
is
used
fluid
amniotic
sac.
obtaining
to
to
the
mother's
guide
withdraw
containing
fetal
the
a
cells
needed
Amniocentesis
through
ultrasound
amniotic
for
chromosomes
karyotype.
needle
using
are
fetal
The
A
second
procedure
sampling
used
abdomen
membranes
needle.
from
This
to
tool
involves
sample
cells
for
obtain
can
be
that
cells
from
done
of
amniocentesis,
the
with
which
earlier
but
it
is
chorionic
from
the
in
is
1%,
villus
through
the
the
chorion,
placenta
the
whereas
amniocentesis
sampling
is
enters
sampling.
vagina
one
the
risk
is
the
develops.
pregnancy
with
of
of
than
miscarriage
chorionic
villus
2%
163
3
G e n e t i c s
Diagram of he age of meioi
Drawing diagrams to show the stages of meiosis resulting in the formation of four
haploid cells.
In
mitosis
prophase,
Meiosis
each
four
can
stage
second
stage
also
be
are
in
twice:
meiosis
mitosis
usually
anaphase
divided
happens
time
in
stages
metaphase,
also
II.
into
in
happen
main
in
actual
telophase.
these
meiosis
The
Usually
recognized:
and
I
stages,
and
but
then
events
of
a
a
each
showing
prophase:
condensation
of
visible
even
metaphase:
attachment
of
spindle
microtubules;
is
why
rather
●
anaphase:
movement
of
often
is
worth
Permanent
in
then
meiosis
it
is
chromosomes
of
we
decondensation
than
draw
stages
to
slides!
of
chromosomes.
Cell has 2n chromosomes (double
nuclear membrane
chromatid): n is haploid number of
chromosomes.
spindle microtubules
and centriole
●
Homologous chromosomes pair (synapsis).
●
Crossing over occurs.
Prophase I
metapae i
Spindle microtubules move homologous pairs
to equator of cell.
bivalents aligned
on the equator
●
Orientation of paternal and maternal
chromosomes on either side of equator
is random and independent of other
Metaphase I
homologous pairs.
Anapae i
●
Homologous pairs are separated. One
homologous
chromosomes
chromosome of each pair moves to each
being pulled to
opposite poles
pole.
Anaphase I
Teopae i
●
Chromosomes uncoil. During interphase
that follows, no replication occurs.
cell has divided
across the equator
●
Reduction of chromosome number from
diploid to haploid completed.
Telophase I
●
164
Cytokinesis occurs.
down
to
slides
but
usually
it
have
temporary
interpret
their
construct
Popae i
●
from
them
attempting
from
The rst division of meiosis
●
at
microscope
slides
than
thepoles;
telophase:
of
difcult
bivalents
usually
microscope
●
structures
looking
is
more
mounts,
the
chromosomes;
structure
●
biological
Preparation
meiosis
challenging.
but
●
draw
microscope.
cells
meiosis:
we
specimens,
appearance.
diagrams
from
of
specimens
This
meiosis
on
3 . 3
m E i O s i s
The second division of meiosis
Popae ii
●
Chromosomes, which still consist of two
chromatids, condense and become visible.
Prophase II
metapae ii
Metaphase II
Anapae ii
●
Centromeres separate and chromatids are
moved to opposite poles.
Anaphase II
Teopae ii
●
Chromatids reach opposite poles.
●
Nuclear envelope forms.
●
Cytokinesis occurs.
Telophase II
Meioi ad geeic variaio
Crossing over and random orientation promotes genetic
variation.
When
two
parents
unpredictable
the
have
mixture
unpredictability
parent
has
genetic
Apart
there
of
the
each
will
parent.
new
child,
they
know
characteristics
due
to
meiosis.
combination
of
that
from
Every
alleles
–
it
will
each
of
gamete
meiosis
is
inherit
them.
an
Much
produced
a
source
by
of
of
a
endless
variation.
from
copies
a
is
a
of
be
genes
gene.
one
There
are
on
In
copy
the
some
of
likely
X
cases
that
to
be
and
Y
chromosomes,
the
allele
in
two
copies
every
thousands
of
are
gamete
genes
humans
in
the
have
same
produced
the
two
allele
by
parent’s
and
the
genome
165
3
G e n e t i c s
where
Actvt
the
chance
a
gene
of
two
alleles
being
with
the
are
passed
alleles
different.
on
A
in
and
a
Each
gamete.
a.
Half
of
of
Let
the
the
us
two
alleles
suppose
gametes
has
that
an
there
produced
by
equal
is
the
If g is the number of genes
parent
will
contain
A
and
half
will
contain
a.
in a genome with dierent
g
alleles, 2
is the number
of combinations of these
alleles that can be generated
by meiosis. If there were
Let
us
now
Again
can
aB
half
result
and
suppose
of
in
ab.
the
that
there
gametes
gametes
There
are
will
with
two
is
another
contain
different
processes
B
gene
and
with
half
b.
combinations
in
meiosis
the
of
that
alleles
However,
these
B
and
genes:
generate
b.
meiosis
this
AB,
Ab,
diversity.
just 69 genes with dierent
alleles (3 in each of the
B
23 chromosome types in
a
B
A
b
a
50%
humans) there would be
probability
b
590,295,810,358,705,
A
700,000 combinations.
B
b
telophase I
Assuming that all humans
A
are genetically dierent, and
a
that there are 7,000,000
50%
humans, calculate the
a
a
b
A
B
probability
prophase I
percentage of all possible
B
genomes that currently exist.
A
metaphase I
▲
Figure 8 Random orientation in metaphase I
1. Random orientation of bivalents
In
of
metaphase
one
Random
the
orientation
does
not
orientation
variation
For
I
bivalent
every
among
genes
additional
combinations
in
of
a
bivalents
that
are
bivalent,
cell
of
bivalents
inuence
the
is
the
on
the
produced
is
process
different
number
by
random
orientation
that
and
any
the
of
possible
doubles.
orientation
the
generates
chromosome
of
meiosis
of
others.
genetic
types.
chromosome
For
a
haploid
number
n
of
n,
the
number
of
possible
combinations
is
2
.
For
humans
with
a
23
haploid
number
of
23
this
amounts
to
2
or
over
8
million
combinations.
2. Crossing over
Without
crossing
chromosomes
chromosome
these
genes
It
over
would
carried
combinations
to
be
increases
meiosis
so
in
be
the
to
number
much
that
it
I,
combinations
linked
combination
could
reshufed,
the
prophase
forever
occur
produce
of
is
in
allele
together.
CD
and
gametes.
new
alleles
another
carried
over
combinations
that
on
example,
Crossing
combinations
effectively
of
For
such
can
be
if
one
cd,
allows
as
Cd
only
linked
and
generated
cD.
by
innite.
Ferilizaio ad geeic variaio
Fusion of gametes from dierent parents promotes
genetic variation.
The
fusion
both
Figure 9
166
for
of
●
It
is
●
It
allows
the
new
gametes
individuals
start
of
alleles
individual.
to
and
the
produce
for
life
from
a
zygote
is
a
highly
signicant
event
species.
of
two
a
new
individual.
different
individuals
to
be
combined
in
one
3 . 3
●
The
●
Fusion
●
Genetic
combination
of
of
gametes
variation
alleles
is
therefore
is
unlikely
ever
promotes
essential
for
to
have
genetic
existed
variation
in
m E i O s i s
before.
a
species.
evolution.
no-dijucio ad Dow ydrome
Non-disjunction can cause Down syndrome and other chromosome abnormalities.
Meiosis
One
is
sometimes
example
of
chromosomes
is
termed
any
of
Both
pairs
the
to
gamete
that
the
decient
involved
be
an
47
to
of
in
other
separate
a
pole.
has
at
The
can
human
to
result
either
13.
with
pole
will
be
If
the
45
gamete
the
result
abnormal
born
of
babies
by
a
having
the
syndrome
or
is
in
humans
not
with
trisomy
can
sex
also
an
18
so
and
the
numbers
chromosomes
XXY.
only
are
trisomy
in
syndrome
having
serious
Babies
result
abnormal
by
are
survive.
Klinefelter’s
caused
chromosome,
is
do
with
chromosomes.
of
is
sex
caused
Turner’s
one
sex
X.
will
or
diploid parent cell with
chromosomes.
An
trisomies
offspring
Non-disjunction
birth
and
chromosome
fertilization,
with
one
other
the
sometimes
This
happen
chromosomes.
extra
chromosome.
individual
that
anaphase.
This
move
an
Most
errors.
homologous
homologous
either
in
to
when
chromosomes
neither
is
fail
subject
is
non-disjunction.
the
of
this
two chromosome 21
number
of
chromosomes
non-disjunction
will
often
lead
syndrome,
signs
or
to
i.e.
a
a
person
collection
symptoms.
For
possessing
of
a
during meiosis
gamete with no
chromosome 21
physical
gamete with two
example
chromosome 21
trisomy
21,
also
known
as
Down
cell dies
syndrome,
event
that
is
due
leaves
to
a
the
non-disjunction
individual
with
fusion of
normal haploid
×
three
of
instead
some
chromosome
of
of
two.
the
number
While
21
individuals
component
features
gametes
gamete
vary,
of
trisomy: zygote with
the
syndrome
include
hearing
loss,
three chromosome 21
heart
and
vision
disorders.
Mental
and
Figure 10 How non-disjunction can give rise to Down syndrome
growth
retardation
are
also
common.
trisomy 2
1
Pareal age ad o-dijucio
all chromosomal
abnormalities
non-disjunction
The
data
maternal
presented
age
and
chromosomal
1
Outline
of
in
the
gure
11
shows
incidence
of
the
relationship
trisomy
21
and
of
between
other
abnormalities.
the
relationship
chromosomal
between
abnormalities
in
maternal
live
age
and
the
incidence
births.
)sht rib evil lla fo %( ecnedicni
Studies showing age of parents inuences chances of
14
12
10
8
6
4
[2]
2
2
a)
For
mothers
40
years
of
age,
a
child
determine
the
probability
that
0
they
will
give
birth
to
with
trisomy
21.
[1]
20
b)
Using
the
mother
of
data
40
chromosomal
in
gure
years
of
11,
age
calculate
will
abnormality
give
other
the
birth
than
probability
to
a
child
trisomy
21.
that
with
40
60
maternal age (years)
a
a
▲
[2]
Figure 11 The incidence of trisomy 2
1
and other chromosomal abnormalities
as a function of maternal age
167
3
G e n e t i c s
3
Only
are
a
small
ever
commonest.
4
Discuss
having
number
found
the
of
among
Suggest
risks
possible
live
reasons
parents
chromosomal
births,
face
for
and
these
when
trisomy
abnormalities
21
is
much
the
trends.
choosing
to
[3]
postpone
children.
[2]
3.4 inetance
Uderadig
Applicaio
➔
Mendel discovered the principles of inheritance
➔
Inheritance of ABO blood groups.
➔
Red-green colour-blindness and hemophilia as
with experiments in which large numbers of
pea plants were crossed.
examples of sex-linked inheritance.
➔
Gametes are haploid so contain one allele of
➔
Inheritance of cystic brosis and Huntington’s
each gene.
disease.
➔
The two alleles of each gene separate into
➔
Consequences of radiation after nuclear
dierent haploid daughter nuclei during meiosis.
bombing of Hiroshima and Nagasaki and the
➔
Fusion of gametes results in diploid zygotes
nuclear accidents at Chernobyl.
with two alleles of each gene that may be the
same allele or dierent alleles.
➔
alleles but co-dominant alleles have joint eects.
➔
Construction of Punnett grids for predicting the
outcomes of monohybrid genetic crosses.
➔
Comparison of predicted and actual outcomes
of genetic crosses using real data.
Some genetic diseases are sex-linked and some
are due to dominant or co-dominant alleles.
➔
➔
Many genetic diseases in humans are due to
recessive alleles of autosomal genes.
➔
skill
Dominant alleles mask the eects of recessive
➔
Analysis of pedigree char ts to deduce the
pattern of inheritance of genetic diseases.
The pattern of inheritance is dierent with
sex-linked genes due to their location on sex
chromosomes.
naure of ciece
➔
Many genetic diseases have been identied in
➔
Making quantitative measurements with
humans but most are very rare.
replicates to ensure reliability: Mendel’s genetic
➔
Radiation and mutagenic chemicals increase
crosses with pea plants generated numerical data.
the mutation rate and can cause genetic
disease and cancer.
168
3 . 4
i N h E r i T A N C E
Medel ad he priciple of iheriace
Mendel discovered the principles of inheritance
with experiments in which large numbers of pea
plants were crossed.
When
living
offspring.
also
blue
this,
whales
on.
However,
tails
of
We
in
acquired
their
parents.
of
it
the
was
not
Mendel’s
nd
out
many
of
pea
inheritance
In
1866
were
was
interest
in
biologists
done
same
pea
female
that
He
also
his
did
just
an
of
used
inheritance
Mendel’s
other
plants
explained
the
For
pea
in
of
the
theories,
and
early
earlier.
theories
characters
between
made
in
those
the
of
▲
in
Figure 1 Hair styles are acquired
characteristics and are for tunately not
rst
inherited by ospring
inheritance,
“Experiments
of
pea
grown
of
plant,
on
its
Plant
result
and
with
grew
the
of
Mendel
male
variety.
each
seven
each
own.
the
another
repeated
over
been
plants
that
They
with
basis
on
cosmetic
pollen
He
them
cross
to
with
different
pairs
principles
of
effect.
have
work.
and
a
be
resemble
blending
demonstrated
isolated
research.
the
transferring
experiment
reasons
experiments
as
can
available.
owers
Mendel
reliably
of
inherit
by
paper
when
in
seen
and
current
biologists
by
than
whale,
Hippocrates
varieties
formed
were.
this
his
Various
using
Scars
intermediate
was
together
were
of
explained
his
their
are
characteristics.
sometimes
Many
that
More
blue
to
to
young
inherited.
offspring
theory
parts
results
not
be
characters
of
published
with
time
parents.
published
were
be
children
a
attacks
According
which
not
of
parents’
whale
cannot
observations
could
the
the
species.
skin
inherited.
the
that
their
characters
pattern
theory
this.
these
alternative
the
ignored.
the
the
the
so
his
of
since
have
Mendel
rediscovered
experiments
Mendel’s
of
peas,
that
as
than
so
seeds
and
Mendel
such
observed
an
their
in
largely
factor
examples
be
killer
characters
to
pea
by
characteristics
same
the
inherit
cannot
caused
varieties
plants.
characters
offspring
on
reproduce,
the
and
that
variety
the
on
in
had
what
of
markings
century
crossed
collected
members
discussed
experiments
one
are
more
until
reliably
carefully
pass
inheritance,
Some
Hybridization”
which
are
been
parents
19th
blue
the
whales
blending
both
whales
the
Aristotle
from
from
that
grandparents
involved
half
as
characteristics
has
they
when
characteristics
blue
example,
reproduce,
they
humans
Inheritance
their
–
such
say
some
some
surgery
but
example,
variations,
passed
For
organisms
For
thirty
years
suggested
and
species.
quickly
animals.
there
In
These
inheritance
in
was
1900
did
his
for
ndings
this.
not
several
cross-breeding
conrmed
all
One
great
plants
that
and
animals.
Replicae ad reliabiliy i Medel’ experime
Making quantitative measurements with replicates to ensure reliability: Mendel's
genetic crosses with pea plants generated numerical data.
Gregor
the
Mendel
father
of
attributed
to
for
research
is
regarded
genetics.
being
into
His
the
by
most
success
rst
to
inheritance.
is
use
Peas
biologists
as
sometimes
pea
plants
have
clear
characteristics
that
to
can
the
easily
next.
hybrids
or
such
be
They
they
as
red
or
followed
can
can
also
be
white
from
be
ower
one
crossed
allowed
to
colour
generation
to
produce
self-pollinate.
169
3
G e n e t i c s
In
fact
Mendel
plants.
was
Thomas
horticulturalist,
Downton
18th
in
and
Philosophical
Knight
had
Castle
century
made
not
the
Andrew
rst
conducted
Transactions
in
the
results
the
important
pea
cross pollinating peas:
English
research
his
of
use
an
Herefordshire
published
some
to
Knight,
to the stigma here
at
late
in
Royal
pollen from another plant is dusted on
the
Society.
discoveries:
pollen is collected
●
male
the
●
and
female
parents
contribute
equally
to
from the anthers
offspring;
characters
that
such
apparently
reappear
in
inheritance
the
is
as
white
ower
disappear
next
in
colour
offspring
generation,
discrete
rather
can
showing
than
that
blending;
– called the keel
●
one
character
can
show
“a
alternative
such
as
stronger
red
ower
tendency”
colour
than
self pollinating peas:
the
– if the ower is left untouched, the anthers
inside the keel pollinate the stigma
character.
▲
Although
Mendel
was
not
as
pioneering
in
Figure 2 Cross and self pollination
his
(a) Prediction based on
experiments
as
sometimes
thought,
he
deserves
blending inheritance
credit
for
was
pioneer
in
a
another
having
seven
Table
in
large
different
1
shows
aspect
of
obtaining
numbers
cross
the
his
research.
quantitative
of
replicates.
experiments,
results
of
his
Mendel
results
He
not
also
just
tall plants
and
3
dwarf plants
did
one.
monohybrid
crosses.
pea plants with an
It
is
now
repeats
standard
in
practice
experiments
to
in
science
to
demonstrate
intermediate height
include
the
(b) Actual results
reliability
of
results.
Repeats
can
be
compared
to
tall plants
see
how
close
identied
tests
can
and
be
differences
they
are.
Anomalous
excluded
done
to
between
from
assess
results
analysis.
the
It
is
3
dwarf plants
be
Statistical
signicance
treatments.
can
also
of
standard
pea plants as tall
practice
to
repeat
whole
experiments,
using
a
as the tall parent
different
organism
or
different
treatments,
to
test
▲
a
hypothesis
in
different
ways.
Mendel
Figure 3 Example of a monohybrid cross experiment. All the
should
hybrid plants produced by crossing two varieties together
therefore
be
regarded
as
one
of
the
fathers
of
had the same character as one of the parents and the
genetics,
but
even
more
we
should
think
of
him
character of the other parent was not seen. This is a clear
as
a
pioneer
of
research
methods
in
biology.
Paenta pant
Tall stem × dwarf stem
Round seed × wrinkled seed
Yellow cotyledons × green cotyledons
Purple owers × white owers
Full pods × constricted pods
Green unripe pods × yellow unripe pods
Flowers along stem × owers at stem tip
▲
170
T
able 1
hbd pant
falsication of the theory of blending inheritance
Opng fo ef-ponatng te bd
rato
All tall
787 tall : 277 dwarf
2.84 : 1
All round
5474 round : 1850 wrinkled
2.96 : 1
All yellow
6022 yellow : 2001 green
3.01 : 1
All purple
705 purple : 224 white
3.15 : 1
All full
882 full : 299 constricted
2.95 : 1
All green
428 green : 152 yellow
2.82 : 1
All along stem
651 along stem : 207 at tip
3.14 : 1
3 . 4
i N h E r i T A N C E
Gamee
Gametes are haploid so contain one allele of each gene.
Gametes
are
start
new
of
a
produced
gametes
cells
when
are
than
gamete
moves
smaller
Parents
one
male
the
pass
and
less
in
or
genes
only
female
and
has
female
at
to
gametes,
It
all.
usually
In
cell
so
are
each
and
the
sex
fuse
The
able
humans,
in
a
its
gene.
The
This
is
parents
Male
is
the
to
of
make
the
female
sperm
to
has
the
a
egg.
contain
of
a
both
an
cell
female
generally
Gametes
true
the
and
swim
nucleus
is
single
whereas
tail
gametes.
that
the
gamete
move
example,
uses
cell
and
zygote.
male
to
haploid.
female
single
cells,
is
for
and
offspring
of
male
called
motility.
egg
type
allele
so
produce
gametes
is
the
their
each
one
and
one.
than
on
of
to
sometimes
size
not
volume
together
are
female
chromosome
therefore
fuse
They
different
smaller
much
that
life.
Figure 4 Pollen on the anthers of a ower
gamete
contains the male gamete of the plant. The
male
equal
male gametes contain one allele of each of
genetic
the plants
contribution
to
their
offspring,
despite
being
very
different
in
overall
size.
Zygoe
Fusion of gametes results in diploid zygotes with two
alleles of each gene that may be the same allele or
dierent alleles.
When
the
male
and
chromosomes
each
If
female
chromosome
of
each
The
type
so
fuse,
their
nucleus
is
of
diploid.
nuclei
the
It
join
zygote
contains
there
were
of
Aa
Some
also
two
either
and
alleles
allele
or
of
a
one
gene,
of
A
and
a,
each.
The
three
the
zygote
two
doubling
two
alleles
of
possible
contain
two
combinations
are
aa.
genes
blood
could
possible
have
more
than
two
alleles.
For
example,
A
ABO
together,
contains
gene.
copies
AA,
gametes
number.
groups
in
humans
combinations
of
has
three
alleles:
I
the
gene
for
B
,
I
and
i.
This
gives
six
alleles:
A
●
three
with
two
of
●
three
with
two
different
the
same
allele,
I
A
alleles,
I
A
I
B
I
B
,
I
B
I
and
A
,
I
i
ii
B
and
I
i.
segregaio of allele
The two alleles of each gene separate into dierent
haploid daughter nuclei during meiosis.
During
nuclei.
meiosis
The
haploid
●
●
If
nuclei
two
a
copies
will
alleles
were
two
of
different
receive
either
every
alleles
one
of
of
copy
a
of
gamete
were
the
twice
two
to
copies
produce
of
each
four
gene,
haploid
but
the
one.
allele
one
divides
contains
only
one
receive
PP
,
nucleus
nucleus
contain
nuclei
If
diploid
diploid
gene
were
this
allele.
will
receive
present,
alleles
present,
or
each
the
For
one
copy
haploid
other
each
of
example,
of
if
the
the
P
.
nucleus
allele,
haploid
two
not
will
both.
For
Figure 5 Most crop plants are pure-bred strains
example,
if
the
two
alleles
were
Pp,
50 %
of
the
haploid
nuclei
would
with two of the same allele of each gene
receive
P
and
50%
would
receive
p.
171
3
G e n e t i c s
The
separation
of
alleles
into
different
nuclei
is
called
segregation.
It
TOK
breaks
up
existing
combinations
to
combinations
form
in
the
of
alleles
in
a
parent
and
allows
new
offspring.
Dd mende ate  eut fo
pubcaton?
In 1936,
the English statistician
Domia, receive ad co-domia allele
R.A. Fisher published an analysis
Dominant alleles mask the eects of recessive alleles but
of Mendel’s data. His conclusion
was that “the data of most, if not
all, of the experiments have been
falsied so as to agree closely with
Mendel’s expectations.” Doubts still
persist about Mendel's data
– a
recent estimate put the chance of
co-dominant alleles have joint eects.
In
each
plant,
the
of
all
other.
pea
plant,
the
Mendel’s
of
the
For
all
parents
example,
the
is
seven
offspring
crosses
showed
in
a
offspring
due
to
one
between
the
cross
were
gene
between
tall.
with
different
character
The
two
a
of
tall
varieties
one
pea
difference
of
the
plant
in
of
pea
parents,
and
height
a
not
dwarf
between
alleles:
getting seven ratios as close to 3:1 as
●
the
●
the
●
they
tall
parents
have
two
copies
of
an
allele
that
makes
them
tall,
TT
Mendel’s at 1 in 33,000.
1
dwarf
parents
have
two
copies
of
an
allele
that
makes
them
dwarf,
tt
To get ratios as close to 3:1 as
Mendel's would have required a
“miracle of chance”. What are the
of
each
each
pass
allele,
on
one
allele
to
the
offspring,
which
therefore
has
one
Tt
possible explanations apar t from a
●
when
the
two
alleles
are
combined
in
one
individual,
it
is
the
allele
miracle of chance?
for
2
Many distinguished scientists,
is
tallness
that
determines
the
height
because
the
allele
for
tallness
dominant
including Louis Pasteur, are
●
the
other
allele,
that
does
not
have
an
effect
if
the
dominant
allele
is
known to have discarded results
present,
is
recessive.
when they did not t a theory. Is it
acceptable to do this? How can we
In
distinguish between results that
was
are due to an error and results that
effect
falsify a theory? What standard do
well-known
you use as a student in rejecting
plant
each
of
Mendel’s
recessive.
when
is
crosses
However,
they
are
present
example
crossed
with
one
some
is
a
the
of
the
genes
together.
ower
alleles
have
They
colour
white-owered
was
pairs
are
of
dominant
of
alleles
called
Mirabilis
plant,
the
and
where
the
co-dominant
jalapa.
offspring
If
a
have
other
both
have
alleles.
an
A
red-owered
pink
owers.
anomalous data?
R
●
there
is
an
allele
for
red
●
there
is
an
allele
for
white
●
these
alleles
owers,
C
W
owers,
C
R
The
a
usual
protein
allele
are
reason
that
codes
is
for
co-dominant
for
dominance
active
a
and
so
of
carries
non-functional
C
one
out
W
C
a
gives
allele
is
172
that
function,
protein.
Figure 6 There are co-dominant alleles of the gene for coat
colour in Icelandic horses.
pink
owers.
this
allele
whereas
the
codes
for
recessive
3 . 4
i N h E r i T A N C E
parents:
Pue grid
genotype
tt
TT
phenotype
dwarf stem
tall stem
Construction of Punnett grids for predicting the
outcomes of monohybrid genetic crosses.
Monohybrid
height
with
two
of
a
two
of
crosses
pea
only
plant,
so
pure-breeding
the
produces
same
just
allele,
one
involve
they
parents.
not
type
of
one
involve
two
character,
only
This
means
different
gamete,
one
for
that
alleles.
containing
example
gene.
Most
the
parents
Each
one
the
parent
copy
of
eggs or pollen
crosses
T
t
start
have
therefore
the
allele.
F
hybrids genotype
Tt
1
Their
offspring
are
also
identical,
although
they
have
two
different
tall stem
phenotype
alleles.
The
offspring
obtained
by
crossing
the
parents
are
called
F
1
hybrids
or
the
F
generation.
different
alleles
of
the
gene,
so
they
can
each
g
two
g
have
1
s
hybrids
T
F
T
The
e
1
TT
produce
two
types
of
gamete.
If
two
F
hybrids
are
crossed
together,
1
or
if
an
F
plant
is
allowed
to
self-pollinate,
there
are
four
possible
1
outcomes.
after
the
cross
This
can
geneticist
between
two
be
shown
who
F
rst
plants
using
used
are
a
2
this
×
2
type
called
the
of
F
1
To
make
a
Punnett
table,
called
table.
The
a
Punnett
offspring
and
outcomes
overall
both
should
ratio
be
below
Tt
tall
of
a
tt
dwarf
generation.
2
grid
the
tT
tall
grid
as
clear
as
possible
the
gametes
should
be
▲
labeled
t
t
tall
alleles
and
shown
the
on
the
the
Punnett
character
grid.
It
is
of
the
also
four
useful
Figure 7 Explanation of Mendel’s 3:1 ratio
possible
to
give
an
grid.
parents:
Figure
7
shows
Mendel’s
cross
between
tall
and
dwarf
plants.
It
R
genotype
explains
the
F
ratio
of
three
tall
to
one
dwarf
plant.
phenotype
C
W
R
W
C
C
C
white owers
red owers
2
Figure
plants
8
shows
of
the
Mirabilis
results
jalapa.
of
It
a
cross
explains
between
the
F
red
ratio
and
of
white
one
red
owered
to
two
pink
2
R
F
hybrids genotype
C
1
phenotype
years
in
a
of
the
similar
20th
way
century,
to
those
many
of
crossing
Mendel.
The
experiments
French
geneticist
used
the
house
mouse,
Mus
musculus,
to
see
C
Cuénot
C
R
Lucien
whether
R
C
the
principles
that
Mendel
had
discovered
also
operated
in
red
C
crossed
normal
grey-coloured
mice
with
albino
mice.
R
C
animals.
W
He
The
hybrid
C
R
W
C
C
pink
mice
that
were
produced
were
all
grey.
These
grey
hybrids
were
W
together
and
produced
198
grey
and
72
albino
W
C
pink
C
crossed
e
early
done
W
C
pink owers
g
the
were
C
R
Data-baed queton: Coat colour in the house mouse
In
W
C
plant.
g
owered
s
white
C
one
R
to
W
C
offspring.
white
1
Calculate
your
2
3
ratio
between
grey
and
albino
offspring,
showing
working.
Deduce
two
the
the
colour
reasons
for
Choose
suitable
and
the
list
symbols,
[2]
of
your
together
of
that
is
due
to
a
recessive
allele,
for
the
[3]
alleles
combinations
with
alleles.
the
coat
Figure 8 A cross involving co-dominance
with
answer.
symbols
possible
combination
coat
▲
of
for
grey
alleles
colours
of
and
mice
associated
albino
using
with
coat
your
each
[3]
173
3
G e n e t i c s
4
Using
5
Punnett
grid,
explain
how
albino
mice
was
produced.
The
albino
mice
had
red
how
▲
a
and
one
gene
can
eyes
determine
the
observed
ratio
of
grey
[5]
in
addition
whether
to
the
white
mice
coats.
had
Suggest
grey
fur
Figure 9
and
black
eyes
or
white
fur
and
red
eyes.
[2]
Data-baed queton: The two-spot ladybird
Adalia
▲
Figure 10 F
bipunctata
called
ladybugs.
There
is
a
rarer
is
a
species
The
of
ladybird.
commonest
form
called
form
annulata.
In
of
North
this
Both
America
species
forms
are
is
ladybirds
known
shown
as
in
are
typica.
gure
9.
hybrid ospring
1
1
Compare
2
The
the
differences
gene.
If
male
offspring
annulata
are
When
is
annulata
the
female
typica.
are
that
typica
and
between
and
forms
conclusions
3
typica
two
typica
Similarly,
mated
can
be
mated
forms
are
forms
are
the
all
of
Adalia
are
mated
due
bipunctata.
to
a
together,
offspring
annulata.
single
all
produced
Explain
[2]
the
when
the
drawn.
with
[2]
annulata,
the
F
hybrid
offspring
are
1
not
▲
Figure 11 F
identical
to
either
parent.
Examples
of
these
F
hybrid
1
ospring
2
offspring
are
shown
in
gure
10.
Distinguish
between
the
F
1
hybrid
offspring
and
the
typica
and
annulata
parents.
[3]
Actvt
4
If
F
hybrid
offspring
are
mated
with
each
other,
the
offspring
1
ABO bood goup
include
It is possible for two parents to have
the
both
same
typica
wing
and
case
annulata
markings
as
forms,
the
F
and
also
hybrid
offspring
with
offspring.
1
an equal chance of having a child with
a)
Use
a
genetic
b)
Predict
diagram
to
explain
this
pattern
of
inheritance.
[6]
blood group A, B, AB or O. What would
be the genotypes of the parents?
the
expected
ratio
of
phenotypes.
[2]
ABO blood group
Inheritance of ABO blood groups.
A
The
ABO
example
blood
of
nd
out
system
co-dominance.
importance:
to
group
before
the
blood
blood
It
is
in
is
humans
of
great
of
a
an
medical
transfused,
group
is
it
patient
is
vital
recessive
alleles
being
that
it
is
matched.
Unless
this
is
may
be
complications
due
to
being
I
B
and
I
.
co-dominant
recessive
are
as
The
and
reasons
the
for
other
two
allele
follows:
All
of
the
three
alleles
cause
the
production
of
done,
a
there
both
and
●
ensure
to
glycoprotein
in
the
membrane
of
red
blood
coagulation
cells.
of
red
blood
cells.
One
gene
determines
the
ABO
A
A
blood
group
of
a
person.
The
genotype
B
blood
group
A
and
the
genotype
I
I
A
●
I
gives
gives
group
B
I
I
alters
the
glycoprotein
galactosamine.
This
by
altered
addition
of
acetyl-
glycoprotein
is
A
A
B.
Neither
I
B
nor
I
is
dominant
over
the
A
allele
a
and
a
different
person
blood
with
group,
the
genotype
called
AB.
I
absent
other
B
I
so
has
There
is
a
allele
of
the
ABO
blood
group
gene,
exposed
i.
A
person
with
the
genotype
ii
is
I
alters
in
A
O.
The
genotypes
I
174
A
and
B
they
not
make
have
anti-A
the
allele
I
antibodies.
the
glycoprotein
This
altered
by
addition
glycoprotein
of
is
not
B
in
people
who
do
not
have
the
allele
I
B
i
and
I
i
give
blood
so
groups
it
do
blood
present
group
to
who
usually
galactose.
called
people
B
●
third
if
from
respectively,
showing
that
i
is
if
exposed
to
it
they
make
anti-A
antibodies.
3 . 4
A
●
The
be
genotype
altered
by
I
B
i N h E r i T A N C E
A
I
causes
addition
of
the
glycoprotein
either
to
acetyl-galactosamine
the
of
the
I
B
or
glycoprotein
I
is
alleles
is
altered
also
by
present
addition
A
and
galactose.
anti-A
nor
As
a
anti-B
consequence
antibodies
neither
are
acetyl-galactosamine
produced.
therefore
give
the
or
same
galactose.
I
phenotype,
of
A
I
A
and
as
do
I
i
B
B
I
I
B
This
genotype
therefore
A
phenotype
to
I
A
gives
B
I
and
I
a
different
B
I
and
I
i
The
allele
A
so
the
alleles
I
and
●
i
is
recessive
because
it
does
not
B
I
are
co-dominant.
A
cause
the
production
of
a
glycoprotein.
I
A
I
A
●
The
allele
i
is
recessive
because
it
and
causes
I
i
do
I
therefore
B
production
of
the
basic
glycoprotein:
if
so
B
I
give
I
same
phenotype
and
i
Group A
Group O
anti-A
anti-B
anti-A
anti-B
Group B
Group AB
anti-A
▲
the
B
and
anti-B
anti-A
anti-B
Figure 12 Blood group can easily be determined using test cards
teig predicio i cro-breedig experime
Comparison of predicted and actual outcomes of genetic crosses using real data.
It
is
in
the
principles
not
just
nature
that
to
of
science
explain
describe
to
natural
individual
try
to
nd
general
phenomena
examples
of
one
face
and
Mendel
discovered
showing
that
have
great
principles
predictive
can
still
use
them
to
predict
the
important
crosses.
Table
2
lists
outcomes
possible
predictions
actual
usually
outcomes
This
is
chance
involved
tossing
of
a
coin
of
genetic
exactly
because
in
is
the
a
crosses
with
there
the
is
coin
to
to
t,
either
the
element
of
analogy.
results,
genes.
We
of
The
due
land
50%
of
times
with
each
An
uppermost,
not
bi ol og y
of
an
is
d ecid ing
ex pe ri men t
pre d i cti o ns
the
resul ts
but
if
we
toss
it
1,000
expect
it
to
land
precisely
500
obvio us
difference
to
for
us
to
ar e
c l os e
a cc e pt
d iffe r ence s
a re
t ha t
too
or
the
p re di ct i on s
gr e at
must
the
less
chance
predictions
do
tr e nd
bet w e e n
lik e l y
and
no t
tha t
the
t
is
tha t
ob se r ve d
the
mor e
the
the
and
g re a ter
e xpe c t e d
di ffe re nc e
l ik el y
t ha t
is
the
r e sul ts .
expect
of
its
assess
objectively
times
times
whether
results
t
two
statistical
tests
are
used.
For
genetic
we
crosses
do
in
whethe r
predictions,
faces
skil l
resul ts
the
or
false.
the
not
predicted
an
inheritance
simple
do
To
the
the
crosses.
correspond
outcomes.
other
in
be
The
the
of
and
monohybrid
with
power.
they
genetic
times
of
enough
We
500
showing.
whether
inheritance
and
a
An
phenomenon.
face
the
chi-squared
test
can
be
used.
This
test
with
is
described
later
in
the
book
in
sub-topic
4.1.
175
3
G e n e t i c s
Co
Pedcted outcoe
Exape
Pure-breeding parents one with
All of the ospring will have the same
All ospring of a cross between pure-
dominant alleles and one with
character as the parent with dominant
breeding tall and dwarf pea plants
recessive alleles are crossed.
alleles.
will be tall.
Pure-breeding parents that have
All of the ospring will have the same
All ospring of a cross between red
dierent co-dominant alleles
character and the character will be
and white owered Mirabilis jalapa
are crossed.
dierent from either parent.
plants will have pink owers.
Two parents each with one
Three times as many ospring have
3:1 ratio of tall to dwarf pea plants
dominant and one recessive
the character of the parent with
from a cross between two parents
allele are crossed.
dominant alleles as have the character
that each have one allele for tall
of the parent with the recessive
height and one allele for dwarf
alleles.
height.
A parent with one dominant and
Equal propor tions of ospring with
1:1 ratio from a cross between a
one recessive allele is crossed
the character of an individual with a
dwarf pea plant and a tall plant with
with a parent with two recessive
dominant allele and the character of
one allele for tall height and one for
alleles.
an individual with recessive alleles.
dwarf height .
T
able 2
Data-baed queton: Analysing genetic crosses
1
Charles
majus
pure
Darwin
plants,
breeding
symmetric.
cr o s s e d
which
pla nts
All
the
pure
hav e
w ith
F
bre e din g
b i l ate ra l ly
pe lo ri c
offspring
wil d- t ype
s ymm et ri c
o w e r s
produced
t h at
Antirrhinum
owe rs ,
a re
wit h
r a di al l y
b i l a ter a ll y
sy m m et r i c
1
owers.
Darwin
the n
cro ss e d
the
F
plants
together.
In
the
F
1
generation
owers
Figure 13 Antirrhinum owers –
there
and
37
were
with
88
p la nts
p e l or ic
2
wi t h
bi la t e ra ll y
s ym m et r i c
owe rs.
(a) wild type, (b) peloric
a)
Construct
between
a
Punnett
the
F
grid
to
predict
the
outcome
of
the
cross
plants.
[3]
1
b)
Discuss
whether
enough
c)
Peloric
to
There
are
called
light,
together,
three
only
buff
pheasants
a)
crossed
Discuss
enough
176
a
with
of
and
141
the
support
all
cross
close
[2]
feather
offspring
buff
there
rare
for
pheasants
produced.
the
are
extremely
reasons
with
light
with
[1]
bred
Similarly,
were
wild
coloration
were
were
in
this.
ring.
75
when
When
light
to
predict
the
outcome
of
pheasants.
actual
the
are
Suggest
were
the
buff.
grid
buff
of
outcome.
pheasant
ring,
Punnett
whether
plants
When
crossed
together
to
majus
species.
buff.
results
predicted
offspring
were
ring
Construct
breeding
b)
and
light
were
68
this
varieties
ring
ring
offspring,
of
actual
the
Antirrhinum
populations
2
the
support
results
predicted
[3]
of
the
cross
outcome.
are
close
[2]
3 . 4
3
Mary
and
character
of
the
are
Herschel
called
fungus
shown
Mitchell
poky
grow
in
the
more
table
mae paent
in
investigated
fungus
slowly
the
inheritance
Neurospora
than
the
crassa.
wild-type.
of
Poky
The
i N h E r i T A N C E
a
strains
results
3.
Feae paent
Wild type
Wild type
Poky
Nube of wd
Nube of pok
tpe opng
opng
9,691
90
Poky
0
10,591
Wild type
Poky
0
7,905
Poky
Wild type
4,816
43
T
able 3
a)
Discuss
table
b)
1
whether
(page
Suggest
a
between
male
c)
data
ts
any
of
the
Mendelian
ratios
in
reason
wild
[2]
for
type
all
the
and
offspring
poky
strains
being
when
poky
a
in
wild
a
cross
type
is
the
parent.
Suggest
cross
is
the
170).
a
[2]
reason
between
the
female
for
wild
a
small
type
number
and
poky
of
poky
strains
offspring
when
a
in
wild
a
type
parent.
[1]
Figure 14 Feather coloration from a bu pheasant
Geeic dieae due o receive allele
Many genetic diseases in humans are due to recessive
alleles of autosomal genes.
A
genetic
diseases
only
usually
person
has
will
recessive
Genetic
in
as
this.
one
not
allele
they
do
illness
a
allele
to
they
for
that
have
the
by
a
parents
show
probability
of
of
do
a
the
have
gene.
the
of
disease
of
a
gene.
but
recessive
one
allele
the
a
can
are
pass
called
If
the
a
allele,
on
the
carriers.
Aa
must
they
child
of
allele.
appear
disease
disease,
having
therefore
allele
dominant
they
usually
the
genetic
disease
dominant
individuals
with
Most
The
the
and
disease,
child
parents
by
a
copies
These
symptoms
of
not
recessive
of
these
caused
two
offspring.
caused
Both
is
allele
genetic
symptoms
their
not
that
recessive
individuals
show
diseases
The
an
by
because
unexpectedly.
but
is
caused
develops
gene,
they
disease
are
are
with
be
unaware
the
Aa
carriers,
disease
of
is
25
a
per
cent
caused
(see
by
a
gure
15).
recessive
Cystic
allele.
It
brosis
is
is
an
described
example
later
in
of
this
a
genetic
A
disease
sub-topic.
Oher caue of geeic dieae
AA
Aa
aA
aa
not carrier
Some genetic diseases are sex-linked and some are due
carrier
to dominant or co-dominant alleles.
A
small
It
is
not
proportion
possible
dominant
allele
to
of
genetic
be
then
a
diseases
carrier
they
of
are
these
themselves
caused
diseases.
will
do not develop the disease
by
If
develop
a
a
dominant
person
the
has
disease.
allele.
one
If
one
develops the genetic disease
▲
Figure 15 Genetic diseases caused
by a recessive allele
177
3
G e n e t i c s
Bb
parent
bb
is
50
has
per
genetic
b
the
cent
allele
(see
disease
for
the
gure
caused
disease,
16).
by
a
A
very
small
alleles.
An
disease
dominant
proportion
example
was
is
of
genetic
sickle-cell
is
bb
does not develop
Hb
a
It
is
child
is
an
inheriting
example
described
later
of
in
it
a
this
described
in
diseases
sub-topic
3.1.
possible
the
sickle
cell
combinations
allele
of
is
alleles
the disease
The
Hb
and
.
caused
by
molecular
normal
Figure
the
co-dominant
basis
allele
that
characteristics
have
as
one
those
for
of
this
hemoglobin
shows
the
three
that
result.
S
Hb
who
17
characteristics
A
Figure 16 Genetic diseases caused
are
The
S
and
Individuals
▲
of
disease
allele.
anemia.
A
Bb
disease
chance
sub-topic.
b
develops the
the
Huntington’s
and
have
one
two
Hb
allele
copies
of
do
not
either
have
allele,
the
so
same
the
by a dominant allele
alleles
Most
some
This
are
co-dominant.
genetic
show
is
diseases
a
called
red-green
affect
different
sex
males
pattern
linkage.
The
colour-blindness
of
and
inheritance
causes
and
females
of
sex
in
in
the
males
linkage
hemophilia,
same
are
and
and
way
but
females.
two
described
examples,
later
in
this
sub-topic.
A
A
alleles : Hb
A
Hb
alleles : Hb
s
Hb
S
alleles : Hb
S
Hb
characteristics :
characteristics :
characteristics :
- susceptible to
- increased resistance
- susceptible to malaria
malaria
- severe anemia
to malaria
- not anemic
- mild anemia
normal red blood
sickle-cell shape
cell shape
A
Figure 1
7 Eects of Hb
▲
S
and Hb
alleles
Cyic broi ad Huigo’ dieae
Inheritance of cystic brosis and Huntington’s disease.
Cystic
brosis
in
parts
of
the
of
CFTR
channel
mucus
the
gene.
chromosome
ion
is
Europe.
and
7
is
This
and
that
commonest
It
is
the
due
to
gene
digestive
is
gene
involved
a
genetic
located
product
in
disease
recessive
allele
a
secretion
mucus
and
on
is
secretions,
chloride
of
sweat,
recessive
chloride
alleles
channels
function
properly.
up
pancreatic
enzymes
reach
the
them
in
the
very
lungs
duct
is
usually
secreted
small
viscous.
causing
by
the
Sticky
infections
blocked
of
of
this
being
gene
result
produced
Sweat
sodium
do
intestine.
that
containing
do
some
have
in
not
excessive
is
an
parts
recessive,
have
of
allele
any
a
Europe
for
cystic
single
effects.
one
copy
The
in
twenty
brosis.
of
the
chance
of
As
people
the
allele
two
allele
does
chloride
is
produced,
but
both
being
a
carrier
of
the
allele
not
parents
1
__
amounts
so
pancreas
juices.
In
The
the
digestive
not
making
builds
is
1
__
×
20
,
20
1
___
digestive
juices
and
mucus
are
secreted
with
which
is
.
The
chance
of
such
parents
having
400
insufcient
enough
178
sodium
water
chloride.
moves
by
As
a
osmosis
result
into
not
the
a
child
with
Punnett
cystic
grid.
brosis
can
be
found
using
a
3 . 4
Because
father
Cc
with
of
late
Huntington’s
children.
A
symptoms
C
the
i N h E r i T A N C E
onset,
many
disease
have
genetic
would
test
can
develop
people
diagnosed
already
show
had
before
whether
a
young
c
person
at
risk
has
the
choose
dominant
not
to
allele,
have
the
but
most
people
test.
Cc
CC
C
About
normal
one
in
10,000
people
have
a
copy
of
normal
(carrier)
the
mother Cc
for
cC
c
cc
Huntington’s
two
can
normal
cystic
(carrier)
brosis
one
parents
both
nonetheless
of
their
allele,
to
so
is
have
develop
parents
it
has
the
the
a
very
unlikely
copy.
disease
allele
A
if
person
only
because
it
is
dominant.
ratio 3 normal : 1 cystic brosis
father
Hh
Huntington’s
allele
of
the
HTT
chromosome
named
still
disease
4
gene.
and
huntingtin.
being
is
due
This
the
to
dominant
gene
gene
The
a
is
located
product
function
of
is
a
on
protein
huntingtin
H
h
is
researched.
Hh
hh
h
The
dominant
allele
of
HTT
causes
Huntington’s
normal
degenerative
disease
changes
in
the
brain.
Symptoms
usually
start
mother hh
when
a
person
is
between
30
and
50
years
old.
Hh
hh
Changes
to
behaviour,
thinking
and
emotions
h
Huntington’s
normal
become
the
increasingly
start
of
severe.
symptoms
is
Life
about
expectancy
20
years.
A
after
disease
person
ratio 1 normal : 1 Huntington’s disease
with
and
or
the
disease
usually
some
eventually
succumbs
other
to
infectious
needs
heart
full
nursing
failure,
care
pneumonia
disease.
sex-liked gee
The pattern of inheritance is dierent with
sex-linked genes due to their location on sex
chromosomes.
Plants
such
female
which
same
●
pea
were
in
When
plants
the
the
are
in
same
female
hermaphrodite
Thomas
the
late
Andrew
18th
whichever
gamete.
–
For
they
can
Knight
century,
character
example,
he
was
produce
did
crossing
discovered
in
these
both
the
two
the
gamete
crosses
and
experiments
that
male
male
gave
and
the
results:
pollen
plant
●
peas
gametes.
between
results
as
with
pollen
plant
from
plant
purple
from
with
a
a
green
stems
placed
onto
on
the
stigma
of
a
stems;
plant
green
with
with
purple
stems
placed
onto
on
the
stigma
of
a
stems.
179
3
G e n e t i c s
Plants
white eye
r
X
red eye
r
are
always
carried
give
out,
the
but
same
in
results
animals
the
when
reciprocal
results
are
crosses
sometimes
such
as
different.
these
An
R
X
X
Y
inheritance
X
r
X
One
r
X
sex
pattern
where
the
ratios
are
different
in
males
and
females
is
linkage
R
called
of
the
rst
examples
of
sex
linkage
was
discovered
by
Thomas
R
X
Morgan
the
fruit
y,
Drosophila.
This
small
insect
is
about
4
mm
long
X
Y
r
red
in
r
r
X
R
X
X
and
Y
completes
its
life
cycle
in
two
weeks,
allowing
crossing
experiments
white
red
to
be
done
quickly
with
large
numbers
of
ies.
Most
crosses
in
Drosophila
r
Y
X
do
not
show
sex
linkage.
For
example,
these
reciprocal
crosses
give
the
white
same
red eye
R
X
white eye
R
results:
●
normal-winged
●
vestigial-winged
males
×
males
vestigial-winged
×
females;
normal-winged
females.
r
X
X
Y
These
gave
different
●
red-eyed
●
white-eyed
males
white-eyed
males.
males
×
results:
white-eyed
females
gave
only
red-eyed
×
females
gave
red-eyed
offspring;
r
R
X
crosses
X
R
X
R
X
red-eyed
females
and
X
Y
R
red
R
X
r
R
X
X
red
Y
red
Geneticists
had
obs e r v e d
tha t
the
inhe ri t a n c e
of
g e n es
an d
of
R
X
Y
chromosomes
sho we d
cle a r
pa r a ll el s
and
so
g en e s
wer e
l ik e ly
to
be
red
located
have
on
two
chromo s o me s .
copies
of
a
It
wa s
a l so
chro mos ome
kn o wn
c a l le d
X
t ha t
an d
fe m a l e
m al e s
Drosophila
on l y
h ave
one
Key
copy.
R
X
Morgan
ded uce d
that
se x
li nka g e
of
eye
c o lo u r
cou ld
t h e r efor e
X chromosome with allele
be
for red eye (dominant)
due
to
the
eye
co l o ur
g e ne
b ei n g
lo c a t ed
on
the
X
ch r om o so m e .
r
X
X chromosome with allele
Male
Drosophila
also
have
a
Y
chro mo s ome ,
but
th i s
do es
not
ca r ry
for white eye (recessive)
the
Y
eye-colour
Y chromosome
Figure
▲
ge ne .
18
explains
the
inheritance
of
eye
colour
in
Drosophila.
In
crosses
Figure 18 Reciprocal sex-linkage
involving
sex
linkage,
the
alleles
should
always
be
shown
as
a
superscript
crosses
letter
on
should
a
letter
also
be
X
to
represent
shown
though
it
the
X
does
chromosome.
not
carry
an
The
allele
Y
of
chromosome
the
gene.
Red-gree colour-blide ad hemophilia
Red-green colour-blindness and hemophilia as examples of sex-linked inheritance.
Many
examples
discovered
to
genes
are
very
X
of
few
of
genes
recessive
cone
specic
They
the
on
X
the
allele
cells
of
a
the
wavelength
all
Y
as
chromosome.
described
due
to
here:
due
there
Two
genes
on
red-green
hemophilia.
gene
proteins.
in
been
almost
conditions
are
and
have
are
chromosome,
colour-blindness
photoreceptor
by
on
chromosomes
Red-green
linkage
sex-linked
colour-blindness
a
sex
humans.
located
examples
the
in
is
caused
for
one
These
retina
of
ranges
the
proteins
the
of
of
by
eye
visible
are
and
made
detect
light.
▲
Figure 19 A person with red-green colour-blindness cannot clearly
distinguish between the colours of the owers and the leaves
180
3 . 4
proteins
involved
expectancy
is
is
untreated.
puried
The
only
for
the
recessive.
allele
is
be
of
carriers
they
The
only
1
in
by
of
VIII
the
In
theoretically
practice,
girls
▲
with
is
there
(
the
hemophilia
VIII,
the
if
X
hemophilia
hemophilia
therefore
Females
both
The
the
can
allele
of
but
their
X
frequency
in
2
=
)
been
due
Factor
hemophilia
allele.
10,000
have
Life
hemophilia
on
is
boys.
disease
the
if
causes
This
1
_____
girls
years
of
in
recessive
carry
blood.
infusing
located
that
10,000.
the
of
donors.
is
allele
disease
develop
chromosomes
ten
frequency
the
of
clotting
is
blood
The
about
frequency
the
about
Factor
chromosome.
is
in
Treatment
from
gene
i N h E r i T A N C E
to
1
in
even
lack
100,000,000.
fewer
of
cases
Factor
of
VIII
Figure 20 Blood should stop quickly owing from a pricked
than
this.
One
reason
is
that
the
father
would
nger but in hemophiliacs bleeding continues for much longer
have
as blood does not clot properly
on
Males
have
inherit
only
from
one
their
X
chromosome,
mother.
If
that
X
which
to
the
be
hemophiliac
condition
to
his
and
decide
to
risk
passing
children.
they
H
chromosome
h
X
H
X
X
Y
KE Y
H
carries
the
the
son
red-green
will
be
colour-blindness
red-green
allele
colour-blind.
In
then
X
X chromosome carrying
the allele for normal
parts
blood clotting
of
northern
Europe
the
percentage
of
males
with
h
h
this
disability
is
as
high
as
8 %.
Girls
are
H
X
red-green
H
X
X
Y
X
X chromosome carrying
the allele for hemophilia.
blind
and
carrying
if
their
they
the
also
father
is
inherit
recessive
red-green
an
gene
X
colour-
chromosome
from
their
mother.
predict
that
the
percentage
of
girls
X
can
X
H
We
with
H
H
X
colour-blindness
in
the
same
parts
of
Europe
to
H
colour-blind
X
be
normal
8%
=
0.64%.
The
actual
percentage
is
about
X
Y
×
h
8%
0.5%,
tting
this
prediction
H
well.
X
h
H
X
X
Whereas
red-green
disability,
colour-blindness
hemophilia
is
a
is
a
mild
life-threatening
genetic
h
X
disease.
the
to
Although
disease,
an
most
inability
to
there
cases
are
of
make
some
rarer
hemophilia
Factor
VIII,
forms
are
one
Y
normal
carrier
of
Y
hemophiliac
due
of
the
Pedigree char
Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
It
isn’t
possible
genetic
experiments.
to
to
diseases
deduce
investigate
in
humans
Pedigree
the
pattern
charts
of
the
by
inheritance
carrying
can
be
out
used
inheritance.
●
of
cross
instead
These
are
conventions
for
constructing
pedigree
to
affected
by
males
are
shown
as
females
are
shown
are
the
shaded
whether
or
an
cross-
individual
is
disease;
parents
top
and
bar
children
of
the
T
are
linked
between
using
the
a
T,
with
parents;
squares;
●
●
circles
indicate
charts:
the
●
and
hatched
the
●
usual
squares
as
Roman
numerals
indicate
generations;
circles;
181
3
G e n e t i c s
●
Arabic
each
numbers
are
used
for
individuals
their
in
generation.
children
expect
large
Example 1 Albinism in humans
1
in
see
will
that
numbers
2
that
to
is
not
our
of
be
if
unexpected
are
we
the
children.
deductions
albinism
albino,
ratio
The
and
about
could
parents
actual
does
the
only
had
very
ratio
not
of
show
inheritance
of
incorrect.
generation I
1
2
Example 2 Vitamin D-resistant rickets
Deductions:
●
generation II
1
2
3
4
Two
unaffected
children
but
children
with
suggesting
Key:
dominant
parents
two
vitamin
that
only
affected
this
have
parents
D-resistant
disease
is
unaffected
have
rickets,
caused
by
a
allele.
normal pigmentation
●
The
are
albino
offspring
all
This
Deductions:
of
suggests
offspring
Two
of
the
parents
both
suggests
allele
children
that
(m)
dominant
have
are
normal
albinism
and
is
normal
allele
albino
and
yet
by
a
pigmentation
This
●
recessive
by
If
vitamin
dominant
a
father
(M).
There
are
both
daughters
and
sons
of
suggesting
that
the
condition
is
only
if
Both
they
albinism
have
allele
males
two
and
females
copies
of
the
in
his
are
data
The
albino
(mm).
children
●
Similarly
have
inherited
for
albinism
from
both
Both
parents
must
also
have
one
allele
pigmentation
parents
therefore
as
they
have
The
chance
are
the
not
of
is
.
a
child
of
Although
these
on
parents
average
1
having
in
4
of
data
the
Key:
vitamin D-resistant rickets
not aected
182
caused
would
the
would
inherit
the
a
the
his
dominant
have
by
of
X
allele,
so
disease.
in
the
pedigree
shows
that
this
and
the
theory.
if
by
vitamin
a
D-resistant
dominant
with
the
rickets
X-linked
disease
in
allele,
generation
is
the
have
one
X
chromosome
II
carrying
the
allele
recessive
for
the
allele.
disease
All
of
her
and
one
offspring
have
a
50%
chance
of
inheriting
this
Mm.
4
▲
is
daughters
albino.
alleles
1
albinism
I
carrying
daughters
chromosome
●
rickets
allele,
generation
dominant
would
The
number
the
for
with
normal
the
of
parents.
the
●
sure
an
would
allele
D-resistant
X-linked
supports
caused
must
be
albino
recessive
mother
●
although
to
I
sons.
not
so
sex-linked.
small
generation
unaffected
with
This
albinism
linkage
too
in
and
pattern.
chromosome
all
●
parents
the
pigmentation.
caused
the
daughters
sex
is
inheritance
●
of
affected
Figure 2
1 Pedigree of a family with cases of vitamin D-resistant rickets
in
the
theory.
and
of
pedigree
having
ts
this
the
disease.
and
so
The
supports
X
3 . 4
i N h E r i T A N C E
Data-baed queton: Deducing genotypes from pedigree char ts
The
pedigree
chart
in
I
gure22
shows
ve
1
generations
of
a
2
3
4
family
II
affected
by
a
genetic
disease.
1
1
Explain,
using
2
3
4
5
6
7
9
8
10
11
12
13
14
15
evidence
III
from
the
pedigree,
1
whether
2
3
4
the
IV
condition
is
due
to
a
1
recessive
or
a
2
3
4
5
6
7
8
dominant
V
allele.
[3]
?
1
?
?
?
2
3
4
unaected male
unaected female
2
Explain
what
the
aected male
probability
is
of
the
aected female
individuals
generation
a)
two
in
V
copies
recessive
b)
having:
one
of
▲
Figure 22 Example of a pedigree char t
a
allele;
recessive
3
and
one
Deduce,
dominant
a)
1
in
b)
13
with
reasons,
generation
the
possible
alleles
of:
III;
allele;
c)
two
copies
of
the
in
generation
II.
[2]
dominant
4
allele.
Suggest
two
examples
of
genetic
diseases
that
[3]
would
t
this
inheritance
pattern.
[2]
Geeic dieae i huma
Many genetic diseases have been identied in humans
but most are very rare.
Several
genetic
including
disease.
(PKU),
There
research
more
genetic
from
no
any
of
by
inheritance.
small
chance
It
is
but
of
now
rare
cause
to
75
genome.
An
to
reason
of
the
disease
that
the
individual
can
that
that
one
as
sub-topic,
Huntington’s
phenylketonuria
large
most
most
of
genetic
us
do
not
must
any
be
of
suffer
diseases
Mendelian
for
diseases
number
genetic
follow
alleles
4,000
this
allele
a
genome
and
large
This
typical
Current
alleles
is
than
Given
which
two
such
this
and
are
patterns
specic
of
disease
inherited
and
the
small.
comparisons.
200
this
inheriting
quickly
alleles
more
surprising
for
in
hemophilia
syndrome.
found.
alleles
sequence
and
disease.
and
be
described
examples,
identied
to
recessive
been
brosis,
Marfan’s
seem
extremely
allow
genetic
between
might
chance
cheaply
to
and
already
The
already
cystic
well-known
remain
develop
is
recessive
a
it
rare
The
this
sequenced
of
has
possible
relatively
other
them.
very
have
anemia,
disease
doubt
diseases,
caused
is
are
Tay-Sachs
Medical
and
diseases
sickle-cell
only
an
research
individual
estimates
among
of
the
individual
numbers
are
a
is
or
child
human
humans
revealing
carrying
that
25,000
produce
is
of
the
so
that
number
genes
with
are
the
a
in
could
is
the
genetic
being
number
▲
human
disease
Figure 23 Alleles from two parents come
together when they have a child. There is a
small chance that two recessive alleles will
come together and cause a genetic disease
due
the
to
one
same
of
rare
these
recessive
alleles
if
the
other
parent
of
the
child
has
allele.
183
3
G e n e t i c s
Caue of muaio
Radiation and mutagenic chemicals increase the mutation
rate and can cause genetic disease and cancer.
A
gene
consists
hundreds
▲
or
of
a
length
thousands
of
of
DNA,
bases
with
long.
a
The
base
sequence
different
that
alleles
of
can
a
be
gene
have
Figure 24 Abraham Lincoln’s features
slight
variations
in
the
base
sequence.
Usually
only
one
or
a
very
small
resemble Marfan’s syndrome but a more
number
of
bases
are
different.
New
alleles
are
formed
from
other
alleles
recent theory is that he suered from MEN2B,
by
gene
mutation.
another genetic disease
A
mutation
types
●
of
is
factor
Radiation
cause
from
can
increases
are
all
tobacco
First
Mutations
mutation
be
benecial.
harmful.
a
cell
to
Mutations
eliminated
into
Almost
diseases.
It
Figure 25 The risk of mutations due to
of
radiation from nuclear waste is minimized
estimates
by careful storage
humans,
is
mutations
of
body
can
cause
of
of
a
gene.
Two
if
it
has
enough
rays
and
ultraviolet
energy
alpha
to
particles
radiation
and
chemical
changes
gas
used
and
as
a
in
DNA
and
nitrosamines
chemical
so
are
found
weapon
in
the
–
there
random
perhaps
mutations
the
genes
and
adding
cells,
are
that
including
individual
passed
one
to
no
mechanism
millions
to
of
into
a
an
is
either
cell
for
allele
years
therefore
control
develop
on
those
dies,
to
particularly
or
the
two
risk
new
of
that
but
a
particular
that
has
unlikely
neutral
division
tumour.
cause
can
to
or
cause
Mutations
This
important
cells
in
is
to
the
mutations
genetic
cancer,
mutations
offspring.
gamete-producing
that
is
change
are
cancer.
the
be
A
over
all
therefore
in
are
rate
Gamma
benzo[a]pyrene
mustard
out.
endlessly
when
gametes
sequence
rate.
short-wave
changes
evolution
cause
in
are
and
carried
Mutations
a
mutation
DNA.
substances
random
divide
therefore
▲
by
in
base
War.
being
developed
the
mutation
isotopes,
smoke
are
the
changes
Examples
World
the
to
mutagenic.
chemical
mutagenic.
change
increase
radioactive
Some
in
random
chemical
X-rays
●
a
the
in
are
cells
that
origin
minimize
ovaries
occur
diseases
in
and
each
of
the
develop
genetic
number
testes.
Current
generation
in
children.
Coequece of uclear bombig ad accide a uclear
power aio
Consequences of radiation after nuclear bombing of Hiroshima and Nagasaki and
the nuclear accidents at Chernobyl.
The
of
common
Hiroshima
accidents
that
at
potentially
of
the
Nagasaki
Three
radioactive
environment
to
feature
and
Mile
Island
isotopes
and
as
a
nuclear
and
were
result
dangerous
the
and
levels
of
into
were
is
the
exposed
radiation.
has
the
atomic
b o mb s
we r e
de to na t e d
The
been
Effects
26,000
followed
people
2011
184
and
Na g a s a k i
have
the
d i r e ctl y
of
or
s i nce
we r e
be e n
us e d
survi v o r s
as
ha d
by
in
no t
a
fe w
1 00, 000
the n
Fo und atio n
who
wi thi n
nea r ly
the
Ra di a t io n
Jap a n .
ex po s ed
a
su r vivor s
co ntro l
de ve lo pe d
An ot h e r
to
gr oup.
17, 448
over
tumours,
Hiroshima
died
health
Research
radiation
By
When
either
months.
Chernobyl
released
people
people
bombing
nuclear
1 50, 00 0– 250 ,00 0
but
only
853
of
the s e
coul d
be
3 . 4
attributed
atomic
to
the
e f fe cts
of
r ad ia tion
fro m
the
into
the
atmosphere
widespread
bombs.
i N h E r i T A N C E
and
in
total.
The
effects
were
severe:
2
Apart
from
radiation
leading
cancer
that
to
the
was
other
main
predicted
stillbirths,
was
effect
of
the
●
mutations,
malformation
or
death.
of
10,000
children
that
were
fetuses
km
of
ginger
Horses
and
atomic
bombs
were
detonated
and
that
Nagasaki
been
found
There
but
has
are
the
were
born
been
monitored.
of
later
mutations
likely
to
number
is
have
too
in
Hiroshima
No
caused
been
small
for
by
it
and
evidence
some
even
with
the
large
the
be
Lynx,
cattle
their
eagle
around
radiation.
in
the
owl,
to
the
felt
the
that
of
evidence
bombs,
they
potential
were
wives
them
or
for
genetic
Bioaccumulation
of
mutations
survivors
stigmatized.
husbands
have
Some
were
of
due
found
reluctant
fear
that
their
children
lamb
accident
as
from
boar
and
thrive
from
other
in
which
a
wildlife
zone
humans
were
caused
caesium
in
high
sh
as
levels
far
of
away
that
and
Germany
was
banned
and
as
with
for
consumption
radioactive
some
time
as
far
away
Concentrations
of
radioactive
iodine
in
the
might
rose
and
resulted
in
drinking
diseases.
at
Chernobyl,
explosions
reactor.
Ukraine,
in
and
a
re
in
the
fatal
Workers
doses
of
at
the
core
plant
radiation.
and
milk
with
unacceptably
high
levels.
1986
of
More
than
6,000
cases
of
thyroid
cancer
a
been
reported
that
can
be
attributed
quickly
to
received
died
Wales.
have
nuclear
plant
glands.
to
●
involved
the
to
contaminated
caesium
sometimes
water
The
wild
started
environment
have
reactor
of
●
marry
the
study.
lack
atomic
of
died.
statistically
numbers
Scandinavia
Despite
near
thyroid
Chernobyl
radioactive
children
and
excluded.
mutations,
to
to
subsequently
has
●
signicant
downwind
brown
77,000
●
children
forest
when
damage
the
pine
turned
The
●
health
4
radioactive
iodine
released
during
the
Radioactive
accident.
isotopes
of
xenon,
krypton,
iodine,
caesium
and
●
tellurium
were
released
and
spread
over
According
Health,
parts
of
Europe.
other
About
radioactive
six
tonnes
metals
in
of
fuel
was
broken
up
into
small
explosions
particles
GBq
of
and
escaped.
radioactive
An
estimated
material
Legacy
Socio-Economic
was
is
produced
no
clearly
by
The
Chernobyl
demonstrated
Forum,
increase
in
by
cancers
or
leukemia
due
to
radiation
in
5,200
the
million
“Chernobyl’s
and
the
solid
the
report
uranium
from
there
reactor
the
Environmental
Impacts”,
and
to
large
most
affected
populations.
released
Incidence per 100,000 in Belarus
12
Actvt
adults (19–34)
Cangng ate of tod cance
10
adolescents (15–18)
When would you expect the cases
children (0–14)
000,001 rep sesaC
of thyroid cancer in young adults to
8
star t to drop, based on the data in
gure 26?
6
4
2
0
1984
▲
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
v
Figure 26 Incidence of thyroid cancer in Belarus after the Chernobyl accident
185
3
G e n e t i c s
Data-baed queton: The aftermath of Chernobyl
Mutations
6.7
at
due
4,000
Green
a
report
to
cancer
from
to
c a n c e r.
a
of
UN
the
1950
warheads.
It
as
at
was
gave
of
exposures,
of
the
an
among
those
published
by
an
“up
but
of
estimate
as
the
Nagasaki
to
in
leukemia
exposed
the
that
of
commissioned
such
due
of
station
d i s a s t e r,
estimate
and
deaths
release
numbers
stated
of
obtaining
Hiroshima
analysis
1990
Forum
The
power
large
Parliament
way
radiation
of
result
which
One
cell.
nuclear
cause
a
European
warheads
and
the
the
die
scientist,
an
tumour
Chernobyl
deaths.
is
a
from
therefore
previous
nuclear
below
become
ultimately
extra
from
of
data
these
The
may
to
material
radiation
between
Research
cell
was
members
data
The
a
1986
60,000
detonation
1945.
in
from
to
use
cause
radioactive
people”
Party
30,000
is
of
Chernobyl
deaths
to
can
tonnes
to
Radiation
and
radiation
Effects
Foundation.
radaton
Nube of deat
Etate of exce
doe ange
n peope expoed
deat ove conto
Pecentage of deat
attbutabe to
(sv)
to adaton
goup
adaton expoue
0.005–0.2
70
10
0.2–0.5
27
13
48
0.5–1
23
17
74
56
47
3391
63
2
0.2–0.5
646
76
12
0.5–1
342
79
23
308
121
39
Leukemia
▲
Figure 27 Humans have been excluded from
a large zone near the Chernobyl reactor. Some
>1
Cancer
plants and animals have shown deformities
0.005–0.2
that may be due to mutations
>1
1
Calculate
due
to
you
have
the
186
in
and
effect
due
with
acceptable
type
to
of
Sv
of
graph
the
to
There
radiation
control
0.005-0.02
groups
Sv
radiation.
or
table,
cancer
(a)
over
chart
to
[4]
represent
including
should
be
the
two
two
what
the
y-axes,
for
deaths
in
the
deaths.
on
data
percentages
[4]
due
to
leukemia
cancer.
reasons,
the
deaths
exposed
of
of
the
excess
>1
calculated.
Compare
Discuss,
(b)
column
deaths
deaths
of
people
suitable
leukemia
and
4
a
in
radiation
right-hand
that
3
of
Construct
the
percentage
leukemia
(sieverts)
2
the
[3]
level
environment.
of
radiation
might
be
[4]
3 . 5
G E N E T i C
m O D i F i C A T i O N
A N D
B i O T E C h N O l O G y
3.5 Genetc odcaton and botecnoog 
Uderadig
Applicaio
➔
Gel electrophoresis is used to separate proteins
Use of DNA proling in paternity and forensic
➔
or fragments of DNA according to size.
investigations.
➔
PCR can be used to amplify small amounts of DNA.
➔
DNA proling involves comparison of DNA .
➔
Genetic modication is carried out by gene
Gene transfer to bacteria with plasmids using
➔
restriction endonucleases and DNA ligase.
Assessment of the potential risks and benets
➔
transfer between species.
➔
associated with genetic modication of crops.
Clones are groups of genetically identical
Production of cloned embryos by somatic-cell
➔
organisms, derived from a single original
nuclear transfer.
parent cell.
➔
Many plant species and some animal species
skill
have natural methods of cloning.
➔
Design of an experiment to assess one factor
➔
Animals can be cloned at the embryo stage by
aecting the rooting of stem-cuttings.
breaking up the embryo into more than one
➔
group of cells.
➔
Analysis of examples of DNA proles.
Methods have been developed for cloning adult
➔
Analysis of data on risks to monarch butteries
animals using dierentiated cells.
of Bt crops.
naure of ciece
➔
Assessing risks associated with scientic research: scientists attempt to assess the risks associated
with genetically modied crops or livestock .
DNA samples
Gel elecrophorei
negative electrode
Gel electrophoresis is used to separate proteins or
sample well
fragments of DNA according to size.
Gel
electrophoresis
eld,
in
is
a
according
gel.
The
applied.
to
gel
is
involves
their
size
separating
and
immersed
Molecules
in
the
in
charged
charge.
a
that
molecules
Samples
conducting
sample
gel
are
are
uid
and
charged
in
placed
an
will
an
in
electric
wells
electric
move
cast
eld
through
1
the
gel.
Molecules
directions.
with
Proteins
negative
may
be
and
positive
positively
or
charges
negatively
move
in
opposite
charged
so
can
positive electrode
be
large fragments
separated
according
to
their
charge.
direction of
The
gel
resists
used
the
in
gel
electrophoresis
movement
of
molecules
consists
in
a
of
a
sample.
mesh
DNA
of
laments
molecules
that
migration
from
small fragments
eukaryotes
are
too
long
to
move
through
the
gel,
so
they
must
be
1
broken
charges
up
so
into
smaller
move
in
the
fragments.
same
All
DNA
direction
molecules
during
gel
carry
negative
electrophoresis,
but
not
▲
Figure 1 Procedure for gel electrophoresis
187
3
G e n e t i c s
at
the
move
to
same
rate.
further
separate
in
Small
a
fragments
given
fragments
time.
of
move
Gel
DNA
faster
than
electrophoresis
according
to
large
can
ones
so
therefore
they
be
used
size.
DnA amplicaio by PCR
PCR can be used to amplify small amounts of DNA .
The
polymerase
of
of
technique
this
amount
a
▲
DNA.
chain
copies
of
single
It
DNA
is
are
is
reaction
almost
described
needed
molecule.
is
Within
used
always
at
in
the
an
to
make
simply
sub-topic
start
hour
or
of
large
called
2.7.
the
two,
numbers
PCR.
The
Only
a
process
millions
–
of
very
in
of
details
small
theory
copies
just
can
Figure 2 Small samples of DNA being
be
made.
This
makes
it
possible
to
study
the
DNA
further
without
ex tracted from fossil bones of a Neander thal
the
risk
of
using
up
a
limited
sample.
For
example,
DNA
extracted
for amplication by PCR
from
fossils
from
blood,
can
be
amplied
semen
or
hairs
using
can
PCR.
also
be
Very
small
amplied
amounts
for
use
in
of
DNA
forensic
investigations.
PCR
is
such
the
not
as
used
blood
person
sperm
PCR
from
cells
is
in
used
copying
by
a
to
primer
The
selectivity
a
presence
primer
is
of
that
amplied
whom
a
of
by
to
blood
semen
DNA
that
set
blood
allows
or
to
greater
but
if
a
man’s
is
A
in
and
entire
of
a
sample
chromosomes
the
together
genome.
sequence
start
is
Instead
selected
desired
of
the
for
sequence.
pairing.
desired
mixture
in
modied
there
all
example,
the
ingredients
genetically
PCR,
for
base
molecules
contain
sequences.
particular
even
DNA
contain
binds
modied
the
of
cells
came,
complementary
genetically
the
of
primer
PCR
binds
entire
White
specic
genome
by
the
the
sample
copy
binds
whole
copy
semen.
using
The
from
to
or
none
sequences
of
DNA.
foods
DNA.
be
the
such
PCR
copied
test
involves
Any
present
to
One
for
the
use
DNA
has
the
of
no
effect.
Data-based questions: PCR and Neander thals
The
be
evolution
studied
DNA.
species
time.
If
a
in
species
base
The
number
Samples
of
fossil
of
living
the
base
separates
sequence
accumulate
“evolutionary
from
groups
into
two
over
differences
the
long
can
be
Neanderthal
can
sequences
between
gradually
of
organisms
groups,
two
periods
used
as
of
an
clock”.
DNA
were
bones
neanderthalensis).
of
a
recently
obtained
Neanderthal
They
were
( Homo
amplied
using
and
between
the
humans
and
the
chimpanzees.
of
fo ycneuqerf
differences
of
comparing
% / secnereid fo rebmun
their
by
25
human–Neander thal
20
human–human
15
human–chimp
10
PCR.
5
A
section
was
of
the
sequenced
Neanderthal
and
mitochondrial
compared
with
DNA
sequences
0
from
994
humans
and
16
chimpanzees.
0
The
bar
chart
sequence
sample
188
of
in
gure
differences
humans,
3
shows
were
how
found
between
the
many
within
▲
the
humans
and
the
5
10
15
20
25
30
35
40
45
50
55
60
65
number of dierences in base sequence
base-
Figure3 Number of dierences in base sequences
between humans, chimps and Neander thals
a
present
3 . 5
1
State
in
2
the
base
most
Humans
in
the
common
sequence
and
genus
classied
in
number
between
pairs
Neanderthals
Homo
the
and
genus
are
G E N E T i C
of
of
differences
humans.
both
Discuss
this
[1]
the
classied
chimpanzees
Pan.
m O D i F i C A T i O N
3
A N D
classication
bar
a
supported
by
the
data
in
[3]
limitation
conclusion
whether
is
chart.
Suggest
are
B i O T E C h N O l O G y
from
to
the
drawing
any
human–Neanderthal
comparison.
[1]
DnA prolig
DNA proling involves comparison of DNA .
DNA
●
proling
A
sample
from
●
involves
of
Sequences
are
DNA
another
in
selected
these
is
obtained,
source
the
and
●
The
copied
●
The
fragments
●
This
produces
is
are
a
such
DNA
are
DNA
stages:
as
that
copied
split
vary
from
or
a
a
known
crime
considerably
individual
or
scene.
between
individuals
PCR.
fragments
separated
of
fossil
by
into
pattern
either
a
using
bands
using
gel
that
restriction
endonucleases.
electrophoresis.
is
always
the
same
with
DNA
▲
taken
from
one
individual.
This
is
the
individual's
DNA
Figure 4 DNA proles are often referred to as
prole.
DNA ngerprints as they are used in a similar
●
The
proles
bands
are
of
the
different
same
individuals
and
which
are
can
be
compared
to
see
which
way to real ngerprints to distinguish one
individual from all others
different.
Paeriy ad foreic iveigaio
Use of DNA proling in paternity and forensic investigations.
DNA
proling
is
used
in
forensic
DNA
investigations.
proling
is
investigations.
●
Blood
stains
on
a
suspect’s
clothing
could
to
come
from
the
Blood
from
stains
the
at
the
victim
crime
could
scene
be
that
shown
to
are
not
come
a
A
single
come
each
the
of
a
hair
to
at
the
come
from
from
scene
sample
If
of
the
a
crime
from
sexual
the
example
crime
victim.
Men
the
highly
scene
could
be
the
is
crime
could
be
shown
to
DNA
a
prole
compared
taken
pattern
of
with
from
bands
that
the
two
the
same
father
to
of
a
nd
out
child.
paternity
There
investigations
are
being
person.
who
of
material
the
the
DNA
suspect
matches
samples
This
can
committed
from
●
prole
or
the
exactly
claim
now
of
DNA
have
many
the
databases
criminal
to
raise
to
that
avoid
they
are
the
having
to
not
pay
the
the
child.
A
provide
crime.
of
DNA
cases
to
who
wish
to
have
ha d
identi f y
mul ti ple
the
pa rtn e r s
bio lo gi cal
fa th e r
of
child
may
man
was
they
are
wish
their
their
to
prove
father
in
that
order
a
to
deceased
show
that
heir.
proles
of
the
mother,
the
child
and
the
are
very
are
needed.
DNA
proles
of
each
of
patterns
of
the
strong
are
prepared
and
the
bands
Some
proles,
be
compared.
If
any
bands
in
the
child’s
prole
which
do
allowed
child
it
are
countries
a
child.
samples
of
of
Women
may
suspect.
DNA
likely
evidence
have
for
sometimes
mother
man
from
the
suspect.
DNA
is
is
requested.
●
Semen
In
paternity
suspect.
shown
●
man
reasons
father
●
in
done
from
●
the
are
victim.
various
●
used
be
whether
shown
also
These
not
occur
in
the
prole
of
the
mother
or
solved.
man,
another
person
must
be
the
father.
189
3
G e n e t i c s
Aalyi of DnA prole
Analysis of examples of DNA proles.
Analysis
two
if
of
DNA
the
DNA
proles
samples
pattern
of
are
in
very
bands
on
forensic
likely
the
to
investigations
have
prole
is
come
the
is
straightforward:
from
the
same
person
same.
victim
specimen
1
2
suspects
3
▲
Figure 5 Which of the three suspects’ DNA ngerprints matches the
specimen recovered from the crime scene?
Analysis
Each
in
of
the
of
DNA
the
biological
prole
must
prole
or
more
proles
bands
be
in
do
prole
paternity
child’s
mother
not,
in
the
checked
the
bands
in
or
to
of
DNA
father’s
make
the
another
investigations
prole
prole.
sure
man
man
that
must
Every
it
have
to
more
the
band
occurs
presumed
must
is
be
be
been
in
the
either
the
the
complicated.
same
in
as
a
band
child’s
the
father.
If
mother’s
one
biological
or
father.
Geeic modicaio
Genetic modication is carried out by gene transfer
between species.
Molecular
be
to
transferred
another
genetic
the
code
amino
is
Genetic
to
milk
crop
the
was
daodil plants to rice, to make the rice
produce
be
These
genes
involved
transfer
genes
from
that
the
from
so
of
from
are
that
allow
genes
It
is
from
possible
transferred
them
is
genes
one
to
species
because
between
unchanged
–
the
species,
the
same
of
been
silk
has
gene
large
used
protein.
to
for
bacteria.
making
quantities
also
been
as
purple
of
it
been
of
One
of
human
this
the
insulin
hormone
to
can
silk
used
have
is
new
characteristics
produced
that
immensely
secrete
strong,
but
commercially.
to
produce
genetically
rather
three
introduce
have
Spider
produce
known
transfer
to
goats
snapdragons
are
the
to
diabetics.
used
are
eukaryotes
that
example,
spider
not
fruits
when
transfer
has
For
modication
example
The
modication.
translated
done
treating
species.
plant.
Figure 6 Genes have been transferred from
rice
for
could
Genetic
of
was
This
containing
spiders
so
transferred
modication
animal
species.
techniques
produced.
examples
produced
developed
genetic
sequence
been
bacterium.
as
universal,
Genes
be
190
between
acid
have
have
known
is
a
produce a yellow pigment in its seeds
is
polypeptide
early
▲
biologists
been
than
genes,
many
modied
or
transferred
red.
two
The
from
new
GM
to
tomatoes
production
daffodil
varieties
crops.
of
plants
For
to
golden
and
3 . 5
one
in
from
the
a
rice
bacterium,
so
that
the
G E N E T i C
yellow
m O D i F i C A T i O N
pigment
β-carotene
is
A N D
B i O T E C h N O l O G y
produced
grains.
Actvt
Scientists have an obligation to consider the ethical implications of their
research. Discuss the ethics of the development of golden rice. β-carotene is
a precursor to vitamin A . The development of golden rice was intended as a
solution to the problem of vitamin A deciency, which is a signicant cause of
blindness among children globally.
techique for gee rafer o baceria
Gene transfer to bacteria with plasmids using restriction
endonucleases and DNA ligase.
Genes
of
can
be
transferred
techniques.
engineering.
Together
Gene
from
these
transfer
one
species
techniques
to
bacteria
to
another
are
known
usually
by
as
involves
a
Bacterial cell
variety
genetic
Plasmid
plasmids,
mRNA extracted from
restriction
●
A
enzymes
plasmid
is
a
and
DNA
small
ligase.
extra
circle
of
DNA.
The
smallest
plasmids
Plasmid obtained
have
about
1,000
base
pairs
(1
kbp),
but
they
can
have
over
from bacteria
1,000
kbp.
They
occur
commonly
in
bacteria.
The
most
mRNA
abundant
Plasmid
plasmids
are
those
with
genes
that
encourage
their
replication
in
cut with
the
cytoplasm
are
therefore
pathogenic
advantage
and
transfer
some
and
on
parallels
natural
a
from
one
with
selection
bacterium
bacterium
viruses
but
favours
rather
than
a
to
another.
plasmids
plasmids
are
that
disadvantage.
There
restriction
cDNA
not
confer
an
mRNA treated
with reverse
Bacteria
transcriptase
use
plasmids
to
exchange
genes,
so
naturally
absorb
them
them
into
their
main
circular
DNA
molecule.
Plasmid and
cDNA fused
and
to make
incorporate
enzyme
Plasmids
using DNA ligase
complementary
Recombinant
are
very
useful
in
genetic
DNA (cDNA)
engineering.
plasmid
introduced into
●
Restriction
enzymes,
also
known
as
endonucleases,
are
enzymes
host cells
that
cut
used
to
DNA
cut
molecules
open
at
plasmids
specic
and
base
also
to
sequences.
cut
out
They
desired
can
genes
be
from
Bacteria
larger
DNA
molecules.
Some
restriction
enzymes
have
the
useful
multiply in
property
of
cutting
the
two
strands
of
a
DNA
molecule
at
different
a fermenter
points.
sticky
This
ends
leaves
single-stranded
created
complementary
by
base
any
one
sections
particular
sequences
so
can
be
called
sticky
restriction
used
to
ends.
enzyme
link
The
and produce
insulin
have
together
Separation and
pieces
of
DNA,
by
hydrogen
bonding
between
the
bases.
purication of
human insulin
●
DNA
by
ligase
making
is
an
enzyme
that
sugar–phosphate
joins
bonds
DNA
molecules
between
together
nucleotides.
rmly
When
Human insulin
the
desired
there
are
gene
still
has
nicks
been
in
inserted
each
into
a
plasmid
sugar–phosphate
using
backbone
sticky
of
the
ends
can be used
by diabetic
DNA
patients
but
An
DNA
obvious
ligase
can
be
requirement
transferred.
It
is
usually
used
for
to
gene
easier
to
seal
these
transfer
obtain
is
nicks.
a
copy
messenger
of
the
RNA
gene
being
transcripts
of
▲
genes
than
the
genes
themselves.
Reverse
transcriptase
is
an
Figure 7 shows the steps involved in one
enzyme
example of gene transfer. It has been used
that
makes
DNA
copies
of
RNA
molecules
called
cDNA.
It
can
be
used
to create genetically modied E. coli bacteria
to
make
the
DNA
needed
for
gene
transfer
from
messenger
RNA.
that are able to manufacture human insulin,
for use in treating diabetes
191
3
G e n e t i c s
Aeig he rik of geeic modicaio
Assessing risks associated with scientic research:
scientists attempt to assess the risks associated with
genetically modied crops or livestock .
There
of
when
Paul
Figure 8 The biohazard symbol indicates any
the
rst
many
fears
was
an
going
expressed
expressed
These
experiments
planned
SV40
biologists
been
modication.
Berg
virus
▲
have
genetic
fears
in
gene
experiment
to
be
be
in
which
into
concerns
the
possible
traced
transfer
inserted
serious
about
can
back
were
being
DNA
the
from
SV40
the
1970s
conducted.
the
bacterium
because
dangers
to
E.
was
monkey
coli.
Other
known
to
organism or material that poses a threat to the
cause
cancer
in
mice
and
E.
coli
lives
naturally
in
the
intestines
of
health of living organisms especially humans
humans.
There
bacterium
Since
have
then
been
scientists
safety
of
many
therefore
cancer
other
identied.
and
the
organisms.
with
was
causing
research
potentially
has
a
risk
risks
led
useful
to
the
associated
has
been
scientists
and
of
genetically
engineered
humans.
There
between
This
in
the
and
of
being
applications
genetic
debate
using
GM
among
about
genetically
imposed
of
modication
both
non-scientists
safety
bans
with
erce
in
crops
some
or
the
modied
countries,
livestock
left
undeveloped.
Almost
everything
eliminate
risk
lives.
natural
It
is
whether
assess
The
▲
or
the
risks
not
●
What
●
How
is
for
go
risks
can
that
entirely,
we
the
assessed
chance
carries
in
humans
ahead
of
assess
it.
with
in
This
their
two
an
risks
science
to
with
associated
be
do
either
or
the
is
and
in
it
is
other
risk
what
of
not
possible
aspects
an
action
scientists
research
before
of
to
our
and
must
do
carrying
it
decide
–
out.
ways:
accident
or
other
harmful
consequence?
Figure 9 GM corn (maize) is widely grown in
harmful
would
the
consequence
be?
Nor th America
If
there
chance
is
of
a
high
very
chance
harmful
of
harmful
consequences
consequences
then
or
research
a
signicant
should
not
bedone.
Rik ad bee of GM crop
is
disagreement,
because
gene
transfer
to
crop
Assessment of the potential risks
plants
and benets associated with genetic
GM
crops
have
that
by
GM
opponents
and
such
reduce
been
many
publicized
produce
issues
192
have
been
as
of
potential
widely
seed,
the
contested.
It
is
the
they
technology.
whether
pesticide
but
benets.
by
GM
and
not
are
questioned
Even
crops
These
corporations
basic
increase
herbicide
surprising
use
that
yields
have
there
a
involved
takes
modication of crops.
is
relatively
are
very
decades
Potential
for
benets
environmental
agricultural
crops
be
are
assessed
evidence.
available
It
complex
disputes
can
a
IB
and
to
in
be
the
science
and
Economic
benets
of
be
because
basis
students
to
they
using
impossible
assess
often
into
benets
here,
issues
it
resolved.
grouped
scientic
would
procedure,
health
included
on
for
be
benets,
benets.
not
recent
in
experimental
the
all
GM
cannot
time
claimed
3 . 5
benets
for
one
claim
one
crop.
all
GM
from
Much
benets
and
Claims
about
GM
●
also
Instead
given
the
to
evidence
risks
is
it
here
is
better
and
freely
to
assess
relating
to
crop
transferring
the
plants.
sprayed
other
Use
for
on
of
GM
of
select
it
for
of
of
can
be
making
so
then
fewer
are
toxin
has
bees
to
be
and
harmed.
reduces
spraying
produced
a
crops,
the
so
need
less
fuel
is
machinery.
fruit
reducing
that
and
vegetables
wastage
have
to
and
be
can
be
reducing
the
grown.
▲
Claims
about
the
health
benets
Figure 10 Wild plants growing nex t to a crop of GM maize
of
crops:
These
●
B i O T E C h N O l O G y
potential
benets
insecticide
crop
varieties
farm
crops
for
insects
and
shelf-life
improved,
area
the
crop
for
varieties
gene
Less
to
plowing
The
a
benecial
needed
GM
A N D
available.
environmental
Pest-resistant
to
●
of
list
m O D i F i C A T i O N
crops:
by
●
crops.
the
G E N E T i C
The
nutritional
improved,
vitamin
for
value
of
example
crops
by
can
diseases
signicantly
be
increasing
of
the
control
killing
content.
cur r e ntl y
and
is
to
insect
t he
red uce
vecto r s
re duce
o nly
cr op
cur re nt
tr a ns mis s ion
of
the
yi el ds
met h od
v ir us e s
by
w it h
insecticides.
●
Varieties
of
allergens
in
crops
or
could
toxins
that
be
produced
are
lacking
naturally
present
A
wide
have
them.
effect
●
GM
crops
could
be
engineered
that
vaccines
so
by
eating
the
on
crop
a
be
vaccinated
against
a
GM
about
agricultural
benets
of
The
health
about
resistant
to
drought,
ground s
cold
risks,
be
produced
by
gene
and
be
transfer,
range
over
which
crops
the
safety
assessed
increasing
total
can
be
a
A
gene
for
case
resistance
can
crop
to
the
be
killed
with
plants
allowing
all
by
kill
all
in
the
herbicide.
crop
plants
growing
With
crop
less
is
●
but
yields
can
conditions
they
are
be
higher.
used
to
is
look
to
for
cannot
can
m a ke
GM
o ve ra ll
cr ops ,
e a ch
usi ng
al l
a nd
ju dg m e n t s
r is k
the
ne e ds
a va i la ble
evid e nce .
basis
Thi s
as
it
ne e ds
is
not
to
be
d on e
p os si ble
risks
and
b e ne ts
of
one
GM
to
c ro p
sowing
be
used
be
diseas e s
by
on
a no t h er
on e.
no
consensus
yet
among
about
GM
all
scientists
crops
and
it
or
is
at
important
the
for
evidence
as
for
many
the
of
us
claims
as
possible
and
risks
that
rather
are
than
included
the
here
publicity.
could
be
Any
of
selected
non-GM
once
p r oduce d
ca use d
p e r f o r med
Herbicides
the
detailed
tha t
are
vi ru s es .
scrutiny.
crop
Claims
varieties
resistant
gr oupe d
create
growing.
Crop
be
r i sk s
by
for
crops
r el e v a n t
can
weed
the
weed-free
of
case
counter-claims,
that
not
other
to
competition
To
experiments
therefore
spraying
ar e
care ful l y,
non-scientists
plants
so
co nce rns
be
There
to
the
yields.
herbicide
transferred
as
as s es s ed
produced
from
●
be
salinity
assess
and
c ro ps
expending
on
the
GM
s uc h
ca nno t
e nv i r o nme ntal
risks.
experimental
can
ab out
the s e,
i nco me s,
remaini ng
agricultural
crops:
Varieties
of
disease.
to
●
S o me
farmer’s
scientic
into
Claims
co nce rns
person
here.
would
of
raised.
produce
on
edible
variety
been
●
made
Proteins
about
produced
translation
of
health
by
risks
of
transcription
transferred
genes
GM
crops:
and
could
be
193
3
G e n e t i c s
toxic
or
cause
livestock
that
allergic
eat
GM
reactions
in
humans
or
plants,
crops.
feed
crops
●
Antibiotic
during
resistance
gene
pathogenic
●
used
as
could
spread
genes
to
Claims
unexpected
GM
could
problems
during
mutate
that
and
were
development
of
them
are
made
about
●
cause
not
GM
made
Some
risk-
environmental
seed
crops.
plants
organisms
than
that
non-GM
risks
agricultural
risks
of
from
that
to
a
must
very
crop
become
be
is
always
controlled,
difcult
spilt
unwanted
if
the
but
crop
and
volunteer
this
could
contains
of
resistance
genes.
crops:
Non-target
organisms
toxins
are
could
be
affected
Widespread
that
intended
to
control
pests
crop
them
transferred
herbicide
plants,
GM
crops
containing
a
that
of
kills
insect
resistance
pests
to
the
will
lead
toxin
in
to
the
the
pests
plants.
that
Genes
of
in
spread
GM
use
by
toxin
●
about
germinates
●
●
and
rather
beinggrown.
herbicide
GM
GM
crops:
become
Claims
insects
where
markers
bacteria.
Transferred
assessed
transfer
genes
plant-eating
on
turning
to
crop
resistant
them
plants
could
into
to
make
spread
to
were
spread
wild
the
of
the
initial
problem
secondary
toxin
but
were
pests
and
that
previously
also
are
to
the
resistant
to
scarce.
uncontrollable
●
Farmers
are
not
permitted
by
patent
law
to
super-weeds.
save
●
Biodiversity
proportion
could
of
be
reduced
sunlight
energy
if
a
lower
passes
to
and
have
weed
re-sow
grown,
conditions
so
GM
seed
strains
cannot
be
from
adapted
crops
to
they
local
developed.
Aalyig rik o moarch buerie of
B cor
Analysis of data on risks to monarch butteries of Bt crops.
Insect
but
pests
that
protein.
ies,
It
kills
Bt
Bt
varieties
In
North
as
maize,
pests
toxin
toxin
or
corn
toxin
in
to
194
is
cob.
insect.
This
from
Data
for
toxin.
contain
are
while
particular
from
toxin
butteries,
corn
is
the
a
moths,
varieties
including
Zea
in
it
larvae
about
engineering
pollen.
attacked
the
The
engineered
produced,
is
insecticides
genetic
transferred
including
corn,
crop
with
by
was
Bt
that
expressed
One
Britain
by
of
the
species
is
various
the
of
of
known
insect
moth
effects
mays.
Ostrinia
Bt
concern
corn
is
on
the
plexippus.
buttery
that
feed
sometimes
with
the
monarch
corn
from
gene
plant
been
The
plant
GM
A
orders
which
dusted
risk
spraying
codes
called
been
by
produced
genetically
the
have
Danaus
a
that
of
crop
monarch
therefore
pollen
insects.
The
borers,
of
been
insect
parts
the
become
experimentally.
of
ants.
have
curassavica.
crops
is
corn
the
controlled
kills
crops
on
species
of
all
this
buttery,
larvae
There
in
Concerns
monarch
Asclepias
and
many
including
non-target
that
members
bees
of
be
recently
thuringiensis
America
nubilalis.
corn
a
can
been
Bacillus
beetles,
produce
crops
have
produce
bacterium
The
of
varieties
crops.
these
on
leaves
grows
of
close
milkweed,
enough
wind-dispersed
larvae
This
risk
experiments
might
has
is
corn
be
been
to
pollen.
poisoned
by
Bt
investigated
available
for
analysis.
3 . 5
G E N E T i C
m O D i F i C A T i O N
A N D
B i O T E C h N O l O G y
)%( eavral hcranom fo lavivruS
Data-baed queton: Transgenic pollen and monarch lar vae
To
investigate
monarch
collected
spatula
old
from
of
dusting.
by
effect
the
of
the
was
leaves
plants
gently
were
buttery
larvae
pollen
from
following
milkweed
pollen
The
monarch
eaten
the
butteries
were
tapped
larvae
was
and
placed
Bt
corn
procedure
in
were
over
on
was
lightly
the
placed
over
on
to
tubes.
each
four
larvae
leaf.
days.
of
Leaves
misted
leaves
water-lled
monitored
the
used.
with
water.
deposit
Five
The
The
were
a
A
ne
three-day-
area
mass
of
of
leaf
100
75
50
25
0
the
1
2
3
4
Time (days)
larvae
was
measured
monitored
treatments
each
The
survival
of
the
larvae
was
days.
were
2
included
in
the
experiment,
with
ve
repeats
treatment:
●
leaves
not
●
leaves
dusted
●
days.
fael evitalumuC
of
four
four
leaves
dusted
with
with
dusted
with
pollen
non-GM
pollen
(blue)
pollen
from
Bt
(yellow)
corn
avral rep noitpmusnoc
Three
over
after
1.5
1
0.5
(red)
0
The
results
are
shown
in
the
table,
bar
chart
and
graph
on
the
1
right.
2
3
4
Time (days)
1
a)
List
the
variables
that
were
kept
constant
in
the
Source: Losey JE, Rayor LS, Carter ME (May 1999).
experiment.
[3]
“Transgenic pollen harms monarch larvae”.
2
b)
Explain
the
a)
Calculate
need
the
to
total
keep
these
number
of
variables
larvae
constant.
used
in
[2]
the
Treatment
experiment.
b)
Explain
the
Nature 399 (6733): 214.
need
for
replicates
in
experiments.
[2]
Mean mass of
surviving larvae (g)
[2]
Leaves not dusted
0.38
with pollen
3
The
bar
Explain
chart
how
and
the
error
graph
bars
help
show
in
mean
the
results
analysis
and
and
error
bars.
Not available
evaluation
non-GM pollen
of
data.
[2]
0.16
4
Explain
the
conclusions
that
can
be
drawn
from
the
pollen from Bt corn
percentage
5
Suggest
survival
reasons
between
the
for
three
of
larvae
the
in
the
differences
three
in
treatments.
leaf
[2]
consumption
treatments.
[3]
Actvt
6
Predict
with
the
mean
non-GM
mass
of
larvae
that
fed
on
leaves
dusted
Etatng te ze of a cone
pollen.
[2]
A total of 130,000 hectares of Russet
7
Outline
this
differences
experiment
might
by
any
Bt
affect
and
between
processes
whether
the
that
monarch
procedures
occur
larvae
are
in
used
nature,
actually
Burbank potatoes were planted in
in
Idaho in 2011. The mean density
which
of planting of potato tubers was
harmed
pollen.
[2]
50,000 per hectare. Estimate the size
of the clone at the time of planting and
at the time of harvest.
Cloe
Clones are groups of genetically identical organisms,
derived from a single original parent cell.
A
zygote,
the
rst
sexual
and
produced
cell
of
a
by
new
reproduction,
develops
into
an
the
fusion
organism.
they
are
adult
of
a
male
Because
all
and
genetically
organism.
If
female
zygotes
it
are
gamete,
produced
different.
reproduces
A
zygote
sexually,
is
by
grows
its
195
3
G e n e t i c s
offspring
Actvt
also
identical
The
a
will
different.
When
they
In
some
do
this,
species
they
organisms
produce
can
genetically
organisms.
of
Although
identical
of
genetically
genetically
we
do
twins
result
develop
genetically
asexually.
production
group
the
be
reproduce
of
a
into
not
is
usually
the
identical
identical
think
smallest
human
zygote
separate
organisms
organisms
of
clone
or
an
in
can
into
is
called
them
that
dividing
embryos,
is
this
two
cloning
and
clone.
way,
exist.
embryo
called
a
a
They
cells,
pair
are
which
splitting
into
of
either
each
two
How many potato clones are there in
parts
which
each
develop
into
a
separate
individual.
Identical
twins
this photo?
are
not
identical
different
rarely
in
all
ngerprints.
identical
their
A
triplets,
characteristics
better
term
for
quadruplets
and
them
and
have,
is
even
for
example,
monozygotic.
quintuplets
More
have
beenproduced.
Sometimes
For
a
clon e
example,
Large
but
clones
even
so
ca n
cons i st
com me r c ia ll y
are
all
fo r me d
the
of
ve ry
gr own
by
cloning
o r g a ni sms
la rg e
pot a t o
ma y
n u m be r s
v a ri e t ie s
h ap pe n in g
be
t r ac ed
a g a in
back
of
a re
to
o rg a n is m s .
hu g e
and
one
c l on e s.
a ga i n,
or ig i n al
parentcell.
naural mehod of cloig
Many plant species and some animal species have
natural methods of cloning.
Although
identical
the
produced
▲
Figure 11 Identical twins are an example
of cloning
twig.
by
●
by
Many
plants
Two
plants
very
examples
A
a
single
A
at
they
garlic
of
are
a
end.
or
the
growing
Natural
are
bulb,
●
and
can
for
in
It
any
the
comes
method
involve
group
early
from
of
of
20th
the
cloning.
stems,
genetically
century
Greek
The
roots,
for
plants
word
for
methods
leaves
or
used
bulbs.
here:
planted,
produce
plant
the
uses
enough
bulbs
g r o ws
in
l ong
p l a ntl e ts
us i ng
plan t.
genetical l y
the
its
food
food
by
group
stores
to
grow
photosynthesis
are
genetically
to
grow
identical
A
hor i zon t a l
g r ow
the i r
roo t s
le a ve s,
he a lthy
i d e ntica l
so
can
s tr awbe r ry
ne w
st e m s
i nt o
p la nt s
th e
with
s oi l
b e c om e
p la nt
in
t h is
p la n t le t s
and
in d ep en d en t
c an
way
pr oduc e
du r in g
t en
a
season.
do
of
cloning
are
less
common
in
animals
but
some
species
it.
Hydra
clones
gure
1,
Female
▲
to
natural
when
All
These
methods
able
used
used
clone.
parent
more
a
given
photosynthesize
of
now
rst
reproduction.
varied
bulbs.
is
was
leaves
strawberry
the
it
have
are
These
group
so
clone
asexual
are
leaves.
●
word
organisms,
itself
page
aphids
by
a
process
called
budding
(sub-topic
1.6,
51).
can
give
birth
to
offspring
that
have
been
produced
Figure 12 One bulb of garlic clones itself to
produce a group of bulbs by the end of the
growing season
196
entirely
meiosis.
from
The
diploid
egg
offspring
cells
are
that
were
therefore
produced
clones
of
their
by
mitosis
mother.
rather
than
3 . 5
G E N E T i C
m O D i F i C A T i O N
A N D
B i O T E C h N O l O G y
Iveigaig facor aecig he rooig of em-cuig
Design of an experiment to assess one factor aecting the rooting of
stem-cuttings.
Stem-cuttings
used
to
from
clone
the
stem,
independent
1
are
Many
the
new
plants
Ocimum
short
plants
lengths
articially.
cutting
can
of
If
stem
roots
that
●
are
develop
become
whether
the
cutting
is
placed
in
water
or
compost
an
●
what
●
how
●
whether
type
of
compost
is
used
plant.
can
be
basilicum
cloned
roots
from
warm
the
cuttings
are
kept
cuttings.
particularly
easily.
a
plastic
bag
is
placed
over
the
cuttings
2
Nodes
are
positions
on
the
stem
where
leaves
●
are
attached.
below
3
a
Leaves
the
4
The
most
species
the
stem
is
cut
whether
holes
are
cut
in
the
plastic
bag.
node.
are
stem.
upper
With
removed
If
half
there
they
lowest
from
are
can
third
of
the
many
also
the
be
lower
large
half
leaves
of
in
You
should
you
design
or
water.
about
these
questions
when
experiment:
the
1
What
2
How
is
your
independent
variable?
reduced.
cutting
is
inserted
Compost
should
be
will
you
measure
the
amount
into
of
compost
think
your
root
formation,
which
is
your
dependent
sterile
variable?
and
contain
plenty
of
both
air
and
water.
3
5
A
clear
plastic
bag
with
a
few
holes
cut
in
Which
variables
should
you
keep
it
constant?
prevents
excessive
water
loss
from
cuttings
4
inserted
in
How
you
6
Rooting
normally
takes
a
few
weeks.
new
different
types
of
plant
should
leaves
usually
indicates
that
use?
Growth
5
of
many
compost.
the
How
many
cuttings
should
you
use
for
each
cutting
treatment?
has
Not
to
all
developed
gardeners
clone
plants
gardeners
ngers”
the
carry
have
using
sometimes
for
an
success
root
biologist
their
about
cuttings
out
factors
your
a
evidence
whether
the
are
but
reason
give
roots.
success.
root
the
list
to
or
have
“green
this
that
You
or
can
determine
can
design
investigate
below,
as
Experiments
not.
to
trying
Successful
reject
factors
experiment
on
said
would
the
when
cuttings.
one
another
and
of
factor
of
own.
Possible
factors
●
whether
●
how
●
whether
the
long
callus
to
stem
the
the
investigate:
is
cut
cutting
end
of
above
or
below
a
node
is
the
stem
is
left
in
the
air
to
over
●
how
●
whether
many
a
leaves
are
hormone
left
on
rooting
the
cutting
powder
is
used
197
3
G e n e t i c s
Cloig aimal embryo
Animals can be cloned at the embryo stage by breaking
up the embryo into more than one group of cells.
At
an
early
stage
pluripotent
theoretically
and
each
This
cells
one
is
embryo
most
separated
Only
to
a
an
▲
in
all
to
an
animal
types
divide
separate
or
by
of
two
individual
up
this
It
or
with
Coral
breaking
because
embryo
tissue).
into
fragmentation.
presumably
egg
still
has
at
embryo
can
could
not
into
be
of
are
is
therefore
more
all
embryos
into
parts
body
smaller
increases
parts.
have
groups
the
of
chance
of
little
stage
interest
it
is
not
vitro
can
be
and
be
this
and
in
allowed
separated
into
obtained
cells
successful
method
possible
cloning
by
naturally.
articially
embryo
most
in
as
this
transplanted
can
the
do
splitting,
However,
some
cases
it
the
embryos.
in
cells
and
clones
usually
to
embryos
fertilized
divisions
is
regarded
multiple
pluripotent
of
be
appear
Individual
number
been
do
animal
develop
embryos
There
the
a
themselves
twins
up
embryo.
are
of
into
cells,
species
number
Splitting
clone
break
limited
certain
embryo
splitting
identical
parts
they
a
the
cells
into
surviving.
multicellular
while
to
all
developing
for
called
single
of
livestock,
of
develop
animal
possible
In
is
even
Formation
but
to
observed
or
development
possible
part
process
been
of
(capable
to
at
of
assess
develop
the
surrogate
this
are
to
from
way,
no
the
articial
stage.
cloning
a
after
pluripotent.
eight-cell
whether
a
mothers.
because
longer
into
embryo
new
because
individual
Figure 13 Sea urchin embryo (a) 4-cell stage
produced
by
sexual
reproduction
has
desirable
characteristics.
(b) blastula stage consisting of a hollow ball
of cells
Cloig adul aimal uig diereiaed cell
Methods have been developed for cloning adult animals
using dierentiated cells.
It
is
relatively
is
impossible
easy
to
characteristics.
assess
This
are
their
is
the
undifferentiated
biologist
nuclei
cells
the
as
from
from
nuclei
carried
tissues
Prize
of
for
Figure 14 Xenopus tadpoles
198
body
cell
there
cells
the
using
Xenopus
or
had
interest
in
out
in
the
frog.
cells
for
an
it
to
is
easy
clone
adult
new
during
and
to
them.
animal
animal
as
and
his
on
cloning
the
body
The
though
egg
they
differentiation
Gurdon
was
pioneering
proved
mammal
to
was
uses
therapeutic
be
them
cells
were
to
the
He
frog
removed
into
into
zygotes.
form
awarded
all
egg
which
They
the
the
Nobel
research.
much
Dolly
of
in
1950s.
transplanted
removed.
reproductive
it
of
a
it
desirable
adults
difcult
experiments
2012
for
stage
needed.
tadpoles
In
in
that
have
into
body
Oxford
been
at
will
more
tissues
developed
cloned
obvious
are
growth
Medicine
first
up
but
grown
much
the
cells
differentiated
The
is
all
Xenopus
cell
embryos
have
make
carried
transplanted
the
also
of
it
student
nucleus
division,
normal
from
is
Gurdon
Physiology
mammals.
Apart
▲
a
that
pluripotent
John
were
but
embryos,
the
embryos
produce
postgraduate
which
out
Cloning
in
a
cells
To
animal
whether
the
characteristics,
because
Xenopus
clone
know
Once
differentiated.
The
to
this
reasons.
more
the
type
If
difficult
sheep
of
this
in
1996.
cloning,
procedure
3 . 5
was
done
stem
with
cells,
Because
adult
the
from
rejection
humans,
which
cells
could
the
be
would
whom
the
embryo
used
be
to
would
was
m O D i F i C A T i O N
consist
regenerate
genetically
nucleus
G E N E T i C
identical
obtained
of
tissues
to
they
A N D
B i O T E C h N O l O G y
pluripotent
for
those
would
the
of
adult.
the
not
cause
problems.
Mehod ued o produce Dolly
Production of cloned embryos by somatic-cell nuclear transfer.
The
production
development
was
used
somatic
a
is
The
Adult
a
normal
were
Dorset
laboratory,
the
cells
●
of
a
a
of
was
cell
method
the
were
that
with
that
transfer.
a
A
diploid
stages:
medium
so
The
nuclear
nutrients.
eggs
Scottish
pioneering
from
and
inactive
Unfertilized
a
these
taken
using
differentiation
body
has
ewe
concentration
in
was
cloning.
somatic-cell
method
cells
Finn
Dolly
animal
called
cell
nucleus.
●
is
of
in
udder
grown
of
in
the
containing
This
the
made
a
low
genes
pattern
of
lost.
were
taken
Blackface
ewe.
from
The
the
ovaries
nuclei
were
▲
removed
cells
to
from
each
around
of
gel.
cause
10%
into
from
egg
the
A
an
Finn
cell,
egg,
small
the
of
the
two
the
these
eggs.
Dorset
inside
which
electric
cells
fused
One
to
cells
the
is
a
was
the
cultured
placed
zona
pellucida
was
the team that produced her
●
coating
used
together.
developed
to
a
The
embryos
seven
could
About
like
Figure 15 Dolly with Dr Ian Wilmut, the embryologist who led
next
protective
pulse
fuse
of
zygote
embryo.
in
the
days
act
as
same
embryos
through
were
old
then
into
injected
uteri
of
surrogate
mothers.
way
IVF
.
as
implanted
a
the
normal
in
when
other
This
about
ewes
was
that
done
Only
one
of
successfully
and
developed
gestation.
This
was
the
29
Dolly.
egg without a
nucleus fused
with donor cell
using a pulse of
electricity
cell taken from udder of
donor adult and cultured
embryo resulting from
in laboratory for six days
fusion of udder cell and
egg transfered to the
surrogate mother
uterus of a third sheep
gives birth to lamb.
which acts as the
Dolly is genetically
surrogate mother
identical with the
sheep that donated
the udder cell
unfertilized egg taken from another
(the donor)
sheep. Nucleus removed from the egg
▲
Figure 16 A method for cloning an adult sheep using dierentiated cells
199
3
G e n e t i c s
Queio
1
Human
while
somatic
our
chimpanzee,
have
the
48
the
primate
human
12
and
have
primate
the
gorilla
chromosomes.
human
from
cells
closest
of
ancestor.
two
The
chromosome
13
and
from
the
orangutan
number
2
2
below
compared
is
was
chromosomes
in
Compare
the
formed
part
a
from
chromosome
the
two
study
gene
this
19
The
(Felis
true,
many
chromosomes,
is
repeats
If
the
predict
region
of
of
endangered
and
variation
out.
samples
analysed
In
were
for
with
samples
Gel
the
East
of
the
one
taken
the
electrophoresis.
compared
blood
an
protein
The
electrophoresis
from
19
domestic
electrophoresis
used
to
separate
proteins
using
the
can
same
as
in
DNA
proling.
The
bands
on
[3]
of
sequence.
gel
is
South
carried
blood
sylvestris).
called
gel
which
the
fusion
what
the
of
same
be
chromosome
hypothesized
to
short
hypothesis
would
have
represent
forms
of
the
protein
telomeres,
transferrin
have
using
level
was
and
in
chromosomes
17).
ends
the
pool
jubatus)
found
2
the
b)
of
study,
for
principles
(gure
cat
cheetahs
were
patterns
chromosome
chimpanzee
of
results
be
with
A
(Acinonyx
large
transferrin
chimpanzee.
human
of
cheetah
that
cats
a)
cheetah
Africa.
all
shows
to
The
species
the
hypothesis
image
3
chromosomes,
the
One
chromosome
fusion
46
relatives,
indicated.
were
found
where
are
DNA
in
the
the
fusion
occurred.
[2]
transferrin
C
H
▲
Figure 1
7
origin
1
2
3
4
5
6
7
8
9
10 11 12
13
14 15 16
1
7 18 19
cheetahs
2
The
pedigree
groups
I
of
in
three
gure
18
shows
generations
of
a
the
ABO
family.
AB
B
O
B
1
2
3
4
B
A
B
O
1
2
3
4
O
A
B
O
?
1
2
3
4
5
transferrin
II
III
▲
O
5
Figure 18
origin
1
2
3
4
5
6
7
8
9
10 11 12
13
14 15 16
1
7 18 19
domestic cats
a)
Deduce
the
genotype
of
each
person
in
the
family.
b)
Deduce
[4]
the
individual
of
possible
III
5,
blood
with
the
groups
▲
of
percentage
chance
each.
Using
Deduce
the
percentage
(i)
of
of
is
200
possible
chance
children
partner
(ii)
gure
19,
deduce
with
reasons:
[2]
a)
c)
Figure 19
who
children
in
of
blood
of
groups
each
blood
individual
is
of
blood
also
III
group
2
in
her
the
and
for
his
group
partner
O
the
b)
[2]
who
[2]
number
number
group:
1
blood
and
AB.
III
and
the
in
c)
domestic
transferrin
gene
number
the
of
cheetahs
number
the
the
in
the
of
gene
of
of
of
the
heterozygous
of
of
[2]
the
transferrin
domestic
alleles
pool
and
were
gene;
alleles
pool
cats
that
of
the
cats;
transferrin
cheetahs.
gene
[2]
gene
[1]
4
E c o l o g y
Intrdutin
Ecosystems
energy
to
energy
lost
of
carbon
require
fuel
as
and
ecosystems
life
a
continuous
processes
heat.
and
Continued
other
depends
chemical
on
supply
to
availability
elements
cycles.
of
replace
The
in
future
survival
depends
of
living
on
Concentrations
signicant
Earth’s
organisms
sustainable
of
effects
gases
on
including
ecological
in
the
climates
humans
communities.
atmosphere
experienced
have
at
the
surface.
4.1 Sps, s   sss
Understandin
Skis
➔
Species are groups of organisms that can
➔
Classifying species as autotrophs, consumers,
potentially interbreed to produce fer tile ospring.
detritivores or saprotrophs from a knowledge of
➔
Members of a species may be reproductively
their mode of nutrition.
isolated in separate populations.
➔
➔
Testing for association between two species
Species have either an autotrophic or
using the chi-squared test with data obtained
heterotrophic method of nutrition (a few
by quadrat sampling.
species have both methods).
➔
➔
Recognizing and interpreting statistical
Consumers are heterotrophs that feed on living
signicance.
organisms by ingestion.
➔
➔
Setting up sealed mesocosms to try to
Detritivores are heterotrophs that obtain organic
establish sustainability. (Practical 5)
nutrients from detritus by internal digestion.
➔
Saprotrophs are heterotrophs that obtain
Nature f siene
organic nutrients from dead organic matter by
external digestion.
➔
A community is formed by populations
of dierent species living together and
➔
Looking for patterns, trends and discrepancies:
plants and algae are mostly autotrophic but
some are not.
interacting with each other.
➔
A community forms an ecosystem by its
interactions with the abiotic environment.
➔
Autotrophs and heterotrophs obtain inorganic
nutrients from the abiotic environment.
➔
The supply of inorganic nutrients is maintained
by nutrient cycling.
➔
Ecosystems have the potential to be
sustainable over long periods of time.
201
4
E c o l o g y
Speies
Species are groups of organisms that can potentially
interbreed to produce fer tile ospring.
Birds
of
paradise
islands.
In
courtship
to
the
dances,
display
their
that
they
reason
is
show
to
Papua
season
repeatedly
exotic
female
the
are
New
the
carrying
plumage.
t
that
and
One
would
they
Guinea
males
are
out
a
a
series
for
type
of
this
suitable
same
other
elaborate
reason
be
the
and
do
Australasian
and
is
to
show
partner.
of
distinctive
movements
bird
of
to
a
Another
paradise
as
female.
There
these
are
each
forty-one
usually
between
of
the
the
characters
types
▲
inhabit
breeding
of
only
different
different
forty-one
that
are
organism
types
reproduces
types
types
are
of
different
such
as
of
with
of
paradise.
of
its
rarely
bird
to
bird
others
of
those
these
type
produced.
paradise
of
other
species .
For
Each
and
this
remains
types.
Although
of
hybrids
reason
distinct,
Biologists
few
with
call
species
have
Figure 1 A bird of paradise in Papua
as
elaborate
courtship
rituals
as
birds
of
paradise,
most
species
have
New Guinea
some
method
members
When
they
two
are
of
trying
their
members
This
paradise.
is
However,
are
species
becoming
The
almost
reproductive
species
being
distinguish
summary,
fertile
of
called
species
a
it
a
to
ensure
that
they
reproduce
with
other
species.
the
interbreeding.
together.
of
of
same
species
Occasionally
cross-breeding.
the
always
offspring
infertile,
mate
and
members
It
of
happens
produced
which
by
produce
different
offspring
species
occasionally
cross-breeding
prevents
the
genes
breed
with
of
birds
between
two
mixed.
separation
recognizable
from
even
species
is
a
the
between
type
of
most
group
of
species
is
organism
closely
the
with
related
organisms
that
reason
for
characters
other
each
that
species.
interbreed
to
In
produce
offspring.
Pps
Members of a species may be reproductively isolated in
separate populations.
A
population
same
area
at
a
the
group
same
they
are
unlikely
they
are
different
still
If
members
two
of
to
they
and
difcult
decide
to
biologists
different
time.
same
of
a
in
are
interbreed
If
If
two
species
each
same
species
live
other.
potentially
never
in
This
could
interbreed
characters.
considered
fertile
whether
sometimes
the
populations
with
they
of
who
live
different
does
not
interbreed,
in
the
areas
mean
they
that
are
species.
their
produce
species.
organisms
interbreed
the
differences
differences,
of
species.
populations
develop
202
is
be
the
offspring.
two
disagree
to
Even
same
In
populations
about
if
then
there
species
practice
have
whether
they
are
it
may
gradually
recognizable
until
can
reached
populations
they
be
this
are
cannot
very
point
the
and
same
or
4 . 1
S P e c i e S ,
c o m m u n i t i e S
a n d
e c o S y S t e m S
aph  hph 
av
Species have either an autotrophic or heterotrophic
Gápgs  ss
method of nutrition (a few species have both methods).
The tor toises that live on
All
organisms
amino
acids.
obtaining
need
They
these
a
supply
are
of
needed
carbon
organic
for
nutrients,
growth
compounds
can
and
be
such
as
glucose
reproduction.
divided
into
two
and
Methods
the Galápagos islands are
of
types:
the largest in the world.
They have sometimes been
grouped together into one
some
●
organisms
make
their
own
carbon
compounds
from
carbon
species, Chelinoidis nigra,
dioxide
and
other
simple
substances
–
they
are
autotrophic,
which
but more recently have been
means
self-feeding;
split into separate species.
some
●
organisms
obtain
their
carbon
compounds
from
other
Discuss whether each
organisms
–
they
are
heterotrophic,
which
means
feeding
on
others.
of these observations
Some
unicellular
gracilis
there
by
for
is
organisms
example
sufcient
endocytosis.
has
light,
use
both
methods
chloroplasts
and
but
feed
Organisms
can
that
also
are
not
of
carries
on
nutrition.
out
photosynthesis
detritus
exclusively
Euglena
or
smaller
autotrophic
indicates that populations
when
organisms
on the various islands are
separate species:
or
●
heterotrophic
are
The Galápagos tor toises
mixotrophic.
are poor swimmers and
cannot travel from one
island to another so
they do not naturally
interbreed.
●
Tor toises from
dierent islands have
recognizable dierences
in their characters,
including shell size and
shape.
●
▲
Figure 3 Arabidopsis
▲
Figure 4 Humming birds
▲
Tor toises from dierent
Figure 5 Euglena – an
islands have been
mated in zoos and
thaliana –the autotroph
are heterotrophic; the plants
unusual organism
that molecular biologists
from which they obtain
as it can feed both
use as a model plant
nectar are autotrophic
autotrophically and
hybrid ospring have
been produced but they
heterotrophically
have lower fer tility and
higher mor tality than
the ospring of tor toises
ts  p  g 
from the same island.
Looking for patterns, trends and discrepancies: plants
and algae are mostly autotrophic but some are not.
Almost
all
complex
plants
organic
substances.
algae
is
A
obtain
therefore
and
supply
by
algae
are
compounds
of
autotrophic
using
energy
absorbing
light.
photosynthesis
is
carbon
needed
Their
and
they
–
they
to
do
method
carry
make
dioxide
it
and
this,
of
out
their
other
which
plants
autotrophic
in
own
simple
and
nutrition
chloroplasts.
▲
This
by
trend
for
plants
photosynthesis
However
the
there
trend,
in
are
because
and
algae
to
chloroplasts
small
make
is
numbers
although
they
their
followed
of
are
both
own
by
carbon
the
plants
majority
and
recognizably
algae
plants
Figure 2 Galápagos tor toise
compounds
of
that
or
species.
do
algae,
not
t
they
203
4
E c o l o g y
do
not
These
them
To
contain
species
and
cause
decide
algae
and
are
whether
groups
are
The
and
It
is
1%
almost
alga
were
them.
all
they
different
of
this
autotrophs,
plant
can
the
and
out
from
parasitic.
theory
whether
to
photosynthesis.
compounds
that
they
consider
plants
are
how
and
just
many
minor
species
the
easily
parasitic
This
is
relatively
ancestral
parasitic
be
lost
species
pattern
from
species
species
from
are
suggests
photosynthetic
ecologists
number
algae
of
small
–
only
species.
original
that
quite
Also,
families.
small
the
or
need
algal
and
repeatedly
a
falsify
we
carry
carbon
therefore
species
plants
and
that
evidence,
with
not
evolved.
developed.
evolved
do
obtain
are
plants
parasitic
Chloroplasts
many
Because
They
autotrophic
certain
be
have
harm.
autotrophic
easily
they
plants,
discrepancies
of
of
and
other
parasitic
of
how
number
about
●
on
them
insignicant
there
●
chloroplasts
grow
regard
plants
exceptional
of
cells,
diverse
that
plant
evolved
but
and
from
cannot
and
occur
parasitic
species.
and
algae
species
as
that
groups
are
of
parasitic.
d-bs qss: Unexpected diets
Although
animals
and
to9
do
we
to
not
show
usually
be
expect
consumers,
always
four
conform
organisms
plants
living
to
our
with
to
be
autotrophs
organisms
are
very
expectations.
diets
that
are
and
varied
Figures
6
unexpected.
1
Which
of
the
organisms
is
autotrophic?
[4]
2
Which
of
the
organisms
is
heterotrophic?
[4]
3
Of
organisms
the
consumer,
which
that
a
are
heterotrophic,
detritivore
and
deduce
which
a
which
saprotroph.
is
a
[4]
▲
Figure 6 Venus y trap: grows in
swamps, with green leaves that
carry out photosynthesis and also
catch and digest insects, to provide
a supply of nitrogen
▲
204
Figure 7 Ghost orchid: grows
▲
Figure 8 Euglena: unicell
underground in woodland, feeding
that lives in ponds, using its
o dead organic matter, occasionally
chloroplasts for photosynthesis,
growing a stem with owers above
but also ingesting dead organic
ground
matter by endocytosis
▲
Figure 9 Dodder: grows parasitically
on gorse bushes, using small root-like
structures to obtain sugars, amino acids
and other substances it requires, from
the gorse
in
plants
4 . 1
S P e c i e S ,
c o m m u n i t i e S
a n d
e c o S y S t e m S
css
Consumers are heterotrophs that feed on living organisms
by ingestion.
Heterotrophs
source
them
of
in.
are
divided
organic
One
Consumers
group
feed
into
molecules
off
of
groups
that
heterotrophs
other
by
they
is
organisms.
ecologists
use
and
called
These
the
according
method
to
of
the
taking
consumers.
other
organisms
are
either
▲
still
alive
or
have
only
been
dead
for
a
relatively
short
time.
A
feeds
on
Figure 10 Red kite (Milvus milvus) is a
mosquito
consumer that feeds on live prey but also
sucking
blood
from
a
larger
animal
is
a
consumer
that
an
on dead animal remains (carrion)
organism
a
that
is
still
alive.
A
lion
feeding
off
a
gazelle
that
it
has
killed
is
consumer.
Consumers
material
ingest
from
digestion.
lions
Consumers
to
and
take
what
are
other
autotrophs;
In
practice,
because
inside
their
sometimes
secondary
their
it
into
organisms
most
that
digest
such
as
up
into
do
feed
not
t
material
they
and
by
on
a
undigested
the
take
into
variety
in
of
by
such
it.
according
feed
consumers
of
food
consumers
groups
any
products
the
consumers
primary
neatly
in
swallowing
trophic
Primary
from
take
absorb
Multicellular
system
consume.
consumers
it
Paramecium
vacuoles.
divided
includes
means
They
digestive
they
consumers
diet
This
consumers
digest
food
food.
organisms.
Unicellular
endocytosis
as
their
other
one
of
trophic
on
and
so
these
on.
▲
groups
Figure 11 Yellow-necked mouse (Apodemus
avicollis) is a consumer that feeds mostly on
living plant matter, especially seeds, but also
groups.
on living inver tebrates
dvs
Spphs
Detritivores are heterotrophs that obtain
Saprotrophs are heterotrophs that obtain
organic nutrients from detritus by
organic nutrients from dead
internal digestion.
organic matter by external digestion.
Organisms
discard
matter,
example:
for
large
quantities
of
organic
Saprotrophs
organic
absorb
●
dead
leaves
and
other
parts
of
the
feathers,
hairs
and
other
dead
parts
of
animal
bodies
●
feces
This
from
dead
ecosystems
of
nutrition
digest
it
ingest
Large
earthworms
Unicellular
The
larvae
is
groups
dead
and
known
the
organisms
rolled
and
as
fungi
are
digestion.
into
the
They
Many
saprotrophic.
decomposers
carbon
compounds
release
elements
so
they
as
a
dead
then
types
in
such
because
dead
as
They
they
organic
nitrogen
are
of
break
matter
into
the
also
down
and
ecosystem
dung
into
that
can
be
used
again
by
other
organisms.
source
heterotroph
–
organic
absorb
dead
ingest
beetles
matter
the
and
products
detritivores
matter
it
into
feed
by
into
food
then
of
such
their
as
gut.
vacuoles.
ingestion
of
▲
feces
of
enzymes
externally.
accumulates
used
of
multicellular
ingest
of
products
it
saprotrophs.
internally
digestion.
rarely
instead
two
and
Detritivores
matter
and
by
detritivores
digestive
digest
animals.
organic
in
and
plants
bacteria
●
secrete
matter
a
ball
by
their
Figure 12 Saprotrophic fungi growing over the surfaces of dead
parent.
leaves and decomposing them by secreting digestive enzymes
205
4
E c o l o g y
TOK
Identifin mdes f nutritin
t h x   h ss
Classifying species as autotrophs, consumers, detritivores
sss (bs  gs) 
or saprotrophs from a knowledge of their mode of nutrition.
s s s  h  pv?
By
answering
a
series
of
simple
questions
about
an
organism’s
mode
of
There are innite ways to divide up
nutrition
it
is
usually
possible
to
deduce
what
trophic
group
it
is
in.
These
our observations. Organisms can be
questions
are
presented
here
as
a
dichotomous
key,
which
consists
of
a
organized in a number of ways by
series
of
pairs
of
choices.
The
key
works
for
unicellular
and
multicellular
scientists: by morphology (physical
organisms
but
does
not
work
for
parasites
such
as
tapeworms
or
similarity to other organisms),
fungi
that
cause
diseases
in
plants.
All
multicellular
autotrophs
are
phylogeny (evolutionary history) and
photosynthetic
and
have
chloroplasts
containing
chlorophyll.
niche (ecological role). In everyday
language, we classify organisms such
Feeds on living or recently
Feeds on dead organic
killed organisms = CONSUMERS
matter = DETRITIVORES
as domesticated or wild; dangerous or
harmless; edible or toxic.
Either ingests organic matter by endocytosis (no cell walls) or by taking it into its gut.
START HERE
av
cg
Cell walls present. No ingestion of organic matter. No gut.
Secretes enzymes into
Enzymes not secreted.
its environment to digest
Only requires simple
dead
ions and compounds
organic matter
= SAPROTROPHS
such as CO
2
▲
Figure 14
= AUTOTROPHS
In a classic essay written in 1972, the
physicist Philip Anderson stated this:
The ability to reduce everything to
simple fundamental laws does not
cs
imply the ability to start from those
laws and reconstruct the universe. At
A community is formed by populations of dierent
each level of complexity entirely new
species living together and interacting with each other.
properties appear.
An
important
part
of
ecology
is
research
into
relationships
between
Clearcutting is the most common
organisms.
These
relationships
are
complex
and
varied.
In
some
cases
and economically protable form of
the
interaction
between
two
species
is
of
benet
to
one
species
and
logging. It involves clearing every tree
harms
the
other,
for
example
the
relationship
between
a
parasite
and
its
in an area so that no canopy remains.
host.
In
other
cases
both
species
benet,
as
when
a
hummingbird
feeds
With reference to the concept of
on
nectar
from
a
ower
and
helps
the
plant
by
pollinating
it.
emergent proper ties, suggest why the
ecological community often fails to
recover after clearcutting.
206
All
species
are
dependent
long-term
survival.
never
in
live
For
isolation.
on
this
relationships
reason
Groups
of
a
with
other
population
populations
of
live
species
one
for
species
together.
A
their
can
group
4 . 1
of
is
populations
known
in
hundreds
▲
living
ecology
or
even
together
as
a
in
an
area
community.
thousands
of
S P e c i e S ,
and
interacting
Typical
species
c o m m u n i t i e S
with
communities
living
together
in
each
consist
an
a n d
e c o S y S t e m S
other
of
area.
Figure 13 A coral reef is a complex community with many interactions between the
populations. Most corals have photosynthetic unicellular algae called zooxanthellae living
inside their cells
Fied wrk – assiatins between speies
Testing for association between two species using the chi-squared test with data
obtained by quadrat sampling.
Quadrats
out
are
using
involves
a
square
quadrat
repeatedly
sample
frame.
areas,
usually
Quadrat
placing
a
marked
●
sampling
positions
in
a
quadrat
habitat
and
frame
The
usual
quadrats
●
of
A
procedure
is
base
●
the
way
table
is
using
Random
a
present
for
each
randomly
placed
the
precisely
two
at
random
the
distances
numbers.
this
procedure
is
followed
correctly,
with
a
large
the
number
of
replicates,
reliable
estimates
of
time.
positioning
this:
line
habitat
all
organisms
is
by
at
recording
enough
numbers
quadrat
determined
If
random
The
marked
a
along
the
numbers
or
a
out
along
measuring
edge
are
random
tape.
of
the
obtained
number
the
It
edge
must
of
the
extend
habitat.
using
either
generator
on
a
calculator.
●
A
a
●
rst
random
distance
number
along
the
distances
along
A
random
a
second
distance
to
the
must
out
tape.
be
the
tape
must
the
distances
equally
used
number
across
All
is
measuring
likely.
is
to
be
All
equally
used
habitat
across
determine
tape.
to
at
the
likely.
determine
right
angles
habitat
▲
Figure 15 Quadrat sampling of seaweed populations on a
rocky shore
207
4
E c o l o g y
population
suitable
not
sizes
for
are
plants
motile.
obtained.
and
Quadrat
populations
of
other
sampling
most
The
method
organisms
animals,
is
not
for
is
that
suitable
obvious
only
2
are
for
Calculate
the
exp e cte d
fr e que nci es ,
assuming
independ e nt
d is tr i butio n,
each
of
Each
reasons.
the
presence
or
absence
of
more
than
four
expected
values
If
the
on
the
sp e ci e s
f or
co mbi na ti on s.
fre q ue ncy
is
conti ng e ncy
ca lcul a t e d
ta bl e
us i n g
f r om
th is
one
equation:
species
is
recorded
sampling
of
a
in
every
habitat,
it
is
quadrat
possible
during
to
test
for
row total × column total
___
an
expected
often
frequency
=
association
unevenly
between
species.
distributed
Populations
because
some
are
parts
of
3
habitat
are
more
suitable
for
a
species
than
two
they
This
species
will
is
occur
tend
to
known
as
in
be
a
the
same
found
in
positive
parts
the
of
same
a
Calculate
be
negative
or
the
degrees
There
species
can
be
of
degrees
of
freedom
of
freedom
=
(m
1)(n
1)
can
distribution
m
and
n
ar e
the
numbe r
of
ro w s
of
and
two
number
equation.
habitat,
quadrats.
association.
associations,
the
this
where
also
total
others.
using
If
grand
the
number
of
co l umns
in
the
co ntin g e n c y
independent.
table.
There
are
two
possible
hypotheses:
4
H
:
two
species
are
distributed
Find
the
table
independently
of
critical
region
chi-squared
for
chi-squared
values,
using
the
from
a
degrees
0
(the
null
of
hypothesis).
freedom
that
signicance
H
:
two
species
are
associated
(either
region
they
tend
to
occur
together
or
negatively
tend
to
occur
can
test
these
is
any
value
in
value
the
hypotheses
using
a
–
the
(5 %).
and
The
a
critical
of
chi-squared
larger
than
table.
Calculate
chi-squared
chi-squared
using
this
equation:
statistical
(f
procedure
calculated
0.05
apart).
5
We
of
so
the
they
have
(p)
positively
1
so
you
level
test.
f
o
e
_
2
X
)2
=
Σ
f
e
The
chi-squared
expected
sample
test
is
frequencies
was
taken
at
only
are
5
valid
or
random
if
all
larger
from
the
and
the
where
the
f
is
the
observed
frequency
o
population.
f
is
the
expected
frequency
and
e
Method for chi-squared test
Σ
1
Draw
up
a
contingency
table
of
6
frequencies,
which
are
the
numbers
of
or
not
containing
the
sum
of.
Compare
the
two
the
calculated
value
of
chi-squared
quadrats
with
containing
is
observed
the
critical
region.
species.
●
Species A
Species A
Row
present
absent
totals
If
the
calculated
region,
for
We
an
there
is
value
reject
in
evidence
association
can
is
at
between
the
the
critical
the
5%
the
hypothesis
level
two
species.
H
Species B present
0
●
If
the
calculated
value
is
not
in
the
critical
Species B absent
region,
because
it
is
equal
or
below
the
Column totals
value
obtained
squared
Calculate
the
row
and
column
totals.
row
the
same
totals
or
Adding
the
column
totals
should
no
evidence
208
total
in
the
lower
right
is
the
table
not
of
chi-
rejected.
at
the
5%
level
for
There
an
give
association
grand
H
0
is
the
from
values,
cell.
between
the
two
species.
4 . 1
S P e c i e S ,
c o m m u n i t i e S
a n d
e c o S y S t e m S
d-bs qss: Chi-squared testing
Figure
16
Caradoc,
The
hill
shows
a
area
hill
is
an
in
grazed
walkers
area
on
the
Shropshire,
cross
by
it
sheep
on
summit
of
Caer
3
Calculate
4
Find
in
grassy
summer
paths.
There
hummocks
growing
in
suggested
of
moss
with
them.
that
A
heather
visual
in
heather
this
(Calluna
survey
Rhytidiadelphus
growing
these
with
area,
of
of
the
hummocks.
heather
and
this
6
site
a
State
a
sample
of
100
the
quadrats,
presence
moss
was
,
the
and
of
freedom.
[2]
positioned
region
level
of
for
chi-squared
at
a
5%.
[2]
chi-squared.
[4]
two
alternative
evaluate
them
hypotheses,
using
the
H
and
calculated
1
value
for
chi-squared.
[4]
or
Suggest
ecological
reasons
for
an
association
recorded
the
heather
and
the
moss.
[4]
randomly.
8
Explain
used
Results
area
Sps
degrees
0
H
species
associated
The
critical
Calculate
between
in
of
are
7
absence
number
vulgaris)
squarrosus,
was
the
signicance
and
5
raised
the
England.
to
of
the
methods
position
that
should
quadrats
have
randomly
in
been
the
study.
[3]
Fq
Heather only
9
Moss only
7
Both species
57
Neither species
27
Questions
1
Construct
a
contingency
table
of
observed
values.
2
[4]
Calculate
the
association
expected
between
values,
the
assuming
no
species.
[4]
▲
Figure 16 Caer Caradoc, Shropshire
Statistia siniane
Recognizing and interpreting statistical signicance.
Biologists
often
signicant”
experiment.
a
statistical
alternative
use
when
This
the
refers
hypothesis
types
phrase
discussing
of
to
the
test.
“statistically
results
of
outcome
There
are
that
an
a
of
H
is
the
null
and
is
the
belief
range
be
false.
of
critical
hypothesis:
hypothesis
is
the
of
region.
two
to
●
it
results
If
A
possible
the
the
and
is
is
a nd
v a l ues
calcul a te d
region,
false
s ta ti s ti c
rese a r ch
nul l
ca l cul a te d
is
ca ll e d
sta ti stic
the
cr it i c a l
is
r e je cte d,
th e
wi t h
ex c ee d s
hyp othes i s
the r e f or e
u si n g
comp ar e d
the
con si de r ed
t h ou g h
that
0
we
there
is
no
relationship,
for
example
that
cannot
say
tha t
thi s
ha s
be e n
p ro ved
two
withcertainty.
means
or
are
equal
correlation
or
that
between
there
two
is
no
association
When
variables.
a
biologist
statistically
●
H
is
the
alternative
hypothesis
and
is
states
signicant
that
it
results
means
were
that
if
the
null
the
1
hypothesis
belief
that
there
is
a
relationship,
for
two
means
are
different
or
that
there
is
between
two
usual
procedur e
hypothesis,
with
t he
is
to
true,
the
probability
of
as
extreme
as
the
observed
results
getting
would
very
small.
A
decision
has
to
be
made
about
variables.
how
The
was
an
be
association
)
0
example
results
that
(H
tes t
the
e x pe ctatio n
nu ll
of
sh owin g
small
known
point
as
for
this
the
the
probability
signicance
probability
needs
level.
of
to
It
be.
is
rejecting
This
the
the
is
cut-off
null
209
4
E c o l o g y
hypothesis
5%
is
one
when
often
in
in
chosen,
twenty.
signicance
That
level
in
fact
so
is
it
was
the
the
true.
A
probability
minimum
published
level
is
●
of
less
In
than
the
example
between
acceptable
pages,
research.
there
two
the
is
a
If
there
is
a
difference
between
the
less
for
the
two
treatments
in
a
statistical
test
results
will
level.
of
If
such
means
the
it
a
is,
large
arising
population
is
difference
there
population
a
is
chance,
are
than
5%
between
even
equal.
signicant
means
signicant
less
difference
by
means
statistically
is
5%
test
association
on
shows
probability
the
observed
previous
whether
of
the
and
being
as
large
as
it
the
is
the
species
being
either
positively
or
show
negatively
whether
an
an
without
experiment,
than
between
for
described
mean
expected
results
testing
chi-squared
difference
●
of
species,
at
We
5%
When
probability
the
when
say
evidence
the
sample
on
the
a
results
bar
usually
there
a
letter
differ.
is
and
such
not
biological
letters
are
signicance.
statistically
the
of
chart,
statistical
that
that
associated.
b,
a
indicate
and
statistically
a
often
Two
signicant
as
research
are
used
different
mean
indicates
to
with
Two
that
indicate
letters,
results
difference.
displayed
of
any
a
the
same
difference
signicant.
Esstems
A community forms an ecosystem by its interactions
with the abiotic environment.
A
community
organisms
living
is
composed
could
not
surroundings
surroundings
as
In
the
some
cases
organisms.
specialized
the
rock
There
For
are
also
the
and
So,
their
not
also
The
can
where
loose
abiotic
and
many
sand
wave
organisms
community
therefore
known
ecosystems
of
be
and
an
an
up
an
on
area.
their
Ecologists
are
wind
complex
and
and
of
an
be
ecosystem.
interactions
a
to
it
These
non-
refer
to
these
area
Ecologists
between
survive.
inuence
more
within
their
the
develop
plants
stabilize
sand
to
abiotic
On
studyboth
the
cliffs,
can
nest.
abiotic
along
grow
the
be
in
sand
deposited.
there
environment
components
them.
Autotrophs and heterotrophs obtain inorganic nutrients
from the abiotic environment.
●
▲
organisms
Carbon,
need
hydrogen
a
supply
and
of
oxygen
chemical
are
elements:
needed
to
make
carbohydrates,
Figure 1
7 Grasses in an area of developing
sand dunes
210
lipids
and
other
carbon
compounds
on
which
life
is
are
interacting
ig s
Living
the
very
environment.
non-living
complex
over
a
birds
communities,
the
highly
creates
which
They
plants
and
and
single
can
specialized
encourage
inuence
shore
on
this.
these
organisms
in
to
powerful
rocky
ledges
of
interactions
between
a
organisms
shore
roots
a
adapted
there
the
The
organisms
the
on
living
considered
as
exerts
example
the
there
in
depend
rock.
are
leaves
are
or
where
blown
living
they
action
whether
cases
interactions
soil
environment
sand.
only
–
environment.
only
break
organisms
water,
the
dunes
is
all
isolation
wind-blown
many
system,
air,
example
Sand
of
in
abiotic
determines
environment.
coasts
of
the
habitat
type
live
based.
of
4 . 1
Nitrogen
●
and
phosphorus
are
also
S P e c i e S ,
needed
to
c o m m u n i t i e S
make
many
of
a n d
e c o S y S t e m S
these
compounds.
Approximately
●
organisms.
are
fteen
Some
nonetheless
Autotrophs
nutrients
obtain
from
Heterotrophs
several
however
obtain
environment,
of
the
abiotic
the
as
other
them
elements
are
used
in
are
needed
minute
by
traces
living
only,
but
they
essential.
all
the
on
others
of
other
part
of
other
elements
hand
the
obtain
carbon
elements
including
that
environment,
as
sodium,
they
need
including
these
two
compounds
inorganic
potassium
as
and
elements
in
their
nutrients
and
inorganic
carbon
nitrogen.
and
food.
from
They
the
do
abiotic
calcium.
n s
The supply of inorganic nutrients is maintained by
Reserves of an
element in the
nutrient cycling.
abiotic environment
There
living
they
are
limited
organisms
have
endlessly
have
run
to
Earth
using
This
is
the
from
the
of
the
chemical
supplies
because
Organisms
nutrients
them
on
been
out.
recycled.
inorganic
return
not
supplies
absorb
abiotic
environment
elements.
for
chemical
the
three
with
elements
the
billion
elements
environment,
atoms
that
use
Although
can
they
them
years,
be
require
and
as
then
Element forming
part of a living
unchanged.
organism
Recycling
diagram
before
vary
of
and
it
is
from
nitrogen
often
element
cycle
nutrient
in
this
for
carbon
it
element
back
to
the
into
The
is
is
rarely
passed
The
described
an
as
from
in
shown
organism
cycle
refer
is
as
environment.
to
often
element
an
cycle
simple
carbon
nutrient
means
as
abiotic
Ecologists
word
nitrogen
is
the
element.
simply
cycle
and
elements
example.
cycles.
context
topic4.2
an
released
as
The
chemical
of
an
a
details
from
schemes
ambiguous
in
the
collectively
biology
organism
nutrient
this
organism
The
different
these
that
example
Option
is
to
in
but
needs.
cycle
in
sub-
C.
Ssb f sss
Ecosystems have the potential to be sustainable over
long periods of time.
The
it
is
concept
clear
that
Something
fossil
fuels
carry
fuels
are
on
Natural
that
our
of
is
is
sustainability
some
current
sustainable
an
nite,
example
are
not
if
risen
human
it
of
has
can
an
to
uses
prominence
of
continue
resources
being
are
indenitely.
unsustainable
currently
recently
activity.
renewed
and
because
unsustainable.
Human
Supplies
cannot
use
of
of
fossil
therefore
indenitely.
ecosystems
children
requirements
for
●
nutrient
●
detoxication
●
energy
can
and
teach
us
how
grandchildren
sustainability
in
to
can
live
live
in
as
a
sustainable
we
do.
There
way,
are
so
three
ecosystems:
availability
of
waste
products
▲
Figure 18 Living organisms have been recycling
for billions of years
availability.
211
4
E c o l o g y
Nutrients
not
be
a
products
species.
Energy
▲
Figure 19 Sunlight supplies energy to a forest
ecosystem and nutrients are recycled
recycled
the
one
and
species
used
Dust
does
supply
light
the
it
not
from
be
to
in
the
energy
an
recycled,
sun.
The
of
toxic
as
released
source
but
by
is
done
life
a
is
resource
by
because
there
based.
should
The
by
of
the
waste
another
decomposers
Nitrosomonas
sustainability
Most
reduced
only
energy
eruption
causing
was
to
this
which
exploited
ions
importance
the
atmosphere
supplies
so
ecosystems.
the
This
energy
if
on
are
bacteria
action
in
of
the
these
accumulate.
afterwards,
starvation.
usually
potentially
consequences
months
are
and
elements
ammonium
for
is
indenitely
chemical
example,
cannot
energy
by
be
of
Ammonium
bacteria
as
of
For
absorbed
soil.
can
lack
a
the
crop
of
in
is
supply
Mount
intensity
the
on
supplied
this
failures
temporary
ecosystems
of
depends
and
phenomenon,
of
ecosystems
be
in
sunlight
globally
form
to
can
Tambora
of
continued
illustrated
1815.
for
some
deaths
due
however,
sunlight
will
to
and
continue
av
for
billions
of
years.
cv sss
Organisms have been found
living in total darkness in
Messms
caves, including eyeless
sh. Discuss whether
Setting up sealed mesocosms to try to establish
ecosystems in dark caves
sustainability. (Practical 5)
are sustainable.
Mesocosms
are
sma l l
e x pe ri menta l
ar e as
t ha t
ar e
set
up
as
Figure 20 shows a
ecological
experime nts .
Fe nce d- off
e nc l os u re s
in
g r as s la n d
or
small ecosystem with
forest
could
be
us e d
as
te r re s tr ia l
m es oc os m s ;
t a nk s
s et
up
in
photosynthesizing plants
the
laboratory
can
be
use d
as
a qua t ic
me s oc os m s.
E c o lo gi c a l
near ar ticial lighting in a
experiments
can
be
d o ne
in
r e pli cat e
m es oc o sm s,
to
nd
ou t
th e
cave that is open to visitors
effects
of
varying
o ne
or
mo re
co nditi on s .
For
ex am pl e,
t an ks
cou ld
in Cheddar Gorge. Discuss
be
set
up
with
and
wi tho ut
s h,
to
i nv e s t ig a t e
the
e f fe c t s
of
sh
on
whether this is more or
aquatic
ecosystems .
less sustainable than
Another
possible
use
of
mesocosms
is
to
test
what
types
of
ecosystems
ecosystems in dark caves.
are
sustainable.
together
You
or
●
with
should
also
soil
or
these
sealing
water
up
a
inside
questions
community
a
of
organisms
container.
before
setting
up
either
aquatic
mesocosms:
glass
be
involves
and
consider
terrestrial
Large
This
air
jars
used.
are
ideal
Should
the
but
transparent
sides
of
the
plastic
container
containers
be
could
transparent
or
opaque?
●
Which
a
of
these
sustainable
groups
of
community:
organisms
must
autotrophs,
be
included
consumers,
to
make
saprotrophs
up
and
detritivores?
●
How
can
we
organisms
will
●
be
How
▲
Figure 20
212
able
can
placed
in
in
ensure
the
to
we
the
that
the
mesocosm
oxygen
as
once
supply
it
is
is
sufcient
sealed,
no
for
more
all
the
oxygen
enter.
prevent
any
mesocosm?
organisms
suffering
as
a
result
of
being
4 . 2
e n e r G y
F l o w
4.2 eg  
Understandin
Skis
➔
Most ecosystems rely on a supply of energy
Quantitative representations of energy ow
➔
from sunlight.
using pyramids of energy.
➔
Light energy is conver ted to chemical energy in
carbon compounds by photosynthesis.
➔
Nature f siene
Chemical energy in carbon compounds ows
through food chains by means of feeding.
➔
Use theories to explain natural phenomena:
➔
the concept of energy ow explains the limited
Energy released by respiration is used in living
length of food chains.
organisms and conver ted to heat.
➔
Living organisms cannot conver t heat to other
forms of energy.
➔
Heat is lost from ecosystems.
➔
Energy losses between trophic levels restrict
the length of food chains and the biomass of
higher trophic levels.
Suniht and esstems
Most ecosystems rely on a supply of energy from
sunlight.
For
most
sunlight.
Three
biological
Living
groups
eukaryotic
organisms
can
autotroph
carry
of
algae
cyanobacteria.
communities,
including
These
the
initial
harvest
out
are
energy
of
by
photosynthesis:
seaweeds
organisms
this
source
that
grow
often
on
referred
energy
is
photosynthesis.
plants,
rocky
to
by
shores,
and
ecologists
asproducers.
Heterotrophs
dependent
on
consumers,
almost
harvested
The
the
and
in
all
by
amount
world.
for
becomes
their
light
are
food
in
as
the
of
The
energy
percentage
example,
the
redwood
in
the
Sahara
to
the
a
producers
in
of
are
to
this
other
they
are
indirectly
heterotroph
in
of
carbon
them
energy.
compounds
ecosystems
energy
that
organisms
of
In
use
most
will
the
energy
in
is
also
sunlight
because
California
more
of
of
All
but
ecosystems:
ecosystems
originally
have
all
been
producers.
intensity
of
much
groups
source
carbon
organisms
forests
but
to
directly,
detritivores.
supplied
available
available
energy
several
and
photosynthesis
In
because
use
There
energy
therefore
Desert,
it.
not
saprotrophs
compounds
or
do
is
there
varies
harvested
varies.
very
are
intensity
becomes
sunlight
high
very
of
In
by
Sahara
but
to
little
of
it
producers.
sunlight
available
producers
the
few
around
is
less
than
organisms
abundant.
213
4
E c o l o g y
d-bs qss: Insolation
av
Insolation
is
a
measure
of
solar
radiation
The
two
maps
in
gure
2
cb  vs
show
Cyanobacteria are
annual
(upper
map)
mean
and
insolation
at
the
at
Earth’s
the
top
surface
of
the
(lower
Earth’s
atmosphere
map).
photosynthetic bacteria that
are often very abundant
Questions
in marine and freshwater
1
State
the
relationship
between
distance
from
the
equator
and
ecosystems. Figure 1
insolation
at
the
top
of
the
Earth’s
atmosphere.
[1]
shows an area of green
2
State
the
mean
annual
insolation
in
Watts
per
square
metre
cyanobacteria on an area
for
the
most
northerly
part
of
Australia
of wall in a cave that is
illuminated by articial light.
a)
at
the
top
of
the
b)
at
the
Earth’s
atmosphere
[1]
The surrounding areas are
surface.
[1]
normally dark. If the articial
3
Suggest
reasons
for
differences
in
insolation
at
the
Earth’s
light was not present, what
surfacebetween
places
that
are
at
the
same
distance
from
other energy sources could
theequator.
[2]
be used by bacteria in caves?
4
Tropical
rainforests
continents.
Evaluate
They
the
insolation.
are
have
found
very
hypothesis
Include
equatorial
high
that
named
in
this
parts
rates
is
of
of
due
the
regions
of
all
photosynthesis.
to
very
world
in
high
your
answer.
▲
[5]
Figure 1
2
0
▲
214
40
Figure 2
80
120
160
200
240
280
320
360
400 w/m
4 . 2
e n e r G y
F l o w
Ener nversin
av
Light energy is conver ted to chemical energy in carbon
Bsh  fs s
compounds by photosynthesis.
Producers
absorb
pigments.
This
make
carbohydrates,
Producers
can
respiration
is
sunlight
converts
eventually
lipids
release
and
then
lost
to
using
the
and
energy
use
the
chlorophyll
light
it
energy
all
the
from
for
cell
to
other
their
and
carbon
carbon
activities.
environment
as
other
chemical
photosynthetic
energy,
compounds
compounds
Energy
waste
which
to
cell
in
However,
used
producers.
by
released
heat.
in
is
this
only
way
some
▲
of
the
carbon
compounds
in
producers
are
used
in
this
way
and
Figure 3
the
Figure 3 shows a bush re in
largest
part
remains
in
the
cells
and
tissues
of
producers.
The
energy
in
Australia.
these
carbon
compounds
is
available
to
heterotrophs.
What energy conversion is
happening in a bush re?
Ener in fd hains
Bush and forest res
Chemical energy in carbon compounds ows through food
occur naturally in some
ecosystems.
chains by means of feeding.
Suggest two reasons for this
A
food
chain
is
a
sequence
of
organisms,
each
of
which
feeds
on
the
previous
hypothesis: There are fewer
one.
There
are
usually
between
two
and
ve
organisms
in
a
food
chain.
It
is
heterotrophs in ecosystems
rare
for
there
to
be
more
organisms
in
the
chain.
As
they
do
not
obtain
food
where res are common
from
other
organisms,
producers
are
always
the
rst
organisms
in
a
food
compared to ecosystems
chain.
The
subsequent
organisms
are
consumers.
Primary
consumers
feed
where res are not common.
on
producers;
consumers
the
last
feed
therefore
falls
▲
in
on
organism
compounds
Figure
secondary
4
in
is
an
secondary
in
the
indicate
a
food
on
direction
of
a
feed
on
consumers,
chain.
organisms
the
example
northern
consumers
primary
and
Consumers
which
of
they
energy
food
chain
so
on.
obtain
feed.
consumers;
No
consumers
energy
The
tertiary
from
arrows
in
feed
the
a
on
carbon
food
chain
ow.
from
the
forests
around
Iguazu
Argentina.
Figure 4
Respiratin and ener reease
Energy released by respiration is used in living organisms
and conver ted to heat.
Living
organisms
●
Synthesizing
●
Pumping
●
Moving
or
ATP
in
need
large
things
or
around
cells
energy
for
molecules
molecules
muscle
supplies
energy
the
for
ions
like
inside
the
activities
DNA,
across
protein
these
cell
RNA
such
that
activities.
as
cause
Every
as
and
membranes
cell,
bres
such
by
these:
proteins.
active
transport.
chromosomes
muscle
cell
or
vesicles,
contraction.
produces
its
own
ATPsupply.
215
4
E c o l o g y
All
cells
can
produce
compounds
oxidation
in
reason
such
as
The
are
ATP
second
never
in
Energy
have
is
law
not
of
is
cell
be
molecules
respiration.
and
make
and
the
and
other
for
in
cell
to
may
heat.
reside
such
eventually
of
states
the
Some
warm
for
as
a
digested
is
time
the
is
in
carbon
cell,
but
large
energy
is
the
ATP
.
The
chemical
transformations
the
to
oxidation
ATP
.
but
for
as
ATP
is
example.
when
when
released
The
when
contract
molecules
proteins,
to
compounds
produced
they
used
activities.
energy
from
also
when
and
in
transferred
heat
up
DNA
the
that
is
transfers
compounds
different
energy
carbon
These
released
respiration
energy
by
process
oxidized.
energy
cell
many
respiration
Muscles
synthesized,
all
this
are
carbon
usable
directly
Not
the
So
chemical
immediately
used
In
lipids
ATP
.
thermodynamics
activities.
are
to
efcient.
ATP
cell
exothermic
that
converted
from
been
by
glucose
is
compounds
remainder
used
this
can
100%
carbon
are
from
doing
glucose
in
ATP
carbohydrates
reactions
energy
for
energy
as
reactions
endothermic
chemical
of
such
they
these
heat.
d-bs qss
20
Figure
shows
the
r e s ul ts
yellow-bill e d
of
ma g p ie s
an
e x pe ri m e n t
(Pica
nuttalli)
in
were
1
be
in
a
cage
in
controlled.
was
The
measured
from
30 ° C
10 ° C
the
w hi ch
at
to
b i r ds ’
seven
+ 40 ° C.
magpies
temperature,
the
but
temp e rat u r e
r ate
of
tem pe r at u r e s,
Between
mai nta i ned
above
30 ° C
c o ul d
r e spi ra tio n
d iffe r ent
10 ° C
constant
body
15
g Wm( etar noitaripser
put
)
which
5
and
body
temperatur e
10
5
increased.
a)
Describe
the
temperature
relationship
and
between
respiration
rate
external
in
0
yellow-
0
10
billed
b)
magpies.
Explain
the
10
[3]
change
in
respiration
rate
20
30
40
50
temperature (°C)
▲
as
Figure 5 Cell respiration rates at dierent temperatures in
yellow-billed magpies
temperature
c)
Suggest
a
drops
reason
respirationrate
from
30 °C
to
from
for
as
the
+10 °C
to
change
temperature
10 °C.
[3]
in
d)
increased
40 °C.
Suggest
two
respiration
[2]
reasons
rate
for
the
between
variation
the
birds
at
in
each
temperature.
[2]
Heat ener in esstems
Living organisms cannot conver t heat to other forms
of energy.
Living
energy
can
chemical
various
Light
●
Chemical
energy
to
kinetic
●
Chemical
energy
to
electrical
●
Chemical
energy
to
heat
cannot
to
perform
●
They
216
organisms
convert
heat
energy
in
energy
in
into
conversions:
photosynthesis.
in
energy
energy
energy
energy
muscle
in
contraction.
nerve
cells.
heat-generating
any
other
form
adipose
of
tissue.
energy.
4 . 2
e n e r G y
F l o w
Heat sses frm esstems
av
Heat is lost from ecosystems.
thkg b g
Heat
This
resulting
heat
can
from
be
cell
useful
respiration
in
making
makes
living
cold-blooded
organisms
animals
warmer.
more
hgs
active.
What energy conversions
Birds
and
mammals
increase
their
rate
of
heat
generation
if
necessary
to
are required to shoot a
maintain
their
constant
body
temperatures.
basketball?
According
to
the
laws
of
thermodynamics
in
physics,
heat
passes
from
What is the nal form of the
hotter
to
cooler
lost
the
bodies,
so
heat
produced
in
living
organisms
is
all
eventually
energy?
a
to
while,
abiotic
but
ultimately
atmosphere.
in
cell
environment.
Ecologists
activities
will
is
lost,
The
for
assume
ultimately
heat
may
example
that
be
all
lost
remain
when
energy
from
heat
in
is
released
an
the
ecosystem
radiated
by
into
respiration
for
the
for
use
ecosystem.
expg h gh f f hs
Use theories to explain natural phenomena: the
concept of energy ow explains the limited length
of food chains.
If
we
consider
chain,
we
leading
that
can
up
fed
to
on
in
the
There
are
might
expect
branches
the
that
occur
how
which
carnivore
many
if
fed
than
chains
innitum.
science,
of
of
top
example,
more
length
a
an
on
that
stages
osprey
is
at
there
the
are
feeds
on
phytoplankton,
end
in
the
sh
of
food
food
such
there
a
are
chain
as
salmon
four
chain.
food
concept
of
out
For
food
ad
of
restricted
is
work
it.
rarely
another
diet
shrimps,
stages
by
the
we
energy
between
to
be
This
try
food
four
stages
limitless,
not
explain
chains
trophic
ve
does
to
ow
or
using
along
levels
with
in
one
happen.
natural
that
chain.
species
In
and
provide
the
an
We
being
ecology,
theories.
chains
can
food
phenomena
scientic
food
a
as
eaten
in
such
In
this
all
as
the
case
energy
it
losses
explanation.
▲
Figure 6 An infrared camera image of an
Ener sses and esstems
African grey parrot (Psittacus erithacus)
shows how much heat is being released to the
Energy losses between trophic levels restrict the length
environment by dierent par ts of its body
of food chains and the biomass of higher trophic levels.
Biomass
tissues
is
of
the
those
compounds
energy,
added
the
be
per
energy
year
The
they
has
by
per
added
square
Most
of
for
the
organisms
a
of
of
the
is
by
each
in
loss
food
trophic
to
of
is
the
measure
their
so
how
that
by
and
other
much
level
carbon
energy
is
are
trophic
is
and
chemical
results
always
is
cells
levels
found:
less.
always
In
less
per
consumers.
between
digested
the
have
The
energy
primary
released
is
trophic
of
of
different
trend
amount
in
and
biomass.
same
energy
is
consists
compounds
successive
than
that
level
can
the
It
carbohydrates
carbon
ecosystem
ecosystem
is
the
done,
example,
trend
organisms.
Because
organisms
this
for
of
Ecologists
biomass
energy
in
of
metre
metre
this
group
including
energy.
When
to
a
contain.
consumers,
reason
of
groups
square
compared.
secondary
●
year
mass
organisms,
that
biomass
per
calculated
can
total
trophic
levels.
absorbed
them
in
by
respiration
▲
for
Figure 7 The osprey (Pandion halietus) is a
sh-eating top carnivore
217
4
E c o l o g y
use
in
cell
available
av
activities.
to
It
is
organisms
carbohydrates
and
therefore
in
the
other
next
carbon
lost
as
heat.
trophic
The
level
compounds
is
that
only
energy
chemical
have
not
energy
been
in
used
S  s
up
in
cell
respiration.
Most salmon eaten by
The
●
humans is produced in sh
by
farms. The salmon have
organisms
organisms
sometimes
traditionally been fed on
parts
sh meal, mostly based on
the
anchovies harvested o the
of
bodies
trophic
next
of
their
in
all
plants
passes
organisms
have become scarce and
a
the
consume
some
material
coast of South America. These
in
in
to
the
level
the
are
prey
such
in
usually
For
an
bones
or
or
entirely
example,
area
Predators
as
trophic
not
level.
plants
eaten.
saprotrophs
next
are
trophic
but
more
may
not
hair.
Energy
detritivores
eat
rather
consumed
locusts
usually
material
in
only
from
uneaten
than
passing
to
level.
expensive. Feeds based on
Not
●
all
parts
of
food
ingested
by
the
organisms
in
a
trophic
level
are
plant products such as soy
digested
and
absorbed.
in
Energy
Some
material
is
indigestible
not
on
and
is
egested
beans are increasingly being
feces.
in
feces
does
pass
along
the
food
chain
and
used. In terms of energy ow,
instead
passes
to
saprotrophs
or
detritivores.
which of these human diets is
Because
of
these
losses,
only
a
small
proportion
of
the
energy
in
most and least ecient?
1
thebiomass
of
organisms
in
one
thebiomass
of
organisms
in
the
trophic
level
will
ever
become
part
of
Salmon fed on sh meal
2
Salmon fed on soy beans
3
Soy beans.
often
quoted,
variable.
less
As
energy
stages
in
enough
trophic
a
to
but
the
the
losses
available
food
in
food
measured
to
carbon
food
of
of
chain
higher
levels.
of
trophic
level
the
in
is
or
levels
all,
of
trophic
is
of
in
a
energy
The
chain,
level.
this
of
10 %is
levels
there
After
remaining
For
gure
trophic
food
trophic
level.
only
would
reasonthe
is
is
lessand
a
few
not
be
number
of
restricted.
also
diminishes
water
from
therefore
a
level.
between
stage
undigested
is
than
each
loss
successive
and
generally
of
at
grams,
uneaten
trophic
energy
amount
chains
dioxide
trophic
There
each
another
Biomass,
loss
of
occur
to
chain
support
levels
level
next
higher
any
parts
of
usually
biomass
other
along
food
respiration
trophic
loss
organisms.
smaller
of
chains,
and
The
than
producers,
the
biomass
that
the
due
from
of
lower
lowest
level.
secondary consumer
decomposers
2
(200 kJ m
2
(16,000 kJ m
Pramids f ener
1
yr
)
1
yr
)
Quantitative representations of energy ow using
primary consumer
2
(2,500 kJ m
1
yr
)
pyramids of energy.
plankton
The
2
of
energy
converted
to
new
biomass
by
each
trophic
level
in
)
an
▲
amount
1
yr
(150,000 kJ m
ecological
Figure 8 An energy pyramid for an aquatic
This
ecosystem (not to scale)
The
is
a
type
community
can
of
with
amounts
bar
of
chart
energy
be
a
should
represented
horizontal
be
per
unit
with
bar
a
for
area
pyramid
each
per
are
kilojoules
should
lowest
be
per
metre
stepped,
bar.
The
not
bars
squared
per
triangular,
should
be
year
(kJ
starting
labelled
m
with
Often
energy.
level.
the
units
1
yr
the
producer,
trophic
year.
2
of
).
The
pyramid
producers
rst
in
consumer,
the
second
secondary consumer
2
(3,000 MJ m
consumer
1
yr
and
so
on.
If
a
suitable
scale
is
chosen,
the
length
of
each
bar
)
can
be
proportional
to
the
amount
of
energy
that
it
shows.
primary consumer
2
(7,000 MJ m
1
yr
)
Figure
8
shows
ecosystem.
To
an
be
example
more
of
a
pyramid
accurate,
the
bars
of
energy
should
be
for
an
aquatic
drawn
with
relative
producers
2
(50,000 MJ m
1
yr
widths
Figure 9 Pyramid of energy for grassland
218
match
the
relative
energy
content
at
each
trophic
level.
Figure
)
9
▲
that
shows
a
pyramid
of
energy
for
grassland,
with
the
bars
correctly
to
scale.
4 . 2
e n e r G y
F l o w
d-bs qss: a simple food web
A
sinkhole
cavern
a
sinkhole
due
in
is
a
surface
collapses.
lled
part
to
feature
Montezuma
with
the
water.
which
Well
It
extremely
is
an
high
forms
in
the
when
an
Sonoran
aquatic
underground
desert
ecosystem
concentrations
of
in
that
Arizona
lacks
dissolved
is
sh,
CO
.
The
2
dominant
grow
to
Figure
1
top
70 mm
10
Compare
3
4
Deduce
7
a
using
P
b)
what
is
the
a
bakeri,
a
giant
water
of
that
can
for
Montezuma
Belostoma
bakeri
Well.
and
Ranatra
montezuma
[2]
which
organism
occupies
more
level.
[2]
values:
be
the
most
preferred
pyramid
the
of
common
prey
of
energy
B.
for
food
chain
in
this
web
[2]
bakeri?
the
rst
[1]
and
second
the
trophic
levels.
Outline
energy
lost
between
the
rst
and
[2]
of
classifying
organisms
into
[2]
additional
the
of
levels.
difculties
the
complete
[3]
percentage
trophic
Discuss
pyramid
information
of
energy
that
for
would
the
third
be
and
required
to
fourth
level.
[1]
Ranatra montezuma
1
235,000 kJ ha
2
P = 1.0 gm
insect
levels.
Calculate
trophic
web
reason,
would
Construct
Belostoma
web.
trophic
what
second
6
roles
a)
trophic
5
food
food
with
one
is
length.
a
the
the
Deduce,
than
in
shows
within
2
predator
Belostoma bakeri
1
1
yr
588,000 kJ ha
1
2
yr
P = 2.8 gm
1
yr
1
yr
Telebasis salva
1
1,587,900 kJ ha
2
P = 7.9 gm
1
yr
1
yr
Hyalella montezuma
1
30,960,000 kJ ha
2
P = 215 gm
phytoplankton - Metaphyton
1
234,342,702 kJ ha
2
P = 602 g C m
▲
1
yr
1
yr
piphyton
1
yr
1
427,078,320 kJ ha
1
yr
1
yr
2
P = 1,096 g C m
1
yr
Figure 10 A food web for Montezuma Well. P values represent the biomass stored
in the population of that organism each year. Energy values represent the energy
equivalent of that biomass. Arrows indicate trophic linkages and arrow thickness
indicates the relative amount of energy transferred between trophic levels
219
4
E c o l o g y
4.3 cb g
Understandin
Appiatins
➔
Autotrophs conver t carbon dioxide into
➔
Estimation of carbon uxes due to processes in
carbohydrates and other carbon compounds.
the carbon cycle.
➔
In aquatic habitats carbon dioxide is present as
➔
Analysis of data from atmosphere monitoring
a dissolved gas and hydrogen carbonate ions.
stations showing annual uctuations.
➔
Carbon dioxide diuses from the atmosphere or
water into autotrophs.
➔
Skis
Carbon dioxide is produced by respiration and
diuses out of organisms into water or the
➔
Construct a diagram of the carbon cycle.
atmosphere.
➔
Methane is produced from organic matter
Nature f siene
in anaerobic conditions by methanogenic
archaeans and some diuses into the
➔
atmosphere.
➔
➔
Making accurate, quantitative measurements:
it is impor tant to obtain reliable data on the
Methane is oxidized to carbon dioxide and
concentration of carbon dioxide and methane
water in the atmosphere.
in the atmosphere.
Peat forms when organic matter is not fully
decomposed because of anaerobic conditions
in waterlogged soils.
➔
Par tially decomposed organic matter from past
geological eras was conver ted into oil and gas
in porous rocks or into coal.
➔
Carbon dioxide is produced by the combustion
of biomass and fossilized organic matter.
➔
Animals such as reef-building corals and molluscs
have hard parts that are composed of calcium
carbonate and can become fossilized in limestone.
carbn xatin
Autotrophs conver t carbon dioxide into carbohydrates
and other carbon compounds.
Autotrophs
it
into
that
absorb
carbon
carbohydrates,
they
require.
This
the
dioxide
lipids
has
concentration
of
atmosphere
currently
and
the
all
from
the
effect
atmosphere.
of
The
the
atmosphere
other
carbon
reducing
mean
CO
the
and
convert
compounds
carbon
dioxide
concentration
of
the
2
mole
is
(µmol/mol)
photosynthesis
220
but
rates
it
approximately
is
have
lower
been
above
high.
0.039 %
parts
of
or
the
390
micromoles
Earth’s
surface
per
where
4 . 3
c a r B o n
c y c l i n G
d-bs qss: Carbon dioxide concentration
The
by
two
maps
NASA.
in
They
concentration
above
the
gure
show
of
the
surface
of
1
were
the
atmosphere
the
4
produced
carbon
Earth,
a)
Deduce
lowest
eight
between
in
kilometres
May
part
mean
May
State
whether
fall(autumn)
2
a)
October
in
Distinguish
the
in
the
Suggest
a)
Distinguish
dioxide
the
in
in
spring
hemisphere.
October
that
had
the
concentration
2011.
[1]
Suggest
reasons
for
carbon
May
and
for
the
between
the
concentrations
and
the
Suggest
being
the
carbon
lowest
in
dioxide
this
area.
[2]
[1]
dioxide
October
[1]
difference.
[2]
carbon
in
May
between
southern
hemisphere.
b)
and
Earth
dioxide
or
hemisphere.
reasons
northern
the
southern
northern
b)
is
between
concentrations
3
the
2011.
concentration
1
of
carbon
and
b)
October
the
dioxide
[1]
reasons
for
the
difference.
Figure 1
[2]
carbn dixide in sutin
In aquatic habitats carbon dioxide is present as a
dissolved gas and hydrogen carbonate ions.
Carbon
dioxide
is
soluble
in
water.
It
can
either
remain
in
water
as
av
a
dissolved
gas
or
it
can
combine
with
water
to
form
carbonic
acid
pH hgs  k ps
(H
CO
2
).
Carbonic
acid
can
dissociate
to
form
hydrogen
and
hydrogen
3
+
carbonate
ions
(H
and
HCO
).
This
explains
how
carbon
dioxide
can
Ecologists have monitored
3
reduce
the
pH
of
pH in rock pools on sea
water.
shores that contain animals
Both
dissolved
carbon
dioxide
and
hydrogen
carbonate
ions
are
absorbed
and also photosynthesizing
by
aquatic
plants
and
other
autotrophs
that
live
in
water.
They
use
them
algae. The pH of the
to
make
carbohydrates
and
other
carbon
compounds.
water rises and falls in
a 24-hour cycle, due to
changes in carbon dioxide
Absrptin f arbn dixide
concentration in the water.
Carbon dioxide diuses from the atmosphere or water
The lowest values of about
pH 7 have been found during
into autotrophs.
the night, and the highest
Autotrophs
use
carbon
dioxide
in
the
production
of
carbon
compounds
values of about pH 10 have
by
photosynthesis
or
other
processes.
This
reduces
the
concentration
been found when there was
of
carbon
dioxide
inside
autotrophs
and
sets
up
a
concentration
bright sunlight during the
gradient
between
cells
in
autotrophs
and
the
air
or
water
around.
day. What are the reasons for
Carbon
dioxide
therefore
diffuses
from
the
atmosphere
or
water
into
these maxima and minima?
autotrophs.
The pH in natural pools or
In
land
plants
stomata
surface
so
in
of
with
the
the
diffusion
leaves
underside
leaves
can
be
and
this
of
diffusion
the
stems
through
leaves.
is
any
usually
In
usually
part
of
happens
aquatic
plants
permeable
these
parts
to
of
through
the
entire
carbon
the
dioxide,
ar ticial aquatic mesocosms
could be monitored using
data loggers.
plant.
221
4
E c o l o g y
Reease f arbn dixide frm e respiratin
Carbon dioxide is produced by respiration and diuses out
of organisms into water or the atmosphere.
Carbon
dioxide
produced
grouped
in
all
is
a
waste
cells
according
that
to
trophic
●
non-photosynthetic
●
animal
●
saprotrophs
Carbon
into
cells
of
out
level
in
aerobic
aerobic
of
the
cell
cell
respiration.
respiration.
It
is
These
can
be
organism:
producers
for
example
root
cells
in
plants
cells
dioxide
the
product
carry
such
as
fungi
produced
atmosphere
or
by
that
decompose
respiration
water
that
dead
diffuses
surrounds
organic
out
these
of
cells
matter.
and
passes
organisms.
d-bs qss: Data-logging pH in an aquarium
Figure
2
shows
the
pH
and
light
intensity
pH sensor (pH)
in
an
aquarium
containing
a
varied
7.50
100
light intensity
community
of
organisms
including
90
pH
newts
and
other
animals.
7.45
The
data
was
obtained
by
stinu yrartibra/ ytisnetni thgil
pondweeds,
data
80
logging
70
using
a
pH
electrode
and
a
light
meter.
7.40
The
aquarium
was
illuminated
60
articially
50
to
give
a
24-hour
cycle
of
light
and
dark
7.35
using
a
lamp
controlled
by
a
40
timer.
30
1
Explain
the
changes
in
light
7.30
intensity
during
the
experiment.
20
[2]
10
2
Determine
how
many
days
the
0
7.25
data
logging
covers.
[2]
0.14:02:31
0.23:13:11
06 February 2013
3
a)
Deduce
the
trend
in
pH
3.08:23:50
14:02:31
4.17:34:30
6.02:45:09
absolute time (d.hh:mm:ss)
in
Figure 2
the
light.
[1]
4
b)
Explain
this
trend.
a)
Deduce
the
b)
Explain
trend
in
pH
in
darkness.
[1]
[2]
this
trend.
[2]
Methanenesis
Methane is produced from organic matter in anaerobic
conditions by methanogenic archaeans and some
diuses into the atmosphere.
In
a
1776
reed
was
on
this
it
is
a
Three
name.
waste
Bacteria
Volta
He
product
had
is
of
groups
that
collected
margins
Methane
different
alcohol,
222
the
inammable.
it
1
Alessandro
bed
hydrogen
Lake
of
bubbles
discovered
type
of
anaerobic
and
in
and
though
anaerobic
from
found
Volta
mud
that
did
not
in
it
give
environments,
as
respiration.
into
dioxide.
emerging
Italy,
prokaryotes
matter
carbon
gas
in
methane,
widely
anaerobic
organic
of
Maggiore
produced
a
convert
of
a
are
involved.
mixture
of
organic
acids,
4 . 3
2
Bacteria
carbon
3
that
use
dioxide
Archaeans
acetate.
that
They
CO
+
CH
organic
this
→
CH
out
→
in
CH
this
Mud
along
●
Swamps,
peat
the
+
mires,
●
Guts
of
●
Landll
sites
from
chemical
2H
to
produce
acetate,
carbon
dioxide,
hydrogen
and
reactions:
O
CO
group
in
are
many
and
in
mangrove
are
termites
alcohol
2
third
shores
deposits
and
2
methanogenesis
●
or
+
4
archaeans
carry
two
4
3
The
methane
by
2
COOH
acids
c y c l i n G
hydrogen.
produce
do
4H
2
the
and
c a r B o n
therefore
anaerobic
the
bed
forests
of
and
methanogenic.
They
environments:
lakes.
other
wetlands
where
the
soil
waterlogged.
and
where
of
ruminant
organic
mammals
matter
is
in
such
wastes
as
that
cattle
and
have
sheep.
been
buried.
Some
of
the
methane
environments
in
the
atmosphere
Methane
produced
diffuses
is
produced
into
the
between
from
by
archaeans
atmosphere.
1.7
organic
and
1.85
waste
in
in
these
anaerobic
Currently
the
micromoles
anaerobic
concentration
per
mole.
digesters
is
Figure 3 Waterlogged woodland–a typical
not
habitat for methanogenic prokaryotes
allowed
to
escape
and
instead
is
burned
as
a
fuel.
oxidatin f methane
Methane is oxidized to carbon dioxide and water
in the atmosphere.
Molecules
on
of
average
the
methane
for
only
stratosphere.
released
12
years,
Monatomic
into
the
because
oxygen
atmosphere
it
is
(O)
naturally
and
persist
there
oxidized
highly
in
reactive
•
hydroxyl
explains
amounts
human
radicals
why
of
(OH
)
are
atmospheric
production
of
involved
in
methane
concentrations
methane
by
are
both
oxidation.
not
high,
natural
This
despite
processes
large
and
activities.
Peat frmatin
Peat forms when organic matter is not fully decomposed
because of anaerobic conditions in waterlogged soils.
In
many
soils
eventually
obtain
the
in
the
of
soils
cannot
In
thrive
saprotrophs
in
and
matter
such
saprotrophic
they
need
these
conditions
also
dead
so
tend
methanogens
leaves
and
respiration
water
waterlogged
conditions
as
bacteria
for
environments
become
Acidic
m a t t e r.
by
that
some
they
decomposed.
organic
organic
oxygen
soil.
so
all
digested
and
is
to
organic
develop,
that
from
unable
to
anaerobic.
dead
might
from
fungi.
plants
is
Saprotrophs
air
spaces
drain
out
Saprotrophs
matter
further
break
is
not
fully
inhibiting
down
the
Figure 4 Peat deposits form a blanket on a
boggy hill top at Bwlch Groes in Nor th Wales
223
4
E c o l o g y
d-bs qss: Release of carbon from tundra soils
Soils
in
tundra
amounts
of
carbon
accumulates
of
dead
ecosystems
plant
this,
from
of
in
Alaska.
the
of
organic
investigate
areas
in
because
form
low
matter
ecologists
tussock
Some
of
typically
of
rates
by
peat.
of
areas
and
This
samples
Toolik
been
and
To
of
the
soil
nitrogen
and
phosphorus
every
or
15°C.
others
the
Some
were
carbon
amount
5
shows
of
the
eight
years
(TF)
and
some
soils
were
incubated
for
had
100-day
were
with
the
kept
water
soils
was
dioxide
monitored.
moist
(W).
The
measured
given
The
(M)
bar
off
during
chart
in
results.
fertilized
year
for
a)
State
the
effect
not
of
increasing
the
the
of
the
soils
on
the
rate
(TC).
of
The
of
carbon
was
temperature
previous
samples
saturated
content
experiment
gure
Lake
1
with
7
initial
decomposition
near
had
either
large
saprotrophs.
collected
vegetation
the
contain
periods
release
of
carbon.
[2]
at
b)
Explain
the
a)
Compare
reasons
for
this
effect.
[2]
40
2
the
rates
of
release
of
carbon
in
TC
C laitini fo egatnecrep
moist
30
soils
with
those
in
soils
saturated
TF
with
b)
water.
Suggest
[2]
reasons
for
the
differences.
[2]
20
3
Outline
release
the
of
effects
carbon
of
fertilizers
from
the
on
rates
of
soils.
[2]
10
4
Discuss
whether
amount
of
differences
water
in
the
in
soil
or
temperature,
amount
of
0
7M
7W
15M
fertilizer
15W
treatment group
release
have
of
the
greatest
impact
on
the
carbon.
[2]
Figure 5
Large
quantities
of
partially
accumulated
in
brown
material
is
acidic
covered
the
total
by
some
peat
called
and
quantities
of
decomposed
ecosystems
as
peat.
the
this
and
organic
become
About
depth
material
is
3%
ten
are
matter
have
compressed
of
the
metres
to
Earth’s
or
more
form
land
in
a
dark
surface
some
places,
immense.
Fssiized rani matter
Par tially decomposed organic matter from past geological
eras was conver ted into oil and gas in porous rocks or
into coal.
Carbon
can
and
remain
are
large
the
result
in
●
deposits
Coal
is
compounds
of
that
coal.
coal
Large
coastal
buried
left
a
the
of
from
were
Carboniferous.
formed
level
coal.
past
chemically
of
of
very
millions
geological
of
peat
compressed
deposits
the
are
hundreds
eras.
organic
of
These
matter
stable
years.
and
There
deposits
and
its
are
burial
rock.
deposits
is
swamps
when
seam
peat
carbon
for
decomposition
when
The
of
rocks
carbon
became
formed
of
in
incomplete
sediments.
falls;
224
of
sediments
period
Figure 6 Coal at a power station
some
unchanged
rose
are
and
formed
There
buried
heated,
during
was
a
as
the
level
and
the
sea
the
cycle
fell
under
turning
Pennsylvanian
of
and
spread
other
gradually
sea
level
were
inland.
rises
and
destroyed
Each
into
sub-
cycle
and
has
4 . 3
Oil
●
and
lakes.
natural
incomplete.
As
decomposed
which
We
largest
these
part
that
above
more
formed
of
other
or
compressed
mixtures
crude
gas.
them
the
mud
mud
is
natural
below
the
anaerobic
complex
hold
in
usually
mixtures
can
and
are
are
matter
produce
call
rocks
gas
Conditions
oil
of
porous
rocks
are
are
gas.
found
that
and
of
seas
deposited
Chemical
carbon
natural
shales
bottom
decomposition
heated.
liquid
and
as
the
so
sediments
and
Deposits
such
at
and
prevent
the
compounds
the
and
partially
there
are
deposit’s
occur,
or
forms
impervious
c y c l i n G
often
changes
Methane
where
also
is
c a r B o n
gases.
the
porous
rocks
escape.
cmbustin
Carbon dioxide is produced by the combustion of biomass
and fossilized organic matter.
If
organic
of
matter
oxygen
it
is
will
heated
set
light
to
its
and
ignition
burn.
The
temperature
oxidation
in
the
reactions
presence
that
occur
Figure 7 Carbon dioxide is released by
are
called
dioxide
In
and
some
forests
the
combustion.
biomass
rapidly
In
other
are
Coal,
in
are
areas
rainforest
leaves
of
complete
combustion
are
carbon
combustion of the leaves of sugar cane
the
the
world
forest
often
it
Carbon
or
well
is
natural
dioxide
is
grassland.
adapted
to
for
there
released
In
these
res
and
to
be
from
periodic
the
areas
the
res
in
combustion
trees
communities
and
of
other
regenerate
afterwards.
sometimes
cane
of
grassland.
organisms
products
water.
parts
or
The
for
due
them
planting
traditionally
burn
oil
res
cause
off,
and
to
to
oil
palms
burned
leaving
natural
natural
occur.
the
gas
causes
Fire
or
is
for
shortly
cattle
before
harvestable
are
are
used
different
very
to
unusual,
clear
areas
ranching.
they
are
but
of
humans
tropical
Crops
of
sugar
harvested.
The
dry
stems.
forms
of
fossilized
organic
Figure 8 Kodonophyllum–a Silurian coral, in
matter.
They
are
all
burned
as
fuels.
The
carbon
atoms
in
the
carbon
limestone from Wenlock Edge. The calcium
dioxide
released
may
have
been
removed
from
the
atmosphere
by
carbonate skeletons of the coral are clearly
photosynthesizing
plants
hundreds
of
millions
of
years
ago.
visible embedded in more calcium carbonate
that precipitated 420 million years ago in
shallow tropical seas
limestne
Animals such as reef-building corals and molluscs have
hard par ts that are composed of calcium carbonate and
can become fossilized in limestone.
Some
animals
(CaCO
have
hard
body
parts
composed
of
calcium
carbonate
):
3
●
mollusc
●
hard
corals
calcium
When
shells
contain
that
build
calcium
reefs
carbonate;
produce
their
exoskeletons
by
secreting
carbonate.
these
animals
die,
their
soft
parts
are
usually
Fig u r e
decomposed
9
E ng la nd.
quickly.
In
acid
conditions
the
calcium
carbonate
dissolves
away
but
or
alkaline
conditions
it
is
stable
and
deposits
of
it
from
parts
can
form
on
the
sea
bed.
In
shallow
tropical
seas
cl i f f s
is
a
on
the
f or m
of
sou th
coast
l i mestone
of
that
a l most
enti r ely
of
90 - m i l l ion- yea r-
hard
old
animal
Cha l k
in
cons i sts
neutral
Cha l k
s hel l s
of
ti ny
u n icel l u la r
a n i ma l s
ca l led
calcium
fo r a m i n i fe r a
225
4
E c o l o g y
carbonate
is
limestone
rock,
visible
as
also
of
carbon
the
by
precipitation
deposited
hard
in
the
parts
water.
of
The
animals
result
are
is
often
fossils.
Approximately
12%
deposited
where
the
are
10%
mass
of
locked
of
the
up
all
sedimentary
calcium
in
rock
carbonate
limestone
rock
on
is
on
Earth
carbon,
is
so
limestone.
huge
About
amounts
of
Earth.
carbn e diarams
Construct a diagram of the carbon cycle.
Ecologists
recycling
studying
of
other
the
carbon
elements
cycle
use
the
and
the
terms
Diagrams
pool
cycle.
and
arrows
ux.
for
diagram
●
A
pool
is
a
reserve
of
the
element.
It
can
or
inorganic.
dioxide
in
the
of
carbon.
ecosystem
The
is
For
example
atmosphere
biomass
an
of
organic
is
an
the
A
ux
one
ux
is
pool
is
the
to
the
transfer
another.
of
in
be
An
absorption
of
element
example
carbon
of
the
atmosphere
and
its
to
plant
to
be
represent
used
Figure
can
be
10
for
shows
converted
shows
ecosystems.
a
for
combined
the
A
labeled
diagram
diagram
cycle
separate
marine
or
of
for
all
for
diagram
aquatic
and
reserve
of
aquatic
could
ecosystems,
ecosystems.
ecosystems,
the
In
inorganic
carbon
carbon
conversion
hydrogen
is
dissolved
carbonate,
carbon
which
is
dioxide
and
by
various
means
biomass.
the
water.
in
cell respiration
in saprotrophs
and detritivores
s
le
u
f
cell respiration
li
s
s
o
f
carbon in
in consumers
organic
compounds
fo
in producers
n
o
it
s
u
b
m
o
c
death
feeding
egestion
carbon in dead
organic matter
incomplete
decomposition
and fossilization
of organic matter
and
absorbed
by
by
2
226
a
and
illustrated
dioxide
CO
Figure 10 Carbon cycle
an
to
carbon
atmosphere
oil
carbon
arrows.
only
marine
into
coal
the
pools
from
producers
photosynthesis
and
constructed
and
from
10
terrestrial
an
pool.
the
can
uxes.
which
boxes
Figure
pool
or
●
used
carbon
inorganic
producers
be
boxes
be
text
organic
can
Text
gas
is
released
back
4 . 3
c a r B o n
c y c l i n G
carbn uxes
Estimation of carbon uxes due to processes in the carbon cycle.
The
carbon
cycle
diagram
in
gure
10
shows
F x/ggs
Pss
processes
another
uxes.
uxes
but
It
is
it
transfer
does
not
them.
not
but
scientists
Estimates
individual
carbon
show
possible
precisely
interest,
in
that
as
global
quantities
on
or
1
to
of

these
are
of
120
Cell respiration
119.6
great
Ocean uptake
92.8
Ocean loss
90.0
for
measurements
in
Photosynthesis
carbon
estimates
many
ecosystems
pool
quantities
produced
based
natural
the
one
measure
these
have
are
to
from
mesocosms.
Deforestation and land use
1.6
changes
Global
carbon
estimates
are
gigatonne
based
on
is
uxes
in
1,015
Ocean
are
extremely
gigatonnes
grams.
large
(petagrams).
Table
Biogeochemical
1
shows
Dynamics,
so
Burial in marine sediments
0.2
Combustion of fossil fuels
6.4
One
estimates
Sarmiento
T
able 1
and
Gruber,
2006,
Princeton
University
Press.
d-bs qss: Oak woodland and carbon dioxide concentrations
Carbon
uxes
deciduous
in
England.
robur
and
have
been
woodland
The
at
trees
Quercus
measured
Alice
are
Holt
mainly
petraea,
with
since
1998
Research
oaks,
some
in
1
on
Quercus
ash,
They
were
planted
in
1935
and
are
20
metres
more
Deduce
dioxide
times
a
concentrations
are
net
is
second.
ecosystem
the
net
From
these
forest
indicate
the
an
forest
decrease
and
production
ux
of
the
can
carbon
be
dioxide
atmosphere.
increase
and
due
in
the
negative
to
shows
net
the
the
months
in
Explain
for
net
year.
[1]
the
in
which
forest
was
the
carbon
pool
highest
of
Positive
carbon
values
loss
daily
pool
indicate
carbon
average
the
reasons
net
pool
of
several
years
ecosystem
for
and
biomass
increases
in
the
in
the
forest
part
of
the
year
and
decreases
in
between
parts.
[4]
values
4
of
the
annual
carbon
ux
to
or
from
forest.
a
dioxide.
State
the
[2]
The
Suggest
a
reason
based
on
the
data
for
ecosystem
also
the
planting
of
more
the
oak
cumulative
the
[2]
encouraging
production
in
decreases
deduced.
5
graph
or
measurements
other
the
the
pool
lowest.
during
This
in
carbon
increases
measured
carbon
the
the
forest
tall.
3
20
days
biomass
and
Carbon
the
now
of
nearly
whether
of
Fraxinus
2
excelsior.
Calculate
biomass
Forest
forests.
[1]
production.
20
25
1
)
20
1
1
)
h
15
15
ah
ah
10
5
5
0
0
0
50
100
150
200
250
300
530
−5
OC t( PEN evitalumuc
2
OC gk( PEN egareva yliad
2
10
−5
−10
−10
−15
day of year
227
4
E c o l o g y
Envirnmenta mnitrin
Making accurate, quantitative measurements: it is impor tant to obtain reliable data
on the concentration of carbon dioxide and methane in the atmosphere.
Carbon
in
the
dioxide
and
atmosphere
effects.
Carbon
methane
have
dioxide
photosynthesis
rates
the
pH
of
above
affect
seawater.
inuence
global
temperatures
and
as
a
600
extent
of
ice
sheets
at
the
poles.
therefore
affect
sea
levels
and
data
lines.
Through
their
effects
the
on
position
heat
the
energy
affect
in
ocean
the
oceans
currents,
and
the
and
extreme
also
the
weather
the
such
and
as
these
hypotheses
and
The
carbon
dioxide
atmosphere
time
in
the
is
severity
past
twenty
over
can
Human
activities
dioxide
and
have
Data
on
higher
million
of
than
the
prerequisite
predictions
methane
long
of
by
a
the
period
past
human
the
at
any
Research
now
years.
of
Organization,
for
of
such
concentration
as
possible
and
possible
future
of
gases
in
the
Atmosphere
atmosphere
Watch
increased
the
the
on
World
agency
in
Meteorological
of
the
various
atmosphere,
Hawaii
has
United
parts
of
but
Nations.
the
world
Mauna
records
from
carbon
concentrations
in
period.
Carbon
dioxide
concentrations
the
been
measured
activity
will
cause
atmospheric
records
from
are
of
1984.
from
1959
These
immense
and
onwards
value
other
and
to
reliable
scientists.
Analysis of data from atmosphere
monitoring stations showing
annual uctuations.
freely
it.
atmosphere
available
There
are
uctuations
data
and
stations
are
in
monitoring
allowing
both
in
Observatory
of
the
data.
Hawaii
data
any
long-term
from
available
The
person
trends
for
and
to
and
Mauna
produces
this
stations
analyse
annual
Loa
vast
other
is
amounts
monitoring
analysis.
Figure 11 Hawaii from space. Mauna Loa is near the
centre of the largest island
228
Loa
the
Trends in atmspheri arbn dixide
from
are
before
atmosphere.
Human
Data
as
atmospheric
activity.
Global
the
an
stations
monitor
methane
●
level
century.
predictions:
have
Earth’s
and
concentrations
collected
longest
methane
and
as
evaluate
Observatory
●
from
a
of
hurricanes.
concentration
currently
essential
measurements
dioxide
programme
●
the
to
of
is
Consider
rise
atmosphere
distribution
frequency
events
an
hypotheses
consequences
rainfall
of
to
2014
amount
we
they
end
in
of
needed
of
are
Reliable
carbon
coast
the
mole
Indirectly
these.
they
by
per
result
evaluating
the
concentrations
Both
Reliable
gases
dioxide
397micromoles
important
concentrations
and
carbon
concentrations
very
4 . 4
c l i m a t e
c H a n G e
4.4 c hg
Understandin
Appiatins
Carbon dioxide and water vapour are the most
➔
Correlations between global temperatures and
➔
signicant greenhouse gases.
carbon dioxide concentrations on Ear th.
Other gases including methane and nitrogen
➔
Evaluating claims that human activities are not
➔
oxides have less impact.
causing climate change.
The impact of a gas depends on its ability to
➔
Threats to coral reefs from increasing
➔
absorb long-wave radiation as well as on its
concentrations of dissolved carbon dioxide.
concentration in the atmosphere.
The warmed Ear th emits longer-wave radiation
➔
(heat).
Nature f siene
Longer-wave radiation is reabsorbed by
➔
Assessing claims: assessment of the claims
➔
greenhouse gases which retains the heat in the
that human activities are not causing climate
atmosphere.
change.
Global temperatures and climate patterns are
➔
inuenced by concentrations of greenhouse
gases.
There is a correlation between rising atmospheric
➔
concentrations of carbon dioxide since the star t
of the industrial revolution two hundred years ago
and average global temperatures.
Recent increases in atmospheric carbon
➔
dioxide are largely due to increases in the
combustion of fossilized organic matter.
greenhuse ases
Carbon dioxide and water vapour are the most signicant
greenhouse gases.
The
in
Earth
the
is
kept
atmosphere
likened
to
that
of
therefore
known
retention
is
The
are
●
not
carbon
Carbon
that
the
as
the
greenhouse
in
much
dioxide
living
retain
glass
than
heat.
that
it
The
retains
greenhouse
gases,
otherwise
effect
heat
of
in
though
a
would
these
be
gases
greenhouse
the
by
gases
has
been
and
mechanism
of
they
are
heat
same.
gases
dioxide
warmer
that
and
is
have
water
released
organisms
and
the
largest
warming
effect
on
the
Earth
vapour.
into
also
by
the
atmosphere
combustion
of
by
cell
biomass
respiration
and
fossil
229
4
E c o l o g y
fuels.
It
is
removed
dissolving
Water
●
in
the
vapour
transpiration
and
Water
liquid
back
continues
the
explains
areas
formed
in
the
atmosphere
by
photosynthesis
and
by
plants.
by
It
evaporation
is
removed
from
from
the
the
oceans
and
atmosphere
also
by
rainfall
snow.
water
to
is
from
oceans.
in
Earth’s
why
with
to
retain
clouds.
the
clear
heat
The
surface
and
temperature
skies
than
after
water
in
it
condenses
absorbs
also
reects
drops
areas
heat
so
the
much
with
to
form
energy
heat
more
cloud
droplets
and
of
radiates
energy
back.
quickly
at
it
This
night
in
cover.
other reenhuse ases
Other gases including methane and nitrogen oxides have
less impact.
Although
carbon
dioxide
and
water
vapour
are
the
most
signicant
Figure 1 Satellite image of Hurricane Andrew in
greenhouse
gases
there
are
others
that
have
a
smaller
but
nonetheless
the Gulf of Mexico. Hurricanes are increasing in
frequency and intensity as a result of increases
signicant
effect.
in heat retention by greenhouse gases
Methane
●
from
sites
is
where
extraction
Nitrous
●
vehicle
two
are
radiation.
than
1%
All
of
fossil
by
is
most
other
signicant
wastes
fuels
bacteria
in
have
and
another
greenhouse
waterlogged
been
from
ice
It
in
greenhouse
habitats
and
gas.
and
dumped.
melting
signicant
some
habitats
also
It
from
is
emitted
released
polar
gas.
by
is
landll
during
regions.
It
is
released
agriculture
and
exhausts.
most
nitrogen,
third
and
organic
of
oxide
naturally
The
the
marshes
abundant
not
of
the
gases
greenhouse
the
in
the
gases
greenhouse
Earth’s
as
gases
they
atmosphere,
do
not
together
oxygen
absorb
and
longer-wave
therefore
make
up
less
atmosphere.
Assessin the impat f reenhuse ases
The impact of a gas depends on its ability to absorb
long-wave radiation as well as on its concentration in the
atmosphere.
Two
factors
●
how
●
the
For
readily
carbon
atmosphere
The
the
its
water
there
atmosphere
for
as
a
it
enters
nine
in
days
twelve
the
much
is
at
a
long
the
on
years
more
on
lower
is
a
greenhouse
gas:
and
the
rate
average
average,
at
it
molecule
is
which
it
remains
is
in
the
methane
dioxide
for
released
there.
immensely
whereas
carbon
per
concentration
less.
atmosphere
and
of
radiation;
warming
much
on
impact
atmosphere.
warming
depends
how
warming
long-wave
global
gas
and
the
gas
causes
on
vapour
only
the
but
impact
of
absorbs
of
methane
atmosphere
which
remains
230
gas
dioxide,
concentration
into
the
the
determine
concentration
example,
than
at
together
The
rapid,
rate
but
remains
even
longer.
it
in
4 . 4
c l i m a t e
ln-waveenth emissins frm Earth
c H a n G e
TOK
The warmed Ear th emits longer-wave radiation.
Qss xs b h 
The
warmed
sun
and
then
re-emitted
The
peak
Figure
2
through
and
the
pass
re-emits
the
the
it,
is
wavelength
shows
of
through
range
of
temperature
of
much
of
but
at
solar
range
the
Earth
of
to
with
longer
the
peak
is
and
of
expected
the
wavelength
of
of
10,000
radiation
emitted
to
Most
the
f s ph. wh
the
sqs gh hs hv f h
nm.
pb pp  sg
f s?
surface
The
from
nm.
solar
Earth’s
(blue).
energy
wavelengths.
400
wavelengths
atmosphere
Earth
a
wavelengths
reach
short-wave
longer
radiation
wavelengths
the
absorbs
much
infrared,
atmosphere
range
the
of
radiation
the
out
show
surface
and
by
smooth
be
the
red
emitted
that
pass
warm
Earth
and
by
it
involves entities and concepts beyond
that
blue
bodies
Much of what science investigates
(red)
everyday experience of the world,
curves
of
such as the nature and behaviour
the
of electromagnetic radiation or the
sun.
build-up of invisible gases in the
atmosphere. This makes it dicult
for scientists to convince the general
ytisnetni lartceps
public that such phenomenon
actually exist – par ticularly when
the consequences of accepting their
existance might run counter to value
systems or entrenched beliefs.
UV
Visible
Infrared
1
0.2
10
70
wavelength (µm)
Figure 2
greenhuse ases
Longer-wave radiation is reabsorbed by greenhouse gases which retains
the heat in the atmosphere.
25–30%
the
is
sun
of
the
that
absorbed
of
light,
which
much
the
of
passing
before
Most
radiation
is
short-wavelength
solar
is
it
radiation
absorbed
therefore
this
is
through
reaches
by
reaches
converted
radiation
the
the
atmosphere
Earth’s
absorbed
ozone.
the
to
is
surface.
ultraviolet
70–75 %
Earth’s
heat.
from
of
solar
surface
and
A
far
higher
percentage
radiation
re-emitted
absorbed
before
70%
the
and
85%
is
atmosphere.
towards
Without
surface
the
it
it
This
would
the
be
longer-wavelength
surface
by
out
effect
is
the
is
Earth
space.
global
at
is
Between
gases
re-emitted,
temperature
about
of
to
greenhouse
energy
The
mean
the
passed
captured
Earth.
the
by
has
of
in
some
warming.
the
Earth’s
18°C.
Key
short-wave radiation
from the sun
long-wave radiation
from earth
Figure 3 The greenhouse eect
231
4
E c o l o g y
Greenhouse
only
absorb
Figure
of
4
below
radiation
shows
gases
the
in
energy
by
the
in
shows
the
bands
Earth’s
specic
total
percentage
atmosphere.
of
atmosphere
individual
wavebands.
The
wavelengths
the
absorption
graph
absorbed
Earth
carbon
also
is
a
some
The
wavelengths
between
dioxide,
absorb
by
gases.
are
of
5
and
methane
these
greenhouse
re-emitted
70nm.
and
Water
nitrous
wavelengths,
oxide
so
by
vapour,
each
all
of
them
gas.
100
tnecrep
75
Total absorption
50
and scattering
25
0
0.2
1
10
70
Water vapour
stnenopmoc rojam
Carbon dioxide
Oxygen and ozone
Methane
Nitrous oxide
0.2
1
10
70
wavelength (µm)
Figure 4
gba temperatures and arbn dixide nentratins
Correlations between global temperatures and carbon dioxide concentrations
on Ear th.
If
the
in
concentration
the
size
atmosphere
of
its
change
can
contribution
and
test
this
global
To
is
drilled
than
trapped
to
in
in
nd
the
greenhouse
can
expect
greenhouse
using
to
the
atmosphere,
in
the
rise
gases
carbon
fall.
to
We
dioxide
because
it
past,
ice
can
columns
years,
the
can
be
so
isotopes
in
ice
has
ice
built
deeper
and
water
up
down
of
air
analysed
concentration.
from
ratios
5
shows
results
for
an
Global
the
present.
They
were
year
obtained
carbon
–
when
the
ice
core
plateau
232
by
drilled
the
in
Dome
European
C
on
Project
the
for
same
Data
that
the
to
of
trend
this
the
current
of
higher
was
Age
periods
periods
striking
concentration
of
Ice
rapid
longer
very
repeatedly
Earth
rises
in
of
correlation
and
global
carbon
coincide
with
warmer.
past
that
some
in
dioxide
the
800,000
It
is
case
in
the
ice
we
does
is
a
temperature
must
increase
always
not
know
cores.
hypothesis
concentration
dioxide
years
other
with
important
correlation
this
carbon
of
found
consistent
effect.
that
but
been
are
carbon
remember
least
has
type
greenhouse
causation,
At
prove
from
other
greenhouse
variation
therefore
gas.
over
have
been
period
to
rises
and
from
Antarctic
Ice
a
periods
periods
of
pattern
much
is
dioxide
the
concentration
concentrations.
an
part
by
There
dioxide
due
before
this
repeating
followed
temperatures
research
of
molecules.
800,000
a
cooling.
between
the
Figure
During
been
warming
gradual
The
have
has
of
has
and
Bubbles
extracted
deduced
the
of
ice
from
surface.
dioxide
be
The
Antarctica.
there
the
effect
or
concentrations
Antarctic.
near
carbon
temperatures
hydrogen
the
of
ice
the
dioxide
the
thousands
older
to
the
we
temperatures
the
carbon
temperatures
over
of
of
considerably.
deduce
been
any
hypothesis
concentration
changed
of
changes,
Coring
in
falls
in
atmospheric
carbon
dioxide
4 . 4
c l i m a t e
c H a n G e
300
vmpp/
250
OC
2
200
erutarepmet(
-380
warm
)yxorp
9°C
-410
%/Dδ
°
-440
cold
800,000
600,000
400,000
200,000
0
age (years before present)
Figure 5 Data from the European Project for Ice Coring in the Antarctic Dome C ice core
d-bs qss: CO
concentrations and global temperatures
2
Figure
6
shows
atmospheric
measurements
The
points
ice
at
show
concentrations
polar
The
red
line
Mauna
carbon
carbon
shows
Loa
0.6
dioxide
direct
)C°( ylamona erutarepmet
concentrations.
Observatory.
dioxide
measured
from
trapped
air
in
cores.
380
Annual average
0.4
Five year average
0.2
0
-0.2
emulov yb noillim rep strap
Direct measurments
360
Ice core measurments
-0.4
340
1880
1900
1920
1940
1960
1980
2000
320
Figure 7
300
2
Compare
the
trends
in
carbon
280
dioxide
260
concentration
temperatures
1750
1800
1850
1900
1950
and
between
global
1880
and
2008.
[2]
2000
3
Estimate
the
change
in
global
average
Figure 6
temperature
Figure
7
shows
temperatures
Institute
annual
for
a
Space
averages
ve-year
from
1961
1990.
1
Discuss
carbon
ice
global
the
average
NASA
The
red
are
is
a)
1900
and
2000
[1]
b)
1905
and
2005
[1]
Goddard
green
curve
values
mean
points
a
given
temperature
are
rolling
as
4
a)
the
Suggest
the
between
measurements
concentration
consistent
measurements
at
with
Mauna
years
of
b)
from
during
trend
Discuss
indicate
direct
Loa.
reasons
temperatures
overall
whether
are
the
The
the
dioxide
cores
of
by
Studies.
and
average.
deviation
and
record
compiled
between
a
global
for
rising
whether
that
global
period
of
does
average
few
an
temperatures.
[2]
falls
dioxide
not
temperatures.
a
with
these
carbon
concentration
[2]
for
falling
inuence
[2]
233
4
E c o l o g y
greenhuse ases and imate patterns
evaporation
of
water
from
the
oceans
and
Global temperatures and climate
therefore
patterns are inuenced by
frequent
bursts
surface
of
the
Earth
is
warmer
than
and
delivered
concentrations of greenhouse gases.
The
is
be
with
no
greenhouse
gases
in
Mean
temperatures
are
estimated
32°C
higher.
greenhouse
and
we
If
the
gases
should
concentration
rises,
expect
more
an
heat
increase
of
will
in
any
be
of
global
average
The
not
all
mean
that
global
likely
are
gas
directly
inuence,
orbit
and
proportional
Other
Milankovitch
variation
in
increases
in
greenhouse
and
to
also
Global
of
cause
higher
more
global
frequent
cycles
sunspot
gas
temperatures
climate.
Higher
very
and
more
of
rain
other
intense
signicantly.
temperatures
cause
In
tropical
to
be
faster
more
wind
frequent
and
speeds.
of
any
rise
unlikely
become
to
in
be
global
evenly
warmer.
Scotland
might
The
average
spread.
west
become
Not
coast
colder
in
activity.
heat
other
temperatures
Atlantic
Current
brought
less
if
warm
from
the
Gulf
distribution
of
Stream
rainfall
to
north-west
would
also
be
Europe.
likely
to
the
with
some
areas
becoming
more
prone
Even
droughts
and
other
areas
to
intense
periods
of
will
and
ooding.
Predictions
about
changes
to
temperatures
intense
inuence
amount
have
concentrations
average
and
with
are
and
North
rainfall
tend
be
to
factors
to
so,
ocean
hurricanes
would
change,
Earth’s
increase
to
average
concentrations.
including
and
powerful,
areas
The
an
to
consequences
water
greenhouse
The
thunderstorms
higher
Ireland
the
temperatures
during
temperature
of
does
protracted.
likely
the
retained
temperatures.
This
are
to
more
be
rain
the
storms
atmosphere.
of
it
addition,
would
periods
weather
patterns
that
a
are
very
uncertain,
but
it
is
clear
waves.
aspects
increase
just
profound
few
degrees
changes
to
of
the
warming
Earth’s
would
cause
very
climatepatterns.
the
d-bs qss: Phenology
Phenologists
of
seasonal
the
are
biologists
activities
opening
of
tree
in
who
animals
leaves
and
study
and
the
the
laying
temperature
timing
plants,
of
such
as
35
of
birds.
Data
climate
The
date
such
as
changes,
in
the
these
can
including
spring
when
provide
global
new
was
been
chestnut
recorded
Figure
year’s
8
trees
in
shows
date
of
Germany
the
leaf
(Aesculus
warming.
leaves
open
hippocastaneum)
every
difference
opening
year
since
between
and
the
Identify
the
a)
the
opening
between
1970
and
indicate
earlier
than
that
b)
mean
1951.
2
Use
the
mean.
date
The
of
leaf
graph
date
between
each
year’s
mean
March
the
and
for
April
these
and
two
the
in
[1]
at
their
March
the
in
the
relationship
[1]
graph
to
deduce
the
and
between
April
and
the
temperatures
date
of
in
opening
leaves
on
horse
chestnut
trees.
[1]
the
whether
there
is
evidence
of
global
of
the
temperature
The
towards
the
end
mean
data
century.
[2]
for
Figure 8 The relationship
15
4
between temperature and
5
1
0
0
1
5
2
10
syad / gninepo fael
C° / erutarepmet
naem ni ecnereid
10
2
fo etad ni ecnereid
3
horse chestnut leaf opening
in Germany since 1951
Key:
temperature
3
15
4
1970
234
and
lowest.
was
shows
overall
months.
earliest
temperatures
data
20th
temperature
opened
were
warming
during
which:
of
b)
difference
in
Negative
opening
also
of
following:
of
the
year
leaves
March
values
records
has
each
mean
2000.
the
on
a)
leaf
from
stations.
evidence
April
horse
obtained
climate
eggs
1
by
German
1980
1990
2000
leaf opening
4 . 4
c l i m a t e
c H a n G e
Industriaizatin and imate hane
There is a correlation between rising atmospheric
concentrations of carbon dioxide since the star t of the
industrial revolution two hundred years ago and average
global temperatures.
The
graph
800,000
of
uctuations.
180
parts
rose
as
atmospheric
years
During
per
high
shown
300
carbon
gure
5
glaciations
million
as
in
by
the
volume.
ppm.
The
dioxide
concentrations
indicates
there
concentration
During
rise
that
warm
during
over
have
dropped
to
interglacial
recent
times
to
the
been
past
large
as
low
periods
as
they
concentrations
Figure 9 During the industrial revolution
nearing
400
ppm
is
therefore
unprecedented
in
this
period.
renewable sources of power including
Atmospheric
carbon
280ppm
until
probably
started
initially
very
the
In
the
late
second
and
18th
but
half
is
carbon
strong
century.
the
Much
the
of
century.
coal,
oil
increases
and
in
for
factors
is
to
say
the
a
when
has
More
countries
natural
gas
an
global
effect
the
when
was
an
by burning fossil fuels
ever
dioxide
between
was
rise
1950.
in
was
some
in
the
industrialized,
more
rapidly,
concentration.
atmospheric
temperatures,
so
wind were replaced with power generated
and
unnatural
starting
globally
increased
rise
since
became
carbon
correlation
as
happened
revolution
260
concentrations
but
exactly
rise
between
industrialization
and
have
were
levels,
atmospheric
concentration
other
of
industrial
impact
20th
This
natural
impossible
evidence
dioxide
explained,
main
of
consequent
There
is
began.
the
combustion
with
it
concentrations
above
century
the
of
18th
rise
slight,
concentrations
countries
late
to
in
dioxide
temperatures
but
as
are
not
already
TOK
directly
since
proportional
the
start
of
the
to
carbon
industrial
dioxide
concentration.
revolution
the
Nevertheless,
correlation
between
wh ss  pb
rising
atmospheric
carbon
dioxide
concentration
and
average
global
v f sk?
temperatures
is
very
marked.
In situations where the public is at risk,
scientists are called upon to advise
governments on the setting of policies
Burnin fssi fues
or restrictions to oset the risk. Because
Recent increases in atmospheric carbon dioxide are
scientic claims are based largely on
largely due to increases in the combustion of fossilized
inductive observation, absolute certainty
is dicult to establish. The precautionary
organic matter.
principle argues that action to protect
As
the
industrial
revolution
spread
from
the
late
18th
century
the public must precede certainty of
onwards,
increasing
quantities
of
coal
were
being
mined
and
burned,
risk when the potential consequences
causing
carbon
dioxide
emissions.
Energy
from
combustion
of
the
coal
for humanity are catastrophic. Principle
provided
a
source
of
heat
and
power.
During
the
19th
century
the
15 of the 1992 Rio Declaration on the
combustion
of
oil
and
natural
gas
became
increasingly
widespread
in
Environment and Development stated
addition
to
coal.
the principle in this way:
Increases
1950s
in
in
the
onwards
atmospheric
that
the
burning
and
carbon
burning
factor
in
the
levels
than
this
rise
of
fossil
dioxide.
fuels
It
of
fossil
of
atmospheric
experienced
fuels
coincides
on
were
with
seems
has
been
carbon
Earth
the
for
most
hard
a
to
major
dioxide
more
rapid
period
than
of
from
the
steepest
doubt
the
Where there are threats of serious or
rises
irreversible damage, lack of full scientic
conclusion
contributory
concentrations
800,000
certainty shall not be used as a reason
for postponing cost-eective measures
to
higher
to prevent environmental degradation.
years.
235
4
E c o l o g y
d-bs qss: Comparing CO
emissions
2
The
bar
chart
in
gure
10
shows
the
cumulative
CO
were
higher
Arab
Emirates,
in
the
year
2000:
Qatar,
United
2
emissions
and
ve
from
fossil
individual
2000.
It
also
forest
clearance
fuels
of
the
countries
shows
the
total
European
between
CO
Union
1950
emissions
reasons
and
for
Kuwait
the
and
Bahrain.
Suggest
difference.
[3]
including
2
3
Although
cumulative
CO
emissions
from
2
and
other
land
use
changes.
combustion
1
Discuss
reasons
for
higher
cumulative
CO
Brazil
of
fossil
between
fuels
1950
and
in
Indonesia
2000
were
and
relatively
2
emissions
from
combustion
of
fossil
fuels
in
low,
total
CO
emissions
were
signicantly
2
the
2
United
States
than
Although
cumulative
1950
2000
and
were
in
Brazil.
[3]
emissions
higher
in
between
the
higher.
4
United
Suggest
Australia
reasons
ranked
emissions
of
for
seventh
CO
in
this.
in
2000,
[3]
the
but
world
fourth
for
when
2
States
four
than
any
countries
other
in
country,
which
there
emissions
were
per
all
capita
greenhouse
reason
for
the
gases
are
included.
Suggest
a
difference.
[1]
30%
Figure 10
CO
from fossil fuels
CO
from fossil fuels & land-use change
2
25%
2
latot dlrow fo tnecrep
20%
15%
10%
5%
0%
U.S.
EU-25
Russia
China
Indonesia
Brazil
Assessin aims and unter-aims
Assessing claims: assessment of the claims that human activities are not causing
climate change.
Climate
almost
change
any
internet
views,
has
other
will
area
quickly
expressed
Michael
scientists
as
use
murder
novel
State
of
more
vociferously.
eco-terrorists
of
Fear.
A
search
The
climate
who
promote
What
debated
diametrically
portrayed
to
hotly
science.
reveal
very
Crichton
mass
been
were
their
reasons
of
than
●
the
and
opposed
the
author
be
prepared
could
in
to
for
such
erce
opposition
to
climate
climate
is
tipping
and
for
what
defend
reason
their
do
ndings
climate
so
questions
many
factors
●
Scientists
are
that
are
worth
could
trained
to
having
be
The
and
to
base
their
an
are
inuence:
about
if
are
expected
to
admit
for
236
evidence
and
is
this
can
weaker
on
changes
about
increases
patterns
occur.
in
There
This
can
where
makes
difcult.
could
be
of
changes
very
severe
in
global
for
climate
humans
other
is
a
species
give
it
need
for
so
many
immediate
feel
that
remain
Companies
and
oil
natural
in
make
gas
action
climate
huge
and
it
even
change
prots
is
in
from
their
their
for
fossil
fuel
combustion
to
continue
evidence.
when
than
climate
more
coal,
there
grow.
the
It
would
not
be
reports
to
be
written
impression
actually
surprising
if
they
paid
are
risks
that
in
science.
for
uncertainties
even
uncertainties
to
They
points
complex
change
There
cautious
ideas
further
concentrations.
consequences
interests
claims
of
very
predictions
vigorously?
discussing.
be
are
make
there
there
These
to
change
and
scientists
gas
massive
prediction
patterns
science
patterns
difcult
consequences
sudden
his
●
be
it
greenhouse
change
work
Global
is.
of
climate
change.
that
minimized
the
4 . 4
c l i m a t e
c H a n G e
oppsitin t the imate hane siene
Evaluating claims that human activities are not causing climate change.
Many
claims
climate
that
change
television
and
human
have
on
activities
been
the
made
internet.
are
in
not
One
Global
causing
newspapers,
example
of
this
warming
increases
on
is:
dioxide
each
by
evidence
“Global
warming
stopped
in
1998,
dioxide
concentrations
have
rise,
so
human
carbon
dioxide
be
causing
global
claim
Earth
are
ignores
greenhouse
and
cycles
variations
factors,
also
gas
in
from
1998
than
that
many
currents
year
was
of
fact
by
to
an
temperatures
factors,
they
year.
some
cause
Because
activity
year
and
have
have
been
be
base
is
such
years
would
on
just
signicant
of
warm
recent
otherwise
not
Volcanic
can
unusually
them
fuels
dioxide
not
with
emitting
and
there
causes
equal
carbon
is
strong
warming,
is
not
supported
by
the
so
evidence.
that
human
change
activities
will
are
continue
not
and
causing
these
claims
need
warming.”
concentrations.
ocean
because
cooler
the
inuenced
fossil
carbon
but
are
emissions
to
This
Humans
continued
climate
cannot
burning
that
claim
Claims
to
continuing
yet
the
carbon
is
year.
evaluated.
our
now
evaluations
gases
Not
all
and
we
gases
and
sources
need
websites
reliable
been.
always
considerable
greenhouse
these
As
the
careful
and
to
the
climate
are
of
effects
of
patterns.
distinguish
that
There
trustworthy
assessments
others
should
emissions
about
internet
we
evidence.
about
changing
objective
evidence
reliable
humans,
about
be
science,
evidence
by
on
to
with
on
in
between
based
show
on
bias.
d-bs qss: Uncer tainty in temperature rise projections
Figure
for
11
shows
average
computer-generated
global
temperatures,
forecasts
based
on
6
eight
AIB
5
different
scenarios
for
the
changes
in
the
AIT
emissions
AIFI
of
greenhouse
gases.
The
light
green
band
includes
4
A2
the
full
range
of
forecasts
from
research
centres
B1
3
around
the
world,
and
the
dark
green
band
shows
B2
IS92a
the
range
forecasts
of
for
most
of
arctic
the
forecasts.
temperatures,
Figure
based
12
on
shows
two
2
of
1
the
emissions
1
Identify
scenarios.
0
the
emissions
code
for
the
least
optimistic
scenario.
1
[1]
9
9
0
2
0
0
0
0
1
0
2
2
0
2
0
2
0
3
0
2
0
4
0
2
0
5
0
2
0
6
0
2
0
7
0
2
0
8
0
2
0
9
0
2
1
0
0
Figure 11 Forecast global average temperatures
2
State
for
the
minimum
average
global
and
maximum
temperature
forecasts
change.
[2]
7
Discuss
whether
forecasts
3
Calculate
and
B2
the
difference
forecasts
temperature
of
between
global
the
Compare
average
8
rise.
the
[2]
forecasts
for
Discuss
average
with
those
whether
environmental
or
in
temperature
inaction.
[4]
livelihood
it
is
risks
risks
possible
with
or
to
balance
socio-economic
whether
priorities
need
arctic
to
temperatures
uncertainty
action
A2
and
4
the
justies
for
be
established.
[4]
global
temperatures.
[2]
7
6
A2
5
Suggest
uncertainties,
apart
from
B2
5
greenhouse
gas
emissions,
which
4
affect
forecasts
for
average
global
3
temperatures
over
the
next
100
years.
[2]
2
6
Discuss
in
how
forecasts
much
based
more
on
condent
data
from
a
we
can
number
be
of
1
0
2000
different
research
centres,
rather
than
one.
2020
2040
2060
2080
2100
[3]
Figure 12 Forecast arctic temperature
237
4
E c o l o g y
cra reefs and arbn dixide
Threats to coral reefs from increasing concentrations of dissolved carbon dioxide.
In
addition
emissions
on
the
its
pH
century
surface
to
when
to
500
there
8.104
in
and
warming,
make
be
billion
tonnes
of
calcium
since
the
dissolved
of
the
been
the
little
mid-1990s
current
in
Earth’s
in
the
of
the
is
In
2012
global
This
seemingly
small
acidication.
are
that
it
severe
if
Ocean
the
change
dioxide
atmosphere
continues
to
There
is
corals
and
animals
such
deposit
calcium
carbonate
need
The
is
to
absorb
will
low,
because
interrelated
reacts
with
dissociates
ions.
they
carbon
concentration
are
even
water
into
ions,
very
as
a
react
result
reducing
in
already
island
coral
of
agreed
monitoring
evidence
reefs.
Ischia
releasing
thousands
In
their
corals,
their
place
and
seawater
than
to
ocean
20
set
up
a
acidication.
for
concerns
Volcanic
vents
about
near
in
the
carbon
Gulf
dioxide
of
Naples
into
the
have
water
of
the
years,
area
reducing
of
acidied
the
pH
water
of
the
there
sea
skeletons
other
reefs
continues
from
algae.
around
to
be
or
other
calcium
organisms
invasive
coral
urchins
could
world
emitted
from
that
carbonate.
ourish
This
the
animals
are
if
such
be
as
the
In
sea
their
grasses
future
carbon
burning
make
of
dioxide
fossil
fuels.
carbonate
of
some
Carbon
acid,
dioxide
which
hydrogen
with
that
soluble.
the
carbonic
and
corals
seawater.
ions
reactions.
form
and
more
of
skeletons
from
makes
hydrogen
ions
their
ions
lower
to
in
not
Seattle
for
existing
threatened.
rise.
carbonate
dioxide
chemical
Hydrogen
carbonate
of
from
so
are
to
existing
become
concentration
reef-building
carbonate
concentration
Dissolved
as
in
dissolve,
corals
ceases
ions,
a
no
Marine
met
scheme
seawater.
the
to
oceanographers
seawater
approximately
represents
acidication
carbon
tends
reef-building
if
carbonate
had
for
more
of
industrialization.
been
30%
of
Also,
solution
carbonate
countries
18th
skeletons.
saturated
skeletons
oceans.
oceans
late
showed
levels
carbon
start
a
the
8.069.
their
effects
8.179
had
the
global
having
have
been
to
are
humans
layers
have
Measurements
fallen
by
revolution
of
estimated
dioxide
Over
released
industrial
contribution
carbon
oceans.
dioxide
The
to
of
carbonate
dissolved
concentration.
+
CO
+
H
2
O
H
CO
2
+
CO
→
H
+
HCO
3
HCO
3
If
→
3
2
+
H
→
2
carbonate
difcult
for
ion
3
concentrations
reef-building
corals
drop
to
it
is
absorb
more
them
to
Figure 1
3 Skeleton of calcium carbonate from a reef-building coral
TOK
av
Draw a graph of oceanic
wh  h p ps f fg bs?
pH from the 18th century
The costs of scientic research is often met by grant agencies. Scientists submit
onwards, using the gures
research proposals to agencies, the application is reviewed and if successful,
given in the text above, and
the research can proceed. Questions arise when the grant agency has a stake in
extrapolate the curve to
the study's outcome. Fur ther, grant applications might ask scientists to project
obtain an estimate of when
outcomes or suggest applications of the research before it has even begun. The
the pH might drop below 7.
sponsor may fund several dierent research groups, suppressing results that
run counter to their interests and publishing those that suppor t their industry.
For example, a 2006 review of studies examining the health eects of cell phone
use revealed that studies funded by the telecommunications industry were
statistically least likely to repor t a signicant eect. Pharmaceutical research,
nutrition research and climate change research are all areas where claims of
funding bias have been prominent in the media.
238
Q u e S t i o n S
Questins
4
The
total
solar
5
5
×
energy
2
l0
kJ
received
m
is
yr
5
.
The
net
×
energy
is
grassland
production
2
is
10
kJ
6
passed
×
m
yr
on
to
and
2
10
kJ
of
the
1
2
production
a
1
2
grassland
by
xednI thguorD
1
gross
1
m
yr
primary
its
.
The
total
consumers
yr
passed
a)
1
m
on
.
Only
to
Calculate
the
the
10
per
cent
secondary
energy
lost
of
this
energy
consumers.
by
plant
respiration.
b)
Construct
[2]
a
pyramid
of
energy
for
this
grassland.
[3]
mk/ytilat rom eert fo aerA
is
kJ
2
1
0
–1
–2
–3
Cool/moist
is
2
2
60
3
2000
1500
1000
500
0
1930
1940
1950
1960
1970
1980
1990
2000
Figure 15 Tree mor tality and drought index
2
Figure
14
shows
temperate
the
forest.
energy
The
ow
energy
through
ow
2
square
metre
per
year
(kJ
is
a)
a
shown
index
per
1
m
yr
Identify
the
two
remained
periods
high
when
for
the
three
or
drought
more
years.
).
lost
b)
(i)
[2]
Compare
the
beetle
outbreaks
in
the
5,223,120
1970s
(ii)
and
Suggest
1990s.
reasons
[2]
for
the
differences
sunlight
between
respiration
the
outbreaks.
[2]
energy
24,024
5,266,800
c)
Predict
rates
of
destruction
of
spruce
1
72
green
consumers
trees
in
the
future,
your
answer.
with
reasons
for
plants
[4]
storage
14,448
decomposers
(e.g. wood)
5,036
4
Figure
16
shows
monthly
average
carbon
Figure 14
dioxide
a)
The
chart
sunlight
shows
energy
that
in
99.17
the
per
cent
temperate
of
the
forest
Zealand
concentrations
and
Alert,
for
Baring
Head,
New
Canada.
is
390
or
Predict
lesser
would
b)
Only
of
be
a
with
a
reason
percentage
lost
small
plants
in
in
a
greater
energy
of
[2]
the
net
temperate
the
forest
reasons
passes
for
to
this.
[2]
OC
Explain
production
385
Key
380
Aler t station,
375
Canada
370
Baring Head,
365
New Zealand
360
2
herbivores.
whether
sunlight
desert.
part
the
of
mpp/noitartnecnoc
lost.
355
350
345
340
3
Warmer
temperatures
favour
some
335
species
330
of
pest,
for
example
the
spruce
beetle.
Since
76 78 80 82 84 86 88 90 92 94 96 98 00 02 04
the
rst
major
outbreak
approximately
Alaska
and
400,000
the
in
1992,
hectares
Canadian
it
of
Yukon.
has
trees
The
year
killed
in
Figure 16
beetle
a)
normally
cycle,
needs
but
it
two
has
years
recently
to
complete
been
able
to
its
do
Suggest
why
areas
Mauna
it
year.
drought
and
The
graphs
index,
a
gure
combination
precipitation,
destroyed
in
and
the
15
of
area
show
Loa,
have
Baring
chosen
Head
such
and
the
locations
for
monitoring
Alert
stations.
[1]
the
temperatures
of
as
in
as
one
scientists
life
spruce
b)
Compare
the
trends
illustrated
in
both
graphs.
trees
[2]
annually.
c)
Explain
why
patterns.
the
graphs
show
different
[3]
239
4
e c o l o G y
5
Figure
17
shows
the
concentration
of
CO
in
the
tundra
above
taiga
2
root
ground
atmosphere,
In
a
forest,
measured
in
parts
concentrations
of
per
CO
million
change
(ppm).
over
above
the
2
ground
course
top
of
of
the
the
day
forest
and
is
change
referred
to
with
as
height.
the
The
root
canopy.
soil
soil
m/thgieh
310 ppm
30
320
Top forest canopy
grasslands
deciduous forest
20
above
above
ground
ground
305
330
10
root
root
340
soil
soil
350
350
0
0
6
12
18
24
time of day / hours
savannah
equatorial forest
Figure 1
7
a)
(i)
State
the
highest
concentration
of
above
above
ground
ground
CO
2
reached
in
the
canopy.
[1]
soil
(ii)
Determine
found
in
the
the
range
of
concentration
canopy.
soil
root
root
[2]
Figure 18 The distribution of nitrogen in the three organic
b)
(i)
State
the
time
of
day
(or
night)
matters compar tments for each of six major biomes
when
the
highest
levels
of
CO
are
2
detected.
[1]
a)
Deduce
what
the
compartment
(ii)
The
highest
levels
of
CO
are
“above
consists
of
ground”
in
an
ecosystem.
[1]
detected
2
just
above
reasons
c)
Give
an
the
why
ground.
this
example
of
is
an
Deduce
the
two
b)
case.
hour
[2]
when
CO
State
which
ground”
c)
Explain
biome
has
the
largest
“above
compartment.
why
it
is
difcult
[1]
to
grow
crops
in
2
concentrations
the
full
range
are
of
reasonably
uniform
over
heights.
an
[1]
cleared
d)
State
by
6
Within
an
ecosystem,
nitrogen
can
be
area
where
of
the
one
above
Figure
in
the
of
three
ground,
18
organic
in
shows
three
roots
the
organic
matter
and
in
matter
the
soil.
of
of
six
major
has
been
of
the
and
[2]
process
detritus
carried
feeders
out
that
stored
CO
e)
nitrogen
compartments
into
the
atmosphere.
[1]
2
Suggest
tundra
why
most
ecosystem
of
is
the
in
nitrogen
the
in
a
soil.
[1]
for
f)
each
name
compartments:
distribution
forest
vegetation.
decomposers
releases
in
its
equatorial
Explain
why
warming
due
to
climate
biomes.
change
might
cause
a
release
of
CO
from
2
tundra
240
soil.
[2]
5
Ev O Lu t I O n
a n d
B I O d I v E r s I t Y
Iocio
There
that
is
the
overwhelming
diversity
continues
ancestry
to
of
of
evolve
groups
evidence
life
by
of
has
for
the
evolved,
natural
species
selection.
can
be
theory
and
comparing
Species
The
deduced
are
their
base
named
internationally
or
and
agreed
amino
acid
classied
sequences.
using
an
system.
by
5.1 Edee  e
ueig
applicio
➔
Evolution ours when heritale harateristis
➔
Comparison of the pentadatyl lim of
of a speies hange.
mammals, irds, amphiians and reptiles
➔
The fossil reord provides evidene for
with dierent methods of loomotion.
evolution.
➔
➔
Seletive reeding of domestiated
Development of melanisti insets in
polluted areas.
animals shows that ar tiial seletion
an ause evolution.
➔
radiation explains similarities in struture when
there are dierenes in funtion.
➔
➔
ne of ciece
Evolution of homologous strutures y adaptive
➔
Looking for patterns, trends and disrepanies:
there are ommon features in the one
Populations of a speies an gradually diverge
struture of ver terate lims despite their
into separate speies y evolution.
varied use.
Continuous variation aross the geographial
range of related populations mathes the
onept of gradual divergene.
241
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Eolio i mmy
Evolution ours when heritale harateristis
of a speies hange.
There
time.
is
strong
scientic
should
the
evidence
Biologists
this
for
be
drawn
of
from
of
between
an
characteristics
process
understanding
lifetime
passed
call
the
parent
to
natural
acquired
individual
of
evolution.
and
offspring.
It
species
lies
world.
at
An
heart
important
characteristics
heritable
changing
the
that
only
a
distinction
develop
characteristics
Evolution
over
of
that
concerns
during
are
heritable
characteristics.
The
▲
mechanism
of
evolution
is
now
well
understood
–
it
is
natural
Figure 1 Fossils of dinosaurs show there were
selection.
Despite
the
selection,
there
still
robustness
of
evidence
for
evolution
by
natural
animals on Ear th in the past that had dierent
is
widespread
disbelief
among
some
religious
characteristics from those alive today
groups.
evolve
There
than
evolution.
are
to
It
stronger
the
is
logic
objections
of
therefore
the
to
the
mechanism
important
to
concept
that
look
at
that
species
inevitably
the
can
causes
evidence
for
evolution.
Eiece fom foil
The fossil reord provides evidene for evolution.
In
the
or
strata
eras
rst
were
various
20th
ages
of
●
layers
the
The
ago
and
would
and
It
of
has
of
that
was
out
the
a
fossils
us
in
in
which
and
fossils
strong
is
of
dating
them.
which
the
the
fossils.
has
branch
evidence
in
In
revealed
There
the
layers
geological
found
sequence
radioisotope
fossils,
given
sequence
worked
there
the
into
Many
that
been
of
the
the
a
science
evolution
on
back
very
ts
land,
and
worms
bony
matches
with
later
sh
mya,
110
in
appear
evolve,
340
appearing
sequences
with
over
60
similar
of
the
bacteria
and
land
appeared
reptiles
sequence
and
vertebrates
about
320
420
mya,
in
simple
later
million
birds
which
algae
250
still.
years
mya
mya.
with
before
plants
fossils
their
members
rhinoceroses
now totally ex tinct
and
mammals
also
to
the
ecology
animal,
suitable
of
plants
for
the
on
insect
groups,
land
with
before
pollination
before
pollinators.
zebras,
hundreds of millions of years but the group is
fungi
amphibians
fossils
organisms
and
fossils
vertebrates,
sequence
insect
which
expected
rst,
placental
The
in
be
the
(mya),
animals
242
–
methods
research
the
was
obvious
different
strata
of
sequence
plant
Figure 2 Many trilobite species evolved over
were
century,
became
palaeontology.
Among
▲
It
reliable
rock
appearing
●
19th
deposited
occurred.
they
●
the
were
named.
amount
called
of
rock
century,
huge
has
half
of
and
a
likely
known,
ancestors.
of
the
genus
tapirs.
An
extensive
million
to
are
years,
links
rhinoceros.
which
For
Equus,
link
example,
are
most
sequence
them
to
together
of
existing
horses,
closely
fossils,
Hyracotherium,
asses
related
to
extending
an
animal
5 . 1
E v i D E n c E
f o r
E v o l u t i o n
Daa-baed qe: Missing links
An
objection
been
for
gaps
in
example
to
fossil
the
a
evidence
record,
link
called
between
for
evolution
missing
reptiles
has
The
links,
and
discovery
particularly
fossils
that
for
ll
in
these
gaps
is
biologists.
birds.
1
Calculate
from
(a)
of
exciting
its
the
length
head
to
the
of
tip
Dilong
of
its
paradoxus,
tail.
[2]
(b)
(g)
(c)
2
(d)
Deduce
three
paradoxus
Earth
similarities
and
reptiles
between
that
live
Dilong
on
today.
[3]
(i)
(h)
3
Suggest
a
function
for
the
protofeathers
of
100 mm
Dilong
paradoxus.
[1]
(j)
(e)
(f)
4
Suggest
would
▲
Figure 3 Drawings of fossils recently found in Western
two
have
features
had
capable
of
Explain
why
to
which
evolve
Dilong
to
paradoxus
become
ight.
[2]
China. They show Dilong paradoxus, a 130-million-year-old
5
it
is
not
possible
to
be
certain
tyrannosauroid dinosaur with protofeathers. a–d: bones of
whether
the
protofeathers
of
Dilong
paradoxus
skull; e–f: teeth; g: tail ver tebrae with protofeathers; h–j:
are
homologous
with
the
feathers
of
birds.
[2]
limb bones
Eiece fom elecie beeig
Seletive reeding of domestiated animals shows that
ar tiial seletion an ause evolution.
Humans
have
thousands
the
wild
of
species
Consider
the
junglefowl
of
Western
other
It
is
clear
The
that
that
very
have
to
cause
in
Asia,
by
of
articial
but
naturally,
with
it
or
to
does
that
breeds
have
for
process
selection
is
is
prove
Blue
and
that
by
over
It
the
in
the
that
of
has
is
been
selection.
time
changes
that
selection
species
evolution
and
individuals
considerable
of
aurochs
their
change
periods
shows
the
cattle
breeds.
articial
evolution
for
and
existed
the
breeding
called
time.
mechanism
that
huge.
the
sheep,
between
for
with
often
and
cattle
of
always
is
shown
animals
geological
not
not
are
hens
breeds
variation
species
compared
differences
Belgian
selecting
animal
are
egg-laying
explanation
This
the
the
different
much
domesticated
comparison
particular
livestock
between
repeatedly
in
of
modern
many
credible
uses.
used
resemble,
or
also
livestock,
human
evolution,
occurred
most
are
only
and
breeds
between
domesticated
The
occurred
short,
they
There
simply
suited
bred
modern
Southern
Asia.
effectiveness
that
▲
of
form.
achieved
If
differences
domesticated
current
most
deliberately
years.
has
natural
are
can
actually
selection.
Figure 4 Over the last 15,000 years many breeds of dog have been developed by ar ticial
selection from domesticated wolves
243
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Daa-baed qe: Domestication of corn
Homology 
A
eolio
wild
grass
probably
is
grown
called
the
as
teosinte
ancestor
a
crop,
it
of
that
grows
cultivated
gives
yields
in
corn,
of
Central
Zea
about
America
mays.
150
kg
When
per
was
teosinte
hectare.
This
Looking for patterns, trends
compares
and disrepanies: there are
at
the
Corn
with
start
was
of
a
world
the
21st
average
century.
domesticated
at
yield
Table
least
7,000
of
1
corn
gives
years
of
4,100
the
kg
lengths
per
of
hectare
some
cobs.
ago.
ommon features in the one
struture of ver terate lims
1
Calculate
and
the
Silver
percentage
difference
in
length
between
teosinte
Queen.
[2]
despite their varied use.
2
Vertebrate
limbs
are
used
Calculate
and
many
different
walking,
running,
swimming,
These
ways,
varied
uses
such
and
world
percentage
average
yields
difference
of
in
yield
between
teosinte
corn.
[2]
as
jumping,
grasping
the
in
ying,
3
Suggest
factors
4
Explain
why
apart
from
cob
length,
selected
for
by
farmers.
[3]
digging.
require
joints
improvement
slows
down
over
generations
of
that
selection.
articulate
velocities
different
be
in
different
of
movement
amounts
reasonable
have
but
very
there
features
found
in
Patterns
are
all
the
As
a
common
vertebrate
piece
of
Teosinte – wild relative of orn
14
Early primitive orn from Colomia
45
Peruvian anient orn from 500 bc
65
Imriado – primitive orn from Colomia
90
common
only
far
legh  b (mm)
to
that
are
Silver Queen – modern sweetorn
limbs.
require
The
so
c aey ad g
would
structure,
structure
this
also
It
them
bone
fact
evolution
ancestor.
expect
[3]
different
and
force.
vertebrate
like
explanation
is
in
bone
explanation.
case
to
of
different
of
ways,
T
able 1
▲
Figure 5 Corn cobs
reasonable
proposed
from
▲
170
a
in
this
common
consequence,
bone
limbs
structure
has
evidence
for
become
of
a
classic
evolution.
Eiece fom homologo ce
Evolution of homologous strutures y adaptive
radiation explains similarities in struture when there are
dierenes in funtion.
Darwin
pointed
structure
dugong
those
between
and
244
a
very
in
the
When
or
tail
we
different.
The
Origin
organisms
whale,
between
structures.
are
out
ns
study
An
are
between
of
of
Species
supercial,
a
whale
whales
them
that
and
closely
evolutionary
some
for
and
a
shes
we
similarities
example
sh.
are
nd
interpretation
between
Similarities
known
that
is
these
that
in
as
a
like
analogous
structures
they
have
had
5 . 1
different
same
or
origins
a
Homologous
may
look
which
of
what
could
in
the
digit
that
be
limb,
same
are
that
many
the
without
Darwin
called
function.
of
These
of
and
have
a
an
teeth
the
of
or
found
pelvis
easily
that
and
–
of
so
are
a
the
structures
function,
gave
the
bat
that
same
appearing
they
pentadactyl
because
asked
the
surface
is
that
but
example
and
“include
structures.
have
or
they
but
they
ve-
perform
thigh
bone
the
are
are
found
gradually
that
as
reveal
to
serve
of
the
in
that
no
them
despite
in
prove
not
structures
examples
appendix
not
do
difcult
the
whales,
evolution
do
and
structures
and
baleen
course
They
ancestry
organs
by
E v o l u t i o n
radiation.
reduced
being
are
and
the
interesting
embryo
explained
and
had
evolution,
and
on
different
vestigial
in
He
explanation
common
organs”
They
they
perform
f o r
evolution.
different
type”.
that
adaptive
of
a
despite
Particularly
snakes,
are
nd
had
they
porpoise
homologous
called
small
function
to
become
called
this.
of
horse,
ancestor
have
is
of
perform
“unity
than
evolved
now
a
mole,
mechanism
some
structures
longer
This
and
because
convergent
converse
positions”,
evolution.
are
toothless,
whales
from
they
similar
called
evolutionary
“rudimentary
They
beginnings
being
The
is
called
examples
explain
the
curious
have
about
are
different
human,
origin,
organisms
This
relative
functions.
anything
the
a
more
and
become
Darwin
of
different.
same
different
There
what
the
completely
had
structures
forelimbs
bones,
have
function.
supercially
have
the
and
similar
E v i D E n c E
are
adults
body
wall
humans.
structures
that
no
lost.
Pecyl limb
Comparison of the pentadatyl lim of mammals, irds, amphiians and reptiles
with dierent methods of loomotion.
The
pentadactyl
limb
consists
of
these
structures:
classes
birds
Be e
femb
that
and
have
a mp hib ia ns,
Ea ch
of
the m
r e pti le s ,
h as
Hdmb
pentadactyl
single one in the
l i mb s :
mamma l s .
humerus
limbs :
femur
●
crocodiles
walk
or
crawl
on
land
and
use
their
proximal par t
webbed
two ones in the
radius and ulna
hind
limbs
for
swimming
tiia and ula
●
penguins
use
their
hind
limbs
for
walking
and
distal par t
their
group of wrist/
arpals
forelimbs
●
ankle ones
echidnas
also
series of ones in
metaarpals and
metatarsals
eah of ve digits
phalanges
and phalanges
●
use
frogs
use
pattern
present
in
mammals,
of
all
bones
or
a
modication
amphibians,
whatever
the
reptiles,
function
of
birds
of
it
use
photos
in
one
example
gur e
of
ea ch
6
s how
of
ippers
for
swimming
all
the
the
four
four
four
for
limbs
forelimbs
limbs
for
for
walking
and
digging
for
walking
the
relative
and
their
jumping.
is
Differences
can
thicknesses
of
be
seen
in
lengths
and
and
their
the
bones.
Some
metacarpals
and
limbs.
phalanges
The
all
their
hindlimbs
The
as
tarsals
s ke le t o ns
of
the
have
penguin’s
been
lost
during
the
evolution
of
forelimb.
v ert ebr at e s
245
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Ay
Peaday mb 
mamma
mole
horse
▲
Figure 6
porpoise
speciio
Populations of a speies an gradually diverge into
separate speies y evolution.
If
two
not
populations
interbreed
of
and
a
species
natural
become
selection
separated
then
acts
so
that
they
differently
on
do
the
two
bat
populations,
human
the
two
will
populations
recognizably
▲
they
evolve
will
different.
If
in
different
gradually
the
ways.
diverge.
populations
The
After
a
characteristics
time
subsequently
they
will
merge
of
be
and
have
Figure 7 Pentadactyl limbs
(not to scale)
the
chance
clear
that
of
interbreeding,
they
have
evolved
but
do
into
not
actually
separate
interbreed,
species.
This
it
would
process
is
be
called
Choose a olour ode for
speciation.
the types of one in a
pentadatyl lim and olour
Speciation
the diagrams in gure 7 to
by
often
show the type of eah one.
species
on
How is eah lim used?
certain
geographical
What features of the ones
are
in eah lim make them well
of
adapted to the use?
different
migrating
an
the
occurs
an
islands.
example
of
archipelago.
species,
divergence.
246
to
after
island.
An
population
explains
endemic
area.
this.
On
a
This
The
One
six
formed
species
lava
species
smaller
by
is
of
to
species
the
is
found
of
is
all
a
island
the
and
by
range
in
a
Islands
main
closely
its
endemic
only
Galápagos
on
there
extends
numbers
that
the
present
islands
migration
a
large
one
lizards
is
of
the
islands
related
but
subsequent
5 . 1
E v i D E n c E
f o r
E v o l u t i o n
Eiece fom pe of iio
Pinta
Genovesa
Continuous variation aross the geographial
Marchena
range of related populations mathes the
Santiago
onept of gradual divergene.
If
populations
gradually
diverge
over
time
to
become
separate
Santa Cruz
Fernandina
species,
to
nd
then
at
any
examples
of
one
all
moment
stages
of
we
would
expect
divergence.
This
is
to
be
San Cristóbal
able
indeed
Santa Fe
what
we
nd
in
nature,
as
Charles
Darwin
describes
in
Isabela
Chapter
II
of
The
Origin
of
Species.
He
wrote:
a
Español
Santa Maria
Many
years
ago,
when
comparing,
and
seeing
others
compare,
key
the
birds
both
from
one
with
mainland,
is
the
the
I
separate
another
,
was
distinction
islands
and
much
with
struck
between
of
those
how
species
the
Galápagos
from
entirely
and
the
Archipelago,
T.albemarlensis
T.delanonis
T.habelii
T.duncanensis
T.pacicus
T.bivittatus
T.grayii
American
vague
and
arbitrary
varieties.
▲
Figure 8 Distribution of lava lizards in the
Galápagos Islands
Darwin
gave
different,
species.
but
One
ptarmigan
species
Because
there
is
being
split
The
to
his
two
for
can
sudden
separate
into
They
therefore
species
are
species
and
as
have
gradually
be
origin
of
variation
were
new
the
clearly
it
been
classied
provides
of
separate
This
is
a
organisms.
time
one
populations
and
species
to
together
or
arbitrary.
distinct
their
as
willow
lagopus.
of
populations
as
the
living
periods
lump
rather
and
Lagopus
classify
long
between
by
separate
Britain
populations
to
created
species
of
and
over
two
across
recognizably
species
name
remains
Instead
of
are
grouse
decision
constant
unchanging.
are
sometimes
being
species
in
they
diverge
the
species
that
red
who
from
species,
that
that
the
varieties
switch
should
the
is
biologists
range
belief
populations
extent
separate
continuous
the
the
Norway.
species
no
of
examples
sometimes
problem
them
either
and
not
of
of
and
common
examples
does
types
geographic
evidence
for
of
not
range
the
match
organism
or
TOK
that
evolution
of
t wha ex e a mpe mde
be ed  e hee?
evolution.
The usefulness of a theory is
the degree to whih it explains
Iil melim
phenomenon and the degree to
whih it allows preditions to e
Development of melanisti insets in polluted areas.
made. One way to test the theory
Dark
varieties
of
typically
light-coloured
insects
are
called
melanistic.
of evolution y natural seletion is
The
most
famous
example
of
an
insect
with
a
melanistic
variety
through the use of omputer models.
is
Biston
betularia,
the
peppered
moth.
It
has
been
widely
used
as
The Blind Watchmaker omputer
an
example
of
natural
selection,
as
the
melanistic
variety
became
model is used to demonstrate how
commoner
in
polluted
industrial
areas
where
it
is
better
camouaged
omplexity an evolve from simple
than
the
pale
peppered
variety.
A
simple
explanation
of
industrial
forms through ar tiial seletion. The
melanism
is
this:
Weasel omputer model is used to
●
Adult
and
Biston
betularia
moths
y
at
night
to
try
to
nd
a
demonstrate how ar tiial seletion
mate
an inrease the pae of evolution
reproduce.
over random events. What features
●
During
●
Birds
the
day
they
roost
on
the
branches
of
trees.
would a omputer model have to
they
and
nd
other
them.
animals
that
hunt
in
daylight
predate
moths
if
inlude for it to simulate evolution y
natural seletion realistially?
247
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
●
In
unpolluted
lichens
●
and
Sulphur
dioxide
blackens
●
●
tree
moths
polluted
areas.
In
polluted
▲
kills
are
well
covered
in
pale-coloured
camouaged
lichens.
are
well
the
camouaged
melanic
variety
over
a
Soot
from
against
variety
of
relatively
▲
Figure 9 Museum specimen of the
against
coal
them.
burning
dark
Biston
short
tree
branches
betularia
time,
but
in
replaced
not
in
non-
Figure 10 The ladybug Adalia bipunctata
peppered form of Biston betularia
has a melanic form which has become
mounted on tree bark with lichens
common in polluted areas. A melanic male
from an unpolluted area
is mating with a normal female here
have
evolution
by
ndings
been
into
criticized
and
selection
ever
Michael
book
in
pale
been
and
used
careful
in
to
a
The
predation
cast
classic
of
example
this,
design
of
doubt
evaluation
Biston
Naturalist
His
nding
melanism
factors
attacked.
and
as
because
the
of
some
moths
over
of
research
early
has
whether
been
natural
occurs.
a
New
2002).
though
of
has
gives
causing
Perhaps
repeatedly
melanism
the
melanism
selection.
actually
of
HarperCollins
pollution
industrial
camouage
this
Majerus
development
strong,
used
natural
have
experiments
rates
are
areas.
Biologists
his
branches
moths
pollution
areas
peppered
polluted
tree
branches.
Melanic
the
in
areas
peppered
other
melanic
in
series
is
that
Biston
than
of
betularia
evidence
and
(Moths,
the
other
camouage
the
of
Michael
evidence
betularia
about
species
and
can
for
other
also
moth
Majerus,
industrial
species
of
inuence
moth
is
survival
varieties.
Daa-baed qe: Predation rates in Biston betularia
One
into
of
the
moths
trunks
roost.
were
and
The
suitable
of
placed
that
1980s
the
moths
is
but
the
original
betularia
exposed
not
were
some
tested
were
in
this
moths
on
the
of
Biston
positions
persisted
248
criticisms
predation
able
even
to
so
effect
placed.
that
positions
normally
websites.
the
experiments
was
move
the
on
where
to
Experiments
of
the
position
Peppered
and
tree
they
have
done
in
in
which
melanic
(fty
in
and
two
the
in
the
a
of
oak
woods,
polluted
Midlands.
in
area
The
percentage
a
trunk.
Forest
of
of
Biston
positions
below
tree
New
each)
exposed
millimetres
at
more
criticisms
forms
placed
the
joint
This
one
near
procedure
in
an
were
trunks
a
major
was
in
eaten
gure
and
11
in
50
branch
area
and
out
of
another
the
show
moths
and
carried
unpolluted
England
Stoke-on-Trent
plots
moths
tree
between
southern
box
betularia
on
the
surviving.
5 . 2
1
a)
Deduce,
with
a
reason
from
the
n A t u r A l
data,
peppered
whether
the
moths
were
more
s E l E c t i o n
likely
to
Stoke on Trent and New Forest
be
New Forest/melanic/BJ
eaten
if
trunk
or
branch
they
were
below
and
the
placed
the
on
the
junction
of
a
60
main
trunk.
New Forest/melanic/ET
38
62
[2]
New Forest/peppered/BJ
b)
Suggest
a
a)
Compare
reason
for
the
difference.
74
and
contrast
the
68
in
b)
of
the
peppered
New
Explain
rate
and
melanic
the
the
Stoke/melanic/ET
[3]
difference
two
in
Stoke/peppered/BJ
survival
varieties
in
Forest.
Distinguish
between
New
woodlands
rates
Forest
of
peppered
the
and
Stoke-on-Trent
Pollution
in
relative
melanic
survival
moths.
due
near
to
50
50
industry
has
Stoke-on-Trent
0%
42
20%
58
40%
60%
80%
100%
key
not eaten
[2]
eaten
BJ = branch junction
decreased
▲
greatly
40
and
ET = exposed trunk
4
60
[3]
melanic
3
28
the
Stoke/peppered/ET
New
72
moths
Forest.
between
32
survival
Stoke/melanic/BJ
rates
26
[1]
New Forest/peppered/ET
2
40
exposed
since
the
Figure 11
1980s.
Source: Howlett and Majerus (1987) The Understanding of
Predict
the
consequences
of
this
change
for
industrial melanism in the peppered moth (Biston betularia)
Biston
betularia.
[4]
Biol. J.Linn.Soc. 30, 31–44
5.2 naa ee
ueig
applicio
➔
Natural seletion an only our if there is
➔
Changes in eaks of nhes on Daphne Major.
➔
Evolution of antiioti resistane in ateria.
variation amongst memers of the same speies.
➔
Mutation, meiosis and sexual reprodution
ause variation etween individuals in a speies.
➔
Adaptations are harateristis that make an
ne of ciece
individual suited to its environment and way of life.
➔
➔
Speies tend to produe more ospring than
the environment an suppor t.
➔
Individuals that are etter adapted tend to survive
Use theories to explain natural phenomena:
the theory of evolution y natural seletion
an explain the development of antiioti
resistane in ateria.
and produe more ospring while the less well
adapted tend to die or produe fewer ospring.
➔
Individuals that reprodue pass on
harateristis to their ospring.
➔
Natural seletion inreases the frequeny of
harateristis that make individuals etter
adapted and dereases the frequeny of other
harateristis leading to hanges within the
speies.
249
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
viio
Natural seletion an only our if there is variation
amongst memers of the same speies.
Charles
causes
his
voyage
the
to
Figure 1 Populations of bluebells (Hyacinthoides
of
of
theory
and
20
to
in
the
understanding
years,
world
on
selection
for
1859.
presents
30
his
many
evidence
Species,
previous
over
natural
accumulate
his
developed
around
theory
Origin
▲
Darwin
evolution
it.
In
HMS
in
the
book
Beagle.
the
He
1830s,
published
of
evidence
of
returning
late
Darwin
this
the
after
nearly
for
it
England
probably
but
his
500
that
mechanism
to
he
then
great
developed
worked
work,
pages,
had
that
from
he
found
The
explains
over
the
years.
non-scripta) mostly have blue owers but
One
of
the
observations
on
which
Darwin
based
the
theory
of
evolution
white-owered plants sometimes occur
by
natural
respects.
blood
may
it
is
all
selection
Variation
group
not
be
there.
and
so
in
variation.
human
many
other
immediately
Natural
individuals
some
is
in
a
individuals
populations
populations
features.
obvious
selection
were
favoured
is
obvious
With
but
depends
population
being
Typical
other
careful
on
than
–
in
many
height,
species
the
observation
variation
identical,
more
vary
within
there
skin
colour,
variation
shows
that
populations
would
be
no
–
way
if
of
others.
soce of iio
Mutation, meiosis and sexual reprodution ause
variation etween individuals in a speies.
The
1
causes
of
Mutation
by
2
gene
Meiosis
an
Sexual
The
a
▲
the
in
new
is
usually
combination
of
in
a
over
reproduction
of
are
diploid
to
carry
and
the
involves
come
alleles
from
New
alleles
Every
different
fusion
of
different
two
understood:
pool
by
cell
alleles
of
a
are
breaking
produced
male
and
individuals.
by
the
the
meiosis
alleles,
of
bivalents.
female
so
This
up
of
orientation
parents,
produced
population.
combination
independent
the
from
well
gene
of
cell.
a
the
now
variation.
enlarges
combinations
likely
crossing
gametes
source
which
combination
of
populations
original
individual
because
3
is
mutation,
produces
existing
in
variation
gametes.
offspring
allows
has
mutations
Figure 2 Dandelions (Taraxacum ocinale)
that
occurred
in
different
individuals
to
be
brought
together.
appear to be reproducing sexually when they
disperse their seed but the embryos in the
In
seeds have been produced asexually so are
of
genetically identical
species
that
variation
not
is
generate
survival
do
not
carry
mutation.
enough
during
times
It
out
is
variation
of
sexual
generally
to
be
reproduction
assumed
able
environmental
to
that
evolve
the
only
such
source
species
quickly
will
enough
for
change.
apio
Adaptations are harateristis that make an individual
suited to its environment and way of life.
One
of
the
structure
correlated
250
recurring
and
themes
function.
with
its
diet
For
and
in
biology
example,
method
is
the
of
the
close
structure
feeding.
The
relationship
of
a
bird’s
thick
coat
between
beak
of
a
is
musk
5 . 2
ox
is
obviously
habitats.
The
infrequent
correlated
water
rainfall
with
storage
in
the
tissue
desert
low
in
temperatures
the
habitats.
In
stem
of
a
biology
in
its
cactus
n A t u r A l
s E l E c t i o n
northerly
is
related
characteristics
Ay
to
such
as
Adapa  bd’ beak
these
that
make
an
individual
suited
to
its
environment
or
way
of
life
The four photographs of
are
called
adaptations.
irds show the eaks of a
The
term
and
thus
this
process.
natural
suited
one
adaptation
that
species
its
as
acquired
not
to
that
It
the
important
direct
They
Characteristics
acquired
is
characteristics
evolutionary
with
environment.
individual.
known
evolve.
According
selection,
to
implies
do
that
characteristics
characteristics
cannot
do
theory
of
develop
a
to
over
imply
making
during
during
widely
an
woodpeker. To what diet
by
individual
lifetime
lifetime
accepted
heron, maaw, hawk and
in
develop
the
a
time
purpose
adaptations
develop
and
be
not
purpose
not
develop
and method of feeding is
eah adapted?
of
are
theory
is
that
inherited.
Oepocio of opig
Speies tend to produe more ospring than the
environment an suppor t.
Living
An
organisms
example
southern
every
other
so
in
of
three
their
species
nucifera
in
which
on
do
have
a
a
bacteria,
there
It
can
number
with
a
and
However
pair
faster
could
the
be
as
needs
a
rate.
breeding
as
7
For
20
raises
for
of
60
the
in
within
living
out
a
a
be
a
the
at
as
least
70
two
years
offspring.
coconut
per
in
the
giant
palm,
year.
fungus
puffball
be
variation
there
is
an
produced
can
that
for
population.
for
for
will
will
the
Darwin
tend
to
existence
There
resources
individual
more
than
support.
this
in
overall
organisms
struggle
competition
every
may
is
edgling
(7,000,000,000,000).
environment
pointed
the
huge
to
of
long
twenty
rate,
offspring
to
as
called
spores
breeding
lead
rate
one
coconuts
all
body
Despite
trend
It
example,
rate
trillion
produce.
breeding
raise
and
fruiting
they
cooperation
live
theoretically
huge
many
slow
the
can
between
fastest
produces
offspring
leadbeateri .
they
breeding
produces
of
relatively
Bucorvus
average
this.
usually
gigantea.
the
hornbill,
lifetime
Cocos
from
to
in
species
years
Most
Calvatia
a
ground
adults
Apart
vary
will
and
obtain
be
not
enough
▲
to
allow
them
to
survive
Figure 3
and
reproduce.
▲
Figure 4 The breeding rate of pairs of
southern ground hornbills, Bucorvus
leadbeateri, is as low as 0.3 young per year
251
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
dieeil il  epocio
Ay
Individuals that are etter adapted tend to survive and
sma  aa
ee
●
Make ten or more
produe more ospring while the less well adapted tend
to die or produe fewer ospring.
ar tiial sh using
Chance
plays
a
part
in
deciding
which
individuals
survive
and
reproduce
modelling lay, or some
and
which
do
not,
but
the
characteristics
of
an
individual
also
have
an
other malleale material.
inuence.
In
the
struggle
for
existence
the
less
well-adapted
individuals
Drop eah of them into
tend
to
die
or
fail
to
reproduce
and
the
best
adapted
tend
to
survive
and
a measuring ylinder of
produce
many
offspring.
This
is
natural
selection.
water and time how long
An
example
that
is
often
quoted
is
that
of
the
giraffe.
It
can
graze
on
eah takes to reah the
grass
and
herbs
but
is
more
adapted
to
browse
on
tree
leaves.
In
the
wet
ottom.
season
●
its
food
is
abundant
but
in
the
dry
season
there
can
be
periods
Disard the half of
of
food
shortage
when
the
only
remaining
tree
leaves
are
on
high
the models that were
branches.
Giraffes
with
longer
necks
are
better
adapted
to
reaching
slowest. Pair up the
these
leaves
and
surviving
periods
of
food
shortage
than
those
with
fastest models and
shorter
necks.
make intermediate
shapes, to represent
their ospring. Random
Iheice
new shapes an also e
introdued to simulate
mutation.
●
Test the new generation
and repeat the
elimination of the
slowest and the reeding
of the fastest. Does
one shape gradually
emerge? Desrie its
features.
Individuals that reprodue pass on harateristis
to their ospring.
Much
of
the
offspring
of
their
–
is
blackcap
some
Spain
Not
all
of
the
broken
of
an
tusk
person
atricapilla
are
signicant
in
and
not
the
of
children
of
skin
on
are
to
not
skin
evolution
with
colour
a
to
Those
broken
from
to
to
skin
colour
north
behaviour
sites
differences
in
in
can
the
their
Germany
genes,
to
Britain.
acquired
inherited.
through
Acquired
of
Due
offspring.
in
overwintering
southwestwards
usually
on
dark
Variation
northwestwards
calves
inherited.
to
passed
the
light-skinned
colour.
example.
others
be
inherit
migration
an
have
darker
not
and
light
can
children
migrate
passed
individual
does
is
a
is
species
winter
develops
skin
example
inherit
individuals
Maasai
direction
this
features
lifetime
darker
The
Sylvia
birds
for
for
parents
heritable.
between
heritable.
parents
European
be
variation
it
An
tusks
for
exposure
characteristics
during
elephant
example.
to
are
the
with
If
sunlight,
therefore
a
a
the
not
species.
Pogeie chge
Natural seletion inreases the frequeny of
harateristis that make individuals etter adapted and
dereases the frequeny of other harateristis leading
to hanges within the speies.
Because
pass
on
adapted
leads
252
to
better-adapted
characteristics
have
an
lower
increase
individuals
to
their
survival
in
the
survive,
offspring.
rates
and
proportion
less
of
they
can
Individuals
reproduce
that
reproductive
individuals
in
a
are
and
less
success.
well
This
population
with
5 . 2
characteristics
that
characteristics
of
natural
make
the
them
well
population
adapted.
gradually
Over
change
the
–
n A t u r A l
generations,
this
is
s E l E c t i o n
the
evolution
by
Ay
selection.
The impulse to reprodue and pass
Major
and
evolutionary
many
them
colours
air.
this
generations,
during
signicant
in
Two
our
that
has
examples
of
are
we
but
there
been
beaks
antibiotic
of
to
occur
not
are
are
in
many
resistance
on
in
to
the
long
be
in
time
able
examples
The
industrial
described
nches
over
expect
observed.
observed
evolution
to
likely
should
have
been
of
changes
development
so
lifetime,
changes
moths
book:
changes
to
of
the
of
with
next
Galapagos
but
dark
wing
Islands
pattern have evolved in lions and
with two or more males so their litters
of
and
infantiide. How ould this ehaviour
other speies? Female heetahs mate
polluted
sections
on harateristis an e very strong.
It an ause adult males to arry out
observe
smaller
evolution
areas
periods
the
have multiple paternity. How does this
protet the young against infantiide?
bacteria.
Daa-baed qe: Evolution in rice plants
The
bar
charts
evolution
in
in
rice
gure
6
plants.
show
F
the
hybrid
results
plants
of
an
were
investigation
bred
by
of
crossing
together
1
two
in
rice
varieties.
Japan.
collected
Each
from
These
year
the
the
hybrids
date
plants,
of
for
were
then
owering
re-sowing
F
grown
was
at
ve
recorded
that
site
F
3
at
in
different
and
the
seed
following
F
4
sites
was
year.
F
5

▲
Figure 5 A female cheetah’s cubs inherit
Sapporo
characteristics from her and from one of
43° N
the several males with whom she mated
Fujisaa
40° N
onasu
36° N
iratsua
singe
35° N
origina
popuation
panted
iugo
out at
33° N
iyaai
31° N
56
70
84
98 112 126
68
82
96
110 124 138
54
68
82
96 110124 138
51
65
79
93
10712
1 135
days to owering
▲
1
Figure 6
Why
was
single
2
the
investigation
pure-bred
Describe
the
done
using
hybrids
rather
than
a
variety?
changes,
[2]
shown
in
the
chart,
between
the
F
and
3
F
generations
of
rice
plants
grown
at
Miyazaki.
[2]
6
3
a)
State
in
the
the
F
relationship
between
owering
time
and
latitude
generation.
[1]
6
4
b)
Suggest
a)
Predict
until
a
reason
the
the
for
results
F
if
this
the
relationship.
investigation
[1]
had
been
carried
on
generation.
[1]
10
b)
Predict
the
results
of
collecting
seeds
from
F
plants
grown
at
10
Sapporo
and
from
F
plants
grown
at
Miyazaki
and
sowing
10
them
together
at
Hiratsuka.
[3]
253
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Glápgo che
Changes in eaks of nhes on Daphne Major.
Pinta (5)
Genovesa (4)
Rabida (8)
Marchena (4)
Santiago (10)
Daphne Major (2/3)
Santa Cruz
Fernandina
San Cristóbal
(9)
(9)
(7)
(a)
G. fortis (large beak)
(b)
G. fortis (small beak)
(c)
G. magnirostris
Santa Fe
(5)
Isabela (10)
Española (3)
Santa Maria (8)
▲
Figure 7 The Galápagos archipelago with the number
of species of nch found on each island
Darwin
and
were
14
species
diet.
and
(see
of
in
From
Galápagos
has
since
particular,
that
related
and
also.
particular
Grant’s
small
ground
called
Both
G.
fortis
can
of
competition
G.
fortis
is
Daphne
Major
of
Peter
a
in
than
birds
“one
of
might
birds
taken
and
Major.
feed
G.
on
Grant
diet
the
are
this
small
seeds.
fuliginosa
size
other
(c) G. magnirostris
does
of
a
is
the
for
the
small
island,
seeds,
In
and
(a) G. for tis (large beak). (b) G. for tis (small beak).
on
fuliginosa,
the
almost
though
absence
small
beak
Figure 8 Variation in beak shape in Galápagos nches.
have
Rosemary
fortis,
▲
closely
other
and
On
on
body
nches.
population
Geospiza
larger
from
smaller
the
and
their
into
Darwin’s
and
Geospiza
eat
research
as
Rosemary
been
nch,
species
also
been
did
islands
paucity
had
changes,
focus
nch,
absent.
intense
one
Daphne
ground
species
and
has
between
that
are
sizes
as
Galapagos
original
characters
when
research
medium
island
beak
the
varied,
hypothesized
an
known
Peter
shown
that
There
ends”.
been
become
the
1835
which
nches.
similarities
one
different
as
in
birds,
nches
over
from
Islands
small
observed
the
Darwin
that
for
have
A
of
overall
archipelago,
modied
what
7),
fancy
There
Darwin
beaks
the
of
identied
distribution
gure
this
all.
the
their
really
In
the
specimens
subsequently
shapes
in
visited
collected
seeds,
size
on
islands.
among
there
months
supply
seeds.
1977,
a
drought
on
Daphne
Major
of
of
G.
of
254
larger,
small
harder
seeds,
individuals
are
population
died
seeds,
so
G.
fortis
able
in
to
which
crack
that
year,
the
fed
open.
with
small,
with
El
soft
bred
small
that
seeds,
year,
and
only
they
and
seeds
breeding
37
per
were
in
population.
In
fewer
With
of
G.
1982–83
a
to
fortis
hard
the
return
until
those
eight
increased
large,
reduced
random
1987,
an
response
stopped
a
In
causing
result
greatly
cent
not
a
and
availability.
and
beaks.
event,
as
rapidly,
conditions
of
food
shorter
Niño
rain
in
to
1987.
alive
in
sample
had
dry
supplies
In
1983
of
the
longer
and
a
beaks
than
the
1983
averages,
correlating
instead
with
on
heavy
fortis
narrower
shortage
severe
weather
bred
caused
a
increase
1983
In
individuals
was
the
reduction
in
supply
of
small
seeds.
larger-beaked
Most
of
highest
the
mortality
Variation
gure
8)
in
is
the
shape
mostly
due
and
to
size
of
genes,
the
beaks
though
the
(see
5 . 2
environment
the
has
variation
Using
and
the
data
breed,
The
the
between
predictions.
by
beak
µm
1983
10
and
µm
and
beak
1987
and
were
to
by
even
was
predicted
6
decrease
120
by
expect
the
by
the
observed
and
increased
of
to
µm.
selection
natural
actually
huge
if
it
had
linked
to
theory
to
have
It
have
followed
1859,
but
have
of
evolution
signicant
selection
changes
natural
the
that
occurring.
been
in
to
is
changes
published
signicant
s E l E c t i o n
objections
natural
caused
to
predicted.
to
was
predicted
decreased
by
width
survived
length
length
One
of
heritability.
close
actually
was
proportion
length
had
very
beak
actually
The
called
that
mean
and
width
is
beak
are
Average
Average
of
in
results
increase
effect.
genes
birds
changes
observed
130
to
heritability
about
the
width
some
due
n A t u r A l
not
is
changes
been
unreasonable
occurred
since
in
the
in
a
Darwin’s
case
occurred
of
that
theory
G.
are
to
species,
fortis,
clearly
selection.
by
µm.
Daa-baed qe: Galápagos nches
When
Peter
nches
there
on
and
the
were
Rosemary
island
breeding
of
Grant
Daphne
began
Major
populations
of
to
in
two
study
the
1973,
G.
fortis
and
Geospiza
scandens.
established
a
breeding
Daphne
Geospiza
island
in
1982,
initially
with
population
just
two
Major
is
100
three
males.
Figure
9
shows
the
m.
G.
magnirostris
and
G.
fortis
on
1997
and
has
an
area
and
of
1
0.34
km
hectare
is
.
100
the
maximum
×
and
females
population
densities
of
G.
fortis
numbers
Daphne
1997–2006.
[4]
Major
Table
between
[3]
hectares
Calculate
during
of
of
on
minimum
and
population
2
km
100
the
the
2
1
magnirostris
in
species,
2
Geospiza
changes
magnirostris.
2
shows
the
percentages
of
three
types
of
2006.
seed
in
the
Daphne
1500
diets
Major.
of
the
Small
three
seeds
nch
are
species
produced
on
by
22
G. for tis
plant
G. magnirostris
species,
srebmun
echios,
1000
and
Tribulus
medium
large
seeds
seeds,
by
which
the
are
cactus
very
Opuntia
hard,
by
cistoides.
500
3
a)
Outline
the
of
on
nch
diet
of
each
Daphne
of
the
species
Major.
[3]
0
1996
1998
2000
2002
2004
b)
2006
There
was
a
very
severe
drought
on
year
Daphne
▲
Figure 9 Changes in numbers of G. for tis and G. magnirostris
Deduce
between 1996 and 2006
a)
Describe
of
G.
and
the
changes
magnirostris
in
the
between
1997
4
2006.
Compare
the
[2]
changes
in
Figure
G.
population
fortis
between
spee
▲
1997
and
2006
10
fortis
the
during
in
the
2003
diet
the
and
of
the
2004.
nches
drought,
using
table.
[3]
shows
from
an
1973
assigned
the
index
to
of
2006,
value
beak
with
zero
size
the
and
of
adult
size
the
in
sizes
in
of
other
G.
data
in
population
1973
b)
how
changed
the
1
Major
years
shown
in
comparison
to
this.
with
Geospiza fortis
Geospiza magnirostris
Geospiza scandens
Yea
1977
1985
1989
2004
1985
1989
2004
1977
1985
1989
2004
sma
75
80
77
80
18
5.9
4.5
85
77
23
17
Medm
10
0.0
5.1
11
0.0
12
26
15
22
70
83
lage
17
19
16
8.2
82
82
69
0.0
0.0
0.0
0.0
T
able 2
255
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
c)
1
In
the
beak
0.5
rst
size
severe
of
G.
second
drought,
data
this
in
xedni ezis kaeb
selection
drought,
fortis
it
decreased.
question,
could
the
increased,
cause
in
Using
explain
these
mean
but
how
the
the
natural
changes
in
0
beak
5
The
size
in
intensity
of
the
two
droughts.
natural
selection
[3]
on
Daphne
0.5
Major
was
droughts.
calculated
The
during
calculated
the
values
two
are
called
1
selection
for
beak
differentials.
length
They
during
the
range
second
from
–1.08
drought,
1.5
to
1975
1980
1985
1990
1995
2000
with
year
▲
+0.88
for
beak
length
in
the
rst
drought,
2005
similar
width
and
These
are
selection
depth
and
differentials
overall
beak
for
beak
size.
Figure 10 Relative beak size in G. for tis between
very
large
selection
differentials,
1973 and 2006
compared
The
graph
change
in
shows
mean
correspond
two
beak
with
periods
size,
droughts
of
both
on
very
of
rapid
Suggest
Major.
beak
on
a)
State
in
b)
two
mean
Suggest
beak
two
changing
a
periods
size
of
of
reasons
most
most
G.
[2]
mean
when
reasons
size
the
of
of
G.
island
in
other
evolution.
for
natural
fortis
of
calculated
being
Daphne
selection
unusually
on
the
intense
Major.
[2]
change
fortis.
for
rapidly
rapid
values
investigations
which
Daphne
to
beak
there
6
Discuss
of
size
for
is
drought.
few
being
[2]
the
advantages
evolution
over
long
long-term
of
investigations
periods
and
the
reasons
investigations
done.
[3]
nl elecio  ibioic eice
Use theories to explain natural phenomena: the theory of evolution y natural
seletion an explain the development of antiioti resistane in ateria.
Antibiotics
medicine
rst
in
the
a
it
but
antibiotic
of
have
resistance
trends
great
of
been
in
triumphs
When
expected
method
there
following
the
century.
was
permanent
diseases,
The
one
20th
introduced,
offer
of
were
they
that
they
were
would
controlling
bacterial
increasing
problems
pathogenic
have
development
of
become
an
of
the
of
develops
what
established:
is
antibiotic
evolution.
theory
understanding
of
bacteria.
example
terms
of
of
very
should
of
It
can
natural
how
useful
be
resistance
be
done
it
to
therefore
explained
selection.
antibiotic
as
is
A
in
scientic
resistance
gives
an
reduce
understanding
the
problem.
16
14
●
After
an
antibiotic
patients,
●
a
bacteria
few
Resistance
and
more
to
introduced
showing
and
resistance
used
on
12
appear
tnatsiser %
within
is
years.
the
antibiotic
species
of
spreads
pathogenic
to
more
bacteria.
10
8
6
4
●
In
each
species
the
proportion
of
infections
2
that
are
caused
by
a
resistant
strain
increases.
bacteria.
▲
The
Figure 11 Percentage resistance to ciprooxacin between
1990 and 2004
4002
3002
2002
there
antibiotic
of
1002
populations
0002
the
9991
of
diseases
in
8991
properties
bacterial
changes
7991
treat
6991
cumulative
5991
used
been
antibiotics
4991
been
have
which
3991
to
over
2991
time
have
resistance
256
the
1991
during
0991
0
So,
5 . 2
n A t u r A l
s E l E c t i o n
aibioic eice
Evolution of antiioti resistane in ateria.
Antibiotic
resistance
is
due
to
genes
in
bacteria
population with no
and
antibiotic-resistant bacteria
so
it
can
be
antibiotic
inherited.
resistance
The
to
mechanism
become
more
that
causes
prevalent
or
antibiotic resistance
to
diminish
The
is
summarized
evolution
of
multiple
in
gure
antibiotic resistance
12.
antibiotic
gene received from a
gene formed by
bacterium in another
mutation in one
resistance
population
has
occurred
evolution
is
in
just
due
to
a
few
the
decades.
following
This
bacterium
rapid
causes:
population with some
antibiotic-resistant bacteria
●
There
has
been
antibiotics,
very
both
for
widespread
treating
use
of
diseases
and
in
antibiotic is used therefore
animal
feeds
used
on
farms.
there is strong natural
selection for resistance
●
Bacteria
can
generation
reproduce
time
of
very
less
than
rapidly,
an
with
a
population with more
hour.
antibiotic-resistant bacteria
●
Populations
increasing
of
the
bacteria
chance
are
of
a
often
gene
huge,
for
antibiotic is not used therefore
antibiotic
there is natural selection
resistance
being
formed
by
mutation.
(weak) against resistance
●
Bacteria
can
pass
genes
on
to
other
bacteria
in
population with slightly
several
ways,
including
using
plasmids,
fewer
which
antibiotic-resistant bacteria
allow
one
resistance
species
genes
of
bacteria
from
to
another
gain
antibiotic
species.
▲
Figure 12 Evolution of antibiotic resistance
Daa-baed qe: Chlor tetracycline resistance in soil bacteria
Bacteria
were
distances
collected
from
a
site
on
from
a
soil
pig
at
farm
different
in
3.0
Minnesota
2.5
from
feed
manure
an
had
animal
given
to
pen
the
subtherapeutic
out
rates.
what
and
pigs
low
chlortetracycline,
growth
been
on
this
of
order
of
farm
the
to
bacteria
percentage
to
overow
accumulate.
doses
in
The
allowed
The
contained
antibiotic
promote
were
them
)%( ecnatsised
where
faster
tested
was
to
nd
resistant
2.0
1.5
1.0
0.5
to
0.0
this
antibiotic.
chart.
The
The
yellow
chlortetracycline
results
bars
are
show
resistant
shown
the
in
the
percentage
bacteria
that
bar
5 m
of
grew
20 m
100 m
distance from animal pen
on
Source: " The eects of subtherapeutic antibiotic use in farm animals
nutrient-rich
the
medium
percentage
on
a
and
the
orange
nutrient-poor
bars
show
medium
that
on the proliferation and persistence of antibiotic resistance among soil
bacteria", Sudeshna Ghosh and Timothy M LaPara, The International
Society for Microbial cology Journal (2007) 1, 191–203
encouraged
1
a)
different
State
the
types
of
relationship
bacteria
to
between
grow.
percentage
2
antibiotic
resistance
and
distance
from
Predict
whether
resistance
animal
pen.
Explain
the
difference
in
between
the
pen
populations
of
and
far
been
antibiotic
lower
from
the
than
at
100
at
200
metres
metres.
[3]
Discuss
the
pen.
use
of
subtherapeutic
doses
of
bacteria
antibiotics
near
percentage
have
antibiotic
3
resistance
would
[1]
from
b)
the
the
in
animal
feeds.
[2]
[4]
257
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
5.3 caa  bd ey
ueig
applicio
The inomial system of names for speies is
➔
Classiation of one plant and one animal
➔
universal among iologists and has een agreed
speies from domain to speies level.
and developed at a series of ongresses.
External reognition features of ryophytes,
➔
When speies are disovered they are given
➔
liinophytes, oniferophytes and
sienti names using the inomial system.
angiospermophytes.
Taxonomists lassify speies using a hierarhy
➔
Reognition features of porifera, nidaria,
➔
of taxa.
platyhelminthes, annelida, mollusa and
➔
All organisms are lassied into three domains.
➔
The prinipal taxa for lassifying eukaryotes are
ar thropoda, hordata.
Reognition of features of irds, mammals,
➔
kingdom, phylum, lass, order, family, genus
amphiians, reptiles and sh.
and speies.
In a natural lassiation the genus and
➔
skill
aompanying higher taxa onsist of all the
speies that have evolved from one ommon
Constrution of dihotomous keys for use in
➔
anestral speies.
identifying speimens.
Taxonomists sometimes relassify groups
➔
of speies when new evidene shows that a
ne of ciece
previous taxon ontains speies that have
Cooperation and ollaoration etween groups
➔
evolved from dierent anestral speies.
of sientists: sientists use the inomial
Natural lassiations help in identiation
➔
system to identify a speies rather than the
of speies and allow the predition of
many dierent loal names.
harateristis shared y speies within
a group.
Ieiol coopeio  clicio
Cooperation and ollaoration etween groups of sientists: sientists use the
inomial system to identify a speies rather than the many dierent loal names.
Recognizable
biologists
many
as
different
language.
of
plant
has
cows
jack
and
French
258
For
lo ca l
to
called
in
bulls,
is
o rg a ni sms
s ame
na me s ,
in
e ve n
as
willy
als o
a
de vi ls
l i ly
a nd
v a r ie ty
kn o wn
can
wit h i n
Eng la nd
s ci e nti sts
p ul p i t,
are
sp ec i e s
the
Arum
lo r d s - a nd- la di e s,
the
there
of
T he
exa mp l e ,
known
been
pint,
group s
speci e s .
o ne
sp ec ie s
maculatum
chandelle,
la
Sainte-Vierge,
Spanish
species
de
del
a ng e ls ,
s na ke ’s
meat.
of
n am e s:
l oc a l
la
In
le
there
of
plant
are
de
p i l e tte
even
the s e
other
le
la
de
ma n t e au
va ch ot t e .
names
j us t
v el a
na me
in
or
mor e
ar e
b a rb a
fue g o ,
The
maculatum
in
la
alcatra x ,
hojas
quemado.
Arum
pi e d - d e - ve a u,
which
culebra,
menor,
cu c ko o-
a nd
to
ha ve
a
a r ón,
de l
fo r
fe w :
lang ua g e s .
but
for
t h is
o ne
c om ida
dr a go nt ia
d ia b lo
pr ima ve ra s
Spanish
de
In
a
is
and
ye r ba
u se d
for
d i ffe r ent
5 . 3
Local
names
culture
of
venture
may
an
so
be
area,
a
valuable
but
scientic
science
names
understood
throughout
system
has
that
cooperation
The
credit
naming
for
is
Linnaeus
who
part
names
the
genius
is
a
still
in
style
many
there
each
was
the
use
of
(used
groups
to
in
anagallis
for
In
the
of
group
το
name,
λενκον
(used
by
of
as
in
and
of
a
was
to
jambu
bol
different
and
by
Fuchs),
(used
jambu
species
of
by
chilli
Eugenia).
of
that
in
that
name
specic
for
name
Ancient
anagallis
Pliny),
Malayan
Malays
(used
mynte
of
used
αδιαυτου
Latin
by
water
mirroring
the
the
and
Seeblumen
and
two-
system
so
Turner)
geel
mynte
of
recognizes
species,
wild
B i o D i v E r s i t Y
scientists.
stroke
been
style
consists
Threophrastus),
This
and
English
(applied
o f
biologist
system
had
The
example
Swedish
a
are
binomial
system
binomial
that
that
The
good
Linnaeus
similar
group
femina
the
the
fact
needed
modern
Seeblumen
the
international
between
century.
before.
a
αδιαυτου
by
18th
today.
species
Greek
to
nomenclature
are
a
introduced
basis
languages
attached
our
given
Carl
in
is
of
an
world.
collaboration
devising
species
are
the
developed
and
part
is
c l A s s i f i c A t i o n
το
μεαυ
mas
German
and
Figure 1 Arum maculatum
▲
weiss
deelopme of he biomil yem
The inomial system of names for speies is universal
among iologists and has een agreed and developed
at a series of ongresses.
To
ensure
that
organisms,
held
for
at
and
International
late
1753
19th
be
plants
150
avec
Botanical
as
fungi
the
to
Linné,
the
as
by
There
same
system
delegates
are
separate
then
the
Species
The
Congresses
The
IBC
starting
this
book
19
vasculaires.”
the
attended
intervals.
century.
kingdom
votes
use
of
from
names
around
congresses
for
the
for
living
world
animals
are
and
fungi.
taken
and
Plantarum,
plant
biologists
congresses
regular
plants
the
all
was
that
gave
that
IBC
(IBC)
in
both
when
consistent
“La
IBC
of
held
in
genera
binomials
Vienna
be
1753)
in
every
1892
in
pour
year
proposed
and
Linnaeus
nomenclature
(ann.
will
were
Genoa
for
year
The
Plantarum
19th
point
the
known.
rule
held
species
published
for
all
1905
Shenzhen,
of
Species
accepted
in
of
the
by
commence
groupes
China,
that
species
botanique
les
during
de
plantes
▲
Figure 2 Linnaea borealis. Binomials
are often chosen to honour a biologist,
or to describe a feature of the
organism. Linnaea borealis is named
2017.
in honour of Carl Linnaeus, the Swedish
The
rst
International
Zoological
Congress
was
held
in
Paris
in
1889.
biologist who introduced the binomial
It
was
recognized
classifying
and
subsequent
valid
names
Systema
The
4th
animal
of
Natura
current
edition
scientists
that
internationally
species
congresses.
animal
in
he
rene
there
the
will
needed
1758
species
which
International
and
were
as
gave
Code
no
methods
accepted
was
this
and
doubt
that
for
Zoological
be
they
as
when
binomials
for
these
chosen
was
rules
more
use
for
were
the
agreed
starting
Linnaeus
all
species
in
naming
and
at
date
this
system of nomenclature and named
many plants and animals using it
for
published
known
Nomenclature
editions
for
naming
the
is
then.
the
future
as
species.
259
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
the biomil yem
When speies are disovered they are given sienti
names using the inomial system.
The
the
system
Linnaea
a
borealis
group
is
that
biologists
international
the
of
name
(gure
species
species
or
use
of
a
2).
that
The
share
specic
is
called
species
rst
name
certain
name.
binomial
consists
of
is
nomenclature,
two
the
words.
genus
characteristics.
There
are
various
An
name.
The
rules
because
example
A
genus
second
about
is
is
name
binomial
nomenclature:
●
The
genus
species
●
In
●
After
name
name
typed
a
or
●
The
binomial
to
or
for
text,
a
used
letter
example:
for
an
upper-case
(small)
binomial
been
initial
published
1758
with
lower-case
has
the
name,
earliest
plants
a
printed
abbreviated
species
begins
with
L.
name
animals,
once
of
shown
in
the
letter
and
the
a
in
piece
genus
italics.
of
text,
name
it
with
can
the
be
full
borealis
for
is
is
(capital)
letter.
a
the
species,
correct
from
1753
onwards
for
one.
ALLIGATORIDAE
the hiechy of x
mississippiensis
Taxonomists lassify speies using a hierarhy of taxa.
Alligator
sinensis
The
word
taxa.
crocodilus
is
of
Caiman
In
taxon
biology,
classied
the
into
genera
is
Greek
species
a
and
are
genus.
and
means
Genera
species
a
arranged
in
a
are
group
or
of
grouped
family
is
something.
classied
into
into
shown
in
The
taxa.
families.
gure
3.
plural
Every
An
is
species
example
Families
are
latirostris
grouped
yacare
kingdom
taxa
and
Melano-
into
or
from
orders,
domain.
the
larger
orders
level
The
taxa
below.
numbers
of
into
classes
form
Going
species,
a
up
and
on
hierarchy,
the
which
so
up
as
fewer
the
each
hierarchy,
share
to
the
and
level
taxon
taxa
of
includes
include
fewer
larger
features.
niger
suchus
palpebrosus
the hee omi
Paleo-
suchus
All organisms are lassied into three domains.
trigonatus
Traditional
▲
classication
systems
have
recognized
two
major
categories
Figure 3 Classication of the alligator family
of
organisms
based
classication
have
been
sequence
there
are
of
two
Members
of
the
but
so
the
eukaryotes.
biologists
very
as
eukaryotes
was
groups
of
and
inappropriate
diverse.
RNA
systems
Eubacteria,
of
types:
In
prokaryotes.
because
particular,
determined,
prokaryotes.
it
the
when
became
They
This
prokaryotes
the
base
apparent
were
given
that
the
names
Archaea.
domains,
some
be
distinct
and
organism,
shows
260
to
cell
regarded
ribosomal
classication
called
and
now
found
of
Eubacteria
Most
is
on
all
therefore
Archaea
organisms
features
that
domains
are
Bacteria
and
archaeans
are
now
and
are
can
Eukaryota.
classied
be
usually
used
less
are
well
three
These
into
to
referred
eukaryotes
often
recognize
three
major
categories
domains.
distinguish
to
as
known.
are
Table
between
bacteria,
relatively
categories
archaeans
familiar
to
1
them.
most
5 . 3
c l A s s i f i c A t i o n
feae
o f
B i o D i v E r s i t Y
Dma
Baea
Histones assoiated
Ahaea
Asent
Ekaya
Proteins similar to histones
with DNA
Present
ound to DNA
Presene of introns
Rare or asent
Struture of ell walls
Present in some genes
Made of hemial alled
Not made of peptidoglyan
peptidoglyan
Frequent
Not made of peptidoglyan;
not always present
Cell memrane
Glyerol-ester lipids;
Glyerol-ether lipids;
Glyerol-ester lipids;
dierenes
unranhed side hains;
unranhed side hains; l-form
unranhed side hains;
d-form of glyerol
of glyerol
d-form of glyerol
▲
T
able 1
Archaeans
deep
are
ocean
Earth.
with
They
very
are
high
methanogens
of
their
of
termites
Viruses
have
found
in
sediments
also
salt
are
are
range
even
in
oil
responsible
classied
coding
for
in
for
any
proteins
habitats
fairly
or
anaerobes
Methanogens
of
deposits
some
concentrations
obligate
are
not
genes
broad
found
metabolism.
and
a
and
such
below
extreme
the
give
in
the
off
the
close
intestines
three
the
the
of
such
to
of
surface,
of
as
a
The
waste
cattle
and
gas”
in
Although
genetic
code
the
water
boiling.
as
“marsh
domains.
same
ocean
surface
methane
production
using
as
the
habitats
temperatures
and
live
of
far
as
product
the
guts
marshes.
they
living
Ay
organisms
they
have
too
few
of
the
characteristics
of
life
to
be
regarded
ideyg a kgdm
as
living
organisms.
This is a denition of the
Bacteria
Archaea
Eukaryota
harateristis of organisms in
Green lamentous
one of the kingdoms. Can you
Slime
bacteria
molds
Spirochetes
dedue whih kingdom it is?
Animals
Gram
Methanobacterium
Proteobacteria
positives
Fungi
Halophiles
Multicellular; cells typically
Methanococcus
Plants
Cyanobacteria
held together by intercellular
Ciliates
junctions; extracellular
Flagellates
matrix with fibrous proteins,
typically collagens, between
two dissimilar epithelia;
sexual with production of an
egg cell that is fer tilized by a
▲
Figure 4 Tree diagram showing relationships between living organisms based on base
smaller, often monociliated,
sequences of ribosomal RNA
sperm cell; phagotrophic and
osmotrophic; without cell wall.
Ekyoe clicio
The prinipal taxa for lassifying eukaryotes are kingdom,
phylum, lass, order, family, genus and speies.
Eukaryotes
into
phyla,
genera.
are
The
phylum,
classied
which
are
hierarchy
class,
order,
into
kingdoms.
divided
of
taxa
family,
into
for
Each
classes,
classifying
genus
and
kingdom
then
orders,
is
divided
families
eukaryotes
is
thus
up
and
kingdom,
species.
▲
Most
biologists
recognize
four
kingdoms
of
eukaryote:
of
the
plants,
animals,
Figure 5 Brown seaweeds have
been classied in the kingdom
Protoctista
fungi
as
and
protoctista.
protoctists
kingdoms.
At
are
very
present
The
last
diverse
there
is
these
and
no
is
should
be
consensus
most
controversial
divided
on
how
up
into
this
more
should
be
done.
261
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Exmple of clicio
Classiation of one plant and one animal speies from
domain to speies level.
Animals
shows
and
the
kingdom
plants
are
classication
down
to
kingdoms
of
one
of
plant
the
domain
and
one
Eukaryota.
animal
Table
species
2
from
species.
tax
Gey w
Dae pam
Kingdom
Animalia
Plantae
Phylum
Chordata
Angiospermophyta
Class
Mammalia
Monootyledoneae
Order
Carnivora
Palmales
Family
Canidae
Areaeae
Genus
Canis
Phoenix
Speies
lupus
dactylifera
▲
T
able 2
Daa-baed qe: Classifying car tilaginous sh
All
the
sh
shown
Chondrichthyes.
found
sh
in
in
gure
They
this
class
are
in
6
are
the
in
most
the
class
1
State
frequently
north-west
in
the
gure
kingdom
6
to
which
all
of
the
species
belong.
[1]
Europe.
2
a)
Four
the
of
the
same
sh
in
genus.
gure
Deduce
6
are
classied
which
these
are.
b)
c)
[1]
Deduce
with
sh
in:
are
whether
these
four
same
or
different
species
[2]
(ii)
the
same
or
different
families.
[2]
State
The
sh
two
that
characteristics
are
of
possessed
these
by
the
four
other
[2]
four
sh
Deduce,
are
not
sh.
other
orders.
Figure 6 Car tilaginous sh in seas in nor th-west Europe
reason
the
four
▲
a
(i)
sh
3
in
sh
split
are
with
into
a
two
classied
reason,
into
how
two
the
four
orders.
[2]
nl clicio
In a natural lassiation, the genus and aompanying higher taxa onsist of all the
speies that have evolved from one ommon anestral speies.
Scientic
that
evolved.
of
a
closely
of
the
of
a
or
is
common
natural
to
this
higher
This
is
follows
Following
genus
ancestor.
262
consensus
most
the
a
in
should
natural
ancestry
to
species
way
convention,
taxon
called
group
classify
we
share
can
in
a
which
all
have
way
species
members
a
common
classication.
expect
many
the
Because
members
characteristics.
An
example
classication
and
all
insects
y.
and
as
differ
to
in
unnatural
be
one
grouped
evolved
do
many
classify
an
would
are
Flight
they
of
not
them
separately
It
articial
which
together,
share
ways.
or
in
a
together
in
these
common
would
not
other
birds,
because
groups
ancestor
be
than
bats
they
they
appropriate
to
place
them
5 . 3
all
in
in
the
the
one
time
they
an
animal
phylum
classied
have
It
cell
articial
separately
are
is
no
share
can
a
be
and
do
classication
to
clear
common
move,
cell
which
other
so
of
natural
Convergent
but
this
walls
than
distantly
bats
were
at
because
shows
groups
and
fungi
presumably
their
each
birds
and
research
ancestor,
problematic.
both
not
as
molecular
similar
always
and
Plants
together,
walls
and
more
not
kingdom
Chordata.
c l A s s i f i c A t i o n
to
organisms
adaptive
visible
of
some
in
sub-topic
was
have
signicant
groups.
More
can
supercially
make
different.
In
attempted
characteristics
methods
caused
appear
radiation
appear
classication
many
have
animals.
species
related
molecular
they
B i o D i v E r s i t Y
organisms
and
as
evolved
that
related
similar
natural
is
o f
been
as
by
possible,
of
to
the
this
past,
looking
introduced
changes
details
closely
the
but
and
at
new
these
classication
are
given
later,
do
5.4.
classication
evolution
can
make
TOK
Wha a ee he deepme  a e e?
Carl Linnaeus’s 1753 ook Species Plantarum introdued
genera and speies. This was inorporated in the Amerian
onsistent two-part names (inomials) for all speies of
“Rohester Code” of 1883 and in the ode used at the Berlin
the vegetale kingdom then known. Thus the inomial
Botanihes Museum and supported y British Museum of
Physalis angulata replaed the osolete phrase-name,
Natural History, Harvard University otanists and a group
Physalis annua ramosissima, ramis angulosis glabris,
of Swiss and Belgian otanists. The International Botanial
foliis dentato-serratis. Linnaeus rought the sienti
Congress of Vienna in 1905 aepted y 150 votes to 19
nomenlature of plants ak to the simpliity and revity
the rule that “La nomenlature otanique ommene ave
of the vernaular nomenlature out of whih it had grown.
Linné, Speies Plantarum (ann. 1753) pour les groupes de
Folk-names for speies rarely exeed three words. In
plantes vasulaires.”
groups of speies alike enough to have a vernaular
1
Why was Linnaeus’s system for naming plants adopted
group-name, the speies are often distinguished y a
as the international system, rather than any other
single name attahed to the group-name, as in the Anient
system?
Greek αδιαυτου το λενκον and αδιαυτου το µεαυ
2
Why do the international rules of nomenlature state
(used y Threophrastus), Latin anagallis mas and anagallis
that genus and speies names must e in Anient
femina (used y Pliny), German weiss Seelumen and geel
Greek or Latin?
Seelumen (used y Fuhs), English wild mynte and water
3
mynte (used y Turner) and Malayan jamu ol and jamu
Making deisions y voting is rather unusual in siene.
Why is it done at International Botanial Congresses?
hilli (applied y Malays to dierent speies of Eugenia).
What knowledge issues are assoiated with this
The International Botanial Congress held in Genoa in 1892
method of deision making?
proposed that 1753 e taken as the starting point for oth
reiewig clicio
Taxonomists sometimes relassify groups of speies
when new evidene shows that a previous taxon ontains
speies that have evolved from dierent anestral speies.
Sometimes
common
closely
from
The
one
related,
genus
species.
assigned
been
to
much
family.
so
species
to
classication
other
this
evidence
ancestor,
Conversely
be
new
so
two
or
another
of
in
all
should
taxa
the
of
a
up
are
more
group
into
if
any,
of
the
great
apes
were
two
or
not
or
species
share
more
found
are
a
taxa.
to
moved
taxa.
controversy
procedures,
family
do
sometimes
united,
higher
caused
and
split
taxa
are
taxonomic
which,
the
be
between
Primates
Originally
members
different
has
standard
about
that
more
or
humans
order
debate
group
classied
Using
the
the
shows
humans
Hominidae.
great
placed
than
apes
in
any
are
There
to
has
include
another
in
family,
263
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
the
Pongidae,
are
closer
same
if
research
This
also
classication
that
and
be
in
is
than
would
suggests
humans
should
but
humans
family.
evidence
so
to
has
to
just
leave
chimpanzees
a
separate
shown
in
that
are
are
so
closer
placed
genus.
gure
chimpanzees
and
orang-utans
chimpanzees
FAMILY
A
in
should
in
the
than
of
SPECIES
gorillas
in
the
Pongidae.
gorillas
different
summary
and
be
to
Most
humans,
genera,
this
gorillas
scheme
for
human
7.
Hominidae
GENUS AND
▲
shown
orang-utans
Pongidae
Gorilla
Homo
Pan
Pan
Pongo
gorilla
sapiens
troglodytes
paniscus
pygmaeus
(gorilla)
(human)
(chimpanzee)
(bonobo)
(orang-utan)
Figure 7 Classication of humans
age of l clicio
Natural lassiations help in identiation of speies
and allow the predition of harateristis shared y
speies within a group.
There
is
great
of
biologists
to
nd
new
out
1
in
are
identied
▲
species
Identication
and
the
it
into
of
is
by
moment
areas
are
sometimes
research
found
at
surveying
what
species
helpful
interest
are
present.
species
is
Even
assigning
it
It
If
what
rst
to
biodiversity
research
in
a
the
specic
specimen
it
is,
kingdom,
world.
been
done
parts
classication
two
species
its
of
has
well-known
Natural
has
easier.
obvious
the
little
discovered.
biodiversity.
not
in
where
of
of
Groups
before,
the
world
species
is
very
advantages.
of
the
an
organism
specimen
then
the
is
can
phylum
be
within
Figure 8 Members of the Hominidae
the
kingdom,
class
within
the
phylum
and
so
on
down
to
species
and Pongidae
level.
Dichotomous
process
Ay
would
example,
colour
cg pa bgh
was
if
not
keys
work
owering
and
a
can
so
be
used
to
well
with
an
plants
were
white-owered
discovered,
it
would
not
with
articial
classied
bluebell
be
help
this
This
classication.
according
Hyacinthoides
identied
process.
to
For
ower
non-scripta
correctly
as
the
species
Phytophthora infestans, the
normally
has
blue
owers.
organism that auses the disease
potato light, has hyphae and
was lassied as a fungus, ut
moleular iology has shown that it
is not a true fungus and should e
lassied in a dierent kingdom,
possily the Prototista. Potato
light has proved to e a diult
disease to ontrol using fungiides.
Disuss reasons for this.
2
Because
have
of
the
within
is
a
found
to
be
was
in
mammary
bats
For
mammalian
were
a
a
that
if
in
a
features.
in
this
related
a
is
of
these
with
all
useful
the
bat
about
heart
predictions
other
ying
a
species
drug
are
species
will
similar
of
as
chemicals
new
predictions
correct:
inherit
characteristics
that
If
classication
they
four-chambered
None
articially
or
natural
the
genus.
many
are
a
of
a
species,
chemical
the
make
they
placenta,
classied
group
genus,
species
could
certainty
glands,
in
a
ancestral
prediction
example,
plant
we
of
common
allows
other
discovered,
reasonable
if
one
in
a
This
group.
found
members
from
characteristics.
other
264
all
evolved
it
of
with
have
and
likely
bat
hair,
many
could
be
made
organisms.
5 . 3
c l A s s i f i c A t i o n
o f
B i o D i v E r s i t Y
dichoomo key
Constrution of dihotomous keys for use in identifying speimens
Dichotomous
keys
are
often
constructed
to
use
for
1
identifying
species
within
a
group.
A
Fore and hind lims visile, an emerge on land
Only fore lims visile, annot live on land
is
a
division
into
two;
a
dichotomous
key
a
of
these
the
numbered
series
should
other
of
clearly
should
pairs
of
match
clearly
be
descriptions.
the
species
wrong.
The
the
designer
of
the
key
chooses
to
Fore and hind lims have paws
..................................... 3
One
and
Fore and hind lims have ippers
................................. 4
features
3
that
use
in
Fur is dark ............................................................
visible.
should
Each
of
to
another
of
in
the
or
key,
the
the
to
therefore
pair
of
reliable
descriptions
numbered
an
be
pairs
of
and
leads
example
of
a
polar ears
easily
either
4
descriptions
External ear ap visile ...........
No external ear ap
sea lions and fur seals
........................................................... 5
identication.
5
An
key
is
shown
in
table
3.
We
Two long tusks
.....................................................
it
to
identify
the
species
in
gure
9.
In
the
of
visible.
6
of
has
key,
They
the
a
the
key.
are
We
blowhole.
we
must
not,
so
must
It
decide
we
now
does
are
if
directed
decide
not,
so
hind
it
if
is
a
limbs
to
the
Mouth reathing, no lowhole
...
dugongs and manatees
are
Breathing through lowholes
stage
species
dugong
true seals
rst
6
stage
walruses
can
No tusks ...............................................................
use
sea otters
the
Fur is white ........................................................
descriptions
................ 6
consists
2
of
..... 2
dichotomy
or
7
......................................... 7
Two lowholes, no teeth .........................
aleen whales
a
One lowhole, teeth ........ dolphins, porpoises and whales
manatee.
to
A
separate
fuller
key
dugongs
would
and
have
another
stage
▲
manatees.
T
able 3 Key to groups of marine mammals
Ay
cg dhm key
Keys are usually designed for use in a par tiular area. All the groups or speies
that are found in that area an e identied using the key. There may e a
group of organisms in your area for whih a key has never een designed.
●
You ould design a key to the trees in the loal forest or on your shool
ampus, using leaf desriptions or ark desriptions.
●
You ould design a key to irds that visit ird-feeding stations in your area.
●
You ould design a key to the inver terates that are assoiated with one
par tiular plant speies.
●
You ould design a key to the footprints of mammals and irds (gure 10).
▲
Figure 9 Manatee
They are all right front footprints and are not shown to sale.
bear
duck
▲
wolf
rabbit / hare
fox
squirrel
cat
deer
dog
heron
Figure 10 Footprints of mammals and birds
265
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Pl
External reognition features of ryophytes, liinophytes, oniferophytes
and angiospermophytes.
All
In
plants
the
life
gametes
formed
which
of
classied
cycle
are
of
it
The
and
into
embryo
is.
together
every
formed
develops
this
plant
into
are
plant,
fuse
an
in
different
The
depends
types
of
example
kingdom.
and
together.
embryo.
develops
one
male
The
way
on
main
female
one
phyla
of
the
smaller
phyla.
The
four
are:
●
Bryophyta
●
Filicinophyta
●
Coniferophyta
●
Angiospermophyta
–
mosses,
liverworts
and
hornworts
in
type
are
–
ferns
put
–
conifers
phyla.
Most
plants
are
in
one
of
four
phyla,
but
other
smaller
phyla.
The
Ginkgo
–
owering
plants.
there
The
are
in
zygote
the
plants
is
plant
biloba
tree
are
Byphya
Vegetative organs – par ts
Rhizoids ut no
of the plant onerned
true roots. Some
with growth rather than
with simple stems
reprodution
and leaves; others
external
recognition
features
of
these
phyla
for
shown
fphya
in
table
4.
cephya
Agpemphya
Roots, stems and leaves are usually present
have only a thallus
Vasular tissue – tissues
No xylem or
with tuular strutures used
phloem
Xylem and phloem are oth present
for transpor t within the plant
Camium – ells etween
No amium; no true trees and
Present in onifers and most angiosperms,
xylem and phloem that
shrus
allowing seondary thikening of stems and
an produe more of these
roots and development of plants into trees
tissues
and shrus
Pollen – small strutures
Pollen is not produed
ontaining male gametes
Pollen is produed
Pollen is produed
in male ones
y anthers in
that are dispersed
Ovules – ontains a female
owers
No ovaries or ovules
gamete and develops into a
seed after fer tilization
Seeds – dispersile unit
Ovules are produed
Ovules are enlosed
in female ones
inside ovaries in
owers
No seeds
Seeds are produed and dispersed
onsisting of an emryo
plant and food reserves,
inside a seed oat
Fruits – seeds together with
No fruits
Fruits produed for
a fruit wall developed from
dispersal of seeds
the ovary wall
y mehanial, wind
or animal methods
▲
266
T
able 4
5 . 3
c l A s s i f i c A t i o n
o f
B i o D i v E r s i t Y
aiml phyl
Reognition features of porifera, nidaria, platyhelminthes, annelida, mollusa and
ar thropoda, hordata.
Animals
table
5.
are
Two
divided
up
examples
into
of
over
each
Phym
30
are
phyla,
shown
Mh/a
based
in
on
gure
their
characteristics.
Six
phyla
are
featured
in
11.
symmey
skee
ohe ex ea
eg eae
Porifera – fan sponges,
No mouth or
up sponges, tue
anus
None
Internal spiules
Many pores over the surfae
(sketetal needles)
through whih water is drawn
sponges, glass sponges
in for lter feeding. Very varied
shapes
Soft, ut hard
Tentales arranged in rings
jellysh, orals, sea
orals serete
around the mouth, with stinging
anemones
CaCO
ells. Polyps or medusae
Cnidaria – hydras,
Mouth only
Radial
3
(jellysh)
Platyhelminthes –
Mouth only
Bilateral
atworms, ukes,
Soft, with no
Flat and thin odies in the shape
skeleton
of a rion. No lood system or
tapeworms
system for gas exhange
Mollusa – ivalves,
Mouth and
gastropods, snails,
anus
Bilateral
Most have shell
A fold in the ody wall alled
made of CaCO
the mantle seretes the shell. A
3
hard rasping radula is used for
hitons, squid, otopus
feeding
Annelida – marine
Mouth and
ristleworms,
anus
Bilateral
oligohaetes, leehes
Internal avity
Bodies made up of many ring-
with uid under
shaped segments, often with
pressure
ristles. Blood vessels often
visile
Ar thropoda – insets,
Mouth and
arahnids, rustaeans,
anus
Bilateral
myriapods
▲
1
Segmented odies and legs or
other appendages with joints
hitin
etween the setions
T
able 5 Characteristics of six animal phyla
Study
and
2
External skeleton
made of plates of
List
the
organisms
assign
the
each
one
organisms
a)
bilaterally
b)
radially
shown
to
that
its
in
gure
11
phylum.
3
List
the
organisms
not
symmetric
symmetric
symmetrical
in
have:
a)
jointed
b)
stinging
appendages
c)
bristles.
are:
4
List
the
their
structure.
tentacles
[3]
organisms
pumping
c)
that
[7]
water
that
lter
through
feed
tubes
by
inside
[3]
their
bodies.
[2]
267
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
veebe
Reognition of features of irds, mammals, amphiians,
reptiles and sh.
Most
Adocia cinerea
species
of
chordate
belong
to
one
of
ve
major
classes,
each
of
Alcyonium glomeratum
which
are
not
are
about
5,700
bony
ve
Nymphon gracilis
Pycnogonum littorale
contains
are
certain
more
and
10,000
mammals.
sh,
with
largest
vertebrates,
By ay-
new
bird
All
of
a
thousand
species
species,
of
more
classes
than
these
than
9,000
30,000
they
Amphba
still
classes
chordate
because
are
are
species.
sometimes
reptiles,
are
species.
a
6,000
The
in
repe
numbers
amphibians
by
the
recognition
table
backbone
the
discovered,
outnumbered
shown
have
Although
6.
All
of
composed
and
ray-nned
features
the
of
Bd
there
of
the
organisms
vertebrae.
Mamma
ed h
Lepidonotus clara
Corynactis viridis
Sales whih
Soft moist
Impermeale
Skin with
Skin has
are ony
skin
skin overed
feathers made
folliles with
plates in the
permeale
in sales of
of keratin
hair made of
skin
to water and
keratin
keratin
gases
Polymastia mammiliaris
Cyanea capillata
Gills overed
Simple lungs
Lungs with
Lungs with
Lungs with
y an
with small
extensive
para-ronhial
alveoli,
operulum,
folds and
folding to
tues,
ventilated
with one gill
moist skin for
inrease the
ventilated
using
slit
gas exhange
surfae area
using air sas
ris and a
diaphragm
No lims
Tetrapods with pentadatyl lims
Fins
Four legs
Four legs (in
Two legs and
Four legs in
suppor ted y
when adult
most speies)
two wings
most (or two
Procerodes littoralis
rays
legs and two
wings/arms)
Loligo forbesii
Arenicola marina
Eggs and sperm released for
Sperm passed into the female for internal
external fer tilization
fer tilization
Remain
Larval stage
Female lays
Female lays
Most give
in water
that lives in
eggs with soft
eggs with hard
ir th to live
throughout
water and
shells
shells
young and
their life yle
adult that
all feed
usually lives
young with
on land
milk from
mammary
Prostheceraeus vittatus
glands
Swim ladder
Eggs oated
Teeth all of
Beak ut no
Teeth of
ontaining gas
in protetive
one type, with
teeth
dierent
for uoyany
jelly
no living par ts
Caprella linearis
types with a
living ore
Do not maintain onstant ody temperature
Maintain onstant ody
Gammarus locusta
temperature
▲
Figure 11 Inver tebrate diversity
▲
268
T
able 6
5 . 4
c l A D i s t i c s
5.4 cad
ueig
applicio
➔
A lade is a group of organisms that have
Cladograms inluding humans and other
➔
evolved from a ommon anestor.
primates.
➔
Evidene for whih speies are par t of a lade
Relassiation of the gwor t family using
➔
an e otained from the ase sequenes
evidene from ladistis.
of a gene or the orresponding amino aid
sequene of a protein.
➔
skill
Sequene dierenes aumulate gradually
so there is a positive orrelation etween the
Analysis of ladograms to dedue evolutionary
➔
numer of dierenes etween two speies
relationships.
and the time sine they diverged from a
ommon anestor.
ne of ciece
➔
Traits an e analogous or homologous.
➔
Cladograms are tree diagrams that show the
Falsiation of theories with one theory eing
➔
superseded y another: plant families have
most proale sequene of divergene in
een relassied as a result of evidene from
lades.
ladistis.
➔
Evidene from ladistis has shown that
lassiations of some groups ased
on struture did not orrespond with the
evolutionary origins of a group of speies.
Cle
A lade is a group of organisms that have evolved from
a ommon anestor.
Species
can
happened
there
are
ancestor.
evolve
now
a
Clades
very
include
a
They
ten
member
can
with
the
and
be
just
thousand
common
been
group
all
species
small
about
of
and
some
groups
groups
A
time
with
of
split
species
species
of
to
highly
can
organisms
form
new
successful
all
be
derived
from
identied
evolved
species.
species,
by
from
a
a
This
so
has
that
common
looking
for
common
shared
ancestor
is
clade.
ancestral
extinct.
large
These
characteristics.
called
over
repeatedly
of
other
ancestral
a
clade
species
species
any
very
a
large
few.
living
For
that
and
The
clade
together
evolved
include
example,
evolved
this
today,
that
species
species.
in
alive
species
all
270
are
form
they
Ginkgo
about
but
it
million
now
of
one
have
biloba
the
and
thousands
birds
because
tree
with
from
is
all
became
species,
large
only
ago.
or
clade
evolved
the
years
common
then
with
from
living
There
have
extinct.
269
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
Ay
the EDGE  Exee pje
The aim of this projet is to identify animal speies
threatened or have lose relatives. In some ases speies
that have few or no lose relatives and are therefore
are the last memers of a lade that has existed for tens
memers of very small lades. The onservation status
or hundreds of millions of years and it would e tragi for
of these speies is then assessed. Lists are prepared of
them to eome extint as a result of human ativities.
speies that are oth Evolutionarily Distint and Gloally
What speies on EDGE lists are in your par t of the world
Endangered, hene the name of the projet. Speies
and what an you do to help onserve them?
on these lists an then e targeted for more intense
http://www.edgeofexistene.org/speies/
onservation eor ts than other speies that are either not
▲
Figure 1 Two species on the EDGE list: Loris tardigradus tardigradus (Hor ton Plains slender loris) from Sri Lanka and Bradypus
pygmaeus (Pygmy three-toed sloth) from Isla Escudo de Veraguas, a small island o the coast of Panama
Ieifyig membe of  cle
Evidene for whih speies are par t of a lade an e
otained from the ase sequenes of a gene or the
orresponding amino aid sequene of a protein.
It
is
not
always
ancestor
The
and
most
amino
objective
acid
ancestor
270
to
evidence
from
have
of
expected
Conversely,
diverged
likely
be
which
therefore
sequences
can
sequence.
but
obvious
should
a
many
species
be
comes
proteins.
to
have
species
common
have
included
from
sequences
that
look
tens
of
from
a
common
clade.
have
differences
might
ancestor
differences.
a
base
Species
few
that
evolved
in
in
a
of
base
similar
genes
recent
in
millions
or
amino
certain
of
or
common
years
acid
respects
ago
are
5 . 4
c l A D i s t i c s
Molecl clock
Sequene dierenes aumulate gradually so there is
a positive orrelation etween the numer of dierenes
etween two speies and the time sine they diverged
from a ommon anestor.
Differences
acid
gradually
occur
clock.
long
For
in
the
sequence
at
over
a
long
species
four
sequence
are
periods
of
split
a
mitochondrial
related
primates
DNA
result
time.
rate
so
differences
from
of
the
of
constant
number
example,
and
base
proteins
roughly
The
ago
of
DNA
evidence
be
used
can
the
that
as
be
in
They
a
amino
accumulate
mutations
molecular
used
to
deduce
how
ancestor.
from
been
is
can
sequence
common
has
therefore
mutations.
There
they
in
and
of
three
humans
European
completely
Japanese
sequenced.
From
hypothetical
in
gure
2.
the
ancestry
Using
differences
has
been
differences
in
base
sequence,
constructed.
in
base
It
is
sequence
a
shown
as
African
a
Common chimpanzee
molecular
between
clock,
groups
●
70,000
●
140,000
●
5,000,000
these
have
years
ago,
years
been
dates
for
splits
deduced:
Pygmy chimpanzee (bonobo)
European–Japanese
ago,
years
approximate
split
Gorilla
African–European/Japanese
ago,
human–chimpanzee
split
split
▲
Figure 2
alogo  homologo i
Traits an e analogous or homologous.
Similarities
between
Homologous
●
example
the
Analogous
●
human
Problems
in
structures
For
this
and
but
reason
rarely
base
or
the
they
are
wing,
are
are
used
amino
acid
similar
eye
led
to
identifying
sequences
arm
homologous
of
and
because
of
similar
other
because
they
(form
and
trusted
in
in
and
a
clade
for
forelimbs.
evolution.
structure
The
and
independently.
analogous
classication
structure)
of
analogous.
ancestry;
evolved
homologous
mistakes
or
pentadactyl
convergent
similarities
members
is
be
because
show
between
morphology
for
either
human
analogous
sometimes
the
can
similar
octopus
distinguishing
have
now
structures
chicken
structures
eye
function
organisms
of
and
in
the
past.
organisms
evidence
is
from
more.
cornea
iris
lens
retina
photoreceptors
optic nerve
▲
Figure 3 The human eye (left) and the octopus eye (right) are analogous because they are
quite similar yet evolved independently
271
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
sruasonid
sdrib
naiva-non
sdrazil
sekans
seltrut
selidocorc
Clogm
Cladograms are tree diagrams that show the most
proale sequene of divergene in lades.
ancestral species A
A
cladogram
is
a
tree
diagram
based
on
similarities
and
differences
between
ancestral species B
the
or
species
amino
in
a
acid
clade.
Cladograms
sequences.
are
Computer
almost
always
programs
have
now
based
been
on
base
developed
that
ancestral species C
calculate
number
▲
how
of
species
changes
in
of
a
clade
base
or
could
amino
have
acid
evolved
with
sequence.
the
This
is
smallest
known
as
the
Figure 4 A cladogram showing the
principle
of
parsimony
and
although
it
does
not
prove
how
a
clade
actually
hypothesized relationship between birds and
evolved,
it
can
indicate
the
most
probable
sequence
of
divergence
in
clades.
the traditional taxonomic group “the reptiles”
The
branching
branch
off
at
points
a
node
on
but
cladograms
sometimes
are
called
there
are
nodes.
three
or
Usually
more.
two
The
clades
node
Ay
represents
Figure 5 shows an ar tist’s impression
species.
of two pterosaurs, whih were the rst
base
a
hypothetical
Option
B
sequences
ancestral
includes
using
species
instructions
computer
for
that
split
to
form
constructing
two
or
cladograms
more
from
software.
hordates to develop powered ight.
Figure
4
is
an
example
of
a
cladogram
for
birds
and
reptiles.
It
has
been
They were neither irds nor dinosaurs.
based
on
morphology,
so
that
extinct
groups
can
be
included.
Where might pterosaurs have tted
into the ladogram shown in gure 4?
●
●
Birds,
non-avian
called
dinosauria.
Birds,
non-avian
part
a
Lizards,
●
This
or
clade
reptiles
are
and
either
be
closely
ancestral
crocodiles
species
and
A
form
ancestral
a
clade
species
B
species
that
divided
related
birds
into
to
C
should
two
birds
form
or
than
a
clade
be
more
to
called
regarded
groups,
other
squamates.
as
as
reptiles
some
reptiles.
Figure 5 Two pterosaurs in ight
Pime clogm
Cladograms inluding humans and
45,000
4.5 Myr ago
other primates.
The
closest
and
bonobos.
species
has
evidence
(gure
relatives
been
for
6).
estimates
The
the
The
of
of
humans
entire
sequenced
population
splits
occurred.
clock
with
These
on
sizes
are
of
the
a
these
very
cladogram
dates
on
a
Figure
7
is
mutation
rate
a
cladogram
for
of
10
are
when
27,000
molecular
–9
a
three
strong
cladogram
and
based
chimpanzees
of
giving
construction
numbers
are
genome
1 Myr ago
–1
yr
primates
and
the
most
12,000
closely
are
for
an
related
order
climbing
gibbons
272
and
other
of
groups
mammals
trees.
that
Humans,
lemurs
are
of
mammal.
have
primates.
Primates
adaptations
monkeys,
baboons,
are
archosaurs.
ancestral
suggests
should
more
and
dinosaurs,
called
snakes
cladogram
that
reptiles
▲
of
dinosaurs
Bonobo
▲
Figure 6
Chimpanzee
Human
5 . 4
c l A D i s t i c s
Cavies and Coypu
alyi of clogm
Porcupines
Mice and Rats
Analysis of ladograms to dedue evolutionary
Beavers
relationships.
Chipmunks
The
pattern
of
branching
in
a
cladogram
is
assumed
to
match
the
Rabbits
evolutionary
origins
of
each
species.
The
sequence
of
splits
at
nodes
is
Primates
therefore
a
diverged.
If
hypothetical
sequence
in
which
ancestors
of
existing
clades
Treeshrews
two
clades
on
a
cladogram
are
linked
at
a
node,
they
are
Figure 7
▲
relatively
of
nodes,
Some
in
related.
are
cladograms
base
are
closely
they
or
amino
assumed
to
less
If
include
acid
occur
two
closely
species
numbers
sequence
at
a
are
only
connected
via
a
series
related.
or
to
in
relatively
indicate
genes.
numbers
Because
constant
rate,
of
genetic
these
Ay
differences
changes
numbers
A adgam  he gea ape
can
The great apes are a family of
be
used
to
estimate
how
long
ago
two
clades
diverged.
This
method
primates. The taxonomi name is
of
estimating
times
is
called
a
molecular
clock.
Some
cladograms
Hominidae. There are ve speies
are
drawn
to
scale
according
to
estimates
of
how
long
ago
each
split
on Ear th today, all of whih are
occurred.
dereasing in numer apar t from
Although
cladograms
history
a
of
group,
constructed
of
on
mutations
sequence
and
using
the
to
of
be
different
cannot
to
were
in
versions
the
for
for
proof.
smallest
base
or
is
convoluted.
of
cladograms
been
the
produced
humans. Figure 6 is a ladogram
evolutionary
Cladograms
possible
assumption
more
have
as
current
this
analysis
that
evidence
regarded
that
account
evolution
strong
be
Sometimes
cautious
several
provide
assumption
occurred
pathways
compare
they
differences.
important
can
for three of the speies. Use
are
this information to expand the
number
amino
ladogram to inlude all the great
acid
apes: the split etween humans
incorrect
It
is
and
and gorillas ourred aout
therefore
where
10 million years ago and the split
possible
etween humans and orang-
independently
utans aout 15 million years ago.
genes.
Daa-baed qe: Origins of tur tles and lizards
Cladograms
based
on
morphology
the
suggest
short-tailed
opossum
or
to
the
duck-billed
platypus.
that
this
turtles
and
hypothesis,
compared
for
lizards
are
not
microRNA
nine
species
a
clade.
genes
of
To
have
been
chordate.
2
Calculate
found
The
but
results
were
gure8.
which
used
The
to
construct
numbers
microRNA
on
genes
the
are
the
cladogram
cladogram
shared
by
a
clade
example,
humans
but
not
there
and
members
are
six
short-tailed
of
other
show
3
microRNA
opossums
genes
but
not
Discuss
other
chordates
on
the
the
Deduce,
whether
using
evidence
humans
are
microRNA
clade
on
genes
the
are
cladogram
clades.
the
supports
any
in
of
4
Evaluate
tetrapod
are
not
the
evidence
the
a
[2]
in
the
hypothesis
that
turtles
clade.
traditional
chordates
[3]
and
into
mammals
classication
amphibians,
using
evidence
of
reptiles,
from
the
cladogram.
cladogram.
1
other
whether
lizards
birds
the
in
many
mammal
For
found
in
not
how
the
cladogram
members
clades.
in
in
and
of
[2]
test
from
more
the
[3]
cladogram,
closely
related
to
273
5
E v o l u t i o n
a n d
b i o d i v E r s i t y
African clawed frog
043
176
167
588
Human
Short-tailed opossum
681
095
378
3
1521
7931
6
Duck-billed platypus
1971
1541
0641
7641
9551
7651
1461
9661
9271
3471
4471
6571
9571
1871
4871
9871
3081
1312
1
4592
4692
094
7931
19
Zebra nch
Chicken
Alligator
7761
1
Painted turtle
▲
0935
1935
2935
3935
4
Lizard
Figure 8
Clogm  eclicio
Evidene from ladistis has shown that lassiations of
some groups ased on struture did not orrespond with
the evolutionary origins of a group of speies.
The
construction
only
the
became
sequence
been
has
classication.
classication
evolutionary
been
data
developed
identication
Cladistics
of
group
and
to
truly
to
274
is
is
from
groups
groups
cases
and
The
as
of
and
20th
amino
acid
century.
computer
of
sequences
Before
software
construction
in
plant
cladograms
does
not
species.
have
species
base
the
had
that
not
cladograms
and
cladistics.
morphology
of
of
revolutions
clear
Some
some
analysis.
known
on
end
available
some
on
origins
of
groups
disruptive
natural
have
some
be
the
now
classications
They
not
based
the
have
animal
traditional
always
As
been
and
that
a
merged,
been
match
result
some
others
transferred
the
groups
have
from
have
been
one
another.
potentially
also
do
based
in
towards
clades
caused
It
Reclassication
a
cladograms
was
to
reclassied.
divided
new
of
possible
based
of
some
signicant
organisms
biologists,
on
classication
revealed
similar.
for
cladistics
so
their
unnoticed
differences
is
but
it
are
time-consuming
is
certainly
likely
predictive
be
value
similarities
between
to
much
will
between
species
and
worthwhile.
be
closer
higher.
groups
previously
The
to
and
assumed
5 . 4
c l A D i s t i c s
Clogm  flicio
Falsiation of theories with one theory eing
superseded y another: plant families have een
relassied as a result of evidene from ladistis.
The
is
a
reclassication
good
theories
and
theories.
on
their
Laurent
revised
example
of
The
of
of
on
replacement
Jussieu
repeatedly
was
in
the
important
classication
morphology
de
plants
an
of
of
Genera
of
theories
discoveries
in
science:
found
to
be
angiospermophytes
begun
during
basis
process
by
the
French
plantarum ,
the
19th
false
into
in
cladistics
testing
with
of
new
families
botanist
published
in
the
based
Antoine
1789
and
century.
Clicio of he gwo fmily
Relassiation of the gwor t family using evidene from ladistis.
There
Until
are
more
recently
than
the
Scrophulariaceae,
gwort
family.
proposed
by
It
de
400
eighth
commonly
was
one
Jussieu
in
name
Scrophulariae
and
based
on
in
more
until
similarities
plants
there
5,000
were
were
families
largest
of
1789.
275
as
He
the
gave
families
it
sixteen
family
with
using
the
morphology.
genera,
Taxonomists
evolutionary
the
original
included
their
angiosperms.
known
the
discovered,
over
of
was
the
compared
the
genes
large
in
a
traditionally
As
genera
that
grew
than
in
and
One
base
in
into
the
sequences
to
related
the
of
one
of
three
in
project
chloroplast
genera
Scrophulariaceae
families.
clades
family
research
species
the
gwort
ve
the
gwort
important
assigned
that
investigated
of
number
closely
species
clade
combined
species.
origins
cladistics.
genera,
more
recently
family
had
It
was
were
and
found
not
incorrectly
a
true
been
family.
Two small families were merged
with the gwort family:
the buddleja family, Buddlejaceae
and the myoporum family, Myoporaceae
Two genera were moved to
Nearly fty genera have
a newly-created family,
been moved to the
The gwort
the calceolaria family,
plantain family,
family
Calceolariaceae
Plantaginaceae
Scrophulariaceae
Thirteen genera have
▲
been
About twelve genera of
transferred to a newly-created
parasitic plants have been
family, the lindernia family,
moved to the broomrape
Linderniaceae
family, Orobanchaceae
Figure 9
275
5
E v o l u t i o n
A
major
Less
in
▲
half
family,
largest
b i o d i v E r s i t y
reclassication
than
the
a n d
of
the
which
among
the
has
species
is
now
now
only
angiosperms.
carried
been
the
A
out.
retained
thirty-sixth
summary
of
the
Figure 10 Antirrhinum majus has been transferred from the
gwor t family to the plantain family
276
been
have
changes
has
before
of
is
been
that
species
▲
shown
in
welcomed
the
gure
as
it
9.
was
This
Scrophulariaceae
rather
than
a
reclassication
widely
natural
appreciated
had
been
a
rag-bag
group.
Figure 11 Scrophularia peregrina has remained in the
gwor t family
Q u E s t i o n s
Qeio
The
bar
three
at
charts
in
gure
populations
different
came
from
Rhosneigr
copper
an
in
undersides
of
the
The
that
growth
Ectocarpus
concentrations.
ships
copper-containing
show
alga,
unpolluted
Wales.
of
12
an
One
environment
other
had
two
been
anti-fouling
4
of
siliculosus,
Which
of
copper
tolerance
the
following
to
processes
develop
in
a
are
required
for
population?
population
(i)
variation
in
(ii)
inheritance
(iii)
failure
copper
tolerance
at
came
from
painted
the
with
of
copper
tolerance
a
of
algae
with
lower
copper
paint.
tolerance
to
survive
or
reproduce.
500
emulov lagla ni esaercni %
Rhosneigr
a)
i)
only
b)
i)
and
ii)
c)
i)
and
iii)
d)
i),
only
0
only
M.V. San Nicholas
500
ii)
and
iii).
0
M.V. Amama
5
In
gure
species.
13,
The
each
number
closer
that
represents
two
numbers
a
are
on
500
the
diagram
The
0
0.0
0.01
0.05
0.1
0.5
1.0
5.0
circles
the
more
represent
similar
the
taxonomic
two
species.
groups.
For
10.0
example,
the
diagram
shows
that
2,
3,
4
and
-3
concentration of copper (mg dm
)
5
are
in
the
same
genus.
Figure 12
1
How
much
higher
concentration
was
the
tolerated
by
maximum
the
algae
copper
from
34
2 3
1
ships
than
the
algae
from
an
unpolluted
6 7
4 5
environment?
a)
0.09
times
higher
b)
0.11
times
higher
8
9 10
c)
1.0
times
higher
d)
10
times
11
higher.
12
13
19
24
14
20
25
15
2
1
16
22
1
7
26
27
28
18
29
23
30
2
What
is
the
reason
for
results
lower
than
zero
31
on
the
bar
32
charts?
33
a)
The
volume
b)
The
algae
c)
Increases
d)
Results
of
all
in
algae
decreased.
died.
Figure 13
volume
were
less
than
100 %
a)
State
with
were
too
small
to
b)
State
with
c)
What
was
the
reason
for
the
difference
tolerance
between
the
The
algae
on
the
ships
the
The
algae
can
develop
absorbed
it
on
to
their
State
The
d)
The
copper
in
copper
tolerance
selection
in
the
for
that
are
in
a
family
species
[2]
that
are
in
an
order
families.
[2]
State
the
species
that
are
in
a
class
with
orders.
[2]
Deduce
whether
species
8
is
more
closely
offspring.
the
the
[1]
and
paint
caused
paint
higher
caused
levels
of
to
species
16
or
species
6.
mutations.
f)
copper
genus
genera.
two
related
c)
a
copper.
e)
pass
in
species.
species
two
three
b)
is
algae?
d)
a)
other
that
in
with
copper
no
species
measure
accurately.
3
one
natural
copper
tolerance.
Explain
been
why
drawn
diagram.
three
concentric
around
species
circles
34
on
have
the
[2]
277
5
E v o l u t i o n
6
The
map
in
in
the
in
Britain
a n d
gure
1950s
of
and
b i o d i v E r s i t y
14
two
shows
forms
Ireland.
the
of
distribution
Biston
Biston
betularia
betularia
is
a
Key
species
of
moth
that
ies
at
night.
It
spends
Non-melanic
the
daytime
roosting
on
the
bark
of
trees.
The
Melanic
non-melanic
with
black
wings.
the
a)
spots.
Before
melanic
wind
form
form
is
wings,
melanic
very
from
has
revolution,
rare.
the
form
peppered
The
black
the
prevailing
Atlantic
Ocean,
to
west.
State
the
maximum
of
Outline
the
the
forms
in
c)
white
industrial
was
percentages
b)
The
the
direction
has
two
gure
Explain
moths
the
trends
of
and
minimum
melanic
in
the
Biston
form.
[2]
distribution
betularia,
of
shown
14.
how
such
[2]
natural
as
Biston
selection
betularia
can
to
cause
develop
Figure 14
camouaged
d)
278
wing
Suggest
reasons
the
forms.
two
markings.
for
the
distribution
[4]
of
[2]
6
H U m A N
p H y S I o l o g y
Intrductin
Research
into
foundation
are
carried
The
blood
to
it
to
and
by
of
medicine.
specialized
the
move,
system
cells
physiology
modern
out
structure
allows
human
of
wall
digest
of
continuously
simultaneously
functions
systems.
small
absorb
intestine
food.
transports
collects
products.
the
organ
the
and
is
Body
The
substances
waste
The
continuous
lungs
are
exchange
the
actively
can
message,
Hormones
widely
skin
threat
and
of
ventilated
occur
used
resist
pathogens.
ensure
that
Neurons
modulate
when
system
by
to
passively.
synapses
are
immune
invasion
the
signals
the
The
gas
transmit
message.
need
to
be
distributed.
6.1 Ds d s 
Understandin
Aicatins
➔
The contraction of circular and longitudinal
➔
Processes occurring in the small intestine that
muscle layers of the small intestine mixes the
result in the digestion of starch and transpor t of
food with enzymes and moves it along the gut.
the products of digestion to the liver.
➔
The pancreas secretes enzymes into the lumen
➔
Use of dialysis tubing to model absorption of
of the small intestine.
digested food in the intestine.
➔
Enzymes digest most macromolecules in food
into monomers in the small intestine.
➔
over which absorption is carried out.
➔
➔
Production of an annotated diagram of the
digestive system.
Villi absorb monomers formed by digestion as
well as mineral ions and vitamins.
➔
Skis
Villi increase the surface area of epithelium
➔
Identication of tissue layers in transverse
sections of the small intestine viewed with a
Dierent methods of membrane transpor t are
microscope or in a micrograph.
required to absorb dierent nutrients.
Nature f science
➔
Use models as representations of the real
world: dialysis tubing can be used to model
absorption in the intestine.
279
6
H u m a n
p H ys i o l o g y
Structure f the diestive sste
Production of an annotated diagram of the digestive system.
The
can
part
be
through
the
of
human
which
anus.
break
the
described
The
down
role
the
in
that
several
of
the
food,
can
to
that
ions
Surfactants
by
mouth
large
and
For
digestion
in
digestion
tube
system
of
absorbed.
occur
a
the
digestive
mixture
polysaccharides
stages
for
as
from
yield
be
used
terms
passes
diverse
compounds
and
body
simple
food
compounds
lipids
in
to
to
to
absorption
is
carbon
smaller
proteins,
involves
different
parts
the
place
some
small
through
small
in
e nzy mes
tha t
sy s te m.
the
the
s ma l l
stoma ch
are
se c r et e d
d ucts
C ontro ll ed,
nutr i e nts
molecul e s ,
the
ha ve
l e ad ing
s e le ct i ve
r el e as e d
inte stine
notab ly
l i ning
by
a nd
a lcohol ,
be for e
di g es ti on
c ol on ,
but
di ffu se
r ea ch in g
t he
intestine.
of
1
is
a
diagram
of
the
human
digestive
gut.
system.
Digestion
droplets
require s
and
Glandular
and
of
takes
o the r
gland s
digestive
Figure
the
and
accessory
s ur f a ctants
enzy me s
cells
intestines
in
the
to
ca ta l yse
l ining
prod uce
to
s ome
of
of
br ea k
up
li pi d
re a ct io n s.
the
the
s tom a c h
e n z ym e s .
The
part
through
the
diagram
can
functions
of
functions
is
of
thorax
be
the
has
esophagus
been
annotated
different
given
in
table
Sc
Mouth
to
parts.
1
that
omitted.
indicate
A
passes
This
the
summary
of
below.
Fc
Voluntary control of eating and
mouth
swallowing. Mechanical digestion
of food by chewing and mixing with
saliva, which contains lubricants and
enzymes that star t starch digestion
Esophagus
Movement of food by peristalsis
from the mouth to the stomach
esophagus
Stomach
Churning and mixing with secreted
water and acid which kills foreign
bacteria and other pathogens in
food, plus initial stages of protein
digestion
gall bladder
Small intestine
Final stages of digestion of lipids,
carbohydrates, proteins and nucleic
liver
acids, neutralizing stomach acid,
stomach
plus absorption of nutrients
pancreas
Pancreas
Secretion of lipase, amylase and
protease
small intestine
Liver
Secretion of surfactants in bile to
break up lipid droplets
Gall bladder
Large intestine
Storage and regulated release of bile
Re-absorption of water,
fur ther digestion especially of
carbohydrates by symbiotic
large intestine
bacteria, plus formation and storage
of feces
anus
▲
280
Figure 1 The human digestive system
▲
T
able 1
6 . 1
D i g e S t i o n
a n D
a b S o r p t i o n
Structure f the wa f the sa intestine
Identication of tissue layers in transverse sections of the small intestine viewed
with a microscope or in a micrograph.
The
wall
of
the
of
living
to
distinguish
outside
small
tissues,
of
in
the
intestine
which
are
sections
wall
going
is
made
usually
of
the
wall.
inwards
of
quite
layers
easy
From
there
the
are
fourlayers:
●
serosa
●
muscle
it
●
–
an
outer
layers
circular
●
lymph
mucosa
with
its
–
the
inner
longitudinal
muscle
and
inside
muscle
sub-mucosa
and
–
coat
–
a
tissue
layer
containing
blood
vessels
the
lining
epithelium
of
the
that
small
intestine,
absorbs
▲
nutrients
on
Figure 2 Longitudinal section through the wall of the small
intestine. Folds are visible on the inner surface and on
these folds are nger-like projections called villi. All of the
surface.
four main tissue layers are visible, including both circular
and longitudinal par ts of the muscle layer. The mucosa is
stained darker than the sub-mucosa
peristasis
acv
The contraction of circular and longitudinal muscle layers
tss  ds f 
of the small intestine mixes the food with enzymes and
s w
moves it along the gut.
To practice your skill at
identifying tissue layers,
The
circular
and
longitudinal
muscle
in
the
wall
of
the
gut
is
draw a plan diagram of the
smoothmuscle
rather
than
striated
muscle.
It
consists
of
relatively
short
tissues in the longitudinal
cells,
not
elongated
bres.
It
often
exerts
continuous
moderateforce,
section of the intestine wall
interspersed
with
short
periods
of
more
vigorous
contraction,
rather
in gure 2. To test your skill
than
remaining
relaxed
unless
stimulated
to
contract.
fur ther, draw a plan diagram
Waves
of
muscle
contraction,
called
peristalsis,
pass
along
the
intestine.
to predict how the tissues
Contraction
of
circular
muscles
behind
the
food
constricts
the
gut
to
of the small intestine would
prevent
it
from
being
pushed
back
towards
the
mouth.
Contraction
of
appear in a transverse
longitudinal
muscle
where
the
food
is
located
moves
it
on
along
the
gut.
section.
The
the
contractions
enteric
Swallowed
one
from
stomach
circular
In
the
the
nervous
food
continuous
away
time
and
for
system,
moves
longitudinal
the
food
progression
of
the
the
The
muscle
is
main
of
is
in
moved
through
the
gut
a
to
of
to
the
are
brain
but
by
complex.
to
occurs
the
in
stomach
one
mouth
used
few
in
direction,
from
rather
centimetres
is
much
peristalsis
mix
the
the
than
the
wall.
intestine
function
food
muscles
only
the
and
only
returned
the
by
esophagus
Peristalsis
food
not
extensive
abdominal
semi-digested
process
is
down
wave.
When
vomiting,
unconsciously
which
quickly
peristaltic
digestion.
up
controlled
mouth.
intestines
churning
speed
the
during
overall
are
it
with
in
at
slower,
the
a
time
intestine
enzymes
so
allowing
and
is
thus
digestion.
281
6
H u m a n
p H ys i o l o g y
pancreatic juice
The pancreas secretes enzymes into the lumen of the
small intestine.
The
the
pancreas
synthesizes
to
a
eating
the
the
The
on
of
is
the wave of muscle contraction (brown) in the
larger
ducts,
nally
pancreatic
by
juice
ducts,
are
by
4.
gland
into
by
the
synthesized
reticulum.
exocytosis.
secreted
in
are
Ducts
day
into
duct,
in
secrete
the
response
structure
of
round
the
secreted.
cells
on
in
pancreas
through
lumen
of
secreted
cluster
processed
the
cells
gut
and
The
gland
then
within
the
the
cells
are
pancreatic
pancreatic
per
system.
enzymes
They
into
gland
of
remainder
synthesized
nervous
of
groups
The
enzymes
groups
which
Small
blood.
hormones
enteric
one
tissue.
the
digestive
Small
into
forming
is
the
gure
secreted
of
secretes
endoplasmic
and
types
glucagon
mediated
also
enzymes
rough
apparatus
is
in
called
digestive
the
and
two
and
and
This
shown
tubes
Figure 3 Three-dimensional image showing
of
meal.
stomach
tissue
ends
esophagus during swallowing. Green indicates
insulin
pancreas
by
▲
contains
hormones
of
which
the
ribosomes
the
Golgi
merge
about
small
into
a
litre
intestine.
when the muscle is exer ting less force. Time
Pancreatic
juice
contains
enzymes
that
digest
all
the
three
main
types
of
is shown left to right. At the top the sphincter
macromolecule
between the mouth and the esophagus is
found
in
food:
shown permanently constricted apar t from a
●
amylase
to
●
lipases
●
proteases
digest
starch
brief opening when swallowing star ts
to
digest
to
triglycerides,
digest
proteins
phospholipids
and
peptides.
secretory vesicles
Diestin in the sa intestine
Enzymes digest most macromolecules in food into
one acinus
monomers in the small intestine.
The
enzymes
small
basement membrane
secretory cells
wall of duct
secreted
intestine
●
starch
●
triglycerides
acids
is
carry
out
digested
and
are
by
to
the
pancreas
these
hydrolysis
maltose
digested
to
monoglycerides
into
by
lumen
of
the
reactions:
amylase
fatty
by
the
acids
and
glycerol
or
fatty
lipase
lumen of duct
phospholipids
●
▲
are
digested
to
fatty
acids,
glycerol
and
Figure 4 Arrangement of cells and ducts in a par t of
phosphate
byphospholipase
the pancreas that secretes digestive enzymes
proteins
●
and
polypeptides
are
digested
to
shorter
peptides
by
protease.
This
does
enough
a
variety
enzymes
in
not
to
be
of
membrane
off
282
other
and
the
juice
of
●
Nucleases
●
Maltase
by
b ut
and
to
wa ll
mo st
be
DNA
ce ll s
wi th
and
maltose
the
RNA
into
m or e
in
nucleotides.
S om e
be
s e c r et e d
p la sma
The y
fo od.
small
p ro du c e s
may
the
e pi t h el iu m
s e m i -d ig e st e d
glucose.
w al l
int e s t in e .
th e
m o le c u le s
s u bs t a n c es .
int e st i n e
the
into
i nt o
in t e s t in e
i m m obil i z ed
wh e n
the
s ma l l
di g es t
l ining
a cti ve
d ig e st i on
the
in
r e mai n
ce l ls
of
of
which
g l and
mi x e d
digest
digests
pr oces s
The
epithe l i um
continue
lining
the
e nzy me s,
produce d
intestinal
there
comp l e te
abso r b e d .
a re
c e l ls
act i ve
are
a bra de d
6 . 1
●
Lactase
●
Sucrase
●
Exopeptidases
amino
until
Because
pass
acids
only
be
of
not
are
digest
cannot
that
a b S o r p t i o n
fructose.
peptides
or
amino
by
removing
terminal
of
single
the
chain
left.
of
time
the
on
into
the
for
amino
small
remain
the
of
most
largely
necessary
to
acids.
intestine,
digestion
substances
passes
digest
a n D
galactose.
and
carboxy
dipeptides
synthesize
and
and
glucose
the
is
length
Some
digested
into
from
dipeptide
great
glucose
proteases
allowing
completed.
into
sucrose
either
a
the
through,
humans
lactose
digests
Dipeptidases
●
is
digests
D i g e S t i o n
large
food
takes
hours
macromolecules
undigested,
enzymes.
intestine
because
Cellulose
as
one
to
to
of
for
the
example
main
▲
components
of
dietary
Figure 5 Cystic brosis causes the pancreatic
bre.
duct to become blocked by mucus. Pills
containing synthetic enzymes help digestion in
the small intestine. The photograph shows one
Vii and the surface area fr diestin
day’s supply for a person with cystic brosis
Villi increase the surface area of epithelium over which
absorption is carried out.
The
process
of
absorption.
taking
In
the
substances
human
into
digestive
cells
and
system
the
blood
nutrients
are
is
called
absorbed
epithelium
principally
the
in
surface
small
the
area
intestine
25–30
small
of
in
the
intestine.
epithelium
adults
millimetres
The
wide
is
rate
that
there
are
absorption
carries
approximately
and
of
out
seven
folds
on
the
process.
metres
its
depends
long
inner
on
The
and
surface,
layer of microvilli
giving
on surface of
epithelium
a
large
Villi
surface
are
small
area.
This
nger-like
area
is
increased
projections
of
the
by
the
presence
mucosa
on
the
of
lacteal (a branch
of the lymphatic
system)
villi.
inside
of
the
blood capillary
intestine
be
as
They
wall.
many
as
increase
A
villus
40
of
the
is
between
them
surface
per
0.5
square
area
by
a
and
1.5
mm
millimetre
factor
of
of
about
long
and
small
there
intestine
can
wall.
10.
goblet cells
(secrete mucus)
Absrtin b vii
Villi absorb monomers formed by digestion as well as
mineral ions and vitamins.
The
epithelium
substances,
useful
Villus
nutrients
cells
glucose,
●
any
●
fatty
●
bases
but
of
covers
the
pass
the
from
twenty
mineral
ions
●
vitamins
must
being
form
a
barrier
permeable
to
harmful
enough
to
▲
Figure 6 Structure of an intestinal villus
▲
Figure 7 Scanning electron micrograph of villi
allow
through.
products
galactose
amino
digestion
absorb
villi
time
of
of
and
acids
monoglycerides
needing
●
the
same
these
fructose,
acids,
also
not
at
to
absorb
●
They
that
while
digestion
other
used
and
of
macromolecules
in
food:
monosaccharides
to
make
proteins
glycerol
nucleotides.
substances
required
by
the
body
and
present
in
foods
digestion:
such
such
as
as
calcium,
ascorbic
acid
potassium
(vitamin
and
sodium
C).
in the small intestine
283
6
H u m a n
p H ys i o l o g y
Some
harmful
subsequently
harmless
of
those
Small
but
that
substances
removed
unwanted
give
numbers
removed
from
food
of
pass
from
blood
substances
its
colour
bacteria
the
through
the
blood
pass
by
are
and
the
epithelium
and
detoxied
also
absorbed,
avour.
through
phagocytic
the
These
and
by
in
the
liver.
including
pass
epithelium
cells
are
the
out
but
in
are
Some
many
urine.
quickly
liver.
methds f absrtin
Dierent methods of membrane transpor t are required to
absorb dierent nutrients.
To
be
the
absorbed
small
must
part
rst
of
be
the
microvilli.
plasma
The
of
and
●
of
be
pass
Fatty
acid
●
of
simple
into
are
inside
into
the
its
pass
pass
in
from
the
through
surface
out
inwards
the
move
of
this
the
villi.
the
area
towards
nutrients
can
digested
are
villus
fatty
be
lumen
The
cell
the
of
nutrients
exposed
enlarged
with
through
lacteal
before
acids
phospholipids
the
and
blood
absorbed
are
by
they
and
the
using
in
fatty
can
be
simple
plasma
the
two
villus
transport
different
absorbed.
cells,
to
triglycerides,
diffusion
as
there
membrane
acids
The
which
as
can
they
membrane.
diffusion
the
epithelium
produce
of
active
monoglycerides,
by
facilitated
proteins
out
glucose.
cells
in
and
diffusion,
illustrated
and
epithelium
which
into
facilitated
triglycerides
be
also
monoglycerides
out
faces
methods
must
transporters,
Once
it
cells
has
then
diffusion,
digestion
between
acids
that
must
lacteals
epithelium
must
where
or
villus.
absorption:
absorbed
can
into
membrane
These
Triglycerides
nutrients
capillaries
mechanisms
cells:
products
●
the
exocytosis.
examples
body,
the
nutrients
different
epithelium
the
to
absorbed
plasma
membrane
capillaries
Many
into
intestine
are
which
of
are
the
combined
cannot
fatty
microvilli.
with
diffuse
back
lumen.
lumen of
small intestine
interior
villus epithelium
of villus
+
Na
+
3Na
blood
+
low Na
capillary
concentration
+
2K
glucose
fatty acids and
monoglycerides
lacteal
lipoprotein
triglyceride
▲
284
Figure 8 Methods of absorption in the small intestine
6 . 1
Triglycerides
●
diameter
and
lipoprotein
plasma
They
or
then
enter
either
the
on
the
it
inside
pump
interstitial
opposite
a
sodium
lumen
to
gradient
Glucose
●
to
form
become
from
into
pumps
This
the
in
droplets
coated
in
with
a b S o r p t i o n
a
phospholipids
sodium
channels
glucose
is
allow
to
capillaries
are
villus
plasma
carried
active
the
a
away
membrane
in
the
cells.
the
lymph,
low
part
transport
villus
by
simple
hydrophilic.
inwards-facing
by
through
epithelium
villi.
and
of
from
the
the
potassium
concentration
of
the
the
it
by
the
of
plasma
cytoplasm
ions
in
sodium
active
glucose
to
microvilli
from
cells.
depends
interstitial
the
in
together
epithelium
but
created
the
in
proteins
molecule
passive
ions
cytoplasm
exocytosis
the
ions
cells.
cytoplasm
diffusion
by
the
therefore
the
ions
of
and
the
co-transporter
a
side
and
creates
epithelium
the
blood
in
inside
and
of
the
polar
spaces
released
lacteal
through
is
ion
facilitated
are
inner
the
sodium
direction.
villus
Sodium–glucose
●
which
capillaries
pass
because
membrane
the
enter
Sodium–potassium
to
cholesterol
µm,
particles
blood
cannot
diffusion
●
with
0.2
membrane
Glucose
●
coalesce
about
a n D
protein.
These
●
of
D i g e S t i o n
on
the
This
the
transfer
intestinal
type
of
concentration
transport.
move
spaces
by
facilitated
inside
the
diffusion
villus
and
on
villus.
Starch diestin in the sa intestine
Processes occurring in the small intestine that result in the digestion of starch and
transpor t of the products of digestion to the liver.
Starch
digestion
processes
illustrates
including
some
catalysis,
CH
important
enzyme
OH
CH
2
specicity
O
OH
and
membrane
permeability.
Starch
is
OH
a
OH
macromolecule,
composed
of
many
OH
2
O
O
O
α-glucose
OH
monomers
linked
together
in
plants
OH
by
CH
OH
CH
2
condensation
reactions.
It
is
a
major
plant-based
pasta.
Starch
membranes
intestine
to
foods
such
molecules
so
must
allow
be
as
bread,
cannot
potatoes
pass
digested
in
OH
CH
2
O
O
of
CH
2
OH
2
constituent
OH
and
through
the
OH
OH
OH
O
OH
▲
O
OH
O
small
absorption.
O
O
OH
O
OH
OH
Figure 9 Small por tion of an amylopectin molecule showing
six α-glucose molecules, all linked bv 1,4 bonds apar t from
All
of
the
reactions
involved
in
the
digestion
of
one 1,6 bond that creates a branch
starch
are
happen
at
molecule
exothermic,
very
in
slow
but
rates.
without
There
a
are
catalyst
two
they
types
of
The
starch:
enzyme
forms
●
amylose
has
unbranched
chains
of
of
by
1,4
amylopectin
by1,4
the
has
bonds,
molecule
the
amylase.
digestion
Saliva
of
both
contains
but
most
starch
digestion
occurs
in
the
bonds;
small
●
begins
is
α-glucose
amylase
linked
that
starch
chains
with
of
some
branched.
α-glucose
1,6
bonds
linked
that
make
intestine,
Any1,4
by
this
least
bond
in
enzyme,
four
catalysed
starch
as
glucose
long
by
pancreatic
molecules
as
there
monomers.
is
can
a
amylase.
be
broken
chain
Amylose
is
of
at
therefore
285
6
H u m a n
digested
p H ys i o l o g y
into
fragments
a
mixture
called
of
maltose
two-
and
and
three-glucose
capillaries
glucose
maltotriose.
enter
Because
of
the
specicity
of
its
active
site,
break
1,6
bonds
in
amylopectin.
the
the
amylopectin
molecule
containing
single
that
dextrins.
Digestion
three
on
enzymes
villus
and
amylase
in
the
epithelium
dextrinase
dextrins
of
into
cannot
starch
digest
is
digest
of
Maltase,
maltose,
layer
is
Blood
by
in
glucosidase
maltotriose
the
villus
co-transport
by
facilitated
with
sodium
the
epithelium
into
ions.
the
It
then
uid
in
inside
the
villus.
The
dense
walls
that
to
consist
of
cells,
with
pores
capillaries
between
have
aiding
the
entry
of
larger
glucose.
glucose
though
The
of
blood
hepatic
glucose
can
be
other
villus
the
in
portal
and
wall
these
vein
to
products
capillaries
of
the
absorbed
is
liver,
by
of
venules
small
venules
the
to
carried
where
to
glycogen
for
storage.
liver
cells
Glycogen
and
is
moves
in
structure
to
amylopectin,
but
with
interstitial
more
spaces
ensures
distance
cells
similar
diffusion
usual,
ows
converted
by
short
Capillary
these
sub-mucosa
intestine.
and
via
into
thin
but
carrying
digestion
microvilli
glucose.
absorbed
of
cells,
than
excess
Glucose
system.
a
called
completed
membranes
cells.
are
epithelium
travel
a
pores
1,6bond
blood
the
to
Fragments
adjacent
of
to
has
amylase
a
cannot
close
only
network
1,6
bonds
and
therefore
more
extensive
of
branching.
mdein hsiica rcesses
Use models as representations of the real world: dialysis tubing can be used
to model absorption in the intestine.
Living
systems
experiments
inuence
control
out
the
all
becomes
are
are
of
results.
the
experiments
carried
rather
much
out
approach
model
of
a
process.
Gastric
the
and
can
A
Model,
human
is
used
very
and
in
of
factors
difcult
analysis
it
is
parts
of
in
results
to
carry
has
tissue
can
to
systems.
physiology
cells
of
better
to
use
a
model
Because
it
is
For
been
culture
investigate
example
is
to
that
digestion
carries
of
real
represent
much
specic
the
out
food
simpler,
aspects
Dynamic
computer-controlled
stomach
chemical
to
recent
a
when
many
organisms.
system.
be
be
only
clones
whole
living
a
can
research
part
a
and
them,
Sometimes
Another
of
It
using
using
than
on
variables
difcult.
example,
complex
done
model
▲
of
Figure 10 The Dynamic Gastric Model with its inventor, Richard
Faulks, adjusting the antrum mechanism
mechanical
samples.
It
can
mimic
be
used
to
investigate
the
effects
of
diet,
the
permeable
alcohol
and
other
factors
on
simpler
made
from
water
freely,
286
example
and
but
is
cellulose.
small
not
the
use
Pores
molecules
large
to
of
the
small
gut,
rather
which
than
is
also
large
more
particles.
digestion.
Dialysis
A
wall
drugs,
of
in
or
dialysis
the
tubing
ions
molecules.
tubing
to
These
allow
pass
through
properties
by
tubing
passive
model
occur
active
in
can
be
diffusion
used
and
transport
living
cells
by
and
to
model
osmosis.
other
absorption
It
cannot
processes
that
6 . 1
D i g e S t i o n
a n D
a b S o r p t i o n
mdein the sa intestine
Use of dialysis tubing to model absorption of digested food in the intestine.
To
make
a
model
length
of
dialysis
a
in
the
knot
thread.
of
the
tubing
Pour
in
small
tubing
a
or
and
tying
suitable
intestine,
seal
one
with
a
mixture
cut
end
piece
of
a
by
of
foods
Suggest
tying
cotton
an
improvements
entirely
need
for
different
to
the
method
method,
of
or
suggest
investigating
the
digestion.
and
2 Investigating membrane permeability using
seal
the
open
end
by
tying
with
a
piece
of
cotton
a model of the small intestine
thread.
made
Two
in
experiments
this
way
are
using
model
intestines
suggestedhere:
1 Investigating the need for digestion using
a model of the small intestine
Cola
drinks
with
different
to
represent
tubing
the
Set
it
up
for
the
one
apparatus
shown
in
gure
11
and
contain
is
wall
a
mixture
particle
food
in
sizes.
the
small
semi-permeable
of
the
small
of
substances
They
so
can
be
intestine.
can
be
used
Dialysis
used
to
model
intestine.
leave
hour.
Predictions
Cola
contains
glucose,
phosphoric
acid
and
Results
caramel,
To
obtain
the
results
for
the
experiment,
bags
out
of
each
tube,
open
them
complex
and
a
brown
solutions
from
them
into
separate
test
the
liquids
have
four
in
the
tubes.
You
should
your
samples
starch
into
and
two
the
of
uid.
halves
other
Divide
and
half
for
test
each
one
of
half
Predict
which
to
of
will
diffuse
out
of
the
bag,
these
with
predictions.
Predict
whether
the
reasons
bag
will
now
gain
samples
colour.
tubes
for
from
added
pour
substances
the
carbohydrate
take
produce
the
a
or
lose
mass
during
the
experiment.
these
for
Instructions
sugars.
1
Make
the
model
2
Rinse
the
outside
traces
of
cola
intestine
and
of
the
then
with
bag
dry
to
the
cola
inside.
wash
off
any
bag.
10 ml of
tube
1% starch
10 ml
solution
of 1%
top of bag sealed
and 1 ml
starch
with cotton thread
of 1%
solution
amylase
cola, left to go at
and 1 ml
solution
before being put
of water
water
into the tube
dialysis tubing
maintained
at 40°C
pure water –
minimum volume
water
water
to surround the bag
base of bag knotted
of dialysis
to prevent leaks
(Visking) tubing
▲
Figure 11 Apparatus for showing the need for digestion
Record
all
the
results
in
the
way
that
you
think
is
spotting
most
appropriate.
tile
Conclusions and evaluation
State
make
carefully
from
Discuss
method
the
of
all
your
the
conclusions
that
you
can
results.
strengths
and
investigating
weaknesses
the
need
for
of
this
pH indicator
digestion.
▲
Figure 12 Apparatus for membrane permeability experiment
287
6
H u m a n
3
Find
p H ys i o l o g y
the
mass
of
the
bag
using
an
vary
electronic
for
these
instructions
balance.
concentration
4
When
place
you
the
are
bag
ready
in
to
pure
start
water
the
in
a
Test
the
water
around
the
bag
test
tube.
6
After
at
suitable
16
A
minutes.
suggested
At
each
range
is
time
lift
mix
the
of
the
Follow
out
the
the
glucose
water.
testing
1,
the
2,
4,
bag
8
the
the
bag,
water
dry
it
for
the
and
last
nd
its
time,
mass
again
time
with
intervals.
strips.
work
experiment,
remove
5
test
and
the
electronic
balance.
and
up
and
Conclusions
down
a
few
times
to
water
in
the
a)
tube,
then
do
these
Explain
about
●
Look
it
●
is
Use
carefully
still
a
drops
clear
dropping
of
spotting
the
tile
indicator.
the
at
or
the
has
with
a
water
a
to
become
pipette
water
Use
and
to
see
them
narrow-range
colour
chart
from
brown.
remove
test
whether
to
a
in
Dip
the
the
change
few
b)
a
conclusions
pH
work
out
the
permeability
tests
in
Compare
and
that
of
mass
and
the
of
you
the
can
in
wall
intestine.
the
villus
dialysis
and
draw
from
tubing
the
bag.
the
[5]
dialysis
membranes
absorption
of
the
water
contrast
plasma
of
that
epithelium
tubing
carry
cells
out
in
the
[5]
pH.
c)
●
the
tests:
a
glucose
record
the
test
colour
strip
that
into
it
the
turns.
water
and
Instructions
Use
the
the
results
direction
osmosis
of
of
across
your
experiment
movement
villus
of
to
water
epithelium
predict
by
cells.
[5]
TOK
W  s f  vs  c scvs s  w s “”?
In some adult humans, levels of lactase are too low
continue to consume milk into adulthood are therefore
to digest lactose in milk adequately. Instead, lactose
unusual. Inability to consume milk because of lactose
passes through the small intestine into the large
intolerance should not therefore be regarded as abnormal.
intestine, where bacteria feed on it, producing carbon
The second argument is a simple mathematical one: a
dioxide, hydrogen and methane. These gases cause
high propor tion of humans are lactose intolerant.
some unpleasant symptoms, discouraging consumption
The third argument is evolutionary. Our ancestors were
of milk . The condition is known as lactose intolerance. It
almost cer tainly all lactose intolerant, so this is the
has sometimes in the past been regarded as an abnormal
natural or normal state. Lactose tolerance appears
condition, or even as a disease, but it could be argued
to have evolved separately in at least three centres:
that lactose intolerance is the normal human condition.
Nor thern Europe, par ts of Arabia, the Sahara and eastern
The rst argument for this view is a biological one. Female
Sudan, and par ts of East Africa inhabited by the Tutsi and
mammals produce milk to feed their young ospring.
Maasai peoples. Elsewhere, tolerance is probably due to
When a young mammal is weaned, solid foods replace
migration from these centres.
milk and lactase secretion declines. Humans who
288
6 . 2
t h e
b l o o D
S y S t e m
6.2 t d ss
Understandin
Aicatins
➔
Ar teries convey blood at high pressure from the
➔
William Har vey’s discovery of the circulation of
ventricles to the tissues of the body.
the blood with the hear t acting as the pump.
➔
Ar teries have muscle and elastic bres in
➔
Causes and consequences of occlusion of the
their walls.
coronary ar teries.
➔
The muscle and elastic bres assist in
➔
Pressure changes in the left atrium, left
maintaining blood pressure between pump
ventricle and aor ta during the cardiac cycle.
cycles.
➔
Blood ows through tissues in capillaries
Skis
with permeable walls that allow exchange of
materials between cells in the tissue and the
➔
blood in the capillary.
➔
capillaries or veins from the structure of
Veins collect blood at low pressure from the
their walls.
tissues of the body and return it to the atria of
➔
the hear t.
➔
Identication of blood vessels as ar teries,
Recognition of the chambers and valves of
the hear t and the blood vessels connected
Valves in veins and the hear t ensure circulation
to it in dissected hear ts or in diagrams of
of blood by preventing backow.
hear t structure.
➔
There is a separate circulation for the lungs.
➔
The hear tbeat is initiated by a group of
Nature f science
specialized muscle cells in the right atrium
➔
Theories are regarded as uncer tain: William
called the sinoatrial node.
Har vey over turned theories developed by the
➔
The sinoatrial node acts as a pacemaker.
➔
The sinoatrial node sends out an electrical
ancient Greek philosopher Galen on movement
of blood in the body.
signal that stimulates contraction as it is
propagated through the walls of the atria and
then the walls of the ventricles.
➔
The hear t rate can be increased or
decreased by impulses brought to the
hear t through two ner ves from the medulla
of the brain.
➔
Epinephrine increases the hear t rate to prepare
for vigorous physical activity.
289
6
H u m a n
p H ys i o l o g y
Wiia Harve and the circuatin f bd
William Harvey’s discovery of the circulation of the blood with the hear t acting
as the pump.
William
Harvey
discovery
he
of
combined
research
theory
is
the
earlier
ndings
for
usually
blood
to
produce
ow
in
opposition
and
touring
by
experiments
provided
theory
became
Harvey
the
to
of
high
for
being
be
veins.
It
blood
He
too
small
tissues
had
of
that
the
not
eye
been
blood
to
the
be
seen
capillaries
about
until
the
1660,
owing
as
he
had
circulation
after
from
his
of
blood
death,
arteries
to
veins
predicted.
results
theories
As
a
ow
vessels
in
heart,
and
result
his
the
too
body
after
theories
to
the
heart
that
the
heart
of
with
arteries
the
far
earlier
and
presence
valves
that
was
as
showed
through
with
return
arteries
seen
linked
though
was
not
overcame
his
showed
consumed
the
overall
blood
theory
was
accepted.
major
the
that
own
his
It
demonstrate
theory.
therefore
in
1628.
it
returns
numerous
in
ne
contemporary
to
veins
in
the
body.
capillaries
naked
to
in
as
his
He
published
the
convincing
body.
also
Harvey
out
with
publishing
that
He
by
predicted
equipment
Blood
must
a
with
blood
unidirectional,
be
out
recycled.
vessels
the
to
pumped
pumps
is
the
previous
his
generally
through
blood
proposed.
and
for
backow.
ow
by
falsied
vessels
prevent
the
Europe
demonstrated
larger
rate
that
evidence
of
discoveries
widespread
also
credited
circulation
are
or
too
with
a
invented
narrow
hand
by
the
to
be
seen
with
lens.
Microscopes
time
that
Harvey
▲
Figure 1 Har vey’s experiment to demonstrate that blood ow
in the veins of the arm is unidirectional
overturnin ancient theries in science
Theories are regarded as uncer tain: William Harvey over turned theories developed
by the ancient Greek philosopher Galen on movement of blood in the body.
During
in
the
the
stimulated
ways
Renaissance,
classical
it
almost
writings
literature
hampered
impossible
interest
of
and
the
progress
to
was
Greece
arts,
in
question
reawakened
and
but
Rome.
in
science.
the
It
This
some
became
doctrines
vital
spirits
arteries.
to
be
then
writers
as
Aristotle,
Hippocrates,
is
from
to
Galen,
pumped
right
passes
290
by
vital
to
“animal
the
the
body
spirits
ow
spirits”,
nerves
to
the
by
to
the
the
which
brain,
are
body.
Harvey
was
unwilling
to
accept
these
Ptolemy
without
evidence.
He
made
careful
Galen.
According
the
into
distributed
observations
and
the
of
doctrines
and
distributed
of
converted
William
such
are
Some
and
ventricle
into
the
to
the
lungs
blood
of
left
and
fro
the
is
formed
between
heart.
ventricle,
becomes
A
in
the
little
where
“vital
it
the
liver
liver
and
blood
meets
spirits”.
air
The
he
deduced
pulmonary
the
not
that
and
existence
veins,
even
and
of
did
blood
circulates
systemic
the
enough
him
of
to
which
through
linking
lenses
for
from
circulations.
capillaries,
though
powerful
experiments,
He
the
predicted
arteries
the
see
time
and
were
them.
6 . 2
The
following
Generation
was
of
extract
is
Animals,
from
Harvey’s
published
in
book
1651
On
when
others:
the
he
73.
hence
it
is
that
admonition
of
observation
and
our
mind
and
to.
goes
senses,
astray
We
are
are,
experience,
in
a
science.
I
Isay,
not
to
to
rely
of
frequent
science,
be
my
the
and
what
experience
to
of
and
truth
actually
so
or
you
your
in
be
natural
therefore,
own
The
on
trust
so
have
of
as
of
at
erroneous
many
said,
things
eyes
method
pursued
held
which
the
properly
of
Generation
commonly
to
can
anything
the
to
one
branch
have
take
others
whether
no
any
judge.
is
foolish,
things
ask
not
appeal
therefore
almost
personal
I
witness
time
to
of
concerning
pursuing
is
appealed
after
would
reader,
me
S y S t e m
which
student
Animals:
phantoms
to
strive
from
observation
every
frequently
due
experiment,
after
Diligent
requisite
senses
the
without
reiterated
appearances.
therefore
the
the
without
b l o o D
without
become
gentle
And
t h e
this
and
enquire
and
omit
themselves
be
not.
Arteries
Ar teries convey blood at high pressure from the ventricles
acv
Dscss qss 
to the tissues of the body.
W h v’s ds
Arteries
the
are
body.
They
The
The
have
arteries,
vessels
main
thick
walls
Elastic
and
Elastic
tissue
a
blood
in
pressure
with
tissue
in
from
chambers
muscle
high
work
muscle
convey
pumping
strong
reaching
artery
that
the
their
at
heart
heart
that
peak
to
walls
the
walls
the
heart
the
of
the
of
used
the
tissues
are
the
ventricles.
pumps
each
facilitate
are
to
do
into
pumping
and
to
blood
control
of
1
to accept doctrines
the
without evidence. Are
cycle.
blood
William Harvey refused
there academic contexts
ow.
where it is reasonable to
this.
accept doctrines on the
contains
elastin
bres,
which
store
the
energy
that
stretches
basis of authority rather
them
at
the
peak
of
each
pumping
cycle.
Their
recoil
helps
propel
the
than evidence gathered
blood
on
down
the
artery.
Contraction
of
smooth
muscle
in
the
artery
from primary sources?
wall
determines
the
diameter
of
the
lumen
and
to
some
extent
the
2
rigidity
of
the
arteries,
thus
controlling
the
overall
ow
through
Harvey welcomed
them.
questions and criticisms
Both
the
elastic
and
muscular
tissues
contribute
to
the
toughness
of
the
of his theories when
walls,
which
have
to
be
strong
to
withstand
the
constantly
changing
and
teaching anatomy
intermittently
high
blood
pressure
without
bulging
outwards
(aneurysm)
classes. Suggest why he
or
bursting.
The
blood’s
progress
along
major
arteries
is
thus
pulsatile,
not
might have done this.
continuous.
The
pulse
reects
each
heartbeat
and
can
easily
be
felt
in
arteries
3
that
pass
near
the
body
surface,
including
those
in
the
wrist
and
the
Can you think of examples
neck.
of the “phantoms and
Each
organ
of
the
body
is
supplied
with
blood
by
one
or
more
arteries.
appearances” that Harvey
For
example,
the
hepatic
each
kidney
is
supplied
by
a
renal
artery
and
the
liver
by
refers to?
artery.
The
powerful,
continuously
active
muscles
of
the
4
heart
itself
are
supplied
with
blood
by
coronary
Why does Harvey
arteries.
recommend “reiteration”
of experiments?
Arter was
5
Harvey practised as
a doctor, but after the
Ar teries have muscle and elastic bres in their walls.
publication in 1628 of
The
wall
of
the
artery
is
composed
of
several
layers:
his work on the
●
tunica
externa
●
tunica
media
–
a
tough
outer
layer
of
connective
circulation of the blood,
tissue
far fewer patients
–
a
thick
layer
containing
smooth
muscle
and
elastic
consulted him. Why
bres
made
of
the
protein
elastin
might this have been?
●
tunica
intima
–
a
smooth
endothelium
forming
the
lining
of
the
artery.
291
6
H u m a n
tunica externa
p H ys i o l o g y
tunica media
tunica
lumen
intima (endothelium)
▲
Figure 3 Structure of an ar tery
acv
ms d sss
Because ar teries are
distensible, blood pressure
in those that pass near
the body surface can be
measured relatively easily.
A common method is to
inate an arm cu until it
squeezes the tissues (skin,
▲
Figure 2 The cardiovascular system. The main ar tery that supplies oxygenated blood to
supercial fat as well as
the tissues of the body is the aor ta, shown as the red vessel that emerges from the hear t
the vessels themselves)
and forms an arch with branches carrying blood to the arms and head. The aor ta continues
enough to stop blood
through the thorax and abdomen, with branches ser ving the liver, kidneys, intestines and
ow. The pressure is then
other organs
released slowly until ow
resumes and the operator
Arteria bd ressure
or instrument can hear the
pulse again. The pressures at
which blood ow stops and
The muscle and elastic bres assist in maintaining
blood pressure between pump cycles.
resumes are the systolic and
The
blood
entering
an
artery
from
the
heart
is
at
high
pressure.
The
peak
diastolic pressures. They are
pressure
reached
in
an
artery
is
called
the
systolic
widening
the
lumen
pressure.
It
pushes
the
measured with a pressure
wall
of
the
artery
outwards,
and
stretching
elastic
monitor. According to the
bres
in
the
wall,
thus
storing
potential
energy.
American Hear t Association
the desired blood pressures
for adults of 18 years or older
measured in this way are:
At
the
for
end
the
of
mechanism
the
each
stretched
artery,
heartbeat
elastic
saves
called
energy
the
the
bres
and
diastolic
to
pressure
squeeze
prevents
in
the
pressure,
the
the
arteries
blood
in
minimum
from
falls
the
sufciently
lumen.
pressure
becoming
too
This
inside
low.
Because
systolic 90-119 mmHg
it
is
relatively
high,
blood
ow
in
the
arteries
is
relatively
steady
and
diastolic 60-79 mmHg
continuous
The
circular
contract,
and
in
the
the
high
muscles
a
density
to
of
is
driven
in
process
lumen
arterioles
the
wall
called
muscle
control
restricts
of
cells
blood
blood
a
pulsating
of
the
heart.
artery
vasoconstriction,
narrowed.
Branches
by
Vasoconstriction
arteries
that
ow
ow
to
to
called
respond
part
the
a
to
of
ring
increases
opposite
process,
called
vasodilation,
when
a
body
is
they
reduced
pressure
particularly
hormone
tissues.
increases
blood
have
various
the
so
circumference
arterioles
downstream
the
form
and
neural
Vasoconstriction
that
Figure 4 Blood pressure monitor
the
292
in
arteries.
signals
▲
although
it.
they
supply
of
and
6 . 2
t h e
b l o o D
S y S t e m
Caiaries
acv
Blood ows through tissues in capillaries with permeable
bss
walls that allow exchange of materials between cells in
Bruises are caused by
the tissue and the blood in the capillary.
damage to capillary walls
and leakage of plasma and
Capillaries
are
the
narrowest
blood
vessels
with
diameter
of
about
blood cells into spaces
10μm.
They
branch
and
rejoin
repeatedly
to
form
a
capillary
network
between cells in a tissue.
with
a
huge
total
length.
Capillaries
transport
blood
through
almost
all
The capillaries are quickly
tissues
in
the
body.
Two
exceptions
are
the
tissues
of
the
lens
and
the
repaired, hemoglobin is
cornea
in
the
eye
which
must
be
transparent
so
cannot
contain
any
broken down to green and
blood
vessels.
The
density
of
capillary
networks
varies
in
other
tissues
yellow bile pigments which
but
all
active
cells
in
the
body
capillary
wall
consists
are
close
to
a
capillary.
are transpor ted away and
The
of
one
layer
of
very
thin
endothelium
cells,
phagocytes remove the
coated
by
a
lter-like
protein
gel,
with
pores
between
the
cells.
The
remains of the blood cells
wall
is
thus
very
permeable
and
allows
part
of
the
plasma
to
leak
out
by endocytosis. When you
and
form
tissue
uid.
Plasma
is
the
uid
in
which
the
blood
cells
are
next have a bruise, make
suspended.
Tissue
uid
contains
oxygen,
glucose
and
all
other
substances
observations over the days
in
blood
plasma
apart
from
large
protein
molecules,
which
cannot
after the injury to follow the
pass
through
the
capillary
wall.
The
uid
ows
between
the
cells
in
a
healing process and the
tissue,
allowing
the
cells
to
absorb
useful
substances
and
excrete
waste
rate at which hemoglobin
products.
The
tissue
uid
then
re-enters
the
capillary
network.
is removed.
The
permeabilities
particular
not
proteins
others.
repair
and
tissues
of
capillary
and
other
Permeabilities
remodel
that
they
walls
large
can
also
themselves
differ
between
particles
change
to
over
continually
in
tissues,
reach
time
enabling
certain
and
response
tissues
but
capillaries
to
the
needs
of
perfuse.
Veins
Veins collect blood at low pressure from the tissues
of the body and return it to the atria of the hear t.
Veins
transport
heart.
By
arteries.
and
the
now
Veins
wall
therefore
than
Blood
by
ow
shorter
sitting
Each
is
this
other
carry
in
because
the
of
falls
arms
The
the
it
a
by
in
heart.
It
is
on
by
It
carries
regarded
carries
is
at
vein
by
as
low
veins
bres.
of
was
is
the
in
as
the
arteries
They
more
blood
like
venous
can
blood
in
the
and
unusual
from
portal
pressure
it
veins
from
on
them
muscle
Walking,
ow.
example
the
because
head
it
than
relatively
blood
in
does
stomach
rather
is
a
pump.
For
the
vein
so
a
exerted
makes
blood
veins.
veins
blood
a
it
wall
pressures
more
is
atria
exercise.
improves
subclavian
a
Contraction
adjacent
portal
the
than
hold
person’s
and
or
to
thick
thus
vigorous
one
as
elastic
and
muscles.
greatly
the
and
gravity
back
pressure
have
sedentary
skeletal
hepatic
to
wider
during
served
lower
muscle
squeezes
is
networks
need
much
assisted
it
liver.
much
fewer
dgeting
to
blood
at
80 %
body
the
back
to
the
is
so
just
veins.
blood
intestines
far
especially
the
from
is
become
veins
wider
of
jugular
to
capillary
therefore
Around
even
part
blood
not
proportion
and
or
from
contains
tissues
carried
the
the
do
dilate
arteries.
though
blood
not
and
an
artery
thin.
293
6
H u m a n
p H ys i o l o g y
Vaves in veins
acv
Valves in veins and the hear t ensure circulation of blood
Sd   d
by preventing backow.
Pocket valves and vein
walls become less ecient
Blood
with age, causing poor
backow
pressure
venous return to the hear t.
heart.
Have you ever performed
three
To
in
veins
towards
the
maintain
cup-shaped
is
sometimes
capillaries
circulation,
aps
of
and
so
low
that
there
insufcient
veins
contain
is
return
pocket
a
of
danger
blood
valves,
of
to
the
consisting
of
tissue.
gymnastic moves such as
If
●
blood
starts
to
ow
backwards,
it
gets
caught
in
the
aps
of
the
headstands or handstands,
pocket
valve,
which
ll
with
blood,
blocking
the
lumen
of
the
vein.
or experienced very high
g-forces on a ride at an
When
●
sides
amusement park? Young
ow
people can mostly do any
blood
of
the
ows
vein.
towards
The
the
pocket
heart,
valve
it
pushes
therefore
the
aps
opens
and
to
the
blood
can
freely.
of these activities easily
These
valves
allow
blood
to
ow
in
one
direction
only
and
make
but older people may not
efcient
use
of
the
intermittent
and
often
transient
pressures
provided
be able to. What is the
by
muscular
and
postural
changes.
They
ensure
that
blood
circulates
in
explanation?
the
body
rather
than
owing
to
and
fro.
Identifin bd vesses
Identication of blood vessels as ar teries, capillaries or
veins from the structure of their walls.
Blood
at
vessels
their
can
structure.
be
identied
Table
1
as
below
a 
Diameter
Larger than 10 μm
arteries,
gives
capillaries
differences
or
that
veins
may
looking
beuseful.
C
Around 10 μm
by
V
Variable but much
larger than 10 μm
▲
Figure 5 Which veins in this gymnast will
need valves to help with venous return?
Relative
Relatively thick
thickness
wall and narrow
wall with variable
of wall and
lumen
but often wide
Extremely thin wall
diameter of
Relatively thin
lumen
lumen
Number of
Three layers,
Only one layer – the
Three layers –
layers in wall
tunica externa,
tunica intima which
tunica externa,
media and intima.
is an endothelium
media and intima
These layers may
consisting of a
be sub-divided to
single layer of very
form more layers
thin cells
Abundant
None
Small amounts
None
None
Present in many
Muscle and
elastic bres
in the wall
Valves
▲
Figure 6 Ar tery and vein in transverse section.
veins
The tunica ex terna and tunica intima are
stained more darkly than the tunica media.
Clotted blood is visible in both vessels
294
▲
T
able 1
6 . 2
t h e
b l o o D
S y S t e m
The dube circuatin
lungs
There is a separate circulation for the lungs.
pulmonary
There
are
valves
in
the
veins
and
heart
that
ensure
a
one-way
ow,
circulation
so
blood
single
circulates
circulation.
oxygenated.
pressure
body
for
to
and
gas
Blood
through
Blood
After
ow
then
is
back
exchange
to
are
capillaries
pumped
owing
directly,
in
arteries,
the
high
the
heart.
In
with
cannot
the
slowly,
contrast,
blood
and
veins.
pressure
gills
relatively
supplied
lungs
at
through
but
capillaries
by
withstand
to
blood
Fish
their
still
gills
has
other
organs
the
lungs
used
separate
high
to
a
be
enough
to
a
have
of
by
the
mammals
circulation.
pressures
so
blood
is
heart
pumped
to
capillaries
to
the
them
of
heart
therefore
the
to
at
lungs
be
have
relatively
the
pressure.
pressure
pumped
two
low
again
separate
of
the
before
it
After
blood
goes
passing
is
to
low,
other
through
so
it
must
organs.
the
return
Humans
circulations:
systemic circulation
●
the
pulmonary
●
the
systemic
circulation,
to
and
from
the
lungs
other
circulation,
to
and
from
all
other
organs,
including
the
organs
heart
Figure
7
muscles.
shows
pulmonary
from
that
the
has
essential
mixed.
systemic
been
that
The
different
the
double
circulation
circulation,
oxygenated
blood
heart
circulation
receives
is
pressures
by
owing
and
the
to
therefore
a
simplied
the
from
double
to
the
blood
systemic
pulmonary
and
a
separately
in
deoxygenated
these
two
It
receives
is
Figure 7 The double circulation
returned
blood
therefore
circulations
delivering
▲
The
has
circulation
circulation.
pump,
two
form.
that
blood
is
not
under
circulations.
semilunar valve
aorta
Heart structure
pulmonary artery
Recognition of the chambers and valves
vena cavae
of the hear t and the blood vessels
pulmonary veins
connected to it in dissected hear ts or in
diagrams of hear t structure.
●
The
heart
pump
has
blood
two
to
sides,
the
left
systemic
and
and
right,
that
pulmonary
circulations.
semilunar
valve
●
Each
a
side
ventricle
arteries
the
●
of
Each
that
and
veins
side
the
an
and
of
heart
has
pumps
atrium
passes
the
atrioventricular
it
heart
valve
the
ventricle
and
a
the
ventricle
and
the
two
blood
that
to
out
into
collects
the
has
chambers,
from
ventricle.
two
between
semilunar
the
blood
valves,
the
an
atrium
valve
and
between
atrioventricular
right atrium
●
Oxygenated
blood
valve
artery.
ows
into
the
left
side
of
left ventricle
right ventricle
the
heart
through
the
lungs
and
the
pulmonary
veins
from
septum
out
through
the
aorta.
▲
Figure 8 Structure of the hear t
295
6
H u m a n
●
p H ys i o l o g y
Deoxygenated
of
the
heart
blood
through
ows
the
into
vena
the
left
cava
side
and
out
4 Left ventricle
in
Identify
the
pulmonary
with
The
heart
is
structure.
is
a
by
a
complicated
The
doing
a
a
way
heart,
are
three-dimensional
learn
A
fresh
with
dissecting
instruments
to
dissection.
mammalian
attached,
best
about
or
structure
specimen
blood
dish
its
vessels
board
scalpel,
line
by
the
removing
around
and
the
has
a
if
vessels
Identify
thin-walled
in
have
incision
gure
Look
cut
an
at
blood
smooth
9.
This
the
vessels.
wall,
as
shown
should
thick
Using
by
open
muscular
a
the
up
wall
the
that
through.
5 Atrioventricular valve
membranes
them.
It
of
dissecting
needed.
blood
ventricle.
pattern
make
X
ventricle.
Extend
up
left
tree-like
dashed
you
still
and
a
sharp
left
of
1 Ar teries and veins
Tidy
the
arteries.
attached
and
the
to
other
the
heart
tissue
thick-walled
from
arteries
the
incision
necessary
until
further
you
can
of
the
atrioventricular
to
the
sides
inverting
towards
see
valve.
of
the
left
into
the
atrium.
the
the
two
Tendons
ventricle
atrium
thin
aps
attached
prevent
the
valve
veins.
6 Left atrium and pulmonary vein
2 Pulmonary ar tery and aor ta
Push
into
a
glass
the
heart
through
of
the
the
rod
artery,
rod
or
through
wall
has
other
of
reached.
through
which
right
through
you
left
the
the
thinner-walled
which
blunt-ended
arteries
heart
to
Identify
you
will
ventricle,
will
reach
instrument
and
where
the
the
the
end
pulmonary
reach
and
feel
the
the
thicker-walled
ventricle.
the
heart
so
that
side
uppermost
underneath.
The
as
the
artery,
now
there
as
surface
of
Extend
the
either
in
dorsal
aorta
is
9.
the
side
its
atrium.
is
no
wall
has
incision
with
the
the
wall
atrium
the
and
(there
a
of
the
look
it.
left
of
outer
already
scissors,
atrium
the
surprisingly
The
appearance.
have
with
at
opening
be
you
or
Look
may
will
inside
wrinkled
that
scalpel
vein.
It
blood
thin
the
as
to
far
wall
made,
cut
as
of
the
the
pulmonary
vein
or
two).
7 Aor ta
gure
and
left
pulmonary
veins
pulmonary
is
the
small
through
aorta,
3 Dorsal and ventral sides
Lay
Identify
of
behind
The
dorsal
an
the
ventral
side
animal
is
itsback.
Find
of
its
the
through
and
the
aorta
lumen,
the
smooth
and
of
the
towards
inner
the
measure
millimetres.
wall
working
stretching
again
in
aorta,
the
left
surface
wall
to
of
see
the
Using
diameter
scissors,
starting
at
ventricle.
the
how
aorta
tough
end
Look
and
it
cut
its
at
try
is.
8 Semilunar valve
aorta
Where
the
will
three
be
aorta
exits
the
cup-shaped
left
ventricle,
aps
in
the
there
wall.
These
pulmonary
form
the
semilunar
valve.
Try
pushing
a
blunt
artery
right
instrument
artrium
into
the
aps
to
see
how
blood
left atrium
owing
closing
backwards
the
pushes
the
aps
together,
valve.
X
9 Coronary ar tery
coronary
artery
Look
carefully
aorta,
near
the
at
the
inner
semilunar
surface
valve.
A
of
the
small
hole
Y
should
be
visible,
coronaryarteries.
lumen
▲
296
Figure 9 Ventral view of the ex terior of the hear t
the
of
wall
this
of
which
the
Measure
artery.
the
is
heart
The
the
opening
diameter
coronary
with
to
oxygen
the
of
arteries
and
the
supply
nutrients.
6 . 2
t h e
b l o o D
S y S t e m
10 Septum
Make
near
line
in
a
transverse
the
base
marked
of
Y
millimetres
ventricles
and
(gure10).
bres,
in
through
ventricles,
gure
9.
the
walls
of
the
septum
septum
help
to
the
along
Measure
of
The
which
section
the
of
the
the
left
stimulate
dotted
thickness
and
between
contains
heart
the
right
them
conducting
the
ventricles
left ventricle
right ventricle
tocontract.
septum
▲
Figure 10 Transverse section through the ventricles
acv
Atherscersis
Sc d fc f
Causes and consequences of occlusion of the
  
coronary ar teries.
Discuss the answers to
One
of
the
commonest
development
of
fatty
current
tissue
health
called
problems
atheroma
in
is
atherosclerosis,
the
artery
wall
the
these questions.
adjacent
1
to
the
endothelium.
Low
density
lipoproteins
(LDL)
containing
fats
Why are the walls of the
and
atria thinner than the
cholesterol
accumulate
and
phagocytes
are
then
attracted
by
signals
walls of the ventricles?
from
fats
endothelium
and
cells
cholesterol
migrate
bulges
cells
into
to
the
by
form
smooth
endocytosis
a
lumen
and
tough
cap
muscle.
and
over
narrowing
it
The
grow
the
and
phagocytes
very
large.
atheroma.
thus
Smooth
The
impeding
engulf
artery
blood
the
muscle
2
What prevents the
atrioventricular valve
wall
from being pushed into
ow.
the atrium when the
Small
traces
of
atheroma
are
normally
visible
in
children’s
arteries
ventricle contracts?
by
the
age
of
ten,
but
do
not
affect
health.
In
some
older
people
3
atherosclerosis
becomes
much
more
advanced
artery
becomes
but
often
Why is the left ventricle
goes
wall thicker than the
unnoticed
until
a
major
so
blocked
that
the
tissues
it
right ventricle wall?
supplies
become
compromised.
4
Coronary
occlusion
is
a
narrowing
of
the
arteries
that
supply
Does the left side of the
blood
hear t pump oxygenated
containing
oxygen
and
nutrients
to
the
heart
muscle.
Lack
of
oxygen
or deoxygenated blood?
(anoxia)
ability
blood
cap
to
causes
contract,
circulation
covering
formation
heart
The
pain,
and
of
atheroma
heart
some
angina,
beats
of
its
blood
that
acute
heart
can
are
shown
not
the
to
faster
are
be
sole
impairs
as
out
ruptures,
block
problems.
atherosclerosis
been
but
clots
and
muscle
sometimes
of
have
the
with
as
atheromas
cause
causes
factors
so
known
not
This
yet
of
tries
of
is
muscle’s
The
in
to
Various
increased
risk
brought by the coronary
the
sub-topic
understood.
an
own supply of blood,
the
blood
Why does the wall
of the hear t need its
brous
stimulates
supplying
with
5
maintain
described
fully
the
to
action.
which
arteries
associated
causes
it
the
of
ar teries?
6.3.
6
Does the right side
of the hear t pump a
greater volume of blood
condition:
per minute, a smaller
●
high
●
chronic
blood
concentrations
of
LDL
(low
density
lipoprotein)
volume, or the same
obesity
high
or
blood
glucose
concentrations,
due
to
overeating,
volume as the left?
diabetes
297
6
H u m a n
p H ys i o l o g y
acv
●
chronic
other
high
blood
pressure
due
to
smoking,
stress
or
any
cause
C d c
ccs
●
consumption
of
the
of
trans
fats,
which
damage
the
endothelium
artery.
A chemical called carnitine
that is found in cer tain foods
There
are
also
some
more
recent
theories
that
include
microbes:
is conver ted into TMAO by
●
infection
●
production
of
the
artery
wall
with
Chlamydia
pneumoniae
bacteria in the gut. Find
out what foods contain the
highest concentrations
of
trimethylamine
N-oxide
(TMAO)
by
microbes
in
theintestine.
of carnitine and discuss
whether this nding should
inuence dietary advice.
▲
Figure 11 A normal ar tery (left) has a much wider lumen than an ar tery that is
occluded by atheroma (right)
The sinatria nde
The hear tbeat is initiated by a group of specialized muscle
cells in the right atrium called the sinoatrial node.
The
heart
is
stimulation
meaning
heart
almost
is
a
that
muscle
adjacent
The
cells,
region
cause
the
298
cardiac
the
of
generated
they
the
also
The
at
heart
of
in
as
node.
its
the
rate
the
other
sinoatrial
of
cells
muscle
node
its
rate
have
are
of
of
the
The
cells
without
myogenic,
membrane
and
this
of
a
activates
therefore
the
spontaneous
wall
few
but
therefore
cells
called
contracts
fastest.
in
cells,
contract
is
contracts
group
the
cells
itself.
cell
fastest
muscle
These
A
of
can
contraction
muscle
when
the
muscles
The
contract.
with
membranes
cycle.
in
the
special
sinoatrial
the
body
neurons.
depolarizes
contraction
because
Figure 12 The sinoatrial node
is
so
group
membranes.
▲
it
cell
in
motor
simultaneously
small
called
unique
from
of
they
of
the
have
initiates
rst
the
to
beating
right
atrium,
proteins
that
extensive
each
heartbeat,
depolarize
in
each
6 . 2
t h e
the
pace
for
If
becomes
b l o o D
S y S t e m
Initiatin the heartbeat
The sinoatrial node acts as a pacemaker.
Because
the
the
beating
defective,
articial
with
sinoatrial
of
its
the
output
electrodes
in
be
This
is
implanted
place
of
initiates
and
may
pacemaker.
heartbeat
node
heart
the
is
each
often
regulated
an
in
or
the
wall
of
the
even
electronic
sinoatrial
heartbeat,
called
sets
replaced
device,
the
it
pacemaker.
entirely
placed
heart
that
it
under
by
the
initiate
an
skin
each
node.
Atria and ventricuar cntractin
The sinoatrial node sends out an electrical signal that
stimulates contraction as it is propagated through the
walls of the atria and then the walls of the ventricles.
The
sinoatrial
sends
This
out
can
across
a
which
so
to
After
to
a
the
the
initiates
the
of
of
a
the
for
electrical
be
signal
cells
signal
contracting
throughout
interconnections
can
the
all
by
spreads
are
signal
passes
second
heartbeat
that
there
electrical
bre
a
signal
because
each
tenth
propagation
atria
node
electrical
happen
branched
than
an
in
propagated.
on
the
causes
to
the
to
Also
the
others.
receive
whole
simultaneously
walls
between
several
atria
and
the
of
the
bres
It
the
both
of
atria.
adjacent
takes
signal.
left
bres
are
and
less
This
right
contract.
time
delay
ventricles.
blood
that
propagated
contract
they
about
time
are
throughout
and
stimulation
of
The
pump
of
the
0.1
seconds,
delay
holding
the
blood
allows
into
walls
out
heartbeat
of
into
are
the
the
the
the
electrical
time
for
the
ventricles.
ventricles,
arteries.
included
in
signal
atria
The
to
is
conveyed
pump
signal
is
stimulating
Details
Option
of
the
▲
then
them
to
Figure 13 Hear t monitor displaying the hear t
rate, the electrical activity of the hear t and the
percentage saturation with oxygen of the blood
electrical
D.
TOK
W s   c dcs k:   csqcs?
There are some circumstances in which prolonging the life of an individual
who is suering brings in to question the role of the physician. Sometimes, an
active pacemaker may be involved in prolonging the life of a patient and the
physician receives a request to deactivate the device. This will accelerate the
pace of the patient’s death. Euthanasia involves taking active steps to end the
life of a patient and it is illegal in many jurisdictions. However, there is a widely
accepted practice of withdrawing life-sustaining interventions such as dialysis,
mechanical ventilation, or tube feeding from terminally ill patients. This is often
a decision of the family of the patient. The withdrawal of life suppor t is seen as
distinct from euthanasia because the patient dies of their condition rather than
the active steps to end the patient’s life in the case of euthanasia. However,
the distinction can be subtle. The consequence is the same: the death of the
patient. The intent can be the same: to end the patient’s suering. Yet in many
jurisdictions, one action is illegal and the other is not.
299
6
H u m a n
p H ys i o l o g y
The cardiac cce
Pressure changes in the left atrium, left ventricle and aor ta during the
cardiac cycle.
The
pressure
chang e s
ventricle
of
a
cycle
cardiac
understand
what
the
are
them
occurs
below
he a r t
at
Typical
it
a
is
ea ch
heart
volumes
the
in
r a te
g ur e
of
of
75
To
wi th
per
is
a l so
of
the
d i r e ctio n
of
blo od
o w
to
achamber
of
the
semilunar
arterial
–
0.1
The
contract
relatively
which
blood
small
causing
pressure
pumps
blood
ventricles,
drains
a
rapid
–
0.45
The
semilunar
from
through
the
in
–
them
0.15
are
arteries
as
but
in
the
atri a
as
into
the m
fr om
the
ve ins
seconds
and
of
the
pressure
ventricular
inside
the
muscles
ventricles
drops
below
the
pressure
in
closed
and
blood
gradually
causing
the
semilunar
valves
no
continues
more
is
to
The
atrioventricular
valves
remain
contract,
build
up
atrioventricular
0.45
in.
–
0.8
seconds
Pressure
in
the
ventricles
pressure
in
the
atria
with
a
so
drops
the
below
that
valves
causes
to
semilunar
valves
the
Blood
and
close.
remain
open.
from
from
slow
the
there
increase
veins
into
in
drains
the
into
the
ventricles,
pressure.
closed.
vein
25 ml
atrium
45 ml
atrium
contracts
25 ml
atrioventricular valve
atrioventricular valve
closed
open
atrioventricular valve
valve open
ventricle
ventricle
relaxing
contracting
ventricle relaxing
ventricle
70 ml
semilunar valve
artery
valve closed
valve open
diastolic
systolic
semilunar valve closed
diastolic
the body
0
0.1
0.15
0.4
0.45
0.8
time (seconds)
Figure 1
4 One cardiac cycle is represented on the diagram, starting on the left with contraction of the atrium. Vertical
arrows show ows of blood to and from the atrium and ventricle
300
the
atrioventricular
rapid
a
▲
closed.
to
ow
pumped
close.
blood
drops
●
tissues of
the
seconds
ventricles
pressure
The
ris e s
ll.
contraction
valves
●
the
the
valves.
valves
the
minimum
The
maximizing
open
●
●
blood
into
atria
the
●
pressure
0.1
and
increase,
to
along
open
ventricles
so
but
arteries,
atrioventricular
its
rises
arteries
pressure.
slowly
they
rapidly
the
The
the
transiently
Pressure
wanes
●
valves
from
the
seconds
atria
●
to
ventricles
in
hea r t.
0.4
●
the
or
and
0.0
in
pressure
pumped
blood
from
the
an
●
indication
seconds
pressure
arteries,
m in u t e .
a nd
0.4
the
Fi g ur e 1 4
tim in g s
s hown
–
The
above
ap pr e cia t e
cy c le .
be a ts
ar e
0.15
●
d u ri n g
15 .
to
the
e ve nts,
blood
an d
a or ta
ne ces s ar y
s ta g e
the
of
a tr ium
the
s ho wn
summarize s
assuming
in
a nd
atria
causing
6 . 2
t h e
b l o o D
S y S t e m
D-sd qss: Hear t action and blood pressures
Figure
15
ventricle
during
one
second
Deduce
from
the
when
the
start
2
Deduce
3
The
the
artery
in
the
to
the
when
one
blood
atrium
and
pressures
on
of
atrium,
the
the
heart,
heart.
pumped
ventricle.
Give
both
times.
ventricle
atrioventricular
the
of
being
the
end
the
life
is
in
side
valve
[2]
starts
is
to
the
contract.
ventricle
gH mm / erusserp
1
shows
and
[1]
120
ar tery
100
valve
80
between
when
the
the
atrium
and
the
atrioventricular
ventricle.
valve
State
closes.
[1]
60
4
The
semilunar
the
ventricle
the
semilunar
valve
and
is
the
the
valve
artery.
between
State
when
40
valve
5
Deduce
when
the
6
Deduce
when
blood
opens.
[1]
semilunar
valve
closes.
[1]
20
from
the
ventricle
is
to
being
the
pumped
artery.
atrium
Give
0
both
7
the
Deduce
start
and
when
the
the
end
volume
times.
of
[2]
blood
in
the
–20
ventricle
is:
0
a)
at
a
maximum
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
[1]
time / s
b)
at
a
minimum.
[1]
Figure 15 Pressure changes during the cardiac cycle
▲
Chanin the heart rate
acv
ls    sds
The hear t rate can be increased or decreased by impulses
Sounds produced by blood
brought to the hear t through two nerves from the medulla
ow can be heard with a
of the brain.
The
sinoatrial
simple tube or stethoscope
node
responds
to
signals
branches
of
two
brain
cause
called
the
healthy
rate.
Signals
act
reects
Low
the
rate
other
the
centre
its
the
pH
carbon
pressure,
in
the
can
nerve
and
the
region
in
and
to
inputs
the
of
the
from
of
a
times
of
the
from
for the ow of blood out of
nerves
the hear t can be felt as the
pulse in a peripheral ar tery.
resting
two
hear t. The consequences
of this whole cardiac cycle
the
In
the
These
placed on the chest near the
heart
signals
heartbeats.
rate.
of
the
medulla
one
three
brake
of
include
from
frequency
decrease
beating
These
Signals
oxygen
dioxide
low
a
increase
throttle
receives
for
heart.
centre.
increase
the
like
and
its
blood
outside
rhythm
originating
to
people
cardiovascular
pressure
the
cardiovascular
rather
blood
●
nerves
from
blood
sets
from
pacemaker
young
branches
The
the
that
nerve
(a)
car.
receptors
concentration.
that
The
pH
monitor
of
the
concentration.
oxygen
concentration
and
low
pH
all
(b)
suggest
rate
of
carbon
that
the
blood
to
heart
the
rate
needs
tissues,
to
deliver
speed
more
up,
to
increase
the
oxygen
and
remove
concentration
and
high
ow
more
dioxide.
▲
●
High
blood
indicators
pressure,
that
the
high
heart
oxygen
rate
may
need
to
slow
pH
are
all
Figure 16 T
aking the pulse: (a)
radial pulse (b) carotid pulse
down.
301
6
H U M A N
P H YS I O L O G Y
Epinephrine
Epinephrine increases the hear t rate to prepare for
vigorous physical activity.
The
by
sinoatrial
increasing
called
adrenalin
secretion
when
In
of
or
▲
Figure 1
7 Adventure spor ts such as rock
is
Thi s
p ro duce d
phy s i ca l
is
to
ep ine ph r in e
h or m o n e
by
the
contr ol l e d
acti vi ty
ma y
be
th e
in
al s o
a dr e na l
by
e pi ne phr in e
is
g la n ds .
br a in
n e c es s ar y
has
the
the
b l ood ,
s ome t im es
an d
Th e
r is es
be c a us e
nic kn am e
of
a
“ g h t
or
hormone”.
the
past
prey
athletes
so
and
re s ponds
r ate .
opportuni ty.  S o
when
epinephrine
for
also
he a r t
epinep hr i ne
vigorous
threat
ight
nod e
the
that
or
when
often
their
activity
huma ns
woul d
ha v e
wer e
be e n
thr e a tened
use
hear t
p r e - r a ce
r a te
is
hun t e r- ga t h e re r s
se cret e d
by
a
p re da t or.
ro utine s
a l re a dy
whe n
to
In
the
s tim u la t e
inc r ea s ed
ra t h e r
hu m an s
th an
we re
mo de rn
a dr e na l in
wh en
vi g or ou s
fa r m e r s,
hu n t i ng
wo rl d
se c r et i on
ph ys ic a l
begins.
climbing cause epinephrine secretion
6.3 Def ence against inf ectious disease
Understanding
Applications
➔
The skin and mucous membranes form a
➔
Causes and consequences of blood clot
primary defence against pathogens that cause
formation in coronary ar teries.
infectious disease.
➔
➔
Cuts in the skin are sealed by blood clotting.
➔
Clotting factors are released from platelets.
➔
The cascade results in the rapid conversion of
Eects of HIV on the immune system and
methods of transmission.
➔
Florey and Chain’s experiments to test penicillin
on bacterial infections in mice.
brinogen to brin by thrombin.
➔
Ingestion of pathogens by phagocytic white
Nature of science
blood cells gives non-specic immunity to
diseases.
➔
➔
➔
Production of antibodies by lymphocytes in
Florey and Chain’s tests on the safety of
response to par ticular pathogens gives specic
penicillin would not be compliant with current
immunity.
protocols on testing.
Antibiotics block processes that occur in
prokaryotic cells but not in eukaryotic cells.
➔
Viral diseases cannot be treated using
antibiotics because they lack a metabolism.
➔
Some strains of bacteria have evolved with
genes which confer resistance to antibiotics
and some strains of bacteria have multiple
resistance.
302
Risks associated with scientic research:
6 . 3
D e F e n C e
a g a i n S t
i n F e C t i o u S
D i S e a S e
Skin as a barrier t infectin
The skin and mucous membranes form a primary defence
against pathogens that cause infectious disease.
There
are
inside
the
are
many
different
human
opportunistic
commonly
inside
The
a
live
primary
entry
of
and
defence
is
damage.
it.
of
the
and
Sebaceous
can
that
are
environment
Some
invade
cause
against
a
body
and
disease
against
associated
can
called
is
the
and
hair
they
only
barrier
physical
with
can
are
pathogens
physical
that
grow
microorganisms
the
specialized
provides
protection
glands
the
disease.
are
body
and
in
a
they
Others
Microbes
tough
pathogens
cause
although
body.
layer
microbes
and
outside
human
outermost
body
also
survive
pathogens.
skin.
Its
against
the
chemical
follicles
and
they
Figure 1 Scanning electron micrograph of
secrete
a
slightly
and
lowers
called
skin
pH.
sebum,
The
which
lower
pH
maintains
inhibits
the
skin
moisture
growth
of
and
bacteria on the surface of teeth. Mucous
bacteria
membranes in the mouth prevent these and
other microbes from invading body tissues
fungi.
Mucous
areas
and
chemical
membranes
such
as
foreskin
the
and
are
nasal
the
a
thinner
passages
vagina.
and
and
The
softer
other
mucus
type
of
airways,
that
these
skin
the
that
head
areas
of
is
of
found
the
skin
in
penis
acv
secrete
i  sk
is
a
sticky
solution
of
glycoproteins.
Mucus
acts
as
a
physical
barrier;
A digital microscope can be
pathogens
and
harmful
particles
are
trapped
in
it
and
either
swallowed
used to produce images of
or
expelled.
It
also
has
antiseptic
properties
because
of
the
presence
of
the dierent types of skin
the
anti-bacterial
enzyme
lysozyme.
covering the human body.
Figure 2 shows four images
Cuts and cts
produced in this way.
Cuts in the skin are sealed by blood clotting.
When
The
the
clotting.
a
skin
bleeding
The
semi-solid
blood
the
and
is
blood
gel.
pathogens
to
blood
stops
seals
up
pressure.
infection
until
vessels
after
emerging
This
blood
barrier
cut,
usually
new
a
from
the
tissue
has
it
a
are
cut
is
by
grown
and
of
from
Clots
heal
the
start
a
to
bleed.
process
being
prevents
important
skin.
to
and
because
changes
also
the
severed
time
wound
Clotting
provided
in
short
a
further
because
prevent
called
liquid
loss
cuts
entry
to
of
breach
of
cut.
pateets and bd cttin
Clotting factors are released from platelets.
Blood
a
clotting
catalyst
for
important
blood
The
that
vessels
process
Platelets
smaller
than
forming
trigger
a
off
next
cascade
is
clotting
either
damage
clots
only
to
temporary
or
plug.
clotting
can
result
vessels
They
platelets
cells.
occurs,
then
of
clots
because
which
very
if
it
produces
rapidly.
occurs
It
is
inside
blockages.
circulate
blood
each
blood
control,
cause
if
that
white
blood
reactions,
a
strict
occurs
fragments
red
of
As
under
resulting
cellular
the
a
reaction.
clotting
the
of
are
involving
involves
the
release
in
the
When
platelets
release
the
clotting
blood.
a
cut
or
are
other
aggregate
clotting
factors.
They
at
injury
the
factors
site
that
process.
▲
Figure 2
303
6
H u m a n
p H ys i o l o g y
Fibrin rductin
The cascade results in the rapid conversion of brinogen
to brin by thrombin.
platelets
red blood cell
The
cascade
from
thrombin.
into
lymphocyte
of
platelets
the
reactions
quickly
Thrombin
insoluble
platelets
and
also
exposed
to
Figure
shows
the
that
in
turn
brin.
blood
air
it
occurs
results
in
after
brin
cells.
to
The
the
the
a
hard
of
soluble
forms
a
clot
of
an
clotting
enzyme
protein
mesh
resulting
form
release
production
converts
The
dries
the
in
is
cuts
factors
called
brinogen
that
initially
a
traps
gel,
more
but
if
scab.
phagocyte
4
red
blood
cells
trapped
in
this
brous
mesh.
Figure 3 Cells and cell fragments from
blood. Lymphocytes and phagocytes
Crnar thrbsis
are types of white blood cell
Causes and consequences of blood clot formation in
coronary ar teries.
In
patients
in
the
coronary
with
to
the
semilunar
supplyingthe
respiration.
thrombosis
If
the
heart
then
coronary
arteries.
oxygen
The
is
the
and
arteries
to
of
disease,
arteries
carry
glucose
name
formation
deprived
unable
They
medical
coronary
is
valve.
heart
These
of
for
produce
blood
to
needed
by
clot
blood
clots
blocked
and
in
ATP
by
off
sometimes
from
wall
of
cardiac
is
the
by
nutrients.
sufcient
clots
the
a
blood
become
oxygen
blood
branch
a
a
the
the
muscle
blood
Cardiac
aerobic
close
heart,
bres
thrombus.
coronary
form
aorta
for
cell
Coronary
arteries.
clot,
part
muscle
of
cells
respiration
the
are
and
their
Figure 4 Scanning electron
contractions
become
irregular
heart
quivering
and
uncoordinated.
The
wall
of
the
micrograph of clotted blood with
makes
movements
called
brillation
that
do
not
pump
brin and trapped blood cells
blood
effectively.
naturally
or
Atherosclerosis
atheroma
damaged
and
a
of
the
risk
There
of
are
increased
calcium
some
risk
the
of
Patches
of
fatal
unless
arteries
coronary
the
the
of
occlusion,
it
resolves
and
arteries.
arteries
artery
tends
wall
atheroma
is
Where
to
become
hardened
sometimes
damage
to
the
rupture
of
atheroma
coronary
●
smoking
●
high
blood
cholesterol
●
high
blood
pressure
●
diabetes
●
obesity
●
lack
factors
that
thrombosis
are
and
correlated
heart
rupture
all
increase
with
an
attacks:
concentration
Figure 5 Early inter vention during a
of
exercise.
heart attack can save the patient’s life
so it is important to know what to do by
being trained
304
Of
course
correlation
nonetheless
advise
does
not
patients
to
prove
avoid
causation,
these
risk
but
by
capillary
thrombosis.
well-known
of
in
especially,
salts.
hardening
prove
endothelium
Coronary
coronary
can
intervention.
occlusion
the
roughened;
lesion.
epithelium,
condition
medical
causes
develops
deposition
causing
This
through
doctors
factors
if
possible.
6 . 3
D e F e n C e
a g a i n S t
i n F e C t i o u S
D i S e a S e
phactes
Ingestion of pathogens by phagocytic white blood cells
gives non-specic immunity to diseases.
If
microorganisms
membranes
of
defence.
and
to
that
sites
digest
infected,
of
formation
of
past
are
the
with
white
physical
white
different
out
infection.
There
of
liquid
called
the
are
and
When
attracted,
mucous
the
blood
walls
next
cell.
of
pathogens
lysosomes.
phagocytes
skin
provide
white
in
engulf
of
cells
of
pores
they
from
barriers
blood
types
through
enzymes
numbers
a
the
body,
many
squeeze
them
large
get
enter
There
phagocytes
move
and
line
Some
are
capillaries
by
and
endocytosis
wounds
resulting
become
in
the
pus.
Antibd rductin
Production of antibodies by lymphocytes in response to
par ticular pathogens gives specic immunity.
If
microorganisms
the
body,
recognized
response.
to
as
an
as
Any
in
antigen
Antibodies
Each
can
small
The
are
a
There
array
are
body.
However,
the
small
group
a
A
to
Antibodies
variable
that
helps
of
types
just
the
they
an
of
the
skin
surface
stimulate
immune
response
is
pathogen.
that
for
too
a
of
a
and
invade
pathogens
specic
response
the
The
on
are
immune
is
referred
production
antibodies
to
antibodies.
few
the
to
ght
that
a
that
produce
has
and
have
the
two
of
bind
to
in
lymphocytes.
our
many
initially
not
bodies
because
the
to
we
cell
cells
of
produce
infected
division
appropriate
type
are
quantities
have
types
previously
of
of
produced
of
the
infection.
functional
antigen
pathogen
is
plasma
enough
clear
but
stimulate
the
called
large
called
of
lymphocytes
specic
the
This
each
pathogen
that
cell
antibody,
producing
secrete
proteins
blood
of
pathogen
pathogen
binds
white
type
lymphocytes
they
the
large
of
of
one
different
antigens
and
body
a
pathogen
readily
preventing
enter
on
and
one
regions:
another
of
a
a
hyper-
region
number
of
ways,
these:
making
more
●
the
by
lymphocytes
control
are
particular
control
clone
days
region
including
●
large
few
antibody
of
and
immune
therefore
to
the
within
a
barriers
stimulates
lymphocytes
antibodies
antibody.
that
produces
of
body
specic
to
physical
molecules
pathogen.
vast
numbers
enough
the
produced
lymphocyte
antibody.
by
response
that
the
other
chemical
on
produce
past
and
foreign
antigen.
antibodies
an
get
proteins
the
Antibodies
more
recognizable
to
phagocytes
so
they
are
engulfed
viruses
from
docking
to
host
cells
so
that
they
cannot
cells.
only
persist
in
the
body
for
a
few
weeks
or
months
Figure 6 Avian inuenza viruses. In this
and
electron micrograph of a virus in transverse
the
plasma
cells
that
produce
them
are
also
gradually
lost
after
the
section, false colour has been used to
infection
has
been
overcome
and
the
antigens
associated
with
it
are
no
distinguish the protein coat that is recognized
longer
present.
However,
some
of
the
lymphocytes
produced
during
an
as antigens by the immune system (purple)
infection
are
not
active
plasma
cells
but
instead
become
memory
cells
from the DNA of the virus (green)
305
6
H u m a n
p H ys i o l o g y
that
the
are
very
same
active
and
infectious
or
long-lived.
pathogen
divide
to
disease
memory
cells
These
infects
the
produce
involves
that
memory
body
plasma
either
allow
cells
again,
cells
having
rapid
remain
in
which
very
rapidly.
antibodies
production
inactive
case
of
unless
they
become
Immunity
against
the
to
an
pathogen,
theantibody.
Huan iundecienc virus
Eects of HIV on the immune system and methods of transmission.
The
production
system
types
is
of
human
and
is
a
a
of
antibodies
complex
process
lymphocyte,
including
immunodeciency
destroys
helper
progressive
antibodies.
In
loss
the
by
the
early
The
diseases
The
a
invades
of
infection,
to
system
makes
antibodies
against
can
be
detected
in
a
person’s
body,
to
be
HIV
is
HIV
.
and
uses
of
its
they
spreads
retrovirus
reverse
once
that
has
genes
transcriptase
it
has
to
entered
a
made
make
host
of
DNA
which
helper
T-cells
are
cell.
destroyed
blood
people.
RNA
can
copies
considerably
and
anti-retroviral
so
antibody
ineffective
infections
by
a
called
said
syndrome
to
have
(AIDS).
HIV
the
infection.
body
for
The
a
virus
short
only
time
normally
only
occurs
if
there
is
and
blood
can
be
slowed
contact
There
drugs.
In
that
strike,
production
most
a
group
which
down
of
healthy
immune
sexual
be
ways
in
and
uninfected
which
this
the
intercourse,
mucous
during
which
membranes
of
abrasions
the
penis
and
by
can
cause
transfusion
becomes
products
opportunistic
system.
infected
various
minor
bleeding
HIV-positive
eventually
would
between
are
HIV
easily
of
such
infected
as
blood,
Factor
or
blood
VIII
fought
●
off
is
is
conditions
The
by
●
patients
by
outside
vagina
using
person
of
for
several
occur:
to
varies
the
of
together
syndrome
deciency
infection,
HIV-positive.
genes
at
existing
the
present,
HIV
collection
are
●
rate
is
of
A
If
to
a
When
immune
infection
said
stages
sarcoma.
conditions
HIV
survives
these
latter
the
AIDS
immune
or
acquired
produce
the
Kaposi’s
syndrome.
due
consequence
to
for
example
different
T-cells.
(HIV)
capacity
stages
diseases
immune
includes
helper
virus
T-cells.
of
the
and
Several
sharing
of
hypodermic
needles
by
intravenous
of
drugusers.
these
are
normally
so
rare
that
they
are
marker
Antibitics
Antibiotics block processes that occur in prokaryotic cells
but not in eukaryotic cells.
An
antibiotic
Most
in
is
prokaryotes
kill
The
a
antibiotics
bacteria
chemical
are
but
inside
processes
transcription,
not
the
antibacterial
fungi
on
which
example
is
by
with
they
fungi
antibiotics
ribosome
penicillin.
It
is
were
feed.
the
growth
are
harm
and
discovered
By
secreting
by
in
bacteria
of
their
some
microorganisms.
that
therefore
bacterial
function
of
processes
can
causing
growth
produced
the
block
and
saprotrophic
both
inhibit
They
without
antibiotics
compete
saprotrophic
inhibits
eukaryotes
body
targeted
These
matter
in
translation,
Many
that
antibacterial.
to
occur
used
human
DNA
cell
be
replication,
wall
formation.
saprotrophic
for
the
dead
antibacterial
bacterial
strains
of
to
cells.
fungi.
organic
antibiotics,
competitors.
the
Figure 7 Fleming's petri dish which rst
fungus,
but
only
when
nutrients
showed the inhibition of bacterial growth by
penicillin from a mycelium of Penicillium
306
bacteria
would
be
harmful.
are
scarce
and
An
Penicillium
competition
with
6 . 3
D e F e n C e
a g a i n S t
i n F e C t i o u S
D i S e a S e
acv
Testin eniciin
Wd aiDS D
Florey and Chain’s experiments to test penicillin on
The red AIDS awareness
bacterial infections in mice.
ribbon is an international
Howard
Florey
in
the
late
to
control
1930s
Ernst
that
bacterial
penicillin,
Chain’s
and
formed
investigated
infections.
discovered
team
Chain
by
developed
the
The
a
method
research
use
most
Alexander
a
of
chemical
promising
Fleming
of
team
in
growing
of
Oxford
symbol of awareness and
substances
these
1928.
the
in
Florey
fungus
support for those living with
was
HIV
. It is worn on World AIDS
and
Day each year – December 1st.
Penicillium
Are you aware how many
in
liquid
culture
in
conditions
that
stimulated
it
to
secrete
penicillin.
people in your area are
They
also
developedmethods
for
producing
reasonably
pure
samples
aected and what can be
of
penicillin
from
the
cultures.
done to suppor t them?
The
test
rst
penicillin
whether
tested
infected
all
the
was
on
Larger
rose
sadly
to
of
eye.
the
of
in
brain
He
were
died.
had
and
He
companies
larger
that
incurable
it
in
was
a
a
do
the
hours
were
tests
on
acute
of
life-
the
face
on
for
policeman
and
four
days
penicillin
from
and
ran
his
out
and
infection.
were
small
of
the
and
cured
child
wall
United
of
the
ve
of
who
the
more
their
States
had
an
infection
carrying
the
child
died
burst.
then
more
effective
patients
infections,
artery
infection,
artery
allowing
highly
penicillin
next
43-year-old
scratch
supplies
the
of
24
quantities.
penicillin
cured
quantities,
bacterial
a
when
the
a
They
with
Four
Within
given
an
produced
All
was
although
had
by
infected
should
larger
the
weakened
hemorrhage
much
but
were
tested.
four
to
humans.
penicillin.
they
He
given
in
needed
pneumonia.
produced,
test.
from
penicillin
the
that
caused
was
died
with
much
been
human
and
them
conrmed
previously
required
they
deliberately
from
but
considerably,
This
brain
Pharmaceutical
penicillin
of
dead
but
infections
were
decided
had
plates,
death
injections
infection
bush.
infections
one
the
suddenly
rst
relapse
quantities
behind
which
the
mice
were
which
agar
bacterial
cause
Chain
improved
acute
blood
mice
bacterial
a
Eight
that
given
and
on
control
penicillin
for
a
suffered
but
were
enough
condition
with
mice.
patients,
chosen
thorn
he
on
Florey
threatening
a
would
untreated
human
bacteria
bacteria
mice
healthy.
When
it
it
Streptococcus
killed
began
to
extensive
treatment
for
produce
testing,
many
infections.
Figure 8 Penicillin – the green ball represents a variable part of the molecule
307
6
H u m a n
p H ys i o l o g y
peniciin and dru testin
Risks associated with scientic research: Florey and Chain’s tests on the safety of
penicillin would not be compliant with current protocols on testing.
When
any
new
that
will
prove
it
patients
These
or
that
risks
are
are
it
that
of
tests
the
will
is
introduced
ineffective
cause
on
it
strict
must
animals
humans.
tested
is
on
to
side
and
a
with
on
drug
last
testing.
that
there
Also
small
pure
passes
the
disease
very
large
whether
the
drug
tocheck
that
numbers
is
there
of
effective
are
no
patients
in
all
severe
to
after
could
the
there
a
very
was
easily
samples
and
methods
tested
a
have
that
could
the
that
brief
new
on
period
type
been
they
drug
of
used
human
of
animal
drug
severe
side
they
were
using
have
been
side
and
effects.
were
effects
not
from
impurities.
the
other
were
all
on
hand,
were
cured
the
the
point
patients
of
death
that
and
they
used
several
and
of
their
infections
as
a
result
of
the
common
treatment.
Because
of
expeditious
effects.
testing
There
are
problems
some
famous
during
cases
testing
or
of
drugs
after
be
causing
Thalidomide
was
quickly
release.
introduced
in
the
a
treatment
for
various
mild
when
sickness
for
that
drug
more
birth
on
it
in
was
found
pregnant
purpose.
the
than
The
fetus
deformities
relieve
side
had
10,000
to
women
been
children
would
in
be
than
possible
June
would
introduced
1944
far
today.
now
more
During
penicillin
was
the
used
to
wounded
bacterial
soldiers
and
infection
the
was
number
greatly
of
deaths
reduced.
prescribed
of
the
tested
were
the
than
landings
was
morning
was
effects
not
before
it
risk-taking
conditions
from
but
greater
penicillin
1950s
treat
as
with
allowed,
D-day
●
only
Penicillin
experimental
side
the
They
test
patients
or
with
tests
On
involve
today
penicillin.
patients
effects.
the
The
for
all
Initial
then
if
drug
risks
or
protocols
Only
treat.
are
some
follow.
patients
intended
there
in
harmful
by
companies
healthy
drug
is
be
performed
numbers
these
to
minimized
pharmaceutical
tests
drug
and
born
problem
with
was
recognized.
In
●
2006
six
TGN1412,
of
leukemia.
All
long-term
very
have
six
rapidly
organ
recovered,
damage
unlikely
been
volunteers
protein
that
allowed
to
to
diseases
became
failure.
they
their
Florey
carry
were
developed
autoimmune
multiple
volunteers
is
new
treatment
suffered
It
healthy
a
may
and
very
and
ill
and
Although
have
immune
out
given
for
systems.
Chain
tests
on
the
suffered
would
a
new
Figure 9 Wounded US troops on Omaha beach 6 June 1944
Viruses and antibitics
Viral diseases cannot be treated using antibiotics because
they lack a metabolism.
Viruses
living
instead
own
308
are
non-living
cells.
of
They
having
means
of
use
a
and
the
can
only
chemical
metabolism
transcription
or
of
reproduce
processes
their
protein
of
own.
when
a
They
synthesis
they
living
do
and
are
host
not
they
inside
cell,
have
rely
their
on
the
6 . 3
host
cell’s
These
enzymes
processes
for
ATP
cannot
be
synthesis
targeted
and
by
D e F e n C e
other
drugs
as
a g a i n S t
metabolic
the
host
i n F e C t i o u S
D i S e a S e
pathways.
cell
would
also
acv
bedamaged.
Dss  w
All
of
the
commonly
chloramphenicol
not
effective
prescribe
antibiotics
and
against
them
and
used
for
antibiotics
tetracycline
viruses.
a
viral
increases
Not
control
only
infection,
in
such
is
but
antibiotic
as
penicillin,
bacterial
it
it
streptomycin,
infections
inappropriate
contributes
resistance
in
for
to
and
are
doctors
the
How can a doctor distinguish
to
overuse
c d v fcs
of
bacteria.
between bacterial and
viral infections, without
prescribing an antibiotic
and seeing if it cures the
There
are
a
few
viral
enzymes
which
can
be
used
as
targets
for
drugs
to
infection?
control
been
viruses
without
discovered
known
as
or
harming
developed
antivirals
rather
to
than
the
host
control
cell.
Only
viruses
in
a
few
this
drugs
way.
have
These
are
antibiotics.
Resistance t antibitics
Some strains of bacteria have evolved with genes which
confer resistance to antibiotics and some strains of
bacteria have multiple resistance.
In
2013
the
government’s
chief
medical
ofcer
for
England,
Sally
Davies,
Figure 10 Many viruses cause
said
this:
a common cold. Children lack
The
danger
along
with
action,
where
able
The
to
posed
we
in
discovered
huge
may
infections
a
lot
kill
of
development
described
soon
of
used
or
after
unless
surgical
antibiotics.
tuberculosis
worldwide
some
all
us
be
as
5.2.
the
a
resistance
of
back
a
threats
in
result
to
of
Another
of
the
or
of
of
WHO
operations.
organ
by
we
an
ranked
don’t
immunity to most of them
so frequently catch a cold.
take
Antibiotics do not cure them
environment
We
natural
won’t
be
selection
resistance
antibiotic.
This
resistance,
(MRSA)
and
which
resists
problem
reported
reaching
be
transplants.
with
patients
has
disease
If
19th-century
multiple
this
should
nation.
bacteria
aureus
example
the
to
routine
develops
hospital
The
antibiotics
almost
introduction
of
to
antibiotics
Staphylococcus
with
an
treatments
Strains
strain
wounds
year
list
cancer
(MDR-TB).
per
a
resistance
methicillin-resistant
blood
on
our
sub-topic
concern
growing
terrorism
then
do
by
is
are
is
for
has
all
is
usually
not
of
example
infected
the
commonly
multidrug-resistant
more
than
epidemic
300,000
cases
proportions
in
areas.
Antibiotic
resistance
is
an
avoidable
problem.
These
measures
are
required:
●
doctors
●
patients
prescribing
antibiotics
completing
courses
only
of
for
serious
antibiotics
to
bacterial
eliminate
infections
infections
completely
●
hospital
staff
maintaining
high
standards
of
hygiene
to
prevent
cross-
infection
●
farmers
●
pharmaceutical
new
not
types
using
have
antibiotics
companies
been
in
animal
developing
introduced
since
feeds
new
the
to
stimulate
types
of
growth
antibiotic
–
no
1980s.
309
6
H u m a n
p H ys i o l o g y
D-sd qss: Antibiotic resistance
Bacterial
resistance
consequence
of
to
the
antibiotics
overuse
of
is
a
these
b)
direct
drugs.
USA,
visits
for
currently
upper
more
than
respiratory
half
tract
of
the
a
reason
for
the
pattern
shown.
Calculate
the
antibiotic
resistance
percentage
difference
in
doctor
infections
between
2002
and
(URIs)
1992.
are
prescribed
most
URIs
are
antibiotics,
caused
by
despite
knowledge
the
early
1990s,
3
viruses.
Finnish
public
Evaluate
began
discouraging
of
the
claim
that
erythromycin
reduction
has
led
to
a
in
the
reduction
health
in
authorities
[2]
that
use
In
the
use
of
theincidence
of
antibiotic
resistance
in
the
S.pyogenes.
antibiotic
the
bacterial
national
capita
The
resistance
Finland,
gure
over
a
antibiotic,
consumption
the
incidence
for
the
2002
responsible
0
1002
antibiotic
0002
is
the
9991
pyogenes
to
5
7991
resistant
Streptococcus
10
8991
that
S.
of
15
6 991
period,
in
20
5991
10-year
are
and
per
cent.
shows
[3]
to
3991
erythromycin.
11
per
response
4991
strains
43
the
in
2991
pyogenes
in
by
URIs
to
erythromycin
dropped
data
for
ecnatsiser citoibitna %
rising
erythromycin
[2]
In
2
the
Suggest
year
condition
known
as
“strep
throat”.
Figure 11 The incidence of Streptococcus
1
a)
Describe
the
pattern
of
erythromycin
pyogenes strains that are resistant to the
resistance
to
over
the
period
from
1992
2002.
antibiotic erythromycin over a 10-year period
[3]
in Finland
6.4 gs  c
Understandin
Aicatins
➔
Ventilation maintains concentration gradients
➔
External and internal intercostal muscles,
of oxygen and carbon dioxide between air in
and diaphragm and abdominal muscles as
alveoli and blood owing in adjacent capillaries.
examples of antagonistic muscle action.
➔
Type I pneumocytes are extremely thin alveolar
➔
Causes and consequences of lung cancer.
➔
Causes and consequences of emphysema.
cells that are adapted to carry out gas exchange.
➔
Type II pneumocytes secrete a solution
containing surfactant that creates a moist
surface inside the alveoli to prevent the sides
Skis
of the alveolus adhering to each other by
➔
Monitoring of ventilation in humans at rest and
reducing surface tension.
after mild and vigorous exercise. (Practical 6)
➔
Air is carried to the lungs in the trachea and
bronchi and then to the alveoli in bronchioles.
➔
Muscle contractions cause the pressure
Nature f science
changes inside the thorax that force air in and
➔
Obtain evidence for theories: epidemiological
out of the lungs to ventilate them.
studies have contributed to our understanding
➔
Dierent muscles are required for inspiration
and expiration because muscles only do work
when they contract.
310
of the causes of lung cancer.
6 . 4
g a S
e x C h a n g e
Ventiatin
Ventilation maintains concentration gradients of oxygen
and carbon dioxide between air in alveoli and blood
owing in adjacent capillaries.
All
organisms
different
dioxide
to
process.
carbon
gases
This
use
in
dioxide
the
inside
one
gas
process
is
from
absorb
oxygen
produced
air.
the
In
by
this
humans
lungs
the
called
photosynthesis
Humans
with
alveoli
absorb
one.
and
for
environment
exchange.
release
use
in
process.
gas
(gure
gas
the
cell
release
oxygen
absorb
occurs
and
small
by
release
organisms
in
a
carbon
produced
respiration
Terrestrial
exchange
and
Leaves
this
the
exchange
air
sacs
called
1).
type I pneumocytes
in alveolus wall
phagocyte
m

0
0
1
network of blood
type II pneumocytes
capillaries
in alveolus wall
Figure 1
Gas
exchange
blood
there
owing
is
a
the
in
of
blood
gradients
removed.
the
by
fresh
This
the
air
and
a
capillary.
must
process
be
is
between
capillaries.
gradient:
oxygen
in
diffusion
adjacent
concentration
concentration
than
happens
the
lower
To
in
in
the
gases
the
into
alveolus
these
the
alveoli
only
concentration
maintain
pumped
called
air
air
The
of
and
diffuse
has
a
carbon
because
higher
dioxide
concentration
alveoli
and
stale
air
must
be
ventilation.
311
6
H u m a n
p H ys i o l o g y
D-sd qss: Concentration gradients
Figure
2
shows
atmospheric
dissolved
in
pulmonary
the
air,
air
typical
air
in
the
returning
composition
alveoli
to
the
and
of
1
gases
lungs
in
Explain
the
the
why
alveoli
is
the
oxygen
not
as
concentration
high
as
in
fresh
air
in
that
inhaled.
is
[2]
arteries.
2
a)
Calculate
the
difference
in
oxygen
oxygen
concentration
between
air
in
the
alveolus
carbon dioxide
nitrogen
and
blood
arriving
at
the
alveolus.
[1]
700
b)
Deduce
the
process
caused
by
this
598
600
concentration
570
570
difference.
[1]
565
gH mm / erusserp lait rap
500
c)
(i)
Calculate
the
difference
dioxide
concentration
inhaled
and
air
Explain
this
difference.
in
carbon
between
air
400
exhaled.
[1]
300
(ii)
[2]
200
d)
159
Despite
the
high
concentration
of
120
105
nitrogen
in
air
in
alveoli,
little
or
none
100
45
40
40
27
diffuses
from
reasons
for
the
air
to
the
blood.
Suggest
3
0
atmospheric air
air in alveoli
blood travelling
this.
[2]
air exhaled
to alveoli
that is inhaled
Figure 2 Partial pressures of gases in the pulmonary system
Ventiatin exerients
Monitoring of ventilation in humans at rest and after mild and vigorous exercise.
(Practical 6)
In
an
investigation
ventilation,
the
the
type
independent
parameter
that
of
the
or
of
and
measured
is
exercise
Either
on
or
variable
in
ventilation
exercise
on
the
dependent
measured
of
exercise
is
enough
variable.
A
simple
approach
for
the
is
to
choose
these
can
be
the
of
the
investigation
ventilation
carrying
reach
given
rate.
a
on
an
constant
below
They
effect
a
of
should
activity
rate.
include
dependent
The
be
for
long
example
simple
and
a
more
independent
advanced
variable
an
of
after
to
methods
●
both
the
intensity
variable
is
effect
levels
of
activity
technique
that
could
be
used
for
the
ranging
investigation.
from
inactive
down,
and
to
the
rates,
a
for
A
same
parameters
per
to
active,
standing,
more
be
at
allows
during
lying
walking,
at
1
jogging
approach
is
Ventilation
●
measured
different
the
correlated
minute
as
different
running
This
such
quantitative
activity
example
treadmill.
joules
very
and
sprinting.
do
on
sitting
to
work
speeds
rate
rate
most
straightforward
ventilation
Count
ventilation
with
The
or
in
as
in
a
maintained
slow
as
is
by
number
inhaled
be
exercise.
the
rate
of
times
minute.
at
a
possible
way
simple
to
measure
observation.
air
is
exhaled
Breathing
natural
rate,
without
should
which
getting
out
is
of
breath.
Ventilation
of
some
fresh
air
some
of
of
drawn
in
and
number
of
times
air
The
expelled
312
the
per
the
lungs
into
stale
the
air
is
carried
lungs
from
expelled
minute
that
is
the
and
the
air
out
then
lungs.
is
is
by
the
expelling
The
tidal
drawn
ventilation
drawing
volume
volume.
in
or
rate.
●
Ventilation
by
is
data
rate
can
logging.
placed
An
around
pumped
in
with
pressure
sensor
also
the
a
is
be
measured
inatable
thorax
bladder.
then
A
used
chest
and
air
belt
is
differential
to
measure
6 . 4
pressure
chest
can
variations
expansions.
be
deduced
ventilations
inside
The
and
may
the
also
the
rate
of
belt
relative
be
due
to
To
ventilations
size
ensure
rigorous,
of
and
recorded.
Tidal
e x C h a n g e
experimental
apart
variables
parameters
times
at
all
should
should
levels
of
design
from
the
be
be
is
independent
kept
constant.
measured
exercise
with
each
volume
person
Simple
●
the
variables
dependent
Ventilation
several
2
that
all
g a S
One
the
apparatus
normal
breath
delivery
volume
this
is
tube
shown
is
air
for
as
in
a
It
vessel
is
not
repeatedly
the
gure
exhaled
into
measured.
apparatus
exhaling
is
CO
3.
in
possible
the
trial.
should
be
As
many
different
people
through
and
safe
the
to
use
inhaling
and
concentration
will
bell jar with
2
rise
too
as
tested.
high.
graduations
delivery tube
●
Specially
designed
available
for
measure
lungs
ow
and
volumes
use
rate
from
can
spirometers
with
into
these
be
data
are
logging.
and
out
of
They
pneumatic trough
the
measurements
lung
Figure 3
deduced.
Te I neuctes
bronchiole
Type I pneumocytes are extremely thin alveolar cells that
are adapted to carry out gas exchange.
The
lungs
area
for
cells,
I
contain
diffusion.
called
the
The
and
of
wall
thin
are
μm
of
They
are
of
each
Most
alveoli
with
alveolus
of
the
attened
cells,
capillaries
also
a
very
consists
cells
in
with
this
the
of
large
a
total
single
epithelium
thickness
of
surface
layer
are
only
of
Type
about
cytoplasm.
of
cells.
numbers
wall
epithelium.
pneumocytes.
0.15
huge
The
the
The
therefore
carbon
adjacent
air
less
in
the
than
dioxide
alveolus
0.5
has
to
μm
and
apart.
diffuse
is
consists
the
The
blood
of
in
distance
therefore
very
a
single
the
layer
alveolar
over
which
small,
of
very
capillaries
oxygen
which
is
an
alveolus
adaptation
to
increase
the
rate
of
gas
0.25 mm
exchange.
Te II neuctes
epithelium of
alveolus wall
Type II pneumocytes secrete a solution containing
nucleus of
epithelium cell
surfactant that creates a moist surface inside the alveoli
basement membrane
to prevent the sides of the alveolus adhering to each other
endothelium of capillary
by reducing surface tension.
Type
II
pneumocytes
alveolar
surface
area.
are
rounded
They
cells
secrete
a
that
uid
occupy
which
about
coats
5%
the
of
inner
alveolus
the
surface
blood plasma
of
the
alveoli.
This
lm
of
moisture
allows
oxygen
in
the
alveolus
to
erythrocyte
dissolve
provides
and
be
and
an
then
area
diffuse
from
to
the
which
blood
carbon
in
the
dioxide
alveolar
can
capillaries.
evaporate
into
It
also
the
air
1 µm
exhaled.
Figure 4 Structure of alveoli
313
6
H u m a n
p H ys i o l o g y
The
uid
secreted
by
the
Type
II
pneumocytes
contains
air in alveolus
water
monolayer of
surface
a
pulmonary
surfactant.
Its
molecules
have
a
structure
surfactant
similar
They
lining
Figure 5 Pulmonary surfactant molecules on the surface of the
the
to
the
a
and
the
causing
air
exhaled
collapse
phospholipids
of
with
the
the
the
the
in
of
the
cell
membranes.
surface
of
hydrophilic
tension
sides
from
the
on
hydrophobic
surface
from
is
of
monolayer
alveoli,
water
reduces
lm of moisture lining the alveoli
that
form
tails
and
the
facing
prevents
alveoli
lungs.
the
This
moisture
heads
to
facing
the
the
adhere
helps
to
air.
This
water
when
prevent
lung.
trachea
Premature
babies
pulmonary
respiratory
giving
the
are
often
surfactant
distress
baby
and
born
can
syndrome.
oxygen
and
with
suffer
insufcient
from
Treatment
also
one
or
infant
involves
more
doses
intercostal muscle
of
surfactant,
extracted
from
animal
lungs.
right bronchus
Airwas fr ventiatin
Air is carried to the lungs in the trachea
bronchioles
right lung
and bronchi and then to the alveoli in
ribs
diaphragm
bronchioles.
Air
enters
the
ventilation
system
through
the
nose
or
Figure 6 The ventilation system
mouth
rings
air
and
of
then
cartilage
pressure
tissues
is
bronchi,
passes
in
inside
high.
also
is
The
with
its
down
wall
low
or
trachea
walls
to
the
trachea.
keep
it
pressure
divides
This
open
in
to
even
when
surrounding
form
strengthened
has
with
two
cartilage.
(a) inspiration
One
ver tebral
bronchus
Inside
the
leads
lungs
the
to
each
bronchi
lung.
divide
repeatedly
to
column
form
ribs
a
tree-like
structure
of
narrower
airways,
called
ribs
bronchioles.
bres
to
diaphragm
in
vary.
groups
The
their
At
of
bronchioles
walls,
the
end
alveoli,
allowing
of
the
where
have
the
smooth
width
narrowest
gas
of
muscle
these
bronchioles
exchange
airways
are
occurs.
pressure chanes durin ventiatin
(b) expiration
Muscle contractions cause the pressure
changes inside the thorax that force air in
and out of the lungs to ventilate them.
Ventilation
If
particles
volume,
air movement
of
of
the
Conversely,
the
gas
lungs
spread
pressure
if
a
gas
is
of
involves
out
the
to
some
occupy
gas
basic
a
becomes
compressed
to
physics.
larger
lower.
occupy
a
smaller
ribcage movement
volume,
the
pressure
rises.
If
gas
is
free
to
move,
it
diaphragm movement
will
always
ow
from
regions
Figure 7 Ventilation of the lungs
regions
314
of
lower
pressure.
of
higher
pressure
to
6 . 4
During
thorax
ventilation,
to
drawn
into
pressure
cause
drop
the
has
risen
out
from
to
the
the
the
thorax
lungs
to
cause
pressure.
atmosphere
atmospheric
inside
from
contractions
atmospheric
lungs
pressure
forced
muscle
below
the
rise
a
pressure
Muscle
above
atmosphere
inside
consequence,
(inspiration)
pressure.
to
the
As
until
contractions
atmospheric,
so
e x C h a n g e
the
air
the
g a S
is
lung
then
air
is
(expiration).
Antanistic usces
Dierent muscles are required for inspiration and expiration
because muscles only do work when they contract.
Muscles
can
Muscles
●
be
do
(tension)
when
they
two
work
that
they
Muscles
●
in
do
when
causes
not
they
contract
particular
while
lengthen
elongated
state
a
force
pushing
a
contracting
and
by
relaxing.
exerting
movement.
a
They
pulling
force
become
shorter
this.
lengthen
do
states:
by
they
are
relaxing,
themselves.
the
Most
contraction
(compression)
of
but
another
while
this
muscles
happens
are
pulled
muscle.
relaxing
so
do
They
no
passively
into
do
work
not
at
–
an
exert
this
time.
Figure 8 Dierent muscles are used for bending
the leg at the knee and for the opposite
movement of straightening it
Muscles
therefore
movement
two
in
muscles
movement,
opposite
the
rst
known
the
be
Inspiration
directions
second
is
caused
When
is
needed
by
pair
the
of
as
in
at
one
and
is
direction.
different
muscle
second
work
elongated
muscle
together
in
times,
contracts
by
If
at
and
the
rst.
contracting
this
way
least
causes
they
a
The
while
are
muscles.
involve
working
one
relaxes
muscles
expiration
required,
movement
When
muscle
antagonistic
and
are
cause
required.
movement
an
only
opposite
will
relaxes.
as
muscles
can
opposite
movements,
antagonistic
so
different
pairs.
Antanistic usce actin in ventiatin
External and internal intercostal muscles, and diaphragm and abdominal muscles
as examples of antagonistic muscle action.
Ventilation
pressure
involves
inside
the
two
pairs
of
opposite
movements
that
change
the
volume
and
therefore
is
e
Diaphragm
Moves downwards and attens
Moves upwards and becomes more domed
Ribcage
Moves upwards and outwards
Moves downwards and inwards
Antagonistic
pairs
the
thorax:
of
muscles
are
needed
to
cause
these
is
movements.
e
Volume and pressure
The volume inside the thorax
The volume inside the thorax decreases and
changes
increases and consequently the
consequently the pressure increases
pressure decreases
315
6
H u m a n
p H ys i o l o g y
Movement
The diaphragm contracts and so it
The diaphragm relaxes so it can be pushed
of the
Diaphragm
moves downwards and pushes the
upwards into a more domed shape
diaphragm
abdomen wall out
Abdomen
Muscles in the abdomen wall relax
Muscles in the abdomen wall contract pushing
wall
allowing pressure from the diaphragm
the abdominal organs and diaphragm upwards
muscles
to push it out
Movement
External
The external intercostal muscles
The external intercostal muscles relax and are
of the
intercostal
contract, pulling the ribcage upwards
pulled back into their elongated state.
ribcage
muscles
and outwards
Internal
The internal intercostal muscles
The internal intercostal muscles contract, pulling
intercostal
relax and are pulled back into their
the ribcage inwards and downwards
muscles
elongated state
Eidei
Obtain evidence for theories: epidemiological studies have contributed to our
understanding of the causes of lung cancer.
Epidemiology
causes
of
is
observational
it
is
rarely
disease
the
disease.
in
study
Most
rather
possible
human
than
to
of
the
incidence
epidemiological
experimental
investigate
populations
the
by
also
and
studies
are
because
causes
carrying
and
factor
a
risk
of
lung
in
other
elds
causes
of
of
scientic
a
disease
research,
are
evidence
for
or
against
a
collected
that
allows
the
theory,
association
disease
For
example,
and
its
survey
theoretical
causes
lung
test
cancer,
the
cause
the
who
have
developed
who
have
not
are
epidemiological
evidence
cancer
for
are
a
theory
smoking
lung
needed.
surveys
link
to
in
and
be
course
correlation
between
a
of
smoking
risk
of
people
very
large
try
to
not
prove
that
the
factor
apart
are
usually
lung
account
the
and
causes
confounding
increased
associated
smoking
is
a
spurious
a
the
factors
compensate
from
the
to
risk.
with
cause
of
Smoking
leanness
lung
association
one
for
reduces
and
cancer.
between
being
to
single
recorded
on
carried
factors
factors.
and
data
This
leanness
Age
out
and
and
sometimes
factors
many
investigated.
be
confounding
of
confounding
collect
procedures
of
effect
This
to
try
sex
it
is
factors
allows
take
to
isolate
are
almost
epidemiological
disease
include
only
males
or
females
or
only
in
sub-
disease.
people
There
an
is
necessary
surveys
does
so
cancer.
statistical
strong
and
To
usually
1.6.
factor
with
the
lung
always
A
that
signicantly
tested.
people
provided
sub-topic
increased
showed
smoking
Examples
that
not
by
an
between
habits
cancer
between
included
that
analysis
is
example,
found
and
can
disease
For
been
leanness
Careful
leanness
it.
a
data
and
to
cause
repeatedly
between
cancer.
and
explains
the
not
They
between
To
of
is
incidence.
theories
proposed.
appetite
obtain
the
does
has
smokers
associated
the
on
associations
that
association
among
about
effect
epidemiologists
out
experiments.
As
an
spurious
an
of
have
cause
in
a
specic
age
range.
which
Causes f un cancer
Causes and consequences of lung cancer.
Lung
cancer
world,
the
316
both
number
is
in
of
the
most
termsof
deaths
common
the
due
cancer
number
to
of
in
the
cases
thedisease.
and
The
general
causes
topic1.6.
The
considered
of
cancer
specic
here.
are
described
causes
of
lung
cancer
are
6 . 4
and
smoke
organic
●
Radon
in
gas
that
granite.
●
from
causes
of
leaks
out
It
Asbestos,
silica
cancer
inhaled.
The
if
This
in
of
and
wood
or
dust
of
or
usually
of
other
other
difculties
with
cases
as
it.
solids
on
can
of
cause
them
are
construction
factories.
cancer
be
such
particles
or
of
radioactive
ventilated
inhale
other
mines
a
rocks
happens
can
is
badly
then
lung
them
in
numbers
It
certain
some
quarries,
Some
disease:
world.
people
consequences
severe.
the
or
coal,
signicant
the
accumulates
and
sites
burning
parts
buildings
lung
e x C h a n g e
matter.
some
gas
g a S
are
used
often
to
help
breathing,
very
diagnose
persistent
Figure 9 A large tumour (red) is
coughing,
coughing
up
blood,
chest
pain,
loss
of
visible in the right lung. The tumour
appetite,
weight
loss
and
general
fatigue.
is a bronchial carcinoma
In
●
Smoking
causes
about
87%
of
cases.
many
when
smoke
contains
many
mutagenic
patients
chemicals.
it
is
cigarette
carries
a
risk,
the
incidence
cancer
increases
with
the
number
day
and
the
number
of
years
of
Passive
smoking
happens
smoke
cases
when
exhaled
will
banned
causes
about
non-smokers
by
decline
indoors
smokers.
in
The
countries
and
in
3%
public
Air
pollution
lung
are
probably
cancers.
most
nitrogen
The
cases.
This
number
early
be
tobacco
where
oxides
are
from
of
about
air
diesel
all
with
secondary
tumours
in
the
elsewhere.
of
Mortality
patients
with
rates
lung
are
high.
cancer
is
enough,
removed
with
of
smoking
than
one
Other
5
years.
all
or
If
part
surgically.
or
more
patients
a
of
the
This
courses
are
tumour
is
of
treated
is
survive
discovered
affected
usually
lung
may
combined
chemotherapy.
with
radiotherapy.
places.
causes
sources
signicant
or
15%
more
The
●
large
have
smoking.
of
inhale
already
also
smoked
for
●
is
may
As
Only
per
and
of
brain
lung
tumour
discovered
metastasized,
every
the
Tobacco
5%
pollution
exhaust
vehicle
that
fumes,
exhaust
minority
cancer,
of
fumes
are
but
likely
to
difculties,
possible
of
patients
have
lost
continue
fatigue
return
of
who
some
to
and
the
of
have
also
are
cured
their
of
lung
pain,
anxiety
lung
tissue,
breathing
about
the
disease.
Ehsea
Causes and consequences of emphysema.
In
healthy
group
of
lung
small
emphysema
of
larger
total
air
tissue
these
sacs
surface
each
thin-walled
are
with
area
for
bronchiole
alveoli.
replaced
much
gas
by
In
a
thicker
exchange
a
leads
smaller
walls.
is
to
patient
a
●
with
infections
number
elastase,
The
them
and
the
distance
over
which
gases
occurs
is
increased,
and
so
a
therefore
An
enzyme
much
less
less
elastic,
so
effective.
gas
The
ventilation
is
molecular
mechanisms
lungs
more
though
there
is
involved
some
inhibitor
are
from
by
to
kill
endocytosis.
called
prevents
alpha
elastase
1-antitrypsin
and
digesting
lung
tissue.
other
In
also
the
number
not
evidence
increases
and
of
they
phagocytes
produce
in
the
more
elastase.
fully
Genetic
factors
affect
the
quantity
and
for
effectiveness
these
enzyme,
formed
lung
produce
difcult.
●
understood,
vesicles
prevent
and
exchange
lungs
The
the
usually
smokers,
become
normally
bacteria
diffusion
proteases
is
alveoli
engulng
protein-digesting
inside
(A1AT)
of
inside
by
considerably
●
reduced
Phagocytes
of
A1AT
produced
in
the
lungs.
theories:
317
6
H u m a n
p H ys i o l o g y
In
about
in
the
of
proteases
walls
30%
of
alveolus
are
is
smokers
wall
not
by
digestion
the
prevented
weakened
and
of
increased
and
than
proteins
nd
alveolus
eventually
normal
result
quantity
the
even
onerous.
destroyed.
during
Emphysema
is
a
chronic
disease
because
to
alveoli
oxygen
is
usually
saturation
in
irreversible.
the
blood
and
In
dioxide
lacks
such
mild
concentrations.
energy
as
cases
and
climbing
there
exercise
is
but
may
stairs
As
a
eventually
too
shortness
eventually
of
breath
even
mild
the
It
causes
it.
Ventilation
is
laboured
and
tends
causes
to
low
tasks
vigorous
activity
damage
carbon
patient
be
more
rapid
than
normal.
higher
D-sd qss: Emphysema and gas exchange
Figure
10
shows
healthy
emphysema,
at
emphysema.
Breathing
1
a)
Place
times
a
b)
2
Explain
the
why
tissue
polluted
of
and
magnication.
air
each
the
several
the
are
tissue
makes
crosses
for
from
Smoking
the
micrograph
ruler
times
results
suitable
Explain
lung
across
edge
this
that
using
same
ruler
the
Repeat
way
the
each
a
a
disease
and
gas
count
State
with
causes
worse.
how
exchange
micrograph,
comparable.
lung
usually
in
your
many
surface.
such
a
results
units.
[3]
conclusions
people
who
that
have
you
draw
from
emphysema
feel
the
results.
tired
all
the
time.
3
Suggest
and
Figure 10 Healthy lung tissue (top) and lung
tissue showing emphysema (bottom)
318
[3]
[3]
why
strained
people
right
with
side
of
emphysema
the
heart.
often
have
an
enlarged
[1]
6 . 5
n e u r o n S
a n D
S y n a p S e S
6.5 ns d sss
Understandin
Aicatins
➔
Neurons transmit electrical impulses.
➔
The myelination of ner ve bres allows for
➔
Secretion and reabsorption of acetylcholine by
neurons at synapses.
saltatory conduction.
➔
Neurons pump sodium and potassium ions
➔
Blocking of synaptic transmission at
cholinergic synapses in insects by binding
across their membranes to generate a resting
of neonicotinoid pesticides to acetylcholine
potential.
receptors.
An action potential consists of depolarization
➔
and repolarization of the neuron.
Skis
Ner ve impulses are action potentials
➔
➔
Analysis of oscilloscope traces showing resting
propagated along the axons of neurons.
potentials and action potentials.
Propagation of ner ve impulses is the result of
➔
local currents that cause each successive par t
of the axon to reach the threshold potential.
Nature f science
Synapses are junctions between neurons and
➔
➔
Cooperation and collaboration between groups
between neurons and receptor or eector cells.
of scientists: biologists are contributing to
When pre-synaptic neurons are depolarized
➔
research into memory and learning.
they release a neurotransmitter into the
synapse.
A ner ve impulse is only initiated if the threshold
➔
potential is reached.
Neurns
Neurons transmit electrical impulses.
Two
systems
endocrine
of
the
a nd
tha t
consists
of
glands
consists
of
nerve
neurons
in
the
electrical
Neurons
also
by
use d
for
ne r vous
r e le a se
ca l le d
in t e r na l
s ys t e m .
hor m o n es .
ne ur ons .
ner vous
tr a ns mitti ng
Th e
Th e r e
s yste m .
ner ve
c o m m u ni c a t io n :
T he
en d oc r in e
n e r vo u s
a re
a bou t
N eu r on s
i m pu l se s .
h e lp
A
the
s yst e m
sys t em
85
bil li on
wit h
n e r ve
in t e rn a l
im pu ls e
is
signa l .
have
have
ce l l s
ar e
the
huma n
communication
an
body
system
a
cell
narrow
body
with
outgrowths
cytoplasm
called
and
nerve
a
nucleus
bres
along
but
they
which
nerve
impulsestravel.
●
Dendrites
are
totransmit
spinal
●
Axons
short
branched
impulses
between
nerve
bres,
neurons
in
for
one
examples
part
of
those
the
used
brain
or
cord.
are
impulses
very
from
elongated
the
tips
of
nerve
the
bres,
toes
or
for
the
example
ngers
to
those
the
that
spinal
transmit
cord.
319
6
H u m a n
p H ys i o l o g y
cell body
axon
skeletal muscle (eector)
dendrites
▲
Figure 1 Neuron with dendrites that transmit impulses to the cell body and an axon that transmits impulses a considerable
distance to muscle bres
meinated nerve bres
The myelination of nerve bres allows for saltatory
conduction.
The
basic
structure
transmitted
membrane
most
A
▲
cases
nerve
is
of
very
enclosing
is
about
bre
with
speed
of
about
Some
nerve
called
myelin.
1
a
nerve
simple:
1
a
µm,
this
are
per
is
which
a
cylindrical
region
though
simple
along
bre
narrow
metre
bres
bre
the
of
some
The
bres
conducts
impulse
shape,
cytoplasm.
nerve
structure
nerve
in
are
with
plasma
diameter
wider
nerve
is
a
in
than
impulses
this.
at
a
second.
coated
along
most
of
their
length
by
a
material
Figure 2 Ner ve bres (axons) transmitting
It
consists
of
many
layers
of
phospholipid
bilayer.
Special
electrical impulses to and from the central
cells
called
Schwann
cells
deposit
the
myelin
by
growing
round
and
ner vous system are grouped into bundles
round
the
double
more
There
myelin
sheath
nucleus of
Schwann cell
nerve
layer
layers
is
a
of
bre.
when
gap
Each
time
phospholipid
the
Schwann
between
the
they
bilayer
cell
myelin
is
grow
around
deposited.
stops
the
There
nerve
may
bre
be
20
a
or
growing.
deposited
by
adjacent
Schwann
cells.
node of
Ranvier
The
gap
is
impulse
can
saltatory
along
a
called
a
jump
node
from
conduction.
nerve
much
more
much
as
bre
rapidly
so
It
of
Ranvier.
one
is
node
much
myelinated
Ranvier
quicker
myelinated
than
of
In
nerve
unmyelinated
to
than
the
bres
next.
continuous
bres
nerve
nerve
transmit
bres.
This
is
nerve
called
transmission
nerve
The
the
impulses
speed
can
be
axon
▲
100
metres
per
second.
Figure 3 Detail of a myelinated ner ve
bre showing the gaps between adjacent
Schwann cells (nodes of Ranvier)
▲
Figure 4 Transverse section of axon showing the myelin sheath formed by the Schwann
cell's membrane wrapped round the axon many times (red)
320
as
6 . 5
Restin tentias
n e u r o n S
a n D
S y n a p S e S
uid outside neuron
Neurons pump sodium and
+
Na
+
potassium ions across their
Na
+
Na
channel
+
K
+
Na
+
membranes to generate a resting
K
closed
+
Na
potential.
+
Na
+
Na
+
A
neuron
that
is
not
transmitting
a
Na
signal
+
has
a
potential
membrane
This
and
difference
that
potential
negative
is
is
called
due
to
charges
or
voltage
the
an
resting
across
imbalance
across
the
Na
its
of
positive
membrane.
+
Na
Sodium–potassium
●
pumps
transfer
+
sodium
(Na
+
Na
potential.
+
/K
pump
+
)
and
potassium
(K
)
ions
+
across
the
membrane.
Na
ions
are
pumped
+
out
and
K
numbers
ions
of
are
ions
pumped
pumped
is
in.
+
The
+
+
K
unequal
–
K
K
channel
when
+
K
+
three
Na
are
pumped
out,
only
two
closed
+
+
ions
+
K
K
Na
+
K
+
K
ions
are
pumped
in,
+
creating
K
+
K
+
concentration
gradients
for
both
K
ions.
+
+
+
K
K
K
+
Also
●
the
membrane
is
about
50
times
K
more
+
+
permeable
to
K
+
K
ions
than
Na
ions,
leak
back
across
the
K
K
protein
ions
+
+
so
+
K
+
K
membrane
+
faster
than
Na
ions.
As
a
result,
cytoplasm
the
+
Na
concentration
gradient
across
the
▲
Figure 5 The resting potential is generated by the sodium–potassium pump
+
membrane
creating
In
●
a
is
steeper
charge
addition
negatively
to
than
the
K
gradient,
imbalance.
this,
there
charged
are
(organic
proteins
anions),
inside
which
the
nerve
increases
bre
the
that
are
charge
imbalance.
These
factors
about
70
together
give
the
neuron
a
resting
membrane
potential
of
mV
.
Actin tentias
An action potential consists of depolarization and
repolarization of the neuron.
An
of
action
two
potential
is
a
rapid
change
in
membrane
potential,
consisting
phases:
●
depolarization
●
repolarization
Depolarization
is
–
–
a
a
due
change
change
to
the
from
back
negative
from
opening
of
to
positive
positive
sodium
to
negative.
channels
in
the
+
membrane,
allowing
Na
ions
to
diffuse
into
the
neuron
down
the
+
concentration
imbalance
the
across
outside.
about
+30
gradient.
This
the
The
entry
membrane,
raises
the
of
so
Na
the
membrane
ions
inside
reverses
is
potential
the
positive
to
a
charge
relative
positive
to
value
of
mV
.
321
6
H u m a n
p H ys i o l o g y
uid outside neuron
uid outside neuron
+
+
+
Na
Na
Na
+
+
Na
Na
+
channel
+
+
K
+
K
K
+
channel
+
K
Na
+
K
K
open
+
+
closed
Na
Na
+
Na
+
Na
+
+
Na
Na
+
+
+
+
Na
K
K
K
+
K
+
K
+
K
+
Na
+
+
+
Na
/K
+
/K
Na
pump
pump
+
+
+
K
+
+
K
Na
+
Na
K
+
K
+
Na
-
Na
-
channel
+
+
Na
K
+
+
+
K
+
closed
K
+
K
Na
Na
+
-
-
-
-
+
-
+
+
K
-
Na
K
K
-
-
+
+
-
K
+
-
-
+
+
+
+
Na
-
+
+
+
-
-
Na
K
+
+
K
Na
+
+
+
Na
K
-
+
Na
+
-
K
+
K
K
Na
+
K
-
-
+
K
K
K
Na
K
+
K
+
K
+
+
K
K
protein
Na
protein
+
+
Na
K
cytoplasm
cytoplasm
▲
open
+
-
K
K
+
channel
Figure 6 Neuron depolarizing
Figure 7 Neuron repolarizing
▲
Repolarization
to
the
closing
channels
in
out
of
the
the
inside
the
the
of
the
down
ce l l
channe l s
potential
ra pi dl y
s o di um
me mb r ane.
neuron,
potassium
a
ha p p e ns
of
close
T hi s
thei r
ne g ativ e
r e m a in
to
70
a fte r
de pol a ri z a t io n
channe l s
al l ow s
o pe n in g
pot a s si u m
conce n t r at i on
a ga i n
op en
mV
.
a nd
The
re la t i ve
unt i l
the
diffusi o n
and
of
io ns
gr a di en t ,
to
the
d ue
to
diffu s e
w h ic h
out s ide .
mem bra n e
of
is
pot a s si u m
has
pota ss ium
m a ke s
T he
fa l le n
to
re p ola r iz e s
impulse movement
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
the
neuron,
but
it
does
not
r e stor e
the
re s t in g
p ote n t ia l
as
the
cell membrane
A
concentration
gra d i e nts
of
s od ium
a nd
p ot a s si u m
ion s
h a ve
n ot
y et
cytoplasm
been
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
+
+
+
+
+
–
–
–
–
–
B
then
re-established .
transmit
T hi s
ano the r
tak e s
ne rv e
a
few
m il li s ec o n ds
and
t he
neu r on
c an
imp ul se .
+
Na
praatin f actin tentias
+
+
+
+
–
–
C
Nerve impulses are action potentials propagated along
+
Na
the axons of neurons.
+
K
A
+
+
+
+
+
–
+
+
–
D
–
+
nerve
impulse
is
an
action
potential
that
starts
at
one
end
other
end
of
of
a
neuron
+
–
–
and
is
then
propagated
The
propagation
along
the
axon
to
the
the
neuron.
+
Na
movements
+
that
of
the
action
depolarize
potential
one
part
of
happens
the
because
neuron
the
trigger
ion
depolarization
K
+
+
+
–
–
–
+
+
+
in
–
–
–
+
E
+
+
–
–
the
neighbouring
part
of
the
neuron.
–
+
Na
Nerve
▲
Figure 8 Action potentials are propagated
along axons
322
impulses
and
other
one
terminal
always
vertebrates.
of
a
move
This
neuron
is
in
one
direction
because
and
can
an
only
along
impulse
be
passed
neurons
can
on
only
to
in
be
other
humans
initiated
neurons
at
or
6 . 5
different
after
a
cell
types
at
depolarization
backwards
along
an
the
other
that
terminal.
prevents
Also,
there
propagation
of
is
an
a
n e u r o n S
refractive
action
a n D
S y n a p S e S
period
potential
acv
axon.
ns   s 
d  s
lca currents
Anemonesh have a nervous
system similar to ours, with a
Propagation of nerve impulses is the result of local
central nervous system and
currents that cause each successive par t of the axon to
neurons that transmit nerve
impulses in one direction
reach the threshold potential.
only. Sea anemones have
The
propagation
of
an
action
potential
along
an
axon
is
due
to
no central nervous system.
movements
of
sodium
ions.
Depolarization
of
part
of
the
axon
is
due
to
Their neurons form a simple
diffusion
of
sodium
ions
into
the
axon
through
sodium
channels.
This
network and will transmit
reduces
the
concentration
of
sodium
ions
outside
the
axon
and
increases
impulses in either direction
it
inside.
The
depolarized
part
of
the
axon
therefore
has
different
sodium
along their nerve bres. They
ion
concentrations
to
the
neighbouring
part
of
the
axon
that
has
not
yet
both protect each other from
depolarized.
As
a
result,
sodium
ions
diffuse
between
these
regions
both
predators more eectively
inside
and
Inside
the
outside
the
axon.
than they can themselves.
axon
depolarized
to
the
part
the
that
are
currents
has
not
is
the
part
shown
reduce
yet
a
higher
axon
part
gradient
polarized
movements
Local
of
neighbouring
concentration
from
there
that
is
in
in
sodium
is
still
the
back
the
so
sodium
to
ions
gure
part
10.
This
diffuse
that
has
are
the
so
in
in
the
inside
the
axon
sodium
just
called
gradient
makes
along
Outside
direction
They
concentration
depolarized.
concentration
polarized.
opposite
the
ion
the
diffuse
These
currents.
part
membrane
axon
the
ions
depolarized.
local
Explain how they do this.
the
of
the
potential
neuron
rise
from
▲
the
resting
potential
of
70mV
to
about
50
mV
.
Sodium
channels
in
Figure 9 Anemonesh among
the
the tentacles of a sea anemone
axon
of
membrane
50mV
Opening
Thus
is
of
local
a
voltage-gated
reached.
the
to
hundred
This
sodium
currents
repolarization
and
are
(or
therefore
channels
cause
be
is
a
open
of
as
a
the
per
membrane
threshold
potential
potential.
depolarization.
depolarization
along
metres
when
known
causes
wave
propagated
more)
and
the
axon
at
and
a
then
rate
of
between
one
second.
impulse movement
+
N
a
di us
io
n
outside
inside
membrane
N
a
▲
+
dius
n
o
par t that has just depolarized
par t that has not yet depolarized
(action potential)
(resting potential)
Figure 10 Local currents
323
6
H u m a n
p H ys i o l o g y
action potential peak
Anasin scisce traces
ira
taz
noi
noi
taz
0
Analysis of oscilloscope traces showing resting
ope
er
lop
iral
d
ecnereid laitnetop
)Vm( enarbmem ssorca
+35
potentials and action potentials.
Membrane
threshold potential
potenti a l s
in
ne ur ons
ca n
be
m e a su r e d
by
pla c i n g
50
electrodes
on
each
side
of
the
me m br a n e.
The
po t en t i al s
can
be
70
displayed
resting potential
using
an
o s ci ll os co pe .
Th e
di s pla y
is
s im il a r
to
a
g ra ph
undershoot
with
0
1
2
3
4
5
6
time
on
the
x-axis
a nd
the
me mbr an e
p ot e n t ia l
on
the
y -a xi s .
7
If
there
is
a
resting
p o te nti a l,
a
hor iz on t al
li ne
ap pe a rs
on
the
time/ms
oscilloscope
stimulus
▲
Figure 11 Changes in membrane polarity
resting
screen
potential
at
of
a
l ev el
of
70
mV
,
assuming
tha t
this
is
the
the  ne ur on.
during an action potential
If
an
action
potential
and
falling
The
oscilloscope
the
phases
70
mV
changes
showing
trace
depolarization
repolarization
occurs,
until
does
not
immediately
gradually
may
narrow
the
show
the
threshold
usually
is
seen,
is
a
resting
and
the
is
with
rising
in
potential
which
is
rising
before
reached.
membrane
phase
the
repolarization.
potential
potential
return
there
the
spike
depolarization
also
the
and
until
a
The
potential
the
to
potential
reached.
D-sd qss: Analysing an oscilloscope trace
The
a
oscilloscope
digital
in
a
trace
oscilloscope.
mouse
in
It
gure
shows
hippocampal
12
an
was
taken
action
pyramidal
from
1
potential
neuron
pulse
of
after
the
neuron
was
stimulated
the
resting
hippocampal
potential
pyramidal
of
the
mouse
neuron.
[1]
that
2
happened
State
with
Deduce
with
a
reason
the
threshold
a
potentialneeded
to
open
sodium
in
this
voltage-gated
current.
3
channels
Estimate
the
time
)Vm( egatlov enarbmem
depolarization,
neuron.
taken
and
the
for
[2]
the
repolarization.
[2]
50
4
Predict
the
time
depolarization
taken
for
the
from
the
resting
end
of
the
potential
0
to
be
regained.
[2]
resting potential
5
Discuss
how
many
action
potentials
50
could
be
stimulated
per
second
in
this
neuron.
0
50
[2]
100
6
time (ms)
Suggest
a
potential
▲
reason
rising
for
the
briey
at
membrane
the
end
of
the
Figure 12
repolarization.
[1]
Snases
Synapses are junctions between neurons and between
neurons and receptor or eector cells.
Synapses
are
there
synapses
the
are
brain
neurons.
324
junctions
and
In
between
between
spinal
muscles
cord
and
cells
sensory
there
are
glands
in
the
nervous
receptor
immense
there
are
cells
system.
and
numbers
synapses
In
sense
neurons.
of
In
synapses
between
organs
both
between
neurons
and
6 . 5
muscle
bres
effectors,
Chemicals
synapses.
and
or
secretory
because
they
called
This
only
cannot
about
20
Muscles
(carry
out)
neurotransmitters
system
post-synaptic
impulses
cells.
effect
is
cells
pass
nm
used
are
at
all
This
a
are
glands
used
by
gap
is
are
response
synapses
separated
across.
and
a
to
to
the
a n D
S y n a p S e S
called
stimulus.
signals
the
uid-lled
called
sometimes
a
send
where
n e u r o n S
across
pre-synaptic
gap,
so
synaptic
electrical
cleft
and
is
wide.
Snatic transissin
When pre-synaptic neurons are depolarized they release
▲
Figure 13 Electron micrograph of a synapse.
a neurotransmitter into the synapse.
False colour has been used to indicate the
Synaptic
transmission
occurs
very
rapidly
as
a
result
of
these
events:
pre-synaptic neuron (purple) with vesicles of
neurotransmitter (blue) and the post-synaptic
A
●
nerve
impulse
is
propagated
along
the
pre-synaptic
neuron
neuron (pink). The narrowness of the synaptic
until
it
reaches
the
end
of
the
neuron
and
the
pre-synaptic
cleft is visible
membrane.
Depolarization
●
of
the
pre-synaptic
membrane
causes
pre-synaptic cell
nerve
2+
calcium
ions
membrane
Inux
●
of
(Ca
into
)
the
calcium
neurotransmitter
membrane
and
to
diffuse
through
channels
in
impulse
the
neuron.
causes
to
vesicles
move
fuse
with
to
containing
the
2+
pre-synaptic
Ca
it.
diuses
into knob
synaptic knob
synaptic vesicles
Neurotransmitter
●
is
released
into
the
synaptic
cleft
by
exocytosis.
pre-synaptic
The
●
neurotransmi tte r
cleft
and
binds
to
d i ffus es
r e ce p tor s
acr os s
on
the
the
s y n ap t ic
membrane
neurotransmitter
pos t - syn a pt ic
(e.g. acetylcholine)
membrane.
synaptic cleft
neurotransmitter
The
●
binding
causes
●
of
the
adjacent
neurotransmitter
sodium
Sodium
ions
into
post-synaptic
the
synaptic
diffuse
membrane
ion
down
channels
their
neuron,
to
to
reach
the
to
open.
concentration
causing
the
20nm approximately
receptors
the
threshold
gradient
ion channel opened
post-
potential.
post-synaptic
membrane
An
●
action
potential
membrane
and
is
is
triggered
propagated
in
on
the
post-synaptic
along
the
neuron.
post-synaptic cell
The
●
neurotransmitter
removed
from
the
is
rapidly
synaptic
broken
down
and
cleft.
▲
Figure 14 A ner ve impulse is propagated across a synapse by the
release, diusion and post-synaptic binding of neurotransmitter
D-sd qss: Parkinson’s disease
Dopamine
that
are
is
used
Parkinson’s
one
at
of
the
many
synapses
disease,
in
there
is
neurotransmitters
the
a
brain.
loss
of
In
metabolic
and
neurons,
initiating
in
many
which
movement,
cases
causes
muscular
shaking.
slowness
rigidity
Figure15
of
involved
in
the
formation
dopamine.
dopamine1
secreting
pathways
breakdown
Explain
how
symptoms
of
Parkinson’s
disease
in
are
relieved
a)
L-DOPA
by
giving
the
following
drugs:
and
shows
the
[1]
325
6
H u m a n
b)
p H ys i o l o g y
selegeline,
which
is
an
inhibitor
of
tyrosine
tyrosine
L-DOPA
COOH
COOH
monoamine
oxidase-B
(MAO-B)
hydroxylase
[1]
CH
CH
HO
CH
2
c)
tolcapone,
which
is
an
2
inhibitor
NH
NH
(FOOD)
of
catechol-O-methyl
2
2
COMT
transferase
dopa
(COMT)
d)
dopamine
[1]
ropinirole,
which
is
an
agonist
CH
CH
CH
of
3
dopamine
decarboxylase
COOH
2
2
NH
2
2
NH
[1]
2
HO
HO
e)
sanamide,
of
which
dopamine
by
inhibits
MAO-B
reuptake
O
pre-synaptic
C
2
neurons.
[1]
H
aldehyde
2
Discuss
how
a
cure
for
Parkinson’s
disease
dehydrogenase
might
in
the
future
be
developed
by:
COMT
CH
O
CH
3
a)
stem
cell
therapy
b)
gene
therapy.
CH
2
COOH
2
[3]
HO
HO
[2]
Figure 15 The formation and breakdown of L
-DOPA and
▲
dopamine. The enzymes catalysing each step are shown in red
Acetchine
Secretion and reabsorption of acetylcholine by neurons
at synapses.
Acetylcholine
including
in
the
diet,
choline
The
used
synapses
with
an
during
binding
group
loaded
synaptic
receptors
site
for
to
the
neuron
acetyl
is
as
neurotransmitter
between
pre-synaptic
acetylcholine
cleft
is
neurons
by
produced
into
and
combining
vesicles
many
muscle
It
is
absorbed
aerobic
then
synapses,
bres.
choline,
during
and
in
produced
from
respiration.
released
into
the
the
The
synaptic
transmission.
acetylcholine
which
in
the
acetylcholine
post-synaptic
will
bind.
The
membrane
have
acetylcholine
a
only
acetyl group
remains
▲
Figure 16 Acetylcholine
one
action
because
cleft
The
bound
acetyl
enzyme
rapidly
choline
converted
the
potential
the
and
to
is
is
receptor
initiated
breaks
into
in
a
short
the
acetylcholine
into
active
the
time,
during
post-synaptic
acetylcholinesterase
reabsorbed
back
for
is
present
down
into
pre-synaptic
neurotransmitter
by
which
neuron.
in
the
choline
neuron,
only
This
is
synaptic
and
acetate.
where
recombining
it
it
is
with
group.
Nenictinids
Blocking of synaptic transmission at cholinergic
synapses in insects by binding of neonicotinoid
pesticides to acetylcholine receptors.
Neonicotinoids
bind
to
central
326
the
are
synthetic
acetylcholine
nervous
system
compounds
receptor
of
insects.
in
similar
cholinergic
to
nicotine.
synapses
Acetylcholinesterase
in
does
They
the
not
an
6 . 5
break
down
receptors
neonicotinoids,
are
blocked,
so
so
the
binding
acetylcholine
is
is
irreversible.
unable
to
bind
n e u r o n S
a n D
The
S y n a p S e S
acv
and
rsc ds 
synaptic
transmission
is
prevented.
The
consequence
in
insects
is
cds
paralysis
and
death.
Neonicotinoids
are
therefore
very
effective
There are currently
insecticides.
intense research eor ts
One
of
the
advanta g e s
of
ne oni co ti n oid s
as
pe s tic i de s
is
t h at
t h ey
to try to discover whether
are
not
highly
tox i c
to
huma ns
a nd
ot h e r
m a m m a ls .
Th i s
is
be c a u se
neonicotinoids are to blame
a
much
greater
pr o p o r ti on
of
sy na ps es
in
t he
cen t r a l
n er vou s
for collapses in honeybee
system
are
choline r g i c
in
i ns e cts
tha n
in
m am m al s
and
a l so
be c a us e
colonies. What are the most
neonicotinoids
bind
much
l es s
str ongl y
to
a c e t yl c h ol in e
re c e pt or s
in
recent research ndings
mammals
than
ins e cts .
and do they suggest that
Neonicotinoid
pes ti ci d e s
particular
neoni cotinoi d,
one
insecticide
the
insects.
the
in
effects
of
the
There
evidence
government
world.
thes e
has
of
are
no w
been
Howe ve r,
on
h u g e a re a s
d is pute d
is
conc e r n s
by
c ro ps .
mos t
wid e ly
h ave
be en
ra i se d
and
con t r over s y
the
of
the
ho ne ybee s
consi de ra ble
is
on
i midaclo pr id,
i ns e ctici de s
ha r m
us e d
ot h e r
ove r
us ed
be banned?
a bo u t
b en e c ia l
t h is
ma n u fa c t u r er s
these insecticides should
In
and
and
so m e
agenci e s .
Threshd tentias
▲
Figure 1
7 Research has
shown that the neonicotinoid
A nerve impulse is only initiated if the threshold
pesticide imidacloprid reduces
potential is reached.
Nerve
impulses
initiated
do
if
the
follow
voltage-gated
opening
of
some
start
channels
and
positive
At
membrane
therefore
a
synapse,
always
the
depolarization
the
threshold
The
that
of
a
pumps
effect.
full
of
to
be
and
open,
causing
inward
more
action
only
this
is
of
sodium
channels
potential
is
only
potential
depolarization.
diffusion
sodium
threshold
potential
at
to
The
ions
open
reached
–
there
depolarization.
membrane
reached
does
in
not
post-synaptic
the
the
An
because
neurotransmitter
membrane
the
to
the
causing
If
pre-synaptic
potential
entered
potassium
be
amount
the
post-synaptic
have
potential
feedback
principle.
reached,
channels
the
will
is
sodium
there
a
all-or-nothing
potential
sodium
increases
is
an
threshold
growth of bumblebee colonies
the
then
neuron
post-synaptic
secreted
may
not
following
be
post-synaptic
depolarize.
are
to
cause
membrane.
The
pumped
membrane
enough
sodium
out
returns
by
to
ions
sodium–
the
resting
potential.
A
typical
not
just
post-synaptic
with
necessary
time
for
for
the
be
initiated
be
used
help
in
to
one
but
several
with
of
threshold
in
the
process
neuron
in
many
these
to
potential
post-synaptic
information
the
brain
or
pre-synaptic
release
to
be
cord
neurons.
It
neurotransmitter
reached
neuron.
from
spinal
This
different
and
type
a
has
may
at
nerve
of
synapses
be
the
same
impulse
mechanism
sources
in
the
to
can
body
to
decision-making.
327
6
H u m a n
p H ys i o l o g y
Research int er and earnin
Cooperation and collaboration between groups of
scientists: biologists are contributing to research into
memory and learning.
Higher
only
functions
partly
actively.
but
being
science
▲
have
used
are
medicine,
the
understood
They
increasingly
are
of
also
at
including
present
traditionally
the
to
brain
techniques
unravel
making
the
and
been
of
and
are
being
and
molecular
work.
contributions,
computer
by
biology
at
learning
researched
investigated
mechanisms
important
pharmacology
memory
are
very
psychologists
and
biochemistry
Other
branches
including
of
biophysics,
science.
Figure 18 Many synapses are visible in this
The
Centre
for
Neural
Circuits
and
Behaviour
at
Oxford
University
is
scanning electron micrograph between the cell
an
excellent
example
of
collaboration
between
scientists
with
different
body of one post-synaptic neuron and a large
areas
of
expertise.
The
four
group
leaders
of
the
research
team
and
the
number of dierent pre-synaptic neurons (blue)
area
of
science
that
●
Professor
●
Dr
Martin
●
Dr
Korneel
●
Professor
Gero
they
Miesenböck
Booth
Hens
Scott
originally
–
studied
are:
medicine
and
–
engineering
–
chemistry
Waddell
–
and
and
optical
physiology
microscopy
biochemistry
genetics,
molecular
biology
and
neurobiology.
The
centre
Neurons
specializes
are
transmission
genetically
or
an
brain
tissue
visible.
in
brain
tissue
respond
There
that
are
are
to
allows
be
many
there
group
to
research
is
a
element
to
national
boundaries.
of the cerebrum—the folded upper par t of
undoubtedly
328
scientic
be
of
groups
memory,
sometimes
make
Figure 19 Memory and learning are functions
countries
patterns
They
to
a
emit
making
are
light
activity
optogenetics.
in
synaptic
specic
engineered
signal
in
as
during
activity
also
light
known
the
with
an
neurons
so
specic
action
of
living
studied.
investigating
Although
rst
This
to
potential,
in
tissue
techniques
engineered
action
neurons
brain
the brain
research
neurons
potential.
▲
in
the
research.
there
This
in
the
and
is
world.
brain
between
also
extends
of
throughout
other
a
across
many
of
world
to
be
the
collaborative
scientic
how
groups
the
functions.
scientists
strongly
understanding
achievement
throughout
universities
competition
discovery,
Success
in
learning
the
disciplines
brain
scientists
works
in
and
will
many
6 . 6
h o r m o n e S ,
h o m e o S t a S i S
a n D
r e p r o D u C t i o n
6.6 hs, sss d dc
Understandin
Aicatins
Insulin and glucagon are secreted by α and
➔
Causes and treatment of type I and type II
➔
β cells in the pancreas to control blood glucose
diabetes.
concentration.
Testing of leptin on patients with clinical
➔
Thyroxin is secreted by the thyroid gland to
➔
obesity and reasons for the failure to control
regulate the metabolic rate and help control
the disease.
body temperature.
Causes of jet lag and use of melatonin to
➔
Leptin is secreted by cells in adipose tissue
➔
alleviate it.
and acts on the hypothalamus of the brain to
The use in IVF of drugs to suspend the
➔
inhibit appetite.
normal secretion of hormones, followed
Melatonin is secreted by the pineal gland to
➔
by the use of ar ticial doses of hormones to
control circadian rhythms.
induce superovulation and establish
A gene on the Y chromosome causes
➔
a pregnancy.
embryonic gonads to develop as testes and
William Har vey’s investigation of sexual
➔
secrete testosterone.
reproduction in deer.
Testosterone causes prenatal development
➔
of male genitalia and both sperm production
Skis
and development of male secondary sexual
characteristics during puber ty.
➔
➔
Annotate diagrams of the male and female
Estrogen and progesterone cause prenatal
reproductive system to show names of
development of female reproductive organs
structures and their functions.
and female secondary sexual characteristics
during puber ty.
Nature f science
The menstrual cycle is controlled by negative
➔
➔
and positive feedback mechanisms involving
Developments in scientic research follow
improvements in apparatus: William Har vey
ovarian and pituitary hormones.
was hampered in his obser vational research
into reproduction by lack of equipment. The
microscope was invented 17 years after
his death.
Cntr f bd ucse cncentratin
Insulin and glucagon are secreted by α and β cells in the
pancreas to control blood glucose concentration.
Cells
the
in
the
glucose
pancreas
respond
concentration
to
changes
deviates
in
blood
substantially
glucose
from
the
levels.
set
If
point
of
1
about
5
mmol
hormones
L
insulin
,
homeostatic
and
glucagon
mechanisms
are
mediated
by
the
pancreatic
initiated.
329
6
H u m a n
p H ys i o l o g y
The
is
pancreas
exocrine
leading
called
to
islets
of
small
directly
Alpha
(α
level
breakdown
the
Beta
●
▲
blood,
Figure 1 Fluorescent light micrograph of the
cells
glucose
tissue
into
falls
blood
below
glycogen
cells)
the
digestive
small
stream.
and
set
Most
the
The
of
enzymes
regions
of
pancreas
two
secrete
point.
glucose
cell
the
into
pancreas
ducts
endocrine
that
tissue
secrete
types
in
the
islets
glucagon
This
in
if
hormone
liver
cells
the
blood
stimulates
and
its
release
into
concentration.
synthesize
concentration
are
organ.
hormones.
into
the
one
through
synthesize
increasing
(β
dotted
the
in
secretes
There
different
cells)
of
glands
that
intestine.
secrete
cells
glucose
two
Langerhans
Langerhans
●
effectively
glandular
the
hormones
of
is
rises
insulin
above
and
the
secrete
set
point.
it
when
This
the
blood
hormone
pancreas showing two islets of Langerhans
stimulates
uptake
of
glucose
by
various
tissues,
particularly
skeletal
surrounded by exocrine gland tissue. Alpha
muscle
and
liver,
in
which
it
also
stimulates
the
conversion
of
cells in the islets are stained yellow and beta
glucose
to
glycogen.
Insulin
therefore
reduces
blood
glucose
cells are stained red
concentration.
cells
it
acts
within
Like
upon,
minutes
so
of
most
its
hormones,
secretion
eating
and
insulin
must
may
be
is
broken
ongoing.
continue
for
down
by
Secretion
several
the
begins
hours
after
ameal.
Diabetes
Causes and treatment of type I and type II diabetes.
Diabetes
is
the
consistently
during
of
glucose
also
it
is
in
If
in
impairs
drinks,
There
the
of
whether
are
two
body
urinate
feels
for
have
main
their
in
urine
an
and
craves
in
and
this
the
years.
while
Until
is
but
the
of
prolonged
to
and
diabetes.
lack
factors
The
last
in
that
treatment
go
the
affect
of
in
over
are
due
65s.
not
two
is
to
are
a
slow
for
this
many
form
under
The
well
50
causes
of
and
of
understood
sugary,
habitual
together
energy
the
people
of
glucose
decades,
factors
exercise,
or
Onset
unnoticed
few
diabetes
obesity
of
cells.
rare
risk
because
receptors
may
very
main
insulin
target
the
only
form
to
insulin
on
was
common
this
disease:
of
disease
diabetes
increase
urine
respond
transporters
sugary
the
or
deciency
proteins.
frequently,
glucose
of
even
presence
elevated
from
developed
types
process
dehydration.
more
tired
test
they
the
resulting
and
has
levels
to
particularly
kidney,
should
person
glucose
leading
reabsorption
urine
to
a
Continuously
tissues,
thirsty,
they
blood
urine.
needs
constantly
where
fasting,
water
in
volume
person
check
the
damages
forming
the
a
elevated
prolonged
glucose
It
condition
fatty
diets,
overeating
with
genetic
metabolism.
types
of
diabetes
is
different:
●
Type
I
diabetes,
characterized
sufcient
destruction
causes
are
In
by
the
and
usually
of
still
beta
children
severe
disease
inability
this
being
of
disease
of
Langerhans
more
early-onset
an
quantities
autoimmune
system.
or
by
insulin.
arising
cells
in
body’s
and
start
●
an
Type
too
people
food
the
of
suddenly.
the
The
diseases
researched.
last
can
Type
II
diabetes,
sometimes
called
is
characterized
by
an
and
too
a
because
in
the
high
are
it
or
often
of
insulin
blood.
is
testing
likely
blood
to
become
before
glucose
Timing
is
a
as
the
very
do
not
treatments
are
implanted
insulin
necessary.
blood
injecting
molecules
Better
using
the
and
done
absorbed.
exogenous
when
by
regularly
peak
and
developed
A
devices
into
the
that
blood
permanent
cure
late-onset
inability
be
achievable
by
coaxing
stem
cells
to
to
become
330
is
digested
release
may
diabetes,
it
prevent
long
being
treated
Injections
important
as
●
when
to
is
is
concentration
high.
meal
autoimmune
diabetes
insulin
of
immune
symptoms
I
glucose
the
islets
own
rather
other
is
from
the
is
produce
It
young
obvious
and
diabetes,
to
fully
functional
replacement
beta
cells.
6 . 6
●
Type
diet
II
to
diabetes
reduce
glucose.
eaten
Small
Foods
avoided.
treated
peaks
amounts
frequently
meals.
be
is
the
rather
with
high
Starchy
by
adjusting
and
of
troughs
food
than
should
content
should
h o m e o S t a S i S
the
of
blood
be
infrequent
sugar
food
h o r m o n e S ,
be
it
it
is
be
large
has
r e p r o D u C t i o n
low
included
are
eaten
a
digested
foods.
should
only
if
a n D
glycemic
slowly.
to
slow
Strenuous
benecial
as
index,
indicating
High-bre
the
digestion
exercise
they
foods
and
improve
of
that
should
other
weight
insulin
loss
uptake
andaction.
D-sd qss: The glucose tolerance test
acv
The
glucose
tolerance
test
is
a
method
used
to
diagnose
diabetes.
Fds f  ii dcs
In
this
test,
the
patient
drinks
a
concentrated
glucose
solution.
The
Discuss which of the foods
blood
glucose
concentration
is
monitored
to
determine
the
length
of
in gure 2 are suitable for a
time
required
for
excess
glucose
to
be
cleared
from
theblood.
person with type II diabetes.
mc 001 gm / noitartnecnoc
3–
400
They should be foods with a
350
low glycemic index.
300
250
diabetic
200
150
unaected
100
50
0
0
0.5
1
2
3
4
5
time after glucose ingestion / h
▲
Figure 3 A person with diabetes and an unaected person
give very dierent responses to the glucose tolerance test
With
reference
metabolism
a)
The
to
to
gure
the
concentration
consumption
of
of
3,
person
b)
The
length
c)
The
maximum
d)
The
time
of
the
time
glucose
required
at
person
with
time
with
normal
respect
zero,
i.e.
glucose
to:
before
the
drink.
to
level
glucose
the
diabetes
glucose
glucose
before
compare
with
return
to
the
level
at
time
zero.
▲
reached.
levels
start
to
Figure 2
fall.
t
Thyroxin is secreted by the thyroid gland to regulate the
metabolic rate and help control body temperature.
The
hormone
chemical
atoms
of
prevents
almost
structure
iodine.
the
all
metabolic
active,
Higher
and
it
in
rate,
such
is
as
so
metabolic
all
of
as
the
cells
are
to
and
supports
generation
more
in
hormone
Thyroxin
are
but
the
protein
body
gland
heat.
so
the
is
the
a
also
most
Its
four
therefore
unusual
as
body’s
metabolically
targets.
and
person
secretion
body
neck.
contains
diet
synthesis
In
the
regulatesthe
main
thyroxin
production
in
molecule
iodine
respond
increased
heat
of
This
brain
of
thyroid
thyroxin
targets.
need
triggers
the
deciency
muscle
stimulates
by
thyroxin.
body
rate
the
cooling
which
secreted
unusual
the
liver,
increases
is
Prolonged
synthesis
cells
physiology,
gland,
thyroxin
growth
with
by
normal
the
temperature
thyroid
rises.
331
6
H u m a n
p H ys i o l o g y
Thyroxin
thus
regulates
the
metabolic
rate
and
also
helps
to
control
bodytemperature.
The
importance
deciency
●
lack
of
energy
●
forgetfulness
●
weight
gain
broken
▲
of
thyroxin
is
revealed
by
the
effects
of
thyroxin
(hypothyroidism):
and
and
feeling
to
all
the
time
depression
despite
down
tired
loss
of
release
appetite
energy
by
as
less
cell
glucose
and
fat
are
being
respiration
Figure 4 Structure of thyroxin with atoms of
●
feeling
cold
all
●
constipation
the
time
because
less
heat
is
being
generated
iodine shown purple
slow
impaired
●
because
contractions
of
muscle
in
the
wall
of
the
gut
down.
brain
development
in
children.
letin
Leptin is secreted by cells in adipose tissue and acts on
the hypothalamus of the brain to inhibit appetite.
Leptin
The
the
is
a
amount
groups
of
control
cells.
of
If
The
inactive
They
type
mice
and
had
of
new
Leptin
a
body
Figure 5 Mouse with obesity due to lack of
were
injected
leptin and a mouse with normal body mass
increased
of
that
recessive
with
and
weight,
a
ob
body
about
allele
was
mass
of
that
in
food
feed
ob.
In
by
by
showed
the
early
of
is
the
these
causing
with
that
in
a
tissue.
wild
the
1990s
When
energy
with
become
adipose
the
cells
leptin.
a
to
rise,
research
compared
Adipose
in
and
hormone
membrane
increased
declined,
30 %
cells).
intake
contribute
supported
produce
appetite
this
ravenously,
experiments
leptin.
storage
food
intake.
grams,
gene
by
of
that
the
(fat
concentrations
through
100
allele,
cannot
dropped
brain
leptin
this
named
their
target
demonstrated
1950s
Breeding
alleles
the
cells
controlled
The
reduced
recessive
leptin
of
mainly
of
is
receptors
was
the
weight
wild-type
hormone
two
in
to
adipose
body.
blood
and
system
grams.
copies
the
binds
by
blood
the
increases,
this
body
the
in
inhibition
20–25
have
tissue
discovered
two
that
of
secreted
in
hypothalamus
tissue
gain
to
leptin
the
appetite
grow
shown
of
appetite.
mice
mice
▲
in
adipose
of
hormone
adipose
importance
strain
a
of
cells
long-term
of
protein
concentration
it
obese
was
synthesis
mice
that
ob/ob
mice
expenditure
month.
letin and besit
Testing of leptin on patients with clinical obesity and reasons for the failure
to control the disease.
The
by
a
discovery
lack
soon
this
in
led
to
way.
to
that
leptin
obesity
and
attempts
Amgen,
California,
rights
332
of
paid
leptin
a
to
treat
mice
by
a
obesity
million
large
could
leptin
biotechnology
$20
and
in
cured
for
clinical
be
caused
injections
in
humans
company
the
in
based
commercial
trial
was
carried
out.
Seventy-three
themselves
or
with
used,
so
knew
were
a
either
placebo.
neither
who
was
analysed.
obese
with
A
the
volunteers
one
double
of
blind
researchers
injecting
injected
several
leptin
leptin
procedure
nor
until
the
the
doses
was
volunteers
results
6 . 6
The
leptin
swelling
The
7.1
a
eight
kg
loss
injections
and
of
of
only
patients
body
1.3
injecting
the
receiving
in
on
the
the
highest
volunteers
dose
the
in
the
results
tissue
lost
with
of
inevitably
fails
are
group
from
a
loss
of
15
kg
to
a
gain
of
5
body
mass
lost
during
the
trial
was
rapidly
are
afterwards.
frequent
in
Such
drug
kg.
very
mice
of
humans
and
other
is
small
are
contrast
humans
leptin
to
have
ob/ob
to
concentrations.
leptin
so
fail
to
concentrations.
and
food
most
The
have
–
high
in
many
obesity
insulin
prevents
extra
if
the
leptin
cause
injections
early-stage
type
II
is
alone
diabetes.
to
of
cases
mutations
in
of
obesity
the
genes
in
or
its
various
receptors
on
for
target
Trials
in
people
weight
with
loss
such
while
obesity
the
leptin
have
shown
injections
ways
continuing.
to
is
cells
it,
even
More
and
and
However
in
shown
the
of
at
leptin
inhibited
of
adipose
to
be
to
have
leptin
injected
affect
in
has
the
children
not
solving
the
most
refused
reproductive
suitable
high
not
the
has
consequently
treatment
resistant
therefore
excessive.
day
blood
target
respond
is
of
the
obese
become
Appetite
intake
leptin
disappointing
research
different
mice,
may
blood
is
a
short-lived
rodents.
exceptionally
hypothalamus
as
proportion
due
synthesis
protein
In
with
in
resistance
Injection
control
just
rise
usually
are
from
to
a
leptin
Also
signicant
physiology
appetite.
ineffective
cells.
outcomes
the
very
leptin
regained
causing
resistance,
humans
any
r e p r o D u C t i o n
but
inhibition
A
widely
develops,
leptin
were
varied
a n D
concentration
trial.
dose
who
h o m e o S t a S i S
and
the
compared
However,
highest
irritation
completed
average
12
placebo.
the
skin
patients
receiving
mass
kg
induced
47
h o r m o n e S ,
it.
several
of
those
Also
leptin
development
system,
and
fullled
human
so
young
its
early
obesity
times
a
offered
and
has
functioning
injections
adults.
this
been
are
All
promise
as
in
a
not
all
means
problem.
meatnin
Melatonin is secreted by the pineal gland to control
circadian rhythms.
Humans
are
behaviour
They
can
the
Circadian
light
daily
the
of
evening
rapidly
The
most
night.
night.
time
drop
the
drops
the
obvious
levels
in
core
kidney,
a
24-hour
are
person
is
because
cycle
known
placed
an
and
as
have
rhythms
circadian
system
in
rhythms.
experimentally
internal
to
grown
brain
a
low
by
body
and
of
two
the
at
dawn
liver,
changes
of
is
is
no
in
used
as
to
as
Melatonin
of
the
increases
the
the
cells
cues
set
about
hormone
in
hormone
concentrations
the
sleep-wake
and
the
is
rise
rapidly
and
fall
at
blocking
the
the
rise
during
have
in
production
at
end
to
through
of
the
the
night-
melatonin
the
been
High
sleep
contributes
articially
urine
cycle.
promote
waking
receptors
decreased
in
secretion.
melatonin
melatonin
cells
These
external
secretion
and
encourage
that
of
(SCN).
secretion
blood
in
temperature,
that
the
drowsiness
levels
shown
temperature.
with
control
groups
nuclei
Melatonin
melatonin
giving
suggesting
they
feelings
have
on
culture
level
these
effect
in
gland.
blood
to
depend
suprachiasmatic
melatonin
core
it
if
cause
Falling
reduces
in
a
These
humans
the
the
Experiments
drop
levels
if
pineal
response
melatonin
the
In
the
from
in
in
even
day.
by
and
removed
in
darkness
called
rhythm
time
live
cycle.
even
or
rhythms
melatonin
to
this
rhythm.
hypothalamus
a
t
continue
continuous
control
adapted
that
day
causes
discovered
night
may
a
in
be
▲
another
effect
of
this
Figure 6 Until a baby is about three months old
hormone.
it does not develop a regular day-night rhythm
When
light
humans
cues
are
placed
indicating
the
experimentally
time
of
day,
the
in
an
SCN
environment
and
pineal
without
gland
usually
of melatonin secretion so sleep patterns do
not t those of the baby’s parents
333
6
H u m a n
p H ys i o l o g y
maintain
a
timing
the
day.
of
A
of
rhythm
special
type
wavelength
indicates
to
melatonin
of
rhythm
of
slightly
is
ganglion
460–480
the
SCN
secretion
longer
normally
nm
the
so
cell
and
timing
that
it
than
24
adjusted
in
the
passes
of
hours.
by
a
few
retina
of
impulses
dusk
and
corresponds
to
the
to
dawn
the
This
indicates
minutes
eye
cells
and
that
so
each
detects
light
in
or
the
allows
day-night
SCN.
it
to
This
adjust
cycle.
Jet a and eatnin
Causes of jet lag and use of melatonin to alleviate it.
Jet
has
lag
is
a
common
crossed
three
travel.
The
awake
during
sleeping
to
and
continuing
rather
of
more
to
day
than
are
daylight
understand:
timing
experience
symptoms
through
headaches
or
the
the
hours
night,
set
a
SCN
someone
who
Jet
air
impulses
are
used
gland
rhythm
point
to
of
be
are
suit
the
try
that
it
eastwards
few
is
to
and
days,
cells
detect
regime.
prevent
time
helping
a
ganglion
new
to
the
for
they
commencing.
and
destination.
by
when
at
shown
the
departure
lasts
sent
to
to
orally
easy
only
SCN
adjust
irritability,
causes
lag
the
remaining
difculty
pineal
the
during
in
fatigue,
and
at
and
The
circadian
night
for
zones
difculty
indigestion.
and
the
time
or
when
Most
light
trials
crossing
help
reduce
at
jet
the
jet
is
ve
It
is
melatonin
more
taken
have
sleep
especially
or
to
ideally
promoting
lag,
to
body
sometimes
lag.
should
of
which
retina
the
Melatonin
sleep
effective
reduce
during
in
if
time
ying
zones.
Sex deterinatin in aes
A gene on the Y chromosome causes embryonic gonads to
develop as testes and secrete testosterone.
Human
egg
reproduction
from
embryos
or
a
and
testes.
whole
●
If
the
of
SRY
is
SRY
●
50%
have
of
a
embryos
embryonic
codes
factor).
testis
copy
on
of
develop
pathway
the
present,
located
determining
cause
is
on
fusion
a
for
of
the
the
Y
a
or
sperm
of
that
presence
the
TDF
of
development
gonads
depends
gene
gene
the
the
developmental
baby
embryos.
that
involves
Initially
embryonic
The
the
This
female.
the
could
embryonic
embryonic
the
of
gonads
DNA-binding
a
either
absence
chromosome,
stimulates
from
male
embryo
so
is
is
the
with
become
gonads
an
same
in
all
ovaries
and
thereby
onegene.
develop
only
protein
called
expression
into
present
of
TDF
other
testes.
in
50 %
(testis
genes
development.
have
the
gonads
two
SRY
X
chromosomes
gene.
develop
as
TDF
is
and
therefore
no
not
Y
so
they
produced
do
not
and
the
ovaries.
Teststerne
Testosterone causes prenatal development of male
genitalia and both sperm production and development of
male secondary sexual characteristics during puber ty.
The
of
testes
about
▲
Figure 7 X and Y chromosomes
334
develop
pregnancy,
early
30mm
stage
at
long.
and
from
the
the
time
The
these
embryonic
when
testes
the
develop
produce
gonads
embryo
is
in
about
becoming
the
a
testosterone-secreting
testosterone
until
about
the
eighth
fetus
week
and
cells
at
fteenth
is
an
week
6 . 6
of
pregnancy.
genitalia
At
to
puberty
the
production
males.
During
develop,
in
of
secretion
the
pubic
hair
also
during
and
weeks
are
of
testes,
Testosterone
characteristics
the
which
of
h o r m o n e S ,
secretion,
shown
in
testosterone
which
causes
puberty
deepening
is
the
the
the
testosterone
gure
increases.
primary
as
This
sexual
of
enlargement
voice
due
causes
a n D
r e p r o D u C t i o n
male
8.
development
such
of
h o m e o S t a S i S
to
stimulates
sperm
characteristic
secondary
of
the
growth
penis,
of
the
of
sexual
growth
larynx.
Sex deterinatin in feaes
Estrogen and progesterone cause prenatal development
of female reproductive organs and female secondary
sexual characteristics during puber ty.
If
the
gene
SRY
Ychromosome,
is
therefore
not
progesterone,
by
the
not
the
present
are
always
ovaries
and
the
female
reproductive
During
puberty
the
but
the
include
enlargement
the
organs
of
of
the
in
of
by
female
female
as
the
rst
In
estrogen
and
are
they
the
and
shown
sexual
growth
of
is
no
Testosterone
estrogen
are
of
fetal
progesterone,
in
gure
9.
increases,
characteristics.
pubic
and
secreted
absence
progesterone
secondary
and
At
placenta.
which
there
ovaries.
hormones,
pregnancy.
estrogen
breasts
because
develop
maternal
develop
of
embryo
two
later
presence
development
an
gonads
present
and
secretion
causing
in
embryonic
secreted,
mother’s
testosterone
is
and
These
underarm
hair.
mae and feae rerductive sstes
Annotate diagrams of the male and female reproductive system to show names
of structures and their functions.
The
tables
female
on
the
next
reproductive
page
indicate
systems
are
functions
that
should
be
included
when
diagrams
of
male
and
annotated.
seminal vesicle
bladder
bladder
sperm duct
sperm duct
prostate
seminal vesicle
gland
erectile tissue
prostate gland
penis
penis
epididymis
testis
epididymis
urethra
urethra
scrotum
testis
foreskin
scrotum
▲
Figure 8 Male reproductive system in front and side view
335
6
H u m a n
p H ys i o l o g y
oviduct
ovary
oviduct
opening
to
uterus
uterus
cervix
ovary
oviduct
bladder
vagina
cervix
large
urethra
intestine
vagina
vulva
labia (vulva)
▲
Figure 9 Female reproductive system in front and side view
m dcv ss
Testis
Scrotum
F dcv ss
Produce sperm and testosterone
Ovary
Produce eggs, estrogen and progesterone
Hold testes at lower than core body
Oviduct
Collect eggs at ovulation, provide a site
temperature
for fer tilization then move the embryo to the
uterus
Epididymis
Store sperm until ejaculation
Sperm duct
Transfer sperm during ejaculation
Uterus
Provide for the needs of the embryo and
then fetus during pregnancy
Seminal vesicle
Secrete uid containing alkali,
and prostate
proteins and fructose that is added
Cervix
Protect the fetus during pregnancy and then
dilate to provide a bir th canal
gland
to sperm to make semen
Urethra
Transfer semen during ejaculation
Vagina
Stimulate penis to cause ejaculation and
provide a bir th canal
and urine during urination
Vulva
Penis
Protect internal par ts of the female
Penetrate the vagina for ejaculation
reproductive system
of semen near the cervix
menstrua cce
The menstrual cycle is controlled by negative and
positive feedback mechanisms involving ovarian and
pituitary hormones.
The
menstrual
menopause,
it
gives
called
the
ovary.
lining
most
In
of
chance
each
the
The
second
of
corpus
of
uterus
half
luteum.
because
egg
is
The
a
rst
group
stimulated
(endometrium)
breaks
women
from
pregnancies.
is
open,
Each
half
of
to
puberty
time
of
the
follicles
grow.
repaired
releasing
and
its
occurs
cycle
developing
the
starts
egg
the
cycle
menstrual
is
At
until
the
same
to
into
in
time
thicken.
the
is
the
the
The
oviduct.
degenerate.
of
follicle
most
pregnancy.
an
follicle
follicles
the
a
in
during
phase
follicle
developed
other
occurs
from
follicular
The
wall
336
the
cycle
apart
the
that
cycle
is
called
released
Continued
an
the
egg
luteal
phase
becomes
development
of
the
a
because
body
called
endometrium
the
the
prepares
6 . 6
it
for
the
implantation
of
an
embryo.
h o r m o n e S ,
If
h o m e o S t a S i S
fertilization
does
not
a n D
r e p r o D u C t i o n
occur
TOK
the
corpus
luteum
endometrium
in
in
the
the
ovary
uterus
breaks
also
breaks
down.
The
thickening
down
and
is
shed
of
the
during
t w   d vs 
menstruation.
w jd   f  c?
Figure
10
including
typical
shows
one
for
measured
so
woman
in
mass
progesterone,
estrogen
of
a
the
is
hormone
complete
who
per
FSH
measured
ovary
and
of
levels
is
not
and
the
LH
a
woman
cycle.
The
pregnant.
millilitre.
in
in
menstrual
The
are
The
actual
(pg).
a
36-day
in
of
are
levels
very
nanograms
Figure
10
also
period,
changes
hormone
masses
measured
picograms
over
pattern
Human eggs can be obtained by
is
using FSH to stimulate the ovaries,
are
then collecting eggs from the ovaries
small,
(ng)
shows
using a micropipette. Women have
and
the
sometimes undergone this procedure
state
to produce eggs for donation to
endometrium.
another woman who is unable to
produce eggs herself.
The
four
cycle
by
hormones
both
hormones
receptors
are
in
negative
produced
in
ovarian
gure
the
and
by
the
all
help
positive
of
gland
follicle
produced
to
control
feedback.
pituitary
membranes
hormones,
10
by
cells.
the
FSH
that
the
and
bind
to
Estrogen
wall
of
menstrual
the
LH
are
FSH
and
protein
and
Recently stem-cell researchers have
LH
used eggs in therapeutic cloning
progesterone
follicle
and
corpus
experiments. The nucleus of an egg is
removed and replaced with a nucleus
from an adult. If the resulting cell
developed as an embryo, stem cells
1000
could be removed from it and cloned.
LH
It might then be possible to produce
tissues or organs for transplanting to
600
400
noitaurtsnem
noitaurtsnem
lm gn/ level enomroh
1–
FSH
800
the adult who donated the nucleus.
There would be no danger of tissue
rejection because the stem cells
would be genetically identical to
200
the recipient.
0
There is a shor tage of eggs both
for donation to other women and
for research. In 2006, scientists
in England got permission to oer
to develop
mature
corpus
luteum
8
lm gp/level negortse
1–
400
progesterone
6
300
estrogen
200
4
100
2
women cut-price IVF treatment, if they
lm gn/level enoretsegorp
follicle nearly
1–
follicle starting
were willing to donate some eggs for
research. In Sweden only travel and
other direct expenses can be paid to
egg donors, and in Japan egg donation
is banned altogether.
1
Is there a distinction to be drawn
between donating eggs for
0
26
28
2
4
5
8
10
12
14
16
18
20
22
24
26
28
days of menstrual cycle
4
therapeutic cloning experiments
and donating eggs to a woman
muirtemodne fo ssenkciht
who is unable to produce eggs
ovulation
herself, for example because her
ovaries have been removed? Can
the same act be judged dierently
depending on motives?
28
▲
2
7
14
21
28
Figure 10 The menstrual cycle
337
6
H u m a n
p H ys i o l o g y
luteum.
they
FSH
●
They
rises
and
towards
uid.
FSH
to
the
a
receptive
more
the
LH
rises
to
follicular
a
of
It
in
end
of
the
the
follicles,
partial
follicle
estrogen
Progesterone
and
Progesterone
of
LH
female
body,
where
development.
menstrual
each
cycle
containing
secretion
after
rise
It
of
and
an
oocyte
estrogen
(negative
of
by
the
at
the
to
the
follicle
the
into
a
start
low
of
the
level
thickening
inhibits
FSH
the
and
and
stimulates
end
of
meiosis
allowing
corpus
the
in
it
of
the
to
burst
the
luteum
which
progesterone.
luteal
by
the
and
LH
after
the
production
the
of
wall
make
development
and
phase.
estrogen
feedback)
towards
feedback)
that
levels
completion
the
follicular
endometrium
estrogen
high
peak
the
the
receptors
(negative
the
of
of
boosting
ovulation
back
also
FSH
promotes
(positive
drop
end
reaches
sharp
also
promotes
endometrium.
it
FSH
and
in
FSH,
digestion
levels
then
to
the
thickening
stimulates
ovulation.
the
secretes
sudden
phase.
and
at
gland
cells
therefore
stimulates
increase
When
secretion
secretion.
oocyte
an
feedback).
LH
peak
of
towards
and
follicles
wall
and
the
also
peak
repair
and
open
many
development
menstruation
inhibits
●
peak
rises
stimulates
(positive
●
by
expression
wall.
Estrogen
It
a
the
follicular
follicle
absorbed
gene
to
stimulates
●
are
inuence
phase,
end
of
reach
this
maintenance
secretion
by
a
phase.
of
the
the
pituitary
feedback).
D-sd qss: The female athlete triad
The
of
female
three
female
and
athlete
athletes:
menstrual
bone
triad
interrelated
mineral
is
a
syndrome
disorders
osteoporosis,
disorders.
density.
It
that
can
can
be
caused
runners
is
in
calcium,
vitamin
D
or
energy,
a)
higher
bone
a
density
in
runners
cycles
b)
lower
by
per
parts
had
year.
for
of
The
shows
the
above
the
the
femur
for
numbers
t-score
young
Outline
11
different
deviations
mass
a)
Figure
is
or
the
bone
a)
Suggest
b)
bone
mean
the
density
than
the
mean
[2]
density
between
than
the
mean.
[4]
reasons
or
for
no
female
athletes
menstrual
low
one
reason
body
for
cycles.
weight
in
eating
[2]
disorders
female
athletes.
[1]
of
peak
women.
relationship
Suggest
and
menstrual
number
below
of
mineral
female
of
some
low
number
)DS( erocs-t
1
two
who
standard
bone
levels.
for
diet
havingfew
estrogen
reasons
having:
eating
by
or
the
reduced
3
low
Explain
affect
disordered
Osteoporosis
2
consisting
1
neck of femur
trochanter of femur
0.5
0
0.5
of
menstrual
cyclesper
year
and
bone
1
density.
[3]
menstrual cycles per year
b)
Compare
femur
the
with
results
the
for
results
the
for
neck
the
of
the
trochanter.
0–3
4–10
▲
Figure 11 Bone mass in women grouped by number of
menstrual cycles
338
11–13
[3]
6 . 6
h o r m o n e S ,
h o m e o S t a S i S
a n D
r e p r o D u C t i o n
In vitr fertiizatin
The use in IVF of drugs to suspend the normal secretion of hormones, followed by
the use of ar ticial doses of hormones to induce superovulation and establish
a pregnancy.
The
in
natural
vivo,
tissues
method
meaning
of
outside
the
the
conditions.
of
that
body.
body
This
occurs
carefully
called
in
in
inside
Fertilization
in
is
fertilization
it
can
humans
the
also
controlled
vitro
a
is
consequence
usual.
living
as
happen
Twelve
many
always
abbreviated
to
IVF
.
This
been
used
extensively
to
the
in
either
the
male
overcome
or
the
are
rst
woman
spray,
or
is
takes
to
LH.
several
stage
a
stop
drug
her
Secretion
therefore
different
usually
female
also
protocols
day,
pituitary
of
for
This
usually
gland
estrogen
stops.
IVF
,
as
a
secreting
and
the
cycle
and
allows
doctors
to
embryo.
wall
is
nasal
to
timing
and
amount
of
egg
given
much
than
is
mm
by
in
an
diameter
injection
they
of
is
normally
secreted
HCG,
eggs
at
is
37
passed
out
50,000
in
°C
mounted
of
to
a
the
through
follicles.
100,000
shallow
until
the
on
by
the
next
uterus
Each
sperm
dish,
an
egg
cells
which
is
in
then
day.
fertilization
is
successful
then
one
or
more
control
production
in
are
placed
in
the
uterus
when
they
are
the
48
hours
old.
Because
the
woman
has
not
ovaries.
Intramuscular
follicles
18
that
scanner
with
incubated
gone
then
IVF
normal
about
woman’s
are
mature
micropipette
conditions
embryos
the
A
wash
mixed
sterile
FSH
progesterone
suspends
to
hormone
ultrasound
but
The
If
menstrual
of
be
parent.
down-regulation.
each
stage
than
can
fertility
the
There
This
there
superovulation.
follicles
stimulated
another
problems
follicles.
develop
and
procedure
are
has
called
follicles
unusual
fertilization,
When
almost
more
not
twenty
therefore
laboratory
far
is
to
injections
daily
for
develop.
higher
during
of
about
The
FSH
ten
FSH
concentration
a
normal
and
days,
LH
to
of
this
menstrual
progesterone
are
in
stimulate
injections
give
and
the
grow
from
as
a
is
vagina,
maintained.
a
hormone
cycle
through
then
a
normal
usually
to
If
the
menstrual
given
ensure
the
that
embryos
pregnancy
pregnancy
that
as
the
a
cycle
tablet
uterus
implant
that
began
by
placed
lining
and
follows
extra
is
natural
is
continue
no
to
different
conception.
Wiia Harve and sexua rerductin
William Harvey’s investigation of sexual reproduction
in deer.
William
Harvey
circulation
life
is
into
sexual
the
William
from
remembered
but
it
mixes
to
he
also
generation
reproduction.
He
which
with
was
the
for
had
to
a
discovery
generation
taught
male
menstrual
his
lifelong
the
blood.
and
“seed
produces
The
a
egg
of
the
obsession
with
pioneered
and
soil”
seed,
theory
which
develops
how
research
of
forms
into
a
an
fetus
mother.
Harvey
are
chiey
blood,
according
when
inside
Deer
is
the
transmitted
Aristotle,
egg
of
tested
seasonal
Aristotle’s
breeders
and
theory
only
using
become
a
natural
sexually
experiment.
active
during
the
▲
autumn.
Harvey
examined
the
uterus
of
female
deer
during
the
Figure 12 IVF allows the earliest stages in a
mating
human life to be seen. This micrograph shows a
season
by
slaughtering
and
dissecting
them.
He
expected
to
nd
eggs
zygote formed by fer tilization. The nuclei of the
developing
in
the
uterus
immediately
after
mating,
but
only
found
signs
egg and sperm are visible in the centre of the
of
anything
developing
in
females
two
or
more
months
after
the
start
of
zygote. There is a protective layer of gel around
the
mating
season.
the zygote called the fer tilization membrane
339
6
H u m a n
p H ys i o l o g y
He
of
regarded
his
reproduction
proceed
from
commixture
was
false,
during
sexual
▲
of
was
false
seed
that
or
today
or
Although
that
that
he
“neither
have
as
female
intercourse)
aware
deer
concluded
male
seed”.
(sexual
well
of
with
and
conclusion
reproduction:
yesterday
of
the
Harvey’s
coitus
Harvey
experiments
was
had
in
not
nor
“seed
did
not
theory
neither
yet
and
from
soil”
result
any
theory
from
events
false.
discovered
philosophers
satisfactorily
Aristotle’s
doth
coition,
fetus
also
that
fetus
Aristotle’s
the
was
the
proof
“the
the
nor
explained,
or
basis
the
of
physicians
solved
the
of
problem
Aristotle.”
Figure 13 William Har vey’s book on the
reproduction of animals Exercitationes de
Generatione Animalium published in 1651
Irveents in aaratus and research breakthruhs
Developments in scientic research follow improvements in apparatus: William
Harvey was hampered in his observational research into reproduction by lack of
equipment. The microscope was invented seventeen years after his death.
Harvey
publish
but
was
he
73
was
his
did
into
eventually
years
Generatione
solved
understandably
research
the
old
in
do
his
Animalium.
mystery
of
reluctant
sexual
so
in
work
He
to
reproduction,
1651
when
Exercitationes
knew
sexual
that
he
he
reproduction:
Harvey
because
effective
when
and
de
had
William
not
I
remain
more
plainly
in
than
sensation,
Let
the
the
see
nothing
uterus
remains
...
I
in
have
learned
after
the
at
braine
invented
and
all
doth
coition,
this
ingenious
...
of
subsequent
after
of
an
stage
of
it;
let
the
supercilious
the
for
the
laugh
scofng
their
ticklish
swinge.
generation,
Because
I
is
no
sensible
thing
in
the
coition;
and
yet
there
is
a
by
research
something
340
render
the
should
be
animal
has
deciencies
being
will
made
Harvey’s
sperm,
eggs
there,
were
death,
and
in
often
been
apparatus,
early
hampered
with
for
a
discoveries
into
the
improvements.
future
and
we
can
uterus
forward
to
further
transformations
in
necessity,
fruitful.
the
small
Microscopes
after
following
continue
of
the
natural
world
as
new
which
techniques
may
in
embryos.
understanding
that
choice
embryos
let
look
after
remained
his
microscopically
period.
of
available
say,
This
there
not
gametes
it:
only
them
of
with
because
years
discovery
mystery
development
remain
long
fusion
unlucky
animal
used
the
were
men
reject
time
and
was
seventeen
Scientic
consider
he
solve
so
embryo
He
unusually
invented
allowing
Fable.
ock
that
to
microscopes
working,
experimental
for
no
was
undiscovered.
deer
When
he
failed
and
technology
are
invented.
our
Q u e S t i o n S
Questins
1
Using
the
data
in
table
accidents
1:
during
disrupted
a)
outline
the
relationship
between
of
the
mother
and
the
success
percentage
IVF
as
a
result
Figure
of
15
oxygen
saturation
of
shows
arterial
during
a
night
of
sleep
in
a
patient
with
[3]
severe
b)
daytime
tiredness.
rate
blood
of
the
and
the
the
age
sleep
outline
the
relationship
between
obstructive
sleep
apnea.
the
100
number
of
embryos
transferred
and
1
70
the
of
chance
of
having
a
baby
as
a
result
IVF
[3]
100
2
c)
discuss
how
should
be
many
allowed
embryos
to
fertility
70
centres
transfer.
[4]
100
3
70
pc f cs  iVF cc
ccd    f s sfd
a f
100
4

1
2
single
twins
70
single
twins
sruoh
single
3
triplets
< 30
10.4
20.1
9.0
17.5
3.6
0.4
30–34
13.4
21.8
7.9
18.2
7.8
0.6
35–39
19.1
19.1
5.0
17.4
5.6
0.6
O
%
2
100
5
70
100
6
70
> 39
4.1
12.5
3.5
12.7
1.7
0.1
100
T
able 1
7
70
100
2
Figure
14
shows
variations
in
liver
glycogen
8
70
over
the
course
of
one
day.
0
a)
Explain
the
variation
in
10
20
30
liver
40
50
60
minutes
glycogen.
[3]
Figure 15
b)
Evaluate
the
contribution
of
glycogen
to
a)
blood
sugar
homeostasis.
Hour
8
shows
a
typical
pattern
due
to
[2]
obstructive
sleep
level negocylg revil
(i)
Explain
the
(ii)
Explain
apnea.
causes
the
of
causes
falls
of
in
saturation. [2]
rises
in
saturation.
(iii)
Calculate
falling
lunch
dinner
Estimate
that
12:00
16:00
how
and
long
rising
each
cycle
saturation
of
takes.
[2]
breakfast
b)
8:00
[2]
20:00
24:00
4:00
the
the
minimum
patient
oxygen
experienced
saturation
during
the
8:00
night,
and
when
it
occurred.
[2]
Figure 14
c)
Deduce
during
the
the
sleep
night
patterns
when
of
the
the
trace
patient
was
taken.
3
Sometimes
This
is
is
the
the
called
ventilation
apnea.
blockage
of
One
the
of
the
lungs
possible
airways
by
cause
the
soft
4
palate
sleep
during
apnea.
sleep.
It
consequences,
has
This
some
including
is
called
The
action
potential
of
a
squid
axon
was
obstructive
potentially
an
[2]
stops.
recorded,
with
The
was
the
axon
in
normal
sea
water.
harmful
increased
risk
+
axon
then
placed
in
water
with
a
Na
of
concentration
of
one-third
of
that
of
sea
water.
341
6
h u m a n
The
p h yS i o l o g y
action
potential
was
recorded
again.
a)
Using
only
the
data
in
gure
17,
outline
the
+
Figure
16
shows
these
recordings.
effect
of
reduced
Na
)Vm( laitnetop ebarbmem
(i)
the
magnitude
(ii)
the
duration
concentration
of
of
on:
depolarization
the
[2]
action
+40
potential.
sea water
[2]
+20
+
b)
Explain
the
effects
of
reduced
Na
0
concentration
on
the
action
potential.
[3]
33%
20
+
c)
Discuss
the
effect
of
reduced
Na
40
concentration
on
the
time
taken
to
return
60
to
the
resting
potential.
[2]
80
1
2
d)
Compare
the
action
potentials
of
shaker
time (ms)
and
normal
fruit
ies.
[3]
Figure 16
e)
Explain
action
5
Geneticists
y
that
with
discovered
shakes
ether.
a
mutant
vigorously
Studies
have
variety
when
shown
of
fruit
anaesthetized
that
the
shaker
+
mutant
has
properly.
normal
K
channels
Figure
fruit
17
ies
that
shows
and
in
do
not
action
shaker
function
potentials
in
mutants.
40
wild-type drosophila
normal action potential
0
Vm/laitnetop ebarbmem
40
4
8
12
16
40
shaker mutant
abnormal action potential
0
40
4
8
12
time (ms)
Figure 1
7
342
16
the
differences
potentials.
between
the
7
N U C L E I C
A C I D S
( A H L )
Introduction
The
discovery
of
revolutionized
coded
form
in
the
structure
biology.
DNA
is
of
DNA
Information
copied
onto
structure
stored
mRNA.
in
a
The
of
Information
translated
DNA
is
ideally
transferred
into
an
suited
from
amino
acid
to
DNA
its
to
function.
mRNA
is
sequence.
7
.1 DN A  and an
Understanding
Applications
➔
DNA structure suggested a mechanism for DNA
➔
Rosalind Franklin’s and Maurice Wilkins’
replication.
investigation of DNA structure by X-ray
➔
Nucleosomes help to supercoil the DNA .
➔
DNA replication is continuous on the leading
diraction.
➔
Tandem repeats are used in DNA proling.
➔
Use of nucleotides containing
strand and discontinuous on the lagging strand.
➔
DNA replication is carried out by a complex
dideoxyribonucleic acid to stop DNA replication
system of enzymes.
➔
in preparation of samples for base sequencing.
DNA polymerases can only add nucleotides to
the 3’ end of a primer.
Skills
➔
Some regions of DNA do not code for proteins
but have other impor tant functions.
➔
Analysis of results of the Hershey and Chase
experiment providing evidence that DNA is the
genetic material.
Nature of science
➔
➔
Utilization of molecular visualization software
Making careful obser vations: Rosalind
to analyse the association between protein and
Franklin’s X-ray diraction provided crucial
DNA within a nucleosome.
evidence that DNA is a double helix.
343
7
N U C L E I C
A C I D S
( A H L )
The Hershey–Chase experiment
Analysis of the results of the Hershey–Chase experiment providing evidence that
DNA is the genetic material.
From
that
and
the
late
1800s,
chromosomes
that
the
hereditary
nature.
Aware
of
protein
both
that
contenders
Until
the
1940s,
class
due
of
to
to
specic
proteins.
two
nucleic
be
the
the
view
was
functions
properties
requirements
and
that
for
acid,
that
that
had
great
been
the
was
variety
Further,
identied
of
function
to
as
be
for
were
essential
and
was
known
protein
that
cells
becoming
bound
then
bursts,
(see
gure
certain
with
The
simple
T2
while
and
cell.
The
are
to
the
often
virus
they
It
has
DNA
a
is
coat
portion
which
of
new
by
their
of
the
cell
viruses
environment
specic
chose
to
to
because
inside
a
work
of
composed
found
was
factories
infected
numbers
them
it
injecting
An
bacteriophage
structure.
protein
the
of
1950s,
particles
non-genetic
Viruses
type.
the
cells
large
releasing
cell
was
the
infectious
host
outside
1).
In
wanted
material
virus-producing
to
manufactures
and
Chase
genetic
DNA.
are
into
material.
remains
the
or
viruses
transform
genetic
Martha
whether
viruses
of
material.
Hershey
ascertain
virus
a
sub-units
expected
hereditary
was
it
sub-units.
had
composed
molecules
material.
as
Alfred
to
chemical
were
protein
specicity
the
a
both
occurring
were
convinced
heredity
had
genetic
nucleotide
Variety
in
favoured,
naturally
four
were
role
material
macromolecules
opposed
many
to
material
twenty
a
chromosomes
and
were
hereditary
scientists
played
its
very
entirely
the
coat.
DNA
protein
▲
Figure 1 Coloured transmission electron micrograph (TEM) of T2
viruses (blue) bound to an Escherichia coli bacterium. Each virus
consists of a large DNA-containing head and a tail composed of a
central sheath with several bres. The bres attach to the host cell
▲
surface, and the virus DNA is injected into the cell through the sheath.
Figure 2 Diagram illustrating the structure of
the T2 virus
It instructs the host to build copies of the virus (blue, in cell)
Daa-bad qn: The Hershey–Chase experiment
Alfred
Hershey
scientists
the
In
who
chemical
their
and
Martha
worked
nature
experiment,
the
fact
that
not
sulphur
but
not
DNA
of
to
resolve
the
they
took
proteins
phosphorus.
They
were
the
genetic
contains
while
Chase
phosphorus.
two
debate
over
material.
advantage
phosphorus
contain
cultured
of
but
with
the
blender
of
the
the
two
to
infected
types
separate
virus
culture
pellet.
They
sulphur
a
viruses
radioactive
from
of
The
cells
viruses.
the
the
solution
separately
They
used
non-genetic
cell
to
and
then
concentrate
were
genetic
bacteria
expected
component
to
of
a
component
centrifuged
the
cells
have
the
in
the
virus
in
35
that
contained
sulphur
and
proteins
they
with
separately
radioactive
cultured
(
S)
viruses
them.
pellet
They
and
measured
the
the
radioactivity
supernatant.
Figure3
in
represents
32
that
344
contained
DNA
with
radioactive
(
P)
the
process
and
results
of
the
the
experiment.
7. 1
D N A
s t r u c t u r e
A N D
r e p l i c A t i o N
35
radioactive protein (
S)
35
virus
radioactivity (
S) in supernatant
35
protein coat with
S
bacterium
bacteria
32
radioactive DNA (
P)
virus
DNA with
32
P
bacterium
bacteria
32
radioactivity (
P) in pellet
Questions
Explain
what
b)
Explain
why
found
in
the
a
supernatant
the
genetic
pellet
and
is.
material
not
the
should
be
supernatant.
32
c)
Determine
the
percentage
of
remains
in
the
supernatant.
Determine
the
percentage
the
P
that
35
d)
in
e)
the
of
S
that
remains
supernatant.
Discuss
which
the
evidence
transforms
that
the
DNA
bacteria
is
the
into
tnatanrepus ni epotosi fo %
a)
percentage of isotope in supernatant after 8 minutes agitation
100%
80%
60%
40%
20%
0%
35
infected
32
S
chemical
▲
P
Figure 3
cells.
X-ay dan an a vdn f ma 
Making careful observations: Rosalind Franklin’s X-ray diraction provided crucial
evidence that DNA was a helix.
Two
names
connection
Watson.
they
are
Flashes
could
not
experimental
other
His
of
usually
with
DNA
is
of
have
the
described
insub-topic2.6
led
achieved
and
One
into
remembered
discovery
insight
work
scientists.
research
the
of
of
to
it
careful
these
in
the
their
was
Erwin
base
and
success,
without
data-based
107).
Crick
but
skilled
observations
percentage
(page
Another
in
DNA,
by
Chargaff.
composition
question
key
gure
Rosalind
Franklin.
associate
in
London.
The
structure
had
the
of
already
institute
in
the
discovery
1950,
biophysics
unit
DNA
was
by
she
unit
other
of
DNA
became
at
King’s
a
diffraction.
X-ray
College,
carboncompounds
the
Franklin
techniques
diffraction
was
research
alreadyinvestigating
X-ray
becomeskilledin
crystallographyand
researching
in
In
of
while
at
an
Paris.
345
7
N U C L E I C
At
of
King’s
a
A C I D S
College
camera,
so
measurements
( A H L )
she
she
of
improved
could
the
make
X-ray
the
resolution
more
diffraction
diffraction
the
detailed
had
previously
been
possible.
She
high
quality
samples
of
aligned
in
narrow
DNA
bres.
Franklin’s
with
Watson
By
and
of
humidity
two
types
of
pure
be
produced
and
as
Franklin
was
represented
investigated
the
normal
after
Franklin
starting
had
work
obtained
diffraction
images
have
described
been
beautiful
ever
X-ray
taken”.
the
next
her
ndings
of
at
structure
the
of
the
or
permission,
best
the
calculations
based
diffraction
on
publish
her
results
it.
Crick
Before
and
had
used
structure.
It
them
is
to
build
widely
their
accepted
model
that
of
Rosalind
DNA,
deserved
in
Their
was
there
embarked
on
are
strong
rigorous
is
described
to
a
Nobel
in
evidence.
of
happened.
prizes
aged
in
1962,
Prize
posthumously,
we
can
discoveries
serendipity
more
for
her
or
She
foundations
the
techniques
but
research,
of
of
science
and
of
Prizes
Rosalind
from
be
life
made
but
rigorous
were
cancer
cannot
in
be
Franklin
prize
her
insight,
are
diligent
Watson
died
many
sometimes
ashes
and
she
Nobel
than
remember
may
Crick
but
thirty-seven.
remembered
What
publish
analysis
never
awarded
They
most
substance
unwilling
was
a
the
any
implications
She
until
of
1958,
X-ray
existence.
“amongst
this
awarded
College,
sharpest
DNA
as
King’s
photographs
section.
therefore
knowledge
shown
both.
but
Soon
was
could
Franklin
she
calculate
unsure
DNA
which
to
sample
Watson
could
her
helix.
careful
Franklin
control
allowed
DNA
the
pattern
molecules
that
the
also
James
produced
of
patterns
Without
than
patterns
dimensions
winners.
is
that
through
the
real
experimental
observation.
Rosalind Franklin’s investigation of DNA structure
Rosalind Franklin and Maurice Wilkins’ investigation of DNA structure by X-ray diraction.
If
a
beam
most
by
is
of
the
of
it
X-ray s
passes
particles
called
in
them
by
particles
d i re cte d
the
diffractio n.
makes
the
is
thr o ug h
at
T he
a
m a ter ia l ,
s ome
m ate ri al .
is
Thi s
wav el e ng th
parti cul a r l y
in
but
s e ns itive
b i o l o gi ca l
to
sc at t e r ed
s c at t e r in g
of
X- r ays
d iffr a c t io n
mo le cul es
includingDNA.
In
a
crystal
repeating
regular
way.
molecules
array
in
pattern
the
particles
pattern,
so
DNA
were
be
cannot
be
in
samples
obtained,
arranged
diffraction
arranged
Franklin’s
to
are
the
in
a
crystallized
an
for
rather
orderly
a
regular
occurs
in
but
a
the
enough
diffraction
than
random
scattering.
▲
An
to
X-ray
collect
rotated
the
be
detector
the
in
of
recorded
placed
scattered
three
pattern
is
rays.
different
scattering.
using
close
X-ray
The
to
the
sample
dimensions
Diffraction
lm.
to
can
be
investigate
patterns
Franklin
can
From
was
high
resolution
camera
containing
the
able
structure
X-ray
obtain
from
these
346
very
DNA.
clear
Figure
diffraction
4
images
shows
patterns.
of
diffraction
the
most
of
make
a
pattern
series
of
in
gure
4
deductions
Franklin
about
the
DNA:
The
cross
in
the
centre
of
the
pattern
indicated
lm
that
to
diffraction
to
developed
●
a
Figure 4 Rosalind Franklin’s X-ray diraction photograph of DNA
sample
the
molecule
was
helical
in
shape.
patterns
famous
of
●
The
angle
(steepness
of
of
the
cross
angle)
of
shape
the
showed
helix.
the
pitch
7. 1
●
The
distance
showed
between
turns
of
the
the
horizontal
helix
to
be
3.4
D N A
s t r u c t u r e
bars
nm
the
apart.
A N D
repeats.
distance
r e p l i c A t i o N
This
turned
between
out
adjacent
to
be
base
the
pairs
vertical
in
the
helix.
●
The
distance
diffraction
there
was
a
molecule,
between
pattern
the
and
repeating
with
a
middle
the
top
structure
distance
of
of
the
showed
that
within
0.34
nm
These
the
deductions
diffraction
between
in
the
that
pattern
discovery
of
of
the
The Watson and Crick model suggested semi-
were
DNA
made
were
structure
from
the
critically
of
X-ray
important
DNA.
toK
conservative replication
Wha n d n hav
DNA structure suggested a mechanism for DNA replication.
whn h and dn
dn’ fy mah xmna
Several
lines
of
experimental
evidence
came
together
to
lead
to
the
vdn?
knowledge
by
the
Nobel
discerned
base
of
the
structure
prize
from
winner
the
composition
DNA:
Linus
careful
studies
of
molecular
Pauling,
photographs
of
Erwin
modelling
X-ray
of
diffraction
Rosalind
Chargaff.
pioneered
But
Franklin
insight
Charga wrote about his
patterns
and
and
observations:
the
imagination
the results serve to disprove the
played
a
role
as
well.
tetranucleotide hypothesis.
One
of
Watson
and
wrapped
around
Rosalind
Franklin
nitrogen
bases
phosphate
Crick’s
one
rst
another
countered
were
with
this
relatively
backbone
and
models
the
had
the
nitrogen
model
with
hydrophobic
would
likely
sugar-phosphate
the
in
point
bases
facing
to
the
that
to
centre
the
of
noteworthy
cannot yet be said
the
sugar-
the
however,
It is,
- whether
this is more than accidental,
outwards.
knowledge
comparison
in
strands
helix.
- that in all
deoxypentose nucleic acids
examined thus far the molar ratios
of total purines to total pyrimidines
Franklin’s
X-ray
diffraction
studies
showed
that
the
DNA
helix
was
and also of adenine to thymine and
tightly
packed
so
when
Watson
and
Crick
built
their
models,
their
choices
of guanine to cytosine were not far
required
the
bases
to
t
together
such
that
the
s