O X
F O
R
D
I B
P
R
E
P A
R
E
D
BIOLO GY
I B
D I P L O M A
Debora M. Primrose
P R O G R A M M E
O X
F O
R
D
I B
P
R
E
P A
R
E
D
BIOLO GY
I B
D I P L O M A
P R O G R A M M E
Debora M. Primrose
1
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C ontents
Introduction
1
iv
Cell biology
1.1
Introduction to cells
2
1.2
Ultrastructure of cells
4
1.3
Membrane structure
6
1.4
Membrane transpor t
7
1.5
The origin of cells
9
1.6
Cell division
2
2.1
Molecules to metabolism
14
2.2
Water
15
2.3
Carbohydrates and lipids
16
2.5
Proteins
Enzymes
9.1
Transpor t in the xylem of plants
103
9.2
Transpor t in the phloem of plants
107
9.3
Growth in plants
110
9.4
Reproduction in plants
113
10
10.1
Meiosis
10.2
Inheritance
Structure of DNA and RNA
23
DNA replication, transcription and translation
24
2.8
Cell respiration
26
2.9
Photosynthesis
28
121
10.3
Gene pools and speciation
125
11
Genes
30
3.2
Chromosomes
32
3.3
Meiosis
33
3.4
Inheritance
35
3.5
Genetic modication and biotechnology
37
11.1
Antibody production and vaccination
128
11.2
Movement
133
11.3
The kidney and osmoregulation
137
11.4
Sexual reproduction
141
12
Data-based and practical questions
A
Neurobiology and behaviour
147
A.1
Neural development
157
A.2
The human brain
159
A.3
Perception of stimuli
161
A.4
Innate and learned behaviour (AHL)
165
A.5
Neuropharmacology (AHL)
167
A.6
Ethology (AHL)
169
B
Biotechnology and bioinformatics
Ecology
4.1
Species, communities and ecosystems
40
4.2
Energy ow
43
4.3
Carbon cycling
45
4.4
Climate changes
47
Evolution and biodiversity
B.1
Microbiology: organisms in industry
B.2
Biotechnology in agriculture
B.3
Environmental protection
178
B.4
Medicine (AHL)
180
B.5
Bioinformatics (AHL)
182
C
5.1
Evidence for evolution
5.2
Natural selection
5.3
Classication of biodiversity
54
5.4
Cladistics
57
6
Animal physiology (AHL)
Genetics
3.1
5
117
21
2.7
4
Genetics and evolution (AHL)
20
2.6
3
Plant biology (AHL)
11
Molecular biology
2.4
9
50
51
172
174
Ecology and conservation
C.1
Species and communities
186
C.2
Communities and ecosystems
188
C.3
Impacts of humans on ecosystems
192
C.4
Conservation of biodiversity
194
C.5
Population ecology (AHL)
19 6
C.6
Nitrogen and phosphorus cycles (AHL)
199
Human physiology
6.1
Digestion and absorption
60
6.2
The blood system
63
6.3
Defence against infectious disease
66
6.4
Gas exchange
69
6.5
Neurons and synapses
72
6.6
Hormones, homeostasis and reproduction
75
D
7
D.1
Human nutrition
D.2
Digestion
202
207
D.3
Functions of the liver
211
D.4
The hear t
D.5
Hormones and metabolism (AHL)
215
D.6
Transpor t of respiratory gases (AHL)
218
212
Nucleotides (AHL)
7.1
DNA structure and replication
80
7.2
Transcription and gene expression
84
7.3
Translation
87
8
Human physiology
Internal assessment
223
Practice exam papers
228
Index
247
Metabolism, cell respiration and
photosynthesis ( AHL)
8.1
Metabolism
91
8.2
Cell respiration
93
8.3
Photosynthesis
97
Answers to questions and exam papers in this book can be found
on your free suppor t website. Access the suppor t website here:
w w w.ox f or dsecondar y.com / ib-pr epar ed-suppor t
iii
I N T R O D U CT I O N
This
book
syllabus
provides
in
full
biology
coverage
and
offers
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support
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Biology
at
the
and
or
of
from
internal
part
2
assessment
their
external
usually
later.
are
page
1
of
are
two
marks
top
grade,
as
day
assessment
the
sat
The
to
(lowest)
give
to
7
one
internal
combined
V
on
as
and
shown
your
overall
(highest).
The
answers
and
examination
and
solutions
papers
to
are
all
practice
given
online
problems
at
www.oxfordsecondary.com/ib-prepared-support.
Blank
answer
available
at
sheets
the
for
same
examination
address.
papers
are
also
Assessment over view
SL
Assessment
Description
HL
Topics
marks
Internal
Experimental work with a written repor t
Paper 1
Multiple-choice questions
—
weight
24
Core:
marks
20%
30
weight
24
20%
20%
40
20%
1–6 (SL)
Paper 2
Shor t- and extended-response questions
50
40%
72
36%
1–11 (AHL)
Section A : data-based and practical
—
15
15
questions
20%
Paper 3
Section B: shor t- and extended-response
24%
Option of your
20
questions
The
final
points
IB
from
diploma
theory
of
30
choice
score
is
calculated
knowledge
and
by
combining
extended
essay
grades
for
six
subjects
with
up
to
three
additional
components.
Command terms
Command
terms
command
For
example,
levels
of
are
term
the
detail,
(“discuss”),
as
pre-defined
specifies
the
command
from
a
shown
and
terms
single
in
words
type
the
state,
word,
next
and
phrases
depth
of
outline,
short
the
used
explain
sentence
in
all
response
or
and
IB
Biology
expected
discuss
numerical
questions
from
require
value
you
in
answers
(“state”)
to
and
a
problems.
particular
with
Each
question.
increasingly
comprehensive
higher
analysis
table.
Question
Possible answer
State the eect of increasing temperature
Rate increases.
on the reaction rate.
Outline how an increase in temperature
For most reactions, the rate approximately doubles when temperature increases by
aects the reaction rate.
10 degrees.
As temperature increases, the average speed and thus kinetic energy of particles also
Explain why an increase in temperature
increase. The particles collide with one another more frequently and with a greater force.
increases the reaction rate.
As a result, the frequency of successful collisions increases, so the rate increases.
Both factors increase the rate by increasing the frequency of successful collisions.
However, an increase in temperature increases the frequency and intensity of all
Discuss the eects of increasing
collisions (successful and unsuccessful) but has no eect on the activation energy.
temperature and the presence of an
In contrast, an enzyme has no eect on the frequency or intensity of collisions but
enzyme on the reaction rate.
lowers the activation energy by providing an alternative reaction pathway and thus
allowing slow-moving par ticles to collide successfully. Thus, the same macroscopic
eect is achieved by dierent microscopic changes.
A list
of
commonly
Understanding
examination.
questions
in
the
used
exact
Therefore,
this
command
meaning
you
terms
of
should
in
biology
frequently
explore
this
examination
used
command
table
and
use
it
questions
terms
is
is
given
essential
regularly
as
a
in
for
the
your
reference
following
success
when
in
table.
the
answering
book.
Command term
Denition
Analyse
Break down in order to bring out the essential elements or structure
Annotate
Add brief notes to a diagram or graph
Calculate
Obtain a numerical answer showing your working
Comment
Give a judgment based on a given statement or result of a calculation
Compare
Give an account of the similarities between two or more items
Compare and contrast
Give an account of similarities and dierences between two or more items
Construct
Present information in a diagrammatic or logical form
Deduce
Reach a conclusion from the information given
Dene
Give the precise meaning of a word, phrase, concept or physical quantity
Describe
Give a detailed account
Design
Produce a plan, simulation or model
Determine
Obtain the only possible answer
Discuss
Oer a considered and balanced review that includes a range of arguments, factors or hypotheses
Continued on page VI
v
INTRODUCTION
Command term
Denition
Distinguish
Make clear the dierences between two or more items
Represent by a labelled, accurate diagram or graph, drawn to scale, with plotted points (if
Draw
appropriate) joined in a straight line or smooth curve
Estimate
Obtain an approximate value
Explain
Give a detailed account including reasons or causes
Identify
Provide an answer from a number of possibilities
Label
Add labels to a diagram
List
Give a sequence of brief answers with no explanation
Outline
Give a brief account or summary
Predict
Give an expected result
Represent by means of a diagram or graph (labelled as appropriate), giving a general idea of the
Sketch
required shape or relationship
State
Give a specic name, value or other brief answer without explanation
Suggest
Propose a solution, hypothesis or other possible answer
A complete
list
of
command
terms
is
available
in
the
subject
guide.
Preparation and exam strategies
In
addition
study
1.
and
Get
ready
drink
night’s
exam
the
for
sleep
day
,
Organize
study
place
Create
make
and
the
this
understanding
the
Check
more
vi
easily
for
you
as
Work
systematically
on
Make
a
can
A
5.
topics
your
rules
you
should
using
the
6.
a
of
follow
studying
complete
tasks
up
can.
of
and
7.
each
y o ur
where
s k il ls .
point
as
this
during
your
preparation
the
ga p s
Sp en d
a nd
on lin e
8.
the
in
ex t r a
is
Do
looking
at
constraint.
papers
papers
not
panic.
improve
attention
answers
axes
exam
Take
on
goals
goals.
approach.
Double-check
a
in
and
all
at
work
learn
future
to
all
as
the
you
end
and
and
this
and
improve.
reflect
from
values
book.
systematically
to
clear
annotate
attitude
can
your
results.
questions
command
numerical
from
you
Read
short
positive
prepared
your
as
graphs
tips
things
and
Be
performance
to
worked
answering
past
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than
reference.
time
from
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your
Use
realistic
f or
a
every
before
Practice
rather
definitions
solve
future
under
exam
Label
you r
re qui re d .
for
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paying
concentrate
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problem
problems
your
Keep
units.
these
the
trial
topics
t i me
Try
notes
questions
possible.
and
task
understanding
points
book.
Optimize
as
and
practice
for
a
on
key
words.
Make
many
Take
terms.
of
th rou g h
imp rovemen t
textbook
information .
f ir st
way
iden tify
an d
ready
diagrams.
your
and
and
carefully
,
large
parts.
time
Get
Focus
Recite
own
answer.
Solve
material.
Break
your
exam-style
organized.
your
actively.
example
the
distractions.
files
Read
memorizing.
by
good
before
Find
manageable
your
well,
lighting,
offline
list
eat
deadline.
book
reference.
and
importance.
agenda
that
simple
score.
Avoid
computer
online
smaller,
sure
before
Use
an
by
your
adequate
ventilation.
papers
them
some
stress
exercise.
environment.
with
studies.
into
are
sleep,
your
important
improve
Plan
tasks
physical
particularly
and
there
enough
reduce
can
useful
arrange
4.
and
Bookmark
your
and
it
your
your
Have
water
is
as
temperature
3.
study.
of
suggestions,
itself.
thinking
comfortable
Keep
above
exam
plenty
positive
2.
to
the
on
Set
to
achieve
your
errors
in
order
Key features of the book
Each
chapter
typically
covers
one
core
or
option
topic,
and
starts
with
Theoretical concepts and key
“You
should
know”
and
“You
should
be
able
to”
checklists.
These
definitions are discussed at a
outline
the
understandings
and
applications
and
skills
sections
of
the
IB
level sufficient for answering
diploma
biology
syllabus.
Some
assessment
statements
have
been
typical examination questions.
reworded
or
combined
together
to
make
them
more
accessible
and
Many concepts are illustrated
simplify
the
navigation.
These
changes
do
not
affect
the
coverage
of
by diagrams, tables or worked
key
syllabus
material,
which
is
always
explained
within
the
chapter.
examples. Most definitions are
Chapters
contain
the
features
outlined
on
this
page.
given in a grey side box like this
one, and explained in the text.
Example
Examples
common
offer
solutions
to
problem-solving
typical
problems
techniques.
Many
and
demonstrate
examples
provide
This feature highlights the
alternative
answers
and
explain
how
the
marks
are
awarded.
essential terms and statements
that have appeared in past
markschemes, warns against
Nature of science relates a biology concept to the overarching
common errors and shows how
principles of the scientific approach.
to optimize your approach to
par ticular questions.
Sample
student
questions
each
(most
response,
answers
of
which
the
correct
show
are
typical
taken
points
student
from
are
past
often
responses
to
examination
highlighted
in
IB-style
papers).
green
In
while
Links provide a reference to
incorrect
or
incomplete
answers
are
highlighted
in
red.
Positive
or
relevant material, within another
negative
feedback
on
student’s
response
is
given
in
the
green
and
red
par t of this book , that relates to the
pull-out
boxes.
An
example
is
given
below.
text in question.
You
will
icon
Number
The
may
on
marks
have
their
the
student
earned
marks
of
on
see
the
question
available
from
a
an
has
past
exam
right
been
IB
paper
when
the
adapted
paper
based
response
Examination
Negative
question
feedback
SAMPLE STUDENT ANSWER
▼
[2]
Describe what is meant by a condensation reaction.
clear
enough,
single
This
answer
could
have
achieved
1/2
condensation
two
A
condensation
reaction
is
an
as
reacting
it
implies
species
a
while
a
marks:
anabolic
reacting
must
involve
species,
which
at
least
can
be
reaction
identical
or
different
molecules
or
ions.
that
builds
a
polymer
from
a
monomer.
▲
“Water”
the
most
although
The
Questions
student’s
not
taken
response
from
past
Positive
IB
examinations
will
not
have
feedback
the
exam
the
molecule”
paper
is
accepted
common
answer
would
as
by-product,
be
“a
small
more
accurate.
icon.
Practice problems
Practice problems are given at the end of each chapter.
problem-solving skills. Some questions introduce
These are IB-style questions that provide you with
factual or theoretical material from the syllabus that can
an oppor tunity to test yourself and improve your
be studied independently.
1
CELL
1
1 . 1
B I O LO GY
I N T R O D U C T I O N
T O
Y sd kw:
✔
all
living
organisms
C E L LS
Y sd e ae :
are
composed
of
cells.
✔
discuss
exceptions
striated
✔
unicellular
that
organisms
carries
out
all
consist
functions
of
of
only
life
one
in
muscle,
to
the
giant
cell
algae
theory
,
and
including
fungal
hyphae.
cell
that
✔
draw
cells
✔
describe
as
seen
under
the
light
microscope.
organism.
✔
cell
size
ratio
of
is
limited
the
by
the
surface
area
to
volume
named
in
multicellular
can
✔
develop
by
differentiation
genes
✔
and
of
life
in
Paramecium
unicellular
and
a
organism.
cell.
✔
✔
functions
photosynthetic
not
organisms,
cell
calculate
tissues
of
differentiation.
involves
others
in
multicellular
organisms
emerge
the
from
specialized
the
a
drawings
expression
cell’s
have
interaction
of
some
✔
explain
genome.
volume
properties
of
the
their
that
✔
treat
and
or
the
the
and
actual
ultrastructures
size
shown
in
micrographs.
limitations
and
describe
cellular
magnication
structures
small
of
therapeutic
Stargardt
a
surface
disease
cell
having
a
large
area.
use
and
of
stem
one
cells
other
to
example.
components.
✔
✔
stem
cell
division
necessary
for
and
differentiation
embryonic
discuss
the
ethics
of
using
stem
cells.
is
development.
All
living
are
formed
organisms
are
formed
of
cells.
Unicellular
organisms
The ultrastructure of cells is
of
only
one
cell
that
performs
all
the
functions
of
life
studied in Topic 1.2. The process
(nutrition,
metabolism,
growth,
response,
excretion,
homeostasis
and
of cell respiration is studied in
reproduction).
Topics 2.8 and 8.2. Nutrition is
studied in Topic 6.1 and metabolism
Multicellular
in Topic 8.1.
specialized
form
organisms
by
organs
which
differentiate,
different
cilia
cells
proteins.
material,
but
resulting
cells
are
composed
differentiation,
if
together
must
All
some
will
make
express
cells
in
genes
be
forming
many
organ
different
an
are
up
of
cells
different
systems.
genes
organism
expressed
that
tissues.
have
and
and
the
In
become
These
order
therefore
same
others
are
tissues
to
produce
genetic
not,
the
different.
contractile vacuole
plasma membrane
• Ces are the basic units of life.
• Dieeiai is the change in a
cell to become more specialized.
nucleus
• Emee ppe ies are proper ties
that appear in a complex system (or
• Sem ces are cells that are capable
an organism) but do not appear in the
of dierentiation.
cytoplasm
food in vesicles
individual units.
Paramecium
Exampe 1.1.1.
Fie 1.1.1.
Paramecium is a
unicellular organism that obtains its
The
food from the environment, digesting it
microscope
micrograph
with
shows
a
onion
epidermal
magnification
of
in food vacuoles
a)
2
(i)
Label
the
nucleus
of
one
cell.
cells
×400.
seen
under
the
light
1 .1
(ii)
Calculate
of
this
the
cell.
actual
Show
IntroDuCtIon
to
C E ll S
Because stem cells have the
width
ability to differentiate into
your
any type of cell, they are used in
working.
the development of medical
b)
Suggest
how
the
surface
area
treatments for a wide range of
to
volume
ratio
of
a
cell
can
conditions. These include physical
affect
its
function.
trauma, degenerative conditions
Solution
a)
(i)
and genetic diseases such as
Any
dark
circle
labelled.
Stargardt disease. However, there
are ethical issues regarding the
(ii)
The
magnication
is
the
size
of
the
image
divided
by
the
use of stem cells in the treatment
actual
size
of
the
cell.
Therefore
the
formula
for
actual
size
is:
of diseases. Much of the debate
size of
image
surrounding stem cells concerns
Actual
size
of
cell
=
magnification
the use of human embryonic cells.
The use of adult stem cells from
To
calculate
the
width
of
the
cell,
you
rst
use
a
ruler
to
sources such as blood from the
measure
the
width
of
the
chosen
cell
(size
of
image).
umbilical cord is more convenient
For
example,
measured
cell
width
=
10
mm
and less controversial.
10 mm
Actual
width
of
cell
=
Actual
width
of
cell
=
400
0.025
mm
You have to check whether your
b)
If
the
ratio
is
too
small
the
exchange
of
substances
will
be
too
result makes sense. 1 mm is
slow,
waste
substances
will
accumulate
and
heat
will
not
be
lost
equal to 1000 μm, therefore the
efciently
.
cell width is 25 μm, which is the
average cell width.
Exampe 1.1.2.
The
pictures
scale.
A
Which
Giant
alga
show
fully
drawings
complies
or
micrographs
with
the
cell
from
different
cells
with
different
magnifications
not
to
theory?
(Acetabularia)
B
White
blood
cell
C
Fungal
aseptate
hyphae
cell wall
cytoplasm
cytoplasm
nuclei
D
Striated
muscle
light
micrograph
×
100
magnification
(longitudinal
section)
20 mm
muscle
fibres
nucleus
connective
tissue
Solution
The
answer
The
giant
typical
many
is
alga
cell.
All
is
The
nuclei.
nuclei.
B,
white
a
fungal
The
these
very
blood
large
aseptate
striated
are
cell,
because
organism
hyphae
muscle
exceptions
to
cells
the
it
is
surrounded
consisting
do
are
cell
not
of
have
much
only
by
one
divisions
larger
than
a
cell
cell.
membrane
The
size
between
any
cells,
average
and
does
cell
not
has
therefore
and
genetic
material.
correspond
also
the
cell
contain
to
the
contains
many
theory
.
3
1
C E LL
BI O LO G Y
S AMPlE StuDEnt AnS WEr
Outline the use of human embryonic stem cells (hESC) to treat Stargardt
disease.
This
[2]
answer
Human
could
embryonic
differentiate
▲ The
it
answer
outlines
the
is
correct
use
of
for
Stargardt
vague
cells
only
reference
are
used
of
for,
makes
what
the
mark.
question
the
therefore
It
is
important
carefully
and
being
asked.
cells
being
cells
or
In
used
this
stem
to
read
answer
to
case,
replace
photoreceptors
unspecialized
cell.
T
hese
hESC
and
are
can
inserted
retina
of
the
eye
and
specialize
to
become
healthy
cells
answer
which
could
allow
have
a
person
achieved
0/2
to
regain
their
vision.
marks:
As
human
embryonic
stem
cells
are
undifferentiated
cells
scoring
the
a
totipotent,
they
are
able
to
be
made
into
any
cell
that
needed.
T
he
Stargardt
disease
can
be
treated
by
stem
cells
stem
as
retinal
was
are
the
what
is
is
any
are
a
and
no
almost
cells
marks:
disease.
This
answer
stem
2/2
cells
retinal
▼ This
into
achieved
as
stem
into
specically
have
adequate
cells
can
be
created
that
the
Stargardt
disease
key
kills.
issue
to
include
in
1 . 2
the
answer.
U LT R A S T R U C T U R E
Y sd kw:
✔
eukaryotes
structure
✔
have
than
prokaryotes
a
much
not
more
complex
cell
✔
describe
have
eukaryotes
have
a
the
organelles
cell
✔
explain
compartmentalization.
✔
C E L LS
Y sd e ae :
prokaryotes.
do
O F
general
within
how
structure
animal
and
prokaryotes
and
function
plant
divide
by
of
cells.
binary
ssion.
compartmentalized
cell
✔
draw
the
ultrastructure
of
prokaryotic
✔
draw
the
ultrastructure
of
eukaryotic
✔
compare
cells.
structure.
✔
electron
microscopes
resolution
than
light
have
a
much
microscopes,
higher
and
of
the
ultrastructure
contrast
the
structure
of
allowing
prokaryotic
observation
cells.
of
and
eukaryotic
cells.
cells.
✔
compare
and
contrast
and
label
animal
cells
and
plant
cells.
✔
interpret
structures
in
electron
micrographs.
Prokaryotic
cells
do
not
have
a
nucleus
or
membrane-bound
An introduction to cells is given
organelles,
their
nuclear
material
DNA is
naked,
is
found
in
the
nucleoid
or
nuclear
in Topic 1.1.
• Maicai is how much an
image has been enlarged.
region
and
have
cell
a
cytoplasm
that
membrane
a
nucleus,
their
wall,
pili
and
contains
enclosing
70S
bound
and
a
ribosomes.
cytoplasm
mitochondria
not
flagella,
and
that
other
to
proteins.
plasma
Eukaryotic
contains
Prokaryotic
membrane
cells
larger
have
(80S)
membrane-bound
cells
enclosing
a
plasma
ribosomes,
organelles.
Plant
• resi is the minimal
distance at which two points
that are close together can be
distinguished.
4
cells
are
which
eukaryotic,
are
not
found
but
in
they
also
animal
contain
cells.
a
cell
wall
and
chloroplasts,
1.2
u lt r A S t r u C t u r E
oF
C E ll S
Exampe 1.2.1.
The invention of electron
microscopes led to greater
Complete
the
table
using
a
tick
(✓)
for
“possible
presence”
or
a
understanding of cell structure.
cross
(✗)
for
“lack
of”
to
distinguish
prokaryotic
and
eukaryotic
The maximum magnification of a
cells.
light microscope is usually lower
Solution
than × 2,000 and the maximum
type f ce
Caaceisic
resolution is 0.2 μm. Beams of
Prokaryotic
Eukaryotic
✗
✓
pili
✓
✗
flagellum
✓
✗
✗
✓
✓
✗
nuclear membrane
electrons have a much shor ter
wavelength compared with light
waves, so electron microscopes
have a much higher resolution. The
maximum magnification of
mitochondrion
modern electron microscopes is
70S ribosomes
around ×10,000,000 and the
maximum resolution is less than
0.0001 μm.
S AMPlE StuDEnt AnS WEr
The electron micrograph shows the structures in a blood plasma cell.
▼ Although
correctly
the
functions
The
RER
across
the
the
electron micrograph with their principal role.
This
answer
could
have
Organelle
achieved
0/2
[2]
charge
The
its
but
correct.
in
in
is
did
organelles,
not
role
ATP
,
of
the
assist
cell,
principal
produce
student
are
does
proteins.
a) Using the table, identify the organelles labelled I and II on the
the
identify
transport
this
to
case
synthesize
mitochondria
but
they
are
not
in
secretion.
marks:
Name
Principal
role
You must be precise with the
I
rough
endoplasmic
transport
proteins
wording used.
reticulum
II
(RER)
mitochondria
across
secretes
cell
A
TP
▲ This
for
student
correctly
) Draw a labelled diagram of a eukaryotic plant cell as seen in an
The
electron micrograph.
vacuole
This
answer
could
have
[4]
achieved
3/4
plasma
▼ The
wall
Nucleus
Plasma
the
the
membrane
also
scored
a
mark
cell
and
wall.
the
mark.
marks:
nucleus,
chloroplast
Cell
scored
labelling
membrane
are
not
and
clear
Although
labelled
scheme
enough
the
the
did
ribosome,
mitochondrion
for
student
cytoplasm,
not
a
mark.
correctly
include
the
a
mark
mark
Lysosome
for
this.
Ribosome
Mitochondria
Cytoplasm
Vacuo le
It is good practice to include
multiple labels when answering
Chloroplast
this type of question because
it increases the likelihood of
identifying all the answers given
in the mark scheme.
5
1
C E LL
1 . 3
BI O LO G Y
M E M B R A N E
S T R U C T U R E
Y sd kw:
✔
membranes
cholesterol,
are
Y sd e ae :
formed
proteins,
by
phospholipids,
lipoproteins
✔
draw
and
the
uid
mosaic
model
in
two
dimensions.
glycoproteins.
✔
✔
membrane
structure,
proteins
position
are
in
diverse
the
in
terms
membrane
explain
of
the
plasma
uidity
and
permeability
of
the
membrane.
and
✔
analyse
electron
micrographs
of
plasma
function.
membranes.
✔
molecules
that
have
hydrophilic
and
✔
hydrophobic
properties
are
said
to
analyse
information
that
led
to
the
proposal
be
of
the
Davson–Danielli
model
and
its
later
amphipathic.
falsication
✔
phospholipids
amphipathic
✔
cholesterol
is
form
bilayers
due
to
their
leading
to
the
Singer–Nicolson
model.
properties.
a
component
of
animal
cell
membranes.
The
cell
membrane
is
formed
by
a
double
layer
of
phospholipids.
The ultrastructure of cells was
Phospholipids
are
amphipathic;
this
means
they
have
a
hydrophilic
studied in Topic 1.2.
part
and
outside
a
hydrophobic
and
the
inside
part.
of
the
The
cell
hydrophilic
while
the
heads
face
hydrophobic
both
part
the
is
in
the
DavsonDanielli model (1935)
middle
of
the
bilayer.
The
low
melting
point
of
phospholipids
in
protein
the
bilayer
acids
is
determined
occurring
at
by
the
unsaturated
kinking
bonds.
of
This
the
long
chain
determines
of
that
fatty
some
phospholipids
phospholipids
solid
state,
embedded
in
permeability
Proteins
are
are
found
proteins),
are
found
making
this
to
the
double
some
crossing
the
liquid
layer
state
fluid.
will
In
while
others
animal
control
this
cells,
fluidity
are
in
the
cholesterol
and
solutes.
embedded
some
in
membrane
in
from
partly
the
side
inside
phospholipid
to
side
bilayer.
(integral
(integral),
Some
proteins
transmembrane
whereas
others
are
only
on
SingerNicolson model (1972)
the
protein
outside
(peripheral).
Lipoproteins
and
glycoproteins
can
also
be
phospholipids
found
on
the
outside
of
the
cell
membrane.
• Ampipaic molecules contain
• Iea peis are embedded in
a ydpiic (water-loving) and a
the phospholipid bilayer and protrude
ydpic (water-repelling) par t.
on only one side of the membrane.
They are dicult to separate from the
• tasmemae peis are
phospholipid bilayer.
integral membrane proteins that span
Fie 1.3.1.
across the membrane. It is very hard
• Peipea peis are temporarily
to separate them from the membrane,
attached either to the surface of the
but this can be done using detergents
phospholipid bilayer or to integral
or solvents.
proteins. They can be separated from
Models of membrane
structure
The structure of phospholipids
is discussed in Topic 2.3, and
transpor t across membranes is
discussed in Topic 1.4.
the membrane using salts.
Davson and Danielli proposed a cell membrane model with two layers of
protein, and a layer of phospholipids between these layers. This model
was falsified by Singer and Nicholson. When the membrane was split open it
revealed irregular rough surfaces and therefore could not be a constant layer.
Membrane proteins were shown to be mobile and not fixed in place,
confirming the fluid mosaic structure.
6
1.4
MEMbrAnE
trAnSPor t
S AMPlE StuDEnt AnS WEr
Draw a labelled diagram that shows the positions of proteins within the
▲ This
cell membrane.
for
This
answer
answer
scored
one
mark
[3]
could
have
achieved
2/3
the
labelled
shown
marks:
integral
crossing
the
(transmembrane).
Inside
of
protein
membrane
The
second
mark
cell
was
for
the
glycoprotein.
Cho lestero l
Phospho lipid
heads—
amphipatic
▼ The
drawn
Peripheral
Integral
1 . 4
particles
move
diffusion,
protein
is
as
shown
is
Also
the
peripheral
not
embedded
on
the
in
membrane
surface;
protein.
hydrophilic
of
of
membranes
diffusion,
by
really
an
integral
T R A N S P O R T
by
simple
osmosis
✔
describe
and
of
allows
materials
endocytosis
or
to
be
released
✔
the
materials
within
cells.
✔
structure
and
sodium–potassium
describe
by
exocytosis.
move
is
cell
transport
membranes
cells
it
Y sd e ae :
across
facilitated
into
vesicles
bilayer,
and
transport.
uidity
✔
labelled
hydrophobic
M E M B R A N E
taken
protein
the
pro tein—
Y sd kw:
✔
bilayer
labelled.
Glycopro tein
Outside
active
not
pro tein—
hydrophilic
✔
phospholipid
but
in
the
structure
potassium
in
axons.
medical
in
a
and
channels
reasons
in
for
the
function
active
axons.
of
provide
explain
pumps
why
of
the
explain
need
same
the
facilitated
tissues
procedures
solution
for
or
to
function
diffusion
organs
be
used
bathed
osmolarity
as
the
cytoplasm.
✔
estimate
samples
The
cell
membrane
and
from
the
transport.
gradient;
require
cell.
Active
osmosis.
charged
it
and
Small
the
Substances
transport
therefore
energy
controls
molecules
can
includes
do
not
pass
usually
requires
molecules
entrance
simple
exit
out
by
by
substances
active
a
the
hydrophobic
bathing
solutions.
given in Topic 1.2 and the structure
in Topic 1.3.
and
However,
part
by
hypertonic
of cell membranes was discussed
not
diffusion
diffusion.
tissues
and
The ultrastructure of cells was
to
passive
does
facilitated
simple
or
in
hypotonic
concentration
transport
diffusion,
through
of
against
Passive
through
diffuse
or
occurs
energy
.
pass
in
and
osmolarity
in
of
the
• Passie asp  is the
movement across the membrane
without the use of energy.
membrane.
Ions
through,
while
negative
charges
larger
with
polar
molecules
positive
or
molecules,
over
pass
their
by
negative
which
surface,
facilitated
charges
have
diffuse
cannot
partial
at
very
diffusion;
easily
positive
low
channel
diffuse
• Faciiaed disi is the
and
rates.
Slightly
proteins
enable
passive transpor t of molecules
or ions across the cell membrane
through specic transmembrane
the
diffusion
of
some
molecules.
Water
molecules
pass
through
by
proteins (channel proteins).
osmosis.
• Acie asp  is the movement
Substances
that
cannot
enter
through
channel
proteins
because
they
across the membrane requiring
are
too
large
require
bulk
transport;
this
is
transport
in
membrane-
energy in the form of ATP
.
bound
vesicles.
Bulk
transport
into
the
cell
is
called
endocytosis
and
• osmsis is the passage of water
bulk
transport
exiting
the
cell
is
called
exocytosis.
In
endocytosis,
through a selectively permeable
the
fluidity
of
the
the
particle
to
be
cell
membrane
allows
the
membrane
to
surround
membrane, from a higher water
ingested.
In
exocytosis,
vesicles
formed
in
the
Golgi
potential (lower solute concentration)
complex
fuse
with
the
membrane
to
transport
the
substances
out
to a lower water potential (higher
of
the
cell.
solute concentration).
7
1
C E LL
BI O LO G Y
Exampe 1.4.1.
The
potassium
configuration.
present
called
a)
on
each
in
the
change
side
of
the
in
axons
can
structure
membrane;
show
an
depends
open
on
therefore
the
these
or
closed
charge
channels
are
voltage-gated.
Explain
how
channel
b)
channels
This
in
Suggest
the
the
the
disposition
membrane
mode
of
of
the
assists
transport
proteins
in
of
the
of
the
potassium
movement
potassium
of
ions.
through
these
channels.
Solution
a)
The
proteins
the
hydrophobic
parts
of
of
fatty
acids
sections
of
the
membrane
the
part
The
of
in
acting
they
the
allow
Facilitated
and
it
are
with
a
a
not
in
of
ions
the
The
surface
of
to
the
the
the
inner
on
the
tails
is
also
through
are
through,
part
of
surface
outside
channels
pass
in
The
hydrophilic
and
inside
water)
same
it
with
the
These
proteins.
embedded
cytoplasm,
(and
because
require
the
contact
ions
have
are
bilayer.
where
channel.
potassium
which
on
the
tunnel,
passage
as
transmembrane
proteins
membrane
make
diffusion,
does
the
are
phospholipid
proteins
only
ions
of
the
therefore
sodium
channel
contact
the
proteins
allowing
b)
of
of
the
the
of
cell.
hydrophilic,
the
centre,
very
not
specic;
smaller
charge.
occurs
through
a
protein
channel
energy
.
Exampe 1.4.2.
Compare
and
contrast
osmosis
and
active
transport.
You do not need to answer the
question in a table, but it helps
to make sure you are really
Solution
The
tick
(✓)
means
it
occurs,
the
cross
(✗)
that
it
does
not
occur.
comparing the two modes of
osmsis
Acie asp 
Meme acss ce memae
✓
✓
tasmemae pei eqied
✓
✓
✗
✓
✓
✗
transpor t. Remember you need
at least one similarity and one
difference. If the question is wor th
Eey eqied
3 marks you need to write at least
I e dieci f a cceai adie
three characteristics.
The
the
sodium–potassium
axons
of
potassium
forming
are
out
is
this
by
using
This
The
by
process
2
ATP
the
the
nervous
impulse
movement
through
gradient
active
protein
molecules.
to
Two
outside
potassium
for
pump
Three
of
the
ions
occur
sodium
allowing
transport.
the
of
to
membrane
sodium–potassium
through
the
a
diffusion
concentration
up
across
allows
involves
facilitated
built
transported
gradient
cell
by
channels.
movements
carries
neurons.
ions
pump
and
proteins
these
protein,
sodium
cell
can
along
which
ions
against
then
a
enter
the
diffusion.
• osmaiy is the measurement of
• A ype ic si has a higher
the solute concentration of a solution,
solute concentration than the tissues
expressed as the total mass of solute
(or cells) it bathes.
(or osmoles) per litre of solution.
• A ypic si has a lower
• An isic si shares the
solute concentration than the tissue
same concentration as the tissues or
it bathes.
cells it is bathing.
8
1.5
thE
or IgIn
oF
C E ll S
S AMPlE StuDEnt AnS WEr
Red blood cell 1 is a normal red blood cell.
Red blood cell 2 and red blood cell 3 are two red blood cells that have
been placed in solutions with dierent concentrations of solutes
(osmolarities).
red blood cell 1
red blood cell 2
red blood cell 3
a) Deduce, with a reason, which red blood cell has been placed in a
hyper tonic solution.
This
Red
answer
blood
could
cell
[1]
have
2,
achieved
because
1/1
all
marks:
water
left
the
cell
by
osmosis
▲ The
to
answer
because
try
to
This
Red
even
out
answer
blood
the
could
cell
1
concentration
have
was
achieved
placed
0/1
in
gradient.
it
it
is
thicker
than
a
the
hypertonic
▼ The
solution,
normal
blood
cell.
cell
answer
ratio in red blood cell 3.
It
has
could
have
achieved
T H E
cells
can
be
formed
pre-existing
1/1
O R I G I N
O F
of
rst
only
by
division
of
✔
analyse
cells.
cells
must
that
have
arisen
from
or
volume
has
evidence
endosymbiotic
Miller
theory
can
from
spontaneous
does
Pasteur ’s
generation
not
now
of
occur
experiments
cells
on
and
Earth.
non-living
✔
eukaryotic
Stanley
its
blood
Y sd e ae :
use
modern
that
the
that
red
shrunk
C E L LS
material.
✔
or
has
marks.
organisms
the
water,
it
not
is
[1]
Y sd kw:
✔
(because
it
decreased.
1 . 5
✔
2
does
that
decreased).
) State what change there has been in the cell surface area to volume
answer
mark
shrunken
marks:
lost
This
one
the
cell.
acknowledge
because
scores
identies
explain
the
repeats
apparatus
Pasteur ’s
to
design
an
experiment
experiment.
origin
cells.
and
Harold
Urey
carried
out
experiments
to
show
In Topic 5.1 you will study the
how
the
first
cells
might
have
arisen
from
non-living
material.
They
evidence for evolution.
passed
steam
representing
used
to
carbon
The
through
the
simulate
early
compounds
from
that
Earth
theory
were
of
methane,
atmosphere.
They
needed
prokaryotic
prokaryotes
mixture
lightning.
endosymbiotic
cells
a
for
found
life
explains
cells.
the
Electrical
that
were
by
amino
evolution
other
and
ammonia,
discharges
acids
and
were
other
produced.
Mitochondria
engulfed
hydrogen
are
of
eukaryotic
thought
prokaryotes
to
be
and
aerobic
remained
9
1
C E LL
BI O LO G Y
inside
the
cells.
photosynthetic
organelles
as
their
double
Likewise,
prokaryotes
maintain
own
chloroplasts
many
circular
membranes
engulfed
of
the
DNA and
produced
are
by
other
features
70S
by
thought
of
have
been
prokaryotes.
prokaryotic
ribosomes,
the
to
and
endocytic
they
Both
cells,
also
these
such
possess
mechanism.
Exampe 1.5.1.
Which
is
not
evidence
for
the
endosymbiotic
theory?
Negative questions are not very
frequent, but you must look out
A.
Prokaryotes
can
carry
out
photosynthesis
for them, as they can lead to
B.
Mitochondria
C.
Chloroplasts
have
a
double
membrane
confusion.
D.
have
Chloroplasts
70S
have
ribosomes
DNA
Solution
The
correct
fact
that
these
In
the
from
had
answer
some
were
past
engulfed
many
non-living
made,
called
such
by
people
as
as
although
are
other
Their
that
a
living
belief
was
appearing
in
true
statement,
does
or
out
to
things
based
rotten
Pasteur ’s
carried
generated
is
not
the
show
that
prokaryotes.
generation.
were
this
photosynthetic
believed
maggots
flasks
spontaneously
pre-existing
A,
materials.
spontaneous
swan-necked
be
is
prokaryotes
they
meat.
This
idea
with
whether
could
spring
up
observations
experiments
prove
whether
could
on
was
broth
microbes
come
only
they
in
could
from
cells.
1. Pasteur poured nutrients
into two asks like this.
Pasteur
investigated
Since
he
broth
in
He
knew
flasks
then
that
to
heated
how
broths
excess
kill
the
heat
could
anything
necks
of
turned
that
the
bad
kill
the
living
might
glass
in
be
flasks
following
things,
living
until
in
he
it
they
way
.
boiled
at
the
were
some
start.
soft,
and
2. He stretched
pulled
them
out
into
a
long,
thin,
curving
tube
called
a
swan-neck.
The
their necks into
broths
in
the
flasks
did
not
go
bad.
Then
Pasteur
broke
open
one
of
the
S-shapes.
flasks
that
and
the
exposed
broth
something
where
the
settled
test
in
his
went
and
into
he
could
be
settled
was
a
it
open
made
whatever
neck
and
dust
currents,
the
broth.
was
it
In
the
not
that
in
must
this
was
be
he
that
noticed
there
was
swan-necked
the
broth
reached
particles
broth
time
conclude
so
whatever
but
this
affecting
flask
other
The
that
and
therefore
and
again.
air
Pasteur
swan-necked
back
air
in
the
affecting
concluded
by
bend
This
clear,
the
to
was
where
tipped
Pasteur
the
bad.
of
bend
broth
that
tipped
carried
in
go
air
bend
he
the
bad.
did
the
broth
the
idea
then
went
in
the
some
may
second
broth.
the
have
causing
heavier
might
the
of
have
To
broth
collected,
flask
the
than
flasks
then
change
air
as
it
swan-neck.
Exampe 1.5.2.
What
theory
did
Pasteur
falsify
with
his
experiments?
3. He boiled the nutrients.
A.
Fie 1.5.1.
Independent
assortment
C.
Endosymbiosis
Pasteur's experiments
B.
Spontaneous
generation
D.
Evolution
Solution
The
correct
that
microorganisms
(covered
10
in
answer
is
B,
as
with
could
microbes)
were
not
his
experiments
grow
allowed
in
a
into
broth
the
Pasteur
unless
flask.
showed
dust
particles
1.6
1 . 6
C E L L
two
genetically
produced
during
from
Y sd e ae :
identical
the
daughter
division
of
the
nuclei
are
✔
nucleus
✔
interphase
✔
the
stages
of
✔
cyclins
✔
mutagens,
are
involved
a
very
by
active
mitosis
see
the
the
correlation
incidence
of
between
cancers.
supercoiling.
phase
occurring
of
in
the
the
identify
with
cell
cycle
✔
a
the
phases
microscope
determine
the
of
or
mitosis
in
mitotic
a
in
cells
viewed
micrograph.
index
from
a
micrograph.
nucleus
is
are
cell
division
in
oncogenes
in
prophase,
metaphase,
telophase.
involved
secondary
the
occurring
the
control
and
of
after
the
metastasis
development
of
mitosis.
cell
cycle.
are
primary
and
tumours.
chromatids
centromere
have
condense
processes
and
cytokinesis
a
to
and
cytoplasm.
✔
by
is
many
anaphase
Sister
data
smoking
✔
chromosomes
and
analyse
mitosis.
✔
with
DI vISIon
D I V I S I O N
Y sd kw:
✔
C E ll
separated
are
in
to
two
the
parts
early
form
of
a
stages
individual
chromosome
of
mitosis.
structures
attached
When
they
sister
are
to
each
other
chromatids
referred
to
as
You will study how DNA
replicates before cell division in
Topic 2.7. You will also study how
chromosomes.
cells divide to produce gametes in
Topic 3.3.
• Iepase is the stage of the cell
• Meapase is the stage where
division before mitosis. Cells grow,
chromosomes are aligned in the
forming organelles (G1 stage), DNA is
equator of the cell.
duplicated (S stage) and synthesis of
• Aapase is the stage where sister
proteins that are involved in nuclear
chromatids (V shape, with the ver tex
division occurs (G2 stage).
pointing to the poles) are separated
• Misis is nuclear division
to the opposite poles of the cell.
consisting of four stages: prophase,
When answering a question
relating to mitosis, you need to be
clear that mitosis is the nuclear
• tepase is the last stage
metaphase, anaphase and telophase.
of mitosis, where a nuclear
• Ppase is the stage where
membrane forms around each set of
chromatin condenses and associates
chromosomes that begin to uncoil.
division while cytokinesis is cell
division.
with histones forming chromosomes,
• Cykiesis is a process that occurs
the nuclear membrane disappears
along with telophase. The cytoplasm
and spindle bres are formed.
of the parental cell divides into two
Chromosomes attach to spindle
daughter cells. Cytokinesis in animals
bres.
is produced by cell strangling while in
plants it is by formation of a plate.
Exampe 1.6.1.
a)
b)
State
(i)
(ii)
two
processes
Dene
occurring
during
prophase.
‘centromere’.
Explain
the
reason
centromeres
are
facing
either
opposite
pole.
c)
Dene
‘mitotic
index’.
11
1
C E LL
BI O LO G Y
Sir Richard Timothy Hunt
Solution
discovered a new protein in
a)
During
prophase
fer tilized sea urchin eggs (Arbacia
histones
punctulata). Cyclin was
disappears
forming
and
chromatin
condenses
chromosomes,
spindle
bres
the
are
and
associates
nuclear
with
membrane
formed.
synthesized soon after the eggs
b)
(i)
The
centromere
that
holds
is
the
structure
of
the
chromosome
(DNA)
were fer tilized and increased in
together
both
chromatids.
It
is
also
the
point
of
levels during interphase, but the
attachment
to
the
spindle
bres.
levels decreased quickly in the
(ii)
middle of mitosis. The fact that the
During
anaphase,
amount of cyclins drops
the
periodically at different cell
attached
division stages proved to be of
towards
impor tance for cell cycle control.
and
c)
spindle
the
Number
under
of
the
to
bres
the
the
cells
One
sister
in
sister
chromatids
opposite
spindle
pole.
other
the
to
bre,
sister
poles.
the
are
the
by
total
to
by
always
migrates
migrates
divided
pulled
centromere
centromere
chromatid
chromatid
mitosis
As
the
to
is
goes
one
opposite
number
of
cells
rst
pole
pole.
seen
microscope.
S AMPlE StuDEnt AnS WEr
During the development of multicellular organisms, cells dierentiate
into specic cell lines. A study was carried out on the early stages of
dierentiation in cells from mouse embryos that were grown in cultures.
Two dierentiated cell lines were studied, one from the inner embryonic
tissue (endodermal cells) and the other from external embryonic tissue
(nerve cells). A culture of undierentiated cells was used as a control
group.
The role of regulators during cell dierentiation was studied. After 96
hours of incubation, a sample was taken of each cell line and the cyclins
separated by gel electrophoresis. The presence of dierent cyclins
D1, D2 and D3 was analysed in the three cell lines. The image shows
the results. The size and intensity of the bands is an indicator of the
quantity of cyclins.
control
endodermal
nerve
cyclin D1
cyclin D2
cyclin D3
a) Compare and contrast the amounts of the dierent cyclins in nerve
cells and control cells.
This
answer
T
here
high
is
▲ This
because
answer
it
scores
compares
full
all
marks
cyclins
is
cells
types
of
D2
most
the
D1
in
ner ve
in
marks:
contro l
ner ve
prominent
least
2/2
cells.
cells
of
cells,
T
here
is
than
the
prominent
is
almost
the
same
tissues.
cells
12
and
in
achieved
while
about
the
three
contro l
cyclins
in
there
in
ner ve
is
very
times
cells.
the
a
as
Cyclin
contro l
cells.
However
,
in
there
both
cyclin
the
have
cyclin
amount
much
D3
no
could
[2]
than
contro l
cells.
amount
of
cyclin
D3
in
ner ve
1.6
C E ll
DI vISIon
) Using the data, discuss the possible role of the three cyclins in the
dierentiation of nerve and endodermal cell lines.
This
answer
could
have
achieved
2/3
[3]
marks:
▲ The
answer
mentions
As
cyclin
D3
is
in
greater
quantity
in
the
endodermal
endodermal
specic
cells,
it
could
indicate
differentiation.
As
that
both
this
the
leads
to
an
endodermal
increase
and
the
same
amount
of
cyclin
D1,
it
may
control
be
the
differentiation
of
undifferentiated
ner ve
present
that
or
in
the
endodermal
ner ve
higher
cells
cell
than
presence
of
lines.
Cyclin
cells,
endodermal
cyclin
D2
D2
cells.
lowers
relation
nerve
to
and
D2
differentiation.
answer
does
not
mention
responsible
but
not
cyclin
causes
group
of
in
cells
that
for
for
D3
differentiation,
in
▼ The
have
correctly
cyclin
is
is
most
differentiation
contains
none
likely
what
as
control
of
the
it.
more
T
his
the
D1
suggests
rate
of
differentiation.
As this is a discussion, the answer could have mentioned that there is limited
data to determine roles of cyclins as there are very complex processes
involved.
Pacice pems f tpic 1
Pem 1
Pem 2
The electron micrograph shows a section of the
Glucose is a six-carbon sugar that provides energy
epithelium of the small intestine.
needed by cells. Because glucose is a large molecule, it
is difficult for it to be transpor ted across the membrane
through simple diffusion. Explain how glucose is
transpor ted into a cell such as a red blood cell down a
concentration gradient.
Pem 3
a) Describe the experimentation that led to the
proposal of the Davson–Danielli model of the
cell membrane and its later falsification leading
to the Singer–Nicolson model.
) Outline the process of endocytosis.
Pem 4
Describe the experiment of Miller and Urey into the
origin of organic compounds.
Pem 5
Identify  w structures present in these cells that show
Cells go through a repeating cycle of events in growth
they are involved in the uptake of food.
regions such as plant root tips and animal embryos.
Outline this cell cycle.
13
M O L EC U L A R
2
2 . 1
M O L E C U L E S
T O
M E TA B O L I S M
Yu shuld be able :
Yu shuld knw:
✔
molecular
via
the
biology
describes
interactions
of
the
living
chemical
✔
processes
explain
urea,
substances
also
involved.
✔
carbon
other
atoms
form
B I O LO GY
four
covalent
bonds
✔
with
that
are
synthesized
draw
molecular
saturated
atoms.
some
carbon
produced
fatty
by
compounds,
living
such
organisms
and
as
are
articially
.
diagrams
acid
and
a
of
glucose,
ribose,
generalized
a
amino
acid.
✔
living
organisms
compounds
proteins
✔
reactions
✔
in
anabolism
from
✔
molecules
nucleic
refers
a
is
simpler
catabolism
created
including
and
metabolism
are
is
cell
the
to
or
from
carbon
carbohydrates,
✔
lipids,
use
acids.
the
molecular
lipids
and
diagrams
amino
to
identify
sugars,
acids.
enzyme-catalysed
organism.
synthesis
of
complex
molecules
molecules.
the
into
breakdown
simpler
of
complex
molecules.
Carbon
atoms
form
four
covalent
bonds
with
other
molecules,
allowing
In 1828, Friedrich Wöler
the
production
of
a
variety
of
compounds.
All
living
organisms
are
synthesized urea, an
created
from
carbon
compounds,
including
carbohydrates,
proteins,
organic carbon compound, from
lipids
and
nucleic
acids.
These
compounds
are
used
by
living
inorganic salts. Carbon
organisms
in
a
complex
web
of
chemical
reactions
called
metabolism.
compounds were called “organic”
from the earlier belief that they
had an inner vital force that could
only be found in living organisms.
• Cabhydaes are molecules
• Pens are macromolecules
composed of carbon, hydrogen and
formed from chains of amino acids.
oxygen which serve as immediate
They contain carbon, hydrogen,
energy and for structural purposes.
oxygen and nitrogen. They can
They have the general formula
also contain sulfur. They have
This theory was called “vitalism”.
Because Wöler did not require any
living organism to obtain urea, the
C
n
(H
2
O)
many dierent functions in living
n
theory of vitalism was falsified.
organisms.
• Lpds are molecules composed
In Topic 1.3 you studied the
molecules that form membranes.
of carbon, hydrogen and, in a lesser
• Nuclec acds, such as DNA and
amount, oxygen. They serve as an
RNA, are molecules in charge of the
energy storage molecule and form
genetic information in cells. They
the cell membrane. They can also act
are composed of a nitrogenous base
as hormones.
joined to a sugar and a phosphate
In Topics 8.1 and D.5 you will study
group.
how these molecules are used in
metabolism.
Example 2.1.1.
The
diagram
Which
14
shows
diagram
the
shows
structure
the
of
structure
different
of
biological
D-ribose?
molecules.
2.2
C
CH
W At E r
OH
2
O
B
HOCH
2
A
O
You should be able to identify
H
=
H
−
−
O
−
−
−
N − C − C
OH
lipids or amino acids from
OH
H
R
D
HO
H
H
biochemicals such as sugars,
OH
HO
OH
H
H
H
H
OH
H
H
OH
H
H
molecular diagrams. You will only
be asked to identify a molecule
O
H
−
−
−
−
−
−
−
−
−
−
−
−
−
type from a series of molecular
H − C − C− C − C− C − C− C − C− C − C− C − C− O − H
H
−
H
−
H
−
H
−
H
−
H
−
H
−
H
−
−
−
−
H
H
structures you already know.
H
Solution
The
formula
the
• In anablsm, two or more
correct
answer
for
right,
an
the
is
diagram
amino
amine
acid;
group
B.
you
on
Diagram
can
the
A
clearly
left
is
see
a
generalized
the
containing
acid
molecules join to form a larger
group
nitrogen,
molecule.
on
and
• In caablsm, molecules
in
the
centre
could
be
a
Diagram
and
is
a
the
All
of
at
living
single
C
a
carbon
continually
organisms
processes
An
example
CH
loss
of
perform
be
seen
1
R
group
more
(side
complex
from
facing
carbons
and
obtain
allow
metabolic
changes
produced
in
the
is
fructose
one
the
to
the
cell.
the
chain)
groups
that
of
six-membered
downwards.
hydrogens
are broken down into smaller
atoms.
molecules.
ring
Diagram D
with
an
acid
reactions.
require
Anabolic
formation
glucose
of
and
These
are
enzymes
and
energy
a
that
series
are
catabolic
needed
reactions
to
perform
live.
molecule
molecule
that
chemicals
them
anabolism
of
or
carbon
monosaccharide
monosaccharide
the
can
the
1.
to
that
of
A six-carbon
of
chain
to
atom
as
biological
being
the
with
group
long
organisms
and
joined
hydrogen
α-glucose,
is
acid,
chemical
allow
α-carbon
hydroxyl
fatty
group
the
to
of
sucrose,
molecule
form
the
joins
common
a
sugar.
six-carbon
disaccharide
sucrose,
water.
CH
OH
OH
2
2
CH
OH
2
CH
OH
2
O
O
O
H
H
O
H
H
H
H
H
H
+
H
OH
H
OH
HO
HO
HO
CH
H
HO
H
HO
OH
O
2
CH
OH
2
glycosidic
H
OH
H
H
OH
OH
OH
bond
H
between
H
C1 and C2
O
2
Fgue 2.1.1.
The formation of sucrose (a disaccharide) from the condensation of glucose and fructose (two
monosaccharides)
2 . 2
W AT E R
Yu shuld knw:
✔
water
end
✔
molecules
and
water ’s
a
negative
cohesive,
properties
bonding
✔
are
can
and
hydrophilic
by
polar,
they
have
a
positive
✔
end.
compare
those
adhesive,
explained
thermal
by
and
solvent
✔
of
explain
the
thermal
properties
of
water
with
methane.
how
water
acts
as
a
coolant
in
sweat.
hydrogen
dipolarity
.
substances
(water-loving)
repelled
be
Yu shuld be able :
and
water
are
attracted
hydrophobic
to
water
substances
are
(water-fearing).
15
2
MOLEC UL AR
BI O LO G Y
Water
is
formed
from
one
atom
of
oxygen
and
two
atoms
of
hydrogen
Carbon compounds and carbon
joined
by
covalent
bonds.
The
hydrogen
atoms
form
a
V
shape
with
cycling will be studied in Topic 4.3.
the
oxygen
in
the
hydrogen
the
vertex.
The
atom
of
oxygen
is
electronegative
while
Topic 4.4 describes how carbon
atoms
are
electropositive.
The
negative
part
of
one
water
dioxide released from metabolic
molecule
is
attracted
to
the
positive
part
of
another
water
molecule,
reactions causes climate change.
forming
are
electromagnetic
weak,
water
but
many
bonds
bonds
called
together
hydrogen
form
a
bonds.
strong
These
bonding
bonds
between
molecules.
+
δ
H
Water
has
particular
thermal
properties.
Each
hydrogen
bond
has
an
1
+
+
δ
δ
H
O
average
δ
energy
of
20
kJ
mol
,
therefore
water
needs
a
lot
of
heat
to
H
change
+
has
δ
δ
a
state,
high
causing
specific
the
heat
boiling
capacity
,
and
a
melting
high
heat
points
of
to
be
high.
vaporization
Water
and
a
high
O
H
heat
+
of
fusion.
Example 2.2.1.
δ
H
a)
Complete
the
table
to
distinguish
the
solubility
of
molecules.
Place
δ
O
a
tick
(✓)
in
the
cases
where
the
molecules
are
soluble
in
water.
+
δ
H
Fgue 2.2.1.
Solution
Hydrogen bonding
a)
Mlecule
glucose
amino
fats
cholesterol
oxygen
sodium
between two water molecules
acids
Slubly
✓
chloride
✓
✓
✓
n wae
b)
Explain
the
possibility
relationship
of
transport
between
in
blood
the
solubility
plasma
of
in
these
water
and
the
molecules.
• Hea capacy is the energy
required to raise the temperature of
Solution
1 g of substance by 1°C.
b)
• Hea f vapan is the energy
Water-soluble
which
required to change 1 g of liquid to
is
soluble
substances
composed
in
water,
can
mainly
such
as
be
of
transported
water.
lipids,
in
blood
Substances
need
to
be
that
plasma
are
transported
not
through
vapour.
vesicles
or
attached
• Hea f fusn is the energy
Cholesterol
required to change 1 g of solid to
to
liquid.
be
cholesterol,
2 . 3
monosaccharide
condensation
and
example
to
proteins,
for
✔
monomers
reactions
to
are
form
joined
by
✔
disaccharides
acids
can
be
saturated,
monounsaturated
A N D
proteins.
molecule
high-density
that
has
lipoprotein
L I P I D S
identify
and
cellulose,
unsaturated
fatty
analyse
starch
function,
acids
can
be
cis
or
trans
and
the
and
✔
explain
are
acids
formed
and
one
by
condensation
from
✔
with
the
glycerol.
compare
energy
✔
structure
and
function
glycogen.
about
✔
of
to
their
molecular
health
fatty
risks
acids
lipids
and
evidence
in
starch
and
structure
visualization
of
trans
the
fats
and
software.
and
diet.
carbohydrates
in
terms
of
the
and
evidence
the
for
methods
health
used
claims
to
made
lipids.
determine
use
respect
cellulose,
storage.
evaluate
obtain
contrast
using
saturated
triglycerides
fatty
compare
glycogen
polyunsaturated.
three
16
insoluble
as
transport.
of
isomers.
✔
an
forming
such
polysaccharides.
fatty
or
of
substances
Yu shuld be able :
✔
✔
soluble
an
C A R B O H Y D R AT E S
Yu shuld knw:
✔
is
attached
to
a
body
mass
nomogram.
index
by
calculation
or
2.3
Monosaccharide
monomers,
such
as
glucose
and
fructose,
can
C A r B o H Y D r At E S
AND
LiP iD S
be
• Cabhydaes are carbon
linked
together
with
glycosidic
bonds
to
form
disaccharides,
such
as
compounds containing hydrogen
sucrose.
Because
this
reaction
liberates
water
it
is
called
a
condensation
and oxygen. They serve as energy
reaction.
Sucrose
is
found
in
plants.
Lactose,
the
sugar
found
in
milk,
storage and structural components
and
maltose,
the
sugar
found
in
seeds,
are
also
disaccharides.
Lactose
of organisms.
is
formed
from
glucose
and
galactose.
Maltose
is
composed
of
two
• Mnsacchades are simple
glucose
molecules
and
is
produced
by
the
hydrolysis
of
starch.
sugars and are the basic building
blocks of carbohydrates.
Polysaccharide
polymers
are
composed
of
long
chains
of
• Dsacchades are two
monosaccharides.
The
most
abundant
polysaccharides
in
nature
are
monosaccharides joined together.
starch
and
mainly
of
cellulose,
found
α-glucose,
while
in
animals.
amylose
amylopectin
joined
through
bonds
are
are
joined
O
H
is
are
found
Starch
and
in
carbon
branched.
H
the
6
main
In
O
plants,
composed
and
of
In
the
glycogen,
two
Amylose
amylose,
bonds.
branch,
is
different
a
linear
glucose
amylopectin,
but
which
is
polymers
molecule,
molecules
these
α-glucose
other
α-1,6-glycosidic
forming
H
is
in
amylopectin.
α-1,4-glycosidic
formed
at
which
• Plysacchades are polymers of
monosaccharides.
are
same
molecules
bonds.
H
Example 2.3.1.
4
1
O
glucose
1
O
units
A disaccharide
O
is
broken
1,6 linkage
α-
down
into
glucose
and
fructose.
1,4 linkage
α6
CH
a)
2
O
H
H
O
H
H
O
H
H
State
side
4
1
O
name
of
the
branch
1
H
the
disaccharide.
5
1
O
O
O
b)
Identify
the
type
of
bond
main
branch
amylopectin
Fgue 2.3.1.
present
Structure of starch
bonds.
of
the
a
polymer
Because
chain
upside
This
is
to
down
makes
the
the
in
hydroxyl
hydroxyl
order
cellulose
body
.
Many
fibres
found
cellulose
in
β-glucose
of
the
to
a
position
walls
on
on
these
of
join
two
1
4,
is
are
by
on
disaccharide.
hydroxyl
to
made
to
opposite
second
groups
digest
form
in
these
side
glucose
is
b)
Glycosidic
by
bond
(formed
condensation)
together.
the
human
microfibres.
from
Sucrose
1,4-glycosidic
the
every
difficult
together
plants
joined
carbon
carbon
molecule,
molecules
cell
molecules
group
group
strong
the
Solution
a)
Cellulose
in
The
cellulose
Lipids in the diet have been
microfibres.
said to be bad for human
health. Never theless, they are
Example 2.3.2.
necessary for many metabolic
processes. Health problems linked
a)
Compare
and
contrast
the
structure
of
glycogen
and
starch.
to dietary lipids include obesity
b)
Explain
affects
how
their
the
bonding
in
starch
and
cellulose
molecules
and coronary hear t disease.
structure.
Solution
a)
Glycogen,
plants,
two
while
glycogen,
an
with
b)
the
in
Starch
in
amylose
and
amylopectin
bond
joining
molecules,
starch,
is
same
In
by
the
in
the
the
chain
molecule
while
In
one
is
both
of
is
a
at
by
linear
and
molecules
carbon
formed
branching
more
group
on
is
starch
occurs
also
in
formed
glucose
cellulose
hydroxyl
the
the
is
Amylose
branching
Glycogen
found
Starch
chain
glycogen
as
starch,
branched.
main
The
α-glucose
α-glucose
of
is
bond.
but
and
molecules.
amylopectin.
the
bond.
therefore
formed
side
animals,
glucose
α-1,6-glycosidic
β-glucose.
the
of
α-1,4-glycosidic
an
branched
than
mostly
polymers
molecules,
molecule
is
found
are
is
6
from
greater
compact.
is
on
formed
carbon
carbon
4,
1
by
is
on
allowing
the
17
2
MOLEC UL AR
BI O LO G Y
• Lpds are carbon compounds
formation
of
the
1,4-glycosidic
bond.
β-glucose,
In
the
hydroxyl
containing mainly hydrogen
groups
are
found
on
different
sides
of
the
chain.
In
order
for
the
and some oxygen. They form a
β-1,4-glycosidic
bonds
to
form,
every
second
β-glucose
needs
to
diverse group containing oils,
be
upside-down
in
order
to
position
the
hydroxyl
groups
on
the
fats, membrane components and
same
side
of
the
chain.
hormones.
• Fay acds are formed by long
chains of carbons (4 to 34) with
Lipids
are
carbon
compounds
such
as
glycerides
and
steroids
that
are
hydrogens attached and an acid
insoluble
in
water.
They
contain
double
the
energy
of
carbohydrates.
group at one end.
Fatty
• Unsauaed fatty acids have
by
double or triple bonds between two
1.
a
acids
long
The
are
the
chain
carbons
of
main
components
carbons
can
be
and
joined
of
simple
hydrogens
by
single
or
lipids.
with
an
double
They
acid
are
group
bonds.
formed
at
When
carbon
the
fatty
or more carbons.
acid
• Sauaed fatty acids do not have
has
double
any double or triple bonds.
have
or
• Cis fay acds have the two
no
double
bonds
only
more
it
one
is
bonds
said
double
double
to
it
is
be
bond
said
to
be
saturated;
unsaturated.
while
if
it
has
one
Monounsaturated
polyunsaturated
fatty
or
fatty
acids
more
acids
have
two
bonds.
hydrogen atoms adjacent to the
Unsaturated
fatty
acids
can
have
the
hydrogen
atoms
next
to
the
double bond located on the same
double
bond
on
the
same
side
or
on
opposite
sides
of
the
chain.
If
the
side of the chain.
hydrogen
atoms
are
on
the
same
side
of
the
chain,
the
unsaturated
• Trans fay acds have the two
fatty
acid
is
said
to
be
cis;
if
they
are
on
opposite
sides
of
the
chain
it
hydrogen atoms adjacent to the
is
trans.
The
tail
in
cis
fatty
acids
kinks,
separating
the
molecules.
This
double bond located on opposite
gives
cis
fatty
acids
a
lower
melting
point
than
trans
fatty
acids.
sides of the chain.
There
the
are
others
H
H
H
−
know
by
−
H
H
H
H
H
only
very
the
lipids.
complex
structure
condensation
These
H
have
of
formed
Some
from
have
glycerol
molecules,
a
simple
and
such
one
as
structure,
fatty
acid,
steroids.
You
such
as
while
from
of
triglycerides.
three
fatty
acids
Triglycerides
and
one
are
need
to
glycerol
formed
molecule.
−
−
−
−
−
−
−
−
O
H
types
H
−
−
−
=
H
C − C − C − C − C − C − C − H
−
−
H
−
C − C −
H
−
−
H
−
C
H
−
−
O
many
monoglycerides,
H
fatty
acids
do
not
need
to
be
the
same.
In
some
cases,
one
H
carbon
joins
to
a
phosphate
group
instead
of
a
fatty
acid,
forming
H
a
saturated fatty acid
phospholipid.
another
group,
phospholipid
H
C−
−
H
an
at
forming
important
part
the
same
time
join
to
phosphatidylcholine,
of
the
cell
a
membrane.
−
C −
−
−
−
−
−
−
−
H
forms
choline,
can
H
−
C −
O
H
that
example
group
H
−
− C − C − C − C
for
phosphate
H
−
=
H
−
C − C
H
−
−
H
−
C
H
−
−
−
H
=
H
O
This
H
H
H
H
H
H
H
C
H
C
glycerol
unsaturated fatty acid
H
Fgue 2.3.2.
C
H
Saturated fatty acid
H
O
H
C
C
H
C
C
H
O
with no carbon–carbon double bonds
three fatty acids
O
and unsaturated fatty acid showing one
H
C
C
carbon–carbon double bond
H
3H
H
H
H
−
O
−
−
−
−
−
−
−
H
H
H
H
C
O
O
C
O
−
H
H
−
C − C− C
O
H
H
=
C − C −
O
H
−
C − C=
H
−
−
− C −
C
H
−
−
−
H −
H
H
triglyceride
H
C
O
C
H
C
O
C
O
H
trans fatty acid
H
O
H
= C
−
C −
−
C −
−
−
−
‘water-repelling’
O
H
O
H
cis fatty acid
18
C
O
C
H
C
P
= phosphate
O
H
H
Fgue 2.3.3.
H
=
C
H
H
tails: hydrophobic
phospholipid
−
H
C
−
C
H
−
−
C
H
H
−
H
C
−
−
−
−
C
−
−
C
H
−
−
−
H
−
H
H
−
H
H
H
Cis and trans fatty acids
Ch
= choline
‘water-liking’
Fgue 2.3.4.
Formation of triglycerides and structure of a phospholipid
2.3
C A r B o H Y D r At E S
AND
LiP iD S
Example 2.3.3.
Explain
the
the
health
risks
of
trans
fats
and
saturated
fatty
acids
in
diet.
Solution
Triglycerides
unsaturated
called
high
trans
so
fats)
density
double
of
bonds
tightly
.
hardening
of
plaques
atheroma
even
can
It
form
or
of
or
branches
the
infarction,
a
the
in
of
are
pack
acids
these
tightly
contacts.
irregular
saturated
on
fatty
with
or
artery
in
shape
trans
fats
walls
of
macrophages,
swelling
in
the
flow
of
other
blood.
heart
artery
The
cardiovascular
a
acids
of
and
may
or
the
are
forming
lipids
cannot
blood
heart
formation
or
An
connective
slows
flow
attack
pack
contribute
and
which
a
with cis
(atherosclerosis).
wall
loss
disease,
from trans
together,
(arteriosclerosis)
the
or
fatty
Hydrocarbons
mainly
coronary
or
made
that
arteries
atheroma
forms
blocks
saturated
(fats
rods
levels
consists
result
from
acids
intermolecular
High
to
tissue.
formed
fatty
to
down
the
or
heart
myocardial
diseases.
S AMPLE StUDENt ANS WEr
The image shows a nomogram.
140
135
130
clinically obese
125
body mass index (BMI)
120
obese
115
50
48
110
40
46
44
105
42
35
100
over weight
38
gk / thgiew
36
95
30
34
32
90
25
28
85
normal
26
80
24
75
22
18.5
20
70
18
65
16
(155 cm, 60 kg)
60
14
55
under weight
50
45
40
145
150
155
160
165
1
70
1
75
180
185
190
195
200
205
▲ On
the
nomogram
where
the
155
the
point
height / cm
intersects
the
cm
height
line
line
between
normal
a) Using the nomogram, state the lower weight limit for a woman with
and
the height of 155 cm to be classified as overweight, giving the units.
This
answer
could
have
achieved
1/1
weight
limit:
60
marks:
▼ This
H
could
have
achieved
1/2
[2]
acid
60
kg
weight.
does
not
show
group.
mark
group
was
and
given
for
hydrogens
the
shown.
marks:
▼ The
H
structure
acid
▲ One
answer
at
kg
b) Draw the structure of a saturated fatty acid.
This
is
[1]
the
Lower
overweight
structure
on
the
left
only
O
has
H
three
carbons
and
the
shortest
C
H
H
fatty
acid
with
4
known
is
butyric
acid,
OH
carbons.
19
2
MOLEC UL AR
2 . 4
BI O LO G Y
P R O T E I N S
Yu shuld knw:
✔
polypeptides
linked
✔
are
together
polypeptides
20
✔
a
different
huge
in
any
are
the
of
from
amino
✔
acids
proteins
living
condensation.
synthesized
amino
range
because
formed
by
in
ribosomes
from
✔
a
polypeptides
acids
can
is
be
genes
a
code
protein
multiple
✔
the
is
very
wide
range
of
functions
in
is
it
the
is
full
set
unique
of
to
proteins
each
in
an
individual.
Yu shuld be able :
together
sequence.
for
the
amino
acid
sequence
describe
spider
may
consist
of
polypeptides
three-dimensional
determined
by
the
one
polypeptide
linked
or
✔
of
acid
of
how
denature
a
protein
✔
draw
a
acids
are
the
of
rubisco,
rhodopsin,
insulin,
collagen
and
heat
building
and
changes
to
pH
can
protein.
molecular
formation
sequence.
Amino
functions
silk.
explain
together.
conformation
amino
the
immunoglobulins,
of
polypeptides.
✔
a
possible
linked
✔
✔
proteome
individual;
acids.
amino
have
organisms.
of
a
diagrams
peptide
blocks
of
to
show
the
bond.
proteins.
There
are
20
different
The synthesis of proteins
amino
acids.
These
amino
acids
are
joined
by
condensation
in
the
through translation will be studied
ribosomes
to
form
polypeptides.
The
bond
between
amino
acids
in Topic 2.7. The industrial use of
is
called
a
peptide
bond.
A DNA molecule
is
used
as
a
blueprint
to
organisms to produce proteins will
produce
RNA that
will
carry
the
information
to
produce
a
polypeptide
be discussed in Topic B.1.
in
a
process
protein
is
called
translation.
determined
by
the
The
three-dimensional
amino
acid
shape
of
a
sequence.
Most organisms assemble
• rubsc is the shor t name for
• Cllagen is a brous protein found
ribulose bisphosphate carboxylase/
in connective tissues.
proteins from the same 20
amino acids. However, pyrrolysine
oxygenase. It is the enzyme involved
• Spde slk is a brous protein made
and selenocysteine, which were
in photosynthesis that takes par t in
by spiders to spin their web.
discovered fairly recently, are two
carbon dioxide xation.
additional amino acids that are not
present in all organisms, and they
• Peme is all of the proteins
• insuln is a hormone that promotes
produced by a cell, a tissue or an
the absorption of glucose by the liver.
are genetically encoded in a
organism.
dierent way from the other 20.
• immunglbulns are globular
• Gel elecphess is a method
proteins that function as antibodies.
used to separate proteins according
They have a number of roles in the
to their size.
body’s immune defence.
• rhdpsn is a pigment involved in
▲ The
answer
scored
a
mark
for
light detection.
showing:
• each amino acid with an acid group
S AMPLE StUDENt ANS WEr
(COOH) at one end and an amine
a) Draw molecular diagrams to show the condensation reaction between
group (NH
) at the other end;
2
two amino acids to form a dipeptide.
•
the
double
Cand
•
the
bond
between
This
O;
α-carbon
in
the
[4]
the
middle
answer
could
have
achieved
4/4
marks:
with
H
H
and
R
group
attached;
N
•
the
peptide
bond
correctly
C
C
N
drawn
OH
OH
H
R
between
Marks
N
would
awarded
for
and
C
also
the
=
have
acid
H
0.
R
1
been
group
at
one
H
H
O
H
H
O
end
of
the
dipeptide
and
the
amine
H
H
at
the
other
end,
plus
another
N
N
OH
for
showing
the
loss
of
R
water.
R
20
O
2
mark
1
2.5
ENzY ME S
Example 2.4.1.
Explain
how
heat
can
denature
a
protein.
It is possible to provide more
correct answers than there are
Solution
Heat
can
thereby
rubisco,
is
detect
a
gel
the
its
would
the
interactions
broken,
in
it
increased,
the
To
modify
affecting
cease
between
the
In
electrophoresis
of
the
catalyse
the
R
a
the
tissue,
of
an
within
the
of
of
a
When
the
have
substrates
amino
can
molecular
enzyme’s
required
to
can still get full marks for another
be
correct point.
proteins
are
extracted
then
separated
run.
an
Yu shuld be able :
active
site
to
which
specic
✔
bind.
design
movement
active
for
site
and
with
collision
the
of
rate
of
activity
pH
of
of
are
✔
sketch
graphs
temperature,
enzymes
and
activity
depends
substrate
activity
enzymes
can
be
denatured.
✔
enzymes
can
be
immobilized
to
be
to
and
test
the
effect
substrate
of
concentration
on
enzymes.
to
pH
of
show
and
the
expected
substrate
effects
of
concentration
on
enzymes.
on
concentration.
✔
describe
and
✔
pH
the
substrate
catalysis.
temperature,
experiments
temperature,
the
the
on the mark scheme because you
cause
acids
the
✔
matter if you missed something
temperature
E N Z Y M E S
enzymes
✔
you write a good answer, it won’t
as
protein.
Yu shuld knw:
✔
such
molecule
different
marks available in the question. If
protein,
enzyme
reaction.
groups
of
structure
case
vibrations
structure
proteome
2 . 5
to
increased
changing
the
three-dimensional
function.
used
its
methods
to
produce
lactose-free
milk
advantages.
in
industry
.
Enzymes
control
cell
metabolism.
They
are
globular
proteins
that
have
How enzymes are used in
a
catalytic
zone
called
the
active
site.
This
site
can
consist
of
around
metabolism, cell respiration and
three
to
twelve
amino
acids.
Changes
in
temperature
and
pH
can
alter
photosynthesis will be discussed in
the
spatial
disposition
of
the
protein,
affecting
the
rate
of
reaction
of
the
Topic 8.
enzyme.
enzyme
If
the
change
unable
to
is
extreme,
the
protein
can
denature,
leaving
the
work.
• An enyme is a globular protein
that acts as a biological catalyst.
• A subsae is the molecule
changed by the enzyme.
• The acve se is the par t of the
enzyme that binds to the substrate.
• Denauan is the loss of the
ter tiary structure of the enzyme.
• opmum describes the ideal
conditions required for an enzyme
to work .
Fgue 2.5.1.
Structure of an enzyme showing its active site in red
21
2
MOLEC UL AR
BI O LO G Y
S AMPLE StUDENt ANS WEr
Keratin is a protein found in hair, nails, wool, horns and feathers. The
graphs show the relative keratinase activity obtained in experiments of
keratin digestion at dierent pH values and at dierent temperatures.
% / ytivitca evitaler
% / ytivitca evitaler
100
80
60
40
20
100
80
60
40
20
0
0
3
4
5
6
7
8
9
10
11
12
13
20
30
pH
40
50
60
70
a) Determine the optimum pH and temperature of keratinase.
This
▲ The
student
optimum
44
to
and
identied
temperature
48°C
and
the
pH
in
80
90
temperature / ºC
answer
could
have
achieved
Optimum
pH =
8.
Optimum
temperature:
1/1
[1]
marks:
the
the
range
between
7.8
45°C.
8.5.
b) Suggest  w changes occurring in the reaction vessel that could be
used to indicate keratinase activity.
This
▲ Marks
could
mentioning
or
absorbance
changes
be
scored
changes
or
in
any
indicating
for
answer
could
have
achieved
[2]
2/2
marks:
T
he
change
in
mass
of
keratin.
T
he
change
in
mass
of
the
colour
newly
produced
amino
acids.
chemical
the
presence
of
c) State two conditions that should be kept constant in both
amino
acids.
experiments.
This
▲ The
answers
amount
of
scored
a
or
as
of
pH,
the
are
buffer
mark,
these
correct.
would
but
not
were
could
have
achieved
2/2
marks:
The
have
T
he
mass
T
he
time
of
keratinase
used.
also
temperature
the
answer
[2]
of
keratinase–keratin
reaction.
variables
experiment.
Increasing
of
substrate
enzymes,
occupied
but
and
concentration
only
the
up
to
enzyme
a
will
point,
will
not
as
be
increase
all
the
able
the
active
to
react
rate
sites
any
of
reaction
will
become
faster.
etar noitcaer
active sites occupied by
Example 2.5.1.
substrate molecules
Describe
pointing
a
method
out
the
to
obtain
a
advantages
named
and
immobilized
disadvantages
of
enzyme,
the
method.
Solution
substrate concentration
Fgue 2.5.2.
Effect of the substrate
Lactase
is
form
produce
to
concentration on the rate of reaction of
alginate
an enzyme
Lactase
are
enzyme
beads
the
the
separated
stabilizes
the
lactose
enzymes
from
the
more
the
of
or
in
the
Milk
found
people.
be
in
industry
in
is
poured
milk
in
into
the
cases,
reducing
the
its
immobilized
this
of
it
in
column.
and
making
times,
galactose,
suitable
immobilization
as
they
can
be
immobilization
reactions
cases
an
glucose
milk,
advantages
many
in
immobilized
through
A disadvantage
some
matrix,
is
many
therefore
values.
and
The
In
in
Lactase
sugar
used
product.
pH
used
milk.
lactose
can
enzyme,
expensive
sequestered
22
column.
amount
temperatures
is
a
lactose-intolerant
that
widely
lactose-free
in
digests
reducing
for
an
can
of
occur
the
enzyme
reactivity
.
at
different
method
has
its
is
that
active
it
site
2.6
2 . 6
S T R U C T U R E
O F
D N A
Yu shuld knw:
✔
the
of
✔
nucleic
DNA differs
type
of
DNA is
RNA are
polymers
✔
explain
a
RNA in
the
DN A
AND
rNA
R N A
how
base
the
number
composition
of
✔
and
draw
the
of
simple
nucleotides
Crick
and
Watson
DNA using
diagrams
of
model
of
DNA and
the
elucidated
structure
RNA,
the
making.
of
pentoses
single
and
bases.
double
hydrogen
base
from
pentose.
antiparallel
helix
strands
bonding
of
composed
of
nucleotides
between
two
linked
by
complementary
pairs.
DNA is
a
aligned
in
bonds
DNA and
structure
present,
oF
Yu shuld be able :
nucleotides.
strands
✔
acids
A N D
StrUCtUrE
chain
an
of
nucleotides
antiparallel
between
forming
manner
complementary
and
a
double
are
held
nitrogenous
helix.
The
together
bases,
C
by
with
strands
are
The genetic modification of DNA
hydrogen
G
and A with
and its use in biotechnology will be
T.
described in Topic 3.5. In Topic 7
the structure of nucleic acids will be
S AMPLE StUDENt ANS WEr
studied in more detail.
Label the par ts of two paired nucleotides in the polynucleotide of
DNA.
This
[3]
answer
could
have
achieved
2/3
marks:
A
nitrogenous
base
▼ “5-carbon
adenine
sugar”
is
too
vague
T
for
5-carbon
a
mark.
The
correct
answer
is
sugar
deoxyribose.
phosphate
group
• DNA (dex ybnuclec acd) is a polymer of nucleotides containing the
genetic instructions responsible for inheritance. The segments carrying the
Use circles, pentagons and
information are called genes.
rectangles to represent
phosphates, sugars and bases
• rNA (bnuclec acd) is a polymer of nucleotides containing the genetic
respectively. The two DNA strands
instructions for protein synthesis.
should be shown antiparallel.
• A nuclede is a molecule containing a phosphate, a sugar and a
nitrogenous base.
• The ngenus bases adenine (A), guanine (G), cytosine (C) and thymine
Crick and Watson created
(T) are found in DNA ; uracil (U) replaces thymine in RNA .
models to discover the
• Cmplemenay nitrogenous bases are linked by hydrogen bonds on
structure of DNA. They used
opposite strands of DNA or double-stranded RNA.
information from Rosalind
Franklin’s X-ray diffraction images
Example 2.6.1.
of DNA and Erwin Chargaff ’s
measurements of the propor tions
The
table
shows
the
ratio
of
nucleotides
in
the
DNA of
different
of each of the four bases.
organisms.
Suce
A  G
A  t
C  t
C  G
human
1.29
1.04
0.57
1.00
salmon
1.43
1.02
0.70
0.98
wheat
1.22
1.00
0.85
1.03
E. coli
1.05
1.09
1.05
1.01
23
2
MOLEC UL AR
BI O LO G Y
a)
State
the
two
nucleotide
ratios
that
are
closest
to
1
for
most
organisms.
b)
Discuss
whether
adenine
pairs
(A)
with
this
always
guanine
data
pairs
(G)
supports
with
by
the
hypothesis
thymine
(T)
complementary
and
that
cytosine
base
pairing
(C)
in
theDNAstructure.
Solution
a)
A to
b)
T
and
DNA is
paired
are
no
close
✔
helicase
the
two
on
its
unpaired
to
1,
while
of
A in
amount
of
T.
that
nucleotides.
A to
the
The
they
are
T R A N S L AT I O N
semi-conservative
the
by
DNA polymerase
template
in
base
double
breaking
and
✔
mRNA is
pairing.
helix
and
hydrogen
uses
the
separates
✔
bonds.
DNA strand
as
from
explain
A to
This
C
one
G
strand
and
is
C
to
that
similar
G.
is
strand;
and
means
organisms
with
DNA base
RNA polymerase
in
processes
how
multiple
This
T
there
are
the
to
not
total
the
total
supports
the
basepairing.
and
Taq
copies
reaction
of
replication,
translation.
DNA polymerase
of
DNA by
the
produces
polymerase
(PCR).
a
✔
the
the
explain
the
the
universality
production
of
of
the
genetic
human
code
insulin
in
sequences
bacteria
by
are.
in
second
complementary
transcription
replication.
copied
by
the
ratios
G
these
happens
explain
using
✔
to
base
in
T R A N S C R I P T I O N
chain
✔
The
C
DNA of
Each
base
Yu shuld be able :
complementary
strands
and
joining
A N D
unwinds
T
same
R E P L I C AT I O N ,
is
helix.
complementary
D N A
DNA replication
depends
G.
double-stranded
with
Yu shuld knw:
✔
to
amount
idea
2 . 7
a
C
as
an
example
of
gene
transfer
between
transcription.
species.
✔
synthesis
of
polypeptides
occurs
on
ribosomes
✔
in
deduce
the
DNA base
sequence
for
the
mRNA
translation.
strand.
✔
mRNA determines
the
amino
acid
sequence
of
✔
polypeptides
according
to
the
genetic
deduce
amino
✔
codons
of
three
bases
on
mRNA correspond
amino
acid
in
a
acid
translation
base
depends
pairing
anticodons
on
between
on
complementary
codons
DNA replication, transcription and
translation in genetic modification
and biotechnology will be studied.
Transcription and gene expression
will be studied in more detail in
Topic 7.2; translation will be covered
24
corresponds
genetic
to
which
code.
analyse
Meselson
on
for
the
and
replication
of
of
is
theory
Stahl’s
of
results
to
obtain
semi-conservative
DNA.
mRNA and
tRNA.
In Topic 3.5 the impor tance of
in Topic 7.3.
codon(s)
the
polypeptide.
support
✔
in
to
✔
one
which
code.
The
central
then
principle
makes
inheritance.
template
is
to
proteins.
In
is
a
link
new
Therefore
replication,
DNA forms
DNA carries
together
because
strand.
that
all
DNA polymerase
nucleotides
semi-conservative
other
genetics
one
to
form
strand
is
the
uses
an
a
RNA which
information
the
new
for
DNA strand
strand.
original
as
a
Replication
strand
and
the
2 .7
DN A
r E P L i C At i o N ,
Example 2.7
.1.
The
on
first,
the
AND
t r A N S L At i o N
Example 2.7
.2.
second
and
messenger
third
positions
RNA (mRNA)
are
of
the
three
shown
in
bases
this
of
the
genetic
codons
code.
Secnd lee
U
U
trANS CriPtioN
UUU
Phe
C
A
UCU
UAU
In
A.
way
enzymes
during
G
Tyr
what
UGU
B.
U
Cys
are
UCC
Ser
UAC
the
produce
Leu
UCA
UAA
Stop
structure
UCG
UAG
Stop
of
by
enzymes
is
DNA
both
enzymes
have
globular
and
DNA
A
UGA
Stop
UUG
RNA
C
UGC
C.
UUA
and
replication
determined
UUC
enzymes
DNA related?
D.
G
UGG
enzymes
shapes
contain
the
code
Trp
for
C
CUU
CCU
CAU
His
DNA
U
CGU
Solution
CUC
Leu
CCC
Pro
CAC
CGC
C
Arg
The
CUA
Fs
CCA
CAA
CUG
CCG
CAG
AUU
ACU
AAU
Gln
thd
G
CGG
lee
lee
A
Asn
AGU
answer
contains
A
CGA
synthesis
will
Ile
ACC
Thr
AAC
AUG
G
Met
GUU
GUC
Val
ACA
AAA
ACG
AAG
GCU
GAU
GCC
Ala
Lys
AGA
Asp
GAC
as
DNA
of
mRNA,
determine
the
for
the
which
of
the
primary
protein,
which
C
AGC
will
AUA
B,
blueprint
U
Ser
structure
AUC
is
the
A
Arg
AGG
G
GGU
U
GGC
the
determine
the
structure
of
enzyme.
C
Gly
• replcan is the semi-
GUA
GCA
GAA
GUG
GCG
GAG
Glu
GGA
A
GGG
G
conservative synthesis of DNA.
• tanscpn is the synthesis of
mRNA copied from the DNA base
A sequence
of
nucleotides
of
mRNA is
shown:
sequences by RNA polymerase.
AUGUUUCCACUAAAUGUAAGCAGA
• tanslan is the synthesis of
polypeptides on ribosomes.
a)
(i)
Identify
the
produce
(ii)
Deduce
DNA sequence
this
the
that
has
been
transcribed
to
mRNA.
peptide
sequence
translated
from
this
mRNA
sequence.
b)
Discuss
when
whether
leaving
all
the
proteins
contain
Met
as
a
first
amino
acid
ribosomes.
To identify the DNA sequence, you
have to find the complementary
c)
(i)
Explain
what
would
have
happened
if
instead
of
AGA you
base: for A it is T and for C it is G.
had
UGA in
the
last
codon
of
this
portion
of
this
mRNA.
Remember that in DNA you have T
(ii)
Suggest
a
reason
how
the
change
in
c)
(i)
could
have
instead of U.
happened.
Solution
a)
(i)
(ii)
b)
TAC
Met
The
AAA GGT
Phe
start
Pro
codon
GAT
Leu
of
TTA CAT
Asn
most
Val
Ser
open
TCG
TCT
Arg
reading
frames
(ORF)
is
AUG.
To deduce the peptide sequence,
Transcription
starts
at
TAC
(or
ATG
in
the
DNA coding
you first separate the sequence of
sequence)
as
this
is
where
the
polymerase
starts
transcription.
mRNA every three nucleotides. You
There
are
some
cases
of
alternative
start
codons,
but
these
are
then look in the table for A as the
very
rare
in
eukaryotes.
first letter, U for the second letter
c)
(i)
UGA is
There
leaves
(ii)
a
is
stop
no
the
A point
codon,
so
the
tRNA capable
ribosome.
mutation
The
translation
of
joining
peptide
replacing
would
this
codon,
produced
A with
U
be
stopped
so
the
would
could
have
be
here.
peptide
and G for the third. This is done for
each codon.
short.
caused
the
change.
25
2
MOLEC UL AR
2 . 8
BI O LO G Y
C E L L
R E S P I R AT I O N
Yu shuld knw:
✔
cell
respiration
energy
from
glucose)
✔
ATP
is
to
an
is
Yu shuld be able :
the
organic
produce
controlled
release
compounds
(such
of
✔
describe
as
ethanol
ATP
.
immediate
the
and
anaerobic
cell
source
respiration
of
energy
in
the
cell.
✔
explain
yields
a
small
in
dioxide
baking
to
through
produce
anaerobic
lactate
production
respiration
is
in
used
humans
to
when
maximize
the
of
muscle
contractions.
ATP
.
✔
✔
yeasts
amount
power
of
of
respiration.
anaerobic
✔
use
carbon
aerobic
cell
respiration
requires
oxygen
analyse
results
from
experiments
using
a
and
respirometer.
gives
a
large
yield
of
ATP
.
Most
living
respiration
processes
through
respiration,
require
the
glucose
is
energy
,
breakdown
broken
down
which
of
to
is
glucose
obtained
from
molecules.
produce
a
small
In
cell
anaerobic
amount
of
ATP
.
You do not need to know all
The
end
products
in
anaerobic
respiration
can
be
lactic
acid
(in
muscles
the metabolic pathways of cell
or
bacteria)
or
carbon
dioxide
and
ethanol
(in
yeast
or
bacteria).
In
respiration. You need to recall
aerobic
respiration,
large
amounts
of
ATP
are
produced
from
the
only substrates and final waste
breakdown
of
glucose;
carbon
dioxide
and
water
are
also
produced.
products.
• Anaebc espan is the
large amounts of energy in the form
catabolic process through which
of ATP
.
small amounts of energy in the form
• AtP or adensne phsphae is a
of ATP are produced from glucose
molecule that is used as a fast source
without the use of oxygen.
of energy. It is formed by a ribose
• Aebc espan is the catabolic
that has a nitrogenous base joined to
process involving the use of oxygen
carbon 1 and three phosphate groups
through which glucose is broken
joined to carbon 5.
down to carbon dioxide, water and
Example 2.8.1.
Describe
the
use
of
a
respirometer
to
measure
cell
respiration
in
In Topic 1.2, the structure of
germinating
seeds.
mitochondria were studied. How
respiration is involved in carbon
Solution
cycling will be studied in Topic 4.3.
In
In Topic 8.2, cell respiration will be
a
explained in more detail.
to
a
simple
mesh.
respirometer,
Underneath,
absorb
CO
.
This
an
germinating
alkali
ensures
such
that
as
seeds
are
sodium
reductions
in
placed
in
hydroxide
volume
a
is
are
tube
on
used
due
to
2
oxygen
use.
prevents
You can illustrate your answer with
a drawing, but you must make
sure to annotate it clearly.
26
Temperature
volume
changes
is
kept
due
to
constant
using
temperature
a
water
bath.
fluctuations.
This
2.8
C E LL
r E S P i r At i o N
S AMPLE StUDENt ANS WEr
The oxygen
oxygen meter linked
to a
computer
consumption rate of
the sh Oplegnathus
insignis was examined
in a respirometer at
three dierent water
temperatures and
water
water
in
out
at four dierent body
masses.
h
1–
1–
300
gk
23ºC
O gm / etar
2
noitpmusnoc negyxo
400
18ºC
200
13ºC
100
0
0
200
400
600
body mass / g
a) Suggest how the oxygen consumption rate is determined using this
apparatus.
This
[2]
answer
could
have
achieved
1/2
marks:
▲ The
answer
because
T
he
“ water
out”
part
of
the
apparatus
contains
water
from
sh
meter
,
has
consumed
which
detects
oxygen.
oxygen
T
he
levels
water
in
the
is
passed
water
.
T
he
to
the
result
oxygen
with
the
oxygen
level
of
the
supplied
water
to
using
the
mark
that
the
the
data
difference
in
concentration.
answer
is
lacking
the
fact
calculate
time
rate
one
is
that
the
measures
oxygen
▼ The
compared
gets
mentions
which
logger
the
it
the
measurement
and
that
the
is
mass
done
of
the
over
sh
computer
.
needs
the
to
be
measured
to
calculate
rate.
b) State the relationship between body mass and the oxygen
consumption of sh.
This
T
he
answer
greater
could
the
consumption
per
[1]
have
body
rate
achieved
mass
it
has.
1/1
of
marks:
the
T
his
sh,
means
the
it
lower
the
consumes
oxygen
less
oxygen
kilogram.
c) Predict the eects of global warming on aerobic respiration
A mark would also have been
in sh.
[2]
given for saying that less oxygen
This
answer
could
have
achieved
2/2
marks:
can dissolve in warmer water so
less aerobic respiration can occur.
A
higher
temperature
causes
a
higher
oxygen
consumption
Another mark could be given for
rate.
T
herefore
global
warming
will
cause
sh
to
have
more
saying that larger fish are favoured
as they have a lower oxygen
metabolism
and
therefore
consume
more
oxygen.
consumption rate.
27
2
MOLEC UL AR
2 . 9
BI O LO G Y
P H O T O S Y N T H E S I S
Yu shuld knw:
✔
photosynthesis
compounds
in
is
Yu shuld be able :
the
cells
production
using
light
of
carbon
✔
energy
.
explain
oceans
changes
and
rock
to
the
Earth’s
deposition
atmosphere,
due
to
photosynthesis.
✔
visible
is
the
light
has
shortest
a
range
and
red
of
the
wavelengths:
violet
longest.
✔
draw
for
✔
chlorophyll
absorbs
red
and
blue
light
and
explain
chlorophyll
an
and
absorption
an
action
spectrum
spectrum
for
most
photosynthesis.
effectively
other
and
reects
green
light
more
than
colours.
✔
design
experiments
temperature,
✔
oxygen
is
produced
in
photosynthesis
from
of
energy
is
needed
✔
carbon
temperature,
to
produce
compounds
light
concentration
the
rate
of
and
the
effect
carbon
of
dioxide
photosynthesis.
carbohydrates
explain
the
are
from
intensity
possible
carbon
and
of
photosynthetic
by
chromatography
.
dioxide.
carbon
limiting
separation
and
pigments
other
investigate
water.
✔
✔
to
intensity
the
on
photolysis
light
dioxide
factors
on
photosynthesis.
Visible
In Topic 2.4, an enzyme involved
in photosynthesis was discussed
In Topic 8.3, knowledge of
photosynthesis will be deepened.
light
wavelength
absorbs
more
some
light
red
than
and
other
a
range
nm)
blue
photolysis
by which green plants (and some
carbon
to
is
to
by-product.
Energy
the
most
with
longest
that
contain
electrons
that
ions
from
and
ATP
nm).
and
occurs
chlorophyll.
molecules
hydrogen
violet
(700
effectively
Photosynthesis
water
release
and
wavelengths
red
light
colours.
split
dioxide
of
and
microorganisms
energy
• Phsynhess is the process
microorganisms) use sunlight to
has
(400
to
reflects
in
the
green
plants,
The
eventually
produce
shortest
light
algae
Photosynthesis
(photolysis).
can
the
Chlorophyll
be
energy
.
hydrogen
purpose
from
used
to
Oxygen
and
uses
of
reduce
is
photolysis
a
are
synthesize nutrients from carbon
used
to
produce
carbohydrates
and
other
carbon
compounds
from
dioxide and water. Light is absorbed
carbon
dioxide.
by pigments and generates oxygen
as a by-product.
Although
other
chlorophyll
pigments
that
is
the
absorb
main
light
pigment
at
found
different
in
plants,
wavelengths.
there
are
Examples
• Chlphyll is a green pigment
of
these
pigments
are
xanthophylls
and
carotenes.
It
is
possible
that absorbs light in most plants.
separate
• An acn specum is a graph
of the rate of photosynthesis
performed by an organism at
dierent light wavelengths.
• An abspn specum is
a graph of the amount of light
absorbed by each pigment at
dierent light wavelengths.
28
photosynthetic
pigments
using
chromatography
.
to
2.9
P H oto S Y N t H E S i S
S AMPLE StUDENt ANS WEr
Outline the production of carbohydrates in photosynthesis.
This
answer
Glucose
is
could
a
have
type
of
achieved
3/4
[4]
marks:
carbohydrate
formed
through
photosynthesis.
T
he
photosynthesis
equation
allows
us
to
see
how
and
when
▲ The
in
the
process
glucose
is
answer
scores
a
mark
produced:
for
photolysis
and
for
mentioning
LIGHT
carbon
dioxide +
+
glucose
oxygen
of
T
here
are
two
stages
to
the
production
of
glucose
and
hydrogen
photolysis.
The
as
products
second
mark
is
or
for
carbon
xation.
carbohydrates.
Stage
about
1:
light-dependent
photolysis,
which
reaction.
is
the
Sunlight
splitting
of
is
used
water
to
bring
molecules
▼ The
answer
mention
into
hydrogen
and
oxygen
2:
T
hrough
light-independent
these
two
stages
of
reaction.
getting
Carbon
xation
hydrogen
and
occurs.
to
chlorophyll
chemical
and
xating
carbon
is
we
get
the
carbohydrate
and
energy
.
energy
is
used
not
absorbed
of
which
for
is
converted
Some
the
of
the
production
oxygen
ATP
is
carbohydrates
ions
does
light
ions.
by
Stage
that
needed
or
to
produce
starch.
molecule
glucose.
Example 2.9.1.
How
A.
is
the
Water
oxygen
released
molecules
split
by
with
photosynthesis
the
energy
from
produced?
ATP
to
liberate
oxygen.
B.
Water
molecules
split
with
the
energy
from
light
to
liberate
oxygen.
C.
Water
molecules
combine
with
carbon
dioxide
molecules
to
form
oxygen.
D.
Carbon
dioxide
producing
molecules
split
with
the
energy
from
light
oxygen.
Solution
The
a
answer
process
and
the
is
B.
called
oxygen
Light
energy
photolysis.
is
liberated
is
used
to
split
The
hydrogen
as
by-product.
a
is
the
water
used
in
molecule
in
photosynthesis
Pacce pblems f tpc 2
Pblem 1
Pblem 3
Describe the proper ties of water that allow
Design an experiment using egg white to show
cooling by sweating.
the effect of heat on proteins.
Pblem 2
Pblem 4
Outline the action of enzymes.
Outline the production of carbohydrates in
photosynthesis.
29
G E N ET I C S
3
3 . 1
G E N E S
Yu suld knw:
✔
every
life
✔
a
living
from
gene
its
each
organism
consists
gene
inherits
a
blueprint
for
✔
explain
parents.
information
✔
Yu suld be able t:
of
for
a
a
length
specic
occupies
a
of
DNA that
carries
✔
explain
characteristic.
specic
place
on
✔
alleles
are
only
few
new
a
a
✔
forms
of
a
gene
that
vary
by
✔
are
by
the
genome
is
the
whole
mutation.
genetic
✔
describe
information
✔
arises
if
there
is
a
hemoglobin.
between
malaria
and
sickle
cell
of
genes
in
humans
and
human
diversity
is
due
to
single
polymorphisms.
the
use
in
of
the
a
database
base
to
determine
sequence
of
a
gene
in
of
two
an
anemia
for
numbers
how
differences
✔
cell
gene
link
the
nucleotide
formed
sickle
the
organisms.
explain
bases.
alleles
the
compare
other
different
in
anemia.
chromosome.
✔
how
mutation
species.
organism.
the
Human
whole
Genome
human
Project
sequenced
the
genome.
Each
gene
is
located
in
a
specific
place
or
locus
on
the
chromosome.
• A gene is a heritable factor that
There
can
be
several
variants
of
the
same
gene;
these
are
called
alleles.
consists of a length of DNA and
Humans
have
around
20,000
genes,
while
some
bacteria
have
5,000.
If
inuences a specic characteristic.
an
organism
has
two
alleles
for
a
particular
gene
that
are
the
same,
it
• The lcus is the place on the
is
called
a
homozygote.
If
an
organism
has
two
alleles
for
a
particular
chromosome where a gene is
gene
that
are
different
(for
example,
alleles
for
both
blue
eyes
and
located.
brown
eyes),
it
is
called
a
heterozygote.
• Alleles are various specic forms
of a gene.
In
sickle
acid
to
cell
be
anemia,
one
substituted
hemoglobin
by
specific
valine
polypeptide.
As
a
base
as
substitution
the
result
sixth
the
amino
structure
causes
acid
of
in
the
glutamic
the
hemoglobin
The development of gene
protein
is
altered
and
it
does
not
carry
oxygen
efficiently
in
sequencers has allowed for
erythrocytes;
the
shape
of
affected
erythrocytes
is
also
altered
(they
are
the sequencing of genes in many
‘sickle-shaped’).There
appears
the
cell
to
be
a
correlation
between
malaria
and
organisms. Frederick Sanger was a
incidence
of
sickle
anemia.
Regions
where
malaria
is
endemic
pioneer in DNA sequencing, as in
also
show
a
high
incidence
of
sickle
cell
anemia
in
the
local
population;
1977, together with his co-workers,
sickle
cell
anemia
has
a
low
rate
of
incidence
in
regions
that
do
not
he developed the chain-termination
have
malaria.
This
is
probably
due
to
the
fact
that
the
malarial
parasite
method. This method consisted of
cannot
enter
into
‘sickle-shaped’
erythrocytes,
so
heterozygotes
for
the selective incorporation of chainthe
sickle
the
gene
cell
gene
are
relatively
protected
against
malaria.
Therefore,
terminating dideoxynucleotides by
can
survive
and
be
inherited
more
often.
On
the
other
hand,
DNA polymerase during replication.
patients
who
are
homozygous
for
the
sickle
cell
gene,
and
therefore
Other faster methods have been
suffer
from
developed since, allowing for larger
of
sections of DNA to be sequenced.
30
malaria.
sickle
cell
anemia,
are
highly
susceptible
to
the
lethal
effects
3 .1
Example 3.1.1.
GE N E S
• A mutatn is a change to the
structure of a gene caused by the
The
ABO
blood
group
gene
locus
is
located
on
the
long
arm
of
alteration of single base units in the
human
chromosome
9,
and
encodes
for
an
enzyme
that
mediates
DNA. A mutation may be inherited
the
B
expression
genes
differ
sequence
acids
of
from
shows
groups
means
in
the
the
part
(an
the
of
of
A and
a
few
allele
B
single-base
for
blood
sequences
a
protein
asterisk
amino
antigens
for
acid
is
not
substitutions.
blood
the
erythrocytes.
group
sequence
means
on
O
differs
groups
sequence
is
The
in
A and
alignment
of
the
The
A and
more
B.
the
may aect only the individual in
amino
The
and
which it occurs. Mutations can be
caused by exposure to radiation
table
alleles
same
by subsequent generations, or
protein
of
a
or carcinogens, or by errors in
blood
replication or transcription.
dash
present).
• Sngle nucletde plymrpsms
are caused by point mutations
Allele
Amn acd
that give rise to dierent alleles
Blood group A
P
K
V
L
T
P
W
K
Blood group B
*
*
*
*
*
*
*
C
Blood group O
*
*
*
*
*
*
*
C
D
V
L
V
V
T
P
W
L
A
P
I
V
W
E
G
T
F
R
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
R
*
*
*
*
*
P
L
G
W
L
P
L
S
G
R
A
H
S
containing alternative bases at a
given nucleotide position within a
locus.
a)
(i)
Identify
the
sequence
(ii)
Suggest
due
to
number
between
whether
single
of
amino
blood
this
group
data
nucleotide
acids
that
A and
shows
that
are
different
blood
group
human
polymorphisms
in
this
B.
diversity
is
(SNPs).
You do not need to study
b)
Explain
gene
how
can
blood
a
base
cause
group
of
substitution
a
difference
a
person.
in
in
the
the
DNA molecule
protein
that
of
one
determines
deletions, inser tions and frame
the
shift mutations.
Solution
a)
(i)
Topic 3.4 shows how genetic
2
information is inherited. Topic 5.4
(ii)
There
are
more
SNPs
between
the
sequence
for
blood
group
explains how cladistics is used to
O
and
both
A and
B.
There
are
few
differences
between
A and
describe the way organisms are
B.
Therefore,
the
SNPs
make
a
difference
in
the
blood
group,
related phylogenetically.
confirming
b)
The
in
ribosome,
cause
a
code
is
codon
the
the
translation
primary
codes
protein
codon,
the
the
contribute
blueprint
A change
will
tRNA to
if
for
the
the
(neutral
protein
in
join
of
by
its
the
change
same
be
the
The
the
If
human
of
in
anticodon,
acid,
no
new
the
mRNA could
determining
Because
nucleotide
mRNA
determine
mRNA enters
change
the
diversity
.
formation
DNA could
the
amino
much
to
protein.
in
mutation).
will
for
When
occur.
sequence
degenerate,
that
can
mRNA codon.
different
different
is
transcription.
change
to
SNPs
DNA molecule
through
a
that
the
genetic
determines
change
codon
is
will
a
a
for
a
occur
stop
shorter.
S AMPLE STUDENT ANS WER
Mutations are the ultimate source of genetic variation and are essential
to evolution.
a) State one type of environmental factor that may increase the
mutation rate of a gene.
▲ Correct
arise
from
such
as
UV
chemical
[1]
answer
could
have
achieved
1/1
papilloma
virus
is
to
presence
or
less
can
radiation
of
carcinogens,
cigarette
smoke.
common,
marks:
by
to
rays,
it
mutations
Exposure
mutations
mutagens,
Although
This
answer:
exposure
could
polymerases
occur
in
from
errors
transcription
or
radiation.
translation.
b) Identify one type of gene mutation.
[1]
▲ Correct
This
answer
could
have
achieved
1/1
occur
could
Base
substitution
answer:
mutations
can
marks:
from
also
base
occur
substitution.
from
They
insertion,
mutation.
deletion
or
frameshift.
31
3
GE N E T I CS
3 . 2
C H R O M O S O M E S
✔
a
karyogram
shows
the
chromosomes
of
an
Yu suld knw:
organism
✔
prokaryotes
have
one
chromosome
in
homologous
pairs
of
decreasing
consisting
length.
of
a
circular
DNA molecule.
✔
✔
plasmids
are
small
circular
sex
are
present
✔
only
in
some
eukaryote
chromosomes
molecules
associated
eukaryotes
carry
have
different
are
with
linear
histone
homologous
sequence
alleles
of
of
DNA
diploid
different
chromosomes
explain
haploid
chromosomes
those
nuclei
but
not
carry
the
compare
coli,
same
necessarily
the
each
species
Cairns’
the
and
autosomes
determine
technique
length
genome
Drosophila
Paris
same
sex.
of
is
used
for
DNA molecules.
size
in
T2
phage,
melanogaster,
Homo
Escherichia
sapiens
and
japonica
genes.
have
pairs
of
compare
Homo
homologous
have
one
chromosome
✔
of
sativa
analyse
Down
has
a
specic
number
✔
of
loci
Chromosome separation during
cell division is studied in Topic 1.6.
diploid
Pan
and
troglodytes,
karyograms
and
the
the
use
chromosome
Parascaris
syndrome
describe
chromosomes.
the
sapiens,
Oryza
eachpair.
✔
how
measuring
that
chromosomes.
✔
sex
not
genes.
genes
nuclei
do
Yu suld be able t:
✔
✔
determine
that
proteins.
✔
✔
chromosomes
prokaryotes.
✔
✔
chromosomes
DNA molecules
in
of
to
numbers
Canis
of
familiaris,
equorum.
deduce
sex
and
diagnose
humans.
databases
protein
products
to
identify
of
genes.
gene
• The karytype is the number and
division, it is where the spindle bres
type of chromosomes present in the
attach.
nucleus.
• A crmatd is a DNA molecule
• A karygram is a photograph of
that is the copy of a newly formed
chromosomes ordered by size.
chromosome.
• The genme sze is the total length
• Sster crmatds are two DNA
of DNA in an organism.
molecules formed by DNA replication
In 1963, John Foster Cairns
used autoradiography to
establish the length of DNA
prior to cell division until the splitting
molecules in chromosomes. E. coli
• The centrmere is the area of
cells were grown with radioactive
the chromosome where the sister
of the centromere at the star t of
anaphase.
chromatids are linked. During cell
thymidine, which was incorporated
into the DNA during replication.
Radioactively labelled DNA from
Chromosomes
broken cells was spread on a glass
proteins.
slide and all the molecules covered
chromosomes
with a light-sensitive emulsion. The
Down
tracks of silver grains resulting
a
from exposure of DNA to
membrane,
radioactive thymidine were used to
the
measure the DNA fibres.
circular
All
the
nucleoid.
genes
have
a
a
few
naked
but
have
one
the
cell.
The
not
half
may
of
of
for
one
also
in
of
the
each
in
have
do
not
plasmids,
pairs
carry
alleles
of
chromosomes
are
of
of
such
consisting
have
in
a
an
nuclear
area
which
found
are
called
small
inside
same
those
sequence
genes.
diploid
Haploid
nuclei—they
pair.
Example 3.2.1.
The
scanning
(×1,600).
32
electron
micrograph
shows
part
of
as
of
homologous
the
as
histone
diseases
cytoplasm
chromosomes
same
with
number
example
contain
nuclei
the
same
chromosome
chromosomes
number
chromosome
associated
the
prokaryotes
found
Eukaryote
necessarily
the
have
Because
Diploid
pairs
have
exceptions,
DNA is
Prokaryotes
of
species
Prokaryotes
DNA molecules.
nucleus
nuclei
(with
DNA molecules
of
DNA molecule.
chromosomes.
of
linear
syndrome).
circular
the
are
members
a
cell
in
mitosis
3.3
a)
On
b)
the
Identify
sister
c)
micrograph,
on
d)
a
centromere.
micrograph
two
chromatids.
Identify
,
of
the
label
MEioSiS
with
mitosis
Describe
a
this
how
karyogram
reason,
cell
is
you
from
the
stage
in.
could
this
make
a
picture.
Solution
a)
and
b)
See
diagram
on
the
right
centromere
c)
highly
condensed,
become
where
apparent.
and
This
chromosomes
chromatids
is
are
the
stage
more
clearly
seen.
d)
Each
chromosome
picture
by
size
and
cut
scissors)
homologous
their
of
(using
is
pairs
the
from
and
the
ordered
according
length
of
to
each
arm
chromatid.
sister
chromatids
The
genome
size
does
not
give
an
idea
of
how
complex
in
form
the
• Gametes have a haploid number
organism
is.
Humans
have
a
genome
of
around
3,000
million
base
of chromosomes in their nucleus.
pairs,
while
pairs.
The
Paris
japonica,
a
woodland
plant,
has
150,000
million
base
• Autsmal cells have a diploid
number
of
chromosomes
is
not
an
indication
of
evolution
number of chromosomes in their
either.
Humans
have
46
chromosomes
in
diploid
cells
(23
in
haploid)
nucleus.
while
dogs
have
3 . 3
78
chromosomes
(36
in
haploid).
M E I O S I S
✔
genetic
variation
is
promoted
by
crossing
over,
Yu suld knw:
random
✔
one
diploid
nucleus
divides
by
meiosis
✔
the
four
haploid
chromosome
sexual
life
cycle
is
halved
fusion
of
DNA is
replicated
chromosomes
✔
pairing
of
crossing
during
before
consist
of
homologous
over
early
is
gametes
to
allow
a
orientation
meiosis
two
so
sister
that
chromosomes
followed
by
of
pairs
how
describe
separation
of
pairs
chromosomes
halves
✔
alleles
the
in
of
separation
combinations
to
during
be
other
cause
chromosome
used
analysis
sampling
(for
and
to
obtain
example,
cells
for
chorionic
amniocentesis)
and
the
risks.
is
random.
✔
draw
the
stages
of
of
four
meiosis
haploid
resulting
in
the
cells.
homologous
rst
chromosome
segregate
and
can
homologous
to
the
parents.
non-disjunction
methods
formation
✔
different
syndrome
karyotype
condensation
villus
of
prior
from
abnormalities.
✔
and
explain
Down
all
chromatids.
meiosis.
chromosomes
fusion
Yu suld be able t:
associated
✔
and
gametes.
✔
✔
chromosomes
nuclei.
number
with
of
to
of
produce
orientation
division
of
meiosis
✔
analyse
microscope
✔
interpret
slides
showing
meiosis.
number.
meiosis
formed
by
allowing
the
fusion
new
of
age
of
studies
parents
investigating
inuences
the
whether
chances
of
the
non-
disjunction.
gametes.
33
3
GE N E T I CS
Meiosis
Cell division is studied in Topic
number
produces
of
chromosomes,
1.6. Topic 10.1 covers meiosis
to
in greater depth and Topic 11.4
Meiosis
is
discusses the formation of gametes
halving
of
in sexual reproduction.
chromosome
is
fuse
gametes.
and
create
an
divided
chromatids.
of
a
into
two
with
meiosis
metaphase
are
two
the
so
I
pair
the
gametes
in
contain
(one
I
and
to
haploid
each
parent)
chromosomes.
where
consist
chromosomes
II.
The
each
opposite
chromosomes
homologous
of
meiosis
I,
the
the
from
number
meiosis
migrates
all
that
meiosis
occurs
that
cells
diploid
processes,
number
homologous
before
In
allowing
embryo
chromosome
replicated
Gametes
pole.
of
DNA
two
pair
sister
up,
Meiosis was discovered by
and
crossing
over
occurs.
The
homologous
chromosomes
are
randomly
careful microscope
orientated
prior
to
separation
in
anaphase
I.
Meiosis
II
is
similar
to
a
examination of dividing germ-line
mitotic
cell
division,
as
each
sister
chromatid
migrates
to
an
opposite
cells. In 1876 Oscar Her twig first
pole.
Overall,
one
diploid
nucleus
divides
by
meiosis
to
produce
four
described meiosis in sea urchin
haploid
nuclei
at
the
end
of
meiosis
II. Alleles
segregate
during
meiosis
eggs, but it was not until 1890 that
allowing
new
combinations
to
be
formed
by
the
fusion
of
gametes.
August Weismann described the
Genetic
variation
is
promoted
by
crossing
over,
random
orientation
of
change from a diploid to four
chromosomes
and
fusion
of
gametes
from
different
parents.
haploid cells.
Example 3.3.1.
The
graphs
stages
in
show
meiosis
undergoes
three
chromosome
progressive
the
I
schematic
and
II
stages:
filament;
increase
of
rye
comparison
(Secale
aggregation
in
diameter;
cereale).
of
condensation
chromosome
The
chromatin
in
and
of
length,
chromosome
into
which
separation
of
a
involves
a
chromatids
in
segregation.
meiosis I
meiosis II
aggregation
condensation
segregation
I
P
M
A
T
I
P
M
A T
I
Key
I
=
P
interphase
=
A =
prophase
M
=
a)
State
T
anaphase
=
telophase
metaphase
the
stage
at
which
the
chromosomes
are
maximally
condensed.
b)
c)
d)
Suggest
Explain
one
and
there
chromosome
Compare
I
reason
and
no
aggregation
condensation
contrast
meiosis
is
at
chromosome
each
in
meiosis
II.
stage
in
meiosis
segregation
in
meiosis
I.
II.
Solution
a)
Metaphase.
b)
Chromatin
meiosis
c)
In
II
aggregates
chromosomes
interphase
prophase
is
prophase
chromosomes
to
form
in
chromosomes
are
chromosomes
when
chromosomes
34
into
are
already
are
not
chromosomes
partly
mitosis.
It
is
can
be
in
meiosis
I,
as
in
formed.
condensed.
start
to
and
metaphase
Early
condense
distinguished.
separated
in
only
In
and
late
constrictions
when
in
mid
prophase
begin
chromosomes
3.4
are
maximally
condensed,
condensed.
they
While
segregate
and
the
chromosomes
move
towards
the
are
i N h E R i TA N C E
still
poles
during
anaphase.
d)
During
pairs
pair
anaphase
are
migrates
each
I
(in
segregated
sister
to
an
the
I),
the
homologous
poles—one
opposite
chromatid
3 . 4
meiosis
at
pole.
migrates
During
to
the
chromosome
chromosome
anaphase
opposite
from
II
each
(meiosis
II),
poles.
I N H E R I TA N C E
Yu suld knw:
✔
the
inheritance
✔
Mendel’s
✔
gametes
of
Yu suld be able t:
genes
experiments
follows
to
patterns.
explain
inheritance.
✔
describe
✔
explain
the
the
red–green
of
each
are
haploid
so
contain
only
one
inheritance
role
the
gene.
two
✔
alleles
different
of
each
haploid
gene
daughter
separate
nuclei
describe
fusion
with
colour
the
✔
describe
same
of
gametes
alleles
allele
or
results
of
each
different
in
diploid
gene
that
zygotes
may
be
✔
construct
the
dominant
alleles
alleles
but
mask
effects
alleles
of
have
compare
recessive
joint
genetic
many
genetic
autosomal
diseases
recessive,
blindness
and
plays
in
hemophilia.
inheritance
of
cystic
brosis
and
disease.
consequences
and
of
radiation
at
Chernobyl.
Punnett
grids
for
monohybrid
genetic
in
humans
dominant
can
or
be
predicted
crosses
and
using
actual
real
outcomes
of
data.
effects.
✔
✔
inheritance
alleles.
the
codominant
groups.
crosses.
✔
✔
the
Hiroshima
two
sex-linked
blood
into
during
meiosis.
✔
ABO
allele
Huntington’s
✔
of
due
analyse
to
pedigree
inheritance
of
charts
genetic
to
deduce
the
pattern
of
diseases.
codominant
alleles.
✔
the
inheritance
✔
some
genetic
radiation
Mendel’s
of
sex-linked
diseases
and/or
and
genes.
cancer
mutagenic
experiments
with
pea
are
due
to
chemicals.
plants
helped
him
to
discover
the
• Segregatn is the separation of
laws
of
inheritance—the
laws
of
segregation,
independent
assortment
alleles into dierent nuclei.
and
dominance.
Because
each
homologous
chromosome
migrates
to
• A dmnant allele is one that
a
different
pole
during
gamete
formation,
the
alleles
for
each
gene
produces its characteristic
segregate
from
each
other,
so
that
each
gamete
carries
only
one
allele
phenotype.
for
each
gene
(law
of
segregation).
The
homologous
chromosomes
• A recessve allele only produces
migrate
in
a
random
way
,
therefore
genes
for
different
traits
can
its characteristic phenotype when
segregate
independently
during
the
formation
of
gametes
(law
of
homozygous.
independent
recessive;
an
assortment).
organism
Some
with
at
alleles
least
are
one
dominant
dominant
while
allele
others
will
are
display
• Cdmnant alleles are those that
are simultaneously expressed in
the
effect
of
the
dominant
allele
(law
of
dominance).
the phenotype of the individual.
In 1866, Gregor Johann Mendel, an Austrian monk and scientist,
• Sex lnkage is the phenotypic
expression of an allele related to
described the cross-breeding of pea plants to show the inheritance of
the sex chromosomes, usually the
seven characteristics. His results were used to establish the rules of
X chromosome.
inheritance, called the laws of Mendelian inheritance. In order to reach these
laws, Mendel performed large numbers of crosses. Mendel’s genetic crosses
with pea plants generated numerical data. Many measurements with
replicates were necessary to ensure reliability of the data obtained.
Topic 1.6 introduces cell
division.
35
3
GE N E T I CS
Example 3.4.1.
What
type
of
inheritance
is
shown
in
the
pedigree?
You may be asked to show genetic
crosses in the exam. It is always
better to use a Punnett grid to
do so and follow annotation
conventions. Alleles carried on X
unaffected male
affected male
chromosomes should be shown
unaffected female
as superscript letters on an upper
affected female
h
case X, such as X
. The expected
notation for ABO blood group
alleles is for the phenotype O, A, B
and AB. For the genotype: ii for O
A
A
and I
A
A
I
group; I
or I
B
i for A ; I
B
I
B
or I
i for B;
A.
B
I
sex-linked
recessive
C.
multiple
dominant
D.
alleles
for AB.
B.
autosomal
codominant
alleles
Solution
B
X
Y
The
B
B
X
X
b
B
B
X
X
correct
answer
is
B
as
it
is
showing
an
autosomal
dominant
B
X
X
b
Y
inheritance.
the
b
X
X
Y
F
pairing
is
not
sex-linked
would
not
be
because
affected,
as
if
it
her
was,
the
mother
daughter
is
in
unaffected,
or
1
both
Fgure 3.4.1.
It
Punnett grid
It
is
daughters
not
would
showing
daughter
in
F
is
be
affected
multiple
not
alleles
if
or
the
mother
were
codominant
a
carrier.
alleles
because
the
affected.
2
Colour-blindness
X
chromosome.
is
The
sex-linked
Punnett
recessive
grid
inheritance
shows
the
on
the
inheritance
of
colour-
In the exam you will be asked
B
blindness
in
a
family
.
(X
b
shows
the
normal
allele
and
X
the
colour-
to construct Punnett grids for
blind
allele.)
For
females,
there
is
a
50%
of
being
a
carrier
and
50%
monohybrid genetic crosses.
chance
of
not
being
a
carrier.
For
males,
there
is
a
50%
of
being
Remember to place the parents’
colour-blind
and
a
50%
chance
of
being
not
colour-blind.
alleles in the top and left-hand
boxes and the offsprings’ in the
S AMPLE STUDENT ANS WER
centre as a result of the possible
The most common form of Stargardt disease is known to be autosomal
combinations. Remember there
recessive. Using a Punnett grid, deduce the probability of a child
is a 1/4 (25%) chance in each
inheriting Stargardt disease if both the parents are carriers of the
pregnancy for each one of the
disease but do not have the disease themselves.
genotypes.
▼ This
parents
student
to
Stargardt
be
has
shown
homozygous
allele
so
got
the
This
answer
could
have
achieved
0/3
marks:
This
answer
could
have
achieved
3/3
marks:
the
for
the
wrong
percentage.
▲ The
grid
mother
are
student
correctly
.
and
both
gametes
are
father
dominant
because
carriers.
The
combinations
shown.
(or
at
36
The
could
the
drew
The
of
are
bottom.
Punnett
four
the
There
recessive
parents
possible
gametes
been
for
shown.
and
both
answer
have
the
gametes
is
are
clear
1/4)
is
also
as
25%
written
3.5
3 . 5
GENETIC
GE N E T iC
M o D i F i C AT i o N
M O D I F I C AT I O N
AND
B i oT E C h N o Lo G Y
AND
B I O T E C H N O L O G Y
Yu suld knw:
✔
there
of
✔
are
DNA,
gel
techniques
cells
PCR
can
of
be
for
articial
separates
✔
to
amplify
to
or
✔
size.
small
✔
explain
using
amounts
of
✔
DNA.
✔
describe
forensic
proteins
DNA according
used
manipulation
organisms.
electrophoresis
fragments
✔
and
Yu suld be able t:
DNA proling
gene
genetic
involves
modication
transfer
between
is
comparison
carried
out
of
by
DNA.
✔
evaluate
explain
clones
are
organisms,
of
✔
derived
genetically
from
a
and
the
potential
with
the
to
bacteria
risks
genetic
production
by
design
experiment
via
and
and
plasmids
DNA ligase.
benets
modication
of
somatic-cell
cloned
of
crops.
embryos
nuclear
transfer.
gene
species.
groups
paternity
endonuclease
produced
an
affecting
✔
transfer
restriction
associated
DNA proling
in
investigations.
the
rooting
to
of
assess
one
factor
stem-cuttings.
identical
single
original
parent
✔
analyse
DNA proles.
✔
analyse
data
cell.
✔
many
have
✔
plant
natural
animals
can
breaking
group
✔
species
up
methods
be
cells.
methods
have
using
A polymerase
cloned
the
of
animals
and
some
of
cloning.
at
the
embryo
been
into
embryo
more
developed
differentiated
chain
animal
reaction
for
species
stage
than
Bt
on
risks
to
monarch
butteries
of
crops.
by
one
cloning
adult
cells.
(PCR)
is
a
technique
by
which
small
Replication, transcription and
amounts
of
DNA can
be
amplified
into
large
quantities.
The
DNA
translation of DNA are studied in
fragments
obtained
by
this
method
can
be
separated
by
size
in
gel
Topic 2.7.
electrophoresis.
larger
to
ones.
compare
The
smaller
A marker
with
molecules
known
migrate
sizes
of
further
than
DNA fragments
the
is
used
sizes.
DNA
primers
primers
1
Heat DNA to 93ºC. This breaks
2
Cool to 55ºC. Primers join to
new strand made from
the hydrogen bonds that hold
the ends of the DNA strands.
new DNA nucleotides
the two strands of the DNA
3
Heat to 72ºC. DNA polymerase
double helix together.
joins new nucleotides on to
the DNA strands. This gives
two copies of the original
DNA sequence.
the cycle can be repeated
Fgure 3.5.1.
Production of DNA molecules by PCR
37
3
GE N E T I CS
Fgure 3.5.2.
• Clnes are groups of genetically
Separation of DNA molecules by gel electrophoresis
Example 3.5.1.
identical organisms, derived from a
A DNA profiling
was
performed
as
a
paternity
test
for
the
boy
single original parent cell.
shown
as
DC.
The
first
pair
of
maternal
grandparents
tested
were
• Endnucleases are restriction
both
heterozygous
for
an
allele
(AB
and
AD)
and
the
possible
enzymes that cut the DNA within
paternal
grandparents
were
also
heterozygous
(AB
and
CD).
Males
the sequence.
are
shown
as
squares
and
females
as
circles.
• DNA lgase is an enzyme that
joins DNA fragments by joining a
AB
AD
sugar to a phosphate.
AD
AC
AA
AC
DA
DC
control
allele a
allele b
allele c
allele d
a)
b)
State
the
Suggest
alleles
with
a
grandparents
A major benefit of GM crops
c)
Describe
this
is increased yields. GM crops
present
reason
AB
briefly
and
how
in
the
supposed
whether
DC
father.
could
have
as
maternal
AD.
the
DNA molecules
were
separated
in
gel.
can be modified to include genes
Solution
for food supplements such as
a)
AC
vitamins, vaccines, stress
b)
DC
could
she
inherited
be
the
grandson
of
AB
and
AD.
His
mother
is
AD
so
resistance and longer shelf life.
one
allele
from
her
mother
(A)
and
one
from
her
Where the introduced genes code
father
(D).
Her
son
DC
inherited
the
allele
D
from
his
mother.
for pest resistance, GM crops could
also lead to a marked reduction in
the use of pesticides and
herbicides, which has many
economic, environmental and
health benefits.
38
c)
PCR
products
current
is
DNA has
positive
of
the
are
applied
a
placed
to
negative
pole.
The
molecules.
the
inside
gel
charge,
speed
The
at
that
the
the
is
of
placed
they
particles
the
gel. An
inside
molecules
which
larger
well
a
buffer.
migrate
move
move
is
the
electric
Because
towards
related
least.
to
the
the
size
3.5
Genetic
to
engineering
another.
the
gene
transfer
plasmid.
to
Usually
produce
are
cut
allow
join
is
Plasmids
a
with
them
these
is
the
what
usually
to
same
be
DNA sections.
transgenic
bacteria
antibiotics
or
by
by
have
are
into
Once
chosen
seeing
genetic
their
is
a
bacteria,
a
protein.
restriction
inserted
of
transferred
performed
fluorescent
the
transfer
is
gene
The
of
by
gene
is
either
and
This
the
the
is
gene
to
“sticky
into
them
one
is
the
in
or
a
in
a
gene
that
used
plasmid,
the
B i oT E C h N o Lo G Y
inserted
ends”
then
AND
When
inserted
be
M o D i F i C AT i o N
species
DNA).
antibiotic
DNA ligase
growing
of
gene
to
leaves
inserted
from
section
resistance
plasmid.
the
(a
usually
plasmid
enzyme.
the
information
gene
GE N E T iC
to
the
presence
of
fluorescence.
Scientists must consider how genetically modified (GM) genes will
move through food webs, in case there are toxic or allergic effects on
non-target species. Gene transfer from GM plants to wild non-GM plants
could also eventually lead to the extinction of wild plants and there are
concerns the GM crops might become agricultural weeds and invade natural
environments, compromising the biodiversity of these habitats. As some GM
crops have pest resistance, this could impose intense selection pressure on
pest populations to adapt to the resistance mechanism, leading to the
development of super-pests that would be difficult to control.
Example 3.5.2.
A gene
gene
A.
was
transfer
Both
B.
Both
C.
All
D.
transferred
one
species
to
another.
Why
was
this
possible?
species
species
species
All
from
species
have
have
have
have
the
same
identical
the
the
same
same
genes
DNA
number
genetic
of
chromosomes
code
Solution
The
correct
because
answer
they
all
is
have
D.
Gene
the
transfer
same
genetic
can
be
done
amongst
species
code.
Practce prblems fr Tpc 3
Prblem 1
Prblem 3
Explain how Cairns’ technique is used for
Explain how cloned embryos may be produced
measuring the length of DNA molecules.
by somatic-cell nuclear transfer.
Prblem 2
Prblem 4
a) ()
Explain the relationship between Mendel’s law of
Define codominant and recessive alleles.
segregation and independent assor tment and
() Define locus and sex linkage.
meiosis.
b) Explain the inheritance of blood groups.
39
EC O LO GY
4
4 . 1
SPECIES,
COMMUNITIES
✔
Y shd k:
autotrophs
abiotic
✔
only
sustainable
continued
communities
survival
of
living
will
allow
species
are
potentially
groups
of
organisms
interbreed
to
that
produce
✔
the
members
supply
a
species
may
be
of
nutrient
✔
fertile
ecosystems
over
of
inorganic
nutrients
from
the
environment.
inorganic
nutrients
is
maintained
cycling.
can
offspring.
✔
obtain
ECOSYSTEMS
for
organisms.
by
✔
AND
long
have
the
periods
potential
of
to
be
sustainable
time.
reproductively
Y shd e ae :
isolated
in
separate
populations.
✔
✔
most
species
have
either
an
autotrophic
or
classify
species
detritivores
heterotrophic
method
of
heterotrophs
can
be
or
autotrophs,
consumers,
saprotrophs.
nutrition.
✔
✔
as
a
consumers,
detritivores
design
sealed
mesocosms
to
try
to
establish
or
sustainability
.
saprotrophs.
✔
✔
a
community
is
formed
by
populations
analyse
data
association
different
species
living
together
and
obtained
by
quadrat
sampling
for
of
between
two
species
using
the
chi-
interacting
2
squared
with
each
✔
✔
a
test
(χ
).
other.
community
interactions
forms
with
an
the
ecosystem
abiotic
by
interpret
statistical
signicance
in
data.
its
environment.
Energy flow in ecosystems
will be studied in Topic 4.2. The
classification of biodiversity
will be studied in Topic 5.3 and
• Aphs are organisms that
• Deves are heterotrophs that
produce their own food.
obtain organic nutrients from detritus
by internal digestion.
• Heephs are organisms that
• Sapphs are heterotrophs that
feed on other organisms.
obtain organic nutrients from dead
Topic C.1 will cover species and
• Cses are heterotrophs that
organisms by external digestion.
communities. Topic C.2 will broaden
feed on living organisms by ingestion.
your knowledge of communities
and ecosystems.
Organisms
own
has
food
one
have
need
while
specific
more
than
energy
others
mode
one
in
order
need
of
to
to
nutrition.
mode
of
live.
feed
on
Some
other
There
are
organisms
organisms.
only
a
few
produce
Each
their
species
species
that
nutrition.
Exape 4.1.1.
The
diagram
Which
A.
V
is
a
model
organisms
and
could
W
C.
representing
be
V
different
feeding
interactions.
saprotrophs?
only
X
Z
V
B.
W
and
Z
D.
Z
only
W
Y
Solution
The
is B.
from
therefore
an
as
40
answer
nutrients
in
this
Saprotrophs
dead
autotroph. Any
energy
are
organisms
flow
heterotrophs
by
other
diagram
the
external
organisms
mode
of
that
obtain
digestion.
could
feeding
V
be
is
a
is
organic
a
producer,
correct
not
answer,
explicit.
4 .1
Mesocosms
are
experimental
systems
that
can
be
set
up
to
SPECiE S ,
C om m u ni t iE S
AnD
E C o S YS t E m S
study
• Speces are organisms that have
natural
environments
under
controlled
conditions.
They
can
range
common characteristics which
in
size
from
a
small
plastic
bottle
to
a
large
tank.
Mesocosms
can
be
are capable of producing fer tile
closed
systems,
allowing
only
energy
exchange
with
the
environment,
ospring.
or
open
systems,
allowing
exchange
of
materials
as
well.
The
• Ppa is a group of organisms
advantage
of
a
mesocosm
is
that
many
environmental
conditions
can
of one species that interbreed and
be
controlled
and
measured,
the
experiments
can
be
replicated
several
live in the same place at the same
times
under
the
same
a
environment.
conditions
and
it
is
easier
to
manipulate
than
in
time.
free
The
disadvantage
is
that
it
does
not
represent
the
• Cy is formed by
real
environment
exactly
,
so
you
could
reach
false
conclusions.
populations of dierent species living
together and interacting with each
Exape 4.1.2.
other.
A mesocosm
of
the
of
a
tiger
lake
Twelve
with
experiment
fish
in
(Hoplias
South
was
set
up
to
malabaricus)
evaluate
affects
the
how
the
plankton
presence
• Ecsyse is a community and
structure
its interactions with the abiotic
environment.
America.
experimental
groundwater,
units
were
including
set
up.
sediment
Each
and
mesocosm
free-floating
was
filled
plants
and
The term sustainability
the
plankton
Daphnia
obtusa.
In
some
cases
Jenynsia
multidentata,
refers to the capability of a
a
fish
eaten
by
the
tiger
fish,
was
added
with
or
without
tiger
fish
system to endure and maintain
of
different
sizes.
The
four
different
treatments
were
randomly
itself. The three main challenges
assigned.
for sustainable ecosystems are
Control:
plankton
(Daphnia
obtusa)
(no
fish)
finding sources of both nutrients
and energy that will not run out
JM:
plankton
(Daphnia
obtusa)
+
Jenynsia
multidentata
and avoiding the accumulation of
HMs:
plankton
(Daphnia
obtusa)
+
Jenynsia
multidentata
+
Hoplias
toxic wastes that will become hard
malabaricus
(small
tiger
fish)
to store or have an impact on the
HMb:
plankton
malabaricus
(Daphnia
(big
tiger
obtusa)
+
Jenynsia
multidentata
+
Hoplias
environment. The sustainable
production of food uses renewable
fish)
raw materials efficiently, avoids
The
abundance
of
plankton
(Daphnia
obtusa)
remaining
in
the
the use of environmentally
mesocosm
was
recorded
as
individuals
per
litre
at
different
times.
unfriendly chemicals in their
L slaudividni
1–
/ecnadnuba asutbo ainhpaD
900
manufacture, uses clean and
800
renewable energy and minimizes
700
the production of waste. Because
600
control
500
JM
400
HMs
300
HMb
of the increase in our global
population, it is becoming more
impor tant that we consider the
sustainability of human activities.
200
100
0
0
2
10
20
30
time/day
a)
(i)
State
of
(ii)
the
the
amount
Calculate
State
one
Daphnia
in
the
JM
mesocosm
at
the
start
experiment.
the
mesocosm
b)
of
percentage
from
variable
the
that
start
is
not
change
to
the
kept
in
end
Daphnia
of
the
constant
in
in
the
JM
experiment.
these
mesocosms.
Solution
1
a)
(i)
180
ind
L
(ii)
Amount
of
Daphnia
at
the
start:
Amount
of
Daphnia
at
the
end:
1
180
ind
L
1
20
ind
L
41
4
E C O LO G Y
First:
work
numbers
out
you
the
are
difference
(increase)
between
the
two
comparing.
Do not forget to provide the units.
Increase
=
New
=
20
number
−
Original
number
1
Then:
−
divide
multiply
180
the
the
=
−160
increase
answer
by
ind
by
L
the
original
number
and
100.
In markschemes, what is not
Increase
%
expected in the answer will appear
increase
160
× 100
=
Original
=
× 100
number
=
−89%
180
in brackets. In this case, because
If
your
answer
is
a
negative
number,
then
this
is
a
percentage
this is a “state” question, the
decrease.
reason is in brackets, as it is not
expected in the answer.
b)
There
are
many
variables
should
are
be
correct
not
only
kept
one
possible
answers:
exposed
to
in
the
(different
(as
the
so
to
a
is
organisms,
could
so
pH
the
the
rays
in
all
all
The
Here
of
mesocosms)
or
some
are
metabolic
acids
answer
are
mesocosms
mesocosms),
from
many
mesocosm.
(different
all
as
variables.
amount
across
different
stop
of
(although
change
variable
question,
each
list
temperature),
could
this
inside
not
temperature
this
plants
constant
variable,
ambient
mesocosm
produced,
answers
activity
alkalis
nutrients
and
sunlight
entering).
2
The
a
chi-squared
significant
observed
want
can
to
a
numbers
chosen
)
test
difference
frequencies
see
use
(χ
if
the
and
in
be
one
or
each
test.
of
You
quadrat
null
the
to
determine
expected
more
distributions
The
used
between
in
chi-squared
species.
can
species
should
record
hypothesis
frequencies
categories.
two
base
the
For
are
your
called
there
and
example,
sampling
or
H
)
on
absence
is
that
is
the
if
independent,
presence
(also
whether
you
you
random
of
the
the
presence
0
of
one
The
species
is
alternative
random
in
hypothesis
relation
(also
to
the
called
H
presence
)
is
that
of
the
the
other
presence
species.
of
one
a
species
the
is
other
associated
species.
with
The
or
dependent
formula
used
to
on
the
presence
calculate
or
absence
the
chi-squared
null
hypothesis
of
test
is:
2
(O
E)
2
χ
=
∑
E
The
alternative
rejected)
results
if
is
the
statistically
probability).
higher
hypothesis
difference
than
association
This
a
accepted
significant
means
tabulated
between
is
between
that
if
the
(with
the
two
the
a
p
<
results
0.05,
calculated
chi-squared
the
(and
observed
(critical
and
where
p
is
chi-squared
value),
it
is
expected
the
result
supports
is
the
species.
Exape 4.1.3.
In
a
field
species
trip,
(1
and
association
the
H
second
(null
a
student
2)
in
an
between
species,
hypothesis)
a
quadrat
ecosystem.
the
a
used
presence
chi-squared
=
The
In
of
count
order
one
test
presence
to
test
species
was
of
to
the
presence
whether
and
the
of
there
two
is
presence
of
performed.
species
1
is
independent
of
0
the
H
presence
of
(alternative
species
2.
hypothesis)
=
The
presence
of
species
1
determines
a
the
a)
presence
The
the
42
of
results
table.
species
for
the
2.
observed
Complete
the
numbers
table
to:
of
organisms
are
shown
in
4.2
i)
identify
the
between
ii)
b)
the
calculate
Using
the
the
of
and
species
the
there
1
if
each
chi-squared
whether
of
results
presence
results
determine
presence
expected
there
and
no
f lo w
association
species
results.
chi-squared
is
is
EnErgY
an
the
distribution
association
presence
of
or
not
species
table,
between
the
2.
Solution
a)
2
Speces
ne  ass
Expeced es 
(ose ved−expeced)
se ved
hee s  assca
1 only
3
2.5
0.1
2 only
1
2.5
2.25
1 and 2
4
2.5
2.25
none
2
2.5
0.1
total
10
10
4.7
expeced
Pay
Deees  eed
0.99
0.95
0.05
0.01
1
0.000
0.004
3.841
6.635
2
0.020
0.103
5.991
9.210
3
0.115
0.352
7.815
11.345
4
0.297
0.711
9.488
13.277
5
0.554
1.145
11.070
15.086
b)
The
are
4
The
of
degrees
possible
critical
5%).
value
is
The
is
freedom
for
a
calculated
and
association
4 . 2
in
scenarios
value
smaller
rejected
no
of
than
the
this
of
p
=
the
study
null
is
7.815
critical
the
is
4.7.
a
the
ecosystems
energy
to
energy
lost
require
fuel
life
as
species
the
This
two
a
(as
1
there
and
calculated
hypothesis
means
there
is
F L O W
continuous
and
supply
to
living
organisms
forms
of
✔
energy
length
heat.
most
ecosystems
from
sunlight.
rely
on
a
supply
of
energy
cannot
so
it
is
convert
lost
from
heat
to
other
ecosystems.
of
replace
losses
of
trophic
✔
2).
level
species.
✔
processes
3
significance
alternative
Y shd k:
✔
of
Because
the
of
therefore
not
accepted.
presence
E N E R G Y
or
1,
(with
value,
hypothesis
between
n −
presence
0.05
chi-squared
the
is
between
food
chains
trophic
and
the
levels
restrict
biomass
of
the
higher
levels.
energy
Y shd e ae :
✔
light
energy
is
converted
to
chemical
energy
in
✔
carbon
compounds
by
design
representations
pyramids
✔
chemical
through
✔
energy
energy
food
converted
is
to
carbon
chains
released
respiration
in
by
from
used
in
of
energy
ow
using
photosynthesis.
compounds
means
carbon
living
of
of
energy
.
ows
✔
analyse
✔
draw
✔
identify
✔
explain
pyramids
of
energy
.
feeding.
compounds
organisms
food
chains.
by
and
a
food
chain
from
a
food
web.
heat.
the
reason
food
chains
have
a
limited
length.
43
4
E C O LO G Y
Biomass
in
terrestrial
ecosystems
diminishes
with
energy
along
Species, communities and
food
chains
due
to
the
loss
of
carbon
dioxide,
water
and
other
waste
ecosystems are studied in
products,
such
as
urea.
The
indigestible
parts
of
organisms
such
as
hair
Topic 4.1. In Topic 2.8 you can
and
nails
are
also
lost
from
one
link
of
the
food
chain
to
the
next.
Heat
see cell respiration as a cause
is
lost
through
respiration.
There
is
a
continuous
but
variable
supply
for the loss of energy in a food
of
energy
in
the
form
of
sunlight
but
the
supply
of
nutrients
in
an
chain. In Topic 2.9 you can see
ecosystem
is
finite
and
limited.
photosynthesis as a mode of
S AmPlE StuDEnt AnS wEr
obtaining energy.
The image shows a food web.
elf owl
Theories can be used to
wolf spider
explain natural phenomena;
for example, the concept of energy
flow explains the limited length of
ground beetle
food chains. Because only around
10% of the energy in a trophic level
ear thworm
woodlouse
snail
can be used by the next trophic
level, the food chains are limited
bacteria
in length.
fungi
dead leaves
plants
Outline the energy ow through this food web.
This
▲ All
answers
answer
could
are
correct.
have
Plants
The
mentioned
energy
level,
webs
could
is
lost
lengths
are
of
at
each
food
restricted.
have
detritivores
also
or
(autotrophs)
chemical
chains
the
material
or
as
heat
to
Primary
that
saprotrophs
soil
energy
to
is
that
obtain
used
are
the
3/3
marks:
producers
and
convert
light
energy
energy.
T
his
energy
is
used
by
the
plant
and
lost
the
surroundings
through
the
process
of
respiration.
consumers
like
snails
consume
plants.
Only
10%
of
decay
accumulates
energy
by
achieved
answer
energy
plant
have
trophic
The
added
could
that
to
as
answer
[3]
and
organisms
is
passed
on
to
the
next
trophic
level
as
energy
is
lost
in
that
as
heat.
Also,
energy
is
lost
as
not
all
of
the
plant
is
eaten
or
for
digested.
metabolism.
Exape 4.2.1.
Pyads  eey are diagrams
The
diagram
is
a
trophic
pyramid
of
energy
(not
shown
to
scale).
that represent the amount of
energy conver ted to biomass at the
X
dierent trophic levels.
Y
a)
Label
b)
State
c)
X
and
the
Explain
units
the
pyramid
Y
.
of
used
loss
of
in
a
pyramid
energy
from
of
one
energy
.
level
to
the
next
in
a
energy
.
Solution
a)
X:
second
Y:
producer
2
b)
kJ
m
(The
c)
1
yr
or
kilojoules
biomass
Autotrophs,
energy
44
consumer
can
also
mainly
during
per
be
metre
squared
measured
plants
and
photosynthesis.
in
algae
in
Plants
per
joules
year.
or
megajoules).
phytoplankton,
are
consumed
by
release
primary
4.3
consumers,
Around
the
to
90%
energy
which
the
which
is
of
the
lost
cannot
other
be
as
are
then
eaten
energy
as
heat
digested
they
are
is
lost
from
are
by
secondary
between
lost
from
The
one
C Y C ling
consumers.
trophic
respiration.
C Arbon
levels.
parts
link
of
of
the
Most
of
organisms
food
chain
egested.
S AmPlE StuDEnt AnS wEr
Outline how the energy flow through food chains limits their length.
[3]
▲ The
This
answer
could
have
achieved
1/3
marks:
(10%)
Food
as
chains
energy
are
often
ows,
of
most
about
of
the
3
to
4
energy
organisms.
is
released
or
T
his
is
lost
because
into
one
of
as
heat.
Only
about
10%
of
the
energy
is
an
energy
level
to
the
next
level.
T
herefore,
the
the
food
chain
is
limited.
Also,
the
energy
is
length
available
answer
for
lost
as
to
which
are
often
predators
or
very
little.
So,
there
could
not
be
a
lot
of
recorded
be
passed
4 . 3
to
the
next
C A R B O N
energy
that
to
✔
availability
peat
forms
when
of
carbon
in
on
carbon
autotrophs
convert
carbon
dioxide
and
partially
other
carbon
in
aquatic
as
dissolved
ecosystems,
carbon
carbon
dioxide
is
present
dioxide
✔
into
carbon
diffuses
from
the
atmosphere
out
methane
in
is
of
is
produced
organisms
by
into
from
conditions
and
respiration
water
or
and
into
water
in
answer
due
to
uneaten
undigested
feces
organic
because
of
in
parts
or
energy
parts,
that
or
are
due
lost
egestion.
matter
acidic
waterlogged
decomposed
oil
carbon
eras
and
was
gas
dioxide
biomass
animals
and
may
of
calcium
in
limestone.
some
by
organic
✔
matter
carbon
methanogenic
diffuses
into
or
accumulates
in
estimate
is
not
and/or
fully
anaerobic
soils.
organic
matter
converted
either
from
into
past
coal
that
accumulate
in
porous
is
produced
fossilized
by
the
organic
combustion
matter.
have
hard
is
oxidized
the
carbonate
parts
and
can
that
are
become
composed
fossilized
to
carbon
carbon
uxes
due
to
processes
in
the
cycle.
the
the
analyse
data
from
air-monitoring
stations
to
ground.
explain
methane
The
mentioned
the
✔
atmosphere
✔
respiration.
Y shd e ae :
produced
anaerobic
archaeans
not
occurs
or
atmosphere.
✔
does
loss
autotrophs.
dioxide
diffuses
it
heat
and
✔
water
because
the
ions.
of
carbon
a
energy
rocks.
✔
hydrogencarbonate
✔
score
that
compounds.
or
✔
not
into
geological
carbohydrates
did
cycling.
✔
✔
from
ecosystems
conditions
depends
pass
next.
C Y C L I N G
decomposed
continued
can
the
consumer
.
Y shd k:
✔
heat
have
through
can
for
carnivores,
losses
is
mark
the
should
consumers,
to
mentioning
that
through
secondary
that
level
a
proportion
passed
specify
of
small
the
mark
from
scored
the
energy
trophic
▼ The
environment
answer
mentioning
dioxide
annual
uctuations.
and
✔
construct
✔
explain
a
diagram
of
the
carbon
cycle.
atmosphere.
the
processes
occurring
in
the
carbon
cycle.
The
continued
cycling.
one
The
carbon
availability
cycle
sink
shows
to
of
the
another.
carbon
in
processes
Carbon
ecosystems
that
fluxes
depends
transfer
should
carbon
be
on
carbon
from
measured
in
15
gigatonnes,
which
are
1
×
10
g
(1,000,000,000,000,000
grams).
45
4
E C O LO G Y
Exape 4.3.1.
The structure of carbon
compounds such as carbohydrates
The
diagram
shows
part
of
the
carbon
cycle.
is studied in Topic 2.3. Carbon
a)
fossil
State
one
process
by
which
CO
2
dioxide’s role in photosynthesis
fuels
is
transferred:
will be studied in Topic 8.3. Carbon
dioxide and climate change will be
(i)
from
fossil
fuels
(ii)
from
plants
(iii)
from
air
to
the
air
studied in Topic 4.4.
CO
to
fossil
fuels
in
2
air and sea
to
plants.
• A ca sk (also known as
plants
carbon reservoir) is a reserve of
carbon.
animals
• A ca  x is the transfer of
carbon from one carbon sink to
another.
b)
The
carbon
flux
from
plants
and
animals
to
CO
in
the
air
and
2
• Pea is organic matter that is not
sea
fully decomposed due to acidic or
which
is
about
this
120
gigatonnes
carbon
is
per
year.
transferred
to
Explain
the
the
process
by
air.
waterlogged soils.
c)
On
the
cycle,
draw
a
box
showing
the
carbon
sink
of
• fss es are par tially
decomposers
and
the
carbon
flux
due
to
decomposition
decomposed organic matter
leading
to
the
carbon
sink
of
decomposers.
from past geological eras that
accumulate in porous rocks.
• lese, a rock composed
of calcium carbonate, is mainly
d)
Describe
the
formation
of
peat.
Solution
a)
(i)
combustion
(ii)
fossilization
(iii)
photosynthesis
formed from sediments containing
the remains of marine organisms
such as corals and molluscs.
b)
Carbon
dioxide
process
of
reactions
that
catabolic,
energy
occurs
out
in
of
the
in
in
c)
A
box
from
d)
as
the
cells
and
acid
resulting
in
in
peat
into
In
in
the
plants
not
of
This
have
aquatic
reactions
oxygen,
full
are
to
(ATP).
or
the
produce
This
dioxide
into
the
carbon
process
diffuses
water
dioxide
ions.
labelled
bacteria
by
chemical
glucose
habitats
decomposers
as
respiration
so
many
carbon
decomposers
anaerobic
conditions,
The
atmosphere,
cycle)
to
animals
triphosphate
cells.
the
Saprotrophic
acidic
energy
.
breakdown
of
plants.
do
soils
conditions.
function
into
the
and
involves
hydrogencarbonate
from
soils
these
plants
adenosine
passes
anywhere
Waterlogged
In
of
aquatic
forming
(added
food
involve
form
by
Respiration
mitochondria
and
of
animals
water.
produced
convert
they
the
case
dissolves
is
respiration.
(usually
all
air
fungi
with
arrows
soil).
gaps
occurs,
and
in
are
full
resulting
are
decomposition
unable
is
S AmPlE StuDEnt AnS wEr
Increasing carbon dioxide concentration in the atmosphere leads to
acidification of the ocean. This in turn reduces the amount of dissolved
calcium carbonate. A study was under taken to investigate the effect
of increasing the concentration of atmospheric carbon dioxide on the
calcification rate of marine organisms. Calcification is the uptake of
calcium into the bodies and shells of marine organisms. The study was
under taken inside Biosphere-2, a large-scale closed mesocosm. The
46
to
inhibited,
formation.
graph shows the results of the data collection.
of
in
4.4
C l i m At E
C H A ngE
120
m
2–
OCaC lomm
3
/ noitaciclac
yad
1–
80
40
0
0
200
400
600
800
/ µatm
pCO
2
Source of data: C. Langdon et al. (2000), Global Biogeochemical Cycles,
14(2), pp. 639–654
a) State the relationship between atmospheric carbon dioxide and
calcication rates.
▲ Although
[1]
in
the
graph
partial
This
answer
could
have
achieved
1/1
rates
dioxide
decrease
pressure
of
concentration
was
carbon
is
the
shown
X
axis
carbon
is
the
dioxide,
marks:
the
As
what
on
concentration
increases,
the
accepted
as
of
an
carbon
dioxide
answer.
calcication
exponentially.
▲ The
mark
answer
for
scored
mentioning
the
the
fact
that
) Outline e way in which reef-building corals are aected by
the
increasing atmospheric carbon dioxide.
carbonate
ion
availability
is
[2]
decreased
with
increased
CO
2
This
answer
could
have
achieved
1/2
marks:
levels.
Reef-building corals require carbonate ions to help build (deposits
▼ The
that
in) their shells. If atmospheric CO
an
answer
does
increase
in
not
CO
mention
increases
2
2
global
temperature
(CO
is
a
2
taken into the water and the CO
reacts with water to form H
2
CO
2
greenhouse
3
+
which dissociates into H
gas).
temperatures
and HCO
Higher
(the
same
ocean
applies
for
, further decreasing the
3
acidication)
carbonate ions available for the reef-building corals to deposit.
zooxanthellae,
coral
4 . 4
C L I M AT E
✔
there
is
a
correlation
atmospheric
concentrations
of
gases
in
the
atmosphere
experienced
at
the
Earth’s
carbon
dioxide
and
water
vapour
are
the
greenhouse
methane
✔
the
and
impact
absorb
nitrogen
of
a
concentration
✔
gas
long-wave
warmed
in
Earth
radiation
oxides
depends
radiation
the
emits
the
start
of
years
ago
have
on
as
its
less
impact.
ability
well
as
on
greenhouse
its
atmosphere.
recent
increases
largely
fossilized
due
✔
✔
that
explain
the
climate
change.
analyse
is
absorbed
inuenced
by
global
temperatures.
atmospheric
increases
in
carbon
the
dioxide
combustion
of
matter.
effect
of
greenhouse
gases
on
data
on
retain
the
and
climate
concentrations
of
coral
of
reefs
from
dissolved
increasing
carbon
dioxide.
by
heat
in
the
✔
analyse
global
temperatures
average
in
to
organic
data
showing
temperatures
concentrations
global
dioxide
revolution
Y shd e ae :
atmosphere.
✔
carbon
industrial
longer-wavelength
radiation
gases
rising
of
to
(heat).
longer-wave
the
and
concentrations
✔
between
concentrations
gases.
are
✔
increasing
bleaching.
most
✔
signicant
therefore
of
surface.
200
✔
rejection
affect
since
climates
to
C H A N G E
Y shd k:
✔
leads
patterns
on
correlations
and
carbon
between
dioxide
Earth.
are
greenhouse
gases.
✔
evaluate
causing
claims
climate
that
human
activities
are
not
change.
47
4
E C O LO G Y
• geehse ases are those
• The eehse eec is the
that produce the greenhouse eect
process by which the Ear th’s surface
(carbon dioxide, water, methane and
is warmed due to entrapment of the
nitrogen are the most impor tant).
radiation re-emitted by the Ear th as
The proper ties of water and
how these control temperature are
studied in Topic 2.2. The production
of carbon dioxide in respiration is
long-wave radiation.
shown in Topic 2.8 and the use of
carbon dioxide in photosynthesis is
S AmPlE StuDEnt AnS wEr
discussed in Topic 2.9.
Using the diagram, explain the interaction of shor t- and long-wave
radiation with greenhouse gases in the atmosphere.
[3]
Claims, such as the claims
This
answer
could
have
achieved
3/3
marks:
that human activities are
causing climate change, need to
be assessed. Scientific evidence
for warming of the climate system
is unequivocal. The global
temperature of the Ear th’s surface
has increased 1.8°C since 1880.
Many scientific models have been
used to explain these changes. It is
likely that this trend is par tially
due to human activity, as it is
unlikely that these changes
occurred only from natural
internally generated variability of
the climate system. Never theless,
there are many uncer tainties that
need to be tested, especially those
related to variability due to natural
causes.
Greenhouse
gases
include
gases
such
as
CO
,
methane,
water
2
▲ The
for
answer
mentioning
radiation
is
scored
that
full
the
long-wave
marks
reected
vapour
,
etc.
penetrate
and
is
reected
radiation
the
is
as
heat.
unable
greenhouse
to
the
(as
UV)
greenhouse
passes
gases
from
the
rays
of
the
Sun
these
gases
in
the
atmosphere,
reaching
the
surface
through
of
the
Earth
and
thus
delivering
heat
energy.
However
,
when
Short-wave
they
radiation
radiations
Long-wave
pass
gases.
Short-wave
radiation
to
reect
from
the
surface,
they
become
long-wave
radiation
through
the
Earth’s
which
is
absorbed
by
the
gases
and
reected
back
to
the
Earth
surface.
or
trapped
warmer
.
48
in
the
atmosphere.
T
his
causes
the
Earth
to
become
4.4
Methane
matter
is
in
methane
an
important
anaerobic
and
water
greenhouse
conditions.
from
gas.
It
is
Methanogenic
carbon
dioxide
and
produced
from
archaeans
hydrogen.
C l i m At E
C H A ngE
organic
produce
They
can
There are two strategies to use to
also
produce
methane
from
acetate.
Some
methane
diffuses
into
identify the correct answer to a
the
atmosphere
or
accumulates
in
the
ground.
Methane
is
oxidized
to
multiple choice question: 1. pick
carbon
dioxide
and
water
in
the
atmosphere,
but
this
takes
the correct answer directly, 2.
many
years.
eliminate all the wrong answers.
Exape 4.4.1.
The
enhanced
global
Arctic
greenhouse
warming.
if
the
A.
Increase
B.
Decrease
Exape 4.4.2.
What
Earth’s
in
area
in
is
effect
likely
surface
of
ice
numbers
has
to
caused
occur
in
temperature
What
the
rises?
habitat
of
pest
to
and
do
methanogenic
methane
that
is
archaeans
liberated
use
into
the
atmosphere?
A.
species
gases
produce
Carbon
dioxide,
hydrogen
B.
Carbon
dioxide,
ethanol
C.
Carbon
monoxide
and
and
oxygen
hydrogen
pathogens
C.
Decreased
D.
Increased
rates
of
decomposition
of
of
predators
acetate
and
ozone
detritus
D.
amount
or
Carbon
dioxide
and
hydrogen
or
acetate
from
Solution
temperate
regions
The
Solution
The
are
is
a
correct
the
answer
opposite
decrease
increase
correct
archaeans
due
of
is
D.
what
in
ice
areas
to
global
All
the
other
happens,
and
in
B
as
answers
in
and
A
C
there
they
reaction
answer
can
of
is
D
produce
carbon
as
methanogenic
methane
dioxide
and
from
the
hydrogen
or
from
acetate.
all
warming.
Pacce pes  tpc 4
Pe 1
Pe 3
Outline the potential energy value of ear thworms as
Discuss the processes in the carbon cycle that affect
primary consumers, grown on household food waste
concentrations of carbon dioxide and methane in the
such as fruit and salad leftovers, as a potential
atmosphere and the consequences for climate
source of food.
change.
Pe 2
a) Describe the production of methane by bacteria.
) Explain the reason carbon dioxide is a more
significant greenhouse gas than methane.
49
EV O LU T I O N
5
5 . 1
BIODIVERSIT Y
EV I D E N C E
FOR
EV O LU T I O N
✔
Yu shuld knw:
continuous
range
✔
evolution
occurs
when
heritable
of
a
species
✔
fossil
✔
selective
provide
breeding
that
across
the
populations
geographical
supports
of
gradual
the
divergence.
change.
records
shows
variation
related
characteristics
concept
of
AND
of
articial
evidence
for
domesticated
selection
can
evolution.
Yu shuld be able t:
animals
✔
explain
the
✔
analyse
processes
involved
in
evolution.
cause
data
on
development
of
melanistic
evolution.
insects
✔
evolution
of
homologous
structures
by
explains
similarities
in
structure
are
differences
in
compare
the
populations
into
of
separate
a
and
limbs
reptiles
of
mammals,
with
different
function.
species
species
pentadactyl
amphibians
methods
✔
areas.
when
birds,
there
polluted
adaptive
✔
radiation
in
by
can
gradually
of
locomotion.
diverge
evolution.
There
is
overwhelming
evidence
for
the
evolution
of
life
on
Earth.
The
The inheritance of genetic traits
fossil
record
provides
evidence
for
evolution.
This
includes
not
only
is studied in Topic 3.4 and Topic 5.2
direct
evidence
such
as
preserved
bones,
shells,
teeth,
and
pine
cones
discusses how natural selection
but
also
indirect
evidence
such
as
footsteps,
feces
and
pollen.
leads to evolution.
Comparative
basically
anatomy
similar
in
has
shown
different
that
species.
certain
This
structural
homology
features
may
be
are
regarded
• Evlutn is the change in
as
evidence
of
evolution
from
a
common
ancestor.
The
forelimbs
of
characteristics that can be inherited
tetrapod
vertebrates
have
similar
structures,
as
they
all
have
a
five-
by dierent generations of a
finger
pattern
(pentadactyl),
but
are
adapted
for
different
purposes.
population.
For
example
bats
use
their
wings
to
fly
while
moles
use
their
front
• Hmlgus structures are those
limbs
to
dig.
Homologous
structures
showing
adaptations
to
different
inherited from a common ancestor.
conditions
or
lifestyles
are
examples
of
divergent
evolution.
• Analgus structures have
similar structures but a dierent
ancestry.
Diversity
Natural
of
life
has
selection
individuals
evolved
increases
better
adapted
and
the
and
continues
frequency
to
of
decreases
evolve
by
selection.
characteristics
the
frequency
of
that
make
other
• Cnvergent evlutn is the
development of similar features
in unrelated species, for example,
wings in birds and insects or the
characteristics
in
species
evolution,
can
as
leading
lead
can
to
be
to
changes
evolution.
seen
in
within
the
Artificial
selective
species.
selection
breeding
of
These
can
also
changes
cause
domesticated
animals.
streamlined bodies of sh and
cetaceans.
• Dvergent evlutn describes
in which the newly diversied
the evolution of new species from
species are adaptively specialized to
a single parent species in response
a par ticular environmental niche.
to evolutionary triggers, for example
• Specatn is the creation of new
Darwin’s nches.
species from one existing species,
50
• Adaptve radatn is a rapidly
often as a result of divergent
occurring type of divergent evolution
evolution.
5.2
N AT U R A L
SELECTioN
Example 5.1.1.
What
A.
evidence
Ancestors
for
of
evolution
can
domesticated
be
seen
animals
in
domesticated
cannot
be
found
animals?
in
the
fossil
record.
B.
Variation
C.
Animals
not
D.
in
domesticated
adapt
to
the
animals
is
environment
due
but
to
sexual
these
reproduction.
characteristics
are
inherited.
Differences
cause
between
species
to
breeds
show
that
artificial
selection
can
change.
Solution
The
correct
natural
have
this
been
is
not
Answer
during
answer
selection.
is
found,
so
evidence
C
is
the
not
D.
The
A
for
is
of
of
incorrect.
to
an
selection
ancestors
evolution
related
lifetime
Artificial
fossils
is
of
Although
for
as
are
faster
answer
domesticated
evolution,
individual
much
domesticated
B
correct,
animals
characteristics
not
is
than
animals
only
.
▲ This
acquired
for
answer
outlining
behaviour—a
heritable.
scored
the
a
process
type
of
mark
of
mating
behavioural
isolation
S AMPLE STUDENT ANS WER
▼ Reproductive isolation can
Outline how reproductive isolation can occur in an animal population. [3]
be
This
answer
could
have
achieved
1/3
marks:
sympatric
other
have
Reproductive
isolation
can
for
example
occur
through
isolation
change
in
mating
behaviour
.
T
he
different
behaviour
can
allopatric.
the
mentioned
isolation,
a
or
methods
answer
are
the
geographic
shown
by
The
could
temporal
isolation,
plants
or
with
be
polyploidy
passed
on
to
practicing
new
one
the
the
any
offspring
old
up
behaviour
more.
to
a
point,
won’ t
S
peciation
has
where
mate
with
occurred
individuals
those
as
the
who
two
do
the
groups
If the question is wor th 3 marks,
won’ t
interbreed
anymore.
you will need to outline at least
three methods.
5 . 2
N AT U R A L
S E L E C T I O N
✔
Yu shuld knw:
individuals
that
characteristics
✔
diversity
evolve
of
by
life
has
natural
evolved
and
continues
natural
selection
✔
natural
selection
can
only
occur
if
there
among
members
of
the
same
mutation,
variation
✔
meiosis
between
adaptations
individual
of
✔
are
sexual
reproduction
individuals
in
characteristics
suited
to
its
a
increases
that
make
the
frequency
individuals
of
better
and
decreases
the
frequency
of
other
cause
leading
to
changes
within
the
species.
species.
that
make
environment
and
Yu shuld be able t:
an
way
✔
describe
✔
explain
adaptations
to
environments.
life.
species
tend
to
environment
✔
and
on
species.
characteristics,
✔
pass
offspring.
is
adapted
variation
their
to
selection.
characteristics
✔
reproduce
to
individuals
survive
and
produce
can
that
more
offspring
than
the
well
are
better
produce
adapted
offspring.
processes
involved
in
natural
support.
adapted
more
tend
offspring
✔
explain
✔
analyse
tend
to
die
or
while
produce
the
process
of
speciation.
to
data
respecting
the
changes
in
beaks
of
the
nches
less
the
selection.
on
Daphne
Major.
fewer
✔
explain
evolution
of
antibiotic
resistance
in
bacteria.
51
5
E VOLUTION
AND
BIODI VERSIT Y
There
The inheritance of traits
is studied in Topic 3.4. The
characteristics of species are
studied in Topic 4.1 and the
evidence for evolution
in Topic 5.1.
origin
of
natural phenomena, for
example, the theory of evolution
of
those
into
and
three
levels
genetic
new
in
frequencies
on
the
by
which
the
caused
moulding
and
third
preceding
recombinations,
obtained
at
novelties
variations
attained
is
Theories are used to explain
are
the
isolating
two
evolutionary
by
the
is
variation.
genetic
the
second
by
The
of
first
natural
Second
structures
fixation
levels.
process
the
is
acts.
is
of
the
is
the
ordering
populations
diversity
attained
selection
First
and
by
already
mutations
the
third
level
mechanisms.
• Varatns are dierences in a
• Natural selectn is a theory
species due to mutation, meiosis and
involving mechanisms that contribute
sexual reproduction.
to the selection of individuals that
reproduce. It can lead to the evolution
by natural selection can explain
• Adaptatns are characteristics
the development of antibiotic
that make an individual suited to its
resistance in bacteria. Methicillin-
environment and way of life.
of species.
resistant Staphylococcus aureus
(MRSA) is a bacterium that causes
Variation
in
species
arises
from
recombination
of
genetic
material.
mild infections on the skin, like
This
can
happen
in
different
ways.
Crossing
over
and
independent
sores or boils. It can also cause
assortment
of
homologous
chromosomes
during
meiosis
I
produce
more serious skin infection or if it
different
combinations
of
gametes.
The
combination
of
male
and
enters the bloodstream it can
female
gametes
when
fertilization
occurs
also
produces
variation.
reach the lungs or the urinary tract.
Mutations
are
random
and
usually
neutral
but
can
be
beneficial
Though most MRSA infections
or
harmful.
These
variations
lead
to
adaptations
which
can
aid
a
aren’t serious, some can be
population’s
chance
of
survival
and
reproduction.
life-threatening. Because it is
resistant to commonly used
antibiotics, it is tougher to treat
Example 5.2.1.
than most strains of
Staphylococcus aureus. This
What
increases
variation
in
a
population?
resistance has arisen by the
I.
Mutation
II.
Meiosis
III.
Sexual
reproduction
excessive use of antibiotics which
A.
I
only
C.
II
and
III
only
selects for the most resistant
strains by competitive exclusion.
B.
I
and
II
only
D.
I,
II
and
III
Solution
The
a
correct
population.
organisms,
gametes
is
D,
Mutations
changing
are
variation
In
during
meiosis
chromosomes
fusion
of
cause
sexually
chromatids.
random
all
promote
a
genotype.
migration
of
they
can
their
inherited.
occurs
as
homologous
the
52
answer
and
female
the
and
in
the
Mutations
reproducing
by
Another
change
variation
crossing
random
source
male
of
within
DNA of
occurring
in
organisms,
over
of
genes
orientation
variation
gametes.
in
between
the
results
from
5.2
N AT U R A L
SELECTioN
S AMPLE STUDENT ANS WER
Some lice live in human hair and feed on blood. Shampoos that kill lice
have been available for many years but some lice are now resistant to
As this is a discussion, valid
those shampoos. Two possible hypotheses are:
statements for both hypotheses
can be mentioned. For example,
Hypthess A
Hypthess B
Resistant strains of lice were present in
Exposure to anti-lice shampoo caused
the population. Non-resistant lice died
mutations for resistance to the shampoo
with increased use of anti-lice shampoo
and this resistance is passed on to
and resistant lice survived to reproduce.
offspring.
variation is necessary for natural
selection to occur, and in this case
both hypotheses include variation
in the population of lice, resistant
and non-resistant.
Discuss which hypothesis is a better explanation of the theory of
evolution by natural selection.
[3]
▲ One
This
answer
could
have
achieved
2/3
marks:
mark
hypothesis
the
resistance
shampoo
Hypothesis
A
is
better
as
it
follows
the
theory
of
Whereby
certain
organisms
possessed
the
resistance
by
the
was
to
the
shampoo,
probably
through
mutation.
anti-lice
shampoo,
there
was
a
ght
for
better
(mutation)
would
be
for
one
to
as
the
present
Due
to
the
use
of
the
sur vival
in
initially
shampoo.
for
saying
best
resistance
of
awarded
the
in
the
natural
population
selection.
was
A as
The
that
not
other
the
adapted
is
and
caused
mark
frequency
increases
passed
on
and
through
which
reproduction.
the
resistant
lice
environment
who
were
sur vived,
better
while
adapted
those
who
to
live
were
in
not,
such
died.
T
he
▼ The
resistant
lice
thus
were
able
to
reproduce
and
passed
on
this
trait
that
the
to
the
offspring
(which
hypothesis
B
answer
lifetime
not
mutations
example
finches,
of
inhabiting
speciation
and
the
Galapagos
adaptive
of
the
to
mention
acquired
during
individual
mentions).
might
Darwin’s
fails
characteristics
archipelago,
radiation.
Their
are
a
common
be
inherited
are
as
not
all
heritable.
good
ancestor
The term trait is accepted instead
arrived
on
the
Galapagos
about
two
million
years
ago.
Fifteen
of
the
of allele or gene, as it is the
currently
recognized
species
evolved
from
this
common
ancestor.
phenotypic expression of the
Changes
in
the
size
and
form
of
the
beak
have
enabled
different
characteristic.
species
sizes.
to
The
utilize
environment
harsh
so
finch,
Geospiza
the
G.
seeds
a
larger
Birds
large
of
a
until
T.
there
seeds,
advantage
over
could
on
next
feed
G.
the
the
small
G.
smaller
G.
can
larger
easily
.
a
fortis
beaks,
The
to
a
Here,
small
are
In
able
1982,
there
strong
with
was
with
finches
was
shift
Daphne
the
little
smaller
with
towards
the
the
to
of
bigger
members
of
island.
crack
the
magnirostris
G.
fortis
beaks
had
beaks,
passed
down
smaller
(a)
G. fortis (large beak)
(b)
G. fortis (small beak)
(c)
G. magnirostris
for
availability
bigger
then
is
ground
members
onto
G.
different
Major
tackle
few
them
of
of
medium
but
to
flew
allowing
compete
trait
a
seeds
the
seeds
population
finches
This
called
magnirostris,
magnirostris
showing
on
beaks
drought,
seeds.
island
cistoides.
bigger
especially
survive.
mainly
enough
During
resources,
Geospiza
have
were
so
generation,
among
with
cistoides
seeds.
the
T
ribulus
finch,
species
of
on
subsists
called
of
food
organisms
population
this
large
few
fortis,
species
cistoides
the
a
plant
seeds
grew,
T.
only
fortis
of
different
beak
of
an
as
to
they
the
size
fortis
Fgure 5.2.1.
Darwin’s finches
53
5
E VOLUTION
5 . 3
AND
BIODI VERSIT Y
C L A S S I F I C AT I O N
O F
✔
Yu shuld knw:
natural
of
✔
species
are
named
and
classied
using
B I O D I V E R S I T Y
classications
species
and
agreed
system—the
help
the
in
identication
prediction
of
an
characteristics
internationally
allow
shared
by
species
within
a
group.
binomial
system.
Yu shuld be able t:
✔
the
binomial
system
is
used
to
name
newly
✔
discovered
determine
and
✔
taxonomists
of
classify
species
using
a
hierarchy
✔
organisms
are
classied
Eukarya,
Archaea
the
taxa
main
and
in
a
and
used
phylum,
to
into
three
state
domains:
natural
species
Eubacteria.
classify
class,
family
,
are
✔
state
genus
recognition
one
plant
domain
recognition
Arthropoda
higher
have
the
taxa
evolved
genus
consist
from
and
of
one
all
✔
state
the
of
features
and
to
Bryophyta,
of
Annelida,
and
Porifera,
Cnidaria,
Mollusca,
Chordata.
recognition
amphibians,
features
reptiles
and
of
birds,
mammals,
sh.
common
construct
a
dichotomous
key
for
use
in
species.
identifying
taxonomists
species
sometimes
when
previous
evolved
features
Coniferophyta
Platyhelminthes,
✔
a
of
from
Angiospermophyta.
eukaryotes
order,
classication,
that
ancestral
of
species
level.
Filicinophyta,
species.
accompanying
✔
classication
animal
taxa.
kingdom,
✔
one
species
✔
✔
the
species.
new
taxon
from
reclassify
evidence
contains
different
groups
shows
species
ancestral
specimens.
that
that
have
species.
Natural
classifications
help
in
identification
of
species
and
allow
The characteristics of species,
the
prediction
of
characteristics
shared
by
species
within
a
group.
communities and ecosystems are
Sometimes
taxonomists
reclassify
groups
of
species
when
new
studied in Topic 4.1. The evidence
evidence
shows
that
a
previous
taxon
contains
species
that
have
for evolution is covered in Topic 5.1.
evolved
from
different
ancestral
species.
For
example,
sequencing
The characteristics of plant species
of
the
16S
rRNA bases
(part
of
the
30S
ribosome
of
prokaryotes)
has
are related to the presence of
resulted
in
the
reclassification
of
many
bacterial
species.
The
binomial
vascular tissues. Transpor t in plants
system
is
used
to
avoid
the
confusion
which
often
arises
from
the
will be studied in Topic 9.1 and
use
of
common
names.
The
genus
and
species
names
are
normally
Topic 9.2.
underlined
case
or
(capital)
letter;
for
written
letter
example,
in
and
italics.
the
Homo
The
species
sapiens
is
genus
name
the
name
with
a
scientific
begins
lower
name
with
case
for
an
upper
(small)
humans.
• Eukaryotes are classed from
Taxonomists
classify
kingdom, phylum, class, order,
the
or
family, genus and species.
plants
higher hierarchy to lower as
presence
to
four
organisms
absence
different
of
by
shared
phylums
assigning
features.
them
The
to
groups
features
based
used
to
on
assign
include:
• The bnmal system of
•
Bryophyta:
Non-vascular
land
plants
including
liverworts,
mosses
classication uses “Genus species”
and
hornworts.
They
do
not
produce
fruits,
pollen
or
seeds.
They
to name organisms.
have
the
•
rhizoids
presence
with
ovaries.
54
of
Filicinophyta:
leaves
instead
water
of
roots.
as
it
Vascular
xylem
and
Reproduction
Fertilization
occurs
plants
including
phloem.
is
by
outside
Do
spores
not
on
of
the
gametes
on
organism.
ferns.
Have
produce
the
depends
roots,
pollen
underside
of
stems
and
have
leaves.
and
no
5.3
•
Coniferophyta:
roots,
are
stems
Vascular
and
produced
in
leaves
cones,
plants
with
including
xylem
where
and
seeds
are
evergreen
phloem.
pine
Pollen
produced.
trees.
and
They
do
C L A S S i F i C AT i o N
oF
BioDi VERSiT Y
Have
ovules
not
Other characteristics can be used
produce
flowers.
to construct the key, but always
•
Angiospermophyta:
roots,
stems
produced
and
in
V
ascular
leaves
flowers,
with
where
flowering
xylem
fruits
and
plants
such
phloem.
containing
as
roses.
Pollen
seeds
are
and
They
have
ovules
try to keep it simple.
are
produced.
Example 5.3.1.
Construct
a
simple
dichotomous
key
to
classify
plants.
Solution
1.
2.
3.
a.
Produce
b.
Do
a.
Seeds
enclosed
b.
Seeds
not
a.
Has
b.
Does
not
seeds
........................................................................
produce
in
tissue
have
...........................................................
ovary
enclosed
vascular
not
seeds
in
................................
ovary
go
go
to
to
2
3
Angiospermophyta
.......................Gymnospermophyta
...................................................Filicinophyta
vascular
tissue
......................................Bryophyta
• inver tebrates are animals that have
have a spinal cord (notochord). These
no ver tebral column, such as the
are classied as Chordata, along with
Ar thropoda.
a few primitive species that have a
notochord but no ver tebral column.
• Ver tebrates are animals that have
a ver tebral column. All ver tebrates
Features
the
used
following
by
six
taxonomists
phyla
to
classify
invertebrates
as
members
of
include:
invertebrates
Lepidonotus clara
Loligo forbesii
Procerodes littoralis
Nymphon gracilis
Adocia
cinerea
Carcinus maenas
Arenicola marina
Polymastia
Alcyonium
mammiliaris
glomeratum
Prostheceraeus vittatus
Lumbricus terrestris
Corynactis viridis
Caprella linearis
Helix aspersa
Gammarus
Coccinella magnica
locusta
Cyanea capillata
Porifera
Cnidaria
Platyhelminthes
Annelida
Mollusca
Arthropoda
• no mouth or anus
• radial symmetry
• bilateral symmetry
• bilateral symmetry
• bilateral symmetry
• bilateral symmetry
• pores on surface
• sting cells
• mouth
• mouth and anus
• mouth and anus
• mouth and anus
• spicules
• tentacles
• no skeleton
• blood vessels
• soft body
• jointed legs
• no skeleton
• hard shell
• exoskeleton
• calcium exoskeleton
Fgure 5.3.1.
The six phyla of inver tebrate taxonomy
55
5
E VOLUTION
AND
BIODI VERSIT Y
S AMPLE STUDENT ANS WER
▼ Although
for
it
is
exoskeleton
is
correct,
not
the
given
mark
Lice are wingless insects that belong to the phylum Ar thropoda. State
because
t w characteristics that identify lice as members of the Ar thropoda.
if
there
is
a
list,
only
the
This
answer
is
too
is
considered
vague
answer
jointed
to
could
score
have
and
a
or
▲ The
for
mouth
answer
bilateral
and
could
have
achieved
1/2
marks:
The
1.
have
head,
legs
and
exoskeleton.
segmented
2.
body
,
answer
“head”
mark.
mentioned
appendages,
[2]
rst
have
bilateral
symmetry.
anus
scored
one
mark
Dichotomous
keys
can
be
used
to
identify
organisms.
A series
of
symmetry
questions
organism
Features
Figure
need
to
be
answered
in
order
to
deduce
to
which
group
an
belongs.
used
by
taxonomists
to
classify
chordate
animals
are
shown
in
5.3.2.
ver tebrates
sh
amphibians
reptiles
birds
mammals
• eggs laid in water
• waterproof eggs
• shelled eggs
• give bir th
• lar vae have gills
• hard scales
• feathers
• produce milk
• wings
• have hair
• gills
• scales
• ns
• naked skin
Fgure 5.3.2.
Features for classifying ver tebrates
Example 5.3.2.
Which
is
A.
moist
B.
soft
dry
a
characteristic
of
reptile
skin?
C.
scaly
hairy
D.
feathery
Solution
The
for
answer
Classifying
facilitating
general.
is
of
as
A
the
more
is
being
genetic
or
for
amphibians,
replaced
protein
sequences
species
by
C
is
easily
and
during
features
the
a
most
known
for
mammals
molecular
has
distinct
recognized
there
is
no
However,
field
trip,
species
among
identification
sequences
DNA.
sequences
million
by
Genetically
are
their
2
communication
taxonomic
protein
morphology
.
is
than
meaningful
distinguished
56
B,
Traditional
rapidly
on
is
and
D
is
birds.
two
which
differences
because
classifying
error
it
is
in
society
observable
Classification
over
in
when
in
traits
based
observation
be
their
visually
DNA or
identifying
difficult
when
and
cannot
organisms
approach
important
on
advantages
human
advantageous
based
approaches.
species
by
is
scientists
to
obtain
using
not
in
genetic
external
a
laboratory
.
5.4
5 . 4
C L A D I S T I C S
✔
Yu shuld knw:
evidence
from
classications
✔
a
clade
is
a
group
of
organisms
that
evolved
from
a
common
did
or
which
✔
amino
species
sequence
there
acid
is
a
number
are
sequences
part
differences
positive
of
of
a
are
time
since
they
has
shown
groups
that
based
not
correspond
with
on
the
gradually—
between
between
of
a
group
or
species.
Yu shuld be able t:
accumulate
diverged
origins
for
clade.
correlation
differences
evidence
two
✔
construct
the
other
species
from
a
cladograms
including
humans
and
primates.
and
✔
the
some
ancestor.
evolutionary
base
cladistics
of
have
structure
✔
C L A D i S T i CS
analyse
cladistic
evidence
that
led
to
the
common
reclassication
of
the
gwort
family
.
ancestor.
✔
✔
traits
can
be
analogous
or
analyse
cladograms
to
deduce
evolutionary
homologous.
relationships.
✔
cladograms
most
are
probable
Evidence
for
tree
diagrams
sequence
which
species
of
that
show
divergence
are
part
of
a
the
in
clades.
clade
can
be
obtained
from
the
The inheritance of traits is
base
sequence
of
a
gene
or
the
corresponding
amino
acid
sequence
of
studied in Topic 3.4. The evidence
a
protein.
In
1977
Carl
Woese,
studying
the
sequences
of
16S
ribosomal
for evolution and how evolution
RNA,
realized
that
Archaea
had
a
separate
line
of
evolutionary
descent
took place are studied in Topic
from
bacteria.
This
determined
the
new
classification
of
domains.
5.1 and Topic 5.2, respectively.
DNA and
FASTA.
protein
The
software
similarities
BLASTn
alignments
sequences
can
and
be
in
are
usually
shown
DNA sequences
protein
performed
sequences
in
BLAST
can
using
or
in
be
a
format
shown
BLASTp.
Classification of species is studied
called
using
in Topic 5.3.
the
Sequence
ClustalW.
• A trat is an identiable, heritable
phenotypic characteristic of an
A cladogram
is
a
tree
diagram
used
in
cladistics
to
show
relationships
organism, such as blue eyes, or
between
organisms. A cladogram
uses
lines
that
branch
off
in
different
red or white owers. It is used in
directions
ending
at
a
clade. A clade
is
a
group
of
organisms
with
a
the description of the observable
last
common
ancestor. At
each
node
a
splitting
event
occurs.
The
node
characteristics expressed by an
therefore
the
stems
represents
represent
the
the
end
of
newly
the
ancestral
formed
taxonomic
species
that
split
group
from
(taxon),
the
and
allele.
ancestor.
57
5
E VOLUTION
AND
BIODI VERSIT Y
Example 5.4.1.
Plant families have been
The
reclassified as a result of
animals.
cladogram
shows
the
evolutionary
relationship
between
some
evidence from cladistics. In 2001,
present day
placental
marsupial
mammals
mammals
egg-laying
Richard Olmstead and Pat Reeve
mammals
studied the DNA sequences of
birds
reptiles
three chloroplast genes through
I
PCR sequencing of 65 taxa of the
amphibians
aquatic angiosperms in the
P
J
Scrophulariaceae, commonly
bony
known as the figwor t family. They
sh
cartilagenous
found that the groups previously
sh
included in this family were not all
M
T
descendants of a common
ancestor; rather, they were five
R
different groups.
V
vertebrate ancestor
a)
State
b)
c)
the
organisms
Identify
the
Identify
the
group
node
that
of
are
closely
organisms
(bifurcation)
that
related
is
where
most
fish
to
reptiles.
distantly
related
to
fish.
diverged.
Solution
a)
birds
b)
mammals
c)
V
Example 5.4.2.
The
FASTA sequences
and
mice
(Mus
Score
Expect
199
2e-73
for
musculus)
bits(507)
Query
Query
b)
c)
1
61
State
M G D V E K G K K
I
F
M G D V E K G K K
I
F +
M G D V E K G K K
I
F
using
in
humans
(Homo
sapiens)
BLASTp.
Method
Identities
Positives
Compositional
96/105(91%)
99/105(94%)
Gaps
0/105
I
(0%)
MK C S Q C H T
V E K G G K H K
T
G P N L H F G R K
T
G Q A P G Y
K C + Q C H T
V E K G G K H K
T
G P N L H F G R K
T
G Q A
S
Y
T
A N K N K G
I
G + S
Y
T
A N K N K G
I
V Q K C A Q C H T
V E K G G K H K
T
G P N L H F G R K
T
G Q A P G F
Y
T
D A N K N K G
I
G E D
T
L M E
Y
L
E N P K K Y
I
P G
T
KM
I
F
V G
I
K K K E E R A D L
I
A
Y
L K K A
T N E
G E D
T
L M E
Y
L
E N P K K Y
I
P G
T
KM
I
F
G
I
K K K
E R A D L
I
A
Y
L K K A
T N E
G E D
T
L M E
Y
L
E N P K K Y
I
P G
T
KM
I
F
A G
I
K K K G E R A D L
I
A
Y
L K K A
T N E
the
these
Suggest
Yeast
from
A
I
W
number
of
amino
acids
in
the
studied
S
60
W
T
W
60
105
105
protein
that
are
different
organisms.
a
reason
cytochrome
(Saccharomyces
human
humans
58
aligned
proteins
matrix adjust.
61
Subject
in
were
c
1
Subject
a)
cytochrome
in
cerevisiae)
cytochrome
the
c
c.
cladogram.
is
useful
to
cytochrome
Identify
construct
c
whether
protein
mice
cladograms.
has
or
64
yeast
differences
are
closer
to
5.4
C L A D i S T i CS
Solution
a)
9
b)
Cytochrome
is
an
evolutionarily
Substitutions
within
are
constant
relatively
cytochrome
c)
c
Mice
are
c
a
closer,
separated;
the
useful
as
the
therefore
primary
over
more
yeast
structure
time,
molecular
conserved
which
protein.
of
cytochrome
makes
c
characterizing
clock.
differences
separated
there
are,
the
earlier
they
earlier.
Practce prblems fr Tpc 5
Prblem 1
Prblem 2
Beak shape in Darwin’s finches is emblematic of natural
Explain how natural selection can lead to evolution.
selection and adaptive radiation. Representatives of
Prblem 3
four distinct beak morphologies of finches that feed
Complete the table to compare and contrast the
on different parts of cacti are: small blunt in Geospiza
following inver tebrates. Use a tick (✓) to show the
fuliginosa, medium blunt in Geospiza fortis, large blunt in
feature is present.
Geospiza magnirostris and medium pointed in Geospiza
scandens. The length-to-width ratios of the beaks were
Phylum
measured and are shown in the scatter diagram.
Feature
Prfera
Cndara
Platyhelmnthes
Annelda
Mllusca
Ar thrpda
Ar tculated
G. magnirostris
(large blunt)
legs
Shape change
Blateral
Size change
size constant
shape approximately
symmetry
constant
G. scandens (sharp)
G. for tis (blunt)
G. fuliginosa
outer shell
(small blunt)
Prblem 4
oitar htdiw-ot-htgnel kaeb
2.0
The image shows par t of a cladogram.
1.8
sh
bird
mammal
1.6
1.4
C
1.2
1.0
0.8
0.6
B
G. scandens
G. for tis
G. fuliginosa G. magnirostris
A
nch species
a) State the median beak length-to-width ratio in
G. for tis
b) Compare the beak shape of G. scandens with that of
G. magnirostris.
a) Using the cladogram, suggest one diagnostic feature
that characterizes the given groups of ver tebrates at
A, B and C.
c) Explain how the shapes of the beaks allow different
feeding habits.
b) State the name of the domain to which these
organisms belong.
d) Using the example of finches, suggest how
populations can gradually diverge into separate
species by evolution.
59
HUMAN
6
6 . 1
DIGESTION
AND
ABSORPTION
Y ld kw:
✔
the
structure
allows
✔
it
to
the
small
enzymes
the
move,
contraction
of
of
of
Y ld e ale :
wall
of
digest
circular
intestine
and
P H YS I O LO GY
moves
the
and
and
intestine
absorb
the
along
food
the
✔
draw
food.
longitudinal
mixes
it
small
the
pancreas
the
small
secretes
enzymes
muscle
✔
explain
enzymes
with
into
the
lumen
digest
monomers
villi
increase
villi
as
most
in
the
the
macromolecules
small
surface
absorption
absorb
well
as
and
structure
in
explain
food
the
digestive
result
occurring
in
the
in
the
digestion
small
of
starch.
of
make
the
annotated
diagrams
of
the
villus.
is
mineral
area
of
and
membrane
are
absorbed
in
the
epithelium
describe
over
the
absorption
use
of
of
dialysis
digested
tubing
food
in
the
to
model
intestine.
out.
formed
ions
molecules
intestine.
carried
monomers
how
villus.
by
explain
digestion
vitamins
sugars
transport
the
use
from
of
amylase
starch
and
in
in
the
the
production
brewing
of
of
beer.
through
✔
different
processes
that
describe
of
✔
✔
of
intestine.
into
which
the
intestine
✔
✔
diagram
gut.
✔
✔
annotated
system.
✔
✔
an
identify
tissue
layers
in
transverse
sections
of
methods.
the
in
✔
small
a
intestine
contains
describe
large
with
a
microscope
or
micrograph.
the
digestion
Food
viewed
molecules
transport
to
the
that
of
the
products
of
liver.
need
to
be
digested
in
order
to
be
In Topic 2.1 you have studied the
absorbed
through
the
gut.
Digestion
can
be
mechanical
or
chemical.
molecules involved in metabolism
Mechanical
digestion
involves
breaking
up
the
food
through
chewing
and in Topic 2.5 the structure of
and
through
muscle
movements.
Chemical
digestion
is
the
catabolism
enzymes and how they work .
of
molecules
and
includes
pancreas
secretes
chemical
digestion.
the
enzymes
use
into
of
the
acids
lumen
or
of
alkalis
the
and
small
enzymes.
intestine
The
for
• De is the process by which
foods are transformed into soluble
Eample 6.1.1.
molecules.
• Ap is the process by
a)
Label
the
digestive
which monomers enter the cells of
diagram
of
the
system.
the intestine wall.
b)
Describe
the
digestion
of
starch
A
• Amylae is the enzyme that
in
humans.
digests starch, a polysaccharide,
into disaccharides.
c)
Explain
the
reason
lipase
is
not
B
involved
in
the
digestion
of
• Lpae is the enzyme that digests
starch.
lipids such as triglycerides into
C
fatty acids and glycerol.
• Peae are enzymes that
a)
A:
esophagus;
digest proteins into peptides and
C:
then into amino acids.
intestine
60
D
Solution
small
B:
stomach;
intestine;
D:
large
6 .1
b)
Starch
food
is
first
and
the
digested
tongue
in
the
helps
mouth.
to
mix
it
The
teeth
with
chew
saliva.
the
The
DigE s t ion
AnD
Ab s orPtion
starchy
starch
starts
You can be asked questions
to
be
digested
of
the
with
salivary
amylase,
which
breaks
down
some
on how starch, glycogen, lipids
starch
molecules
into
maltose.
Starch
is
a
polysaccharide
and nucleic acids are digested
while
maltose
is
a
disaccharide.
The
food
is
then
taken
to
the
into monomers. Remember that
stomach
and
from
there
to
the
small
intestine.
The
small
intestine
cellulose remains undigested.
has
circular
along
the
lumen
gut.
of
the
molecules
glucose
and
longitudinal
The
pancreatic
small
into
muscles
intestine.
maltose.
molecules
that
amylase
It
is
Maltose
is
then
move
secreted
continues
(monomers).
help
the
into
can
by
now
food
the
digestion
digested
Glucose
the
of
starch
maltase
be
into
absorbed
by
• Vll are small nger-like
the
intestinal
villi
to
enter
the
blood.
projections of the intestinal wall
c)
Lipase
down
is
an
enzyme
triglycerides
specific—their
Lipase
its
is
no
active
that
into
active
good
digests
fatty
site
for
lipids.
acids
will
and
usually
digesting
starch
Specifically
glycerol.
accept
one
starch
facing the lumen.
breaks
Enzymes
only
because
it
are
• Mcvll are small projections
substrate.
does
not
fit
found on the surface of the
epithelial cells of the villi.
site.
• A laceal is the lymphatic vessel
found in each villus which aids lipid
absorption.
The
small
intestine
is
lined
with
villi.
Villi
absorb
monomers
formed
• The mca is the layer of
by
digestion
as
well
as
mineral
ions
and
vitamins
through
different
epithelial tissue where food
methods.
Villi
increase
the
surface
area
of
epithelium
over
which
absorption occurs.
absorption
is
carried
out.
Each
villus
has
a
central
lacteal
into
which
• Ccla ad ldal mcle
lipids
are
absorbed
and
a
network
of
capillaries
into
which
the
rest
of
contract in dierent directions,
the
useful
substances
from
digestion
are
absorbed.
allowing the movement of food
through the gut.
Eample 6.1.2.
a)
b)
c)
State
one
type
the
route
State
State
(i)
one
of
of
molecule
amino
function
circular
absorbed
acids
into
into
the
the
lacteal.
villus.
of:
muscle
(ii)
mucosa.
Solution
a)
b)
c)
fatty
acids
from
(i)
the
lumen
contract
(ii)
to
absorption
of
the
move
of
small
food
intestine
along
the
to
capillaries
in
the
villus
gut
foods
Eample 6.1.3.
The
micrograph
epithelial
cells
shows
of
a
The structure and function of
villus.
the intestine wall is difficult
a)
On
the
micrograph
label:
to study, as mechanisms to do so
are invasive. Models can be used
as representations of the real
(i)
a
(ii)
microvilli
mitochondrion
world. Dialysis tubing can be used
to model absorption in the
(iii)
a
nucleus.
intestine because it is selectively
permeable.
61
6
HUMAN
P H YS I O LO G Y
b)
Suggest
one
absorption
adaptation
other
than
of
the
many
epithelial
cells
mitochondria
of
for
the
villus
to
energy
.
Solution
a)
Labels
cell,
cell
b)
as
follows:
and
Villi
the
have
many
absorption
of
to
the
is
also
the
villi
epithelium
increase
basal
Enzymes
ensure
for
at
occur
the
the
top
of
the
throughout
surface
channels
that
expressed
close
on
proximity
absorption.
increase
yellow
and
the
blue.
that
contain
substances.
shown
orange
shown
epithelium
to
are
shown
microvilli
They
intestinal
molecules
are
nucleus
absorption.
of
microvilli
mitochondria
The
of
blood
area
help
the
for
in
the
surface
the
food
capillaries
close
absorption.
Once
digested,
sugars
polysaccharides
have
or
become
villus
monosaccharides,
lipids
such
triglycerides
become
as
rich blood
have
fatty
supply produces
acids
and
glycerol,
and
proteins
a steep
have
concentration
become
amino
acids.These
gradient for
monomers
can
now
be
absorbed
ecient
by
the
epithelial
cells
of
the
villi.
diusion
Glycerol
is
diffusion,
large surface
absorbed
as
it
can
by
pass
simple
through
area for diusion
the
cell
membrane.
Fatty
acids
are
and active
absorbed
by
facilitated
diffusion.
transpor t
Glucose
and
absorbed
thin wall (only
amino
by
acids
co-transport
are
with
one cell thick)
sodium.
This
process
itself
so there is only
does
not
require
energy
,
but
to
a shor t distance
maintain
across which
diusion takes
the
sodium
sodium–potassium
gradient,
pump
the
must
place
move
the
of
cell
the
active
sodium
to
the
transport.
from
other
This
one
side
through
does
require
lymph system
energy
Fe 6.1.1.
in
the
form
water-soluble
Adaptations of the
absorbed
villus to absorption
by
of
ATP
.
vitamins
simple
Most
are
diffusion.
• sdm c-ap  is the
process by which sodium is
Eample 6.1.4.
transpor ted outside the cell by
How
is
glycerol
absorbed
into
the
epithelium
of
the
intestine
active transpor t to allow the
wall?
entrance of other substances such
as glucose into the cell by co-
A.
Simple
diffusion
C.
Facilitated
diffusion
transpor t with the sodium ions.
B.
Osmosis
D.
Endocytosis
Solution
Glycerol
is
absorbed
osmosis, diffusion and active
Glycerol
is
soluble
transpor t.
layer
In Topic 1.4 you studied
62
of
the
cell
in
by
simple
lipids,
membrane
diffusion,
therefore
without
it
the
so
can
the
correct
pass
need
for
answer
through
a
the
channel.
is A.
bilipid
6.2
6 . 2
T H E
B L O O D
the
blood
system
substances
waste
to
and
transports
simultaneously
✔
collects
arteries
carry
ventricles
veins
to
blood
the
at
high
tissues
of
pressure
the
arteries
in
blood
from
vessels
the
as
structure
arteries,
of
their
capillaries
or
walls.
from
the
their
have
muscle
walls
which
cells
pump
how
capillaries
and
elastic
maintain
blood
the
are
structure
suited
to
of
arteries,
their
veins
and
function.
bres
sketch
the
diagrams
heart
and
of
the
the
chambers
blood
vessels
and
valves
connected
of
to
it.
pressure
✔
between
explain
body
.
✔
✔
identify
products.
✔
✔
s Ys t E M
Y ld e ale :
continuously
cells
bLo o D
S Y S T E M
Y ld kw:
✔
thE
explain
the
double
circulation
of
blood
in
the
cycles.
heart.
✔
blood
ows
✔
capillaries
exchange
through
have
of
tissues
permeable
materials
in
capillaries.
walls
between
that
cells
✔
identify
✔
explain
and
in
and
the
blood
in
the
veins
collect
blood
at
low
pressure
from
of
the
body
and
the
return
it
to
the
atria
heart
describe
in
veins
and
the
heart
ensure
blood
✔
there
✔
the
by
preventing
is
a
separate
sinoatrial
a
circulation
for
the
node
the
by
pressure
and
the
initiates
heart
rate
of
the
the
be
the
out
heartbeat,
an
as
atria
it
electrical
is
during
in
the
the
left
atrium,
cardiac
left
cycle.
describe
William
of
the
Harvey’s
blood
discovery
with
the
of
heart
the
acting
as
pump.
acting
explain
the
causes
coronary
and
consequences
of
occlusion
of
arteries.
signal
discuss
social
implications
of
coronary
heart
disease.
propagated
and
increased
to
the
physical
twice
the
medulla
increases
vigorous
flows
can
brought
from
adrenaline
Blood
sends
contraction
walls
impulses
for
changes
aorta
then
the
walls
ventricles.
nerves
✔
node
stimulates
through
the
of
pacemaker.
sinoatrial
that
✔
and
lungs.
✔
of
node
control
backow.
✔
the
sinoatrial
hormonal
circulation
the
✔
the
and
rate.
circulation
as
of
nervous
heart.
valves
of
valves.
of
✔
✔
function
the
ventricle
the
of
the
✔
tissues
function
capillary
.
the
✔
the
the
describe
tissues
describe
allow
of
or
heart
the
heart
decreased
through
two
brain.
rate
to
prepare
activity
.
through
the
heart,
once
to
be
oxygenated
in
the
In Topic 2.2 you studied the
lungs
and
a
second
time
for
circulation
to
the
rest
of
the
body
.
structure of water and how some
molecules can dissolve in it to be
pulmonary
pulmonary
lungs
ar tery
vein
transpor ted. In Topic 2.3 you have
learned about carbohydrates and
lipids, which are transpor ted in
blood. In Topic 6.4 you will study
vena cava
gas exchange occurring between
aor ta
blood and lung tissues. In Topic 6.6
you will study the hormones that
head and
can be carried in blood and how
body
they help in homeostasis and
Fe 6.2.1.
Double circulation in the hear t
reproduction.
The
heart
three
and
main
blood
types
of
vessels
blood
make
vessels:
up
the
circulatory
arteries
that
carry
system.
blood
There
away
are
from
63
6
HUMAN
P H YS I O LO G Y
the
heart,
connect
veins
both
that
these
carry
blood
towards
the
heart
and
capillaries
that
vessels.
ar tery
capillary
vein
lumen
lumen
lining layer
lumen
lining layer
lining layer
elastic layer
elastic layer
muscle layer
muscle layer
tough outer layer
tough outer layer
Fe 6.2.2.
Blood vessels
Theories are regarded as
uncer tain. In 1628 William
Eample 6.2.1.
Harvey described how blood flow
Compare
and
contrast
the
structure
of
arteries,
veins
and
capillaries.
in the body was unidirectional,
with valves stopping the blood
Solution
from backflowing, and that blood
A ee
Ve
Capllae
thick walls to
thin wall to allow
wall one layer
withstand high
muscles to exer t
of cells thick to
pressure
pressure on them
allow diffusion of
returned to the hear t to be
Wall
recycled by pumping. With this, he
over turned theories developed by
the ancient Greek philosopher
substances
Galen on the movement of blood in
Fe 
collagen and elastic
thin outer layer of
wall
fibres in outer layer
collagen and elastic
to give wall strength
fibres for protection
no fibres
the body.
and flexibility
Lme
narrow lumen
wide lumen so
narrow lumen to fit
to maintain high
greater volume of
in small spaces
pressure
blood can pass
You do not need to answer the
question in the form of a table, but
Valve
no valves
valves to avoid
no valves
backflow
it helps to ensure you are really
comparing and contrasting.
Dec
away from hear t
towards hear t
connect ar teries to
veins
Pe
no pores
no pores
pores to allow
lymphocytes to
leave
64
6.2
The
to
pressure
whether
the
contraction
pressure
the
different
ventricles
(diastole).
graph.
The
curve
larger
are
where
part
the
a
heart
cycle
heartbeat
are
the
the
(systole),
heartbeat
of
atria
where
of
contracting
A whole
first
curve,
chambers
contracting
ventricles
are
or
can
can
changes
relaxing
be
be
according
seen
seen
(atrial
as
on
a
the
systole)
contracting
after
bLo o D
s Ys t E M
semilunar
semilunar
valves open
valves close
a
aor ta
heart
first
and
the
(ventricular
erusserp
parabolic
second,
in
thE
atrioventricular
valves open
atrioventricular
systole).
In
healthy
adults
you
can
hear
two
normal
heart
sounds
in
left
valves close
atrium
each
heartbeat.
These
are
often
described
as
a
“lub”,
the
closing
of
left
the
ventricle
atrioventricular
(A
V)
valves,
and
a
“dub”,
the
closing
of
the
semilunar
valves.
time
systole
diastole
Eample 6.2.2.
a)
Figure
6.2.4
shows
a
human
heart.
hear t
sounds
Label
b)
(i)
A to
D
Explain
during
(ii)
The
in
the
(iii)
Describe
the
in
the
valves
time
these
the
the
of
the
heart.
pressure
in
“lub”
the
ventricle
“dub”
Fe 6.2.3.
Cardiac cycle
Fe 6.2.4.
The human hear t
increases
contraction.
pressure
the
diagram
reason
atrial
semilunar
at
the
aorta
open.
valves
change
semilunar
in
valves
is
around
Predict
80
the
mmHg
pressure
just
in
the
before
the
ventricle
open.
pressure
in
the
left
ventricle
after
close.
Solution
a)
b)
A:
aorta;
(i)
B:
During
open;
the
(ii)
pulmonary
blood
blood
be
from
letting
is
just
the
pressure
blood
left
the
increasing
must
flowing
ventricular
valves,
the
ventricle,
pressure
C:
contraction,
therefore
left
The
atrial
artery;
ventricle
atrioventricular
flowing
the
above
out
be
of
80
the
mmHg
into
high
the
from
D:
vena
(A
V)
left
cava.
valve
atrium
is
into
pressure.
ventricles
must
wall;
the
enough
to
allow
aorta.
to
the
The
open
the
heart.
Par t (b) in example 6.2.2 is
(iii)
The
the
of
pressure
ventricle
the
the
body
.
A
V
in
and
The
(mitral)
ventricle.
the
left
ventricle
entered
atria
valve
are
is
the
decreases,
aorta
filling
closed,
to
with
no
be
blood
carried
blood,
blood
as
is
but
to
has
the
left
rest
because
flowing
into
the
referring to the left ventricle, but
as the same happens in both
ventricles simultaneously, no
marks will be taken off if you just
refer to the ventricles instead of
the left ventricle.
• The medlla laa is the par t
of the brain involved in the control
of the hear t rate.
• Adeale is a hormone that
accelerates the hear t rate.
65
6
HUMAN
P H YS I O LO G Y
The
heartbeat
is
initiated
by
a
group
of
specialized
muscle
cells
in
the
There are social implications
right
atrium
called
the
sinoatrial
node.
The
sinoatrial
node
acts
as
a
of coronary hear t disease.
pacemaker,
sending
out
an
electrical
signal
that
stimulates
contractions
Diets rich in glucose and trans fats
as
it
is
propagated
through
the
walls
of
the
atria
and
then
the
walls
of
can lead to obesity, which at the
the
ventricles.
The
heart
rate
can
be
affected
by
nervous
and
hormonal
same time increases the chances
control.
Two
nerves
link
the
heart
to
the
medulla
oblongata
of
the
of atherosclerosis. High blood
brain.
One
of
these
nerves
carries
messages
to
increase
the
heart
rate,
pressure is also a cause of
the
other
to
decrease
the
heart
rate.
Adrenaline
is
a
hormone
that
coronary hear t disease. Smoking,
increases
the
heart
rate
to
prepare
for
vigorous
physical
activity
.
stress, cer tain drugs and a diet rich
Atherosclerosis
in salt can contribute to increasing
called
blood pressure. Coronary hear t
lipoprotein
disease can lead to disabilities;
arteries,
therefore it is impor tant to keep a
the
healthy lifestyle to reduce your
infarct
6 . 3
DEFENCE
(LDL)
area
skin
and
defence
mucous
against
flow
the
the
the
dead
AGAINST
formation
is
mainly
and
of
heart
properly
.
of
white
blood.
can
heart
This
If
a
blood
the
suffer
plaque
by
cells.
artery
damage
muscle
damage
of
formed
tissue.
can
the
It
due
clogs
to
this
to
a
arteries
density
occluded
If
lead
in
low
the
(blocked)
lack
of
happens
heart
is
oxygen
the
attack
heart
or
an
tissue).
INFECTIOUS
DISEASE
Y ld e ale :
Y ld kw:
✔
the
reaching
contract
(an
by
atheroma
cholesterol
artery
,
nutrients
cannot
caused
The
impeding
coronary
and
chances of developing it.
is
atheroma.
membranes
pathogens
form
that
a
✔
primary
cause
explain
mechanisms
of
defence
against
pathogens.
infectious
disease.
✔
✔
clotting
factors
allowing
cuts
are
in
released
the
skin
to
from
be
sealed
by
describe
explain
platelets
clot
blood
the
the
process
causes
formation
in
of
and
blood
clotting
consequences
coronary
and
of
blood
arteries.
clotting.
✔
✔
the
cascade
brinogen
✔
ingestion
cells
of
gives
results
to
brin
in
the
by
pathogens
non-specic
rapid
conversion
outline
the
production
of
antibodies
by
lymphocytes.
of
thrombin.
by
phagocytic
immunity
to
white
✔
outline
✔
explain
how
lymphocytes
act
as
memory
cells.
blood
the
action
of
antibodies
against
diseases.
pathogens.
✔
production
of
antibodies
by
lymphocytes
in
✔
response
to
particular
pathogens
gives
explain
the
evolution
of
antibiotic-resistant
specic
bacteria.
immunity
.
✔
✔
antibiotics
block
processes
that
occur
describe
Florey
penicillin
prokaryotic
cells
but
not
in
eukaryotic
viruses
lack
a
metabolism
and
cannot
✔
treated
some
that
with
strains
confer
strains
of
of
Chain’s
bacterial
experiments
infections
in
to
test
mice.
describe
the
effects
of
HIV
on
the
immune
therefore
system
be
on
cells.
✔
✔
and
in
and
methods
of
transmission.
antibiotics.
bacteria
resistance
bacteria
have
to
have
evolved
antibiotics
multiple
with
and
genes
some
resistance.
Pathogens
are
organisms
that
cause
disease.
The
human
body
has
In Topic 5.2 you have seen
structures
and
processes
that
resist
the
continuous
threat
of
invasion
how natural selection can result in
by
pathogens.
Skin
and
mucous
membranes
form
a
primary
defence
bacterial resistance to antibiotics.
against
pathogens
organisms
wound,
skin
to
to
clotting
be
a
protein
from
66
of
body
.
by
are
blood
fibrinogen
that
flowing
the
cause
factors
sealed
conversion
is
enter
that
makes
through
a
infectious
To
released
clotting.
to
fibrin
mesh
the
avoid
not
organisms
from
The
using
joining
wounds.
disease,
the
the
entering
platelets
cascade
allowing
through
allowing
results
enzyme
platelets,
in
cuts
the
in
the
rapid
thrombin.
stopping
a
Fibrin
the
blood
6.3
DEFEnCE
AgAinst
inFECtious
DisE A sE
Eample 6.3.1.
An understanding of
immunity has led to the
What
sequence
of
reactions
occurs
during
blood
clotting?
development of vaccinations and
A.
Fibrinogen
is
broken
down
into
trypsin
by
fibrin.
treatment of cancer. In 2018,
George P
. Smith and Gregory Winter
B.
Fibrin
is
broken
C.
Fibrinogen
down
into
fibrinogen
by
trypsin.
by
thrombin.
both became Nobel Laureates in
is
broken
down
into
fibrin
Chemistry. They were inspired by
D.
Fibrin
is
broken
down
into
fibrinogen
by
the power of evolution and used
thrombin.
the same principles—genetic
Solution
change and selection—to develop
The
correct
answer
is
C.
Fibrinogen
is
a
globular,
soluble
protein
proteins to solve medical
found
in
blood
found
in
an
plasma.
In
the
event
of
a
cut,
an
enzyme
that
is
problems. They used
inactive
form
is
transformed
into
active
thrombin.
bacteriophages to evolve new
Thrombin
breaks
down
part
of
the
soluble
fibrinogen
protein,
now
proteins which can be used in the
transforming
it
into
a
smaller
but
insoluble
fibrous
protein
called
pharmaceutical industry for the
fibrin.
Molecules
of
fibrin
form
cross-linking
bonds
resulting
in
a
production of antibodies that
large
polymer
which
attaches
to
platelets,
and
thus
clots
blood.
neutralize toxins, counteract
autoimmune diseases or cure
Once
organisms
activates
of
a
have
series
pathogens
by
of
entered
the
mechanisms
phagocytic
tissues,
to
white
the
defend
blood
immune
the
cells
body
.
gives
system
metastatic cancer.
Ingestion
non-specific
lymphocytes recognize
immunity
to
diseases.
Production
of
antibodies
by
lymphocytes
in
antigens on bacteria
response
are
to
particular
proteins
flagging
that
them
Lymphocytes
plasma
cells
remember
can
for
attach
other
mature
(or
how
B
to
pathogens
to
gives
pathogens,
lymphocytes
to
cells).
become
to
immunity
.
destroying
engulf
them
cells
particular
are
a
clone
antibodies,
of
Antibodies
them
by
antibody-producing
Memory
produce
specific
antibodies
phagocytosis.
cells
called
plasma
and
and release specic
or
cells
therefore
that
antibodies attach to
are
antibody
very
useful
if
there
is
a
second
encounter
with
the
same
antigens on bacteria
pathogen.
molecules
ydobitna fo noitartnecnoc
secondary response
phagocytes are
attracted towards
primary response
bacteria and
small vacuoles
engulf them
contain enzymes
bacteria are
0
10
20
30
40
50
60
digested within
time / days
food vacuoles
rst encounter
second encounter
with antigen
with antigen
Fe 6.3.1.
Fe 6.3.2.
Specific immune
Production of antibodies
response
• Lympcye are white blood
• An ady is a protein that
cells involved in the production of
attaches to the antigen to destroy or
antibodies.
ag the pathogen.
• Plama cell are mature
• Memy cell produce antibodies if
lymphocytes that can produce
a pathogen carrying a specic antigen
antibodies in the primary response.
is re-encountered. This is called the
In Topic 11.1 you will cover
antibody production in more detail,
along with how vaccinations work .
secondary response.
• An ae is par t of the pathogen
(usually a protein) recognized by the
• hiV is a virus that causes the
immune system.
disease AIDS.
67
6
HUMAN
P H YS I O LO G Y
s AMPLE stuDEnt Ans WEr
Some blood proteins are involved in the defence against infectious
In an eight-mark question you
diseases. Explain the roles of amed types of proteins in different
should mention many proteins,
defence mechanisms.
[8]
not just explain how one type of
This
answer
could
have
achieved
1/8
marks:
protein is made.
Lymphocytes
▲ The
for
student
saying
that
scored
one
are
phagocytes
against
infectious
bacteria
carry
diseases.
that
are
When
involved
the
in
infection
defence
occurs,
the
mark
lymphocytes
create
antigens
on
their
surface,
which
the
lymphocytes
antibodies.
could
▼ The
student
clotting
factors
failed
and
to
that
mention
brin
as
recognize.
is
responsible
that
Although
the
permits
blood
antibodies
student
does
not
are
in
the
producing
specic
cells
defend
mentioned,
mention
of
large
antibodies
retain
specic
role
the
plasma
amounts
or
ability
how
to
for
the
will
antigen.
then
T
here
are
nd
a
phagocyte
different
types
of
T
he
lymphocyte
would
have
to
multiply
cells
that
clotting.
from
different
bacteria.
When
the
lymphocyte
is
found,
their
it
specicity
,
lymphocytes
a
antigens.
protein
T
he
will
now
begin
rapid
cell
division
to
increase
the
number
of
cells
of
lymphocytes
creating
antibodies.
T
he
phagocyte
would
then
memory
engulf
produce
the
bacteria
and
digest
it.
T
he
lymphocytes
are
now
able
antibodies.
to
recognize
same
antigen
quickly
Antibiotics
or
which
are
on
the
cell
are
can
the
the
cell
and
so
some
they
of
have
but
usually
not
the
strains
have
be
the
a
part
by
of
eukaryotic
with
genes
multiple
treated
with
the
living
a
Antibiotics
membrane,
so
if
lymphocyte
destroy
microorganism’s
evolved
cannot
in
plasma
to
bacteria,
synthetically
.
membrane.
or
body
on
produced
produced
cells
wall
transcription
bacteria
chemicals
be
or
the
phagocytes
pathogen,
wall
antigens
enters
make
prokaryotic
of
similar
recognize
Some
a
confer
be
or
the
able
as
to
fungi
glycoprotein
that
occur
the
Some
resistance
lack
to
a
that
of
in
formation
replication
material.
Viruses
such
antigens
block
inhibit
genetic
resistance.
or
processes
others
that
would
organisms
protein
cells.
similar
bacteria.
They
block
a
or
strains
of
antibiotics,
metabolism,
antibiotics.
cell with gene conferring
bacterium divides
resistance to antibiotic
many times
bacteria grown
with antibiotic
population
of bacteria
bacteria divide. One
only resistant
cell undergoes a
cell sur vives
mutation
Fe 6.3.3.
Human
immunodeficiency
reducing
loss
of
the
the
acquired
68
Antibiotic resistance in bacteria
number
ability
to
immune
of
virus
active
produce
deficiency
(HIV)
acts
lymphocytes
antibodies,
syndrome
on
the
(or
T
leading
(AIDS).
immune
cells)
to
the
and
system,
causing
a
development
of
6.4
Eample 6.3.2.
gA s
E xC h A ngE
Florey and Chain’s tests on
the safety of penicillin would
How
does
HIV
affect
the
immune
system?
not be compliant with current
A.
Reduces
the
number
of
phagocytes
protocol on testing. After testing
penicillin on eight mice, Florey and
B.
Reduces
the
C.
Increases
number
of
active
lymphocytes
Chain decided to test it on humans.
the
amount
of
antibiotics
For tunately it proved to be
D.
Increases
the
amount
of
clotting
effective in most cases and
factors
penicillin star ted to be produced in
Solution
large quantities. Nowadays more
The
correct
answer
is
B.
HIV
is
a
virus
that
destroys
active
testing must take place before a
lymphocytes
or
T
helper
cells.
These
cells
are
involved
in
the
drug can be used on humans.
immune
reaction
against
pathogens;
therefore
the
person
infected
Drugs must first be tested on
with
HIV
will
have
a
poor
response
to
any
other
disease.
animals, then on healthy
volunteers, only then on
consenting infected patients.
Randomized controlled trials
which are double-blind, placebo-
controlled trials must be
performed to eliminate bias.
6 . 4
G A S
E X C H A N G E
Y ld e ale :
Y ld kw:
✔
ventilation
of
oxygen
in
alveoli
maintains
and
and
concentration
carbon
the
dioxide
blood
gradients
between
owing
in
the
✔
draw
the
✔
explain
respiratory
system.
air
lung
ventilation
including
the
muscles
adjacent
involved.
capillaries,
so
gas
exchange
occurs
passively
.
✔
✔
type
I
pneumocytes
cells
that
type
II
are
are
adapted
extremely
to
carry
out
thin
gas
pneumocytes
containing
secrete
surfactant
that
a
inside
the
alveoli
creates
to
and
describe
the
function
of
a
alveolus
surface
adhering
to
each
the
sides
explain
is
structure
other
by
gas
they
carried
bronchi
outline
to
the
lungs
in
the
trachea
causes
and
of
an
of
alveoli
and
the
exchange
are
suited
to
occurs
their
in
the
alveoli
function.
and
then
to
the
alveoli
in
contractions
cause
the
the
thorax
that
force
air
consequences
and
of
discuss
lung
of
these
the
social
diseases.
bronchioles.
pressure
in
and
emphysema
and
design
experiments
and
to
monitor
ventilation
in
changes
humans
inside
structure
capillary
.
reducing
✔
muscle
the
tension.
consequences
✔
show
pneumocytes.
how
how
cancer
air
to
adjacent
of
✔
✔
an
moist
prevent
and
the
diagram
solution
✔
surface
a
alveolus
exchange.
✔
✔
draw
alveolar
out
of
at
rest
and
after
mild
and
vigorous
the
exercise.
lungs
✔
to
different
and
ventilate
muscles
expiration
when
they
them.
are
required
because
for
muscles
inspiration
do
work
only
contract.
69
6
HUMAN
P H YS I O LO G Y
V
entilation
In Topic 1.4 you studied
membrane transpor t. Oxygen and
carbon dioxide are transpor ted
across membranes in the alveoli
to and from the blood system you
studied in Topic 6.2. Cancer is
excessive cell division, which you
studied in Topic 1.6.
called
is
the
breathing.
exchange
can
gradients
of
blood
sets
the
muscles.
action.
muscles
and
allowing
two
sets
air
of
contract
In
into
and
during
or
and
chest
the
and
belt
In
contrast,
in),
the
air
in
the
four
or
be
by
also
gas
of
and
different
muscles,
and
antagonistic
intercostal
thoracic
(breathing
are
can
is
that
alveoli
by
inhalation,
muscles
It
ensure
external
exhalation
during
lungs.
concentration
examples
apparatus
pressure
to
intercostal
are
V
entilation
simple
and
the
performed
expanding
abdominal
exhalation.
between
internal
lungs.
In
of
maintains
is
muscles
contract,
out
ventilated
It
(breathing
the
and
dioxide
capillaries.
inhalation
relax.
into
actively
carbon
external
flow
air
V
entilation
abdominal
observation
spirometer
are
diaphragm
muscles
only
simple
The
and
the
to
and
adjacent
muscles
intercostal
by
in
lungs
of
passively
.
oxygen
diaphragm
muscle
The
occur
flowing
of
movement
out),
the
relaxed.
cavity
,
They
monitored
data
these
internal
either
logging
with
meter.
Eample 6.4.1.
• Vela ae is the amount of
air breathed in a period of time.
The
diagram
shows
the
D
• tdal vlme is the amount of air
respiratory
system.
breathed in one breath.
a)
(i)
Label
(ii)
On
A to
the
D.
diagram
identify
a
bronchus
and
bronchioles.
A
b)
Outline
the
function
of
B.
C
c)
State
at
the
process
E
occurring
E.
B
Solution
a)
(i)
A:
C:
(ii)
ribs;
B:
lungs;
b)
The
function
diaphragm
in
c)
At
D:
Bronchus
between
the
E,
diaphragm;
between
bronchus
of
the
B
is
to
contracts,
thoracic
in
windpipe
cavity
.
alveoli,
or
trachea.
trachea
and
contract
the
rib
This
and
bronchioles;
bronchiole
alveoli.
to
allows
gaseous
allow
cage
gets
air
inspiration.
larger,
to
exchange
rush
When
reducing
into
the
the
the
pressure
lungs.
occurs.
s AMPLE stuDEnt Ans WEr
The lung volume was recorded as a student breathed into a spirometer.
The air was exhaled over a soda lime chamber that absorbs carbon
dioxide to avoid suffocation.
6
5
mc / emulov
3
4
3
2
1
0
5
10
15
time / s
70
20
25
a
6.4
a) Describe the ventilation pattern of this student.
This
T
he
answer
could
student’s
have
achieved
ventilation
2/2
the
tidal
volume
is
marks:
pattern
a
bit
is
normal
for
5
breaths,
each
▲ The
less,
and
suddenly
at
17
student
a
deep
inspiration
and
then
slowly
breaths
described
at
the
the
beginning
seconds
of
makes
E xC h A ngE
[2]
normal
time
gA s
the
experiment
breath
expires.
after
5
and
breaths
the
(or
deep
at
16/17
seconds).
) Use the data to estimate the ventilation rate during normal breathing.
Show your working.
This
answer
could
[2]
have
achieved
1/2
marks:
▲ One
ventilation
rate =
breaths
per
mark
for
the
correct
for
the
answer
minute
working.
15
seconds:
4
.5
60
seconds ×
breaths
breaths
=
60
×
4
.5
/15
=
18
breaths
▼ No
Answer
=
18
the
breaths
marks
units
breaths
are
per
incorrect;
it
as
should
be
minute.
c) Sketch on the diagram the results expected for the student after mild
exercise star ting from time 0 seconds.
This
answer
could
have
achieved
2/2
[2]
marks:
6
5
▲ The
student
mc
3
ventilation
rate
drew
the
higher
(this
is
the
4
/
breaths
emul ov
the
3
occurring
tidal
oxygen
volume
more
often)
higher,
to
and
increase
uptake.
2
1
0
5
10
Gaseous
adapted
exchange
to
capillaries
this
close
Fe 6.4.1.
occurs
function.
20
15
time
in
/
the
They
25
s
alveoli
are
of
moist,
the
are
lungs.
one
cell
The
alveoli
thick
and
are
have
by
.
Gaseous exchange in the alveoli
71
6
HUMAN
P H YS I O LO G Y
T
ype
Cancer is uncontrolled cell
I
pneumocytes,
where
division. For fur ther information on
gaseous
shaped
and
which
exchange
occur
are
numerous,
occurs.
amongst
the
Type
type
I
II
very
large
and
pneumocytes,
cells,
produce
flat,
which
are
are
cube
surfactant.
cell division see Topics 3.2, 3.3
Cancer
is
a
disease
in
which
some
of
the
cells
of
the
body
multiply
and 10.1.
out
of
control
caused
by
and
spread
smoking,
into
surrounding
carcinogens
such
as
tissue.
asbestos
Lung
and
cancer
air
can
be
pollution.
• type i pemcye are attened
The
consequence
is
the
formation
of
tumours
causing
pain,
breathing
epithelial cells allowing gaseous
difficulties
and
fatigue.
It
can
progress
to
metastasis
of
the
tumour
and
exchange.
death.
Smoking
causes
lung
cancer
because
cigarette
smoke
contains
• type ii pemcye are
carcinogens
that
damage
the
cells
that
line
the
lungs.
Emphysema
is
a
cuboidal epithelial cells producing
progressive
disease
of
the
lungs
caused
by
destruction
of
lung
tissue
surfactant.
involved
• L cace is the presence of
and
the
in
air
gaseous
sacs
exchange.
larger.
This
is
The
walls
caused
by
of
the
the
alveoli
presence
become
of
thicker
elastase,
an
tumours growing in the lung tissue.
enzyme
• Empyema is the destruction of
alveoli
alveolar walls by elastase leading to
alveoli,
impaired gaseous exchange.
6 . 5
produced
to
stretch.
therefore
impaired,
N E U R O N S
neurons
transmit
✔
myelination
of
shortness
the
of
digests
the
number
breath
elastin,
number
of
and
of
protein
that
phagocytes
elastase.
possibly
a
Gaseous
leading
in
allows
the
exchange
to
is
death.
S Y N A P S E S
Y ld e ale :
electrical
nerve
that
increases
increasing
Y ld kw:
✔
phagocytes
Smoking
causing
A N D
by
impulses.
bres
allows
for
saltatory
✔
draw
the
structure
✔
explain
electrical
✔
explain
an
✔
explain
the
✔
analyse
of
a
myelinated
impulses
across
neuron.
neurons.
conduction.
✔
neurons
across
pump
their
sodium
and
membranes
to
potassium
generate
a
action
potential.
ions
effect
of
myelination
on
conduction.
resting
oscilloscope
traces
showing
resting
potential.
potentials
✔
an
action
and
✔
potential
consists
repolarization
nerve
impulses
of
are
the
of
the
axons
of
✔
describe
action
potentials
propagation
of
✔
explain
chemical
the
currents
axon
to
the
propagation
that
impulses
is
the
result
synapses
between
are
cause
the
each
successive
threshold
junctions
neurons
nerve
impulses
explain
the
secretion
and
part
by
neurons
reabsorption
at
of
synapses.
of
potential.
between
receptor
and
of
✔
✔
of
neurons.
nerve
reach
synapses.
synapses.
acetylcholine
local
potentials.
propagated
✔
✔
action
neuron.
across
along
and
depolarization
neurons
or
explain
the
blocking
at
cholinergic
of
neonicotinoid
of
synaptic
synapses
in
transmission
insects
by
binding
and
effector
pesticides
to
acetylcholine
cells.
receptors.
✔
when
presynaptic
release
✔
a
nerve
a
neurotransmitter
impulse
potential
neurons
is
is
are
into
initiated
depolarized
the
only
if
they
synapse.
the
threshold
reached.
Neurons
are
nerve
cells
that
have
differentiated
to
perform
a
function.
In Topic 1.4 you studied the
They
transmit
electrical
impulses.
There
is
a
gap
between
neurons
different methods of membrane
called
a
called
neurotransmitters.
synapse.
The
message
must
cross
this
gap
using
chemicals
transpor t.
modulate
the
axon.
which
72
is
the
message.
Myelination
much
faster
Neurons
Some
of
neurons
nerve
than
transmit
fibres
have
the
a
allows
conduction
in
message;
myelin
for
synapses
sheath
saltatory
unmyelinated
covering
conduction,
nerve
fibres.
6.5
Eample 6.5.1.
nEurons
AnD
s Yn APsE s
• Memae peal is the
dierence in voltage between
The
diagram
shows
a
motor
neuron.
the outside and inside of the cell
C
B
D
membrane.
• re peal is the
membrane potential as long as
there is no per turbance; it is around
70 mV.
A
cell
• Ac peal is the
body
depolarization and repolarization
Which
label
shows
the
myelin
sheath?
of the neuron allowing impulse
transmission.
Solution
The
correct
answer
is
• Deplaza is the opening of
C
sodium ion channels, increasing
the membrane potential.
Nerve
impulses
neurons.
that
cause
potential.
placing
are
action
Propagation
each
potentials
nerve
successive
Membrane
electrodes
displayed
of
using
part
of
potentials
on
an
each
propagated
impulses
side
the
in
of
is
the
axon
neurons
the
to
along
result
reach
can
be
membrane.
of
the
axons
local
the
• replaza is the closing of
the low membrane potential.
by
potentials
sodium ion channels and opening
of potassium ion channels restoring
threshold
measured
The
of
currents
can
be
• hypeplaza is when
the membrane potential is at its
oscilloscope.
lowest. This is caused by the delay
The
resting
potential
is
the
potential
across
the
membrane
caused
by
in closing of the potassium ion
the
exchange
of
three
sodium
ions
moving
out
of
the
cell
and
two
channels.
potassium
use
of
and
one
ions
ATP
into
the
cell
molecule.
repolarization
of
the
by
An
the
sodium–potassium
action
potential
consists
pump,
of
with
the
depolarization
neuron.
Eample 6.5.2.
Ions
move
action
across
potential.
generated
in
a
the
The
plasma
membrane
oscilloscope
neuron
during
trace
three
of
a
neuron
shows
action
during
voltage
an
changes
potentials.
The question refers to a section
X
50
labelled X, so do not answer
Vm / laitnetop enarbmem
referring to what occurs before or
after the section labelled X, as no
0
marks will be given or marks can
be lost due to contradictions.
V
threshold
–50
–90
time
a)
b)
Describe
Explain
depolarization.
the
observed
movement
during
the
of
ions
interval
which
labelled
causes
X
on
the
the
voltage
changes
graph.
Solution
a)
Depolarization
allowing
is
sodium
concentration
caused
ions
to
by
the
diffuse
opening
into
the
of
the
sodium
neurone
down
channels,
a
gradient.
73
6
HUMAN
P H YS I O LO G Y
+
b)
At
the
peak
the
sodium
(Na
)
channels
close
and
the
potassium
+
(K
)
+45
channels
mV
.
occur.
There
The
The
is
a
open.
The
potassium
membrane
delay
in
ions
flow
potential
the
hyperpolarization,
membrane
closing
and
a
potential
out,
causing
reaches
of
approximately
repolarization
approximately
potassium
membrane
is
channels,
potential
of
70
to
mV
.
causing
around
78
mV
.
myelin sheath
axon of presynaptic
neuron
membrane of
presynaptic neuron
smooth endoplasmic
mitochondrion
reticulum
synaptic
vesicle
2+
Ca
containing
acetylcholine
calcium ion
2+
Ca
channel
membrane
of postsynaptic
acetylcholine
neuron
molecule
sodium ion channels
synaptic cleft
+
Na
acetylcholine
empty receptor site
molecule in
one of ve protein sub-units
receptor site
that make up the sodium ion
channel
Fe 6.5.1.
Synapses
and
are
are
effectors
Cholinergic synapse
the
junctions
such
depolarized
as
they
Neurotransmitters
gap
around
20
nm
are
neurotransmitters
as
acetylcholine
receptor,
ion
The
have
a
similar
acetylcholine
system
no
of
longer
synaptic
74
are
the
the
insects.
capable
in
of
is
resting
binding
between
the
to
the
causes
the
the
used
neurons
synapse.
synaptic
it
are
cleft
down
is
as
such
to
a
sodium
the
enzyme
recovered.
insecticides.
bind
in
postsynaptic
and
They
irreversibly
the
blocked,
paralysis
of
by
(a
examples
attaches
opening
synapses
are
the
neurotransmitter
They
receptors
into
neuron,
potential
nicotine.
neurons
presynaptic
dopamine
broken
chemicals
to
the
This
cross
and
by
then
cholinergic
Because
transmission.
to
Once
potential
synthetic
or
When
postsynaptic
action
composition
receptor
used
Acetylcholine
mammals.
and
neurons
glands.
neurotransmitter
acetylcholine
acetylcholinesterase
Neonicotinoids
in
the
a
or
chemicals
reaches
inducing
channels.
release
wide).
of
between
muscles
central
to
the
nervous
acetylcholine
membrane,
death
of
is
inhibiting
insects.
6.6
6 . 6
H O R M O N E S ,
horMonE s ,
h o M E o s tA s i s
H O M E O S TA S I S
AnD
rEProDuCtion
A N D
R E P R O D U C T I O N
Y ld kw:
✔
✔
hormones
when
distributed.
insulin
and
cells
blood
of
thyroxin
is
body
are
pancreas
need
to
be
✔
secreted
by
respectively
α
to
and
✔
is
outline
type
control
by
metabolic
the
thyroid
rate
and
gland
the
hormonal
control
of
blood
glucose
II
causes
and
treatment
of
type
I
and
diabetes.
help
secreted
by
cells
in
adipose
✔
explain the regulation of metabolic rate by thyroxin.
✔
explain
✔
outline
testing
obesity
and
to
the
effect
of
leptin
on
appetite.
control
temperature.
leptin
explain
concentration.
secreted
the
signals
levels.
glucagon
the
glucose
regulate
✔
used
widely
β
✔
are
Y ld e ale :
tissue
of
leptin
reasons
for
on
the
patients
failure
with
to
clinical
control
the
and
disease.
acts
on
the
hypothalamus
of
the
brain
to
inhibit
✔
appetite.
describe
how
therapies
✔
melatonin
control
✔
a
gene
is
secreted
circadian
on
gonads
to
the
Y
by
the
pineal
gland
chromosome
as
testes
causes
and
as
are
used
replacement
in
a
variety
of
therapies.
to
rhythms.
develop
hormones
such
embryonic
✔
explain
✔
outline
the
the
melatonin
secrete
action
of
melatonin.
causes
of
jet
to
alleviate
lag
and
use
of
it.
testosterone.
✔
testosterone
of
male
causes
genitalia
pre-natal
and
both
✔
explain
✔
draw
sperm
development
of
male
secondary
during
of
testosterone.
and
annotate
diagrams
reproductive
systems
of
to
the
male
show
and
the
names
sexual
of
characteristics
action
production
female
and
the
development
structures
and
their
functions
(front
and
side
puberty
.
views).
✔
estrogen
and
progesterone
cause
pre-natal
✔
development
of
female
reproductive
explain
the
roles
progesterone
and
female
secondary
sexual
the
menstrual
outline
cycle
is
controlled
by
positive
the
use
in
feedback
mechanisms
secretion
of
articial
estrogen
and
cycle.
IVF
and
pituitary
of
drugs
describe
sexual
chemicals
hormones,
to
suspend
followed
the
by
doses
of
hormones
to
the
induce
and
establish
a
pregnancy
.
hormones.
✔
are
of
involving
superovulation
ovarian
Hormones
LH,
menstrual
negative
use
and
FSH,
the
puberty
.
normal
✔
in
characteristics
✔
during
of
organs
secreted
by
glands.
They
travel
through
used
when
signals
William
Harvey’s
reproduction
in
investigation
of
deer.
Developments in scientific
blood,
affecting
target
organs.
Hormones
are
research follow improvements
need
to
be
widely
distributed.
Their
effect
is
usually
long
lasting.
For
in apparatus—William Harvey was
example,
insulin
and
glucagon
are
secreted
by
the α
and
β
cells
of
the
hampered in his observational
pancreas,
respectively
,
to
control
blood
glucose
concentration.
research into reproduction by lack of
equipment. William Harvey failed to
• il induces the uptake of glucose
• Lep is secreted by cells in
from blood to be stored in the liver as
adipose tissue and acts on the
glycogen when glucose levels are high.
hypothalamus of the brain to inhibit
solve the mystery of sexual
reproduction because effective
microscopes were not available
appetite.
when he was working. The
• glca induces the breakdown of
glycogen into glucose to be released
• Mela is secreted by the pineal
when glucose levels are low in blood.
gland to control circadian rhythms. It
microscope was invented 17 years
after his death. Fusion of gametes
promotes sleep when it is dark . It is
and subsequent embryo
• ty is secreted by the thyroid
used to alleviate the eects of jet lag.
gland to regulate the metabolic rate
development remained
and help control body temperature.
undiscovered till many years later.
75
6
HUMAN
P H YS I O LO G Y
s AMPLE stuDEnt Ans WEr
▲ The
for
student
scored
mentioning
that
one
mark
a) Glands are organs that secrete and release par ticular chemical
melatonin
substances. Melatonin is an impor tant hormone secreted in the pineal
regulates
the
circadian
rhythm
gland in the brain. Describe its role in mammals.
(or
biological
mark
the
is
saying
sleep–wake
marks
are
for
clock).
that
for
the
that
be
that
This
affects
The
by
the
detected
in
is
level
a
high
the
night
the
day;
the
and
this
directly
retina
of
a
of
and
low
level
means
to
achieved
2/2
marks:
controls
the
circadian
rhythms
in
mammals
as
it
is
the
pattern
of
sleep
by
inducing
sleep
when
it
is
night
time
there
(and
dark)
and
waking
the
mammal
up
during
the
daytime
during
during
secretion
proportional
have
light
that
secretion
could
Melatonin
obtained
production
amount
answer
other
sets
controlled
[2]
other
it
cycles.
could
fact
The
when
it
is
bright.
is
night-time
) Describe how the hormone leptin helps to prevent obesity.
[3]
duration.
This
T
he
▲ The
for
student
saying
appetite
that
and
scored
leptin
one
hormone
mark
it
reduces
food
not
▼ The
student
that
a
mark
leptin
adipose
is
could
for
and
need
to
with
higher
tissue,
leptin
the
the
of
have
acts
the
amount
greater
produced.
people
have
T
herefore
in
calories
the
on
in
losing
brain.
of
the
brain
that
we
are
full
and
do
any
more.
An
experiment
on
mice
showed
that
inhibitors
became
obese.
If
leptin
is
given
to
he/she
he/she
is
is
more
less
likely
likely
to
to
feel
eat
full
too
having
much,
eaten
retain
too
less.
many
and
In
them
become
obese.
Studies
conducted
on
humans
with
leptin
have
not
been
successful
so
far
,
although
slight
The
adipose
the
leptin
for
to
marks:
the
weight
amount
humans,
losses
have
been
noticed.
of
obese
resistance;
Diabetes
therefore
eat
leptin
human,
increased
hypothalamus
signals
2/3
mentioning
produced
tissue
leptin
achieved
intake.
a
scored
have
for
those
saying
could
mark
inhibited
another
answer
leptin
is
no
is
a
medical
condition
in
which
blood
glucose
levels
are
help
higher
weight.
urine.
than
Type
normal,
I
diabetes
destruction
of
This
the
causes
glucose
caused
in
by
even
β
the
It
an
cells
body
blood.
is
to
is
resistance
after
Glucose
autoimmune
of
the
lack
islets
insulin,
treated
to
fasting.
with
insulin.
It
of
disease
insulin
be
be
that
Langerhans
therefore
can
can
causes
of
raising
injections.
caused
by
detected
the
the
pancreas.
level
Type
in
the
II
of
diabetes
obesity
.
s AMPLE stuDEnt Ans WEr
▲ The
for
answer
scored
mentioning
produce
the
one
mark
inability
to
Outline the cause of type I diabetes in humans.
This
▼ Although
the
student
did
marks,
would
that
have
the
there
to
B
are
avoid
been
cells
confusion,
better
were
blood
to
B
specify
cells
is
▼ This
mark
answer
because
did
it
is
not
caused
function
type
when
it
I
diabetes
should
autoimmune
destruction
reducing
76
1/1
marks:
by
an
inability
to
produce
insulin.
B
cells
do
not
too.
It’s
score
answer
the
could
result
of
have
achieved
genetic
0/1
marks:
transfer
from
the
parents
to
the
implying
is
have
inherited,
said
condition
of
the
achieved
properly.
offspring.
that
have
as
This
a
could
it
pancreatic,
immune
answer
score
It
full
[1]
insulin.
beta/β
it
is
an
involving
cells,
production
of
thus
insulin.
childhood.
It
is
a
genetic
development
with
the
onset
during
is
6.6
A gene
on
gonads
causes
to
the
Y
chromosome
develop
pre-natal
production
during
and
as
testes
found
and
development
development
only
secrete
of
of
male
male
in
males
causes
testosterone.
genitalia
and
secondary
horMonE s ,
h o M E o s tA s i s
AnD
rEProDuCtion
embryonic
Testosterone
both
sexual
sperm
characteristics
puberty
.
Eample 6.6.1.
The
diagram
system.
shows
Which
a
section
structure
through
represents
the
the
male
• tee are the male reproductive
reproductive
prostate
organs that produce sperm and
gland?
testosterone.
A
• The cm holds the testes.
B
• The epddym is a duct where
sperm are stored until ejaculation.
• spem dc transfer the sperm
C
from the epididymis to the urethra
during ejaculation.
• semal vecle and the
pae lad secrete uid that
D
makes semen.
Solution
• The pe is the organ that
The
correct
answer
is
C.
A
shows
the
bladder
which
is
part
of
the
penetrates the vagina during sexual
urinary
system
and
where
urine
is
stored.
B
shows
the
seminal
intercourse.
vesicles
sperm
that
are
Estrogen
seminal
fluid
and
D
the
epididymis
where
stored.
and
reproductive
during
produce
progesterone
organs
and
cause
female
pre-natal
secondary
development
sexual
of
female
characteristics
puberty
.
Eample 6.6.2.
The
diagram
shows
the
female
reproductive
system.
• ovae are the organs where
eggs, estrogen and progesterone
are produced.
• ovdc are the canals that
receive the eggs at ovulation and
are the site of fer tilization.
• The e is the organ where
K
the embryo is implanted after
fer tilization.
L
• The ce v is the lower par t of the
uterus. Its muscles dilate to provide
a bir th canal.
• The vaa is the duct joining
the vulva with the uterus allowing
a)
Which
structures
do
K
and
L
identify?
sexual intercourse.
K
L
A
endometrium
uterine wall
b
placenta
endometrium
C
amnion
placenta
D
fetus
uterine wall
• The vlva protects the internal
par ts of the female reproductive
system.
Solution
The
correct
answer
is
B
77
6
HUMAN
P H YS I O LO G Y
The
menstrual
cycle
is
controlled
by
negative
and
positive
feedback
• Fsh stimulates the development
mechanisms
involving
ovarian
and
pituitary
hormones.
Follicle
of follicles and the secretion of
stimulating
hormone
secretion
estrogen
(FSH)
stimulates
the
development
of
follicles
and
estrogen by the follicle wall.
of
by
the
follicle
wall.
Estrogen
stimulates
the
repair
• Ee stimulates the repair
and
thickening
of
the
endometrium
after
menstruation.
High
levels
of
and thickening of the endometrium.
estrogen
inhibit
the
secretion
of
FSH
(negative
feedback)
and
stimulate
• Lh stimulates the development of
luteinizing
hormone
(LH)
secretion.
LH
stimulates
the
completion
of
follicles, leading to ovulation.
meiosis
• Peee promotes the
the
thickening and maintenance of the
and
wall
secretes
of
allows
the
ovulation.
follicle
estrogen
after
(positive
LH
also
ovulation
feedback)
promotes
into
and
the
the
development
corpus
luteum
progesterone.
of
which
Progesterone
endometrium.
promotes
also
the
inhibits
thickening
FSH
and
and
LH
maintenance
secretion
by
the
of
the
endometrium.
pituitary
gland
It
(negative
feedback).
In
vitro
used
ova.
fertilization
to
stimulate
Human
Fertilization
then
take
chorionic
is
in
lining
is
fertility
method
is
is
used
in
the
outside
woman.
maintained.
treatment
widely
used
in
of
cases
infertility
.
causing
(HCG)
the
body
are
potential
throughout
the
is
is
risks
world
to
in
to
and
to
that
health;
the
that
drugs
are
many
ova.
embryos
ensure
the
LH
of
mature
fertilized
used
aware
FSH
ovulation
used
and
Progesterone
Scientists
pose
of
follicles,
gonadotropin
performed
implanted
uterus
(IVF)
development
are
the
women
nevertheless
treating
infertile
this
couples.
Pacce plem f tpc 6
Plem 1
Plem 2
In an experiment on food digestion and absorption, a
a) Describe William Harvey’s discovery of the circulation
student placed amylase and starch inside a dialysis
of the blood with the hear t acting as the pump.
tube. The dialysis tube was then placed in a test tube
) Explain what is meant by the double circulation of
containing a solution of water and maltase. The tube
blood through the hear t.
was left for three hours. The amount of glucose was
Plem 3
measured outside the dialysis tube.
The bar graph shows the life expectancy of non14
78
10
76
sraey / ycnatcepxe efil
md gm / noitartnecnoc esoculg
3–
smokers and smokers.
12
8
6
4
2
0
0
20
40
60
80
100
120
140
160
180
74
72
70
68
66
64
200
62
time / minutes
60
non-smokers
smokers
a) State the reason a dialysis tube is used in this
experiment.
a) ()
Calculate the percentage difference in the life
expectancy of smokers and non-smokers.
) State the glucose concentration outside the dialysis
tube 1 hour after the start of the experiment.
()
Suggest whether this data suppor ts the
hypothesis that smoking adversely affects life
c) Explain the source of glucose:
expectancy.
()
outside the dialysis tube
) Explain gaseous exchange in the lungs.
() inside the dialysis tube.
c) Discuss the social consequences of lung cancer and
emphysema.
78
6.6
horMonE s ,
h o M E o s tA s i s
AnD
rEProDuCtion
Plem 4
The body mass of rats was recorded every five days
Botulin or Botox is a neurotoxic protein produced by
during 20 days and compared with that of control rats.
the bacterium Clostridium botulinum. Intramuscular
neurotransmitter acetylcholine at the neuromuscular
junction from presynaptic motor neurons causing
muscle paralysis. It is used in cosmetics to reduce
wrinkling of skin. In a study to see its side effects, ten
g / ssamoib ydob
administration of botulin inhibits the release of the
440
420
control rats
400
380
360
with botulin
340
320
0
5
10
15
20
25
brown rats (Rattus norvegicus) were injected with
time after injection / days
different doses of botulin. Their muscles were examined
under the microscope for atrophy and classified
according to severity as normal, mild and severe.
c) Compare and contrast the effect of botulin with
time on the body mass of botulin-treated rats and
untreated control rats.
Mcla apy ( =
10)
d) Evaluate all the data on the effect of botulin on
De f l /
1
 k
nmal
Mld
sevee
rats.
1
day
( apy)
Plem 5
0
10
0
0
1
3
7
0
3
0
10
0
9
0
2
8
Explain how an electrical impulse is propagated along a
a) ()
myelinated neuron.
State the number of rats that had atrophied
muscles with a dose of 1 ng per kilogram of mass
per day.
() Identify the lowest dose that caused all rats to
have some atrophy in their muscles.
) Suggest whether the results suppor t the hypothesis
that botulin causes muscle atrophy.
79
N U C L EOT I D E S
7
7 . 1
D N A
S T R U C T U R E
A N D
single
Y hd knw:
and
✔
the
structure
of
DNA is
ideally
suited
to
(AHL)
R E P L I C AT I O N
strand
binding
proteins,
DNA polymerases
I
and
DNA primase
III
in
replication.
its
✔
describe
the
function
of
non-coding
regions
of
function.
DNA such
✔
✔
nucleosomes
help
DNA structure
to
supercoil
suggested
a
the
DNA polymerases
only
✔
at
the
3′
end
DNA replication
can
of
is
a
start
mechanism
for
✔
adding
✔
on
introns,
telomeres
explain
the
and
discontinuous
on
the
the
DNA replication
is
carried
out
lagging
by
a
of
some
but
samp les
of
s top
DNA
for
tRNAs.
conta ini n g
rep lica ti on
ba se
in
th e
s equ en c i n g.
describe
Rosalind
Wilkins’
investigation
Franklin’s
of
and
Maurice
DNA structure
by
diffraction.
strand.
analyse
results
of
the
Hershey
and
Chase
complex
providing
evidence
that
DNA is
the
enzymes.
regions
have
expression,
for
n u cleotides
to
genetic
✔
of
genes
preparation
experiment
system
gene
leading
✔
✔
use
and
dideoxyribose
X-ray
strand
of
nucleotides
primer.
continuous
regulators
DNA.
DNA replication.
✔
as
of
other
DNA do
not
important
code
for
proteins
✔
material.
analyse
functions.
the
association
DNA within
a
visualization
between
nucleosome
protein
using
and
molecular
software.
Y hd be abe :
✔
✔
explain
DNA replication
describing
the
function
(only
of
in
explain
prokaryotes),
helicase,
in
DNA gyrase,
DNA consists
how
tandem
DNAproling
electrophoretic
of
a
double
strand
of
repeats
and
are
analyse
used
prole
gels.
nucleotides
in
the
form
of
a
In Topic 2.6 you have already
helix.
In
eukaryotes
it
is
associated
with
histone
proteins
forming
studied the basic structure of DNA
nucleosomes.
This
allows
the
DNA to
be
condensed.
A nucleosome
and RNA. Here you will see more
consists
of
a
core
of
four
pairs
of
histone
proteins
with
around
150
base
detail and study the replication
pairs
of
DNA coiled
around
the
proteins.
A short
section
of
naked
DNA
of DNA.
connects
one
molecule
nucleosome
binds
the
to
DNA to
the
the
next.
core
An
additional
histone
protein
particle.
Rosalind Franklin’s X-ray diffraction studies provided crucial evidence
that DNA is a double helix. Rosalind Franklin and Maurice Wilkins used
novel techniques with a high resolution X-ray camera to obtain very clear
images of diffraction patterns from DNA. They were able to deduce that the
DNA molecule was helical in shape. This helped Watson and Crick figure out
the structure of DNA.
Alfred
Hershey
provided
as
was
and
evidence
believed
at
Martha
that
the
Chase
DNA is
time.
In
devised
the
their
genetic
an
experiment
material
experiment,
and
they
that
not
proteins
cultured
35
viruses
that
contained
proteins
with
radioactive
(
S)
sulfur
and
they
32
separately
cultured
phosphorus.
viruses.
80
They
They
viruses
infected
separated
that
contained
bacteria
the
DNA with
separately
non-genetic
with
component
radioactive
the
by
two
(
types
P)
of
centrifugation
7. 1
and
measured
the
radioactivity
in
the
pellet
(where
the
DN A
structurE
AND
r E p l i c At i o N
infected
Baehage are viruses
bacteria
where)
and
the
supernatant
(where
the
virus
coats
were).
They
that create a channel across the
found
using
that
most
radioactivity
radiolabelled
was
found
in
the
infected
bacteria
when
bacterial cell membrane and wall
DNA.
to transfer the viral genome DNA to
the host cell cytoplasm, initiating
infection in the bacterium.
’phage coat
’phage DNA
labelled
labelled
35
with
32
S
with
P
’phage absorbed
onto . coli and
DNA injected
’phage coats
separated
from host
cells
% radioactivity
75
15
supernatant uid
containing ’phage coats
25
Fge 7
.1.1.
pellet (bacteria)
85
The Hershey and Chase experiment
Eame 7
.1.1.
Scientists
wanted
bacterium
and
used
recorded
to
Bacillus
to
in
infect
the
study
subtilis.
the
The
bacteria,
importance
DNA of
with
supernatant
and
(left)
a
of
without
and
calcium
in
bacteriophage
the
calcium
percentage
channelling
was
being
of
marked
present.
infected
of
bacteriophage
with
The
bacteria
radioactive
amount
of
calculated
DNA to
the
host
phosphorus
radioactivity
was
(right).
without
100
100
P evitcaoidar % / tellep ni AND
P evitca oid ar % / tn at anrep u s ni AN D
calcium
90
80
70
60
50
40
30
with calcium
20
10
0
90
80
70
60
50
40
30
20
10
0
0
15
30
60
45
75
90
with calcium
without calcium
time / seconds
a)
(i)
State
and
(ii)
the
percentage
without
Explain
the
radioactive
phosphorus
in
the
supernatant
at
30
seconds
for
infection
with
calcium.
results
obtained
in
(i)
81
7
N U C L E OT I D E S
b)
Suggest
for
c)
whether
the
(AHL)
results
obtained
in
both
graphs
support
the
hypothesis
that
calcium
is
necessary
infection.
Discuss
the
results
in
term
of
the
Hershey–Chase
theory
of
genetic
inheritance.
Solution
a)
(i)
12
(ii)
%
with
With
calcium
calcium
disappears
cannot
the
b)
The
c)
The
In
their
for
calcium.
phosphorus
supernatant.
channel
the
experiment,
that
pellet
Bacillus
the
supports
Hershey–Chase
was
radioactive
the
the
without
the
In
the
of
the
viral
infection
DNA to
enter
DNA enters
occurring
the
the
without
bacterium,
bacterium
calcium,
therefore
the
and
the
viral
therefore
bacteriophages
DNA remains
in
hypothesis,
as
there
is
no
or
little
infection
when
calcium
is
missing,
as
seen
in
graphs.
viruses
the
make
100%
supernatant.
data
both
the
from
and
experiments
they
contained
was
due
subtilis,
possible
bacterial
to
the
(with
cells
provided
cultured
DNA with
results
calcium).
and
was
and
were
When
found
that
radioactive
phosphorus
same
viruses
evidence
that
in
the
the
material
was
lagging strand
in
of
not
out
by
a
it
cell
with
due
was
was
in
system
the
In
pellet
in
the
of
and
sulfur
not
and
proteins.
other
radioactivity
the
the
in
experiment
only
when
on
infection
DNA did
not
enter
pellet.
duplication
mitosis
or
of
the
genetic
meiosis.
chromosomes.
In
eukaryotes
DNA replication
is
enzymes.
• DNA gyae (topoisomerase II)
• DNA ymeae iii adds
relieves the strain on the coil, ready
complementary nucleotides at the
for helicase to star t working.
3'
the
sulfur.
by
in
that
calcium),
the
division
chromatids
complex
to
found
for
material
radioactive
(without
little
needed
of
sister
genetic
observed
was
possible
very
DNA is
the
They
phosphorus;
advance
produces
carried
leading strand
for
the
proteins
supernatant
supernatant;
Replication
it
contained
DNA is
phosphorus.
obtained
infection
in
that
primer in the 5′–3′ direction.
5'
5'
3'
• Heae breaks hydrogen bonds
• DNA ymeae i removes the
between strands, allowing the helix
primer.
DNA
e
id
to uncoil.
• DNA gae seals the nicks.
lo
o
y
n
o
i
r
e
m
c
e
s
a
polymerase
• snge and bndng en
• DNA ymeae i and DNA
avoid re-binding of complementary
lo
f
o
p
A
A
N
D
D
N
p
ymeae iii proofread the new
DNA.
• DNA mae star ts adding RNA
primer at the 5′ end.
c
e
it
m
n
o
3'
base pairs.
e
s
r
id
a
e
5'
Eame 7
.1.2.
Explain
replication
in
eukaryotes.
[8]
Solution
The
enzyme
uncoiling,
or
5'
unwinds
or
topoisomerase
strains
DNA double
in
the
helix,
II
double
prepares
helix.
separating
or
DNA for
Helicase
unzipping
uncoils
by
breaking
hydrogen
bonds
between
the
two
the
strands
of
DNA replication
DNA.
of
DNA primase
RNA.
Next
nucleotides
in
a
5′
to
3′
replacing
sections
strand.
at
the
primer.
RNA with
of
adds
RNA primer
starts
synthesizes
DNA ligase
DNA,
replication
III
It
III
DNA polymerase
DNA.
replicated
Once
an
DNA polymerase
direction.
polymerase
82
the
the
3'
strands
Fge 7
.1.2.
DNA gyrase
relieving
is
proofread
or
Okazaki
completed,
for
mistakes.
which
the
I
is
a
replication
short
by
length
adding
complementary
removes
seals
the
the
nicks
fragments,
in
strand
primer
by
linking
the
DNA polymerase
lagging
I
and
DNA
7. 1
Non-coding
regions
are
regions
of
DNA that
do
not
code
for
DN A
structurE
AND
r E p l i c At i o N
proteins
• rega f gene een
but
have
other
important
functions
such
as
regulators
of
gene
are non-coding regions of DNA
expression,
introns,
telomeres
and
genes
for
tRNAs.
Regulators
of
gene
that increase or decrease gene
expression
can
be
areas
of
the
DNA such
as
the
promoter,
where
the
expression.
RNA polymerase
joins
to
start
transcription.
Many
promoters
require
• inn are sections of mRNA
activator
proteins
to
start
transcription
and
can
be
down-regulated
that are edited out (spliced) before
by
repressor
proteins.
Introns
are
sections
found
in
eukaryotic
DNA
translation.
that
are
transcribed
to
mRNA but
are
edited
out
before
translation.
• temee are the non-coding
Telomeres
are
the
extremes
of
chromosomes
and
protect
the
DNA from
DNA extremes of chromosomes.
damage.
There
are
170
to
570
genes
coding
for
tRNAs
in
eukaryotes.
• Gene f rNA are DNA
sections that are transcribed to RNA
Eame 7
.1.3.
molecules that act as tRNAs.
Which
I
are
examples
telomeres
A.
I
B.
I
of
II
non-coding
promoter
III
only
and
regions
C.
II
only
I
D.
II
DNA?
exons
and
I,
of
III
only
and
III
Solution
The
correct
answer
is
B,
as
exons
are
the
coding
regions.
Eame 7
.1.4.
Tandem
of
one
or
remain
can
repeats
more
inherited
us
in
DNA when
nucleotides
adjacent
show
occur
to
each
patterns
traits
of
an
is
repeated
other.
that
a
regions can cause diseases
and
Tandem
help
Tandem repeats in coding
pattern
such as Huntington’s disease. If
repeats
identify
they occur in non-coding regions
the
they are usually harmless,
individual.
although diseases such as the
In
a
paternity
test,
a
PCR
was
performed
fragile X syndrome are caused by
on
each
organism
tested
and
the
amplified
tandem repeats in non-coding
material
was
run
through
electrophoresis.
The
regions. When a PCR is performed,
results
are
shown
in
the
gel.
if there are tandem repeats,
a)
(i)
State
the
most
probable
father
of
fragments of different sizes will be
the
obtained. These are directly
child.
propor tional to the number of
(ii)
Explain
the
choice
in
(i)
repetitions; this means that if a
b)
Describe
the
process
of
electrophoresis.
tandem repeat appears six times,
the fragments produced in a PCR
Solution
will be double the length of one
a)
(i)
Father
1.
(ii)
Father
1
that is repeated three times.
as
the
child
mother
father
b)
In
1
nor
one
that
in
share
nucleotide
agarose
current
is
positive
The
gel.
smaller
as
is
the
2.
This
The
is
ladder
fragments
the
means
of
that
DNA)
in
a
negative
are
are
to
than
separated
known
size
is
from
the
the
placed
buffer
due
more
both
child
and
repeat.
obtained
placed
move
fragments
of
in
height
DNA fragments
DNA is
fragments
same
tandem
products
gel
the
compare
the
present
sequences
therefore
of
not
at
common
The
applied.
pole
band
father
a
electrophoresis,
(short
an
has
and
will
the
in
an
move
the
PCR
a
well
larger
placed
in
a
of
electric
towards
phosphate
according
reaction
the
groups.
fragments,
to
their
well
in
size.
A
order
to
sizes.
83
7
N U C L E OT I D E S
(AHL)
Sequencing
Sanger
is
used
determined
nucleotides
to
determine
the
containing
preparation
of
samples
sequence
the
DNA nucleotide
termination
dideoxyribose
for
base
to
order.
method,
stop
Frederick
using
DNA replication
in
sequencing.
Stages 1–2: DNA strand chopped up, mixed with primer, bases, DNA polymerase + terminator bases
A
T
C
G
T
A
G
C
A
T
G
C
C
T
A
G
T
A
C
primer
T
Stage 3:
Each time a terminator base is added a strand terminates until all possible chains produced
T
A
G
G
A
A
A
T
T
T
T
C
C
C
C
C
C
C
C
C
C
C
G
G
G
G
G
G
G
T
T
T
T
T
T
T
T
A
A
A
A
A
A
A
A
Stage 4:
Readout from capillary tubes: DNA fragments separated by electrophasis in capillary tubes
Fge 7
.1.3.
Sequencing
7 . 2
T R A N S C R I P T I O N
Y hd knw:
✔
✔
gene
expression
bind
to
the
specic
is
have
an
regulated
impact
of
on
by
sequences
a
cell
gene
and
proteins
in
in
transcription
DNA is
copied
of
that
✔
explain
gene
✔
explain
the
✔
transcription
occurs
✔
nucleosomes
help
expression
and
its
regulation.
an
organism
process
nucleosome
of
transcription
regulation
of
and
the
it.
expression.
information
onto
E X P R E S S I O N
DNA.
✔
✔
G E N E
Y hd be abe :
base
environment
A N D
stored
as
a
code
in
explain
and
post-transcriptional
how
they
affect
gene
changes
to
RNA
expression.
mRNA.
to
in
a
5′
to
regulate
3′
✔
explain
alternative
✔
describe
splicing.
direction.
transcription
in
the
non-coding
promoter
as
DNA with
a
an
example
of
function.
eukaryotes.
✔
✔
eukaryotic
cells
modify
mRNA after
splicing
of
different
84
mRNA increases
proteins
an
the
organism
number
can
changes
patterns.
transcription.
✔
analyse
of
produce.
in
the
DNA methylation
7. 2
Gene
expression
information
but
can
also
regulators.
cells,
only
insulin
gene
in
is
is
the
be
the
tRNA or
Although
some
expressed
modification
is
are
only
which
gene
RNAs
genome
of
in
the
α
that
gene
can
product
are
act
different
of
the
RNA processing
is
gene
the
can
and
be
made
For
This
E x p r E ss ioN
In Topic 2.7 you studied DNA
all
its
example,
is
GE N E
replication, transcription and
expression
in
AND
using
proteins,
same
tissues.
pancreas.
expression
is
usually
as
organism
in
cells
Gene
a
products
an
expressed
regulated.
initiation,
of
by
These
small
the
genes
expression
transcriptional
process
genes.
trANs criptioN
translation and Topic 7.1 looked at
replication in more detail.
because
modulated
by
post-translational
proteins.
Eame 7
.2.1.
Explain
the
control
of
gene
expression
in
eukaryotes.
Solution
The
mRNA conveys
ribosomes,
where
expression
transcribed
in
certain
changes
usually
Most
at
and
in
thereby
splicing.
by
expression.
the
The
growing
remains
gene
as
enhance
is
the
or
for
or
the
certain
times
which
Such
to
such
as
DNA,
can
be
mRNA
appear
to
control
DNA methylation
that
contain
chemical
are
RNA polymerase.
factors
acetylation
one
is
involves
expression
Some
the
may
being
determines
positive
or
X
negative
environment
of
a
cell
expression.
synthesis
of
are
between
the
Gene
of
modification
example
not
expression
transcription.
binding
protein
Introns
at
factors,
transcription
factors.
mRNA,
RNA polymerase
adds
the
Gene
differentiation
decrease)
transcription.
Hormones
bonds
5′
end
broken,
nucleus
or
binds
the
the
separated
first
of
the
free
The
leaves
via
a
to
the
of
the
the
promoter
nucleotides.
to
hydrogen
mRNA.
nuclear
gene
breaking
RNA nucleotide
temporary
liberating
step
DNA at
due
complementary
mRNA molecule.
the
of
epigenetic
gene
RNA are
in
(or
gene
only
the
mRNA through
therefore
that
Transcription
access
DNA strands
hydrogen
DNA and
or
the
off,
Cell
DNA to
production.
expressed
increase
silencing.
The
two
polymerase
the
can
inherited,
affect
Transcription
site.
are
from
specific
means
tissues.
expression.
limit
regulators.
also
genes
of
turned
This
post-transcriptional
chromosome
can
are
DNA methylation
are
polypeptide
time.
different
prevent
expression
patterns
information
production
genes
one
regulating
regulated
gene
of
gene
may
the
some
cells
Nucleosomes
gene
any
proteins,
proteins
guides
requires
transcription.
regulated
it
genetic
The
of
RNA
the
3′
bonds
end
of
between
mRNA either
pore.
area of effect of
RNA polymerase
direction of
U
movement of
A
messenger
G
RNA leaving
C
G
the nucleus
having been
A
nuclear
G
spliced
pore
A
nuclear
envelope
template
strand of
DNA
Fge 7
.2.1.
DNA transcription
85
7
N U C L E OT I D E S
(AHL)
Eame 7
.2.2.
Which
statement
applies
to
transcription
in
eukaryote
cells
but
It is now well known that
not
in
prokaryote
cells?
there are epigenetic factors
that can modify gene expression.
A.
Initiation
of
transcription
requires
a
promoter
sequence
of
DNA.
There is mounting evidence that
B.
Uracil
C.
It
replaces
thymine
in
RNA.
the environment can trigger
heritable changes in epigenetic
occurs
in
the
nucleus
and
is
followed
by
translation
in
the
cell
cytoplasm.
factors. The nature versus nur ture
debate concerning the relative
D.
RNA polymerase
transcribes
DNA to
produce
a
strand
of
RNA.
impor tance of an individual’s
Solution
innate qualities versus those
The
acquired through experience is still
correct
answer
eukaryotes,
under discussion.
The
promoter
is
the
the
into
joining
in
a
the
of
occurs
do
regulation
join
to
enhance
the
occur.
the
the
not
outside
of
DNA usually
not
repressor
can
prokaryotes
cannot
mRNA will
of
activator
NH
as
usually
sequence
RNA polymerase
replication
by
C,
essential
non-transcribed
If
is
translation
have
the
gene
found
promoter
Gene
of
In
upstream
on
the
other
the
nucleus.
expression.
expression
promoter.
binding
a
In
nucleus.
of
be
is
the
DNA,
can
It
a
gene.
the
inhibited
occasions,
an
RNA polymerase
to
NH
2
2
the
promoter,
increasing
gene
expression.
DNA
CH
3
Methylation
methyltransferase
HN
the
addition
of
a
methyl
group
(–CH
)
to
a
3
nucleotide,
are
O
is
HN
N
O
areas
a
DNA in
cytosine
or
close
found
to
the
in
a
CpG
promoters
island.
where
CpG
there
islands
is
a
N
cytosine
nucleotide
followed
by
a
guanine
nucleotide
in
a
linear
H
H
sequence
Fge 7
.2.2.
usually
of
the
DNA methylation
in
the
cytosines
this
affects
of
5′
to
3′
these
direction
islands
transcription
(5′-C-phosphate-G-3′).
are
not
methylated,
but
if
Normally
they
are,
inversely
.
Eame 7
.2.3.
The
of
diagram
shows
homologous
the
methylation
chromosomes
in
two
pattern
of
the
homozygote
DNA promoters
organisms.
Organism 1
promoter
exon
CpG
methylated CpG
gene expression
Organism 2
promoter
exon
no gene expression
If
the
result
A.
second
of
The
organism
CpG
gene
were
a
heterozygote,
what
would
be
the
methylation?
would
be
expressed
at
the
same
level
as
in
the
first
organism.
B.
There
C.
Only
would
half
the
be
no
gene
gene
expression,
would
be
as
in
expressed,
the
second
producing
protein.
D.
86
Only
the
methylated
strand
would
be
expressed.
a
organism.
shorter
7. 3
t r A N s l At i o N
Solution
The
correct
answer
unmethylated,
this
case
strand
is
chromosome
of
eukaryotes
as
splicing,
If
is
is
is
one
as
the
a
from
can
will
of
the
same
promoter
of
be
gene
the
3′
by
as
promoter
to
RNA.
therefore
Usually
replication,
In
the
only
therefore
one
the
change.
post-transcription
the
used
has
transcribed
transcribed.
for
not
introns
are
be
transcription,
template
mRNA suffers
removal
can
inhibiting
expression
sequences
chromosome
strand
methylated
used
the
If
polyadenylation
alternative
obtained
not
gene
In
Splicing
A.
that
methylation
that
amount
is
then
end
and
special
proteins
introns,
(alternative
modifications
capping
different
of
and
the
5′
such
end.
enzymes.
peptides
can
be
splicing).
star t codon
DNA
exon
intron
exon
intron
exon
exon
intron
exon
intron
exon
transcription
5'
immature RNA
3'
splicing
5
mature RNA
only exons
3
translation
Fge 7
.2.3.
polypeptide
NH
Transcription and
COOH
2
translation in protein synthesis
7 . 3
T R A N S L AT I O N
✔
the
tertiary
structure
is
the
further
folding
of
the
Y hd knw:
polypeptide
✔
information
transferred
from
DNA to
into
an
amino
acid
initiation
of
translation
✔
synthesis
cycle
✔
of
involves
assembly
of
the
quaternary
of
disassembly
free
bound
for
✔
of
of
the
can
nuclear
the
by
the
one
exists
polypeptide
a
repeated
in
proteins
with
chain.
Y hd be abe :
follows
✔
explain
translation.
✔
explain
tRNA-activation
phosphorylation
proteins
use
occur
for
use
✔
describe
✔
explain
in
proteins
primarily
acids
lysosomes.
immediately
prokaryotes
and
is
due
R
after
to
the
✔
absence
helices
hydrogen
of
primary
structure
and
beta
bonding.
the
are
by
enzymes
amino
acid
through
binding.
structure.
is
amino
acids
in
the
✔
the
describe
how
binding
sheets
of
stabilized
✔
the
and
non-polar
bonds
identify
describe
can
be
quaternary
of
two
group
or
to
polysomes
prokaryotes
formation
pleated
polar
to
formed
amino
between
groups.
the
structure.
reason
relevant
prosthetic
number
the
protein
and
cell.
synthesize
for
in
secondary
alpha
involves
membrane.
sequence
polypeptide
✔
than
process.
components
synthesize
or
transcription
✔
the
ribosomes
secretion
a
the
polypeptide
within
translation
of
out
translation.
ribosomes
primarily
✔
the
carry
structure
the
events.
termination
✔
that
between
groups.
more
components
interactions
sequence.
✔
✔
by
mRNA is
R
translated
stabilized
and
how
used
eukaryotic
form
in
a
may
peptides
or
conjugated
electron
involve
of
a
protein.
micrographs
of
eukaryotes.
molecular
to
structure
more
analyse
ribosomes
visualization
the
and
structure
a
software
of
tRNA molecule.
87
7
N U C L E OT I D E S
(AHL)
Information
amino
In Topic 2.7 you studied DNA
cycle
replication, transcription and
acid
of
transferred
sequence.
events.
components
translation. In Option B you can
by
study bioinformatics.
energy
.
to
that
the
a
carry
specific
To
begin
small
The
large
out
in
the
subunit
of
the
the
the
acid
to
of
a
involves
Firstly
the
determined
an
involves
tRNA,
binds
then
a
of
tRNA is
an
repeated
the
activated
enzyme
using
ATP
mRNA molecule
mRNA binding
methionine
ribosomes
an
into
assembly
A tRNA-activating
translation,
at
translated
polypeptide
process.
cytoplasm.
subunit
carrying
of
mRNA is
translation
process
ribosomal
tRNA molecule
of
amino
the
DNA to
Synthesis
Initiation
phosphorylation
attaches
from
site.
at
the
start
joins
the
small
An
for
binds
initiator
codon
(AUG).
subunit.
It
has
Answers should be written inside
three
sites,
the
A (aminoacyl)
site,
P
(peptidyl)
site
and
E
(exit)
site.
The
the answer box as continuations
initiator
tRNA is
in
the
P
site
of
the
ribosome.
The
next
codon
signals
below the box or to the side
another
tRNA to
bind
at
the
P
and
A site.
A peptide
bond
is
formed
between
may not be seen. If you need to
the
amino
acids
in
the
A sites.
The
ribosome
translocates
three
continue the answer on another
bases
along
the
mRNA (in
the
E
the
5′–3′
direction),
moving
the
tRNA in
sheet, then you should state this
the
P
site
to
site.
This
tRNA is
now
free
in
the
cytoplasm
to
be
clearly where the answer in the
activated
again.
The
tRNA with
the
appropriate
anticodon
will
bind
box ends. Continuation answers
to
the
next
codon
and
occupy
the
vacant
A site.
This
will
continue
till
should be fully labelled, for
a
stop
codon
(UAG,
UGA or
UAA)
is
reached.
The
disassembly
of
the
example, 2(a)(ii), not just (ii).
components
follows
termination
of
translation.
s AMplE stuDENt ANs WEr
Outline the roles of the different binding sites for tRNA on ribosomes
during translation.
This
answer
Ribosomes
2
▲ The
student
scores
the
tRNA
P
saying
and
and
E
that
the
binding
third
marks
ribosome
sites.
are
The
for
has
in
fourth
the
for
P
site.
saying
formed
The
that
the
between
the
A site
the
P
and
the
start
amino
is
bond
acid
polypeptide
been
E
Another
given
binding
for
site
mark
including
is
where
could
that
the
During
P
site
the
to
the
marks:
sites;
site.
A,
P
and
T
ranslation
E.
At
any
happens
time,
from
an
mRNA
containing
the
amino
corresponding
to
the
start
codon
AUG
arrives
of
the
ribosome.
Another
tRNA
with
the
amino
corresponding
to
its
anticodon
mRNA
along
attaches
at
the
A
site.
As
to
acid
at
acid
the
of
moves
the
ribosome,
the
tRNA
moves
from
the
at
site
to
the
E
site,
leaving
the
ribosome.
T
he
tRNA
from
the
A
have
the
site
moves
to
the
P
site
and
a
peptide
bond
forms
between
amino
tRNA
T
he
binding
sites
are
present
on
the
large
subunits
ribosome.
ribosome.
large
ribosomal
initiator
subunit
tRNA
initiator
tRNA
3
U
A
e
M
A
U
C
G
in
the
5
3’
P
site
e
M
t
E
3
5
start
mRNA
site
codon
binding
small
t
A
3
5
88
5′
only
is
acids.
exits
bind
binding
translation,
methionine,
P
site.
can
3
4/4
codon,
mark
peptide
the
the
have
achieved
that
the
to
have
A,
second
saying
met-tRNA binds
could
marks
3′.
for
[4]
ribosomal
subunit
of
the
7. 3
Ribosomes
proteins
are
that
synthesize
to
the
are
site
used
proteins
Translation
due
the
can
translation.
primarily
primarily
occur
absence
of
within
for
a
nuclear
ribosomes
the
secretion
immediately
of
Free
after
cell
or
synthesize
while
for
use
t r A N s l At i o N
bound
in
transcription
ribosomes
lysosomes.
in
prokaryotes
membrane.
Eame 7
.3.1.
The
diagram
shows
the
structure
of
a
The use of computers has
polysome.
enabled scientists to make
advances in bioinformatics
X
applications such as locating
genes within genomes and
identifying conserved sequences.
For example, scientists can
diagnose diseases by comparing
Y
DNA sequences. Von Willebrand
disease is the most common
hereditary blood-clotting disorder
in humans. It arises from a
deficiency in a protein required for
mRNA
platelet adhesion during clotting,
a)
Identify
X
and
Y
.
the von Willebrand factor. The gene
for this factor is found on the shor t
b)
Indicate
with
an
arrow
the
direction
of
the
mRNA
arm of chromosome 12 and has
movement
in
this
diagram.
52 exons. Patients whose DNA
c)
(i)
State
where
polysomes
can
be
found
in
eukaryotic
cells.
sequence for this clotting factor
is different to the norm could
(ii)
Suggest
a
reason
why
the
presence
of
polysomes
enhances
be liable to clotting problems
translation.
and suffer severe bleeding. A
Solution
simple genetic sequencing test
a)
X:
polypeptide
and
Y:
ribosome
and a BL AST comparison enable
b)
Arrow
shown
from
left
to
diagnosis of the disease before the
right.
symptoms occur.
c)
(i)
Free
in
the
cytoplasm
or
attached
to
rough
endoplasmic
reticulum.
(ii)
Many
ribosomes
to
synthesize
of
a
greater
the
can
simultaneously
same
amount
of
protein.
the
This
same
read
one
allows
protein
in
for
a
mRNA chain
the
formation
shorter
period
of
time.
89
7
N U C L E OT I D E S
(AHL)
Proteins
can
have
different
structures.
Hemoglobin
is
a
globular
protein
• The may e of proteins
that
has
a
quaternary
structure.
It
is
formed
by
four
polypeptides
that
or polypeptides is the sequence
have
alpha
helix
secondary
structures.
The
four
prosthetic
groups
in
and number of amino acids.
hemoglobin
are
the
same,
one
heme
group
joined
to
each
polypeptide.
• The enday e is the
The
heme
group
is
a
molecule
containing
iron,
which
oxidizes
allowing
formation of alpha helices and
the
transport
of
oxygen
in
red
blood
cells.
beta pleated sheets stabilized by
hydrogen bonding.
• The e ay e is the
fur ther folding of the polypeptide
into globular or brous forms,
stabilized by interactions between
R groups. The bonds maintaining
ter tiary structure are disulde
bridges, hydrophobic interactions,
electrostatic attractions and
hydrogen bonds.
• A qaenay e exists
in proteins with more than one
polypeptide chain. It can have
Fge 7
.3.1.
Quaternary structure of hemoglobin showing the four
other molecules such as a
polypeptides and four heme groups (red)
prosthetic group.
pae bem f t 7
pbem 1
a) ()
Explain the use of nucleotides containing dideoxyribose
Describe the histone acetylation patterns of the
twins.
to stop DNA replication in the preparation of samples for
()
Explain how the acetylation of histones affects
base sequencing.
gene expression.
pbem 2
b) ()
Suggest a reason for the differences in CpG
Acetylation and methylation are epigenetic changes that
methylation patterns between the twins.
can occur in peptides. The epigenetic differences were
recorded in twins at the ages of 4 years and 40 years.
Explain how the methylation of DNA can affect
gene expression.
70
% / noitalyhtem GpC
% / senotsih fo noitalyteca
90
()
60
50
40
30
20
10
0
5.0
4.0
pbem 3
3.0
Explain how a DNA sequence can eventually determine
2.0
the primary structure of a protein.
1.0
0.0
4-year-old
40-year-old
4-year-old
40-year-old
twins
twins
twins
twins
METABOLISM, CELL
8
RESPIRATION AND
PHOTOSYNTHESIS (AHL)
8 . 1
M E TA B O L I S M
Yu suld knw:
✔
metabolic
the
✔
✔
reactions
are
in
response
to
✔
explain
how
pathways
consist
enzyme-catalysed
enzymes
lower
chemical
reactions
enzyme
regulated
needs.
metabolic
of
✔
cell’s
Yu suld be able t:
the
inhibitors
of
chains
and
cycles
✔
explain
reactions.
activation
that
can
they
be
metabolic
product
Enzymes
energy
of
the
✔
describe
catalyse.
competitive
or
non-
✔
need
and
can
be
controlled
by
end-
✔
distinguish
globular
graphs
proteins
that
lower
the
activation
at
threonine
are
rates
of
used
and
processes.
inhibition
anti-malarial
plot
pathways
metabolic
databases
new
experimental
pathways
metabolic
in
converts
how
calculate
for
work
end-product
that
potential
inhibition.
are
the
pathway
competitive.
✔
the
enzymes
of
the
to
isoleucine.
to
search
for
drugs.
reaction
from
raw
results.
different
specied
types
of
substrate
inhibition
from
concentration.
energy
In Topic 2.5 you studied how
of
the
chemical
reactions
they
catalyse.
Metabolic
pathways
are
enzymes work . In Topic 2.7 and
enzyme-mediated
biochemical
reactions
that
lead
to
the
synthesis
Topic 7 you studied DNA replication,
or
breakdown
of
natural
substrates
into
products
within
a
cell
or
transcription and translation that
tissue.
The
glycolysis
reactions
in
respiration
and
the
Calvin
cycle
in
lead to gene expression.
photosynthesis
are
examples
of
metabolic
pathways.
Example 8.1.1.
reaction without
enzyme
Explain
how
activation
the
active
site
of
an
enzyme
helps
to
lower
ygrene
a)
energy
.
Compare
and
contrast
the
primary
and
secondary
without
enzyme
energy
an
with
overall
enzyme
energy
structure
catalysed by
of
energy
activation
reaction
b)
activation
enzyme.
released
enzyme
during
reaction
Solution
time
a)
The
active
site
is
formed
by
the
amino
acids
responsible
for
the
Fgure 8.1.1.
catalytic
activity
of
enzymes.
It
is
an
area
of
the
protein
Enzymes lower
where
activation energy
the
substrate
The
b)
enzyme
by
bringing
by
straining
Both
the
of
sequence
structure.
beta
It
the
and
specific
energy
held
The
Where
The
acids
by
in
in
a
the
secondary
no
each
for
join
in
catabolic
is
substrate.
the
an
help
structure
the
These
folding
bonds,
structure
can
it
is
is
to
occur
reaction
determine
the
are
joined
are
be
the
number
pattern
which
structure
reaction
anabolic
or
reaction.
structures
protein.
hydrogen
is
to
primary
structure
there
for
needed
closer
secondary
protein.
amino
is
is
molecules
secondary
bonds.
sheets.
and
substrates
the
the
of
The
peptidic
lowers
the
primary
structure
bonds.
enters
of
by
the
weaker
peptide
primary
than
alpha-helices
called
loops.
final
and
the
or
For questions that ask you to
cmpare and cntrast, remember
to include at least one difference
and one similarity.
91
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
Malaria
to
is
a
disease
around
2
million
parasites
to
drug
caused
deaths
by
per
treatment
the
parasite
year.
Plasmodium,
Increased
requires
the
that
resistance
development
of
of
leads
malaria
new
therapies.
Remember that questions are
Plasmodium
nucleic
acid
synthesis
metabolic
pathways
are
different
often based on more than one
from
those
of
their
human
hosts.
Thus,
targeting
these
metabolic
topic. This question is linked
pathways
provides
a
promising
route
for
novel
drug
development.
to Topic 7, so you can add
Bioinformatic
analysis
has
provided
an
improved
route
to
inhibitor
information from that topic too.
design
targeted
synthesis
to
specific
metabolism.
enzymes,
Scientists
can
including
use
those
of
experimental
nucleic
acid
information
as
Developments in
well
as
training
artificial
neural
networks
to
predict
the
outcome
of
bioinformatics, such as the
novel
drugs
on
different
targets.
interrogation of databases, have
Enzyme
inhibitors
can
be
competitive
or
non-competitive.
Competitive
facilitated research into metabolic
inhibitors
compete
with
the
substrate
for
the
active
site.
This
means
pathways. Databases such as
that
increasing
the
and
eventually
substrate
concentration
reduces
the
inhibition
Kegg have curated most metabolic
the
reaction
is
similar
to
that
without
the
inhibitor.
pathways, the enzymes involved
Conversely
,
non-competitive
inhibitors
bind
to
the
enzyme
in
a
and their inter-relationships.
different
place
concentration
from
will
the
not
active
affect
site,
the
so
increasing
inhibition.
the
Many
substrate
enzyme
inhibitors
• A rate f reactn is the speed at
have
been
used
been
used
to
in
medicine.
For
example,
ethanol
and
fomepizole
have
which a chemical reaction takes
act
as
competitive
inhibitors
for
antifreeze
poisoning.
place. It can be measured according
to the concentration (or amount) of
product formed in a unit of time or
S AMPLE STUDENT ANS WER
as the concentration (or amount) of
substrate that disappears in a unit
of time.
no inhibitor
The graph shows the
relationship between the
etar noitcaer
reaction rate and substrate
• An nbtr is a molecule that
binds to an enzyme, decreasing its
concentration in the presence
catalytic activity.
and absence of a competitive
with inhibitor
inhibitor.
• A cmpettve nbtr joins at the
active site. Its binding is aected by
a) Explain the eect of the
substrate concentration
the substrate concentration.
competitive inhibitor on the
• A nn-cmpettve nbtr
reaction rate.
[2]
joins away from the active site.
This
answer
could
have
achieved
0/2
marks:
Its binding is not aected by the
substrate concentration.
T
he
means
▼ The student confuses rate
of
reaction
and
competitive
should
have
competitive
The
active
mentioned
inhibitor
rate
site.
similar
as
The
shape
certain
point
in
the
time
the
rate
of
the
substrate
reaction.
T
his
concentration
the
presence
it
that
slows
competes
competitor
or
of
a
competitive
inhibitor
will
be
higher
than
answer
the
the
substrate
concentration
in
the
absence
of
the
competitive
the
inhibitor
reaction
a
increases
substrate
with
concentration.
that
inhibitor
for
has
composition
at
the
same
point
in
time.
the
a
to
the
b) On the graph, sketch the relationship between the reaction rate
substrate,
binding
to
the
enzyme
in
and substrate concentration in the presence of a non-competitive
a
reversible
way
. As
the
substrate
inhibitor.
concentration
substrate
than
rate
the
binds
as
the
the
The
active
and
with
no
the
reaction
maximum
This
site
starting
without
with
a
lower
at
an
rate
plateau,
same
inhibitor
rate
of
point
but
reaction
have
achieved
2/2
no
then
inhibitor
as
the
with
92
a
plateau
at
a
lower
non -compe titive
inhibitor
always
and
substrate
making
marks:
the
inhibitor.
the
could
noitcaer
one
answer
reaction
▲ The student drew the correct
line,
[2]
more
etar
same
to
competitor
increases.
reaches
increases,
point.
concentration
8. 2
Metabolic
reactions
Metabolic
pathways
reactions.
reactions
Because
that
Metabolic
This
they
the
This
regulated
consist
enzymes
catalyse,
pathways
means
reaction.
are
can
initial
avoids
be
of
response
chains
lower
the
and
the
reactions
is
excess
the
the
cycles
can
by
of
cell’s
occur
by
the
R E S P i R AT i o N
needs.
enzyme-catalysed
energy
at
a
end-product
inhibited
of
to
activation
controlled
reaction
an
in
C E LL
of
the
higher
chemical
rate.
inhibition.
product
of
the
final
product.
negative feedback
end
product
E1
E2
Fgure 8.1.2.
E3
E4
E5
Negative feedback by end-product inhibition
Example 8.1.2.
Explain
how
isoleucine
controls
its
As
own
the
reaction
isoleucine
production.
allosteric
takes
increases.
site
of
the
place,
the
Isoleucine
first
concentration
then
enzyme
in
binds
the
to
of
the
chain,
Solution
threonine
The
production
of
isoleucine
is
controlled
deaminase.
inhibition.
It
inhibits
the
converts
threonine
to
isoleucine.
series
of
five
enzyme-catalysed
therefore
Isoleucine
When
the
acts
as
a
level
of
isoleucine
non-competitive
is
low
again,
Through
the
a
is
pathway
inhibitor.
that
enzyme
by
inhibited.
end-product
This
reactions,
enzyme
will
start
breaking
down
threonine
the
again.
amino
acid
threonine
8 . 2
is
converted
C E L L
to
isoleucine.
R E S P I R AT I O N
✔
Yu suld knw:
in
the
Krebs
groups
✔
energy
is
converted
to
a
usable
form
in
is
cycle,
coupled
the
to
oxidation
the
of
reduction
acetyl
of
hydrogen
cell
carriers,
liberating
carbon
dioxide.
respiration.
✔
✔
cell
respiration
involves
the
oxidation
energy
to
reduction
of
electron
the
phosphorylation
of
cristae
of
by
oxidation
the
reactions
mitochondria
by
is
carried
reduced
carriers.
NAD
✔
released
and
molecules
makes
them
and
FAD.
less
✔
transfer
of
electrons
between
carriers
in
the
stable.
electron
✔
in
glycolysis,
in
the
glucose
is
converted
to
pyruvate
cristae
glycolysis
the
use
of
gives
a
small
net
gain
of
ATP
without
in
aerobic
an
cell
acetyl
coenzyme
respiration
and
oxidized,
compound
A to
form
pyruvate
and
acetyl
is
converted
attached
coenzyme
to
A
the
proton
membrane
of
the
pumping.
link
in
chemiosmosis
to
protons
generate
diffuse
through
ATP
ATP
.
oxygen
is
needed
maintain
the
electrons
from
pathway
,
to
bind
hydrogen
the
end
resulting
in
with
ion
of
the
the
free
gradient
the
electron
formation
protons
and
to
to
accept
transport
of
water.
in
✔
the
to
in
oxygen.
decarboxylated
into
coupled
synthase
✔
✔
is
chain
cytoplasm.
✔
✔
transport
the
structure
the
functions
of
a
mitochondrion
is
adapted
to
reaction.
it
performs.
93
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
✔
Yu suld be able t:
analyse
electron
tomography
images
of
active
mitochondria.
✔
explain
how
energy
is
made
available
through
✔
respiration.
analyse
diagrams
respiration
✔
outline
the
reactions
in
glycolysis,
the
and
the
Krebs
explain
the
electron
involvement
✔
explain
of
transport
NAD
and
chemiosmosis
synthase
in
the
the
pathways
where
of
aerobic
decarboxylation
oxidation
reactions
occur.
cycle.
✔
✔
of
deduce
link
and
reaction
to
chain
FAD
and
production
the
of
in
and
annotate
a
how
adapted
diagram
of
a
mitochondrion
to
show
the
it
is
to
its
function.
respiration.
function
of
ATP
ATP
.
Cell
respiration
involves
the
oxidation
and
reduction
of
electron
carriers.
In Topic 2.8 you studied cell
Oxidation
and
reduction
are
chemical
processes
that
always
occur
together
respiration and in Topic 1.2 the
in
what
is
called
redox
reactions.
Oxidation
is
when
electrons
are
lost
from
ultrastructure of cells, including
a
substance
and
reduction
is
when
electrons
are
gained.
Phosphorylation
mitochondria, was covered.
is
the
addition
phosphate
ion
transferred
transfer
of
of
is
are
phosphate
added
part
of
hydrogen
to
a
molecule,
for
to ADP to
form ATP
.
hydrogen
atom,
a
atoms
in
both
so
example,
In
this
redox
respiration
when
process,
reactions
and
an
inorganic
electrons
happen
by
photosynthesis.
Example 8.2.1.
Which
A.
of
the
following
Production
of
processes
includes
oxidation?
FADH
2
B.
Production
of
NADH
C.
Production
of
ADP
D.
Production
of
from
from
acetyl
NAD
ATP
CoA from
pyruvate
Solution
The
correct
answer
is
D.
In
decarboxylated
and
and
coenzyme
In
attached
glycolysis,
Glycolysis
anaerobic
lactate
an
a
lactic
the
net
reaction,
converted
A to
form
gain
to
of
pyruvate
the
same
name
in
be
used
produces
When
from
‘-ic
the
in
a
cytoplasm.
of
alcoholic
acid.
proton
acid’
compound
A.
use
carbon
lactic
is
acetyl
the
without
produces
changes
an
coenzyme
pyruvate
can
thing.
pyruvate
into
acetyl
ATP
fermentation
fermentation
effectively
acid
link
converted
the
Alcoholic
while
organic
is
small
respiration
are
oxidized,
glucose
gives
fermentation.
alcohol,
to
the
to
is
oxygen.
or
dioxide
Lactic
and
acid
given
In
lactic
up
and
from
‘-ate’.
Example 8.2.2.
What
is
the
total
net
number
of
ATP
molecules
produced
during
glycolysis?
A.
0
B.
1
C.
2
D.
4
Solution
The
net
answer
of
amount
is
glucose
produced
As
of
C,
there
four
to
are
is
what
two
ATP
glucose
when
two
leaving
a
left
at
the
molecules
phosphate
triose
of
is
6-phosphate
triose
molecules
produced,
94
as
net
and
is
phosphate
ATP
.
end
are
of
the
two
in
ATP
molecules,
two
process.
the
two
are
into
this
used
molecules
The
of
correct
phosphorylation
molecules
transformed
Therefore,
total
of
used
are
pyruvate.
produces
and
ATP
four
a
total
are
produced.
8. 2
After
glycolysis,
respiration
into
an
pyruvate
pyruvate
acetyl
coenzyme
called
the
the
citric
of
released
mitochondria
The
acid
reduction
Energy
reduced
A in
by
the
It
link
cycle),
mitochondrion.
and
then
the
In
oxidation
carriers,
and
to
the
of
is
In
oxidized,
aerobic
and
coenzyme
Krebs
acetyl
liberating
reactions
NAD
FAD
and
attached
reaction.
oxidation
reduced
NAD
is
hydrogen
by
the
decarboxylated
compound.
acetyl
to
is
enters
to
the
cell
form
(sometimes
groups
carbon
carried
R E S P i R AT i o N
converted
A to
cycle
C E LL
is
coupled
dioxide.
cristae
of
the
FAD.
(NADH
and
FADH
,
respectively)
2
produced
in
carried
the
to
carriers
is
in
linked
chain
pass
glycolysis,
cristae
the
to
electron
proton
include
the
This
the
link
to
a
reaction
transport
chain
The
complexes
more
liberates
and
mitochondria.
pumping.
protein
electron
reactions.
of
the
in
as
the
that
will
of
membrane
of
the
used
of
to
are
the
electron
acceptor
be
cycle
electrons
cytochromes.
electronegative
energy
Krebs
Transfer
molecules
such
the
cristae
transport
Each
donor
through
build
between
up
will
redox
a
proton
+
(H
the
to
)
gradient
final
bind
acceptor
with
resulting
Energy
in
the
the
can
glucose,
across
be
of
the
inner
electrons
free
protons
formation
released
amino
acids
in
or
of
mitochondrial
in
to
the
membrane.
transport
maintain
the
chain.
Oxygen
Oxygen
hydrogen
ion
is
is
needed
gradient,
water.
the
lipids
mitochondrion
and
stored
as
from
the
breakdown
of
ATP
.
glucose
2 × ATP
glycolysis
alcoholic fermentation
2 × ethanol + 2 × CO
2
2 × pyruvate
NADH
lipids
lactate fermentation
2 × lactate
cytosol
mitochondrion
2 × CO
2
β-oxidation
2 × acetyl CoA
respiration
n × acetyl CoA
2 × NADH
34–36 × ATP
citric
6 × NADH
electron transpor t chain
2 × ATP
The chemiosmotic theory
acid
2 × FADH
led to a paradigm shift in the
cycle
O
H
2
O
field of bioenergetics. Peter
2
Mitchell’s chemiosmotic theory
4 × CO
2
encountered years of opposition
Fgure 8.2.1.
Summary of the processes producing energy in a cell
before it was finally accepted.
Previously it was believed that the
proteins in the electron transpor t
Chemiosmosis
membrane,
generate
comes
are
from
the
they
enzyme
The
of
build
up.
enable
ions
protons
energy
to
of
membrane
When
the
across
diffuse
they
the
come
partially
the
the
the
mitochondria,
ATP
hydrogen
permeable
synthase
ion
transport
of
through
the
gradient
chain.
intermembrane
back
phosphorylation
In
through
electron
into
a
gradient.
maintain
reactions
the
of
electrochemical
when
redox
out
they
movement
their
occurs
ATP
.
pumped
where
the
down
chemiosmosis
to
is
Protons
space
ATP
synthase
chain flowed freely, but Mitchell
showed they were found in the
mitochondrial cristae and that the
difference in pH required to drive
phosphorylation of ATP is obtained
thanks to the small gap between
mitochondrial membranes.
ATP
.
95
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
Example 8.2.3.
• o xdatve psprylatn is the
phosphorylation of ADP to ATP using
What
occurs
during
chemiosmosis
in
cell
respiration?
the oxidation of molecules such as
reduced NAD (NADH) and reduced
A.
NADH
and
FADH
provide
energy
through
their
phosphorylation.
2
FAD (FADH
).
2
B.
Protons
move
to
the
intermembrane
space
along
a
concentration
• The electrn transpr t can is
gradient.
the process by which electrons are
passed from one carrier to another
C.
liberating energy that is used to
ATP
synthase
transports
protons
to
the
matrix
of
the
mitochondrion.
transfer protons across the inner
D.
A six
carbon
molecule
is
broken
down
into
a
four
carbon
membrane from the matrix to the
molecule.
intermembrane space.
• Cemsmss is the process
Solution
by which protons move across the
The
inner mitochondrial membrane,
out
down the concentration gradient,
correct
of
build
the
up.
answer
is
C.
membrane
When
they
In
into
chemiosmosis,
the
come
protons
intermembrane
back
to
the
are
space
matrix
pumped
where
through
the
they
ATP
releasing the energy needed for the
synthase
enzyme
they
enable
the
phosphorylation
of
ATP
.
Answer
enzyme ATP synthase to make ATP
.
A.
is
incorrect
because
NADH
and
FADH
(which
are
reduced)
2
• The Krebs cycle is a series of
become
chemical reactions to reduce NAD
B
is
oxidized
incorrect
to
supply
because
the
energy
,
not
movement
phosphorylated.
to
the
Answer
intermembrane
space
and FAD, by oxidation of two-carbon
requires
energy
provided
by
the
redox
reactions
in
the
electron
acetyl groups. It occurs in the
transport
chain.
Answer
D
relates
to
the
Krebs
cycle.
matrix of the mitochondrion.
The
structure
performs.
reaction
and
oxidation)
has
a
inner
The
area
for
pumping
ATP
has
inorganic
It
ribosomes
folds
in
synthesis
and
adapted
cycle.
is
with
membranes
electron
synthetase)
is
matrix
many
membrane
are
ATP
mitochondrion
Krebs
outer
cristae
a
mitochondrial
and
double
and
of
The
has
the
by
also
a
the
inner
a
site
and
small
where
transport
of
the
functions
enzymes
oxidation
DNA for
gradient
membrane
chains
particles
as
of
give
is
it
a
where
ATP
ATP
link
(β
synthesis.
between
can
It
the
develop.
large
the
synthase
generate
it
the
fats
gap
protons
that
this
occur.
that
of
for
protein
intermembrane
chemiosmosis,
stalked
to
contains
surface
proton
(also
from
called
ADP
and
phosphate.
Portion of a mitochondrion
Stereogram of the mitochondrion
matrix
outer membrane
mitochondrial
outer membrane
inner membrane
envelope
inter-membranal space
cristae
inner membrane
ATP synthase complex
ATP synthase complex
(stalked particle)
enlarged view of this region
but with only one ATP
hydrogen atoms
synthase complex shown
ATP synthase complex (stalked particle)
(from Krebs cycle)
in detail
head piece
2e
2H
(site of catalysis and
2e
ATP
protons
synthesis of ATP
, facing
+
the matrix side of the
H
O
2H
2
stalked
inner membrane)
ADP+Pi
par ticle
1
O
stalk
2
2
ATP
ADP
+
P
base piece
inner mitochondrial
membrane
(portion of ATP synthase
complex embedded in the
inter-membranal space
phospholipid bilayer of the
inner membrane)
+
Fgure 8.2.2.
96
outer mitochondrial
membrane
H
The mitochondrion is adapted to its function
8. 3
P h oTo S Y N T h E S i S
S AMPLE STUDENT ANS WER
▼ The
answer
mentions
Mitochondria are thought to have evolved from prokaryotic cells.
but
not
the
that
is
too
double
it
is
vague.
It
membrane,
needed
for
a
Describe two adaptations of the mitochondrion, each related to its
gradient
function.
of
but
answer
could
have
achieved
0/2
not
from
membranes,
energy
to
all
supply
processes
the
cell
it
is
happen
by
itself
.
that
could
have
achieved
production
ATP
particles
synthase
that
1/2
answer
this
helps
oxidative
have
two
membranes
phosphorylation
and
the
which
are
electron
needed
space
is
ATP
does
in
not
the
mention
oxidative
transport
vital
to
the
production
of
or
the
electron
chain.
for
chain.
▼ The
intermembrane
has
generate
marks:
transport
T
he
It
energy
in.
phosphorylation
Mitochondria
of
ADP
.
▼ The
answer
the
Produces
how
This
develop.
marks:
stalked
T
wo
to
[2]
mentions
This
protons
A
TP
the
in
answer
building
does
up
of
not
the
mention
proton
gradient.
these
Also
steps.
the
folded
cristae
increase
surface
area
for
the
processes
▲ The
of
cellular
respiration
and
A
TP
mark
increased
production.
is
scored
surface
area
for
for
ATP
synthesis.
8 . 3
P H O T O S Y N T H E S I S
✔
glycerate
3-phosphate
is
reduced
to
triose
Yu suld knw:
phosphate
✔
light
energy
is
converted
✔
light-dependent
into
chemical
take
place
in
space
of
the
light-independent
reactions
and
ATP
.
triose
phosphate
produce
is
used
to
regenerate
RuBP
carbohydrates.
thylakoids.
✔
✔
NADP
the
and
intermembrane
reduced
energy
.
✔
reactions
using
take
place
in
ribulose
bisphosphate
is
reformed
using
ATP
.
the
stroma.
Yu suld be able t:
✔
reduced
NADP
and
ATP
are
produced
in
the
✔
light-dependent
✔
absorption
of
light
by
photosystems
diagrams
adapted
to
photolysis
of
water
generates
electrons
for
the
describe
the
light-dependent
transfer
carriers
✔
excited
explain
of
in
excited
electrons
thylakoid
electrons
contribute
ATP
to
synthase
occurs
from
photosystem
generating
in
the
a
thylakoids
proton
excited
electrons
how
✔
describe
II
are
involved
to
reduce
in
the
in
the
light-
photosynthesis.
generating
in
the
excited
chloroplasts
electrons.
✔
explain
the
process
of
photolysis.
proton
the
in
transfer
of
thylakoid
excited
electrons
between
membranes.
gradient.
generates
explain
how
NADP
and
ATP
are
produced
in
ATP
light-dependent
reactions.
gradient.
from
photosystem
I
are
explain
Calvin’s
experiment
to
elucidate
the
used
of
RuBP
.
NADP
.
✔
light-independent
reactions
a
analyse
the
carboxylation
of
diagrams
of
the
pathways
carboxylase
of
catalyses
of
photosystems
carboxylation
✔
is
used
✔
✔
chloroplast
between
the
using
a
membranes.
✔
✔
steps
reactions
lights,
carriers
to
how
reactions.
absorb
✔
show
use
✔
in
to
function.
electrons.
dependent
✔
its
generates
✔
excited
annotate
reactions.
photosynthesis
to
deduce
where
ribulose
decarboxylation
and
oxidation
reactions
occur.
bisphosphate.
97
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
In
the
light-dependent
reactions
of
photosynthesis,
the
absorption
of
In Topic 2.9 you studied
light
by
photosystems
generates
excited
electrons.
Photolysis
of
water
photosynthesis. In Topic 4.2 you
generates
electrons
for
use
in
the
light-dependent
reactions.
Reduced
have seen how producers that
NADP
and
ATP
are
produced
in
the
light-dependent
reactions.
photosynthesize are the first step
of energy flow in an ecosystem.
In Topic 4.3 you studied carbon
cycling.
• Tylakds are membrane-bound
• Ptsystems are proteins that
compar tments inside chloroplasts,
absorb light and transfer electrons.
formed by a membrane surrounding a
• Ptlyss is the breaking down of
thylakoid space. They form stacks of
water molecules by photons present
disks called grana.
in light.
• A tylakd membrane is the site
• Reduced NADP (NADPH) is the
of light absorption and the electron
molecule produced in the last step
transpor t chain.
of the electron transpor t chain. It
• A tylakd space is the site of
is used as reducing power for the
photolysis and proton build-up.
biosynthetic reactions in the Calvin
cycle.
2e
CYCLIC
5
PHOTOPHOSPHORYLATION
electron
9
2e
accepter
8
+
2
NADP
2H
NADPH
+
+ H
2ADP
+
NON-CYCLIC
2P
PHOTOPHOSPHORYLATION
to the light-
electron
independent
carrier
reaction
2ATP
system
+
2H
3
(protons)
PHOTOSYSTEM
increasing
H
O
2
energy
P700
electrons
7
2e
4
6
Electrons
PHOTOSYSTEM
2e
P680
1
1
O
2
LIGHT
LIGHT
Fgure 8.3.1.
98
Light-dependent reactions in photosynthesis
2
level
8. 3
P h oTo S Y N T h E S i S
S AMPLE STUDENT ANS WER
The diagram represents a detail of the chloroplast showing light-
dependent reactions linked to chemiosmosis.
oxygen
thylakoid
membrane
1
O
2
2
+
H
2
2H
O
2e
+
ADP
P
2e
ATP synthase
thylakoid
space
ATP
electron
+
light
carrier
2e
2H
chlorophyll
to the
stroma
light-
independent
stage
+
+
NADP
NADPH + H
a) State the reaction occurring in the ATP synthase.
This
answer
could
have
Phosphorylation
of
achieved
ADP
to
1/1
[1]
marks:
A
TP
.
b) Using the diagram, suggest how the chloroplast is adapted to perform
the light-independent process of photosynthesis.
This
T
he
answer
could
chloroplasts
photosynthesis.
the
thylakoid
provide
a
generates
such
as
are
allows
the
in
the
these
to
that
electrons
in
7/8
the
area.
embedded
cytochrome
of
have
surface
Light-dependent
space
adapted
T
hey
excited
membrane
achieved
membrane
large
photosystems
have
inner
into
Absorption
are
take
to
process
light
to
occurs
membrane
by
one
place
in
next
the
lost
in
and
carriers
membranes.
be
electrons
of
called
grana
carried
thylakoid
T
he
of
thylakoid
which
reactions
the
membrane
stacks
proteins
thylakoids.
marks:
perform
the
[8]
to
T
he
the
other
.
intermembrane
from
photosystem
▲ This
II
get
replaced
by
the
oxidation
of
water
,
which
is
lysed
into
its
protons
and
membrane
the
oxygen.
causes
thylakoid
T
he
these
electron
protons
membrane
into
transfer
to
the
be
in
the
actively
thylakoid
ow
down
their
electrochemical
pumped
space.
potential
A
TP
synthase,
creating
A
TP
by
the
to
in
the
process
chloroplasts.
reduce
NADP
independent
of
chemiosmosis.
T
he
protons
Excited
electrons
forming
reactions
in
from
NADPH
the
to
stroma
be
of
diffuses
photosystem
used
the
the
perform
▼ Although
to
the
score
answer
many
was
good
marks,
it
has
gradient
phosphorylation
Oxygen
how
to
across
of
not
just
ADP
explains
adapted
function.
some
through
is
thylakoid
enough
then
answer
chloroplast
in
the
I
out
are
faults.
For
oxidized
protons
example,
and
and
it
is
not
water
lysed
is
into
oxygen.
of
used
light-
chloroplast.
99
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
The
light-indepen den t
rea ctions
occ ur
in
th e
st roma
of
the
• The Calvn cycle is the
chloroplast.
A
carbox y la se
cata ly ses
the
c a r boxyl a t i on
of
r i bul ose
light-independent stage of
bisphosphate
(5C
s u g a r).
In
a
carbox y l a t i on,
c a r bon
d i ox i de
is
photosynthesis consisting of
added
to
the
molecu le.
T he
6C
sug a r
f orme d
is
brok en
d own
carbon xation, reduction reactions,
into
and ribulose 1,5-bisphosphate
to
(RuBP) regeneration.
two
triose
3C
phospha te
phosphate
•
Carbn
fxatn is
the
molecu les .
is
used
carbon
dioxide
to
(3 C )
to
usin g
3- phosp h at e
redu c e d
regenera te
(3 C)
NAD P
ribu lose
a nd
is
re du c e d
ATP
.
bi sp hosph a t e
Tr i os e
an d
produ c e
addition
carbohydrates
of
Glycera te
usin g
AT P
.
orga nic
molecules.
• Rbulse bspspate
carbx ylase xdase (RubisCo)
Example 8.3.1.
is the enzyme that catalyses the
incorporation of carbon dioxide.
Scientists
• The strma is a uid par t of the
chloroplast and is the site of the
Calvin cycle.
wanted
to
of
photosynthesis
to
normal
carbon
and
very
dioxide
evaluate
of
the
maidenhair
cold
effect
tree
of
temperature
(Ginkgo
temperatures
at
biloba)
different
on
the
leaves,
rate
exposed
atmospheric
concentrations.
6
5
C and
autoradiography enabled
biochemical details of the Calvin
4
m lomorcim
experiment used to work out the
2–
carbon fixation. The lollipop
s
Calvin to elucidate the pathways of
1–
/ sisehtnysotohp fo etar
14
Sources of
normal carbon dioxide
elevated carbon dioxide
2
cycle shows considerable
creativity. At the star t of the
experiment, in the lollipop vessel,
–20
–10
0
10
20
30
14
radioactive carbon dioxide with
C
temperature / °C
was supplied to algae. Samples of
the algae were removed at time
a)
Calculate
the
difference
in
rate
of
photosynthesis
between
intervals and carbon compounds
normal
and
elevated
carbon
dioxide
levels
at
0°C.
in the algae containing radioactive
b)
14
(i)
Outline
the
effect
of
temperature
on
rate
of
photosynthesis
at
C were recorded.
different
CO
levels.
2
(ii)
Suggest
plant
c)
Suggest
by
cold
how
the
change
in
photosynthetic
rate
will
affect
growth.
which
reactions
of
photosynthesis
could
be
affected
temperatures.
Solution
−2
a)
b)
3.3−1.5
(i)
At
=
1.8
micromol
20°C,
with
m
either
−1
s
normal
or
elevated
CO
levels,
the
2
plants
have
the
same
rate
of
photosynthesis.
As
the
Remember to write the units.
temperature
much
rates
(ii)
The
faster
are
as
starch.
the
normal
rate
carbon
decreases,
dioxide
but
levels.
it
At
decreases
−10°C
both
0.
lower
grow,
decreases
in
the
rate
of
photosynthesis
photosynthesis
This
is
used
to
produces
produce
the
less
glucose
energy
and
the
that
for
is
plant
will
stored
as
structural
growth.
c)
Temperature
reactions
bisphosphate
affected.
enzyme.
100
affects
will
In
be
en z y mes;
a ffected.
carbox y la se
In
th eref ore
th e
Cal vi n
ox idas e,
chemios mosis ,
ATP
f or
th e
e n z yme - c a t al yse d
c yc l e ,
r i bul ose
e xamp le ,
s yn t h as e
is
the
c oul d
be
a ff e c t e d
8. 3
P h oTo S Y N T h E S i S
Example 8.3.2.
Outline
adaptations
of
the
chloroplast
to
its
function.
Solution
Adaptations
•
a
•
internal
of
double
the
chloroplast
membrane
are:
enclosing
and
protecting
the
chloroplast
Three answers from this list are
thylakoid
membranes
exposing
photosystems
to
expected in a three-mark question.
capture
•
light
presence
of
energy
large
amounts
of
light-absorbing
pigments
in
the
photosystems
•
internal
hold
•
spaces
small
for
•
thylakoids
the
surface
•
fluid
•
ribosomes
•
DNA for
to
increase
the
surface
area
to
thylakoid
membranes
to
allow
a
build-up
of
chemiosmosis
spaces
established
membranes
carriers
between
protons
•
thylakoid
electron
inside
with
thylakoids,
fewer
stacked
into
grana
area:volume
stroma
holding
for
protein
the
proton
gradient
is
to
save
space
while
increasing
ratio
enzymes
protein
so
protons
for
the
Calvin
cycle
synthesis
synthesis.
Practce prblems fr Tpc 8
Prblem 1
a) Calculate the percentage difference in α-glucosidase
The enzyme α-1,4-glucosidase catalyses the breakdown
activity after 120 minutes in bacteria grown with only
of maltose to two glucose molecules. Its activation by
maltose compared with bacteria grown with a mixture
maltose and inhibition by glucose was studied. The
of both maltose and glucose. Show your working.
activity of α-glucosidase was measured in bacteria which
b)
Analyse the effect of incubating the bacteria with
were grown in a medium containing 2% maltose only,
either maltose or glucose in terms of metabolic
2% glucose only or a mixture of 1.5% maltose and
pathways.
0.5% glucose.
c)
Acarbose, an α-glucosidase inhibitor, competitively
2% maltose
2% glucose
and reversibly inhibits α-glucosidase in the
1.5% maltose + 0.5% glucose
intestines. Discuss whether acarbose may be used to
450
prevent the development of diabetic symptoms.
nim lomorcim
1–
350
Prblem 2
300
Explain how the rate of reaction of an enzyme can be
g
1–
/ ytivitca esadisoculg- a
400
250
controlled inside a cell.
200
Prblem 3
150
a) Outline the light-dependent reactions of
100
50
photosynthesis.
0
0
30
60
90
time / minutes
120
150
b) Explain the effect of light intensity and temperature
on the rate of photosynthesis.
101
M E TA B O LI S M ,
8
AND
C E LL
R E S P IR AT I O N
P H OTO S Y N T H E S I S
(AHL)
Fomepizole
acts to inhibit the breakdown of methanol into active
toxic metabolites. It is a competitive inhibitor of the
enzyme alcohol dehydrogenase found in the liver. This
enzyme plays a key role in the metabolism of methanol.
Patients who had accidentally ingested antifreeze
50
10
40
8
30
6
methanol
20
4
10
2
formic acid
0
were treated with fomepizole and their blood plasma
0
0
levels of methanol and formic acid with time.
40
60
80
time / hours
methanol and formic acid levels were measured after
several hours. The line graph shows the changes in
20
L lomm / level amsalp dica cimrof
it down to formic acid, which is very toxic.
ld gm / level amsalp lonahtem
ingestion. Methanol is toxic because enzymes break
1–
Fomepizole is a drug used to treat antifreeze (methanol)
1–
Prblem 4
a) State the reason the breaking down of methanol is
considered a metabolic pathway.
b) Compare and contrast the trends in methanol and
formic acid metabolism with time.
c) Suggest whether the treatment with fomepizole is
efficient for antifreeze intoxication.
alcohol
formaldehyde
dehydrogenase
dehydrogenase
methanol in
formaldehyde
antifreeze
102
inhibition by
metabolic acidosis
fomepizole
and tissue damage
PLANT
9
9 . 1
T R A N S P O R T
B I O LO GY
I N
T H E
transpiration
gas
✔
✔
is
exchange
the
in
plants
transport
leaves
to
the
of
✔
of
explain
vessels
the
from
of
water
allow
roots
to
✔
the
explain
are
transpiration.
and
the
transport
✔
structure
using
lter
the
adhesive
generate
✔
active
property
tension
uptake
absorption
of
of
of
forces
water
in
mineral
water
by
leaf
ions
and
cell
in
✔
evaporation
the
how
the
causes
✔
measure
✔
design
✔
stems
polar
deserts
and
transport
pots
of
function
are
plants.
in
saline
soils
conservation.
water
transpiration
in
including
and
on
xylem
blotting
capillary
primary
based
experiments
effect
calculate
stomata
are
of
of
apparatus,
porous
of
xylem
using
or
tubing.
vessels
microscope
rates
and
the
partial
negative
charge
on
to
test
temperature
transpiration
molecules
P L A N T S
in
images.
potometers.
osmosis.
the
Water
in
water
structure
of
and
xylem
plants
for
models
sections
roots
the
simple
paper,
draw
walls.
structure
in
adapted
design
under
tension.
✔
how
correlated
from
losses
property
xylem
consequence
leaf.
water
replace
cohesive
the
inevitable
the
O F
Y  be abe t:
Y  k:
✔
X Y L E M
(AHL)
or
humidity
about
on
rates.
stomatal
from
hypotheses
apertures
light
and
micrographs
distribution
or
leaf
of
casts.
the
In Topic 2.2 you studied the
oxygen
atom
in
one
water
molecule
attracts
the
hydrogen
atom
in
proper ties of water and in Topics 2.9
another
water
molecule,
causing
cohesion.
Water
is
also
attracted
to
and 8.3 you studied the process of
hydrophilic
parts
of
the
cell
walls
of
xylem.
This
is
adhesion.
As
a
photosynthesis.
result
of
the
cohesion
through
the
xylem
Water
transported
is
in
between
what
in
the
is
the
molecules,
called
plant
the
water
can
transpiration
through
xylem
be
pulled
up
pull.
vessels.
It
enters
• Ce is the attraction
through
the
root
hair
cells
in
the
epidermis
of
the
roots
and
reaches
between water molecules due to
the
xylem
in
the
vascular
the
centre
bundles
of
till
the
it
root.
reaches
It
then
the
travels
leaves,
up
where
the
it
stem
exits
through
their hydrogen bonds.
by
• Ae is the attraction of water
transpiration
as
water
vapour
through
the
stomata.
to other substances, for example
the xylem walls.
Exae 9.1.1.
• Xye is the tissue that carries
A student
set
up
the
following
apparatus
leafy shoot
water from root to leaf.
• A ec is the concave
and
measured
the
reser voir of water
movement
of
syringe
surface tension.
cut end
air–water
surface of a liquid resulting from
the
meniscus
of shoot
along
the
scale
in
tap
the
rubber
capillary
calibrated
air–water
capillary tube
meniscus
tube.
tube
a)
State
this
the
name
of
apparatus.
3
scale calibrated in mm
103
9
PL A N T
BI O LO G Y
(AHL)
b)
Describe
c)
Explain
affect
d)
the
function
how
the
Suggest
changing
results
an
humidity
of
of
this
the
this
this
environmental
temperature
would
experiment.
experimental
in
apparatus.
way
to
modify
the
environmental
experiment.
Solution
a)
Potometer.
b)
This
in
a
apparatus
twig.
plants.
water
It
The
is
is
a
used
to
model
capillary
reservoir
is
measure
to
measure
tube
used
to
the
the
rate
rate
of
of
water
represents
the
top
capillary
up
the
uptake
transpiration
xylem
vessels.
tube
to
in
The
start
a
new
measurement.
c)
If
the
and
Use models as
This
representations of the real
temperature
water
means
move
world—mechanisms involved in
unit
water transpor t in the xylem can
the
be investigated using apparatus
at
of
a
that
faster
time
faster
is
vapour
the
the
eliminated
air–water
pace.
(for
the
increased,
is
The
example
stomata
by
meniscus
distance
therefore
in
the
the
moved
minutes).
movement,
of
transpiration
The
a
be
warmer
rate.
tube
measured
the
the
open
faster
capillary
can
increasing
leaves
at
will
in
a
temperature,
rate
of
water
3
uptake
and materials that show
(measured
increase
similarities in structure to plant
so
tissues. Experiments using the
the
more
rate
water
in
of
mm
per
minute).
photosynthesis.
will
be
taken
up
by
Warmer
This
the
temperatures
process
requires
water,
leaves.
potometer have allowed scientists
d)
A way
of
increasing
the
atmospheric
humidity
is
by
placing
to work out how different
the
apparatus
under
a
bell
jar
or
in
a
plastic
bag.
This
will
conditions affect transpiration
maintain
the
water
vapour
eliminated
by
transpiration
in
rates. The introduction of image
the
environment.
A method
of
decreasing
the
environmental
processing software and digital
humidity
is
using
a
fan.
The
fan
blows
away
the
transpired
microscopes has fur ther increased
water
vapour,
drying
the
environment.
By
placing
a
fan
at
the capacity to gather even more
different
distances
from
the
potometer,
one
can
model
different
data to ensure reliability.
environmental
Transpiration
is
humidities.
the
inevitable
During
photosynthesis
oxygen
is
in
the
produced.
leaf
exchange,
is
the
These
epidermis
water
in
gases
called
also
consequence
leaves,
lost
are
stomata.
by
of
carbon
gas
exchanged
As
the
exchange
dioxide
in
is
in
structures
stomata
the
required
open
for
leaf.
and
found
gaseous
transpiration.
Exae 9.1.2.
Design
area
in
an
experiment
the
lower
and
to
compare
upper
the
surfaces
number
of
a
of
stomata
per
unit
leaf.
Solution
A leaf
cast
leaf
painted
is
Once
a
dry
,
slide
(total
area
use
to
be
can
the
is
the
seen
field
same
This
two
off
is
or
very
with
under
is
three
the
the
done
by
by
lower
times
with
The
the
of
easy
in
a
of
off
of
ruler
cast
nail
is
on
The
the
It
is
deviation.
plants
surface
stage.
The
needs
stomata
The
such
on
field
important
of
epidermis
the
varnish.
per
experiment
number
of
placed
stomata
leaf.
The
the
succulent
surface
counted.
the
mean
standard
peeling
is
times.
the
leaf
number
placing
both
The
transparent
upper
surface
and
the
simply
particularly
layers
and
magnification
several
varnish.
microscope)
calculated
for
nail
easily
.
microscope
calculated,
be
blossfeldiana.
104
the
repeated
area
prepared
with
repeated
also
leaf.
be
peels
image
to
unit
it
under
of
same
can
per
experiment
from
the
as Kalanchoe
9 .1
The
light
of
leaf
a
micrograph
surface
of
1
shows
mm
TrAnspor T
in
ThE
X YlEm
of
pl A n Ts
part
by
There are different possible
1
mm.
The
number
of
stomata
answers to this question. This is a
2
in
this
case
would
be
4
per
mm
.
reasonable answer.
Both
must
the
upper
be
and
lower
investigated
stomatal
epidermis
to
compare
distribution.
In experimental design questions
it is useful to sketch how you
would perform the experiment.
In this case it is complicated, but
you could sketch what the results
Evaporation
of
water
in
the
mesophyll
of
the
leaf
creates
a
tension
or
would look like.
negative
pressure
transpiration
in
the
pull.
vascular
cellulose.
allows
water
Xylem
vessels
to
the
to
water
into
roots
leaf
causes
up
a
to
the
cell
not
Plants
walls
in
in
the
transport
ions
the
collapse
water
force
action
force
tension
do
pulling
capillary
suction
of
a
through
by
replace
transport
from
creates
under
and
walls.
xylem
Active
the
drawn
tension
lignified
the
which
the
pulled
resist
in
transpiration.
be
is
of
pressure
and
leaves
Water
bundle
Low
thickened
potential,
of
to
the
xylem
water
the
roots
they
from
the
pull.
have
the
roots
leaves
enables
to
Cohesion
transpiration
from
the
adhesion
xylem.
because
lost
into
out
due
called
by
osmosis
of
soil.
Exae 9.1.3.
The
a)
b)
diagram
Label
the
shows
a
vascular
bundle
in
the
stem
of
a
plant.
xylem.
Structure
Explain
below
and
function
adaptations
of
are
correlated
xylem
vessels
in
the
xylem
to
their
of
plants.
function.
Solution
a)
xylem
b)
Xylem
after
vessels
the
are
other.
lignified.
This
continuous
These
cells
tubes
have
strengthens
the
of
piled
thickened
walls,
so
cells
walls
that
arranged
that
they
can
one
become
withstand
You can sketch your answer in an
low
pressures
without
collapsing.
The
cells
in
xylem
vessels
die
annotated diagram, but remember
after
some
time,
leaving
only
the
walls
of
the
non-living
cells.
This
it must be very clear.
provides
that
are
the
no
cells
larger
water
space
for
movement
mitochondria
also
allow
a
disappear,
substances
to
to
water
in
these
supply
making
pass
in
transport,
a
vessels
energy
.
and
out
of
must
The
continuous
the
and
also
be
passive,
divisions
tube.
determines
as
there
between
Small
holes
or
pits
vessels.
105
9
PL A N T
BI O LO G Y
(AHL)
Plants
that
live
xerophytes.
of
water
or
Deep
night
loss.
of
area
rolled
reduce
of
Stems
are
and
high
no
also
the
reduce
the
usually
as
water
root
or
systems
or
the
hot
reflect
are
xerophytes
and
instead
of
Hairs
of
of
that
have
reduces
reduce
the
to
in
leaf
stomata
are
surface
for
at
water
amounts
adapted
have
the
pits
open
reduce
large
They
structures
chances
stomata
storing
Plants
the
called
surface
on
conditions,
are
leaves
The
halophytes.
some
leaf
presence
capable
called
increase
the
sunlight.
daytime
they
are
of
evaporation.
and
photosynthetic.
conditions
conservation
cuticle
thorns
stomata
leaf
during
for
waxy
leaves
Few
will
are
to
or
thick,
succulent
salt
adaptations
The
near
than
adapted
wide-ranging
leaves.
flow
rather
in
or
Small
leaves
air
water
live
deserts
absorption.
transpiration.
surface
in
to
similar
removing
salt.
SAMPLE STUDENT ANSWER
a) Outline the proper ties of water molecules that permit water to move
upwards in plants.
This
▼ Although
score
full
the
marks,
answer
it
answer
includes
the
xylem
water
vessel
up
in
wall
an
of
with
If
the
water
draw
or
water
water
vessel
sap,
up
through
cells,
though,
from
them
▲ This
if
by
can
are
only
polar:
molecules
is
already
the
water
this
allows
for
hydrogen
bonding
between
water
creating
cohesion
(when
one
molecule
of
water
pulls
adhesion
cell
water
It
cannot
can
walls
has
they
are
all
pulled).
Polarity
also
allows
adhesion
to
xylem
walls
which
enables
the
transpiration
pull
to
work
by
draw
of
leaf
been
dragging
water
up
in
a
continuous
mass,
hence
the
transport
lost
can
be
passive.
This
answer
evaporation.
answer
scored
adhesion
to
marks:
lled
one
move
of
water
could
have
achieved
1/2
marks:
mark
Water
for
2/2
air-lled
higher.
the
achieved
water
upwards,
vessel.
have
a
T
hey
draw
could
did
misconception—adhesion
to
[2]
evaporates
from
the
surface
of
the
leaf
,
creating
negative
allowing
upwards.
pressure.
xylem
Water
to
the
ows
leaves.
under
Water
tension
forms
from
cohesive
the
roots
forces
through
with
other
water
▼ This answer is incomplete.
It
does
not
mention
evaporates
by
that
molecules
water
transpiration.
It
which
not
the
mention
polarity
that
of
cohesion
the
water
is
and
adhesive
forces
between
water
and
xylem
vessels
does
due
enable
them
to
move
upwards.
to
allowing
b) In hot, dry conditions plants lose water rapidly due to transpiration.
for
a
hydrogen
continuous
bonding,
water
thus
forming
Explain how the structures and processes of the plant allow this water to
column.
be replaced.
This
•
▼ This answer does not score marks,
as
it
does
There
is
not
no
structure
answer
the
explanation
is
adapted
to
[8]
answer
Mass
could
ow
through
of
have
achieved
water
allows
0/8
marks:
plants
to
replace
water
being
lost
transpiration.
question.
of
how
the
•
T
he
xylem
takes
up
water
from
the
roots
and
takes
it
upwards
function.
to
•
the
rest
Cohesion
taken
•
of
allows
plant.
the
water
to
stick
to
each
other
while
being
up.
Adhesion
This
the
answer
allows
could
water
have
to
stick
achieved
4/8
to
the
walls
of
the
xylem.
marks:
▲ The marks are for less stomata
in
rolled
absorb
leaves
and
long
water. A third
roots
mark
Plants
to
was
in
hot,
functions
for
stomata
water
loss.
saying
water
106
that
loss
open
The
the
by
at
night
fourth
waxy
to
mark
cuticle
transpiration.
dry
places
develop
many
structures
and
given
to
preser ve
water
.
One
structure
is
the
presence
reduce
was
for
of
rolled
up
leaves
to
prevent
loss
of
water
by
way
of
the
reduces
stomata.
Also,
these
plant
leaves
typically
have
less
stomata
9.2
TrAnspor T
in
ThE
p h lo E m
of
pl A n Ts
▼ The answer did not mention
for
this
reason
as
well.
T
hese
plants
also
have
long
roots
in
that
the
order
to
reach
water
and
minerals
that
are
below
the
evaporation
pressure
same
T
hese
photosynthetic
processes
take
advantage
of
night
and
by
opening
their
stomata
for
transpiration
during
time
potential
the
day
it
is
cooler
and
there
is
no
sun
to
water
quickly.
T
hese
plants
also
have
a
water
loss
by
way
of
waxy
transpiration.
cuticle
that
to
water
or
store
water
for
long
or
T
hese
plants
periods
I N
of
time.
T H E
Y  k:
✔
plants
transport
sources
✔
✔
to
organic
compounds
by
of
along
pressure
transport
compounds
is
into
a
called
The
walls
pulling
molecules
does
to
not
of
thickened
to
travel
water
and
force
bonds
is
in
up
xylem
making
cohesive
xylem
and
walls.
by
collapse
walls
from
replace
P H LO E M
from
✔
explain
is
incompressibility
active
force
The
the
allowing
roots
osmosis)
losses
O F
because
by
water
(where
to
the
it
is
leaves
transpiration.
P L A N TS
Y  be abe t:
sinks.
hydrostatic
the
also
to
T R A N S P O RT
at
pressure
pull.
cell
hydrogen
absorbed
9 . 2
a
pulling
adhesive
xylem
compartmentalize
creates
through
stem
also
prevents
lowers
that
evaporate
due
the
water
the
the
because
of
leaves
transpiration
drawn
night
in
ground.
water
used
to
phloem
allows
transport
✔
explain
gradients.
load
sieve
to
at
the
how
✔
explain
✔
identify
structure
their
compounds
organic
tubes
how
related
plants
from
water
of
phloem
sieve
tubes
function.
load
and
sources
uptake
in
to
transport
organic
sinks.
plant
tissues.
the
xylem
and
phloem
in
microscope
source.
images
✔
high
concentrations
of
solutes
in
the
phloem
✔
source
raised
of
the
Plants
lead
to
water
hydrostatic
phloem
transport
to
uptake
pressure
ow
organic
by
causes
towards
stem
and
root.
at
✔
the
of
analyse
data
phloem
transport
from
experiments
measuring
osmosis.
the
contents
radioactively
rates
labelled
using
carbon
aphid
stylets
and
dioxide.
sinks.
compounds
from
sources
(photosynthetic
You studied membrane transpor t
tissues
and
storage
organs)
to
sinks
(roots
and
parts
of
the
plant
in Topic 1.4 and water transpor t in
requiring
energy).
A
concentration
gradient
of
sucrose
is
required
xylem in Topic 9.1.
for
transport
compounds
actively
in
the
into
phloem.
phloem
transported
out
Active
sieve
of
transport
tubes
the
at
the
companion
is
used
source.
cells
to
load
organic
Hydrogen
using
ATP
.
ions
The
are
build-
• ogac c are formed
up
of
hydrogen
ions
makes
them
flow
down
a
concentration
gradient
by carbon joined to atoms of
back
into
the
companion
cells
through
a
protein
that
co-transports
other elements, most commonly
sucrose
into
the
cells.
The
incompressibility
of
water
allows
transport
hydrogen, oxygen, or nitrogen.
along
hydrostatic
in
phloem
pressure
gradients.
High
concentrations
of
solutes
• Tacat is the transpor t
the
at
the
source
lead
to
water
uptake
by
osmosis.
Raised
of organic compounds in plant
hydrostatic
pressure
causes
the
contents
of
the
phloem
to
flow
phloem. It requires energy.
towards
sinks.
• A ce is a par t of the plant
where carbohydrates and amino
acids are loaded into the phloem.
• A k is where the carbohydrates
and amino acids are unloaded to be
used.
107
9
PL A N T
2
BI O LO G Y
(AHL)
Companion cell: sucrose loaded
from mesophyll cell moves into
Living cells of stem and root
7
sieve tube element along
actively remove solutes for
plasmodesmata. In some plants
metabolic purposes and water
these are modied companion
xylem
phloem sieve
vessel
tube element
potential of sieve tube elements
cells, transfer cells, with increased
rises.
companion cell
surface area, which actively
chloroplast
transpor t sucrose into the sieve
tube element. These cells contain
a very large number of mitochondria.
source
eg, photosynthesing
3
Sieve tube element: loading of sucrose
cell
lowers the water potential in these cells.
sucrose
1
Mesophyll cell in leaf synthesises organic
sucrose made
4
solutes (sucrose) and ‘loads’ them into
Water diuses by osmosis
in cytoplasm
phloem companion cell by active transpor t –
from the xylem vessels down a water
potential gradient into the phloem sieve
this process requires ATP to pump protons
water
tubes. This raises the hydrostatic pressure
from companion cell to mesophyll cell and
companion cell
then uses the proton gradient to ‘co-transpor t’
in the phloem.
sucrose
sucrose into the companion cell.
vacuole
5
Sieve plates: the volume of the sieve tubes
is limited by their cellulose cell walls so
that the continuously increasing uid
sink
volume is reduced as solution
eg, respiring cell
(sucrose + water) is forced through the
sieve plates.
6
Translocation of a solution of organic solutes
water
occurs from leaf phloem to stem phloem to
root phloem along a gradient of hydrostatic
nucleus
starch
pressure: mass ow
grain
8
Water diuses by osmosis (ie down the water potential
gradient) from the sieve tube elements. This water joins
the water absorbed by root hairs and diuses into the
xylem vessels.
fge 9.2.1.
Transpor t in plant cells
Exae 9.2.1.
In
a
dicotyledonous
transported
which
I
I
B.
II
the
the
leaves
products
to
the
rest
of
of
photosynthesis
the
plant
are
through
tissues?
Xylem
A.
from
plant,
vessels
II
Companion
only
cells
C.
only
II
D.
I,
III
and
II
III
and
Sieve
tube
cells
only
III
Solution
The
are
correct
companion
The
phloem
tissue
of
living
have
and
sieve
no
companion
elements
by
in
is
the
C,
as
although
sieve
tube
most
cells,
of
some
the
are
carbohydrates
transported
in
the
cells.
composed
with
108
answer
transported
is
composed
tube
nucleus.
cells.
of
elements
Sieve
These
cells
plasmodesmata.
sieve
which
tube
are
tubes.
are
Sieve
cells
elements
connected
tubes
that
are
to
are
are
no
closely
the
sieve
longer
associated
tube
9.2
Sieve
tube
elements
concentration
that
maintain
has
been
the
sucroseand
established
by
organic
active
TrAnspor T
molecule
transport.
Companion
in
ThE
p h lo E m
of
pl A n Ts
longitudinal
sieve plate with
view
pores
cellulose cell wall
cells
are
rich
in
mitochondria
and
have
a
large
surface
area
of
cell
of companion cell
membrane
in
the
allow
flow
by
to
to
support
phloem.
for
of
the
sap
The
the
cell
active
walls
establishment
in
perforated
the
phloem.
walls
called
of
of
transport
the
the
sieve
and
elements
necessary
sieve
plates,
sucrose
tube
pressure
Individual
sieve
of
tube
aid
are
to
quick
rigid
achieve
elements
allowing
transport
are
flow
to
nucleus of
the
companion cell
separated
from
cytoplasm of
companion cell
cell
cell.
cellulose cell wall of
sieve tube element
cytoplasm of sieve
tube element
SAMPLE STUDENT ANSWER
The image shows a severed aphid stylet embedded in plant tissue.
a) Identify the tissue labelled II.
[1]
transverse
This
answer
could
have
achieved
1/1
marks:
lumen
view
cellulose cell
wall
sieve pore
stylet
sieve plate
companion cell
with nucleus
sieve tube
element
I.
cytoplasm
fge 9.2.2.
Structure of the sieve
tubes
II.
b) Outline e piece of evidence that the tissue labelled I is phloem
tissue.
This
[1]
answer
could
have
achieved
1/1
marks:
▲
T
he
stylet
is
located
in
the
tissue
labelled
I
and
not
in
The
tissue
tissue
labelled
II.
Aphid
stylets
only
phloem
sap;
go
into
the
phloem
tissue
food.
been
to
obtain
the
content
of
therefore
tissue
I
answer
recognizes
the
the
is
phloem
than
are
as
the
place
Another
that
the
it
is
answer
closer
xylem.
smaller
aphids
than
the
could
to
Also
go
the
that
for
have
surface
its
xylem
cells
tissue
tissue.
and
it
has
adjacent
smaller
to
the
companion
larger
sieve
cells
tube
c) Explain how aphid stylets can be used to study the movement of
cells.
solutes in plant tissues.
This
answer
Aphids
could
take
up
have
[3]
achieved
solutes
from
3/3
marks:
the
phloem
of
plant
tissues
using
▲
The
marks,
the
stylet.
As
an
aphid
is
taking
up
phloem
sap,
its
stylet
can
answer
but
gained
could
mentioned
that
also
if
full
have
plants
are
grown
14
in
be
severed.
Once
this
occurs,
the
phloem
sap
(which
radioactive
continues
to
ow
out,
and
the
closer
the
stylet
was
the
the
sink,
the
greater
the
ow.
T
he
ow
of
phloem
sap
be
for
content
and
rate
of
transportation.
It
detected
Stylets
parts
analysed
can
tissue
for
that
transportation
transports
of
solutes
solutes
in
in
phloem,
)
which
is
2
carbohydrates,
labelled
later
in
carbon
the
of
the
which
inserted
plant
at
phloem
can
different
show
be
different
analysed
CO
can
sap.
be
into
radioactively
can
to
(
2
incorporated
solutes)
CO
contains
is
rates
of
movement.
a
plants.
109
9
PL A N T
9 . 3
BI O LO G Y
(AHL)
G R O W T H
I N
P L A N TS
Y  k:
✔
plants
adapt
their
Y  be abe t:
growth
to
environmental
✔
conditions.
✔
undifferentiated
allow
✔
mitosis
and
provide
and
cells
indeterminate
cell
cells
in
the
division
of
of
plants
plant
hormones
and
✔
identify
✔
design
for
in
the
shoot
extension
apex
of
the
using
stem
gels
undifferentiated
meristems
tissue
and
from
growth
control
growth
in
the
shoot
rapid
of
uses
of
bulking
virus-free
shoots
respond
to
the
environment
auxin
efux
gradients
✔
auxin
the
of
pumps
auxin
inuences
pattern
of
can
in
cell
gene
used
for
plant
micrographs.
the
experiments
shoot
apex,
of
plants
nutrient
agar
set
plant
up
micropropagation
up
of
of
new
of
varieties,
existing
orchids
such
and
as
production
varieties
other
rare
and
species.
by
tropisms.
✔
are
hormones.
strains
propagation
plant
in
micropropagation
explain
apex.
✔
cells
micropropagation.
leaves.
✔
✔
how
growth
growth.
needed
development
meristems
explain
concentration
✔
explain
✔
design
the
action
of
experiments
auxin
to
in
show
plants.
tropisms.
tissue.
growth
rates
by
changing
expression.
Plants
adapt
their
growth
to
environmental
conditions.
Plant
cells
In Topic 3.5 you studied genetic
have
the
ability
to
generate
a
whole
plant;
this
means
their
cells
are
modification and biotechnology in
totipotent.
Plants
grow
mainly
cells
indeterminate
at
meristems
where
undifferentiated
plants.
allow
final
cell
size
or
fixed
division
in
number
the
shoot
growth;
of
this
parts
apex
means
such
provide
as
that
there
branches.
cells
needed
is
no
Mitosis
for
fixed
and
extension
• Tttet ce are able to
develop into any dierentiated cell
of the organism.
of
the
stem
and
development
micropropagation,
production
of
which
virus-free
is
of
leaves.
used
strains
for
of
Meristems
rapid
existing
can
bulking
varieties
up
be
of
and
used
new
for
varieties,
propagation
• mete are totipotent
orchids
and
other
rare
species.
undierentiated dividing cells
located at the tips of a plant’s
SAMPLE STUDENT ANSWER
shoots and at the ends of its roots.
Achieving successful rooting of cuttings is difficult in some shrub
• A x are plant hormones with
species. An experiment was under taken to determine whether juvenile
impor tant roles in the coordination
shoots of trees root more successfully than mature shoots.
of many growth processes.
100
• mcagat is the
using small pieces of plant tissue. It
is done in sterile conditions in vitro
using agar gel containing nutrients
and hormones.
90
% / sseccus gnitoor
multiplication of a selected plant
80
70
Key:
60
mature shoots (M)
50
40
juvenile shoots (J)
30
20
10
0
M
J
C. japonica
M
J
P
. nigra
M
J
M
P
. alba
J
S. caprea
M
J
S. babilonica
a) Distinguish between the rooting success of the juvenile shoots and
Remember to use a comparative
that of the mature shoots.
[1]
word in a “distinguish” question.
This
answer
could
have
achieved
1/1
marks:
An answer saying that juvenile
shoots have a high rooting
Overall
the
juvenile
mature
shoots.
success would not have scored a
mark .
110
shoots
had
greater
rooting
success
than
the
of
9.3
▲ The
b) Suggest e reason for the dierences in rooting success in the
juvenile shoots and the mature shoots.
[1]
answer
understanding
tissues.
This
answer
Juvenile
could
shoots
have
achieved
contain
1/1
more
Gr o w T h
in
pl A n Ts
shows
of
A more
undifferentiated
correct
answer
marks:
undifferentiated
cells
in
would
have
been
shoots
have
a
that
faster
juvenile
response
to
the
auxin.
meristems,
allowing
for
more
successful
rooting.
c) Outline e variable that would need to be controlled in this
▼ Leaf
experiment.
This
[1]
answer
could
have
achieved
0/1
area,
of
cutting
in
all
groups.
moisture
amounts
of
hormones
mass
be
Light,
and
kept
length
similar
temperature,
marks:
nutrients,
Equal
size,
should
should
be
maintained
rooting
should
mixture
be
the
or
same
for
all
because
plants.
hormones
can
impact
the
development
and
growth
of
shoots.
▼ Auxin
has
an
effect
on
rate
) Auxin is a hormone that can be applied to improve the percentage
of
mitosis.
of
gene
It
changes
the
pattern
success of rooting in those study plants with poor rooting success.
Explain the eects of auxin on plant cells.
expression,
transcription
This
answer
could
have
achieved
1/3
Auxin
marks:
also
auxin
is
a
hormone
produced
by
the
meristem.
cell
wall,
proton
•
auxin
•
plant
promotes
fruit
and
seed
development
in
have
auxin
receptors
on
their
can
bind
and
either
inhibit
or
membrane
promote
to
which
walls,
cell
growth.
hormones
control
growth
in
the
shoot
apex.
3-acetic
acid
(IAA),
are
involved
in
plant
shoots
respond
to
the
environment
by
can
set
phototropism
up
influences
and
concentration
cell
zone of cell
growth
negative
gradients
Auxins,
growth
tropisms.
rates
by
gravitropism.
of
auxin
changing
in
the
pattern
the
of
cross-links
auxin
in
wall
cell
plasticity
.
concentrations
effects
in
different
have
parts
of
especially
Shoots
answer
for
the
scored
last
the
point,
that
auxin
have
efflux
tissue.
of
bres
cell
behaviours.
Auxin
plant
of
and
activity
breaks
cellulose
increases
positive
pH
plant.
mark
Plant
It
increasing
▲ The
indole
increasing
different
the
Plant
genes.
the
plants.
Varying
auxin
some
environment
pumps.
between
cells
of
changes
extracellular
•
promoting
[3]
cell
growth.
pumps
Auxin
gene
expression.
auxins synthesized in meristem cells
division
auxins diuse away from tip
auxins bind to receptor sites
vacuoles form and low
pH develops
zone of cell
elongation
low pH of cell walls keeps them
exible allowing cells to expand
as they absorb water. Vacuoles
get bigger and cell walls stretch
large central vacuole formed.
Auxins destroyed by enzymes.
Cell walls become rigid.
No futher cell elongation is
possible
zone of cell
dierentiation
fge 9.3.1.
The effect of auxin on apical shoot growth
111
9
PL A N T
BI O LO G Y
(AHL)
Improvements in analytical
Exae 9.3.1.
techniques allowing the
The
brown
planthopper
(Nilaparvata
lugens)
is
a
destructive
detection of trace amounts of
piercing-sucking
insect
pest
of
rice
(JA)
plays
(Oryza
sativa).
The
plant
substances has led to advances in
hormone
jasmonic
acid
an
important
role
in
plant–
the understanding of plant
pest
interactions.
JA induces
the
rice
gene
JAmyb
that
encodes
a
hormones and their effect on gene
transcription
factor
necessary
for
plant
defence.
Total
RNAs
were
expression. The demand for
isolated
from
rice
seedlings
following
infestation
with
different
increased crop productivity and
numbers
of
brown
planthoppers.
The
levels
of
expression
of
mRNA
the predicted challenges related to
of
JAmyb
in
rice
seedlings
were
determined
at
different
numbers
of
plant survival under adverse
infesting
insects
per
plant.
Ribosomic
RNA is
a
housekeeping
gene;
environmental conditions have
it
is
always
expressed,
therefore
it
is
used
as
a
control.
renewed the interest in research in
root biology. Research in the areas
of hormone signalling,
understanding metabolism
involved in hormone action and
the transpor t of plant hormones
can be used for investigating the
impact of abiotic stress factors on
molecular mechanisms.
a)
Describe
the
production
effect
of
b)
Suggest
one
c)
Suggest
whether
is
involved
infestation
of
reason
in
by
the
JAmyb
number
data
planthoppers
RNA is
supports
defence
affecting
of
on
the
rice.
ribosomic
the
the
in
of
gene
rice
used
the
as
a
control.
hypothesis
plants
expression
in
a
of
that
JA
planthopper
JAmyb.
Solution
a)
The
of
greater
JAmyb
constant
b)
c)
The
amount
till
of
a
be
good
correctly
of
JAmyb
in
infestation
the
effect
modified
rice
of
the
instead
the
JA on
data
the
one
a
numbers
to
of
to
this
the
add
of
the
sure
that
number
give
that
the
any
JAmyb.
different
brown
is
the
amount
maintained
the
RNA has
control).
conclude
really
it
gel).
supporting
not
greater
where
make
with
could
(thus
does
in
45
positive
expression
experiment
of
is
increases
therefore
to
precise
control
(it
planthoppers,
response
planthoppers,
approximately
cannot
RNA is
extracted
Nevertheless,
112
number
(values
Ribosomic
been
the
produced
of
it
is
infesting
expressed
hypothesis).
information
One
could
JA concentrations
planthoppers.
on
have
to
9.4
9 . 4
R E P R O D U CT I O N
I N
reproduction
by
✔
the
biotic
owering
in
✔
the
the
switch
✔
of
success
most
and
abiotic
to
is
✔
inuenced
in
gene
plant
is
dark
relationships
a
✔
expression
response
periods
reproduction
fertilization
owering
distinguish
plants
with
and
use
in
to
many
depends
seed
the
seed
design
day
and
pl A n Ts
P L A N TS
and
environments.
change
owering
light
in
a
plants
apex.
pollination,
✔
owering
involves
shoot
length
in
in
Y  be abe t:
Y  k:
✔
rEproduCTion
between
pollination,
fertilization
dispersal.
experimental
plants
to
ower
✔
draw
the
internal
✔
draw
half-views
✔
design
experiments
factors
affecting
methods
out
of
to
induce
short-
season.
structure
of
seeds.
plants.
of
animal-pollinated
owers.
on
to
test
hypotheses
about
dispersal.
germination.
mutualistic
pollinators
in
sexual
reproduction.
stigma
Flowering
plants
reproduce
style
anther
by
sexual
reproduction.
carpel
stamen
The
lament
flowers
are
the
ovary
reproductive
ovule
structures
apical
the
meristem
gametes.
ovules
Male
in
produced
are
that
found
or
in
the
shoot
contain
Female
gametes
the
by
gametes
the
pollen
or
ovary
.
are
found
anther.
petal
sepal
In Topic 1.6 you have seen cell
division.
fge 9.4.1.
Flowering
shoot
involves
apex.
In
a
many
change
plants,
in
the
gene
expression
switch
to
in
Half-view of an animal-pollinated flower
the
flowering
is
a
R
response
plants
(Pr)
to
that
or
the
affects
far-red
mainly
red
is
length
the
Pr
the
inactive
light
(not
activated
light
and
phytochromes.
(Pfr)
light
of
to
far
Pfr.
dark
periods
Phytochromes
photoreceptors.
red),
At
therefore
night,
Pfr
in
are
Sunlight
during
slowly
many
FR
red
contains
the
Pr
Pfr
inactive form
active form
day
,
returns
to
fge 9.4.2.
Pr
transcription
inhibits
this
form.
of
In
genes
long-day
for
plants
flowering,
Pfr
while
promotes
in
Phytochromes
the
short-day
plants
Pfr
• lg-ay at ower with shor t
transcription.
nights (summer).
Success
in
plant
reproduction
depends
on
pollination,
fertilization
and
• s t-ay at ower only if
seed
dispersal.
Most
flowering
plants
use
mutualistic
relationships
with
nights are long (autumn).
pollinators
for
sexual
reproduction.
• pytce are pigments that
absorb light and can detect the
length of night.
113
9
PL A N T
BI O LO G Y
(AHL)
As
Ex ternal structure
the
with
seed
germinates,
positive
the
gravitropism
radicle
emerges
(geotropism).
from
The
the
shoot
testa
(plumule)
seed coat
grows
from
the
cotyledon.
(testa)
scar where seed
Exae 9.4.1.
was attached to
the ovary
What
does
a
long-day
A.
Days
with
a
lot
of
B.
Long
dark
nights
C.
Days
D.
Long
plant
require
to
flower?
sunlight
Internal structure
embryo shoot
with
more
days
and
light
long
hours
than
dark
hours
nights
(plumule)
Solution
Although
embryo root
they
are
called
long-day
plants,
what
they
cotyledon–
(radicle)
really
require
are
short
nights
to
avoid
too
much
Pfr
one of two
changing
in the seed
back
to
Pr,
therefore
the
correct
answer
is C.
seed coat
fge 9.4.3.
Internal structure of a seed
Exae 9.4.2.
A series
of
experiments
(Xanthium
for
in
• pat is the transfer of
pollen from the anther to the
germination.
a
jar
and
pressure
of
the
was
pennsylvanicum)
was
at
Each
of
subjected
recorded
shoot
lot
below
with
determine
seeds
to
room
the
conducted
to
was
certain
put
the
on
for
seeds
of
conditions
wet
conditions
temperature
cotyledon
the
10
(hypocotyl),
of
cocklebur
necessary
absorbent
cotton
atmospheric
days.
The
followed
elongation
by
the
stigma.
geotropic
response,
was
used
as
a
criterion
of
germination.
• fe tzat is the union of the
Ja
Atec
o x yge
Teeate
Geate
Aveage egt
ee / 
ee /
age / °C
ee / %
 ycty
female and male gametes.
• see ea is the transpor t

/ 
of the seed away from the parent
A
99
20
19–22
75
15
B
90
19
21–22
80
23
11
plant.
C
72
15
20–28
45
D
72
15
20–22
30
6
E
28
6
21–24
0
0
a)
State
the
jar
with
the
best
conditions
for
germination
in
this
Paradigm shift—more than
experiment.
85% of the world’s 250,000
species of flowering plant depend
b)
on pollinators for reproduction. The
Describe
shoot
the
effect
of
oxygen
pressure
on
germination
and
elongation.
University of Göttingen, in
c)
Suggest
with
effect
temperature
a
reason
which
jars
could
be
used
to
see
the
Germany, found that 87 of 115 of
of
on
germination.
the leading global crop plants
depend to some degree upon
d)
animal pollination, including bees.
Evaluate
the
experimental
to
the
results
obtain
design
that
allowed
the
researcher
shown.
This knowledge has led to
Solution
protecting entire ecosystems
a)
Jar
B.
rather than individual species. The
European Commission (EC) and
the United States Environmental
Protection Agency (EPA) have
prohibited the use of cer tain
neonicotinoid pesticides when
bees are present.
114
b)
The
lower
the
pressure,
lower
the
pressure,
6
the
seeds
mm
did
the
not
the
lower
shorter
the
the
germinate.
germination
hypocotyl.
At
rate.
The
pressures
of
9.4
c)
All
temperatures
temperature.
as
the
rest
changes.
a
higher
of
In
d)
The
the
C
been
condition
atmospheric
oxygen
not
the
design
are
have
is
difficult
could
the
be
has
been
and
a
the
jars
of
flaws.
each
jar.
at
temperature
Temperature
wide
C
pl A n Ts
of
and
D,
reached
higher
greater.
There
should
environmental
time,
kept
a
effect
in
temperature
and
was
was
One
a
the
range
there
elongation
many
a
see
are
wider
changed
through
to
used
same—only
temperatures
changed.
varied
it
had
shoot
replications
pressure
pressure
constant,
higher
and
should
so
that
temperature
At
rate
many
ones
conditions
experimental
have
similar,
only
the
value.
germination
are
The
rEproduCTion
for
fixed
should
example,
and
have
then
been
the
the
kept
range.
pactce be  Tc 9
pbe 1
pbe 2
The drawing shows the rolled leaf of marram grass
In an experiment, the pressure inside the xylem and the
(Ammophila arenaria).
rate of water flow were measured at different times of
the day in common oak trees (Quercus robur). The graph
shows the results obtained during one day.
8
0.0
7
pressure
6
–1.0
rate of
potential
water flow
5
inside
in xylem /
xylem /
4
–2.0
3
mm
MPa
per
3
minute
2
–3.0
1
0
–4.0
Explain how the marram grass is adapted to live in a dry
00.00
12.00
00.00
environment.
time of day
a) State the rate of water flow in the xylem at noon
(12.00).
b) Calculate the change in pressure potential in the
xylem from midnight (00.00) to noon (12.00).
c) Explain the changes in water flow at different times of
the day.
) Suggest a reason for the change in water pressure in
the xylem.
115
9
PL A N T
BI O LO G Y
(AHL)
pbe 3
pbe 5
Compare and contrast the structure of xylem and
In a study, the percentage of insect visitors to flowers
phloem vessels.
and the crop yields were recorded across small and
large farms in different continents over 5 years. The
pbe 4
percentage of flower visitors was calculated as the
In three experiments, seedlings were kept in the dark
number of bees visiting 100 flowers in determined
for two days and then two shoots were cut and placed
quadrats.
on a gel for a few hours. One shoot was kept intact and
100
the other was split in half. The concentration of auxin
90
−1
in the gel was measured in nmol g
fresh weight in all
80
Experiment 1: Seedlings kept in the dark and the auxin
concentration measured.
intact
split
shoot
shoot
% / dleiy porc
three experiments.
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
8
ower visitors / %
a)
State the crop yield at 3% flower visitors.
−1
25.5
24.1
auxin concentration / nmol g
b)
Experiment 2: The measurement was repeated after the
() Describe the effect of flower visitors on crop
yield.
shoots were exposed to unilateral light (shown with an
() Suggest e reason for the results obtained
arrow).
in (i).
−1
26.2
23.4
auxin concentration / nmol g
Experiment 3: The gel itself was cut in half and the
concentrations on the left and right sides of the gel were
recorded after unilateral light exposure.
−1
auxin concentration / nmol g
31.0
12.5
23.0
24.7
a) Calculate the concentration difference between the
left and the right sides of the gel in the intact shoot
and in the split shoot in experiment 3.
b) Compare and contrast the results for intact and split
shoots on the concentration of auxin measured in
experiments 1 and 2.
c) Explain the results obtained in experiment 3.
) In reality, the intact shoot in experiment 3 will look
different to how it is shown here. Draw the resulting
shape of this shoot.
116
9
G E N ET I C S
10
1 0 . 1
EV O LU T I O N
meiosis
leads
to
chromosomes
alleles
✔
(AHL)
M E I O S I S
Yu huld knw:
✔
AND
in
independent
and
a
daughter
chromosomes
unique
assortment
composition
of
✔
sister
✔
independent
random
of
in
interphase
separate
assortment
orientation
chromosomes
cells.
replicate
chromatids
in
of
in
of
genes
pairs
meiosis
meiosis
of
is
II.
due
to
the
homologous
I.
before
Yu huld be able t:
meiosis.
✔
crossing
between
✔
crossing
alleles
✔
over
over
on
the
chiasmata
exchange
produces
new
chromosomes
can
of
result
in
an
gametes
chromatids.
the
haploid
of
describe
✔
explain
✔
draw
the
separate
of
in
haploid
the
processes
in
meiosis.
consequences
diagrams
crossing
cells.
non-sister
exchange
with
✔
DNA material
combinations
between
chromosomes
produces
of
homologous
formation
homologous
Meiosis
the
non-sister
chromatids
✔
is
✔
explain
✔
analyse
to
show
of
crossing
chiasmata
over.
formed
by
over.
the
outcome
of
meiosis.
alleles.
meiosis
cells.
micrographs
to
identify
cells
in
meiosis.
I.
Gametes
are
haploid
In Topic 1.6 you studied cell
so
that
the
chromosome
number
after
fertilization
is
diploid.
Meiosis
division and in Topic 3.3 you looked
occurs
in
two
divisions,
meiosis
I
and
meiosis
II.
Chromosomes
at meiosis. In Topic 11.4 you will
replicate
in
interphase
before
meiosis.
In
meiosis
I
the
number
of
study sexual reproduction.
chromosomes
to
each
pole
chromatids
The
total
is
halved
and
of
the
each
outcome
chromosomes
of
as
cells
the
homologous
divide
into
chromosome
is
the
four
are
different
parent
two.
chromosomes
In
meiosis
separated
cells
with
into
half
II
the
two
the
migrate
sister
new
cells.
number
of
cell.
Example 10.1.1.
In
which
stage
of
meiosis
is
the
number
of
chromosomes
halved?
A.
Prophase
I
B. Anaphase
I
C.
Metaphase
II
D.
T
elophase
II
Solution
The
correct
migrates
number
to
of
answer
the
is
B
as
opposite
one
pole,
chromosomes
in
from
each
making
telophase
pair
two
of
cells
chromosomes
with
half
the
I.
117
10
GE N E T I CS
AND
E VOLUTION
(AHL)
Meiosis I
Interphase
Immediately before meiosis DNA
nuclear
envelope
replicates so that the cell now contains
four rather than the original two copies
Meiosis II
spindle bres
of each chromatid
Prophase II
centrioles moving
re-forming at right
Where the nuclear envelope has
to opposite ends
Prophase I
angles to previous
re-formed, it breaks down again.
of the cell
he chromosomes shor ten and fatten and
spindle axis
come together in their homologous pairs
The nucleolus disappears, the
point of
chromosomes shor ten and
crossing over
to form a bivalent he chromatids wrap
thicken and the spindle re-forms.
around one another and attach at points
centrioles
chromosomes
called chiasmata he chromosomes may
replicate and
seen to comprise
two chromatids
brea at these points and swap similar
sections of chromatids with one another
move to poles
Nuclear envelope
chromosomes
disintegrating
in a process called crossing over inally
Metaphase II
lying on the
the nucleolus disappears and the nuclear
spindle
The chromosomes arrange
equator of
envelope disintegrates
bres
themselves on the equator
the cell
Metaphase I
of each cell.
equator
entromeres attach to the spindle and the
bivalents arrange themselves randomly on
centriole
the equator of the cell with each of a pair of
homologous chromosomes facing opposite
piece of sister
poles
chromatid
chromatid
Anaphase I
moving towards
Anaphase II
exchanged
the pole
during
ne of each pair of homologous chromosomes
The centromeres divide and the
crossover
in prophase 1
is pulled by spindle bres to opposite poles
chromatids are pulled to opposite
poles by the spindle bres.
one of the
Telophase I
homologous
icrotubules pull two sides of the cell surface
chromosomes
membrane together so that the cell becomes
narrower towards its
par ts of the
being pulled
centre until the opposite
Telophase II
to a pole
The tetrad of four cells is formed.
membrane fuse to give two
ach cell has the haploid number
nuclear envelope
separate cells In most animal cells a nuclear
re-forming
of chromosomes. rossing over
envelope re-forms around the chromosomes
during prophase  has produced
at each pole but in most plant cells there is
genetic variety which, in this
cell divided by
no telophase I and the cell goes directly into
constriction
example, has given four cells
metaphase II
Fgure 10.1.1.
of dierent genetic composition.
Stages in meiosis
• Hmlgu chrmme are
non-sister chromatids of homologous
one set of maternal and one set of
pairs.
paternal chromosomes that have the
• The chama is the point where
same genes in the same loci. They
genetic material is exchanged in
pair up during meiosis.
crossing over.
• Crng ver is the process in
which DNA is exchanged between
Meiosis
a gene
same gene, but can be a
dierent allele
leads
to
chromosomes
in
AND fo edam
emosomorhc a
I.
daughter
It
is
sister
the
cells.
to
cells.
the
of
chromosome
from father
from mother
Fgure 10.1.2.
118
A homologous pair of chromosomes
assortment
composition
over
occurs
DNA material
chromatids,
on
the
orientation
meiosis
I.
of
in
prophase
between
producing
pairs
of
non-
new
assortment
of
of
alleles
chromosomes
independent
random
in
of
alleles
The
chromosomes
chromosome
unique
Crossing
homologous
haploid
independent
a
exchange
combinations
due
an
and
of
of
the
genes
is
homologous
10 . 1
MEiosis
Example 10.1.2.
The
diagram
shows
chromosomes
of
a
six
diploid
A
cell
in
early
(although
metaphase
not
shown
F
I
as
bivalents).
B
Which
of
is
one
pair
E
homologous
chromosomes?
D
A.
B.
A and
B
A and
C.
B,
D.
D,
C
C
E
There
and
is
F
no
pair
of
homologous
chromosomes.
Solution
The
homologous pair
correct
answer
centromere
in
length.
incorrect,
same,
C
is
they
the
is
are
B.
same
not
a
The
homologous
place
as
chromosomes
and
the
chromatids
although
the
chromosomes
pair—there
are
four
not
two
are
of
all
have
the
the
same
look
the
chromosomes.
Example 10.1.3.
The
light
a
thin
through
lily
an
(Lilium
The
is
a)
b
section
anther
sp.),
cells
B
Y
of
a
showing
Z
pollen
a
crossing over
micrograph
X
shows
A
recombinants
dividing.
magnification
A
A
a
a
B
b
B
b
×70.
Identify
meiosis
and
the
for
stage
cells
of
X,
Y
Z.
gametes
b)
Explain
the
reason
why
cells
in
the
anthers
of
Lilium
must
Fgure 10.1.3.
undergo
Formation of
meiosis.
recombinants
Solution
a)
X:
prophase
I;
Y:
telophase
II;
Z:
telophase
Careful observation and
I.
record keeping revealed
b)
Cells
in
the
anther
of
Lilium
must
undergo
meiosis
because
they
anomalous data that Mendel’s law
will
form
the
pollen
which
will
fertilize
the
egg
cell
in
the
ovary
of independent assor tment could
of
the
plant.
The
number
of
chromosomes
must,
therefore,
be
not account for. Thomas Hunt
reduced
to
half.
This
occurs
by
the
migration
of
homologous
Morgan developed the notion of
chromosomes
during
anaphase
I
to
opposite
poles
and
the
linked genes to account for these
separation
into
two
cells
in
telophase
I,
forming
haploid
cells.
anomalies.
Crossing
over
is
the
exchange
of
DNA material
between
non-
10 µm
sister
homologous
single
sister
strand
in
an
break
chromatids
chiasma)
chromatids
formation
exchange
of
(SSB)
of
in
occurring
the
DNA is
homologous
between
alleles.
cut
prophase
between
chromosomes.
non-sister
This
a
during
of
alleles
can
can
A
non-
Chiasmata
chromatids
exchange
the
I.
(or
result
produce
recombinants.
Crossing
over
chromosomes
produces
of
the
new
haploid
combinations
cells.
of
alleles
on
the
Fgure 10.1.4.
Micrograph image of
crossing over during meiosis
119
10
GE N E T I CS
AND
E VOLUTION
(AHL)
When
with
four
crossing
strange
over
shapes
chromatids)
chromatids
occurs,
pull
or
called
homologous
tetrads
bivalents
away
from
(named
(named
each
chromosomes
after
after
other
but
the
two
are
form
presence
structures
of
chromosomes).
held
together
at
The
the
chiasmata.
s AMPLE sTUDENT ANs WER
The diagram shows the changes in the amount of DNA per cell in the
anther of a plant.
AND fo tnuoma
C
D
a) State the process occurring at A .
This
answer
DNA
could
have
achieved
[1]
1/1
marks:
replication.
b) Explain the reason the mass of DNA decreases at B.
This
At
▲ The
answer
process
and
identies
stages
of
answer
B
each
the
the
could
cell
is
have
achieved
going
chromosome
2/2
through
have
[2]
marks:
mitosis.
migrated
to
the
T
he
sister
opposite
chromatids
pole
in
of
anaphase,
DNA
in
telophase
the
nuclear
membrane
reappears
and
the
cell
has
reduction.
divided
into
two
cells
in
cytokinesis.
c) Suggest what is happening at C.
This
At
answer
C
the
DNA
could
process
decreases
chromosome
producing
▲ This
answer
is
II,
each
two
sister
opposite
form
cells
of
in
pole
to
meiosis
half
in
to
half
is
a
anaphase
the
compared
II.
In
with
In
each
II,
the
pole
the
▼ Replication
gradually
(as
makes
shown
answer
could
DNA
in
A).
Here
the
Replication.
amount
once.
120
of
DNA is
Fertilization
doubled
is
all
at
occurring.
have
new
in
the
0/1
amount
each
cell
four
of
homologous
anaphase
number
I,
of
division,
in
migrates
nuclear
cells
chromosomes
original
achieved
as
second
are
and
meiosis
to
the
membranes
formed.
1/4
the
T
hese
amount
cell.
d) State the name of the process occurring at D.
This
T
he
chromosome
and
of
I,
half
cytokinesis
number
with
meiosis
different
cells
of
marks:
occurring.
cytokinesis.
chromatid
in
2/2
during
different
telophase
have
DNA
of
achieved
migrates
chromosomes
complete.
have
[2]
marks:
[1]
10 . 2
1 0 . 2
I N H E R I TA N C E
Yu huld knw:
✔
gene
i N H E R i TA N C E
loci
are
said
Yu huld be able t:
to
be
linked
if
on
the
same
✔
construct
✔
describe
Punnett
squares
for
dihybrid
traits.
chromosome.
✔
unlinked
result
of
genes
segregate
independently
as
a
ratios
in
variation
the
to
can
be
phenotypes
show
discrete
or
continuous.
of
polygenic
continuous
Chi-squared
whether
and
an
the
characteristics
non-Mendelian
tests
expected
statistically
are
used
to
✔
ratio
of
involving
genotypic
offspring
unlinked
of
and
dihybrid
autosomal
genes.
identify
recombinants
in
crosses
involving
two
genes.
determine
between
frequency
predicted
tend
variation.
difference
the
phenotypic
linked
✔
of
Drosophila.
calculate
crosses
✔
discovery
meiosis.
✔
✔
Morgan’s
an
observed
distribution
✔
deduce
is
from
results
dihybrid
of
a
chi-squared
test
on
data
crosses.
signicant.
✔
explain
height
how
may
polygenic
also
be
traits
such
inuenced
by
as
human
environmental
factors.
Genes
may
be
linked
or
unlinked
and
are
inherited
accordingly
.
Gene
In Topic 3.4 you studied
loci
are
said
to
be
linked
if
they
are
on
the
same
chromosome.
Unlinked
inheritance.
genes
segregate
autosomal
or
located
the
Alleles
AaBb.
show
on
are
In
independently
sex-linked;
X
usually
as
as
a
result
sex-linked
of
meiosis.
inheritance
Linkage
the
genes
can
are
be
usually
chromosome.
shown
representing
them
in
vertical
side
crosses
pairs,
by
side
in
involving
for
dihybrid
linkage,
it
crosses,
is
for
more
example,
common
to
example:
The lines symbolize chromosomes
A
B
in the notation used for linked
genes.
a
b
• Lnked gene are those on the
Example 10.2.1.
same chromosome.
The
sketch
shows
two
pairs
of
human
chromosomes,
1
and
12.
On
• A mnhybrd cr is a genetic
chromosome
1,
the
gene
for
CHD5
is
represented
by
the
alleles
R
cross involving one gene locus.
and
r,
and
the
gene
for
CLIC4
by
S
and
s.
On
chromosome
12,
the
• A dhybrd cr is a genetic cross
gene
for
ZNF26
is
represented
by
T
and
t.
involving two gene loci.
r
• A ch-quared tet is a statistical
test to determine whether the
S
S
s
s
dierence between an observed
and an expected frequency
T
T
t
t
distribution is signicant.
chromosome 1
a)
State
two
b)
Suggest
genes
with
combination
chromosome
c)
Draw
the
chromosome 2
a
of
that
are
reason
alleles
linked.
the
R
process
and
r
on
that
the
resulted
in
homologous
this
pair
of
1.
possible
chromosomes
genotypes
using
a
of
Punnett
gametes
formed
with
these
square.
121
10
GE N E T I CS
AND
E VOLUTION
(AHL)
Solution
a)
The
linked
answer
is
genes
CHD5
chromosome
b)
The
alleles
sister
case
on
chromosome
chromatids
on
the
same
CLIC4
(R
chromosome,
and
S),
as
they
therefore
are
the
on
1.
one
chromatid
through
are
and
the
formed
process
was
of
chromosome
is
the
by
of
should
crossing
exchanged
be
replication
with
homologous
over,
the
r
the
of
the
of
same,
the
R
one
as
other.
from
of
the
one
In
this
one
non-sister
pair.
c)
Rs
rs
R
r
T
RST
rST
RsT
rsT
t
RSt
rSt
Rst
rst
A dihybrid
two
Data
tests
and
cross
different
from
are
an
is
a
genetic
cross
involving
two
gene
loci,
each
with
alleles.
dihybrid
used
to
crosses
determine
expected
can
be
tested
whether
frequency
the
distribution
with
a
chi-squared
difference
is
between
statistically
test.
an
These
observed
significant.
Example 10.2.2.
The
can
seeds
have
over
a
wrinkled
between
two
offspring
a)
of
plant
yellow
(G)
and
or
be
round-shaped
green
yellow
plants
were
can
with
is
dominant
round
round
and
yellow
284
round
and
green
322
wrinkled
and
yellow
109
wrinkled
and
green
unlinked
colour.
and
(R)
or
Round
over
yellow
wrinkled
shape
green.
seeds
In
the
is
a
(r)
and
dominant
cross
following
produced:
947
Calculate
(g)
the
seeds
seeds
expected
seeds
seeds.
ratio
characteristics.
of
phenotypes
Show
your
assuming
results
in
a
these
are
Punnett
square.
b)
Use
to
the
chi-squared
determine
your
formula
whether
these
and
table
shown
characteristics
are
in
example
linked.
Show
working.
Solution
a)
The
Mendelian
crossing
for
unlinked
traits
is
as
follows:
R = allele for round seeds
r = allele for wrinkled seeds
G = allele for yellow seeds
g = allele for green seeds
Parental
round, yellow seeds
round, yellow seeds
phenotypes
Parental
RrGg
RrGg
meiosis
meiosis
genotypes
Gametes
122
RG
Rg
rG
rg
RG
Rg
rG
rg
4.1.3
10 . 2
Ospring (F
i N H E R i TA N C E
) genotypes
2
Gametes
Gametes
RG
Rg
rG
rg
RRGG
RRGg
RrGG
RrGg
RRGg
RRgg
RrGg
Rrgg
RrGG
RrGg
rrGG
rrGg
RrGg
Rrgg
rrGg
rrgg
RG
Rg
rG
rg
Ospring (F
9 round, yellow seeds
)
2
3 round, green seeds
phenotypes
3 wrinkled, yellow seeds
1 wrinkled, green seed
b)
There
are
two
hypotheses:
the
null
hypothesis
(H
)
and
the
0
alternative
hypothesis
(H
).
1
H
=
The
characteristics
assort
=
The
characteristics
do
independently
(are
not
linked).
0
H
not
assort
independently
(thus
are
1
linked).
The
To
total
number
calculate
obtained
in
the
(a)
The
add
the
expected
is
shown
done
in
the
1662.
frequencies
947
for
×
all
for
=
of
green
frequencies:
9/16
we
ratios
yellow:wrinkled
frequency
the
is
expected
expected
calculatedas:
This
seeds
expected
for
green:wrinkled
First
of
round
9
+
use
of
3
the
round
9:3:3:1.
+
yellow
data
yellow:round
3
+
is
1
=
16
9/16
so
it
is
935
possible
characteristics.
The
results
are
table:
2
Phentype
round yellow
round wrinkled
wrinkled yellow
wrinkled green
Ttal
The
value
The
degrees
(number
Then
for
of
use
your
reject
is
below
In
this
critical
of
the
(o − E)
947
935
−12
0.2
284
312
28
2.4
322
312
−10
0.3
109
104
−5
0.3
1662
1662
freedom
the
−
5%)
give
critical
value
is
1)
to
=
find
and
a
3
(ie,
value
1)
the
the
3.2
characteristic
critical
of
value
at
freedom.
the
critical
the
accept
not
p
=
as:
0.05
The
value
the
null
is
insignificant),
are
calculated
that
the
linked.
value
in
alternative
chi-squared
confirming
seed
is
3
accept
for
statistically
of
=
above
you
/E
3.2.
each
and
value
accepted,
colour
−
=
degrees
value,
the
is
for
(4
hypothesis
example,
the
squared
table
at
null
hypothesis
and
(o − E)
chi
results
the
Expected (E)
rows
(significant
If
ober ved (o)
the
is 7.815
table,
you
hypothesis.
If
it
hypothesis.
below
therefore
shape
It is a convention to use the same
the
of
the
the
null
seed
letter for alleles of the same
gene, using a capital letter for the
dominant characteristic.
123
10
GE N E T I CS
AND
E VOLUTION
(AHL)
W
w
W
red-eyed
white-eyed
P
1
female
male
W
W
w
F
red-eyed
red-eyed
1
female
male
w
W
W
W
W
w
F
2
red-eyed
red-eyed
red-eyed
white-eyed
female
female
male
male
Fgure 10.2.1.
Morgan
with
discovered
Drosophila.
melanogaster
red-eyed
The
Linked genes inheritance
with
flies,
expected
males,
2:1:1:0
a
the
the
of
• Dcrete varatn is a
white-eyed
discontinuous variation found in a
trait
was
of
the
and
females.
connected
the
When
ratio
of
in
his
female
he
did
F2
experiments
fruit
crossed
not
fly Drosophila
heterozygous
assort
did
generation
not
hypothesized
red-eyed
occur.
were
white-eyed
F1
independently
.
females,
females
males,
therefore
sex
Mendel’s
red-eyed
white-eyed
red-eyed
Morgan
with
in
red-eyed
progeny
phenotypes
females,
ratios
a
male.
F2
1:1:1:1
males,
observed
red-eyed
crossed
white-eyed
traits
Mendelian
white-eyed
Instead,
non-Mendelian
Morgan
a
ratio
males,
that
the
of
and
eye-colour
factor.
number of distinct categories.
Variation
can
be
discrete
(discontinuous)
or
continuous.
In
discrete
• Cntnuu varatn is the
variation
a
characteristic
is
found
in
two
or
more
distinct
forms.
An
combined eect of many genes
example
of
discrete
variation
is
the
blood
groups.
The
phenotypes
of
and/or the eect of the environment
polygenic
characteristics
tend
to
show
continuous
variation.
Polygenic
on genes. It can be plotted as a
traits
such
as
human
height
may
be
influenced
by
environmental
normal distribution curve.
factors
such
as
diet.
25
20
latot fo %
noit roporp
15
10
5
0
AB
O
A
type of blood group
B
136–
140–
144–
148–
152–
156–
160–
164–
168–
139
143
147
151
155
159
163
167
1
7
1
heights of 12-year-old girls / cm
Fgure 10.2.2.
124
Discrete variation (left) and continuous variation (right)
10 . 3
1 0 . 3
G E N E
P O O LS
A N D
Yu huld knw:
✔
gene
pools
change
GE N E
PooL s
AND
s P E C i AT i o N
S P E C I AT I O N
Yu huld be able t:
over
time.
✔
explain
evolution
in
terms
of
changing
of
allele
frequencies.
✔
a
gene
pool
different
consists
alleles,
of
all
present
the
in
genes
an
and
their
interbreeding
✔
explain
speciation
✔
compare
due
to
isolation.
population.
✔
allele
frequencies
change
with
time
in
and
and
contrast
geographic
temporal,
reproductive
behavioural
isolation.
populations.
✔
✔
reproductive
temporal,
isolation
of
behavioural
populations
or
can
compare
be
speciation
due
populations
to
can
divergence
be
of
isolated
speciation
A gene
pool
can
is
examples
of
geographically
of
directional,
stabilizing
and
selection.
gradual.
occur
the
identify
disruptive
✔
✔
frequencies
populations.
geographic.
✔
✔
allele
isolated
sum
explain
abruptly
.
of
all
the
speciation
in
the
genus
Allium
by
polyploidy
.
population’s
genetic
material
at
In Topic 5.1 you studied
a
given
time.
Gene
pools
change
over
time
through
evolution.
For
evidence for evolution.
example,
mutated
in
sickle
allele
cell
and
a
anemia
normal
natural
allele
in
selection
the
tends
genetic
to
pool,
maintain
as
a
heterozygous
• A gene pl is all the genes and
organisms
do
not
develop
sickle
cell
anemia
and
are
resistant
to
their dierent alleles present in an
malaria.
interbreeding population.
In
speciation,
the
gene
pool
is
split
if
populations
are
reproductively
• Reprductve isolation is
isolated
and
populations
in
the
same
Allopatric
there
are
therefore
can
be
place
not
interbreed.
sympatric
and
isolation
different
do
is
or
includes
allopatric.
temporal
geographic
selection
Reproductive
and
isolation.
pressures
as
Sympatric
isolation
isolation
behavioural
In
there
different
are
of
a mechanism that prevents
occurs
isolation.
of populations can be temporal,
environments
different
production of ospring. Isolation
behavioural or geographic.
habitats
• Plypldy is the multiplication of
or
niches
to
frequencies
exploit.
change,
These
changes
causing
the
cause
natural
populations
to
selection.
The
allele
diverge.
sets of chromosomes. It can lead to
speciation as it produces hybrids.
s AMPLE sTUDENT ANs WER
Outline how reproductive isolation can occur in an animal population. [3]
This is a three mark-question,
This
answer
could
have
achieved
2/3
marks:
therefore three isolations are
expected.
Reproductive
species
are
isolation
unable
to
occurs
mate
when
with
organisms
another
species.
from
a
Reproductive
▲ Although
isolation
can
be
temporal,
behavioural
or
geographic.
mentions
implied
T
emporal
-
the
species
mate
at
different
times
in
the
hence
Behavioural
the
resulting
in
reproductive
species
have
different
courtship
that
places
hence
-
the
species
cannot
are
in
geographically
patterns.
there
members
due
to
reproduce.
divergence
of
isolated
populations
was
of
occur
a
for
temporal
different
at
This
saying
isolation
by
populations
different
in
behaviours.
courtship
can
be
gradual
or
a
mark
a
answer
for
did
by
times
and
not
geographic
population
being
differences
score
isolation
separated
abruptly
.
gradualism,
gradual
is
the
speciation.
mark
isolation
because
In
a
behavioural
by
can
it
from
different
▼ The
Speciation
species,
were
before
scored
reproducing
Geographical
they
species
answer
isolation.
that
-
candidate
year
same
(seasonally),
the
different
and
the
evolution
continuous
occurs
uniformly
transformation
of
at
the
a
steady
species,
rate
with
with
a
long
it
example
river,
did
of
not
mention
barrier,
mountain
or
for
the
example,
a
road.
125
10
GE N E T I CS
AND
E VOLUTION
(AHL)
sequence
of
intermediate
forms.
In
punctuated
equilibrium,
speciation
In some plants, the
occurs
abruptly
and
the
population
becomes
stable
immediately
.
duplication of the genetic
Punctuated
equilibrium
change
short
implies
long
periods
without
appreciable
material has led to speciation. In
and
periods
of
rapid
evolution.
species such as those of the
genus Allium (for example onions)
• Gradualm is the process by which
• Drectnal electn favours one
speciation occurs at a steady rate
extreme phenotype over the other.
the number of chromosomes has
duplicated by polyploidy. When a
with a long sequence of intermediate
• stablzng electn favours
diploid organism (two sets of
forms.
middle phenotypes.
chromosomes) duplicates its sets
• A punctuated equlbrum is the
it becomes a tetraploid (four sets
• Druptve electn favours both
speciation that occurs abruptly
of chromosomes). Polyploidy is a
extreme phenotypes over middle
without intermediate forms.
phenotypes.
type of sympatric speciation,
because polyploids cannot breed
with the original diploids. Many
crop species have been created to
Example 10.3.1.
be polyploid. Polyploidy increases
Describe
the
pace
of
evolution
in
the
theory
of
punctuated
allelic diversity and permits novel
equilibrium.
phenotypes to be generated,
leading to hybrid vigour. The
Solution
domestication of wheat involved
There
multiple polyploidization events
periods
between several species to obtain
occurs
hexaploid bread wheat (Triticum
causing
are
long
of
in
stable
rapid
the
evolution.
case
sudden
periods
of
a
with
An
volcanic
climatic
or
little
change
example
of
eruption
sudden
punctuated
or
environmental
and
a
meteor
short
evolution
impact,
changes.
aestivum). This new species has
larger grains which produce more
Evolution
requires
that
allele
frequencies
change
with
time
in
flour than the wild ancestral
populations.
Natural
selection
can
occur
due
to
directional,
stabilizing
species.
or
disruptive
selection.
How does the trait change?
Directional selection
Stabilizing selection
selection against one
selection against both
extreme
extreme
Disruptive selection
selection against the mean
population
population
population
after selection
after selection
after selection
shor t
original
original
population
population
medium
long
shor t
for: moderate traits
against: the other ex treme
against: both ex tremes
long
population
shor t
medium
long
for: both ex tremes
against: moderate traits
eg, Long wiggly tails look like a
eg, Shor t tails mess up the cat’s
eg, Shor t tails help keep predators
snake and scare predators. The
balance. Long tails drag on the
from catching them on the ground.
longer the tail, the more it looks
ground. Medium tails are best.
like a snake.
Fgure 10.3.1.
126
medium
for: one ex treme trait
original
Types of selection
Long tails are good for balance in
the trees. Medium tails don’t help.
10 . 3
GE N E
PooL s
AND
s P E C i AT i o N
Practce prblem fr Tpc 10
Prblem 1
Prblem 2
The diagram shows a pair of homologous chromosomes
Two genes determine the coat colour in mice. One
during meiosis in a cell in the human testis. The
gene controls whether the coat is coloured and the
positions of the alleles of some genes are indicated.
other controls the colour. The gene for coloured (C) is
dominant over non-coloured or albino (c). Agouti (A) is
A
B
C
for grey-coloured hair and is dominant over black (a).
Albino mice (cc) do not have coat colour because these
mice are unable to produce any colour.
a) Using a Punnett square, predict the possible
genotypes for colour of coat of the offspring of a
crossing of two agouti mice heterozygous for both
genes.
a
b
c
b) Identify the possible phenotypes for the offspring
a) ()
Draw the possible chromosomes that could be
in (a).
found in the gametes formed.
Prblem 3
() Identify in your diagrams in (i) which
chromosomes are recombinant.
Star ting from the concept of a gene pool, explain
briefly how populations of early ver tebrates could have
evolved into different groups.
b) Explain the consequence of crossing over on
variability.
127
ANIMAL
11
1 1 . 1
(AHL)
ANTIBODY
PRODUCTION
Y sl kw:
✔
every
organism
surface
✔
of
its
pathogens
others
has
be
cross
unique
molecules
on
the
✔
describe
B
lymphocytes
in
✔
species-specic
species
although
✔
explain
barriers.
blood
are
activated
by
T
plasma
B
✔
cells
cells
multiply
and
to
memory
form
plasma
cells
✔
antibodies
✔
immunity
secrete
immune
antibody
the
cells
reason
a
response
in
mammals,
production.
antigens
stimulate
with
clones
explain
on
antibody
different
the
effects
immune
system.
blood
surface
of
red
production
the
in
a
group.
describe
how
of
vaccination
on
the
of
cells.
✔
disease
✔
VA C C I N AT I O N
lymphocytes
mammals.
activated
the
including
person
✔
AND
Y sl be able t:
cells.
can
can
P H YS I O LO GY
of
smallpox
humans
to
was
have
the
rst
been
infectious
eradicated
by
antibodies.
vaccination.
memory
aid
the
destruction
depends
upon
the
of
pathogens.
persistence
✔
analyse
✔
explain
vaccines
but
✔
do
white
✔
contain
not
fusion
of
a
antigens
the
release
which
producing
✔
cause
cells
allergens
data.
the
use
of
monoclonal
antibodies
to
cells.
HCG
✔
epidemiological
of
histamine
tumour
monoclonal
hybridoma
trigger
pregnancy
test
kits.
immunity
disease.
cause
plasma
that
in
in
allergic
cell
cell
antibodies
with
an
creates
are
response
to
symptoms.
a
antibody-
hybridoma
produced
cell.
by
cells.
Immunity
is
based
on
the
recognition
of
self
and
the
destruction
In Topic 6.3 you studied defence
of
foreign
material.
Every
organism
has
unique
molecules
on
the
against infectious diseases.
surface
of
its
antibodies.
Antibodies
antigen.
B
secrete
cells
the
are
Lymphocytes
to
mature
Immunity
Once
by
foreign
are
clones
B
in
by
are
that
a
of
by
in
event
the
of
the
antibodies,
phagocytes.
matter.
of
T
a
that
are
recognized
attach
white
to
blood
white
blood
lymphocytes.
plasma
aid
upon
the
type
lymphocytes
the
which
proteins
when
activated
depends
marked
destroyed
any
are
form
antibodies
antigens,
produced
antibodies
are
called
Antibodies
lymphocytes
multiply
128
cells
cells
and
that
of
matter
are
encounter
In
how
B
cells.
to
with
memory
such
as
the
mammals,
pathogens.
encounter
persistence
foreign
of
remember
Phagocytes
cell.
specific
antigens.
Activated
memory
destruction
second
the
cells
by
cells
Plasma
cells
Memory
produce
the
antigen.
cells.
bacteria
non-specific,
as
is
they
destroy
11 . 1
AnTiBodY
• An ate is a molecule (usually a
• T lympytes are white blood cells
peptide or glycoprotein) found on the
that activate B lymphocytes.
ProducTion
And
v A c c i n AT i o n
surface of the cells of pathogens.
• Plasma ells are mature B
• An atby is a protein of the
lymphocytes that produce
immune system produced by plasma
antibodies.
cells that attacks antigens.
• Memy ells are mature B
• B lympytes are white blood
lymphocytes that remember how
cells that mature into either plasma
to produce the antibodies.
cells or memory cells.
lymphocyte
Key
1 Lymphocytes recognize antigens on
antibody
the surface of bacteria as 'foreign'
antigen
and produce antibodies against them.
phagocyte
4 Bacteria are enclosed
in a vacuole where they
are killed.
bacteria
2 Antibodies stick to the
antigens on the bacteria.
clump of
The bacteria clump together.
bacteria
3 Pseudopodia of the phagocyte flow
around the bacteria.
Fe 11.1.1.
Defence against disease
Eample 11.1.1.
Which
A.
B.
cells
produce
antibodies?
erythrocytes
immature
B
C.
lymphocytes
plasma
D.
mature
cells
T
lymphocytes
Solution
The
correct
no
need
chemicals
which
Some
one
do
are
has
the
T
into
are
produce
red
plasma
blood
proteins.
lymphocytes,
which
Salmonella
or
is
reservoirs
species.
with
affect
as
cells
B
such
and
enterica
types
(or
associated
in
others
that
cells;
they
lymphocytes
as
only
a
broad
However,
the
cytokines,
then
can
with
affect
more
immunity
subspecies
serovars)
range
type
can
trigger
species-specific
disseminated
only
but
antigens
different
Typhimurium
animal
associated
fever
by
contain
disease.
containing
mammalian
is
cannot
species-specific
non-species-specific
and
Erythrocytes
mature
Vaccines
cause
Salmonella
C.
they
produced
them
pathogens
not
is
so
they
antibodies.
species.
bacterium
as
nucleus
make
produce
it
answer
have
that
enterica
can
pathogens.
gastroenteritis
of
reptilian,
Salmonella
septicemic
in
is
a
such
is
a
either
type
humans
avian
typhi
infections
act
The
than
but
and/or
specialist;
as
typhoid
humans.
129
11
A NIM A L
P H YS I O LO G Y
(AHL)
Eample 11.1.2.
The
graph
shows
vaccination
(on
the
day
concentration
0)
and
after
a
of
antibodies
second
in
blood
encounter
with
after
the
antigen.
80
stinu yrartibra / doolb ni
seidobitna fo noitartnecnoc
70
60
50
40
30
20
10
0
0
20
40
60
80
100
120
140
time / days
a)
b)
State
(i)
the
concentration
Identify
second
(ii)
c)
the
the
antibodies
person
on
day
30.
encountered
the
antigen
for
a
time.
Suggest
Explain
day
of
a
the
possible
body’s
source
of
response
this
to
a
encounter.
second
encounter
with
the
antigen.
You must always write the units.
In this case as they are arbitrary
Solution
units it is not really necessary, but
a)
24
(arbitrary
units)
it is always better to include them.
b)
(i)
day
(ii)
50
The
person
could
c)
Following
plasma
start
the
cells
in
a
of
collection
of
the
in
a
the
T
as
shot
the
Some
soon
of
the
have
antigen.
B
how
as
matured
Plasma
After
30
lymphocytes
to
they
antibodies
vaccine
or
pathogen.
lymphocytes.
against
remember
therefore
the
lymphocytes
of
decreasing.
that
second
with
B
help
activated
make
the
days
mature
antibodies.
encounter
are
into
cells
the
produced
antigen
immediately
quantity
.
data
data
determine
start
time,
diseases
the
cells
are
had
antibodies
greater
Epidemiological
to
with
memory
second
and
have
infected
vaccination,
cells
producing
These
factors
been
antibodies
into
the
could
have
usually
a
and
policies
shows
defined
statistical
to
the
distribution,
population.
analysis.
eradicate
and
It
It
is
helps
prevent
causes
usually
and
based
provide
on
risk
a
information
diseases.
Eample 11.1.3.
Cholera
is
cholerae.
The
pain
John
in
and
an
cramps.
Snow’s
1854,
local
handle.
130
It
each
water
council
The
caused
can
completed
shows
communal
the
infection
symptoms
of
lead
map
case
as
pumps.
to
to
the
one
watery
cholera
one
outbreak
water-borne
are
dehydration
of
After
disable
cholera
by
cholera
dot.
The
of
the
in
black
analysing
soon
and
cases
the
water
ended.
bacterium Vibrio
diarrhoea,
stomach
death.
Soho,
London,
squares
data,
pumps
show
Snow
by
the
persuaded
removing
its
11 . 1
AnTiBodY
ProducTion
And
v A c c i n AT i o n
There are ethical
implications of research.
Jenner tested his vaccine for
smallpox on a child. Nowadays it
d
or
xf
O
t
e
re
St
would be regarded as completely
L
e
x
i
n
g
t
o
n
D
e
a
n
S
t
r
e
e
t
W
a
r
d
o
u
r
S
t
r
e
e
t
campaign for the global eradication
of smallpox in 1967. Vaccination
a global level and the fact that
S
t
r
e
e
t
n
g
S
t
r
e
e
t
S
a
v
i
l
l
e
r
B
e
w
w
humans are the only reservoir of
the smallpox virus (there are no
r
e
w
i
c
k
W
a
r
n
e
d
e
l
r
o
a
G
u
q
S
e
S
t
r
e
e
t
e
e
t
S
t
r
Health Organization initiated the
policies that led to immunization at
r
t
S
R
o
t
e
e
r
t
S
first on many animals. The World
t
e
t
i
u
d
n
o
C
R
e
g
e
n
t
t
e
e
r
t
S
K
i
d
a
o
r
B
w
i
c
k
S
t
r
e
e
t
.
t
G
S
t
r
e
e
t
t
e
e
r
t
S
h
g
u
o
r
o
lb
r
a
M
B
e
r
P
lo
a
n
d
unethical to do so without testing it
other carriers) played an impor tant
role in the decline of the disease.
Inadequate repor ting of cases and
N
y
l
l
i
d
a
c
c
i
P
the impossibility of funding the
0
100
vaccination or reaching
Metres
inaccessible areas of some
countries slowed down the
a)
State
two
streets
with
relatively
higher
numbers
of
cholera
cases.
process. The campaign was
deemed a success and smallpox
b)
Outline
how
the
information
in
this
map
might
have
helped
was globally eradicated in 1977,
to
stop
the
cholera
outbreak.
only 10 years later.
Solution
a)
Broad
Street
Lexington
b)
The
map
was
information
more
has
pump
inactivated
stopped,
most
a
good
way
gathered
cholera
water
the
cases.
In
second
place
it
could
be
Street.
cases.
in
It
Broad
this
water
therefore
by
to
represent
Snow.
shows
Street
It
that
and
pump,
the
eradicating
the
clearly
most
epidemiological
identifies
cases
Lexington
source
the
of
were
Street.
the
areas
close
to
When
with
group of antibodies against many
the
antigens.
Snow
contamination
• Plylal atbes are a
was
• Mlal atbes
outbreak.
are specic against only one
determined antigen.
Fusion
a
of
a
tumour
hybridoma
cell
cell
which
with
an
antibody-producing
produces
monoclonal
plasma
cell
creates
antibodies.
cells taken
hybridoma cells
from spleen
produced by
fusion
culture of tumour
shor t-lived
cells (myeloma)
antibodytumour cells that
mouse injected
producing cells
grow and divide
with antigen
continually
limitless supply
of an antibody
Fe 11.1.2.
Production of monoclonal antibodies
131
11
A NIM A L
P H YS I O LO G Y
(AHL)
Monoclonal
kits.
In
They
these
antibodies
have
kits,
chorionic
also
the
have
been
been
very
monoclonal
gonadotropin
used
useful
for
in
disease-detecting
pregnancy-detection
antibodies
(anti-HCG).
many
used
Human
are
kits.
anti-human
chorionic
gonadotropin
▲ This answer scored a mark for
is
the
following.
phagocytes
step
2,
In
step
engulf
1,
the
macrophages
a
glycoprotein
hormone
that
is
synthesized
by
the
placenta,
and
macrophage
pathogen.
then
In
therefore
appears
only
during
pregnancy
.
display
S AMPLE STudEnT AnS WEr
the
antigen
antigens
of
from
a
the
pathogen
pathogen
and
correspond
Explain the production of antibodies.
to
a
specic
each
antibody
specic
are
T
helper
In
corresponds
antigen
activated
cell.
and
by
to
a
This
5,
some
memory
▼ The
that
antigen
activated
binding.
cells
act
immunity
or
In
failed
are
to
2,
it
to
does
the
macrophage
pathogen.
correct
In
that
step
T
3,
cells
pathogen
digests
is
this
not
is
through
done,
but
6/7
marks:
B
hormones
through
engulfed
by
a
macrophage.
Macrophage
presents
hormones
3.
helper
T
he
T
to
cells
the
antigen
activate
bind
to
T
the
on
helper
its
surface
and
cells.
antigen
and
thereby
obtain
the
information
as
to
what
specic
antibody
is
needed.
It
say
releases
hormones
to
activate
B
cells
and
passes
on
the
the
although
activate
is
releases
it
is
information.
cells,
4
.
it
achieved
for
infectious
not
A
then
that
have
In
say
necessary
resistance
step
could
as
2.
answer
disease.
B
cells.
antibodies
answer
lymphocytes
1.
step
[7]
step3,
B
cells
start
to
divide
by
mitosis
and
produce
and
secrete
that
peptides
antibodies.
such
The
B
as
interferon
answer
cells
clones
should
divide
of
plasma
by
plasma
cells
and
that
cytokines.
have
mitosis
cells
said
to
and
secrete
that
5.
Some
be
able
B
cells
remain
in
the
body
as
memory
cells
to
form
it
is
to
produce
antibodies
the
next
time
this
pathogen
these
specic
invades
the
body.
antibodies.
Allergies
occur
when
allergy-causing
allergens
are
the
antigen
pollen,
immune
called
dust
an
and
system
over-reacts
allergen.
foods
such
The
as
most
to
a
specific
common
peanuts.
In
response
It can be useful to use annotated
to
allergens,
white
blood
cells
release
histamine
which
causes
the
diagrams to explain an answer.
allergic
symptoms.
Histamines
found
blood
can
in
eventually
and
Antigens
on
production
determine
before
a
damage.
132
the
the
a
body
,
dea th.
be
surface
person
in
urine
can
lead
shutting
to
red
of
to
off
red
a
avoid
due
as
to
Some
r a sh
f ood s
T h e se
blood
cells
different
donor
an
c e l l s)
that
p er me a bil i t y
and
a re
swe l l i n g
nat u r al l y
include
fever,
as
blood
stimulate
blood
are
of
that
high
in
f e r me n t e d
f ood s
possibilities.
chills,
blood
and
clotting
supply
to
the
This
Blood
will
is
reaction.
breathing
damage
antibody
group.
incompatibility
kidney
death
the
itchin g,
(ma st
th e
win e).
blood
such
ce l l s
in cre a se
a voided.
with
different
symptoms
It
to
blood
tiss ues
ca us es
(especia lly
in
blood
wh ite
sh ou ld
transfusion
includes
ache,
T h is
lea d
and
alcohol
by
conn ective
capillaries.
histamines
the
released
the
tested
This
difficulty
,
jaundice
may
main
occur
reaction
muscle
due
to
liver
throughout
organs.
11 . 2
MovEMEnT
Eample 11.1.4.
Compare
groups
and
by
contrast
antigens
completing
the
and
antibodies
in
different
blood
table.
Solution
Bl type
Feate
A
B
AB
o
Membae
ates
O
A
B
anti-B
Plasma
AB
anti-A
none
anti-A and
anti-B
atbes
at-bl
p
pe
B and O
Bl type
A and O
A , B, AB and O
only O
tat a be
eee  a
tasfs
1 1 . 2
M O V E M E N T
Y sl kw:
✔
bones
and
muscles
✔
exoskeletons
and
synovial
Y sl be able t:
act
joints
as
provide
anchorage
for
✔
describe
levers.
allow
insect
certain
movements
but
not
antagonistic
pairs
of
muscles
in
an
leg.
✔
annotate
✔
draw
a
diagram
of
the
human
elbow.
others.
✔
movement
work
✔
in
of
the
antagonistic
skeletal
muscle
contain
body
muscles
to
labelled
are
multinucleate
muscle
endoplasmic
✔
explain
bres
up
of
✔
analyse
contain
many
contractile
the
contraction
achieved
by
of
the
structure
of
a
muscle
the
contraction.
electron
myobrils,
of
micrographs
muscle
to
nd
the
state
of
bres.
each
design
experiments
using
grip
strength
data
sarcomeres.
loggers
✔
the
reticulum.
✔
made
of
and
contraction
✔
diagrams
sarcomere.
pairs.
bres
specialized
requires
skeletal
sliding
of
muscle
actin
and
to
assess
muscle
fatigue.
is
myosin
laments.
✔
ATP
hydrolysis
necessary
✔
calcium
ions
troponin
of
for
and
the
and
control
The
roles
and
protection.
the
cross
bridge
laments
the
to
proteins
muscle
formation
are
slide.
tropomyosin
and
contractions.
musculoskeletal
system
are
movement,
support
In Topic 2.8 you studied cell
Movement
is
achieved
mainly
by
muscles
pulling
respiration and ATP production and
on
bones,
while
bones
provide
most
support
and
protection.
Bones
in Topic 1.2, the ultrastructure of
and
exoskeletons
provide
anchorage
for
muscles
and
to
in
act
as
levers.
cells.
Movement
of
the
body
requires
muscles
work
antagonistic
pairs.
133
11
A NIM A L
P H YS I O LO G Y
(AHL)
• Abt is the movement of a
limb away from the midline of the
biceps muscle
relaxes
biceps muscle
body.
contracts and
triceps muscle
• At is the movement of
pulls
triceps muscle
relaxes
a limb towards the midline of the
contracts and
body.
pulls
• Lamets attach bone to bone.
• Tes attach muscle to bone.
arm bends
• Atast msles produce
arm
straightens
opposing movement at a joint—
when one contracts, the other
relaxes.
Fe 11.2.1.
Movement of the human arm
• ca tlae prevents the friction of
bones.
Synovial
• Syal  provides lubrication
joint,
type
preventing friction.
joints
where
of
flexion
joint
allow
the
certain
femur
allows
(bending)
joins
movements
the
movement
and
pelvis,
in
extension,
all
is
but
a
not
ball
directions
abduction
others.
and
The
socket
including
and
hip
joint.
This
rotation,
adduction.
The
elbow
• The jt apsle seals the joint
allows
less
movement
because
it
is
a
hinge
joint,
allowing
flexion
and helps to prevent dislocation.
extension
only
.
S AMPLE STudEnT AnS WEr
The diagram shows a human elbow.
A
B
X
Y
D
C
a) Label A to D.
This
▼ Label A is
vague.
The
correct,
correct
but
answer
[4]
could
have
achieved
3/4
marks:
too
answer
was
the
A:
bone,
B:
ligament,
C:
synovial
uid
and
D:
cartilage.
humerus.
b) State the function of C in this elbow.
This
C
134
answer
could
lubricates
the
have
achieved
joint
and
1/1
[1]
marks:
prevents
friction.
and
11 . 2
) Explain the function of bones X and Y.
This
X
is
answer
the
biceps
could
radius
muscle
have
and
achieved
Y
the
through
4/4
[4]
marks:
ulna.
T
he
tendons
radius
while
the
is
attached
ulna
is
to
the
attached
to
▲ The
the
triceps.
T
hese
muscles
are
antagonistic.
When
the
the
lower
arm
lifts;
when
the
triceps
contracts
answer
function
biceps
and
contracts,
MovEMEnT
the
and
explains
anchorage
function
of
the
the
of
muscles
system
as
a
and
lever.
the
biceps
together
using
Muscles
with
this
the
lever
,
contain
Myofibrils
containing
secured
relaxes
at
are
the
lower
humerus
less
many
force
fibres,
organelles
actin
and
either
arm
to
is
levers.
which
the
bound
cell
are
of
down.
T
his
required
composed
myosin
end
as
moves
to
is
a
lift
formed
units
T
hese
third
class
act
lever—
objects.
by
called
together.
bones
The
many
myofibrils.
sarcomeres
myofibrils
are
membrane.
A-band
Z-line
I-band
whole muscle
H-zone
single muscle
bundle of muscle
bre
bres
single
myobril
nucleus
striations
sarcomere
ner ve
blood
capillary
Fe 11.2.2.
Muscle
are
cells
are
which
cell.
suited
They
stores
Muscle
sarcomeres.
section
and
fibres
through
alternate
with
also
for
the
light
a
between
their
function.
nuclei
contain
releases
contain
The
thick lament
of actin
of myosin
Structure of muscles
multinucleate
muscle
thin lament
a
specialized
calcium
many
light
and
ions
to
myofibrils,
micrograph
myofibril
Skeletal
displaced
in
(×900).
dark
to
endoplasmic
each
A number
are
of
up
of
shows
the
contraction.
contractile
a
repeating
visible.
of
reticulum,
muscle
made
11.2.3
fibres
periphery
regulate
Figure
bands
muscle
the
These
longitudinal
units
are
that
the
sarcomeres.
Fe 11.2.3.
Light microscope
image of a myofibril
135
11
A NIM A L
P H YS I O LO G Y
(AHL)
Eample 11.2.1.
Annotate
diagrams
differences
when
of
the
relaxed
structure
of
a
sarcomere
showing
the
and
relaxed muscle
contracted.
thick and thin laments slide past one
another, causing the muscle to contract
Solution
In
a
of
the
relaxed
apart,
the
the
inwards,
ions
changing
actin
its
actin
allows
The
and
it
to
movement
for
the
the
The
that
of
a
of
of
actin
the
the
The
and
muscle
myosin
of
ion
to
ATP
is
the
binds
starting
and
cross
with
to
site
causes
achieved
then
tropomyosin,
releases
binds
binding
myosin
to
bridge
potential
myosin
return
hydrolysis
bound
cross
calcium
and
skeletal
is
a
action
The
actin
filaments.
(T)
forming
nerve
cell.
exposing
binding
the
troponin
from
muscle
and
requires
to
band
head
contraction
filaments
Contracted muscle
of
in A
light
shows
myosin
release
of myosin
smaller.
the
shape
thick lament
of actin
becomes
propagation
filament.
contract.
centre
myosin
into
thin lament
filaments
bands
below
The
(purple)
the
myosin
the
and
and
When
which
dark
the
wider
actin
much
diagram
preventing
filament.
the
the
closer
becomes
The
bands
towards
The
become
of
pull
Z-lines
further
longer.
sarcomere,
shorter.
the
are
contracts,
filaments
H
light
sarcomere
muscle
the
muscle,
sarcomere
by
actin
calcium
troponin,
on
the
the
the
muscle
the
ATP
,
sliding
which
position.
bridge
to
This
formation
slide.
2+
Ca
myosin head
ion
bending of
myosin head
troponin
ADP + Pi
ADP + Pi
tropomyosin
T
T
2+
actin
1. Star t position in relaxed
2. Binding of Ca
ion to troponin, interaction
lament
muscle bre
between actin and myosin
ATP
hydrolysis
Pi
ATP
ADP
T
T
4. ATP binding. Actin and myosin
3. Movement of tropomyosin
slide back to their former position
Fe 11.2.4.
ATP
Muscle contraction
Eample 11.2.2.
Fluorescent
micrograph
calcium
shows
ions
the
have
been
calcium
used
levels
in
a
to
study
muscle
muscle
cell
(red
contraction.
being
the
The
fluorescence
highest)
before
and
contracting.
Explain
136
how
the
increased
level
of
calcium
ions
triggers
the
contraction
of
muscle
cells.
decomposition
while
11 . 3
ThE
K idnE Y
And
o S M o r E g u L AT i o n
Solution
When
end
the
muscle
its
actin
it
The
and
to
1 1 . 3
potential
the
release
calcium
exposing
filament.
muscle
action
induces
cell.
shape
the
nerve
plate,
The
ion
the
reaches
of
binds
myosin
binding
of
the
calcium
to
troponin,
binding
actin
muscle
ions
and
into
the
changing
site
on
myosin
the
causes
contract.
T H E
K I D N EY
A N D
Y sl be able t:
Y sl kw:
✔
animals
are
either
O S M O R E G U L AT I O N
osmoregulators
✔
or
compare
osmoconformers.
✔
the
Malpighian
kidney
of
carry
tubule
out
nitrogenous
system
in
insects
osmoregulation
and
and
✔
the
describe
the
from
of
that
blood
in
the
in
the
renal
renal
artery
draw
the
ultrastructure
Bowman’s
✔
the
of
capsule
proximal
reabsorbs
the
the
loop
convoluted
useful
of
conditions
is
state
ADH
the
controls
collecting
the
tubule
by
✔
annotate
the
✔
length
annotated
diagram
of
the
human
functions
of
the
different
parts
of
the
✔
explain
maintains
diagrams
of
the
nephron.
osmoregulation
in
humans
and
transport.
the
consequences
of
dehydration
and
overhydration.
hypertonic
medulla.
reabsorption
of
water
in
explain
the
treatment
hemodialysis
the
or
of
kidney
kidney
failure
by
transplant.
of
the
with
loop
the
of
Henlé
need
for
is
state
water
that
drugs
positively
blood
are
cells,
detected
in
glucose,
urinary
proteins
and
tests.
conservation
animals.
the
type
of
correlated
All
and
duct.
correlated
in
kidneys
selectively
active
✔
✔
of
kidney
.
and
✔
✔
structures
tubes.
ultraltration.
substances
Henlé
in
and
vein.
glomerulus
facilitate
an
describe
✔
osmoregulator
animals.
kidney
.
✔
✔
contrast
wastes.
composition
different
the
Malpighian
removal
✔
✔
and
osmoconformer
animals
nitrogenous
with
waste
evolutionary
excrete
in
animals
history
nitrogenous
waste
and
is
habitat.
products
and
some
animals
In Topic 1.3 you studied the
also
balance
water
and
solute
concentrations.
Nitrogenous
wastes
membrane structure and in
are
produced
from
the
breakdown
of
amino
acids
and
nucleic
acids.
Topic 1.4, membrane transpor t.
The
Malpighian
carry
out
tubule
system
osmoregulation
and
in
insects
removal
and
of
the
kidneys
nitrogenous
in
humans
wastes.
Not
all
• osmfmes are organisms
animals
are
osmoregulators;
some
are
osmoconformers.
that change according to the
external environment.
• osmelats maintain their
internal environment regardless of
the external environment.
• Keys are the organs in humans
used to carry out osmoregulation and
removal of nitrogenous wastes.
• Malpa tbles are excretory
organs in ar thropods (insects).
137
11
A NIM A L
P H YS I O LO G Y
(AHL)
The
Malpighian
alimentary
from
the
These
canal
body
in
transport
canal.
and
n
ia
h
ig
lp
a
M
by
are
is
series
are
reabsorbed
f
o
branched
They
and
from
ions
together
e
n
o
(
of
arthropods.
released
wastes
le
u
b
tu
a
diffusion
Mineral
water
nitrogenous
are
most
fluids
substances
alimentary
as
tubules
absorb
mineral
the
by
osmosis.
by
by
reach
and
active
tubules
the
The
undigested
that
water
ions
Malpighian
reabsorbed
with
tubes
wastes
wastes
transport.
into
rectum
the
by
are
the
active
excreted
food.
)
y
n
a
m
+
NH
4
+
Na
Cl
water
uric acid
uric acid
mid gut
hind gut
Fe 11.3.1.
• The lmels is the high-
rectum
Malpighian tubule
Eample 11.3.1.
pressure capillary causing
The
diagram
shows
a
ultraltration in the Bowman’s
human
kidney
.
capsule.
A
• The Bwma’s apsle is where
a)
glomerular ltrate collects to be
Which
label
shows
the
cortex?
B
fur ther processed.
b)
Which
label
shows
• The pmal lte tble
the
blood
vessel
selectively reabsorbs useful
carrying
blood
into
the
substances by active transpor t. It
glomerulus?
C
contains many mitochondria and
microvilli for absorption.
c)
What
is
the
pelvis
of
the
kidney?
• The lp f helé maintains
D
hyper tonic conditions in the
Solution
medulla. Animals adapted to dry
a)
The
cortex
is
A
habitats have long loops of Henlé.
b)
The
blood
vessel
carrying
• The stal lte tble
blood
to
the
glomerulus
regulates mineral ion levels and
is
B,
the
renal
artery
.
It
maintains pH.
can
be
distinguished
from
the
renal
vein
(C)
by
the
width
of
• The llet t is the
vessel.
D
is
the
ureter,
where
all
the
collecting
ducts
join.
site where the amount of water
reabsorption can be varied as a par t
of osmoregulation.
• Adh is the antidiuretic hormone
that controls water reabsorption.
138
c)
The
pelvis
is
the
funnel-like
structure
leading
to
the
ureter.
the
11 . 3
ThE
K idnE Y
And
o S M o r E g u L AT i o n
S AMPLE STudEnT AnS WEr
▲ The answer scored marks for
saying
Explain how the structure of the nephron and its associated blood
vessels enable the kidney to carry out its functions.
This
answer
could
have
achieved
7/8
the
[8]
the
glomerulus
of
the
larger
than
the
nephron,
efferent
bringing
taking
the
afferent
arteriole
was
pressure,
forcing
arteriole.
T
his
creates
out
the
urea,
glucose,
of
mineral
ions
from
the
the
blood
vessels.
T
he
blood
rest
proximal
is
lined
by
but
enters
podocytes,
leaving
the
the
proteins
Bowman’s
which
wrap
T
he
ltrate
moves
to
the
substances
for
reabsorption.
Here,
the
glucose
and
T
his
Another
is
convoluted
of
ions
by
active
transport.
T
he
cells
have
with
this.
Water
ows
by
osmosis.
T
he
mitochondria
large
loop
of
reabsorption
in
the
proximal
to
loop
surface
uid
then
moves
-descending
to
loop
the
is
loop
of
of
in
loop
is
convoluted
structure
allows
for
a
high
to
water
but
not
to
ions.
to
ions
but
not
to
medulla.
T
he
longer
the
loop
concentration
of
Henlé
limb
were
give
of
salt
ions
in
Henlé,
the
more
water
a
the
to
the
distal
is
reabsorbed
and
to
the
excretion
urea.
of
if
ADH
is
convoluted
tubule,
where
are
vessels
collecting
duct,
where
water
the
bloodstream.
Glucose
nephron
is
to
allow
as
well
as
ions
reabsorbed
and
water
limb
the
for
a
the
high
solute
medulla.
water
T
wo
reabsorbed
which
has
in
microvilli
area.
water
,
but
have
been
that
is
a
function
osmoregulation
the
waste
or
such
candidate
ultraltration,
not
walls
and
mention
in
to
the
the
that
glomerulus
smaller
that
with
the
basement
podocytes
capsule
preventing
act
the
as
loss
of
a
the
lter
of
large
reabsorption
into
the
urea
is
such
cells.
The
as
protein,
answer
and
failed
to
blood
mention
capillaries
for
nitrogenous
does
Bowman’s
blood
the
the
Although
molecules,
to
large
is
present.
surround
a
impermeable
surface
permeable
thus
Blood
for
one
was
saying
mention
membrane
reabsorbed
in
could
for
molecules
more
and
creating
large
capillary
moves
given
being
for
kidney
answer
then
has
marks.
is
conser ved.
uid
two
descending
mark
duct,
▼ Marks
does
T
he
which
water
.
as
the
useful
proximal
tubule.
of
T
his
and
the
Henlé.
permeable
permeable
in
was
the
Henlé
obtained
-ascending
in
tubule.
area
to
T
he
useful
ions
selective
scored
One
collecting
the
and
glucose
tubule,
mark
water.
marks
increases
(selective)
mineral
the
of
concentration
help
the
are
to
reabsorbed
as
occurs
area,
ascending
tubule
the
One
capsule,
capillaries.
proximal
for
convoluted
that
reabsorbed
ultraltration.
than
water
surface
which
in
larger
large
convoluted
in
a
blood.
glucose
such
reabsorption
and
pressure
to
blood
away
given
reabsorption
is
Explaining
of
due
arteriole
the
amounts
blood
is
arteriole
substances
much
high
marks:
mark
In
that
glomerulus
removed
as
the
active
active
pumping
out
the
of
of
transport
sodium
ascending
limb
or
ions
from
the
urine.
ltrate
T
he
nephron
is
in
the
kidney
and
functions
to
lter
the
blood.
to
the
distal
the
pH
the
medulla.
convoluted
The
fact
tubule
that
adjusts
+
and
+
K
of
Na
,
+
and
the
H
is
not
collecting
water
varies
aquaporins
or
concentration
mentioned.
duct
with
and
amount
of
collecting
mentioned
for
by
of
have
to
of
ADH
varying
reabsorbed
could
a
number
amount
water
duct
permeability
the
osmoregulation
That
the
in
the
been
mark.
No marks are given for
ultrafiltration in the Bowman’s
capsule because this answer is
too vague.
139
11
A NIM A L
P H YS I O LO G Y
(AHL)
ADH
the
or
antidiuretic
hypothalamus
reabsorption
of
hormone
and
water
stored
by
is
a
in
peptide
the
changing
hormone
pituitary
the
produced
gland.
permeability
It
by
controls
of
the
the
collecting
Although you may find
ducts.
When
ADH
is
present,
more
is
reabsorbed
the
collecting
ducts
become
permeable
vasopressin mentioned in books,
to
water
and
into
blood,
therefore
the
urine
you should use the term ADH in
becomes
less
concentrated
and
less
urine
is
produced.
Aquaporins
the exam rather than vasopressin.
are
of
integral
water
membrane
across
collecting
the
ducts,
under
The
of
water
The
highly
of
paste,
marine
and
while
soon
as
this
in
it
is
allows
in
water.
less
as
Uric
to
Birds
retain
ammonia
amount
The
acid
it
the
and
is
is
in
the
the
transfer
kidney
sites
to
the
of
ADH
urea.
less
plasma
need
but
in
with
uric
acid
which
wastes
it
in
is
Aquatic
safely
the
form
animals
they
is
insoluble
water.
where
for
produced.
Ammonia
toxic
Terrestrial
urea
the
nitrogenous
water,
water.
with
correlated
soluble
excrete
into
is
main
acid
but
into
correlates
excrete
uric
toxic
directly
them
in
intracellular
the
habitat.
excreted.
convert
water,
does
animals
and
also
from
channels
expressed
positively
ammonia,
ammonia
mammals
dissolved
is
are
as
ADH.
as
waste
soluble
as
of
animals,
are
serve
They
Henlé
history
urea
excrete
as
in
of
that
move
control
loop
animals
toxic
diluted
they
nitrogenous
by
water,
animals
a
the
evolutionary
excreted
in
the
conservation
type
their
membrane.
where
membrane
length
proteins
of
and
excrete
urine.
Deser t animals prevent water loss in a number of ways. Some live in
burrows, some have thick outer coverings to reduce moisture loss and
some have lower resting metabolic rates or lower body masses to avoid heat
production and water loss. Some produce small amounts of highly
concentrated urine by modulating the amount of ADH.
• Amma is a toxic nitrogenous
vomiting, fever, excessive sweating
waste that is soluble in water.
or increased urination. It can lead
to hear t injury, kidney problems,
• u a is a less toxic nitrogenous
seizures and low blood volume.
waste that is insoluble in water.
• oeyat is excess of water
• uea is a less toxic nitrogenous
in the body, usually caused by over
waste that is soluble in water.
drinking. The symptoms are swelling
• deyat is loss of total body
of cells by excess osmosis.
water. It can be caused by lack of
• hemalyss is the extracorporeal
drinking or by excess diarrhoea or
purication of blood.
Blood
cells,
Doctors
glucose,
can
substances
monitor
that
hemodialysis
the
blood
filtered
matter,
then
or
the
is
returned
the
a
donor
greatly
the
to
the
the
in
the
Kidneys
the
in
the
be
the
expectancy
.
In
The
urinary
machine
that
takes
purified
could
every
few
are
the
failure,
hemodialysis,
kidney
.
kidney
tests.
to
kidney
transplanted
advantages
dialysis
of
dialysis
blood.
can
in
according
event
membrane
malfunctioning
but
inconvenient
working
In
transplanted
system,
life
and
permeable
a
detected
osmoregulation.
patient
replace
are
are
urine.
substances
that
increase
drugs
kidneys
in
patient.
immune
of
the
selectively
the
and
maintain
of
useful
to
hours
to
out
procedure
patient’s
how
present
used
through
keeping
through
can
are
taken
deceased
with
140
is
proteins
be
days
out
from
a
are
waste
also
is
living
risks
rejected
having
and
is
blood
There
not
it
by
to
go
that
it
11 . 4
1 1 . 4
S E X U A L
spermatogenesis
mitosis,
and
cell
Y sl be able t:
and
growth,
oogenesis
two
both
divisions
of
involve
✔
explain
meiosis
formation
and
of
gametes
in
oogenesis.
differentiation.
processes
result
in
in
spermatogenesis
different
numbers
of
and
annotate
oogenesis
gametes
and
amounts
of
in
to
show
of
the
the
seminiferous
stages
of
tubule
gametogenesis.
annotate
diagrams
of
a
mature
sperm
and
egg
cytoplasm.
to
fertilization
diagrams
ovary
with
✔
different
✔
the
spermatogenesis
✔
✔
rEProducTion
R E P R O D U CT I O N
Y sl kw:
✔
SE xuAL
animals
can
be
internal
indicate
their
functions.
or
✔
describe
internal
and
✔
explain
implantation
✔
explain
pregnancy
✔
explain
birth
✔
analyse
external
fertilization.
external.
✔
fertilization
involves
mechanisms
that
polyspermy
.
✔
implantation
of
endometrium
the
is
blastocyst
essential
for
in
the
in
mammals.
prevent
the
continuation
and
and
the
the
hormones
hormones
involved.
involved.
of
graphs
showing
the
correlation
between
pregnancy
.
animal
✔
HCG
stimulates
progesterone
✔
the
placenta
between
✔
✔
the
mother
and
placenta
once
is
Sexual
early
the
and
it
has
reproduction
at
secrete
birth
in
the
development
of
the
young
mammals.
exchange
of
materials
fetus.
are
secreted
by
the
formed.
by
estrogen
to
and
pregnancy
.
progesterone
mediated
involving
ovaries
facilitates
estrogen
birth
the
during
size
positive
and
feedback
oxytocin.
involves
the
development
and
fusion
of
haploid
In Topic 3.3 you studied meiosis
gametes.
Gametes
therefore
need
to
undergo
a
reduction
in
the
number
and in Topic 6.6, hormones,
of
chromosomes
of
the
through
meiosis.
Spermatogenesis
is
the
development
homeostasis and reproduction.
male
gametes
seminiferous
female
and
tubules
gamete
oogenesis
(spermatozoa
both
of
(ovum)
involve
the
and
testes.
occurs
mitosis,
or
sperms)
Oogenesis
in
cell
the
and
is
the
ovaries.
growth,
occurs
two
in
the
formation
of
the
Spermatogenesis
divisions
of
and
meiosis
differentiation.
141
11
A NIM A L
P H YS I O LO G Y
(AHL)
(a)
(b)
primordial germ cell –
primordial germ cell –
2n
2n
divides by mitosis
noitacilpitlum
2n
2n
2n
esahp
2n
2n
2n
2n
divides by mitosis
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
spermatogonia
growth
2n
2n
2n
2n
2n
2n
2n
oogonia
growth
esahp
htworg
primary
primary
2n
2n
spermatocyte
oocyte
secondary
rst meiotic
rst meiotic
spermatocyte
division
division
n
n
rst polar
secondary
esahp noitarutam
n
n
oocyte
body
second meiotic
division (usually
second
n
n
n
meiotic
n
spermatids
occurs after
fertilization)
division
dierentiation
n
n
n
second
ovum
n
additional polar
polar body
bodies—may not be
spermatozoa
formed
Fe 11.4.1.
(a) Spermatogenesis and (b) oogenesis
S AMPLE STudEnT AnS WEr
It is always good to use a diagram
to explain an answer, but in this
Describe the different cell types in the seminiferous tubules that are
case it did not get more marks as
involved in the process of spermatogenesis.
[4]
it was not annotated to add more
This
answer
could
have
achieved
2/4
marks:
information than that given in the
text, therefore it was a waste of
epithelial
cells
(diploid)
precious time.
primary
▲ The
answer
primary
by
scored
a
spermatocytes
meiosis
I
into
mark
spermatocyte
(diploid)
for
dividing
secondary
secondary
spermatocytes.
The
second
mark
spermatocyte
is
(haploid)
for
Sertoli
or
nourishment
nurse
to
cells
these
providing
developing
serto li
cells.
cell
spermatozoa
nished
sperm
▼ The
answer
mentioned
(2n)
are
cells.
could
that
spermatogonia
undifferentiated
The
germ
spermatogonia
T
he
divide
by
mitosis
spermatocytes.
The
cells
into
score
a
mark
answer
spermatocytes
spermatids
for
primary
that
it
is
The
answer
that
spermatids
or
mature
Leydig
or
does
into
it
by
the
most
mature.
spermatocyte
undergoes
the
rst
cell
division
in
I.
Secondary
into
does
meiosis
not
spermatocytes
are
undergoing
the
second
cell
not
to
become
haploid.
II.
mention
Sertoli
sperm
nor
cells
that
T
hey
cells
can
produce
stored.
142
are
nurse
the
spermatozoa
till
they
develop
agella.
differentiate
interstitial
testosterone.
inside
did
division
mention
furthest
secondary
dividing
because
are
primary
meiosis
not
which
mature
A
and
cell(haploid)
have
detach
and
swim
into
the
epididymis,
where
they
are
11 . 4
Fertilization
in
animals
can
be
internal
or
external.
Aquatic
SE xuAL
rEProducTion
animals
• Fe tlzat is the joining of the
often
use
external
fertilization.
Usually
many
eggs
are
fertilized
ovum and the nucleus of the sperm.
because
there
is
a
great
risk
of
loss
by
predation.
In
terrestrial
animals
• An asme eat is the
and
marine
mammals,
fertilization
is
usually
internal.
This
increases
release of antigens and enzymes
the
likelihood
of
success,
so
fewer
organisms
need
to
be
produced.
for binding to the membrane and
In
humans,
fertilization
involves
the
acrosome
reaction,
fusion
of
the
digesting through the ovum’s zona
plasma
membrane
of
the
egg
and
sperm
and
the
cortical
reaction.
pellucida.
The
process
of
fertilization
in
humans
occurs
in
the
oviduct
• A  tal eat is the release
(fallopian
tube).
of cor tical granules to prevent any
additional sperm from fer tilizing the
Eample 11.4.1.
egg, avoiding polyspermy.
The
diagram
shows
an
ovum.
II
a)
b)
Label
to
Outline
of
c)
I
III.
one
function
I.
State
the
which
organ
the
in
ovum
is
I
formed.
III
d)
Explain
by
the
which
germ
process
the
cell
diploid
becomes
a
haploid
ovum.
Solution
a)
I
are
cortical
layer)
b)
and
When
III
are
exocytosis,
enzymes
d)
the
zona
II
of
the
activated.
the
the
zona
cells
ovum
These
the
cortical
pellucida,
is
follicle
producing
of
preventing
c)
are
fertilization
granules
the
granules,
(corona
by
the
vesicles
cortical
granules
not
pellucida
allowing
radiata).
sperm
occurs,
release
reaction.
produce
more
(glycoprotein
their
In
this
to
cortical
reaction,
changes
sperm
the
contents
that
enter
by
the
harden
the
ovum,
polyspermy
.
Ovary
.
The
process
haploid
the
ovary
.
mitosis
by
ovum
The
shortly
after
(growth
meiosis
I
a
a
cells
II
are
in
will
oocyte
ovum
the
which
is
follicles
much
is
the
are
At
only
another
than
into
Each
start
by
of
I
turns
The
into
a
polar
division.
II,
one
body
.
male
No
into
follicle
further
into
a
phase).
secondary
cell
oocyte
called
halts
secondary
When
cell
The
a
smaller
the
of
menstrual
(maturation
fertilization,
meiosis
primary
or
oocytes
prophase
mature
secondary
of
before
primary
them.
to
by
month
each
FSH
in
divide
Just
into
transforms
meiotic
the
fourth
around
meiosis
cell
Upon
undergoes
larger
the
fetus
enter
a
occurs
meiosis.
formed.
one
degenerates.
II.
becomes
the
the
by
cells
stimulated
second
of
oocytes
follicle
other
cell
process
differentiate
completing
the
other
ovary
primary
and
This
Around
oogonia
metaphase
finish
germ
dividing
produced.
by
which
the
phase).
produced,
secondary
and
in
start
follicle
survives;
body
meiosis
oocyte
ovum
oocyte
and
polar
the
These
oocytes
two
cells
diploid
oogenesis.
cells
primary
one
primary
secondary
oocyte
the
birth,
and
of
primary
the
germ
phase).
consists
Of
the
called
(multiplication
development,
cycle,
which
is
the
becomes
result
is
one
the
ovum
sperm.
143
11
A NIM A L
P H YS I O LO G Y
(AHL)
Eample 11.4.2.
The risks to human male
The
diagram
shows
fer tility were not adequately
structure
of
a)
part
a
Middle
the
section
–
full
of
mitochondria
sperm.
Acrosome
assessed before steroids related to
Which
is
involved
in
the
Nucleus
progesterone and estrogen were
acrosome
reaction?
released into the environment as a
b)
result of the use of the female
Which
for
contraceptive pill. Studies have
part
provides
Tail
energy
movement?
shown that males have a lower
Solution
sperm count than expected, and
a)
The
answer
is
D,
as
it
is
showing
the
acrosome.
B,
as
it
is
showing
the
mitochondria.
this could be attributed to the
b)
The
answer
is
presence of estrogen in water
systems.
After
fertilization,
embryo.
The
blastocyst.
require
cells
The
an
month
facilitates
The
the
of
the
to
uterus
involving
inhibit
to
through
is
by
the
of
birth
food.
the
the
it
has
and
of
The
to
during
Estrogen
is
As
the
place
as
The
mother
HCG
to
dilates
baby
by
is
placenta
fetus.
which
are
the
by
secretion
and
pushed
more
the
of
feedback
the
the
helps
secreted
fetus
wall
sensory
produce
of
the
neurons
oxytocin
amniotic
out
through
sac
the
vagina.
Eample 11.4.3.
The
graph
birth
and
shows
the
gestational
relationship
period
in
between
some
offspring
body
mass
at
mammals.
stinu yrartibra
/ doirep lanoitatseg
body mass / arbitrary units
What
A.
B.
does
Body
The
this
mass
longer
graph
and
the
show?
gestational
gestational
period
period,
are
the
not
related.
smaller
the
size
of
the
baby
.
C.
D.
There
is
of
young
the
There
is
number
144
a
a
correlation
at
birth
between
in
correlation
of
offspring
body
mass
and
the
development
mammals.
between
per
gestational
gestation.
period
the
the
stimulates
positive
induces
a
now
in
After
contractions
produced
perceived
called
ovum
and
inhibits
by
the
blastocyst
progesterone
Oxytocin
cervix
the
ball
the
pregnancy
.
inhibiting
gland
the
of
from
pregnancy
,
mediated
are
hollow
control.
early
Hormones
pituitary
a
forming
formed.
the
Progesterone
contractions
take
of
fully
and
thus
Birth
oxytocin.
feedback.
will
is
between
progesterone.
the
form
nutrients
hormonal
gland,
mitosis,
Implantation
placenta
by
to
on
by
continuation
formed.
pituitary
messages
positive
migrate
materials
pregnancy
.
secretion
and
of
for
produced
feeding
progesterone
once
estrogen
broken,
cervix
supply
endometrium.
contract.
send
were
maintained
during
the
uterus
that
is
are
embryo
pregnancy
placenta
oxytocin
the
cells
essential
secrete
the
the
that
exchange
pregnancy
maintain
by
is
of
the
ovary
in
cells
external
endometrium
third
many
and
the
11 . 4
SE xuAL
rEProducTion
Solution
The
correct
mass
at
longer
the
smaller
is
in
shown
a
It
can
longer
period
is
an
the
in
there
is
increasing
be
correlated
no
is
not
graph,
in
the
graph
period
with
correct,
correlation,
a
but
is
but
incorrect
usually
the
that
for
it
can
using
is
larger
body
organism. A
development
be
all
the
seen
the
that
data,
opposite
because
opposite
a
that
greater
as
trendline. Answer B
graph. Answer D
the
seen
gestational
birth. Answer A
organisms
draw
shown
not
at
is C.
means
gestational
young
could
answer
birth
not
one
of
only
of
in
is
what
this
occurs.
Pate pblems f Tp 11
Pblem 1
Pblem 2
A blood test was performed in a laboratory to test blood
The diagram shows some of the muscles in the leg of an
groups. The picture shows some results obtained for
insect.
different blood groups with different antibodies. Where
X
exoskeleton
there are open circles the results are not shown.
tendons
of femur
exoskeleton
of tibia
Y
a) State the function of the exoskeleton in
movement.
b) ()
Label muscles X and Y.
() Muscles X and Y are said to be antagonistic.
Explain the term antagonistic using these
muscles as an example.
) Describe how the contraction of a muscle is
achieved.
a) Determine the results that would be expected when
mixing the given antibodies and blood groups by
completing the table.
Atby
Bl p
at-o
at-A
at-B
no reaction
reaction
no reaction
no reaction
reaction
no reaction
at-AB
A
reaction
reaction
no reaction
no reaction
B
AB
no reaction
O
b) Explain the reason this test needs to be performed
before a blood transfusion.
145
11
A NIM A L
P H YS I O LO G Y
(AHL)
An experiment using a grip strength data logger to
assess muscle fatigue was performed. The maximum
60
gk / ecrof mumixam
50
40
Females
30
800
md lomµ
contractions was measured in females and males.
1000
3–
force exer ted and the endurance after many
/ noitartnecnoc eninitaerc amsalp
Pblem 3
600
400
200
0
0
20
40
60
80
100
120
140
160
Males
3
GFR / cm
20
–1
min
10
a) State the plasma creatinine concentration at a GFR of
0
3
30
40
50
60
70
80
90
100
40 cm
−1
min
endurance / %
b) Describe the relationship between GFR and plasma
creatinine concentration.
a) Calculate the difference in the highest maximum
force exer ted in this experiment between males and
females.
b) The students hypothesized that there was a
difference between males and females in maximum
force and in endurance. Analyse the data to see
) Explain what could be happening to a patient if the
levels of creatinine in blood plasma were high.
Pblem 5
Compare and contrast the blood composition in the
renal ar tery and the renal vein.
whether the hypothesis is suppor ted.
Pblem 6
Pblem 4
Glomerular filtration rate (GFR) describes the flow rate
of fluid that is filtered through the kidney. One method
of determining GFR is to determine the amount of
creatinine in blood plasma. The graph represents the
relationship between plasma creatinine concentration
and GFR.
146
Describe the exchange of materials between the mother
and the fetus in the placenta.
D ATA - B A S E D
12
P R A CT I CA L
( S ECT I O N
You should know:
✔
experimental
variety
✔
of
data
data
communicated
✔
graphical
quantitative
random
human
be
form
are
qualitative
errors
using
a
✔
interpret
are
of
an
and
by
recorded
table
effective
or
way
associated
the
and
✔
identify
graphs.
quantitative
always
caused
a
and
of
✔
data.
using
with
apparatus
✔
systematic
the
procedures
errors
in
experimental
accuracy
qualitative
correctly
and
often
lead
discuss
to
set-up
validity
affects
of
the
precision,
✔
suggest
obtained.
is
to
A of
carry
out
to
maintained
theoretical
past
are
Section
guide.
that
The
in
in
is
can
also
important
going
to
a
be
of
and
tissues,
light
2.
data
form.
independent
variables
trends
and
plots
sketch
graphs
axes.
and
and
their
diagrams.
suggest
analyse
be
Estimation
hypotonic
of
or
Experimental
4.
Separation
of
in
three
questions
students
reality
and
Questions
experiments.
experiments
with
other
remember
can
or
virtually
.
also
that
include
Reference
to
laboratory
impact
on
the
results.
the
accuracy
experiment
and
their
a
evaluate
can
and
be
precision
of
a
improved.
hypotheses
using
evidence.
historical
biological
experiments
producing
well
facts.
on
should
controls
estimate
in
know
It
must
the
actual
or
that
you
may
be
assessed
experimental
these
not
are
the
skills
only
on
from
in
the
IB
experiments
are:
to
drawing
drawings
investigate
of
cells,
and
the
along
the
structure
with
actual
size
of
cells
calculation
of
of
structures
the
shown
micrographs.
osmolarity
and
3.
whether
or
all
errors
included.
microscope
with
of
these
along
to
two
that
of
tested.
magnification
drawings
to
asked
measurements
experiments.
practicals
Use
be
techniques
laboratory
,
specific
3,
will
or
accurate
any
Paper
specified
in
you
skills
the
stress
several
A of
It
are
3,
background
models
There
1.
Paper
experimental
important
be
from
and
how
particular
known
how
graphical
quantities
sources
experimental
the
data
the
experiment
measurement.
✔
Section
and
labelled
unknown
experimental
general
experimental
and
relationships.
uncertainties
✔
In
analyse
tabular
dependent
estimate
and
in
limitations.
experimental
✔
and
their
identify
✔
✔
A)
presented
commonly
the
data
obtained
techniques.
techniques
representing
✔
can
are
in
Q U E ST I O N S
You should be able to:
biological
quantitative
AND
in
hypertonic
tissues
by
bathing
samples
in
solutions.
investigation
of
photosynthetic
a
factor
affecting
pigments
by
enzyme
activity
.
chromatography
.
147
12
D ATA - B A S E D
QUE STIONS
AND
PRACTIC AL
(SECTION
A)
5.
Setting
6.
Monitoring
up
vigorous
7.
(HL
There
of
ventilation
Measurement
many
A of
mesocosms
in
to
try
to
humans
establish
at
rest
sustainability
.
and
after
mild
and
exercise.
only)
are
Section
sealed
of
experiments
Paper
transpiration
and
models
rates
that
can
using
be
potometers.
tested
in
3.
Example 12.1.
The
electron
Zinnia
a)
The
actual
Calculate
your
b)
shows
mesophyll
cells
in
a
young
leaf
of
diameter
the
of
the
central
magnification
of
mesophyll
the
electron
cell
is
20
μm.
micrograph.
Show
working.
Identify
seen
c)
micrograph
elegans.
in
two
an
Outline
an
electron
structures
animal
seen
in
this
cell
that
cannot
be
cell.
advantage
microscope
and
over
a
a
disadvantage
light
of
using
an
microscope.
Solution
a)
You
first
using
For
a
measure
example,
change
this
if
to
micrometres,
You
M
diameter
then
the
diameter
micrometres.
thus
calculate
of
the
central
mesophyll
cell
image
size
actual
size
4
cm
the
is
measures
One
40,000
4
cm,
centimetre
you
is
first
equal
have
to
to
10,000
μm.
magnification
using
the
formula:
=
40, 000
M
the
ruler.
m
=
= 2 , 000
Remember this is a practical
20
m
question, therefore the answer
The
must include structures that can
magnification
of
the
electron
micrograph
is
×
2,000.
be seen at this magnification.
a)
Chloroplasts,
vacuole.
b)
An
cellulose
(Only
advantage
microscope
resolution,
is
of
the
that
it
that
starch
granules
a
microscope
greater
observation
the
cells
artefacts
preparation.
Another
not spend time giving more than
and
required
one.
the
microscope.
need
to
use
of
to
and
large
this
the
killed
from
and
a
higher
of
in
the
A
preparation
specimen
disadvantage
type
light
ultrastructures.
be
resulting
important
over
magnification
the
disadvantage are required, so do
light
the
has
of
training
and
electron
Only one advantage and one
148
slides
is
wall,
needed.)
allowing
disadvantage
the
two
cell
is
the
microscope
cost,
size
compare
to
Example 12.2.
The
graph
shows
the
change
in
length
of
cytoplasm
in
–3
salt solution / mol dm
cells
placed
in
salt
solutions
of
different
concentrations
0
0.1
0.2
0.3
0.4
and
the
0.5
0.6
0.7
0.8
0.9
1.0
0
compared
with
the
solution.
a)
the
b)
State
length
the
cells
in
an
–1
concentration
Determine
of
the
of
salt
percentage
in
the
change
isotonic
in
length
% / htgnel ni egnahc
isotonic
mean
solution.
for
cells
−3
placed
c)
in
Identify
a
0.5
the
mol
dm
dependent
salt
and
solution.
independent
variables
in
–2
–3
–4
–5
–6
–7
this
experiment.
–8
Solution
3
a)
0.22
b)
c)
mol
dm
5%
The
is
independent
measured)
is
variable
the
(what
percentage
is
varied)
change
in
is
the
length
salt
in
concentration
the
diameter
of
dependent
variable
(what
cells.
SAMPLE STUDENT ANSWER
A common reaction occurring in cells is the decomposition of hydrogen
peroxide, which breaks down into oxygen (producing the foam) and
In Example 12.2 par t (b), it
is impor tant to either use the
water. Catalase (also known as hydrogen peroxide oxidoreductase)
negative sign or mention decrease
protects human cells from the toxic effects of hydrogen peroxide, which
in length.
is a powerful oxidizer produced as a biochemical by-product.
Catalase is present in pieces of potato. In an experiment to see the effect
of enzyme concentration on the rate of reaction, discs of potato were
placed in hydrogen peroxide and the height of the foam was measured
Make sure the answer refers
with a ruler. The first conical flask had 5 discs, the second 10 and the
directly to the question.
third 20 potato discs.
a) State two conditions of the potato discs that must be kept
▼ The experiment mentioned
constant.
[2]
here
This
answer
could
have
achieved
0/2
so
marks:
is
does
this
not
of
potato
discs
in
the
replicates
and
time
of
T
o
experiment.
answering
the
question.
refer
score
volume
the
kept constant in this experiment.
achieved
a
of
light
and
the
1/2
have
achieved
of
the
the
each
the
answer
surface
disc
discs
potato.
in
two
▲ The
[1]
could
does
discs
area
must
must
The
directly
.
had
be
be
discs
to
or
the
from
they
must
must
have
not
their
contact
with
conditions
the
peroxide.
needed.)
temperature.
experiment.
answer
it
The
marks:
c) Suggest one reason a conical ask is not appropriate for this
This
experiment
potato
mark
that
same
(Only
amount
the
touching;
surface
T
he
the
as
[2]
be
have
of
to
same. All
b) State two conditions not related to the potato discs that need to be
could
replicates,
correct,
mention
answer
to
not
the
not
This
refer
is
duration
Number
not
answer
1/1
temperature
must
be
kept
constant.
marks:
▼ The light will not affect this
T
he
conical
ask
is
not
straight,
so
the
volume
is
not
experiment
not
constant
all
along
the
height.
A
test
tube
would
have
been
appropriate.
therefore
as
has
correct.
been
Other
more
directly
,
considered
be
conditions
constant
are
concentration
The
volume
asks
need
of
and
to
that
the
be
need
volume
hydrogen
shape
the
of
to
and
peroxide.
the
conical
same.
149
12
D ATA - B A S E D
QUE STIONS
AND
PRACTIC AL
(SECTION
A)
d) Explain the dierences in enzyme-catalysed reactions in the three
conical asks.
This
answer
Each
disc
number
of
enzyme,
the
More
oxygen
why
student
there
reactions
are
of
explains
conical
achieved
approximate
is
different,
three
faster
asks.
the
enzymes
the
2/2
rate
formed,
means
forming
amount
the
T
he
of
substrate
marks:
of
amount
greater
reaction,
they
more
of
the
enzyme
chances
therefore
the
is
of
forming
more
and
If
amount
thus
have
(peroxide)
enzymes.
more
of
more
foam.
clearly
differences
the
an
the
with
is
have
discs
in
collision
▲ The
has
different
foam.
[2]
could
in
the
asks.
e) Predict what would happen if the discs were boiled before the
It
was
important
to
realize
that
experiment.
each
of
disc
represents
enzyme
number
the
and
of
that
discs
amount
of
an
[1]
amount
increasing
means
This
the
answer
could
have
achieved
0/1
marks:
increasing
enzyme.
Boiling
the
potato
discs
will
kill
the
potato,
so
no
reaction
occurs.
▼ The
answer
the
potato
the
catalase
rate
of
will
be
is
discs
in
too
would
them,
reaction
vague.
to
be
Boiling
denature
causing
nil,
so
the
no
foam
formed.
Example 12.3.
Melvin
Calvin,
James
Bassham
and
algae in nutrient media
Andrew
Benson
independent
an
reactions
experiment
Calvin,
discovered
green
of
similar
algae
to
the
light-
photosynthesis.
that
performed
(Chlorella)
were
In
air and carbon
dioxide
by
placed
light
within
a
lollipop
was
thin
container)
added
intervals
into
hot
transparent
to
the
the
and
container
radioactive
apparatus.
samples
methanol.
of
At
algae
Samples
carbon-14
10-second
were
were
dropped
analysed
valve that can be
using
two-dimensional
which
separates
out
paper
the
light
(the
chromatography
,
different
carbon
syringe for injecting
14
radioactive
sample of algae at
hydrogencarbonate
intervals
compounds.
The
results
showed
carbon
of
these
experiments
at lollipop vessel
that
carbohydrates
reactions
of
dioxide
during
the
was
converted
to
light-independent
photosynthesis.
hot methanol
a)
Determine
a
transparent
lollipop
b)
Suggest
and
not
for
the
dark
use
of
glass
in
the
vessel.
one
methanol.
150
reason
reason
for
the
use
of
hot
C as
opened to remove
c)
The
10
substances
seconds
found
and
at
30
at
different
seconds
times
that
are
were
recorded
missing
Time / seconds
Radioactive molecules
0
carbon dioxide
in
the
in
a
table.
Identify
the
substances
detected
at
table.
10
20
triose phosphate
glycerate 3-phosphate
30
40
glycerate 3-phosphate
triose phosphate
glucose
ribulose bisphosphate
A mathematical
model
wa s
ma de
to
p rov i d e
140
a
high CO
of
the
effects
of
varia tion s
in
stinu bra / noitalimissa nobrac
description
CO
2
concentrations
increasing
line
on
th e
rubisco
indicates
the
a ss imila tion
en z y me
a vera ge
of
c a r bon
con centr a t i ons .
rubisco
at oms
Th e
at
d as h e d
con c e n t r a t i on
in
algae.
d)
Experimental
factor
at
low
results
CO
show
levels,
that
but
rubisco
not
when
is
the
the
2
concentration
is
limiting
CO
2
high.
Suggest
with
reasons
2
120
low CO
2
100
80
60
40
20
whether
0
this
mathematical
model
matches
the
experimental
0
100
200
400
300
500
results.
enzyme concentration / arb units
Solution
a)
Transparent
needed
for
reduced
glass
the
NAD
allows
light
production
(NADH
)
of
to
pass
through.
hydrogen
and
ATP
ions
required
to
in
Light
is
produce
the
light-
2
independent
b)
Hot
c)
At
30
d)
methanol
10
seconds
seconds
The
reactions.
graph
is
used
to
glycerate
glycerate
shows
stop
chemical
3-phosphate
3-phosphate,
that
at
low
CO
reactions
appears
triose
or
to
(some
phosphate
concentrations,
kill
algae.
carbon
and
as
dioxide
glucose
the
might
might
enzyme
be
still
remain)
and
at
found.
concentration
increases,
the
carbon
2
assimilation
high
CO
increases,
matching
concentrations,
which
the
experimental
does
not
match
results.
the
It
also
shows
experimental
that
results.
At
the
same
enzyme
occurs
for
concentrations
2
greater
than
(matching
CO
normal
the
for
the
experimental
concentrations,
not
algae,
the
results)
matching
increase
but
the
it
also
in
enzyme
has
no
experimental
concentration
effect
on
the
does
affect
assimilation
of
the
assimilation
carbon
for
low
results.
2
151
12
D ATA - B A S E D
QUE STIONS
AND
PRACTIC AL
(SECTION
A)
SAMPLE STUDENT ANSWER
In an experiment to determine the effect of diet on response to leptin,
mammals were fed a control diet or a high fructose diet for 8 months.
One group was injected with leptin while the other remained as a control.
The food intake of the different groups was monitored over a period of
48 hours.
800
700
Jk / ekatni doof latot
600
500
no leptin
400
leptin
300
200
100
0
control
high fructose
diet
▼ This
does
question.
describe
It
the
injection;
not
was
answer
the
important
effect
of
therefore
a) Distinguish between the eect of leptin injection on the to tal food
to
intake in the mammals fed the control diet and the mammals fed the
leptin
the
high fructose diet.
This
had
to
compare
without
what
injection
injection
and
expected
was
no
answer
effect
(statistically
in
food
group
in
intake
compared
was
diets.
that
in
the
to
no
achieved
0/1
marks:
injection
given
to
the
control
diet
group
resulted
food
intake
compared
to
that
of
the
high
fructose
diet
leptin
b) Discuss the implications of these results for recommending leptin
leptin.
This
answer
From
marks
answer
because
scored
it
on
effectiveness
mentioned
diet
and
mammals
that
may
of
leptin
results
not
be
The
awarded
obese
diet,
marks
people
then
appetite
mark
for
the
it
will
and
saying
a
not
that
high
these
to
suppressing
those
a
control
diet,
it
implies
that
[2]
marks:
leptin
would
be
benecial
as
it
lowered
food
intake
compared
not
injected
with
leptin.
However
,
on
a
high
fructose
leptin
would
in
fact
increase
intake,
suggesting
that
its
that
if
effectiveness
on
these
mammals
is
debatable.
Furthermore,
fructose
obese
will
appetite,
also
leptin
injections
have
a
different
effect
on
humans
as
they
these
mammals,
with
previous
experiments
suggesting
some
suppress
appetite.
humans
have
gained
weight
when
injected
leptin.
c) Leptin is a hormone. Hormones are chemicals produced in one par t of
the body that have an eect in another par t of the body. State the tissue
that produces leptin in humans.
This
answer
Adipose
could
have
achieved
[1]
1/1
marks:
tissue.
This type of question is about
scientific research and its
d) State the target that leptin normally acts on.
biological background rather than
This
answer
could
experiments you might have done
Hypothalamus.
in the laboratory.
152
do
people
on
with
it
2/2
for
suppress
for
results
achieved
that
same
scheme
for
have
have
depends
diet,
humans.
these
could
full
in
the
diet
group.
injections as an appetite suppressant for humans.
▲ This
in
but
reduction
with
leptin
lower
diet
control
injected
have
The
there
fructose
signicant)
when
could
with
both
with
answer
happened
T
he
leptin
[1]
answer
have
achieved
1/1
marks:
[1]
Example 12.4.
Non-pathogenic
culture
two
E.
coli
bacterial
media
at
differen t
examples
of
th e
pH
res u lts
colonies
va lues.
w ere
Th e
obta ined.
grown
Petri
E ac h
d ot
on
d i sh e s
is
one
s h ow
bact e r i a l
colony.
The
table
standard
shows
the
deviation)
mean
number
measured
pH
in
of
10
colonies
replicates
(plus
at
or
each
minus
pH
one
value.
Number of colonies
4
11 (±2)
5
138 (±4)
6
361 (±7)
7
558 (±11)
8
310 (±51)
9
191 (±155)
10
121 (±21)
a)
Identify
the
b)
Identify
a
c)
State
d)
Describe
e)
Suggest
independent
variable
that
variable
needs
to
in
be
this
experiment.
controlled.
In (b) just mentioning temperature
the
optimum
pH
a
to
for
the
growth
of
E.
coli
would not score a mark , as it is
method
count
the
number
of
colonies
in
the
dishes.
the temperature of the incubator
or at which they were grown that
with
a
reason
which
results
are
not
reliable.
matters and not the temperature
Solution
when the colonies are counted.
a)
The
independent
b)
V
olume
of
bacteria
grown;
(Only
bacterial
should
be
amount
one
variable
of
is
culture
even;
the
pH
placed
in
on
temperature
growth
medium
the
the
at
growth
dish;
which
used;
time
media.
spreading
bacteria
left
in
of
were
incubator.
needed.)
Although pH = 7 might seem
c)
pH
=
d)
The
7
(or
close
to
this
value).
the most obvious answer, as the
1
×
dishes
1
and
cm).
the
e)
of
be
divided
colonies
value
squares.
are
that
The
is
into
quadrats
counted
in
obtained
divisions
example
squares
is
can
(for
chosen
multiplied
also
be
by
shown
squares
of
at
number of colonies is the greatest,
randomly
the
as
the optimum should really be
total
determined by drawing the curve.
sections
in
chart.
Results
not
The
mean
number
pie
can
a
In the exam students are not
expected to draw graphs.
pH
reliable.
=
9
This
have
a
means
large
that
standard
there
is
a
deviation,
great
therefore
variability
are
between
replicates.
153
12
D ATA - B A S E D
QUE STIONS
AND
PRACTIC AL
(SECTION
A)
Example 12.5.
In
a
an
experiment
strong
beaker
sugar
of
water.
recorded.
The
a)
State
the
b)
Determine
c)
Explain
to
demonstrate
solution
The
coloured
apparatus
experiment
was
independent
two
the
movement
was
food
left
for
repeated
variable
conditions
reason
the
with
in
that
coloured
need
of
molecules
was
several
with
this
water
dye
attached
minutes
different
through
to
a
and
sugar
osmosis,
clear
the
Visking
capillary
height
of
concentration
tube
tubing
and
coloured
containing
submerged
liquid
in
the
in
a
tube
was
solutions.
experiment.
to
be
goes
kept
up
the
constant
in
this
experiment.
tube.
Solution
a)
The
independent
b)
Conditions
beaker,
that
c)
Osmosis
that
the
is
of
and
the
equalizes
water
need
diameter
temperature
variable
passes
pressure
be
glass
the
kept
the
concentration.
constant
time
of
the
two
the
size
on
either
an
Visking
left,
across
side.
increase
solution
is
tube
(and
type),
environmental
volume
of
conditions
water
such
in
as
needed.)
molecules
causes
coloured
of
tube
conditions
solvent
This
are
Visking
concentrations
tubing.
forcing
sugar
(Only
movement
solute
into
the
tube,
pressure.
net
and
to
is
up
As
in
the
a
semi-permeable
the
the
sugar
volume
capillary
membrane
solution
of
is
liquid
in
more
the
in
a
direction
concentrated,
tubing,
increasing
tube.
Example 12.6.
A model
a)
showing
Identify
the
modelled
b)
Suggest
could
the
c)
of
d)
error
in
contracted
state
of
the
sarcomere
was
made
by
students.
blue.
structure
the
in
Identify
and
that
by
balls.
muscle
shown
pale
represented
silver
Describe
relaxed
structure
in
one
be
the
contraction
sarcomeres
the
with
this
as
model.
a
reason
one
model.
Solution
a)
Z-line
b)
Myosin
heads
or
c)
Myosin
forms
thick
actin
filaments
contraction,
the
d)
They
are
should
moved
represented.
154
also
towards
all
be
(Only
pull
in
the
tails.
sarcomere
are
model.
error
is
the
The
out.
myosin
In
the
needed.)
myosin
length
of
heads
the
the
centre
total
of
should
be
contracted
model,
the
too
short
with
using
the
muscle
heads
is
(silver)
cross-bridges
towards
myosin
fibre
The
creating
filaments
muscle,
spread
The
(pink).
connected
actin
the
this
evenly
one
the
They
along
errors
their
ATP
in
blue).
heads
stretch
several
or
fibres
(dark
these
filaments
There
calcium
in
is
During
to
the
thin
muscle
shortening
it.
As
shortened.
contact
to
attached
sarcomere,
myosin
respect
are
ATP
.
the
with
heads
actin
the
actin
should
fibre.
filaments.
have
Troponin
is
not
Example 12.7
.
A model
of
lung
ventilation
was
made
into
the
using
a
plastic
bottle,
straws
and
bung
balloons.
A hole
was
drawn
a)
State
the
muscle
represented
b)
State
the
structure
by
lid
the
of
the
bottle
to
pass
the
straw.
balloon
bell jar
rubber.
(lung)
represented
by
the
straw
with
its
top
part
outside
the
bottle.
c)
Explain
what
happens
when
the
rubber
is
pulled
out
in
terms
of
lung
ventilation.
Solution
a)
Diaphragm
b)
Trachea
c)
The
rubber
being
diaphragm.
cavity
increases,
atmospheric
the
alveoli
balloons
air.
in
to
pulled
When
the
out
lowering
This
the
represents
diaphragm
the
causes
lungs.
In
pressure
air
this
the
contraction
contracts,
to
in
enter
model,
the
the
lungs
through
pulling
of
volume
the
compared
the
the
the
of
airway
rubber
thoracic
to
passages
will
rubber
the
cause
to
the
inflate.
Practice problems for Chapter 12
Problem 1
The electron micrograph shows human DNA from a
a) Estimate the length of one strand of DNA in the
replication bubble.
cancer cell, showing a stage of DNA replication. The
b) John Forster Cairns demonstrated by
strand of DNA has a replication bubble, where the
autoradiography that the DNA of bacteria was a single
DNA has unwound into two single strands forming a
molecule that replicated at two replicating forks
Y-shaped molecule termed a replication fork . It is here
(unlike humans that have only one) at which both
that daughter strands form as the parent DNA acts as a
new DNA strands are being synthesized. Describe
template for the construction of a new matching strand
Cairns’ technique for measuring the length of DNA
in DNA replication.
molecules by autoradiography.
0.1
μm
155
12
D ATA - B A S E D
QUE STIONS
AND
PRACTIC AL
(SECTION
A)
Problem 2
Problem 3
The picture shows a thin layer chromatogram of an
Glass jars containing cultures of Chlorella vulgaris
extract of leaves of annual meadow grass (Poa annua).
microalgae were used as mesocosms. The carbon
Plastic sheets were coated with silica gel. A drop of
dioxide released from the combustion of the waste was
extract was spotted at the bottom of the sheet. The
pumped into the jars to promote photosynthesis and
sheet was then placed in a beaker of solvent
therefore growth of the algae. The jars were kept at 25°C.
(75% acetone and 25% petroleum ether).
a) State one other condition required in this mesocosm.
b) Identify, with a reason, whether this is an open or
solvent front
closed mesocosm.
c) One of the jars was kept at a temperature of 30°C.
Suggest a difference that could be seen in this jar
carotene
with respect to the rest of the jars.
Problem 4
Describe how the ventilation rate of someone breathing
pheophytin
chlorophyll A
chlorophyll B
carotenoids
a) Identify the most soluble pigment.
b) Calculate the R
for pheophytin. Show your
f
working.
c) Suggest what would have happened to the pigments
if the solvent had been different.
156
can be monitored.
N E U R O B I O LO GY
A
A . 1
B E H AV I O U R
N E U R A L
D EV E L O P M E N T
Y  knw:
✔
the
neural
formed
tube
by
elongation
of
Y  e ae t:
embryonic
infolding
of
the
of
chordates
ectoderm
is
followed
✔
describe
✔
annotate
neurons
in
✔
the
are
immature
✔
an
axon
✔
neurons
to
some
axons
reach
other
✔
a
✔
synapses
produced
by
differentiation
used
migrate
from
each
chemical
extend
parts
developing
neural
of
an
embryonic
animal
tissues
model,
in
during
neurulation
are
the
not
a
nal
immature
✔
explain
✔
state
neural
pruning
pruning.
location.
neuron
in
that
cultural
acquisition
stimuli.
beyond
of
neuron
that
to
of
a
experiences,
language,
including
results
in
the
neural
pruning.
the
neural
tube
to
✔
describe
✔
outline
the
plasticity
of
the
nervous
system.
body
.
forms
used
multiple
do
not
synapses.
how
promote
persist.
✔
describe
involves
the
loss
of
events
such
reorganization
how
embryonic
✔
as
tube.
grows
response
diagrams
tube.
initially
neural
neurulation.
by
Xenopus,
✔
AND
as
of
incomplete
neural
tube
strokes
brain
closure
can
may
function.
cause
of
the
spina
bida.
unused
neurons.
✔
the
plasticity
change
The
with
of
the
nervous
system
allows
it
to
experience.
modification
of
neurons
starts
in
the
earliest
stages
of
In Topic 6.5 you studied neurons
embryogenesis
and
continues
to
the
final
years
of
life.
The
neural
tube
and synapses.
of
by
embryonic
elongation
chordates
of
the
is
formed
by
infolding
of
ectoderm
followed
tube.
Xenopus is a genus of African frogs that are commonly known as the
African clawed frogs. Their worldwide use in research is due to the fact
that it is easy to obtain large amounts of their eggs inexpensively, which are
easily manipulated. The embryonic tissues of Xenopus are a good model for
human disease because most essential cellular and molecular mechanisms
are the same as in humans. Nematode worms (Caenorhabditis elegans), fruit
• Neatn is the development
of the dorsal nerve cord by the
infolding of the neural plate.
• Nea pnng is the elimination
of unused neurons or synapses.
flies (Drosophila melanogaster), zebrafish (Danio rerio), chickens (Gallus
• Nea patty is the ability of
gallus) and mice (Mus musculus) have also been used to discover the
molecular mechanisms fundamental to life, thereby providing a shor tcut to
understanding human biology.
the brain to change in time by gain
or loss of neurons, par ts of neurons
or synapses.
157
A
N E U R O BI O LO G Y
AND
BE H AV IO U R
Exape A .1.1.
The
diagram
(Xenopus
shows
the
stages
of
neurulation
during
the
first
two
weeks
in
the
African
clawed
frog
laevis).
A
B
dorsal surface
X
C
endoderm
gut cavity
a)
b)
c)
Label
A to
Annotate
Suggest
C.
the
what
diagram
to
happens
in
explain
what
humans
if
is
occurring
neurulation
at
X.
does
not
occur
properly
.
Solution
a)
and
b)
lateral edges of neural plate
neural plate
join together forming a tube
neural groove
dorsal surface
neural tube
endoderm
gut cavity
c)
Incomplete
closure
of
the
embryonic
neural
tube
Modification
and
by
chemical
parts
Neural
so
pruning
acquisition
Neurons
of
a
is
neural
Some
earliest
life.
tube.
from
Immature
extend
the
language,
via
that
brain
of
unused
Cultural
result
these
plasticity
.
of
loss
stimuli.
are
in
used
a
lot
This
such
so
not
as
are
used
to
a
response
tube
multiple
there
are
in
neural
to
reach
synapses.
more
do
not
stimuli.
neurons,
experiences,
neural
neurons.
Events
that
between
the
produced
migrate
neuron
forms
synapses,
embryogenesis
initially
neurons
beyond
neuron
of
are
immature
Synapses
interference
stages
Neurons
each
multiple
neurons.
less
synapses
reorganization
the
of
axons
form
involves
faster
neural
in
years
grows
bifida.
body
. A developing
between
and
accessed
axon
between
there
interference
system
the
the
spina
starts
final
neurons
connections
persist,
in
stimuli.
of
Developing
is
the
location. An
other
cause
neurons
to
differentiation
final
to
of
continues
can
again
reducing
including
the
pruning.
are
reinforced
process
strokes
gives
may
so
the
information
nervous
promote
function.
SAMPLE STUDENT ANSWER
The synaptic density is the number of synapses per unit volume. The
graph shows the synaptic density for a human from bir th to 4 years old.
7
01 / ytisned
8
citpanys
mm
3–
6
5
4
3
2
1
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52
age / months
a) Determine the age when the synaptic density is highest.
This
answer
Remember to write the units,
8
otherwise no mark is given.
158
months.
could
have
achieved
1/1
marks:
[1]
A .2
ThE
humAN
brAiN
) Explain how the synaptic density decreases after the age determined
in (a).
This
[3]
answer
During
neural
neurons
T
here
are
is
could
achieved
pruning,
through
also
also
have
loss
of
to
the
A . 2
brain
by
T H E
are
which
dendrites
T
his
marks:
they
apoptosis,
eliminated.
damage
if
3/3
can
and
is
used,
branches.
happen
or
there
programmed
axon
also
strokes
not
by
due
to
chemical
H U M A N
the
anterior
form
the
part
of
cell
loss
of
death.
Synapses
old
age,
abuse.
B R A I N
Y  e ae t:
Y  knw:
✔
is
the
neural
tube
expands
✔
to
identify
parts
diagram
brain.
or
medulla
✔
different
✔
the
parts
of
the
brain
have
specic
nervous
system
processes
in
the
mainly
in
the
brain
body
using
the
outline
cerebral
the
cortex
brain
and
is
forms
more
a
larger
highly
the
than
in
other
photograph,
including
cerebellum,
the
hypothalamus,
gland
and
cerebral
hemispheres.
the
functions
of
the
visual
cortex,
area
brain
and
nucleus
with
accumbens
specic
as
areas
functions.
proportion
developed
describe
swallowing,
breathing
and
heart
rate
in
as
humans
a
stem.
✔
of
in
brain
centres
of
✔
brain
the
controls
Broca’s
located
of
roles.
✔
involuntary
the
oblongata,
pituitary
autonomic
of
scan
examples
of
activities
coordinated
by
the
animals.
medulla.
✔
the
human
cerebral
cortex
has
become
enlarged
✔
principally
by
an
increase
in
total
area,
analyse
brain
extensive
folding
to
accommodate
it
correlations
within
size
✔
describe
cerebral
hemispheres
are
responsible
different
Angelman
inherited
the
in
condition
order
size
and
syndrome
that
is
as
a
genetically
diagnosed
from
for
characteristically
higher
body
animals.
the
cranium.
✔
between
with
abnormal
patterns
on
an
functions.
electroencephalogram.
✔
the
left
cerebral
hemisphere
receives
sensory
✔
input
from
sensory
receptors
in
the
right
explain
brain
of
the
eld
body
in
and
both
the
eyes,
right
and
side
vice
of
the
versa
for
the
✔
right
explain
lesions
brain
the
left
cerebral
contraction
vice
versa
in
for
hemisphere
the
the
right
right
side
controls
of
the
use
of
the
pupil
of
animal
reex
to
evaluate
damage.
visual
hemisphere.
✔
the
side
the
use
and
fMRI
to
experiments,
identify
the
role
of
autopsy
,
different
parts.
muscle
body
✔
and
discuss
how
depending
hemisphere.
the
on
denition
local
and
of
living
national
varies
laws
and
culture.
✔
brain
The
metabolism
brain
and
spinal
requires
cord
large
are
energy
mainly
inputs.
formed
of
neurons.
These
In Topic A.1 you studied the
neurons
communicate
with
other
neurons
through
synapses.
Synaptic
formation of the neural tube.
communication
functional
The
cerebral
The
outer
In
the
body
neurons
circuits
hemispheres
part
of
posterior
brainstem
between
neural
and
through
the
part
the
the
that
form
cerebral
of
the
the
to
the
cerebral
The
establishment
sensory
largest
part
hemispheres
cerebellum.
spinal
leads
mediate
is
and
of
is
the
called
hemispheres
brain
motor
human
the
we
brain.
cerebral
can
connected
of
processing.
to
find
the
cortex.
the
rest
of
the
cord.
159
A
N E U R O BI O LO G Y
AND
BE H AV IO U R
Exape A .2.1.
The
diagram
shows
a
human
brain.
The par t labelled as A could
A
be cerebral cor tex or cerebral
a)
Label A to
C
shown
in
the
of
the
diagram.
hemisphere. If in doubt, it is better
to be as precise as possible.
b) Outline
the
function
Broca’s
You could have answered:
area
and
nucleus
accumbens.
cerebral cor tex of the cerebral
hemispheres.
c)
On
the
diagram
label
the
visual
B
C
cortex.
Solution
a)
A:
cerebral
b) The
Broca’s
brain
• The ea ngata controls
cortex,
with
area
B:
is
a
medulla
region
functions
breathing and reexes such as
processing.
swallowing, coughing, sneezing and
human
vomiting.
involved
The
brain
in
in
linked
nucleus
associated
laughter,
oblongata
the
to
frontal
speech
accumbens
with
fear,
and
lobe
cerebellum.
of
the
production
is
a
pleasure
aggression
C:
group
and
and
of
human
and
language
cells
reward.
It
in
is
the
also
addiction.
• The eee controls of
c)
Area
of
the
brain
above
the
cerebellum
shown
and
labelled.
equilibrium and posture.
• The yptaa regulates
metabolic processes and
The
autonomic
body
using
nervous
centres
system
located
controls
mainly
in
involuntary
the
brain
processes
stem.
The
in
the
autonomic
hormones.
system
• The pttay gan secretes
many
hormones.
the
• The eea epee are
involved in learning and memory.
is
divided
opposing
“fright
situations,
“rest
and
heart
and
flight”
while
the
digest”.
rate
into
while
parasympathetic
functions.
system,
and
sympathetic
as
it
example,
sympathetic,
system
prepares
parasympathetic
For
the
The
the
the
system
system
body
for
it
have
dangerous
the
system
slows
which
considered
prepares
sympathetic
parasympathetic
is
body
to
accelerates
the
down.
• The a  tex processes the
light images perceived in the eyes.
• ba’ aea controls speech.
The
cerebral
forms
a
humans
cortex
larger
than
is
the
outer
proportion
in
other
of
layer
the
animals.
of
brain
The
the
and
cerebral
is
human
more
hemispheres;
highly
cerebral
it
developed
cortex
has
in
become
• The ne aen is the
enlarged
principally
by
an
increase
in
total
area,
with
extensive
folding
pleasure reward centre.
to
accommodate
it
within
the
cranium.
Exape A .2.2.
The
The neuroscientist Wilder
graph
mass
Penfield experimented on
in
shows
some
the
relationship
between
body
mass
and
brain
mammals.
6
human brains, trying to identify
5
the areas responsible for epilepsy.
brain cor tex using a small electric
current and asked his patients
what they felt. With all the
information gathered, he mapped
gk gol / ssam niarb
He stimulated the surface of the
4
3
2
the areas of the cor tex that control
different par ts of the body.
1
Penfield developed a homunculus,
0
a car toon drawing of a human
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
body, sized propor tionally to the
body mass / log kg
amount of brain space devoted to
processing motor functions, or
a)
Describe
the
relationship
between
body
mass
and
brain
mass.
sensory functions, for different
b) Discuss
whether
the
data
provides
par ts of the body.
are
160
more
intellectually
developed.
evidence
that
larger
animals
A .3
PEr cEPTioN
of
s T im u li
Exape A .2.3.
Solution
a)
There
is
mass:
the
a
positive
correlation
between
body
mass
and
brain
Explain
larger
the
animal,
the
larger
the
contralateral
brain.
processing
b)
This
graph
does
not
provide
any
information
of
images.
about
Solution
development.
The
positive
correlation
between
body
mass
The
and
brain
mass
does
not
mean
that
the
organism
is
left
cerebral
receives
developed,
as
many
large
animals
that
have
a
large
brain
as
developed
as
smaller
organisms
that
have
a
small
is
determined
by
the
infolding
of
the
of
which
increases
the
brain
surface
area:volume
resonance
of
the
some
imaging
brain
functions
is
can
energy
,
the
of
to
meet
process
the
up
vessels
called
by
these
a
many
large
that
areas,
areas
energy
supply
rate
of
back
used
or
brain
cells
with
The
shows
P E R C E P T I O N
receptors
the
right
the
the
visual
right
and
the
optic
right
visual
even
field
versa
hemisphere.
processing
chiasma,
brain
field
vice
is
due
where
processes
from
and
the
vice
left
versa.
more
which
it
brain
for
require
lactate
use
the
the
energy
.
generates
that
this
aerobically
O F
in
detect
S T I M U L I
Y  e ae t:
changes
in
the
environment.
✔
explain
the
rods
of
eyes,
information
that
can
glucose
supply
Y  knw:
✔
the
the
specific
brain
they
glycolysis
which
the
stroke.
means
to
in
and
cycle.
A . 3
✔
the
Although
astrocytes
neurons,
a
to
identification
imagery
neurons
requirements.
to
the
that
as
inputs.
undergoes
in
body
Contralateral
magnetic
Although
and
such
the
these
cells
cells
functional
functions.
certain
energy
sent
be
disturbance
glial
glial
extra
is
to
and
can
specific
over
metabolic
generates
Krebs
spread
requires
cells
taken
in
following
high
lesions
scanning
attributed
are
blood
other
Glucose
ATP
be
itself
by
(fMRI)
involved
metabolism
served
help
part
activities
reorganize
Brain
experiments,
side
both
for
animal
receptors
the
ratio.
in
Nowadays,
from
cerebral
right
cortex,
input
brain.
side
Development
sensory
are
sensory
not
hemisphere
more
and
cones
are
photoreceptors
located
the
many
detection
different
of
chemicals
olfactory
in
the
air
by
receptors.
in
retina.
✔
label
a
diagram
of
the
structure
of
the
human
to
show
eye.
✔
rods
and
light
cones
differ
intensities
and
in
their
sensitivities
to
wavelengths.
✔
annotate
types
✔
bipolar
cones
✔
✔
cells
to
send
ganglion
cells
the
optic
nerve.
the
information
from
both
visual
the
ganglion
from
rods
messages
to
the
brain
via
✔
explain
✔
describe
of
from
the
right
is
sent
to
and
vice
versa.
the
eld
left
of
part
vision
of
✔
the
structures
in
the
amplify
sound.
sensory
hairs
middle
ear
transmit
and
specic
✔
impulses
hair
the
cochlea
detect
retina
in
which
light
the
cell
moves.
sounds
how
a
is
red–green
normal
label
light
detected
of
the
eye.
colour-blindness
trichromatic
diagram
by
the
as
a
variant
vision.
structure
of
the
human
explain
how
sound
waves
are
detected
by
the
of
explain
the
use
of
cochlear
implants
in
deaf
patients.
wavelengths.
caused
transmitted
✔
of
the
ear.
✔
✔
of
direction
ear.
✔
✔
the
and
cells.
send
eyes
cortex
impulses
diagrams
and
cells
in
movement
to
the
the
of
by
sound
brain
perception
via
the
semicircular
the
are
auditory
canals
nerve.
detect
head.
161
A
N E U R O BI O LO G Y
AND
BE H AV IO U R
Living
In Topic 3.4, you studied the
inheritance of traits.
the
organisms
environment.
chemoreceptors,
olfactory
have
Humans’
in
the
that
sensory
thermoreceptors
receptors
chemicals
receptors
in
the
nose
are
are
able
receptors
and
to
detect
are
changes
in
mechanoreceptors,
photoreceptors.
chemoreceptors,
as
For
they
example,
detect
air.
SAMPLE STUDENT ANSWER
• meaneept detect
Odorants are very small molecules with varied chemical formulae.
mechanical forces and movement.
Volatile odorants that enter the nose are detected by millions of
olfactory neurons. The discriminatory capacity of the mammalian
• ceeept detect
olfactory system is so specic that a vast number of volatile chemicals
chemicals.
are perceived as having distinct odours.
• Teeept detect
The table shows the response of olfactory receptors to dierent
dierences in temperature.
substances. Acids and alcohols with the same number have the same
• Pteept detect light.
formula except for the rst carbon, where one has an acid and the other
an alcohol group.
cea
oaty eept
t
(ant)
1
2
3
4
5
6
7
8
9
10
acid 1
alcohol 1
acid 2
alcohol 2
acid 3
alcohol 3
acid 4
alcohol 4
Key
response
no response
a) State the name given to the type of receptor the olfactory receptors
belong.
This
▼ This
answer
is
too
answer
is
answer
could
have
achieved
0/1
marks:
vague—the
a)
correct
[1]
Smell
receptors.
chemoreceptors.
) Identify the receptor that:
()
[2]
detects most odorants
() does not perceive the odorants shown.
This
answer
could
have
achieved
2/2
marks:
Remember that in the options the
examiners are expecting more in-
(i)
4
depth knowledge of the topics.
(ii)
9
) Identify the chemical that is the least perceived by these
receptors.
This
▲ Only
two
response
to
receptors
this
show
chemical.
answer
[1]
could
have
achieved
1/1
marks:
a
Alcohol
2
) A slight alteration of the odorant will be perceived as a completely
dierent smell. Comment on this statement referring to the results
obtained in this experiment.
162
[2]
A .3
This
answer
could
have
achieved
2/2
PEr cEPTioN
▲ Recognizing
substance
with
the
same
chemical
formula
as
ones
scored
from,
changing
the
rst
carbon
group
from
acid
(for
example,
acid
1
and
alcohol
1),
is
perceived
different
receptors,
thus
smelling
by
by
If
a
change
in
group
can
be
then
this
is
a
true
acid
and
number
one
mark.
to
be
were
The
compared
the
were
fact
that
perceived
different
second
receptors
mark.
Another
completely
considered
a
for
slight
could
have
commenting
this
alteration,
the
same
had
completely
mark
different.
that
substances
gained
completely
that
the
to
both
alcohol
with
another
,
the
apart
s T im u li
marks:
alcohol
A
of
change
was
been
that
not
scored
perhaps
only
a
slight
statement.
alteration.
The
eye
is
organism
from
the
organ
with
both
that
vision.
eyes
is
sent
can
The
to
receive
light
information
the
left
part
stimuli
from
of
the
the
and
right
visual
provide
field
cortex,
of
the
vision
and
vice
versa.
Exape A .3.1.
The
a
drawing
cross
shows
section
human
of
the
eye.
a)
Label
I
to
b)
Outline
IV
.
II
the
function
I
of
I.
IV
c)
State
the
the
name
tissue
of
containing
In exams you may be asked to
photoreceptors.
III
Solution
a)
I:
lens;
optic
identify some par ts of the eye
including the sclera, cornea,
II:
retina,
nerve;
IV:
III:
conjunctiva, eyelid, choroid,
cornea.
aqueous humour, pupil, lens, iris,
vitreous humour, retina, fovea,
b)
The
function
of
the
lens
is
to
bend
the
light
rays
so
they
are
optic nerve and blind spot.
focused
c)
on
the
retina.
cones
are
photoreceptors
Retina
Rods
and
located
in
the
retina.
Rods
and
• r are photoreceptors that
cones
differ
in
their
sensitivities
to
light
intensities
and
wavelengths.
detect monochromatic images.
Impulses
cells
they
travel
pass
from
to
the
rods
and
ganglion
cones
cells
to
that
bipolar
carry
cells.
the
From
the
information
bipolar
to
the
• cne are photoreceptors that
detect colour.
brain
through
the
optic
nerve.
• bpa e send the impulses
from rods and cones to ganglion
Exape A .3.2.
cells.
The
diagram
shows
part
of
the
retina
of
the
human
eye.
• Gangn e send messages to
the brain via the optic nerve.
D
A
B
C
a)
Label
parts
A to
D
in
the
diagram.
163
A
N E U R O BI O LO G Y
AND
BE H AV IO U R
b)
Draw
c)
Annotate
from
d)
an
the
Describe
arrow
the
eye
showing
diagram
to
the
to
direction
show
the
of
light.
direction
of
the
nerve
impulse
brain.
red–green
trichromatic
the
colour-blindness
as
a
variant
of
normal
vision.
Solution
a)
A:
bipolar
b)
Arrow
from
left
c)
Arrow
from
ganglion
d)
Trichromacy
retina,
cell;
the
the
properly
these
colours.
close
to
cell;
C:
cone;
D:
rod
right
cell
that
and
that
the
Because
together
in
from
three
person
cones
work
very
ganglion
means
giving
blindness
B:
top
types
normal
detect
person
the
the
to
bottom
of
cones
vision.
red
has
light
In
spectrum,
of
most
present
red–green
and
difficulty
wavelengths
are
green
in
red
in
the
colour-
light
do
not
distinguishing
and
affected
green
light
people
are
have
• oe are the bones of the
problems
with
both
these
colours.
middle ear (hammer, anvil and
stirrup) that transmit and amplify
sound.
The
ear
is
the
organ
of
hearing.
Sound
waves
are
detected
by
the
ear
• seny a of the cochlea
through
the
movement
of
the
eardrum
and
ossicles.
The
eardrum
detect sounds of specic
and
ossicles
amplify
the
sound.
This
causes
the
vibration
of
cochlear
wavelengths.
fluid.
• The aty ne e sends
hair
All
along
cells.
the
These
basal
hair
membrane
cells
are
in
of
the
different
cochlea
positions
there
and
are
sensory
have
cilia
of
impulses caused by sound
different
lengths.
These
cilia
different
nerve
signals
vibrate
at
different
wavelengths,
each
perception to the brain.
sending
• ha e in the semicircular
canals detect movement of the
by
sound
nerve.
perception
Hair
cells
in
are
the
in
the
transmitted
semicircular
auditory
to
the
canals
nerve.
brain
detect
via
Impulses
the
caused
auditory
movement
of
head.
thehead.
outer ear
middle ear
inner ear
The discovery that electrical
ossicles (bones)
stimulation of the auditory
semicircular
system can create a perception of
pinna
hammer
anvil
stirrup
canals
sound has had a huge impact on
oval
the treatment of hearing loss and
auditory
window
impairment. Cochlear implants can
ner ve
now be used to help those who are
deaf to hear. Sounds are detected
by an external microphone placed
on the external ear. These sounds
are transmitted through wires to
electrodes that are implanted in
round
the cochlea of the inner ear. The
window
electrodes then transmit the sound
eardrum
(membrane)
as electrical impulses to the
auditory nerve, which carries the
message to the brain, allowing
hearing.
fge A .3.1.
164
Structure of the ear
oval window
(membrane)
cochlea
A .4
A .4
I N N AT E
AND
i N N AT E
LEARNED
ANd
lE ArNEd
bE h Av io u r
B E H AV I O U R
✔
learning
✔
memory
is
the
acquisition
of
skill
or
(Ahl)
(AHL)
knowledge.
Y  knw:
✔
innate
so
✔
behaviour
develops
autonomic
is
inherited
independently
and
from
of
involuntary
the
parents
and
responses
is
accessing
environment.
the
process
of
encoding,
storing
and
information.
are
Y  e ae t:
referred
to
as
reexes.
✔
✔
reex
arcs
comprise
the
neurons
that
explain
the
withdrawal
reex
of
the
hand
from
mediate
a
painful
stimulus.
reexes.
✔
✔
reex
conditioning
involves
forming
describe
Pavlov’s
experiments
into
reex
new
conditioning
in
dogs.
associations.
✔
✔
learned
behaviour
develops
as
a
result
explain
the
role
of
inheritance
and
learning
in
of
the
development
of
birdsong.
experience.
✔
✔
imprinting
is
learning
occurring
at
analyse
data
experiments
particular
life
stage
and
is
independent
of
of
operant
conditioning
is
a
form
of
learning
of
Behavioural
trial
and
patterns
of
the
behaviour
effect
and
on
chances
of
reproduction.
draw
error
can
be
a
labelled
diagram
of
a
reex
arc
for
a
that
pain
consists
invertebrate
terms
behaviour.
✔
✔
in
the
survival
consequences
from
a
withdrawal
reex.
experiences.
inherited
or
learned.
Inherited
behaviours
are
In Topics 3.3 and 3.4 you
said
to
be
innate.
Learned
behaviour
develops
as
a
result
of
experience.
studied inheritance of alleles
through meiosis and in Topic 6.6
Exape A .4.1.
you studied reproduction.
Compare
and
contrast
learned
and
innate
behaviour.
Solution
feate
innate
leane
type of behaviour in humans
yes
yes
Laboratory experiments and
field experiments both have
their strengths and limitations.
inherited
yes
no
instinctive
yes
no
affected by the environment
no
yes
can be modified by experience
no
yes
produces variability in a population
no
yes
Laboratory experiments have the
advantages that it is much more
possible to precisely control the
variables and it is far easier to
replicate the experiment. However,
the ar tificial setup of a laboratory
Reflexes
are
an
example
involuntary
responses
the
that
neurons
forming
new
of
are
mediate
innate
behaviour.
referred
reflexes.
to
as
Autonomic
reflexes.
Reflex
Reflex
conditioning
and
arcs
comprise
involves
study can produce unnatural
behaviour or biased results. Field
studies have the advantage that
the results are more likely to
associations.
reflect real life and therefore have
dorsal root
cell body of
more validity. Predictions and
(sensory ganglion)
relay neuron
results obtained in the laboratory
cell body of
do not always correspond with
sensory neuron
studies performed on organisms in
spinal ner ve
field conditions.
impulses from
receptor
grey
impulses to
ventral root
cell body of
eector
(motor neuron)
motor neuron
matter
fge A .4.1.
Learned
The reflex arc
behaviour
develops
as
a
result
of
experience.
165
A
N E U R O BI O LO G Y
AND
• ipntng is learning occurring
BE H AV IO U R
Exape A .4.2.
at a par ticular life stage and is
independent of the consequences
a)
of behaviour.
With
respect
between
a
to
Pavlov’s
conditioned
experiments
and
an
with
dogs,
unconditioned
distinguish
stimulus.
• opeant ntnng is a form of
b)
Outline
the
differences
between
classic
conditioning,
as
seen
in
learning that consists of trial and
Pavlov’s
dogs,
and
operant
conditioning.
error experiences.
c)
Describe
an
example
of
imprinting.
• leanng is the acquisition of skill
or knowledge.
• mey is the process of
Solution
a)
An
unconditioned
encoding, storing and accessing
therefore
information.
salivation
neutral
in
b)
Both
for
the
and
reaction
is
a
the
a
learning
is
a
voluntary
learned
is
independent
duckling
as
it
either
learned
of
the
first
occurring
would
human
follow
its
bell,
and
a
or
in
that
is
response,
sound
before
Operant
error
classic
for
food.
behaviours
operant
and
becomes
learned.
depends
which
will
conditioning
experiences.
conditioning
at
a
of
particular
behaviour.
after
mother
hatching
life
stage
An
example
and
and
follows
before they scored was
recorded. They were then
asked to train for two
weeks and the same test
was performed again. The
results are shown in the
graph.
gnirocs erofeb slairt fo rebmun
ball . The number of trials
subdivisions on the Y axis,
15
10
mean
5
0
trained
a) State the highest number of trials attempted by an untrained student
and by a trained student before scoring a basket.
[1]
therefore it is hard to give the exact
This
answer
could
have
achieved
1/1
marks:
answer. The markscheme will have
a range, but you should not give
18
trials
for
untrained
and
5
for
trained
a range, but an exact number. The
reason for this is that if your range
) Calculate the dierence in the mean number of trials before scoring
is larger and does not match the
between untrained and trained students.
range in the markscheme, you do
This
answer
could
have
not score a mark.
Untrained =
T
rained
=
4
Difference
166
=
9
trials
trials
5
trials
achieved
1/1
marks:
is
is
duck.
not trained
This graph does not show the
a
a
that
20
score a basket using a
is
It
is
SAMPLE STUDENT ANSWER
Students were asked to
on
conditioning
punishment
trial
triggers
previously
reflexes.
consequences
a
a
conditioning
while
on
a
is
involve
while
of
automatically;
naturally
conditioned
Classic
behaviour
sees
a
hearing
behaviour.
consists
of
stimulus
reward
depending
learning
that
to
stimulus
food
stimulus
conditioning
learned
that
behaviour
Imprinting
human
to
the
a
response
of
sound
triggers
response
to
response
control
of
the
environment.
therefore
form
in
operant
reflexes
in
example
a
smell
conditioned
stimulus
by
or
unconditioned
salivation
classic
triggers
sight
The
controlled
there
c)
with
conditioned
example
The
dogs.
stimulus,
associated
The
stimulus
innately
.
[1]
A .5
▼ This
) Deduce whether scoring a basket is an innate or learned
behaviour.
This
reason
[2]
answer
could
have
achieved
1/2
N E u r o P h A r m A c o lo G Y
answer
must
of
answer
In
this
to
a
incomplete.
given
for
“deduce”
the
A
choice
question.
marks:
case,
learned
Learned
is
be
(Ahl)
the
behaviour
because
once
is
students
behaviour
.
were
trained,
required
) Explain how training aects the nervous system.
nearly
[3]
to
half
the
score
the
number
a
basket
number
of
trials
was
before
training.
This
answer
could
Developing
many
not
of
have
neurons
connections
used
do
unused
stimuli.
neurons.
basket,
not
form
neurons,
so
so
and
while
Neural
there
A . 5
is
less
is
that
some
not
there
are
used
faster
will
be
the
are
are
loss
between
a
by
neurons
used
that
involves
interference
accessed
are
so
Synapses
pruning
synapses
that
synapses,
neurons.
reinforces
others
marks:
multiple
information
T
raining
3/3
between
persist.
Neurons
reinforced
achieved
lot
are
these
to
help
score
a
pruned.
N E U R O P H A R M A C O L O G Y
✔
anesthetics
( A H L )
act
by
interfering
with
neural
Y  knw:
transmission
✔
communication
between
neurons
can
be
the
reception
✔
some
in
of
manipulation
chemical
the
release
neurons
excite
✔
and
nerve
others
stimulant
in
and
by
the
✔
inhibit
addiction
can
be
predisposition,
impulses
postsynaptic
are
initiated
neurons
as
or
a
the
drugs
provided
dopamine
nerve
sensory
CNS.
mimic
the
stimulation
sympathetic
nervous
system.
impulses
them.
✔
of
and
messengers.
neurotransmitters
postsynaptic
of
areas
altered
perception
through
between
affected
social
by
genetic
environment
and
secretion.
inhibited
result
of
the
Y  e ae t:
summation
of
all
excitatory
neurotransmitters
received
and
from
inhibitory
✔
presynaptic
explain
✔
many
the
action
of
excitatory
and
inhibitory
neurotransmitters.
neurons.
different
modulate
fast
slow-acting
synaptic
✔
neurotransmitters
transmission
in
explain
the
the
action
of
slow-acting
neurotransmitters
in
memory
explain
on
and
learning.
brain.
✔
✔
memory
in
and
neurons
learning
caused
by
involve
the
stimulants
changes
effects
and
two
the
nervous
system
of
two
sedatives.
slow-acting
✔
describe
✔
explain
✔
evaluate
the
effect
of
anesthetics
on
awareness.
neurotransmitters.
✔
psychoactive
either
drugs
increasing
or
affect
the
brain
decreasing
how
endorphins
can
act
as
painkillers.
by
data
showing
the
impact
of
MDMA
postsynaptic
(ecstasy)
on
serotonin
and
dopamine
transmission.
metabolism
Neurotransmitters
are
chemicals
released
by
vesicles
in
the
in
the
brain.
presynaptic
In Topic 6.5 you studied neurons
neuron
that
enable
neurotransmission.
They
are
chemical
messengers
and synapses.
which
transmit
synapse.
neurons
in
Some
and
others
postsynaptic
and
signals
inhibitory
from
one
neuron
neurotransmitters
inhibit
neurons
as
them.
a
excite
Nerve
result
neurotransmitters
of
to
another
nerve
impulses
the
across
impulses
are
summation
received
from
the
in
neural
postsynaptic
initiated
of
all
the
presynaptic
or
inhibited
excitatory
neurons.
167
A
N E U R O BI O LO G Y
AND
BE H AV IO U R
Exape A .5.1.
An innovative method of
treating cancer patients is
Explain
how
nerve
impulses
depend
on
the
summation
of
through immunotherapy. Because
excitatory
and
inhibitory
messages.
it is a relatively new treatment,
there is little data about the
long-term effects of immune cell
therapy. There are still concerns
about long-term survival as well as
pregnancy complications in female
patients treated with these cells.
Some immune therapy drugs have
been approved, although they
produce serious side effects.
Patient advocates have pressed for
the speeding up of drug approval
processes, encouraging more
tolerance of risk .
Solution
The
axon
neurons.
More
same
of
than
of
given
released,
being
and
neurotransmitters. They excite
they
affect
only
can
than
neuron.
a
of
of
an
does
a
They
or
excitatory
rise
effect
can
the
action
above
potential.
the
of
The
excitatory
prevent
the
neurotransmitter
slow-acting.
to
of
the
is
occur.
millisecond
attach
The
must
action
not
with
combining
signals
potential
cancels
other
neurons.
synapse
involves
excitatory
fast-acting
less
form
balance
an
action
of
between
neurotransmitters
when
the
be
take
one
the
membrane
Inhibitory
dendrites
neurotransmitters.
generation
reached,
therefore
neurotransmitters
on
The
the
can
neurotransmitters
neurotransmitters.
Neurotransmitters
• stant are excitatory
for
the
Summation
inhibitory
depending
inhibitory
threshold
and
with
connections
neuron
neuron.
signals.
threshold
of
connects
multiple
presynaptic
form
inhibitory
effect
be
excitatory
potentials
a
one
neuron
can
postsynaptic
effects
and
one
There
to
The
cross
receptors
fast-acting
the
in
synapse
the
and
postsynaptic
nerve impulses in postsynaptic
neuron
which
are
protein
ion
channels.
Slow-acting
neurotransmitters
neurons.
on
• seate are inhibitory
neurotransmitters. They inhibit
the
more
cause
other
than
the
hand
one
can
take
neuron.
release
of
hundreds
They
do
secondary
not
of
act
milliseconds
through
messengers.
ion
to
act.
They
channels,
Examples
of
affect
but
instead
slow-acting
nerve impulses in postsynaptic
neurotransmitters
are
noradrenalin,
dopamine
and
serotonin.
neurons.
Psychoactive
drugs
affect
the
brain
by
either
increasing
or
decreasing
• satn is the result of
postsynaptic
transmission.
Stimulant
drugs,
such
as
nicotine,
cocaine
all excitatory and inhibitory
or
amphetamines,
mimic
the
stimulation
provided
by
the
sympathetic
neurotransmitters received from
nervous
system.
Sedatives
such
as
benzodiazepines,
alcohol
or
presynaptic neurons.
tetrahydrocannabinol
(THC)
mimic
inhibition. Anesthetics
act
by
• sw-atng netantte
interfering
with
neural
transmission
between
areas
of
sensory
perception
act through secondary messengers.
and
the
central
nervous
system
(CNS).
They
prevent
the
transmission
They modulate fast synaptic
of
nerve
of
sodium
impulses
by
binding
to
sodium
channels,
inhibiting
the
influx
transmission in the brain.
ions
through
these
channels. Addiction
can
be
affected
by
• mey and eanng involve
genetic
predisposition,
social
environment
and
dopamine.
changes in neurons caused by
slow-acting neurotransmitters.
Exape A .5.2.
a)
Outline
the
effect
of
benzodiazepines
and
alcohol
on
the
nervous
system.
b)
State
the
c)
Outline
effect
the
of
use
MDMA on
of
synapses.
anesthetics
in
surgery
.
Solution
a)
Both
benzodiazepines
synaptic
transmission.
receptors
Alcohol
b)
for
enhances
which
the
effect
neurotransmitter
MDMA is
also
Anesthetics
such
This
as
called
levels
preventing
in
act
as
is
an
of
sedatives,
increase
inhibitory
GABA and
affecting
the
effect
of
neurotransmitter.
decreases
the
glutamate.
ecstasy
.
synapses,
It
increases
enhancing
the
its
serotonin
release
and
and
reuptake.
act
by
ketamine
interferes
perception
168
alcohol
Benzodiazepines
excitatory
dopamine
c)
GABA,
and
interfering
prevent
with
and
the
neural
glutamate
neural
CNS,
with
receptors
transmission
preventing
transmission. Anesthetics
from
between
pain
being
areas
of
duringsurgery
.
active.
sensory
A .6
A . 6
E T H O L O G Y
E T h o lo G Y
(Ahl)
( A H L )
✔
explain
migratory
behaviour
in
blackcaps
is
an
Y  knw:
example
✔
behaviour
can
be
innate
or
ethology
is
the
study
of
animal
behaviour
change
natural
selection
observed
explain
animal
can
change
the
frequency
behaviour
and
in
a
of
behaviour
and
natural
selection.
how
that
example
blood
of
by
the
sharing
in
vampire
development
natural
of
bats
as
altruistic
selection.
behaviour.
increases
reproduction
will
the
chances
become
more
of
explain
foraging
example
survival
optimal
prevalent
of
behaviour
increasing
prey
in
shore
chances
of
crabs
survival
as
an
by
choice.
population.
✔
✔
by
behaviour
of
✔
✔
basis
conditions.
an
✔
genetic
in
✔
natural
the
learned.
its
✔
of
learned
behaviour
population
innate
or
be
can
lost
spread
from
it
through
more
explain
breeding
populations
a
rapidly
affecting
than
as
strategies
an
chances
example
of
in
of
survival
Coho
salmon
behaviour
and
reproduction.
behaviour.
✔
explain
courtship
example
of
mate
in
birds
of
paradise
as
an
selection.
Y  e ae t:
✔
✔
explain
how
natural
selection
favours
explain
in
types
of
✔
describe
examples
✔
describe
different
behaviours
foraging,
crabs
oestrus
in
female
lions
a
pride
as
an
example
of
innate
behaviour
behaviour.
that
Shore
synchronized
specic
such
of
types
as
breeding
(Carcinus
innate
of
animal
strategies
maenas)
reproduction
behaviours.
migration,
✔
learned
explain
blue
altruistism,
and
choose
increases
loss
courtship.
middle-sized
mussels
to
of
feeding
tits
of
the
as
an
chances
survival
and
offspring.
on
cream
example
learned
of
of
from
the
milk
bottles
development
in
and
behaviour.
feed
In Topic 5.2 you studied natural
on
in
preference
to
large
mussels,
despite
the
fact
they
provide
less
selection.
energy
.
larger
This
is
mussels
example
of
because
is
not
the
time
worth
increasing
the
the
taken
to
trouble.
chances
of
break
This
the
harder
foraging
survival
by
shells
of
behaviour
optimal
prey
is
an
choice.
SAMPLE STUDENT ANSWER
a) The sketch shows the growth rate of two types of the same species of
migratory sh (Coho salmon, Oncorhynchus kisutch). The mean age at
maturity is shown with a circle.
7
fish 1
stinu y ratibra / ezis
6
fish 2
5
4
3
2
1
0
0
2
4
6
8
10
12
age / years
Use the graph to explain breeding strategies in Coho salmon populations
as an example of behaviour aecting the chances of survival and
reproduction.
[6]
169
A
N E U R O BI O LO G Y
▲ This
The
in
answer
student
the
graph
is
uses
to
very
the
AND
complete.
BE H AV IO U R
This
answer
explain
the
of
salmon
and
have
achieved
6/6
marks:
different
One
types
could
information
their
part
of
the
population
stays
in
one
habitat,
reaching
a
breeding
strategies.
small
the
Experiments to test
hypotheses on the migratory
size.
graph
when
T
hese
that
they
sh
2.
size
before
are
reaches
become
T
he
called
other
a
plateau
adults,
sh
jacks.
rst
which
grow
at
a
T
hese
is
are
represented
(Fish
at
slower
a
1).
T
he
younger
rate,
dot
age
reaching
by
shows
than
a
larger
behaviour of blackcaps have been
returning
to
the
breeding
site.
T
hese
are
called
carried out. Birds are tagged and
followed through GPS recordings. The
hooknoses.
T
he
hooknoses
are
usually
larger
in
size
so
they
bird known as the blackcap (Sylvia
ght
to
fertilize
females,
while
the
smaller
jacks
do
not
ght
atricapilla) traditionally migrated
but
hide
and
wait
for
the
right
moment
to
fertilize
females.
from its summer breeding grounds in
Central Europe to warmer areas in
T
he
larger
jacks
may
behave
like
the
hooknoses,
as
it
is
Spain and Portugal for the winter.
difcult
for
them
to
hide.
Lately they have been seen to
migrate to the UK. The abundance of
garden birds increased with levels of
Many
birds
show
sexual
dimorphism.
This
means
the
males
are
bird feeding. Studies found that
very
different
may
have
from
the
females.
The
males
may
be
very
colourful
or
blackcaps migrating to the UK from
distinctive
feathers
to
attract
females.
Others
show
special
Germany had become adapted to
courtship
behaviours
such
as
dances.
Birds
of
paradise
show
both
of
eating food supplied by humans. In
these
behaviours,
in
a
very
exaggerated
manner.
Females
choose
their
contrast blackcaps migrating to
mates
according
to
their
plumage
and
dance.
Natural
selection
has
led
Spain had bills adapted to feeding on
to
the
selection
of
these
exaggerated
traits.
fruit such as olives. The birds
migrating to the UK have an
evolutionary advantage, as they
Exape A .6.1.
need to travel less so expend less
a)
Outline
the
behaviour
of
feeding
on
cream
from
milk
bottles
by
energy. Therefore the genetic basis
blue
tits.
of behaviour has been changed by
natural selection.
b)
Outline
one
increases
way
the
in
which
chances
of
synchronized
survival
and
oestrus
in
reproduction
female
of
lions
offspring.
Solution
a)
Blue
tits
started
behaviour
are
few
bottles
of
b)
the
soon
blue
are
tits
no
to
feed
spread
on
showing
longer
development
cream
from
throughout
this
behaviour,
delivered
and
loss
milk
Europe.
of
bottles.
probably
door-to-door.
a
learned
This
Nowadays
This
there
because
is
an
milk
example
behaviour.
The advantage of synchronized oestrus in female lions is that the
females have their cubs and are lactating all at same time, therefore
some females can suckle and take care of others’ cubs while they
hunt. The cubs are more likely to survive when they are raised in a
nursery rather than by a solitary mother
. Another advantage is that a
group of male cubs of the same age leave the pride at the same time,
so can compete for dominance of another pride more effectively
.
170
A .6
E T h o lo G Y
(Ahl)
Pate pe  optn A
Pe 1
Pe 4 (Ahl)
The growth of the axon and one dendrite were measured
Outline the processes occurring when a person touches
in a developing neuron. The graph shows the length of
a rough surface with their hand and then moves the
the axon and dendrite from the tip to the cell body over
hand away.
time.
Pe 5 (Ahl)
The volume of the left and right nucleus accumbens was
measured in tetrahydrocannabinol (THC) consumers
350
and compared with those of control par ticipants who do
300
not consume cannabinoids. The bar graph shows the
250
results of several recordings.
axon
200
1000
dendrite
150
800
100
50
0
0
1
2
3
4
5
6
7
8
time / days
mm / emulov
3
sertemorcim / pit ot ydob morf ecnatsid
400
600
400
200
a) State the process occurring in this neuron from day 1
0
control
to day 7.
THC
control
left
THC
right
) Calculate the difference in length of the axon and
dendrite after 7 days’ growth.
a) State the mean volume of the left nucleus
accumbens in THC consumers.
) Explain the difference in trend of growth of the axon
and dendrite.
) Compare the volume of the accumbens in THC
consumers and control par ticipants.
) Outline what could happen to the dendrite if it is not
used.
) Explain the effect of THC on the nervous system.
Pe 2
Pe 6 (Ahl)
The following is a magnetic resonance image (MRI) of a
Common vampire bats (Desmodus rotundus) feed only
human brain.
on blood and die after 70 h of fasting. Unfed bats often
receive food from other bats by regurgitation. The graph
shows the changes in weight at the time of feeding
compared to the pre-feeding weight (100%) of donor
and recipient bats before and after blood donation.
120
cerebellum, hypothalamus and pituitary gland.
% / gnideef-erp thgiew egatnecrep
a) On the image, label the medulla oblongata,
100
80
before
60
after
40
20
) Explain how functional MRI can be used to detect the
functions of different par ts of the brain.
0
donor
recipient
Pe 3
Explain how, in humans, colour in the environment is
detected by the eyes and relayed to the brain.
Using the data, explain blood sharing in vampire bats is
an example of the development of altruistic behaviour
by natural selection.
171
B I OT EC H N O LO GY
B
B . 1
AND
B I O I N F O R M AT I C S
M I C R O B I O L O G Y:
ORGANISMS
Y  kw:
✔
microorganisms
✔
the
are
IN
INDUSTRY
Y  be be :
metabolically
diverse.
✔
compare
and
contrast
batch
and
continuous
fermenters.
genetic
and
regulatory
microorganisms
can
be
processes
within
modied.
✔
explain
the
production
of
penicillin
of
citric
by
batch
fermentation.
✔
pathway
produce
engineering
metabolites
is
of
used
industrially
to
interest.
✔
explain
the
continuous
✔
fermenters
of
✔
used
for
large-scale
microorganisms
their
probes
own
are
in
fermenters
waste
used
to
become
limited
✔
explain
how
✔
explain
zones
products.
monitor
bacterial
conditions
within
✔
describe
fermenters.
✔
conditions
for
the
are
growth
biogas
of
the
at
by
of
optimal
is
produced
inhibition
in
around
fermenters.
cultured
growths.
Gram
staining
Gram-negative
maintained
acid
fermentation.
production
metabolites.
by
✔
are
production
of
Gram-positive
and
bacteria.
levels
microorganisms
being
cultured.
Microorganisms
are
allows
to
small
cells
that
reproduce
very
quickly
.
This
In Topic 2.1 you studied
scientists
modify
them
and
use
them
in
different
industrial
molecules involved in metabolism.
processes.
Genes
can
be
introduced
into
microorganisms
by
genetic
In Topic 4.3 you have seen carbon
engineering
so
that
they
will
make
a
desired
product.
The
modified
cycling. In Topic 6.3 you studied
microorganism
is
placed
in
a
fermenter.
In
batch
beginning
of
the
fermentation
the
defence against infectious disease.
substrate
is
introduced
is
obtained
at
the
is
continuously
end,
added
at
the
while
and
in
the
continuous
product
is
process
and
fermentation
harvested
the
the
product
substrate
throughout
Alexander Fleming
the
process.
Continuous
fermentation
is
more
efficient,
but
any
discovered penicillin in
contamination
will
affect
the
whole
process.
England in 1928, on a discarded
petri dish. Many perceive this as
Exmpe
B.1.1.
serendipity, a lucky accident.
However, Fleming had spent many
Complete
the
table
to
compare
and
contrast
batch
and
continuous
years studying organisms and this
fermentation
according
to
the
time
when
each
process
occurs.
prepared him to understand what
he saw in the dish. He could
Solution
connect his observations with
Pce
Bc
C
substrate added
at the beginning
 e me
product harvested
 e e
at periodic intervals
oxygen monitored
 e me
all the time
production of foam check
all the time
 e me
what he already knew about
microorganisms to recognize what
was happening.
172
B .1
Exmpe
Citric
starch
can
(CB)
be
produced
using
consumed
changes
or g a ni s M s
in
industrY
B.1.2.
acid
bagasse
M i C r o B i o l o g Y:
in
pH
fermentation
the
by
due
are
the
to
by
continuous
filamentous
fungal
citric
shown
in
Aspergillus
fermentation
acid
the
fermentation
fungus
production
(left
axis)
(right
of
cassava
niger.
and
axis)
The
the
during
the
graph.
30
BC yrd fo g 001
35
25
30
20
25
20
15
15
10
10
5
5
0
starch
pH
citric acid
rep g
/ dica cirtic
/ demusnoc hcrats
BC yrd fo g 001 rep g
40
0
0
24
48
72
96
120
144
time / h
Source of data: F. C. Prado et al. (2005),
Brazilian Journal of Chemical Engineering, 22(4),
pp. 547–555.
a)
State
b)
(i)
(ii)
(iii)
c)
one
use
State
a
of
mode
Describe
Suggest
Explain
citric
the
the
one
of
acid
of
the
detection
changes
reason
production
consumption
in
of
for
of
food
of
pH
the
the
citric
pH
over
pH
industry
.
in
time
value
acid
in
the
in
fermenter.
this
after
fermenter.
144
relation
to
hours.
the
starch.
Solution
a)
Citric
b)
(i)
(ii)
acid
can
A probe
The
pH
can
is
decreases
(iii)
The
pH
used
be
4
as
used
alkaline
to
is
addition
be
at
(acid)
alkaline
preservative
to
detect
the
at
prevented
of
a
the
pH
beginning
48
hours.
from
It
or
of
in
the
the
remains
becoming
substances
flavouring.
such
experiment
constant
more
as
fermenter.
acidic
by
hydroxide
and
after
48
h.
the
or
bicarbonate.
c)
Starch
is
bagasse
down
the
substrate
(CB)
to
this
and
eventually
acid
reaction
fermentation.
molecule.
is
as
the
it
to
It
or
produced
It
is
found
hydrolysed
glucose
product
is
is
(both
primary
during
in
or
cassava
broken
smaller
sugar
metabolite
the
Krebs
of
the
cycle.
B.1.3.
Aspergillus
to
of
storage
Citric
fermentative
used
a
maltose
molecules).
Exmpe
as
niger
produce
is
glucose
citric
hexokinase
acid
by
continuous
trehalose 6 phosphate
fermentation. Glucose is
synthase
G-6-P
converted
by
to
trehalose 6-phosphate
pyruvate
glycolysis.
T
rehalose
6-phosphate
pyruvate
normally
inhibits
hexokinase,
an
acetyl CoA
important
enzyme
in
CoA
the
glycolysis
pathway
.
citric acid
Krebs cycle
173
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
Suggest
factor
how
which
pathway
reduces
engineering
yields
of
could
citric
be
used
to
address
this
acid.
Solution
The
molecule
inhibiting
the
feedback.
modified
In
to
production
to
trehalose
order
synthase
another
already
of
a
in
of
the
water,
can
need
B . 2
pH,
cell
and
probes.
These
alert
the
such
bicarbonate
B I OT EC H N O LO GY
organisms
can
be
modied
to
include
at
protein
enzyme
breed
of
enzyme
type
can
least
of
be
hexokinase
negative
genetically
reduce)
approach
that
trehalose
the
could
breaks
trehalose
strains
kept
such
dioxide
acid
be
down
6-phosphate
6-phosphate,
of Aspergllus
in
also
the
foam
system
to,
and
to
for
acids
These
levels
these
the
in
niger
can
that
pH
of
the
tanks,
when
alkaline
it
dissolves
otherwise
include
nutrients,
monitored
add
the
medium.
conditions
oxygen,
are
change
respiration
acidifies
example,
raise
that
fermentation
metabolism.
dioxide. All
alkalis
as
produced
which
constant
gets
using
substances
too
low
.
A G R I C U LT U R E
recombinant
physical
✔
a
niger
(or
production
carbon
I N
✔
Y  kw:
the
a
metabolites
density
,
or
the
is
activity
.
carbon
the
block
produces
carbonic
be
to
This
6-phosphate. Another
Because
produce
to
to
selectively
The
binds
acid.
this, Aspergllus
microorganism
products
as
to
citric
gene
that
TPS
medium.
temperature,
waste
is
low
producing
affect
a
catalyses
method
have
Conditions
they
gene
6-phosphate.
(TPS)
of
avoid
trehalose
Microorganisms
pH
to
incorporate
incorporate
trehalose
6-phosphate
production
DNA can
and
chemical
be
introduced
methods
or
by
direct
indirectly
by
DNA
vectors.
from
✔
other
these
that
organisms.
transgenic
were
not
organisms
previously
produce
part
of
proteins
their
Y  be be :
species’
✔
explain
how
transgenic
organisms
can
be
proteome.
produced.
✔
genetic
modication
can
be
used
to
produce
✔
novel
describe
(Ti)
✔
plants
can
be
genetically
environmental
✔
the
modied
resistance
bioinformatics
can
be
to
used
to
increase
in
overcome
crop
identifying
target
plasmid
introduce
yields.
✔
describe
mosaic
target
control
the
gene
its
is
linked
to
other
sequences
B
an
the
tumour-inducing
open
expression.
reading
frame
✔
is
a
signicant
tumefaciens
resistance
into
to
soybean
genetic
to
modication
allow
vaccine
in
bulk
of
tobacco
production
tobacco
of
plants.
that
describe
the
(Solanum
✔
of
Agrobacterium
glyphosate
virus
hepatitis
a
of
crops.
genes.
✔
use
products.
length
production
tuberosum)
for
of
Amora
the
paper
potato
and
adhesive
of
industries.
DNA from
a
start
codon
to
a
stop
codon.
✔
✔
recombinant
DNA can
be
introduced
into
evaluate
data
on
the
glyphosate-tolerant
plants,
leaf
discs
or
recombinant
DNA must
be
inserted
into
cell
and
chloroplast
taken
identify
up
by
its
chromosome
an
open
marker
DNA.
uptake
174
genes
of
a
are
✔
target
used
to
gene.
indicate
the
reading
databases
frame
to
nd
(ORF)
an
and
use
ORF.
or
use
bioinformatic
genes
✔
of
the
bioinformatic
plant
impact
soybeans.
protoplasts.
✔
✔
environmental
whole
successful
in
other
software
organisms
to
identify
(BLASTn).
similar
B.2
In
order
to
genetically
modify
an
organism,
an
open
reading
B i ot E C h n o lo g Y
in
a g r i C u lt u r E
frame
• An pe e fme (orF)
(ORF)
is
found
using
bioinformatics.
This
target
gene
sequence
is
is a signicant length of DNA from
linked
to
DNA is
other
sequences
formed
DNA or
the
antibiotic
when
the
that
target
mitochondrial
resistance
are
control
or
used
gene
its
expression.
forms
chloroplast
to
indicate
part
DNA.
of
Recombinant
either
Marker
successful
the
genes
uptake
a star t codon to a stop codon. It
nuclear
of
such
the
as
contains sucient nucleotides to
code for a polypeptide chain.
target
• tec describes an
gene.
When
the
transgenic
organism’s
cells
divide
by
mitosis,
the
target
organism that has foreign DNA
DNA is
incorporated
into
the
new
cells.
included in its own DNA .
Exmpe B.2.1.
Find
an
open
reading
frame
(ORF)
in
the
following
DNA
In Topic 1.5 you studied the
sequence.
origin of cells and in Topic 3.5 you
GATCCATGCTGCTGCTGACTCGGAGCCCCACAGCTT
studied genetic modification and
GGCACAGGCTCTCTCAGCTCAAGCCTCCGGTCCT
biotechnology.
CCCTGGGACCCTGGGAGGCCAGGCCCTGCATCTGAGGT
CCTGGCTTTTGTCAAGGCAGGGCCCTGCAGAG
ACAGGT
GGGCAGGGCCAGCCCCAGGGCCCTGGGCTTCGAACCCG
GCTGCTGATCACAGGCCTGTTTAGGC
TGGACTCGGT
Solution:
The
the
start
codon
beginning
TGA.
Starting
groups
of
appears.
the
stop
Plants
through
a
large
and
to
for
produce
Genetic
selection,
and
The
then
the
a
of
formation
such
as
allow
one
infect
B
many
use
from
TAA and
sequence
these
into
sequences
between
the
diseases
start
a
and
in
plants.
against
obtained
so
requires
tools,
increase
reduces
plants
are
to
cold,
constantly
the
has
plants
hepatitis
the
to
starch.
achieved
mosaic
eaten
and benefits associated with
scientific research, for example,
of herbicide resistance genes
by
virus,
by
Scientists must assess risks
the need to evaluate the potential
frost
changing
been
tobacco
The
pests
used
high-amylopectin
vaccines
antigens
be
withstand
insects
tolerance
in
can
can
transgenic
grow
edible
and
and
and
or
can
transgenic
traits,
vitamins
antibodies
TAG,
generations
of
longer
Some
tobacco
are
conditions
desired
keep
to
nucleotides
the
of
codons
increased
easier
of
the
to
6
ORF.
takes
pesticides.
crop
of
that
resistance
hepatitis
to
this
with
crops
may
20
an
at
codons
divide
when
Through
production
used
must
see
environmental
plants
more
making
see
found
but
time.
molecules
incorporation
induce
of
you
and
have
Improving
useful
ATG
stressful
modification
is
stop
approximately
produce
environment.
which
can
The
you
herbicides
drought,
the
to
produce
disease.
need
or
can
you
the
are
investment
scientists
yields
there
natural
which
sequence.
(codons)
codons,
resistant
ATG,
the
from
three
If
is
of
animals
escaping into the wild population.
Wild relatives of genetically
engineered crops can acquire
transgenic traits such as herbicide
B.
resistance. This can happen by
spontaneous transgenic crop–wild
Exmpe B.2.2.
hybridization. In agricultural crops,
Starch
from
resistance to herbicides is often a
63
different
62
sources
contains
proportions
amylose
of
and
amylopectin.
about possible problems that
61
C° / erutarepmet
different
beneficial trait, but little is known
potato (high amylopectin)
could result if this trait persists
60
when herbicides are not used.
potato (normal)
59
58
Another problem is the appearance
57
of herbicide-resistant weeds.
Potatoes
56
(Solanum
55
barley (high
amylose)
barley (normal)
tuberosum)
have
Source of graph data: H. Frediksson et al
54
0
been
10
20
30
40
50
(1998), Carbohydrate Polymers, 35,
genetically
amylose concentration / %
modified
produce
pp. 119–134.
to
high-amylopectin
starch
(Amflora
potatoes).
175
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
aeme p
Heat
the
induces
gel
starch
formation
to
form
a
gel
temperature
at
in
excess
different
water.
The
amylose
graph
shows
concentrations.
When looking at the data, check
a)
Discuss
the
hypothesis
that
the
temperature
at
which
the labels on the x and y axes
starches
form
a
gel
depends
on
the
degree
of
cross-linking
of
and make sure you use the same
amylopectin.
wording in your answer. The x
(independent) variable affects
b)
State
the y (dependent) variable; in this
one
advantage
of
potatoes
with
a
high
amylopectin
content.
case, the amylose concentration
c)
The
Amflora
potato
was
approved
for
industrial
applications
in
affects the temperature at which
the
European
Union
(EU)
in
2010
and
was
withdrawn
in
January
the gel is formed. Use all the
2012
due
to
opposition.
Discuss
reasons
for
people
supporting
or
data to answer the question. In
opposing
the
introduction
of
the
Amflora
potato
in
the
EU.
a discussion you should try to
include a statement that suppor ts
Solution
the hypothesis and one that does
a)
not suppor t it.
High-amylopectin
potatoes
molecules
is
so
amylopectin
(or
temperature
than
• Ccm ce promotes the
hypothesis
binding of plasmid DNA to the cell
amylose
membrane, alllowing the plasmid to
there
which
is
normal
similar
amylopectin
cross-linking.
form
a
therefore
However,
the
more
of
potatoes
potatoes,
very
support
have
chance
low-amylose)
show
not
will
great
supported.
barley
does
a
normal
gel
gel
we
at
a
can
barley
formation
High-
higher
say
and
the
high-
temperature,
hypothesis.
enter the cell using heat shock .
b)
High-amylopectin
potato
starch
is
used
in
adhesives
production
• A pme is a spherical lipid
as
it
forms
a
sticky
paste.
It
can
be
stored
for
long
periods
of
vesicle used as a vehicle to carry
time.
transgenic DNA.
c)
There
is
some
support
for
the
production
of
Amflora
potatoes.
• Eecp is the application
They
of an electric eld to cells in order
are
a
cheap
deforestation.
to increase their permeability to
Opposing
trangenic DNA.
and
This
natural
benefits
arguments
transgenic—that
source
local
include
they
have
of
adhesives,
farmers
that
and
Amflora
foreign
reducing
reduces
potatoes
DNA in
their
pollution.
are
genome.
This
• Mcjec is the use of a
could
represent
a
health
risk
to
the
population
as
they
could
be
glass micropipette to inject the
allergenic
trangenic DNA into cells.
and
the
or
toxic.
future
There
effects
of
is
also
this
a
are
risk
of
horizontal
gene
transfer,
unknown.
• Bc is the sticking of DNA
to “micro bullets” that are red into
a cell.
A transgenic
crop
is
a
genetically
modified
organism.
A transfer
of
• Agrobacterium tumefaciens is a
genes
has
occurred
incorporating
DNA from
a
different
species.
vector used to infect plant tissue
The
gene
of
interest
is
amplified
or
added
to
a
plasmid,
and
then
and the tumor-inducing plasmid (Ti)
introduced
into
the
cells
of
whole
plants,
leaf
discs
or
protoplasts.
is used to carry transgenic DNA.
The
new
DNA is
incorporated
into
DNA in
the
nucleus
of
the
plant
• tbcc mc  is a vector
cell
or
the
chloroplast
DNA.
Chemical
methods
of
introducing
genes
used to incorporate recombinant
into
plants
can
include
calcium
chloride
or
liposomes
while
physical
DNA into tobacco plants by infection.
methods
include
Recombinant
Agrobacterium
electroporation,
DNA can
also
tumefaciens
be
and
microinjection
introduced
tobacco
using
mosaic
and
biolistics.
vectors
virus.
The
such
two
as
most
aeme p
common
methods
methods.
are
Biolistics
biolistics
involves
and
tumour-inducing
sticking
DNA to
small
plasmid
(Ti)
micro-bullets
and
Limit the chemical methods of
then
firing
these
into
a
cell.
This
technique
is
clean
and
safe
but
it
can
introducing genes into plant cells
result
in
the
gene
of
interest
being
rearranged
upon
entry
or
the
target
to calcium chloride and liposomes.
cell
sustaining
damage
upon
bombardment.
The
Ti
method
involves
Limit the physical methods of
the
use
of
Agrobacterium
tumefaciens,
which
infects
plant
cells.
The
introducing genes into plant cells
transgenic
piece
of
DNA is
integrated
into
the
plant’s
chromosomes
to electroporation, microinjection
using
a
Ti
plasmid
as
a
vector.
A plasmid
is
a
large
circular
DNA
and biolistics. Limit vectors to
particle,
which
replicates
independently
of
the
bacterial
chromosome
Agrobacterium tumefaciens and
and
can
take
control
of
the
plant’s
cellular
machinery
tobacco mosaic virus.
make
176
many
copies
of
its
own
bacterial
DNA.
and
use
it
to
B.2
B i ot E C h n o lo g Y
in
a g r i C u lt u r E
SAMPLE STUDENT ANSWER
Succinate is industrially produced by continuous fermentation. It is
used as a raw material in the production of flavour enhancers, drugs
and industrial chemicals. One method of increasing the production
of succinate is to genetically modify E. coli to express high levels of
formate dehydrogenase (FDH1). This results in the production of higher
concentrations of NADH. The engineered pathway is shown as a bold
dotted line in the image.
glucose
+
NAD
NADH
succinate
+
2NAD
2NADH
+
NADH
pyruvate
NAD
lactate
+
formate
CO
NADH
2
NAD
FDH1
acetyl CoA
2NADH
+
2NAD
formate
acetate
ethanol
) Using the diagram, suggest a reason for high concentrations of NADH
favouring the production of succinate.
This
answer
High
of
could
have
achieved
concentrations
succinate
because
of
[1]
1/1
NADH
succinate
marks:
favour
is
the
production
produced
using
the
+
conversion
the
greater
of
NADH
the
to
NAD
(the
concentration
of
oxidation
NADH
the
of
NADH),
more
NADH
so
there
+
is
available
produce
to
more
be
oxidized
creating
more
H
,
e
and
energy
to
succinate.
b) Predict one metabolite other than succinate that will be produced in a
greater amount if the amount of NADH available is increased.
This
answer
could
have
achieved
1/1
[1]
marks:
aeme p
+
CO
,
because
the
reduction
of
NAD
to
NADH
leads
to
the
Remember to include a reason for
2
a “predict” or “suggest” question.
formation
of
CO
from
formate.
2
c) Outline one reason this process represents pathway
engineering.
This
T
his
answer
[1]
could
represents
being
altered
results
the
in
achieved
pathway
to
concentrations
altering
have
express
of
terms
of
marks:
engineering
higher
succinate.
original
1/1
levels
because E.
of
Pathway
metabolic
FDH1
to
coli
form
engineering
pathway
to
is
achieve
greater
involves
better
yields.
177
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
B . 3
E N V I R O N M E N TA L
Y  kw:
✔
biotechnology
and
can
mitigation
industrial,
of
P R OT ECT I O N
Y  be be :
be
used
in
the
contamination
agricultural
and
prevention
✔
explain
from
municipal
properties
bioremediation
clearing
up
uses
microorganisms
pollution
to
aid
describe
some
of
of
the
emergent
microorganisms
in
biolms.
in
for
the
sewage
use
of
biolms
in
trickle
lter
beds
treatment.
incidents.
✔
✔
advantages
wastes.
✔
✔
the
microorganisms
metabolize
describe
specic
the
elemental
conversion
mercury
by
of
methyl
mercury
into
Pseudomonas
pollutants.
✔
✔
biolms
that
are
have
sensing,
aggregates
emergent
formation
of
properties
of
a
describe
microorganisms
such
matrix
and
as
degradation
of
benzene
degradation
of
oil
quorum
✔
describe
✔
evaluate
data
or
environmental
bacteriophages
water
are
used
in
the
halophilic
by
Pseudomonas
antibiotic
resistance.
✔
by
bacteria.
disinfection
media
reports
problems
on
caused
by
biolms.
of
systems.
Industrial
contamination
or
pollution
can
affect
all
of
the
organisms
In Topic 1 you have studied cell
inhabiting
that
area.
Microorganisms
are
capable
of
metabolizing
some
biology.
pollutants,
is
called
rendering
them
bioremediation.
necessary
to
remove
the
less
harmful
Physical
and
pollutants
to
the
ecosystem.
chemical
from
water
This
procedures
or
process
may
also
be
soil.
• A bm is a layer of
• Emee ppe e arise from
microorganisms attached to a
the interaction of the members of
surface, forming an organized
a biolm that are not present in the
structure with complex structural and
single-celled microorganism.
functional characteristics.
Exmpe B.3.1.
Compounds
help
The
extract
process
cyanide,
a
results
toxin
bacterium
ammonia
gold
from
in
that
),
cyanide
can
rock
inhibit
that
is
less
is
cellular
fluorescens
which
group
gold-containing
waste
Pseudomonas
(NH
the
(CN)
rocks
are
used
called
contaminated
respiration.
degrades
100
% / dedarged edinayc
to
containing
ore.
with
The
cyanide
to
toxic.
3
cyanide
carbon
+
oxygen
dioxide
+
+
organic
ammonia
carbon
+
source
80
60
40
20
→
0
nitrates
sterile
To
research
the
degradation
samples
of
of
conditions
cyanide,
that
result
researchers
cyanide-processed
ore
in
sprayed
with
solution
maximum
one
a
sterile
•
a
solution
containing
a
culture
of
P
.
fluorescens
•
a
solution
containing
a
culture
of
P
.
fluorescens
solution
a)
Outline
b)
Sugest
178
the
how
evidence
the
that
addition
P
.
of
fluorescens
sucrose
can
and
sucrose.
degrade
promotes
the
P
.
fluorescens
and sucrose
Journal of Soil Contamination, 3, pp. 271–283.
three
solutions:
•
fluorescens
Source of data: C. White and J. Markweise (1994),
different
of
P
.
cyanide.
degradation
of
cyanide.
B.3
E n v i r o n M E n ta l
P r ot E C t i o n
Solution
a)
With
the
sterile
degradation
b)
Sucrose
and
In
provides
sucrose,
control
solution,
with
the
with
P
.
the
of
energy
amount
sucrose
bioremediation
which
is
the
control,
there
is
no
degradation
of
cyanide
but
there
is
fluorescens
of
or
carbon
source
degradation
only—this
contaminated
would
soils,
of
in
this
cyanide
help
reaction.
is
establish
higher
In
the
than
solution
without
containing P
.
sucrose.
There
fluorescens
was
no
causality
.
microorganisms
are
used
to
• Beme is the use
degrade
pollutants
such
as
hydrocarbons,
oil,
heavy
metals,
pesticides,
of microorganisms to degrade
herbicides
and
dyes.
This
technique
takes
advantage
of
the
ability
contamination.
of
certain
microorganisms
to
metabolize
these
pollutants.
It
is
an
• Pem is a genus of
environmentally
friendly
,
low-cost
and
efficient
environmental
clean-
bacteria used in the bioremediation
up
technique.
A few
examples
of
bioremediation
are
the
conversion
of oil and mercury.
of
methyl
mercury
degradation
oil
by
in
and
plastic
a
public
chains.
(Hg)
by
mercury
halophilic
is
Biofilms
better
not
able
concern
by
Pseudomonas,
bacteria
by
populations
on
a
present
to
in
survive
which
because
of
of
of
and
and
the
the
degradation
of
and
changes
in
the
the
health
by
the
less
of
mercury
substance
biomagnify
to
result
methyl
in
toxic
food
element
putida.
be
emergent
individual
metal
may
affects
neurotoxic
mercury
can
the
contamination
microorganisms,
which
involving
electrodes,
adversely
the
methyl
present
the
those
bioaccumulate
Pseudomonas
surface
biofilms
as
lights
Environmental
can
transformation
These
are
wildlife.
performed
are
such
fluorescent
substance
together
liquid.
activities,
contamination,
and
health
This
The
mercury
grow
urban
beings
mercury
.
that
benzene
industries,
mercury
human
is
elemental
Pseudomonas
Industrial
and
of
into
generally
solid
(living
properties;
organism.
bacteria,
or
these
Biofilms
environment,
for
that
non-living)
are
or
properties
are
example
bacterium
changes
altered
in
so
pH.
they
they
live
on,
This
matrix
The
can
biofilm
organisms
produce
which
in
have
substances
many
cases
is
their
binding proteins
bacterium
metabolisms
including
the
matrix
exopolysaccharide
(EPS).
bacterium
acts
bacteriostatic
as
a
protective
substances
from
layer,
preventing
affecting
the
antibiotics
organisms.
or
bacterium
They
bacterium
form
channels
synchronize
quorum
their
sensing;
organisms
these
through
and
gene
this
only
advantages
which
food
expression
means
then
allow
one
does
it
can
travel
through
organism
express
microorganisms
a
faster.
mechanism
senses
certain
in
They
there
called
are
proteins.
biofilms
to
bacterium
bacterium
acid
more
All
of
survive
area of tooth decay
in
different
environments,
for
example,
in
water
pipes
and
on
tooth
teeth,
catheters
and
shower
caps.
SAMPLE STUDENT ANSWER
Using the diagram on the right, explain the emergent properties of biofilms.[3]
This
answer
Y
ou
can
could
have
achieved
0/3
marks:
▼ This
see
that
the
tooth
is
attacked
because
it
presents
could
Each
bacterium
has
proteins
that
join
them
together
student
described
what
cavities.
attacking
the
be
seen,
question,
but
did
therefore
not
answer
scored
no
marks.
the
tooth.
Bacteriophages
unaffected
by
are
viruses
antibiotics
Bacteriophages
replicate
that
and
infect
are
within
able
their
bacteria.
to
kill
host
These
bacteria
cells,
viruses
within
amplifying
are
biofilms.
the
179
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
bacteriophage
spreading
the
EPS
can
through
matrix,
also
B . 4
M E D I C I N E
of
infection
the
by
a
presence
its
within
eliminating
destroy
the
systems,
released
EPS.
as
they
the
the
the
bacteria
biofilm.
that
By
produce
Bacteriophages
Bacteriophages
destroy
biofilm.
are
biofilms
used
that
in
form
the
in
pipes
tanks.
( A H L )
Y  be be :
pathogen
of
are
biofilm,
degrade
water
Y  kw:
✔
the
which
bacteriophages
themselves
disinfection
and
numbers
can
genetic
be
detected
material
or
by
by
✔
describe
its
how
pathogens
can
be
detected
in
organisms.
antigens.
✔
✔
predisposition
detected
to
through
metabolites
in
a
genetic
the
blood
disease
presence
or
urine
of
or
can
markers
through
biopharming
protein
✔
products
tracking
study
techniques
for
used
therapeutic
experiments
the
are
interactions
are
of
used
a
to
predisposition
can
be
or
produce
✔
explain
✔
analyse
✔
explain
of
localize
desired
genetic
the
use
of
genetic
markers.
DNA
use.
to
how
detected.
microarrays.
✔
describe
be
✔
and
simple
the
strains
✔
use
the
of
describe
explain
the
Infection
of
an
interpret
organism
by
use
a
of
use
vectors
PCR
in
the
treatment
of
to
transferin
to
detect
biopharming
of
detect
different
virus.
probes
how
production
✔
viral
inuenza
luminescent
✔
of
SCID.
describe
protein.
DNA microarrays.
linked
to
tumours.
can
be
used
in
the
antithrombin.
results
of
pathogen
ELISA diagnostic
can
be
tests.
detected
by
presence
of
polymerase
Developments in scientific
chain
reaction
(PCR)
techniques
that
show
the
the
genetic
research and technology
material
of
the
pathogen.
This
test
is
usually
performed
on
a
blood
have allowed scientists to
sample.
Another
method
of
detecting
pathogens
is
by
observing
the
diagnose and treat diseases.
reaction
of
antibodies
specific
to
the
pathogen
antigens.
Preventative medicine is becoming
a desirable therapeutic approach
and patients are beginning to
Exmpe B.4.1.
demand fast and early qualitative
Tobacco
plants
were
transformed
to
include
the
hepatitis
B
virus
diagnosis. Rapid developments in
gene
coding
for
surface
antigen.
Surface
antigen
gene
expression
technology have facilitated the
levels
were
determined
by
ELISA.Transformed
tobacco
plant
callus
production of tests and devices
cells
were
analysed
for
the
integration
of
the
gene
by
PCR.
A band
that can detect diseases. Using
of
681
base
pairs
confirms
the
transformation
(gel
on
the
right).
ar tificial intelligence and web-
now monitor disease
blood test that can detect prostate
gland cancer and can distinguish
between benign cancers and
metastatic disease. This test
detects molecular changes in
the prostate-specific antigen in
2.5
1
sullac fo marg rep
epidemiology. One example is a
smargorcim / noitcudorp negitna
based knowledge systems we can
4
5
1.0
681 bp
0.5
0
control
transformed
tobacco plant
180
3
1.5
blood, reducing the need for
biopsies.
2
2.0
B.4
a)
Suggest
b)
Explain
c)
a
reason
how
hepatitis
B
Describe
the
why
the
this
is
ELISA test
an
is
example
used
to
of
MEdiCinE
(ahl)
biopharming.
detect
the
presence
of
the
antigen.
expression
PCR
of
the
method
antigen
used
in
this
experiment
to
detect
the
gene.
Solution
a)
Biopharming
and
plants
is
the
production
genetically
and
engineered
use
to
of
transgenic
produce
animals
pharmaceutical
In Topic B.2 you studied
substances
for
use
in
humans
or
in
other
animals.
In
this
case
the
biotechnology in agriculture.
gene
for
order
a
b)
the
to
vaccine
In
this
to
a
in
ELISA,
sample
This
bind
in
antibody,
antigen.
enzyme
that
to
is
added,
used
to
and
On ce
well s
an
inserted
of
this
to
the
any
in
tobacco
protein
that
plants
will
in
the
by
a ntigen
in
serve
as
is
colou r
an
t h is
at t ac h
T he
a
we l l s
wh en
of
th e
con c entration
the
of
a re
the
f i xe d
an y
linked
an
an t i ge n
the
is
a n t i bod y
ag ai n
e n zy me
pre se n t .
pre se n c e
a n t i g en
f re e
to
wa she d
f or
e n zy me
the
se c ond
of
the
any
su bstr at e
indica tion
dilu tions
to
p la n t s
prote i n s
a void
a n t i ge n
wh e n
t h em.
t obac c o
th e
to
to
on
f i xe d
Th e se
antigen
of
bou n d
c l e an e d
La s tly,
B
plac e d
c al l u se s
w ill
an tibody.
a n ti gen .
is
are
we l l s) .
pu r i f yi n g
has
a ga ins t
an tibody
ch a n g es
Different
detect
he pa ti t i s
thorou ghly
fix ed
colou r
a nd
an t i bodi e s
man y
pl an t s
crus hing
cells
the
a re
wit h
the
toba cco
by
a nt i ge n
dish
ca pture
T h is
free
which
s urfa ce
a n tibody
added.
change
antigen.
B
obta in ed
them.
bound
This
is
Next,
remove
is
s p ecia l
transformed
the
is
to
a
transformed
sample
present
antigen
amounts
hep a titis
(usually
of
containing
B
large
humans.
surface
antibodies
a
hepatitis
produce
of
can
the
be
p re se n t
in
th e
sample.
c)
PCR
An
is
a
method
enzyme,
primers,
thermal
DNA
stick
cycler.
the
Th e
will
a mplify
and
is
bu ffer.
temp era ture
(meltin g
DNA
polymerase
to
p oly mera se,
nucleotid es
stra nds
to
u s ed
DNA
sta ge).
beca us e
th en
Th e
is
T he
th ey
a dd
s ma l l
a moun t s
a dde d
a re
to
t u bes
a
are
i n c re a se d
of
t u be
pl a c e d
to
comp le me n t ar y.
in
a
5′
to
in
s ep a ra t e
comp l e me n t ar y
n ucleotide s
DNA.
c ont ai n i n g
3′
a
th e
pr i me r s
Th e
DNA
aeme p
direction,
You can give your answer as an
extending
the
DNA .
T h ere
is
a
forwa rd
pri me r
whi c h
wil l
annotated diagram, as shown.
copy
the
one
strand
opposite
increasing
and
a
direction .
the
amou n t
reverse
Th is
of
p rim e r
proces s
DNA
wh i c h
occ u r s
wi l l
in
c opy
ma n y
c yc l es ,
ex pon en t i al l y.
5′
template
in
3′
GAATATACCC ATATGAGCC ATATATCC ATATACCT T TC ACCC AT TAAATCCCGTCCCGC ACT
CT TATATGGGTATACTCGGTATATAGGTATATGGAAAGTGGGTAAT T TAGGGCAGGGCGTGA
DNA
3′
5′
5′
3′
GAATATACCC ATATGAGCC ATATATCC ATATACCT T TC ACCC AT TAAATCCCGTCCCGC ACT
3′
GGTAATTTAGGGCAGGGC
5′
primers bind
to template
5′
TATACCCATATGAGCC
3′
CT TATATGGGTATACTCGGTATATAGGTATATGGAAAGTGGGTAAT T TAGGGCAGGGCGTGA
3′
5′
5′
3′
GAATATACCC ATATGAGCC ATATATCC ATATACCT T TC ACCC AT TAAATCCCGTCCCGC ACT
3′
TAGGTATATGGAAAGTGGGTAATTTAGGGCAGGGC
5′
T
aq polymerase
ex tends primers
5′
TATACCCATATGAGCC ATATATCC ATATACCT T TC
3′
CT TATATGGGTATACTCGGTATATAGGTATATGGAAAGTGGGTAAT T TAGGGCAGGGCGTGA
3′
5′
181
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
cycle:
B . 5
1
2
B I O I N F O R M AT I C S
Y  kw:
✔
databases
protein
✔
✔
store
( A H L )
Y  be be :
information
on
DNA,
RNA and
✔
deduce
✔
predict
information
allow
scientists
information
and
databases
increasing
is
searches
the
body
can
easy
of
access
data
to
✔
different
gene
allows
different
organisms.
BLASTn
✔
allows
BLASTp
model
and
stored
similar
sequence
comparison
nucleotide
allows
organisms
can
functions
using
bioinformatic
in
✔
compare
✔
explain
sequences
using
alignments.
exponentially
.
identify
organisms
software
while
databases.
tools.
how
of
be
used
its
a
gene
can
be
used
to
function.
alignment
sequences
sequence
protein
mutating
sequences
determine
in
from
sequences.
databases
BLAST
3
from
✔
identify
✔
analyse
genes
EST
chromosome
bioinformatic
alignment
using
21
mining.
genes
using
tools.
alignment.
to
predict
✔
use
software
✔
design
such
as
BLASTp
to
align
proteins.
gene
phylogenetic
cladograms
from
sequence
functions.
alignments.
✔
databases
can
identied
sequences
function
✔
EST
is
in
an
identify
be
other
searched
with
to
compare
sequences
newly
of
known
organisms.
expressed
sequence
tag
used
to
genes.
A bioinformatic
a
way
many
gene
that
different
search
sequences.
and
U.S.
by
Basic
amino
be
view
the
part
of
of
used
cladograms.
high
The
to
data
of
Center
to
perform
proteins
for
sequence
sequence
for
alignment
of
advances
and
with
an
protein
to
Health
is
a
tool
produce
analyse
Information
(NIH)
of
the
health
information.
for
comparing
sequence
BLASTn
sequences.
are
organized
and
genomic
entire
similarity
.
and
or
are
science
(BLAST)
such
chromosome
(PDB)
databases
Institutes
Tool
a
in
There
Biotechnology
biomedical
Search
organized
information.
sequence
NCBI
BLASTp
sequence
users
National
access
DNA and
for
the
of
useful
structure
National
of
of
access
significant
nucleotide
regions
collection
allowing
the
Alignment
or
a
can
Health.
providing
acid
sequences
182
is
Local
identifying
can
by
Department
research
an
databases,
Particularly
which
is
scientists
(Embl),
maintained
(NCBI)
The
database
other
is
library
,
used
BLAST
for
software
phylograms
and
B.5
B i o i n F o r M at i C s
(ahl)
Exmpe B.5.1.
The
image
The
combination
“address”
obtained
on
a
of
from
chromosome
numbers
and
21
letters
in
Ensemble
provides
a
is
shown.
gene’s
chromosome.
snoitairav
CG %
staeper
senegoduesp
non gnol
seneg gnidoc
non t rohs
seneg gnidoc
nietorp
seneg gnidoc
3.22q
2.22q
21.22q
31.22q
11.22q
3.1
2q
2.1
2q
1.1
2q
2.11q
2.11p
31p
1
2
emosomorhc
a)
State
b)
Identify
c)
Explain
to
the
find
meaning
the
of
address
how
the
of
letters
one
expressed
p
gene
and
q
close
sequence
tag
on
to
the
the
(EST)
chromosome.
centromere.
mining
could
be
used
genes.
Solution
a)
p
signifies
b)
The
c)
An
genes
EST
is
the
short
p11.2
a
obtained
is
by
and
short
approximately
as
a
of
the
on
mRNA,
aligned
800
the
They
the
the
are
the
the
of
long
template
be
of
the
the
the
This
ESTs
as
strand.
using
the
The
DNA
Because
in
ESTs
EST
(cDNA)
sequence
represent
reverse
The
chromosome.
centromere.
cDNA
mRNA.
represented
or
locations.
genome
to
of
complementary
mRNA,
may
arm
closest
nucleotides.
sequence
chromosome
with
q
transcription
to
cDNA/mRNA
specific
q11.2
to
reverse
genes.
and
sequence
500
complementary
expressed
arm
DNA
portions
databases
of
either
complement
can
be
shown
sequence
bioinformatic
the
of
is
can
be
software.
183
B I OT E C H N O LO G Y
B
AND
B I O I N F O R M AT I C S
SAMPLE STUDENT ANSWER
International agreement limits the hunting of whales. Only the meat
of the minke, fin and humpback whales from Southern Hemisphere
populations is allowed to be sold on the domestic market in Japan.
Scientists obtained five samples of food that were being sold as “whale
meat” in a Japanese market place. They identified the species and
probable geographical origin of the meat using genetic analysis. The
results were used to construct the cladogram.
100%
minke whale (Antarctic)
minke whale (Australia)
minke whale (Nor th Atlantic)
sample 1
humpback whale (Nor th Atlantic)
98%
humpback whale (Nor th Pacific)
sample 2
>92%
sample 3
fin whale (Mediterranean)
fin whale (Iceland)
sample 4
92%
sample 5
Hector ’s dolphin
Commerson’s dolphin
) Using the data in the cladogram, state the reason for sale of sample 1
meat being illegal in Japan.
This
answer
Sample
the
1
could
meat
minke
Sample
North
meat
1
have
is
whale
illegal
from
organism
Atlantic.
from
the
[1]
achieved
is
in
the
1/1
Japan
North
likely
T
herefore
Southern
marks:
it
is
to
since
it
Atlantic,
be
from
illegal
a
since
Hemisphere
is
is
closely
related
suggesting
nearby
only
allowed
area
that
to
minke
to
be
to
the
the
whale
sold
in
Japan.
b) Using the data in the cladogram, state the reason for the sale of
sample 4 meat being illegal in Japan.
This
answer
Sample
with
the
is
whales,
have
illegal
dolphins
because
184
4
could
it
only
and
is
achieved
in
Japan
since
likely
whales
1/1
it
not
are
is
to
[1]
marks:
since
it
located
be
a
allowed
shares
in
whale.
to
be
a
a
common
different
T
herefore
sold
in
ancestor
clade
it
Japan.
is
than
illegal
B.5
B i o i n F o r M at i C s
(ahl)
c) Outline how the polymerase chain reaction (PCR) might have been
used in this study.
[3]
▼ The
This
answer
could
have
achieved
0/3
student
described
but
Polymerase
chain
reaction
is
used
to
amplify
DNA.
It
the
genetic
used
alongside
gel
question
electrophoresis
to
identify
markers
used
for
to
In
genes.
Scientists
may
have
compared
a
specic
gene
in
The
primers
“legal”
the
organism
’s
by
amplifying
DNA.
T
hey
could
have
compared
the
specic
DNA,
cutting
it
with
restriction
running
compare
the
the
fragments
fragments.
T
he
on
an
gene
electrophoretic
or
enzymes
fragments
gel
for
similarities
and
differences
been
PCR
be
of
included).
were
of
was
amounts
from
the
conserved
such
as
18S
C
ribosomes
oxidase.
occurs
If
then
no
the
test
to
obtained
with
to
used
samples
cytochrome
could
was
negative.
was
very
known
If
the
different
gene
from
obtained
the
be
legal
compared
small
had
amplication
and
not
case
gene
genes
the
has
this
amplify
DNA (small
certain
correctly
ngerprinting,
could
answered.
be
has
marks:
samples.
gene,
then
the
sample
was
“illegal”.
) Explain how sequence alignment software might have been used in
this study.
This
[2]
answer
could
have
achieved
2/3
marks:
▲ The
student
identied
Sequence
alignment
software
is
used
to
align
DNA,
proteins
differences
or
between
mRNA
to
identify
sequences.
T
he
similarities
DNA
of
the
similarities
and
samples
protein
been
aligned
organisms
to
alongside
determine
the
known
similarities
sequences
between
the
of
two
percentage
through
of
similarities
sequence
alignment
and
certain
software
been
Gene
function
sequences
be
or
the
by
“legal”
whale
inactive
in
can
be
an
physiology
,
studied
knockout
organism
researchers
(in
this
nd
with
case
a
the
the
sequence)
in
order
to
cladogram.
sequences.
identied
used
student
mention
the
be
such
used,
failed
software
as
to
that
BLASTn
could
for
DNA
to
or
BLASTp
for
protein
sequences.
cladogram.
using
of
to
might
sequences
construct
used
other
differences
have
correctly
differences
sequence
▼ The
T
he
and
are
known
construct
have
has
sequences
sequences
DNA or
of
that
using
model
technology
.
and
can
observing
infer
the
organisms
By
causing
any
with
a
differences
probable
similar
specific
function
in
of
gene
to
behaviour
the
gene.
Pcce pbem f op B
Pbem 1
Pbem 4
In India around 5% of the biogas consumed is produced
Microorganisms such as bacteria can be used in
in small-scale family-run biogas plants. Describe
response to pollution incidents. Explain how bacteria
and explain the production of biogas from organic
can be used in response to an oil spill.
matter.
Pbem 5 (ahl)
Pbem 2
Explain how simple DNA microarrays can be used to
Describe an inhibition zone experiment to show the
detect disease.
resistance of bacteria to three different antibiotics.
Pbem 6 (ahl)
Pbem 3
Explain the use of viral vectors in the treatment of SCID.
Explain how plants can be genetically modified to
Pbem 7 (ahl)
overcome environmental resistance to increase crop
Explain how mutating a gene can be used to determine
yields.
its function.
185
EC O LO GY
C
C . 1
C O N S E RVAT I O N
SPECIES
AND
COMMUNITIES
Yu shuld knw:
✔
the
AND
distribution
of
Yu shuld be able t:
species
is
affected
by
limiting
✔
factors.
describe
plant
zones
✔
community
by
structure
keystone
can
be
strongly
each
species
plays
a
✔
unique
role
distribution
of
to
illustrate
of
one
limits
animal
of
and
tolerance
one
and
stress.
affected
species.
describe
of
✔
the
species
within
ways
local
in
examples
which
to
species
illustrate
can
the
interact
range
within
a
a
community
.
community
of
its
because
spatial
habitat
of
the
and
unique
combination
interactions
with
other
✔
species.
explain
the
symbiotic
zooxanthellae
and
relationship
reef-building
between
coral
reef
species.
✔
interactions
can
be
between
classied
species
according
in
to
a
community
their
effect.
✔
analyse
data
between
✔
two
species
same
cannot
habitat
if
survive
their
niches
indenitely
are
in
that
illustrate
and
the
distinction
realized
niche.
the
identical.
✔
explain
the
use
distribution
abiotic
The
sets
fundamental
distribution
of
species
of
of
transects
plant
or
to
correlate
animal
species
the
with
an
variable.
is
affected
by
limiting
factors.
Plant
In Topic 4.1 you studied species,
distributions
are
affected
by
abiotic
factors
such
as
light,
temperature,
communities and ecosystems.
water,
by
pH,
food,
Aquatic
biotic
salinity
and
temperature,
organisms
factors
water,
are
affecting
minerals.
also
Animal
breeding
affected
distribution
distributions
sites
by
and
light,
such
as
are
affected
geographical
pH
and
salinity
.
predation,
factors.
There
herbivory
are
and
competition.
• A keystne speces is one
in which its presence has a
dispropor tionate impact on
The
community
which
means
ecosystem and its removal often
exist
because
leads to signicant changes.
community
.
structure
the
of
whole
the
is
an
emergent
community
interactions
of
has
the
property
certain
of
an
ecosystem,
properties
individual
that
organisms
only
within
that
• A nche is the role or function
of an organism or species in an
Zones of stress and limits of tolerance graphs are models of the real
ecosystem.
world that have predictive power and explain community structure.
• A fundamental nche of a species
Each species has a range of values for biotic and abiotic factors that can be
is the potential mode of existence.
tolerated. Never theless, within a population there is variability, where some
• A realzed nche is the actual
mode of existence, depending on
are more tolerant than others. An example of such limits of tolerance of abiotic
factors is shown in populations of the marine fish Cheilodactylus spectabilis
adaptations and competition with
in the Tasman Sea. Here, increasing temperatures coincide with increased
other species.
growth but only up to a cer tain temperature. Increasing water temperatures
• Cmpette exclusn is a
principle which states that two
have pushed the species past the point where warming is beneficial, as these
high temperatures result in higher metabolic costs and less availability of
species cannot occupy the same
energy for growth and reproduction. As a result, C. spectabilis will be absent in
niche.
those areas where water temperatures surpass their limits of tolerance.
186
C .1
The
keystone
organisms
keystone
dogs
species
affect
the
species
and
a
disproportionate
environment
are
mountain
has
the
sea
star
more
effect
than
Pisaster,
sea
because
expected.
otters,
even
a
Examples
elephants,
SPECiE S
AND
C oM M U Ni T iE S
few
of
prairie
lions.
S AMPLE STUDENT ANS WER
Outline what is meant by a keystone species.
This
answer
could
have
achieved
1/2
[2]
marks:
▲ This
for
Keystone
species
are
those
that
have
a
destabilizing
that
on
disruptive
impact
on
the
ecosystem
they
live
in.
T
hey
can
could
be
who
like
overfeed
ants
on
that
the
have
prey
both
in
a
the
ecosystem,
positive
and
or
is
the
a
on
other
insect
species
other
be
plays
a
species.
classified
competition,
of
Interactions
according
to
predation,
mark
a
species
overfeeds
of
the
implying
organism
is
answer
fails
to
mention
species.
unique
combination
be
negative
the
impact
unique
that
therefore
impact
removal
organism
the
one
could
signicant.
they
that
Each
scored
it
predator
prey
,
the
▼ The
impact
that
be
that
predators
answer
saying
role
its
within
spatial
between
their
community
species
effect.
grazing,
a
habitat
and
in
These
a
because
interactions
community
interactions
mutualism,
symbiosis,
has
on
the
a
of
the
keystone
disproportionate
ecosystem.
of
with
can
can
be
parasitism
and
commensalism.
Many students just mention
that keystone species are very
impor tant to the environment.
Competition
can
be
for
resources
such
as
food,
water,
sunlight,
Although this is true, it is not really
breeding
sites
or
territory
.
Intraspecific
competition
is
between
explaining what it is.
members
different
habitat
of
a
species
species.
if
their
while
Two
niches
interspecific
species
are
cannot
identical
competition
survive
due
to
is
between
indefinitely
competitive
in
the
same
exclusion.
• Cmpettn is a situation in which
one organism or species contends
for the same resources as another.
Example C.1.1.
• Predatn is when an organism
Acanthocephalus
tahlequahensis
is
a
parasitic
worm
often
found
in
(predator) kills a prey to feed on it.
fish
intestines.
The
percentage
of
fish
infected
by
Acanthocephalus
• Grazng is when herbivores feed
parasites
was
measured
in
freshwater
fish.
on plants or algae.
acanthocephalus
• Symbss is a long-term interaction
(Acanthocephalus tahlequahensis)
between dierent biological species.
It can be mutualism, parasitism or
commensalism.
rocksh
sunsh
(Umbra pygmaea)
(Lepomis gibbosus)
• Mutualsm is when both organisms
benet. For example birds feeding on
ectoparasites of cattle.
pirate perch
bream
(Aphredoderus sayanus)
(Lepomis macrochirus)
• Parastsm is when an organism
lives on/in a host and feeds from it,
causing the host harm. For example,
a)
Define
parasitism
using
the
data
provided
as
examples.
worms in animal intestines.
b)
State
the
species
where
most
fish
presented
parasites.
• Cmmensalsm is when one
species gains benets while the
c)
The
bream
(Lepomis
macrochirus)
are
recent
invaders
of
this
other species is neither beneted
environment
and
are
relatively
resistant
to
the
parasite.
nor harmed. For example remora
Comment
on
this
statement
based
on
the
results
shown.
sh feed on the parasites found on
d)
Suggest
and
the
with
a
sunfish
reason
whether
(Lepomis
the
gibbosus)
bream
show
(Lepomis
macrochirus)
intraspecific
the skin of sharks.
competition.
187
C
E C O LO G Y
AND
C O N S E R V AT I O N
Solution
a)
Parasitism
it
harmed
and
case
the
b)
c)
is
causing
is
the
hosts
Pirate
The
are
bream
They
from
to
in
most
cannot
the
C O M M U N I T I E S
species
multiple
✔
a
food
web
a
community
.
the
is
the
an
type
area
of
is
it
would
in
different
shows
all
of
the
trophic
possible
ingested
dependent
stable
on
energy
the
ecosystem
predictable
closed
ecosystems
exchanged
✔
with
disturbance
change
based
the
levels
in
that
as
of
in
tahlequahensis)
fish
reasons:
therefore
they
they
they
are
infected
one
may
supporting
have
have
only
not
competition
from
interspecific
is
this
and
the
by
be
that
recently
had
they
statement.
time
been
to
the
because
same
they
genus.
If
are
not
they
do
competition.
EC O SYST E M S
✔
analyse
food
chains
✔
explain
in
food
webs.
converted
respiration
that
on
will
energy
the
conversion
production
explain
to
ratio
in
sustainable
food
practices.
how
humans
interfere
with
nutrient
cycling.
rate.
emerge
compare
in
pyramids
of
energy
from
different
ecosystems.
climate.
but
not
matter
analyse
is
structure
climographs
between
surroundings.
inuences
within
be
A N D
✔
✔
two
intraspecific
species,
✔
✔
host
chains.
percentage
biomass
percentage
to
environment,
have
same
✔
✔
the
organism
sayanus).
due
be
parasitic
fish.
parasite,
could
the
(host),
therefore
Yu shuld be able t:
occupy
food
the
The
another
it;
(Acanthocephalus
lowest
be
off
killing
infected.
Yu shuld knw:
✔
the
could
feeds
benefits.
different
shows
reason
compete,
C . 2
parasite
the
This
introduced
d)
normally
(Aphredoderus
resistant
become
organism
not
acanthocephalus
perch
Another
one
but
the
are
parasites.
when
harm
showing
temperature,
the
rainfall
relationship
and
the
type
of
ecosystem.
and
rate
of
✔
construct
ecosystems.
Gersmehl
relationships
in
taiga,
✔
analyse
✔
design
desert
data
ecosystem
is
a
and
experiments
community
made
to
of
show
stores
inter-
ows
succession.
determine
living
the
and
rainforest.
primary
disturbance
up
to
nutrient
tropical
showing
environmental
An
diagrams
between
on
an
the
effect
of
an
ecosystem.
organisms
and
its
You studied energy flow in
interaction
with
the
abiotic
environment
such
as
air,
water
and
Topic 4.2.
mineral
soil.
Changes
Most
Examples of aspects investigated
in the ecosystem that you could
be tested on could be species
diversity, nutrient cycling, water
movement, erosion and leaf area
index, among others.
188
in
community
species
therefore
A food
chains
it
is
web
in
a
occupy
not
is
a
structure
different
very
more
practical
realistic
community
.
affect
trophic
to
and
levels
show
model
as
are
in
these
it
affected
multiple
by
relationships
shows
all
the
organisms.
food
chains;
in
a
possible
chain.
food
C.2
C oM M U Ni T iE S
AND
E C o S YS T E M S
Example C.2.1.
The
diagram
is
of
an
ocean
food
web.
polar
gull
humans
bear
fulmar
harp
ringed
guillemot
nar whal
beluga
seal
seal
Arctic cod
arrow worms
amphipods
walrus
copepods
bivalve
molluscs
kelp
algae
a)
b)
c)
State
a
State
producer
the
Predict
most
detritus
phytoplankton
in
trophic
what
this
web.
level(s)
would
of
the
happen
to
gull.
this
web
if
a
disease
killed
guillemots.
Solution
a)
Algae,
b)
Third
c)
kelp
and
or
fourth
Amphipods
guillemots.
will
on
be
will
This
eaten
will
consumer
increase
means
more.
guillemots,
these
phytoplankton
they
At
in
that
the
will
number
algae
same
feed
as
and
time,
more
they
kelp
as
on
stop
will
gulls
fulmar
being
eaten
decrease,
can
and
no
as
longer
Arctic
by
they
feed
cod,
so
In a), only one of these answers is
expected and in b), both answers
are needed to score the mark .
decline.
Pyramids of energy model the energy flow through ecosystems. Energy
is lost from one trophic level to the other. Most of the energy is lost as
• A bme is a community of living
organisms that share the same
climate.
heat. The percentage of ingested energy conver ted to biomass is dependent
on the respiration rate. Energy can also be lost as indigestible material (eg,
cellulose and fibre for humans) and as uneaten par ts such as hair and teeth.
The loss of energy from one trophic level to the other can be shown with a
pyramid of energy.
third consumers
second consumers
rst consumers
producer
The
type
based
on
of
stable
climate.
temperature
of
living
habitats.
(snow
and
ecosystem
that
Climographs
precipitation
organisms
Examples
living
of
in
a
biomes
will
emerge
represent
of
a
location.
common
are
the
in
area
A biome
climate.
deserts,
an
monthly
It
tropical
is
can
is
predictable
average
a
community
comprise
rainforests
many
and
taiga
forests).
189
C
E C O LO G Y
AND
C O N S E R V AT I O N
Example C.2.3.
The
diagram
shows
a
climograph.
100
40
75
mm / llafniar
50
0
25
–20
0
–40
Jan
a)
b)
c)
C° / erutarepmet
20
State
State
Feb
the
Apr
May
maximum
the
Identify
Mar
warmest
the
biome
Jun
Jul
Aug
Sep
precipitation
month
in
this
represented
Oct
in
Nov
this
Dec
location.
location.
in
the
climograph.
Solution
a)
78
mm
Gersmehl
nutrient
of
the
the
diagrams
stores
circles
arrows
b)
and
is
gives
direction
an
an
of
are
models
flows
c)
of
between
indication
indication
the
July
of
of
the
inter-relationships
biomass,
the
taiga
litter
amounts
amounts
and
stored,
flowing
and
between
soil.
the
the
The
width
arrow
diameter
of
the
shows
flow.
• A taga is a temperate forest with
taiga
deser t
tropical rainforest
cold winters and warm summers.
B
B
There is little precipitation. Its main
B
store is litter (pine needles) with
little ow between stores.
L
• A deser t is very dry with very hot
L
L
days and cold nights. Its main store
S
S
is in soil and there is major ow
S
from biomass to litter.
• A trpcal ranfrest is rainy and
hot. Biomass is its main store with a
Fgure C.2.1.
Gersmehl diagrams for taiga, deser t and tropical rainforest
high rate of ow.
S AMPLE STUDENT ANS WER
Distinguish between tropical rainforest and taiga in terms of nutrient
stores, nutrient flows and climate. Gersmehl diagrams can be used to
suppor t your answer.
This
▲ This
for
answer
scored
distinguishing
the
two
marks
levels
answer
could
have
[6]
achieved
2/6
marks:
T
ropical rainforest has the largest plant species biodiversity
of
of all the land biomes. It has an abundant amount of life,
precipitation
both
and
temperature
in
biomes.
and therefore the amount of nutrient for each energy level
is very abundant. T
aiga is the largest terrestrial biome, but
▼ This
address
store,
answer
the
needed
differences
nutrient
ow
to
in
and
the diversity of its plant and animal life is much lower
,
nutrient
climate.
consisting of large mammals and coniferous trees. Because
the rainforest is so diverse, the amount of predators and
190
C.2
C oM M U Ni T iE S
AND
E C o S YS T E M S
prey ensure that there are many trophic levels. Consumers
like monkeys can also be secondary consumers and in
turn be consumed by tertiary consumers. T
aiga does not
have as many levels or such complex food webs due to the
The Gersmehl diagrams are based
lesser amount of species. T
ropical rainforests have heavy
on biomass, nutrient storage in
precipitation and the air is usually humid and hotter
litter and nutrient storage in soil
than many biomes all year round. T
aiga is much drier
,
and the flow between these. The
answer had to be focused on
the temperature is cooler as most taiga are near or in the
these, as the question clearly
mountains, and there is heavy snowfall but not as much
stated you could use these
diagrams.
precipitation.
Living
organisms
energy
into
can
kinetic
energy
.
it
matter
have
of
the
an
is
is
ecosystem
lost
cannot
from
the
exchanged
energy
These
into
are
environment,
energy
be
interconvert
the
can
is
also
as
In
be
into
rates
the
which
measured
in
can
other
The
into
of
heat
energy;
energy
environments
depend
on
the
primary
per
converted
form
ecosystems
net
mass
Light
be
converted
any
closed
average
energy
.
which
surroundings.
conversion
measured
energy
,
converted
ecosystem.
with
which
can
chemical
Chemical
energy
different
involved.
in
converted
energy
.
Heat
therefore
not
be
unit
but
can
organisms
productivity
area
per
unit
2
time
(eg,
Feed
at
g/m
conversion
converting
It
is
of
the
food
body
mass
ratio
their
of
temperature)
they
have
a
is
food
the
produced).
homeotherms
as
/yr).
how
into
input
efficient
the
(food
desired
given)
Poikilotherms
are
more
(animals
higher
that
rate
the
output
divided
(animals
effective
maintain
of
bodies
that
of
milk
the
have
of
regulated
conversion
organisms
(eg,
by
producers
a
of
food
meat).
output
a
(mass
variable
protein
body
to
or
are
than
temperature)
biomass.
Example C.2.4.
• Bmass is the total dry organic
matter.
The
efficiencies
of
production
of
some
food
meat
products
and
of
• Grss prductn is the total
crickets
are
shown
in
the
table.
amount of organic matter produced
per unit area per unit time by a
Crcket
Beef
Chcken
Feed cnersn rat (FCR)
1.7
10
2.5
Edble pr tn / %
80
40
55
trophic level in an ecosystem.
• Net prductn is the amount of
gross production remaining after
the amount used for respiration
a)
State
the
least
efficient
food
source.
by the trophic level has been
b)
(i)
Distinguish
between
beef
and
chicken
as
food
subtracted.
sources.
• Feed cnersn rat (FCR) is
(ii)
Explain
reasons
for
the
differences.
the eciency of production of an
c)
Using
the
data,
discuss
whether
crickets
are
a
good
source
of
animal food source.
food.
• Pkltherms are animals whose
body temperature varies with the
Solution
environment.
a)
b)
Beef
(i)
Chicken
FCR
has
than
a
larger
beef.
percentage
of
edible
parts
and
a
lower
• Hmetherms are animals that
maintain their body temperature.
191
C
E C O LO G Y
AND
C O N S E R V AT I O N
(ii)
Chicken
FCR,
is
this
amount
animal
more
mean
of
efcient
that
meat
to
therefore
c)
If
Crickets
FCR.
are
are
This
edible,
eating
due
they
a
is
Ecological
is
to
is
less
is
due
lost.
to
fed
energy
that
to
the
One
be
source
fact
that
is
because
may
be
they
most
that
of
it
maintain
as
it
obtain
around,
food,
problem
just
to
move
to
because
chickens
of
because
less
probably
source
sometimes
religious
food
allowed
good
mainly
little
This
reason
not
very
insects,
to
are
a
needs
eat.
requires
perature. Another
cages.
it
as
taste,
the
is
its
a
this
a
same
body
in
the
of
energy
.
lowest
their
everybody
but
other
tem-
small
saves
have
lower
smaller
kept
parts
not
has
body
likes
times
issues.
successions
are
processes
where
the
species
structure
of
an
• Prmary successn occurs in
ecological
community
changes
over
time.
Primary
succession
occurs
areas that were not inhabited by
in
environments
where
there
were
no
soil
or
organisms,
such
as
lava
living organisms.
flows
or
glacier
retreats.
Secondary
succession
occurs
in
areas
that
• Secndary successn occurs in
previously
supported
organisms
before
an
ecological
disturbance
such
areas that were already inhabited
as
a
fire,
flood
or
agricultural
practices.
Disturbance
influences
the
but suered disturbance.
structure
C . 3
I M PA C T S
O F
and
introduced
alien
ecosystems
✔
and
competitive
predators
of
endemic
species
become
lead
species
to
change
within
O N
ecosystems.
EC O SYST E M S
Yu shuld be able t:
exclusion
can
of
H U M A N S
Yu shuld knw:
✔
rate
can
escape
into
local
✔
invasive.
and
the
when
alien
in
the
species,
absence
reduction
explain
the
of
✔
numbers
species
become
alien
of
especially
evaluate
control
effect
the
the
eradication
as
measures
introduction
cane
toads
in
programmes
to
reduce
the
of
an
alien
Australia.
and
biological
impact
of
species.
invasive.
✔
✔
pollutants
of
become
organisms
at
concentrated
higher
trophic
in
the
levels
tissues
analyse
data
illustrating
consequences
of
the
causes
and
biomagnication.
by
✔
discuss
the
trade-off
between
control
of
the
biomagnication.
malarial
✔
macroplastic
and
accumulated
in
microplastic
debris
and
DDT
pollution.
has
✔
marine
parasite
explain
the
impact
of
marine
plastic
debris
on
environments.
Laysan
albatrosses
and
one
other
named
species.
In Topic 4.1 you studied species,
The use of biological control has associated risk and requires
communities and ecosystems.
verification by tightly controlled experiments before it is approved. One
of the most well-known invasive species was introduced as a biological
control. The cane toad (Rhinella marina) was introduced to Australia to control
the cane beetle (Dermolepida albohir tum). The cane toad and their tadpoles
In Topic 5.4 you studied
are highly toxic to most animals if ingested. As they do not have natural
reclassification of organisms using
predators, they have become a competitor for food resources and have
evidence from cladistics. You will
spread throughout the country. Decreases in the populations of cer tain
find many books refer to the cane
species of frogs (Limnodynastes peronii), large lizards (Bellatorias major,
toad as Bufo marinus, but it has
Intellagama lesueurii, and Varanus varius) and snakes (Pseudechis
now been reclassified as Rhinella
porphyriacus) occurred following the introduction of R. marina.
marina
192
C.3
Introduced
alien
species
can
escape
into
local
ecosystems
and
i M PA C TS
oF
HUMANS
oN
E C o S YS T E M S
become
• Bmagncatn is the
invasive.
Competitive
exclusion
and
the
absence
of
predators
can
lead
increasing concentration of toxins
to
reduction
in
the
numbers
of
endemic
species
when
alien
species
in the tissues of organisms at
become
invasive.
Biological
control
has
been
used
to
try
and
control
successive higher levels in a food
alien
species.
Pollutants
trophic
become
levels
pesticides,
and
chain.
by
concentrated
industrial
microplastic
in
the
biomagnification.
wastes,
debris
heavy
have
tissues
Examples
metals
accumulated
of
and
in
organisms
of
pollutants
plastics.
marine
at
higher
are
Macroplastic
environments.
S AMPLE STUDENT ANS WER
a)
Outline the concept of biomagnification of plastic pollution in
oceans.
[3]
▲ This
mark
This
answer
could
have
achieved
2/3
answer
for
level
is
when
toxins
released
from
primarily
the
up
general
waste
or
antibiotics
are
passed
along
to
level.
T
he
toxins
increase
in
destructive
pass
toxins
from
that
prey
could
to
have
predator
,
such
and
an
capacity
by
as
plastic
effect
on
rafts
the
contain
achieved
2/2
on
these
rafts
is
can
not
know
what
it
is.
hazardous
Birds
macroplastic
Microplastics
can
be
can
might
choke
ingested
to
other
animals
that
consume
them
as
food;
are
by
the
bird
animals
or
worsen
and
the
its
in
biomagnication.
T
he
toxins
means
this
can
affect
a
not
is
a
pesticideused
used
reduction
in
of
the
to
reduce
reduction
mosquitoes
led
of
to
fact
that
wide
these
selection
pests
that
mosquitoes
a
ratesof
biomagnification
in
health
islands
of
the
reduced
top
predators.
reproductive
reduction
food
For
success
organisms
from
prey
to
about
have
plastics
in
toxins
the
(not
of
are
on
animals.
disease
carrying
in
vectors.
malaria.
malaria.
chainscaused
a
example,
in
birds
It
negative
of
that
such
as
answer
just
does
microplastics
or
consumed
birds.
metabolized
in
As
by
the
are
by
toxins
organisms
tissues.
This
answer
saying
that
scored
birds
one
macroplastics
that
can
mark
and
plastics
choke
another
can
for
worsen
health.
was
This
Unfortunately
,
thethinning
of
The
are
▼ The
that
answer
these
failed
islands
into
to
can
areas
mention
introduce
where
the
impact
is
not
found.
Another
eggshells
issue
and
that
ingested
pathogen
on
absorbed
was
release
pathogens
the
are
should
accumulate
their
widely
it
mention
saying
DDT
for
can
for
motile
the
is
health.
▲
result
mark
mention
wastes).
directly
they
ingesting
(although
not
marks:
animals
do
so
mentioned
[2]
not
plastic
is
level
question
human
T
he
chain
toxins
trophic
they
plastics,
ocean
have
are
successive
ecosystem.
mobility of plastic rafts and the communities they host.
could
food
second
that
lower
▼ The
answer
each
predator).
b) Other than biomagnication, outline t w concerns associated with
This
one
toxins
each
(when
they
in
destructive
The
saying
trophic
the
term
ideal).
human
that
marks:
concentrated
Biomagnication
scored
saying
not
mentioned
is
that
the
prey
.
introduced
species
may
become
invasive.
S AMPLE STUDENT ANS WER
State one advantage and one disadvantage regarding the use
of DDT.
This
[2]
answer
DDT
could
prevents
insects
and
have
the
then
achieved
spread
of
prevents
2/2
marks:
illnesses
humans
such
as
getting
malaria
that
through
illness
from
▲ This
them.
However
,
DDT
releases
toxins
as
soon
as
those
for
mentioning
levels
with
it
are
consumed,
and
biomagnication
ensures
that
impacts
other
species.
scored
of
the
the
one
mark
reduction
malarial
in
parasite
the
and
it
the
detrimentally
answer
infected
of
other
DDT.
mark
The
maximum
for
biomagnication
student
achieved
marks.
193
C
E C O LO G Y
C . 4
AND
C O N S E R V AT I O N
C O N S E R VAT I O N
O F
Yu shuld knw:
✔
entire
order
✔
an
communities
to
preserve
indicator
assess
a
specic
Yu shuld be able t:
need
to
be
conserved
in
✔
describe
biodiversity
.
species
B I O D I V E R S I T Y
is
an
cases
of
reintroduction
organism
environmental
used
to
✔
analyse
condition.
on
the
captive
of
an
impact
diversity
endangered
of
limited
breeding
and
animal
biogeographical
to
island
size
and
species.
factors
edge
effects.
✔
relative
used
✔
in
to
situ
numbers
calculate
ex
situ
of
outside
may
is
their
species
can
a
biotic
index.
require
active
value
nature
conservation
species
indicator
the
conservation
management
✔
of
of
reserves
the
or
national
preservation
natural
be
✔
dene
biotic
✔
dene
biodiversity
parks.
biogeographical
✔
richness
and
factors
of
✔
analyse
habitats.
evenness
affect
are
species
in
terms
of
richness
and
evenness.
the
biodiversity
communities
of
✔
index.
using
of
two
Simpson’s
local
reciprocal
index
diversity
.
diversity
.
components
of
biodiversity
.
The preservation of species involves international cooperation through
In Topic 4.1 you studied species,
intergovernmental and non-governmental organizations. The Andean
communities and ecosystems.
condor (Vultur gryphus) was in danger of extinction. In 1991, the Andean Condor
Conservation Program (PCCA) of Argentina developed ar tificial incubation
• In situ cnser atn refers to
programmes and techniques for hand rearing birds using puppets (without
conservation of species in their
human contact) and worked to rescue and rehabilitate wild condors. The venture
own natural habitat, for example in
included public and private funding from different countries. In 20 years more
natural reserves or national parks.
than 160 condors have been released in all South America. Andean condors
• Ex situ cnser atn is the
routinely cross borders between countries and, therefore, it was essential that
preservation of species outside
international stakeholders unite to coordinate in its conservation.
their natural habitats, for example,
in zoos, botanical gardens or seed
banks.
An
indicator
species
environmental
used
to
calculate
pollution
is
the
that
one
or
in
of
the
is
a
of
pollution
used
to
numbers
biotic
If
environment,
If
on
present,
pollution
intolerant
assess
of
index.
intolerant.
polluted.
species
Examples
while
organism
Relative
pollution
found
intolerant
unpolluted.
an
value
environment
pollution
worms
the
tolerant
only
this
is
condition.
then
ones
a
is
the
a
species
species
pollution
other
tolerant
specific
Indicator
there
the
a
indicator
tolerant
high
hand,
include
are
stonefly
be
be
species
probability
there
environment
organisms
can
can
are
must
be
leeches
larvae
and
and
caddisflies.
The
formula
for
biotic
index
is
the
following:
1
∑
(n
× a
i
)
i
n = 1
Biotic
index
=
N
Where
n
is
the
number
of
individuals
of
a
species
and
a
i
of
means
and
of
that
this
collected.
194
of
for
value
species
is
the
level
i
tolerance
that
given
each
is
have
species.
species
added
been
to
its
the
added.
The
number
next
N
sign
is
is
total
means
“the
multiplied
species
the
Σ
and
so
number
by
on,
of
sum
the
until
of”;
this
tolerance
all
i
number
individuals
C.4
C o N S E R v AT i o N
oF
BioDi vERSiT Y
Example C.4.1.
The
graph
shows
ecological
biotic
the
groups
index
(BI)
evolution
(from
from
very
1990
of
the
percentage
tolerant
to
2005
to
very
recorded
of
different
sensitive)
in
an
and
the
estuary
.
100
6
90
5
% / sepyt fo egatnecrep
80
very tolerant
70
4
tolerant
60
IB
50
3
indierent
slightly sensitive
40
2
very sensitive
30
20
1
10
0
0
1990
1995
2000
2005
year
a)
State
the
b)
Using
of
c)
the
the
the
with
data,
quality
Suggest
to
year
greatest
amount
of
very
sensitive
species
in
estuary
.
a
explain
of
the
reason
how
the
biotic
index
gives
an
idea
water.
for
the
lowering
of
the
BI
from
the
year
2000
2005.
Solution
a)
1990
b)
In
(with
this
data,
species
and
pollution
species,
c)
for
higher
the
nature
and
shape
that
and
have
a
little
see
only
therefore
there
in
are
higher
very
this
tolerant
year
many
pollution,
The
the
are
that
the
large
must
affect
in
are
the
the
very
therefore
biotic
and
of
a
of
This
sensitive
they
index,
can
the
diversity
.
is
by
The
in
banning
due
a
to
factory
the
there
of
For
a
is,
so,
perimeter
are
of
a
(like
a
the
larger
biodiversity
more
effective
also
affects
reserve
ideally
,
calculating
biodiversity
example,
reserve
edge
Any other reasonable suggestion
will be accepted.
corridors
edge
when
probably
preserving
shape
to
small
is
species
estuary
.
close
considered
index
sensitive
example
the
it
connected
differs
for
into
species
connected.
area
2000).
efficient
amount
be
reciprocal
none
slightly
pollution,
more
not
and
chemicals
Biodiversity
evenness
Simpson’s
stop
factors
is,
determines
should
1990.
were
to
their
reserves
biodiversity
.
can
When
is
sensitive
(there
taken
reserve
those
there
in
one
species,
greatest.
means
sending
small
than
sensitive
the
very
Biogeographical
a
2000,
pollution.
reappeared
from
year
example
the
measures
the
no
this
2005,
in
was
thrive,
In
30%)
a
and
the
reserve
circle).
Richness
biodiversity
.
considers
both
of
these
numbers.
N (N
1)
D =
∑
Where
and
n
value
n (n
D
is
is
the
for
D
1)
the
diversity
number
means
of
index,
N
organisms
there
is
a
lot
of
is
of
the
total
each
number
individual
of
species
species.
found
A large
biodiversity
.
195
C
E C O LO G Y
AND
C O N S E R V AT I O N
Example C.4.2.
• indcatr speces are organisms
The
diagram
represents
four
A
B
C
D
that indicate the health of an
different
communities.
Each
ecosystem or level of pollution.
geometric
figure
represents
a
• Bdersty measures the
different
species.
variation of species in a community.
a)
Deduce
with
a
reason
the
• Rchness is the number of
community
with
the
largest
dierent species present in a
evenness.
community.
b)
• Eenness is how close in
numbers each species in an
Calculate
the
reciprocal
environment is – how equal the
Simpson’s
diversity
community
B.
index
Show
for
your
working.
community is numerically.
c)
Suggest
which
community
has
the
smallest
biodiversity
.
Solution
a)
D
because
the
b)
D
other
c)
C . 5
C
(both
(with
low
P O P U L AT I O N
dynamic
density
✔
biological
and
sampling
✔
the
processes
population
3
1
a
+
1
×
0
3
organisms
1
×
12/2
diversity
EC O LO GY
impact
population
✔
used
to
pattern
evaluate
of
estimate
✔
occurs
in
growth
reaches
carrying
the
species
is
the
same
as
each).
6
index
of
1).
This
is
because
it
has
a
( A H L )
the
methods
commercial
describe
the
slows
as
a
capacity
stock
use
of
recapture
method
size
animal
of
an
used
of
the
to
to
estimate
marine
the
size
resources.
capture-mark-release-
estimate
the
population
species.
an
environment.
population
=
one
0)
✔
discuss
the
effect
immigration
✔
in
of
richness.
growth.
are
growth
unlimited
+
Simpson’s
size.
exponential
ideal,
×
organisms
Yu shuld be able t:
techniques
population
have
4
of
=
×
Yu shuld knw:
✔
number
=
(2
Always show your working.
the
and
of
natality
,
mortality
,
emigration
on
population
size.
population
of
the
✔
environment.
analyse
the
effects
reproductive
of
status
population
on
size,
sustainable
age
and
shing
practices.
✔
the
phases
explained
shown
by
immigration
in
the
relative
and
sigmoid
rates
of
curve
natality
,
can
be
mortality
,
✔
emigration.
explain
bottom-up
shortage
of
control
nutrients
and
of
algal
blooms
top-down
by
control
by
herbivory
.
✔
limiting
factors
can
be
top-down
or
bottom-up.
✔
design
models
organism
Sampling
techniques
are
used
such
to
of
as
the
growth
yeast
estimate
or
curve
species
population
using
a
simple
of Lemna.
size.
The
capture-
In Topic 4.1 you studied species,
mark-release-recapture
method
is
frequently
communities and ecosystems.
population
196
size
of
an
animal
species.
used
to
estimate
the
C.5
P o P U L AT i o N
E C o Lo G Y
(AHL)
S AMPLE STUDENT ANS WER
The population sizes of
Explain how the Lincoln index is used to determine population size.
commercial stock of marine
[4]
resources can be estimated by
This
answer
could
have
achieved
4/4
marks:
echo sonography or by inferring it
according to the catch age
distribution. In the fishing industry,
T
he
Lincoln
index
is
calculated
from
the
capture-markyields depend on natural
release-recapture
method.
It
is
calculated
according
to
the
processes such as growth,
number
of
individuals
caught
and
marked
initially
mor tality and reproduction.
and
Therefore it is impor tant to allow
those
recaptured
in
the
second
sample
divided
by
the
number
fish to grow to a reasonable size
of
the
recaptured
which
are
x
N
before being caught. It is impor tant
N
1
Population
marked.
2
to predict the effect of changes in
size =
size of net and of mesh and the
N
3
Where
N
is
the
number
caught
and
marked
initially,
amount of fishing on the rates of
N
1
2
reproduction and survival. This can
is
the
total
number
caught
in
2nd
sample
and
N
is
the
3
number
of
marked
individuals
help prevent the thinning of fishing
recaptured.
stocks.
▲ This
Exponential
population
environment.
by
relative
the
The
rates
sigmoid
growth
phases
of
curve,
occurs
shown
natality
,
in
the
mortality
,
population
in
an
ideal,
sigmoid
unlimited
curve
immigration
growth
is
can
and
exponential
be
points
explained
emigration.
and
then
it
answer
of
the
covers
Lincoln
all
the
diversity
index.
In
slows
• The Lncln ndex uses data
until
the
population
reaches
the
carrying
capacity
of
the
environment.
obtained from the capture-mark-
release-recapture method to
estimate the size of a population.
small uctuations
• A sgmd grwth cur e shows
due to factors such
changes in population over time.
carrying capacity
as food supply
700
mc snoillim / airetcab fo rebmun
3–
• Natalty is number of bir ths.
exponential
stationary
(log) phase
600
• Mr talty is number of deaths.
phase
rapid growth
no growth
500
• immgratn is when organisms
arrive at an environment.
400
• Emgratn is when organisms
300
leave an environment.
lag
• Carryng capacty is the
200
phase
maximum population an
slow
100
environment can hold due to food,
growth
territory or breeding sites.
0
0
10
20
30
40
50
60
70
time / hours
Fgure C.5.1.
Sigmoid growth curve
You can be asked to draw this
curve for different organisms.
• Tp-dwn factrs aect the
population from a trophic level
above it.
• Bttm-up factrs aect the
population from a lower trophic
level or from a nutrient store.
197
C
E C O LO G Y
AND
C O N S E R V AT I O N
Example C.5.1.
An
up
experiment
control
grown
salina)
on
with
in
was
salt
(+)
performed
marsh
and
without
mesocosms
repeated
with
grass
with
addition
(
or
of
to
examine
(Spartina
)
a
top-down
densiflora).
herbivore
without
salt.
and
The
planthopper
The
bottom-
grass
was
(Prokelisia
experiment
was
nutrient.
14
12
mc / htworg tnalp
10
8
6
nutrient added
4
no added nutrient
2
0
–
+
–
+
herbivores
salt absent
salt present
condition
a)
b)
State
Outline
of
c)
the
plant
d)
Use
the
mode
the
in
the
effect
these
by
the
which
of
marsh
grass
nutrients
herbivores
mesocosms
information
planthopper
with
where
are
grows
the
bottom-up
most.
controls
growth.
Outline
grasses
conditions
to
on
explain
herbivores
on
the
without
the
marsh
growth
of
marsh
salt.
top-down
grass
effect
grown
in
of
mesocosms
salt.
Solution
a)
Marsh
grass
without
b)
Nutrients
example
by
marsh
grasses
marsh
plants
might
nutrients,
d)
the
no
marsh
ions
in
with
nutrients
for
formation
needed
added
and
for
plant
of
growth.
nucleic
these.
For
acids
Nutrients
and
are
plants.
present
more.
less.
needed
the
also
of
and
But
This
with
herbivores
are
no
when
could
the
are
nutrients
are
nutrients
be
marsh
of
This
plant
is
due
to
added,
are
the
grasses
added,
fact
and,
the
controls
because
leaves.
herbivores
nutrients
reducing
grass.
top-down
added.
destroying
presence
environment,
198
salt,
that
with
the
the
other
the
more.
because
marsh
is
compete
nutrients
the
probably
the
grow
grasses,
present,
used
are
grow
grow
Planthopper
when
mineral
is
roots
herbivores
plants
without
Phosphorus
absorbed
When
include
nitrogen
proteins.
c)
grown
herbivores.
allow
other
damage
When
increases
by
marsh
feed
nutrients
marsh
plants
done
of
they
to
the
grasses
on
are
grass
grow
the
in
growth,
the
planthoppers
to
C.6
C . 6
N I T R O G E N
A N D
Ni T R o GE N
AND
PHoSPHoRUS
P H O S P H O R U S
C YCLE S
(AHL)
C Y C L E S
( A H L )
Yu shuld knw:
✔
nitrogen-xing
nitrogen
✔
to
Rhizobium
Yu shuld be able t:
bacteria
convert
atmospheric
✔
draw
a
labelled
✔
explain
diagram
of
the
nitrogen
cycle.
ammonia.
associates
with
roots
in
a
mutualistic
the
nitrogen
impact
of
waterlogging
on
the
cycle.
relationship.
✔
✔
in
the
absence
reduce
✔
nitrate
phosphorus
cycle
of
by
oxygen
in
can
the
be
harvesting
the
rate
of
bacteria
of
much
✔
to
the
fertilizer
agricultural
turnover
lower
availability
to
✔
of
of
agriculture
leaching
land
to
than
of
into
the
the
the
rivers
phosphorus
or
removed
✔
by
nitrogen
affect
the
of
phosphorus
may
nutrients
causes
is
key
plants
availability
as
in
an
adaptation
waterlogged
experiments
of
a
soil
to
assess
the
nutrient
sample.
cycle
is
outline
of
cycle.
soil
how
crop
nutrients
rotations
by
allow
allowing
an
the
area
renewal
to
remain
“fallow”.
become
limiting
✔
describe
✔
explain
the
phosphorus
cycle.
future.
from
agricultural
eutrophication
biochemical
cycle
rate
design
content
oxygen
and
may
leads
very
important
ecosystem
the
reason
become
availability
limiting
to
of
phosphate
agriculture
in
the
future.
demand.
✔
The
insectivorous
nitrogen
crops.
nitrogen
phosphate
in
mineral
increased
in
low
soils.
✔
✔
describe
to
soil.
added
application
the
denitrifying
because
nitrogen
explain
availability
eutrophication.
can
processes.
In Topic 4.1 you studied species,
communities and ecosystems.
nitrifying bacteria
eg Nitrobacter
Nitrites (NO
absorption by roots
Nitrates (NO
)
Protein in
)
• Dentrcatn is the turning
3
2
green plants
in soil
in soil
of nitrates to atmospheric
nitrogen.
• Ntrcatn is the
transformation of ammonium
denitrifying
nitrogenbacteria
nitrifying
compounds to nitrites and
xing bacteria
feeding
nitrates.
bacteria
eg Rhizobium
and
eg Nitrosomonas
(mutualistic)
digestion
lightning
• Ammncatn is the
transformation of proteins to
ammonia.
Ammonium
Atmospheric
Protein in
nitrogen
animals
• Ntrgen xatn is
compounds
the transformation from
(in soil)
atmospheric nitrogen to
protein.
chemical
excretion
death
combination
(natural or in
fertilizer manufacture)
ammonication by
Protein in
Nitrogenous
putrefying bacteria
dead organisms
waste, eg urea
Ammonia
ammonication by putrefying bacteria
Fgure C.6.1.
The nitrogen cycle
199
C
E C O LO G Y
AND
C O N S E R V AT I O N
Example C.6.1.
Our huge population growth
has led to an increase in the
a)
Outline
the
impact
of
waterlogging
on
the
nitrogen
cycle.
demand for food, which, in turn,
has led to intensive methods of
b)
Describe
nitrogen
agriculture. Intensive agriculture
insectivorous
availability
plants
in
as
an
adaptation
waterlogged
for
low
soils.
involves labour-intensive and
Solution
costly practices in order to obtain
a)
Waterlogging
fills
the
air
gaps
in
the
soil
with
water.
In
the
high yields per unit of land.
absence
of
oxygen
denitrifying
bacteria
reduce
nitrate
in
the
soil
Intensive animal farming methods
to
atmospheric
nitrogen.
An
example
of
denitrifying
bacteria
are often criticized for involving
is
Pseudomonas
denitrificans
which
uses
nitrate
as
an
electron
low standards of animal welfare,
acceptor
to
produce
ATP
.
which rely on the overuse of
b)
Insectivorous
plants
obtain
their
food
through
photosynthesis
antibiotics to be viable. Issues
and
make
organic
products
using
light.
Nevertheless
these
associated with intensive crop
carnivorous
plants
live
in
nutrient-poor
habitats
where
there
farming methods are the use of
are
almost
no
nitrates
available,
therefore
need
to
trap
insects
in
toxic pesticides which are often
order
to
obtain
their
nitrogen.
carcinogenic and bioaccumulate,
harming non-target species, and
the use of chemical fer tilizers
Phosphorus
is
pres en t
in
a ll
living
org an i s ms.
It
is
p re s en t
in
which can cause eutrophication of
the
phospholipids
of
cell
membra ne s,
is
re qui re d
f or
mak i n g
waterways.
ATP
,
DNA
and
after
phosphoryla tion ,
Phosphorus
fertilizer
or
turnover
in
cycle
the
RNA ,
can
be
therefore
foun d
an d
a dded
removed
the
is
by
is
to
prot e i n s
neede d
the
cycle
a va ila bility
to
and
f orm
p hos phoru s
ha rvestin g
phos p horus
its
in
bon e s
cyc l e
a gr i c u l t u r al
is
may
car boh yd r a t e s
much
than
li mi t i n g
teeth.
a pp l y i n g
c rops .
l ower
become
a nd
by
The
in
to
rate
th e
of
n i t rogen
a gr i c u l t u re
in
future.
S AMPLE STUDENT ANS WER
• Eutrphcatn is the enrichment
with nutrients of a body of water
leading to the excessive growth of
The graph shows the global phosphorus fer tilizer use from 1960 to
2011.
plants and algae, causing oxygen
25
depletion.
the amount of dissolved oxygen
needed by aerobic organisms to
break down organic material.
snotagem / su rohpsohp
• Bchemcal x ygen demand is
forecast
20
15
developing countries
10
developed countries
world
5
0
1
6
2
2
0
0
2
1
2
0
0
8
0
0
4
2
2
0
1
9
9
0
0
6
1
9
9
2
1
9
8
8
9
8
4
1
1
9
8
0
are
in
1
fertilizers,
soil
9
fact
that
phosphate may become limiting to agriculture in the future.
[6]
fertilizers
the
the
phosphorus
the
7
make
from
6
Suggest whether the data suppor ts the hypothesis that availability of
The
use
This
answer
have
achieved
5/6
marks:
is
order
enough
could
last
T
urnover
removed
9
that
in
7
and
and
2
years;
crops
increased
1
for
fertilizers
the
in
and
that
1
needed
of
slow;
9
are
is
6
turnover
8
the
agriculture.
turnover
9
for
of
6
future
denition
phosphates
1
the
of
most
with
1
availability
addresses
associated
9
answer
issues
4
6
the
0
▲ The
of
of
phosphate
refers
to
the
replacement
of
phosphate
to
for
ve
once
it
has
been
removed.
T
urnover
of
phosphate
is
slower
than
marks.
nitrogen.
levels
to
200
When
within
replenish
the
the
farmers
soil
remove
their
continually
mineral,
therefore
crops,
deplete
the
the
and
need
to
phosphate
there
add
is
no
way
fertilizer
.
T
he
C.6
Ni T R o GE N
AND
PHoSPHoRUS
▼ The
phosphate
removed
by
crops
is
replaced
by
fertilizers,
which
answer
to
developed
same
time
are
obtained
from
sedimentary
rocks.
is
removing
the
phosphate
from
the
land
to
fertilizer
at
far
greater
rate
than
it
can
produce
possibly
If
P
fertilizers
this
be
T
he
graph
shows
that
the
use
of
phosphorus
be
fertilizers
trend
of
increased,
especially
after
1940,
but
has
levelled
off
in
P
are
last
years.
If
the
turnover
is
slower
than
the
to
agriculture
Leaching
of
of
in
phosphate
the
mineral
eutrophication
and
may
future,
nutrients
leads
to
become
thus
from
a
depletion,
limiting
supporting
agricultural
increased
the
is
amount
decreasing.
the
to
the
predicted
factor
The
could
answer
that
from
phosphates
the
detergents
eventually
also
soil
and
to
that
these
the
lakes
to
and
ow
into
produce
the
rivers
and
eutrophication.
hypothesis.
land
biochemical
in
transferred
mention
detergents
availability
the
countries,
removed
produce
the
is
used
fertilizers
reduced.
failed
has
make
that
turned
use
over
.
fact
countries
developing
this
the
Human
of
activity
not
(AHL)
at
reference
the
did
C YCLE S
into
rivers
oxygen
causes
demand.
Practce prblems fr optn C
Prblem 1
a) Compare and contrast the nutrient stores in taiga and
Most reef-building corals contain photosynthetic
tropical rainforest.
algae, called zooxanthellae, that live in their cells. Coral
b) Describe the flw of nutrients in taiga.
bleaching can occur as a result of human-induced
changes, leading to the zooxanthellae being ejected
c) Draw a Gersmehl diagram for the tropical
rainforest.
from the coral.
a) State the type of interaction that occurs between
zooxanthellae and reef-building corals.
b) State the trophic level of zooxanthellae
d) Suggest ne reason the nutrient store above the
ground is so high in both biomes.
Prblem 3
Explain the effect alien species can have on an
c) When coral is bleached, cer tain organisms become
ecosystem.
more common in the ecosystem such as the
cnidarian Gorgonia, the echinoderm Diadema,
other algae and cer tain sponges. State the term
that is used for organisms whose presence
Prblem 4
Explain the impact of island size and edge effects on
community structure.
provides evidence of the existence of a par ticular
Prblem 5 (AHL)
environmental condition.
Explain how the carrying capacity of the environment
d) A coat of algae builds up on coral reefs as a
affects population growth.
consequence of eutrophication. Explain the
Prblem 6 (AHL)
relationship between eutrophication and algae
Explain the reason for the presence of insectivorous
growth.
plants in waterlogged soils.
e) Explain how excessive growth of algae on coral reefs
can be controlled by top-down factors.
Prblem 2
The pie char ts show the nutrient levels in two biomes.
tropical rainforest
taiga
above
above
ground
ground
root
soil
soil
root
201
HUMAN
D
D . 1
H U M A N
N U T R I T I O N
Yo shod kow:
✔
essential
body
,
nutrients
therefore
Yo shod be abe o:
cannot
they
P H YS I O LO GY
have
be
to
synthesized
be
included
by
in
the
✔
explain
the
need
for
a
balanced
✔
explain
the
production
diet.
the
of
ascorbic
acid
by
some
diet.
mammals,
✔
dietary
minerals
are
essential
chemical
but
not
others
that
need
a
dietary
supply
.
elements.
✔
vitamins
are
compounds
chemically
that
diverse
cannot
be
✔
describe
by
✔
explain
appetite
✔
explain
how
fatty
acids
and
some
amino
acids
✔
of
essential
production
of
amino
acids
affects
type
outline
of
lack
control.
II
obesity
the
how
risk
of
cholesterol
coronary
malnutrition
imbalance
or
may
be
excess
✔
caused
of
by
a
nutrients
lead
to
hypertension
in
blood
heart
is
an
indicator
disease.
the
proteins.
explain
the
cause
phenylketonuria
✔
can
diabetes.
are
essential.
✔
malnutrition.
the
and
some
of
carbon
synthesized
body
.
✔
causes
and
treatment
of
(PKU).
deciency
,
in
the
✔
diet.
explain
breakdown
of
heart
muscle
due
to
anorexia.
✔
a
lack
bone
of
vitamin
D
or
mineralization
calcium
and
cause
can
affect
rickets
✔
or
design
content
osteomalacia.
✔
appetite
is
experiments
controlled
by
a
centre
in
of
food
by
to
determine
the
energy
combustion.
the
hypothalamus.
✔
overweight
individuals
hypertension
✔
starvation
and
can
type
lead
to
are
II
more
likely
to
suffer
diabetes.
breakdown
of
body
tissue.
A balanced
diet
is
essential
to
human
health.
Essential
nutrients
are
Topic 2.3 covered the
those
that
cannot
be
synthesized
by
the
body
and
therefore
they
determination of body mass index
have
to
be
included
in
the
diet.
Certain
fatty
acids,
amino
acids
and
by calculation or using a nomogram
dietary
minerals
are
essential.
Vitamins
are
chemically
diverse
carbon
and in Topic 6.1 digestion and
compounds
that
cannot
be
synthesized
by
the
body
(with
the
exception
absorption were studied.
of
or
vitamin
there
The
is
D).
Vitamin
formerly
System
World
and
known
(MDIS),
Health
deficiencies
202
Non-essential
another
at
nutrient
Mineral
as
the
was
can
Nutrition
be
established
global
to
in
either
used
for
be
the
Deficiency
1991
strengthen
level.
can
Information
Micronutrient
Assembly
the
nutrients
that
made
same
System
by
the
body
purpose.
(VMNIS),
Information
following
surveillance
a
request
of
by
the
micronutrient
D .1
• Baaed die is one that contains
• Sa aio is the deciency of
the accepted and dened propor tions
nutrients in a diet.
HuMAn
nutrItIOn
Scurvy is caused by a
deficiency of dietary
of carbohydrates, fats, proteins,
• Body mass idex (BMI) is the body
ascorbic acid (vitamin C) since
mass measured in kilograms divided
humans are unable to
by the square of the body height
metabolically make this chemical.
vitamins, minerals and water
essential to maintain good health.
• Maiio is caused by eating
measured in metres.
The symptoms of scurvy are
in excess or undereating or by a diet
abnormal bleeding. Ascorbic acid is
• Obesiy is a medical condition
lacking in an essential element. It
−2
involved in the synthesis of
where the BMI is above 30 kg m
may lead to severe deciencies,
collagen fibres; therefore the lack
illness or even death.
of this vitamin will cause defective
connective tissues and thus fragile
The
nine
essential
amino
acids
humans
cannot
synthesize
are
capillaries. Scurvy was thought to
phenylalanine,
valine,
threonine,
tryptophan,
methionine,
leucine,
be specific to humans, because
isoleucine,
lysine
and
histidine.
Threonine
can
be
synthesized
by
attempts to induce the symptoms
the
human
body
when
phenylalanine
is
present
in
the
diet.
Arginine
in laboratory rats and mice were
cannot
be
synthesized
by
infants
so
it
must
be
present
in
the
diet
of
unsuccessful.
small
children.
omega-6.
Essential
These
fatty
fatty
acids
acids
can
be
are,
for
found
example,
in
fish
and
omega-3
in
and
seeds.
Exampe D.1.1.
Vitamin
caused
rattus)
to
C
by
and
avoid
with
The
a
is
also
the
known
lack
guinea
ascorbic
hexose
amount
of
pigs
acid
sugar,
of
as
l-ascorbic
ascorbic
(Cavia
acid.
a
precursor
acid
an
porcellus)
production.
ascorbic
acid.
In
On
in
was
were
day
the
Scurvy
is
a
experiment,
2
fed
a
in
(Rattus
restricted
animals
synthesis
measured
disease
rats
of
were
ascorbic
urine
every
diet
injected
acid.
day
.
The ethics of the use of animals in
experiments could be discussed.
In this case, only 10 days
6
experimentation will cause no
rats
yad gm / eniru ni dica cibrocsa
1–
harm to the guinea pigs.
5
guinea pigs
4
3
2
1
You should give only two
0
symptoms, as only the first two
0
1
2
3
4
5
6
7
8
9
10
11
will be marked. Just writing “death”
time /days
will not score a mark .
a)
b)
List
two
Suggest
their
c)
An
a
health
of
scurvy
.
reason
sailors
used
oranges
and
lemons
in
trips.
attempt
was
to
entirely
Suggest
d)
symptoms
induce
the
symptoms
unsuccessful
whether
Explain
the
the
reason
data
but
was
pigs
scurvy
successful
supports
guinea
of
this
in
in
laboratory
guinea
rats
pigs.
statement.
develop
scurvy
.
Solution
a)
Scurvy
is
bruising
gums
b)
used
are
The
data
sugar,
tiny
swollen
citrus
rich
quantities
c)
disease
with
and
Sailors
fruits
a
in
or
and
the
were
skin
by
to
cure
acid
cures
to
patients
and
weakness,
the
C)
friable
may
prevent
(vitamin
statement
able
apathy
,
hemorrhages,
Untreated
fruits
prevents
rats
large
legs.
ascorbic
supports
the
characterized
easy
bleeding
die.
scurvy
which
in
as
these
adequate
disease.
because,
synthesize
using
ascorbic
a
precursor
acid
while
guinea
203
D
HUMAN
P H YS I O LO G Y
• S  y is caused by lack of
pigs
vitamin C (ascorbic acid).
were
days
not.
after
the
precursors
• rikes and oseomaaia are
to
The
levels
injection,
of
ascorbic
showing
synthesize
acid
that
ascorbic
the
were
rats
reduced
require
a
few
these
acid.
caused by lack of vitamin D.
d)
Guinea
• Pheykeoia (PKu) is caused
for
by a deciency of an enzyme
the
pigs
cannot
production
tissues,
tendons
synthesize
of
and
collagen
blood
ascorbic
found
vessels.
in
acid
which
skin,
Ascorbic
is
needed
connective
acid
cannot
be
that conver ts phenylalanine
synthesized
by
guinea
pigs
because
they
have
a
mutation
in
into tyrosine, causing excess
the
gulonolactone
oxidase
(GLO
or
GULO)
gene
which
codes
phenylalanine in blood.
for
• type II diabees is caused by
an
enzyme
l-ascorbic
that
acid.
is
(The
needed
same
is
for
true
the
in
last
step
in
the
synthesis
of
humans.)
resistance to insulin.
• Hype esio is blood pressure
Malnutrition
above the norm.
nutrients
Lack
can
is
of
be
in
may
the
seen
in
by
distended
dermatitis
diet
they
in
cases
is
have
and
severe
teeth
lack
a
deficiency
,
protein
and
of
and
a
imbalance
lead
or
to
production
marasmus.
consumption
large
liver.
Marasmus
on
is
People
with
effect
the
produces
protein.
(emaciated),
can
affects
kwashiorkor
loss.
long-term
cases
by
acids
sufficient)
a
thin
a
of
abdomen
including
extremely
amino
insufficient
consumption
a
caused
or
excess
of
diet.
essential
caused
be
There
is
caused
by
physical
and
and
of
if
the
This
an
feet,
hair,
deficient
marasmus
loss.
mental
and
of
energy
from
fat
energy
ankles
thinning
suffering
muscular
proteins.
Kwashiorkor
(even
swelling
of
In
both
are
cases,
development
death.
SAMPLE STUDENT ANSWER
The diameter of the left ventricle and left atrium of the hear t was
Make sure you read the question
measured in 20 healthy subjects and in 19 patients with anorexia.
[2]
properly. In this case, what was
expected was a discussion on the
60
data itself, not on the biological
effect of anorexia on the hear t.
offer a considered and balanced
review that includes a range of
arguments, factors or hypotheses.
mm / retemaid
When you discuss, you must
40
20
Opinions or conclusions should be
presented clearly and suppor ted
0
by appropriate evidence.
healthy
anorexia
healthy
left ventricle
▲ This
mark
answer
for
scored
mentioning
one
that
anorexia
left atrium
Discuss the suppor t provided by the data for the claim that anorexia
the
data
leads to the breakdown of hear t tissue.
supports
this
statement
as
This
structures
are
smaller
in
[3]
both
answer
could
have
achieved
1/3
marks:
anorexic
patients.
In
▼ Although
mention
in
this
some
student
important
all
structures
diameter
the
answered.
that
in
question
The
is
not
statement
anorexia
there
is
the
have
are
heart.
The
mentioned
differences
anorexic,
bars
and
there
that
that
is
it
mentions
the
too
the
small.
size
The
correlation
of
fact
does
the
that
not
there
healthy
204
causality
.
to
decrease
healthy
is
most
likely
due
to
malnutrition
among
that
is
due
to
lack
of
carbohydrates,
fats
and
forcing
the
body
of
the
anorexic
to
resort
to
their
in
be
muscles
as
a
source
of
energy
for
respiration.
Although
and
error
the
body
would
focus
on
degrading
skeletal
muscle
rather
reliable
sample
there
cardiac
muscle,
the
cardiac
muscle
will
still
gradually
is
is
degenerate,
as
is
evidenced
necessarily
hearts
establish
T
his
anorexic
than
because
compared
a
really
although
not
showed
should
overlap
may
subjects
each
breakdown
answer
between
anorexia
measured,
of
protein,
of
were
does
facts
subjects.
anorexia,
in
that
of
the
anorexic.
in
the
decreased
diameters
of
the
and
D .1
Lack
of
rickets
vitamin
or
D
or
calcium
osteomalacia.
such
as
the
production
with
exposure
to
UV
can
There
of
affect
are
positive
vitamin
rays
which
bone
D
as
can
mineralization
effects
well
cause
as
of
exposure
health
skin
and
risks
cancer
to
HuMAn
nutrItIOn
cause
sun
associated
such
as
melanoma.
Appetite
is
controlled
information
from
stimulate
inhibit
or
the
by
a
centre
digestive
in
the
system
hypothalamus.
and
adipose
It
receives
tissue
to
either
appetite.
hypothalamas
stimulates
inhibits
appetite
appetite
insulin
ghrelin
stimuli from
pancreas
stomach
stretch receptors
leptin
PYY
3-36
intestines
adipose tissue
Fie D.1.1.
BMI
values
Appetite control
are
overweight.
a
good
way
Underweight
of
assessing
subjects
if
someone
typically
have
a
is
under
BMI
or
under
−2
18.5kg
m
−2
,
overweight
subjects
a
BMI
of
between
25.1
and
29.9
kg
m
−2
and
obese
subjects
individuals
are
Hypertension
Normal
and
70
those
diabetes,
form
of
these
a
when
for
diet
also
patients
on
a
the
to
30.0
suffer
patient’s
is
around
diastolic
kg
m
blood
120
Obese
pressure
mmHg
pressure.
known
as
non-insulin-dependent,
develop
the
cells
cells
in
insulin
are
no
the
due
to
pancreas
resistance,
longer
above
systolic
genetic
is
still
which
stimulated
overweight
type
Hypertension
sodium
β
or
and
and
is
for
in
The
salt
.
hypertension
rich
diabetes.
receptors
above
likely
pressure
mmHg
with
BMI
more
is
blood
a
can
occur
factors.
the
most
means
diabetes.
pressure
produce
by
II
normal.
II
common
insulin
that
in
Type
the
but
insulin
insulin.
Exampe D.1.2.
The
incidence
of
amongst
20,000
and
were
BMI
follow-up
the
values
coronary
subjects.
recorded.
interviews.
of
the
heart
disease
Baseline
The
The
evidence
bar
measured
(CHD)
parameters
chart
of
CHD
shows
was
of
the
investigated
waist
was
to
hip
ratio
identified
results
in
according
to
parameters.
205
D
HUMAN
P H YS I O LO G Y
waist to hip ratio
15
BMI
elpoep 000,1 / DHC
10
5
0
low
medium
high
very high
parameters
a)
(i)
Deduce
BMI
(ii)
b)
with
most
Suggest
Explain
higher
the
risk
a
reason
clearly
whether
reason
of
whether
correlates
the
to
the
parameter
overweight
waist
incidence
and
chosen
obese
to
of
in
hip
ratio or
the
CHD.
(i)
causes
people
have
CHD.
a
CHD.
Solution
a)
(i)
Waist
to
hip
incidence
(ii)
ratio
while
A correlation
as
increasing
increasing
does
not
ratio
BMI
shows
does
necessarily
increasing
CHD
not.
mean
a
causation.
−2
b)
Overweight
These
high
and
people
cardiac
people
output
increase
and
acid
an
enzyme
restriction
reduction
or
of
raise
raise
the
It
is
of
larger
most
by
is
intellectual
a
as
of
arteries
25
kg
m
of
HDL.
have
a
Waistline
becoming
higher
obesity
stiffer
pressure.
congenital
deficiency
of
phenylalanine
relatively
disability
disorder
of
phenylalanine
into
tyrosine.
successful
in
associated
the
with
PKU.
SAMPLE STUDENT ANSWER
a) Outline what is meant by the term “essential amino acid”.
This
▼ The
that
answer
an
fails
essential
to
mention
amino
acid
An
answer
essential
obtained
cannot
The
be
body
essential
amino
from
the
diet
synthesized
cannot
amino
by
as
acid
from
amino
achieved
acid
is
0/2
one
marks:
required
by
the
human
in
order
to
remain
at
a
homeostasis
state
and
to
carry
it
the
synthesize
have
[2]
must
body
be
could
body
.
out
functions
and
processes.
T
he
human
body
requires
the
other
the
essential
amino
acids
along
with
other
substances
to
acids.
conduct
metabolic
processes.
Phenylalanine is conver ted into tyrosine by the enzyme phenylalanine
hydroxylase.
COOH
COOH
phenylalanine hydroxylase
NH
NH
2
2
HO
phenylalanine
206
.
cholesterol,
they
pressure.
common
converts
than
concentrations
with
blood
phenylalanine
prevention
low
blood
caused
that
BMI
hypertension
resistance
can
is
metabolism.
hydroxylase,
Dietary
which
a
concentrations
and
have
can
have
high
LDL
can
which
(PKU)
people
have
of
vascular
narrower
Phenylketonuria
amino
usually
concentrations
Overweight
can
obese
tyrosine
D. 2
DIgE S t IOn
b) (i) Deduce the reason that tyrosine is considered to be a
“conditionally” essential amino acid.
This
answer
T
yrosine
could
is
have
achieved
considered
to
be
[1]
0/1
a
marks:
conditionally
essential
▼ Tyrosine
amino
amino
acid
as
it
may
be
required
for
a
process
but
is
not
required
in
cases
acid.
of
general
sense
or
for
the
entire
body.
T
yrosine
is
also
food
ingested
human
and
can
aid
or
provide
assistance
for
is
that
non-essential
only
The
necessary
answer
tyrosine
fails
can
only
in
to
be
present
synthesized
in
a
It
PKU.
mention
a
is
in
the
the
when
phenylalanine
is
diet.
body.
(ii) When infants with the condition PKU are left untreated, they have a
build-up of phenylalanine in the blood and high levels of phenylalanine
in the urine. State the cause of this condition.
[1]
▼ The
This
answer
could
have
achieved
0/1
marks:
It
a
T
he
infant's
body
doesn’ t
have
a
control
or
regulation
of
fails
answer
to
recessive
condition
enzyme
is
too
mention
inherited
where
vague.
that
PKU
is
genetic
there
is
phenylalanine
lack
of
the
hydroxylase
phenylalanine.
or
the
gene
for
this
enzyme
is
mutated.
In
order
easy
to
determine
experiment
water
and
its
measured.
The
final
of
to
capacity
food
is
temperature
the
water
the
be
of
the
heat
times
of
energy
water
D . 2
is
of
by
the
and
water
the
food,
divided
is
the
food
The
mass
under
the
water
mass
of
of
a
is
volume
the
food
the
by
the
nervous
and
exocrine
body
water
the
specific
is
mass
heat
food.
or
of
hormonal
digestive
glands
the
Yo shod be abe o:
of
control
the
✔
describe
✔
identify
the
volume
and
are
controlled
to
the
content
by
the
formation
of
gastric
ulcers.
juices.
secrete
lumen
mechanisms
the
surface
of
the
Helicobacter
stomach
pylori
infection
as
a
cause
of
ulcers.
gut.
✔
✔
in
the
as
also
water.
change
calculated
times
is
of
an
of
D I G E S T I O N
secretion
✔
or
gained
Yo shod kow:
✔
combustion
container
and
heat
energy
in
by
mass
recorded
As
the
rise
by
of
initial
placed
calculated.
temperature
all
The
measured.
ignited
water
lost
the
content
performed.
temperature
The
temperature
equal
can
of
nervous
gastric
and
secretions
explain
by
the
proton
reduction
pump
of
stomach
inhibitor
acid
secretion
drugs.
hormonal
✔
explain
✔
identify
dehydration
due
to
cholera
toxin.
mechanisms.
✔
acid
conditions
in
the
stomach
favour
exocrine
digestive
hydrolysis
reactions
and
help
to
in
ingested
juices
and
cells
villus
that
secrete
epithelium
cells
control
that
pathogens
gland
some
absorb
digested
foods
from
electron
food.
micrographs.
✔
the
structure
of
cells
of
the
epithelium
of
the
✔
villi
✔
the
is
adapted
rate
of
intestine
to
transit
is
the
of
absorption
materials
positively
of
through
correlated
explain
adaptations
of
villus
epithelial
cells.
food.
with
the
their
large
bre
content.
✔
materials
not
absorbed
are
egested.
207
D
HUMAN
P H YS I O LO G Y
Nervous
and
hormonal
mechanisms
control
the
secretion
of
digestive
Topic 1.2 covered the
juices.
The
volume
and
content
of
gastric
secretions
are
controlled
by
ultrastructure of cells and in
nervous
and
hormonal
mechanisms.
Topic 6.5 the structure of neurons
Exocrine
glands
body
ducts.
secrete
substances
onto
epithelial
surfaces
of
the
and synapses is studied.
via
clusters
The role of gastric acid in
digestion was established
by William Beaumont while
are
of
For
(known
exported
to
as
example,
acini).
the
duodenum
protein-secreting
endoplasmic
pancreatic
These
cells,
they
cells
via
a
have
exocrine
secrete
pancreatic
a
large
cells
form
digestive
duct
nucleus
glandular
enzymes
system.
and
lots
that
Typical
of
rough
reticulum.
observing the process of digestion
Acid
conditions
in
the
stomach
favour
some
hydrolysis
reactions
and
in an open bullet wound.
help
to
control
pathogens
in
ingested
food.
Excess
acid
can
damage
Beaumont extracted gastric juice
the
mucus
of
the
stomach
that
can
lead
to
an
ulcer. Helicobacter
pylori
by introducing an elastic tube
infection
is
a
cause
of
stomach
ulcers.
Reduction
of
stomach
acid
through the wound and observed
secretion
can
be
achieved
by
taking
proton
pump
inhibitor
medication.
digestion of different foods.
• The paasympahei system
the small intestine in response to the
accelerates digestion.
presence of acid uid. It stimulates
the production of alkali by the
• The sympahei system slows
pancreas.
down digestion.
• Somaosai is an inhibitory
• gasi is a hormone produced in
hormone secreted by the gut that
response to the presence of food and
inhibits acid production. It also
stimulates the production of gastric
prevents the release of gastrin and
juice by the stomach.
secretin, thus slowing down the
• Seei is a hormone produced in
digestive process.
Exampe D.2.1.
Describe
the
formation
of
gastric
in
the
ulcers.
Although not asked, it is neat to
star t the answer describing in one
Solution
sentence what an ulcer is, as this
Gastric
leads into the explanation on how
be
they are formed. Never theless,
symptoms
make sure you don’t take too
bleeding
long on this and always focus on
is
what the question is asking. For
bacterium
example this answer would score
inflammation.
4 marks, as it identifies the excess
damages
of acid and its damage on the
with
lining and it identifies H.pylori and
acidification
ulcers
formed
due
to
by
are
are
presence
The
of
or
the
the
feces.
in
lining.
proton
the
the
stomach.
the
vomiting
of
response
Ulcers
pump
due
to
the
the
pylori
the mode it damages the stomach
through the immune response.
SAMPLE STUDENT ANSWER
No mark would have been given
for the last sentence, as it refers
The diagram shows a cell of the lining of the stomach.
to the treatment and not the
proton pump inhibitor
formation of ulcers.
ADP + Pi
+
H
+
K
potassium channel
ATP
+
K
+
CI
K
CI
chloride channel
208
sometimes
are
ulcers
This
that
immune
(PPIs)
stomach.
The
gastric
stomach
H.
inhibitors
of
pylori.
by
can
layer.
and
cause
Helicobacter
lumen
They
mucus
Another
bacterium
inflammatory
by
of
damages
heartburn,
the
toxins
stomach
antibiotics
in
of
lining
which
pain,
appears
produces
the
acid
stomach
which
the
sores
excess
cause
system
treated
which
inhibit
D. 2
▼ The
answer
should
DIgE S t IOn
have
a) Outline the impor tance of the proton pumps in the digestion of
mentioned
foods.
proton
pumps
[1]
pump
protons
allowing
This
that
answer
could
have
achieved
0/1
for
the
pumps
help
fasten
the
process
of
digestion
in
accelerates
the
enzymes
stomach.
It
pumps
nutrients
the
stomach,
production
of
marks:
hydrochloric
Proton
into
in
and
out
of
the
cell
in
acid.
This
digestion
or
gives
as
acid
it
activates
optimal
pH
for
the
enzyme
(pepsin)
digestion.
stomach.
▼ The
answer
mentioned
should
that
the
have
proton
pump
b) Explain the use of proton pump inhibitors to treat patients
is
complaining of stomach pain.
a
answer
could
have
achieved
0/3
marks:
to
proton
the
ions
With
proton
pump,
it
can
help
the
ow
of
potassium
and
into
the
stomach.
T
he
channel
protein
is
between
not
gastric
Avoids
the
stomach
villus
epithelium
cells
decrease
pain.
absorb
digested
foods
from
the
lumen
of
the
▼ The
the
Villi
are
finger-like
absorption
of
food.
projections
Within
the
that
increase
columnar
the
surface
epithelium
of
the
are
prevent
transports
The
goblet
the
structure
absorption
of
absorption.
form
of
cells,
self-digestion.
capillaries
products
of
cells
food.
They
ATP
to
of
which
The
of
are
rich
active
villus
or
central
lubricate
of
the
lacteal
the
to
villi
to
that
is
adapted
the
where
into
to
production,
will
pH
of
thus
relieve
gastritis
did
saying
stomach.
This
symptoms
or
not
that
it
of
ulcers.
score
a
reduces
pain,
as
this
is
already
in
outer
question.
that
the
area
energy
of
of
in
network
absorption
stomach
reduction
fats.
surface
the
a
and
supply
absorbs
provide
nutrients
lacteal
food
blood
increase
mitochondria,
transport
the
a
of
microvilli
in
to
contains
and
epithelium
have
also
mucus
core
digestion
the
They
enable
the
of
secrete
central
hydrogen
the
area
the
surface
the
student
for
stomach
for
the
into
causes
acid
reux,
mark
intestine.
When
bind
the
acid
The
inhibitors
pump
sent
This
increasing
cells.
pump
proton
are
lumen.
of
chloride
protein.
[3]
the
This
transmembrane
the
of
fats
occurs.
lumen of
interior
small intestine
villus epithelium
of villus
+
Na
+
3Na
blood
+
low Na
capillary
concentration
+
2K
glucose
glucose
fatty acids and
monoglycerides
lacteal
lipoprotein
triglyceride
Fie D.2.1.
The
rate
of
correlated
Absorption in the villus of the small intestine
transit
with
of
their
materials
fibre
through
content.
the
large
Materials
not
intestine
is
absorbed
positively
are
egested.
The structures in Figure D.2.1
should be seen in intestine
electron micrographs.
209
D
HUMAN
P H YS I O LO G Y
Exampe D.2.2.
The
to
graph
pass
The
shows
through
more
dietary
the
fibre
the
the
length
gut
as
digestible
of
a
time
that
function
matter
of
present
the
content
digestible
in
the
of
a
meal
matter
meal,
the
takes
content.
lower
the
content.
90
sruoh / emit ecnediser naem
80
70
60
50
40
30
20
10
0
0
10
30
20
40
50
60
70
80
90
digestible material / % mass of meal
a)
Estimate
the
digestible
The mark scheme will probably
mean
residence
time
of
a
meal
with
50%
matter.
have a range for this answer, for
b)
Explain
the
relationship
of
digestible
matter
and
mean
example from 35 to 39 hours. In
residence
time.
your answer, it is better not to write
Solution
a range, as if your range is outside
a)
37
hours
the accepted range, you will score
no mark . It is always better just to
b)
write one value and its units.
A higher
time.
due
digestible
This
to
water
to
hardens
a
the
cells
stool
toxin
with
into
leave
the
an
a
slower
is
an
contents.
water
means
bowel
a
A higher
longer
into
or
material
amount
constipation
residence
movement
indigestible
absorption
causing
active
infected
caused
Vibrio
the
(enterocytes),
becomes
in
Fibre
content
the
and
of
peristalsis
that
attracts
digestible
large
intestine.
further
This
increases
time.
disease
contaminated
cholera
derive
fibre.
increases
residence
is
of
intestinal
material
Cholera
will
lack
matter
by
the
cholerae
intestinal
triggering
enzyme
ingestion
bacteria.
lumen.
enterocytes,
to
or
food
bacterium
toxin
of
activates
leading
water
This
The
endocytosis
which
of
the
binds
toxin.
chloride
watery
to
releases
epithelial
The
ions
toxin
and
then
water
diarrhoea.
SAMPLE STUDENT ANSWER
Outline how infection by V. cholerae can lead to dehydration.
This
▲ This
is
complete
a
very
concise
answer
that
answer
marks.
have
that
been
V
.
Another
scored
cholerae
obtained
mark
saying
produces
for
could
a
stating
have
that
cholerae affects
water
to
diarrhoea
the
and
dehydration.
210
marks:
intestine
vomiting
the
large
intestine.
Once
in
the
large
intestine
cells
it
promotes
the
pumping
of
chloride
ions
into
toxin.
lumen
of
the
intestine.
Via
osmosis,
water
follows
the
been
the
loss
chloride.
of
3/3
could
the
Another
achieved
scored
mark
for
have
and
Vibrio
full
could
[3]
leads
that
Via
osmosis
once
more,
water
leaves
the
blood
to
lead
to
capillaries
into
the
intestine
cells
to
replenish
water
.
from
to
D. 3
D . 3
F U N C T I O N S
O F
T H E
Yo shod kow:
✔
the
liver
removes
detoxies
✔
OF
tHE
lI v E r
L I V E R
Yo shod be abe o:
toxins
from
the
blood
and
✔
explain
the
✔
compare
✔
explain
dual
blood
supply
to
the
liver.
them.
components
the
F unctIOnS
of
red
blood
cells
are
recycled
and
contrast
sinusoids
and
capillaries.
by
how
the
liver
regulates
toxin
levels
in
liver.
blood.
✔
the
breakdown
phagocytosis
✔
iron
is
carried
hemoglobin
surplus
✔
endoplasmic
the
liver
regulate
✔
some
blood
the
new
cholesterol
hepatocytes
✔
erythrocytes
red
to
in
✔
of
of
bone
red
is
intercepts
nutrient
nutrients
by
blood
and
blood
to
to
✔
explain
recycling
✔
explain
nutrient
✔
explain
causes
✔
label
of
erythrocytes.
cells.
regulation
by
the
liver.
produce
cells.
Golgi
plasma
with
Kupffer
marrow
converted
reticulum
produce
starts
cells
bile
salts.
apparatus
and
microscopic
consequences
mounts
of
of
jaundice.
hepatocytes.
in
proteins.
from
the
gut
to
stored
in
levels.
in
excess
can
be
the
liver.
The
of
liver
breaks
to
is
a
large
detoxifying
down
urea;
hepatic
leaves
from
and
the
that
it
glycogen,
flows
liver.
The
into
performs
maintains
regulates
vitamins
phospholipids;
artery
the
organ
blood;
erythrocytes;
stores
proteins
the
the
hepatic
and
many
blood
blood
and
and
portal
clotting;
iron;
produces
liver
the
vein
functions.
It
temperature
converts
synthesizes
bile.
The
the
in
charge
Topic 6.1 covered digestion and
pressure;
ammonia
absorption and in Topic 6.2 the
blood system is studied.
plasma
oxygenated
deoxygenated
reaches
is
and
liver
hepatic
vein
carrying
food
• Hepaoyes are liver cells
that perform functions such
as: detoxication; metabolism
intestines.
of carbohydrates; secretion of
SAMPLE STUDENT ANSWER
bile; and synthesis of proteins,
Outline the ways in which the liver regulates the chemical and cellular
composition of the blood.
cholesterol and phospholipids.
[6]
• Kpe es are macrophages in
This
answer
could
have
achieved
2/6
marks:
T
he liver regulates chemical
charge of erythrocyte breakdown.
▲ One
that
mark
the
liver
is
scored
lters
for
saying
chemicals
▼ The
answer
expected
was
and cellular composition
not
required,
and
one
mark
for
that
of the blood by creating a
saying
the
removing
ltration. Blood is rst taken
The
rest
liver
detoxies
toxins
of
the
from
answer
the
is
blood
the
liver
no
more
marks
glucose
as
by
glycogen
or
releases
inuence
of
insulin
it
under
the
blood.
too
are
and
glucagon
vague;
respectively
therefore
stores
depending
on
blood
scored.
into the liver by the vein and
glucose
excess
taken out through the artery
(such
cells
levels.
can
as
be
Some
stored
vitamin
engulf
nutrients
in
A or
bacteria,
the
D).
in
liver
Kupffer
therefore
and carried back through the body. T
he liver intercepts blood from
removing
the gut to regulate nutrient levels.
cells
pathogens.
break
down
phagocytosis.
Kupffer
erythrocytes
Hemoglobin
is
by
split
Some nutrients in excess can be stored in the liver
. T
he liver lters
into
the
heme
heme
and
globin.
group
of
Iron
from
hemoglobin
all matter not required in the blood. It also lters chemicals not
is
required or that can be harmful to the human body. One example
carried
produce
to
the
new
erythrocytes.
bone
marrow
hemoglobin
Excess
iron
in
is
to
new
stored
of that is alcohol. T
he liver lters out cellular composition not
in
required in the body. Blood is ltered owing through the liver
.
the
liver.
converted
produce
Surplus
to
bile
plasma
cholesterol
salts.
is
Hepatocytes
proteins
such
as
Levels of minerals and proteins are ltered through the liver
.
albumin.
211
D
HUMAN
P H YS I O LO G Y
Exampe D.3.1.
a)
Compare
and
contrast
sinusoids
and
capillaries.
This type of question can be
answered without the table, but
b)
Outline
adaptations
of
hepatocytes
to
their
function.
you must make sure you compare
Solution
the same feature in both vessels.
a)
vesse
For example, if you say capillaries
capiay
are small in size and sinusoids
have fenestra, you do not score
Sisoid
coe
any marks.
blood
Size
small
a bit larger
Poes
very small
large (called fenestra)
Baseme membae
continuous
discontinuous
Iaea spae
small
large
lme
round
no definite shape
Kpffe es
absent
present
Scientific studies have shown
that high-density lipoprotein
(HDL) could be considered “good”
cholesterol. HDL is the smallest
lipoprotein and it is the densest
because it contains the highest
b)
Hepatocytes
proportion of protein to lipids. HDL
are
has been shown to help prevent and
complexes,
even improve atherosclerosis by
protein
removing harmful low-density
nutrient
rich
in
are
involved
mitochondria
rough
synthesis.
in
for
many
metabolic
energy
.
endoplasmic
Glycogen
There
reticulum
granules
and
processes.
are
many
and
They
Golgi
ribosomes
lipid
droplets
for
are
for
storage.
lipoprotein (LDL) from blood.
D . 4
T H E
H E A R T
Yo shod kow:
✔
internal
and
external
Yo shod be abe o:
factors
inuence
heart
✔
function.
✔
✔
structure
explain
the
regulate
of
cardiac
propagation
of
signals
the
from
contraction
muscle
stimuli
sinoatrial
cannot
cells
through
pass
allows
the
node
heart
that
directly
✔
explain
✔
analyse
the
the
of
heart
articial
pacemakers
to
rate.
cardiac
cycle
to
a
normal
ECG
trace.
wall.
cause
from
use
atria
systolic
and
diastolic
blood
pressure
measurements.
to
✔
explain
causes
and
consequences
of
ventricles.
hypertension
✔
there
is
on
a
a
delay
between
the
arrival
and
stimulus
at
the
atrioventricular
describe
the
this
delay
allows
time
for
atrial
systole
atrioventricular
valves
conducting
bres
contraction
of
ensure
entire
design
experiments
rate
ventricle
normal
heart
sounds
atrioventricular
closing
causing
are
valves
caused
and
changes
treat
life-
under
to
measure
different
and
interpret
conditions.
analyse
epidemiological
in
by
of
coronary
heart
relating
to
the
disease.
the
semilunar
blood
data
wall.
incidence
✔
to
conditions.
coordinated
✔
the
debrillation
close.
heart
✔
of
cardiac
before
✔
the
use
node.
threatening
✔
thrombosis.
passing
✔
of
and
valves
ow.
The
of
structure
stimuli
of
cardiac
through
the
muscle
wall
of
cells
the
(myocytes)
heart.
Cardiac
allows
muscle
propagation
is
a
striated
Topic 6.2 covered the blood
muscle
that
has
thick
and
thin
muscle
fibres
with
myofibrils
containing
system and in Topic 11.2
myofilaments
similar
to
those
found
in
skeletal
muscle.
The
striations
movement is studied.
are
given
muscle
212
by
cells
the
is
structure
found
in
of
the
the
sarcomeres.
centre
of
the
cell
The
and
nucleus
there
of
are
cardiac
many
D. 4
mitochondria
Unlike
and
skeletal
muscle
has
resulting
glycogen
muscle,
numerous
in
long,
granules
which
short,
branched
has
found
adjacent
multinucleate
cylindrical
cells
to
cells,
the
the
arranged
tHE
HE Art
myofibrils.
cardiac
end-to-end,
fibres.
Exampe D.4.1.
Explain
cardiac
the
reason
muscle
electrical
cell
to
the
impulses
can
pass
rapidly
from
one
other.
Solution
The
cardiac
muscle
end-to-end,
cells
are
These
that
resulting
joined
gap
has
by
in
long,
are
discs
arrays
intercellular
short,
joined,
intercalated
junctions
permit
numerous
of
passage
cylindrical
branched
fibres.
containing
densely
of
ions
arranged
The
adhering
packed
and
cells
protein
small
cardiac
junctions.
channels
molecules.
R
Electrical
current
muscle
so
the
activation
via
gap
allows
linked
of
the
junctions.
electrical
cells
heart
This
requires
characteristic
impulses
contract
cell-to-cell
to
almost
pass
transfer
structure
rapidly
of
from
of
cardiac
cell
to
cell,
simultaneously
.
P
The
sinoatrial
cells
that
(SA)
contract
node
consists
rhythmically
of
at
involuntary
around
70
myogenic
beats
per
T
muscle
minute.
Q
S
Following
the
each
contraction,
atrioventricular
move
into
the
the
as
lungs
the
via
the
and
QRS
node.
ventricles.
electrocardiograph
ventricles,
(A
V)
to
wave
This
(ECG).
bundle
the
rest
an
of
Contraction
His.
the
on
spreads
contraction
The A
V
of
complex
impulse
node
The
body
.
the
of
is
the
seen
atria
as
transmits
ventricles
The
ECG.
through
The
T
P
wave
on
to
sending
contraction
is
the
to
blood
wave
impulse
contract
ventricular
atria
causes
the
the
the
to
the
the
blood
is
to
seen
relaxation
of
Fie D.4.1.
the
A normal ECG trace
ventricles.
showing the cardiac cycle
SAMPLE STUDENT ANSWER
▲ This
Outline the events of the cardiac cycle that are occurring during the QRS
interval.
This
for
[2]
answer
could
have
achieved
1/2
electric
signal
is
sent
signal
then
through
continues
the
atrium
to
the
ventricle.
the
through
the
connecting
bres
answer
septum
sent
of
the
from
valves
the
sinoatrial
node
that
cause
contraction
cannot
pass
from
atria
to
A
V
mention
and
node.
carry
ventricle
His
a
that
signal
The
impulses
wall
ventricles.
There
is
a
delay
between
the
The
is
(Purkinje
depolarize
close
valves).
systole
directly
the
bres
the
of
ventricles
from
to
and
the
ventricles.
bundle
Signals
mark
ventricle
to
through
contraction
fails
depolarizes
conducting
cause
one
the
marks:
is
T
he
scored
that
contracts.
▼ The
An
answer
mentioning
and
(bicuspid
atria
bres).
the
and
tricuspid
repolarize
initiated
(the
The
A
V
and
the
ventricles
arrival
contract).
and
passing
time
for
ensure
on
atrial
of
a
systole
coordinated
pacemakers
stimulus
can
be
before
at
the
contraction
used
in
the
A
V
A
V
of
cases
valves
the
of
node.
This
close.
entire
delay
Conducting
ventricle
SA problems
allows
to
wall.
fibres
Artificial
regulate
the
heart
rate.
Do not feel tempted to write about
The invention of the stethoscope led to improved knowledge of the
the P and T waves, as no marks will
workings of the heart. The stethoscope is an acoustic device that allows
be given for this.
doctors to listen to heart sounds. Normal heart sounds are caused by the AV
valves (lub sound) closing before the ventricles contract and semilunar valves
closing (dub) after the ventricles are emptied.
213
D
HUMAN
P H YS I O LO G Y
SAMPLE STUDENT ANSWER
The diagram shows the use of a sphygmomanometer in the
In this case the units are already
measurement of blood pressure.
given for the answer so they are
180 mm Hg
pressure gauge
cu
not needed. Never theless, it is
arm
(rubber bag
impor tant to remember to add the
ar tery
ar tery collapsed
inated with air)
units in answers if they are not
cu
explicit.
115 mm Hg
▼ Although
pressure
needed
is
a
both
mark,
was
90 mm Hg
77 mm Hg
diastolic
correct,
for
pressure
the
115
and
were
the
systolic
sound audible
louder
in stethoscope
noise
no noise
mmHg.
a) Identify the systolic pressure and diastolic pressure for this adult
male.
▼ This
answer
confuses
This
contraction
of
the
marks
that
of
the
ventricles.
the
artery
To
answer
pressure
is
with
score
should
the
force
[1]
the
the
is
arteries.
The
measured
contracts,
systolic
when
when
pumped
out
pressure
is
of
the
Systolic
said
is
being
the
heart
are
is
lled
marks:
pressure
(mmHg):
180
mmHg
pressure
(mmHg):
77
mmHg
b) Explain the meaning of systolic and diastolic pressure.
when
with
[3]
Diastolic
This
ventricles
0/1
pressure
heart.
measured
achieved
ventricle
blood
the
have
blood
Diastolic
on
could
three
have
of
answer
that
answer
could
have
achieved
0/3
marks:
the
blood
and
Systolic
relaxed.
pressure
makes
pressure
is
the
is
the
relaxing
systole
and
contracting
pressure.
diastole
is
pressure
and
Contracting
the
of
diastolic
the
artery
opposite.
) During cardiac arrest, the ventricles of the hear t might begin to
Be careful to write that it is the
contract in an uncoordinated fashion. Outline the treatment used for this
ventricles that are contracting, not
condition.
the hear t.
This
[1]
answer
could
have
achieved
0/1
marks:
▼ This answer is too vague for
A
a
mark.
the
or
use
reset
an
It
should
of
a
(or
shock
to
rhythm.
or
indirectly
restore
This
discharge
to
treatment
the
the
heartbeat
this
condition
is
that
purposefully
sending
signals
or
to
the
atrium.
gives
to
the
heart),
Coronary
restoring
for
mentioned
debrillator
normal
electric
chest
a
have
heart
disease
(CHD)
refers
to
the
reduction
of
blood
flow
in
natural
the
coronary
arteries
to
the
heart
muscle.
The
lack
of
oxygen
causes
rhythm.
muscle
a
high
cells
lipid
diabetes
attacks.
to
diet,
and
It
is
die.
Risk
factors
obesity
,
alcoholism.
the
lack
include
of
high
exercise,
Atherosclerosis
narrowing
of
an
artery
blood
high
is
blood
the
due
to
pressure,
main
fatty
smoking,
cholesterol,
cause
of
deposits
heart
on
its
Because it is an “outline” question,
inner
walls.
The
deposits
are
made
of
atheroma,
a
substance
containing
just mentioning the defibrillator is
cholesterol,
decaying
cells,
blood
cells
and
fatty
proteins.
Narrowing
which
puts
strain
the
of
not enough to score a mark .
blood
vessels
Chronic
narrowing
arrhythmia
disordered
instead
This
of
which
heart
blood
of
the
can
electrical
arrest.
using
a
the
pressure,
coronary
cause
During
causes
causing
heart
from
the
can
be
can
ventricles
or
blood,
fibrillation,
vital
lead
fibrillation.
arrhythmia
pumping
ventricular
defibrillator
arteries
ventricular
activity
contracting,
prohibits
cardiac
214
raises
for
to
on
to
ventricular
This
abnormal
an
when
(fibrillate)
heartbeats.
collapse
electric
survival.
is
quiver
causing
heart.
shock
and
to
the
D. 5
HOrMOnE S
AnD
M E tA B O l I S M
(AHl)
Exampe D.4.2.
Describe
the
use
of
defibrillation
to
treat
life-threatening
cardiac
conditions.
Solution
An
electrical
the
heart
pacemaker.
are
placed
is
in
Either
on
defibrillator
heart
impulse
muscle
the
monitored
two
or
is
metal
through
in
the
an
the
defibrillator
re-establish
paddles
chest,
whether
through
D . 5
by
to
patient’s
detects
arrhythmia
delivered
sent
order
the
cardiac
the
or
close
a
to
patient
arrest.
electrodes
and
few
the
is
is
used
function
to
of
adhesive
heart.
having
A series
usually
of
natural
electrodes
Once
a
the
depolarize
the
on,
the
dangerous
electrical
patient
shocks
is
ECG.
H O R M O N E S
A N D
M E TA B O L I S M
✔
Yo shod kow:
hormones
growth,
✔
endocrine
glands
secrete
hormones
directly
✔
the
developmental
pituitary
changes,
control
reproduction
homeostasis.
bloodstream.
steroid
in
by
into
and
the
secreted
( A H L )
the
hormones
cytoplasm
bind
of
to
the
receptor
target
cell
proteins
to
form
Yo shod be abe o:
a
✔
receptor–hormone
describe
hormonal
secretion
by
endocrine
complex.
glands.
✔
the
receptor–hormone
complex
promotes
the
✔
transcription
of
specic
compare
and
contrast
steroid
and
peptide
genes.
hormones.
✔
peptide
hormones
bind
to
receptors
in
the
✔
plasma
membrane
of
the
target
explain
and
✔
binding
of
hormones
to
membrane
a
cascade
mediated
by
a
inside
the
the
hypothalamus
explain
the
anterior
pituitary
controls
Hormones
and
the
hypothalamus
the
control
of
milk
secretion
by
oxytocin
prolactin.
hormone
outline
how
posterior
lobes
some
athletes
take
growth
secretion
hormones
by
by
cell.
✔
✔
control
gland.
second
and
messenger
pituitary
receptors
✔
activates
hormonal
cell.
of
to
build
muscles.
the
gland.
are
these produce
not
hypothalamus
In Topic 6.6 hormones,
hormones that
secreted
at
a
uniform
pituitary gland
rate
and
exert
their
regulate production
effect
of other hormones
at
low
homeostasis and reproduction were
studied.
concentrations.
Endocrine
glands
secrete
thyroid gland:
produces thyroxine
hormones
the
directly
bloodstream.
endocrine
pituitary
,
The
glands
pineal,
into
are
the
adrenal glands:
thymus,
produce adrenaline
thyroid
and
adrenal
pancreas:
glands,
and
the
pancreas.
produces insulin
In
addition,
women
ovaries (in females):
produce
hormones
in
their
produce estrogen
ovaries
and
men
in
their
and progesterone
testes.
testes (in males):
produce testosterone
Fie D.5.1.
Main endocrine glands
215
D
HUMAN
P H YS I O LO G Y
Exampe D.5.1.
The International Council for
the Control of Iodine
The
thyroid
hormones
found
in
the
bloodstream
are
Deficiency Disorders includes a
tetraiodothyronine,
also
called
(T3)
(rT3).
levothyroxine
(T4),
triiodothyronine
number of scientists who work to
and
reverse
T3
Reverse
T3
is
formed
by
the
elimination
eliminate the harm done by iodine
of
one
iodine
from
T4,
inactivating
this
hormone.
The
levels
of
rT3
deficiency. Iodine is a mineral that
have
been
recorded
to
increase
in
cases
of
cirrhosis.
is necessary for the correct
functioning of the thyroid gland.
This gland produces two similar
hormones, triiodothyronine (T3)
that contains three iodine atoms
The
levels
of
The
results
the
normal
are
shown.
T3
are
and
rT3
recorded
range
of
rT3
were
in
measured
the
and
scatter
lower
in
the
graph
limit
for
blood
and
the
the
serum
upper
normal
of
men.
limit
range
of
for
T3
and tetraiodothyronine (T4) that
upper limit of normal
contains four iodine atoms. These
range of rT3
hormones are involved in
metabolism. The inability to
to lack of iodine means that the
hypothalamus and the anterior
pituitary continuously stimulate
the thyroid and this leads to goitre
(enlargement of the thyroid).
3T fo slevel gnisaercni
produce the thyroid hormones due
lower limit of normal
range of T3
• Seoid homoes act directly on
receptors on cell membranes.
increasing levels of rT3
• Pepide homoes act through
The
data
show
that
many
of
these
men
have
thyroid
and
liver
second messengers.
issues.
Comment
on
the
health
information
that
can
be
provided
by
• Seod messees are
this
data.
molecules that are activated when
the peptide hormone attaches
to the receptor. These second
Solution
The
data
show
that
most
of
these
men
are
not
healthy
.
If
you
divide
messengers activate a series of
the
graph
in
four,
the
men
in
the
top
left
are
healthy
,
and
as
can
reactions. Examples are cyclic AMP
be
seen,
they
are
the
minority
.
Those
on
the
right
upper
and
lower
and calcium calmodulin.
sections
have
cirrhosis).
low
of
Those
levels
iodine
elevated
of
in
T3
the
in
rT3
the
and
and
left
are
bottom
therefore
therefore
have
might
sick
correct
have
(perhaps
levels
thyroid
of
with
rT3
problems
but
or
lack
diet.
Exampe D.5.2.
Compare
and
contrast
the
mode
of
action
of
steroid
and
peptide
hormones.
Solution
Both
peptide
target
for
a
but
the
long
hormone
the
a
of
plasma
to
second
enzymatic
hormones
216
to
form
complex
hormones
by
Both
to
cell
bind
while
receptor
to
the
genes.
membrane
not.
the
of
the
target
inside
Peptide
the
to
where
it
a
which
hormones
the
bind
of
cascade
ATP
do
of
receptor–
to
the
the
receptors
peptide
mediated
produces
require
on
lasts
cytoplasm
The
promotes
Binding
activates
cell
in
act
receptors,
hormones
complex.
hormones
and
hormones
specific
peptide
cell.
blood
steroid
proteins
nucleus
Peptide
receptors
through
and
receptor–hormone
travels
messenger
travel
peptide
hormones
bind
a
specific
reactions.
both
enter
membrane
do
hormones
of
these
hormones
cell
transcription
in
effect
hormones
Steroid
target
steroid
The
time.
steroid
not.
and
organs.
a
series
while
of
steroid
D. 5
HOrMOnE S
AnD
M E tA B O l I S M
(AHl)
SAMPLE STUDENT ANSWER
Explain the role of receptors in mediating the action of both steroid and
protein hormones.
This
As
answer
could
receptors
are
have
achieved
specic
for
6/6
marks:
each
hormone,
the
receptors
allow
▲ This
both
cells
steroid
and
and
protein
hormones
to
affect
specic
given
cross
plasma
T
hough
steroid
hormones
can
the
plasma
cytoplasm
membrane
of
their
desired
cells
target
hormone
into
and/or
the
specic
receptor–hormone
nucleus,
it
is
not
until
the
hormone
bind
receptor
for
that
hormone
that
complex
binds
directly
to
the
DNA
(once
the
nucleus)
and
acts
as
a
transcription
factor
for
expression.
(T
he
complex
can
either
promote
or
to
and
thereby
affect
protein
inhibit
cell
a
hormone:
Requires
plasma
production.)
membrane
complex
coupled
to
internal
proteins
such
and
bind
cytoplasm
form
a
The
peptide
the
second
in
the
target
of
receptor–
other
three
hormones
plasma
cell,
acting
as
messenger
inside
cAMP
.
obtained
answers
are
full
were
proteins;
the
marks,
that
in
steroid
receptor–hormone
promotes
specic
genes;
the
and
transcription
that
the
receptors
of
receptors
are
of
answer
other
binding
(which
for
such
receptors
certain
of
Peptide
to
receptors
hormones
expression
the
gene
but
gene
marks
hormones
the
The
the
steroid
complex.
were
through
in
and
Three
membrane
in
cell
membrane
to
clear
pass
marks
binds
for
receptors
the
the
very
tissues.
hormone:
through
a
answer.
were
to
Steroid
is
complete
target
as
hormones
activates
a
to
membrane
cascade
of
G-protein)
reactions.
to
affect
the
messenger
The
gene
such
as
hypothalamus
posterior
lobes
Hormones
changes,
of
expression
cyclic
controls
the
secreted
by
the
the
hormone
through
second
secretion
by
the
anterior
and
gland.
pituitary
and
cell
AMP
.
pituitary
reproduction
of
control
growth,
developmental
homeostasis.
Exampe D.5.3.
Explain
hormonal
control
by
the
hypothalamus
and
pituitary
gland.
Solution
The
hypothalamus
and
posterior
by
the
secrete
the
the
respectively
males.
induces
Milk
in
the
the
cell
by
in
in
gland
the
the
pituitary
to
or
controlled
in
and
anterior
and
by
of
in
This
The
milk
(FSH)
sperm
and
gland
in
a
and
and
It
luteinizing
ovulation
in
hormone
(GH)
released
control
anterior
other
testes
that
thyroid
stimulates
bones
and
prolactin,
is
are
that
formation
is
thyroxine
are
production.
and
follicles
regeneration
gland.
in
(TSH)
changes,
they
neurons
hormone
oxytocin
secreted
which
where
has
pituitary
.
hormone
produce
anterior
hypothalamus
oxytocin
hormone
growth
and
the
involved
growth
females,
reproduction
is
the
the
Hormones
pituitary
,
prolactin,
by
developmental
cells
(ADH)
stimulating
thyroid
The
stimulating
ovaries
gland.
hypothalamus
of
involved
secretion
growth,
posterior
The
Somatotropin
secretion
produced
to
produces
Thyroid
hormones.
growth,
hormone
follicle
(LH),
pituitary
control
functions
gland
produces
the
hormone
homeostasis.
down
endocrine
hormone
in
and
bloodstream.
pituitary
also
of
gland
antidiuretic
transported
into
lobes
pituitary
reproduction
controls
under
soft
two
the
tissues.
hormones
control
of
the
hypothalamus.
217
D
HUMAN
P H YS I O LO G Y
hypothalamus
• The hypohaams is par t of the
inhibition by
brain that controls the pituitary
dopamine
positive
gland.
anterior
posterior
pituitary
pituitary
feedback by
• The piiay ad is an
suckling
endocrine gland.
• O x yoi is a peptide hormone
prolactin
oxytocin
produced by the hypothalamus
in charge of childbir th and milk
secretion.
breasts
• Poai is a peptide hormone
produced by the pituitary gland in
synthesis
milk ejection
charge of milk secretion.
of milk in
by muscle
milk gland
contraction
Fie D.5.2.
Control of milk secretion
Exampe D.5.4.
Outline
how
some
athletes
take
growth
hormones
to
build
muscles.
Solution
Some
athletes
HGH
increases
also
increases
take
human
body
sprint
cell
capacity
testosterone. Anabolic
They
can
coronary
D . 6
T R A N S P O R T
produce
heart
O F
growth
mass
disease
and
and
body
administered
hormones
mental
are
(HGH)
decreases
when
steroid
sexual
hormone
and
toxic
have
the
build
mass.
together
several
problems,
to
to
fat
can
muscles.
It
with
adverse
increase
effects.
the
risk
of
liver.
R E S P I R AT O R Y
G A S E S
( A H L )
✔
Yo shod kow:
✔
oxygen
dissociation
hemoglobin
✔
carbon
to
for
dioxide
hemoglobin
curves
show
the
afnity
carbon
into
✔
the
is
carried
the
Bohr
✔
is
in
solution
the
transformed
explains
and
bound
the
to
placenta
are
in
red
blood
cells
in
cells
increased
to
release
of
✔
tissues.
changes
in
outline
within
blood
fetal
how
explain
✔
analyse
cells
in
micrographs
the
✔
rate
of
ventilation
control
is
controlled
centre
in
the
adult
of
oxygen
in
hemoglobin.
pH
of
narrow
causes
capillary
light
of
lung
blood
range
and
is
of
endothelium
micrographs
and
tissue.
regulated
7.35
treatments
to
of
to
stay
7.45.
emphysema.
by
the
dissociation
exercise
response
to
the
the
rate
of
amount
ventilation
of
for
hemoglobin
and
myoglobin.
explain
gas
during
curves
medulla
✔
CO
2
218
the
pneumocytes,
and
electron
respiring
sensitive
identify
the
consequences
oblongata.
in
from
transfer
pH.
respiratory
✔
the
Yo shod be abe o:
ions.
the
hemoglobin
chemoreceptors
blood
✔
shift
by
different
blood.
hydrogencarbonate
oxygen
is
allowing
oxygen.
in
dioxide
hemoglobin
hemoglobin
of
✔
✔
fetal
in
changes
the
blood.
exchange.
of
high
altitude
for
D. 6
Emphysema
is
a
lung
disease
where
the
walls
of
the
alveoli
trAnSPOr t
break
OF
r E S P I r AtO r Y
gA SE S
(AHl)
down,
Scientific research has led to
so
air
sacs
are
fewer
and
larger.
The
enzyme
elastase
is
a
protease
that
a change in public
digests
elastin,
a
protein
that
gives
alveoli
their
elasticity
.
It
is
caused
perception of smoking. The carbon
mainly
by
smoking
or
pollution. Another
cause
of
emphysema
is
the
monoxide produced in smoking
lack
of
alpha-1
antitrypsin,
a
protease
inhibitor.
This
is
a
genetic
disease.
binds irreversibly to hemoglobin,
T
reatment
consists
of
the
use
of
bronchodilators,
corticosteroids
to
decreasing gaseous exchange
reduce
inflammation,
oxygen
supplementation,
and
antibiotics
if
there
causing breathlessness. Nicotine
are
signs
of
infection.
The
most
important
step
is
to
quit
smoking.
increases hear t rate, blood
Surgery
or
even
lung
transplant
is
done
in
very
severe
cases.
pressure and the chance of
Red
blood
gases.
cells
Oxygen
(erythrocytes)
dissociation
are
vital
curves
in
show
the
the
transport
affinity
of
of
respiratory
hemoglobin
thrombosis. Tar coats the lining of
for
oxygen.
alveoli, increasing the risk of
emphysema. Infections and
irritation of breathing pathways are
100
c
the hemoglobin becomes
c
saturated at very high pO
increased because the cilia are
burnt or damaged. This induces
2
90
as all the heme groups
coughing. Scientists have proven
become bound
that smoking affects lung function.
80
% / ne gyx o h t iw n i b o l go m eh f o n o i t a ru t a s
There are increased chances of
b
developing lung, throat or mouth
70
cancer and cardiovascular disease.
60
• type I pemoyes are cells in
50
at higher pO
b
more heme
2
normal physiological range
groups are bound to oxygen,
of oxygen partial pressures
making it easier for more
40
the alveoli involved in the process
of gas exchange.
oxygen to be picked up
• type II pemoyes secrete
pulmonary surfactant, a uid that
30
decreases the surface tension
a
, few
at low pO
20
within the alveoli. They are also
2
heme groups
capable of cellular division, giving
are bound to
rise to more type I pneumocytes.
10
a
oxygen, so
• gaseos exhae is the process
hemoglobin
by which gases move passively
0
does not carry
5
10
15
by diusion across a surface. For
much oxygen
partial pressure of oxygen / kPa
Fie D.6.1.
example, the intake of oxygen and
Graph showing oxygen dissociation curve for human hemoglobin
release of carbon dioxide between
the alveoli and blood capillaries of
the lungs.
Exampe D.6.1.
Explain
how
carbon
dioxide
is
transported
in
blood.
Solution
Inside
red
blood
cells
or
erythrocytes
CO
reacts
with
H
2
carbonic
acid
(H
CO
carbonic
anhydrase.
2
).
This
reaction
is
O
forming
2
catalysed
by
the
enzyme
3
The
carbonic
acid
breaks
down
to
hydrogen
+
ions
(H
)
and
hydrogencarbonate
(HCO
).
Most
of
the
carbon
3
dioxide
The
rest
is
therefore
of
the
CO
transported
in
the
red
as
hydrogencarbonate
blood
cells
2
is
transported
as
carbaminohemoglobin.
binds
to
in
blood.
hemoglobin
and
Topic 6.2 covered the blood
system and in Topic 6.4 gas
exchange was studied.
219
D
HUMAN
P H YS I O LO G Y
The
Bohr
shift
explains
the
increased
release
in
respiring
tissues.
The
% / negyxo htiw nibolgomeh fo noitarutas
• Hemoobi is a protein in
oxygen
the erythrocytes formed by four
dissociation
curve
is
shifted
to
the
peptides with four heme groups,
right
as
the
oxygen
binding
affinity
each with an iron molecule.
is
inversely
related
to
acidity
and
• O x yhemoobi is hemoglobin
carbon
dioxide
shift
the
concentration. A
that carries oxygen.
to
right
in
the
sigmoid
• cabamiohemoobi is
dissociation
curve
means
a
hemoglobin that carries carbon
decrease
in
O
affinity
,
therefore
O
2
2
dioxide.
is
released.
• The Boh ee is the shift of the
In
the
aorta
and
the
carotid
artery
,
oxygen dissociation curve to the
of
oxygen
there
are
special
hemoglobin
100
low carbon dioxide
concentration
(2 kPa)
medium carbon
dioxide concentration
50
(5 kPa)
high carbon dioxide
concentration
(8 kPa)
0
5
right with the increased acidity or
by
10
15
20
chemoreceptors
par tial pressure of oxygen / kPa
that
in blood.
CO
detect
the
levels
of
carbon
2
Fie D.6.2.
dioxide
in
the
The Bohr shift
blood. Additionally
,
• Emphysema is when the walls of
the
carotid
receptors
detect
changes
in
the
pH
of
blood.
Blood
pH
the alveoli break down, air sacs are
is
regulated
to
stay
within
the
narrow
range
of
7.35
to
7.45.
The
fewer and larger.
respiratory
ventilation
external
control
in
centre
response
intercostal
ventilation
to
in
in
medulla
changes
muscles
increases
the
and
in
pH
oblongata
by
sending
diaphragm.
response
to
the
controls
high
the
impulses
During
exercise
amount
of
CO
rate
to
the
in
of
the
rate
the
of
blood.
2
SAMPLE STUDENT ANSWER
Explain how low blood pH causes hyperventilation (rapid breathing).
This
▼ This
mark
answer
because
did
it
is
not
not
score
question.
the
student
becomes
that
in
this
CO
In
due
but
to
lowering
that
blood
not
pH.
are
not
T
he
of
increase
blood
blood
muscles
the
and
occurs
to
that
the
blood
has
become
more
acidic.
of
an
acid
substance
can
reduce
the
afnity
T
his
means
it
is
not
able
to
carry
as
oxygen.
diaphragm
CO
T
his
means
that
an
individual
would
have
to
centre,
V
entilation
expel
means
hemoglobin.
breathe
faster
in
order
to
obtain
a
normal
amount
of
oxygen,
rate
therefore
increase
marks:
The
respiratory
mentioned.
pH
binding
much
intercostal
0/2
say
2
chemoreceptors,
achieved
sentence
does
an
have
answering
rst
mentions
acidic
is
the
could
any
Low
the
answer
[3]
causing
ventilation.
rather
2
than
to
obtain
oxygen.
Exampe D.6.2.
a)
b)
Compare
Sketch
and
contrast
curves
hemoglobin
to
myoglobin
compare
with
adult
the
and
fetal
saturation
of
hemoglobin.
myoglobin
and
fetal
hemoglobin.
Solution
a)
Myoglobin
peptide
bind
that
one
in
is
chain
with
oxygen
muscle
hemoglobin.
saturated
transfer
at
of
It
a
in
muscles.
one
heme
molecule,
hemoglobin,
respiring
220
found
taking
cells.
has
a
lower
oxygen
but
the
Fetal
greater
partial
in
the
It
consists
group.
this
binding
oxygen
from
hemoglobin
affinity
pressure
placenta
of
to
only
Myoglobin
for
of
is
is
only
stronger
than
hemoglobin
different
oxygen,
oxygen.
the
one
can
fetal
in
from
adult
becoming
This
allows
hemoglobin.
the
D. 6
b)
trAnSPOr t
OF
r E S P I r AtO r Y
gA SE S
(AHl)
100
myoglobin
In the sketch you do not need to
% / negyxo htiw noitarutas
fetal
80
hemoglobin
be too precise with the values
of saturation and oxygen par tial
60
adult
pressures, but you need to clearly
hemoglobin
show the trends of saturation. In
40
this case, the curves for fetal and
adult hemoglobins are sigmoid,
20
with the fetal hemoglobin above
the adult. The curve for myoglobin
0
is less sigmoidal and above both
0
2
4
6
8
10
12
14
hemoglobins. The three curves
par tial pressure of oxygen / kPa
plateau close to 100% saturation.
At
high
altitude
number
of
because
there
(EPO).
for
there
is
erythrocytes
EPO
doping
is
is
in
an
less
in
increased
produced
some
partial
blood
pressure
are
production
naturally
in
of
produced
the
of
the
body
,
oxygen.
in
A greater
response
hormone
but
has
to
this
erythropoietin
also
been
used
sports.
Paie pobems fo Opio D
Pobem 1
Pobem 2
The graph shows the sodium, potassium and
Explain the hormonal mechanisms that control the
cholesterol consumption in a diet of 1,000 children in a
secretion of digestive juices.
school compared to the recommended dietary intake.
Pobem 3
500
recommended intake
Explain the causes and consequences of jaundice.
actual intake
400
gm / ekatni
300
200
100
0
sodium
potassium
cholesterol
a) State the nutrient for which the diet of the children in
this school is below recommended values.
b) Outline one problem these children might have in the
future due to their cholesterol intake in diet.
) These children have high chances of hyper tension in
the future if they do not change their diet. Comment
on this statement.
221
D
HUMAN
P H YS I O LO G Y
Pobem 4
Pobem 6
Explain the need for the time delay between the arrival
A factor which adapts organisms to survive under low
and passing on of a stimulus at the atrioventricular
oxygen conditions is the presence of a substance in red
node.
blood cells called diphosphoglycerate (DPG). It affects
the percentage saturation of hemoglobin as shown
Pobem 5
in the graph.
The diagram shows a section through the pancreas
showing an islet of Langerhans.
100
pancreatic cells
pancreatic juice
(secrete pancreatic
juice)
islet of
a cells
Langerhans
% / nibolgomeh fo noitarutas
duct carries away
normal
low DPG
90
high DPG
80
70
60
50
40
30
20
10
0
b cells
0
10
20
30
40
50
60
70
80
90
100
oxygen pressure / mmHg
a) Identify the effect of DPG on hemoglobin
blood capillary
saturation.
Identify the structures that show that the pancreas is
b) Suggest with a reason the DPG levels in organisms
both an exocrine and an endocrine gland.
living at high altitude.
222
INTERNAL
For
to
a
your
carry
internal
out
report.
an
This
assessment
individual
report
(IA)
you
will
investigation
should
be
be
and
between
six
ASSESSMENT
asked
write
and
Collect sufficient data over a meaningful range, with
12
pages
long
and
will
form
20%
of
your
final
IB
adequate repeats, and use the most precise apparatus
Biology
grade.
you have access to.
The
Assessment criteria
independent
changed.
Your
investigation
is
assessed
using
the
six
out
of
a
total
of
be
measured
be
or
controlled.
necessarily
Personal
Explo
Ana
Evalua
Comm
ration
lysis
tion
unication
engage
Total
ment
but
a
variable
variable
observed.
6
6
6
4
The
the
value.
It
investigations
variable
Maximum
include
derived
certain
2
the
is
the
that
will
variable
be
All
other
that
variables
24marks.
must
Criterion
dependent
is
criteria
will
below,
The
variable
(eg
studying
research
actual
is
question
dependent
understood
there
the
will
be
that
no
may
not
variable
for
independent
relationship
between
the
24
distributions
marks
of
two
species
in
a
named
ecosystem).
Percen
tage of
8
25
25
25
17
100
▼
Bad
▲
question
Good
question
mark / %
How
affect
▲
does
the
ow
of
water
insects?
What
ow
is
the
rate
inuence
of
water
in
of
the
the
Table 1. IA assessment criteria
Ibicui
river
in
distribution
Brazil
of
leptobranchus
on
the
Paracloedes
nymphs?
Choice of research question
▲
If
you
look
above,
for
is
you
at
the
can
see
exploration,
why
it
is
so
assessment
that
data
the
most
analysis
important
criteria
that
the
marks
and
the
in
are
Table 2. Good and bad research questions
table
available
evaluation—that
investigation
yields
Make sure your research question is focused and
good
data.
You
can
be
adventurous
in
the
choice
precisely expressed. For example, “Measuring the effect
of
your
investigation,
but
you
must
make
sure
it
of light on photosynthesis” is too vague as it does not
will
provide
you
with
enough
data
for
analysis.
indicate what the dependent and independent variables
Choosing
an
interesting
research
question
that
are. The independent variable could be light intensity,
yields
little
data,
or
insufficiently
useful
data,
will
wavelength, photons, type of lamp, etc, while the
score
very
poorly
.
dependent variable could be rate of photosynthesis,
presence of starch, and many others.
Research and try out your ideas to make sure you can
generate sufficient useful data before you embark on a
Analyse
Draw
data
conclusion
State
full investigation.
problem
Collect
Scientic
data
Not
all
IAs
are
based
on
primary
data.
You
can
Method
Formulate
use
data
generated
from
online
databases.
In
Hypothesis
Design
cases
where
you
work
with
a
group
of
candidates
experiment
collaborating
generate
to
your
generate
own
a
unique
database,
research
you
must
question.
223
INTERN AL
When
formulating
A SS E SS M E N T
your
hypothesis,
To
consider:
gain
the
exploration
marks,
include
the
following
sections:
•
the
independent
being
•
the
•
the
it
the
•
a
of
the
limited
the
and
scientific
prediction
independent
to
dependent
variable)
•
or
two
variables
•
your
research
•
your
hypothesis
question
•
background
•
a
•
apparatus
•
method
•
safety
correlated
range
keep
variable
a
variable
how
you
name
of
variable
reasonable
of
what
(or
are
the
you
(try
to
value)
derived
going
to
organism
think
is
statement
information
of
the
variables
dependent
measure
it
considerations.
used
going
to
happen.
If you use secondary data (or data from models and
Once
can
you
add
have
the
an
investigative
statistical
“null”
hypothesis,
and
then
“alternative”
you
test
simulations) instead of collecting primary data in the
lab, you will need more than one source of data so
that the variance between sources can be evaluated.
hypotheses:
This will make your error analysis and evaluation more
•
The
null
hypothesis
will
state
a
lack
of
successful.
correlation/association
variables
or
or
impact
between
groups.
After
•
The
alternative
hypothesis
will
state
a
stating
include
correlation/association
or
differences
or
research
question
you
need
to
suitable
background
information,
the
of
which
between
should
variables
your
significant
focus
on
specifics
your
chosen
research
groups.
question
your
and
methodology
.
question
and
existing
Describe
the
context
for
knowledge.
Criterion 1: Personal engagement
This
criterion
exploration
assesses
and
how
your
you
engagement
have
made
it
with
your
the
own.
Remember, the background information provided for the
For
this
criterion,
make
•
communicate
that
sure
you:
investigation should be entirely relevant and enhance
•
pose
a
know
•
do
your
question
the
not
•
the
which
in
you
your
do
investigation.
not
the understanding of the context of the investigation.
already
You
will
and
how
need
to
include
a
statement
of
the
variables
answer.
use
a
known
modifications
in
to
interest
design
to
of
explain
why
chosen.
Ensure
method
without
it—examiners
your
you
are
making
value
any
originality
method
using
the
helpful
you
to
will
use
investigation
when
method
you
a
to
writing
control
table
like
make
your
them.
this
sure
You
whilst
you
do
may
find
planning
not
miss
it
your
any
out
statement.
have
Independent variable
that
the
method
works,
and
if
it
(state the range)
does
not,
modify
it
and
explain
how
and
why
Dependent variable
you
modified
it
in
your
what will be measured (be precise)
report.
Reason for
Controlled variable
Control method
controlling variable
The examiners will be looking for the personal
significance of your research question.
▲
Table 3. Planning around variables
Include
Criterion 2: Exploration
used
will
This
criterion
is
about
establishing
a
stating
a
clear
and
focused
your
enable
and
techniques
your
in
using
your
awareness
considerations.
224
of
appropriate
method.
safety
,
In
list
of
the
investigation.
you
to
collect
apparatus
Choose
reliable
and
materials
apparatus
data,
for
that
example,
using
graduated
pipettes
and
measuring
research
cylinders
question
detailed
scientific
by
context,
in
a
concepts
addition,
environmental
and
it
assesses
and
ethical
to
measure
volume
rather
than
beakers.
You
▼
Bad
naming
of
▲
apparatus
Good
naming
of
need
to
record
independent
3
measuring
cylinders
3
×
measuring
0.5cm
data
dependent
about
the
variables
to
enable
meaningful
processing
should
record
and
interpretation.
You
cylinders
eg,
▲
and
3
±
25.0cm
enough
apparatus
also
fieldwork
qualitative
should
always
observations,
have
some
form
of
Table 4. Good and bad descriptions in an apparatus
site
description;
this
could
take
the
form
of
maps,
section
sketches
photos
Make
for
so
sure
any
that
your
reader
an
gained.
It
idea
is
a
repeat
of
the
good
how
you
chose
This
narrative
data
you
are
method
to
to
help
the
give
part
in
your
explain
is
sufficient
and
uncertainties
describe
and
which
in
investigation
developed
collecting
decision-making,
written
associated
idea
and
will
is
the
a
can
be
paragraph
amount
the
and
be
methodology
.
insight
of
detail
also
not
“personal
engagement”
You
will
in
advance
need
method
to
how
take
must
for
allow
many
a
valid
After
the
is
sufficient
repeats
conditions,
the
relevant
▼
Bad
basic,
safety
section,
safety
,
to
of
the
such
glasses,
IB
you
the
your
as
but
animal
forms,
ensure
sites.
If
you
should
ethical
and
best
data
noting
could
the
also
need
add
This
for
include
experimentation
you
that
under
will
be
Good
graph
is
the
y
axis
straight,
Graph
a
a
better
but
Axes
has
a
curve
have
title
Data
t
labels
points
Scale
of
are
graph
clearly
is
marked
appropriate
Table 5. Good and bad aspects of a graph
in
a
short
you
might
have
of
waste
cannot
identify
problems,
a
you
have
at
gloves
the
policy
,
and
the
data,
include
the
any
use
safety
,
to
uncertainty
and
evaluate
in
a
the
table.
You
need
uncertainty
in
to
the
data
and
and
the
size
and
those
of
any
discrepancy
between
your
results
application
the
literature
(if
they
exist).
This
gives
indication
of
how
accurate
your
data
is.
on
ethics
this
considered
in
of
impact
statement
least
collected
be
you
are
familiar
with
statistical
analyses,
you
can
or
the
impact
of
measurement
uncertainty
on
effect
your
show
on
t
indicates
be
consider
will
picture
for
environmental
methodology
.
disposal
environmental
Also,
photos,
each
If
field
▲
missing
of
would
your
an
consent
one
use
data.
respirometer
where
graph
interpret
quite
qualitative
unnecessary
a
you
supporting
for
associated
issues
of
if
are
valid.
method
about
set-up
these
enough.
Once
section
the
written
include
of
your
and
to
to
different
▲
measurement
not
However,
that
should
measurements
conclusion,
that
example
Line
plan
sure
of
into
evidence
criterion.
photographs.
replacing
careful
Units
the
or
make
results
using
the
following
techniques:
them.
•
propagate
the
errors
through
numerical
calculations
Criterion 3: Analysis
•
The
analysis
that
you
have
interpreted
research
criterion
is
selected,
the
data
question
in
and
about
providing
recorded,
ways
can
that
processed
are
support
sufficiently
large
to
the
•
draw
of
a
line
deviation
(if
you
have
a
data
set)
best
fit
on
your
graph
consider
including
error
bars
and/or
the
reach.
maximum
In
standard
conclusion
•
you
the
and
relevant
the
calculate
evidence
your
analysis,
you
should
include:
with
the
values
•
raw
•
sample
•
qualitative
•
statistical
or
minimum
data
at
you
each
have,
data
slopes
based
that
on
can
the
be
drawn
range
of
point.
data
Statistical
calculations
for
processed
layout
and
quantitative
data
of
your
associated
•
graphical
uncertainty
of
your
data
is
expected.
The
this
other
will
depend
means,
statistics
upon
medians,
can
be
the
tools
standard
presented
at
used.
deviations
the
end
of
data
the
•
of
Percentages,
or
analysis
analysis
data
column
or
row
of
data
they
represent.
For
more
table
complex
analysis.
such
as
processing
correlation
of
data
using
coefficient,
spreadsheets,
t-test
and
2
X
(chi-squared)
other
less
variance
test,
orthodox
(ANOV
A)
screenshots
processing
tests,
a
are
such
worked
acceptable.
as
analysis
example
For
of
may
be
necessary
.
Remember that bar char ts are of limited analytical use
and are used only if you have discontinuous variables.
225
INTERN AL
A SS E SS M E N T
different
• Mean: the sum of the
the regression predictions
values divided by the
perfectly t the data.
to
data
evaluate
from
a
sources
(secondary
reproducibility
.
database
you
need
If
to
data
you
are
show
examples)
using
you
data
have
done
number of values; ie, the
• ttest: a statistical test
some
average.
research
into
the
uncertainties
associated
with
used to determine if there
database
• Median: value found
is a signicant dierence
exactly in the middle of a
between the means of two
data set.
groups of data. A t-test is
data
and
applied
it.
most commonly applied
• Statistical signicance:
when the data sets follow a
In all of this section you need to keep an eye on your
these statistical tests are
use of both significant figures and decimal places—
normal distribution.
all about proving that any
they need to be consistent.
2
dierence between sets
• X
of data is not random. The
a statistical test used to
result of a test is said to be
determine whether there
statistically “signicant”
is a signicant dierence
when a test shows that
between the expected
your data sets are reliably
(chisquared) test:
• A random error is a
measurement possible
statistical uctuation (in
with the device.
frequencies and the
either direction) in the
dierent, and therefore not
observed frequencies in
dierent by chance.
one or more sets of data.
• An outlier is any value
measured data due to the
that is numerically distant
precision limitations of the
from most of the other data
• Standard deviation: a
• ANOVA (analysis of
measurement device.
points in a set of data.
measure that is used to
variance) test: a collection
• Systematic error is a
quantify the amount of
of statistical models that
variation or dispersion of a
help you calculate how
set of data values.
much of the total variance
• Accuracy refers to the
problem which persists
closeness of a measured
throughout the entire
value to a standard or
experiment that can be
comes from variance
known value.
• Correlation coecient
solved through a better
between groups of data
(r): a numerical measure
• Precision refers to the
experimental design.
and from variance within
of some type of correlation.
closeness of two or more
groups of data. ANOVA is
• The uncer tainty of
useful for comparing three
a measurement is as
or more groups of data. It
accurate as the tool
will show if there are any
being used to make
statistically signicant
this measurement; it is
dierences between the
one half of the smallest
It shows if there is a
measurements to each
statistical relationship
other.
between two variables.
• Reliability is the degree
• Coecient of
of consistency of a
2
determination (r
): a
measurement.
statistic that will give some
means of three or more
information about the
independent groups of
goodness of t of a model.
data.
2
An r
of 1 indicates that
Using error bars and lines of best fit on graphs will help
you to por tray the data as realistically and honestly as
possible.
When presenting your data, check you have considered:
✔
degrees of precision of instruments used
✔
variation in the material used
✔
standard deviations
Criterion 4: Evaluation
✔
This
criterion
investigation
standard errors
✔
ranges (maximum–minimum)
✔
outlier data.
research
also
Outliers
need
to
be
and
should
not
You
should
check
outlier
by
exclude
do
not
Their
be
recorded
used
“fit
exclusion
the
from
well”
the
whether
repeating
outliers
in
in
but
statistical
any
data
is
experiment.
processing
the
marked
general
requires
a
trend
such
analysis.
really
You
just
as
an
should
because
of
the
not
data.
Drawing
justification.
data
relevant
this
by
data
Completing
several
trials
will
make
it
easier
to
decide
which
results
are
inconsistent.
to
226
it
would
be
good
to
compare
the
data
and
your
evaluation
results
in
accepted
ability
is
the
most
conclusion
fairly
to
of
relation
scientific
identify
or
justifying
comparisons
much
other
challenging
that
is
your
to
the
context.
limitations
more
your
to
the
available
accepted
through
scientific
However,
experimentally
data
with
and/or
you
can
any
are
trends
in
line
and
with
checking
relationships
accepted
do
determined
that
you
from
and
correctly
conclusion
difficult.
your
but
for
If
It
criterion.
consistent
straightforward,
comparing
identify
can,
is
is
whether
you
a
describing
context
your
your
improvements.
Evaluation
the
they
question
assesses
suggest
assesses
and
theory
.
you
Repor t checklist
• A correlation indicates
• A causal link indicates
a predictive relationship
that one event is the
between two variables.
result of the occurrence
Complete
this
checklist
before
you
submit
your
report.
of the other event; ie, the
• A trend is a pattern or
independent variable
Tasks
general tendency of a
aects the dependent
series of data points.
The repor t is within the 12-page limit
variable.
The title page has the candidate name and number on it
You
must
identify
improvements
to
limitations
your
and
There is a contents page and all pages are numbered
suggest
investigation.
Try
to
identify
The research question is specific
and
address
any
systematic
and
random
errors
in
All background information included is relevant to the research
detail.
Include
a
discussion
of
the
likely
effect
of
question
systematic
volume
behind
of
errors;
an
each
for
example,
enzyme
time
you
with
will
a
if
you
pipette
have
a
measured
and
left
smaller
a
the
drop
The apparatus is listed precisely
volume
The methods are described clearly (and are repeatable)
than
recorded.
Do
not
be
tempted
to
suggest
things
All illustrations have figure numbers
that
are
unnecessary
,
had
sufficient
calculate
the
results
such
that
percentage
as
more
agreed.
error
of
repeats
You
your
if
can
you
Raw data has been included
also
results.
All graphs/tables have units and all graphs have labelled axes
Lastly
,
if
you
can
see
a
good
extension
to
your
Sample calculations have been included for processed data
investigation,
suggest
it
here.
Data is shown honestly, eg, using lines of best fit or error bars
Safety, ethical and environmental issues have been included
All sources are correctly referenced
✔
Make sure you have a basis to your conclusion
There is a conclusion
which you can then compare with secondary data
The evaluation makes recommendations for improvements
or a scientific theory.
✔
Identify whether errors are random or systematic.
✔
Suggested improvements should address the
errors identified.
Criterion 5: Communication
The
communication
report
and
In
effectively
outcomes
general
do
well
in.
structured
Include
this
so
a
can
is
anything
Do
not
the
to
that
waste
information
as
(if
understand
it
the
in
by
does
your
process
worked
that
Do
not
the
processed
from
have
to
of
well.
the
example
data.
references
It
for
source.
unnecessary
include
to
you
examiner
your
and
another
not
for
appropriately
information
including
pictures.
examiner
so
is
description
citations
come
space
one
be)
you
the
your
least
need
how
whether
focus,
criterion
report
presents
at
the
easiest
your
include
has
or
assesses
investigation.
detail
and
calculation
be
sure
that
enough
important
your
will
Make
methodology
,
of
of
criterion
communicates
read
an
appendix,
it.
227
P R A CT I C E
At
this
point,
Biology
approach.
papers,
course.
you
syllabus.
1,
It
2
is
will
now
and
3,
Answers
have
re-familiarized
Additionally
,
time
with
to
to
the
these
you
put
will
these
same
papers
structure
are
yourself
have
skills
E XA M
with
picked
up
to
the
test;
as
the
external
available
at
in
the
content
some
this
key
PA P E R S
from
the
techniques
section
you
assessment
will
you
topics
and
find
will
and
skills
options
to
practice
complete
at
refine
of
the
your
IB
exam
examination
the
end
of
the
DP
www.oxfordsecondary.com/ib-prepared-support.
Paper 1
SL:
45
HL:
1
minutes
hour
Instructions
•
•
Answer
For
all
each
sheet
to
candidates
the
questions.
question,
(provided
at
choose
the
answer
you
consider
to
be
the
best
and
indicate
your
choice
on
the
answer
www.oxfordsecondary.com/ib-prepared-support).
•
The
maximum
mark
for
the
SL
examination
•
The
maximum
mark
for
the
HL
paper
examination
is [30
paper
marks].
is [40
marks]
SL candidates: answer questions 1–30 only
HL candidates: answer all questions.
1.
Which
property
suitable
A.
for
Their
of
stem
therapeutic
cells
and
3.
them
use?
chromosomes
transfer
makes
are
What
a
role
of
ideal
for
gene
A.
Reduces
membrane
permeability
B.
They
can
divide
C.
They
can
differentiate
D.
They
can
produce
cholesterol
in
mammalian
cell
membranes?
cloning
by
is
meiosis
into
to
form
gametes
specialized
B.
cells
Clogs
to
transport
uidity
some
and
solutes
proteins
disabling
facilitated
diffusion
antibodies
C.
Forms
part
of
lipoproteins
recognized
by
antibodies
2.
Two
epithelial
larger
these
than
cells
cells
the
is
were
other.
compared;
Which
one
statement
D.
was
Produces
channels
for
transport
through
membranes
about
correct?
Questions 4 and 5 refer to the drawing at the top of page 229.
A.
The
to
B.
small
its
The
cell
had
less
surface
area
relative
The drawing shows how proteins are secreted from a cell.
volume
big
cell
produced
more
waste
per
unit
of
4.
Which
process
is
being
shown
volume
C.
The
small
excess
D.
228
Less
cell
was
more
efcient
at
A.
Diffusion
B.
Exocytosis
C.
Osmosis
D.
Facilitated
losing
heat
waste
diffused
out
of
the
big
cell
diffusion
in
the
diagram?
OH
H − N− C
=
R
− C
− C −
−
C
N −
H
−
−
H
H
−
−
O
−
C
O
−
−
R
−
−
H
endoplasmic
H
−
−
HO − C − C − N − N − C
rough
O
=
R
−
=
H
−
proteins expelled
H
R
−
membrane
=
O
cell surface
nuclear pore
H
H
reticulum
5
C.
nucleus
D.
cisternae
secretory vesicle
ribosome
9.
Which
statement
refers
to
DNA and
RNA?
2
A.
cisternae
RNA usually
comes
in
three
forms
and
DNA
1
only
B.
comes
They
in
always
one.
show
complementary
base
pairing.
cis face
4
3
C.
They
are
formed
D.
Only
RNA is
by
the
same
nucleotides.
trans face
proteins
a
helix.
transpor t
vesicles
Golgi apparatus
10.
Which
A.
It
statement
always
is
related
requires
Taq
to
DNA replication?
DNA polymerase
to
occur.
5.
Which
organelle(s)
other
than
the
nucleus
B.
show(s)
that
this
is
a
eukaryotic
DNA polymerase
separates
I
Golgi
II
apparatus
C.
Ribosomes
III
Rough
A.
I
B.
III
New
reticulum
only
only
C.
I
D.
I,
D.
and
II
III
and
The
new
and
a
diagram
shows
occurs
between
water
the
interaction
DNA strands.
bases
attach
the
original
one
original
strand
strand.
Which
graph
best
the
represents
substrate
the
effect
concentration
of
on
activity?
molecules?
−
H
H
−
−
−
O
O
−
H
−
−
H
H
H
H
H
H
−
−
H
H
H
−
−
H
H
B.
O
−
A.
O
−
H
−
O
ytivitca emyzne
H
ytivitca emyzne
H
−
O
H
O
C.
D.
substrate concentration
substrate concentration
A.
What
is
a
difference
between
amylose
Only
amylose
is
a
larger
C.
Only
amylopectin
is
molecule.
made
is
of
β-glucose.
made
of
glucose
ytivitca emyzne
Amylose
B.
ytivitca emyzne
A.
B.
and
amylopectin?
molecules.
D.
to
backbone.
that
O
7.
that
III
enzyme
−
enzyme
DNA contains
new
increasing
Which
an
only
11.
6.
the
nucleotide
sugar–phosphate
endoplasmic
is
cell?
Amylose
is
unbranched
while
amylopectin
substrate concentration
substrate concentration
is
branched.
C.
8.
Which
diagram
shows
a
peptide
bond
12.
two
amino
D.
between
Which
molecule
is
the
source
of
the
oxygen
acids?
produced
−
−
H
N − C −
photosynthesis?
O
=
H
in
C −
−
−
A.
Ribulose
B.
Carbon
C.
Glucose
D.
Water
bisphosphate
OH
dioxide
H
R
−
OH
N − C −
O
=
=
=
C −
−
C−
−
−
−
−
H
−
C −
OH
13.
What
is
the
relationship
between
Mendel’s
law
H
H
H
A.
R
−
N−
O
R
−
C−
H
−
−
−
N − C −
O
H
R
H
H
of
segregation
and
meiosis?
B.
A.
The
separation
chromosomes
of
paternal
shows
no
and
maternal
pattern.
229
PRACTICE
B.
Only
one
of
E X AM
a
pair
PA P E R S
of
genes
appears
in
a
gamete.
C.
Dominant
and
recessive
alleles
18.
Variation
only
results
after
All
the
D.
All
of
biotic
one
and
the
species
of
abiotic
sh
in
factors.
the
pond.
always
separate.
D.
C.
two
divisions.
What
is
the
direction
photosynthesis
in
A.
From
fossil
B.
From
plants
of
the
fuels
the
flow
carbon
to
of
carbon
by
cycle?
atmospheric
CO
2
14.
A man
has
hemophilia,
a
condition
caused
by
to
atmospheric
CO
2
a
recessive
What
is
allele
the
carried
possibility
on
of
the
X
having
chromosome.
a
C.
From
plants
D.
From
atmospheric
to
animals
hemophiliac
CO
to
plants
2
child
if
his
wife
is
homozygous
normal
for
the
gene?
19.
A.
0%
B.
25%
C.
50%
D.
100%
The
pie
chart
greenhouse
shows
gases
the
that
are
nitrous oxide
15.
In
goldfish
in
colour
(TT)
are
(Carassius
pattern.
common
auratus)
The
orange
recessive
crossed,
produce
they
type
of
Co-dominance
B.
Non-mendelian
C.
Non-disjunction
D.
Dihybrid
goldfish
(tt)
are
the
In
mice
(Tt).
What
is
carbon dioxide
What
grey
does
colour
is
due
dominant
allele
(G)
and
the
allele
for
Most
(g)
is
recessive.
Grey
mice
were
albino
mice.
A total
of
6
of
the
grey
and
4
albino.
The
null
suggest
production
is
about
the
gases?
probably
due
to
cattle
probably
due
to
burning
fermentation.
Most
production
is
fossil
fuels.
offspring
C.
were
graph
greenhouse
crossed
of
with
of
albino
B.
colour
this
to
gut
a
area.
chlorouorocarbons
called?
musculus)
an
methane
production
(Mus
in
When
A.
16.
produced
dominant
and
fish
of
variation
transparent.
mottled
inheritance
A.
is
homozygous
homozygous
this
there
proportion
Least
production
is
due
to
burning
of
to
burning
of
hypothesis
chlorouorocarbons.
is
that
the
alleles
segregate
independently
D.
(are
unlinked)
heterozygous.
therefore
The
the
grey
chi-squared
parent
value
is
Least
production
is
due
biogas.
was
0.4.
The
Questions 20 and 21 relate to the following data.
table
below
shows
the
probability
values:
The
number
of
snails
(Cepaea
nemoralis)
eaten
by
Probability
birds
Degrees of
and
0.99
0.95
0.05
was
early
counted
during
summer
(days
late
10
to
spring
20),
(days
when
1
the
to
10)
trees
0.01
freedom
turn
1
0.000
0.004
3.84
6.64
2
0.020
0.103
5.99
9.21
greener.
background
eaten
when
More
is
green
brown
the
snails
and
more
background
is
are
eaten
brown
when
snails
the
are
green.
100
0.115
Which
of
the
0.352
statements
is
7.82
correct
yad rep netae slians fo rebmun
3
11.35
about
the
null
hypothesis?
A.
B.
It
is
accepted
is
less
It
is
than
the
chi-squared
value
3.84.
rejected
than
because
because
the
probability
is
less
90
80
70
60
brown snails
50
green snails
40
30
20
10
0.05.
0
1
C.
It
is
accepted
because
the
chi-squared
3
5
7
9
11
13
15
17
19
21
value
time / day
D.
is
less
It
is
than
5.99.
rejected
because
the
chi-squared
value
is
20.
greater
than
This
pattern
years.
17.
What
is
a
continually
probable
B.
All
All
the
the
throughout
A.
Balanced
B.
Convergent
C.
Divergent
D.
Competition
outcome?
polymorphism
What constitutes a population in a pond ecosystem?
A.
230
occurs
0.352.
living
organisms
animals
and
in
plants
the
in
evolution
pond.
the
evolution
pond.
the
21.
What
statement
refers
to
green
and
brown
220
/ tluda sa level loretselohc doolb naem
snails?
belong
to
a
B.
They
belong
to
the
same
C.
They
belong
to
the
nemoralis
D.
They
belong
to
the
Cepaea
Studies
the
It
biochemistry
evolutionary
was
in
from
found
gorillas
that
in
genus.
phylum.
the
by
provide
of
amino
chimpanzees
evidence
between
sequence
one
family
.
order.
relationships
differs
hemoglobin
different
hemoglobin
acid
and
of
primates.
from
humans,
210
200
mc 001 gm
They
3–
22.
A.
190
180
170
160
150
whose
130
sequence
is
the
same.
Models
were
140
160
150
170
180
constructed
mean blood cholesterol level when young /
showing
the
humans,
chimpanzees
possible
relationships
between
–3
mg 100 cm
and
gorillas.
What
Which
model
according
to
best
represents
hemoglobin
A.
the
relationship
does
cholesterol
this
graph
show
about
blood
levels?
structure?
A.
They
increase
B.
They
are
C.
Low
as
men
grow
older.
B.
human
gorilla
chimpanzee
3
human
chimpanzee
never
below
160
mg
in
100
cm
gorilla
blood
cholesterol
levels
in
youth
are
healthier.
D.
They
remain
lifetime
25.
common ancestor
What
is
of
true
a
constant
throughout
the
man.
about
antigens?
A.
They
are
produced
B.
They
are
only
C.
They
may
in
found
the
in
bone
white
marrow.
blood
cells.
common ancestor
C.
stimulate
the
formation
of
D.
antibodies.
chimpanzee
gorilla
human
chimpanzee
human
gorilla
D.
They
can
only
be
found
on
the
walls
of
bacteria.
26.
common ancestor
23.
What
not
A.
24.
characteristic
in
Bilateral
present
in
arthropods
but
27.
Articulated
Calcium
D.
Notochord
legs
shell
cholesterol
group
of
year.
teenage
Years
levels
boys
later,
were
once
when
a
measured
month
they
in
28.
a
Alveoli
B.
Bronchi
C.
Trachea
D.
Diaphragm
During
the
were
results
measured
were
again
recorded
in
in
the
the
represents
the
level
way
.
graph.
as
and
as
an
adult
for
each
cycle,
progesterone
Growth
of
follicle
Growth
of
uterine
C.
Menstruation
D.
Ovulation
What
occurs
during
place
what
in
humans?
event
occurs
falls?
surrounding
the
egg
lining
transmission
of
a
nerve
a
There
is
of
membrane
man
a
change
in
the
permeability
to
ions
The
the
in
the
axon.
Each
+
The
resting
condition
is
restored
by
Li
ions
young
owing
teenager
of
take
adults,
same
scatter
cholesterol
menstrual
level
B.
B.
dot
the
exchange
A.
A.
they
gas
impulse?
during
were
does
A.
as
symmetry
C.
Blood
is
molluscs?
B.
one
common ancestor
Where
in
out
of
the
neuron.
the
+
C.
During
depolarization,
K
ions
ow
out
of
study
.
the
neuron.
+
D.
In
hyperpolarization,
K
ions
ow
into
the
neuron.
231
PRACTICE
29.
What
II
is
true
for
E X AM
type
I
PA P E R S
diabetes
but
not
for
type
34.
What
occurs
during
chemiosmosis?
diabetes?
A.
A.
Glucose
can
be
detected
in
Oxidation
urine.
NAD
of
molecules
(NADH)
and
such
reduced
as
reduced
FAD
(FADH
).
2
B.
High
C.
Blood
insulin
levels
blood
insulin
levels.
D.
levels
Insulin
of
glucose
receptors
are
are
detected
lower
in
than
blood.
B.
Electrons
normal
another,
C.
are
Protons
blocked.
What
is
the
sinoatrial
A.
A blood
B.
The
C.
A group
passed
move
concentration
D.
30.
are
liberating
across
compounds
a
of
into
one
carrier
membrane,
gradient,
Transformation
node?
from
to
energy
.
releasing
energy
stored
down
a
energy
.
in
organic
ATP
.
vessel
35.
wall
of
of
the
The
diagram
and
the
shows
two
stems,
one
untreated
ventricle
cells
that
initiate
other
placed
in
ink
for
a
day
.
myogenic
contraction
D.
A node
formed
by
sensory
neurons
untreated
stem placed in
stem
ink for a day
The following questions are for HL candidates only
31.
What
forms
a
eukaryotic
chromosome?
What
A.
One
DNA molecule
B.
Several
and
one
large
A.
DNA molecules
and
causes
many
One
DNA molecule
D.
Several
and
DNA molecules
many
and
difference
in
these
stems?
Coloured
water
transported
through
the
proteins
xylem
C.
the
protein
has
passed
to
the
phloem.
proteins
one
B.
Coloured
C.
The
water
has
entered
the
phloem
only
.
large
ink
was
transpired
through
the
stomata
protein
of
D.
the
The
stems.
ink
has
stained
all
living
tissues.
Questions 32 and 33 refer to the following diagram.
The
diagram
fragments
in
shows
the
the
formation
replication
of
of
Okazaki
DNA in
36.
prokaryotes.
Scientists
species
in
investigated
of
three
plants.
ways:
Each
some
the
of
pollination
the
plants
species
had
their
of
four
was
treated
flowers
leading strand
covered
5'
were
parental DNA
to
not
exclude
pollinators,
manipulated,
pollinate
them,
and
a
other
allowing
third
plants
birds
group
was
to
pollinated
5'
Okazaki fragments
by
hand
using
a
paintbrush.
The
percentage
3'
of
the
was
total
flowers
that
developed
into
fruit
recorded.
3'
32.
What
enzyme
links
the
Okazaki
fragments
together?
33.
A.
Gyrase
C.
Helicase
B.
Ligase
D.
Primase
Why
is
the
necessary
formation
during
of
Okazaki
fragments
% / stiurf otni depoleved taht srewol f
lagging strand
no pollinators allowed
90
pollination allowed
80
hand-pollinated
70
60
50
40
30
20
10
0
replication?
A.
B.
C.
D.
species of plant
A.
DNA polymerase
nucleotides
in
the
adds
5′–3′
complementary
direction
only
.
Which
B.
The
RNA primer
cannot
be
attached
to
species
pollinated
lagging
C.
more
D.
replication
is
faster
and
efcient.
Okazaki
coding
232
strand.
A discontinuous
fragments
regions.
only
replicate
non-
of
plant
the
by
birds?
is
most
efficiently
37.
A student
carried
comparing
each
of
When
out
of
t
a
in
probability
the
the
of
100
data
cress
seedlings
collected
Looking
up
appropriate
value
between
drawn
B.
investigation
environmental
the
t-test.
conclusion
an
growth
different
processing
carried
value
the
two
out
table
0.15
from
the
C.
the
gave
state
continuous
D.
Evolution
of
What
There
B.
signicant
The
difference
39.
result?
What
the
difference
between
species
between
the
two
seedlings
prefer
one
samples
environment
is
is
A.
forms
over
are
species
long
long
a
steady
transformation
sequence
of
a
of
species
periods
where
a
number
equilibrated
in
source
the
of
glucose
Bowman’s
in
the
fluid
capsule?
over
Filtrate
B.
Urine
C.
Blood
D.
Cells
in
in
in
of
the
the
the
the
distal
convoluted
collecting
tubule
duct
glomerulus
medulla
other
There
What
the
A.
is
insufcient
data
to
carry
out
a
40.
t-test
What
of
38.
a
at
the
conditions
signicant
Cress
D.
a
environmental
not
C.
is
two
with
uniformly
is
flowing
A.
with
intermediate
a
0.25.
occurring
Evolution
student
calculated
and
this
in
conditions.
Evolution
is
punctuated
Long
and
periods
short
happens
the
sperm
immediately
into
the
after
the
penetration
egg?
equilibrium?
without
periods
of
appreciable
rapid
change
evolution
A.
Development
of
the
secondary
B.
Development
of
the
primary
C.
Acrosome
D.
Cortical
oocyte
oocyte
reaction
reaction
Paper 2
SL:
1
HL:
hour
2
15
hours
15
Instructions
•
Answers
are
minutes
minutes
to
candidates
must
provided
be
at
is
written
within
the
answers
boxes
(answer
sheets
www.oxfordsecondary.com/ib-prepared-support).
•
A calculator
required
for
this
paper.
•
The
maximum
mark
for
the
SL
•
The
maximum
mark
for
the
HL
examination
paper
examination
is [50
paper
marks]
is [72
marks]
SL candidates: answer questions 1–4 from section A and one question from
section B.
HL candidates: answer all questions from section A and two questions from
section B.
Section A
1.
T
ransgenic
another
plants
species
engineering.
a
variant
Bacillus
(a)
Some
maize
The
levels
gene
next
to
been
one
Cry
protein
gene
for
is
the
or
into
modified
expresses
This
the
which
to
more
the
resist
protein
pests.
from
poisonous
Cry
genes
genome,
protein
to
is
from
using
Bt
the
corn
genetic
is
bacterium
certain
added
insects.
to
the
[3]
of
for
of
uptake
the
for
the
Cry
DNA,
thickness
results
that
in
introduced
corn.
amounts
and
how
plants
been
have
thuringiensis.
Outline
Bt
the
of
are
have
of
the
plant,
protein
were
mRNA and
the
leaves
by
of
band
three
respective
is
transcription
and
measured.
order
protein
an
indicator
different
ladders
were
on
plants
the
of
In
translation
detected.
amounts
(1,
2
and
following
3)
to
do
The
so,
the
darkness
present.
are
of
The
shown
page.
233
PRACTICE
E X AM
PA P E R S
(b)
In
order
to
detect
performed.
Cry
due
to
promoter.
Cry
(c)
(d)
an
presence
the
(an
the
a
extra
plant
that
gene
for
slightly
sequence
has
the
Cry
,
larger
of
a
PCR
gene
DNA)
larger
in
gene
was
for
the
for
the
[1]
reason
the
data
successful
Common
cornfields
of
monarch
across
Information
plant,
Region
be
the
detected
whether
most
plant
genetic
3.
[1]
modification
plants.
[2]
is
corn-growing
(Danaus
plants.
to
the
in
Bt
a
produce
a
is
that
regions.
plexippus)
corn
plant
live
exists
The
and
larvae
feed
corn
that
has
protein
that
is
on
been
poisonous
to
pests.
research
from
impact
genetically
three
not
(Asclepiassyriaca)
modified
insect
information
would
confirm
butterflies
A collaborative
the
to
the
milkweed
genetically
certain
in
mRNA was
milkweed
in
common
of
11
Bt
was
corn
on
sought
modified
exposed
to
common
effort
regions
the
the
toxic
scientists
develop
monarch
on
and
by
to
degree
milkweed,
a
produced
formal
butterfly
percentage
amounts
to
of
found
of
which
Bt
in
corn
assessment
that
is
monarch
pollen
and
risk
populations.
on
its
around
larvae
host
cornfields.
Percentage
Percentage of
Percentage of
Probability
of arable land
corn that is
corn area that
of exposure
planted with
Bt / %
is a breeding
of monarch
site for monarch
butterfly to Bt
butterfly / %
corn pollen
corn / %
234
of
presented
insertion
Identify
one
Evaluate
of
the
plant
protein.
Suggest
was
One
1
42
26
19
0.0040
2
42
14
18
0.0026
3
38
7
10
0.0007
4
12
26
4
0.0002
5
13
11
2
0.0001
6
21
8
4
0.0002
7
29
30
8
0.0028
8
12
22
5
0.0002
9
39
26
7
0.0011
10
13
11
0
0.0001
11
26
37
9
0.0004
Mean
26
23
8.6
0.0 011
(e)
(i)
State
the
monarch
(ii)
be
corn
support
another
plants
(Bt
from
1
that
is
area
with
[1]
region
of
this
current
percentage
sites.
a
leaves
from
monarch
Bt
pollen
corn
larvae
non-Bt
the
from
with
and
of
greatest
where
pollen
of
Bt
corn
milkweed.
2-year
commercial
negligible.
[1]
study
Bt
that
the
corn
Analyse
the
on
impact
of
monarch
data
to
conclusion.
study
,
dusted
corn
with
on
reason,
populations
this
the
breeding
a
concluded
pollen
butterfly
In
with
found
Scientists
Bt
with
butterfly
Identify
,
could
(f)
region
2)
fed
[3]
butterfly
from
and
two
their
milkweed
larvae
were
brands
survival
plants
of
fed
Bt
rate
was
dusted
milkweed
corn
compared
with
pollen
corn.
1
gnivivrus noitroporp
0.8
0.6
0.4
non-Bt corn
Bt corn 1
0.2
Bt corn 2
0
0
20
40
60
80
100
120
time / hours
(g)
Compare
when
(h)
Using
and
using
all
contrast
non-Bt
the
data,
the
corn
survival
pollen
discuss
the
of
and
monarch
Bt
effect
of
corn
Bt
butterfly
larvae
pollen.
corn
on
[3]
monarch
butterflies.
2.
Camellia
used
to
sinensis
produce
mRNA for
C.
[2]
is
a
species
tea.
The
sinensis
are
of
evergreen
nucleotide
given
in
plant
whose
percentages
the
in
leaves
the
are
DNA and
table.
Bases / %
Adenine
Guanine
Cytosine
Thymine or uracil
DNA
31.7
18.6
18.3
31.4
mRNA
25.7
29.8
23.9
20.6
(a)
(b)
State
(i)
the
base
Distinguish
DNA and
(ii)
(c)
The
where
leaves
diagram
in
mRNA but
between
the
not
DNA.
percentages
of
[1]
bases
found
in
mRNA.
Determine
Outline
the
3.
found
of
a
[2]
reason
for
DNA and
C.
shows
this
difference.
mRNA can
be
found
[1]
in
sinensis.
the
structure
the
cells
of
[2]
of
a
human
heart.
235
PRACTICE
E X AM
PA P E R S
(a)
(b)
On
the
(i)
left
(ii)
semilunar
(iii)
pulmonary
4.
The
label
the:
[3]
atrium
Annotate
blood
(c)
diagram
the
valve
through
Explain
the
vein.
diagram
the
show
the
direction
show
parts
width
of
in
the
different
1)
No
plants
2)
3)
of
classification
and
of
plants
shown
(not
ventricles.
to
[3]
scale).
in
the
pictures
using
the
[3]
tissue
.................................Bryophyta
vascular
tissue
..........................
present....................................
spores
Flowers
the
key
.
vascular
Spores
No
of
D
the
Presence
walls
B
C
dichotomous
deoxygenated
[2]
in
A
Determine
of
heart.
difference
photographs
to
presence
of
to
2
Filicinophyta
.......................................................
present.........................
go
go
to
3
Angiospermophyta
No
flowers
cones........Coniferophyta
Question 5 is for HL candidates only
5.
(a)
List
two
structures
endosymbiotic
(b)
Explain
present
in
mitochondria
that
support
the
theory
.
chemiosmosis
[2]
in
mitochondria.
[4]
Section B
Questions 6 and 7 are for SL candidates only. Answer one of the questions. Up to one
additional mark is available for the construction of your answer.
6.
7.
Starch
is
produced
(a)
Draw
(b)
Explain
(c)
Describe
Bacteria
(a)
a
can
the
chloroplasts.
chloroplast
Outline
in
in
how
how
be
how
show
enzymes
useful
food
to
chloroplasts
to
its
in
the
produce
organisms
industry
to
ultrastructure.
produce
such
starch
digestive
foods
as
produce
but
[4]
photosynthesis.
system
can
bacteria
foods
by
or
digest
also
be
yeast
through
starch.
pathogenic.
can
be
used
anaerobic
respiration.
(b)
Bacteria
can
(c)
236
[4]
can
develop
Explain
the
[7]
[4]
be
killed
by
resistance
immune
antibiotics.
to
Describe
how
some
antibiotics.
reaction
to
a
bacterial
bacteria
[4]
infection.
[7]
The following questions are for HL candidates only. Answer two of the questions.
Up to one additional mark is available for the construction of your answers for
each question.
8.
Starch
is
produced
(a)
Draw
(b)
Explain
a
(c)
Describe
in
chloroplasts.
chloroplast
how
to
show
chloroplasts
how
enzymes
its
ultrastructure.
produce
in
the
starch
digestive
by
[4]
photosynthesis.
system
starch.
9.
Bacteria
(a)
[4]
can
be
Outline
Bacteria
10.
Waste
toxic
(a)
the
matter
develop
needs
in
Compare
and
excretion
by
Outline
(c)
Uric
the
acid
but
ethanol
can
and
also
be
carbon
pathogenic.
dioxide
in
antibiotics.
resistance
reaction
a
of
of
labelled
to
eliminated
a
how
some
antibiotics.
bacterial
to
structural
tubule
ADH
normal
by
to
Describe
avoid
[4]
infection.
harmful
[7]
effects
from
organism.
contrast
role
is
be
[4]
by
Malpighian
characterized
a
to
the
concentrations
Draw
foods
produce
killed
immune
substances
(b)
produce
bacteria
be
can
Explain
to
respiration.
can
bacteria
(c)
useful
how
anaerobic
(b)
[7]
digest
in
acid
can
of
of
lead
inflammation
structure
functional
and
aspects
of
kidneys.
[7]
osmoregulation.
component
uric
and
systems
of
the
urine.
to
gout.
joints,
[4]
High
blood
This
such
as
disease
the
is
elbow.
elbow.
[4]
Paper 3
SL:
1
HL:
hour
1
hours
15
Instructions
•
Answers
(answer
to
minutes
candidates
must
be
sheets
written
are
within
provided
at
the
answers
boxes
provided
www.oxfordsecondary.com/
ib-prepared-support).
•
A calculator
is
required
for
this
paper.
•
The
maximum
mark
for
the
SL
•
The
maximum
mark
for
the
HL
examination
paper
examination
is [35
paper
marks].
is [45
marks].
Section A
SL and HL candidates: answer all questions.
1.
In
an
experiment,
solutions
water
seen
and
test
bath. A positive
in
tubes
Benedict’s
varying
test
densities
were
reagent.
results
in
the
filled
The
in
with
tubes
an
different
were
orange
glucose
then
heated
precipitate,
in
a
which
is
tubes.
237
PRACTICE
E X AM
PA P E R S
Two
food
shown
in
samples
the
(a)
Estimate
(b)
Suggest
the
2.
To
test
glucose
with
Describe
0.1%
tested
in
the
same
way
and
the
results
are
photograph.
measuring
(c)
were
a
the
one
concentration
reason
whether
glucose
method
in
this
is
foods
a
1
and
precise
2.
[2]
method
of
concentration.
to
obtain
the
[1]
glucose
solutions
of
1%
and
concentration.
the
following
effect
of
light
apparatus
[3]
intensity
was
set
in
a
the
rate
of
photosynthesis,
the
laboratory
.
wide plastic
3
5 cm
up
on
syringe
tubing
capillary tube
thermometer
scale (mm)
shoot of lodea
pond water or potassium
hydrogencarbonate solution
water bath
(a)
Suggest
this
one
way
light
intensity
could
have
been
modified
in
experiment.
(b)
Identify
the
(c)
Explain
how
[1]
reason
the
a
thermometer
rate
of
is
placed
photosynthesis
in
was
the
water
recorded
bath.
in
[2]
this
experiment.
[3]
3.
Polyacrylamide
separate
the
nucleic
electrophoresis
acids
in
forensic
(PAGE)
chemistry
.
is
a
technique
The
diagram
used
to
illustrates
process.
Explain
how
the
electrophoresis.
238
gel
nucleic
acids
separate
in
the
gel
during
[3]
Section B
Answer all of the questions from one of the options.
Option
A:
Neurobiology
and
behaviour
SL candidates: answer questions 4–7
only
HL candidates: answer questions 4–10.
4.
The
graph
mammal
shows
during
the
neurogenesis
embryonic
stages
and
and
dendritic
after
growth
in
a
birth.
htworg fo tnet xe
neurogenesis
dendrite growth
bir th
(a)
Neurogenesis
is
the
development
of
new
neurons.
Describe
neurogenesis.
(b)
Neurulation
stages
(c)
State
are
5.
It
has
mass
name
of
variable
rate
that
was
if
the
occur
before
neurogenesis.
Outline
the
and
has
a
could
are
that
been
not
the
by
from
which
or
synapses
[1]
evolution
accompanied
longevity
many
neurons
used.
corresponding
affect
analysed
[3]
process
they
hypothesized
mammals
mortality
mass
the
to
neurulation.
eliminated
been
in
of
[3]
needs
of
by
increase
is
brain
mammalian
a
in
increasing
reduction
body
of
longevity
.
mass.
Data
on
the
Another
brain
species.
100
sraey / ytivegnol
10
1
10
1
100
1,000
10,000
brain mass / g
Analyse
the
increasing
6.
The
data
body
diagram
to
see
mass
whether
can
illustrates
a
affect
it
confirms
the
hypothesis
that
longevity
.
transverse
section
[3]
of
a
human
eye.
II
IV
III
239
PRACTICE
E X AM
PA P E R S
(a)
Identify
the
(i)
light
(ii)
sends
(iii)
adjusts
label
matching
detection
by
impulses
in
function:
[3]
photoreceptors
to
order
each
the
to
brain
bend
the
light
rays
to
be
focused
on
the
retina.
(b)
Draw
an
arrow
observing
(c)
The
ear
cells
in
is
an
also
the
showing
the
direction
of
the
light
rays
when
object.
a
[1]
sensory
cochlea
and
organ.
the
hair
Distinguish
cells
in
the
between
the
hair
semicircular
canals.
7.
Explain
the
[2]
mode
of
action
of
the
autonomic
nervous
system.
[4]
The following questions are for HL candidates only
8.
The
diagram
shows
the
reflex
arc.
Label
the
parts
1
to
4.
[2]
1
2
3
4
9.
The
number
recorded
Melospiza
of
the
in
of
different
two
species
melodia.
passerines
results
are
A group
and
shown
songs
of
in
the
the
and
lengths
passerines,
of
birds
birds’
bar
was
songs
of
these
Melospiza
bred
were
songs
lincolnii
isolated
also
were
and
from
recorded.
the
rest
The
charts.
12
3
Melospiza lincolnii
Melospiza melodia
2.5
s / sgnos fo htgnel
sgnos tnereid fo rebmun
10
8
6
4
2
Analyse
240
1
0
control
10.
1.5
0.5
0
that
2
the
isolated
data
birdsong
Discuss
the
is
to
see
innate
health
control
whether
in
the
data
passerines.
effects
of
cocaine.
supports
the
isolated
hypothesis
[2]
[6]
Option
B:
Biotechnology
and
bioinformatics
SL candidates: answer questions 11–14 only
HL candidates: answer questions 11–16.
11.
Fermenters
by
allow
microorganisms.
mycoprotein
produced
every
(a)
by
for
The
production
diagram
fermentation.
human
of
shows
metabolites
the
Mycoprotein
consumption.
production
is
a
fungus
Mycoprotein
is
of
protein
harvested
day
.
State
this
(b)
large-scale
two
conditions
that
should
be
monitored
by
probes
in
fermenter.
State
one
[2]
reason
for
the
use
of
paddles.
[1]
waste
gases
water
out
water
jacket
feedstock
lter
ex tract
mycoprotein
air
ltrate
water
in
12.
Bagasse
juice
a
is
nutrient
using
(a)
the
from
the
fibrous
sugar
cane.
solution
fungus
State
a
use
of
is
ordinary
that
were
it
is
Citric
that
acid
containing
Aspergillus
citric
Fermentation
an
matter
on
acid
trays
much
different
in
of
cheaper
for
after
the
obtained
by
extraction
of
fermentation
concentrations
of
of
bagasse
niger.
the
food
different
fermentation.
collected
remains
was
The
than
evaluation
industry
.
depths
was
advantage
using
of
a
citric
[1]
of
compared
tray
fermenter.
acid
with
fermentation
Samples
production.
rettam y rd g001 rep g / dica cirtic
30
25
20
fermenter
tray (2 cm)
15
tray (6 cm)
10
5
0
bagasse / %
(b)
Identify
the
best
conditions
to
obtain
citric
acid
in
this
experiment.
(c)
Based
on
the
effectiveness
[1]
results
of
of
fermentation
tray
these
experiments,
of
comment
bagasse.
on
the
[3]
241
PRACTICE
E X AM
PA P E R S
13.
The
is
mixture
known
common
(a)
S.
as
of
plaque.
bacteria
mutans
used
The
to
It
in
are
saliva
is
a
tooth
and
cause
of
biofilms
Gram-positive
detect
thickness
was
the
bacteria,
that
of
measured
a
for
percentage
of
the
3
tooth
are
of
weeks.
decay
are
The
(caries).
Describe
on
The
teeth
most
mutans.
the
method
Gram-positive.
Streptococcus
bacteria
found
Streptococcus
bacteria.
bacteria
biofilm
live
carbohydrates
viability
over
the
mutans
was
total
[3]
bacteria
measured
after
as
exposure
to
antibiotics.
30
100
25
80
% / ytilibaiv
mµ / ssenkciht
20
15
60
40
10
20
5
0
0
1
2
1
3
2
week
(b)
Suggest
reasons
3
week
for
the
change
in
thickness
of
the
biofilm
over
time.
14.
[2]
(c)
Calculate
(d)
Suggest
Transgenic
genes
have
for
plants
different
one
been
difference
reasons
rice
from
Explain
the
the
have
method
by
viability
change
been
species
genetically
in
to
in
viability
genetically
promote
which
between
these
weeks
over
transgenic
to
rice
and
3.
[1]
time.
modified
resistance
2
by
[2]
adding
herbicides.
plants
could
modified.
[4]
The following questions are for HL candidates only
15.
Part
of
the
different
the
(a)
sequence
organisms.
amino
State
acid
the
similar
(b)
On
the
to
protein
cytochrome
alignment
and
whose
a
is
shown
space
that
cytochrome
c
there
c
was
below.
is
compared
A dash
no
sequence
amino
is
in
shows
acid.
most
humans.
sequence,
Outline
the
repeated
organism
conserved
(c)
is
of
The
in
how
all
the
this
[1]
use
a
box
to
species
sequence
identify
an
amino
acid
that
shown.
alignment
is
[1]
was
obtained
using
bioinformatics.
[2]
Human
G
D
V
E
K
G
K
K
I
F
I
M
K
C
S
Q
C
H
T
V
E
K
Pig
–
–
–
–
–
–
–
–
–
–
V
Q
–
–
A
–
–
–
–
–
–
–
Fish
–
–
–
–
–
–
–
–
V
–
V
Q
–
–
A
–
–
–
–
–
–
N
Wheat
N
P
D
A
–
A
–
–
–
K
T
–
–
A
–
–
–
–
–
N
A
Yeast
S
A
K
–
–
A
T
L
–
K
T
R
–
Q
L
–
–
–
–
–
–
16.
Using
an
therapy
.
242
example,
explain
the
use
of
viral
vectors
in
gene
[6]
Option
C:
Ecology
and
conservation
SL candidates: answer questions 17–20 only
HL candidates: answer questions 17–22.
17.
Lettuce
in
coral
shallow
Colonies
into
The
the
U.
tenuifolia
medium
number
year
of
starting
(2)
tenuifolia)
semi-exposed
of
small,
times,
(Undaria
and
and
colonies
in
Southern
in
in
the
the
dominant
Southern
classified
coral
species
Caribbean
according
to
the
Sea.
colony
size
large.
according
spring
ending
reefs
were
is
of
the
spring
to
first
of
their
year
the
size
(1),
were
then
second
year
recorded
autumn
(3)
in
a
of
three
the
first
location
in
Caribbean.
140
120
seinoloc fo rebmun
100
small colony
medium colony
80
large colony
60
40
20
0
0
2
1
3
time / recording
(a)
State
each
the
(b)
Describe
(c)
Suggest
18.
Describe
Serratia
predator,
trends
colonies
nutrients
at
in
reason
recorded
numbers
for
the
how
the
first
spring
for
colonies.
in
[2]
population
of
small
and
(first
aurelia
on
this
is
an
trophic
(second
(small
two
[1]
bleaching
level)
trophic
nasutum
food
(third
chain
marcescens
only
•
microcosm
2:
S.
marcescens
and
•
microcosm
3:
S.
marcescens,
population
after
density
7
of
the
P
.
stress
bacterium
is
level)
in
(low
aurelia
aurelia
three
S.
corals.
eaten
[2]
by
by
a
effect
closed
were
set
up
as
andhigh):
only
and
bacterium
on
eaten
The
microcosms
levels
S.
of
which
studied
1:
P
.
a
trophic
The
nutrient
is
level)
was
mesocosms).
different
indication
microcosm
measured
of
change
•
The
in
corals.
Didinium
microcosms
follows
of
[1]
marcescens
Paramecium
of
the
one
medium
(d)
number
colony
.
D.
nasutum.
marcescens
was
days.
1 000 000
lm rebmun
1−
/ snecsecram .S fo ytisned noitalupop
100 000
microcosm 1
10 000
microcosm 2
microcosm 3
1 000
100
low
nutrient level
high
243
PRACTICE
E X AM
PA P E R S
(a)
State
S.
(b)
the
effect
marcescens
Explain
adding
the
a
of
in
nutrient
level
microcosm
effect
trophic
on
the
level
the
density
of
population
1
S.
in
on
[1]
marcescens
each
population
microcosm
at
a
density
high
of
nutrient
level.
[2]
(c)
Suggest
(d)
Using
one
the
between
reason
data
in
nutrient
for
this
little
change
investigation,
levels
and
the
at
low
nutrient
predict
length
of
a
a
levels.
[1]
relationship
chain
in
a
food
web.
19.
The
[1]
table
sand
shows
the
number
of
plants
of
each
species
counted
in
a
dune.
Species
Number
sea holly (Acanthus ebracteatus)
3
sand couch (Sporobolus virginicus)
6
baby grass (Sporobolus pungens)
1
Total
10
(a)
of
Calculate
the
following
Simpson
data
for
reciprocal
this
diversity
community
,
using
index
the
from
formula
the
given
below.
N (N
D
1)
[1]
=
Σn ( n
(b)
Comment
− 1)
on
the
richness
and
evenness
of
this
sand
dune
community
.
The
sand
where
240
Simpson
(c)
20.
Discuss
pest
community
organisms
diversity
Distinguish
forest
[2]
dune
were
index
between
the
was
compared
counted
of
this
in
forest
biodiversity
a
total
was
of
with
of
that
10
of
a
forest
species.
The
14.
the
sand
dune
and
the
studied.
the
[2]
biological
and
ethical
issues
surrounding
biological
control.
[4]
The following questions are for HL candidates only
21.
The
study
of
species
environments
can
processes
to
(Quercus
due
robur)
determine
(a)
in
two
urban
graph
nitrogen
and
244
and
in
in
the
The
habitats
of
leaves
of
in
versus
Q.
±
that
of
the
could
in
English
areas
leaf
rural
shifts
were
assessed
nitrogen
affect
ecological
oak
the
nitrogen
[2]
standard
of
to
content.
robur.
leaves
large,
of
rural
affected
soil
mean
concentration
rural
urban
adjacent
the
leaves
shows
in
understanding
urbanization
factors
concentration
The
the
urbanization.
whether
Outline
interactions
improve
Q.
medium
deviation
robur
and
of
the
growing
small
cities.
in
urban
30
g gm / noitartnecnoc negortin
1−
25
ssam fael y rd
20
urban
15
rural
10
5
0
large
medium
small
city size
(b)
Describe
leaf
22.
Explain
the
effect
nitrogen
of
city
size
and
urbanization
on
the Q.
robur
concentration.
bottom-up
and
[2]
top-down
limiting
factors
in
a
pond
environment.
Option
D:
[6]
Human
physiology
SL candidates: answer questions 23–26 only
HL candidates: answer questions 23–28.
23.
Phenylketonuria
decreased
by
the
deficiency
converts
in
(PKU)
metabolism
foods
of
an
the
inherited
amino
phenylalanine
phenylalanine
that
is
of
contain
into
disease
acid
hydrolase,
tyrosine.
phenylalanine
that
an
Treatment
and
results
phenylalanine.
the
It
enzyme
is
with
addition
of
a
in
is
caused
that
diet
low
special
supplements.
Serum
phenylalanine
restricted
does
not
brain
did
diet
follow
damage
not
stick
levels
therapy
.
the
and
to
the
diet.
the
are
Brain
The
important
damage
scattergraph
plasma
indications
might
occur
shows
phenylalanine
if
the
levels
for
the
protein-
patient
incidence
of
patients
of
who
diet.
6
stinu y rartibra / noitcnuf niarb
5
4
3
2
1
0
0
5
10
15
20
25
30
−1
phenylalanine plasma levels / mg dl
(a)
Describe
and
(b)
24.
brain
Discuss
in
Orally
relationship
use
with
administered
at
which
of
1
means
to
the
of
plasma
levels
the
drug
drugs
by
is
drug
but
protein-free
diet
to
improve
brain
function
PKU.
happens
all
phenylalanine
[1]
a
eliminated
this
between
function.
the
patients
completely
bind
the
do
[3]
that
the
called
has
not
are
liver
the
been
not
by
excreted
hepatic
removed.
catabolize
in
enzymatic
it.
urine
extraction
ratio.
Competitive
The
must
reactions.
graph
be
The
rate
A ratio
inhibitors
shows
the
245
PRACTICE
E X AM
PA P E R S
relationship
inhibition
between
by
a
the
hepatic
competitive
extraction
ratio
and
percentage
inhibitor.
1.0
oitar noitcart xe citapeh
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
inhibition / %
(a)
It
has
cause
been
suggested
drug
damaging
plasma
the
that
drug
competitive
concentrations
liver.
Discuss
this
to
inhibitors
increase,
hypothesis
can
permanently
using
the
data
provided.
(b)
25.
List
A study
two
was
investigate
(a)
a
functions
of
performed
the
Define
For
[3]
effects
the
on
of
liver
other
patients
exercise
than
with
on
detoxification.
hypertension
heart
[2]
to
functions.
hypertension.
period
treadmill.
of
At
the
non-exercise
recorded
in
10
[1]
weeks
same
per
group
time,
conditions.
beats
a
of
patients
excercised
control
patients
were
The
mean
minute
resting
heart
kept
rate
using
a
under
was
(bpm).
79.0
78.5
78.0
mpb / etar t raeh gnitser
77
.5
77
.0
76.5
76.0
75.5
75.0
74.5
74.0
exercise
(b)
Describe
(c)
Outline
The
(d)
the
Explain
the
heart
walls
how
propagation
26.
effect
how
heart
Explain
control
exercise
is
contract
the
of
of
rate
nervous
during
structure
stimuli
on
of
resting
heart
rate.
[2]
of
the
[2]
heart
cardiac
through
control
the
measured.
the
beats.
muscle
heart
cells
allows
wall.
[2]
digestion.
[4]
The following questions are for HL candidates only
27.
The
human
that
stimulates
bone,
and
increases
promotes
Outline
28.
Fetal
this
246
growth
the
muscle
the
mode
hemoglobin
statement.
hormone,
growth,
mass,
is
action
of
different
in
of
glucose
body
a
peptide
It
hormone
strengthens
uptake
by
the
liver
fat.
somatotropin
from
is
childhood.
reduces
breakdown
of
somatotropin,
especially
adult
on
target
hemoglobin.
cells.
Comment
[4]
on
[6]
Index
Key
terms
are
in
bold.
B
lymphocytes
bacteria
abduction
134
60–2,
absorption
spectrum
actin
reaction
136,
spectrum
site
active
transport
95,
7,
8,
50,
136,
26,
62,
209
138,
aerobic
65,
66
agriculture
26
tumefaciens
176
30,
allergies
35,
alveoli
amino
ammonia
72,
219
20,
amphipathic
amylase
60,
amylose
17
anabolism
203,
respiration
structures
11,
kidneys
production
128–33
141–6
muscles
antibodies
68,
67,
134
appetite
arteries
128,
control
64,
assessment
atheroma
iv
,
19,
96,
v
,
181
system
63–6
vessels
63–4
body
mass
index
Bohr
effect
136,
209
96
164
nervous
autosomal
cells
autotrophs
40
auxins
111,
33
26,
62,
160
factors
197,
198
capsule
138,
139
71
of
103,
46–7
72,
176
155,
168,
180,
64
competition
14,
carbon
45–7
cycling
fixation
carbon
fluxes
carbon
sinks
cardiac
cycle
cardiac
muscle
cells
45,
65
15,
35
226
138
36
v–vi
187
skills
40–3,
227
186–92
187
exclusion
competitive
inhibitors
186
92
nitrogenous
reaction
17,
bases
23
20
163
of
biodiversity
exam
questions
variation
convergent
evolution
heart
205–6,
124
50
disease
227
correlation
coefficient
reaction
crossing
cyanide
(CHD)
66,
214
correlation
cortical
194–6
243–5
40
continuous
over
226
143
118,
119–20
contamination
cytokinesis
197
Darwin’s
data
60
227
2–13
division
29
190
178–9
11
212–13
134
links
46
46
capacity
catabolism
16–19,
100
45,
220
182
competitive
coronary
carbohydrates
cartilage
219
61
105
terms
consumers
100
59,
determination
duct
practice
chloride
cycle
117–22
muscles
175
communication
cones
34,
20
collecting
condensation
160
32,
47–9
complementary
70,
101
63–5
alleles
88,
conservation
causal
116
206
30,
58,
189,
communities
79
carrying
system
205,
100,
54–6
commensalism
203,
159–61
carbon
triphosphate)
25,
command
(BMI)
226
18
colour-blindness
220
area
145
123,
164
collagen
133,
214
carbaminohemoglobin
214
autonomic
110,
133,
223–7
100,
nerve
158
132,
205
66,
synthase
auditory
129,
214
(adenosine
95,
blood
66,
132
132,
122,
38
codons
89,
124,
99,
11,
change
cohesion
66–7,
31,
121,
210
57,
codominant
194
220
42–3,
57–8
cladograms
clones
natality
capillaries
67,
acids
cochlea
pressure
cancer
181
antigens
241–2
disease
99
162,
system
climographs
questions
82
longitudinal
classification
163
170,
fatty
climate
blood
calcium
175,
178–80
37–9
161
32
and
cladistics
180–2
groups
Calvin
128–33,
cis
protection
clotting
Broca’s
10,
130–1,
circulatory
test
69
68,
179
172–85
blood
breathing
variance)
28
chloroplasts
chromatids
174–7
blood
brain
128–33
of
178,
160,
119
chlorophyll
cholera
193
118,
coefficient
also
Bowman’s
137–40
193
194–5
calcification
52,
192,
172–4
59,
bottom-up
226
antibiotics
144
blood
133–7
(analysis
birth
botulin
reproduction
antagonistic
axons
50
137–40
vaccination
94,
26
182–5
modification
cells
53,
see
128–46
osmoregulation
180,
6
118
movement
92,
159,
heart
95–6,
test
chromosomes
exam
80–1,
coronary
chemoreceptors
circular
index
birds
Martha
see
chiasma
189
bipolar
61
antibody
ANOV
A
206–7
199
molecules
physiology
sexual
204,
15
analogous
anaphase
biotic
62,
32
hemispheres
chi-squared
191
medicine
140
anaerobic
44,
practice
ammonification
225,
43,
224
71,
89,
control
industry
42,
201
179–80
environmental
125
hypothesis
acids
animal
122
200,
176
genetic
isolation
alternative
123,
119,
demand
194–6
108
4–5
77
Chase,
CHD
of
160
chemiosmosis
oxygen
agriculture
118,
239–40
161–4
93–7
plants
17
cerebellum
54
50–8,
biotechnology
132
allopatric
system
bioremediation
193
165–7
questions
biodiversity
biomes
150–1
species
alleles
exam
26–7,
in
centromeres
learned
7–9
9–10
transport
cellulose
biochemical
biomass
200–1
134
perception
178,
of
6–7
135
ultrastructure
biomagnification
174–7,
Agrobacterium
joints
cells
respiration
cervix
biological
respiration
origin
169–70
bioinformatics
105
179–80
203
cerebral
biofilms
hormone)
transport
167–8
binomial
(ATP)
structure
membrane
157–9
biolistics
adrenaline
ATP
53
membrane
development
stimuli
100,
103,
155,
neuropharmacology
practice
140
adhesion
ATP
107
triphosphate
96,
153,
157–71
and
neural
52
(antidiuretic
139,
alien
91
134
adenosine
129,
159–61
innate
radiation
adduction
algae
28
81,
202,
socket
ethology
21
adaptations
diet
behaviour
73
energy
active
adaptive
143
and
brain
action
ADH
balanced
137
potential
activation
129
101,
muscle
bacteriophages
28
ball
action
94,
209
226
acrosome
128,
80–2,
179–80
absorption
accuracy
68,
finches
analysis
data-based
databases,
59
practical
questions
bioinformatics
Davson–Danielli
11–13
53,
225–6
defibrillators
model
147–56
182
6
214–15
247
INDE X
dehydration
140
denaturation
ethical
21
denitrification
199
deoxyribonucleic
dependent
deserts
diabetes
149,
223
evenness
digestion
dihybrid
diploid
12,
121,
32,
eye,
129
fatty
126
138
24–5,
50
fertilization
acid)
82–4,
23–4,
transcription
translation
32,
37,
fertilizers
84–7
gyrase
DNA
ligase
DNA
polymerase
I
DNA
polymerase
III
DNA
primase
food
39
82
food
82
35
57,
of
fusion
of
vaporization
16
B
175,
84
frogs
FSH
124
heterotrophs
histamines
(FCR)
191–2
HIV
172–4
143
plants
59
44,
120,
human
(FSH)
78
188
(HIV)
of
207
50
gas
(follicle
niches
hormone)
78
structure
ecology
of
40–9,
carbon
164
186–201
cycling
climate
ecosystems
human
gaseous
47–9
40–3,
gastrin
186–8
40–3
flow
on
ecosystems
cycle
phosphorus
population
species
elbow,
cycle
exam
emergent
186,
of
188–93
96
176
219,
glands
endonucleases
endosymbiotic
flow
energy
178
model
220
38
9,
10
191
189
60,
estrogen
248
61,
91,
178–80
92
77
77,
pools
30,
78,
219,
144
2,
genetic
221
35–6,
32,
37–9
of
respiratory
bonds
hydrophilic
questions
6,
16,
7,
121–4
204,
73
205,
solution
160,
solution
internal
immigration
206
8
217,
218
8
immune
assessment
197
system
67,
immunoglobulins
33
imprinting
114–15
in
190,
191
vitro
128
20
166
fertilization
independent
(IVF)
variables
78
149,
153,
223
138,
139
indicator
75
industry
,
61,
218–21
8
hyperpolarization
hypotonic
gases
85
8
6,
hypertension
245–6
77–8
117–20
161
76,
94,
91,
94–5,
GM
38,
39
gradualism
74
transport
IA see
glycolysis
101
161
125–6
inhibitors
effect
gases
production
48
48
191
35–6,
92,
20,
integral
greenhouse
194,
internal
75,
165–7
76,
85,
11,
61–2,
205
6
assessment
interphase
172–4
93
proteins
intestine
196
121–4
behaviour
insulin
187
species
biotechnology
inheritance
innate
greenhouse
gross
202–7
125–7
33–5,
glomerulus
crops
34
215–18
215–18
hypothalamus
32–3,
69–72
exam
hypertonic
37–9
30,
diagrams
26,
176
30–1
size
cells
172
175,
modification
meiosis
grazing
160
9,
gene
39,
117–27
biotechnology
glucose
enzymes
erythrocytes
modification
glucagon
protection
epididymis
genetic
30–9,
84–7
66–9
72–4
hydrophobic
engineering
glial
theory
83,
83
genetic
Gersmehl
43–5
21–2,
tRNAs
disease
207–10
75–6,
synapses
hydrogen
expression
for
genetics
38
30–1
germination
environmental
epilepsy
gene
20,
202–22
63–6
60–2,
reproduction
inheritance
2,
215
ecosystems
energy
2,
genes
chain
practice
125–7
virus
211–12
nutrition
219
208
genome
72,
163
chromosomes
197
emphysema
endocrine
243–5
134
properties
emigration
energy
,
questions
transport
electroporation
196–8
186–8
40–3,
structure
electron
200–1
ecology
40–3,
ecosystems
199–200
cells
215–18
212–15
neurons
exchange
pools
genes
nitrogen
34
electrophoresis
genes
192–3
practice
gel
gene
43–5
impacts
33,
ganglion
45–7
change
communities
energy
gametes
50
112,
60–79,
against
exchange
liver
118,
60–2
system
hormones
186
117,
69
physiology
heart
stimulating
111,
68,
digestion
158
fundamental
structures
75–6,
defence
46
record
chromosomes
127
67,
blood
169
69
191
absorption
189
82
immunodeficiency
immunodeficiency
human
behaviour
fuels
hormone
content
188,
116
80–1,
30
68,
homologous
113–14,
stimulating
157,
67,
homologous
53,
175
experiment
132
homeotherms
119,
220–1
181
40
(human
virus)
219,
211
metabolism
ear,
90,
180,
resistance
heterozygotes
ratio
94,
16
140
30,
hepatocytes
8
214
82
herbicide
7,
205–6,
16
heat
hepatitis
165
75
heat
hormones
webs
fossil
alleles
228–46
57
Darwin’s
foraging
38
dominant
vi,
62
114,
energy
fossil
30,
66,
capacity
hemoglobin
200–1
chains
food,
DNA sequencing
disease
64,
212–15
hemodialysis
187–8
follicle
82
DNA profiling
heart
67
flowering
82
38,
66,
finches,
fish
87–90
DNA
Drosophila
155
80–4
24–5,
24–5,
51–3
163
conversion
fibrin
of
of
18,
fermentation
155
structure
50,
147–8,
63–6,
helicase
diffusion
acids
feed
(deoxyribonucleic
replication
125–7
FASTA sequences
66–9,
tubule
evolution
50–1
106
William
heart
heat
125–7
structure
164
Hershey–Chase
124
selection
Harvey
,
126
against
convoluted
86
117–27
papers/strategies
facilitated
variation
85,
201
selection
experiments
17
defence
divergent
122
34
selection
disaccharides
exam
82,
57–8
speciation
207–10
crosses
disruptive
13
80,
200,
for
pools
natural
2,
60–2,
directional
disease,
gene
155
nuclei
discrete
205
32,
50–8,
evidence
204,
9,
cells
halophytes
196
evolution
40
76,
hair
eutrophication
73
differentiation
83,
DNA
4,
cladistics
diaphragm
DNA
see
190
detritivores
distal
acid
3
169–70
eukaryotes
variables
depolarization
issues
ethology
118
209
(IA)
223–7
154,
INDE X
introns
83,
87
microbiology
invertebrates
iodine
(in
vitro
8
78
microvilli
capsule
134
mitochondria
karyotype
keratin
32
kidneys
species
186,
187
cycle
Kupffer
95,
cells
161
DNA
and
enzymes
lactic
61
acid
lactose
large
17
water
leptin
209
166,
75,
76,
165–7
structure
168
ovaries
(luteinizing
hormone)
78
28–9
movement,
animal
46
mucosa
197
121,
lipase
60,
61
lipids
14,
16–19,
liposome
liver
locus
of
lumen
lung
myoglobin
myosin
Henlé
133–7
83,
85–9
145,
146
system
71,
138,
114
139,
NADP
,
140
220–1
137,
30,
nerve
hormone
67,
magnification
3,
(LH)
78
4,
net
5
Malpighian
17,
tubules
61,
137,
138
101
mechanoreceptors
medulla
33–5,
see
peat
46
memory
cells
Gregor
Johann
cycle
DNA
41–2,
198
mesophyll
108,
messenger
RNA (mRNA)
metabolism
metaphase
215–18
118
49
methylation
148
91–3,
11,
gene
83,
85–9
nucleus
human
74,
79,
plants
167
see
in
phloem
138,
inhibitors
139,
140
92
plastic
structure
80–90
and
replication
84–7
202–7
39,
123,
107–9
113–16
plants
67,
175
103–7
128,
129
193
72,
114
193
antibodies
polymerase
181–2,
219
191
178–9,
polyclonal
224
112
176
pneumocytes
pollutants
43,
58
66
pollination
160
218
126
poikilotherms
87–90
42,
80–4
217,
54–5,
111,
pollution
platelets
84–7
accumbens
160,
transport
cells
plasmids
85
hypothesis
xylem
plasma
14
23–4,
113
transport
transgenic
137,
physiology;
110–12
speciation
23
wastes
animal
reproduction
199
bases
150–1
103–16
hormones
fixation
97–102,
physiology
gland
growth
199–200
163
28–9,
classification
199
translation
null
167–8
158
expression
nutrition
86
157,
transcription
25,
162,
98
phytochromes
186
nucleotides
110
mesocosms
161–4
200–1
54–5
pituitary
neuropharmacology
nucleosomes
179
239–40
18
98
photosystems
perception
non-competitive
78
6,
photoreceptors
72–4
acids
116
cycle
28,
physiology
nitrogenous
35
photolysis
questions
6
128
photosynthesis
exam
216–17
122–3
107–9,
phyla
nucleic
contamination
meristems
methane
129
72,
phosphorus
158
reaction
200
167–8
nitrogenous
103
menstrual
157,
180
chain
88
proteins
phospholipids
158
20,
hormones
157–9
nitrogen
128,
phloem
157,
129,
172
bonds
phenotypes
157–71
cycle
10
67,
77
development
nitrogen
68,
69,
208
7
polymerase
pesticides
169–70
nitrification
67,
66,
neuropharmacology
niches
73
170
159–61
neurulation
168
Louis
phagocytes
neurotransmitters
76
potential
166,
mercury
220
7–9
memory
meniscus
160,
6–7
transport
Mendel,
66,
cell
structure
membrane
65,
117–20
75,
membrane,
pruning
neurons
oblongata
melatonin
neural
stimuli
180–2
126,
160
plasticity
practice
226
medicine
51–3,
191
neural
neural
162
50,
167–8
system
production
ethology
226
meiosis
PCR
system
transport
peptide
74
impulses
brain
218
187–8
peripheral
neurobiology
203
96
220
parasympathetic
penis
98
selection
nervous
128
92
malnutrition
median
parasitism
penicillin
154
197
neonicotinoids
155
96
217,
pathogens
52
reduced
natality
72
72,
lymphocytes
maltose
phosphorylation
Pasteur,
133–7
187
136,
natural
luteinizing
mean
113,
64
malaria
94,
oxidative
peptide
plants
cancer
lungs
133–7,
31,
mutualism
176
25,
30
long-day
loop
61,
mutations
211–12
140
77
oxidation
passive
musculoskeletal
62
RNA)
61
muscles
124
77
oxytocin
physiology
limestone
index
154
204
oxyhemoglobin
17
mRNA (messenger
genes
121
108,
197
134
linked
131–2
137–40
105,
overhydration
antibodies
ligaments
Lincoln
8,
226
oviducts
crosses
8
osteomalacia
15–16
mortality
7,
107
137
164
outliers
monosaccharides
152
23–4
20–1
monohybrid
osmosis
ossicles
21–2
monoclonal
behaviour
learning
24–5
16–19
proteins
intestine
learned
LH
94
and
175
166
21
osmoregulation
transcription
(ORF)
compounds
osmolarity
26–7
143
frame
osmoconformers
16–19
photosynthesis
iv
142,
conditioning
optimum
14–29
RNA
141,
reading
organic
biology
206
resources
operant
96–7
205,
162
oogenesis
95,
replication,
lipids
lacteal
9–10,
translation
211
online
217–18
respiration
DNA
137–40
179
open
carbohydrates
cell
178,
11
molecular
22
keystone
Krebs
32
174,
110
209
secretion
mitosis
karyograms
61,
203,
odorants
172,
micropropagation
fertilization)
obesity
176
microorganisms
solution
milk
joint
172–4
microinjection
216
isotonic
IVF
55
chain
131
reaction
(PCR)
37,
83,
185
polyploidy
125,
126
249
INDE X
polysaccharides
population
17
saprotrophs
ecology
196–8
populations
41
pores,
vessels
blood
saturated
practice
exam
practice
problems
precision
64
papers
scurvy
187
structure
primary
succession
progesterone
prokaryotes
prolactin
77,
4,
prophase
132
78,
77,
proteome
proximal
14,
20–1,
57,
62,
87,
90,
204
20
pseudomonas
punctuated
of
138
36
energy
44–5
95
quorum
sensing
90
rate
of
errors
226
reaction
realized
niches
red
blood
219,
redox
163,
cells
220
(erythrocytes)
9,
30,
reduction
reflexes
94
of
reliability
gene
expression
83
82–4,
155
sperm
reproduction
resolution
spider
isolation
cells
26–7,
gases,
respiratory
system
potential
rhodopsin
218–21
70
ribulose
88,
richness
rickets
see
RNA
carboxylase
196
stroma
acid)
23–4,
83,
85,
112
sucrose
node
species
sample
student
Sanger,
Frederick
250
3,
answers
30,
84
of
144
141,
108
proteins
104,
6,
227
18,
19,
62
rainforests
136,
190
137
I
type
II
pneumocytes
diabetes
type
II
pneumocytes
62
unsaturated
72,
204,
of
219
205
72,
219
measurement
fatty
acids
10
126
226
175–6
140
77,
78
128–33,
175
77
blood
4
veins
161–4
52
ventilation
rate
vertebrates
55,
61–2,
visual
71,
155,
160
theory
202,
14
203–4,
Willebrand
vulva
70,
56
209
cortex
vitamins
V
on
64
64
vitalism
216–17
vessels
65
variations
villi
226
106
205
disease
89
77
water
22
xylem
web
168
synovial
41
system
208
158–9
fluid
systematic
biology
transport
resources
whale
meat
wheat
126
134
errors
226
xerophytes
xylem
iv
184
106
103–7,
115,
15–16
103–7
187
74,
225
18
140
acid
molecular
21,
8
106
valves
142
17
synapses
vii
107,
type
vagina
100
sympathetic
129
176
88
vaccination
168
sustainability
sinoatrial
Salmonella
186–8
generation
61,
175,
87–90
208
symbiosis
SA see
data
tropical
uric
203
summation
20
24–5,
transpiration
heart
104–5,
substrate
(ribonucleic
organisms
uncertainties
8,
77
perception
stomata
163
54,
168
19
84–7
125–7
selection
2,
24–5,
translocation
uterus
hormones
stomach
62
pump
significance
cells
stimuli
100
18,
176
198
31
164
deviation
stimulants
89
acids
fatty
troponin
20
17–18,
steroid
204
rubisco
silk
statistical
bisphosphate
oxidase
starch
stem
acid
110
urea
53,
structure
starvation
73
20
ribonucleic
40–3,
standard
of
163–4
ribosomes
209
107
50,
spontaneous
93–7
transport
cells
175,
197,
57
tRNA 83,
208
plants
stabilizing
respiratory
rods
125
totipotent
triglycerides
nucleotide
spermatogenesis
4
respiration,
RNA
141–6
113–16
reproductive
retina
77–8,
213
219
ducts
sperm,
animals/human
resting
61,
perception
species
73
82
32
co-transport
speciation
24–5,
repolarization
66,
131
72,
virus
factors
trends,
node
neurotransmitters
(single
source,
proteins
107
(SA)
somatostatin
226
replication
plants
binding
intestine
sound
6
70
mosaic
transcription
polymorphisms
sodium–potassium
165
regulators
model
216
75
transmembrane
plants
sodium
98
197
98
hormones
volume
traits
98
98
top-down
trans
chromatids
SNPs
94
NADP
125
curve
polymorphisms)
reactions
reduced
30,
31
strand
smoking
221
141–6
113
nucleotide
smallpox
35
space
translation
small
alleles
113–14,
162
thylakoid
transgenic
sister
77
membrane
tobacco
108–9
slow-acting
162,
170
90
thylakoid
tidal
growth
186
recessive
35
plants
92
receptors
structure
Singer–Nicolson
sinks,
118
77
thyroxin
anemia
sinoatrial
random
11,
134
Simpson’s reciprocal diversity index 195–6
single
179
164
reproduction
single
structure
telophase
thyroid
sexual
tubes
83
thylakoids
77
dimorphism
(SNPs)
quaternary
35
hairs
sigmoid
54–6
telomeres
testes
114
sexual
sieve
126
190
taxonomy
129
thermoreceptors
vesicles
cell
taiga
tertiary
192
122–3
linkage
226
testosterone
dispersal
sickle
179
equilibrium
grids
pyramids
tubule
90
168
114,
lymphocytes
t-test
tendons
208
short-day
convoluted
216
structure
sex
19
204
succession
sensory
180
18,
223
messengers
seminal
60
6,
203,
segregation
118
acids
secondary
seeds
218
gland
fatty
154
secondary
seed
32
T
method
sedatives
144
40
135–6,
77
secretin
192
DNA 86–7
11–12,
proteases
kits
90
9–10,
217,
promoters,
pyruvate
scrotum
second
primary
Punnett
228–46
vii
pregnancy-detection
proteins
scientific
226
predation
prostate
sarcomeres
116
220
O X
F O
R
D
I B
P
R
E
P A
R
E
D
BIOLO GY
Author
Offering an unparalleled level of assessment suppor t at SL and HL ,
IB Prepared: Biology has been developed directly with the IB to provide
Debora M. Primrose
the most up-to-date and authoritative guidance on DP assessment.
You can trust IB Prepared resources to:
➜
Consolidate essential knowledge and facilitate more effective
exam preparation via concise summaries of course content
FOR FIRST ASSESSMENT
➜
Ensure that learners fully understand assessment requirements
IN 2016
with clear explanations of each component, past paper material
and model answers
➜
Maximize assessment potential with strategic tips, highlighted
common errors and sample answers annotated with exper t advice
What's on the cover?
➜
Build students’ skills and confidence using exam-style questions,
Water droplets on a
practice papers and worked solutions
peacock feather
C
E C O LO G Y
AND
C O N S E R V AT I O N
Example C.6.1.
Key syllabus material is explained
Our huge population growth
has led to an increase in the
a)
Outline
the
impact
of
waterlogging
on
the
nitrogen
cycle.
demand for food, which, in turn,
alongside key definitions
b)
has led to intensive methods of
Describe
nitrogen
agriculture. Intensive agriculture
insectivorous
availability
in
plants
as
an
adaptation
waterlogged
for
low
soils.
involves labour-intensive and
Solution
costly practices in order to obtain
a)
Waterlogging
fills
the
air
gaps
in
the
soil
with
water.
In
the
high yields per unit of land.
absence
of
oxygen
denitrifying
bacteria
reduce
nitrate
in
the
soil
Intensive animal farming methods
to
Assessment tips offer guidance and
atmospheric
nitrogen.
An
example
of
denitrifying
bacteria
are often criticized for involving
is
Pseudomonas
denitrificans
which
uses
nitrate
as
an
electron
low standards of animal welfare,
acceptor
to
produce
ATP
.
which rely on the overuse of
warn against common errors
b)
Insectivorous
plants
obtain
their
food
through
photosynthesis
antibiotics to be viable. Issues
and
make
organic
products
using
light.
Nevertheless
these
associated with intensive crop
carnivorous
plants
live
in
nutrient-poor
habitats
where
there
farming methods are the use of
are
almost
no
nitrates
available,
therefore
need
to
trap
insects
in
toxic pesticides which are often
order
to
obtain
their
nitrogen.
carcinogenic and bioaccumulate,
harming non-target species, and
Assessment questions and sample student
the use of chemical fer tilizers
Phosphorus
is
present
in
all
living
organisms.
It
is
present
in
which can cause eutrophication of
the
responses provide practice oppor tunities
phospholipids
of
cell
membranes,
is
required
for
making
waterways.
ATP
,
DNA
after
phosphorylation,
and
Phosphorus
and useful feedback
fertilizer
or
turnover
in
cycle
the
RNA,
can
be
removed
the
therefore
is
found
and
added
by
is
to
proteins
cycle
availability
to
and
form
phosphorus
harvesting
phosphorus
its
in
needed
the
agricultural
is
may
carbohydrates
bones
cycle
much
than
limiting
teeth.
applying
crops.
lower
become
and
by
The
in
to
rate
the
of
nitrogen
agriculture
in
future.
S AMPLE STUDENT ANS WER
Eutrophication
Also available, from Oxford
is the enrichment
with nutrients of a body of water
leading to the excessive growth of
978 0 19 839211 8
The graph shows the global phosphorus fer tilizer use from 1960 to
2011.
plants and algae, causing oxygen
25
depletion.
is
the amount of dissolved oxygen
needed by aerobic organisms to
break down organic material.
snotagem / su rohpsohp
Biochemical ox ygen demand
forecast
20
15
developing countries
10
developed countries
world
2
2
0
1
6
2
2
2
0
2
1
8
1
9
0
0
0
9
0
0
0
2
6
4
0
1
1
1
1
9
9
8
1
9
9
9
9
7
8
in
8
soil
are
8
the
2
from
6
the
the
phosphorus
fertilizers,
4
make
0
1
fact
Suggest whether the data suppor ts the hypothesis that availability of
that
phosphate may become limiting to agriculture in the future.
[6]
fertilizers
use
This
answer
order
enough
could
have
achieved
5/6
marks:
last
is
T
urnover
removed
1
1
in
1
and
9
crops
increased
that
9
and
9
for
fertilizers
year
the
in
The
and
that
9
needed
of
years;
slow;
7
6
are
is
6
turnover
most
with
phosphates
agriculture.
turnover
6
the
addresses
associated
of
for
of
4
answer
issues
future
denition
8
the
availability
the
0
▲ The
of
of
phosphate
refers
to
the
replacement
of
phosphate
to
for
ve
once
it
has
been
removed.
T
urnover
of
phosphate
is
slower
than
marks.
nitrogen.
levels
to
When
within
replenish
the
the
farmers
soil
remove
their
continually
mineral,
therefore
crops,
deplete
the
the
and
need
to
phosphate
there
add
is
no
way
fertilizer
.
T
he
200
I B
D I P L O M A
P R O G R A M M E
Suppor t material available at www.oxfordsecondary.co.uk/ib-prepared-suppor t
ISBN
web
978-0-19-842363-8
www.oxfordsecondary.com/ib
9
780198
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