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Contents
A1.1
C1.1
Nucleic
acids
s
s
A1.2
16
C1.2
C1.3
Cell
structure
49
C2.1
A2.3
l
n
O
o
n
i
o
D2.1
D2.2
t
a
D2.3
Water
potential
648
u
D3.1
796
Index
802
D3.2
D3.3
D4.1
D4.2
D4.3
D
Internal assessment: The scientic investigation
egnahc dna ytiunitnoC
a
B
E
v
B4.2
l
f
x
O
noitcnuf dna mroF
B4.1
d
r
o
B3.1
D1.2
D1.3
B2.2
B2.3
D1.1
C
U
B2.1
C4.2
C
v
i
n
B1.2
p
A
B1.1
C4.1
y
P
C3.2
y
A4.2
B3.3
C3.1
r
e
A4.1
y
A3.2
C2.2
t
i
s
ecnednepedretni dna noitcaretnI
ytisrevid dna ytinU
A3.1
B3.2
r
A2.2
e
A2.1
Answers: www.oxfordsecondary.com/ib-science-support
iii
Introduction
The aim
of the International Bacc alaureate biology syllabus is to
combine a conceptual approach to biology,
an understanding
Leve
l
of
orga
nizat
ion
1.
Mole
cules
2.
3.
ted
in
the
rich
biodiv
A
specic skills.
All of these elements are embedded
ersity
Wate
diver
map
life
on
Earth
Origin
s
of
A1.2
nism
s
4.
Nucle
[HL
ic
Diver
sity
only]
acids
is shown in Figure 1.
organ
of
A4.1
Evolu
isms
speci
Cell
struc
ture
A3.2
Virus
es
and
[HL
only]
Class
cladis
ificati
ation
e
A2.2
A2.3
on
A4.2
tics
Cons
biodiv
[HL
Topics are organized
The theme and
four levels of
B
level of organization shows
B1.1
Form
and
and
Carb
ohyd
rates
B2.1
Mem
lipids
mem
brane
brane
funct
ion
B1.2
Prote
B2.2
Orga
teachers are encouraged
nelles
artme
ntaliz
and
B3.1
port
and
ation
to personalize
Cell
motili
speci
B4.1
Adap
tation
nge
envir
onme
Trans
ty
niche
le
[HL
and
C1.1
n
Enzy
and
gical
only]
meta
ce
mes
and
C2.1
bolism
Chem
signa
C1.2
It
is structured
in the same way as the syllabus,
C1.3
divided
into numbered
ration
synth
C2.2
esis
Some understandings will also include
D1.1
D2.1
D1.2
Prote
gene
and
Muta
tions
editin
and
nucle
expre
ar
D3.1
D2.3
Wate
r
poten
•
and
lead
Measurements
lity
Clima
te
and
chan
ge
Hypotheses
n
unexpected
to a possible explanation. The
it
requires
further veric ation.
•
F alsic ation
Hypotheses c an be proved false using other
to serendipitous results.
u
f
x
t
a
Sometimes the observations in experiments are
Natur
al
tion
Stabi
ge
forms an important
hypothesis is this provisional view and
o
r
o
i
Observations and experiments
r
y
C
U
•
in the following eleven aspects:
s
of
matte
of the scientist’s work whatever the science.
Patterns lead
which c an
d
be summarized
Nature of Science,
fer s
and
Patterns and trends
part
theories depends on the
D4.1
selec
D4.2
y
is
D4.3
Recognition of a pattern or trend
•
tion
ostas
lation
unitie
s
Trans
tial
or the study of language. Science has particular
The eective pursuit of modern scientic work and its
Repr
oduc
Inher
itance
Home
Popu
comm
energ
chan
pursuits such as the arts, social sciences, mathematics,
methodologies and purposes.
C4.1
ce
disea
se
ssion
D3.3
p
•
st
o
from other
of
ms
Defen
C4.2
D3.2
Gene
g
r
e
dierent
v
make it
i
n
Science has features that
Integr
ation
syste
and
C3.2
again
only]
Figure 1
Nature of science
body
lling
on
esis
[HL
(NOS).
C3.1
only]
signa
in
D2.2
synth
D1.3
Cell
tion
divisi
chan
ge
the nature of science
ical
[HL
DNA
eplica
reference to the applic ation of skills and
lling
Neur
al
O
D
understandings.
respi
Photo
t
i
s
chapter corresponding to a topic and
Cell
with each
n
nden
y
actio
depe
to
nt
Ecolo
s
C
Inter
inter
of
port
B4.2
Musc
This textbook allows you
to sequence the course by theme or level of organization.
and
ion
l
their approach to the syllabus.
alizat
ion
tion
ervat
ersity
Gas
excha
B3.2
B3.3
B2.3
ystem
s
evidence,
has led
but
it
c an't
to paradigm
be proved
denitely true. This
shis in science throughout
Measurements c an be qualitative or quantitative, but
all data are prone to error.
Evidence
is important
history.
to know the
a
O
•
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Unity
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Molecules
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3
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molecule and form one pole. The oxygen atom forms the opposite pole.
4
Molecules
Positively charged particles (positive ions) and negatively charged particles (negative
water
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hydrogen
per
unit
bonds
volume
(Figure
of
5)
water.
which
As
a
result,
collectively
there
give
+
δ
water
its
unique
properties.
These
properties
are
H
very important to living things.
δ
δ
H
Demonstrating
the
strength
y
3
•
a
•
a
tube
clip
needed
open
and
add
plunger
is
≅
to
the
seal
overcome
and
gate
the
with
clip
inner
the
the
tightly
the
tube.
empty.
one
by one
surface
much
force
of
the
barrel?
half-lled with air
needed
closed.
10
cm
the
How
much
3
syringe
force
to
is
1
with
avoid
needed
to
the
syringe
accidents
increase
the
to
heavy
volume
of
with
with a dotted
covalent
water
Cohesion of water
to
or dashed
line,
whereas
bonds within water molecules are
water and no air bubbles. Be
weights
u
f
x
A1.1.3
half-lled
due
i
step
c areful
Hydrogen bonds between
water molecules c an be represented
Figure 6
volume of air in the
t
a
Repeat
?
r
o
3.
to
δ
o
increase
d
to
Figure 5
+
H
represented with a continuous line
between the
▴
is
▴
down to the
How
friction
syringe
syringe
syringe
weights
N).
syringe
O
n
1
1
the
close
pulled
barrel (100 g
step
the
and
to
clamp
U
Repeat
used
of
a
the
H
o
syringe
the
be
nozzle
in
of
C
of
and
clip
the
down
barrel
i
n
the
end
plunger
2.
c an
unweighted
until
is
gate
to
the
p
the
Begin
that
upside
from
connected
gate
Keep
held
hanging
v
1.
syringe
δ
+
δ
y
10 cm
weights
r
e
•
H δ
O
t
i
s
Assemble the apparatus as in Figure 6, with:
+
n
of the hydrogen bond
•
O
l
techniques:
y
P
+
Applying
H
O
r
are
and
e
Although
s
s
force that forms when a slightly positive hydrogen atom in one polar molecule is
falling.
How
much
force
3
10 cm
?
molecules due
l
O
for
organisms
is
a
mutual
them.
molecules
stick
organisms
use
and
the
attraction
E
between
use
of
v
There
a
to hydrogen bonding and consequences
Energy
is
together.
this
between
required
The
property.
water
to
scientic
Two
molecules
break
these
term
examples
for
are
and
bonds.
this
the
hydrogen
In
simple
property
is
conduction
bonds
form
terms,
water
cohesion.
Living
of
water
in
xylem
water surfaces as a habitat.
5
Unity
and
diversity
Conduction of water
Cohesion
upwards
are
roots
in
the
leaves
to
columns
forces),
develops
upwards
the
Water
in
xylem
a
rope
bec ause
these
is
lost
water
the
at
both
between
by
forces
in
in
ends
in
a
to
the
leaves
of
“tug
particles
cell
Water
xylem
column
the
the
plants.
E ach
soil
and
in
vessels
evaporation
molecules
pulling
tension
tubular
vessels.
pulled
attractions
water
between
in
under
along
are
of
For
is
there
more
bec ause
column
water
simultaneously
If
in
at
a
remains
xylem
one
vessel
point
were
easily
fewer
and
hydrogen
trees
would
to
along
available—hydrogen
break,
the
bonds
be
it
will
many
vessel.
columns
able
This
a
pond
eect
is
known
as
(such
as
mercury)
is
bec ause
than
tension,
even
cohesion
attractions
through
the
simultaneously.
is
All
energy
the
to
acts
like
bec ause
are
to
water
water
this
this
than
oat
denser
water,
do
have
tension
possible
they
between
of
is
liquids
surface
between
surface
The
it
though
water
This
more
of
water
grow so tall.
in
an
elastic
water
xylem
membrane that
molecules
are much
hydrogen bonding than to air particles. This
tension.
stronger
n
U
greater
break
surface
water,
by
of
area.
C
This
of
of
other
surface
have
i
n
surface
each
body
o
to
other
possible
v
attracted
Bec ause
or
minimum
pulled
takes
to
y
of
the
p
more
to
r
e
surface
shrinks
be
hydrogen bonds
c an withstand surprisingly
bonds,
not
Water
hydrogen bonds make it
continuous,
Use of water surfaces as habitats
The
cells.
O
break
of
normally
tensions.
would
tensions
water
t
i
s
large
column
broken
than
leaf
n
be
energy
the
y
must
a
withstand
as
Tension
Tension
l
upwards.
c an
long
P
As
war ”.
water.
greater than the
roots.
cohesive.
There
atmosphere; it is also
walls
has to be strong enough to withstand
considerable tension forces
sucked
water is under
of
and
is
tissue.
objects
and
we
molecules
and
the
many
may
property
due
oating
be
such
might
hydrogen
not
but
only
a
few
water.
to
as
steel pins on the
expect them to sink.
hydrogen bonds is
object.
bonds
For
an
must
object to
be
broken
available.
o
Water striders (also known as pond skaters) walk on the water surface with their six
i
legs. Mosquito larvae live just below the surface, hanging from it using their siphon.
u
l
a
E
v
O
f
x
t
a
r
o
d
Living organisms make use of this property by using water surfaces as a habitat.
▴
Figure 8
The ra spider Dolomedes mbriatus hunts prey on the water surface. It detects
prey by means of vibrations passing through the water. It has a coat of unwettable hairs that
help it to remain on the surface, even though its mass is about 30 g and it is denser than water
6
y
in
by
as
leaves
water
like
tension in xylem
water
r
forces
the
of
generated
attractions
moves
The rope in a tug of war
roots
of
e
to
is
under
transport
s
s
the
the
the
(pulling
in
due
Figure 7
from
continuous
tension
▴
allows
Molecules
Data-based questions: Tall trees
The
tallest
trees
in
the
world
(Sequoia sempervirens)
C alifornia.
including
side
season
(late
which
measured
branches
is
the
at
September
are
4.
redwoods
At
climbed
ve
of
these
within
xylem
are
height
trees,
a
116 m tall (the tallest in the
pressure
pressures
xylem
Redwoods State
trees.
maximum
State
tissue
of
below
prone
Park.
to
−2.0 MPa,
Use
height
Explain
columns
of
the
for
data
in
the
redwood
your
graph
taken
group
before
to
early
[2]
October).
In
Figure
9,
0.6
height
above
ground
was the
pressure
the
it
relationship
and
xylem
dependent
the
variable.
dependent
between
pressure
variable.
height
before
[1]
1.2
1.4
above
1.6
dawn.
[1]
reasons
a.
Compare
and
pressures
with
for
the
relationship.
[2]
y
Suggest
r
e
1.8
b.
O
the
ground
was
makes
1.0
m e l yx
State
what
[1]
2.0
a
reason
pre-dawn
pressures
for
at
xylem
30
midday.
[2]
dierences.
[1]
▴
i
n
C
question
hypotheses
this
clues
should
the
“suggest”,
possible
does
not
as
to
be
what
mean
is
possible
need
that
You
every
possible.
and
to
et
al.
The
120
ground / m
limits
to
tree
height.
Nature 428,
https://doi.org/10.1038/nature02417
propose a solution,
may
propose
answer
Bec ause
testable.
available data.
is
you
However,
a
a
range of
good
are
one. The data
“suggesting”,
they
do
not
your
need to be
u
f
x
A1.1.4
you
answer.
i
by
to
t
a
proven
you
another
but
gives
statements
or
r
o
usually
asks
G.
(2004).
90
above
n
hypothesis
o
a
a
d
If
Koch,
851–854
U
command terms
Source:
Figure 9
Communic ation skills: Responding to
ATL
60
height
o
Suggest
the
the
v
b.
contrast
p
3.
n
variable.
l
variable. Explain what makes it an
independent
0.8
y
independent
Xylem
a.
represents
midday.
research,
Explain
2.
at
group
y
taken
lower
measurements
t
i
s
b.
this
The
represents
P
In
points
apM / erusserp
a.
data
dawn.
measurements
1.
of
predict
answer.
dierent heights during the dry
r
upper
to
trees in Humboldt
0.4
the
water in
breaking. This limits the maximum
e
They
in
small
Researchers
Hyperion
world).
currently
Humboldt
s
s
Park,
in
Adhesion of water to materials that are
l
O
Hydrogen
polar
c alled
bonds
adhesion.
glass
water-lled
of
energy.
formed
paper
exert
is
between
large
strong
drawn
c an
results
air
also
This
in
between
c auses
is
c ause
formation
glass
and
amounts
the
forces
narrow
by
and
movement,
c apillary
of
many
water
water,
of
water
the
surface
of
a
solid
composed
water to stick to the surface of the solid and is
c alled
replaced
suction
through
form
This
tubes.
As
have
It
E
narrow
c an
molecules.
v
of
a
polar or charged and impacts for organisms
so
surface
through
spaces
as
when
action.
The
hydrogen
along
the
energy
area
is
bonds,
tube,
between
We
so
many
released.
attractive
adhesion.
water
to
drawn
from
there
through
air-lled to
is
a
hydrogen
release
bonds
are
Porous solids such as
water.
observe
cellulose
is
change
This
this
means
when
molecules
in
they
c an
water is
paper
towels.
7
Unity
and
diversity
Water
is
drawn
by
from
an
attracted
action
•
If
as
in
there
water
is
a
walls
useful
water
the
moist
to
so
it.
gravity
in
to
soil
tends
plants.
starts
If
This
is
to
Water
dry
out
is
walls
be
they
generates
in
leaves
drawn
c an
the
out
absorb
low
and
of
in
deciduous
due
to
the
air-filled,
vessel
trees
adhesion
are
helps
to
lost
air-filled
the
sap
with
c arbon
rise,
between
For
the
draw
In
for
spring,
wall
xylem
c apillary
O
100
µm
y
p
o
C
n
a group
water from
fog or dew and
o
d
paraphyllia around
the
the
vessels.
t
i
s
r
e
Some mosses have narrow hair-like structures on their stems,
Dicranum majus.
and
example,
the
vessel.
needed
1 mm
walls of these structures attract
on the le is
atmosphere,
water up in
water
winter.
refilling
the
xylem
dioxide
that
water.
through
to
to
nearest
pressures
adhesion
refill
v
i
n
Figure 10
U
▴
rewetted
n
action
help
down.
adheres to cellulose
is
the
y
vessels
becomes
c an
it
water is
c an rise up
The moss on the right
(at
store it,
c alled
paraphyllia. The cellulose cell
helping to keep
the moss hydrated.
The moss
higher magnic ation) is Climacium dendroides, with
of developing leaves
i
t
a
r
o
Measuring variables: Determining wet and dry mass
u
Figure 11
1665,
l
a
E
v
O
f
x
◂
Natural
In
Robert Hooke
published
a drawing of
the structure of natural
sponge.
protein
Spongin
is
(phylum
is
the
so
skeleton
Porifera).
spongin,
resistant
which
to
The
of
animals
skeleton
unusually
digestion
by
is
c alled
composed of
contains
most
iodine.
proteases and
He described
as “A confus’d
adheres
to
it.
Bec ause
it
has
a
porous
structure and
heap
large
surface
area,
large
amounts
natural
sponge
c an absorb and hold
of the brous parts
of
water.
This
is
why
it
has
been
used
over
curiously jointed and
thousands
of
years
for
washing and other daily tasks.
implic ated. The joints
More
recently,
articial
sponge
has
almost
entirely
are for the most part
where three bres onely
meet,
for I had
seldom
that
8
the
water
it
sponge
sponges
met
had
very
with any
four ”
replaced
reduces
marine
c ause
natural
the
sponge.
need
for
ecosystems.
harm
to
has
harvesting
But
ocean
This
similar
of
wild
properties but
sponges
from
‘sponges’ made of plastic could
ecosystems
in
another
way.
y
vessel
vessel
pull
water
l
the
porous,
automatic ally
vessels.
xylem
is
how
available.
cell
water
also
though
that
soil.
r
of
from
c ause
It
of
is
wall
in
wetting
P
a
any
soil,
e
the
so
substances
dry
even
adhesion
source
forces
keeps
xylem
If
to
walls,
photosynthesis.
•
source,
evaporates
adhesive
This
due
cell
chemic al
through
s
s
molecules
long
many
action
underground
C apillary
as
to
c apillary
Molecules
s
s
e
r
l
a
sample
source
and
of
n a t u ra l
compare
it
sponge
with
from
some
s p o n g e.
1.
Examine the structures using a microscope.
2.
Dry the sponges—for example, by placing them in
Solvent properties of water
Allow the sponges to soak up as much water
5.
Find the mass of each saturated sponge.
6.
C alculate the amount of water retained by each
sponge as a percentage of the dry mass.
linked to
i
metabolism and for
t
a
r
o
its role as a medium for
4.
n
o
d
A1.1.5
Find the mass of each dry sponge.
as they can.
U
an oven at 80°C for 24 hours.
3.
C
i
n
sy n t h e t i c
obtain
p
c an,
o
sustainable
v
you
a
n
O
an iPhone in
2021 (more than 350 years aer Hooke’s drawing)
If
y
Image of natural sponge made using a Meiji microscope and
y
P
y
t
i
s
Figure 12
r
e
▴
transport in plants and animals
substances
particles
are
solutes.
forms
them
partially
positive
dissolve.
Water
of
pole
hydrogen
both
The
is
polar
charged
so
attracted
is
particles
liquid
the
of
the
substance
solvent
and
the
become
separated
solvent and solutes is a solution.
together
is
the
The
properties.
pole
hydrogen
forms
dissolve,
liquid.
around
clumping
oxygen
E
negative
a
mixture
solvent
shells
from
partially
The
sugar
into
a
it
as
l
important
that
prevents
such
dispersed
v
O
has
means
and
u
separated
Water
f
x
When
they
to
attracted
bonds
remain
in
the
water
molecule
molecules. This
solution.
Water ’s
charged ions and its
negatively
polar
of
polar
positively
to
with
nature
and
charged ions, so both
molecules.
9
Unity
and
diversity
All
substances
These
with
positive
or
“hydrophilic”
water.
Substances
c an survive
complete dehydration are c alled
cell walls,
hydrophobic.
instead,
or
charges.
may
are
they
hydrophobic
dissolve
to
but
that
are
does
chemic ally
not
attracted to
dissolve—for
not
are
if
more
they
Hydrophobic
in
other
Although
repelled
this
by
attracted
are
solvents
to
non-polar
substances
such
as
term
water.
other
and
are
literally
They
example,
do
insoluble
propanone
means
“water-
are simply not
hydrophobic substances.
they
not
in
have
negative
water although
(acetone).
All
lipids
are
is
a
by c apillary action.
aer which it
turns green again
summary,
universal
in
it.
and
water
solvent
Water ’s
for
dissolves
bec ause
solvent
many
there
dierent
are
also
substances.
many
properties
allow
transport.
Metabolism
it
to
be
However,
substances
used
as
a
that
do
medium
it
not
for
not
dissolve
metabolism
O
starts to grow
In
n
swells and opens out in
y
and
are
substances
are
they
substances
adheres
hydrophilic.
Molecules
positive
water
t
i
s
a few hours,
it;
charges, such as sodium and chloride ions. The term
describe
hydrophobic, including fats and oils.
Selaginella lepidophylla is an example: the
dry ball of the plant
by
“water-loving”).
l
desicc ated
attracted
(literally,
r
e
y
Cytoplasm is a complex mixture of dissolved substances. It is an aqueous solution,
because the solvent is water. The solutes in this aqueous solution can move
p
around and interact. Dissolved enzymes catalyse specic chemical reactions. The
v
many dierent chemical reactions catalysed in cytoplasm are collectively known
o
as metabolism. Without water, the components of these reactions could not move
i
n
and come together on the active sites of enzymes. Therefore, water is the medium
C
for metabolism.
Transport
animals.
aqueous solution in both plants and
transported
in
systems:
xylem
sap.
o
t
a
a
E
nutrients they need;
Amino
a
diverse
chloride
is
an
range
ionic
of
substances.
compound
that
For
is
example:
freely
soluble
in
water; it
+
to
form
acids
they
are
part
sodium
of
have
soluble
the
dissolved
•
Gl u c o s e
both
in
ions
(Na
in
is
in
po l a r
Their
which
others.
blood
a
negative
water.
molecule,
hydrophobic
in
in it.
)
and
chloride
ions
(Cl
),
which
are
c arried
All
is
and
positive
solubility
hydrophilic
amino
acids
charges.
varies
in
are
Bec ause
depending
some
amino
soluble
on
acids
enough
to
of
the
this
variable
and
be
c arried
plasma.
mo l e c u l e.
It
is
f re e l y
s o l u bl e
in
water
so
is
also
c arried
pl a s ma .
Other
this is known as total
parenteral nutrition (TPN). An emulsier is
in TPN.
an
which is water with
chloride dissolved
patients are given water containing all the
10
u
l
v
intravenously. Sometimes the
“saline”,
required
transports
Sodium
dissolves
Hospital patients are oen
uid
sodium
as
transport
Sucrose and other products of photosynthesis are transported in phloem sap.
•
are
such
•
Blood
ions
two
Mineral
•
given uid
is just
transported
•
i
d
r
o
Figure 14
be
have
in blood plasma.
f
x
O
▴
c an
Plants
n
U
Substances
C an you explain why?
•
Oxygen
is
a
non-polar
sometimes
c alled
to
in
dissolve
molecule,
dioxygen.
water
The
sparingly.
composed
small
Water
size
of
of
two
this
becomes
oxygen
atoms
and
molecule
allows
it
saturated
with
oxygen
y
Rehydration involves
water being drawn rapidly through the
these
hydrophilic
molecules such as glucose and particles
P
resurrection plants.
substances
are
polar
e
almost
Several plants that
that
also
fearing”,
to
water
s
s
Figure 13
used
in
both
r
▴
dissolve
include
negative
is
cellulose—are
Other
that
substances
Molecules
at
relatively
solubility
less
low
of
dissolved
transport
transport
F at
are
this,
of
at
20°C
or
lower.
the
body
to
provide
cells
contain
greatly
water
37°C
rises,
c an
Blood
for
hold
plasma
aerobic
haemoglobin.
increases
the
are
than
the
much
c annot
cell
H aemoglobin
c apacity
of
the
blood
small
fat
around
are
c an
to
are
to
coated
hydrophilic
prevent
remain
the
and
coalesce
in
at
larger
form
a
single
one
contact
large
end
oxygen
so
droplets
in
they
are
blood.
To
layer of phospholipids.
and
between
hydrophobic at the
water
and
fat,
allowing
suspended in blood plasma while being
l
transported
to
droplets
they
droplets
non-polar
tend
molecules
means
fat
They
body.
O
Physic al properties of water and the
consequences for animals in aquatic habitats
is
a
characteristic
changing
properties,
with
its
of
a
chemic al
major
material
that
structure.
consequences
for
c an
Water
living
be
has
force
be
The
and
less
densities
water.
the
object
gravity
of
living
lung
However,
it
living
for
energy
to
the
due
the
are
quite
organisms
oat
to
at
use
a
to
control
vesicles
which
they
use
to
adjust
less
dense
Organisms
than
has
high
uid
a
tube,
there
viscosity.
moves
is
viscosity
the
to
their
the
relative
is
to
is
friction.
The
of
be
the
by
greater
object
as
a
force on the
the
object. It is
than
is
density
habitat,
depth.
the
higher,
force due
buoyancy
example, bone is denser than
storage
overall
organisms
as
due
in
fat
overall
to
are
both
close
bec ause
Bony
density.
of
a
sh
to
less dense than
that
they
have
an
of
do
water.
not
need
air-lled
Cyanobacteria
to
internal
part.
provides
For
li
uid
propanone
the
more
and
generate
stickiness
another
greater
upward
swim
have gas
how close to the surface they oat.
have
such
Viscosity
velocity
internal
resistance
is
solvents
E
a
terms,
Organic
v
ow.
a
simple
c an
water
l
O
In
living
therefore
Viscosity
an
for
u
f
x
use
much
will
variable—for
particular
they
is
an
displaced
lower than the density of the uid,
density
tissue
have
which
buoyancy.
is
buoyancy
the
adipose
them
exerts
uid
object will sink.
bladder
Air
If
the
object
to
oat.
tissues
and
of
uid
of
t
a
much
and
tissue
easier
will
the
i
makes
use
on
r
o
This
density
uid,
weight
o
while
the
object
a
d
water
in
the
If
the
than
to
n
will
to
acting
gravity
equal
U
to
buoyancy.
immersed
is
C
the
is
force
o
v
c alled
object
This
i
n
an
object.
distinctive
organisms.
Buoyancy
When
observed or
some
p
physic al
property
without
y
physic al
measured
r
e
A
n
y
t
i
s
A1.1.6
y
small
and
at
P
the
This
entirely
water.
Phospholipid
other.
blood
plasma
r
prevent
in
red
oxygen
temperature
oxygen.
molecules
insoluble
why
for
plasma
around
the
blood
e
•
is
sites
than
oxygen
As
so
s
s
to
This
binding
decreases,
oxygen
enough
respiration.
has
concentrations.
oxygen
friction
viscous
of
a
the
low
airborne.
determines
viscosity,
how
easily it
whereas
treacle
c aused when one part of
when
tube
uid,
negligible amounts of
stay
which
have
example,
centre
to
the
a
than
uid
ows
through
at
the
edges, so
greater
the
friction and the
ow.
11
Unity
and
diversity
Pure
water
bonds
does
not
bec ause
it.
has
c ause
The
ow
of
a
higher
internal
as
the
viscosity
friction.
easily
as
water.
dissolved
viscosity
of
air
is
than
organic
Solutes
salts,
about
Seawater
with
50
solvents,
increase
has
the
a
higher
consequences
times
smaller
bec ause
viscosity
for
than
hydrogen
even
viscosity
further, so blood
than
organisms
that
of
water
freshwater
that
at
swim in
the
same
s
s
temperature.
Thermal conductivity
rate
at
which
has
about
25%
is
of
useful
water
when
to
as
air
hand,
body
is
blood
and
dissipate
than
need
allows
contracting
excess
required
specic
heat
to
raise
the
c apacity.
specic
air,
has
amount
remains
equally
large
maintain
constant
o
between
i
consequences
t
a
seal
(a
mammal)
moderate
their
and
size
young
the
a
in
of
loon
through
than
Water
has
than
and
body
the
it.
easier
for
than
it
is
a
more
There
is
about
heat
c apacity
the
thermal
in
air
to
is
a
material
of
of
example, the
body
more
by
water
bec ause
of
water
do
where
heat or parts
1°C
is
(or
kelvin,
this.
increase,
This
is
energy.
result,
with
mammals
As
air
4.18 J g
K)
−1
K
.
hydrogen bonds
to
of
terrestrial
of
a
hydrogen
why
water.
a
To
the
relatively
cool
down,
temperature
temperatures and aquatic
habitats.
(which
air
for
The
are
high
mostly
specic
heat
composed of
to
so
800times
same
(a
bird).
spend
so
it
stay
the
due
seal
more
in
to
drag
on
land
on
a
rearing
Arctic loon ies
the
water.
far
the
use
ringed
are both of
The
dierences
than
must
the
They
time
the
provides
alo
have major
Consider
However,
vary
dense,
energy
water
submerged
habitats
less
loon
Both
food.
time
and
habitats.
habitats.
viscous,
less
in
buoyant
ringed
more
body
energy
buoyancy
seal
energy to
moving
through
velocity.
conductivity
animals,
maintain
need
For
the
−1
to
dierent
more
more
is
at
of
black-throated
these
Air
expend
submerged
loon
far
in
medium.
air
in
foraging
spends
of
and water
overlapping
water
Water
through
of
or
heat.
temperature
properties
living
Arctic
are at much
temperatures.
physic al
movement
greater
bodies
have
the
must
water.
water
the
seal
for
move
the
in
ringed
The
oating
and
the
compared
birds
organisms
and
and
viscosity
force.
for
the
1 g
needed
raise
stable
helps
is
animals
parts
that
c apacity
c apacity
amount
stable
thermally
also
to
n
U
l
12
to
water
energy
needed
relatively
more
requirements
a
than
while
air
air
so
acts
temperature
it
as
conducts
an
heat
insulator.
above
that
of
It
the
away
is
from
therefore
environment
seal (Pusa hispida)
above water in the Laptev
A ringed
longer than 150 cm
of
Dierences
while
v
E
A ringed
Sea near Russia.
an
is
of
heat
heat
heat
therefore useful as
environment.
temperature
Physic al properties of air
u
f
x
Figure 16
peeks its head
65 cm
r
o
a wing span of 120 cm
O
▴
heat
black-throated loon
(Gavia arctica) has a length of about
and
d
An adult
lose
are
c apacity
water)
of
and
the
C
water
habitats
broken
i
n
of
be
parts
K
specic
For
to
o
must
high
motion.
are
transfer
from
−1
1.01 J g
v
bonds
must
only
relatively
molecular
water
Figure 15
a
is
restrict
large
▴
value
and
conductivity.
conduct
warm-blooded animals.
p
Water
the
materials
heat
thermal
y
−1
For
the
temperature
The
as
oils
O
heat
its
c arry
to
and
warm-blooded
muscles)
heat
known
land-based
absorb
to
r
e
is
to
it
Specic heat
The
These
aquatic
heat
a
5%.
is
F ats
n
able
other
of
there
of
(such
water,
material
t
i
s
are
the
loss
content
generated
that
On
the
as
a
conductivity.
l
is
quickly
through
thermal
y
high
risk
passes
high
seal rarely grows
thermal
for
a
ringed
so
it
seal
resists
environment
for
in
water.
changes
the
seal
At
in
the
same
time,
temperature.
than
air
does
water
Thus
it
has
a
higher
provides
for the loon.
a
specic
more stable
y
Water
it
as
insulators.
greater
heat
relatively
P
heat
a
r
Water
e
The
Molecules
Extraplanetary origin of water on
Earth and reasons for
are
is
in
liquid
in
the
was
nearly
1.4
state.
atmosphere.
formed,
boiled
for
origin
of
is
unlikely
is
solid
that
temperatures
and
the
that
kilometres
vast
of
ice
water
water
and
was
would
have
lost
to
space.
There
amounts
of
water
been
water
this
in
was
delivered
to
on
the
on
on
are
E arth.
gas
as
above
water
100°C
competing
The
by
or
vapour
E arth when the planet
been
E arth
E arth and 98.3% of this
snow,
most
so
widely
colliding
water
hypotheses
supported
asteroids.
r
is
cubic
remainder
e
have
the
It
bec ause
would
hypothesis
billion
The
its retention
s
s
There
a
LHA
A1.1.7
the Earth about once every 20 million years. This rate of bombardment could not
of water. However, there is evidence of much heavier bombardment during the rst
t
i
s
n
y
taken from an asteroid and brought back to Earth contained only a small proportion
l
account for all of the water on Earth, especially as a sample of material recently
few hundred million years aer Earth’
s formation. Also, it is likely that asteroids that
O
collided with Earth early in its history contained more water. Asteroids that have
been in orbit for billions of years have lost nearly all of their water due to heat from
the Sun evaporating the water and gravity being too weak to retain water vapour.
The
explain
factors
distance
of
to
tightly
its
to
hydrogen
is
evidence
and
has
the
Sun
water
due
to
relatively
holding
esc ape
the
aer
hydration
of
these
aer
presence
the
reactions
minerals
of
planet’s
were
strong
its
the
water
so
from
the
delivery
on
M ars
It
in
surface
is
is
never
but
raises
hydrogen bonding.
holding
the
into
space
this
seems
thought
M artian
water
by
retained much
oceans
atmosphere. Some
atmosphere
minerals
less
sunlight
water
gravity,
within
formation.
with
that
Liquid
o
in
for
soon
boil.
cohesion
gases
from
ensures
to
that
rock.
was
but
On
not
to
most
very
little
have
of
this
water
E arth, the
used
up.
u
l
a
E
v
O
f
x
t
a
r
o
i
quantities
vapour
E arth
helium
for
d
used
from
vapour.
disappeared
was
the
E arth
n
There
water
surface
and
E arth
enough
U
water
size,
its
on
C
Due
than
retained
i
n
•
easily
was
o
more
the
high
water
signic ant.
v
temperatures
how
are
p
•
to
two
y
trying
asteroids,
r
e
When
y
P
Currently, large asteroids (with a diameter greater than 5 km) only collide with
◂
Fig ure
Co m e t s
dust.
17
a re
T he y
k i l o m e t re s
hi g hl y
have
and
a
a
tail
comet
of
the
a ro u nd
orbits.
S u n,
ga s
H y a k u t a k e.
fo rm e d
diameter
go
e l o n ga t e d
a p p ro a c he s
fo rm
The
m o st l y
and
t he
of
ice
of
t he
a
S un
Wh e n
ice
and
few
a
in
comet
v a p or i z e s
to
d u st
13
LHA
Unity
and
diversity
Data-based questions: Were comets the source of water in E arth’s oceans?
−4
Scientists have analysed the ratio of deuterium to hydrogen (D/H) of water in the Earth’
s oceans (1.56 × 10
). They have
compared it with the same ratio in:
comets
originating
(asteroids
•
comets
of
the
that
from
Jupiter
have
the
family
passed
Oort
through
Cloud
including
the
including
67P/C-G,
E arth’s
atmosphere)
Halley’s comet
which
was
explored
by
the
Rosetta
r
n
y
 amil
Space
Agency
C
The graph in Figure 19 shows these D/H ratios, arranged on the x-axis according to their distance from the Sun.
obtainedremotely.
The
4.
The
5.
Using
the
of
E arth’s
graph
changes
have
ratio
the
D/H
likelihood
data
in
the
uses
found
for
the
ratio
comet
a
on
11
that
logarithmic
Halley’s
comets
that
water
was
on
discuss
which
that
of
measured
E arth
was
whether
water.
sc ale.
Outline
what
has
comet.
for
matches
67P/C-G
graph,
u
l
a
E
v
O
14
data
a
for
y-axis
ratio
f
x
the
D/H
shows
comets
D/H
19. The
the
n
Figure
a
D/H
water
i
3.
the
at
t
a
Determine
d
Look
2.
r
o
1.
o
U
Diamond-shaped data points represent measurements from in situ samples; circles show astronomical data,
by
on
the
derived
asteroids
ratio
meant
by
a
logarithmic
sc ale.
[2]
[1]
been
measured.
Identify
how
many of
E arth.
Rosetta
from
or
is
[2]
spacecra
in
2014.
Discuss
how
this
ratio
comets.
comets
are
[2]
more
likely
to
have
been
the
source
[3]
y
l
O
P-M-/P4
eltra /P301
G-C/P76

00 / C
ella /P
P
1P
European
1 /C
The
B
drarra G
Source:
Figure 19
uiter
o
i
n
▴
deuterium
Comets of the
Oort Cloud
p
On
1 in 6,420 atoms of hydrogen are
eatua 
Comets of the
Asteroid
v
is the isotope deuterium.
0
E arth,
the
Belt
In this model of a water
one of the hydrogen atoms has a
neutron so it
r
e
Meteorites
from
molecule,
y
/
E arth
Figure 18
elttu/
1 /C
t
i
s
oitar
–4
10
▴
100 / C
10
–3
10
4
electron
AE 7 00/C
AE
neutron
ah-a e/P31
oB-ela 
proton
spacecra.
e
meteorites
•
s
s
•
Molecules
LHA
A1.1.8
Relationship between the search for
extraterrestrial life and the presence of water
the
of
porridge.
fairy
tale,
bowl
is
zone
around
known
too
far
the
away
right
star,
forms
and
one
them
temperature.
oen
on
c alled
E arth.
water
allows
of
If
water
to
This
the
a
freezes.
too
hot
is
used
is
too
However,
in
a
for
liquid
a
young
another
as
Goldilocks
planet
exist
and
a
girl
too
tries
cold
metaphor
zone.
close
Liquid
to
planets
a
in
star,
the
three
but
bowls
the
third
for the habitable
water
is
water
will
essential to
Goldilocks
vaporize;
zone, the
state.
r
temperature
loc ation of the Goldilocks zone depends on the size of the star and the
amount
of
energy it emits. It also depends on the size of the planet, which
the
zone”.
The
strength
is
more
the
of
gravity
estimated
planets
chance
that
that
there
and
there
are
in
the
atmospheric
pressure. Within our
are 40billion planets within a “Goldilocks
the
extra-terrestrial
Goldilocks
life
has
zone
around
other
stars, the
evolved.
▴
the
various
intermolecular
forces
of
attraction
Outline
to
the
things.
Describe
the
properties
of
cohesion
role
of
hydrogen
bonding
biologic al
Outline
an
(A1.1.3)
Describe
processes
example
the
role
of
of
only
happen
how
the
cell
(C2.1.6)
Explain
the
relationship
at
surface
near
of
of
in
the
DNA.
structure
surfaces?
water acts as a habitat.
receptors
between
structure
interactions
or
surface
are important
in
chemic al signalling.
surface-area-to-volume
ratio and
a
exchange. (B2.3.6)
E
v
O
materials
l
c.
hydrophobic
(B2.1.2)
u
f
x
b.
of
membrane.
t
a
a.
importance
i
What
the
plasma
r
o
2.
the
d
of
the
o
Explain
in
adhesion
n
(A1.2.6)
c.
and
(A1.1.3)
U
b.
how
living
biologic al
C
i
n
a.
aect
p
do
systems?
Will the porridge in the large
bowl be too hot or too cold?
o
How
v
1.
Figure 20
y
r
e
Linking questions
O
t
i
s
greater
it
n
alone,
y
galaxy
l
determines
y
P
The
a
life
nds
e
all
just
Goldilocks and the Three Bears,
She
s
s
In
15
A1.2
Nucleic
acids
s
s
How does the structure of nucleic acids allow hereditary information to be stored?
All of the information encoded on a computer is ultimately
1.
Binary code
Character
Binary code
A
01000001
N
A computer byte is 8 binary digits.
01001110
B
01000010
O
converted
to binary code.
0 1 0 0 1 1 1 1
C
01000011
P
represented
D
01000100
Q
E
01000101
F
01000110
G
01000111
H
01001000
How would
the term
I
“DNA” be
in binary code? Bec ause each digit
possible values,
DNA codons with three symbols have 64
compared
For this reason,
01010010
01010011

01010100

01010101
01001001

01010110
01001010

0 1 0 1 0 1 1 1
K
01001011

01011000
L
01001100

M
01001101

scientists have
DNA computers.
J
p
o
U
C
i
n
reproduction. Why must dividing cells produce new DNA? The
guides accurate replication. Chromosomes are mainly composed of
01011010
y
r
e
v
Cells divide for the purposes of maintenance, repair, growth and
always paired with T and C is always paired with G. Complementarity
01011001
Figure 1
How does the structure of DNA facilitate accurate replic ation?
structure of DNA is dependent on complementary base pairing—A is
O
t
i
s
▴
n
y
to develop
symbols.
01010001

l
possibilities using eight
with a binary byte which has 256
01010000

DNA. These chromosomes (Figure 2) are seen during the early stages
n
of cell division. The double structure of each chromosome shows
that the DNA has replicated to form two identical strands, known as
o
▸
Figure 2
genetic
Components
A1.2.3
Sugar–phosphate
a
nucleotide
bonding
and RNA
A1.2.5
RNA
in
as
each
a
nucleic
polymer
acid
formed
and
that
by
HL
living
the
AHL
A1.2.11
organisms
A1.2.12
sugar–phosphate
“backbone” of
form the basis of a code
condensation
of
nucleotide
monomers
Purine-to-pyrimidine bonding as a
component of DNA
helix stability
A1.2.13
Structure
of
a
A1.2.14
Evidence
from
Chase
experiment
material
two strands linked by hydrogen bonding between complementary base pairs
A1.1.15
E
A1.2.7
Dierences
A1.2.8
Role
A1.2.9
of
of
replic ated
complementary
and
Diversity
DNA
A1.2.10
for
pairing
in
allowing
genetic
information to
expressed
of
storing
base
possible
DNA
base
sequences
and
the
limitless
c apacity
information
Conservation
of
the
universal common ancestry
genetic
code
Charga ’
s
amounts
between DNA and RNA
across
all
life
forms as evidence of
only
Directionality of RNA and DNA
A1.2.6 DNA as a double helix made of two antiparallel strands of nucleotides with
be
16
a
Bases
v
O
A1.2.4
all
l
DNA
of
and
of
u
A1.2.2
SL
material
i
the
t
a
as
sc anning electron micrograph of two human chromosomes
r
o
DNA
f
x
A1.2.1
A coloured
d
chromatids. These strands are linked by a region called the centromere.
across
of
nucleosome
the
Hershey–
for DNA as the genetic
data
on
the
relative
pyrimidine and purine bases
diverse
life
forms
y
of two,
c an have four
P
values instead
worked
Figure 1 shows the letters
r
Character
on binary code—a code based on two options, 0 and
e
based
Molecules
A1.2.1
DNA as the genetic material of all
living organisms
material
cell
also
and
sometimes
hereditary
full
c alled
name
of
to
information.
ospring.
hereditary
If
copied,
Bec ause
information.
All
it
c an
genetic
living
be
passed
material
organisms
is
use
from cell to
inherited it is
DNA
to
store
for
acid
DNA
or
name.
They
which
deoxyribonucleic acid. The other type of nucleic acid is
link
Nucleic
are
to
very
form
acids
large
a
were
rst
molecules,
discovered in the cell nucleus,
made
from
subunits
c alled
polymer.
Figure 3
The virus shown in the centre
(black structure) uses DNA as its genetic
l
HIV
. This observation does not seem to t the theory that genes are made of DNA
material.
in all living organisms. However
, reproduction is a fundamental property of living
DNA has spilled
The virus has burst open and its
where it
O
t
i
s
they do not falsify the claim that all living organisms use DNA as their genetic material.
Components of a nucleotide
which
a
phosphate
three parts:
five
group,
c arbon atoms so is a pentose sugar
which
is
the
acidic
and
negatively
•
a
base
that
contains
nitrogen and has either one or two rings of atoms in its
phosphate
sugar
base
1
O
C
2
shows
the
Figure
5
base
sugar.
base
a
parts
and
The
and
the
ve
they
are
linked
phosphate
how
are
both
c arbon
atoms
in
the
Figure 5
Simple diagram
together
linked
pentose
by
to
of a nucleotide
form an RNA
covalent bonds to
sugar
are
numbered,
linked to C1 and the phosphate to C5.
shows
phosphate,
these
The
pentose
with
▴
Parts of a nucleotide
E
the
a
4
nucleotide.
l
Figure
OH
v
O
Figure 4
u
f
x
3
OH
▴
N
C
4
o
O
t
a
2
5
r
o
CH
O
i
d
O
P
n
U
structure.
O
charged part of
C
nucleic acids
o
•
of
has
v
sugar,
i
n
a
p
consist
•
y
r
e
Nucleotides
of the polyhedral head,
is stored
for this process so they are not considered to be true living organisms. Therefore,
A1.2.2
out
n
y
organisms and viruses cannot reproduce themselves. Instead, they rely on a host cell
y
▴
Some viruses use RNA as their genetic material, for example, coronaviruses and
P
nucleotides
is
RNA.
r
the
store
information.
ribonucleic
hence
a
parent
e
The
is
from
s
s
Genetic
a
nucleotide
pentagon
for
in
the
symbolic
pentose
form,
sugar
with
and
a
a
circle
to
represent the
rectangle
for
the
base.
17
Unity
and
diversity
O
O
A1.2.3
O
P
Sugar–phosphate bonding and
thesugar–phosphate “backbone” of DNA
and RNA
O
link
nucleotides
together
into
a
chain
or
polymer,
covalent
bonds
s
s
To
CH
are
formed
the
next
2
O
between
HC
base
CH
the
one
nucleotide
and
the
pentose
acids
are
produced
by
living
being
added
polypeptide
is
linked
by
a
in
organisms,
the
same
P
of
O
nucleotide.
alternating
sugar
together
phosphate
covalently
groups,
bonded
with
together.
a
in
DNA
and
RNA
molecules
A1.2.4
OH
The oxygen atom
shown in red
the
are
four
dierent
fourth
one
diers.
to
as
DNA
bases
in
RNA
adenine (A)
cytosine
(C)
cytosine
(C)
guanine
(G)
guanine
(G)
is
The
uracil (U)
to
a
oxygen and
strong sugar–
conserve the
is
in
RNA.
contain
sugar
almost
of
used
along
is
base
to
a
so
c an
make
DNA
there
be
the
or
are
linked
bond
RNA
bases
four
to
are
types
each
the
molecule
is
of
the
same but
they
are oen
nucleotide in DNA
other,
same.
are
why
bec ause the
Any
base
and
the
number
The
information
sequence
of
possible
innite.
bases
form—this
one
nucleotides
Three
nitrogen—this
the
is
how
information
universal
genetic
is
stored.
code
that
is
shared
by
all
is
stored in a
organisms.
i
t
a
r
o
Table 1
two
possible
sequence
coded
contains
o
(T)
d
thymine
and
therefore
sequences
Any
n
(A)
phosphate
U
adenine
RNA.
and
o
in
nucleotide
in
DNA
bases
C
and
i
n
E ach
in
the
nitrogenous bases.
nucleotide and the pentose sugar of the
nucleotide
of
v
forms links between the phosphate of one
referred
bases
All
p
There
Figure 6
helps
y
the basis of a code
OH
forms
Bases in each nucleic acid that form
CH
r
e
HC
that
creates a series
O
base
CH
chain
way
c arbon,
t
i
s
O
HC
this
of
n
backbone
in
chain
This
sequence of bases.
2
are
covalent bond to the pentose sugar of
nucleotides
y
phosphate
CH
▴
nucleotides
l
atoms
and
Linking
O
bases
the
way: the phosphate of
Data-based questions: Bases in DNA
the
molecular
models
in
one
other
2.
E ach
dierence
of
the
Deduce
nucleotide
18
E
le).
bases
atom
is
has
in
how
a
a
answer the
atom
position
nitrogen
assembled
is
bonded to a
(shown
Identify
three
similarities
between adenine and
its
subunits.
[3]
4.
Compare
the
structure
5.
Although
the
bases
one
distinctive
has
a
Remembering
lower
important
used when a
from
3.
guanine.
[1]
nitrogen
similar
this
being
and
between adenine and the
bases.
hydrogen
7
a
State
v
O
1.
Figure
l
following questions.
u
at
f
x
Look
[2]
for
the
each
of
have
cytosine
some
chemic al
function
base
to
of
be
and
thymine.
shared
features,
structure
DNA,
and
explain
distinctive.
[4]
each
shape.
why it is
[5]
y
previous
growing
P
nucleotide
the
the
r
to
the
phosphorus
next
of
e
nucleic
added
OH
O
▴
sugar
CH
always
O
of
nucleotide.
Whenever
HC
phosphate
Molecules
Guanine
O
N
NH
s
s
NH
N
NH
2
e
Adenine
r
NH
2
N
l
NH
N
2
N
Thymine
O
O
Figure 7
skills:
o
d
Communic ation
ATL
n
U
▴
C
i
n
NH
o
v
NH
y
O
p
r
e
NH
O
t
i
s
NH
n
y
Cytosine
y
P
N
Interpreting
and
evaluating
i
r
o
information presented in dierent forms
of
7
e ach
in
me ans
to
the
make
e ach
third
an
is
questions
is
a
structural
a
space
appraisal
type
of
lling
by
shows
model.
weighing
l
questions?
three
formula,
representation.
dierent
second
The
command
up
Which
strengths
was
is
representations
the
and
most
a
ball
term
and
stick
“evaluate”
limitations.
useful
in
answering
a
v
O
data-based
A1.2.5
rst
u
and
Evaluate
data-based
The
f
x
model
the
the
base.
t
a
Figure
RNA as a polymer
formed by
E
condensation of nucleotide monomers
RNA
is
a
subunits
single,
of
molecule
a
of
unbranched
polymer,
RNA
condensation
is
so
polymer
of
nucleotides.
they
are
monomers.
unlimited,
but
they
reaction.
are
The
always
The
nucleotides
number
linked
in
of
are
nucleotides in a
the
same
way,
by a
▴
Figure
using
8
circles,
RNA
polymers
pentagons
c an
and
be
represented
rectangles
19
Unity
and
diversity
In
a
condensation
molecule
one
of
and
nucleotide
the
other
OH
and
groups
OH,
the
is
is
on
the
molecules
are
Hydroxyl
pentose
removed
producing
two
two
eliminated.
sugar
entirely.
It
is
of
water.
The
remaining
This
is
another
oxygen
in
S
HC
C
S
bonds
P
OH
P
C
S
▴
Figure 9
t
a
P
G
S
G
S
base
CH
HC
CH
OH
OH
A1.2.6
DNA as a double helix made of two
antiparallel strands of nucleotides with the
DNA
is
e ach
nucleotide
composed
is
of
strands
or
deoxyribose
polymers
and
the
of
nucleotides.
bases
are
The
adenine,
pentose
cytosine,
sugar
in
guanine
sugar–phosphate
v
S
and
thymine.
backbone
P
P
S
P
P
O
HC
between complementary base pairs
C
a
P
O
T
2
two strands linked by hydrogen bonding
S
P
l
S
A
CH
u
S
P
S
f
x
T
S
O
Condensation reaction between two nucleotides
i
r
o
S
P
OH
P
P
O
2
o
A
T
S
d
P
H
CH
S
G
S
P
n
U
hydrogen
P
+
E
S
S
A
DNA
by
their
molecule
bases.
consists
The
links
of
two
strands
between
the
of
nucleotides
bases
are
linked
hydrogen
to
each other
bonds.
Adenine (A)
P
G
S
C
only
forms
hydrogen
bonds
with
thymine
(T).
Guanine
(G)
only
forms
hydrogen
S
3’end
bonds
with
cytosine
(C).
This
results in complementary base pairing. A and T
P
complement
each
other
by
forming
5’end
each
▴
20
Figure 10
The double helix
other
by
forming
pairs.
base
pairs and similarly G and C complement
y
P
A
T
base
CH
OH
n
HC
C
i
n
complementary
o
3’end
O
p
O
CH
O
v
5’ end
S
O
HC
y
r
e
O
O
l
OH
base
CH
O
OH
2
2
y
t
i
s
CH
OH
P
covalent bond,
O
HC
base
CH
One
from the
P
CH
2
HC
S
new
O
O
HC
pairs
used.
9.
P
O
base
a
are
hydrogen
e
O
O
CH
CH
the
r
P
P
with
O
O
O
form a single
nucleotide
forms
Figure
O
O
to
(OH) on the phosphate of
combined
nucleotides.
shown
combined
groups
s
s
linking
reaction,
water
Molecules
The
two
strands
opposite
ends
with
ends
with
the
a
group
usually
Figure
the
structure
structure
of
the
simply
on
paper
molecule.
a
shape.
this
nucleotide
were
(2 nm).
However, they run in
For
oriented
bonds
A
in
with
helix
Bec ause
is
a
of
reason,
while
the
the
coiled
strand
strand
same
each
the
one
other
direction,
other.
structure that has
two
strands, DNA is a
features.
DNA
in
other.
c annot
Figure
11
show
shows
all
features
how
the
of
the
three-
structure of DNA
diagram.
l
covalent bond
Key
A
C
–
G
T
S
G
P
P
S
A
T
P
G
S
C
formed
between two bases
four
bases
in
The
The
and
bases
RNA
of
dierences
polymers
polymers
RNA
in
are
E
instead
4
1
H
H
OH
3
2
OH
OH
is
are
ribose
between the two types of nucleic acid:
of
CH
nucleotides
in
DNA,
whereas
there is only
2
OH
5
H
O
often
referred
to
as
strands, so DNA is double-
a
stranded
The
H
O
t
a
RNA.
two
l
O
in
important
usually
v
2.
one
are
u
three
There
OH
Dierences between DNA and RNA
f
x
are
1.
2
Complementary base pairing between the antiparallel strands of DNA
A1.2.7
There
i
r
o
Figure 11
CH
5
o
are
d
bonds
n
P
hydrogen
U
S
C
i
n
P
o
v
S
y
C
p
r
e
S
3.
nitrogenous bases
P
P
▴
– phosphate
P
S
T
O
A
t
i
s
– sugar
S
S
n
y
P
y
represented
of
terminal
helic al
its
each
hydrogen
nanometres
shows
to
antiparallel.
strands
form
a
be
the
two
to
adopt
2
10
the
of
to
r
of
of
If
able
parallel
said
e
helix.
be
are
are
P
be
not
diameter
dimensional
c an
they
deoxyribose.
molecules
Drawings
so
phosphate
would
constant
double
nucleotides
s
s
a
the
bases
DNA
of
directions
4
1
single-stranded.
DNA
are
H
adenine,
cytosine,
cytosine,
guanine
guanine
and
thymine.
The
H
four
OH
3
adenine,
and
uracil,
so
uracil
is
2
present
OH
H
thymine in RNA.
pentose
deoxyribose
sugar
ribose.
Figure
ribose.
The
12
full
within
shows
names
DNA
that
of
is
deoxyribose,
deoxyribose
DNA
and
RNA
has
are
whereas the sugar in RNA is
one
fewer
oxygen atom than
based on the type of sugar in
them—deoxyribonucleic acid and ribonucleic acid.
▴
Figure 12
an H
atom
Ribose has an OH
attached
to c arbon 2,
group and
whereas
deoxyribose has two H atoms
21
Unity
and
diversity
parental DNA
A1.2.8
in allowing genetic information to be
C
C
C
T
G
C
G
replic ated and expressed
G
In
DNA,
adenine
guanine.
T
molecule
A
to
is
be
c an
only
pair
with
complementary
made
in
a
thymine
base
process
and
pairing.
c alled
It
cytosine
allows
c an only pair with
an
exact
replic ation.
In
DNA
E ach
original
copy of a DNA
replic ation, the
e
T
A
two
C
strands
of
the
double
helix
separate.
of
the
strands
serves as a
strands
are
G
guide,
replic ation
This
s
s
A
Role of complementary base pairing
or
template,
for
the
creation
of
a
new
strand.
The
new
fork
T
by
G
adding
nucleotides
one
by
one
and
linking
them
r
A
together.
C
T
E ach nucleotide that is added must be c arrying the base that is complementary to
G
C
C
the
T
T
A
T
G
C
G
each
the
of
base
the
on
other
two
the
template
template
strand.
template
strands
This
strand.
should
means
Replic ation
have
changes
one
C
G
A
DNA
molecules,
and
one
strand.
each
with
A
new
This
is
c alled
A
T
T
A
T
one
the
synthesized
same
original
strand
from
semi-conservative
T
A
newly
base
DNA
the
molecule into
original
replic ation.
strand on
sequence as
molecule
O
identic al
t
i
s
two
A
T
the
exactly
n
C
A
y
C
next
A
l
T
A
Genetic information consists of sections of DNA called genes. Each gene contains
information needed for a particular purpose. When the information in a gene has
G
C
T
A
y
an eect on the cell, this is called gene expression. The rst stage in expressing a
T
A
T
r
e
C
A
gene is the copying of its base sequence, but the copy is made of RNA rather than
T
A
G
G
strand
strand
DNA. Only one of the two DNA strands is used as a template for this. The rules
parental
strand
p
new
of complementary base pairing are followed but adenine on the template strand
pairs with uracil on the new strand of RNA, rather than thymine. This process of
o
strand
new
v
parental
Figure 13
Semi-conservative
RNA
that
is
produced
or
Again,
sequence
protein.
translation
it
of
the
are
be
by
transcription
used
RNA
in
protein
molecule
is
complementary
more
fully
may
have
synthesis.
translated
base
regulatory
or
synthesize
a
into
pairing
described in
a
To
is
the
amino
involved.
structural
acid
Both
role in
protein, the base
sequence of a
transcription and
Topic D1.2
o
Diversity of possible DNA base
i
sequences and the limitless c apacity of DNA
for
storing information
Genetic
u
DNA
•
l
information
molecule.
There
are
Any
four
is
stored
in
sequence
the
of
possibilities
base
bases
for
sequence
is
each
of
one
of
the
two
strands of a
possible.
base
in
the
sequence—A,
C,
G
or
T.
2
•
a
E
v
O
f
x
t
a
r
o
d
A1.2.9
There
and
are
so
4
or
16
4
or
64
so
on.
possibilities
for
a
sequence
of
two
bases—AA,
AC,
AG
on.
3
•
There
are
AAG
and
With
n
possibilities
for
a
sequence
of
three
bases—AAA,
AAC,
n
•
of
DNA
bases,
over
a
The
feature
for
4
c an
possible
immense.
sequences.
With
a
As
n
sequence
increases,
of
just
10
the
number
bases,
there
possibilities.
be
range
an
are
becomes
million
molecules
sequences.
ideal
there
possibilities
are
22
may
n
cell,
U
the
C
replic ationof DNA
i
n
making an RNA copy of the base sequence of DNA is called transcription.
▴
any
of
length,
possible
information
adding
to
sequences
storage
the
is
system.
potential
eectively
diversity of base
limitless, which is an
y
P
A
formed
Molecules
The
diameter
DNA
c an
devised
up
and
be
by
the
of
a
DNA
stored
in
humans,
amount
molecule
a
very
DNA
of
is
is
small
very
material
just
2
nanometres, so immense lengths of
volume.
Compared
with
data-storage
systems
economic al, both in terms of the space it takes
used to make it.
s
s
e
r
l
is a DNA delivery system. These
chromosome
genes.
of
the
of
thymine.
are
that
has
a
for
has
an
173,904
of
224
coat
is
single-stranded
one
DNA.
Suggest
disadvantage of this DNA
store
[2]
genetic
information
C alculate the
17
base
in
small
circular
c alled plasmids. A plasmid with
pairs
has
been
found in the bacterium
Acetobacter pasteurianus.
bacterium
What
proteins. A surprisingly
is
the
and
the
C an
you
has
ratio
length
The
main
3.155 Mb (Mb
=
chromosome of
megabase
pairs).
between the length of the plasmid
of
the
main
chromosome?
[2]
adenine, cytosine and
genome
only
of
5.
in
nd
examples
of
DNA
molecules
from
[3]
2,063 bases with
nanometres
l
animals,
bacteria,
than
examples
the
example
of
DNA
viruses
given
with
or
plasmids
here?
less
than
C an
that
are shorter
you nd an
7.3%
guanine?
[2]
diameter.
a
v
O
A1.2.10
that
c an
molecules
1,440
this
protein-coding genes. This type of virus has a
protein
is
and
single-stranded.
Bacteria
DNA
estimate
guanine.
are
just
u
two
circovirus
f
x
C anine
with
code
bases
bases
4.
[1]
t
a
percentage
194
3.08 billion
i
7.3%
genome,
these,
being
pairs.
material
advantage
percentage of this does
Carsonella ruddii
its
base
has
contain?
r
o
low
Of
in
what
genome
genetic
one
o
pairs
57
,227
,415
d
base
3.
total,
Its
n
pairs
the
The bacterium
has
human
base
Y
in
the
chromosome (and
molecule) is the Y
U
2.
which
that
DNA
how wide is
y
Assuming
smallest
C
chromosome
the
shortest
and
p
the
o
Homo sapiens,
therefore
r
e
In
i
n
1.
How long is each sperm
where the DNA is stored?
v
Data-based questions: DNA lengths
over 3 billion base
The microscope image has a grid of lines 50
micrometres apart.
the head
2 metres and
O
cells each contain 3.3 picograms of DNA,
with a total length of about
pairs in total.
n
A sperm
human sperm
y
P
y
Figure 14
t
i
s
◂
Conservation of the genetic code
E
across all life forms as evidence of universal
common ancestry
The
sequence
The
information
are
c alled
of
bases
is
codons
in
DNA
or
RNA
decoded
during
and
meanings
have
contains
protein
in
information
synthesis.
the
code.
in
Groups
There
are
a
of
64
coded
form.
three bases
dierent
23
Unity
and
diversity
codons,
bec ause
combinations.
most
•
one
•
three
Details
codons
codon
of
base
the
in
64
a
codon
codons
c an
has
a
be
any
of
four,
so
there
are 4
×
4
×
4
meaning:
specify one particular amino acid
signals
codons
the
of
that
signal
genetic
protein
that
code
synthesis should start
protein
are
synthesis
described in
should
s
s
•
each
E ach
stop.
Topic D1.2
e
It is an extraordinary fact that—with a few minor exceptions—all living organisms
r
and all viruses use the same genetic code. It represents a sort of genetic language.
Humans use many dierent spoken languages, each of which is an eective form
and they would probably function perfectly well, but all life forms use essentially
l
the same version. For this reason, it is called the universal genetic code.
the
have
been
a
code
over
small
for
billions
changes
has
genetic
code
a
specic
of
to
codons.
years
the
changed
it
little
most
is
genetic
so
found
In
amino
so
in
that
language.
some
c ases,
acid
not
organisms
one
instead.
surprising
code
and
p
below
were
awarded
in
1968
at
immediate
all
which
and
birds,
lasts
it
to
of
all
living
saw
really
this
the
knew
and
I
so
things
a
1.
I
we
were so
2.
understood
and
the
of
Life
that
the
are
three
has
been
there
in
some
organisms. It is
all
forms
of
life
still
speak
that
all
when
I
related.
3.
c ame in
nature
is
genetic
the
Why
did
such
a
same
the
very
real
universality
profound
eect
of
on
at
the
time?
What
are
the
implic ations
unity
of
Are
life,
there
to
scientists
other
c ausing
a
To
extent
in
fact
the
is
genetic
M arshall
of
the
and
examples
profound
and
very true: we
language.
of
change
to
have
recognition of the
other
scientic
in
code
Nirenberg and
people?
discoveries
attitudes?
squirrels and some
profound
think
are
with
use
others
everything about
ndings
bec ause
plants,
had
day.
code.
life on this planet use the
instructions
to
I
these
profound,
forms
genetic
all
universal had a terric
eect
the
on
4.
what
do
emotional
responses such as
me,
the
one
described
here support or run counter to
feeling of being
stereotypic al
representations
of
scientists?
u
l
f
x
t
a
garden
the
so
me.
but
the
one
Nirenberg,
Physiology or
i
related
on
time,
r
o
of
or
genetic
We’re
the
and
on
is
in
o
most
same
work
code
eect
the
M arshall
d
that
his
the
by
Prize
n
philosophic al
evolution
for
that
spoken
Nobel
U
nding
the
o
was
The
Thinking skills: Evaluating the role of languages in science
a
code
What
2.
For
are
the
benets
E
1.
scientists,
terminology
which
why
a
is
v
O
language
symbols.
ascribes
agreed
meanings to
3.
Esperanto
created
of
sharing
a
common
language?
a
viewed
the
Figure 15) an international language
Zamenhof
universal
second
language
and
understanding.
in
1887
.
would
What
He
hoped that
promote world
are the diculties in
standardization of
creating
as
(see
Ludwik
peace
is
is
by
a
new
language?
essential?
persist
24
64
y
code
genetic
the
C
words
Medicine
A
to
of
Thinking skills: Evaluating the role of emotions and attitudes in science
who
ATL
same
i
n
The
very
the
universal
one
v
ATL
few
the
changed
evolution
that
of
r
e
noteworthy
essentially
has
by
the
O
codons
diversifying
to
meaning
t
i
s
stop
exceptions
to
n
minor
changes
y
The
widely
today?
Why
does
Esperanto not
y
P
of communication. Many dierent versions of a genetic code could be devised
Molecules
flava
blanka
verda
griza
blua
nigra
P
ways
sugar
of
terminal
available
linkage
phosphate
unlinked.
This
nucleotide
the
is
to
one
end
C5
of
at
the
a
in
of
the
the
strand
the
other
bec ause
the
of
same
sugar
of
way:
the
next
same
way and the
DNA
or
strand
a
antiparallel
end
within
pentose
t
a
l
Figure 16
E
▴
v
O
ending
with a phospate
of
u
f
x
at the 3’ terminal
5’ terminal
orientated
ends
in
pentose
nucleotide.
terminal,
attached
r
o
pentose sugar
at
linked
the
is
RNA
c an
unlinked.
(c arbon atom number 3) in this sugar is
nucleotide
c alled the 5′
group
C3
another
of
two
all
i
phosphate
group
is
all
to
Figure 16.
bec ause
to
are
The
are
o
The
for
the
RNA
linked
n
This is the 3′
in
is
LHA
pentose
nucleotides
directionality.
shown
or
y
The
has
as
DNA
C
whole
distinguished
the
of
nucleotide
o
result,
strand
one
d
•
a
a
a
of
U
•
as
As
within
group
i
n
be
extinction
p
nucleotides
strand
and
Directionality of RNA and DNA
phosphate
nucleotide.
diversic ation
v
the
language
speciation?
r
e
A1.2.11
The
is
to
O
what
analogous
t
i
s
In
n
Colours
in Esperanto
4.
l
Figure 15
y
◂
purpura
y
bruna
e
oranĝa
s
s
roza
r
ruĝa
a
of
the
strand is
nucleotide the
sugar.
phosphate
at the 5’ terminal
strands
of DNA
3’ terminal
with a
ending
sugar
25
LHA
Unity
and
diversity
The
5’
directionality
of
RNA
and
DNA
aects
processes
c arried
out
by enzymes or
3’
ribozymes:
•
replication in which DNA polymerases and other enzymes make copies of DNA
•
transcription
in
which
RNA
polymerase
makes
an
RNA
copy of a DNA base
s
s
sequence
3’
5’
5’
3’
•
translation
acid
at
a
ribosome
sequence
of
a
with
an
RNA
base
sequence determining the amino
polypeptide.
e
direction of
Bec ause
of
their
directionality,
DNA
and
RNA
strands
and
nucleotides must
replic ation
r
5’
be
facing
in
the
correct
direction
for
them
to
t
the
active sites of enzymes and
3’
For
this
reason,
replic ation,
transcription
and
translation
Replic ation
happen
In
the
same
replic ation,
the
to
is
therefore 5′ to 3′
of
a
translation,
replic ation,
molecule
by
linking
along
of
is
this
therefore works in a 5′ to 3′
RNA
nucleotides
are
nucleotides. The 5′
sugar at the 3′
end
always
added to the 3′
phosphate
of
of
the
n
3’
DNA
the
the
of
the
growing
sequence
together.
molecule
C
i
n
5’
U
3’
c arries
acids
free
nucleotide is
polymer. DNA
The
free
nucleotide
polymer.
information
ribosome
towards the 3′
that
end.
for making
c arries out
Translation
direction.
Replic ation
3’
the
therefore 5′ to 3′
RNA
amino
of
the
added to the 3′ end of the
phosphate
end
of
growing
o
v
moves
always
the
p
polypeptide
translation
5’
are
of
y
In
r
e
like
a
nucleotides
nucleotides. The 5′
linked to the ribose sugar at the 3′
Transcription,
end
O
RNA
polymer
added to the 3′ end of the
phosphate
t
i
s
is
always
deoxyribose sugar at the 3′
transcription,
growing
are
nucleotides. The 5′
always
n
linked
nucleotides
of
y
polymer
In
•
DNA
growing
replic ation
•
direction.
l
•
in
growing
free
end
of
the
nucleotide
polymer.
DNA
is
growing polymer of
linked
replic ation
to
is
the
deoxyribose
therefore 5′ to 3′
Both of the strands in DNA are used as templates during replication. The two
transcription
in the same direction as the overall process of replication. On the other strand, it
i
Transcription
strands are antiparallel. On one strand, 5′ to 3′ assembly of a new strand moves
moves in the opposite direction. As a result, there are dierences in what happens
on the two template strands. These dierences are described in Topic D1.1.
Transcription
u
RNA nucleotides are always added to the 3′ end of the growing polymer of
nucleotides. The 5′ phosphate of the free nucleotide is linked to the ribose sugar at
l
a
E
v
O
f
x
t
a
Figure 18
r
o
▴
o
direction of
d
5’
the 3′ end of the growing polymer
. Transcription, like replication, is therefore 5′ to 3′
Only
one
of
transcript.
move
in
the
This
the
two
is
strands
always
same
the
direction
of
DNA
strand
as
the
is
used
that
as
allows
overall
a
template
the
process
for making an RNA
assembly
of
of
the
RNA
strand to
transcription.
Translation
A
molecule
of
RNA
c arries
the
sequence
information
for making a polypeptide
direction of
by
linking
amino
acids
together.
The
ribosome
that
c arries
out
translation
moves
translation
along
▴
26
Figure 19
Translation
to 3′
this
RNA
direction.
molecule
towards the 3′
end.
Translation
therefore works in a 5′
y
Figure 17
P
ribozymes.
▴
Molecules
LHA
A1.2.12
Purine-to-pyrimidine bonding as a
adenine
thymine
component of DNA helix stability
nitrogenous
•
Adenine
bases
and
in
DNA
guanine
are
are
in
two
purine
chemic al
bases
with
groups:
mole cules
that
have
two
s
s
The
rings
guanine
cytosine
of
•
atoms.
Cytosine
and
thymine
are
pyrimidine
with
purine
and
molecules
that
have only
e
bases
one ring of atoms.
guanine
pair
in
consequence,
helps
to
two
base
has
pairs
one
are
of
equal
one
width
pyrimidine
and
require
base.
the
As
same
between the two sugar–phosphate backbones in the double helix. This
make
a
the
DNA
of
DNA
stable
and
allows
any
sequence of bases in
thymine
Figure 20
DNA
electron
are
of
eukaryotes
microscope.
eight
approximately
DNA
the
Plants,
a
between
animals
and
and
their
molecule
nucleus
adjacent
other
DNA
is
is
of
The
may
preparing
eukaryotes
viewed using an
the
core
of
H1
also
to
have
bec ause
is
DNA
reinforces the binding
help
divide.
not
H1 histone
nucleosome
molecule is wound
in
the
There
nucleosomes.
it
a
dierent types of histone
DNA
nucleosomes.
“naked”
At
core.
c alled
H1
four
U
nuclei
when
protein
core.
when
packaging of
is
a
short
Bacteria
do
section of
not
C
DNA
protein
beads
each
structure.
this
nucleosome
of
nucleosome.
i
n
chromosomes
linker
around
histone
to
copies
disc-shaped
twice
a
p
additional
the
Two
is
nucleosome
o
of
a
string
v
An
up
a
Purine bases have two rings
pyrimidine bases have only one
y
make
proteins.
like
“bead”
r
e
together
histone
looks
E ach
n
▴
Structure of a nucleosome
and
The
adenine
O
t
i
s
A1.2.13
structure
molecule.
l
on
cytosine
y
genes
the
therefore
y
distance
DNA
P
a
base
r
E ach
30nm
fibre
have
associated with histones.
n
▴
Figure 21
Nucleosomes
o
d
Using molecular visualization soware: Visualizing nucleosomes
i
r
o
Molecular visualization soware can be used to analyse the
t
a
association between protein and DNA within a nucleosome.
1.
Visit
the
search
Rotate
“3D
that
like
the
that
twice
the
the
extends
22,
the
out
two
they
core.
from
150
bp
octamer
N-terminal
tail
that
each
tail
involved
the
protein.
in
regulating
of
core.
protein
core
with
the
negatively
by
protein has a
core.
DNA
wrapped
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from the histone
modic ation of this
gene
expression.
charged amino acids on the
▴
nucleosome
the
each
identied
E ach
projects
Chemic al
positively
copies
are
the
of
the
for
is
from
of
structure”.
around
core
Visualize
see
approximately
E
Note
extend
v
Note
this
to
Figure
a
the
In
association
charged DNA.
www.rcsb.org and
l
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protein.
nearly
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molecule
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the
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nucleosome
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Click
3.
5.
data
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f
x
2.
4.
protein
for
the
Suggest
how
they
play
a
Figure 22
role in
27
and
diversity
LHA
Unity
A1.2.14
Evidence from the Hershey–Chase
experiment for DNA as the genetic material
From
the
in
known
clear
late
that
of
these
viewed
amino
the
many
specicity
as
material
of
that
chromosomes
had
a
chemic al
protein
and
played a
nature.
DNA
but
it
It
was
was not
was the genetic material. Until the 1940s, most
more
likely
whereas
functions
function
convinced
composed
the
subunits,
specic
of
were
molecules
protein
acid
were
hereditary
were
of
c andidate,
DNA
proteins
considered
has
just
had
bec ause it contains 20
four
types
of
already
been
identied.
essential
for
nucleotide. In
r
addition,
scientists
that
e
dierent
and
chromosomes
which
biologists
and
1800s,
heredity
s
s
role
Variety
hereditary material.
l
genetic material. It has a coat composed entirely of protein, with DNA inside the coat.
n
y
In the 1950s, it was known that a virus can transform a host cell so that it produces viral
proteins; for this to happen, viral genes must have been injected into the host cell.
not
experiment,
contains
Hershey
phosphorus
phosphorus.
They
and
but
Chase
not
cultured
some
35
radioactive (
S)
group
in
a
bacterial
virus.
pellet.
of
the
cells,
Then
virus.
cells
were
28
It
transmission electron micrograph (TEM) of T2 viruses
cell surface,
radioactive (
to
the
E ach virus consists of a large DNA-
of a central sheath with several bres. The
and
instructs the host
the virus DNA is injected into the cell
to build
copies of the virus (blue, in cell)
P)
expected
contain
to
and
separate the non-genetic
culture
Chase
solution
the
to
concentrate
radioactive genetic
measured
the
radioactivity in
o
i
through the sheath.
blender
DNA
protein
Figure 24
Diagram
structure of the T2 virus
a tail composed
bres attach to the host
a
t
a
a
and
used
▴
(blue) bound to an Escherichia coli bacterium.
containing head
with
groups of bacteria with the two viruses.
u
l
v
E
Coloured
proteins with
32
DNA
n
U
d
r
o
f
x
O
Figure 23
contained
contained
centrifuged
Hershey
the pellet and the supernatant.
▴
they
they
Finally,
that
separate
C
i
n
component
The
viruses
proteins contain sulfur but
that
o
cells
of
the
v
the
of
infected
viruses
y
each
component
they
other
advantage of the fact that
while
p
For
Then
and
r
e
phosphorus.
sulfur
took
sulfur
O
their
DNA
t
i
s
In
illustrating the
y
P
Alfred Hershey and Martha Chase chose to use the T2 bacteriophage to identify the
Molecules
LHA
Data-based questions: The Hershey–Chase experiment
These
diagrams
show
the
process
of
the
Hershey–Chase
experiment.
35
s
s
radioactive protein (
35
T2 virus with
S)
35
virus
S
radioactivity (
in its protein coat
S)
in supernatant
bacterium
bacteria
e
r
of
the
experiment.
n
results
y
the
o
shows
U
C
26
p
r
e
Figure
v
i
n
Figure 25
O
t
i
s
bacterium
bacteria
▴
l
P)
virus
P in its DNA
y
P
y
32
radioactive DNA (
T2 virus with
32
32
radioactivity (
P)
in pellet
percentage of isotope in supernatant aer 8 minutes agitation
Figure 26
a
why
the
l
State
the
supernatant
genetic
v
Explain
a
material
E
Determine
5.
Discuss
the
the
32
P
and
a
should
pellet.
be
found
[2]
in
the
pellet
and
not
the
supernatant.
[2]
32
percentage of
4.
n
S
between
o
35
u
0%
Distinguish
i
20%
t
a
40%
O
3.
60%
r
o
%
2.
80%
f
x
ni epotosi fo
1.
d
tnatanrepus
▴
100%
P
that
remains
in
the
supernatant.
[1]
32
percentage of
evidence
that
DNA
P
that
is
the
is
spun
down
chemic al
into
which
the
pellet.
transforms
the
[2]
bacteria
into
infected
cells.
[3]
29
and
LHA
Unity
diversity
Experiments: Use of radioisotopes as research tools
Two
if
atoms
they
of
properties
protons
an
isotopes
number
in
atom
their
are
have
same
dierent
of
the
same element
protons
atomic
but
dierent
nucleus.
by
the
The
chemic al
levels
of
properties.
nuclear
atomic
nuclei
radiation
as
be
they
repulsive
electric
release
assume
more
force.
energy
stable
in
forms.
has
16protons
and
S
has
to biological systems, these unstable variants of common
16neutrons and is stable
an
positively
electric al
19neutrons
charged
force.
and
However,
and
repel
at
is
atomic elements can be traced as they move through
unstable.
biological systems. György Hevesy won the Nobel Prize in
Chemistry in 1943 for pioneering the use of radioisotopes
each other
in biological research. In 1923, Hevesy published the
very close
l
212
distances
attract
each
bec ause
the
protons
attractive
and
a
nuclear
neutrons
nuclear
force
rst study using radioactive
force.
are
Pb as a tracer to follow the
absorption and translocation of minerals in plants.
c annot
A1.2.15
O
t
i
s
unstable
of
with
n
combinations
other
y
Certain
they
Charga ’
s data on the relative
y
r
e
amounts of pyrimidine and purine bases
p
across diverse life forms
v
Before the structure of DNA was known, scientists hypothesized that it would
o
i
n
contain a repeating sequence of the four bases. This would mean the four
nucleotides occurred in equal numbers. The tetranucleotide hypothesis was
C
formulated in 1910. However
, if DNA had a tetranucleotide structure, it would not be
able to vary enough to be the genetic material. This is why scientists thought it was
U
more likely that the 20 amino acids making up proteins were the genetic material.
test
the
samples
is
range
shown
i
Source
of
DNA
of
in
hypothesis,
species
to
Erwin
nd
their
Charga
and
others
analysed DNA
nucleotide composition. A portion
Table 2.
Guanine
Cytosine
M ammal
31.0
19.1
18.4
31.5
C attle
M ammal
28.7
22.2
22.0
27.2
S almon
Fish
29.7
20.8
20.4
29.1
32.1
u
l
a
E
v
O
f
x
Adenine
Human
Sea
urchin
Group
Thymine
Invertebrate
32.8
17.7
17.4
Wheat
Plant
27
.3
22.7
22.8
27.1
Yeast
Fungus
31.3
18.7
17.1
32.9
Mycobacterium
Bacterium
15.1
34.9
35.4
14.6
tuberculosis
Bacteriophage
Polio
▴
30
data
a
o
their
tetranucleotide
from
t
a
r
o
d
of
n
To
virus
Table 2
T2
Virus
32.6
18.2
16.6
32.6
Virus
30.4
25.4
19.5
0.0
y
with
are
and
radiation
P
Protons
16protons
result,
research tool. When introduced in minuscule quantities
For
35
but
This
r
S
a
form of
detected.
32
example,
As
the
For scientists in the 1950s, radioisotopes were a valuable
However,
stability.
the
unstable
c an
numbers of
neutrons—so isotopes of an
chemic al
counterbalance
e
the
of
determined
electrons—not
have
may
same
neutrons
of
and
element
dierent
the
s
s
numbers
they
are
have
Molecules
LHA
Data-based questions: Charga ’
s data
Use
the
1.
Compare the base composition of
data
in
Table
of
the
(a
to
answer
the
4.
following questions.
shown
in
Table
2.
C alculate
for
the
base
ratio A
+
G / T
+
of
between the amounts of bases
and
prokaryotes in terms of the
DNA.
C,
Mycobacterium tuberculosis.
how
these
[2]
results
falsify
the
tetranucleotide
hypothesis.
for humans
Show
Explain
[2]
your
6.
working.
Suggest
reasons
for
the
e
and
ratios
[2]
5.
2.
the
eukaryotes
structure
prokaryote) with the base composition
eukaryotes
Explain
in
Mycobacterium
s
s
tuberculosis
2
dierence in the base
[2]
3.
Ev a l u a t e
claim
a re
th a t
the
e qu a l
a re
the
D NA
and
th e
of
of
amounts
polio
e u k a r yo te s
adenine
of
viruses.
and
guanine
equal.
[2 ]
patterns
have
inductive
there
about
we
to
the
have
reasoning.
no
the
The
observed.
world
observed
that
of
all
This
is
that the four DNA bases occur in equal amounts. The
known
problem with induction is
the
generalization;
natural
not
been
certainty
Charga’
s analysis falsied the tetranucleotide hypothesis
draw conclusions about
which
is
we
there
anything
c an be certain when
c ases?
n
U
makes
RNA
the
c.
Compare
the
of
role
and
enzymes
of
RNA
contrast
the
a
the
E
Explain
in
role
of
been
and
the
the
cellular
the
c atalyst.
structure
in
properties
between
function
rst genetic material,
of
processes
of
DNA
of
and
RNA.
(A1.2.7)
properties?
glucose
reactions
the
associated with
(A2.1.6)
emergent
condensation
relationship
structure
a
the
result
between
v
Outline
(B1.1.2)
as
l
O
Distinguish
b.
the
role
polymerization
a.
c.
have
u
f
x
Outline
c an
to
(D1.1.8)
b.
How
likely
i
Explain
heredity.
2.
more
DNA?
t
a
a.
than
r
o
rather
d
What
o
Linking questions
1.
protein is the genetic material. The work of these scientists
provided certainty of what was not the case.
unobserved things will
thus,
Hershey and Chase experiment falsied the hypothesis that
C
conform
is
yet
to
i
n
that
generalizations. These
used
not
certain of what is not the case, by nding a counter-example.
then
form
Falsiability is the idea that in science we can at least be
gathered
observations,
o
as
that
evidence
make
v
things
are
on
Scientists
p
generalizations
and
based
O
detect
are
y
senses.
the
r
e
claims
through
n
y
t
i
s
F alsic ation: The nature of the genetic material
Knowledge
[2]
l
cytosine
in
a mo u n ts
y
thy mi n e
and
th e
p ro k a r yo t e s ,
P
and
r
composition of bacteriophage T2 and the
in
and
starch.
(B1.1.5)
forming nucleic acids.
sequence of amino acids and
proteins.
(B1.2.10)
31
Unity
and
diversity
TOK
How can we know that current knowledge
s
s
is an improvement on past knowledge?
Levene
established
DNA;
the
he
1928
existence of the sugar–phosphate backbone
acids;
and
Figure
signic ant contributions to the
understanding of nucleic acids. He
he
identied
coined
the
name
rough
The
deoxyribose as the sugar in
2
strain
heat-killed
nucleotide.
stated
that
DNA
of
the
was
four
known
DNA
as
nucleotides
the
of
not
c ause
the
mixing
the
living
version
of
c ause
death.
the
death
smooth
hypothesis.
death
of
strain
the
did
the
heat-killed
the
non-deadly
stacked
tetranucleotide
c ause
the
c arried out in
Injecting mice with the
of
the
mice.
mice. The
not
c ause
smooth
rough
version
version
Somehow the genetic material of the
t
i
s
This
version
However,
did
did
experiment
n
units
did
together.
virus
an
viruses.
was made up of
with
repeating
a
strain
of
l
incorrectly
of
results
involving
y
also
the
Griths
smooth
death.
He
shows
by
heat-killed version was able to transform the living non-
hypothesis
led
Levene to state that DNA could not be
O
This
virulent version to the virulent version. In 1944, Avery,
the
hereditary
material,
not
suciently
variable
bec ause
the
tetranucleotides
were
McC arty and McCleod took the experiment further. From
to
be
the
basis
of
the
code
for the
Grith’
s experiment, they were aware that dead virulent
diversity
of
life
that
exists.
This
idea
was widely
y
r
e
tremendous
strains of bacteria could transform living strains to make them
accepted.
Instead,
proteins
hereditary
material,
were
thought
to
form the
virulent. In dierent experiments, they attempted to establish
they
were
known
to
have
great
p
bec ause
what the transforming material was by adding enzymes that
variety
of
structure.
o
2
O
n
N
O
O
O
O–
O
P
O
u
l
O
P
O
O
O
N
a
2
H
N
O
N
HN
O
dTMP
N
N
E
v
O
f
x
t
a
O
i
O
O
r
o
d
o
O
O
P
P
N
N
U
O
N
O
N
Figure 1
dCMP
O
N
HN
NH
O
O
O
▴
32
C
HN
i
n
2
dGMP
v
would break down dierent chemicals to determine if they
dAMP
A tetranucleotide molecule
y
nucleic
made
our
P
in
of
r
development
e
Phoebus
Molecules
could interfere with the transformation process. They added
evidence
RNA ase, proteinase and DNA ase. The DNA ase was able to
was
interfere with the transformation process. This established
support
to
establish
incorrect.
the
The
theory
that
weight
that
the
of
DNA
tetranucleotide
evidence
was
the
was
hypothesis
beginning
genetic
to
material.
that the hereditary material was DNA.
The
1950,
Erwin
composition
found
that
not
of
equal
of
the
cells
to
from
amount
guanine
the
analysed
of
(G),
a
number
adenine
and
amount
the
of
the
nucleotide
of
(A)
dierent
was
amount
cytosine
(C).
not
of
species.
This
was
and
Chase
that
DNA
combination
of
to
the
establish
(T)
was
upon
equal
thymine
He
Hershey
convincingly
that
past
the
the
experiment
three
new
in
1952
showed
was the genetic material. The
experiments
knowledge
was enough to
was
an
improvement
knowledge.
sucient
r
e
amount
Charga
s
s
In
l
n
O
y
p
o
C
n
McCleod
and
McC arty were aware that
i
transform
non-virulent
heat-killed virulent bacteria
bacteria.
They worked to identify the
t
a
r
o
could
o
Avery,
a chemic al that
y
P
y
t
i
s
r
e
v
i
n
U
Figure 2
contained
d
▴
transforming chemic al was
u
l
f
x
a
E
v
O
33
Unity
and
diversity
End of chapter questions
1.
Table
1
compares
the
physic al
Water
4.18 J°C
and
1
1.01 J°C
1
g
27°C
1
1
0.028 W m
1
K
16°C
e
K
0.6 W m
air.
Condition
1
g
1
Thermal
water
Air
1
heat
of
s
s
Property
Specic
properties
conductivity
r
3
3
1000 kg m
1.225 kg m
15°C;
Buoyancy
650 N
0.8 N
Assuming
sea
level
a
body
of
volume
3
0.0664 m
18.6 × 10
Pa·s
27°C
Table 1
heat
takes
change
to
refers
to
the
the
amount
temperature
of
of
d.
energy it
one
Viscosity
gram of
i.
substance
is
C alculate
by 1°C.
water
which
substance
(air
or
water)
is
more
ii.
resistant
to
changes
in
temperature.
[1]
the
Identify
the
resistance
Identify
the
habitat
that
would
have
a
more
e.
thermal
Thermal
conductivity
the
medium
the
air.
a
seal
possible
air
would
or
a
bladders
the
be
of
more
surrounding
upward
counteract
the
would
swimming
having
the
of
counteract
Suggest
a
to
density
E
v
O
to
of
of
object.
organism
energy
it
i
the
the
that
l
Which
of
medium
they
bird
to
of
was
results
more
gravity: a
[1]
[2]
▴
34
study
the
[1]
Figure 1
flying
bird
are
and
c arried
flow.
of
air.
offers
the
[2]
greater
[1]
the
to
for
out
shown
a
to
air
compares the
and
swimming
exposure
heat
stress
This
survive
is
an
model
to
that
c an
and
air
is
water as a
seal.
[4]
low
tide,
affect the ability
human
thermal
Figure 2.
at
characteristic
reproduce.
important
subsistence
in
that
of
adapted to a marine
during
to
Lottia gigantea
are
that
environment.
and
resisting
by which the viscosity of
viscosity
representation
organisms
birds
area
disadvantages
animals
terrestrial
shore
between fish
buoyancy.
a
However,
The limpet
for
and
unit
movement.
visual
subjected
intertidal
force
flight?
relationship
and
the
gravity. It is
expend
effects
in
of
medium and the
have
the
are
u
of
above
measure
a
f
x
function
volume
ii.
a
which
for
intertidal
t
a
by
in
Most
existence.
[2]
organisms to sustain their internal
r
o
is
provided
heat.
2.
o
medium
habitat
degree to
exceeds the thermal
d
the
for
of
the
a
advantages
n
water
difficult
of
by which the thermal
of
Identify
measure
conductor
factor
of
Buoyancy
i.
a
a
conductivity
medium.
a
is
conductivity
temperatures
c.
is
[3]
U
C alculate
ii.
this.
Construct
C
which
i.
discuss the
i
n
b.
of
and
the
medium
to
o
implic ations
environment
v
stable
factor
p
ii.
per
y
Identify
force
exceeds
r
e
i.
the
O
Specific
t
i
s
a.
n
y
▴
−6
Pa·s
0.7978 × 10
l
−3
Viscosity
at 15°C
food
source
harvesters. A
stress. Some of
y
P
Density
Molecules
A
40
C
40
minimum l et hal te mp er atur e
air
35
30
30
25
25
20
20
15
15
0
minimum l et hal te mp er atur e
D
40
water
20
15
15
10
10
5
5
500
1000
1500
0
2000
Exp
Biol
(2006)
209
(13):
2420–2431
over time between air (graph C) and water
(graph D).
lethal
over
to
limpets
A
and
time
in
(graph
Graph
two
low
level
water
line.
Deduce,
which
a
0.5 m
and
1.5 m
reason,
which
mortality
rate
loc ation
due
to
B).
which
[1]
temperature
the
above
position.
Deduce
the
above
u
f
x
ii.
with
graph
2000
a.
it
is
adenine
19.5%
and
30.4%, guanine 25.4%,
thymine
0.0%
From this data, what is the evidence that the polio
virus is
i.
an
RNA
virus
ii.
single-stranded
[1]
average
the
i
line
and
viewed as being
graph
[1]
average
t
a
water
r
o
level
A
is
represent
areas:
low
i.
B
that
that
cytosine
n
Graph
temperature
o
c.
the
U
Identify
d
b.
1500
da ys
Analysis of the base composition of the polio virus
shows
[2]
1000
o
3.
Compare and contrast the temperature variations
C
i
n
a.
J
v
Source:
Figure 2
500
p
da ys
y
r
e
0
0
n
25
20
O
30
25
y
30
t
i
s
35
l
yd ob
35
0
▴
0
r
40
5
P
B
10
e
5
y
C° / eutarepmet
C° / eutarepmet
10
s
s
35
represents
[2]
results in a higher
thermal
stress.
[1]
l
a
E
v
O
35
Unity
and
A
s
s
d i v e rs i t y
e
r
2
Cells
l
y
P
n
y
Common ancestry has given living organisms many shared
features while evolution has resulted in the rich biodiversity of
The fundamental unit
p
Most
y
cell theory.
All cells come from
These are the two main propositions of the
r
e
pre-existing cells.
of life is the cell.
O
t
i
s
life on Earth.
living organisms are single cells and most of the
v
biomass on E arth is formed
from
single-celled
organisms.
o
i
n
Even complex multicellular organisms begin their life cycles
C
as single cells:
the whole organism
is generated
by cell
divisions from a single cell. This cell includes the machinery
U
to gather raw materials from
n
these materials to construct
the environment and to use
a new cell in its own image,
All cells store their hereditary information using the same
i
linear chemic al code:
DNA.
The genetic code is described
as universal bec ause the same code is used
across nearly all
forms of life.
u
l
a
E
v
O
f
x
t
a
r
o
d
o
complete with a new copy of its hereditary information.
All cells function as biochemical “factories”, utilizing the same
basic molecular building blocks. All cells use proteins called
enzymes as catalysts. Each protein is coded for by a specic
gene or set of genes. All cells copy their hereditary information
through templated polymerization, transcribing portions of
their hereditary information into the same intermediary form
(RNA). All cells translate RNA into protein in the same way.
A2.1
Origins of cells
What plausible hypothesis could account for the origin of life?
s
s
Is there a consensus view of the conditions that existed on the
pre-biotic earth? If there is one, what were these conditions? How
r
did living things cause some of the changes to conditions on the
early earth?
e
do they dier from the conditions that exist today? In what ways
showing concentric layers of rock (white) and coal-like organic
l
material (black). The layers of organic material were laid down by
Figure 1
O
▴
t
i
s
be found? Do they oer conclusive proof of life?
n
y
cyanobacteria (blue-green algae). How far back can such layers
y
P
Figure 1 shows a cross-section through a fossilized stromatolite,
Cross-section through a fossilized stromatolite
y
r
e
What intermediate stages could there have been between non-living matter and the rst
living cells?
p
is not known when or where life on Earth began. However, some
i
n
of the earliest habitable environments may have been submarine
of microbial life have been found in precipitates associated with
seaoor hydrothermal vents. For the rst living cells to have
U
C
hydrothermal vents. The oldest known fossils providing evidence
o
v
Figure 2 shows a “white smoker” which is a hydrothermal vent. It
appeared, catalysis would have to have occurred. What were
n
some of the some of the necessary developments that would
need to have occurred for the rst life to emerge? How might
o
d
hydrothermal events provided the correct conditions for this
emergence?
early
AHL
E arth
and
compounds
Cells
as
the
smallest
Challenge
A2.1.4
Evidence
A2.1.5
Spontaneous
for
bilayers
RNA
A2.1.7
Evidence
as
a
the
origin
A2.1.8
Approaches
for
a
last
used
of
the
of
formation
presumed
E
A2.1.6
units
explaining
v
spheric al
of
a
O
A2.1.3
l
A2.1.2
i
on
Figure 2
A "white smoker" hydrothermal vent
only
u
Conditions
t
a
r
o
f
x
A2.1.1
▴
the
pre-biotic
self-sustaining
formation
of
c arbon
life
spontaneous origin of cells
c arbon compounds
of
vesicles
by
coalescence
of
fatty acids into
rst genetic material
universal common ancestor
to
estimate
dates
of
the
rst living cells and the last
universal common ancestor
A2.1.9 Evidence for the evolution of the last universal common ancestor in the
vicinity of hydrothermal vents
37
and
diversity
LHA
Unity
A2.1.1
Conditions on early Earth and the
pre-biotic formation of c arbon compounds
The Sun formed about 4,500 million years ago, two-thirds of the way through the
s
s
time that our Universe has existed. The Earth formed soon aerwards, as gravity
caused gas and dust in the early solar system to come together
. At rst, there was no
life—there was a pre-biotic period in the Earth’
s development. Gases accumulated
e
but in very dierent concentrations to those in today’
s atmosphere. Evidence from
ancient rocks has helped scientists to describe the pre-biotic atmosphere:
There
Methane
meteorite
bec ause
with
were
iron
higher
to
it
reacted with other elements.
produce
than
today
iron
due
concentrations
were
also
probably
volc anoes.
higher
C arbon
higher
to
aerosol
rainfall
have
hydrothermal
droplets
of
haze.
into
water
was
emitting
and
raised
temperatures.
have
on
asteroid
formed
the
in
UV
the
or
oceans.
creating
layer that
by absorbing
this
have
layer,
more
penetrated
radiation
energy
There
may
lightning
other
also
on
today
variety
provides
chemic al
have
early
chemic al
possible
a
and
for
may
of
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processes.
have
c arbon
environments such as hot springs on
would
a
ozone
us
estimates
11.
surface. UV is a high-
of
result,
C arbon
creating
compounds
seas,
form
more
a
w as;
pH
bec ause of the lack
would
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not
As
to
Without
activation
are
specialized
the
atmosphere,
c arbon
lakes
in
that
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5
radiation (UV) would not
oxygen.
triggering
reactions
pre-biotic
oce ans
pH
existed,
been
exist as a
the
protects
reactions.
orbits our nearest
vents
in
These
pools,
Sun
comet
stratospheric
solar
dierences,
of
f rom
ultraviolet
of
spontaneously
may
y
a
E
in
or
pH
have
This planet
these
energy,
will
currently
the
compounds
land
less
range
for life to evolve on this planet?
of
occurred
are
o
C
l
Bec ause
the
n
are needed
p
r
e
water,
now.
methane
Estimates of temperatures on pre-biotic
in the habitable zone where water could
liquid
have
the
although
impacts
o
i
from
and
to
are
and
20%
v
i
n
apart
v
O
38
t
a
conditions,
dioxide
they
emissions
Earth vary widely. It is also uncertain what
U
What
u
liquid.
likely
than
to
greenhouse gases
energy
An artist’s impression of conditions on Proxima b.
are
due
heat-trapping
The
d
r
o
f
x
Figure 3
volc anic
O
t
i
s
been
neighbouring star Proxima Centauri,
intense
bombardment.
Temperatures
▴
oxide.
to
n
dioxide
oxygen
y
from
of
reacted
concentrations
and
C arbon
traces
oxygen
l
activity
•
only
compounds
what
then
“soup”
of
has
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have
may
have
c alled
been
an
formed
organic
deposited
c arbon compounds.
by
y
•
were
example,
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For
r
•
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is
unsure
much
which
many
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and
living
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in
the
bases
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atmosphere
against
organisms
c aused
UV.
had
probably
may
life—such
part
of
zero
as
DNA
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time,
on
have
c arboxylic
and
they
pre-biotic
increased
They
oxygen
levels
increased,
greenhouse
made
it
from
also
eect
non-living
impossible
for
scientists
are
However,
aldehydes, amino
possibilities.
c aused enormous changes to
organisms
20%.
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all
so
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acids,
RNA—are
to
evolved
E arth
spontaneously
life
the
reduced
an
was
concentration
c arbon
ozone
layer
reduced.
It
of
dioxide
oxygen
to
very
formed, giving
is
ironic that once
r
living
had
As
of
are
O ver
from
concentrations.
protection
blocks
that
organisms
on
conditions
matter, the changes that they
to
evolve again.
e
low
building
the
about
compounds
s
s
Once
the
uncertainty
c arbon
LHA
There
l
S aturn’s
in
largest
make
Titan’
s
up
moon.
more
atmosphere
G as
The
than
due
atmosphere
1%
to
of
ethane,
Titan
reasons
the
for
the
on
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There
is
a
Table
thick
hydroc arbons.
1
shows
orange
n
dene
as
that
nutrition
maintain
a
what
crying
life
and
life,
is.
a
to
o
to
(such
required
those
Titan.
▴
Figure 4
Image of Titan taken by NASA’s C assini spacecra
t
a
recognize
v
O
life”
to
easy
l
so
not
It
u
easy
[5]
[5]
i
d
r
o
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x
is
atmospheres
to
and
Cells as the smallest units of
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not
similar
E arth
atmospheres being so
dierent?
A2.1.2
other
the
o
between
Titan?
the
and
of
C
are
dierences
i
n
What
the
and
U
2.
are
processes
y
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propene
by
surface
p
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e
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it
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Table 1
of
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methane
▴
around
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nitrogen
oxygen
It
the
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smog
that
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is
gases
t
i
s
the
y
Titan
y
P
Data-based questions: Titan’s atmosphere
baby
is
is
respiration).
life
alive
common
while
to
use
However,
a
a
lump
of
rock is not. It is
checklist of “functions
these
are
just
processes
itself.
A key dierence between living and non-living things is that living things use
E
energy to keep themselves in a highly ordered state. They are self-sustaining. This
highly ordered state would be extremely dicult to achieve starting with non-
living components. A complex device such as a smartphone can be assembled
from individual components and work when it is switched on. In contrast, living
organisms are just too complex. Currently, the only way to produce a living thing is
by reproducing an existing one. Passing on the ability to maintain a highly ordered
state to ospring is a second key dierence between living and non-living things.
39
and
diversity
LHA
Unity
An
individual
one
cell
organism
(unicellular)
multicellular
or
organism
is
certainly
many
is
cells
alive,
or
alive.
Living
organisms
(multicellular).
just
the
whole
To
may
decide
organism,
be
composed of
whether
we
c an
each cell in a
look
at
various
types of evidence:
Individual
•
Some
cells
cells
clearly
in
a
dead,
use
to
multicellular
for
c an
divide
•
Cells
c an
be
been
kept
to
organism
hair
produce
taken
from
cultures
the
since
cells
a
highly
may
or
ordered
stop
cells
in
doing
the
state.
this.
outer
These
cells
layers of skin.
more cells.
body
and
cultured.
For
example,
1951.
are
e
Cells
example,
maintain
r
•
in
energy
s
s
•
HeL a
cells
have
components
are
not
self-sustaining.
For
that
reason,
the
smallest
units
of
self-sustaining
life.
electron micrograph have the smallest
genome (473 genes) of any self-replic ating
which have base
A2.1.3
Challenge of explaining the
sequences found in Mycoplasma mycoides,
was transplanted into a cell of Mycoplasma
been
According
This pared-down bacterium,
to
from
the
theory
non-living
of
to study the roles of genes in cells. The
by
Louis
currently
Evidence
was
in
chickens
pre-existing
from
it
some
and
cell.
frogs.
This
and
gained
He
biologists
Robert
discovered
principle
remarkable
other
from
U
C
a
i
n
cells
natural cell?
Pasteur
also
Is this an articial cell or a modied
generation,
o
false.
known.
v
Experiments
function of 149 of the genes is not
spontaneous
matter.
bec ame
deductions
living
p
formed
developed in 2016, enables scientists
y
removed.
spontaneous origin of cells
r
e
capricolum whose own DNA had
considered to
O
An articial chromosome
containing these genes,
are
t
i
s
organism.
cells
n
be
y
The bacteria in this sc anning
l
cell
Figure 5
c an
that
an
be
showed
Remak’s
every
organisms
that
this
c an be
claim
was
observational studies of
cell
essential
is
part
formed
of
the
by division of
cell
theory and
made.
Consider the trillions of cells in your body. Each one was formed by division of
n
a pre-existing body cell, starting with a zygote produced when one sperm from
your father fused with an egg from your mother. The sperm and egg cells were
i
through many generations of human ancestry. If you accept that humans evolved
from pre-existing ancestral species, you can trace the origins of your cells back
through vast numbers of generations over thousands of millions of years of life.
life
u
generations,
they
l
a
E
v
O
f
x
However,
have
has
you
travelled
not
from
developed
from
non-living
how
by
means?
natural
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argued
there
the
existed
eventually
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question:
It
always
must
to
was
rst
a
could
that
cells
series
cells
of
a
the
too
more
to
you
keep
cells
deduction
a
a
are
going
to
have
universe,
cell
arisen
over
These
the
as
have
stages
feasible.
in
This
complex
complex
If
earliest
else
material.
as
intermediate
becomes
E arth.
somewhere
structure
are
on
reach
arise
by
long
back
these
leads
through the
existed.
to
Unless
rst cells must
a
very dicult
from non-living material
evolution.
period
of
developments
However, if
time,
evolution of
required
for the
origin of cells:
•
c atalysis—to
•
self-assembly—c arbon
form
40
o
in your parents’ bodies back to the zygote from which they developed—and so on
t
a
r
o
d
produced by cell division in your parents. You can trace the origins of all the cells
give
polymers
control
over
which
compounds
chemic al
such
as
reactions occur
amino
acids
must
assemble to
y
P
The evidence is strong enough for us to regard cells as living. However, individual
▴
Cells
compartmentalization—a
•
self-replic ation
successful
There
are
of
membrane
molecules—as
a
must
basis
LHA
•
develop to enclose cell contents
for
inheritance
and
the
persistence of
variants.
hypotheses
for
how
each
development
could
have
occurred.
s
s
F alsic ation: The origin of the rst cells
rst
the
conditions
were
dierent.
found.
conditions
the
on
of
and
Other
to
test
billions
most
found
to
of
about
of
specimens
it
is
not
possible
existed.
the
methods
fossils of the
crystals. Scientists
but
have
hypotheses
years ago
ancient
be
E arth
would
hypotheses
unscientic.
the
pre-biotic
that
hypotheses and
dicult
Well-preserved
Some
conditions
that
very
happened
re-analysed
mean
therefore
very
be
this
including
is
origin
testing
of
cells
c an
be
are
used.
▴
For
example,
the
genomes
of
living
organisms
contain
Figure 6
3.77 billion year old
vast amounts of data
iron rock from
one
approach
is
to
examine
this
data
for
he
the
of
c arbon
made,
hypothesis
the
early
simulate
a
the
week,
was
indeed
This
showed
on
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dark
E
had
been
that
before
apparatus
the
and
water
A
c arbon
in
to
been
variety
some
produced,
of
including
possible
for
life
had
evolved,
as
of
for
a
more
They
structures visible could
be the result of
metamorphosis of sedimentary rocks
In
variety
on
an
dioxide
on
a
mixture
substances
from
which
experimentally
a
water
electric al
vapour to
discharges
produced, then the
water.
the
water
variety
than
20
of
turned
pink.
Aer
c arbon compounds
dierent amino acids.
compounds
long
the
conditions
tested
added
used
c arbon
as
acts
there are signs
ve-litre ask, they
substances
day,
that
c arbon
that
Others believe that the
mixture of gases they thought
then
the
life.
a
hypothesis
materials
a
of
which
organic
was
In
origin
in
light
of
the
Urey.
boiling
showed
was
pre-biotic
ask,
cooled
ask
it
simulated
Harold
atmosphere.
running
Analysis
this
vapour,
ultraviolet
vast
the
soup”
based
compounds
and
another
the
on
dilute
water
ammonia—the
condenser
had
red.
of
Miller
pre-biotic
returned
experiment
it
a
article
He
“when
apparently
a
Aer
of
boiling
was
origin
hydrogen
lightning.
condensate
and
Stanley
v
O
to
by
the
by
representative
mixture
that:
ammonia,
l
the
for
1950s
methane,
formed.
contained
u
was
sugars
an
“hot
up”.
f
x
mixed
and
a
i
in
claimed
dioxide
as
t
a
This
H aldane
built
have
atmosphere
including
are
could
wrote
ocean
r
o
proteins
the
c arbon
H aldane
o
are
that
ammonia.
water,
J.B.S.
pre-biotic
d
of
the
compounds
assumption
and
biologist
described
n
1929,
it,
U
In
C
i
n
compounds
of life in this rock.
p
the origin of c arbon
Some scientists claim
o
Evidence for
v
A2.1.4
banded
Isua in western Greenland.
information about the origins of
rst cells.
y
the
r
e
and
n
not
to
been
model
do
bec ause
it
O
and
have
certainty
diculties
untestable
E arth
science,
t
i
s
These
to
with
cells,
unlikely
fossils
attempted
replic ate
on
are
of
in
Unfortunately,
l
have
as
claims
y
described
to
origin
protocells
that
testable.
y
when
to
be
P
relating
understand
must
r
theories,
e
Biologists
to
conditions
form
in
the
spontaneously
Miller–Urey
accurately enough.
41
and
diversity
LHA
Unity
ammonia
)
(NH
water vapour
3
electrode
)
methane (CH
4
hydrogen
s
s
(H
)
2
e
condenser
r
l
n
y
cooled water containing
y
chemical analysis
p
Miller and
O
t
i
s
Figure 7
Urey’s apparatus
o
v
i
n
A2.1.5
sample taken for
r
e
▴
organic compounds
Spontaneous formation of vesicles
C
by coalescence of fatty acids into spheric al
Figure 8
Phospholipids naturally
U
▴
bilayers
form
spheric al bilayers in water, with the
bilayer and
from the
the hydrophobic tails (green)
are
common
exosomes.
membrane
a
phospholipid
it
is
polar.
more
The
u
When
l
a
E
v
O
f
x
hydrophilic
The
hydrophobic
these
the
If
basis
of
c arbon
into
the
42
Figure 9
Butterfat
droplets
is
water,
heads
face
or
and
into
been
played
to
non-polar
is
outwards
inwards,
away
form
a
a
(two
membrane.
produce
part
water
substances
parts
in
also
composed
attracted
of
in
the
to
early
hydrophilic
water.
A
are
very
vesicles,
evolution of cells.
phospholipids.
(the
hydrophobic
than
They
extracellular
tails).
One end of
head)
These
bec ause
tails
are
molecule with both
c alled amphipathic.
phospholipids
other
so
naturally
assemble
into
they
in
with
from
stable
out
amphipathic
on
vesicles
and
hydrophobic
own
mainly
cells
are
water.
contact
Experiments
spheric al
structures;
bilayers.
water. The
have
such
shown that
structures
are
vesicles.
bilayers
have
is
face
compounds
their
is
spontaneously
phospholipids
of
enclosed
Some
vesicles
hydrophobic
tails
bilayers
uid,
probably
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with
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of
cells.
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molecule
to
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molecules
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of
i
The
droplets
o
c alled
small
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t
a
r
o
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forming the core
Vesicles
n
hydrophilic heads (blue) facing out
pre-biotic
would
of
these
membrane
internal
chemistry,
cell-like
even
very
likely
spheric al
core.
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dierent
though
molecules
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they
a
they
have
were
would
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part
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from
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not
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the
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self-assembled
Movement of polar
would
vesicles
were
of
have
have
been
limited
could
have
developed
by
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proper cells.
y
P
cold
water in
Cells
LHA
A2.1.6
RNA as a presumed rst genetic
material
Living
organisms
replic ate
However,
RNA
as
Some
to
make
have
DNA
virus
a
to
using
DNA
Living
cells
of
the
molecules
process
c atalyst
bec ause
precise
it
c an
It
stability
or
of
the
is
form
interactions
less
bec ause
accurate
much
be
an
have
proteins
complex
in
cells
to
of
in
two
the
a
been
may
have
to
enc apsulated
that
such
on
pre-biotic
by
a
a
to
be
structures
The
molecules.
bonds
which
how
with
c atalysed
core of the
Together,
between amino acids.
polypeptide.
RNA
structures
c an act as
that
more
self-replic ating
1.
grow
and
▴
Figure
10
dimensional
c an
Protocells
and
ribozyme
RNA
c an
shapes,
which
has
as
form
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two
complex
this
three-
hammerhead
loops
and
three
helices
divide.
with
(lower
(upper
a.
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could
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molecules.
model
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three-dimensional
u
f
x
existed
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few
organism with
act
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protocells
a
n
to
equivalent
only
found
enclosed in a phospholipid
used
all
only
biologic al cells or components of cellular
organization
thought
living
enzymes,
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peptide
produce
other
a
t
a
are
the
with
o
compartment
in
enough
have
polypeptides
of
of
i
a
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than
virus
example,
polymerase
advantage in helping
were
d
complex
is
a
the
been benecial.
thousands
was
complex
r
o
protocell
membrane.
in
before genes
(for
more important so a change to
Data-based questions: Protocells
A
used
material
However,
much
composed
with
rate,
matter
even
been
is
that
times
have
genetic
system.
formation
many
much
may
processes
of
is
not
even
structure
their
mutation
would
thought
ribosome
repeated
rate.
immune
synthesis
c atalyse
does
could
as
U
undergo
is
same
p
subunit
the
high
sequence
material
was
number
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the
o
a
small
in
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it
RNA
RNA
i
n
these
a
very
hundreds
time
evolution,
c atalyst.
v
RNA.
large
host’s
that
with
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genetic
three-dimensional
However,
by
one
a
base
genetic
produce
At
a
in
y
whose
the
as
phase
information
r
e
proteins.
have
DNA.
the
genes,
as
theory
Viruses
reproduction
evade
of
act
earlier
store
O
thousands
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the
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high
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c atalysts.
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and
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it
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need enzymes.
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genes
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copies
and
RNA
enzymes
y
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genes!
use
organisms
l
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need
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considered to be non-living) use RNA as their genetic
evolved.
coronaviruses)
of
ospring,
material.
self-replic ating
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they
genetic
made
to
r
of
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genes
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made
it
have
pass
enzymes,
been
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material.
and
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way
may
today
DNA
s
s
To
curve
curve
in
Compare
RNA
were
unlabelled
in
radioactively
vesicles
that
labelled
contained
Figure 11) or did not contain RNA
Figure 11).
and
contrast changes in the size of
the
radioactively
are
mixed
with
labelled
protocells when they
vesicles containing RNA and not
l
O
containing RNA.
In an experiment, researchers used a simple protocell
a
consisting of a self-replicating RNA molecule encapsulated
b.
Suggest
what
might
have
happened to make the
by a membrane. For growth to occur
, new membrane
v
radioactively
labelled
protocells
become
smaller.
material is needed. However
, there were no cellular
mechanisms to manufacture new membrane material. It has
E
been hypothesized that protocells containing RNA can grow
by capturing new membrane material from the environment.
43
and
LHA
Unity
diversity
a.
Analyse
b.
Evaluate the hypothesis that the presence of RNA
the
results.
1.3
capture membrane material from other protocells.
1.1
1.0
40
50
fo
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The
radioactively
which
makes
protocells
them
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were articially
likely
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material
mixed
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(lower
curve
from
unswollen
in
other
protocells.
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were
protocells containing RNA
▴
Figure 12) or not containing RNA
Figure 12
Source
in
Figure 12).
&
of
Figure
Szostak,
between
J.
model
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20
time /
11
and
W.
(2004).
protocells.
p
view
it.
investigate
should
protein
molecules
23S rRNA
the
and
search
“ribosome”.
be
and
able
RNA
which
to
rotate the image to
components.
together
Roberts, R.
Science
(New
York,
N.
Y
.),
https://doi.org/10.1126/
act
as
a
There
are
ribozyme:
i
In this image,
t
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o
23S rRNA is shown
u
f
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in green and
5S rRNA is shown in orange
l
a
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v
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A2.1.7
Evidence for
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ancestor
Living
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in
code,
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not
matter
does
consistency.
have
44
A.,
large subunit of the ribosome
and 5S rRNA.
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emergence of competition
o
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Figure
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science.1100757
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curve
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t
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swollen,
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specic
The
referred
to
information
codons,
and
using
each
a
genetic
codon
is
a
code.
There
sequence
of
are
three
64
“words”
bases.
Every
meaning; it is either an amino acid or a stop or start signal.
how
same
meanings
is
true
anything
but
of
are
assigned
language—for
now
have
a
to
codons,
example,
specic
as
the
meaning.
long
as
letters
there is
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could
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30
minutes
e
20
time /
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evitaler
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e c af r u s
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s
e c af r u s
sllecotorp
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inside vesicles increases the likelihood that they will
1.2
Cells
LHA
It would be perfectly possible for dierent species to use dierent genetic codes,
just as humans use dierent languages around the world. However
, when the
genetic code was investigated, it was found to be universal—it is the same in all
species, with only a small number of minor variations. The meanings of the 64
dierent codons could be assigned in an almost limitless number of ways, having
s
s
dierent meanings for dierent species. This makes it highly unlikely that two species
would use the same genetic code by chance. Instead, the obvious explanation for
species using the same code is that they inherited it from a common ancestor
.
e
It is possible for strikingly similar structures to evolve in organisms that do not have
r
a recent common ancestor. This is called convergent evolution. However, this
is not thought to be the reason for the universal code because living organisms
cells—such as the ribosome and the enzymes that synthesize DNA and RNA—are
l
essentially the same in all organisms. More than 350 widely occurring protein
that can be traced back to a common ancestor. The most recent common ancestor
It
is
likely
forms
other
from
rst
of
life
This
forms
life
evolved.
of
is
the
life
over
At
some
stage,
due
to
competition
process
of
natural
onwards.
Figure
14
however,
from
selection,
represents
LUCA
which
the
or
has
continued
C
o
v
i
n
n
U
o
i
d
t
a
r
o
LUCA
life
species that
evolution and
time.
◂
u
l
f
x
Figure
14
On
line ages
are
line ages
with
of
life
from
diagram
a
v
O
origins
this
shown
there
lines.
matter
scientists
actually
diagram,
dotted
continuous
non-living
but
tree
with
are
Three
are
not
extinct
lines
and
shown
yet
extant
origins
sure
on
how
this
many
were
Approaches used to estimate dates
E
A2.1.8
these
p
extinction
LUCA.
evolution
of
presumably
y
the
forms
extinct,
r
e
evolved
from
that
bec ame
O
t
i
s
to have existed is called LUCA—the last universal common ancestor.
n
y
families have been identied in prokaryotes, each with an evolutionary ngerprint
y
P
have so many other shared features. For example, key parts of structures within
of the rst living cells and the last universal
common ancestor
Palaeontology
has
e vo l u ti o n ,
is
last
so
c o mm o n
it
p rovi d e d
an
o bv i o u s
u n i ve rs a l
i nv a l u a bl e
a p pro a c h
a n c e s t o r.
T h e re
evidence
fo r
a re
dating
about
th e
re l a ti ve l y
th e
f i rs t
pa thw ays
l i vi n g
cells
w e l l - p re s e r ve d
of
and
the
ro c k s
45
and
diversity
LHA
Unity
da t i n g
like
f ro m
o rg a n i s ms .
of
th e s e
ro c ks
in
be e n
3 .0
s t r u c t u re s .
We s te r n
l a rg e
billion
i s o to pe
How e ve r,
ye a rs
ra ti o s
a l t e r n a ti ve
The
e arliest
A u s tra l i a ,
s tr u c tu re s
(Gy a ).
These
they
exp l a n a ti o n s
u n c o n t e s te d
k n ow n
th a t
a go
s u g ge s t i n g
as
the
re s e mb l e
ro c k s
a re
h ave
th e
be e n
evidence
St re l l e y
fo ss i l i z e d
Po o l
contain
re m a i n s
fo ss i l -
of
s u g ge s te d
of
l i fe
comes
Fo r m a t i o n .
s tro m a t o l i t e s
In
l i vi n g
fo r
these
h ave
is
thousands
of
Strelley
Pool
other
forms
of
that
earliest
and
than
the
life
cells
must
cyanobacteria
plausible
which
cells
of
c arbonate,
date
for
from
have
3.42Gya.
based
that
existed
on
form
before
in
shallow
building
explanation
LUCA,
bacteria
slowly
has
been
This
is
fossils.
seawater
rocky
proposed
so
there
we
c an
by
th e
all
clearly
been
metamorphosed
recognizable
from
isotope
by
heat and
fossils. The only evidence of
ratios.
C arbon
originating
from
12
C/
C
ratio.
Banded
iron
rock
from Akila and Isua in
13
further
n ew
have
comes
13
remains
fo r m e d
c re a te
nd
low
shows this
the
te c to n i c
e ro s i o n ,
to
a
O
u
l
a
E
v
O
f
x
E arth
has
E arth
contain
y
cells
be c a u s e
and
be
p
may
simplest
Th e
hope
Greenland
rocks
on
not
n
y
c an
organisms
i
west
we
do
o
that
living
found
they
t
a
r
o
d
life
rocks
so
o
oldest
pressure,
n
The
C
Western Australia
U
Shark Bay,
are
deduce
3.42Gya.
t
i
s
Stromatolites in shallow water
Hamelin Pool M arine Nature Reserve,
over
for the
therefore a minimum
However,
stromatolites,
r
e
Figure 15
v
at
i
n
▸
trap
mounds
l
simpler
the
No
structures,
earliest
mats
back
a bo u t
C
of
in
ro c k
4 .5 Gy a .
f ro m
and
if
dates
from
3.70
to
3.85Gya. These
so, this would push the origin of the
time.
p ro c e ss e s
h a rde s t
depletion
stromatolites;
No
ro c k s
continuously
m a g ma .
f ra g me n t s
o l de r
How e ve r,
c an
th a n
d e s troy
p e rs i s t
when
and
a bo u t
ro c k
by
ro c k
4 .0 Gy a
re m a i n
s u b du c t i o n
is
g ro u n d
become
pa r t
of
dow n
n ew
13
s e di me n ta r y
ro c ks .
Zi rc o n
pa r t i c l e s
w i th
depleted
C
dating
f ro m
4 .1 Gy a
13
h ave
been
ra ti o
is
fo u n d
consistent
exi s t e n c e
of
in
yo u n ge r
w i th
a
ro c k s
bi o g e n i c
at
Jack
o r i gi n
Hi l l s ,
bu t
We s te r n
th i s
is
far
A u s tra l i a .
f ro m
pro o f
The
of
12
C/
C
th e
l i fe.
Scientists trying to date the origins of life can also analyse genomic information.
The number of dierences between the genomes of two species is proportional
to the time since they diverged from a common ancestor. A recent study using this
approach suggested that LUCA and the rst living cells existed nearly 4.5Gya,
soon aer the Earth is thought to have been impacted by the planet Theia. This
impact would have sterilized the Earth and led to the formation of the Moon.
46
y
the
years.
when
c alcium
P
for
formed
secrete
r
and
e
stromatolite
ma ny
f ro m
d i s c ove re d.
sediments
date
to
with
s
s
ro c ks ,
A
3 .5
s t r u c t u re s
Cells
LHA
Millions of
years ago
art formed
4,600
by accretion
impact
e
4,000
s
s
eia
oldest known rocks
r
for life
l
life on land
Western Australia,
2,000
the evolution of the
is
possible
organisms
archaea.
this
to
have
LUCA
in
the
lived
E
water
There
are
smokers)
emerge
c arrying
various
have
at
are
types
had
the
have
in
the
compounds
60°C
ammonia
energy,
into
are
and
algae
shared gene and it matches
archaea,
deductive
reasoning
animals
500
vertebrates
355
protein
genes
families
needed
nitrogen.
with
are
E arth’s
(unoxidized)
high
From
for
this,
that
are
anaerobic
we
concentrations
found
to
and
alkaline
the
90°C
in
and
around
early
of
life.
contain
These
cells
C arbon
characterized
chemic als
such
hydrothermal
origin
and
suldes.
which
polymers.
to
surface,
inorganic
suited
of
1,000
flowering plants
c an
of
hydrogen,
hydrothermal
▴
Figure 17
Timeline for life based on
evidence from
rocks. Most of these dates
are still hotly debated
most
methane,
archaea. A wide
early common
gene.
conditions
conditions
supplies
a
today.
groups of
and
an
1,500
(>3.5Gya),
0
However,
accessible
for
from
ago
alive
the
life—bacteria
and
They
dioxide
vent.
of
organisms
among
inherited
identied
of
temperatures
of
years
from a common ancestor of bacteria and
environment
cracks
reduced
hydrogen,
c arbon
an
These
v
vents
hot
bacteria
genome.
c arbon
in
iron.
oceans.
Hydrothermal
for
LUCA
LUCA’s
were
using
widely
constructed
researchers
xing
and
is
occur
history
inherited
a
dioxide
in
for
that
the
genes
l
vents
been
tree
been
suggests
and
that
O
c arbon
has
technique,
metabolism
deduce
evolutionary
gene
tree
make-up
that
u
likely
This
evolutionary
f
x
Using
a
in
million
o
that
early
these
3,500
t
a
us
that
genetic
genes
than
i
accepted
tells
originated
more
d
an
its
identied
suggests
lived
r
o
the
If
investigate
have
that
distribution
ancestor.
to
probably
eukaryotes
n
Researchers
LUCA
U
it
though
C
hydrothermal vents
o
i
n
last common ancestor in the vicinity of
Even
2,500
so far discovered
p
Evidence for
potosyntesis
where there are zircon particles
fragments of the E arth’s crust
v
A2.1.9
These are the oldest
O
S atellite view of Jack Hills,
oxygen production by
y
Figure 16
dating to 4.4Gya.
r
e
▴
n
y
t
i
s
3,000
y
P
undisputed evidence
3,500
The
high
dioxide
have
would
as
iron
sulde.
vents (white
hydrothermal uids
concentrations of
chemic als
would
by gushing
represent
needed
also
have
to
readily
assemble
been
47
and
diversity
LHA
Unity
required;
the
rst
There
this
cells
are
evolving.
many
matter.
amazing
present in much higher quantities at the time when
problems
However,
it
in
understanding
seems
likely
that
how
the
rst
cells
hydrothermal
evolved
vents
from
were the site
s
s
this
probably
still
non-living
of
was
were
event.
e
r
l
i
n
it
n
O
y
This is why this type of vent
porous deposits and
It
has vents
a depth of over a mile.
minerals are precipitated
is known as a “white smoker ”. The
is in these pores that
C
non-living matter,
of Indonesia.
surrounding water,
o
v
water meets the cold
producing pale “smoke”.
from
is a submarine volc ano o the coast
chemic al-laden water into the ocean at
When this superheated
minerals form
p
K awio Barat
the rst
cells may have evolved
4.5billion years ago
U
1.
what
reasons
o
a.
Outline
b.
Explain
i
d
the
is
heredity
processes
why
meiosis
an
that
is
essential
are
feature
dependent
uniquely
necessary
of
living
on
cell
for
sexual
things?
division.
(D2.1.8)
reproduction.
t
a
r
o
(D2.1.9)
c.
u
l
f
x
2.
Discuss the relationship between heredity and natural selection. (D4.1)
What
is
needed
a.
Compare
b.
Distinguish
c.
Discuss
a
E
v
O
48
For
n
Linking questions
(C.4.1.10,
for
structure
discrete
and
between
to
be
able
polygenic
intraspecific
to
evolve
by
inheritance.
and
natural
selection?
(D3.2.14)
interspecific competition.
C4.1.11)
the
role
of
diversity
in
the
process
of
natural
selection.
(D2.1)
y
P
y
t
i
s
Figure 18
releasing superheated,
r
e
▴
A2.2
Cell structure
Figure 1 shows a hot
picture is made up
of sulfur bacteria (purple),
organisms.
algae and
protozoa, all
How does the cell theory take into account the
are unique to certain cells? What
implic ations of the cell theory? What
are the limits to what
are
are the
the cell theory
l
predicts or explains?
Sc anning electron
micrograph of a hot
community
What
is the actual limit
was used
electron microscopes? A sc anning electron microscope
to prepare the image shown in Figure 2,
What
which is an embryo on the head
U
of a pin.
and
of prey like an eagle? How large are
is the resolving power of the dierent type of
C
microscopes like light
o
cells? Organelles? Membranes? What
does resolution refer to with
to the resolving power of the
i
n
human eye? How does this compare to a bird
p
resolving power.
to optic al devices? What
v
respect
spring extremophile
y
r
e
How is microscopy used to investigate cell structure?
The human eye has limited
O
Figure 1
n
y
t
i
s
▴
y
features of cells are universal? What
some examples of features that
P
diversity of cell structure? What
r
one celled
spring extremophile community. This community
water in the hills of New Mexico. The community in the
e
thrives in 75°C
s
s
What are the features common to all cells and the features that dier?
is the value of a SEM over a transmission electron microscope?
n
o
HL
AHL
u
f
x
Origin
A2.2.2
Microscopy skills
A2.2.13
Cell
A2.2.3
Developments
Prokaryote
common
cell
Eukaryote
cell
A2.2.7
Processes
of
A2.2.8
Dierences
E
A2.2.6
cells
specialized
in
all
living
organisms
sc anning
A2.2.14
of
eukaryotic
dierentiation
tissues
in
only
cells
as
the
multicellular
by
endosymbiosis
process
for
developing
organisms
Evolution of multicellularity
structure
structure
life
in
to
a
Structures
A2.2.5
v
O
A2.2.4
l
A2.2.12
microscopy
Coloured
human embryo on the tip of a pin
A2.2.1 Cells as the basic structural unit of all living organisms
in
Figure 2
electron micrograph (SEM) of a
t
a
and
i
d
r
o
SL
▴
in
unicellular
eukaryotic
cell
organisms
structure
between
animals, fungi and plants
A2.2.9
Atypic al
cell
Cell
electron
micrographs
A2.2.11
types
structure
A2.2.10
Drawing
and
and
cell
in
eukaryotes
structures
annotation
viewed in light and
based
on
electron
micrographs
49
Unity
and
diversity
A2.2.1
Cells as the basic structural unit
of all living organisms
Individual
cells
but
fundamental
larger
units
single
organisms
are
a
70 kg human consists of 3.8 × 10
of
life.
Some
multicellular.
small
organisms consist of
It
been
has
estimated that
s
s
cell
are
a
13
multicellular
the ory
of
tissues
cells.
cells.
They
trend
that
of
Since
development
the
not
allowe d
living
are
of
described
and
it
the
organisms
has
later.
not
cell
to
not
general
Sometimes
their
the
as
observations
theory.
natural world and
observers and make
biologists
Theories
and
notice
from
developed
from
observations
going
living
the
all
of
new
all
tissue
were
organisms
organisms
have
but
they
about
the
discovered some
however,
organism
cell
develop
all
an
example
of
is
the
cell
discovered,
to
theory,
the
specic
discovery
consisted
of
the
inductive
specic
organisms
specic
are
the
cells
general.
led
that
to
o
u
cells
All living organisms
consist of
cells
l
a
Theory developed by
inductive reasoning
E
Observations
The cell theory was developed
by inductive reasoning
In
theory
we
c an
reasoning—
the
parts
the
organisms consist of cells.
consists of cells
Figure 4
that
of
pre dictions
consists of cells
▴
types
typic al cells; some of these
from
Toad cartilage
50
of
By
Elder pith
v
O
f
x
Embryos
consist of
trend or
i
cells
structure
t
a
r
o
of
a
they
d
Cork
consists
this
of
general
p
a
in
in
act
C
pattern
it—they
n
observations.
interested
at
parts
the ory.
from
mic roscope.
Both
exceptions,
a
the
a
o
v
i
n
are
c arefully
a
of
biologists
reasonably condent that some or all of it will consist of cells.
U
look
If
at
with
researchers
these
Observations, theories and inductive reasoning
Biologists
all
example
conclude d
consist
rejected.
look
an
other
examine d.
make
theory,
do
Despite
been
at
to
is
and
view
scientists
them
that
to
be
looke d
cells
y
structures
be
this,
r
e
in
useful
had
e asy
also
organisms.
structures
still
mic roscopes
could
From
of
Hooke
for a
c ase of the
of
diverse
generalization that
y
use d
relatively
are
consist
Robert
L arge
n
a
when
cells
structure
is
cells.
specialized
l
Hooke’s drawing of
each
O
Robert
trillion
P
Figure 3
cork cells
types,
t
i
s
▴
of
found
organisms
onw ards
animal
consist
made
had
cell
y
are
to
living
develope d
P lant
century,
found
that
w as
century
organisms.
19th
dierent
40
r
statement
This
17th
many
nearly
role.
The
the
have
is
e
particular
organisms
cells—that
Cells
inner
layer of
tadpole-like
larvacean house
by
mucus
larvacean
house
it
(dwarfed
secretes)
s
s
e
r
l
makes and
food
an
as
a
e ss e n ti a l
( 2 0 × ).
be c a u s e
w i th
fo r
A
to
see
single
two
th i s
or
c o mb i n e d
ma gn i f i c a t i o n
of
w i th
c o nvex
is
not
mo re
m a g n i fi c a ti o n
lens
0.0 0 0 1 m i l l i me tre s
s ki l l
s ma l l
How e ve r,
the
e ye p i e c e
to ta l
too
mi l l i m e t re s .
M i c ro s c o p e s
10 ×
g i ve s
small
a re
is about
3 to 5 centimetres long but the non-cellular house
living organisms make everything out of cells
n
is
as
a
a
mi c ro s c o p e
lens
cells.
that
0.1
times
vi s i bl e
ex a m pl e,
s t r u c t u re s
20
l
see
to
of
s t r u c t u re s
Fo r
o bj e c ti ve
E
v
O
pow e r
to
s t r u c t u re
smaller
mu l ti pl i e d.
up
about
view of a larvacean (the blue tadpole-like
o
th e
s tr u c tu re s
i
ma gn i f y i n g
at
than
u
mu c h
look
f
x
s tu dy i n g
to
s ma l l e r
t
a
fo r
The actual organism
there are some exceptions to the theory that
r
o
us
shows a magnied
the larvacean pumps water through the inner and outer mucus
The MBARI research shows there are still exciting discoveries to be made about
Microscopy skills
a l l ow
e ye — a ny th i n g
u s e fu l
also shows that
d
A2.2.2
It
the surrounding seawater.
to a metre in diameter.
U
the natural world.
Lenses
particles from
lives inside c an be up
o
it
By beating its tail,
has been researching marine
The inner ne-mesh structure c aptures smaller food particles. The
The photograph on the right
of its mucus house.
by K akani K atija,
which consists of two non-cellular mucus structures.
C
lters to extract
to the inner part
particles.
i
n
larvacean itself is too small to be seen in this image.
organism) adjacent
v
The large coarse-mesh outer structure excludes coarse non-food
led
n
Research Institute (MBARI),
O
Monterey Bay Aquarium
The photograph on the le shows a larvacean’s “house”
y
of researchers at
larvaceans.
p
A team
y
P
y
t
i
s
Figure 5
organisms c alled
r
e
▴
of
400 ×.
lenses
a
This
naked
lens
is
enough
th e
with
the
lenses
40×
is
h i gh -
a l l ows
(0.1 mi c ro m e t re s) .
fo r
make
us
Us i n g
a
b i o l o gi s ts .
51
Unity
and
diversity
Using a light microscope
•
If
you
want
to
increase
the
magnic ation,
move the
camera
slide
so
higher
of
most
the
promising
eld
of
region
is
exactly in the
view and then change to a
magnic ation lens.
eyepiece
Use
these
hints
to
troubleshoot
when
you
are
focusing:
e
objective lens
M ake
sure
when
under
the
you try to
the
specimen is actually
lens,
condenser
fine focus
focus
positioning
by
c arefully
slide
and
using
rst.
light source
coarse focus
see a
There
Parts of a light
your
microscope
black rim.
c an.
•
Learn
•
Understand
at
using
microscopes as much as
There
names
of
how
parts
to
of
focus
the
the
are
blurred
Either
the
clean them.
when
you
on
them.
focus it as well as
possible
image.
you
aer
your
microscope
so
it
stays
in
perfect
The
Know
Look
focus
further
apart.
sure
the
support
the
and
before
weight
of
the
at
up
of
with
the
When
you
have
smaller
the
with
slide
have
teacher to
the
diaphragm
to
increase
the
specimen.
The image looks
Adjust
rather
the amount of light passing through
bleached.
each
other.
stage.
▴
with
your
the
the
diaphragm
to
decrease
specimen.
Table 1
Making temporary mounts of cells and tissues and
using stains
The
slides
you
examine
permanent
or
skilled
takes
the
most
promising
and
made
by
using
very
with
temporary.
M aking
do
this
a
experts.
thin
long
a
microscope
M aking
time,
Permanent
slices
temporary
for
larger
c an be
permanent
of
so
these
slides
of
slides
slides
is
very
are normally
tissues
are made
tissue.
slides
is
quicker
and
easier,
so
you
c an
yourself.
even
if
you
need high-
Place
the
one cell
cells
on
the
slide,
in
a
layer
not
more than
help
structures
thick.
eventually.
•
coarse-focusing
nearly
ne-focusing
•
rst,
got
the
image
knobs
in
rst.
that
to
make
it
a
drop
are
of
pale
water
or
or
stain.
Stains
transparent
to
show
a
onto
up
more
clearly.
focus, use the
•
knobs
Add
really
C arefully
lower
cover
slip
sharp.
avoid
52
the
your
specimen
window in the stage that
power
magnic ation
Focus
Adjust
or
Ask
through.
low
E
•
stage,
a
power
comes
focus
the
centre
slide.
your
c arefully with a hand under it to
l
light
Always
on
the
v
O
the
•
slide
in
the
u
the
region
on
securely.
f
x
Put
it
lenses
Course and ne focusing
•
to
else.
microscope
its
the
lower surfaces of the slide
putting
surfaces
anything
and
closer
t
a
C arry
or
upper
dry
lens
them
i
touch
ngers
•
the
and
the
move
r
o
Never
moving
Never
very
the
the amount of light passing through
following these guidelines:
o
clean
by
by
problems.
d
are
•
microscope
Always
M ake
troubleshoot
is
n
•
your
to
U
•
aer
how
image
dark.
C
•
order.
i
n
working
c an.
o
v
Look
p
best
•
lenses
even
microscope to get the
on
improve
for making slides so
dirt
microscope.
to
are no air bubbles.
parts of the image
r
e
the
bubble
try
y
you
skill
air
and
technique
there
to
an
it
O
Figure 6
improve
t
i
s
▴
Try
is
Ignore
n
c an
circle with a thick
y
You
low
l
power
the
trapping
any air bubbles.
the
drop.
Try to
y
Solution
Nothing is visible
P
Problem
r
stage
s
s
middle
the
Cells
•
Remove
putting
piece
of
lightly
excess
the
paper
on
uid
slide
the
or
inside
towel
cover
stain
a
by
cover
c arefully
slip
cover slip
lower the
gently
folded
and
squeeze
to remove excess
pressing
fluid
slip.
s
s
stain or water
cover slip
▸
Figure 7
M aking a temporary mount
shown
Table 2.
in
are
very
leaves. Mount a
Peel
methylene blue
drawn
leaf
moss
leaf
4
plant
in
a
with
drop
of
thin
water
or
stain.
Leaf
lower
the
water
epidermis
lower
here
or
in
epidermis
was
from
blue.
on
a
so
slide.
tissue
Mount
in
a
drop
5
and
of
your
add
previously
add
methylene blue to stain.
a
(not
E
v
O
l
frozen).
cut
Smear
6
surface
onto
5
a
cell
to
scrape
cheek.
cells
of
liver
slide
and
White
Smear
slide
a
blood
thin
and
µm
cell
layer
stain
of
with
mammalian
blood
over a
Leishman’
s stain.
µm
2
▴
from the
Smear them on a slide
methylene blue to stain.
10
cell
freshly
bud
o
i
a
cheek
cotton
t
a
liver
from
u
cells
d
r
o
f
x
M ammalian
Scrape
a
inside
20 µm
3
Human
Use
n
U
of iodine solution.
from
µm
y
place
the
20
p
and
of
C
banana
cell
amount
leaf. The cell
o
fruit
small
a
O
t
i
s
r
e
a
a
v
Banana
Scrape
i
n
2
o
Centranthus. Mount in
methylene
10 µm
towel
n
cell
y
single
types
paper
dierent
l
a
six
y
Moss
Use
for
P
1
instructions
r
and
e
slide
folded
Sketches
µm
Table 2
53
Unity
and
diversity
Photography
Observing, drawing and photographing cells
When
cells,
you
it
typic al
a
useful
cell.
focused
to
at
record
Alternatively,
photo
through
high
your
of
power on plant or animal
observations
by
one
drawing a
biologist’
s
microscopes
you could use a smartphone to
the
is
very
microscope.
an
photographs
is
alternative
that
they
subjective
are
to
drawings.
contain
real
The
data
interpretation
of
advantage
rather than
it.
Digital
increasingly common and they make it
s
s
take
is
have
easy to take photos.
cell
e
good
bad
good
Qualities in drawings
l
Measuring sizes using an eyepiece graticule
n
y
You can measure the actual sizes of structures visible
through a microscope by using a scale inside the eyepiece,
t
i
s
O
called a graticule. The graticule has to be calibrated so
you know what size each unit on the scale indicates. This
will be dierent for each objective lens. For example,
if one unit on the scale represents 2.5micrometres
y
r
e
at 400× magnication (high power), it will represent
25micrometres at 40× magnication (low power).
circles are air bubbles; this is
in temporary microscope slides.
introduced
the
unnecessary
membrane
is
and
edges
detail
too
you
it
Drawings
and
forms
a
name,
or
to
You
you
of
than
magnied.
the
same
structures
the
actual
and
a
a
drawing.
blood
▴
Figure 10
smartphone,
For
sc ale.
the
using
if
they
from
diagram.
identify
a
the
are
seen
using
a
microscope
such
the
shows
should
be
appear
larger than
e ach
actually
are.
Most
microscopes
have
more than one
Then
objective
lens,
factors.
typic al
so
you
c an
magnify
specimens
by
dierent
structure
microscope
drawing
a graticule
100graticule units = 5millimetres or 5,000micrometres
C alculating actual size, magnication and sc ale
line
details
Microscope image photographed using a
showing a fruit of Centranthus ruber and
cell.
they
drawing
and
indic ated.
cell
its
Structures
o
other
The
deduce
your
a
drawing
as
A
school
microscope
the
magnic ation:
seen
on
a
show
informative
simply
add
c an
straight
position
size—the
Everything
in
of
more
draw
might
magnic ation
c alculated
54
E
larger
a
it
not
features
on
shading.
you
edge
are
to
c an
function.
Drawings
outer
ruler
interest
there.
include
diagram
lines
Do
faint
but
a
a
should
use
see,
of
some
the
l
with
of
notes
only
to
diagrams
Use
type
with
structures.
and
the
a
Usually
v
O
annotated.
add
of
thin
is
u
example,
structure
nucleus.
f
x
position
the
cell
shown
t
a
represent
as
a
is
i
such
of
structure
r
o
only,
drawing
cell
was
o
biologic al
bec ause
that
during preparation of the slide
d
A
They are a
naturally present
n
type of artefact—something not
U
a common fault
p
Some of the cells have a red pigment in their
The black-edged
C
cytoplasm.
o
Onion epidermis cells photographed with a
smartphone.
v
Figure 8
i
n
▴
are
•
40×
(low
•
100×
•
400×
power)
structures
(medium
power)
shown to
magnic ation should be
(high
power)
has
three
levels of
y
Figure 9
bad
P
▴
good
r
bad
cell
Cells
If
you
the
is
take
a
image
c alled
a
photo
even
c an
Electron
microscope,
the
of
When
drawing
the
you
the
is
bars
abbreviated to
labelled
are taken using an
example,
or
not
Sc ale
c an magnify
shown
draw
larger
drawing
of
oen
you
microscope image
a
a
may
be
alongside
with
a
the
on
actual
10 mm
magnic ation of
specimen,
put
them.
long
micrographs
A
sc ale
size
that
sc ale
×10,000
bar
is
the
or
a
drawings, or
straight
bar
bar
on
a
would
be
labelled 1 µm.
smaller, so the
necessarily
the
nd
the
same as
microscope.
magnic ation
of
a
micrograph
or
a
drawing,
The
need
to
length
drawing
an
or
the
that
has
is
30 mm.
actual
size
It
use
this
the
image.
represents
3 µm.
a
Determine
formula:
Either:
l
=
−3
30 mm
you
know
the
size
of
the
of
=
30 × 10
m
specimen
image
and
the
magnic ation,
−6
3 µm
c an
c alculate
the
actual
size
of
a
=
3 × 10
specimen.
m
t
i
s
you
−3
magnic ation
=
=
10,000
O
30 × 10
When using this formula, you must make sure you use the
×
−6
3 × 10
same units for the size of the image and the actual size of
Or:
the specimen. They could both be millimetres (mm) or
=
30,000 µm
30,000
magnic ation
to micrometres by multiplying by 1,000. You can convert
micrometres to millimetres by dividing by 1,000.
=
=
3
y
30 mm
the calculation will be wrong. You can convert millimetres
10,000
×
o
C
i
n
v
p
r
e
micrometres (µm) but they must not be dierent, otherwise
n
If
size
y
actual
the
y
you
of
size of image
magnic ation
of
P
Then
an
micrograph) and the actual size of the
magnic ation
specimen.
image
know two things: the size of the image (in
structure
the
of
r
you
For
micrograph with a
Worked example
To
line,
represents.
e
magnic ation
of
micrographs
microscope.
make
magnic ation
the
a
photo
s
s
you
A
photomicrograph,
micrograph.
electron
down
more.
Data-based questions: Size, magnic ation and sc ale
a.
Determine
the
b.
magnic ation of the
cells
in
in
the
micrograph.
[2]
i
11
Figure 12
Mitochondrion
with false colour (red)
Thiomargarita
3.
The
magnic ation
of
the
human
cheek
cell
from a
cells (one whole cell
compound
microscope
(Figure
13)
is
2,000×
and two in part). The
f
x
a.
C alculate the length of a 20 µm
sc ale bar on
sc ale bar represents
u
l
the
v
a
Determine
magnic ation
of
the
image.
[2]
0.2 µm
b.
Determine the maximum length of the cheek cell.
[2]
the
electron
[2]
◂
E
C alculate the length of a 5 µm
this
c.
◂
Figure
t
a
r
o
◂
micrograph.
b.
o
cell
is8 µm.
a.
[3]
Figure 12, the actual length of the mitochondrion
O
In
11.
d
whole
2.
Figure
Determine the maximum diameter of the
n
Thiomargarita
U
1.
stained
electron
Determine
Figure 13
micrograph.
width
of
the
with methylene blue
[2]
4.
the
Human cheek cell
sc ale bar on
mitochondrion.
a.
Using
the
width
of
the
hen’
s
egg
as
a
guide,
[1]
estimate
the
actual
length
of
the
ostrich
egg in
55
Unity
and
diversity
Figure
b.
14.
Estimate
micrometres.
[2]
the
magnic ation
of
the
image.
c.
[2]
Convert
to
the
millimetres.
convenient
[2]
dimensions
Which
with
an
from
length
micrometres
units
organism
of
are
this
more
size?
[3]
s
s
model
organism
in
been
research.
widely
Most
used
adults
Figure 15
Caenorhabditis elegans together with an
are
and
have
exactly
959 cells.
Measure the maximum width and total length of
b.
One
worm,
unit
in
on
eyepiece
the
sc ale
units
(EPU).
indic ates
[2]
9.5micrometres.
measuring
instrument.
a
microscope
are
qualitative
likely
yellow and
data
is
Two
in
table
with
two
observations”
and
your
about
record
An
algae
the
many
the
advantages
of
qualitative
5.
Do
all
quantitative
instrument?
legs a
Or
observations
numbers?
Or
involve
units?
example of a
larva
appears
(centre
Synura
green.
headed
“quantitative
organisms in the
0.8 mm
in
your
table.
▴
with
those
of
a
classmate.
and
quantitative
observations.
by
descriptions
are visible:
columns
them
observations
E
56
a
Compare
16.
copepod
and
simply
Consider the
l
3.
of
how
involve
Pandorina morum
observations
micrograph
the
types
v
O
M ake
count
Figure
observations”.
2.
obtained
subjective.
that
Discuss
u
a
“qualitative
100.
water
f
x
Create
might
observations
observation
transparent.
appears
1.
pond
be
we
more
4.
measuring instrument.
c an
it
is
obtained with
(graticule) in
i
is
of
be
a
sc ale
t
a
right)
to
if
of
data
r
o
micrograph
qualitative
see
usually
o
contrast,
that
to
is
d
In
example,
has,
and
eyepiece
example
quantitative
For
centipede
an
An
n
counting.
is
numeric al
U
Sometimes
is
C
data
a
i
n
Quantitative
y
Quantitative versus qualitative observations
o
v
p
r
e
C alculate the actual dimensions of the worm in
O
a.
the
t
i
s
eyepiece sc ale
hermaphrodite
Figure 16
A micrograph of pond
water
a
measuring
y
a
n
has
▴
as
l
Caenorhabditis elegans
e
r
Ostrich egg
y
5.
Figure 14
P
▴
Cells
A2.2.3
Developments in microscopy
Microscopes were rst invented in the 17th century. Since then, there have been
many technological developments in microscopy, which have made new and
more detailed observations possible. Improved light microscopes in the second
s
s
half of the 19th century allowed the discovery of bacteria and other unicellular
organisms. Chromosomes were seen for the rst time and the processes of
mitosis, meiosis and gamete formation and fertilization were discovered. More
and the presence of mitochondria, chloroplasts and other structures in cells.
r
Leeuwenhoek microscope of
1670 (le) and
Zeiss microscope of
but
become
A
there
hand
is
a
becomes
smaller.
lens
limit
or
increasingly
Imagine
a
Eventually,
of
it
of
will
dicult
dots
be
distortions
impossible
c aused
by
in
50s.
parts
of
maximum
rst
an
eyes
1930s.
Some
object
using
of
produce
10 point
to
see
of
microscopes
the
wavelength
4 point
that
use
beams
3 point
electrons is much shorter than
electron
the
microscopes
They
electron
c ame
were
designed
into
use
in
microscopes
c an
give
2 point
research
1 point
▴
distinguishable
by
eye
is
c alled
Figure 18
of
the
unaided
eye,
the
light
for punctuation c an be used to
microscope
test
three
Size of printed periods (full
resolution.
stops) used
resolution
microscope,
E
Unaided
and
a
electron
The
during
1,000,000×
v
O
the
separate
the
light.
development
wavelength
u
shows
to
the
l
the
Table
up
by
The
Germany
1940s
f
x
M aking
3
visible
in
the
magnic ations
light.
o
laboratories
and
of
constructed
of
i
wavelength
and
overcome
t
a
the
was
instead
d
problem
electrons
r
o
of
to
appear
allows smaller details to be
of light.
This
that
20 point
5 point
microscope
bec ause
pair
y
they
dots.
it
microscope.
p
distinguished
light
o
as
separate
a
C
together
as
more than 400×,
n
them
of
with
U
closer
image
O
t
i
s
r
e
magnic ations
focused
30 point
v
a
i
n
At
n
y
l
2020 (right)
y
Figure 17
about
P
◂
e
advanced microscopes also revealed the complexity of organs such as the kidney,
the resolution of the naked
eye, and of
dierent SI size units.
the eye aided
by one or more lenses.
size is the maximum
height
Font
of letters and is
Resolution
Resolution
Resolution
measured in “points”. In desktop publishing
millimetres /
micrometres /
nanometres /
fonts,
mm
µm
nm
0.1
100
1point
is 0.353 mm. The diameter
of a period
is just
overall font
size,
less than one-tenth of the
so a period
at
font size 30
100,000
has a diameter of approximately 1 mm. The
Light
microscopes
Electron
microscopes
0.0002
0.2
200
0.000 001
0.001
1
table shows a row of 10 periods at
from
30 to 1.
font sizes
Which sizes of period
c an you
distinguish as individual dots?
▴
Table 3
57
Unity
and
diversity
Bec ause
electron
magnic ation.
microscope.
Electron
cell
Electron
microscopes
the
do
contrast,
light
is
a
have
any
In
used
any
vacuum
widely
give much higher
to
investigate the
ultrastructure
between
disadvantages.
electron
prepare
the
be
both
material
would
beams
used
types
die
of
to
of
They
micrographs
for
the
inside
examine
be
living
very
microscope
destructive. In
material
are
used.
very
give black
added
microscope
electron
are
microscope
only
to
electron
an
electrons
c an
has
and
useful
produce
in
l
19
t he
An
e l e c t ro n
M a x-P l a nc k
m i c ro sc o p e
Ins t i t u t
in
H a l l e,
Most
of
t he
m a ny
of
the
m i c ro s c o py
unless
cells
stained.
are
Stains
white
used
a re
bind
to
some
chemic als
but
not
he re
to
DNA
and
RNA
when
a
and
stains
re-emit
fluorescent stain
to
particular
of
loc ated.
c an
be
image
There
used
to
is
a
are
c an
then
many
nd
out
for
blue
light,
for
if
and
emit
a
built
single
(antigens)
are
be
linked
of
in
example.
with
lighter
blue.
re-emits it at a longer
100
years. Some absorb
Special
uorescence
intense
light
sources such as
wavelength.
This
light
is
absorbed
to
uorescent staining. Antibodies that
the
cell
these
produced
research
one
then
over
a
generating particularly bright images.
development
colours
and
used
methylene blue binds
cytoplasm
showing
applic ations
specic
are
type
of
produced.
antibodies.
of
where
this
protein
A
Then
the
chemic als
technique;
is
uorescent
multicoloured
being
for
are
example, it
produced in a cell.
o
i
d
r
o
secondary
that
sample,
chemic als
dierent
uorescent
antigen
t
a
antibody
u
l
f
x
a
E
v
O
fluorescent stain
antigen
Figure 20
lasers
the
light
been
designed
n
U
markers
primary
or
by
Immunouorescence
bind
antibody
LEDs
absorbs
and
are dicult to
coloured substances
example,
blue
have
C
antibody
power
re-emitted
i
n
and
been
as
For
dark
they
are
o
high
have
v
microscopes
it
others.
nucleus
substance
Fluorescent
light
the
so
y
ultraviolet
is
stains
colourless
microscopy
p
wavelength.
it
r
e
Fluorescence
so
or
in
O
in
that
d e s c ri b e d
in
t e c h no l o gi c a l
distinguish
d e ve l o p m e nt s
chemic als
t
i
s
Th re e
n
y
at
research
The uorescent stain (yellow)
may be linked directly to the antibody
that binds to the target antigen (green).
Alternatively, it may be linked indirectly by an
▴
Figure 21
In this image produced by immunouorescence, DNA in the nuclei is stained cyan.
antibody that binds to the primary antibody
Microtubule proteins of the cytoskeleton, which are normally invisible, are stained magenta. This
image was produced using a Nikon RTS2000MP custom laser scanning microscope
58
y
be
in
P
to
in
cells
c an
Therefore,
scientists
Variations
c an
seen than with a light
1. Fluorescent stains and immunouorescence
Fig ure
use
Ge r m a ny.
▴
and
microscopes
colour.
to
c ase,
be
later.
some
colour
allowed
cells.
they
c an
r
there
continue
described
methods
cells.
bec ause
and
so
have
of
resolution,
structures
e
The
always
in
are
images,
articially.
kill
(ultrastructure)
types
better
smaller
s
s
dierent
white
have
much
microscopes
structure
images
in
means
detailed
and
▴
microscopes
This
Cells
2. Freeze-fracture electron microscopy
This
technique
plunged
then
into
used
of
to
fracture
the
cells.
vaporization,
vapour
to
Cell
frozen
of
enhance
or
the
the
coating.
This
sample.
ice
at
texture
c arbon
is
of
of
red
creates
The
the
it
the
fracture
replic a
cells.
freezes.
goes
This
is
A
A
is
sample is
steel blade is
through
surface
surface.
the
within
rapidly
fractured
onto
a
surfaces
so
the
removed
weakest
by
c alled etching. Then a
fracture surface at an angle of about
of
the
fracture
surface.
P
l
of
the
3D
angle
2
which
through
in
is
cells
The
sample
nanometres
the
and
c an
thick
coating
is
on
be
shadowing.
usually
the
middle
freeze-fracture
When
these
images
theories
about
membrane
were
rst
of
is
thickness
between the two
they
surface
is
replic ated
led to a fundamental
described in
Topic B2.1
n
OW
a
E
v
O
l
u
f
x
t
a
r
o
i
o
d
PM
vacuole
the
gives the
Fractured
gives a unique image of this
produced,
This
but
This
membranes,
process
structure.
examined using an
average
applied.
U
in
at
frozen
image
phospholipid.
cells.
the
about
4.
o
point
is
etched
C
of
change
a
of
from
It
is
v
part
of
Cell
O
bec ause
weakest
layers
removed
i
n
The
3.
The freeze-fracture process
is
microscope.
impression
fractured
p
varies
is
y
electron
Cell
r
e
replic a
2.
n
y
Figure 22
The
frozen
t
i
s
▴
is
y
1.
a
the
images
at –190°C
r
form
produce
propane
Some
platinum
to
to
e
35°
of
used
s
s
points
is
liqueed
cytoplasm
◂
Figure 23
Freeze-fracture image of a yeast cell, showing
LD
a large vacuole,
smaller vesicles (unlabelled), plasma
membrane (PM),
vacuole,
cell wall (CW) and
vesicles and
a lipid
droplet
(LD). The
plasma membrane appear convex
or conc ave bec ause the fracture followed
the centre of the
0.2 µm
membrane,
fractured
which was curved.
bec ause it
is not
The lipid
surrounded
droplet
is cross-
by a membrane
59
Unity
and
diversity
3. Cryogenic electron microscopy
This
the
a
technique
structure
grid.
The
of
is
d e t e c to rs
of
when
Since
that
2010,
resolutions
a
in
in
mo l e c u l e s
di ffe re n t
pa tt e r n s
one
protein
an
a re
pa tte r n s
a re
them
form
other
have
This
in
O ver
the
they
rapidly.
protein
Dubochet,
cryo-EM.
ralloc
Tail
fibres
knurt
etalpesab
components of the protein before and aer
spike
it
60
contracts
24
now
Frank
and
o
C
n
o
c) show
3D
research
structures
(c)
Post
i
images of pyocin (b and
to
c an
Joachim
Figures
a
coloured
The sc ale bar
Using
a
give
have
now
Bank (EMDB). The 2017 Nobel
The cryo-EM
Two computer-generated
pro du c e
proteins at the instant
They
Pre
t
a
u
l
v
E
post-contraction.
represents 30 nm.
to
c arry out their function.
image (a) shows pyocin pre-contraction
and
o r i e n ta te d
pro du c e d.
generation of images of individual
10,000
D ata
Jacques
developing
(b)
as
m i c ro s c o p e
i n di vi du a l
scientists
Pyocin is a protein produced
membrane.
prevent
produced images of a
analyses
allows
improved
Microscopy
to
This
another
allows
molecule.
awarded
work
froze.
to
only
cryo-EM
by
ra n d o m l y
a re
by bacteria to kill other bacteria by bursting
their cell wall and
applied to
and
e l e c t ro n
c o mb i n e d
structure
However,
techniques
was
their
i
n
U
d
r
o
Figure 24
f
x
O
▸
from
Electron
example of this.
(a)
around
v
for
or
the
Chemistry
Henderson
form.
0.12nanometres.
protein
in
tra n s mi tt e d
p
Prize
in
shared
pl a c e d
y
been
th e s e
is
e l e c t ro n s
pro t e i n
r
e
atoms
of
ma ny
analysing
water
cryo-EM
of
ice
above its melting point
molecules.
stable
change
vitreous
researching
is
O
proteins
the
the
s o l u ti o n ,
for
for
solution
n
time
most
just
t
i
s
in
its
s o l u ti o n
p a tt e r n
algorithms,
methods
in
smooth
ethane
used
protein
l
protein
create
Liquid
p ro t e i n
the
Be c ause
pro t e i n
principally
y
Previous
th e
is
pure
25
and
Richard
show an
y
of
to
It
a
P
i ma ge
f roz e n
f roz e n
c o m pu ta ti o n a l
crystals.
of
used as the coolant.
re c o rd
molecules.
l aye r
layer
r
th e
cryo-EM.
thin
ash-frozen,
water
the
A
e
grid
and
in
w i th
is
usually
Th e
c alled
s
s
–182.6°C
pro te i n
oen
proteins.
solution
theformation
of
is
of
Cells
◂
collar
Figure 25
This
sequence of diagrams
shows how pyocin binds to
and
then pierces its target
tail
s
s
sheath
fibre
membrane
attachment
considerably
in
size,
shape
and
structure,
but
they
share some
features:
membrane
even
if
the
entry
concentration
entry
of
substances
The
or
of
substances.
the
even
that
permeability
of
cell
toxic
is
very
are
very
the
plasma
dierent
cell
itself
the
c aused
(autolysis).
is
those
in
relies
on
or
suspended
hundreds
or
even
in
leads
of
this
thousands
of
down
even
and
replace
v
are
with
up
a
cell
its
of
DNA,
contain
genes
hold
so
which
a
are
needed
cell
It
This
c an
death
of
c annot
energy
the
is
and
the
chemic al
and
structure
not
there
in
a
be
cell;
are
a
surrounding
structure
as
lysis and
c arried
this
out
by the
shows that the
many substances
reactions.
cell.
the
known
cytoplasm
produces
of
is
even
the
eective at
all
the
c atalyse
These
reactions
are
proteins and
Proteins
are
quite
easily
growing the cytoplasm must continuously
proteins.
M any
structural
without
E
made
functions.
cell
make
when
3. DNA
Genes,
a
a
so
that
bursts.
Enzymes
dierent
l
damaged,
break
provides
substances
the
u
f
x
O
other
to
cytoplasm
water.
the metabolism of the cell.
Metabolism
cell
viruses.
structure.
component
dissolved
a
by
i
main
vital
of
or
t
a
the
always
r
o
is
a
pressure
very
o
membrane
Lysis
2. Cytoplasm
Water
membrane
excess
also
allows a cell to maintain
from
d
plasma
plasma
by
is
It
n
be
It
membrane
U
c an
c an pump substances
low.
substances.
based on lipids.
Occ asionally
of its contents. The plasma
It
C
environment.
outside
unwanted
and encloses all
exit
i
n
concentrations
of
and
o
preventing
the
v
in,
controls
p
This is the outer boundary of the cell
y
r
e
1. Plasma membrane
n
vary
common
O
t
i
s
living organisms
Cells
l
y
Structures common to cells in all
y
inner tube
A2.2.4
membrane
P
contraction
r
outer
cytoplasmic
e
baseplate
the
the
for
information
instructions
growth
control
and
needed
for
making
repair.
chemic al
for
a
a
cell
to
protein.
c arry out all its
Some
proteins
Others act as enzymes,
reactions
and
does
not
have a
functioning metabolism.
61
Unity
and
diversity
DNA
is
c an
be
heritable.
DNA.
Bacteria
Use of DNA
of
copied
Plant
this
DNA
do
as a
is
are
be
m a ny
is
it
they
units,
a
Some
of
and
other
nuclear
do
evolve
skin,
from
not
not
on
small
in
our
cells,
loc ation
eukaryotes.
organisms
Bacteria
(such as
envelope consisting of a
have a nucleus.
E arth
in
size
and
they
and
are
intestines
including
This
and
still
have
found almost
even in pools of
prokaryotic cells, also
structure
cells
is
thicker
prokaryotes,
interior
and
stronger
by
are
still
cell
wall
lled with
membranes;
therefore
contain
a
very
many enzymes.
organs
Prokaryotes
Prokaryote
that
and
do
the
are
not
have
are
ribosomes
rate
at
analogous
organelles
ribosomes
eukaryote
of
the
entirely
cells
they
organelles
Both
measure
is
compartments
Prokaryotic
contains
whereas
a
the
into
including
functions.
are
so
In
cells—although
organisms.
70S
which
cell
chamber.
ribosomes.
are
bursting.
divided
eukaryotic
specialized
ele ctron
u
than
the
molecule
of
l
E
v
a
eukaryotic
cytoplasm
contains
appe ar
DNA,
darker
other
m i c r o g ra p h s
rest.
of
and
instead.
eukaryotic cells is the nucleus, which
by
membrane.
biochemic als
from
of
mostly
our
prokaryotic
eukaryotic
unlike
it
cytoplasm
cells, but the
are
cytoplasmic
smaller
are
to
distinct
80S.
than
The
which
a
particle
of
cytoplasm
those
S
stands
sinks
centrifugation.
lighter
the
a
than
o
t
a
Svedberg
single
prevent
in
of
of
apart
eukaryotes:
during
the
protects the cell, maintains its shape and supports the
multicellular
with
stores
n
of
cell
uninterrupted
i
d
r
o
f
x
O
62
cytoplasm
organelles
In
one
mixture
structures
for
the
cytoplasm
simpler
organs
in
prokaryotes
variety
cells
C
is
on
to
a
o
nucleus
The
are
membrane.
n
U
complex
of
It
to
i
n
it
structurally
the
They
peptidoglyc an.
no
instead,
organisms
v
is
it
l
membrane
feature
Prokaryotic
water,
outside
and
bounded
areas.
plasma
wall
cytoplasm.
The
in
membrane.
contains
There
soil,
key
is
groups,
fungi
p
plasma
is
y
the
a
rst
structure.
volc anic
have
cell
the
two
r
e
than
a
DNA
common to all
O
cells
have
their
t
i
s
everywhere—in
All
and
is therefore
y
cell
in
The
This
membrane.
were
water
information
in
This
DNA
DNA,
is
that
it
c alled
but
it
is
is
prok aryotes,
contains
forms
not
the
not
ele ctron
proteins.
of
re gion
a
loop
a
or
a ss o c i a t e d
nucleoid.
true
It
is
The
usually
DNA
proteins.
similar
Other
They
the
There
c i rc l e.
with
is
nucleus.
m i c r o g ra p h s .
part
DNA.
to
a
of
the
a
“naked”:
lighter
nucleus
parts
contain
The
is
a p p e a rs
only
re gion
bec ause
cytoplasm
ribosomes,
enzymes
y
of
into
animals,
eukaryotic.
the
hot
divided
Plants,
Prokaryotes
simplest
the
universal.
chromosomes.
layer
so
e
double
nucleus
a
material
cells,
P
contains
have
not
daughter
Prokaryote cell structure
c an
prokaryotic.
Amoeba)
to
have a nucleus that contains almost all their
r
are
on
cells
s
s
Organisms
passed
animal
genetic
not
A2.2.5
and
and
Cells
Data-based questions: Ultrastructure of Clostridium
Figure
26
shows
an
positive bacterium
electron
micrograph
of
Clostridium botulinum.
the
Gram-
This bacterium
cytoplasm
a
neurotoxin
that
is
the
most
poisonous
with
nucleoid containing
70S
protein
naked DNA
ribosomes
so
far
discovered.
treatments
2.
This
so
under
dark
in
the
image
of
name
the
is
to
you
see
Clostridium
to
a
[2]
section:
going
in
from
you
end
transverse
to
c an
see a thin
end.
section
What
(going
side)?
[1]
There
cell. What does this suggest it is getting ready to do?
sc ale
bar
on
the
[2]
t
i
s
a
micrograph. Use this to
the
magnic ation
of
the
micrograph.
[3]
cell
membrane
of
showing as a dark line
5.
Use
of
the
the
magnic ation
to
c alculate the actual length
cell.
▴
[2]
Figure 26
is
to
research
the
connection
aected?
are
between
facial
injections.
c
Clostridium botulinum
site:edu
What
Which
search
“What
is
Your primary purpose is to use web-based sources to
U
C
cellular
processes
cosmetic
i
n
and
o
task
Clostridium botulinum
the
terms
and
enabled
connection
peptidoglyc an
y
p
r
e
Your
v
Research skills: Using search engines eectively
ATL
wall made
O
plasma
c alculate
n
4.
l
There are two nucleoids visible in the cytoplasm of this
y
3.
is
μm
appear
micrograph?
longitudinal
bacterium
would
side
electron
a
0.5
Botox®.
y
shape
from
brand
used in cosmetic
P
slice
the
c auses the cytoplasm of
is
e
What
neurotoxin
r
1.
This
s
s
produces
cosmetic
you
to
between
facial
injections
answer the questions:
Clostridium botulinum
nd information. You should use precise language in your
and
n
search terms, including scientic language. For example,
cosmetic
processes
you might search “Clostridium botulinum” and “cosmetic
facial
injections?”
aected
by
and
“What cellular
Clostridium botulinum?”
o
d
facial injections”. However, this is likely to return results
are
for businesses oering cosmetic treatments. These will be
r
o
i
sites with domain names ending in “.com”. For this task,
t
a
you want information from organizations whose primary
purpose is education. Such sites have domains ending
in “.edu”. To lter your search results, include the search
f
x
term “site: edu”.
the
following
of
Botox®
the
terms
dierent
in
your
search
engine.
Compare
searches.
l
treatment
a
b.
O
a.
the
results
u
Enter
Clostridium botulinum
and
cosmetic
facial
injections
▴
Figure 27
Injecting Botox®
v
E
63
Unity
and
diversity
A2.2.6
Eukaryotes,
cytoplasm
wall
of
the
the
of
other
a
living
plasma
eukaryotic
the
Whereas
cells
cytoplasm
compartments
are
by
are
In
the
cells
a
basic
cell
cytoplasm
or
from
structure with
eukaryotes,
of
a
double
there is also a cell
prokaryotic cell is one
compartmentalized.
single
described in
eukaryotic
have
some
Areas
membranes.
Topic B2.2.
Three other fundamental
proteins
replic ated.
are
histones,
around
the
except
The
molecules
DNA
arranged
outside.
than
Svedberg
prokaryotic
units
(S).
histones.
DNA in eukaryotes
There are many of these histones
Romualdi, Patrizia. (2017). Epigenetic Approaches
Nuclei,
mitochondria
important
organelles
An electron micrograph
Saccharomyces
cerevisiae (baker ’s yeast). The nucleus (N),
f
x
mitochondria (m) and
The cell wall (CW) is the thicker
pale outer layer.
The plasma membrane
ribosomes
eukaryotic
in
centrifuged;
are
80S
prokaryotes,
c auses
this
whereas
are
cells
examples
are
of
l
O
but
m
N
many are present.
V
m
v
The labelled ribosomes look like a string
of beads. This cell is 8 µm
long.
What is
m
E
the magnic ation of the micrograph?
Remember that 1 µm = 1,000 nm
m
PM
64
there
more
of
a
are
prokaryote
Section A2.2.10
m
a
to see,
but
sink
organelles. All the
described in
80S ribosomes (R) are smaller and
more dicult
to
quantied using
those
(PM) is the thinner dark line inside the cell
wall.
them
is
R
u
visible.
vacuole (V) are easily
and
of
o
i
t
a
r
o
d
in Neuroblastoma Disease Pathogenesis. 10.5772/
Figure 29
as
This
circular.
beads, with the
eukaryotes they are only lacking in cells that never respire aerobically.
n
Source: C aputi, Francesca & C andeletti, S anzio &
of the unicellular fungus,
when
ribosomes
size.
than
small
to increase the surface area. Mitochondria carry out aerobic cell respiration, so in
appearance of a string of beads
▸
proteins,
in
like
The cytoplasm of a eukaryotic cell contains mitochondria. A mitochondrion is
U
giving the overall
intechopen.69566
groups
preparing to divide
rather
surrounded by a double membrane. The inner membrane is usually folded inwards
to groups of proteins c alled
along the chromosome,
ribosomes
Eukaryotic
C
is attached
larger
is
o
prokaryotes is naked,
are
v
Whereas the DNA of
i
n
Figure 28
synthesize
they
70S.
Mitochondria
▴
cells
and
cell
linear
p
are
eukaryotic
globular
a
are
y
quickly
in
dierences
r
e
structural
in
when
O
80S ribosomes
Ribosomes
chromosome consists of one long
proteins,
t
i
s
wound
is
to
chromosomes. The nucleus has a double
E ach
n
The
DNA
DNA
attached
it.
l
the
cell’
s
y
and
the
through
CW
y
molecule
holds
pores
r
DNA
with
P
compartment
membrane
separated
advantages
prokaryotic cells:
Nucleus
This
are
The
e
distinguish
organisms,
membrane.
membrane.
space,
rest
having
features
all
s
s
from
like
inside
outside
undivided
Eukaryote cell structure
Cells
A2.2.7
Processes of life in unicellular
organisms
Living organisms are very diverse in their activities. However, some vital processes
either
universal
or
very
widespread:
•
homeostasis—maintenance of a constant internal environment in an organism
•
metabolism—the
nutrition—supplying
in
an
of
all
the
biochemic al
the
nutrients
response to stimuli—perception
of
waste
metabolism
an
stimuli
and
c arrying
out
appropriate
of
a
cell
types
unicellular
Paramecium
unicellular
either
are
sexually
specialized
organism
and
must
asexually.
to
perform
perform these
perform them all.
Chlamydomonas
organisms
the
(Figure 30 and
functions
organisms that
be controlled
by
the cell
digested
it
moves in
a
particular
direction
in
response to
changes
the Paramecium
Paramecium
has
Metabolic reactions
the nutrients are
into
take
the cytoplasm,
provide energy
and
place in
the
where
cytoplasm,
including
materials
the reactions that
needed
for
n
U
the environment.
they
smaller
Figure 30
These are gradually
and
absorbed
▾
C
i
n
consumed.
that
life.
vacuoles contain
moves
the water.
of
o
v
ood
of whip-like cilia
or
p
two
offspring,
dierent
cell
diagrams of
how
of
n
of
y
single
Paramecium through
This can
organism
O
organism,
the
show
Beating
from
response
annotated
31)
of
r
e
but
products
y
in
multicellular
functions,
in
repair
increase in size or number of cells
reproduction—production
so
and
t
i
s
actions
Figure
growth
y
•
The
energy,
l
growth—an
a
for
P
excretion—removal
•
In
required
organism
•
•
reactions that occur in a
organism
r
•
sum
e
living
s
s
are
growth.
release energy
respiration.
i
o
the cytoplasm
catalyse
these
reactions.
u
l
a
v
O
f
x
t
a
r
o
d
in
by
Enzymes
The nucleus of the cell
E
can
divide to
the etra
when
produce
nuclei
the cell
needed
The contractile
reproduces.
The cell
of the cell
eproduction
is
often
chemicals enter
and
allows the
of oygen
leave.
with
the parent
entry
fill up
dividing
to
form
two
respiration.
Ecretion
water
each
and
end
then
it
through
the plasma
membrane
for
of the cell.
cell
with
t
epel
aseual,
vacuoles at
membrane controls what
This is a
type of homeostasis,
happens
keeping the water content of the cell
daughter
cells.
by
waste products diffusing
within tolerable limits.
out
through
the membrane.
65
Unity
▸
and
diversity
Figure 31
Chlamydomonas
The cell
wall
The plasma
wall
is freely permeable.
membrane inside the
Photosynthesis occurs
controls which chemicals
inside the large cup-shaped
enter and leave the cell. For
chloroplast. arbon dioxide
example, oxygen (a
is converted into compounds
waste product
s
s
of photosynthesis) is excreted
needed for growth. ther
by outward diffusion through
metabolic reactions happen
the plasma
in the cytoplasm.
membrane.
e
ontractile vacuoles
r
 store of starch
at the base of the
is visible inside
fill up with
water and then expel
it through the plasma
the chloroplast.
l
Food vacuoles
membrane. This is a
type of homeostasis,
observations:
t
i
s
which eeps the water
content of the cell
within tolerable limits.
community of life
under a microscope
see
unicellular
organisms,
1.
Collect
pond
water.
v
identical
possible, centrifuge the
to
i
n
sample
nearby. t allows the cell
concentrate the
a
pond
slide.
Add
slip
water on a
can also
of sexual
form
reproduction. n this
image, the nucleus is concealed
by the cup-shaped chloroplast.
n
microscope
U
concentrated
by asexual
fuse and then divide in a
respond by swimming towards it.
drop of the
C
Place
to sense
where the brightest light is and
organisms in it.
3.
nuclei
reproduction. uclei
o
If
can
divide to produce genetically
carotenoid pigments is visible
2.
endocytosis.
The nucleus of the cell
through the water.  light-
sensitive eyespot containing
some
ingested by
 μm
p
procedure.
organisms are
beat to move the
follow
cell
this
when other
y
r
e
The two flagella
To
are formed
O
Examining a
n
y
Making c areful
Data-based questions: Processes of life in a
4.
a
cover
and
view with
testate amoeba
see
unicellular
a
pure
habitats.
you could obtain
culture of unicellular
Paramecium
Chlamydomonas
It
has
a
is
a
unicellular
hard
structure
resembling
aperture
in
through
or
a
E
v
O
l
u
f
x
organisms such as
66
Arcella gibbosa
organisms.
t
a
Alternatively,
r
o
to
i
You will almost certainly be able
o
microscope.
d
a
nuclear
this,
test
then
structures
vacuole
are
C alculate
food
the
testate
coat
and
nger-like
(nm),
(cv)
again.
outer
and
diameter
In
A
of
the
with
is
c alled
the
Figure
of
in
sc ale
of
32,
ve
(to),
is
and
test
in
freshwater
light
test.
plasma
(at).
The
but
There
structures
shown
the
a
cytoplasm
test
the
bar
cell
lives
chitin,
protrusions
surface
that
of
This
aperture
vacuoles.
amoeba
made
honeycomb.
retract
membrane
contractile
1.
the
outer
strong
is
a
circular
c an push out
are
labelled:
membrane (pm),
unlabelled
coloured
lower right.
magnic ation of the
micrograph.
the
[3]
2.
Deduce
3.
Explain
the
maximum
4.
Predict
whether
need
a.
growing
b.
preparing
for
this
a
size
of
food
contractile
cell
particle
vacuole
that
in
could
this
be
ingested.
organism.
[2]
[3]
was:
[2]
to
divide.
[2]
y
P
flagella
Cells
5.
Suggest
a
hypothesis
for whether the cell has
nm
to
mitochondria
suggest
how
in
its
your
cytoplasm.
hypothesis
Give
could
reasons and
be
tested.
[3]
s
s
pm
e
r
cv
l
outer
of
organelles with two
membranes and internal
wall
layer outside the plasma
to
strengthen and
protect the cell
exible
Small
uid-lled compartment
surrounded
by
a
single
membrane
l
organise
organelles that
the
assembly
E
composed
v
Cylindric al
a
O
Centrioles
u
A
f
x
Vacuole
t
a
membrane
of
of
structures
microtubules
Undulipodia
Cilia
and
agella
movement
of
a
food
or
to
generate
movement of
temporary
excess
or
Cells
vacuoles
of
There
water or digest
taken
chloroplasts
as
varied types
in
by
(for
photosynthesis) and
fungi
and
of chitin in fungi
pathogens
of
such
cells
is
of
oen
fungi
substances
a
plants
walls,
store
starch)
composed
and cellulose in plants
large
and
and
have
(to
permanent
plants,
used
vacuole in
for
storage of
pressurizing the cell
endocytosis
Used to construct the spindle
Absent,
that
swimming
moves
chromosomes
in mitosis and the 9+2
except in fungi and plants with
male
gametes,
which
have a centriole
at the base of the agellum
microtubules in cilia and agella
Cilia
used
cell
expel
Plastids
amyloplasts
None
i
rigid
r
o
A
Plants
None
o
Cell
sacs
None
d
membrane
n
family
Fungi
n
A
O
U
Plastids
C
Animals
y
o
i
n
structure between animals, fungi and plants
Feature
50 μm
p
Dierences in eukaryotic cell
y
P
y
t
i
s
Arcella gibbosa
v
A2.2.8
Figure 32
r
e
▸
at
and
agella
are
present in
many animal cells, including the
Absent
except in fungi and plants with male
gametes
that
swim
using
agella
(tails)
tail of male gametes
uid adjacent to a cell
▴
Table 4
67
Unity
and
ATL
It
is
are
diversity
Thinking skills: Reecting on the reasonableness of results
claimed
10
that,
for
prokaryotic
reasonable
it
using
claim?
artist’
s
one
living
One
of
in
your
your
human
body.
cells,
Does
there
this
3.
Construct
seem
times
way to test this claim is to model
Obtain
model
in
of
every
a
eukaryotic cell that is 10
dimension:
100 mm
×
50 mm
50 mm.
clay.
4.
1.
a
larger
some
modelling
Using
these
models,
does
the
claim
seem
clay.
reasonable?
Construct
a
model
of
a
dimensions
10 mm
×
5 mm
e
2.
prokaryotic cell, with
×
×
s
s
a
every
cells
5 mm.
r
two).
patterns.
skeletal
cell
have
theory,
one
However,
Some
muscle
some
examples
and
are
aseptate
cells
do
it
is
structures
in
red
cells,
blood
fungal
not
are
made
preparing
organisms
to
do
phloem
of
cells.
divide,
not
follow
a
nucleus.
there
the
typic al
sieve tube elements,
hyphae.
have
E ach cell
when
y
these
organisms
(unless
At a late stage in their
p
mammals,
living
r
e
Red blood cells
In
all
nucleus
n
be
to
O
may
l
expected
the
t
i
s
is
Atypic al cell structure in eukaryotes
to
y
According
development in bone marrow, the nucleus is moved to the edge of the cytoplasm
the
small
but
have
a
the
they
of
c annot
lifespan
of
cell
the
containing
nucleus
repair
only
it
is
makes
to
120
pinched
red
themselves
100
C
they
of
o
exible,
part
Removal
i
n
phagocyte.
v
and
if
o
blood
they
are
and
cells
destroyed
smaller
damaged.
and
For
by a
more
this
reason,
days.
n
U
Phloem sieve tube elements
Plants move sap through tubular vessels, made from columns of cylindrical cells.
The ow of sap would be impeded if these cells had a typical structure. In xylem
o
body?
the
transport. The subunits in a sieve tube are usually called elements rather than cells
because of their atypical structure. Sieve tube elements are connected to adjacent
companion cells, which have a nucleus and mitochondria. These companion cells
help the sieve tube elements to survive and carry out their function.
Skeletal muscle
sartorius
muscle
Some
600 mm
these
i
Are
break down, but the plasma membrane remains as it is essential for phloem
human
extend
t
a
68
as
that
cells are sieve-like, with large pores for the sap to pass through. During
u
other.
human
much
bres
conducting vessels are called sieve tubes. The dividing walls between adjacent
a
the
as
contents break down. This creates a hollow tube that no longer consists of cells.
In phloem, which conducts sugary sap from the leaves to other parts, the
l
be
muscle
The
between adjacent cells are removed and the plasma membrane and all of the cell
development of sieve tubes, the nucleus and most of the other cell contents
v
c an
33
E
Figure
d
r
o
f
x
O
▴
vessels, which conduct watery sap from the roots to the leaves, all the dividing walls
long.
from
It
one
longest
large
multinucleate
structures
are
formed
when
groups of cells fuse
contains
end
cells
in
to
the
together.
This
Columns
of
then
together
fuse
type
cells,
of
structure
each
to
with
form
a
is
a
syncytium.
nucleus,
long
are
muscle
Muscle
formed
bres.
bres
develop
in
this
way.
by cell division. These cells
y
P
A2.2.9
Cells
Aseptate fungal hyphae
In
some
cell
growing
division.
coenocyte.
so
the
hyphae
The
cells,
the
results
in
nucleus
an
thread-like
hyphae
of
without
other
these
divides
unusually
hyphae
types
of
divisions
of
repeatedly
large
some
fungi
are
fungi
into
without
multinucleate
develop
uninucleate
any
subsequent
structure,
in
this
cells
known as a
way.
are
Walls that
s
s
divide
This
c alled septa,
aseptate.
e
r
l
are also visible
n
c ause of mucormycosis.
them
O
frequent
produced
Spores
n
U
C
the sporangia that
y
p
o
A micrograph of aseptate hyphae of the fungus Rhizopus
which is the most
y
P
y
t
i
s
r
e
and
v
Figure 34
arrhizus,
i
n
▴
A2.2.10 Cell types and cell structures viewed in light and
electron micrographs
micrographs,
in chains
small
size—cells
usually
arranged
oen
less than
rod-shaped (bacilli),
(cocci)
or
no
present
nucleus;
paler
E
a
wall
v
•
cell
instead
•
•
whether
a
cell
is
from
apart
from
a
prokaryote, a plant or an animal.
always
Animal cells
multicellular
there is
larger
and
•
zygotes
size—cells
usually
•
shape
at
tends
sides
visible
in
•
cell
•
nucleus
region of cytoplasm
wall
always
multicellular
gametes,
more
•
than 5 µm
helic al
a
(spirilli)
•
l
O
spheroidal
identify
gametes
5 µm
•
to
Plant cells
u
f
x
•
sometimes
us
i
cells,
help
t
a
single
features
r
o
•
these
o
light
Prokaryotic cells
d
In
larger
apart
from
zygotes and blood cells
size—cells
usually
more
than 5 µm
to
and
be
cell
regular with
junctions
•
easily
shape
tissues
hard
present
normally
present but not
tends
junctions
to
no
•
nucleus
always visible
cell
see
•
to
be
rounded with
between cells oen
in
tissues
wall
normally
present but not
always visible
(nucleoid)
•
simple
•
no
internal
•
structure with no
membrane-bound
present, such as
chloroplasts,
organelles
vacuoles or other internal
plastids
storing
•
large
or
•
amyloplasts
chloroplasts
but
starch
vacuole
no
cytoplasm
other
oen
present
•
only
or
stored
contains
starch
many
organelles
small
vacuoles
are
present
membranes
69
Unity
and
diversity
Table
5
describes
the
structure
and
functions
of
all
the
main
organelles of
eukaryotic cells.
▾
Table 5
The
double nuclear
it.
The
membrane
of
DNA
nuclear pores
nuclear
membrane
nucleus
associated
chromosomes
that
appear
more
densely
the
nucleus,
coiled
histone
up
replic ated
and
proteins.
grainy.
mostly
parts
of
The
The
exported
via
the
transcribed
nuclear
to
cisternae.
protein
synthesized
c alled
are
larger
than
in
prokaryotes and
then
the
c arried
Golgi
appears
U
attached.
tubular
as
or
smooth
Smooth
reticulum
consists
membranes.
circles
is
ER
the
rER
cell.
Protein
passes into its
vesicles, which bud o and
p
of
the
apparatus.
o
endoplasmic
network
membrane
by
from
of
y
is
to
secretion
ribosomes
Smooth
it
sacs,
attached to the outside of
for
the
C
i
n
reticulum
It
moved
v
Smooth endoplasmic
by
r
e
cisternae.
cisterna
They
membrane
are
classied as 80S. The main function of the rER is to
synthesize
are
attened
n
are
of
Ribosomes
where
form mRNA, which
O
these
consists
t
i
s
ribosomes
rER
have
is
l
cisternae.
nucleus
y
The
reticulum
edge of
that
pores to the cytoplasm.
chromatin
Rough endoplasmic
areas that
the
chromsomes
chromatin
is
Uncoiled
small
around
(condensed).
and
through
through the nucleus in the
stained,
contain
pores
ovals
of
bec ause
has
a
In
of
electron
a
branched
micrographs,
membrane. The
there
variety
are no ribosomes
of
functions.
It
is
n
to synthesize lipids, phospholipids and steroids. A
type
of
smooth
ER
stores
used
special
c alcium ions in muscle when it is
relaxed.
o
i
70
v
E
lysosome membrane
t
a
digestive enzymes
a
Lysosome
u
l
O
f
x
vesicles
r
o
cisterna
d
Golgi apparatus
This
organelle
consists
(as
long,
are
oen
curved,
have
many
vesicles
and
processes
of
these
proteins
are
for
them
not
brought
are
have
nearby.
then
in
The
cisternae
in
sacs
c alled
are not as
attached ribosomes
Golgi
vesicles
c arried
are
apparatus
from the rER. Most
vesicles to the plasma
spheric al with a single
formed
concentrations
densely
contain
do
membrane
these
secretion.
They
high
attened
However,
approximately
membrane.
contain
rER).
proteins
membrane
These
in
of
cisternae
staining
digestive
down
ingested
break
down
in
in
organelles
vesicles. They
micrographs. They
which
vesicles.
or
Golgi
protein, which makes
electron
enzymes,
food
from
of
c an
These
be
used
to
enzymes
even whole cells.
break
c an also
y
is
pale
has
P
DNA
with
spread
and
chromosomes, consisting
r
are
remained
dense
are
double
the
e
areas
is
contains
s
s
Nucleus
Cells
A
inner
outer
membrane
membrane
double
inner
membrane
membrane
cristae.
The
uid
mitochondria
is
produce
F at
digested
is
surrounds mitochondria. The
invaginated
inside
is
variable
ATP
for
here
if
to
form
structures
but
usually
the
cell
it
being
is
by
spheric al
aerobic
used
as
or
cell
an
ovoid.
respiration.
energy
in the cell.
not
appear
ribosomes
diameter
ways.
nucleus
double
of
or
variety
organelles
M any
than
half
of
from
Some
unicellular
of
and
are
same
20 nm in
synthesize
cells
the
in
they
of
a
have
cell
and
a
region of
chloroplast. Inside
attened
is
sacs of
variable but
produce glucose
organic compounds
chloroplasts
rapidly,
outside
the
are
They
other
If
constructed
chloroplasts
consist
plant
foods
excess
are
which
ovoid.
of
o
C
t
a
microtubules
E
v
a
O
l
triple
u
vesicles
Microtubules and centrioles
o
i
d
r
o
f
x
large vacuole
more
rER—about
ribosomes
surrounds
shape
photosynthesis.
inside.
containing food
The
photosynthesizing
These
vacuole
the
nucleolus.
thylakoids,
spheric al
wide
n
U
thylakoid
Vacuoles and vesicles
by
a
the
p
r
e
membrane
v
i
n
double
and
the
Free
Ribosomes
c alled
membrane
stacks
usually
have
releasing it to work in the cytoplasm, as enzymes
other
membrane.
stroma
to
cytoplasm
O
are
the
They
y
A
starch grain
80S).
t
i
s
Chloroplast
in
n
the
attached
as
y
in
granules
membrane.
l
protein,
(known
a
y
as
dark
by
P
size
or
as
surrounded
r
These
source
e
matrix
crista
Free ribosomes
c alled
c alled the matrix. The shape of
s
s
They
is
have
may
single
large
volume.
digest
organisms
starch
membrane
vacuoles
Some
them
use
been
contain
with
that
animals
inside
vacuoles
grains.
uid
occupy
absorb
vacuoles.
to
expel
water.
Vesicles
are
very
small
vacuoles
used
to
transport
materials inside the cell.
The
cytoplasm
c alled
including
cells
moving
Animal
cells
consist
of
during
cell
and
contains
They
structures
groups
form
have
small
a
cylindric al
variety
of
bres
roles,
chromosomes during cell division.
h av e
two
Centrioles
cilia
of
microtubules.
an
division
of
anchor
and
c alled
nine
point
also
centrioles,
triple
for
for
which
mic rotubules.
mic rotubules
mic rotubules
inside
flagella.
71
Unity
and
diversity
The cytoskeleton is constructed from several types of protein
bre. Tubulin is used to make microtubules and actin is
used to make microlaments. These structures can easily
be constructed or deconstructed, so the cytoskeleton is
s
s
dynamic. Microtubules guide the movement of components
within the cell. They help plant cells to construct cell walls.
A layer of microlaments just inside the plasma membrane
helps animal cells to maintain their shape.
These
are
one
is
central
present,
c an
also
Flagella
are
a
sperm.
Cilia
and
agella
c an
used
to
create
cell.
a
membrane
microtubules
larger and usually only
are
be
smaller
used
current
and
many
for locomotion.
in
the
O
microtubule
from the cell
double
t
i
s
double
plasma
be
in
nine
uid
next
n
to a
as
Cilia
projecting
of
y
Cilia
ones.
ring
l
present.
a
y
r
e
A2.2.11 Drawing and annotation based on electron micrographs
that
earlier
Table
and
Electron
cell
an
shows
of
also
are
electron
how
a
the
labelled.
in
structure
to
cell
show
Using
your
of
detail.
However, they sometimes include artefacts as well. (An artefact
introduced
may
show
organelles
(Figure
its
as
35)
knowledge
and
of
the
c an
structure
a
the
specimen
structure
be
shown
eukaryotic
c an
these
be
more
in
cell
was
Basic
by
staining
drawing
(Figure
you
36)
are
Organelles
should
be
shown.
in
the
able
to
A
(region containing
membrane
cytoplasm
naked
DNA)
a
v
E
interpret
Electron micrograph of Escherichia coli (1–2 µm
the micrograph
described
in length),
micrograph of
draw the whole cell to
nucleoid
plasma
sectioning.)
were
drawing of the
electron
t
a
u
l
cell wall
and
skills
drawings.
interpreted.
organelles,
prepared
clearly.
o
i
d
r
o
f
x
O
Figure 35
help
was
how
ultrastructure.
▴
great
but
micrograph
prokaryotic
included,
ribosomes
72
present
n
its
is
structure
U
cell
eukaryotic
show
5
of
micrographs
prokaryotic
a
drawing
cell
naturally
C
a
show
not
i
n
Therefore,
is
p
micrographs
something
o
is
v
Electron
with a drawing to
y
two
structures
contain
P
plus
are
whip-like
They
r
surface.
e
Cilia and agella
Cells
free
mitochondrion
nucleus
ribosomes
s
s
e
r
l
viruses
ingest
enzymes
added
therefore
organism
E
relationship,
both
to
o
piece
a
the
killed.
if
it
the
are
Endosymbiosis
almost
According
living
prokaryotes
prokaryotes
that
to
In
and
on
to
other
The
and
studied in
a
could
that
they
down
the
is
the
use
For
closest
form
to
make
It
a
is
enters
vesicle
described
example, phagocytes
organisms such as
feed.
host
In
endosymbiont
membrane.
cells.
unicellular
c ases,
cells
plasma
smaller
The
the
In
those
ingested
c an
gain
c ases,
digestive
organisms,
more
from the
endosymbiosis. In a mutualistic
endosymbiont benet. Examples of mutualisic
Topic C4.1
certainly
contributed
developed
only
the
host).
host.
break
result
the
the
endosymbiosis, one
(the
which
well-established
that
of
other,
vacuole
of
process
ingest
bacteria,
alive.
host
endosymbiosis
cells.
is
cell
is
organisms
the
v
are
the
to
or
a
This
a
Paramecium
ingested
LHA
endocytosis
ingest
are
n
pinching
inside
In
another
u
use
O
by
association.
inside
l
c an
y
vacuole
humans
which
lives
endocytosis.
close
Topic B2.1
O
in
by
f
x
Cells
a
lives
o
small
fully in
endosymbiont
cell
in
i
or
host
together
endosymbiont)
t
a
the
the
Part of the cell on the
n
U
this,
living
d
of
is
(the
r
o
organism
lysosome
apparatus
Origin of eukaryotic cells by
endosymbiosis
Symbiosis
p
The plasma membrane is visible as a dark line.
right is not visible
A2.2.12
o
Electron micrograph of a liver cell.
Golgi
C
Figure 36
i
n
▴
y
P
y
t
i
s
r
e
reticulum
v
rough endoplasmic
the
respire
to
theory,
the
evolution
mitochondria
process
of
aerobic
of
eukaryotic
were
once
respiration.
free-
L arger
anaerobic ally took in these smaller
73
and
diversity
LHA
Unity
prokaryotes
the
in
by
engulfed
the
endocytosis;
cells
to
live
endosymbiont
host’
s
own
supplied
this
energy
respiration.
by
the
host.
mutualistic
of
killing
cytoplasm
At
to
the
Natural
as
and
the
host,
same
far
time,
selection
endosymbiotic
digesting
them,
endosymbionts.
they
Aerobic
allowed
respiration
more eciently than the
the
endosymbiont
therefore
was
favoured cells that
s
s
developed
food
instead
the
supplied
anaerobic
with
in
relationship.
If the endosymbionts grew and divided as fast as the host cell, they could persist
e
inside host cells for many generations. According to the endosymbiotic theory, we
can deduce that they have persisted inside eukaryotic cells for hundreds of millions
r
of years, evolving to become the mitochondria of eukaryotic cells alive today.
l
y
P
O
n
y
t
i
s
embrane invagination
Outgrowths of the plasma
suggest that
membrane expanded the
eukaryotic cells
cytoplasm. The archaean
evolved from
DA
the cells of an
centre and the membrane
archaean,
around it started to develop
usually known
into the inner nuclear
as Asgard.
membrane.
r
e
Shared features
The aerobic eubacterium
y
and vesicle formation
became totally enclosed by
generated organelles which
endosymbiosis and developed
p
became more complex and
remained in the
into the mitochondrion. n
v
diverse. An association
some cells, a cyanobacterium
o
developed with an
i
n
aerobically respiring
eubacterium.
Figure 37
Origins of the nucleus,
mitochondria and
had
o
survive,
also
grow
explains
photosynthesis
and
divide,
it
the
was
could
origin
taken
have
developed into chloroplasts.
in
of
by
chloroplasts.
a
developed
host
into
cell
the
and
If
a
prokaryote
allowed
chloroplasts of
photosynthetic eukaryotes—algae and plants. Again, both the endosymbiont and
host
i
the
This
would
bec ause
u
l
a
E
v
O
f
x
mitochondria
•
•
benet
explanation
theory
They
a
They
a
the
double
their
relationship.
evolution
be
of
mitochondria
conclusively
chloroplasts
plasma
have
the
c annot
and
have
single
for
it
from
provide
membrane.
membrane
was
own
genes,
their
own
on
proved.
strong
This
a
circular
chloroplasts
evidence
would
ingested
and
However,
be
the
remains a
features of both
for it:
expected
if
a
prokaryote with
by endocytosis.
DNA
molecule like that of
prokaryotes.
•
They
own
•
The
transcribe
ribosomes
They
DNA
and
use
the
mRNA
to
synthesize some of their
proteins.
more
•
typic al
c an
of
only
chloroplasts.
74
theory
developed
t
a
r
o
d
to
endosymbiotic
n
that
chloroplasts
U
The
C
▴
also became enclosed and
they
use
for
prokaryotic
be
protein
cells
produced
by
synthesis
than
have
a
size
(70S)
and
structure
eukaryotic.
division
of
pre-existing mitochondria and
Cells
LHA
Eukaryotes
Bacteria
Archaea
s
s
e
r
in was a member of the domain
by uniting
and
membrane
which
would
double
would
have
to
make
predictions:
membrane.
have
Predict
prokaryotic
eukaryotic
features
features.
are ribosomes within the matrix of
mitochondria.
70S
(like
those
of
i
in
are
prokaryotes) or
eukaryotes).
t
a
(as
Predict whether the ribosomes within
r
o
mitochondria
80S
a
o
There
have
d
2.
endosymbiosis
n
which
of
C
theory
U
the
Mitochondria
o
v
i
n
Theories: The theory of endosymbiosis
1.
p
two branches rather than by splitting o a branch
Use
n
took it
the domain Eukaryota was therefore formed
y
In the tree of life,
the mitochondrion was originally a member
cell that
r
e
Archaea.
the host
l
Evidence suggests that
O
Figure 38
of the domain Bacteria and
t
i
s
▴
y
P
y
LUCA
Use the theory of endosymbiosis to explain these features:
Mitochondria
rather
and
have
circular DNA,
Human mitochondrial DNA has only 16,569 base
compared
base
of
pairs
with
human
only
v
are
DNA,
compared
E
There
an
of
143,000,000
chromosomes
loc ated in the
a
O
pairs,
nucleus.
3.
chloroplasts
linear DNA with two ends.
l
2.
than
u
f
x
1.
average
more
Figure 39
than
500
in
Inside this protozoan (Paramecium bursaria),
there are individual cells of a green alga.
have a mutualistic relationship.
inside the
37 genes in human mitochondrial
with
▴
Paramecium,
The two organisms
The algae photosynthesize
providing it
with sugars and
oxygen,
while deriving protection and
c arbon dioxide from their host.
In what
the theory of endosymbiosis?
way does this support
free-living
prokaryotic cells.
75
and
diversity
LHA
Unity
A2.2.13
Cell dierentiation as the
process for
developing specialized
tissues in multicellular
organisms
dierently
perform
the
to
features
other
cell
development
cells
begin
take
and
plants
and
were found
in the liver cluster.
This image shows
in
fungi
genes
in
a
genes
act
in
from
tiny
dierent
a
a
early stage
dierent
the
are
process
“switched
proteins and other gene
cell
is
c alled
once
multicellular
organism
to
in
the
eukaryotic
form
have
Multicellularity
origins
algae
multicellular
lost
the
ability
of
are
plants
has
gene
expression.
evolved
and
at
multicellular.
least once
Even some
aggregates. Most cells within a
to
live
independently
or
to
divide.
o
all multicellular
some multicellular, some unicellular
mostly unicellular, some multicellular
t
a
all unicellular or colonial
plants
mostly unicellular, rarely colonial
all unicellular
u
charophycean algae
red algae
rhizaria
chlorophycean algae
l
dinoflagellates
E
v
a
prasinophytes
ciliates
lobose amoebas
diatoms
dictyostelid slime
other
moulds
stramenopiles
slime
excavates,
e.g.
shows all the major groups of
fungi
shows that multicellularity
choanoflagellates
separately in dierent
acrasid
groups
animals
76
very
is
are
are
expression
embryo,
This
that
they
This evolutionary tree
eukaryotes and
evolved
and
their
genes
moulds
diagram
in
by
cells
type.
development.
particular
energy
human
vary
cell
happens
Even
cells,
multicellular.
and
cooperate
i
d
r
o
f
x
O
Figure 41
M any
are
than
prokaryotes
plasmodial
▸
more
n
cells as a two-dimensional distribution
U
similarities in gene use between individual liver
animals.
makes
of
genes
single
of
in
Evolution of multicellularity
animals
independently
cell
which
C
All
For example, 17 distinct cell types
a
more
protein
o
A2.2.14
dierent
i
n
tissues or organs of the
E ach of these clusters contained
the
in
types
dierentiated
of
Other
organisms.
pathways
release
detected
p
which genes they were using.
A total of 102 cell clusters were discovered,
cell types.
so
control
cells from all parts of the human
corresponding to dierent
In
cell
as
them
the
protein but do not
housekeepeing
active
v
out
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dierent
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roles.
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Biologists recently analysed
The
only
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products.
body.
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specialized
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cells,
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proteins
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body to nd
to
red
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Figure 40
need
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Some
▴
they
For
an
e
ecient.
have
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Multicellular
Cells
to
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have
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types
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biomass
and
within
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they
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an
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generally
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single-celled
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Multicellular
one
single-celled
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consists
traits
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Multicellular
so
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on
death
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single-celled
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organisms
unicellular
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r
lifespans
individual.
organisms,
although
longer
the
Multicellularity
cell
most
the
multicellularity.
organisms must
advantage in some situations.
e
of
of
to
bec ause
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s
suggests
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Nonetheless,
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of
c annot.
dierentiation
and
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lifespans,
LHA
There
l
n
O
y
show coordinated
The bacteria are also able to
are resistant to
They have
u
f
x
when conditions become more favourable, the
cells will reactivate as a swarm
p
and
when the availability of nutrients is limited.
the adaptive advantage that
o
is found in
multicellular inactive (resting) spores that
They form
C
n
as a collective unit
in response to environmental cues.
dierentiate to form
drying out.
which act
t
a
movement
swarms,
It
i
c alled
Gram-negative bacterium
feeds on other species of bacteria.
r
o
clusters,
o
Myxococcus xanthus is a rod-shaped
lives in the soil and
y
P
y
t
i
s
r
e
v
i
n
U
Figure 42
that
d
▴
▴
Figure 43
A slime mould
slow-moving single-celled
solid
c an exist as a number of
protists,
each of which engulfs
food particles. Under certain conditions, the single
cells group
together to form
the plasmodium.
spore tower.
Most
feeding on dead
a multicellular body c alled
This c an then form
into a reproductive
slime moulds are saprophytes,
or dec aying organic matter
l
a
E
v
O
77
LHA
Unity
and
diversity
Data-based questions: Diversity in green algae
1.
a.
State
of
shape
of
the
cells
in
the
two
species
[2]
s
s
b.
the
algae.
Most of the cells of K. klebsii have only one
chloroplast. Describe the features of these
chloroplasts that can be seen in the micrograph. [3]
Explain
a
K. klebsii
for
must
the
hypothesis that some
contain
two
chloroplasts.
[1]
r
d.
reason
cells
Spherical lipid droplets are visible in the cytoplasm
▴
Figure 44
Two species of green algae, with
[1]
Klebsormidium klebsii above and Crucigenia fenestrata below
multicellular.
unicellular
Staurodesmus convergens
two
a
two
bridge
symmetric al
where
the
“semi-cells”
circular
parts
nucleus
contains
of
starch.
wall.
In
impregnated
with
other
or
other
is
their
one
large
There
the
cells,
loc ated.
outer
are
linked
chloroplast with
two
layers in the
layer the cellulose is
substances
and
oen
Suggest
c.
This
spines.
for
the
[2]
spines.
[2]
of
one
in
of
which
this
are
mucus.
these
always
bacteria.
[1]
Discuss
to
the
alga.
alga
is
The alga on the le is the desmid
brebissonii
and the alga
protozoan
that
has
three
Between
similarities
The
cilated
E
15
that
Discuss
the
is
cells.
two
[2]
a
ciliated
visible
has
in
the
Chlorella
dierences
B. brebissonii
protozoan
Chlorella
largest of these
c.
are
v
b.
two.
Bambusina
them
and
a
between the cells of
S.senarium
or
engulfed cells of the alga
l
O
Identify
and
micrograph.
engulfed
[5]
more than
C alculate the diameter of the
Chlorella
relative
cells.
advantages
78
cells.
25
μm
[2]
to
the
ciliated
▴
protozoan of digesting or not digesting the
Chlorella
Staurodesmus convergens
on the right is the desmid
by endocytosis.
a.
cell
u
f
x
Staurastrum senarium.
Figure 45
[3]
one
i
this
▴
t
a
r
o
whether
μm
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d
Suggest benets of the mucus to the bacterium,
also
25
C alculate
n
length
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visible
U
are
d.
and
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secretes a mucus coat outside its cell
Cylindric al
present,
the
function
i
n
alga
wall.
the
without
a
o
b.
v
C alculate the maximum length of the cell,
and
forms
protrusions.
a.
with
by
E ach of the
p
spines
to
y
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[3]
desmid. These algae
r
e
cellulose
store
is a
C. fenestrata
O
a
and
t
i
s
have
3.
or
Figure 46
Bambusina brebissonii (le),
Staurastrum senarium (right) and
[4]
protozoan (centre)
a ciliated
n
K. klebsii
are
y
2.
Discuss whether
l
e.
y
P
of both species, but nuclei are not visible. Outline
how the nuclei could be made visible.
e
c.
Cells
Linking questions
1.
What
explains
the
use
of
certain
molecular building blocks in all living
cells?
the
Explain
how
c.
Describe
cells.
diverse
roles
of
proteins
in
living
cells.
(B1.2.12)
hydrophobicity contributes to compartmentalization in
(A2.1.5)
the
diverse
forms that the genetic material takes in cells.
r
(A2.2.10)
a.
are
A
the
new
the
theory
of
selection,
ii.
multicellularity.
is
useful
the
Predict
the
features that
organism.
and
the
theory
of
evolution
by
evolution of:
(A2.2.12)
(A2.2.14,
such
natural
as
A4.1.1)
the
theory
selection,
of
endosymbiosis
discuss
the
for:
observations.
(A4.1.1,
A2.2.12)
(A4.1.1,
theory
A2.2.12)
n
U
C
o
observations
predicting
the
v
explaining
ii.
i
n
i.
or
extent to which the
p
theory
by
the
y
evolution
of
r
e
of
discovered.
cells
endosymbiosis
cells
theory,
is
the
O
eukaryotic
one
in
explain
i.
Using
plant
observed
theory?
t
i
s
natural
c.
be
compelling
n
Using
multicellular
a
y
b.
of
l
would
features
y
What
P
2.
e
Outline
b.
s
s
a.
o
i
d
t
a
r
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u
l
f
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a
E
v
O
79
LHA
A2.3
Viruses
s
s
How c an viruses exist with so few genes?
Figure 1 shows a human cell infected with inuenza (u) virus. Viruses vary in
8 genes while the human HHV-6 virus (Figure 2) has more than 100genes.
r
What is the minimum number of genes found in any cell? How does this
compare to the virus with the largest number of genes? How can viruses
hosts? Are there any types of genes which are found in all viruses? Do RNA
l
viruses have genes?
AHL
only
structure in viruses
cycle of a virus
several
O
R apid
origins
evolution in viruses
Figure 2 Herpes viruses about to be taken
up by a white blood cell
cycle of a virus
for
y
A2.3.6
▴
features common to viruses
of
p
Evidence
o
Lysogenic
A2.3.5
i
A2.3.4
t
a
Lytic
u
Diversity
A2.3.3
viruses show
a
A2.3.2
v
E
Structural
by white blood
generalizations c an
are some of the ways that
l
f
x
O
A2.3.1
What
is the dierence between the lytic cycle and the
r
o
lysogeniccycle?
80
The virus is also taken up
B-lymphocytes.
all viruses? What
structural variability? What
resulting in a variety of symptoms
d
be made about
o
roseola.
T-lymphocytes and
infects
C
cells c alled
by a
HHV-6,
The micrograph shows a human cell
infected with inuenza (u)virus
n
including a rash c alled
U
nearly all humans in early childhood
to be taken up
This virus,
Figure 1
n
y
t
i
s
r
e
cell which will become their host.
v
white blood
i
n
The herpes viruses shown in Figure 2 are about
▴
of
viruses
from
other
organisms
y
P
endure with so few genes? In what ways are viruses dependent on their
In what ways do viruses vary?
e
the total number of genes they have. For example, the inuenza virus has just
Cells
Viruses
living
are
LHA
A2.3.1
Structural features common to viruses
non-cellular
organisms,
agents
which
share
that
infect
common
cells
and
features
reproduce inside them. Unlike
bec ause
they
are
all
descended
nm =
from
a
single
ancestor
relatively
few
(LUCA),
viruses
probably
1 nm =
as
they
share
features.
Features
that
they
do
have
in
common
are
pm =
examples
of
convergent
evolution—they
developed
for
functional
reasons:
1 pm =
fm =
•
nanometre
have multiple origins,
1000 pm
s
s
common
picometre
1000 fm
femtometre
Small size—Most viruses are between 20 and 300 nanometres in diameter
. This
e
is smaller than almost all bacteria and much smaller than plant or animal cells.
–7
10
Viruses must be smaller than their host cells so they can enter them. Viruses are
r
smallest viruses
also small because they lack cytoplasm and other structural features.
diameter
–8
Fixed
size—Viruses
assembled
inside
do
a
not
host
grow
cell,
so
they
do
not
a
similar
way
to
and
a
c ar
their
increase
a
c ar
in
size. A virus is
being
assembled
from
DNA
molecule
diameter
=
–9
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with
a
M any
fixed
viruses
size,
so
are
are
composed
of
this
determines
the
full
a
size
as
soon
as
10
assembly is
fixed number of components,
overall
size.
hydrogen atom
t
i
s
–10
10
Nucleic
or
RNA
acid
and
as
genetic
they
use
material—All
the
universal
viruses
genetic
have genes made of DNA
code.
This
is
diameter
O
•
essential as their
–11
10
proteins
are
synthesized
by
the
nucleic
acid-to-polypeptide
translation
C apsid
genetic
made
the
c apsid,
enclosed
but
most
have
viral
genetic
produced
material,
that
for
virus
bec ause
are
no
host
a
c apsid. This
of
the
repeating
structure that is strikingly
cytoplasm
infected
and
host
contain
cell,
no
(or
–1
10
–1
10
proton
very
relatively
few
of
the
to
release
100 pm
diameter
=
2 fm
–1
10
viral
rely on the metabolism of the host.
are
cells
the
have only one type of
Self-assembly
symmetric al
viruses
produced
infecting
required
or
for
for
replic ation
bursting
host
cells
▴
Figure 3
This logarithmic sc ale shows
virus’s
the relative size of viruses
u
l
a
E
v
O
f
x
t
a
r
o
i
o
new viruses.
has
d
the
are
enzymes
a
have
c alled
C
The
when
a
coat
viruses
–12
10
from their host cell,
n
enzymes
Even
cells
few
U
enzymes.
host
A
several.
of
from
viruses
released
protein
from the shape of living cells.
released
gives
a
different
few)
c apsid
in
subunits.
subunits
Viruses
the
is
protein
are
i
n
•
in
material
repeating
viruses
o
protein
of
protein—Before
v
is
of
p
their
made
=
y
•
r
e
mechanisms of their host cell.
2 nm
n
each
virus
y
completed.
a
20 nm
l
in
=
y
•
P
10
◂
Figure 4
of mimivirus,
Cryo-electron microscope images
an exceptionally large virus, that
uses Amoeba as its host.
distances from
Colouring indic ates
the centre of the virus.
area (0 – 180 nm
from
The grey
the centre) holds double
stranded DNA that is the genetic material of the
virus.
The rainbow colouring (red to blue =180
to 250 nm) shows the c apsid.
A distinctive
feature of this virus is the starsh shaped
vertex
on the surface of the c apsid
81
and
diversity
LHA
Unity
A2.3.2
Viruses
Based
are
on
Diversity of structure in viruses
very
this
diverse
in
shape
observation,
and
scientists
structure. No genes occur in all viruses.
have
deduced
that
viruses
have multiple
evolutionary origins.
Diversity of genetic material
Viruses
host
have
cell,
genes
the
DNA
circular
variation
no
ends
replic ate
or
their
length
linear
genetic
single-stranded
RNA
material
RNA
viruses
viruses
RNA
nucleic
two
use
viruses
ends.
it
use
one
of
their
genes
transcribe
released
infect it.
the
protein
in
how
synthesis.
For
dierent methods:
as
to
messenger RNA
make
messenger
strand
of
the
DNA
to
produce mRNA.
in
viruses
a
that
virus
it
in
a
process
during
this
c alled
lysis.
process. This is
infect animal cells. The phospholipids in
are
mostly
burst
membrane
derived
from
the
glycoproteins,
plasma
come
membrane of
from
the
virus
itself.
enveloped virus to make contact with a host cell
become
enclosed
viruses
summarizes
that
in
a
infect
some
key
membrane.
bacteria
or
properties
They
plant
of
are
cells
three
c alled non-
are non-
dierent viruses.
n
o
lambda
i
t
a
through
its
pairing
to
has
proteins at the tips of its tails which bind to the outer
Escherichia coli (E. coli).
tubular
tail.
convert
strategies
c an
cycle—The
molecule,
so
new
The
the
then
Lysogenic
viral
whole
viral
DNA
molecule
be
The
has
from
DNA
of
this
virus
enters the host
single-stranded ends, which link
a
linear
to
a
circular
form.
Two
followed:
DNA
virus
becomes
particles
integrated into the bacterial DNA
are
not
produced.
This
is
described in
Section A2.3.4.
•
Lytic
it.
cycle—The
This
is
virus
illustrated
Bacteriophage
A cladogram
viruses
the
proteins,
Most
may be
Lytic cycle of a virus
Bacteriophage
base
1
in
helps
not
Table
A2.3.3
u
Figure 5
E
▴
do
viruses.
cell,
C
viruses
it
variation
o
and
i
n
membrane
alternative
a
v
amphibians
The
surface of its host,
l
reptiles
cell.
The
U
d
r
o
f
x
O
and
genes
p
host
host
covered
around
v
the
enveloped.
birds
negative-sense
their
common
membrane
enveloped
cell
from
become
the
Other
•
three
y
viruses
particularly
mammals
during
There is
and
double-stranded DNA copies of their RNA genes and
the
r
e
be
Some
by
further
Enveloped and non-enveloped viruses
To
enters a
n
2.
make
transcribe
virus
O
then
is
directly
their
a
stranded.
molecule
There
use
t
i
s
retroviruses
acid
and
RNA
•
When
double
lambda
reproduces
in
Figure 6.
is
virulent
and
when
it
then
bursts out of the host cell, killing
follows
the
lytic
cycle
bec ause it
showing
destroys
relationships between coronaviruses,
its
host.
It
c an
spread
to
more
and
more
E. coli
bacteria
but as it kills
based
them
it
must
continue
to
nd
new host cells. If lambda or other bacteriophages
on base sequences of their RNA genomes.
kill
Dierent
host.
an
entire
82
bacteria,
they
are
at
risk
of
dying
out
themselves.
that
infect
cells
in
plants
or
animals
oen
follow
a
lytic
cycle.
As
a
result,
class of host?
they
Source:
of
for a virus to change to a
Viruses
dierent
population
colours indic ate the class of the
How easy is it
Shi,
M.
et
al.
Nature
556,
197–202 (2018).
spread
from
cell
to
cell
within
the
host
organism.
The
viral
infection
becomes
y
negative-sense
the
with
RNA.
or
l
positive-sense
•
of
or
single
y
•
DNA
be
P
example,
in
either
could
r
viruses
with
of
RNA
e
considerable
made
or
s
s
1.
Cells
more
the
of
a
lytic
Usually,
cycle.
virus
become
within
the
the
if
host
body.
has
host,
it
If
humans
a
viral
and
be
produce
infection
the
able
eects
to
ght
of
antibodies
remains
the
o
disease
viruses
that
uncontrolled,
disadvantages
or
it
may
lose
for
its
a
virus.
host
by
The
killing
virus
it.
In
may
however,
be
either
c an
detected and
c ase, the virus
r
lambda
Bacteriophage (a DNA virus that
Coronavirus (an RNA virus with
Retrovirus
uses either a
a
its RNA
bacterium or an
crown-like shape that uses an
One
One
material
molecule
enveloped
48,502
positive and
sense
base
single-stranded
sense
strands and
RNA
molecule
bases.
pairs.
The
16
genes
code
Two
with
positive-sense
for 29
proteins and 6 enzymes.
cycle
virus
it
kills
or
a
follow either a lytic
the
it
reproduces and
host
cell
lysogenic
as
it
bursts
r
o
a
are
viral
9
genes,
coding
for
proteins, including 4
enzymes.
The virus contains the enzyme
reverse
it
a
a
zoonosis,
to
species,
Human
Gram-negative bacterium
15
example
i
Escherichia coli—
molecule of
c aused a pandemic,
in
It
is
an
bec ause
humans
was
from another
probably a bat.
o
d
the host).
single-stranded
RNA
2020.
passed
integrates its DNA and does not
kill
a
starting
of
cycle (in which
of
COVID-19
n
out)
c an
which
U
then
(in
copies
There
structural
C
The
4
o
v
29 proteins including 4 enzymes.
i
n
proteins,
features
29,903
aer
9,749 bases.
There are 32 genes which code for
Distinctive
including
positive-
p
negative
with
r
e
double-stranded DNA
Enveloped
O
Genetic
converts
infecting a host)
y
Enveloped
that
n
as its host)
t
i
s
Non-enveloped
virus
y
cell
(a
genome to DNA
cells
and
y
HIV
l
COVID-19
non-
Host
it
spreads to another host.
animal
or
by
destroy all copies
archaean as its host)
Enveloped
become
multiplying
P
of
virus
will
for a multicellular host.
Bacteriophage
Type
body
e
persist
the
s
s
by
within
animal
example,
therefore
destroyed
only
For
an
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Virulence
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widespread
severe.
LHA
increasingly
transcriptase which makes
double-stranded
of
the
then
viral
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DNA
copy
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integrated into a host cell
chromosome.
possibly cells in
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T-helper cells in the human
immune
system
t
a
u
l
f
x
a
E
v
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membrane
RNA
envelope
with globular
with three types
proteins
matrix protein
packaged
proteins
embedded in
of protein
protein
embedded in it
coat
the membrane
(capsid)
spike proteins
that bind to
reverse
host cells
transcriptase
lipid
bilayer
envelope
▴
Table 1
RNA
associated with globular proteins
83
and
diversity
LHA
Unity
1 Attachment
Proteins in the tip of the tail
bind to maltoporin, a
protein in the outer membrane of
E. coli
used for
absorption of carbohydrates.
2 DNA entry
via
s
s
The viral DNA
molecule enters the host
the pore in maltoporin and another
pore protein in the inner membrane of
r
e
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l
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DNA
circle.
is replicated
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n
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essener NA
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The lytic cycle
100 viruses. The viruses
3 DNA replication
o
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of the host cell.
to mae viral
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v
E
5 Protein synthesis
iral
proteins are synthesied usin host cell ribosomes. nitially,
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hile the virus is inside the host. Then lare uantities of head and tail
proteins are made. These selfassemble to form capsids, ith one copy
of the viral
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84
Figure 6
The lytic cycle
DNA
molecule inside each capsid.
y
P
y
t
i
s
r
e
7 Spread
Cells
The
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A2.3.4
Lysogenic cycle of a virus
lysogenic
cycle,
shown
in
Figure
7,
is
an
alternative
to
the
lytic
cycle.
s
s
The lysogenic cycle
4 Cell division
When the bacterial
prior to cell
host replicates its DNA,
division, it also replicates the
contain the prophage.
1 Attachment
r
roteins in the tip of the tail bind to maltoporin,
used
for absorption of carbohydrates.
l
molecule enters the host via
the pore in maltoporin and another pore
inserted into one specific position in the
by the viral
enzyme integrase.
Aer this, the virus only eists as a
remains
c auses
in
the
state
DNA.
is
lysogenic
harm.
inherited
The
by
uninfected cells.
temperate
to
existing
lytic
must
be
bacterial cell.
Temperate
transferred
bacterial
the
viruses
DNA
bacterial
a
with
the
facilitating
c ause
the
viral
host
is
to
cell
host.
“temperate”: it does not kill its
cells
undetectable
but
c annot
as
a
spread
“lysogenic”
prophage in
by
infecting
bec ause it could
For this to happen, genes in the
stimuli
from inside or outside the
bec ause
These
genes.
is
c alled
lysis.
response
previous
it
remains
daughter
prophage
in
benet
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genes
as
and
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change
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cycle,
virus
u
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bacterial
the
minimal
n
it
i
virus
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x
the
a
and
t
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host
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o
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The lysogenic cycle
o
Figure 7
length
called the prophage.
d
▴
U
of DNA
C
bacterial DNA
o
becomes circular. Then it is
i
n
The viral DNA
v
3 Integration
cycle
y
bacterium.
lysogenic
p
r
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protein in the inner membrane of the
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The viral DNA
n
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a protein in the outer membrane of
e
prophage. Both of the daughter cells
This
their
genes
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increases
the
may include
integrated into the
genetic
diversity of
evolution.
85
LHA
Unity
and
diversity
Justifying hypotheses:
ATL
Data-based questions: M arine viruses
C auses of the switch
Water
to the lytic cycle in
every
samples
two
were
for
taken
13
from
the
months.
counted.
The
St
The
Petersburg
city
pier
in
Tampa, Florida
numbers of bacteria and viruses in the
concentrations
of
chlorophyll
a
were
s
s
samples
were
weeks
measured
Herpes simplex viruses
to
In
everyday
an
oen
“educ ated
is
a
reasonable
This
salinity
correlation
referred to as
guess”.
estimate
were
means
of
the
of
the
water
coecients
taken,
there
is
abundance
of
samples
were
between
these
most
rainfall
in
photosynthetic
also
measured.
variables.
In
algae.
Table
the
area
2
for
the
theoretic al
is
viruses
generated, it
Numbers
worded as a testable statement
of
Numbers
be
investigated
A
well-worded
of bacteria
Chlorophyll
a
Chlorophyll
0.725
hypothesis will suggest the method
be
followed to test it.
Temperature
S alinity
Source: Jiang
of
a
b.
a
variant of the Herpes simplex virus,
is
positive
Numbers
of
a
viruses
and:
b.
chlorophyll
c.
salinity.
period of time symptom free. What
t
a
causes the virus to convert to the
lytic cycle?
Hypothesis 1:
then
lytic
the
will
convert to
If the host is in
O
l
Hypothesis 2:
4.
Discuss
5.
Bacteria
the
of
C alculate
seawater
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163–172.
1.00.
some
[1]
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coecient.
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7
between
0.22 × 10
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7
and
between
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3.0 × 10
3
per
cm
.
numbers of viruses
bacteria
a
[1]
concentration
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the
of
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analysing
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prophages.
the
at
and
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from
contained
coecient
positive
−0.534
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Four
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St
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Petersburg
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coecients.
[2]
tested to nd out whether they
bacteria
of
tested
positive.
lysogeny in bacteria in
pier.
[1]
health, then the virus will
convert
to
the
lytic
cycle.
v
a
robust
virus
cycle.
u
the
f
x
health,
If the host is in poor
o
r
o
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coecient
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reason
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and an active lytic phase; during the
lytic phase, it causes painful blisters.
by
indic ated
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between a dormant lysogenic phase
correlation
negative
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known as HSV1. This virus alternates
indic ated
Progress
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what
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Temperature
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1994.
p
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what
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Paul.
v
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Table 2
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should
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concentration
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bacteria
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that
While viruses are not living, they are
subject
in
to
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t
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adaptations
encoded
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Viruses
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theory
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simpler
natural
rst.
structure
organisms
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these
All
viruses
use
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cells,
same
suggesting
genetic
code,
the
with
hypothesis that they
a
few
insignic ant
selection to justify
dierences.
of
in
reproduction. Use the
evolved
If
they
did
evolve
before
cells,
the
universality of the genetic code
hypotheses.
implies
86
several origins of
viral DNA will determine
successful
both
Evidence for
pressures and
E
the
a
single
ancestral
virus
with
this
code,
from
which
all
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y
hypothesis
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is
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samples
summer.
hypothesis.
of
Once
shows
where
Numbers
justic ation
Temperature
r
there
and
language, a
is
an
e
hypothesis
give
Cells
descended.
viruses
common
Viruses
in
structure and genetic constitution of
suggests
multiple
origins
rather than a single
use
this
cells.
parasites.
is
that
essentially
code.
There
It
the
seems
are
two
They
cells
need
must
same
of
host
cell
evolved
genetic
reasonable
types
a
have
to
code,
for
which
inherited
deduce
hypothesis
in
to
replic ate. An
before viruses. All living
that
the
from
viruses
LUCA. Viruses
must
mechanism
of
have
evolved
evolution.
Progressive hypotheses
are
built
in
in
ts
some
a
series
with
of
the
cells,
for
steps
by taking and modifying cell
observation
example
that
there
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retrotransposons.
l
Retrotransposons are sequences of nucleotides that occur widely in the
t
i
s
make more DNA copies of the transposon by reverse transcription of the RNA,
O
then insert these copies into the cell’
s chromosomes in random positions.
There
are
striking
eukaryotic
have
evolved
material
from
host
between
method
into
a
used
host
cell’
s
retrotransposons,
cell
this
by
method
of
retroviruses
propagating DNA in a
such
chromosomes.
c apsid
proteins
would
observation
the
viruses
are
small
and
Others
smallpox
virus.
Mimivirus
0.75micrometres
to
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of
larger
components,
more
enzymes
of
are
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cells
expected
inside
perform
one
with
a
cell
independent
certain
has
time,
a
a
to
be
host
their
diameter
wall
of
and
organism
base
own
Some
for
pairs.
and
example,
only
These
but
there
of
are
bec ame
parasitic
bacteria
For
have
example, the
0.6micrometres
bacteria
large and
perform functions that
types
functions.
membrane.
that
variation in
complex, such as the
self-reliant
cell.
metabolic
Chlamydia
show
example, with a diameter of
1.2million
u
are
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even
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some
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an
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few
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o
bacteria
ability
600
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with
larger
have had to
loss of cell components.
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leave to their host.
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bacterium
have
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simple
much
by
i
the
steps
viruses
t
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lost
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of
both
d
cells
bacteria
and
are
r
o
The
viruses
viruses
series
n
virus.
most
a
that
self-reliance.
polio
complex
in
U
Some
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also
C
complexity
cells
integrate
o
from
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develop
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to
v
Regressive hypotheses
the
HIV
retroviruses to
proteins.
Viruses
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as
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p
from
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y
genetic
similarities
and
r
e
their
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cell
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RNA and this RNA is translated, several enzymes are produced. These enzymes
y
genomes of eukaryotes. When a retrotransposon is transcribed to produce
y
components
up
This
P
components.
r
Viruses
e
1.
diversity
s
s
organisms
from
obligate
deduction
use
the
Section A2.3.2)
ancestor.
are
obvious
also
However,
(described in
LHA
are
and
as
few as
were thought to be viruses but
They
are
likely
to
have
evolved
parasitic, entering host cells and
reproducing inside them.
These
observations
respiration
may
help
explain
to
convergent
of
bacteria
and
have
by
protein
E
Viruses
suggest
v
intraparasitic
arisen
their
by
that
loss
of
viruses
more
might
and
have
more
originated
from
life functions, including
synthesis.
various
diversity.
evolution—they
progressive
Shared
are
features
shared
for
and
of
regressive
viruses
functional
could
reasons
routes. This would
be
the
rather
result of
than
bec ause
ancestry.
87
and
diversity
LHA
Unity
H
N
O
H
N
s
s
N
N
H
N
r
N
H
Scientists have discovered
of viruses and
from
and
RNA
detecting
and
target
antigen
changes,
l
u
the
immune
are
destroyed.
as
of
the
As
a
c an
of
less
than
The
an
an
infection
evolve.
generation
average
There
and
are
the
next,
generation time is
hour.
ultimate
a
inv ading
as
source
no
or
multiply,
a
rapid
evolution
not
in
plant
on
longer
the
on
on
viruses.
proteins
of
this
perform
or
natural
recognize
those
has
example,
surface
variation
any
checks
of
it.
a
to
high.
antibodies
the
virus.
Viruses
the
is
be
mechanisms
membrane
with
selection
in
tends
animal,
For
the
variation
viruses
enveloping
where as
consequence,
evolution.
do
acting
selection
bacterium,
c apsid
rapid
which
selection
natural
such
and
be
one
the
during
c an
replic ation of their genetic material.
antibodies
the
between
humans,
variation.
natural
destroying
in
In
coronaviruses,
whether
system
encourages
it
during
antigens
protein
happen
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changes—it
with
c an
previous
powerful
If
in
the
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new
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form
and
this
H1N1 inuenza viruses with
haemagglutinin (H1) and
neuraminidase
v
O
f
x
of
evolution.
rates tend to be high in viruses. This is particularly
intensity
humans
variant
such
organism,
of
heritable
time.
genetic
made
result
The
i
for
only
viruses
on
o
the
population.
host
in
viruses
is
c an
mutation
errors
Evolution
The
but
rates
rapidity.
generation
depends
correct
t
a
r
o
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in
this
n
U
or
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years
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Figure 10
25
Evolution
is
for
change
limited
about
2.
▴
reasons
rapid
undergo
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is
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C
it
extremely
virus
Evolutionary
so
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i
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person,
v
three
our understanding of the origin
R apid evolution in viruses
show
p
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This modic ation makes the DNA more heat-stable
How does this aect
r
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c an
attack by the host.
the genetic code?
A2.3.6
Viruses
so the DNA of the bacteriophage has Z–T base pairs
have A–T
.
O
protects it
base,
t
i
s
and
uses the universal
has diaminopurine instead of adenine in its DNA. The
n
for this modied
where other organisms would
a bacteriophage (S 2-L) that
y
letter Z is used
it
l
Figure 9
genetic code with one dierence:
Two
examples
of
are
the
inuenza
virus
and
HIV.
(N1) proteins visible in the enveloping
membrane
The inuenza virus
E
Inuenza
is
stranded
RNA
replic ase
which,
This
leads
consists
c an
88
to
of
a
as
if
by
its
a
enveloped
DNA
cell
from
is
virus
material.
mutation
separate
host
molecules
an
genetic
unlike
high
eight
appear
RNA
c aused
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that
polymerase,
does
rate.
of
Instead
a
molecules.
Bec ause
invaded
two
each
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strain
by
are
negative-sense single-
replic ates its genetic material using RNA
not
proofread
single
of
this,
dierent
combined.
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a
or
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molecule, the genome
new
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strains of the virus and some
The
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y
P
thymine
diaminopurine
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Cells
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in
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by
Ho n g
H 1N 1
also
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in
s t ra i n s
a
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host
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p ro te i n s
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Sp a n i s h
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19 18
H3 N2 .
e ve r y
act
n e u ra mi n i da s e
c h a n ge
th e
c o n tra c t
v a c c i n a ti o n
vi r u s
and
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c aused
p e rs o n
on
the
a
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19 6 8
h ow
de pe n d s
of
These
St ra i n s
Fo r
of
to
was
R a pi d
of
c aused
e vo l u ti o n
influenza
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pu t
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re pe a te dl y
v accine
vi r u s .
a
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genome
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by
of
tw o
vi r u s .
pro d u c e
two
m o re
Th e s e
mo re
to
ma ny
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ma de
s t ra i n s ,
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by
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to
pro o f re a d
m u t a ti o n s .
to ge th e r
within
di ffe re n t
not
enzyme
f a c to rs
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m a ny
an
does
the
v i ra l
its
s i n g l e - s t ra n de d
c o r re c t
Mutations
th e
HIV
host
the
i n fe c t e d
di ffe re n t
or
s t ra i n s .
ge n e s
that
one
Wh e n
c an
also
c o nve r ts
highest
by
e r ro rs
a re
k n ow n
s tra i n
a
of
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d i ve rs i t y.
cell
is
l e a di n g
v
o
Most of the mutations that occur in HIV are harmful to the virus, so the action of
y
e ve n
will
l e a di n g
de a m i n a s e,
a ny
tra n s c r i p ta s e
e n z y me
p
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e
i nv a d e d
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ra t e
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p o l y m e ra s e),
cytidine
to
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th a t
D NA .
t
i
s
(u n l i ke
to
n
is
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l
The HIV virus
y
s e ve ra l
cell.
pa n d e m i c .
exp l a i n s
bi n d
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pro te i n s .
Ko n g
vi r u s
to
P
c o n ta i n s
a
me mb ra n e
used
birds and humans. This is
r
and
and
i n fl u e n z a
the
between
frequently.
e
p o t e n ti a l
th e
is
c o mb i n a t i o n s ,
c o m bi n a ti o n
of
particularly
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with
to g e t h e r
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s
s
h e l ps
th e
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c ause
LHA
transmitted
i
n
cytidine deaminase may be protective to the host. Even so, the rapid generation of
C
new strains within a person helps the virus to evade the immune system. As a result,
most infections are chronic rather than curable. HIV has a protein on its surface that
it uses to bind to and enter a host cell. Mutations in the env gene that codes for this
U
protein allow HIV to evolve to use dierent cell types in the human body as hosts.
n
HIV can also evolve to become resistant to the antiretroviral drugs used to treat
patients infected with HIV
, so a combination of two or more drugs is necessary.
0.7
becoming HIV+
i
0.2
1.2
2.2
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aer
5.9
7
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8.9
9.9
5.3
u
l
a
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v
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r
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years
◂
Figure 11
the
env gene evolved
This tree diagram
the 10-year period
positive.
E ach dot
shows how
in one patient
over
aer they bec ame HIV-
represents a new version
Source: Dapp MJ, Kober KM,
of the gene,
with the colour showing when
Chen L, Westfall DH, Wong K,
it
was rst
identied. A change in colour in
et al. (2017) Patterns and rates of
the branches on the tree diagram shows that
viral evolution in HIV-1 subtype
B infected females and males.
PLOS ONE 12(10): e0182443
the
env protein would
host
bind
to a dierent
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89
and
LHA
Unity
diversity
Data-based questions: Progression in HIV infection
HIV
of
targets
the
CD4
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T-cells
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humans.
used
to
These
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cells
infectious
1.
are part
Describe
patient
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with
changes
typic al
in
CD4
T-cell
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of
numbers in a
the
infection.
blood,
of
the
of
CD4
infected
relatively
rare
HIV-infected
cells
falls
individual
opportunistic
individual
is
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200 cells mm
to
to
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display a number
infections.
said
of
have
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At this point,
AIDS
syndrome).
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blood
contrast
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levels
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virus
found
typic al
progressors and long-term
the
length
of
[3]
(acquired
Determine
time
it
takes
for
AIDS to
vary in their
develop in:
CD4
infection.
The
concentration
typic al
level
of
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the
in
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progression.
progress
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curves with black
4.
of
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13
shows
COVID-19.
the
early
stages
graph
coronaviruses.
90
of
shows
of
an
investigation into the origin
investigation
the
E
The
results
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a
Figure
v
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Data-based questions: COVID-19
how
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was
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similar
chart
c arried out during
c aused
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above
shows
by this virus.
is
to
ve other
how the genome
of
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the
four
and
is
organized.
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have
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proteins:
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spike,
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numbers
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membrane,
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numbers of genes.
for
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y
and
patients
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graphs
P
squares)
four
o
the
HIV
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to
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response
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immunodeciency
the
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how
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4.
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Deduce,
with
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coronaviruses
Compare
[1]
the
which
most
part
of
the
HKU3-1
including
coronavirus
genes.
[2]
5.
is
most
closely
Deduce
b.
Suggest
least
related
to.
[2]
contrast
the
the
genome
genomes
of
the
which
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a
to
that
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most.
[1]
SARSo
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Zhou,
probable
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origin.
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Nature
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Compare
is
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what
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or simplicity?
a.
l
Explain
what
to
explain
concept
and
of
meant
the
et
30,000
al.
A
pneumonia
outbreak
associated
with
a
new
coronavirus of
270–273 (2020)
i
example,
the
v
To
contribute
u
f
x
O
c.
2.
an
Outline
XG.
25,000
t
a
r
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mechanisms
Wang,
579,
20,000
nucleotide position
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Figure 13
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coronaviruses,
COVID-19 genome is
ORF1b
10,000
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[3]
part
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5,000
of
other
COVID-19.
a.
reason, which of the other
COVID-19
and
with
s
s
3.
many
coronaviruses.
LHA
1.
the
rapid
analogous
by
history
contrast
convergent
a
of
the
evolution of viruses. (A2.3.5)
structures. (A3.2.8)
selection
life
evolution?
pressure.
characterized
structure
of
(D4.1)
by
typic al
increasing
complexity
prokaryotic and
eukaryotic cells. (A2.2.5 and A2.2.6)
b.
Outline
the
theory
of
c.
Discuss
the
evidence
endosymbiosis.
(A2.2.12)
for multiple origins of viruses. (A2.3.5)
91
Unity
and
diversity
TOK
Are some things unknowable?
some
are
from
exact
to
scientists
test.
have
to
Abiogenesis
non-life.
It
conditions
is
struggle
is
the
impossible
on
prebiotic
with
process
for
hypotheses that
self-replic ating
by
and
which
researchers
E arth,
bec ause
to
life
all
replic ate
they
of
and
the
rst
protocells
did
not
fossilize.
In
the
Miller
demonstrated
that
it
was
example,
the
70
or
acids
so
from
years
simple
since
inorganic
then,
precursors.
scientists
have
life
form
from
non-living
simulation
it.
is
to
Through
occurred
and
know
reason,
that
it
it
However,
exposed
as
them
well
as
to
to
wet-dry,
moisture,
precursors—despite
through
scientists
involved
the
chamber
high
levels
reason
rather
that
are
The
purpose
the
agree that
thought
of
have
these
emergence
emergence of
To
to
of
of
been
is
RNA
a posteriori is
oxidizing
to
on
to
the
prebiotic
molecules.
know
it
bec ause it has
y
p
o
C
n
o
i
The planetary simulator at
McM aster University in Hamilton
a
Figure 2
two dierent
Sugars have been detected on
meteorites:
Murchison meteorite
E arth.
investigate
u
l
E
v
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x
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a
Figure 1
placed
Figure 1)
seasonal
temperature,
present
experiments
r
e
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o
◂
◂
92
and
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in
radiation and other conditions
self-c atalytic
know something
nitrogenous
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day-night
high
of
wafers.
n
observing
abiogenesis
a priori
solutions
silicon
O
by
a
eorts.
know something
than
in
t
i
s
To
on
been unable to
environments,
signic ant
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mixture
achieve
l
simple
the
y
a
researchers
dried
samples
cycles,
create
then
c atalysis
to
y
amino
and
in
able
laboratory conditions.
possible to
these
form
under
P
Stanley
separately
been
early
bases,
1950s,
steps
have
r
known
these
compartmentalization,
Researchers
are not
For
fully
molecules,
polymerization.
e
arose
the
c ases,
dicult
s
s
In
NWA 801 and the
Cells
been
observed
biochemic al
A priori,
based
we
on
know
is
the
form
the
diversity
many
not
of
possible
to
life
know the
is
with
water
following
essential
evolution,
different
key
for
and
and
chemic ally
interface
surrounding
permeable
cellular. This
materials
factors:
compounds
other
or
element
types
of
The
strength
c an
explain
as
would
need to be semi-
exchange
of
waste
of
a
and
theory
the
the
four
major
c ategories
of
comes
predictions
from
it
the
c an
observations it
support.
to
account
for
amino
acids,
cells—accounts
the
and
all
been
prokaryotes
Rocky
greater
water
range
is
of
found
chromosome
is
tendency
for
planets
form
around
stars,
the
a
them
to
contain
large
evidence
there
original
volumes of
event
phenomenon
condensed
water,
and
water
exists
as
a
liquid
over a
the
relatively
large
temperature
allow
a
living
organism
that
to
cells
achieve
maintain
the
is
essential
conditions
be
a
for
membranes
of
millions
directly
and
c ause
of
years
observable.
explains
all
provide
endosymbiosis. Since
the
ago, the
However,
bec ause
observations, we hold it
pragmatic truth—one that “works”.
p
C
o
v
i
n
n
U
o
i
t
a
u
l
a
v
E
Figure 3
d
r
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f
x
O
▴
predicts
the
prokaryotic type single
theory
occurred
not
a
double
the
observation of
y
compartmentalization
is
r
e
to
The
theory
range.
for
the
Rickettsia,
O
When
and
observations.
fever. Within mitochondria,
ribosomes,
molecules
t
i
s
universe.
type
spotted
throughout
empiric al
the
by
of
intracellular
n
addition,
range
as
theory
l
a
circular
In
supported
y
dissolves
water.
is
parasitic bacteria such as
Mountain
prokaryotic
solvent
than
wide
meteorites.
of
No
a
originated
found
intracellular
c arbon-rich
mitochondria
nucleobases, the
sugars — have
The
evolution of
y
lipids,
that
P
of
for
biologic al
theory
raw
e
of
and
communic ation.
endosymbiosis—used
mutualistic
components
to
well
for
r
subunits
molecule—including
•
allow
c an
The
•
environments.
c arbon.
The
in
diverse
structure
eukaryotic
•
physic ally
environment
to
as
and
between the compartment and the
life’s functions and
no
of
as
in
The
a posteriori.
life on other planets is likely to be
on
process
as
is
s
s
for
It
life on other planets
associated
based
Molecular
of
that
c arbon,
reasoning
•
directly.
features
The red
cells in this micrograph are intracellular parasites in the cytoplasm
of yolk sac cells
93
Unity
and
diversity
End of chapter questions
1.
Figure
1
represents
Identify,
a
a
prokaryotic
ii.
part
The
a
from
a
multicellular
or
root
eukaryotic
tip
magnific ation
or
of
a
the
C alculate
how long a 5 µm
to
the
of
the
cell.
[2]
sc ale bar should
drawing.
[1]
alga.
C. reinhardtii
2
shows
a
as
is
a
a
unicellular
model
c.
section
Organelle
research
green
d.
Structure
growth
aids
detection
in
the
the
labelled
an
C,
D,
eyespot.
of
G
This
light.
and
is
Suggest
the
adaptive
H.
an
When
Chlamydomonas reinhardtii
light.
[4]
organelle that
with
is
the
c alled
vacuole.
function
mutant
5%
cells
CO
that
and
Compare
normal
towards
a
and
cells
lack
normal
a
the
Figure
pyrenoid
air
with
[1]
3
shows the
cells
(purple)
(green), in air
0.04%
CO
2
contrast
and
Conduct
contractile
the
growth
mutant
cells
rates of the
at
low
CO
2
concentrations.
advantage of this
U
ii.
State
the
reason
[2]
photosynthetic
organisms
[2]
require
n
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
94
Figure 2
a
normal
CO
.
[1]
2
A
B
C
D
E
F
G
▴
of
pyrenoid.
C.reinhardtii
2
i.
exposed to
moves
behaviour.
H
and
Deduce the identity of
E
rates of
C
light,
is
contractile
p
A
shown.
a
state
o
Organelle
organelles
are
v
b.
the
organelles
i
n
Eight
is
vacuole.
(single-celled)
system in genetics and
cellular motion studies.
a.
B
and
y
used
Figure
r
e
organism
in
Chlamydomonas reinhardtii
n
micrograph
O
electron
through a single
Figure 1
t
i
s
The
y
▴
2.
l
added
size
y
ii.
is
[1]
P
the
it
tip.
drawing is 2,500×
C alculate
if
actual
[1]
finger
i.
be
organism.
e
i.
of
cell
reason, whether the cell is:
r
b.
with
s
s
a.
Cells
f.
300
Discuss
what
is
signified
by
the
error
Figure
1–
normal
3.
[3]
cells
yad
g.
State
the
dependent
and
independent
variables
mutant cells
3–
ni
100
in
The
example.
microscope
[3]
image
in
Figure
(centre
bottom) and a filament of
longer
numbered
4
shows
a
Spirogyra
s
s
rotifer
(right).
100
a.
The
rotifer
is
ticks
on
the
multicellular,
sc ale
about
1,000
cells.
being
composed of
Outline
two
O.
et
eciency,
68,
Issue
14,
8
limitations
Journal
September
in
of
loss
CO2
in
supply,
Experimental
2017,
that
c an
and
be
two
made
qualitative
from the
Chlamydomonas
but
not
Botany,
micrograph.
thylakoid
Volume
Pages 3903–3913
Estimate the length of the main body of the
d.
Distinguish
t
i
s
c.
rotifer
Suggest
based
Structure
F
in
explain
the
for
pyrenoids
data.
Figure
the
function
2
is
photosynthetic
as
sugar.
cells
a
starch
for
as
granule.
storage
starch
of
e.
Research
field
rather than
[2]
of
a
size
of
cells.
the
[4]
[1]
rotifer cells and
[2]
possible combination of ocular and
lens
that
were
view.
used to obtain this
[1]
C
o
v
i
n
n
U
o
i
d
t
a
r
o
u
l
f
x
a
v
O
▴
Deduce
objective
c arbohydrate
the
Spirogyra
p
in
the size of the
[2]
reasons
between
y
and
on
possible
r
e
e.
a
O
iii.
n
c auses
operating
Pyrenoid
y
reinhardtii
al.
[4]
l
C aspari,
multicellular.
quantitative
observations
Source:
being
y
b.
Figure 3
of
air
2
advantages and
P
CO
the
r
disadvantages
5%
Discuss
The
are 122 µm apart.
e
llyhporolhc
egnahc %
mc
3.
this
0
▴
bars in
Key
Figure 4
E
95
Unity
and
A
s
s
d i v e rs i t y
e
r
3
Organisms
things.
plants
All
in
the
life
forms
adaptive
n
U
o
it
i
p r e ss u r e s
The
o r g a n i s m ’s
arise
are
s u c c e ss f u l
of
and
when
to
a
are
very
Fo r
form
past
by
by
the
adapted
to
its
is
a
c o m p l ex
their
the
selection
changes.
that
Sempervivum
are
typic al
a
an
genus
long
of
evolutionary
succulents
for
enhance
e nv i r o n m e n t .
collection
the
live
of
evolve
through
f rom
and
d i v e rs i t y
e nv i r o n m e n t
and
image
d r o u g h t - t o l e ra n t
to
particular
produce d
d ra s t i c a l l y.
The
to
c h a ra c t e r i s t i c s
a
basis
billion
p ro c e ss
e nv i r o n m e n t
in
the
four
the
to
organisms’
population
the
ex a m p l e ,
changed
f a c t o rs
a l l ow
non-living
changes.
for
adapt
survive
species
Plants
background
a
limiting
adaptations
the
these
become
inherited
ability
coordinate d
p r o c e ss e s .
and
ability
survive
that
to
that
the
has
in
p h o t o sy n t h e s i s
shaped
accounted
g e n e ra t i o n s
to
Ad a p t a t i o n s
u
l
E
v
O
f
x
t
a
r
o
d
m a ny
Every
be
evolve
e nv i r o n m e n t .
enables
been
responses
c an
ra d i a t i o n .
Po p u l a t i o n s
over
has
o
of
D uring
e nv i r o n m e n t
life
use
compounds
C
i
n
evolutionary
of
f rom
nutrition.
image
metabolism.
E a r t h ’s
d i v e rs i t y
c h a ra c t e r i s t i c s
y
energy-rich
v
The
re quire
background
p l a n t ’s
these
organisms
p
y e a rs ,
living
r
e
the
t o g e t h e r,
organisms
the
g e n e ra t e
of
Ta k e n
distinguish
c h a ra c t e r i s t i c s
O
to
t
i
s
us
certain
n
common.
h av e
l
organisms
y
P
living
y
All
s h ow n
in
that
t i m e.
in
they
A3.1
Diversity of organisms
Biologists dene a species as a group
traits that
interbreed
denition work for organisms that
other challenges exist
Charles D arwin wrote,
every naturalist
knows vaguely what he
means when he speaks of a species”.
What
are the reasons
l
that
establishing a denition of a species is so dicult? What
To what
Figure 1
The light
morph (le) and
extent is it surprising that
n
early naturalists use? Consider the
▴
two jaguars in Figure 1.
y
classic ation systems did
y
yet
with this denition? In 1859,
“No one denition has satised
P
all naturalists;
How does this
reproduce asexually?
r
What
of organisms with
in the wild.
e
shared
s
s
What is a species?
the “melanistic” or
dark morph (right) of the jaguar (Panthera onca) interbreed in
to be the same species?
thewild
O
t
i
s
they are considered
What patterns are seen in the diversity of genomes within and between species?
ways do genomes vary across the kingdoms of
Red
size,
composition,
association with
number of chromosomes? In
C
what
loc ation,
i
n
proteins,
ways does the genome within a species vary? The
visc acha rat
It
any mammal,
102.
chromosome number of
Its closest
living relative is
▴
Why is this condition more likely to
A3.1.2
Species
A3.1.3
Binomial
A3.1.4
Biologic al
as
groups
f
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system
and
organisms
of
for
HL
as
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organisms
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i
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of
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traits
organisms
species concept
u
Variation
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A3.1.1
visc acha (Tympanoctomys barrerae, le) and
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A3.1.5 Diculties distinguishing between populations and species
A3.1.12
Diculties
species
concept
and
to
bacteria
in
to
that
have
A3.1.13
Chromosome
within
species
a
l
O
A3.1.14
Engagement
species
to
A3.1.7
K aryotyping
A3.1.15
Identic ation
A3.1.8
Unity
DNA
a
A3.1.9
Diversity
a
karyograms
v
of
of
genomes
within
species
in
the
biologic al
reproducing
horizontal
number
with
as
a
gene
species
transfer
shared
trait
loc al plant or animal
develop a dichotomous key
habitat
of
using
species
from
environmental
barcodes
eukaryote genomes
E
A3.1.10
and
diversity
only
applying
asexually
A3.1.6 Diversity in chromosome numbers of plant and animal species
due to divergence of non-interbreeding populations during speciation
and
of the same family (right)
o
in plants?
d
be found
The red
Octomys mimax,
the Andean visc acha rat (right), which has
56 chromosomes.
Figure 2
Octomys
n
mimax,
is one of the few identied polyploid
has the highest
U
animals.
o
life in terms of structure,
v
what
y
of an organism; that is, the total amount of DNA. In
p
r
e
The genome is the whole of the genetic information
Comparison of genome sizes
A3.1.11 Current and potential future uses of whole genome sequencing
97
Unity
and
diversity
A3.1.1
Variation between organisms as a
dening feature of life
An
organism
variety
between
a
2.
Even
less
members
humans,
same
the
There
bec ause
genes
by
and
but
adds
to
natural
of
is
a
brightly
closely
related—are
the
in
they
twins
of
are
into
but
there
are still
they
the
Variation
is
formed when a
two
acquire
which
richness
subject.
species,
individuals.
dierences
develop
is
Such
through
never
identic al.
natural world and helps to
also
essential
for
the
future of
selection could not happen without it.
p
y
more as they grow older
coloured
variation when two individuals
develops
r
e
some dierences at birth and accumulate
A3.1.2
are
single
least
even
environment
fascinating
evolution
we
monozygotic
divides
Even monozygotic twins show
life
which
and
above 80°C and pHs
n
a
soil
Species as groups of organisms with
v
shared traits
o
i
n
If organisms in an area are studied, it soon becomes obvious that each individual
C
is a member of a group with recognizable traits or characteristics. These groups of
organisms are oen given a name in the local language, especially if they are used by
people or have an impact in other ways. For example, when Māoris arrived in New
U
Zealand about 800 years ago, they found tree ferns growing in the forests and used
n
them to build the walls of their houses. They recognized seven dierent types of tree
fern, which they named whekī, kuripaka, tuokura, mamuka, punui, ponga and kātote.
biologists
by
seven
have
these
The
Alsophila dealbata.
species
M āoris
in
inner
New
described
of
tree
If
a
asked
of
is
and
as
a
the
the
biologists
Biologists
who
other
typic al
species
about
traits.
Linnaeus,
Linnaeus
structure
onwards,
shared
worked
group
of
of
of
a
the
of
term
“species”
for
a
group of
naming
and
classifying
18th
century,
was
a
time
described
his
that
concept
species,
the
been
species.
organisms
morphologic al
origins
in
biologists
members
used
have
This
share
of
Linnaeus
a
is
a
the
known
as
particular
species
pioneer of this
outer
form and
morphology. The
outer
form and
species.
and
his
contemporaries would
In
probably have said that they were the work of a creator. They would have thought
fern
that
Zealand,
three
C arl
structure
of
o
the
for
ponga.
i
to
name
is
a
addition
is
research.
century
with
since.
inner
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name
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idea
v
O
scientic
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17th
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a
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Zealand
d
r
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Figure
New
f
x
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From
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When
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describing
from
the
nothing
morphology
and
of
remained
species,
unchanged aer its
early
biologists
believed
more:
they
were
looking
at
evidence
of
a
creator ’s work.
Alsophila colensoi, Alsophila milnei and
E
Alsophila kermadecensis
A3.1.3
The
international
system
binomial
system.
E ach
borealis.
The
name
have
98
Binomial system for naming organisms
similar
rst
traits.
The
that
biologists
species
is
the
name
genus
second
name
use
for
consists
name.
is
the
A
naming
of
two
genus
species
species
words,
is
or
a
for
group
specic
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example,
of
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species that
name.
y
In
organisms
such
the
individuals.
embryo
the
the
temperatures
to
dierences
l
Figure 3
among
all
bec ause
of
biology
through
the
metres, fungi that consist of
ways.
identic al.
with
and
at
100
any other living thing.
O
▴
variation
diversity
make
many
between
out
growing
than
or
Consider
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s
mutations
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in
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pools
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twins
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us
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growing
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r
from
dierences
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plant,
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is
of
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organisms
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bacteria
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genus
•
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•
In
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initial
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letter
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of
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shown in italics.
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used
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genus
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with
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the
of
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it
c an
species
L. borealis
morphologic al
a
selection
in
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species is an unchanging
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internal
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However, this does not t with the concept of
proposed
concept
denition
concept,
that
to
ts
by
Charles
describe
all
D arwin
species,
contexts.
So
but
far,
at
it
in
least
▴
1857
. Biologists
has
proved
30
Figure 5
have
been
suggested!
plant
that
of C arl Linnaeus,
successfully
how
a
group
garlic,
and
these
but
deliberately
Similarly,
occur,
they
occurring
crossing
there
are
for
are
is
such
have
The
than
unit—the
This
members
partly
junipers
to
and
with
of
a
species
organisms.
in
conifer
conifer
there
and
is
some
was
and is
hybrids
conifers
genera
named
interbreeding
conifer
many
and
natural habitats
Allium macleanii
bec ause
species.
of
of
the binomial system
many plants and animals using it
explains
“Globemaster ”
interspecic
pines,
identify
reported
i
easy
In
groups
introduced
organisms that
concept
species, including onion
variety
species
Ginkgo biloba.
of
been
Where
is
some
garden
600
unusual.
where
have no
speciation
interspecic
t
a
u
l
f
x
a
E
v
O
Figure 6
as
less
with
hundreds
hybrids
sterile.
r
o
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Allium christophii
more
example,
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usually
rapidly,
and
Allium
usually
species
coherent
of
This
o
relatives,
hybridization
▴
concept
d
is
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by
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close
bred
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share genes in a gene pool.
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sterile.
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and
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biologic al
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and
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interbreed
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y
biologic al
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or to describe a feature
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dierent
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denitions
Binomials are oen chosen to
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a
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i
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other
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Biologic al species concept
to
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letter.
l
evolution
a
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the
example,
organisms
between
or
to
text,
nomenclature:
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of
begins
an
r
According
binomial
with
P
A3.1.4
have
name
binomial
for
about
begins
printed
abbreviated
name,
group
rules
name
s
s
•
Allium christophii (le),
Allium Globemaster (centre) and Allium macleanii (right).
Globemaster is a hybrid of A. christophii and
A. macleanii
99
Unity
and
diversity
In
other
dicult
is
groups
to
described in
closely
related
have
to
and
animals,
Section A3.1.5.
but
the
apparently
biologic al
those
sometimes
Further
distinct
species
species
are
hybridized,
but
same
species
hybrids
diculties
arise
species
concept,
producing
are
denition
×
example,
known
lion).
fertile.
therefore
when
hybridization
For
female
concept
gradual
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together.
ospring
sometimes
would
species
and
as
M ale
A
of
species
lions
and
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ligers
rigorous
consider
two
c aptive
lions
and
tigons
are
interpretation of the
r
biologic al
female
biologic al
separation
not distinct.
female tiger) or tigons (male tiger
infertile
the
geographic al
e
×
to
that
plants
due
s
s
According
suggests
of
apply,
and
tigers to be the
species, but this is not acceptable to biologists or the wider public.
l
grizzly bears meet,
If polar bears
they c an mate and
The photo shows
such a hybrid
C
i
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A3.1.5
o
v
produce fertile ospring.
n
and
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bears are spreading north.
p
r
e
usually geographic ally separated but grizzly
O
Polar bears (Ursus maritimus)
grizzly bears (Ursus arctos horribilis) are
Diculties distinguishing between
U
n
populations and species due to divergence
of non-interbreeding populations during
o
population
at
the
same
interbreed
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same
is
with
they
u
if
l
a
genetic ally
two
of
organisms
populations
other.
This
physic ally
populations
physic al
very
may
of
live
does
and
the
in
not
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species,
dierent
areas,
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genetic ally
dierent.
separate
E
The
to
it
c arry
speciation.
c an
species
natural
If
a
species
out
is
may
similar,
to
living
they
mean
both
in
the
same
area,
are unlikely to
that
they
are
populations
which
the
to
dierent
are part of
with
Bec ause
whether
sometimes
animal
c an
diverge.
become
two
this
process is
populations
have
disagree. (It would be
species
diverge
Topic A4.1.
they
populations
accumulate, the two
species.
decide
species
described in
interbreed,
as
continue
biologists
experiments
by
not
separate
dicult
and
do
develop
dierences
become
be
process
This
of
dierences
eventually
gradual,
inappropriate
issues.)
If
each
more
populations
become
group
are
two
Recognizable
usually
a
time.
species.
However,
v
O
f
x
the
c alled
100
i
A
t
a
r
o
d
speciation
to
to
form
try
to
new
resolve these
species is
y
P
y
Figure 7
and
t
i
s
▸
Organisms
s
s
e
r
plants
most
is
male
a
and
gamete
and
is
immense
useful
our
nearest
searching
relatives,
O xfo rd
h ave
been
of
a bo u t
s ma l l e r
c h ro m o s o m e s
and
16
o th e rs
in
h ave
e ve n
2.
Their
o r i gi n s
in
a
m a ny
of
and
s ma l l
ye a s t
f i n d i n gs
of
with
have
c an
from
gametes
All
cells
two
of
starts
chromosomes.
by fusion of a
produces
produced
a
zygote with
from
the
zygote
Gametes with one set of
sets
are diploid.
two
T h e re
to
s u g ge s t e d
to
of
n u mb e r
ones.
chromosomes
nd
is
a
20
of
l a rge
of
Re s e a rc h e rs
Table
a
1
vo l u me s ,
This
th e
few
th e
or
that
th e
a c tu a l
long
as
in
n u mb e rs
l a rg e
c h ro m o s o m e
n u mb e r
of
numbers
shows
e ach
by
numbers
containing
a
could
l a rge r
and
sizes
of
c h ro mo s o me s
exp e r i m e n te d
re d u c e
chimpanzees,
i n fo r m a ti o n
vo l u me s
with
h ave
and
chromosome
w o rd s .
l a rg e r
p a ra l l e l
Some
other
hundreds.
me a n i n g s
animals.
cells
46
easily
c o n s i s ts
and
s ma l l e r
vo l u me s .
pl a n ts
c h ro mo s o me s
You
D ictionary
the
pu bl i s h e d
E
n u m be r
E n gl i s h
are also
However,
chromosome number among plants and animals.
range
species.
life
decrease if
There
there is no change in a
number
new
chromosomes.
cells
occur.
double.
usually
even
A
to
number.
c an
each gamete containing one set of
fusion
humans
48.
They
of
Body
in
an
c abbages).
sets
that
have
databases.
i n fo r ma ti o n
in
a
Th e
diversity
remember
have
with
This
l
some
two
v
O
for
to
cells
u
is
(18
haploid.
f
x
It
are
and
reproduction.
gamete,
c abbages).
these
rare
t
a
chromosomes
There
female
chromosomes
inherit
body
sexual
splits
i
mitosis
of
if
it
o
of
a
are
change:
number
years.
animals,
in
number
chromosome
c an
increase
d
sets
(9
or
chromosome
r
o
by
of
consequence
chromosomes
two
chromosome
millions
together,
the
its
n
In
c ause
is
number
U
over
This
O
the
species
c an
fused
species
this
y
to
that
any
C
changes
become
of
species,
i
n
mechanisms
a
C abot’s
is a separate
o
chromosomes
of
p
characteristic
evolution
v
the
it
Populations of T
. sandvicensis live in Europe whereas T
. acuavidus
Diversity in chromosome numbers of
fundamental
During
in 1787
.
n
all biologists agree.
South Americ a
plant and animal species
A
as a species by John Latham
phylogenetic research suggests that
r
e
A3.1.6
Not
recognized
recent
t
i
s
species, Thalasseus acuavidus.
lives in North and
Thalasseus sandvicensis (le) was rst
as a subspecies of the sandwich tern but
l
The sandwich tern
y
P
Figure 8
tern (right) was classied
y
▴
by
fusing
n u mb e r
to
th e
4
or
c h ro mo s o m e s
in
a
▴
Figure 9
Who has more
chromosomes—a dog or its owner?
s pe c i e s
s a me
is
not
ve r y
s i gn i f i c a n t ,
as
all
me mb e rs
of
th e
species
h ave
th e
n u mb e r.
101
Unity
and
diversity
Data-based questions: Dierences in chromosome number
Plants
no
Number
plant
species
yet
discovered
(in
the
(woodrush)
Crepis capillaris
(in
Vicia faba
bean)
(eld
lily)
brome
(coee)
(porcupine
grass)
tree)
dierent
Explain
Table
chromosomes
in
a
Ovis aries
60
Capra hircus
discuss
of
numbers
the
78
Canis familiaris
13
but
some
black
bear)
(dog)
numbers
are
not
seen,
for
example,
chromosomes.
4.
Using the data in Table 1, identify a change in chromosome structure that may have occurred during human evolution.
and
its
complexity.
to
c alculate
the
genome
is
a
positive
correlation
between the number of
[4]
size
of
a
species
from
its
chromosome
number.
[1]
[2]
u
f
x
t
a
r
o
i
impossible
there
[3]
Explain
it
that
1
(armadillo)
(Americ an
3.
species
hypothesis
Ursus americanus
Table
has
Dasypus novemcinctus
Using
makes
the
in
species
sheep)
(goat)
2.
what
1,
none
(chimpanzee)
(domestic
76
o
in
chromosome
why
d
data
Pan troglodytes
n
the
13.
U
many
and
48
54
C
shrub)
(golden hamster)
(modern human)
o
deciduous
Table 1
are
Homo sapiens
i
n
(evergreen
11
Mesocricetus auratus
46
64
Rhododendron keysii
7
,
44
c at)
(mouse)
y
(hickory)
small
5,
Mus musculus
(mink)
(domestic
p
grass)
Magnolia cordata (a
There
40
v
Carya tomentosa
Felis catus
(saxifrage)
daisy)
(manna
Mustela vison
38
r
e
(Michaelmas
30
(desert locust)
(vampire bat)
O
(peanut)
Desmodus rotundus
t
i
s
bay)
Schistocerca gregaria
n
tea)
(sweet
24
28
y
(Chinese
grass)
(grasshopper)
(Chinese hamster)
l
(Texas
(house y)
A3.1.7 K aryotyping and karyograms
view.
To
to
study
chromosomes
the
and
spread
slip.
The
the
with
c areful
cell
with
no
each
on
a
become visible when
Chromosomes
giving
dierence:
of
an
the
clearest
•
slide.
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searching,
The
it
oen
Some
three types of
stains
give
with
chromosomes
different
banding
distinctive banding
in
each type of
is
usually
stained
Originally,
from
a
each other
possible to nd a
chromosomes
analysis
print
involved
and
•
process
c an
now
be
Chromosomes
(chromosome
c an then
the
cutting
shortest
vary
1)
is
in
size.
more
In
than
humans,
the
largest
five times longer than
(chromosome 21).
arranging them
done
E ach
chromosome visible in metaphase consists
digitally.
of
102
on
pressing on the
overlap
•
This
based
chromosome.
chromosome
manually.
classied
are
patterns,
by
are
organism, cells
microscope
chromosomes
overlaps.
photographed.
out
metaphase
chromosomes
but
be
placed
E
cover
organism
with
stained
burst
an
dividing,
v
are
of
a
are
l
chromosomes
cells
O
The
two
strands
c alled
chromatids, held together
y
Cricetulus griseus
mosquito)
(fruity)
r
22
Glyceria canadensis
1.
Drosophila melanogaster
threadworm)
fever
(watermelon)
Chrysosplenium alternifolium
▴
8
(horse
(yellow
Chorthippus parallelus
Arachis hypogaea
Aster laevis
Aedes aegypti
Musca domestica
Magnolia virginiana
Stipa spartea
6
18
Camellia sinensis
Coea arabica
( jack jumper ant)
12
(royal
Bromus texensis
family)
Parascaris equorum
P
Lilium regale
aster
Myrmecia pilosula
4
(c abbage)
Brassica oleracea
Citrullus vulgaris
the
family)
e
Luzula purpurea
aster
s
s
Haplopappus gracilis
Animals
2
Organisms
by
a
the
centromere. The position of
centromere
chromosomes
so
the
the
so
of
length.
In
near
is
the
centre,
chromosomes
other
centromere
the
is
the
are
s
s
equal
arms
varies. In some
it
chromosomes
nearer to one end,
chromosome has a shorter and
characteristic
in
species
a
showing
is
c alled
are
chromosome
karyotype.
karyotype of an
karyogram. The
arranged
in
l
chromosomes
the
a
of
the
pairs,
with the smallest.
O
K aryogram
t
i
s
Figure 10
of a human female,
with uorescent
staining to generate
o
i
n
v
p
y
banding patterns
r
e
▴
n
y
starting with the longest pair and ending
y
image
organism
types
c alled
P
An
are
r
The
e
a longer arm.
Human somatic (body) cells have 46 chromosomes. Our closest primate
U
C
Data-based questions: Primate chromosome numbers
2
relatives—chimpanzees, gorillas and orangutans—all have 48. Human chromosome
12
n
types are numbered from 1 to 22. One hypothesis is that human chromosome 2 was
formed from the fusion of two chromosomes in a primate ancestor
. Figure 11 shows
The
be
the
strength
of
of
the
fusion
region
has
just
second
a
the
evolution
a
If
the
two
telomeres,
of
u
chromosome
of
with
chimpanzee
have
many
hypothesis
the
were
chromosome
chromosomes.
true,
predict
where the fusion
the
[2]
one
centromere,
centromere.
evidence
chromosome
[3]
repeats of the
occurred.
l
the
a
have
remnants
v
O
are
to
in
2
c alled
sequence.
found
hypothesized
Discuss
in
DNA
f
x
short
would
Normally
chromosome
chromosomes,
what
there
4.
human
of
same
is
3.
ends
t
a
Compare
2.
r
o
1.
o
from chimpanzees.
i
d
banding patterns of human chromosome2 compared with chromosomes 12 and 13
for
a
but
Explain
fusion
of
in
this
chromosome 2
observation.
chimp
[2]
chromosomes
13
2
in
humans.
[3]
▴
Figure 11
Human
E
chromosome 2 (le) aligned
with chimpanzee chromosomes
12 and 13 (right)
103
Unity
and
diversity
F alsic ation: Testable versus non-testable statements
The
nature
of
scientic
and
observations
are
a
theory,
it
predicted
becomes
observation
or
theories enables both
predictions.
the
predicted,
enhanced
to
address
James
the
with
creation
the
that
predictions
biblic ally
of
huge
the
from evidence in
the
E arth must be
based
on
biblic al
reconstructed date
E arth
timesc ale
was
▴
early enough to
implied
by
Figure 12
marine life.
geology,
down,
from
Knowledge
followed
paleontology.
claims
based
on
vertic al to horizontal.
religious faith
oen
not
falsiable
by
observation or
is
not
the
and
Hutton’
s
notion
that
are
to
not
say
they
testable.
are
observations
the
biblic al
were
“days”
explained
were
Another
thinker
proposed
underwent
omnipotence
to
occur
that
You
in
13
in
an
meant
he
the theory that
could
periods
learned
2
these layers were
observations
geologic al features
about
arose
ancestral
of
the
from
primate.
c ause
long
geologic al ages
time.
theory that the human
fusion
Is
this
of
chromosomes 12 and
theory
testable?
o
Unity and diversity of genomes
i
within species
Among
biologists
information
u
l
a
E
v
O
f
x
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a
r
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A3.1.8
have
away,
Hutton used
transformation over long periods of time
short
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God’
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theory”).
but
metaphoric al
corresponded to much longer periods of time (the
“interval
of
one
information
is
each
DNA
A
of
the
genome
c arrying
a
members
of
their
during
the
genes.
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contains
a
or
of
species
promoting
the
alleles
of
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The
is
forms
gene
units
the
the
of
genome
even
same
is
organisms. Genetic
the
genetic
of
a
a
species
a
gene,
is
the
in
of
the
entire
a
base
in
bases.
species
and
sequence of
due
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in
to
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without
along
each
exchanged
any genes being
arrangement of genes
living
organisms.
variation in individual
oen
base
Typic ally, the
sequence,
the
unity
alleles,
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of
same
chromosomes
the
largely
c alled
each
in
species
illustration
of
from
of
diversity
genome
an
thousands
genes,
parts
of
dier
means all of the genetic
group
c alled genes. A gene is a length of DNA
or
allows
thus
genomes
so
or
(chromosomes).
hundreds
This
“genome”
organism
DNA,
have
duplic ated.
Alternative
word
functional
chromosomes
in
in
molecules
sequence
of
the
individual
contained
meiosis,
omitted
on
today,
chromosomes.
Diversity
104
xed
For
C
by
they
i
n
example,
rather,
o
valid;
v
This
were not
not
changed their orientation
by further layers of sediment.
of rock formations such as this to support
experimentation.
that
Aer being partly eroded
p
subsequently covered
are
appearance indic ates many years of sediment being
by a geologic al event
y
and
r
e
laid
zoology
The lower layers of rock in this drawing contain evidence of
The striated
exist
within
a
species.
sequence. Usually only one
y
t
No
argued that the
inferred
and
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than
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be
not
n
rocks
chronology.
for
time.
c an
were
transformation
y
older
constant
t
i
s
present-day
much
of
history
developed the
features
l
periods
E arth’s
observation, or
(1726–1797)
geologic al
underwent
long
result is not well
theory is either
P
but
that
by
new
falsied.
Hutton
theory
the
a
r
considered
the
If
e
or
explained
consensus.
experimental
explained
When enough
and
s
s
explanations
Organisms
or
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very
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small
at
a
number
certain
of
base
bases
position.
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results
loss of gene function.
in
in
nucleotide
M any
a
gene
larger
where
sections
more
polymorphisms,
thousands
of
dierent—for
while
of
than
another
a
gene
one
individual
human
to
may
SNPs
genomes
be
and
have
one
might
become
base
abbreviated
example,
allele
allele
might
have
have cytosine in that
altered, but this usually
present
are
c alled single-
pronounced
been
s
s
Positions
are
position
“snips”.
sequenced,
allowing
have
been
therefore
all
from
of
each
genomes.
base
humans—another
there
are
dierent
diversity
other
typic ally
from
but
these
(unless
we
This
in
illustration
about
have
genome.
of
occurring
humans.
an
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rather
have
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a
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than
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others
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TT
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parents
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for this
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heteroygous
for
bec ause the alleles
inherited
i
r
o
father
is
o
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from the mother and
◂
have
a
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Figure 13
SNPs are inherited
from
base
f
x
t
a
our parents
of
plants,
than
the
and
other
genome
genome
eukaryotes
and
variation
a
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larger
animals
of
l
size
u
Diversity of eukaryote genomes
overall
far
the
d
their
genomes
is
homoygous
from
base
species
is
bec ause
n
U
child
o
v
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n
allele
SNP
present it
p
from
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regarded as a mutation
y
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r
e
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The
the
feer
least 1% of
maternal allele
in
in
(SNPs)
at
may
identic al twin!).
nucleotide polymorphisms
paternal
both
This
are the main factor in making humans
are
bec ause
are
SNPs, so only about
in
than 1% of individuals f a
base
The
bases
regarded as single-
individuals
A3.1.9
Most
unity.
4,000–5,000
commonly
SNPs
seems a huge number but
our
O
positions
that
pairs
t
i
s
These
human
n
level
is
in
y
individual,
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dierent
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threebillion
y
a
same
so
over
l
in
are
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one
1
seem
there
the
Within
base
discovered
r
remember
e
researchers to assess the frequency of SNPs. More than 100 million dierent SNPs
in
base
within
vary
by a huge amount,
sequences.
a
Variation
between
species.
Variation in genome size
genome
and
contain
some
a
lot
functioning
genome
no
size
E
size
of
is
species
measured
have
a
non-functional
genes
consists
known
v
O verall
than
in
base
surprising
DNA,
smaller
so
pairs.
There
amount
they
genomes.
do
For
of
not
a
huge
DNA.
is
L arge
necessarily
range in genome
genomes
contain
c an
more
example, about half of the human
of
transposons
(transposable
function.
Transposons
are
sequences),
sometimes
referred
to
most
as
of
“junk
which
have
DNA”.
105
Unity
and
diversity
Table
2
shows
the
range
of
genome
Organism
sizes
Genome
million
dierent
size /
base
Description
pairs
27
Apis mellifera
Unicellular
217
Honey
3,080
Pan troglodytes
Human
3,175
Chimpanzee
r
Paris japonica
150,000
Woodland plant
gene
a
over
to
for
result,
be
the
time.
protein
there
may
Dierent
species
also
genome
hundreds
make-up,
of
dierent
removed
millions
especially
no)
of
numbers
from
it,
years
ago
when
they
so
has
an
base
and
base
sequence
not
that
of
role
infrequent.
in
example,
respiration.
dierences,
genes.
diverged
developed
to
are
change—for
essential
types
adapted
sequence.
dierences will
sequence
species
have
are
base
does
in
more
Genes
even
c an be
from a common
dierences in their
dierent
ways
of
life.
n
U
o
i
t
a
120 bases in the sequences of the gene that
codes for cytochrome oxidase 1 in nine species.
l
using additional soware to allow comparison
a
E
v
O
106
which
(or
in
that
species.
have
or
few
species,
You c an use the GenBank website to compare base sequences of specic genes between species. This image
shows the rst
been aligned
u
Figure 14
d
r
o
f
x
▴
relatively
c,
C
genetic
be
dierences
changes
function
cytochrome
related
i
n
ancestor
a
genes,
vital
some
separate
o
to
a
have
form
p
distantly
some
with
v
between
added
In
genes
will
to
y
As
tend
species
diverge
r
e
the
a
O
accumulate
These
of
populations
n
populations
these
t
i
s
If
l
y
Variation in base sequence
The sequences have
y
P
Table 2
Two
organism
bee
e
Homo sapiens
organisms.
s
s
Paramecium tetraurelia
▴
in
Organisms
Data-based questions: Genome sizes
graph
number
in
of
Figure
genes
15
that
compares genome size with the
code
for
proteins
in
species of
trend
does
curve
the
number
that
of
proportional
What
t
to
genome
line
on
show?
graph
genes
is
[2]
shows that
not
directly
size.
the
graph
would
the
indic ate
variables?
[1]
3.0
01
genes
reasons
not
for
the
being
number
directly
of
protein-
proportional
genome
size.
[2]
2.0
t
i
s
has
been
c alculated
and
is
a.
What is the statistic R
for this data
0.919.
▴
Figure 15
2
?
[1]
Source:
Hou
Y
,
Lin
does
a
value
as
high
as
0.919
indic ate?
[2]
Eukaryotes
Content
4.
The
sc ales
on
the
axes
are logarithmic.
If
the
log
protein-coding
gene
number
is
4.0,
is
the
actual
number
of
protein-coding
[1]
If the log
genome
size
(kbp)
is
6.0, what is the
10
actual
number
of
base
pairs?
[2]
for
ONE
C
b.
i
n
genes?
Distinct Gene
Relationships
for
Dinoagellate
4(9):
e6978.
o
what
PLOS
v
10
(2009)
Non-Eukaryotes: Gene
Estimation
Genomes.
a.
and
S
Size
size / kbp
y
What
p
r
e
Number-Genome
b.
6.0
genome
10
O
The statistic R
4.0
log
2
3.
n
2.0
to
l
the
coding
y
Discuss
gol
b.
y
between
4.0
P
proportion
graph
the
protein-coding
to
trend
direct
been
the
r
a.
has
in
e
The
data
gnidoc-nietorp
2.
the
eneg
What
s
s
eukaryote.
1.
5.0
rebmun
The
n
U
o
d
A3.1.10 Comparison of genome sizes
of
the
into
to
estimate
the
sequencing
a
cost
gamete
(C-values),
It
of
Genome
form the basis
c an
also
be
in
Plant
DNA
Gardens
C-values
D atabase
hosted
by
Kew
(https://cvalues.science.kew.org.com)
future genome
sizes
units
or
l
content
=
a
animal,
in
grams)
(1 Mbp
data
fungus
v
O
DNA
of
either
a.
used
are
of
b.
Animal Genome Size Database (www.genomesize.com)
c.
Fungal
typic ally
number
of
base
Genome
Size
D atabase
(www.zbi.ee/fungal-
genomesize.com)
mass (usually
pairs
d.
Microbial
Genomes
(https://www.ncbi.nlm.nih.gov/
6
pairs
Nuclear
these
diculty
−12
1 pg = 10
megabase
plant,
and
c an
nuclear DNA contents of a haploid cell such
picograms;
or
genomes
evolution.
u
as
as
of
programmes.
f
x
given
size
genome
t
a
research
r
o
of
i
Knowledge
10
for
and
base
more
pairs).
genome/microbes.com)
than
microbe
is
10,000
available
species
from
four independent databases:
E
107
Unity
and
diversity
Thinking skills: Evaluating alternative perspectives
ATL
Knowledge
For
claims
example,
criteria
size
for
are
aected
answer
correlate
judgement.
to
with
In
the
by
criteria
question,
for judgment.
regulation
“How does
many
tissue
types
fewer
tissue
types?
complexity?” depends on our
particular,
what
do
we
gene
expression.
more
W.
McShea,
quoted in
Single-celled
organisms
c arry
the
know
a
paleobiologist
Scientic American,
term
how
to
complexity:
put
a
“It’s
number
on
at
Duke
discusses
not
it.
just
the
that
They
University
multicellular
problems
they
don’t
activities.
don’t
different
by
the
more
complex?
More
recently
example:
which
are
metabolic ally
Multicellular
organisms
have
more
complex than animals.
a
greater
than
prokaryotes,
due
to
evolved
of
organisms
more
longer
we
agree
agree
on
on
a
an
denition
of
on
inquiries
types
of
c annot
be
successful
extended
it
is
question.
raw data into
internal
in
not
with
a
know
questions
essential
An
are
to
have
the
answer
example:
a.
Do
For
angiosperms,
than
b.
or
Do
be
followed. The dependent and
should
on
be
easy
average,
to
have
identify
from the
larger genomes
pteridophytes?
fungi
Generate
“no” and the
before they start.
so
to
question.
been
“complexity”,
and
animals
have
similar
genome
sizes?
begin with
“yes”
expressed
method
variables
open-ended question
simple
the
independent
assessment
biology
o
does
essays
suggests
stored
c arried out using databases.
project,
answered
clearest
turn
d
researcher
M any
to
data
that
the
n
open-ended
The
researchers
of
D ata mining is
U
both
and
system.
o
based
by
information.
investigations
collection
computer
C
useful
used
organized
a
i
n
process
in
p
an
term
y
r
e
is
v
database
electronic ally
the
answer to the question.
Thinking skills: Answering open-ended questions
ATL
have a
O
c annot
often
ago. Does this make them
complex?
complex
range of
organisms
novel adaptations than those
t
i
s
types
evolved
number
diversity of
Until
cell
smaller
n
•
more
a
l
Plants
out
singled-celled
y
•
c arries
make
word”.
greater
For
that
wording
i
t
a
r
o
using
a
one
research question about genome size and test
or
more databases.
Current and potential future uses of
u
whole genome sequencing
l
a
E
v
O
f
x
A3.1.11
it
Whole
genome
organism’s
bec ause
most
sequencing
DNA.
their
in
was
relatively
organisms.
shown
This
Table
Some
3.
is
rst
small
of
the
determining
done
in
genomes
e arly
the
the
entire
1990s
made
landmarks
it
base
with
e asier.
in
sequence
of
bacteria
and
It
fe asible
whole
is
now
genome
an
archae a,
with
sequencing
are
y
mean
organism
Does
P
they
108
many
know what
•
an
out
single cell within a
r
with
In
organisms with
e
D aniel
a
organisms with
than
“complexity”?
activities per cell, while a
A
Are
complex
mean
•
by
of
s
s
genome
the
Organisms
Year
Organism
1995
Haemophilus inuenzae
Number
(a
pathogenic
1996
Saccharomyces cerevisiae
(yeast—a
1998
Caenorhabditis elegans
nematode
(a
Arabidopsis thaliana—rst
Homo sapiens—complete
eukaryote
multicellular
base
100 million
plant
135 million
sequence
published
3,080 million
the
data
also
both
developments
example,
years, the size of the genomes being
has
This
increased
have
was
the
continued.
dropped
from
made
speed
The
$100
possible
of
by
sequencing and
cost
of
million
in
sequencing
2001
to
less
been
exponential
has
genome
to
been
growth
sequences
sequence
the
in
completed,
will
soon
genomes
of
the
so
be
all
number
any
gure
of
exceeded.
known
species
quoted
The
for which at
for the number
E arth BioGenome
species.
A principal goal of sequencing the genomes of a wide range of species is
p
investigation of evolutionary origins. Comparisons between genomes allow
v
researchers to identify relationships between species and trace the diverging
y
r
e
aims
10
thousand.
2020.
sequence
complete
Project
in
for
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y
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than
of
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least
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less
t
i
s
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genome,
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factor
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l
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3.
by
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one
Table
P
technologic al
reduced
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increased
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at
sequenced
pairs
12 million
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Table 3
Look
of
fungus)—rst
worm)—rst
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e
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unicellular
prokaryote
s
s
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2003
bacterium)—rst
o
pathways from common ancestors. Knowledge gained from studying the genomes
i
n
of dierent species will make it easier to conserve and protect biodiversity.
C
Research into the genomes of pathogenic bacteria and viruses will help in the
control and prevention of infectious diseases caused by these organisms.
are
far,
this
ambitious
over
one
number
has
will
to
treatments
it
and
for
about
be
the
every
genetic
possible
to
development
genetic
health
eight
have
been
months.
sequenced, and
This
has
increased
migrations in all parts of the world. It is also
ever
other
that
and
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to
predict
diseases
person.
and
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of
features
problems
and
genes
the
that
genome
aect
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medicine. If it is
are
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prescribe
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person’
s
genome,
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a
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v
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l
f
x
other
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origins
than
future,
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data
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about
more genomes of individual humans.
genomes
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it
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human
human
t
a
person.
known
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health.
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o
human
of
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providing
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for
individual
d
understanding
aims
million
n
So
U
There
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Figure 16
Sequencing read
from the DNA of the Pinot Noir
variety of grape
109
and
diversity
LHA
Unity
A3.1.12
Diculties in applying the
biologic al species concept to asexually
reproducing species and to bacteria that
The
biologic al
methods
it
of
species
works
less
horizontal
concept
works
well
species
with
gene
well
with
that
many
groups
reproduce
of
sexually,
will
and
as
a
are
of
the
species to
asexually, but as long as
coherent
have
and
is
to
great
eorts
recognize
abandoned
other
species
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sexual
are
genetic ally
a
are
that
experts
made
these
and
therefore
to
clones
is
a
c an
of
dierent
of
parents.
parent.
species
clones
may be
clones
have
some
longer
species
the
their
distinguish
dandelions
no
to
separate
conserve
are
plant
sexually but ospring
identic al
hundreds
blackberries,
reproduction
it
M any
example,
few
are
clones,
concept.
for
Both
reproducing
reproduction
with
blackberries,
species.
are
C
separate
and
asexual
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Among
policy
by
interbreed
asexually.
they
y
the
though
mitosis
n
U
better
biologic al
been
between these
of
the
and
species
rarer clones.
other
species
according to the
species concept.
o
i
d
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a
r
o
u
l
f
x
a
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v
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Figure 17
The yellow ower head of a dandelion
▴
Figure 18
The dandelions in this eld
develops into a spheric al array of wind-dispersed
members of the same clone.
fruits,
producing seed
each with a single seed.
produced
traits
signic ant
members
remain
o
to
not
i
n
as
by
produced
does
“microspecies”
110
allow
sexually
p
clone
recognized.
▴
they
reproduce
as
v
ospring
named
look
produced
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according
and
r
e
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of
species—such as blackberries (Rubus fruticosus) and dandelions
All
A
reproduction,
development
O
group.
produce
a
Shared
reproduce
(Taraxacum ocinale)—only
are
the
n
reproduce
sexual
l
individuals.
species
by
prevents
t
i
s
Some
This
y
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sometimes
unied
interbreed
asexually,
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all the seeds are genetic ally identic al
asexually so they are not
biologic al species
may all be
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y
species
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between
identied.
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members
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If
species.
asexually
e
However,
s
s
have horizontal gene transfer
Organisms
LHA
Species with horizontal gene transfer
The
evolution
trunk
from
individual
their
branches.
genes
gene
genome
even
so
much
less
Genes
transfer
is
genes
gene
Among
and
has
are
distantly
distinguish
species
frequent
interbreed
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with
other
species so
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it
related
from
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from
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species to
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species
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bacteria.
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eukaryotes,
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transfer
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move
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concept
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species.
vertic al
frequent
c an
revealed
sometimes
example,
to
is
it
is
how
another. In fact,
debateable whether
species concept) works with
horizontal
gene
transfer
has
occurred,
dene.
n
is
not
leads to
and
O
it
do
eventually
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t
i
s
prokaryotes.
remains
y
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sequencing
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species
tree, starting with a single
l
the
branch
a
branching
y
there
gene
resemble
P
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way,
a
to
Repeated
separate.
between
to
formed,
same
complete.
transfer,
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the
thought
emerge.
r
another,
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Once
remain
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branches
species.
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life
s
s
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of
which
y
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r
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v
i
n
n
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i
d
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r
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l
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v
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Figure 19
tree diagram,
D arwin’s famous evolutionary
drawn in about
1837 in one of
his notebooks
111
and
diversity
LHA
Unity
A3.1.13
Chromosome number
as a shared
trait within a species
E arlier
in
this
same
reproducing
For
topic,
number
sexual
23
to
a
and
haploid
sperm).
halves
produce
of
a
species
diversity
is
the
females
number
In
the
with
the
nucleus,
chromosomes
c arrying
reliably
the
into
into
two
as
of
these
diploid
chromosomes
one
sequence
other
of
chromosomes
dierent
separate
sets
genes
same
homologous
separated
chromosomes
of
daughter
daughter
cells
M ale
number
and
up
cells.
halves
are
the
and
of
each
are
female
chromosomes
chromosome
Two
said to be homologous.
with
The
(for
gametes
chromosome.
genes
pair
produce
each
O
meiosis,
are
t
i
s
During
there
sequence
have
n
same
species
number.
y
the
usually
consequence of
chromosomes
eukaryotes,
chromosome
zygote
of
of
humans).
c arries
a
other,
so
they
c an
separation of homologous
chromosome
number.
r
e
y
If two organisms with dierent chromosome numbers mated and produced
ospring, the ospring would almost certainly have problems in carrying out
p
meiosis. Some of the chromosomes would not be able to pair up because they
v
would not be homologous to any other chromosome. As a result, there would not
i
n
o
be an orderly segregation of chromosomes into two groups. The cells produced
by meiosis would not be viable and gametes could not be produced. This is why
n
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o
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r
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l
f
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v
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▴
C
ospring of parents with dierent chromosome numbers are usually infertile.
Figure 20
apple tree,
instead
These owers are on a Bramley
which is triploid,
of the usual 34.
with 51 chromosomes
Meiosis therefore fails and
the anthers in the owers produce no pollen, so a
Bramley c annot
112
pollinate any other apple tree
▴
Figure 21
All the cells in these Bramley
apples are triploid, like the tree on which they
grew. Bramley apple trees can produce fruit even
though they cannot carry out meiosis, because
cells in the fruit are produced by mitosis
y
diploid
which
males
the
and
of
l
In
fuse
eggs
lack
asexually.
occur,
have
members
P
then
in
be
human
meiosis,
(46
to
gametes
than
the
This
r
my
in
that
e
example,
a
rather
reproduction
These
gametes
learned
chromosomes.
sexually
gametes.
formed
you
of
s
s
the
Organisms
LHA
Data-based questions: Chromosome numbers in Sphagnum mosses
Researchers
c an
using
that
a
of
light
is
estimate
binds
the
DNA
specic ally
passed
through
a
content
of
cells
to
A
narrow
DNA.
by
1.
Compare
2.
Suggest
of
light
absorbed
by
the
DNA
reason
content
for
six
of
of
the
the
bog
species
mosses.
of
bog
stained nucleus and the
on
amount
the
a
stain
is
the
Svalbard
islands
having
the
same number of
measured. This
chromosomes.
gives
estimate
estimates
(Sphagnum)
of
for
on
the
leaf
the
quantity
cells
in
of
DNA.
eight
Table
species
of
4
[2]
shows
bog
3.
moss
S. arcticum
species
Svalbard islands.
and
when
S. olai
meiosis
probably
arose
Number
DNA / pg
of
a.
S. aongstroemii
Deduce
the
nucleus
of
0.47
of
chromosomes
species.
answer.
Give
two
in
a
leaf cell
reasons
0.92
S. teres
0.42
19
S. tundrae
0.44
19
S. warnstori
0.48
19
4.
It
is
having
mosses
of
for
leaf
plants
and
chromosomes
c an
r
e
their
more DNA than other
mosses.
unusual
number
have
odd
animals
in
their
numbers
cells.
to
have an odd
nuclei.
of
[1]
Explain
how
chromosomes in
[2]
o
i
n
v
p
Table 4
of
t
i
s
bog
and
n
S. olai
S. olai
S. arcticum
l
19
disadvantage to
O
19
0.48
a
y
0.45
S. mbriatum
y
S. balticum
Suggest
for
[3]
0.95
b.
▴
these
19
your
S. arctium
number
chromosomes
y
species
r
of
P
M ass
new
failed to occur in one of their
ancestors.
Sphagnum
as
e
such
an
[2]
moss
s
s
beam
stain
A3.1.14 Engagement with loc al plant or animal species to develop a
key
match
species
be
the
key,
Keys
All
in
are
the
leads
to
an
other
and
either
to
for
identic ation
numbered
should
easily
An
groups
designed
or
species
the
organisms
in
designed.
Choose
your
own
trees
in
loc al
•
water
plants
•
birds
•
invertebrates
E
descriptions
particular
in
visit
which
forest
using
that
for
a
a
of
wrong.
E ach pair
particular
that
may
species
within
a
group.
descriptions.
The
features
In
A
each
that
the
dichotomy is a division into two; a
pair,
one
designer
description
of
the
key
should
chooses
clearly
to
describe
area
be
key
a
area.
c an be
bear
wolf
fox
c at
squirrel
deer
dog
group of
has
never
been
from these suggestions or come up
idea:
the
There
a
a
your
•
area
v
O
with
key.
in
in
be
of
pairs
numbered pair
u
using
use
l
f
x
identied
for
found
of
example key is
Figure 22.
usually
clearly
visible.
another
identic ation.
series
t
a
shown
or
reliable
a
i
descriptions
in
the
r
o
of
and
of
o
therefore
constructed
d
must
the
are
consists
n
keys
dichotomous
U
Dichotomous
C
dichotomous key
of
or
on
your
school
c ampus,
duck
rabbit
/
hare
heron
leaves or bark
loc al pond
bird-feeding
stations
▴
in
your
area
Figure 22
These images show the right
of mammal and
bird
(not
to sc ale).
front
footprints of 10 types
They c an be used
to develop skills in
constructing dichotomous keys
that
plant
are
associated with one
species.
113
LHA
Unity
ATL
and
diversity
Communic ation
skills:
Construction
of
dichotomous
keys
for
use
in
identifying
specimens
visible. They are not, so you are directed to step 6 of the
key must be reliable and easily visible. An example key is
key. You must now decide if the species has a blowhole. It
shown in Figure 23. We can use it to identify the species
does not, so it is a dugong or a manatee. A fuller key would
in Figure24. In step 1, you must decide if hind limbs are
have another step to separate dugongs and manatees.
hind
limbs
Fore
and
hind
limbs
2
6
have
paws...................................
3
have
ippers................................
4
Fur
is
white...............................................................
External
ear
Two
long
ear
visible............................................
sea
ap..................................................
bears
lions
and
tusks.........................................................
walruses
dugongs
through
blowhole,
blowholes....................................
no
7
teeth..........................................
teeth.................................................
seals
and
manatees
p
blowholes,
One
blowhole..................................
baleen whales
v
Two
dolphins, porpoises and whales
A dichotomous key to groups of marine mammals
n
U
C
o
Figure 23
no
seals
o
i
d
t
a
r
o
u
l
f
x
E
v
a
▴
Figure 24
y
true
Mouth
breathing,
fur
5
No tusks...................................................................
O
114
otters
polar
O
external
ap
sea
A marine mammal,
photographed in Florida
n
dark................................................................
l
is
i
n
▴
emerge on land...........
live on land...................
Fur
Breathing
7
c an
c annot
y
and
visible,
visible,
r
e
6
limbs
limbs
e
Fore
No
5
hind
t
i
s
4
fore
y
3
and
Only
P
2
Fore
r
1
s
s
The distinguishing features described in a dichotomous
Organisms
LHA
A3.1.15
Identic ation of species from
environmental DNA in a habitat using
barcodes
barcodes
genes,
of
the
which
gene
for
DNA
of
that
cytochrome
barcoding
might
distinguish
oxidase
allows
otherwise
leaves
these
that
of
DNA
enough
are
to
from
subunit
scientists
be
oval
dicult
with
a
one
identify
1
to
to
a
is
gene,
species.
used
identify
as
at
For
end.
most
For
several
example, part
barcode
species
recognize.
pointed
a
or
from
for animal
small
example,
Barcodes
pieces
▴
many plant
make
it
Figure 25
possible
sampling of wastewater and
of pathogens.
species.
soil
or
a
any
environment.
barcodes
advance
c ase,
using
samples
DNA
taken
barcodes.
an
DNA
c arnivorous
many
be
in
mammal
to
from
This
snow
in
waterholes
analysis
rare
tracks
with
and
northern
species,
used
Australia
to
had
visited
conrm
the
b.
Distinguish
Figure 26
Tracks of a sher
(Pekania pennanti) in fresh snow in winter
correlation
top-down
species
and
extinction
between
form
bottom-up
including
c auses
consequences. (A4.2.3)
exemplify
reference
inheritance.
o
With
of
▴
extinct?
the
between
examples
a
species
E
a.
do
examples,
named
go
demonstrate
(B4.1.8)
(C4.1.17)
or
Idaho.
C
two
ecologic al
persist
waterholes.
n
O utline
variation?
to
u
factors.
and
plants.
using
limiting
How
of
in
v
O
2.
Distinguish,
species
l
c.
function
f
x
b.
a
adaptations
the
presence of a
for
o
and
c ause
how
i
might
Explain
t
a
a.
were
v
i
n
U
d
What
r
o
1.
sampled
conservation.
c alled a sher (Pekania pennanti) in
Linking questions
the
organisms. This
showed that Gouldian nches
bird
was
these
ecology
in
for new strains of COVID-19 and
resurgence of polio
Typic ally, this contains
interacted
identify
applic ations
increasingly
le
used
have
from
p
small
c ase,
c an
environment.
that
collected
y
another
abiotic
DNA,
r
e
(Erythrura gouldiae),
In
has
the
organisms
environmental
O
recent
of
of
using
t
i
s
a
analysed
part
diversity
DNA
technologic al
In
other
wide
possible
n
from
now
y
DNA
is
testing for DNA
This technique has been used
l
water,
identic ation
by regular
y
to test
Species
E arly warnings of the spread
of diseases c an be obtained
P
to
have
sections
r
species
short
distinctive
e
species.
tissue
are
are
s
s
DNA
to
an
both
continuous
example,
outline
and
what
discontinuous
is
meant
by
patterns
polygenic
(D3.2.14)
between
codominance
and
incomplete
dominance.
(D3.2.9)
c.
With
reference
disruptive
to
natural
a
named
example,
selection.
explain
the
mechanism behind
(D4.1.12)
115
A3.2
Classic ation and cladistics
Historic ally,
scientists have used
Relicanthus daphneae.
one? It
7feet
observable features to
shown in Figure 1 is
looks like a sea anemone, does that make
is unusually large for an anemone, with tentacles up to
long.
Across several genes,
its DNA sequence is distinct
is c ategorized
to see if that
as a cnidarian.
What
from
features
is the classic ation? Anemones are
l
unique among cnidarians in having aps over their stinging cells.
▴
the classic ation of this
Figure 1
O
t
i
s
How do cladistic methods dier from traditional taxonomic methods?
might
be dropped
by the crocodile.
reptiles that
What
are the
have led them to be
v
p
dierences between birds and
as separate classes of vertebrates? Molecular analysis has
that
the bird
is more closely related
o
established
to the crocodile
i
n
than the crocodile is to other reptiles such as snakes and turtles.
and
as reptiles?
classic ation
A3.2.4
Clades
A3.2.5
Gradual
groups
of
organisms
accumulation
of
sequences
cladograms
cladistics
the
traditional
investigate
to
common
whether
ancestry
as
the
sequences
the
hierarchy of taxa
evolutionary
dierences
acid
Figure 2
of
and
basis
relationships
shared
proteins
classic ation
of
characteristics
for estimates of when clades
as
the
groups
basis
for
corresponds to
relationships
Classic ation
E
sequences
to
amino
a
Using
or
l
Analysing
A3.2.8
with
sequence
genes
v
O
A3.2.7
evolutionary
of
cladograms
into
corresponding
from a common ancestor
Base
constructing
A3.2.9
organisms
classic ation
u
A3.2.6
of
f
x
diverged
as
classifying
i
Advantages
only
t
a
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A3.2.3
AHL
organisms
r
o
A3.2.2
of
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prevents birds from being
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for
what
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Need
dinosaurs,
n
from
reclassied
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crocodiles share? If birds
U
descended
A3.2.1
116
what
physiologic al features do birds and
C
Other than greater homology of DNA,
of
all
organisms
into
three
domains
using
evidence
from rRNA base
y
a marabou stork is waiting for an opportunity to c apture
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all other anemones.
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it
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classify groups of organisms.
s
s
What tools are used to classify organisms into taxonomic groups?
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Millions
every
of
species
day.
species.
Need for
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To
poses
make
Classic ation
been
have
a
classic ation of organisms
named
considerable
this
easier,
involves
and
accumulated
have
organisms
in
and
amounts
challenge
biologists
placing
described,
huge
in
terms
devised
groups
of
of
more
are
discovered
knowledge about these
information
systems
according
for
to
storage and
classifying
their
s
s
retrieval.
have
Biologists
LHA
A3.2.1
life.
traits or
evolutionary origins.
hierarchic al
All
broadest
we
reach
would
be
is
in
animal
see
it
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about
so
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immediately
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know the domain
are
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and
we
one
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it
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60
c an
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of
the
easy
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we
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the
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the
genus
c an
easily
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family, which
and
species:
access
Pekania
C
name
this
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species.
relatively
so
species of mammal.
Figure 3
What
is this organism?
large amounts of
groups to which it belongs. This is the
classic ation.
n
of
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fisher.
the
about
an
270species.
way,
know
and
kingdom
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power
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the
show
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we
this
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p
similar
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the
species.
hair
that
traits
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Without
Consider
o
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are the
v
•
a
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species.
i
n
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unknown
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subdivided again and again
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identify
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r
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O
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level
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large
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pictured
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type
of
are
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until
system
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r
years.
e
A
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Thinking skills: Evaluating alternative perspectives
ATL
i
r
o
Are classific ation systems invented or discovered?
is
natural
make
it
The
to
them.
study
groups
clouds
innite
is
that
is
and
and
E
unlikely
if
invented
of
the
or
things
in
process
the
The
are
bec ause
it
genera
are
in
an
Meteorologic al
such
are
This
enables
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arranging
classic ation
varieties.
weather.
clouds
a
groups, to
of
appear
recognized,
These
then
sky
World
developed
cumulus.
worthwhile
prediction
has
genera
species
in
a
into
see
forms.
l
stratus
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we
of
v
O
clouds.
The
classic ation.
variety
Organization
arrange
u
1.
in
humans
to
f
x
things
for
easier
t
a
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cumulus.
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of
cirrus,
subdivided
classic ation
more
example,
as
accurate
rainfall
this
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classic ation
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Figure 4
The 10 genera of clouds
discovered?
117
LHA
Unity
and
2.
In
diversity
how
square
their
many
be
ways
c an
classied
similarities
classic ations
and
the
into
tree
oval, triangle and
two
groups,
fur.
based on
branches.
Southern
uterus
dierences? Is one of these
in
better?
with
their
have mammary glands and
pouch.
assessing
foetuses
Sugar
glider
Which
the
develop in the
foetuses
features
relationship
between the
organisms?
Figure 5
animals
in
Figure
6
both
have
a
tail
for aiding
Figure 6
l
▴
(le) Southern ying squirrel (Glaucomys volans)
balance and a parachute-like membrane that stretches
y
wrist
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ankle
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allows
them
to
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O
t
i
s
A3.2.2
n
and (right) sugar glider (Petaurus breviceps)
from
Diculties classifying organisms into
the traditional hierarchy of taxa
y
r
e
Any classicatory group is a taxon, for example, “phylum”. The plural is taxa.
Assigning organisms to groups is taxonomy. Biologists have developed a hierarchy
p
of taxa with ranks from species up to kingdom. This traditional hierarchy is shown
v
in Figure 7
, with two examples. A genus contains one or more species, a family
o
contains one or more genera and so on. Moving up through the hierarchy, the taxa
i
n
contain larger and larger numbers of species that share fewer and fewer traits.
practice,
Even
when
oen
genus;
might
another
dicult
over
think
might
to
agree
what
the
classify
over
taxonomic
traits
think
organisms
which
in
they
a
rank
group
are
according
species
of
the
should
grouping
species
dierent
are
enough
to
to
be
this
should
similar
be
a
Grey
wolf
family.
D ate
palm
t
a
u
l
f
x
a
E
v
O
Animals
Plants
Phylum
Chordates
Angiosperms
Class
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Order
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Palmales
F amily
C anidae
Arec aceae
Genus
Canis
Phoenix
Species
lupus
dactylifera
Traditional classic ation in the hierarchy of taxa
together,
have.
enough
Kingdom
Figure 7
hierarchy.
classied
o
i
d
r
o
Taxon
▴
118
be
disagree
taxonomist
a
c an
n
U
they
it
taxonomists
C
In
One
to
form
y
The
e
r
3.
P
▴
develop
are most
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s
in
gliding
also
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mother ’s
important
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a
They
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Organisms
u n c e r ta i n ti e s
l a rge r
gro u ps
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ove r
ove r
o t h e r,
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into
th o u s a n ds
a re
tw o
or
a
ti me.
re s u l t
Fo r
will
or
e ve n
of
th e
g ra d u a l
ex a m pl e,
e ve n tu a l l y
m o re
as
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of
di ve rge n c e
s pe c i e s
s u f fi c i e n t
s e p a ra te
millions
the
g e n e ra .
ye a rs ,
th e s e
in
a
of
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As
s pe c i e s
ge n u s
fo r
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ge n e ra
will
and
B
di ve rge
th e
LHA
Th e s e
ge n u s
time
c o n ti n u e s
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di f fe re n t
A
to
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in
di ffe re n t
h a p pe n
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c annot
be
The
i n s ta n t
de te r m i n e d
in
time
when
o bj e c ti ve l y.
these
Th i s
is
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th e
boundary
pa ra d ox
and,
be c a u s e
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it,
ta xo n o m i c
ra n k i n gs
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Figure 8
E ach line represents a species
inevitably
e
over time.
ra th e r
s
s
enough
How many genera are there at A
a r b i t ra r y.
and
at
B? How c an you justify your answer?
r
Advantages of classic ation
classic ation
c an
Every
organism
same
taxonomic
In
each
that
be
used
has
should
to
mirror
judge
evolved
from
the
whether
a
evolutionary origins of
a
common
classic ation
ancestor
is
included in the
group.
taxonomic
group,
all
the
species
are
evolved
from
the
as
members
from
synapomorphies.
group
examples
allows
are
given
their
This
biologists
of
a
sharing
to
taxonomic
common
of
traits
make
here.
of
bat
placenta
new
mammalian
species
and
of
discovered.
c an
immediately
bat
will
therefore
features.
a
have
a
navel
button),
i
r
o
types
been
drug
predict
for
treatment
c alled
alkaloids.
Narcissus
evolved
that
alkaloids
other
to
now
are
a
of
produce
is
common
synthesized
been
found
in
know
that
bats
bat,
Murina beelzebub was recently
in Vietnam.
It
is a tube-nosed
with a mass of only 5 to 6 grams. It
is aggressive when c aptured, hence the
species name
with
are
heart,
reasonable
plus
hair, mammary
many other
disease and is one of a
strong
evidence
ancestor.
by
classic ation.
Figure 9
discovered
galanthamine. This substance
Alzheimer ’
s
There
on
▴
It
is
Narcissus
that
all
therefore
species.
species in
reasonable
O ver 80
species in the genus, some of which
a
are
have
from
l
alkaloids
prove useful as drugs.
E
v
O
dierent
likely
a
compounds
the genus
to
as
u
of
daodil (Narcissus species)
f
x
group
of
used
t
a
has
we
predictions
four-chambered
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Species of daodil
Some
based
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make
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members of a
o
a
glands,
sometimes
we
d
certainty:
a
are
mammals,
share
shared
n
as
U
species
classied
will
Such
between
predictions
Species of bat
New
group
ancestor.
C
Two
all
inherited
i
n
taxonomic
satised,
o
known
are
have
y
they
v
are
criteria
that
p
these
traits
same
r
e
commonancestor.
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achieves this:
O
•
that
criteria
t
i
s
•
agree
Two
n
species.
y
Biologists
l
corresponding to evolutionary relationships
y
P
A3.2.3
▴
Figure 10
Narcissus poeticus
119
and
diversity
LHA
Unity
A3.2.4
Clades
common
Species
c an
evolve
of
all
Clades
based
on
(shared)
include
also
shared
species
alive
that
ancestral
a
not
comes
in
a l w ays
should
f ro m
ba s e
is
(non-owering
nested
tree
three
species
a
all
clade
Those
species
plus
other
below
and
clades,
be
Taxus
Th e
Wh e re
to
only
just
one.
11
one
bec ause
of
clade
a
10
(the
the
in
have
c o m mo n
a
clades
monkey
two
species
with
all
fo ss i l s .
“nested”
gymnosperm
below
of
tree)
it
in
radiata
Finally,
these
in
the
and
those
species,
Taxus baccata
(yew)
u
l
Cupressus sempervirens
a
E
v
O
f
x
Cephalotaxus fortunei
(cypress)
(monkey
Podocarpus totara
Pinus radiata
(Monterey
Ephedra sinica
Gnetum africanum
Ginkgo biloba
Figure 11
is
They
gymnosperms.
Araucaria araucana
▴
which
not
c l a de s .
puzzle
Pinus
10
f ro m
ancestor.
ancestry.
includes
ancestor
w h e re
are
of
been
pro te i n s .
is
to
f ro m
species
common
clade
of
ex ti n c t,
c o me s
from
evidence
da ta
o rg a n i s ms
common
that
a
large
evolved
is the only living
Welwitschia mirabilis
120
species, or
i n fo r ma ti o n ,
Smaller
shows
araucana
nested
a
all
There
s e qu e n c e
evidence
and
in
of
o bj e c ti ve
be c o me
baccata
are
from a
species.
form
sequences
of
a ss i gn
h ave
have
it—again
have
f ro m
acid
they
are
birds
ago.
mo s t
amount
used
not
they
e vo l ve d
amino
that
Figure
thousands
years
bec ause
species
biloba
or
the
ancestral
Ginkgo biloba
million
c l a d e.
Araucaria
totara
with
ve
Gingko
i
plus
in
diagram.
c an
evolved
extinct.
deduced.
example,
plants).
Podocarpus
o
9
seed
For
t
a
r
o
d
the
multiple
tree
huge
s pe c i e s
av a i l a b l e
n
U
are
with
in
clades.
a
the
example,
p
larger
clade
not
include
For
bec ause
h ave
a
ge n e s
be
tra i t s
w i th
270
C
species
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is
in
c o n ta i n
c an
the
now
species
of
and
o
da ta
useful
i
n
Every
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m o r ph o l o g i c a l
s e qu e n c e
a
sequences
p a r ti c u l a r l y
are
included
o rga n i s ms
v
is
which
be
about
all
with
y
of
e vo l u ti o n a r y
av a i l a b l e,
Th i s
o bv i o u s
but
organisms
groups
c an be
from the common ancestor and then
species.
contrast,
evolved
clade
th e re fo re
genomes
th e i r
that
that
In
together
species,
r
e
Th e
clade
living
large
species
n
of
species
species.
large
few
of
now
of
O
is
and
thousand
today,
evolved
very
a
group
are
groups
clade.
t
i
s
other
10
be
just
A
there
These
l
common
member
It
about
ancestor.
species. With some highly
so
y
a
with
c an
with
a
new
Smaller clades are nested
within larger ones
pine)
puzzle)
y
small
form
with
characteristics
P
Clades
be
clade
c alled
species
extinct.
to
repeatedly,
characteristics.
is
the
they
very
common
any
bec ame
c an
split
happened
a
ancestor
all
include
from
and
shared
r
They
derived
time
has
organisms
e
common
over
this
and
of
s
s
species,
identied
groups
ancestry
successful
species
as
Organisms
LHA
Paradigm shis
A xed ranking of taxa (kingdom, phylum and so
Taxon
Grey
Kingdom
Animals
wolf
Taxon
D ate
Kingdom
Plants
palm
on) is arbitrary as it does not reect the gradation
s
s
of variation. Cladistics oers an alternative
approach to classication using unranked
Clade
ParaHoxozoa
Clade
Tracheophytes
Clade
Bilateria
Clade
Angiosperms
clades. This is an example of a paradigm shi in
e
scientic thinking.
Increasingly,
the
in
classic ation
traditional
date
been
from
species
1.
grey
wolves
Clade
Chordata
Order
Clade
Olfactores
F amily
up
to
assigned
to
Vertebrata
Tetrapoda
Clade
Amniota
using
in
clades
is
the
and
hierarchy
the
are all
number
of
levels
Class
M ammals
Order
C arnivores
advantage
of
this
approach to
F amily
C anidae
Genus
What
a
this
a
paradigm
shi
rather
Canis
Species
lupus
modic ation?
v
▴
Figure 12
o
C
i
n
A3.2.5
Classic ation using clades
p
than
makes
Phoenix
dactylifera
y
r
e
classic ation?
2.
Species
traditional taxa. The
the
xed.
What
Genus
order, and the kingdom,
levels
as
Clade
Clade
Arec ales
Arec aceae
O
not
ranks in
Figure12
t
i
s
is
the
classied using clades. The taxa
intermediate
referred
Monocotyledons
Commelinids
n
still
of
taxa.
and
Clade
Clade
y
are
palms
of
Nephrozoa
Deuterostomia
l
have
instead
hierarchy
Clade
Clade
named and
y
how
being
P
shows
are
r
used
clades
Gradual accumulation of sequence
dierences as the basis for estimates of when
U
Dierences
over
as
between
two
estimate
most
years
recent
sequence
of
ago.
on
has
rate
the
have
dierences accumulate
this
happens
the
ancestor
DNA
roughly
chimpanzee
bonobo
ancestor. This method of estimating time is
the
they
the
c an
number
diverged
of
sequence
from
a
dierences
common
ancestor.
1 Myr ago
molecular clock, it is important to
vary
clock
on
and
c an
used
a
same
is
the
only
to
aected
intensity
by the length of the
of
selective
when
all
as
million
hominid
humans
a
rate of 10
assumptions,
one
years
ago.
species
and
Using
clock,
our
humans
split
from
4.5 Myr ago
−1
yr
common
existed.
molecular
pressure and
give estimates.
estimate
mutation
other
of
a
been made—that mutations accumulate
been
from
at
human
−9
split
mitochondrial
These
that
dierences to estimate the time since
larger
recently—around
common
of
assume
population,
Based
Using
humans
we
since
molecular
relatives.
more
when
this
dierences
living
split
the
The
based
that
of
If
therefore in the amino acid
mutations.
u
bonobos
size
of
common
a
4.5million
fact,
Thus,
sequence
nearest
In
the
E
the
timings
DNA—and
number
longer
assumption
rate.
a
time.
clock”.
the
v
O
Base
species,
time,
factors.
the
from
“molecular
the
constant
other
use
of
of
result
l
a
c an
considering
generation
periods
diverged
the
remember
at
we
f
x
When
long
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i
rate,
species
known
sequence
t
a
two
base
r
o
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127
LHA
Unity
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diversity
Data-based questions: Mustelid classic ation
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to
the
[2]
Procyon lotor
Mustelidae
family.
should be
O
t
i
s
moved
in the cladogram to suggest that some species should be
y
p
r
e
C
o
v
i
n
n
U
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
128
y
smaller
Lutrinae and Mustelinae. A further proposed subdividsion
seven
n
c.
be
dierent
l
the
a
[2]
y
genus
b.
to
P
the other species from Aonyx capensis to Taxidea taxus are
Figure 26
[2]
Using evidence from the cladogram, discuss whether:
dierent family and were used for reference purposes.
▴
c an
from the number of base substitutions
lotor, at the bottom of the cladogram, are members of a
3.
are
e
maximum parsimony. Bassariscus astutus and Procyon
on
indic ated
s
s
Base sequences of 22 gene segments were analysed to
is
Organisms
LHA
F alsic ation: Reclassic ation based on phylogeny
A
cladogram
Bec ause
they
it
is
are
a
hypothesized
knowledge
not
claims
evolutionary
are
true.
Certainty
property
Hypotheses,
becomes
possible
Elephant
theories
be
shrews
are
Popper
knowledge claims “falsiability”.
other
small
scientic
knowledge
claims
may
insect-eating
name,
elephant
mammals
shrew,
native
comes
to
Afric a.
from a
between their long noses and the trunk of an
their
supercial
that
similarity
elephant
with
shrews
shrews.
should
not
Phylogenetic
be
classied as
▴
shrews;
in
fact,
they
are
more
closely
Figure 27
related to elephants than
E ast
Afric an black and
t
i
s
true
rufous elephant
shrew or Sengi (Rhynchocyon petersi)
shrews!
Classic ation of all organisms into
p
three domains using evidence from rRNA
based
is
now
regarded
given
that
are
all
organisms
usually
and
eukaryotes
are
less
well-known.
distinct
therefore
Archaea
now
and
classied
referred
to
relatively
as
to
of
recognize
the
c ategories of
three
This
are
were
three
diverse. In
determined, it
major
and
They
are
c alled
Members of the
eukaryotes.
but
were
c ategories
c ategories
domains.
biologists
classic ation
so
prokaryotes.
These
archaeans
most
u
f
x
Bacteria
Green
into
RNA
groups
Eukaryota.
bacteria,
familiar
prokaryotes
ribosomal
Archaea.
major
i
with
two
of
the
two
prokaryotes.
t
a
domains
systems
Eubacteria,
are
and
r
o
domains,
there
Eubacteria
classic ation
organism,
sequences
and
o
of
base
recognized
bec ause
d
Most
names
have
eukaryotes
inappropriate
the
apparent
the
types:
n
bec ame
when
as
systems
cell
U
particular,
on
C
classic ation
organisms
i
n
Traditional
o
v
base sequences
y
r
e
A3.2.9
O
to
n
shown
y
English
likeness
and
has
c an nd a
K arl
y
analysis
we
l
elephant,
and
if
c ase.
falsied.
common
perceived
scientic
the
P
Their
of
not
r
eventually
empiric al
e
this
relationship.
on
possible to claim with absolute certainty
counterexample and establish what is
c alled
based
s
s
evidence,
that
depicts
scientic
archaeans
Archaea
Bacteria
are oen
Eukaryota
filamentous
a
Spirochetes
moulds
Animals
Gram
Proteobacteria
Cyanobacteria
Methanobacterium
Halophiles
Fungi
positives
E
v
O
l
Slime
bacteria
Methanococcus
Plants
Ciliates
Flagellates
◂
Figure 28
Tree diagram
showing
relationships between living organisms
based
on base sequences of ribosomal RNA
129
LHA
Unity
and
diversity
Social skills: Actively considering the perspective of others
ATL
During
debates,
someone.
If
this
consider
you
are
not
example,
tree
other
using
is
depending
dierent
on
are
to
not
your
yourself
take
people’s
possible
shrews
nd
time
Approach conversations with the understanding that you
be
fair-minded
might be mistaken and that other people might have valid
Be
ideas. The consensus is that classication should be based
perspective.
criteria
argue
for
that
related,
criteria
disagreeing with
to
or
sure that
judgement.
the
that
elephant
they
are
on evolutionary relationships, as this allows us to make
For
predictions. For example, two closely related organisms
shrew
should have similar metabolism. However, in some
related,
e
and
it
may
s
s
and
you
happens,
contexts it is also reasonable to classify an organism by its
for judgement.
r
niche. In this case, the elephant shrew could be considered
related to other shrews as they are all insectivores.
l
n
29
shows
the
plasma
2.
Compare
the
cell
3.
Distinguish
4.
a.
Compare
and
b.
Construct
a
Deduce
which
of
the
the
cell
contrast
of
the
ve
the
cell
wall
structures
wall
of
Group
structures
based
groups
on
is
the
Z
the
other
the
cell
wall
in
comparisons
and
contrasts.
fungi.
groups.
X
sugar
D-alanine
phosphate
v
glycerol phosphate
proteins
E
N-acetylmannosamine
glucose
▴
Figure 29
Source:
Nature
130
Chen,
553,
Y
.,
Fischbach,
427–436
M.
(2018).
&
Belkaid,
Y
.
Skin
microbiota–host
X
and
interactions.
https://doi.org/10.1038/nature25177
Y
mannose
arabinose
arabinogalactan
phosphate
[2]
[2]
[2]
Y
.
[4]
[4]
[1]
o
amino
ribitol
W,
n
a
N-acetylglucosamine
V,
microorganism.
o
O
N-acetylmuramic acid
u
variable
l
f
x
highly
W
t
a
r
o
V
i
d
wall
Groups
of
C
i
n
outer
membrane
membrane
groups
and
U
lipopoly-
plasma
ve
outside
these
saccharide
cell
in
microorganisms.
microorganisms.
the
cladogram
and
of
v
5.
walls
between
membrane
membranes
O
plasma
y
the
p
Compare
r
e
1.
t
i
s
Figure
Z
y
P
y
Data-based questions: Similarities and dierences in microbial cell wall structure
Organisms
Linking questions
1.
c an
similarities
a.
Outline
b.
Describe
c.
Explain
some
mechanism
mechanism
examples
the
material.
Explain
how
evolution
by
convergent
ideas
that
over
organisms
be
explained?
niche. (B4.2)
natural
which
conrmed
selection.
evolution.
biologists
DNA
and
(D4.1)
(A4.1.5)
disagree?
not
protein
was the
(A1.2.14)
using
the
principle
of
parsimony
could
lead
to
an
error in
l
classic ation. (A3.2.6)
why
c ategorization
distinct”
and
therefore
a
of
some
higher
populations
priority
for
as
“evolutionarily
conservation might be
O
t
i
s
controversial. (A4.2.8)
n
Suggest
y
c.
y
genetic
related
ecologic al
of
of
of
evidence
distantly
an
P
b.
are
Describe
of
r
a.
the
the
between
concept
e
What
the
s
s
2.
How
y
p
r
e
C
o
v
i
n
n
U
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
131
Unity
and
diversity
TOK
How does the way in which we organize or
s
s
classify knowledge aect what we know?
is
most
of
which
realizing
it.
see
a
not.
and
There
hear
the
from
a
In
as
you
a
direction
plant,
you
everyday
domestic ated
threat
might
you do
as
without
loud
sound,
threat; or
it
a
c ame.
you
you
might
dangerous
classify
or
on.
are
innite
ways
to
interpret
w allaby
terms
of
habitat,
forest
dwellers.
names
names
level;
fur
c an
in
have
a
For
be
they
from
a
are
not);
and
or
so
on.
E ach
features
of
c ategorization
the
in
looks
This
referred
other
name,
to
as
folk
have
segments.
in
like
is
as
refers
small
are
both
lynx
quoll
c at)
and
This
to
is
w allaby
in
family
some
bugs”.
“stink
the
both
In
bec ause
focus
on
a
names
given
to
Pentatomidae
shield
folk
when
taxonomies,
Bec ause
they
they
bugs”.
fact
are
particularly
everyday
heraldic
(a
the
herbivores.
are
threatened,
to
together
marsupials.
perception,
the
a
as
the
listener
why,
when
taxonomies
Pentatomidae,
ve
our
the
“shield
spray
focuses
o
a
v
E
le) and a spotted-tailed quoll (bottom right)
to
organism.
i
l
f
x
O
A Siberian musk deer (top le);
a lynx (top right); a whiptail wallaby (bottom
which
above.
a
and
the
taxonomy—the
strong-smelling
n
feature
conservation status
they
organism.
insects
of
together
de er
and
impact
the
classied
marsupial or placental; niche or habitat;
monochrome;
folk
of
example,
shape
viewed
t
a
Figure 1
They
u
▸
or
dierent
1.
apparent
things.
role).
d
a
Figure
ways.
phylogeny
(ecologic al
r
o
on
in
of
U
(threatened
or
animals
number
aspect
C
trophic
organisms),
niche
a
by morphology
quoll
o
four
the
or
in
i
n
Consider
other
them
the
relationships.
groupe d
spotte d-taile d
niche
groupe d
be c ause
c an
the
are
y
to
history)
organisms
group
the
predispose
particular
v
similarity
classify
might
while
level,
the
evolutionary
de er
p
they
(evolutionary
patterned
132
used
organize
r
e
scientists
example,
(physic al
by
together
observations.
Similarly,
are
trophic
at
musk
occupies
of
dierent
For
that
In
terms
looks
the
mammals,
harmless;
and
and
whiptail
The
so
your
lynx
placental
groupe d
When
classify it as ripe or not,
wild;
classic ation
the
marsupial
even
not
which
language,
or
a
or
Thus,
O
or
organisms
ways—oen
representing
identify
on
When
What
N atural
information,
t
i
s
edible
as
of
information. The
sensory
unimportant.
variety
example:
it
fruit
a
as
sensory
endless
n
you
or
For
in
with
y
might
ignore
classify
classify
you
you
interpreting
you
l
might
of
that
are
The
their
release
referred
L atin
family
antennae
y
you
act
P
notice,
the
presents
r
environment
e
Perception
Organisms
The Cerion snail is endemic to the Caribbean. Folk taxonomies refer
to it as the peanut snail or the honeycomb snail. Figure 3 shows
some of the varieties of snail from the three islands of the Netherlands
Antilles. Nineteenth century naturalists classied Cerion snails into a
large number of dierent species based on physical dierences (such
s
s
as colour, lip thickness and number of grooves). In the 20thcentury,
molecular biologists were able to show that the variety represented
a much smaller number of species. All of the snails shown in Figure
on gene expression and how the snails develop. On windy, wavy
r
shores, the snails develop thicker and stronger shells. On low energy
dierent
more
individuals
prone
to
who
classied!
as
classify
organisms.
“Lumpers”
varieties
emphasize
of
these
Taxonomists
are those who tend to
the
same
dierences
species.
as
“Splitters”
indic ative of
▴
Figure 2
A shield bug or stink bug
y
p
r
e
C
o
v
i
n
n
U
o
i
t
a
u
l
a
v
E
Figure 3
d
r
o
f
x
O
▴
O
t
i
s
uniquespecies.
n
are
scientists
be
y
see
are
c an
l
themselves
y
Taxonomists
P
coastlines, colour dierences are more pronounced.
e
3 belong to the species Cerion uva. The environment has an impact
Cerion uva snails
133
Unity
and
diversity
End of chapter questions
1.
Evidence
suggests
a
of
species
areas.
humans
of
The
are
species
the
humans
ape
that
are
has
most
descended
c.
from
C anine
or
spread to colonize
closely
related to
chimpanzee and the gorilla. Studies
biochemistry
and
chromosome
numbers
of
the
evolutionary
Model
C.
type
teeth
of
primates.
relationships
on
are
which
shown
the
in
Humans,
models
shown
in
model
molars
were
appears
of
the
models
correct,
why
eating
evidence.
the
Model B
gorillas
grinding
H
C
G
H
adapted
matter
is
less
for
on
broad,
p
o
C
chimpanzee and
u
chimpanzee
Suggest
teeth while
flat
molars.
[2]
chromosome 2
[3]
Key
n
by one amino acid
as
o
i
from
gorilla
a
E
v
O
l
f
x
t
a
diers
same
C
v
i
n
r
o
chimpanzee
Haemoglobin
molar
relatedness of humans, gorillas
CA
common ancestor
H
human
G
gorilla
C
chimpanzee
Gorilla
48
same as gorilla and
Myoglobin
from
matter.
grinding.
requires
reliant
evidence
Chimpanzee
d
proteins
the
G
CA
U
Human
46
possess
plant
Model C
CA
number
all
have.
y
C
Evidence
134
plant
chimpanzees.
[3]
Figure 1
Table 1
not
[1]
according to the
CA
▴
are
eating
O utline
r
e
G
humans
based on the
number.
Model A
Deduce the
O
biochemic al
Plasma
and
for
large
n
each
and
y
chromosome
teeth.
t
i
s
Evaluate
Chromosome
teeth
constructed
and
▴
molar
Lion
of
from
groups,
teeth supports
l
which
evidence
H
chimpanzees
flat
Table 1.
Identify
b.
large
chimpanzees
Figure 1. Some of
diagrams
e.
a.
have
two
showing
meat
is
that
into
c anine
48
same
as
human
same
as
same
as
and
gorilla
same
as
human
and
chimpanzee
gorilla
same
as
chimpanzee
human
diers
from human and
chimpanzee
by one amino acid
y
evidence
Three
Gorillas
from
P
the
three
divided
r
possible
these
be
relationship
broad
between
c an
evidence
e
evidence
The
provide
d.
conflicting
teeth
small.
s
s
new
that
Afric an
Organisms
2.
One method used by microbiologists to distinguish between Archaea and
Eubacteria is based on the conditions they need for survival. Both groups include
thermophiles—species that are adapted to live at high temperatures. The graph
in Figure 2 shows the optimum temperature and minimum pH required for
growth by selected species of Archaea and thermophilic Eubacteria.
s
s
110
/
r
l
80
1
2
3
4
5
6
7
Minimum pH supporting growth
thermophii uateria
i
n
o
rhaea
v
e
8
y
0
p
r
e
50
O
60
n
y
70
y
P
90
t
i
s
erutarepmet htworg mumitpO
e
C°
100
oure apte rom   aentine 2007 ‘aptations to energ stress itate the eoog an
Figure 2
the
highest
State
the
relationship
the
Eubacteria.
Wi th
re fe re n c e
a l w ays
be
th e r m o p h i l i c
a
the
fo r
possible
habitat
for
recorded
supporting
for the
[1]
growth and
Archaea.
Archaea
data,
E u ba c t e r i a .
a
State
the
suitable
E
v
O
e.
to
for
for
pH
with
s u g ge s t
[1]
those
w hy
u
not
results
l
f
x
d.
temperature
minimum
i
growth
Compare
temperature
t
a
c.
between
r
o
optimum
growth
d
b.
optimum
Eubacteria.
o
thermophilic
n
State
U
a.
C
▴
d i s ti n g u i s h i n g
methanogenic
for the thermophilic
[2]
th i s
method
between
would
A rc h a e a
and
[2]
Archaea.
[1]
135
Unity
and
A
s
s
d i v e rs i t y
Ecosystems
e
r
4
l
y
P
homologous structures exemplify the
diversity.
n
theme of unity and
y
Analogous and
Both patterns arise due to the
t
i
s
factors provide the pressures that
selection and
are adapted
to their environment.
i
n
o
v
p
the characteristics of those members of
the population that
more common.
y
r
e
O ver generations,
The structure–
exists bec ause natural selection
favours individuals that
survive to reproductive age become
The change in species over time is known
C
as evolution.
contribute both to natural
to species diversic ation.
function relationship
O
selection pressures within an ecosystem. Biotic and abiotic
When unrelated
species encounter the same
selection pressures, they can develop analogous structures
U
n
that are similar in appearance and function but have dierent
histories. For example, the long-eared jerboa (Euchoreutes
o
However, they have both developed long ears for heat
i
exchange, movement by hopping and an extended tail
for balance. These features are an example of convergent
evolution, a result of both organisms living in arid habitats.
u
l
a
E
v
O
f
x
t
a
r
o
d
naso) and kangaroos have distinct evolutionary histories.
Yet, they have signicantly dierent reproductive strategies
as the jerboa develops a placenta during pregnancy and the
kangaroo is a marsupial which means its young complete
development in a pouch outside of the uterus. These
examples show that the habitat of an organism can drive both
convergence and divergence. It follows that loss of habitat
and unique environments is a signicant factor increasing the
threat of extinction of species. Biodiversity is the variety of life
in all its forms, levels and combinations, including ecosystem
diversity, species diversity and genetic diversity.
A4.1
Evolution and speciation
s
s
What is the evidence for evolution?
The theory that
species change over time by the
of natural selection has such strong
predictive and
explanatory power that it is unlikely
Figure 1 shows both fossil and human
pentadactyl limb
evolution.
The ve-ngered
by humans with ancestors
going back over 300 million years of evolution.
Here,
which is approximately 280 million years
anatomy of limbs with
diverse functions provides evidence forevolution.
O
Explain how the shared
t
i
s
old.
Figure 1
y
p
r
e
◂
n
y
predatory North Americ an Permian reptile c alled
C aptorhinus,
l
is shown with the foot bones of a small
y
is shared
P
pentadactyl hand
a human hand
r
to be falsied.
e
mechanism
How do analogous and homologous structures exemplify commonality and diversity?
a seagull are similar in form and function.
pressures in evolution? What
how did these
is the role of selection
is the distinction between
n
U
homologous structures?
Why do organisms with a common ancestry that
to dierent
C
of common ancestry,
analogous structures develop? What
analogous and
o
and
a result
v
If this is not
i
n
The wings of a bat
are subjected
selection pressures become increasingly dierent?
o
d
How do homologous structures provide evidence of evolution?
Are the hands of a human and bonobo ape ( Pan paniscus)
SL
as
change
and
in
a population
Evidence
RNA
A4.1.3
and
for
amino
Evidence
domestic ated
for
for
A4.1.5
Convergent
E
Evidence
A4.1.6
Speciation
A4.1.7
Roles
selection
in
of
from
sequences
evolution
animals
A4.1.4
structures
evolution
acid
heritable
a
or
v
O
A4.1.2
HL
the
and
u
Evolution
to evolution?
l
f
x
A4.1.1
from
base
in
is the signic ance of
t
a
the opposable thumb
i
r
o
homologous or analogous structures? What
characteristics of
sequences in DNA
proteins
selective
breeding of
from
structures
evolution as the origin of analogous
by
splitting
reproductive
of
pre-existing
isolation
and
Dierences
A4.1.9
Adaptive
Barriers
hybrids
as
A4.1.11
and
only
similarities
between
sympatric and
speciation
A4.1.10
between
homologous
Figure 2
AHL
A4.1.8
allopatric
crop plants
evolution
▴
radiation
to
means
as
a
source
hybridization
of
and
of
biodiversity
sterility
of
interspecic
preventing the mixing of alleles
species
Abrupt
speciation
in
plants
by
hybridization and
polyploidy
species
dierential
speciation
137
Unity
and
diversity
A4.1.1
Evolution as change in the heritable
characteristics of a population
There
and
is
lies
only
strong
evidence
Biologists
at
the
heart
concerns
This
this
of
a
the
characteristics
of
evolution.
how
scientic
heritable
is
for
process
It
is
understanding
characteristics—traits
populations
of
that
the
the
are
changing
diversity
natural
of
life
world.
inherited
by
over
developed
Evolution
ospring
emphasized in the denition:
from
e
parents.
c all
s
s
time.
Evolution is change in the heritable characteristics of a population.
mechanism
also
strong
•
c an
trees
evidence
their
for
lifetimes.
develop
a
well
very
by
the
For
asymmetric
inuenced
by
hearing
song
use
tennis
hold
children
known
for
proponent
one
environment
for
not
it
and
arm
again,
the
and
a
the
was
from
No
new
to
a
of
acquired
L amarck,
tree
growing
are
exposed
they
player ’
s
they
exposed
develop their
so
to
not
mechanism
has
been
genes.
evolution.
attempts
to
to
the
Therefore,
the
it
is
the
leading
known as
the
same
develop
environment
stronger
discovered
base
has
for the
sequence of genes,
acquired
L amarckism
revive
1859,
asymmetric ally will not
will
changes
in
characteristics. The
children
adaptive
of
lead
repeated
position
speak.
Jean-Baptiste
unless
other.
specic
not
parents
inheritance
seeds
tennis
creation
do
despite
that
a
when
On the Origin of Species
on
ospring
than
c ausing
c ausing
inherited
theory
Similarly,
i
or
hawthorn trees on
a Welsh hilltop
in
this
o
bones
of
based
obvious
asymmetric
parent.
characteristics
been
are
falsied again
theory.
u
f
x
t
a
Windswept
d
Figure 3
r
o
▴
into
the
is
singing
in
organisms
stronger muscles and bones in the arm they
their
published
was
grow
D arwinism.
characteristics.
n
U
as
It
acquired
D arwin
evolution
L amarckism.
languages
parents
C
Charles
theory
grow
as
i
n
Before
main
the
they
selection
c alled
individual
o
are
learn
develop
racket
v
These
players
the
if
p
•
to
natural
also
y
human
their
r
e
•
form
of
is
is
O
are
characteristics
t
i
s
birds
selection
example:
to wind
•
understood—it
natural
n
during
now
y
changing
is
Evolution
Theories: Pragmatic truth
everyday
language,
agrees
a
“true” statement is one that
corresponds
theory
For
pragmatic
example,
the
of
v
correspondence
to
a
O
everyone
l
In
truth
reality.
is
not
However, the
the
only
possibility.
theory of truth holds an
assertion to be true if it “works”.
E
Knowledge claims in science are based on observations of
a fraction of possible cases or instances. Scientists use their
observations to form generalizations that are then tested.
If the generalizations are supported, a theory emerges. If
the theory can explain and predict future observations, it is
said to be a pragmatic truth: a truth that works.
138
The
theory
and
explains
antibiotic
of
is
of
evolution
a
and
broad
pesticide
homologous
unlikely
makes
it
be
and
by
is
supporting
natural
natural
of
to
resistance
prove
the
formally
is
regarded
evidence.
and
also
structures.
However,
selection
therefore
selection
predicts
observations, such as
analogous
falsied.
impossible
evolution
truth
to
and
by
range
true.
as
a
existence
the
theory
nature of science
that
It
the
Thus
is
a
the
theory of
pragmatic
theory, despite all the
y
is
evolution
l
There
of
Topic D4.1).
P
(explained in
r
The
Ecosystems
A4.1.2
Evidence for
evolution from base
sequences in DNA or RNA and amino acid
sequences in proteins
evolution
expect
to
happen
in
the
evolution
likely
also
For
comes
from
example,
Similarities
ancestry,
the
the
same
other
traits,
the
fewer
dierences in
to
explain
species
of
by
develop
of
gene
Hox
are
closely
splits
over
dierences
only
evolution.
match
without
with
families
gene
that
family
is
evolution. It is
time,
natural
easily
This
between
in
related
gradually
selection.
accounted
why
for
cladograms
classic ations
based
lineages.
occur
across
diverse
occurs widely in
and
in
and
all
between
with
for
dierent
animals
vertebrates;
with
clear
species
reasonably
be
explained
in
dierent
lineages.
Hox genes occur
form
a
clade
known as the bilateria.
o
i
t
a
u
of dierent
only
a
Scr
Antp
The fruit y Drosophila has eight
tail development
c an
give multiple copies of the gene and
head-to-tail axis, including annelids,
d
l
v
E
Figure 4
Dfd
genes
to
functions
a
these
r
o
f
x
O
pb
Hox
duplic ation
n
modic ation
cnidaria
arthropods
▴
usually
of
closely
dierences
sequence
sequences
more
U
common
lab
of
base
the
result
species
viral
genomes. Genes in this family help to determine the body plan during
gradual
in
ancestral
dierences
organisms.
development.
by
combinations
of
a
the
spreading
y
of
as
in
C
animal
of
ancestor
ones
seen:
dicult
that
M any base
aecting
is
i
n
groups
theory
(COVID-19).
earlier
sequences
o
Evidence
and
the
than
acid
evolution of the
coronavirus,
comparing
and
is
the
O
sequence
from
amino
evolved.
relationship
trend
2020
this
c an
p
on
morphology
by
common
splitting
virus
the
v
on
This
in
of
in
Consider
successful
morphology
are.
observed
repeated
based
their
there
a
more
clear
starting
genes
we
y
addition,
by
in
the
comes
A
and
population,
r
e
In
also
species.
explained
from
were
RNA
a
t
i
s
convincingly
pandemic
in
or
sequences.
of
occurs. These changes will
n
are,
DNA
population—the
evolution
sequence
diverging
variants
of
base
evolution
l
for
dierent
a
occurred
human
species
base
c aused
new
the
those
characteristics
whenever
P
two
that
sequence
using
changes
Some
in
base
heritable
y
gene
the
genes
r
sequence
Evidence
in
in
made
coronavirus
through
change
changes
the
proteins
traits.
a
e
of
is
see
s
s
If
Ubx
Hox genes which help
parts of the body.
Abd-A
Abd-B
to organize head-to-
Humans have 39 Hox genes which help to
organize our head-to-tail development
139
Unity
and
diversity
Data-based questions: Convergence and divergence of sequences
The hypothesis that there is ancestral convergence in
and amino acid sequences of the separated clades. The
sequences was tested using two plant clades (monocots
more time has passed since the split, the more dierences
and eudicots). There is strong evidence for monocots and
we expect due to this evolution. It therefore follows that
eudicots having a common ancestor
. Amino acid sequences
if we look back at the ancestry of two related clades, the
of 51 proteins in 24 species of monocot and 44 species of
closer we get to a common ancestor, the fewer sequence
eudicot were compared. Sequence convergence in the
dierences there will be. Figure 5 shows a theoretical
ancestors of the two clades was found: the probability of
cladogram, with a common ancestor (P) that split to
the observed pattern of sequence dierences being due to
produce two ancestral clades (Q and R), which then split
anything other than evolution was calculated as 1 × 10
repeatedly to form multiple clades.
This is an innitesimally small chance.
s
s
Aer a clade splits, there can be divergence of the base
the
most
probable
ancestor
whether
more
base
3.
Explain
the
Q
e
species
There
y
i
n
z
protons
picking
the
row?
research
cladev
or
is
free
data
in
the
same
to
are
between
[3]
from multiple
universe.
proton
at
[2]
What is the
random twice
[2]
access
online
(https://
journals.plos.org/plosone/article?id=10.1371/
journal.pone.0069924).
Reasonable
Doubt:
Sequences”.
It
is
c alled
Evolution
Discuss
from
whether
this
“Beyond
DNA
is
a
U
name.
[3]
n
o
i
for
breeding
and
plants
crop
u
have
bred
animals
evolution
of
selectively
from
domestic ated
over
thousands
of
years
for
animals
a
range of
purposes, including:
l
a
E
v
O
f
x
t
a
r
o
d
Evidence
selective
•
meat
•
transport;
•
pets;
If
modern
and
for
resemble,
and
the
is
also
for
the
of
livestock
of
variation
the
are
are
c attle
of
dog
compared
huge.
Asia
and
between
diversity
example,
oen
Southern
Blue
for
sheep
horses
c ats.
dierences
Belgian
by
production;
example,
example,
breeds
much
shown
milk
junglefowl
consider
140
of
suitable
A4.1.3
Humans
80
C
Figure 5
a
This
using
o
v
5.
and
[2]
dierences
proteins.
p
in
x
for
multiple
are 10
chance
w
e
sequence
y
4.
R
clade
sequences of
determined.
ancestorQ.
reasons
and
r
e
v
and
be
O
ancestorP
d
▴
between
t
i
s
expected
c an
base
b
c
Q
n
Discuss
and
y
2.
P
l
ancestor
the
from
with
which
aurochs
dierent
breeds.
the
Consider
they
(now
breeds
of
wild
species that they most
modern
have
extinct)
egg-laying hens
been
of
developed; or
Western
domestic ated
Asia.
There
livestock, as
y
how
a
P
e
r
Explain
.
P
1.
−132
Ecosystems
s
s
by articial selection, starting with
patterns
of
plant
•
bres;
•
cut
obvious
uses.
considerable
plants
years
rapid
during
domestic ated
This
changes
which
If
The
only
repeatedly
relatively
evolution.
wild
process
that
of
selection
have
grown
and
and
in
time
but
some
crop
plants
is
are
markedly
crop plant
have
that
not
always
changes
have
breeding the individuals most
selection.
domestic ated animals and
show
achieved
crops
plant
of
explanation
articial
occurred
periods
articial
humans
animals
credible
c alled
of
varieties
selecting
is
have
short
species
dierent
and
that
this
articial
over
reared
selection
n
c ause
over
many
U
crop
resemble
are
forms.
by
roses.
o
human
plants
that
simply
wheat
cotton
there
current
bred a
p
is
their
selectively
C
to
crop
have
v
It
in
example,
example,
addition,
plants.
i
n
The
In
achieved
suited
for
livestock,
species.
been
example,
owers;
dierent.
existed
for
for
crop
y
with
humans;
among
various purposes, including:
r
e
As
for
for
O
food
observed
t
i
s
•
are
species
n
Humans
range
l
Similar
y
years
y
M any breeds of dog have been developed
grey wolves—perhaps as long ago as 30 to 40 thousand
e
r
Figure 6
P
▴
the
c an
12,000 or so
livestock,
it
seems
o
changes
over
the
billions
of
years
l
8
6
2
1995
E
0
v
4
E arth.
Source:
a
O
% CH T
10
on
u
12
f
x
14
life
i
16
of
t
a
r
o
18
d
reasonable to assume that natural selection could have c aused major evolutionary
University
National
2000
2005
2010
2015
Institute
of
on
Mississippi /
Drug Abuse
2020
year
▴
Figure 7
Herbal c annabis is the dried
contains tetrahydroc annabinolic acid,
by heat.
Through articial selection,
quadrupled
in 23years,
owers and
fruits of the plant Cannabis sativa. It
which is converted
the average THC
to tetrahydroc annabinol (THC)
content
increasing the risk of early-onset
of c annabis sold
psychosis and
to users has
schizophrenia
141
Unity
and
diversity
A4.1.4
Evidence
homologous
D arwin
relative
are
found
were
it
curious
apparently
positions.
pentadactyl,
are
an
anatomic al
D arwin
which
excellent
position
the
forelimbs
dierent,
c alled
means
of
of
inside
such
they
example
and
yet
a
human,
them
similarities
have
ve
despite
mole,
the
“unity
digits
homologous
structure
are
of
(toes
horse, porpoise and
same
bones
or
ngers).
consists
dierences in function.
these
structures:
Hindlimb
proximal part
radius
group of wrist or
c arpals
bones
in
each
metatarsals and
p
phalanges
Table 1
tarsals
metac arpals and
ve digits
phalanges
n
U
C
i
n
o
v
▴
of
tibia and bula
y
series
ulna
r
e
ankle bones
of
and
part
O
distal
femur
t
i
s
two bones in the
n
y
humerus
o
i
d
t
a
r
o
u
l
a
E
v
O
f
x
▴
All
a
amphibians,
modic ation
show
the
limbs:
•
Figure 8
reptiles,
of
it),
skeletons
amphibians,
Crocodiles
birds
whatever
of
one
or
mammals
function
example
reptiles,
walk
and
the
birds
crawl
on
from
and
land
of
have
their
each
of
mammals.
and
use
the
same
limbs.
the
All
their
pattern
The
vertebrate
have
of
photos
bones
in
classes
(or
Figure 8
that
have
pentadactyl limbs.
webbed
hind
limbs
for
swimming.
•
Penguins
use
their
hind
limbs
for
walking
and
their
forelimbs
as
ippers
for
swimming.
142
•
Echidnas use all four limbs for walking and also use their forelimbs for digging.
•
Frogs
use
all
four
limbs
for
walking
and
their
hindlimbs
for
jumping.
y
Forelimb
single bone in the
l
structure
of
Pentadactyl
r
Bone
limb
same
P
pentadactyl
the
structures—features with similar
Pentadactyl limbs
The
in
type”. These limbs
e
limbs
from
structures
that
so
evolution
s
s
bat
for
Ecosystems
You
c an
Some
see
penguin
The
dierences
metac arpals
they
of
all
beginnings
toothless;
the
They
that
about
organs”
of
no
not
easily
explained
the
are particularly
and
in
now
by
evolution:
they
no
longer
thigh
have
a
these
insects
horse
the
also
we
similar
similarities
are
nd
in
that
some
they
are
supercial.
Such
features
analogous
they
evolution.
whether
similar
Consider
deduce
the
l
vertebrates
as
a
E
v
O
and
to
u
structures.
used
an
central
the
t
a
determine
increasingly
structures
perform
the
dierent.
that
they
had
are
known
dierent
same or a similar function.
structures
bat
human
in
evolutionary
nervous
example.
is
o
convergent
to
of
bec ause
very
porpoise
respects but close
i
similar
d
explanation
are
origin
n
that
structures,
are
so
y
the
structures.
dicult
arthropods
as
function
p
structures
study
reveals
f
x
their
found
between the tails of shes and the tail ns of whales.
and
bec ame
is
baleen
bones
o
we
birds
evolution
U
of
c alled
Cladistics
known as
embryo
C
when
evolutionary
be
mole
evolution.
found
pelvis
organisms
mechanism of
v
similarities
but
same basic
prove that
of
function,
teeth
small
do
groups
without
serve
the
y
that
retain
type”.
n
the
or
anything
“rudimentary
are homologous or analogous.
and
forms
explain
structures
of
l
being
to
“unity
O
are
ways
pentadactyl limbs, which it
descendants
structures.
reveal
Convergent
analogous
c an
c alled
diverse
r
adults
its
present
they
reduced
Examples
had
of
D arwin’
s
dicult
r
o
It
D arwin
are
in
r
e
are
wings
is
are
evolved
wall of whales and some snakes; and the appendix in humans. These
examination
This
they
is
All
homologous
do
pentadactyl limbs is that
have
dierent functions. The common ancestor
land.
their
as
but
i
n
are
origins
Activity
evolution of the
gradually lost.
However,
The
of
into
such
ancestor
vertebrates)
on
Nor
analogous
There
as
that
despite
A4.1.5
The
evolved
organs.
structures
of
examples
These
for
bones—this
However,
body
being
the
P
the
thicknesses of the bones.
during
y
whales,
and
lost
t
i
s
vestigial
been
structures
common
adapted
ancestry.
structures
a
walking
limb
have
interesting.
in
of
common
evolution.
from
(four-legged
for
many
organisms
The
lengths
have
e
used
arrangement
had
relative
homologous
become
tetrapods
are
for
inherited
have
probably
There
the
s
s
were
as
in
phalanges
forelimb.
explanation
they
and
systems
dierent
organisms
▴
Figure 9
(not
origins
of
organisms
(CNS) of annelids,
to sc ale)
Choose
type
of
limb,
a
dierent
bone
then
diagrams
the
Pentadactyl limbs
How
e ach
to
its
limb
colour
for
e ach
pentadacty l
and
Figure
What
in
a
copy
in
bones.
use d?
in
is
colour
9
to
e ach
fe atures
make
it
of
the
identify
limb
the
well
bones
adapte d
use?
143
Unity
and
diversity
Are central nervous systems homologous or analogous?
There
is
bodies
and
clade
of
animals
with
bilateral
evolved
symmetry. Their
an
and
a
need
posterior.
for
communic ation
Annelids,
arthropods
rather
between anterior
and
independently
example
than
of
in
these
convergent
homologous
three
evolution.
phyla
They
so
they
are
are analogous
s
s
ends
a
have le and right sides, anterior and posterior
structures.
vertebrates
Annelids
achieve
this
communic ation
running
along
via
a
single
nerve
cord
Nemerteans
midline
of
the
organism, with an
Brachiopods
enlarged
section
at
the
anterior
end.
In
vertebrates,
there
Platyhelminths
a
spinal
cord
and
r
is
brain.
Rotifers
of
nerve
cords
and
vertebrates
associated
in
annelids,
arthropods
Nematodes
is
with
a
similar
pattern of
Arthropods
expression
of
a
suite
of
genes
c alled
homeobox genes.
suggests
that
the
nerve
cords
l
Vertebrates
This
are homologous.
y
nervous
system
development
in
other
groups
n
Hemichordates
However,
Xenacoelomorphs
of
bilaterians
ancestors
vertebrates
did
not
homeobox
gene
dierent. This suggests that
of
have
annelids,
the
expression.
The
▴
arthropods and
characteristic
nerve
cords
must
Figure 10
In annelids,
development
pattern of
arthropods and
of a central nervous system
in other bilaterian groups
n
optic nerve
o
i
The human eye (le) and
u
A4.1.6
l
a
E
v
O
f
x
t
a
However,
the octopus eye (right) are strikingly similar in some
the human eye has nerve bres in front
These two types of eye are the product
Speciation
of convergent
by
pre-existing
species
If
species
two
populations
natural
selection
dierent
Aer
a
ways.
time,
merged
and
it
be
would
y
o
C
lens
whereas in the octopus the nerve bres are behind
c alled
144
p
r
e
v
i
n
nerve fibres
U
d
r
o
spot
retina
blind spot
Figure 11
respects.
vertebrates
is associated with a
similar pattern of homeobox gene expression but this has not
have
been found
▴
O
common
markedly
t
i
s
the
is
of
then
The
they
had
clear
a
acts
characteristics
will
be
the
chance
that
speciation.
of
the
recognizably
they
of
had
separated
on
the
two
two
interbreeding,
evolved
into
so
of
they
c annot
populations,
populations
dierent.
there is a blind
there is no blind spot.
evolution so are analogous structures
splitting
become
dierently
of the retina and
the retina and
If
the
but
not
will
evolve in
gradually
populations
did
separate
will
interbreed and
they
actually
species.
diverge.
subsequently
This
interbreed,
process is
y
development
P
The
e
the
Ecosystems
s
s
e
r
speciation has happened
Figure 12
This fractal tree shows a sequence of
In what
ways does it
white-eyes.
resemble speciation? How
This has occurred in Zosterops, a genus of
There are now over 100 species in this genus,
Afric a though Asia to Australia and
does the evolution of species dier from
the pattern in
New Zealand.
two
and
a
the
two
this
by
to
the
split
into
separate
Interbreeding
whereas
to
the
must
be
of
barriers
populations.
This
a
an
existing
species, they must stop
depends
population
preventing
c an
of
reproductive isolation of
c auses a mixing of genes and
speciation
genes
splitting
happen:
be
a
gene
achieved
r
o
reproductive isolation.
on
as
o
of
for
selection.
traits,
there
speciation
i
pools
occur,
required
other.
refer
in
species
d
gene
of
Biologists
to
c an
each
blending
divergence.
speciation
with
new
n
therefore
dierential
populations
interbreeding
are
a
U
Before
processes
of
y
populations
selection
formation
o
Two
the
and
C
species.
is
isolation
i
n
Speciation
reproductive
v
dierential
of
p
Roles
r
e
A4.1.7
from
This is the Abyssinian white-
eye, Zosterops abyssinica
the fractal?
leading
This is known as
O
birds c alled
splits.
many times,
n
t
i
s
explosive species diversic ation.
▴
over a wide area.
l
In some groups,
to large numbers of species spread
y
P
Figure 13
y
▴
by
separation and
gene
ow
pool.
For
between the
any method of
▴
Figure 14
The bonobo (shown foraging
for insects in the river) and
the chimpanzee
t
a
are both primates from the genus Pan.
Geographical separation is the most obvious and probably the most common cause
Bonobos are smaller and
have markedly
of reproductive isolation. There may be gaps in the range of a species, which divide
u
f
x
dierent
it into separate populations. These gaps could be due to physical barriers that are
behaviours from chimps. The
range of the bonobo and
do not
between two islands. Such barriers prevent interbreeding between populations, so
separated
O
l
dicult to cross—for example, a mountain range, a wide river or a stretch of ocean
the gene pools are separated. Geographical separation is usually associated with
a
it
selection
operates
the
signic ant
c an
the
same
c ause
same
E
remain
in
v
if
and
they
in
will
by the Congo River which
is renowned
for being deep. Neither
to be able to swim.
It is thought that at one point in history
the
way
traits
two
not
of
a
population
populations
become
of
a
separate
to
change.
species,
species.
However,
their
the water level fell drastic ally for a time
traits will
Where
there
are
allowing chimpanzees to cross temporarily.
It
is thought
that
these migrants bec ame
geographic ally isolated
dierences
in
the chimpanzee
as they are geographic ally
species is thought
dierences in selection pressures, which are also required for speciation.
Natural
overlap
selection,
this
is
c alled
dierential
or
divergent
from
their ancestors
selection.
when the water level of the Congo rose
Dierential
selection
c auses
the
traits
of
the
populations
divergence
is
judged
to
become
more and
again.
more
dierent;
when
this
by
taxonomists
to
be
This founder population, being
signic ant,
subject
the
populations
are
classied
as
separate
to dierent
selection pressures,
species.
diverged
from
chimpanzees to become
bonobos
145
Unity
and
diversity
To
of
understand
a
species
these
how
that
factors
there
has
might
c an
been
be
dierent
climate—temperatures,
•
predation—there
from
rainfall
might
be
by
the
and
selection,
migration
other
other
dierent
to
parts
consider
an
of
a
island.
the
new population
Any or all of
species
range:
aspects
predators
or
even
no
predators
in
are as
competition—there
The
lava
lizards
of
the
be
G alápagos
more
or
less
archipelago
competition
are
an
for
example
resources.
of
geographic al
r
and
might
speciation.
e
•
isolation
dierential
s
s
•
some
be
established
numbers
species
geographic al
endemic
one
that
is
an
a
species
This
explains
of
islands
by
G alápagos
Islands
are
the
archipelago.
is
an
the
example.
islands
On six smaller
to
dierential
suggests
lizards
One
of
that
from
these
the
but
dierent
species,
reproductive isolation
selection.
there
were
mainland
migrations
other
two
South
separate
Americ a to
populated
S an
populated all the other
Genovesa.
o
t
a
▴
Figure 16
Galápagos lava lizard Microlophus
albemarlensis on S anta Cruz Island
Española
Maria
island,
o
i
Santa Fe
an
M archena;
from
related
to
San Cristóbal
u
l
a
M. bivittatus
Distribution of lava lizards in the Galápagos Islands
E
146
Santa
v
Figure 15
f
x
O
▴
r
o
Isabela
key
d
Santa Cruz
Fernandina
lava
and
apart
closely
n
U
Santiago
of
C
 
Genovesa
Marchena
due
v
i
n
Pinta
six
research
Galápagos.
Cristóbal
present on all
are
migration
divergence
migrations
the
of
there
formed
Cladistics
area.
lizards
islands,
and
species on islands. An
found only in a certain
species (Microlophus albemarlensis)
larger
of
island.
p
the
population
to
y
lava
One
a
r
e
The
of
is
aer
migrating
n
large
endemic
by
l
the
occurs
O
range
its
None
y
P
oen
extends
t
i
s
Speciation
y
Speciation in lava lizards
Ecosystems
Data-based questions: Flightless steamer ducks
Steamer
inhabit
ducks
are
southern
members of the genus
Chile
that
there
ightless
and
live
on
species
c an
y
third
with
species.
M alvinas
This
the
and
range
fourth
or
species.
coast
of
Two
Chile
of
and
and
them
are
overlapping
F alklands
of
those
steamer
islands
to
of
the
duck
the
east
c an
shows
the
and
ranges
only
of
ice
these
the
four
and
species.
ducks.
about
a
million
was
lower
M aximum
as
Suggest
it
how
with
and
15,000
sea
of
with
reasons,
interbreeding
Chile
Argentina
–200 metres
ago,
did
4.
breed with
U
5.
isolated,
n
ightless
allowing
there
is
[2]
currently
[2]
T.leucocephalus
from a common ancestor
[2]
T.patachonicus is
T.pteneres and
Predict whether
into
cover
ago.
Discuss whether
T.brachypterus is
and
ying
likely
to
cross-
T.leucocephalus.
likely
to
[2]
diverge
species.
[2]
o
i
t
a
▴
Figure 18
B
(2012)
using legs and wings
resembling a paddle steamer. The genus name Tachyeres
means “fast
Soc.
T. brachypterus showing the rapid method of
swimming characteristic of steamer ducks,
and
R.
evolved
years
ice
drop as much.
T. pteneres and
T.pteneres and
o
have
15,000
the
was
L ast
u
Proc.
could
how
not
the
a
al,
Suggest
level
GPG ice limit
l
2339–2346
et
v
Fulton
E
Figure 17
Source:
d
r
o
f
x
O
▴
3.
C
i
n
v
sea level
sea
from the continental
whether
between
T.leucocephalus
by
steamer duck could
y
Discuss,
p
r
e
2.
extensive
inhabited
During
years
levels
diverge
the
is.
species.
fling steamer duck (T. patachonicus)
from a
ago.
areas
three
years
Patagonian Glaciation
reproductively
T. brachypterus to
(T. brachypterus)
the
ago, much of southern Chile
populations
become
the
from
million
diverged
years
currently
and
0.6
O
have
in
Great
years
(LGM)
extensive
Malvinas/Falklands flightless steamer duck
species
ice-covered
than
and
n
not
the
2.2
glaciations
levels
t
i
s
1.
Chubut flightless steamer duck ( T.leucocephalus)
During
sequences suggests
diverged
15,000
y
was
about
sea
base
l
Glacial
between
repeated
low
Argentina
DNA
M alvinas
continental
been
and
200metres
Fuegian flightless steamer duck ( Tachyeres pteneres)
the
ancestor
have
(GPG)
breed on inland lakes.
the
species
that
cover
on
y
ightless coastal populations and also
mitochondrial
P
has
and
There
Argentina.
that
of
species
common
ightless
species
map
ago
occurs on
of
the
continental
Argentina. A
populations
The
that
occurs both on the coast and
species
y
Analysis
research
r
the
its
The
four
Tachyeres
Recent
e
inland,
are
Argentina.
s
s
suggests
and
rower ”
279,
doi:10.1098/rspb.2011.2599
147
and
diversity
LHA
Unity
A4.1.8
Dierences
sympatric
Speciation
is
the
process
It
isolated.
Geographic al
It
is
also
to
into
is
c alled
means
is
isolation
speciation
geographic al
speciation
to
area
be
could
diverge
means
If
to
populations
and
much
whether
product
migration.
temporal
less
closely
of
true
common
of
obvious
one
geographic al
remain
separate
species.
“same homeland” and
be
a
consequence of
than
allopatric
species
sympatric
given
in
they
form
an
living
in
speciation
the
same
speciation, or allopatric
reproductive isolation due to
here.
C
o
v
p
y
are
is
geographic al
dierences in animals or plants.
related
Examples
separation
may
separate
yellower) and sensitivity of retinal pigments to dierent
wavelengths of light. Genetic dierences have been found
between the two forms and experiments have shown that
feed near the shore (littoral) and the other in deeper water
females tend to select a mate who is genetically similar to
(benthic). The two forms have adaptations corresponding
themselves. This is an example of behavioural separation,
to these preferences—body size and shape, structure of
which reduces the mixing of genes between the two forms.
i
o
d
Over time, this may result in speciation.
t
a
r
o
u
l
f
x
a
E
v
O
▴
n
U
700metre wide crater lake in Tanzania. One form prefers to
the jaw and teeth, coloration of breeding males (bluer or
Figure 19
Lake M asoko with a male littoral (yellow) morph Astatotilapia calliptera, a male
benthic (blue) morph and
148
the
by
animals
certainly
sure
temporal
i
n
calliptera) have been discovered in Lake Massoko, a
sympatric
in
r
e
and
Behavioural separation
Two forms of a species of cichlid sh (Astatotilapia
in
is
are
followed
behavioural
together
interbreed.
Sympatric
chapter,
occurred.
“dierent homelands”.
dierences
dicult
this
dierent
has
more
n
it
living
or
reproductively
O
and
not
two
are
in
in
speciation
species
do
populations
speciation.
earlier
t
i
s
Sympatric
a
into
y
behavioural
the
of
that
splits
species
populations
allopatric
population
isolated,
described
When
populations
sympatric
Reproductive
species,
a
l
allopatric
separation,
of
a female mouthbrooding eggs
y
This
a
species
P
reproductively
for
two
one
populations
isolation.
separate
possible
split
which
if
speciation
r
area
by
happen
reproductive
become
allopatric
between
e
areas
of
only
similarities
s
s
species.
means
c an
and
and
Ecosystems
LHA
Temporal separation
The
winter
pine
life
cycle
summer
During
or
that
brief
trees.
head-to-tail
the
sites
next
year
as
did
their
area
of
Portugal,
of
this
feed
In
quickly
and
the
common
The
timing
in
this
of
life
The
in
assume
dierent
summer
enough,
or
that
at
winter.
sympatric
develop
the
the
adaptations
If
the
two
are
to
has
the
in
same
the
cycle
is
by
the
moth,
a
with
are
larvae
of
grow
September.
winter
larvae,
sympatric.
trait so must
forms
never mate
a
will
have
Figure 20
Winter processionary moth larvae in a procession
source
o
as
n
U
biodiversity
▴
C
radiation
v
Adaptive
two
for all
rather than the
the
end
heritable
The
timings
summer,
Portugal—they
genetic ally.
discovered a
M ay or June and
conditions,
pupate
of
have
dierent
forms
needed
divergence
speciation
migrate in
pupae
emerging
emerge
through
of
great
separation: the two
dierent times of
trees and to their
i
n
A4.1.9
of
the
determined
that
Adults
form
area
active
to
at
y
lives
soil.
researchers
summer
ready
in
adults,
larvae
reasonable
bec ause
temporal
happen
occurred.
leaves of pine and
the
larvae
becomes
is
p
more
also
grow
warm
the
from
by
lay
larvae that
life
parents.
species
cycle.
are
of
on
then
into
seems
r
e
The
be
life
and
winter.
M arch,
down
females
hatch
It
diverge,
there
O
its
and
eggs
days.
as
adult
t
i
s
larvae
in
will
winter
underground
population
stages
or
generation
year.
or
of
n
one
February
emerge in
three
mate
The
and
processions
Adults
two
just
other
days
y
In
of
autumn
complete.
live
for
each
three
l
time
In
they
eggs.
or
Mediterranean.
y
into
time
to
and
the
P
pupation
the
year
around
r
cedar
one
autumn
fertilized
during
countries
e
100–200
feed
takes
early
in
s
s
Its
with
processionary moth (Thaumetopoea
pityocampa) lives
Characteristics that make an individual suited to its environment or way of life are
called adaptations. This term is used because the t between structure and function
o
d
is developed over time, by a process of modication. The process of modication is
“adaptation” and a trait developed by this process is “an adaptation”.
i
t
a
r
o
Species extend their range if a group of individuals migrates to a new area. These
individuals are the founders of a new population. If they cannot interbreed with
other populations, the traits of the new population will tend to diverge from the rest
u
f
x
of the species. This is partly due to chance, oen aided by the small initial number
of founders. It is also partly a result of adaptation to dierences in the environment.
Another factor that can cause rapid adaptation in a new population is the availability
l
O
of an ecological niche that is not being fully exploited by other species.
out.
In
this
evolved
source
is
of
the
dened
a
as
a
of
c an
niches
radiation;
is
pattern
of
live
is
rather
a
of
than
the
means
geographic.
which
of
between
allopatric,
repeatedly in some
“radiation”
in
range
Bec ause
competition
speciation
happened
word
diversic ation
occupy
biodiversity.
then
have
the
ecologic al,
ancestor
minimizes
process
new
radiation
considerable
species
to
adaptive
common
radiation
the
related
adaptation
c alled
c ase,
from
adaptive
if
is
E
radiation
Even
and
This
v
groups.
a
Speciation
species
ecologic al
diversity
species
migration
of
so
spreading
Adaptive
that
have
roles. It is a
ecologic al niches,
they
c an
coexist.
c an occur and closely
sympatric ally.
149
and
LHA
Unity
diversity
Darwin’s nches
Galápagos
adaptive
the
of
nch
islands
of
have
leaves,
fruits,
seeds,
insects
of
evolved
adapted
nectar,
leaves
show
possible
without
archipelago. These
dierent
so
insects
nch
food
seeds,
under
sources:
large
bark.
hard
The
beaks
clear adaptations. Up to
have
been
found living
loc ality. It is unlikely that this would be
adaptive
radiation—there would be too
l
much competition.
later wrote:
“The most
He studied the nches on these
curious fact
in the size of the beaks in the dierent
as large as that
of a hawnch to that
of a chanch,
group
of birds,
one might
really fancy that
an original paucity of birds in this archipelago,
modied
for dierent
ends”
one species had
(D arwin, 1839)
o
C
i
n
v
been taken and
y
intimately related
… even to that
diversity of structure in one
p
from
and
gradation
from one
r
e
of a warbler… Seeing this gradation and
small,
is the perfect
species of Geospiza,
Brocchinias—adaptive radiation of bromeliads on the Guiana Shield
Brocchinia is
the
a
genus
of
bromeliads.
Guiana
Shield
in
southern
Brocchinia
from
20
other
bromeliads
last
have
a
competitive
a
For
diversity
smell,
the
and
has
a
tank
which
leaves
uid
are
absorb
mineral
is
and
contains
insects
strategies
killed.
solely
in
than
its
vertic al
which
into
the
attracts
any other
roots
Specialized
to
insects.
The
The
enzymes,
hairs
released
collects.
give
slippery,
esc ape.
digestive
leaves
water
uid
particularly
c annot
nutrients
on
therefore
have
for a supply of nutrients.
curved
v
nectar-like
the
of
relies
soil
secreted
E
are
acidic
for at
Plants which
strategies
Brocchinias
a
the
form
Chemic als
into
diverged
happening
growth.
l
O
through
together
plant
example:
Brocchinia reducta
fall
150
limit
advantage.
greater
plants.
covering
been
nutrient-c apture
Brocchinia prismatica
that
has
u
of
growing
•
c an
f
x
genus
species
years ago and
rock of the Guiana Shield yields nutrient-
that
successful
developed
genus
years.
grow
Guyana.
t
a
develop
soils
the
million
and
i
sandstone
decient
•
within
13
r
o
The
the
species
o
least
million
d
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20
n
The common ancestor of
all
The
Venezuela
U
on
on
it
so
uid
so
the
a
sweet
wax
insects
is
very
trapped
leaves
by digestion.
▴
Figure 22
Venezuela
Brocchinia reducta,
Mount
Roraima,
n
This statue depicts the young Charles D arwin stepping
O
islands and
y
Figure 21
onto the Galápagos islands in 1835.
t
i
s
▸
y
one
years,
from a common ancestor
to
particularly
example of
million
P
in
2.3
small
and
Galápagos
together
known
past
Galápagos
pollen,
nches
species
the
best
the
r
10
the
have
become
on
the
O ver
e
nches
of
are
s
s
14species
on
nches
radiation.
Ecosystems
Brocchinia acuminata
creating
chambers
ants
detritus
and
uids
at
the
the
from
base
uid
has
of
and
expanded
which
ant
these
absorb
ant
activities
are
chambers.
the
leaf bases
colonies
live.
Roots
nutrients
Dead
digested in
grow
released
s
s
into
in
LHA
•
by
digestion.
•
Brocchinia micrantha
of
rainwater
at
grows
the
very
base
of
large
each
and
of
its
collects
leaves.
leaves and other plant detritus falling into
these
water
tanks
are
digested,
r
Dead
providing a supply of
Brocchinia tatei
falling
also
plant
has
debris.
leaf
It
bases
c an
live
that
on
collect
the
water
ground or as
▴
growing
on
the
trunks
and
Figure 23
Brocchinia micrantha,
branches of
Guyana
trees.
Nitrogen-xing
supply
the
plant
cyanobacteria
with
grow in its tanks
nitrogen compounds.
Barriers to hybridization and sterility
Th e
hy br i d s
Hy br i d i z a ti o n
d o n ke y
th o s e
is
o f te n
pro b a b l y
( Eq u us
two
th e re fo re
f i rs t
c a b a l lus
s pe c i e s
been
do n e
the
and
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h ave
de l i be ra t e l y
d o n ke ys
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th a t
re a s o n
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and
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k n ow n
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h ave
m o re.
63 .
di ffe re n t
b re e d e rs .
c o mb i n e
has
Ho rs e s
This
h ave
c auses
i n c o m pa ti bi l i ti e s ,
s te r i l e.
of
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as
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me mb e rs
th a t
i
r
o
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what
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th e
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by
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mu l e
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nutrients to the plant.
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Plant breeders oen use interspecic hybridization to produce new varieties. The rst
person known to have done this was Thomas Fairchild who, in the early 18th century,
f
x
u
crossed carnations with Sweet Williams (Dianthus caryophyllus × Dianthus barbatus).
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s Mule”.
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s Mule was sterile.
l
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This is very common in interspecic hybrids produced by breeders.
interspecic
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evolutionary
hybrid
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produced
species
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permanent
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related
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it
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in
an
totally
to
die
partially
the
that
surprising,
development
likely
or
between
resources
not
happens
naturally
ecosystem.
of
during
hybrid
the
so
ranges of
hybrids,
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c ause
natural
little or no
species.
parent
therefore,
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articial
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parent
a
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that
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producing a sterile
species
hybrid
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zygote
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151
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LHA
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few e r
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individual
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of
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a
is
if
not
mating
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di s p l aye d .
to
among
be
To
bi rds — b i rds
is
if
th e
p re ve n t
of
a
between
Th i s
Th e re
of
its
a re
i n te rs p e c i f i c
pa ra di s e
in
th e
P a pu a
c ases,
species
hy b r i d i z a t i o n ,
i m me n s e
New
there
remained
may
if
be
geographic ally
mixing
bring
a
result,
loss
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barriers
alleles
species
For
and
speciation
example,
on
Anas wyvilliana
faces
biodiversity.
with
hybrid
closely
display
ospring.
these
dierences
separate
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in
related
and
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possible
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their
have
courtship
species.
of
be
Western
these
n
U
either
same
c an
C
the
that
western
viewed
do
hypotheses
not
had
reversed. This
of
traits
Americ a has an
video clips on the internet.
sometimes
explain
enough
or
they
this
time
mate
since
should
and
not
diverging
be
t
a
establish and
in Clark’s grebes involves a
coordinated actions, which
reinforce the bond
between male and
to
evolve
regarded as
a
Courtship
produce
apparent anomaly:
u
l
v
E
Figure 24
sequence of distinctive and
mallard
from both
hybridization, with a
o
i
d
r
o
f
x
O
▴
have
grebe (Aechmophorus occidentalis)
species
displays,
be
naturally
non-native
through
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in
newly
y
the
has
display
the
have not
Hawaiian islands the
mixture
p
However,
i
n
courtship
o
grebe (Aechmophorus clarkii)
elaborate
a
extinction
r
e
v
Clark’
s
some
introduced
with
Courtship in Clark’s grebes
may
would
where
brings
hybridization
that
swarms
happen
migration
together
hybridizing
hybrid
to
overlap and
c an
O
As
consequent
is
forming
If
that
This
but
t
i
s
species.
of
ranges
hybrids.
speciation
again.
separated.
native duck (Anas wyvilliana)
(Anas platyrhynchos),
allowed
together
humans
have
n
happen
do
l
also
back
has
species
interspecic
y
c an
separation
species
developed,
fertile
Guine a,
female
y
separated
related
P
geographic al
closely
produce
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b e h av i o u r
e
some
an
ow n
o ft e n
c h a ra c t e r i s ti c
ex pl a i n s
d i f fe re n t
be h av i o u r :
m e mb e r
fe a t u re s .
s ta ge
di s t i n c t i ve.
place
c o u r ts h i p
exa mp l e.
these
152
of
pa r t n e r
be h av i o u ra l
at
ta k e s
fu n c ti o n s
po te n t i a l
re j e c ti o n
needs
no
th e
r
In
th e
one
d i s ti n c ti ve
with
b e h avi o u r
wasted
is
w h e th e r
fo r
c o u r t s h i p,
courtship
fo r
che ck
l o o ki n g
a re
th i s
s
s
pa tte r n
c an
by
in
re s o u rc e s
a n i ma l s ,
Ecosystems
LHA
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s
s
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l
and
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to
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so
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be
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have
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diploid
in
an
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Western
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in
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que ens
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cell,
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the
copulate
will
pheromone
antennae
lay
with
over
by
up
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one
mating
10–20 m
que ens
and
Crowds
20drones.
ye ars.
How
of
drones
This
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ight.
above
drones
(e)-9-oxo-2-de cenoic
(right).
several
Both
on
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acid
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provides
interspe cic
all
the
typic ally
as
a
que ens
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hy bridization
chromosomes.
in
evolution.
result
an
four sets
autotetraploid.
bec ause
mis-pairing
that
is
Bec ause all the sets of
c alled
fertility,
changes
an
the
there.
(drones)
which
duplic ation. Genome
times
tetraploid.
low
assemble d
males
are as,
chromosomes in a cell
many
become
is
homologous
of
diploid
is
plants
the
and
is
there
are
four
very likely during
overcome
this
problem,
established.
example of the establishment of
of
this
Europe.
species
Part
of
autotetraploids
Sc andinavia,
individual
fuse
in
rele ase
their
fertile
(with
this
16
chromosomes)
area, in the
C arpathian mountains, has both diploids and
that
Europe
autotetraploid
triploid
ight,
successful
whole-genome
with
southeastern
thought
western
gametes.
vigorously
is
E
It
spreading
Meiosis
and
v
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autotetraploids.
been
a
eastern
is
genetic
populations
populations.
of
organism,
associated
of
sets
happened
happens
l
O
Balkan
is
it
two
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rock-cress (Arabidopsis arenosa)
in
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i
autotetraploid
than
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u
O ver
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mating
that
t
a
from
usually
chromosomes
autotetraploid
Q ue ens
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polyploidy
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that
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o
come
allowing
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is
the
e ggs
have
with
congre gation
o
cell
meiosis.
S and
more
show
f
x
homologous
has
chromosomes,
Autotetraploidy
of
are a.
pheromone
mate
C
studies
chromosomes
D uring
this
colonies
ever
drone
n
subsequent
genome
for
speciation
and
consequence
homologous
congre gation
only
spe cial
o
whole
of
sky.
d
If
the
dierent
to
v
a
sequencing
f rom
(que ens)
aernoon
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n
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drone
females
e arly
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thousands
Abrupt
organism
is
fertile
the
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a
have
in
U
polyploid
Polyploidy
of
y
be es?
hybridization
A
re ach
ac ross
hundre ds
honey
A4.1.11
diameter.
which
shooting
fertilize
mellifera)
they
y
comets
to
in
colony
drones,
(Apis
mate,
p
ne e de d
to
100 m
their
for
be es
re ady
about
attractant
resemble
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r
e
sex
In
are
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ground
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25
que ens
n
y
Figure
When
t
i
s
▴
y
P
O
r
H
with
are
produces
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produced
unlikely
to
here
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autotetraploid plants
cells
and
therefore
from an individual that
Figure
perform
only
diploid
gametes
(see
originated
where
26).
meiosis
These
may
successfully,
grow
so
are
sterile.
153
and
diversity
LHA
Unity
According
should
very
be
to
similar
recognize
perhaps
the
biologic al
regarded
in
as
morphology
them
as
species
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new
to
denition,
species.
diploids,
species.
They
diploids
However,
so
taxonomists
are
also
and
autotetraploids
autotetraploids
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relatively
be
are usually
reluctant to
uncommon
in
nature,
bec ause the similarities with the original diploid population make
s
s
competition
likely.
e
diploid
AA
r
polyploidy
AAAA
l
meiosis
haploid gamete
from a
with a diploid yields
AAA
p
Figure 26
i
n
AA
BB
haploid
parents
species
interspecific
Another
1.
sterile
AB
type
of
polyploidy
Individuals
from
hybrid
two
has
polyploidy
so
2.
meiosis
f
x
l
Fi g u re
sym b o l s
ha p l o i d
154
A
27
of
B
the
hybrids
any
cell
in
does
not
then
re p re s e n t
are
Allotetraploids
diploid
mixture
be
divide,
traits
these
will
with
two
process.
The
one
set
species
pairs
four
hybrid
have
sets
of
allotetraploid
allotetraploid
resulting
from
are
when
interspecic
each of the two
very
closely
meiosis
is
related,
attempted,
cells
duplic ates
four
of
will
be
c an
be
able
to
of
allopolyploid,
chromosomes but
are
from
produced
divide
each
the
its
chromosomes. It is an
chromosomes
cells
chromosomes
an
sets
type,
by
two
meiosis
which
interspecic
dierent
by mitosis. It is
c an
bec ause
reliably
hybrid will
problems.
interbreed
species.
from
two-stage
homologous
cell
the
becoming
c an
a
cross-breed.
interspecic
the
these
fertility
of
the symbol A represents one
sterile.
sterile
homologous
By
its
Unless
form
bec ause
parent
of
will
these
pairs.
species.
of
result
species
chromosomes,
not
the
two
overcome
a
both
with
They
other
are
parent
allotetraploids, but not with either of
therefore
species,
a
new
they
are
species
usually
and,
as
they
have
recognized and
t he
d i f fe re nt
c hro m o so m e s
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will
More
likely
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A l l o t e t ra p l o i d y:
a nd
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E
▴
v
allotetraploids
If
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a
O
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u
AB
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sets
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i
AABB
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r
o
allotetraploids
d
hybrid
the
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U
hybridization
Autotetraploidy:
of chromosomes
C
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o
v
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diploid
diploid
y
r
e
but interbreeding
a sterile triploid
O
t
i
s
be produced
n
y
gametes may
named
as
process,
a
distinct
especially
species.
in
the
M any
plant
species
have
kingdom—for
been
produced
by this two stage
example, in the genus
Persicaria
y
P
autotetraploid
Ecosystems
LHA
Horse chestnut trees
Horse
to
chestnut
northern
native
were
to
sterile.
fertile
hybrid
and
A
trees
the
the
both
parents but
developed
seeds
same
likely
was
traits as the
regarded
carnea.
that
germinated
explanation
are
species
hybridized.
Figure
28
for these
as
a
new
shows a
l
author ’s
These
trees
×
from
then
Both
they
garden.
over
for
by
and
=
44
(It
is
in
the
genus
an
Research
hybridization
One of these is
is
Persicaria
native to
introduced alien in other parts
indic ates
between
chromosome
which
There is
having
that
this
species
Persicaria foliosa
(2n
=
22),
followed
(2n
=
number.
by a doubling
n
▴
the
theory
features
the
relationship
E
Discuss
c.
O th e r
the
than
e vo l u ti o n
selection
the
predict
concept
of
and
explain
adaptive
the
radiation.
unity
and
diversity
of
life
on
E arth?
(A4.1.9)
by all cells. (A2.2.4)
between
a
the
emergence
selection.
b.
shared
natural
outline
Persicaria maculosa
niche
and
convergent
evolution.
(B4.1.7)
strong evidence in biology?
how
v
natural
as
by
example,
l
counts
Explain
an
u
the
Discuss
f
x
Outline
c.
What
to
evolution
b.
a.
reference
of
With
t
a
does
a.
O
2.
How
Figure 29
o
i
d
r
o
Linking questions
1.
arose
22) and
U
the
species
chromosomes),
Persicaria lapathifolia
of
world.
allopolyploidy.
Asia.
world.)
the
C
the
of
i
n
of
by
(2n
15
Persicaria, with
parts
o
maculosa
least
most
v
originated
at
species in the genus
in
p
evidence
Europe
100
occurring
y
are
species
r
e
There
Figure 28
O
t
i
s
Hybridization and polyploidy in the genus Persicaria
n
y
◂
y
hybrid
Aesculus
the
traits
tree
with
is
States.
where
P
in
the
seeds.
What
The
c alled
specimen
on
native
r
more
observations?
species,
combined
shoot
hybrid.
United
Germany,
produced
produce
original
to
are
trees (Aesculus pavia)
e
initial
was
buckeye
southern
introduced
The
to
the
Red
s
s
are
trees (Aesculus hippocastanum)
Greece.
experimental
th e
by
of
antibiotic
resistance
is
predicted
and
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evolution
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(A4.1.1)
evidence
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that
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e vi de n c e
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(A1.2.14)
s u pp o r ts
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(A 4 .1 )
155
A4.2
Conservation of biodiversity
s
s
What factors are c ausing the sixth mass extinction of species?
A number of factors threaten biodiversity, including the loss
from invasive species and climate change. The image
r
shows a Red fox (Vulpes vulpes) consuming an Arctic fox
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e
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change? How is climate change impacting the distribution
l
of its prey, its predators and competitor species that
Is the range of temperate species
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Red
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loss and
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measures? What
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fed
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A4.2.7
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A4.2.8
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all
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current
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A4.2.3
conservation
156
the
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A4.2.2
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A4.2.1
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O
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its
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yellow,
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157
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There have been no mass extinction events for 66 million years now. As a result,
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seilimaf fo
be the sixth mass extinction, so this peak of biodiversity is unlikely to be sustained.
0
The graphs show numbers
kingdom.
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total numbers
C,
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Adl S, Simpson
450
400
350
300
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B
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biodiversity of animals in marine habitats is probably higher now than it
Are
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groups of organisms are likely to have followed
9(8):
e1001127.
https://doi.
org/10.1371/journal.pbio.1001127
o
Biology
d
PLOS
50
This graph shows the numbers of marine animal genera known from
evidence over the 542 million years since the start
AGB,
250
there was a major diversic ation of animals and
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other multicellular organisms,
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i
8
much
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of
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Traill’s
1973:
Americ an
Americ an
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and
century,
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birds.
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▴
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159
Unity
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they
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may not adapt
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examples
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largest of
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were the giant moas—Dinornis novaezealandiae
approximately
160
at
prey.
began
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fuels,
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on
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a
and
ago.
last
i
were
Zealand.
years
the
to
extinction.
well-understood
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the
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temperature,
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happened
there
fossil
up
t
a
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o
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about
and
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this
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during
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have
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i
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i
s
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of
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l
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described
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other
transport on boats and airplanes.
y
gradually,
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parts
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in
took
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settled
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by
century,
▴
Figure 9
Painting of
▴
Figure 10
Skeleton of
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less than 200
hunted
to
Dinornis novaezealandiae
novaezealandiae in the British
by William
Natural History Museum
extinction.
Frohawk
y
and
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ice,
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vast
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other
have
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e
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s
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domestic
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Atitlán grebe (Podilymbus gigas)
C ats,
one
other
major
bird
have
the
will
remain
Atitlán
1958,
when
dolomieu and
to
the
lake
to
foods
and
for
of
to
Numbers
species
of
promote
grebes.
of
birds
and
the
were
Atitlán
the
marked
surviving
pied-billed
seen
grebe
in
L ago
of
the
black
lake
in
1983.
but
they
declared
Island’
s endemic
Atitlán
it
de
is
too
for
The
the
bass
grebe
were
grebe
began
introduced
anglers. These
crabs and sh that
also
predated
declined
grebes
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and
bird
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of
the
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from 200 in
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Atitlán grebe,
C
i
n
o
v
1960 to 80 in 1965.
water
numbers,
these
were
then
disappeared
extinct.
late.
Atitlán in
Atitlán
by
bed
decline
However, until all
bass (Micropterus
tourism
Atitlán
Unfortunately an
grebe (Podilymbus podiceps).
1989
was
1,700 m. It had small wings
decline
competed
the
Two
grebes
the
a
p
chicks.
to
led
with
fractured
c aused
for
1973.
y
multiplied
were
numbers.
Micropterus salmoides)
try
32
hybrids
pigeon
1976
by
extinction.
altitude
two
only
extinction
species of land
Henderson
endemic
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with
to
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e
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risk
earthquake
for
programme,
grebe (Podilymbus gigas)
grebe
Guatemala,
rat
refuge
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numbers
y
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been
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from
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in
were
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Inv asive
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factor.
the
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w ater
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of
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land
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plant
ecosystem
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A4.2.4
extinction
of
v
stre ams
of
he ctares
infe ctious
three mountain
declined
1980.
a
the
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c ause
populations
by
spe cies
an
contribute d
relatively common in mountain
l
of
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range
its
When
in
u
10,000
rainforests
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be
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f
x
probably
over
to
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was
in
and
have
t
a
streams.
lived
also
vulnerable
i
in
it
frog
r
o
1966,
was
so
d
ranges
torrent
spe cies
water but spend most of their adult
extinction due to habitat destruction. The Mount
Glorious
of
in
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o
to
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n
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Amphibians
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Glorious torrent
frog
loss
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direct—the
other
Figure 12
areas,
consists
of
loss
of
natural
ecosystem
the
c auses
of
loss
interacting and
161
Unity
and
diversity
interdependent
Activity
may
collapse
changed
Species
have
become
to
be
parts
of
the
world.
the
area
outside
This
the
so
if
c an
range
key
parts
happen
of
are
if
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tolerance
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entire
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of
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ecosystem
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Eight
c ategories
of
direct
or
indirect
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of
species in an
ecosystem
where
you
loss
are
here.
s
s
in
lost.
Research an
described
example
be
extinct in
ecosystem.
all
components,
and
live.
1.
Land-use change for agricultural expansion is the main cause of ecosystem loss.
In temperate zones, most areas suitable for farming were cleared of natural
forests, grasslands and wetlands before the 1970s. For example, the prairies
e
of North America were mostly plowed up in the 19th century. Since the 1970s,
it is mostly old-growth tropical forest ecosystems that have been lost.
Urbanization
rapidly
to
growing
major
the
and
fuel
c an
ecosystem
have
been
destroy
with
loss
of
forests.
and
some
Even
harvesting of a single
example
This
is
is
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overshing of
explored in
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from
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bushmeat and shing in
An
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these
Topic D4.2.
directly
activities
c an
through
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example, nickel mining and smelting in
to
o
soils
of
lakes
copper,
and
nickel
U
C
i
n
of
for
examples.
pollution
For
damage
pollution
dams
are
destroyed
animals
ecosystems.
areas
addition,
and
of
of
Newfoundland.
damage.
c aused
natural
of
v
widespread
has
habitats
threaten
railways.
has
p
In
and
resources
hunting
Banks
smelting
change.
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ecosystems
y
and
roads
r
e
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of
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marine
species
the
Ontario
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and
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n
freshwater
more
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wood,
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land-use
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human
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area
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over
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metals.
irrigation
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lead
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acid
has
to
rain
led to the
loss of
natural river and lake ecosystems. For example, the Colorado River now rarely
as
far
industrial
longer
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or
bec ause
diversion
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other
Mesopotamian
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and
hectares
u
7
.
l
blooms.
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8.
Rivers
Perhaps
the
Ecosystems
lost.
is
of
dams
of
water
hold
southern
in
the
extraction
back
uses
parts
Iraq
1990s.
for
agricultural,
water
from monsoons in
of
has
the
were
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world.
drained
About
the
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by
loss of
example, the
diversion of the
two-thirds of the two million
bec ame desert.
and
have
been
excessive
lakes
in
c auses
which
lost.
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growths
eutrophic ation and algal
organisms
of
Erie
for
algae
nutrient-enriched
are
adapted
example
has
to
low
been
every summer since
water
out
to
sea,
where algal
occur.
widespread
variables.
replaced
of
human
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rivers
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adapted
types
for
in
ecosystems,
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ecosystem
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uses.
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6.
the
occurs
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other
162
as
and
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ows
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to
When
replaced
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and
forest
if
climate
climate
threat
specic
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these
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variables
scrubland
temperatures
is
change
explored
are
of
or
ecosystems
is
temperature,
change,
entire
grassland
rise.
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if
Theme B
Theme D.
change.
ecosystems
rainfall
relationship
more fully in
considered in
climate
rainfall and
decreases.
between
and the likely
y
the
The
P
loss.
r
2.
Ecosystems
Two
live
specic
or
examples
attend
school,
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are
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examples
that
here
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but
wherever
worthy
of
you
study.
s
s
Mixed dipteroc arp forest of southeast Asia
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valuable
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timber.
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large
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legal
have
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more dicult.
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that
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areas
This
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to
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lowland
both
particularly
to
15 m
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o
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typic ally has particularly high quantities of
merchantable
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deep-peat
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the
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the
sandy soils.
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these
over
of
threat—rising
extremely high
of
in
n
to
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l
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rarely
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700
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20
about
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used
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tree
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example,
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e
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o
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Loss of the Aral Sea—an ecologic al disaster
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to
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the
of
water
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salinity
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species
area
much
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now
about
sh
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the
in
were
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former
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fed
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by
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freshwater
the
This
was
rivers but
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lake.
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were
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lake
is
and
depth
now desert.
of
the
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risen
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compared
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it
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major
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from
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levels
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K azakhstan
in
higher
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an
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u
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x
As
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i
it
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fourth
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o
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to
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Twenty-
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▴
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Figure 14
A comparison of the Aral Sea in 1989 (le)
disappeared.
and 2014 (right)
163
Unity
and
diversity
A4.2.5
Journalists
of
Evidence
use
the
ecosystems
before
declaring
that
source
which
useful
most
i
population
detection
of
or
is
a
has
play
over
which
in
example,
an
of
pairs of gannets in
a
of
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changes
such
as
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number
ecosystem—these
Brazilian
ecosystem—for
key
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harmful
M any types
of
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sh
found
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rainforest
example,
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monitoring
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species.
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an
an
species
serious
an
biodiversity
Hawaii
within
o
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u
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scientists
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by
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there
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biodiversity and
opportunities
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individuals
many
still
years.
time
for all citizens to
“citizen
for
science”. Some
who
This
them
have
c an
to
monitored
allow the
be
reversed.
Applying techniques: Use of Simpson’
s diversity index
O
l
The Simpson’
s reciprocal index quanties biodiversity by
highest
greater the biodiversity in an area, the higher the value of D.
species,
a
of
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where
v
The formula for Simpson’
s reciprocal index of diversity is:
164
The
taking into account species richness and evenness. The
D
=
diversity
N
=
total
n
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number
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could
in
occur
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where
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evenness
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forest
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the
with
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succession.
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and
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there
many
are high.
species
or
numbers
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glade
found in an
in
the
same
You could use a phone app
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such as
index
number
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so
undisturbed
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forest
n(n
values
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Picture This
individual
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individuals
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species
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reports.
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diversity
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species
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number
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intergovernmental body
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example,
example,
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losses
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number
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Science-Policy
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richness
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One
term
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Data-based questions: Using Simpson’
s diversity index
Groups of students studied the species diversity of the beetle fauna found on
two upland sites in Europe. The same number of students searched for a similar
s
s
length of time in each of the two sites. The two sites were of equal area.
The
number
of
individuals
of
the
four
species
found
at
Site
B
each
site
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given in
Table 1.
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15
8
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of
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the
the
two
Suggest
a
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at
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Heath.
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in
used
when
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11
12
13
14
15
16
17
18
19
20
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E
165
Unity
and
diversity
Data-based questions: S atellite monitoring
Sentinel
Agency
are
They
vedays.
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operated
provide
data
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by
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images
made
Europe an
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worldwide
charge
and
c an
be
used
for
monitoring
changes
Suggest
Sustainable
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plowing
Resource
benets
plowing
wet
growth
are
light
brown.
harvest
darker
In
the
are
brown.
18
show
season,
green
dry
light
and
season,
brown
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with
the
same
grassland
recently
grassland
and
trees
recently
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in
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in
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was
leaf is
19
shows
produced
2019
to
identify
season
the
show
designated
satellite
the
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that
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satellite
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burned
burned
Green outlines
loc al community
size
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the
area
shown
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the
satellite
images.
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Figure 19
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Deduce what the state of the land is at these co-
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U
wet
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n
what
dry
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[2]
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with
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y
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Figure 17
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of
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40years?
presence
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y
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satellite
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at
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Science as a shared endeavour
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has
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allows
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come
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methodology
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as
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to
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example
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checked.
of
data
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s
s
Consider
This
by
volunteer “citizen scientists”.
Discuss
the
strengths
2.
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the
advantages
data
collected
by
and
other
limitations
and
of
data
collected
in
this
way.
disadvantages of undertaking inquiries using
people.
r
e
1.
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According
to
a
report,
marine
actions.
environments
Current
than
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when
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single
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unfolded
over
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largely
the
of
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clearance
forms
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of
land
of
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people
species.
these
on
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100years.
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towns
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hunting
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land
have
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A4.2.4,
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environment and 66%
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thousands
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and
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Sections A4.2.3
as
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Five
climate
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terrestrial
altered”
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sixth
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higher
history
almost
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rising.
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in
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Causes of the current biodiversity crisis
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twobillion
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human
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O verpopulation is
most
other
species
collapse.
167
Unity
and
diversity
Data-based questions: Human population increases
Figure
20
shows
estimated
worldwide
human
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2100.
12
s
s
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2050
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1950
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the
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what
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greatest absolute rise in the human
greatest
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Partially
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nature
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168
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stored material
One of the conservation
methods has been transloc ations to ve small predator-
free oshore islands
169
Unity
and
diversity
s
s
e
r
l
A new approach to conservation is to create “mainland
a mainland
by fencing o
The fence in
island
near Dunedin
p
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A4.2.8
other threats c an be controlled.
of the boundary of Orokonui Ecosanctuary,
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Figure 22
areas within which alien invasive species and
Selection of evolutionarily distinct
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Lists
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excluded
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species lists
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universally
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Global impact of science
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they be classied
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If red
wolves are as similar to coyotes as to grey wolves,
as a separate species or a subspecies of grey wolf ?
171
Unity
and
ATL
diversity
Thinking skills: Evaluating and defending ethic al positions
When
yield
evaluating
dierent
an
ethic al
results.
question,
dierent
Consequentialism
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standard
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and
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understanding the intentions of an action is
hundreds
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evaluating
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of
millions
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people.
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vaccines
were
ethic al.
introduced
to
give
immunity
to
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1967
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Issues such as which species should be prioritized for
the
World
Health
Organization
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eliminate
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disease
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r
political, social, cultural and economic implications and
last
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in
1978.
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therefore need to be debated. Of the 85,604 species
of
the
viruses
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humans
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diseases
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eukaryotic cells.
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b.
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DNA
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l
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contribute
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pioneer
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stability
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communities?
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construct
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(D4.2.12)
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s
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hypothesis testing:
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An
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project
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The
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Perhaps the most widely discussed false positives in
medical screening come from the breast cancer screening
procedure known as a mammogram (Figure 1). The US
rate of false positive mammograms is the highest in the
there
world; one study found it to be as high as 15%. Women are
diverse
oered mammograms annually, starting in middle age. The
aecting
consequence of the high false positive rate in the US is that,
aecting
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aected
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Netherlands has the lowest rate in the world, with just 1%
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in Northern Europe where mammography lms are read
scientists
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When contrasting the two jurisdictions, what dierences in
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prioritization
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accuracy
to
hypotheses.
inuenced
It
under-researched
lead
report
o
scientic
between
the
a
community
of
times.
under-funded,
2008
of
positive.
c an
possible to minimize the likelihood of one type
example,
may
results
i
are
Health
tropic al
M any
ancient
of
u
since
not
disproportionately
v
O
are
women.
a
US
research,
diseases
in
in
reported
claims
l
diseases
In
common
f
x
and
humanity
World
tropic al
the
was
studies
been
research.
and
sponsor
not
error
type
grant
t
a
are
studies,
containers
have
UN
communities
children
them
the
A
the
is
of
concluded that the bisphenol
pharmaceutic al
neglected
conditions
(FDA)
It
research
suppressing
example,
r
o
20
to
For
research
change
by
interests and publishing those
industry
plastic
the
when
outcome.
groups,
d
climate
poor
their
There
including
According
are
in
study’
s
research
arise
of
U
found
Independent
areas,
the
applic ations
Q uestions
industry.
chemic al
conclusions.
and
to
their
Administration
(BPA)
risk.
counter
on
in
reviewed
false
o
support
A
stake
is
i
n
run
that
Drug
begun.
applic ation
applic ations ask scientists to
suggest
dierent
that
based
even
or
each
grant
false.
research
v
fund
has
and
Some
outcomes
it
agency
agencies
submit
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p
before
to
panel.
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funding
alloc ated?
r
e
a
are
reject the null
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research
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limited and the costs of scientic
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n
Research
true.
is
y
dierent
when
t
i
s
have
mistakenly
it
endeavour, so it is not surprising that
hypothesis
scientists
c an
l
Science
y
or
e
useful
P
Individuals
r
knowledge?
error
In
everyday
language,
this
is
the
idea that the simplest
c an occur in
explanation
or
more
probable
c ause is most likely to be
173
Unity
and
true.
In
diversity
cladistics,
groups
c an
indic ate
likely
the
the
criterion
for
c ase;
for
example,
the
the
practitioners
hypothesis
to
and
by
It
the
vector
of
for
ancient
the
the
as
or
least
the
likely
more
rarer conditions.
motivation
but
worst
likely
blindness.
neglected
times.
of
the
an
2
adult
lead
It
is
a
disease
Onchocerca
diseases as no
disease
Figure
c an
c ase
explanation.
parasitic worm
despite
antenna
toward
prot
river
the
20
hear the
aecting
shows
black
the
parasite
y. The black y
disease.
n
U
o
i
d
t
a
r
o
u
l
a
v
E
174
Figure 2
f
x
O
▴
▴
Onchocerca volvulus parasite coming out of the antenna of a black y
o
since
out
of
available
you
Figure 1
C
a
one
“If
i
n
coming
towards
is
is:
zebras, but it is most likely
approach is to start with the
the
known
general,
v
humanity
with
with
is
be
progress
infection
vaccination
aphorism
In
true.
p
volvulus.
is
oen
separately.
eye
evolved
y
c aused
an
is
they
r
e
Onchocerciasis
theory
rare
vertebrate
birds and
evolved
avoidance
test
of
always the
in
have
and
start
the
not
warm-bloodedness
rational
risk
and
is
O
extreme
eye
This
that
could
scenario
likely.
cladograms
number
t
i
s
S adly,
most
the
smallest
A woman having a mammogram
n
The
most
constructing
is
diagnosis,
likely
the
the
octopus
to
less
y
horses”.
when
with
but
simplest
it
is
consensus
believed
hooves,
It
l
of
twice.
y
medic al
sound
evolved
r
however,
has
between two
Alternatively, it could
P
is
be
similar
Similarly,
mammals
is
history
to
shared
ancestry.
evolved twice or multiple times, so
judgement
assumed
remarkably
most
traits
is
separately.
In
shared
e
are
a
characteristic
complex
parsimony—the
events
characteristic
s
s
is
that
that
a
indic ate
Ecosystems
End of chapter questions
1.
About
in
the
2.5
through
Panama.
years
together
This
a
ago,
of
narrow
event
falling
land
allowed
sea
levels
c.
resulted
bridge, the isthmus
total
two-way
between
redistribution
of
the
formerly
families
and
number
occurred.
of
known
South
ninemillion
native
and
Americ a
(plural
form
years
ago
to
the
a
Figure
1
time
span
ranging
e.
Discuss
why
is
greater
much
in
the
onemillion
apparent
is
the
land
Referring
genera
bridge.
M any
the
[1]
were
decline in the number of
Americ an
native families and the number of
North
Americ an
immigrant families within the last
based.
to
the
why
the
immigrant
and
of
With
of
Suggest
placental
[1]
exclusion
principle,
native families and
the
native mammals
what
rather
of
[2]
were placental
is
the
than
adaptive
marsupial
[2]
to
this
adaptive
example,
radiation.
outline the
[3]
o
Number of genera
50
C
20
100
150
n
5
i
o


of
mammals
number
p
v
i
n
d


u
South American native families
l
a
E
v
O
f
x
t
a
r
o
oga sraey fo snoillim
3

0
U
1
2
a
reference
South America
Number of families
Present
number
marsupials.
concept
30
competitive
the
y
h.
20
[2]
gestation.
[1]
10
percentage
declined.
of
advantage
r
e
years.
[1]
genera
form of evidence on which the data in the
years
South
1.5million
the
O
for
than
families.
t
i
s
reason
Americ a.
in
n
families
of
in
mammals
a
increase
l
immigrant
formation
percentage
y
native families and the number of North
Americ an
the
a
suggest
Americ an
Suggest
the
present.
Compare the changes in the number of South
after
State
graphs
from
g.
b.
increase in the
South
show the total
f.
a.
in
for
immigrant families and
over
found
y
in
genera
isolated continents.
genera
in
years ago and the
percentage
P
genera
graphs
of
ninemillion
the
r
number
The
from
traffic of land
increase
genus)
data
c alculate
e
A
the
present,
d.
mammals
Using
Americ a and South
North
s
s
Americ a
of
million
joining
▴
North American immigrant families
Source: Marshall. 12. Science. ol. 215. P 1351–135.
Figure 1
175
Unity
2.
and
diversity
The
mountain
was
once
a
yellow-legged
common
(C alifornia,
USA).
It
due
to
introduction
as
in
part
trout,
into
the
has
naturally
d.
frog (Rana muscosa)
inhabitant
of
the
Sierra
The
2
shows
the
achieved
from
the
by the
experimental
O utline
a
measure.
method
that
[2]
could
be
used to determine
s
s
Figure
was
trout
fish-free habitats. The bar chart
e.
in
group
of
Discuss the challenges of such a
conservation
non-native fish, such
trout”
removal
waterways.
declined during the past century
of
“without
intentional
Nevada
average number per lake of
the
population
of
frogs
in
the
lake.
[3]
tadpoles.
In
order
to
restore
without
trout.
Compare
removed
Basin
study
results
for lakes with and
trout.
[2]
trout
might
by
tadpoles
affect
the
competing
in
or
the
the
removal
number
of
which
frogs
for
trout
in
resources.
might
and
opyriht 2004 ational
from
the
from
forest
before,
trout.
nature
The
the
646650
caemy o Sciences S
n
far
in
the
o
how
far
effects”.
b.
graph in
With
respect
adapted
effects in the Amazon
l
a
O
Determine
edge
quite
i
detected
t
a
are
some
establishing
“edge
u
rainforest
that
with
of
show the
lakes
O
U
d
shows
3
r
o
f
x
Figure
removal
graphs
the
Source:  reenbur 2004 PNAS ol 101 p
0
about
the
in
o
10
C
i
n
latot
15
v
rebmun
20
associated
The
frogs
y
without trout
200
concerns
after
p
400
5
2001.
and
t
i
s
with trout
is
tadpoles
r
e
ekal rep
600
trout
LeConte
trout populations just prior to
in
[1]
Key
challenge
the
Suggest one
Lake status
reserves
of
and
trout
affect the number of
lakes.
Figure 2
of
frogs or
800
One
of
shows the distribution of mountain
frogs
1,000
to
the
beetles,
indic ator
example of disturbance-
suggest
what
is
meant
by an
species.
[2]
edge.
edge
c.
an
increase
in disturbance-adapted beetles would be detected.
v
E
176
introduced
n
way
map
y
other
The
l
tadpoles
a.
population,
lakes.
[1]
Explain
how
influence
this
the
information
design
of
about
reserves.
edge
effects
c an
[3]
y
The
area
yellow-legged
during,
3.
frog
the
[1]
contrast
population
c.
from
P
without
and
were
r
b.
▴
the
State the number of tadpoles per lake with and
e
a.
Ecosystems
Key
Lae

0
0.25
no trout tadpole or ro
m
no trout tadpole and
s
s
ro preent
trout preent
no tadpole or ro
pper
preent
r
Stream
trout aent
arrer to trout
l
Lower
movement
200
40
150
trout
30
30

removed
4
o
2
0
0
5
0
4
2
0
2
2
0
0
3
0
2
2
0
0
i
t
a
u
l
a
v
100
in
in
species
o
o
o
penetration
WF
tree mortalit
presence
o
Figure 3
o
disturanceadapted
disturanceadapted
utterflies
eetles
lealitter communit
understoradapted
200
Source:
in
disturanceadapted
disturanceadapted
edge
◂
presence
ricness
presence
o
in
Source: Knapp et al. 2007.
ncreased
ncrease
ncrease
presence
presence
0
0
2
r
o
in
E
0
1
0

0

1
1


1


f
x
ncrease
d


7

1


e gd e
O
tceffe
ncrease
in
0
year
ecrease
ecrease
10
n
2
 o r
U
 e l opd a t
trout
C
20

p
Lower Leonte Lae
o
remun  ytned
v
0
0
10
i
n
remun  ytned
01
01
10
y
20
50
ro
r
e
removed
100
0
▴
O
tadpole
enlero
m
1–
enlero
m
1–
50
t
i
s
Key
pper Leonte Lae
250
n
y
Leonte Lae
y
P
trout preent
natural
e
trout tadpole and ro
Leonte Lae
trees
irds
understor plants
00
400
00
distance / m
L aurance. 2008. Biological Conservation. Vol.
141.
Pp.
11–144.
Figure 4
177
B
Fo r m
function
s
s
1
and
Molecules
of
c an
with
built
Ad a p t a t i o n s
c arbon
are
the
o
i
i nv o l u n t a r y
p r e y.
The
binding
u
l
a
E
v
O
f
x
t
a
r
o
d
acetylcholine
in
functions.
the
muscle
asite
preventing
of
image
the
to
by
living
pre dation
functions
to
the
it
f ro m
nerves.
c o n t ra c t i o n s
on
g e n e ra t i o n
surviv al
contains
binds
sy n a p s e
b a c k g ro u n d
to
to
d e f e n s e,
Their
c an
are
forms.
mamba
which
a c e t y l c h o l i n e s t e ra s e
of
that
function.
produce d
metabolism,
unique
black
fasciculin
y
f rom
molecule
their
chances
cov alent
things
molecules
to
double
polar
Living
of
underlying
c arbon.
s i n g l e,
g e n e ra t i o n
molecules
for
other
n
U
Ve n o m
of
on
used
on
and
correspond
f rom
the
The
C
i
n
ra n g e
dependent
that
p e rs i s t
inc re ase
are
form
chains.
d i v e rs i t y
o
v
organisms
c an
backbones.
forms
a g e.
It
cov alent
p
they
reproductive
a
and
adaptations
bec ause
and
rings
s t r u c t u ra l
r
e
These
form
and
O
be
form
the
bonds.
c an
based
t
i
s
on
It
shape
n
It
depend
four
its
are
l
bonds.
form
bonds.
to
y
c an
triple
r e f e rs
molecules
y
and
molecule
P
C arbon
a
Biologic al
e
form
s t r u c t u re.
r
The
which
s h ows
e n z y m e.
the
enzyme
bre aking
This
d ow n
c auses
immobilizes
fasciculin
the
( p u r p l e)
B1.1
C arbohydrates
and
lipids
In what ways do variations in form allow diversity of function in c arbohydrates and lipids?
properties
of
properties
molecules.
are
of
have
Compare
lipids
are
both
dierences
been
and
relatively
composed
in
the
form
identied
contrast
insoluble
the
in
in
c arbon,
their
amounts
compared
oxygen
molecules.
watermelon
relative
water
of
of
plants.
of
to
and
A
hydrogen.
total
Figures
oxygen,
of
1
1,679
and
c arbon
2
and
However,
dierent
show
some
hydrogen
they
have
c arbohydrates and lipids.
c arbohydrates?
O
H
NH
HO
O
O
OH
O
NH
raffinose
Figure 1
Some sugars
HO
chitotriose
o
v
p
▴
2
OH
OH
y
r
e
OH
OH
O
HO
HO
O
O
O
t
i
s
OH
O
n
HO
HO
O
2
y
OH
l
OH
O
N
2
y
P
OH
HO
OH
dierent
examples of both types of
in
OH
HO
very
molecules with a wide
r
Why
lipids
e
range
and
bec ause
s
s
C arbohydrates
How do c arbohydrates and lipids compare as energy storage compounds?
the
oxygen
gram
form
oils
stable
cell
in
the
or
of
c an
and
molecule
or
used
energy
respiration.
the
starch
be
How
aect
is
glycogen and lipids
as
released
does
how
What
advantages
energy
sources?
What
advantages
the
stores. They
when
they
much
energy per
fats
and
oils
do
c arbohydrates
OH
are
relative amount
do
O
nervonic acid
have as
O
arachidic acid
OH
o
releases?
d
it
energy
n
by
in
fats
chemic ally
oxidized
of
of
U
are
form
C
in
i
n
C arbohydrates
have?
12, 13(S)-epoxylinolenate
O
C an both c arbohydrates and lipids be used in either aerobic
of
function
B1.1.5
Polysaccharides
B1.1.6
Structure
B1.1.7
Role
B1.1.8
Hydrophobic
B1.1.9
Formation
B1.1.11
E
B1.1.10
of
polymers
v
of
Form
a
O
Digestion
B1.1.4
of
of
as
of
glycoproteins
Dierence
B1.1.12
Formation
B1.1.13
Ability
of
into
is
OH
more
easily
O
SL
atom
by
▴
allowing
for
condensation
monomers
by
and
the
Figure 2
Some fatty acids
HL
formation
reactions
that
of
link
diverse
compounds
monomers
to
upon
which
life
isbased
form a polymer
hydrolysisreactions
storage compounds
related
in
to
its
cell–cell
function
as
a
structural
polysaccharide in plants
recognition
properties of lipids
between
of
form
monosaccharides
triglycerides
Triglycerides
energy
organism toanother?
c arbon
energy
cellulose
of
a
an
macromolecules
B1.1.3
and
of
t
a
properties
Production
Which
part
u
Chemic al
one
l
B1.1.2
f
x
B1.1.1
respiration?
from
i
anaerobic
transported
r
o
or
in
and
adipose
tissues
phospholipid
non-polar
phospholipids
saturated,
for
energy
bilayers
steroids
to
by
condensation
monounsaturated
pass
as
a
and
reactions
polyunsaturated
fatty acids
storage and thermal insulation
consequence
through
the
of
the
hydrophobic
phospholipid
and
hydrophilicregions
bilayer
179
Form and function
nucleus with six protons and
B1.1.1
Chemic al properties of a c arbon
six, seven or eight neutrons
atom allowing for
the formation of diverse
compounds upon which life is based
not
is
exist.
only
Its
produced,
the
15th
chemic al
so
the
most
abundant
properties
range
of
allow
functions
is
element
many
on
E arth,
dierent
almost
but
forms
without
of
it
limitless.
e
+
+
C arbon
atoms
bond
formed
is
c an
form
by
covalent
sharing
a
pair
bonds
of
A
covalent
This
in
form
complex
one
double
unsaturated
four
covalent
covalent
fatty acids.
them in the outer shell
Stylized
C arbon
atoms
of
elements
c an
form
covalent
as
atoms
c an
hydrogen
bond
atoms
apart
spread
chain
of
zig-zag.
The
ring
may
be
synthesized
oxygen
or
of
mint
nitrogen.
A
the
by
as
the
of
to
20
using
so
atoms
angles,
c arbon
they
is
or
chains
are
phosphorus.
example,
found,
for
C arbon
with
four
more than one other
form ethanol.
to
form
a
chain
atoms.
of
any length.
Chains
c an also
oxygen atom.
to
bonds
a
rotate,
formed
tetrahedral
straight — the
of
covalent bonds or
bonds
to
form
not
to
atoms
covalent
charged
between
c arbon atoms or with atoms
c arbon
an
bond
produced.
single
covalent
bond
bonds
bonded
The
possible
entirely
up
made
of
c arbon
plants.
of
be
element — for
also
positively
of
molecules containing
nitrogen
hydrogen
covalent
other.
bond
c an
and
chains
both
other
They
oen
each
much
made
by
allow
to
bonded
Bec ause
i
is
as
o
a
apart
up
branch
bonds
c arbon
atoms — for
but
by
a
not
shape.
straightest
atoms
c an
to
move
c arbon
So, a
it
c an be
form rings.
example, in menthol which
Or contain an atom of another element, usually
molecule
may
contain
a
single
ring
as
in
the
base
thymine,
u
l
a
E
v
O
f
x
t
a
r
o
d
is
linked
the
one
oxygen
unbranched
nearer
covalently
with
n
atom
or
methane.
other
o
covalent
U
further
with
be
of
with
c an
four
Double
oxygen,
C
branched,
Single
c an
contain
atoms
v
be
atoms
acids
form
example,
i
n
F atty
to
four
so
be
p
element — for
C arbon
with
c an
the
type
y
c arbon atom
hydrogen,
r
e
such
c arbon
bonds,
bond.
to
strongest
on
There
bonds
drawing of a
other
based
structures.
attracted
the
n
example,
and
c an
molecules
are
are
l
single
atom
have
stable
electrons
bonds
O
six electrons with four of
c an
shared
Covalent
t
i
s
two
means
c arbon
c arbon
charged
atoms.
y
E ach
both
▴
Figure 4
The plant
unusual molecule that
Chrysanthemum cinerariifolium produces chrysanthemic acid,
has a ring of three c arbon atoms.
this molecule being rather unstable and
You could
the benets to the plant
a very
research the reasons for
of producing it
y
of
atoms.
180
atoms.
P
nuclei
Figure 3
other
between two adjacent atoms.
+
Thenegatively
▴
with
electrons
r
+
life would
molecule to be
+
+
s
s
C arbon
Molecules
or
two
rings
composed
as
in
adenine,
entirely
of
or
more.
Cholesterol
molecules
have
four rings all
c arbon.
H
methane — a single carbon
H
N
with four single covalent
H
to hydrogen
C
s
s
bonds all
N
H
H
H
C
C
N
N
H
H
atoms and bonds to two
adenine — with two rings both
different other elements
H
r
H
H
sharing of electrons in the ring
O
ethanoic acid — single
C
C
one double bond
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
C
C
H
H
OH
H
p
linolenic acid — an omega-3 fatty acid with a
a
protein
molecule
C an
you
that
is
nd
an
acts
chain
as
of
example
molecular
of
a
spring
atoms,
molecule
in
muscle. The backbone
linked
in
by
single
covalent
your body with a chain of
t
a
r
o
i
o
atoms?
a
100,000
d
1,000,000,000
a
n
bonds.
over
giant
titin
C
i
n
is
the
U
of
o
Some common naturally occurring c arbon compounds
Activity: M acromolecules
Titin
v
Figure 5
O
C
chain of 18 carbon atoms containing 3 double bonds
▴
O
H
y
H
r
e
H
t
i
s
H
H
n
y
covalent bonds and
O
l
H
y
P
with carbons and nitrogens and
H
e
C
ethanol — two carbon
H
Science as a shared endeavour: SI units
The
International
1960.
System
From
unit
c an
be
thousand
but
the
given
time
“centi”
is
it
updated.
is
larger
or
metric
are
7
smaller.
used
to
units
base
of
measurement,
units
The
and
22
preferred
indic ate
a
other
agreed
units
prexes
by
scientists
derived
change
the
newton
(N)
force
(kg m s
v
hertz
(Hz)
frequency
E
mass
ampere
•
kelvin
•
mole (mol) amount of substance
•
pasc al
•
joule
•
watt
•
volt
(Pa)
pressure
9
(G) 10
giga
(s
•
mega (M) 10
6
)
(N m
(million)
3
)
•
kilo (k)
10
•
milli
•
micro 10
•
nano 10
(thousand)
3
current
temperature
( J)
energy
(W)
(N m)
power
(J s
(m) 10
(V)
voltage
(W A
•
lux
(lx)
illuminance
(millionth)
9
)
2
(cd) luminous intensity
(thousandth)
6
)
1
c andela
(billion)
•
1
•
by a factor of a
Metric prexes
)
2
•
(K)
size
2
•
around the
from the base units.
hundredth.
Examples of derived units
•
kilogram
electric
it
for
There
1
•
(A)
scheme
sometimes
metre (m) length
(kg)
the
make
still
a
(s) time
(SI)
that
is
l
O
•
second
Units
to
prexes
prex
Base units
•
of
time
u
E ach
in
f
x
world
(cd m
(billionth)
12
)
•
pico 10
(trillionth)
181
Form and function
B1.1.2
Production of macromolecules by
condensation reactions that link monomers
to form a polymer
with
of
a
relative
are
macromolecule
The
acids.
subunits
E ach
are
living
of
composed
above
organisms
these
is
monomers
made
and
the
of
10,000
are
a
very
atomic
large number of atoms,
mass
units.
The
main
classes
polysaccharides, polypeptides and
by linking together subunits into a chain.
chain
is
a
polymer.
In
each
c ase, the
r
chemic al
in
mass
e
nucleic
molecules
molecular
s
s
M acromolecules
process that links another monomer onto the end of the polymer is a
reaction.
In a condensation reaction, two molecules are linked together and at the same time a
l
smaller molecule is released. When polysaccharides, polypeptides and nucleic acids
n
y
are constructed, the simpler molecule is always water
. It is produced by removing a
hydroxyl group (–OH) from one of the molecules being linked and a hydrogen from
t
i
s
OH
HO
required
polysaccharides
H
nucleic
is
acid
two
in
is
supplied
detail
here.
Glucose
is
starchand
molecules
are
linkages
formed
condensation,
linked
up
with
by
ATP
.
The
Polypeptide
H
OH
a
Structure of glucose.
synthesis of
synthesis
is
described in
linked
the
together.
A
polysaccharide is a
monosaccharide
used to make the
cellulose.
glycosidic
using
bonds.
hydroxyl
These
groups.
The
are C–O–C
hydroxyl on C
(hydroxyl) group
and
of
a
1
glucose
is
linked
to
the
hydroxyl on C
at
the
end
of
the
growing chain.
4
In
an
unbranched
the C
of
a
chain,
glucose
all
the
glycosidic
is
linked to theC
a
side-branch,
1
1→6
of
a
bonds
are 1→4.
glucose
To
form
branches,
already in the chain. This
6
linkage
forms
and
more
glucose
molecules
c an
be
added
There is always
one –H
to it with1→4 bonds.
group on
The upper group is –H in α-glucose and –OH
1
in β-glucose
O
2
Topic A1.2.
monosaccharides
Glucose
by
H
H
N
production in
glycogen,
N
H
polysaccharides, polypeptides and nucleic
energy
monosaccharides.
H
OH
OH or H
C
2
v
O
Figure 7
one –OH
E
182
OH
u
C
3
.
H or
l
f
x
HO
of
This
described
polysaccharides
C
OH
is
disaccharide
chain
1
construct
o
H
C
4
and
i
H
C
A
O
5
▴
Topic B1.2
t
a
r
o
C
d
OH
2
to
condensation.
y
is
by
N
H
p
acids
n
U
Energy
O
2
C
reaction
CH
H
O
monomer to a polymer by a condensation
H
OH
o
Two methods of linking a
6
v
Figure 6
i
n
▸
r
e
HO
O
the other
. This allows a bond to be made to bridge the two molecules.
Cellulose
that
in
liver
c an
or
molecules
contain
muscles
cells
glucosemolecules.
in
plant
15,000
are
or
cell
more
walls
are
glucose
unbranched chains of
molecules.
branched chains of
α
Glycogen
glucose,
with
up
β
glucose
molecules
to
60,000
y
P
condensation
Molecules
H
H
H
H
monosaccharides, C
H
6
O
12
6
e.g. glucose, fructose, galactose
OH
H
s
s
condensation
hydrolysis
O
2
(water removed)
(water added)
O
22
11
e.g. maltose, sucrose, lactose
OH
O
bond
hydrolysis
t
i
s
H
olysaccharide
e.g. starch, glycogen
O
HO
Formation of 1–4 glycosidic bonds by condensation and
p
and
In a hydrolysis reaction,
water
to provide hydrogen
hydroxyl groups.
These are used to
o
monosaccharides,
used
so
as
the
a
monomers
source
of
in
them
energy.
beenbroken
c an
be
Hydrolysis
C
deconstruct
or
make bonds to replace the bond that has
reused to
reactions
5
are
CH
amino
acids
and
nucleotides.
These
are
the
O
reactions that
occur during digestion.
OH
2
polysaccharides, polypeptides and nucleic acids into
n
to
Figure 9
molecules are split
v
used
deconstructed
polymers
U
new
i
n
are
build
▴
HO
Digestion of polymers into monomers
by hydrolysis reactions
Polymers
OH
their breakage
byhydrolysis
B1.1.3
O
y
Figure 8
OH
O
r
e
▴
O
OH
O
H
+
n
y
condensation
O
2
l
H
y
P
O
HO
e
H
12
r
disaccharide, C
OH
4
C1
C
H
H
H
H
o
d
3
C
C2
OH
OH
Digestion of polysaccharides, polypeptides and nucleic acids can be carried out by
i
r
o
all cells. Digestion also happens outside the cell in the gut of animals. Decomposers
ribose — a pentose
t
a
release digestive enzymes into the environment around them in order to break down
6
polymers by hydrolysis so they can absorb and use themonomers.
OH
2
5
C
O
H
H
u
f
x
B1.1.4
CH
H
4
C
1
C
OH
H
C
C2
H
OH
Form and function of
OH
HO
l
3
ve
c arbons
molecules
with
a
between
ring
of
have
three
and
seven
c arbon
atoms.
Pentoses
have
glucose — a hexose
six.
atoms.
Both
There
is
pentoses
one
and
oxygen
hexoses
atom
in
normally
the
ring
have
and
four or
CH
6
OH
2
c arbon atoms.
Monosaccharides
by
have
hexoses
E
ve
and
a
Monosaccharides
v
O
monosaccharides
living
O
organisms.
OH
C
C2
5
have
properties
Glucose
is
a
that
allow
widely
them
used
to
be
used
in
monosaccharide.
a
variety
of
ways
H
H
H
1
4
C
C3
OH
OH
CH
OH
2
fructose — a hexose
▴
Figure 10
183
Form and function
Use of molecular models: Modelling glucose
Pentoses
in
and
hexoses
straight-chain
form
are
as
unusual
well
in
in
that
ring
they
form.
c an
They
exist
to
need
be
in
the
ring
form
in
order
to
form
disaccharides and
polysaccharides.
s
s
H
as
O
1
C
6
6
CH
2
CH
OH
2
OH
2
5
H
H
H
C
e
H
H
5
O
OH
3
H
H
4
r
HO
4
1
C
C
OH
H
OH
1
H
4
C
C
3
2
2
HO
OH
OH
OH
H
structure
Using
structure C
This
Twist
model
is
the
so
attached
straight-chain
that
to
c arbon
c arbon
5
1
as
4.
Attach carbon 1 to the oxygen on carbon 5 and reposition
5.
Place
form.
comes
shown
the detached hydrogen as shown in structure C.
near the
in
structure B.
ring.
hydrogen attached to the oxygen attached to carbon 5.
Is
and
on
–OH
which
your model
a
table. Identify the plane of the
groups
are
are
above the plane of the
below it?
α-glucose or
β-glucose?
o
i
n
v
6.
model
p
ring
Break the double bond on carbon 1 and remove the
the
Which
y
A.
oxygen
3.
molecule model kit, construct a model of
structure
the
B
r
e
2.
a
structure
Figure 11
O
1.
A
OH
t
i
s
▴
OH
n
2
y
CH
l
H
6
Obesity
(excessive
issues,
In
a
study,
mice
dierent
Use
the
divided
sweetener
between
graph
in
or
the
Figure
as
obesity.
into
four
groups.
structure
12
to
of
group
and
was
of
and
has
fructose,
given
the
been
now
same
correlated
widely
amount
used
of
with
as
a
a
large number of
sweetener,
has
been
food and either a so drink
fructose.
contrast
the
body
[1]
fat
accumulation
sweetener
stinu
a
ekatpu
yratibra / yawhtap
gnicudorp-esobir otni
t
a
l
E
yd ob
0
v
t af
2
and
problem
u
f
x
O
g / n o it a l um u c c a
diet drink wit artificial
water
4
health
consumption
E ach
sucrose
compare
so drink wit sucrose
6
global
water.
so drink wit fructose
8
a
increased
i
Distinguish
2.
were
in
r
o
1.
increase
The
o
a
the
recognized
deaths.
d
with
with
is
and
n
associated
weight)
diseases
U
health
C
Data-based questions: Health consequences of the consumption of fructose
in
the
four
groups
of
mice.
30
25
20
15
10
5
0
0
10
20
30
40
50
60
glucose
70
fructose
time / days
▴
184
Figure 12
Body fat
accumulation in four groups of mice
▴
Figure 13
Uptake of sugars in pancreatic cells
[3]
y
C
3
HO
5
H
P
O
H
Molecules
Studies
cells
investigated
were
grown
measured.
The
Discuss
if
4.
Determine
the
graph
the
role
equal
in
Figure
results
which
of
glucose
and
concentrations
13
provide
sugar
is
shows
clear
of
fructose
each
the
range
evidence
primarily
used
in
in
the
sugar
of
of
a
the
development
and
the
uptake
uptake
of
dierence
production
sugars
in
of
of
of
and
uptake
ribose
pancreatic
each
c ancer
cells.
Pancreatic
ribose-producing
the
mean
the
two
of
by
into
sugars.
pancreatic
[2]
c ancer
cells.
[1]
so it is easily transported. It circulates in blood, dissolved in the plasma.
other
is
if
glycogen
yields
or
cells
in
chemic ally
large
very
glucose
quantities.
stable. This
would
c ause osmotic
Therefore, it is usually
starch.
when
it
is
oxidized.
It
c an
therefore
be
used as a
forrespiration.
▴
B1.1.5
Figure 14
energy yield, so plants put glucose (and
p
usually alsofructose) in the esh of animal-
in animals. Both of these substances are composed of large numbers of α-glucose
v
molecules, which can be used a substrate in aerobic and anaerobic cell respiration.
of
Bec ause
Amylopectin
molecule.
of
has
bonds
the
the
bond
same
making
structure
the
CH
α-glucose
angles,
the
as
molecule
linked
chain
is
amylose
but
OH
O
OH
f
x
H
CH
l
H
O
2
O
C
H
2 O
OH
H
a
H
O
O
O
H
O
H
O
E
v
O
O
2
C
u
O
H
O
i
O
straight.
t
a
H
than
o
d
r
o
O
2
H
in the nectar of animal-
are some 1→6
branched.
O
C
there
owers
glycosidic
rather
2
OH
H
by 1→4
helic al
fruits and
pollinated
n
glycosidic
starch
unbranched chain of
U
•
an
C
bonds.
types
is
dispersed
o
two
i
n
are
Amylose
Foods containing glucose
are attractive to animals bec ause of their
Starch and glycogen are used as energy stores. Starch is used in plants and glycogen
•
berries.
y
r
e
compounds
There
A black bear is feeding on
Polysaccharides as energy storage
wild
O
substrate
energy
in
is
However,
n
to
stored
glucose
storage.
t
i
s
Glucose
was
food
y
converted
•
it
for
l
problems
c arbohydrates,
useful
y
most
property
P
Like
e
r
Like all monosaccharides, glucose is soluble and is a relatively small molecule,
•
was
value.
Properties and uses of glucose
•
c ancer
pathways
s
s
3.
in
OH
H
O
O
H
O
H
CH
OH
2
O
H
O
O
H
O
O
▴
Figure 15
all linked
Small portion of an amylopectin molecule showing six α-glucose molecules,
by 1→4 bonds apart
from one 1→6 bond
that
creates a branch
185
Form and function
Glucose
A
c an
hydrolysis
molecule
used
in
be
from
the
removed
reaction
the
cell.
end
You
glucose
there
shortage.
is
a
amylopectin
of
c an
c an
than
starch
a
chain.
think
be
of
This
amylose
or
glycogen
allows
starch
deposited
Adding
and
glycosidic
and
when
removing
bec ause
the
molecules
bond
it
to
to
be
when
it
is
needed.
separate one glucose
transported
elsewhere or
glycogen as a sort of bank account
there
is
glucose
a
surplus
c an
branched
and
happen
structure
withdrawn when
s
s
bec ause
from
breaks a 1→4
more quickly with
provides
more ends
of chains.
1
in
10
has
glucose
store
in
by
large
them
The
compact
property
in
despite
the
a
have
limitless
xed
without
huge
of
than
3
to
be
addition
molecular
expressed
and
mass,
so
glycogen
cell
in
or
swelling
and
they
contribute
c an
up
with
be
water
little
used
drawn
amylopectin makes them
mass. This is another useful
removal
so
amylopectin
starch
glycogen
molecular
and
large size of these
glucose,
means
the
subunits
very
of
molar
percentage
glucose
solutions
terms
is
that
starch and
c annot
be
made.
(grams of substance
o
v
Concentrations
of solution).
C
i
n
B1.1.6
This
structure
their
The
y
of
have
100 cm
solubility
cells.
glucose
branched
not
per
of
of
glucose
thousand.
lower
branched.
p
do
much
of
linked
glycogen, about
compared with about 1 in 20 in
more
storage compound.
consequence
glucose
thousands
r
e
relatively
A
of
hundred
concentration
amounts
osmosis.
a
a
molecules
In
n
gives
tens
than
are
bonding.
y
contain
bond,
molecules
α-glucose
by 1→6
O
to
glycogen
more
osmotic
amylopectin:
t
i
s
the
to
branched
y
molecules
and
molecules has a 1→6
so
c an
contain
structure
bonds
l
Glycogen
to
similar
P
amylopectin,
c an
a
glycosidic
r
by 1→4
e
Glycogen
Structure of cellulose related to
n
U
its function as a structural polysaccharide
inplants
like
markedly
o
are
starch
i
t
a
β-glucose
are 1→4
contain
u
l
In
at
end
than
overall
β-glucose,
is
composed
on
a
free
of
glucose,
β-glucose
β-glucose
but
the
of
the
10,000
length
–OH
of
so
properties
molecule to C
α-glucose.
on the
4
growing
bonds,
its
rather than
1
the
more
glycogen,
bec ause it is a polymer of
reactions link C
glycosidic
an
and
dierent
Condensation
giving
a
v
E
Figure 16
d
r
o
f
x
O
▸
Cellulose,
it
is
cellulose
an
molecule. All the links in cellulose
unbranched
β-glucose
molecules
more
10 µm.
than
group on C
is
angled
chain.
each
A
with
upwards
and
cellulose
a
size
the
of
molecule
about
–OH
c an
1 nm,
group
1
on C
is
angled
downwards.
To
bring
these
–OH
groups
together
and
allow
4
a
condensation
be
inverted
in
therefore
face
CH
OH
2
H
O
reaction
relation
to
to
occur,
the
alternately
previous
upwards
CH
OH
OH
H
H
OH
each
2
H
β-glucose
one. The glucose subunits in the chain
and
downwards.
CH
OH
O
added to the chain has to
OH
OH
H
H
OH
2
H
OH
O
OH
OH
H
H
OH
H
OH
OH
H
H
H
Beta glucose molecules c an
H
HO
H
HO
HO
H
O
H
only form a 1→4 glycosidic bond if one
faces up
186
and
the other faces down
CH
2
OH
OH
Molecules
The chains of
α-glucose
in
orientation of
β-glucose
results
bundles
along
the
of
each
cellulose
molecules.
are
the
bec ause
of
molecules
and
bursting,
entry
of
bundles
plant
strong
the
allowing
of
covalent
when
bonds
in
high
This
molecules
the
have
them.
The
are
c alled
high
regularly
to
form
spaced
between
microbrils
tensile
strength
molecules, the number of
strength
have
formation of
are
bonds
very
cellulose
pressures
allows
groups
hydrogen
Microbrils
between
very
chain.
Hydroxyl
many
cellulose
walls.
cross-links
even
water
cell
straight
parallel.
prevents plant cells
developed inside the cell due
by osmosis.
r
e
from
the
of
a
in
molecule,
These
basis
in
arranged
s
s
and
to
molecules
starch wind into a helix, but in cellulose the alternating
and
from
the side,
showing eight glucose
hydrogen green
c arbohydrate
plasma
cells
recognized
of
recognize
in
or
red
cell–cell
By
helps
infected
blood
with
body
cells
are
an
a
glycoproteins
function,
Any
three
two
of
containing
who
will
be
glycoprotein
themself.
is
A
glycoprotein
not
all
tissues
and
A
it
produce
are
is
glycoproteins
providing
the
means
Key
if
a
person
glycoprotein
monosaccharide
B.
One or
present
in
every
it
has
does
the
not
not
same
produce
c ause
structure
part of the glycoprotein that projects out from the
less, so is not
plasma
as
furanose
A
glycoprotein.
does
O
B
recognized
N acetyl-galactosamine
aect
transfused into
as
one
allow
themself, the
bec ause
with
also
Similarly, blood containing
rejected
However,
c an
destroyed. The ABO
membranes
that
and
problems,
and
of
and
three.
not
rejected.
B
the
O,
rejection
A
of
their
on
glycoprotein
does
E
it
of
but
c alled
a
blood
types
v
O
blood
identied
possible types of
present
are
in
but
u
oligosaccharides
blood,
of
be
l
f
x
c an
The
person
organization
be
example
known
transfusion.
a
to
o
have
have
these
attached
glycoproteins, cells
glycoprotein on the surface of one cell is
i
cells
oligosaccharide
If
are a component
the
recognition.
not
person’s
distinctive
with
t
a
blood
Glycoproteins
positioned
d
do
The
the
cells
r
o
blood
that
are
displaying
them.
ABO glycoproteins
Red
bonds.
and
receptors on the surface of another cell.
recognition
cells
antigens
outwards.
cells
attached.
n
foreign
to
glycosidic
U
Cell-to-cell
by
by
animal
c arbohydrate
C
other
facing
in
with
oligosaccharide — a short chain of
i
n
c arbohydrate
allow
linked
membranes
an
o
of
polypeptides
is
v
monosaccharides
of
y
composed
the
c ases,
p
are
In
r
e
Glycoproteins
O
Role of glycoproteins in cell–cell
recognition
most
t
i
s
B1.1.7
oxygen red
n
of a cellulose molecule viewed
l
Part
C arbon atoms are grey,
y
P
Figure 17
subunits.
y
▴
membrane of the red blood cell
foreign.
▴
Figure 18
O,
A and
B glycoproteins in red blood cells
187
Form and function
B1.1.8
Lipids
are
Hydrophobic properties of lipids
a
diverse
group
of
non-polar
solvents.
Ethanol,
non-polar
solvents.
Lipids
For
misleading
this
reason,
term,
are
only
they
are
bec ause
lipids
in
and
living
sparingly
said
are
to
not
organisms
propanone
be
soluble
in
by
This
dissolve in
are
aqueous
hydrophobic.
repelled
that
(acetone)
examples of
(water-based)
is
water — they
a
s
s
solvents.
substances
toluene
rather
are
just
more
attracted to non-polar substances.
problem
is sewers.
Warm
and
steroids
are
classes of commonly occurring lipids.
does not
liquid
fat
Oils
have
a
melting
point
below
•
F ats
have
a
melting
point
between
solidies in sewers
temperature
dissolve in water. This
so
and
liquid
at
body
20°C
they
and
solidify
37°C
so
at
low
temperature.
they
temperatures.
are
solid
at
room
in London has large
Steroids
have
a
have
melting
point
molecules
above
with
a
37°C,
so
they
characteristic
liquify
four-ring
at
temperatures.
O
t
i
s
B1.1.9
high
structure.
n
Waxes
•
y
•
fat accumulations
l
sewer under the Strand
20°C,
from
Formation of triglycerides and
y
r
e
phospholipids by condensation reactions
A triglyceride is made by combining three fatty acids with one glycerol. Each of
p
the fatty acids is linked to the glycerol by a condensation reaction, so three water
v
molecules are produced. The linkage formed between each fatty acid and the
i
n
o
glycerol is an ester bond. This type of bond is formed when an acid reacts with
the hydroxyl group (–OH) in an alcohol. In this case, the reaction is between the
C
carboxyl (–COOH) group on a fatty acid and a hydroxyl on the glycerol. These
groups are the only hydrophilic parts of fatty acid and glycerol molecules and are
used up in the condensation reaction, so triglycerides are entirely hydrophobic.
U
Depending on the type of fatty acids they contain, triglycerides may be oils orfats.
C
(CH
)
2
n
triglyceride (fat)
H
CH
t
a
H
HO
O
3
O
l
u
H
condensation
(CH
)
2
n
CH
O
3
C
C
(CH
)
2
n
CH
O
3
H
C
O
E
v
O
2
Ester
Figure 20
)
2
n
CH
3
(CH
)
2
n
CH
3
O
O
▴
(CH
(water removed)
C
3H
C
O
O
HO
a
H
i
d
r
o
f
x
O
188
HO
H
o
fatty acids
H
n
glycerol
Formation of a triglyceride from
glycerol and
bond
three fatty acids
(CH
)
2
n
CH
3
y
waste cools and
bec ause it
waxes
•
P
food
oils,
Fatbergs are an increasing
r
Figure 19
e
F ats,
▴
Molecules
Phospholipids
have
acids
glycerol,
linked
to
a
structure
with
a
similar
to
triglycerides,
phosphate
group
but
instead
there
of
a
are
third
two
fatty
OH
hydrophilic
fatty acid. The
O
phosphate
is
hydrophilic,
so
phospholipid
molecules
are
partly
O
P
phosphate
hydrophilic and
O
head
partly
hydrophobic.
H
C
H
O
B1.1.10
C
r
C
fattyacids
acids
a
bonded,
c arboxyl
group
so
it
is
a
).
The
of
c arbon
hydroc arbon
(–COOH)
group (–CH
chain
at
one
length
of
end
the
atoms,
chain.
of
the
The
with
acid
chain.
hydroc arbon
At
hydrogen atoms
part
the
chain
of
the
other
is
molecule
end
there is a
variable but most of
y
methyl
unbranched
the
fatty
acids
used
by
living
organisms
have
between
14
and
20
c arbon atoms.
others
atoms.
have
C arbon
atoms
saturated
fatty
Nearly
the
all
fatty
side
of
c alled
or
hydrogen
more
than
if
usually
a
This
is
in
a
done
but
a
in
the
to
the
are
H
C
H
C
H
H
C
H
C
H
H
H
H
H
C
H
H
H
C
H
H
H
C
H
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
H
H
C
H
H
H
H
c alled
there is a bend in the
▴
Figure 21
The molecular structure of
a phospholipid. The phosphate oen has
other hydrophilic groups attached to it, but
triglycerides containing
in
So,
these are not
regular
shown in this diagram
arrays than
temperature — they
the
C
hydrogen atoms
atoms — these
together
room
are
there is one
at
triglycerides with cis-
are oils.
hydroc arbon chain at the double
melting
articially
produce
to
If
point.
serious
US
could.
c alled
hydrogens to be on opposite
acids,
makes
is
bonds
melting
higher
produced
foods,
(FDA)
liquid
and
This
have
the
cis-fatty
packing
low
bend
chains
are
a
at
double
and
hasmore than one double
c arbon
for
between all of
could
they
i
oils.
processed
Administration
have
have
They
bond.
good
In
is
u
sh
not
acids.
l
f
x
or
less
they
straight
organisms
arrangement
double
are
living
double-bonded
trans-fatty
the
so
in
it
t
a
do
have
acids
two
acids
acids
temperature.
other
at
acids,
fatty
fatty
the
fatty
acids
they
O
Drug
one
C
hydrogen atoms.
bonds
possibly
H
C
tails
whereas
c arbon in the chain,
single
it
monounsaturated;
r
o
fatty
unsaturated
some
as
two
o
chain
cis-unsaturated
vegetable
is
less
d
hydroc arbon
room
acid
have
to
adjacent
with
hydrogen
that
contain
alternative
are
Trans-fatty
acids
an
atoms,
n
The
sides — these
bond;
they
unsaturated
acids.
saturated
F atty
much
to
acid
polyunsaturated.
same
cis-fatty
the
as
fatty
c arbon
hydrocarbon
c arbon atoms in the chain.
bond
U
on
is
acid.
bec ause
bond,
it
contains
bond
A
of
the
between the
C
bond,
double
also
all
i
n
double
a
hydrogen.
c an
pairs
bonding
o
unsaturated
by
one
between
some
bonds
covalent
y
c arbon
to
the
bonds
between
single
is
v
a
linked
bond
acids
single
bonds
by
fatty
p
its
have
linked
atoms
only
of
r
e
c an
Some
double
atoms
C arbon
feature
H
C
O
c arbon
variable
H
H
C
t
i
s
Another
H
C
C
hydrophobic
C
H
n
3
O
l
is
an
H
H
C
y
covalently
have
P
F atty
O
e
monounsaturated and polyunsaturated
C
O
Dierence between saturated,
C
H
H
s
s
C
solid
health
ban
by
use
point.
partial
fats
for
concerns
of
They
are solid at
hydrogenation of
use
in
have
industrial
margarine and
led
the
Food and
trans-fats.
v
E
189
Form and function
OH
O
C
C
OH
O
C
H
C
C
H
C
C
H
C
C
C
C
C
C
C
C
H
H
C
H
H
H
C
H
H
C
H
H
C
H
H
H
C
H
H
H
C
H
C
H
C
H
C
H
C
H
H
C
H
o
C
n
C
C
C
C
H
H
C
H
C
i
n
U
n
H
H
o
palmitic acid
linolenic acid
palmitoleic acid
• saturated
• polyunsaturated
• monounsaturated
• non-essential
• all
• cis
i
d
t
a
r
o
u
l
f
x
▴
Figure 22
from
cis
• essential
• non-essential
• omega
• omega
3
Examples of fatty acids.
the methyl group
the rst
7
The omega number indic ates how far
double bond
is loc ated
a
E
v
O
Figure 23
H
C
C
C
H
C
y
C
H
p
H
H
r
e
C
H
C
v
H
C
l
H
H
O
C
H
r
H
C
P
H
H
y
C
H
C
t
i
s
H
C
Sunower oil is pressed
from
the seeds.
▴
Figure 24
Butter is made by churning cream
from
cow’s milk.
Two-thirds of the fatty acids in the oil are polyunsaturated
Two-thirds of the fatty acids in butter are saturated and most of the
and
most
of the rest
are monounsaturated
rest
190
is monounsaturated
y
H
e
C
C
▴
C
C
s
s
H
OH
O
C
Molecules
H
C
H
H
C
C
C
cis
s
s
H
trans
▴
Figure 25
Double bonds in fatty acids
e
r
l
hand,
a
of
small
number
press
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engine
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essay
or
scientists
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On the other
challenged the
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shows the Google Scholar
dierent journal articles
the
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there
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saturated fat in the diet?
saturated fats. Google Scholar
literature.
for
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What
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e
▴
191
Form and function
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▴
Figure 27
This annotated
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entries take a dierent
view on the
C
o
v
i
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B1.1.11
The two dierent
p
role of saturated fat in the diet
y
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energy storage and thermal insulation
triglycerides
humans,
also
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The
properties
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organs
tissue
triglycerides
chemic ally
very
They
are
immiscible
with
•
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cytoplasm
which
l
release
E
v
a
important
They
in
are
are
so
specialized
the
make
groups
immediately
of
cells
c alled adipose
beneath the skin and
kidneys.
them
particularly
as
that
stable,
so
energy
water,
so
they
have
much
enough
that
conductors
need
liquid
example,
not
animals
poor
animals
They
for
do
twice
c arbohydrate,
•
in
loc ated
suitable
for long-term
storage.
are
•
is
including
They
•
storage in plants and animals. In animals, the
stored
u
•
for
and
adipose
some
t
a
energy
used
fats
o
In
i
d
r
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f
x
O
192
tissue.
are
are
n
Triglycerides
at
around
to
body
the
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energy
energy
move
of
and
heat,
conserve
other
gram
be
in
so
they
body
c an
lost
over
form
time.
droplets in the
effects on the cell.
cell
stored
especially
temperature,
kidneys.
not
naturally
or
per
c an
is
in
for
be
respiration as
half
the
birds
body
and
mass. This is
bats
that
fly.
used as a thermal insulator
heat.
so
they
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shock
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All 7 versions
Molecules
Thermal
insulation
maintain
have
is
needed
most
a
body
temperature
thick
layers
of
c alled
blubber.
overheating
warmer
animals
impedes
than
the
subcutaneous
adults
such
dissipation
water
in
the
of
sea
heat
live in cold habitats and that
the
environment.
Such animals
tissue. In marine mammals it is
lions
onto
that
than
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as
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animals
higher
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s
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blubber
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when
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ocean habitat.
Figure 28
e
▴
A typic al 40 kg male emperor
r
B1.1.12
Formation of phospholipid bilayers
penguin has 12.7 kg of body fat at the
of winter, but only 2.4 kg at the end.
y
P
start
as a consequence of the hydrophobic and
Whydo male emperor penguins need such
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a large amount of body fat at the start of
l
thewinter?
not
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with
to
water
water
property
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basis
oen
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circle
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head and the
water the phosphate
tails
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are
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phospholipids
become
hydroc arbon tails facing
outwards
to
bilayers.
membranes.
t
a
l
the
water
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stable
side.
structures
hydrophilic phosphate head
hydrophobic hydrocarbon tails
a
v
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Simplied
with
u
f
x
O
Figure 30
phosphate
mixed
phospholipid
phospholipid
▴
the
are
Bec ause
the
heads
c alled
bilayer
c alled
i
form
the
to
hydrophilic
layers
the
r
o
they
to
than
double
the
double
are
phospholipids
o
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molecule
d
inwards
and
attracted
other
using
hydroc arbon chains.
of a phospholipid
molecule
When
phospholipids
simply
n
each
the
of
represented
the
hydrophobic.
hydrophilic part
hydrophobic part consists of the
structure
U
heads
of
tails.
diagram
for
is
The
p
parts
lines
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part
o
two
hydroc arbon
c an
The
and
amphipathic.
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The
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two
group.
as
are unusual
v
Figure 29
and
hydrophilic
described
chemic al
structure
is
Other substances that
Phospholipids
i
n
▴
The
molecule
are
phosphate
The
hydrophilic.
hydrophobic.
y
phosphate
the
c alled
r
e
Section B1.1.9.
are
c alled
phospholipid
this
two
in
are
O
Substances
to
t
i
s
bec ause
of
attracted
attracted
n
are
y
Substances
diagram
of a phospholipid
bilayer
193
Form and function
B1.1.13
Ability of non-polar
steroids to pass
through the phospholipid bilayer
Steroids
are
B
C
•
four
•
three
fused
of
these
lipids
with
molecules
similar
to
sterol.
They
c arbon atoms
31;
rings
(Figure
31;
A,
B
and
C)
and
one
cyclopentane ring
D)
c arbon atoms in total in the rings.
The four-ring structure
are
and
structure.
them
examples
the
Steroids
to
pass
of
steroids,
functional
are
groups
mostly
through
which
such
phospholipid
bilayers
CH
the c arbon atoms are
attached
are.
Hydrogen atoms
to the c arbon are not
shown
O
c an be inferred
bec ause each
has a total of fourbonds
C
i
n
Linking questions
How
c an
become
a.
Describe
succession
Outline
i
b.
t
a
c.
2.
u
l
E
v
a
b.
relationship
and
changes
events
O utline
four
activity.
(C4.2.19)
What
a.
the
are
the
Outline
sinks
roles
the
synthesized
of
role
of
the
from
living
organisms accumulate and
of
NADP
in
in
process
cycle.
ecologic al
(C1.3.17)
is
being
reduction
the
of
in
release
photosystem
1
released due to human
biologic alsystems?
of
energy
and
the
O utline
one
example
of
chemoautotrophy.
from
C alvin
(C1.3.13)
c.
OH
3
(D4.2.13)
c arbon
and
oxidation
Explain
the
biomass.
C alvin
oxidation
of
(B1.1.4)
role
between
in
which
c arbohydrates.
the
by
leave cells.
sinks?
the
o
d
r
o
f
x
O
194
compounds
c arbon
n
U
1.
hydrophobic.
or
oestradiol
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testosterone
c arbon atom
HO
v
but
enter
y
individually shown but the bonds
between them
and
CH
p
r
e
not
3
eects on the body. In these
added to the
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structures despite their markedly
skeletal diagrams,
are
therefore
n
3
Testosterone and
oestradiol have very similar molecular
dierent
that
and
t
i
s
CH
–OH
hydroc arbon
OH
Figure 32
dier in the position of C=C
as
y
allows
of
in
l
four-ring
This
hundreds
bonds
(C4.2.7)
cycle.
y
double
P
There
e
17
of
r
•
rings
ofsteroids
▸
c an be
features:
cyclohexane
(Figure
Figure 31
group
D
A
▴
a
using
s
s
identied
B1.2
Proteins
What is the relationship between amino acid sequence and the diversity in form and function
Every
protein
contains
any
length
are
and
sequence
are
or
much
amino
relatedto
its
function?
possible,
longer
acids
in
than
There
but
are
only
a
small
words—most
polypeptides
The
20
parallels
the
hundreds
their
amino
used
to
assemble
of
the
alphabet
to
form
possibilities
are
used.
linking
proportion
have
determine
dierent
with
of
the
or
acids
of
even
that
letters
c an
thousands
three-dimensional
of
shape?
be
amino
How
is
A
acids.
the
words:
dierence is that
How does the
shape
of
a
l
performed.
does
heat
aect
environmental
environments
such
be
altered?
c ause
the
as
lead
proteins
high
or
How
misfolding
structure
changes
of
the
physic al
do
heavy
proteins?
of
proteins?
to
denaturation?
that
low
of
function
in
Why do
temperatures?
Low or
forming dipeptides and
Eect
of
pH
of
and
▴
Figure 1
as
a
Chemic al
basis
for
the
diversity
immense
in
only
the
R-groups of amino acids
diversity
in
protein
form and
function
for amino acids
B1.2.7
Impact
ofproteins
temperature
B1.2.8
on
Some protein structures
AHL
B1.2.6
possible peptide chains
a
E
v
O
B1.2.5
requirements
variety
l
Innite
o
reactions
u
f
x
Dietary
i
HL
longer chains of amino acids
B1.2.4
t
a
and
structure of an amino acid
Condensation
B1.2.3
n
U
B1.2.2
Generalized
d
r
o
SL
B1.2.1
C
values of pH?
What
extreme
o
examples
to
to
i
n
some
high
mercury
sensitive
How do changes of pH
v
some
structure
as
are
molecules
for functions to be
p
How
such
interactions
environment.
protein
metals
protein
y
c ause
are
These
chemic al
within
needed
r
e
and
interactions
conformation
O
weak
the
t
i
s
maintain
n
y
How are protein molecules aected by their chemic al and physic al environments?
Relatively
protein
y
of
polypeptides.
P
sequence
is
more
diverse.
r
polypeptides
one
chemic ally
e
polypeptides
s
s
ofproteins?
protein
structure
of
Pleating
primary
and
structure
coiling
of
on
the
secondary
conformation
structure of
proteins
B1.2.9
Dependence
bonds,
ionic
bonds,
hydrophobic
B1.2.10
of
conjugated
brous
structure
on
hydrogen
covalent bonds and
interactions
proteins
Q uaternary
B1.2.12
tertiary
Eect of polar and non-polar amino acids on tertiary
structure
B1.2.11
of
disulde
structure
of
non-conjugated and
proteins
Relationship
of
form and function in globular and
proteins
195
Form and function
B1.2.1
Generalized structure of an amino acid
Amino
acids
are
central
c arbon
atoms.
One
is
c arbon
atom
the
accept
of
a
amino
c arbon
covalent
c an
be
the
proton
acids
also
links
any
one
a
a
an
to
range
a
of
bond
side
to
a
chain,
c an
hydrogen atom. The
c alled
the
R-group.
O
H
N
C
COOH
N
2
C
H
C
N
C
H
n
O
C
t
i
s
R
O
H
H
informative?
R
H
R
O
dipeptides and longer chains of amino acids
“R-group”
stands
form
a
dipeptide,
for
More
amino
acids
c an
is
2.
When
a
residue?
chains
does
become
a
the
R-group
rather
of
residue?
Amino
the
a
made
are
peptide
between
linked
a
condensation
reactions
reaction.
to
create
any number of amino acids, though
usually
referred to as oligopeptides
are
main
the
bonds.
the
by
condensation
amine
These
component
are C
group (
N
NH
of
bonds
proteins.
formed
by
) of one amino acid
2
COOH)
group
using
i
the
contain
acids
directional
c arboxyl
are
further
Polypeptides
with
group (
is
o
are
It
whatever
at
groups
R-groups
of
another.
process:
the
that
of
end
the
of
The
reaction
amine
the
group
growing
is
of
c atalysed in cells
a
chain.
free amino acid is
Bec ause peptide
are part of all amino acids, the bond is the
the
amino
acids
are.
peptide bond
amino
group
group
u
l
f
x
a
E
v
O
C
the
carboxyl
H
H
condensation
O
H
H
O
O
N
linked
c arboxyl
to
amino
reaction
by
t
a
r
o
d
bonds
same,
H
are
ribosomes.
linked
20
acids
c an
n
by
H
acids
condensation
and
H
than
polypeptides.
U
a
Polypeptides
fewer
than
linked
C
What
chain.
i
n
1.
longer
amino
be
o
a
two
v
in
p
To
R
Condensation reactions forming
y
B1.2.2
residues
r
e
Activity: Researching
residue.
H
O
(water removed)
H
+
C
N
OH
C
H
C
N
C
N
C
R
R
O
2
Figure
3
adipeptide
Condensation
joins
two
aminoacids
with
C
OH
R
H
C
H
OH
R
▴
196
it
a
peptide
bond
to
produce
y
O
H
four
in dierent
H
The
to
l
Which of these is most
bec ause
possibilities.
y
ways.
c an be represented
bonds
(–COOH) is acidic
basic
H
amino acid
molecule has a
group and another
group
is
acid
covalent
amine
group
covalent
c arbon
wide
H
structure of an
of
amino
single
c arboxyl
amine
single
alpha
of
atom
The
the
E ach
with
amphiprotic.
has
the
group.
and
are
proteins.
c arbon,
nitrogen
c arboxyl
a
atom
bond
is
of
alpha
P
The generalized
these
donate
so
R-group
of
blocks
the
r
The
Figure 2
one,
alpha
other
c an
c alled
e
The
it
building
s
s
other
bec ause
▸
the
atom
Molecules
Activity: Drawing dipeptides and oligopeptides
To
of
test
the
your
skill
amino
at
showing
acids
in
how
Figure
4.
peptide
There
are
bonds
16
are
formed,
possible
try
showing
dipeptides
that
c an
the
be
formation
produced
of
a
peptide
from
these
bond
between two
four amino acids.
s
s
COOH
OH
H
C
H
N
C
COOH
H
H
C
H
N
C
COOH
2
H
COOH
H
H
glycine
oligopeptide
of
four
amino
acids,
linked
by
three
peptide
features.
bonds.
If
y
Some common amino acids
you
do
this
n
an
following
C
2
l
draw
the
N
alanine
correctly,
O
t
i
s
•
also
see
2
H
P
could
should
H
COOH
y
You
C
C
glutamic acid
Figure 4
H
H
N
H
serine
▴
H
r
2
H
H
C
e
H
H
you
A chain of atoms linked by single covalent bonds forming the backbone of the oligopeptide, with a repeating sequence
→
N
hydrogen
double
atom
bond
The amine (
to
NH
is
linked
by
single
one
of
and
c arboxyl (
)
the
a
two
bond
C
to
each
C
C
c arbonatoms.
COOH)
groups
are
used
chain.
R-groups
of
These
each
are
amino
c alled
acid
the
amino
remain
and
Bond
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quantities
An
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oxygen
bond
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linked
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remain at the
backbone.
◂
Figure
5
This
glycine-alanine
web-based
from
molecule
of
the
dipeptide
constructed
computer
ChemM agic
Similar
image
was
the
using
applic ation
University
builder
apps
the
c alled
of
Illinois.
exist
on
otherwebsites
The app begins with a molecule of
methane. Students then substitute
individual atoms with desired atoms.
1.
Using
Figure
colours
nitrogen
2.
Identify
and
5,
deduce what
represent
and
the
oxygen,
c arbon,
hydrogen.
R-groups
of
glycine
alanine.
Dietary requirements for amino acids
dierent
c an
peptide
an
Ation
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Plants
and
Diole
B1.2.3
Twenty
v
Oter odel
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in
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i
n
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and
in
o
The
the
v
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of
atom
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2
ends
) the bond angles are closer to being correct.
nitrogen
y
•
. If this is shown as a zigzag (N
r
e
a
C
→
A
C
→
•
N
→
→
C
of
amino
all
of
essential
the
acids
these
are
by
amino
animal
so
used
by ribosomes to make polypeptides.
photosynthesis.
acid
must
be
is
one
that
obtained
Animals
c annot
from
obtain
be
the
amino
acids
from
synthesized in sucient
diet.
A
non-essential amino
197
Form and function
acid
one
c an
be
amino
synthesized
acid
into
by
an
animal
using
metabolic
pathways
that
transform
another.
Nine of the 20 amino acids are essential in humans. The others are non-essential,
though several become essential in special circumstances. For example, the amino
s
s
acid phenylalanine is essential because it cannot be synthesized by the human body;
tyrosine is non-essential because it can be made from phenylalanine.
e
COOH
COOH
phenylalanine hydroxylase
+ O
NH
2
r
NH
2
HO
Figure
6
Conversion
acids.
and
amino
acids
have
dierent
foods
low
in
humans.
each
successful
of
example,
are
It
amino
that
people
amino
do
is
similar
as
Both
is
to
eat
lysine
a
a
a
(sh,
meat, milk,
needed in the human
are
low
decient
in
specic
lysine content, and
methionine
diet,
acid
protein-rich diet and
is
some
and
vegan
a
amino
foods
what
have
consumed.
such
to
and
wheat
eating
acid
provide
possible
Animal-based
balance
such
methionine.
So,
essential
civilizations
a
cereals
is
acid.
non-essential
must
Traditional
are
essential
ensure that
plant-based diets
balance.
o
v
Data-based questions: Essential amino acids
1
amino
in
classied
as
1.0
and
as
of
all
relative
being
each
other
foods.
content
“conditionally
amino
values
acid
are
of
Cysteine
in
a
essential
and
essential”.
hen
a.
tyrosine
b.
egg is set
relative to the hen
c.
eggstandard.
1.1
1.0
1.4
1.0
1.0
1.0
methionine
tryptophan
E
v
lysine
a
O
1.0
and cysteine
essential
amino
Phenylalanine
1.0
0.9
1.1
0.7
1.6
1.3
1.0
1.3
1.0
1.0
0.9
0.9
1.1
from
Robert
McGlivery,
Biochemistry: A Functional Approach,
S aunders.]
198
term
“essential
overall
source of
[2]
converted
the
reason
infants
an
acids.
is
phenylalanine
the
tyrosine
by the
hydroxylase.
that
essential
with
to
tyrosine
amino
is
considered
acid.
condition
are
le
untreated,
they
phenylalaninein
their
blood
phenylalanine
their
urine.
of
1.0
1.0
as
Deduce
(PKU)
1.0
1.0
obtained
milk
enzyme
When
the
[1]
phenylketonuria
have a build-up of
1.3
◂
D ata
by
[2]
aconditionally
d.
meant
human
and tyrosine
histidine
is
Evaluate
phenylalanine
[Source:
what
acid”.
1.1
u
threonine
1.0
l
f
x
valine
milk
o
leucine
cow’s
milk
i
isoleucine
human
t
a
r
o
eggs
d
hen’
s
Outline
amino
n
Thequantity
the
dierent
U
are
summarizes
acids
C
Table
i
n
1.
y
of
for
content.
a
p
in
beans
acids
enough
For
acid
essential
into
r
e
amino
amino
an
balance
Plant-based
amino
peas
a
in
acid
n
diet.
have
their
amino
O
eggs)
in
essential
l
decient
an
y
vary
still
of
t
i
s
Foods
be
tyrosine
1970,
W
. B.
Table 1
this
in
condition.
and
high
Suggest
levels of
the
c ause
[1]
y
▴
P
phenylalanine
Molecules
B1.2.4
Innite variety of possible
Activity: F amous
peptidechains
Ribosomes
acids,
of
The
so
all
amino
ribosome
c an
sequences
are
acids.
They
dierent
amino
acids
The
number
of
are
included
acids
in
acid
in
a
a
time, until a polypeptide is fully
bonds
Ribosomes
instructions
amino
amino
at
peptide
possible.
receive
possible
Both
make
one
the
in
the
between
do
not
form
of
vegans
any pair of amino
make
random
genetic
code.
sequences
Twenty
code.
sequences
dipeptide
c an
c an
be
be
c alculated starting with
any
of
the
20,
so
there
r
dipeptides.
together
are
20
possible
sequences (20
).
There
are 20
× 20
×
20
possible tripeptide
3
sequences (20
tens
of
For a polypeptide of
number
of
amino
n
acids
amino
in
a
acids,
there
polypeptide
are 20
c an
be
possible
anything
from 20
thousands.
400
example,
acid
c alculators
in
a
if
a
polypeptide
sequences.
simply
polypeptide
This
express
c an
be
it
has
is
an
as
tens
400
innity.
of
amino
incredibly
acids,
large
there
are 20
possible
number, and some online
▴
Figure
thousands,
the
number
of
possible
innite.
not
his
want
is
But
the
only
an
extremely
organism’s
small
proportion
are
made
proteome.
is
natural
pain
killer
secreted
v
Beta-endorphin
a
small
Alpha
amylase
protein that contains two short polypeptides, one with 21
and
the
other
the
enzyme
is
with
in
30.
saliva
that
of
starts
the
digestion
of
great
to
and
be
a
was
C anyou
thinkers
da
that
is
did
tomb
for
probably
nd
who
Vinci
he
other
bec ame
examples
vegan
orvegetarian?
o
acids
U
C
is
amino
i
n
•
Insulin
vegetarian.
by the pituitary gland that is a
polypeptide of 31 amino acids.
•
by an
p
Examples of polypeptides
•
said
body
creatures
y
This
have
sequences
r
e
eectively
organism.
Leonardo
to
Given that the number of amino acids
other
is
7
reported
O
amino
t
i
s
For
n
y
to
n
).
The
l
sequences.
y
×
P
2
20
e
amino
vegetarians and
acids
s
s
formed.
link
starch. Itis a
single polypeptide of 496 amino acids, with one chloride ion and
one
c alcium
Titin
is
the
ion
associated.
largest
polypeptide
discovered
so
far.
It
is
part
n
•
of
thestructure of
o
d
muscle. In humans, titin is a polypeptide of 34,350 amino acids, but in mice
it
is
even longer with 35,213amino acids.
Eect of pH and temperature on
u
f
x
protein structure
The
three-dimensional
broken.
This
and
interactions
results
denaturation.
denatured
denaturation
precipitate.
becoming
E
A
in
protein
is
R-groups
a
bonds
conformation
the
l
these
between
a
does
not
permanent.
This
is
due
exposed
to
are
change
v
O
interactions
i
t
a
r
o
B1.2.5
to
to
the
water
the
proteins
weak
return
proteins
hydrophobic
by
the
is
acids
stabilized
by bonds or
within
molecule. Most of
and
conformation
normally
Figure
viewed
amino
relatively
Soluble
the
of
of
▴
to
its
oen
in
they
of
c an
the
former
in
the
be
Month
This
image
rotated
on
of
the
insulin
PDB
c an
be
Molecule
of
website
disrupted or
protein
and
is
c alled
structure — the
become
R-groups
change
the
8
and
insoluble
centre
of
and
the
form a
molecule
conformation.
199
Form and function
Heat
that
c an
c an
c ause
break
tolerance.
Some
geothermal
or
higher.
denaturation
that
It
works
at
Nevertheless,
proteins
was
80°C
heat
example
discovered
and
that
that
in
bec ause
c auses
it
or
c auses
live
are
is
in
not
DNA
hot
of
vibrations
interactions.
volc anic
this
denaturation
it
of
springs
denatured
by
polymerase
springs
is
in
or
proteins
in
in
molecule
their
hot
in
at
National
much
lower
e
white
and
are
yolk
are
insoluble
heated,
in
both
both
yolk
bonds
he at,
the
have
denatured.
so
ionic
and
whitesolidify
within
dissolved
the
contents
this
is
protein
the
of
the
optimum
in
pH
for
or
oen
are
the
c an
on
c ausing
structure
water
stomach
alkaline,
charges
of
new
the
ionic
protein
become
normally
c ause
R-groups
denaturation.
This
are
bre aking
bonds
is
acidic,
with
to
altered
insoluble.
protein-digesting
changed,
a
form.
and
There
are
pH
low
enzyme
as
pepsin
stomach.
As
is
with
proteins
that
exceptions:
as
1.5,
that
but
works
O
t
i
s
inthe
the
three-dimensional
been
and
n
become
the
eggs
dissolved
acidic
negative
y
They
When
were
and
l
the
9
that
both
r
e
denaturation experiments
to
close
emit
blue
choice,
the
light
is
of
one
egg
of
of
pH
the
c an
tubes
the
used,
than
main
of
extent
in
measure
as
be
how much light
how much light
test
in
tube
at
investigated
egg
c an
white. A
be
which
it
heated in a
denatures.
by adding acids and
egg albumen solution.
of
▴
Figure
10
denatured
These
albumin.
tubes
The
contain
increasing
concentration
of
quantities
albumin
in
of
urine
is
an
denaturation, a colorimeter
denatured
dissolved
proteins
a
temperature
albumen
albumen.
The
absorbs
solution
a
E
v
O
l
moreturbid.
200
measure
u
light
will
f
x
be
means that it will
there is a function
i
eects
test
the
albumen
nd
to
to
passes
sample. If the function is set at
machine
to
quantify
c an
the
the
it
that
500 nm or
absorbed.
bath
alkalis
To
transmittance
through
If
at
t
a
The
possible
r
o
water
as
sample.
set
are both
light
o
solution
the
is
d
Albumen
colorimeter
of
n
been
a
range
into
choose
passed
absorbance,
has
UV
If
amount
U
has
sample.
the
o
as
spectrophotometer
C
a
a
measure
i
n
through
and
that
p
colorimeter
instruments
v
A
y
Applying techniques: Using a colorimeter to measure turbidity:
important
diagnostic
for
determining
kidney
function.
Albumin
more
will
in
urine
in
turbidity.
is
precipitated
using
sulphosalicylic
acid,
which
results
become
should
not
This
c an
be
measured
using
normally
be
present
urine
in
a
colorimeter.
Protein
y
Figure
proteins
pH,
P
▴
of
positive
Park.
biotechnology.
r
bec ause
near
Thermus aquaticus,
temperatures.
Extremes
heat
water
temperatures of 80°C
from
used
the
vary
Yellowstone
widely
most
within
Proteins
s
s
prokaryote
best
have
best-known
a
bonds
microorganisms
vents
The
bec ause
intermolecular
Molecules
Elements
Chemic al diversity in the R-groups
in
Number
R-group
amino
LHA
B1.2.6
of
acids
of amino acids as a basis for the immense
H
only
C
and
1
diversity in protein form and function
the
20
amino
chemic al
shown
of
ribosomes
their
use
R-groups.
to
The
make
polypeptides
elements
present
are
in
very
the
varied in
R-groups
C,
H
and
S
C,
H
and
N
only
only
C,
H
and
O
only
C,
H,
one
used
end
are
to
linked
make
up
into
peptide
a
polypeptide,
bonds.
This
their
leaves
an
amine
amine
and
c arboxyl
group (–NH
N
and
of
the
chain
and
a
c arboxyl
group
O
)
▴
(–COOH) at the other end. The
Table
2
Variation
the
properties
chemic al
or
living
of
the
the
−)
polypeptide;
Some
hydrophilic
by
acting
organisms
to
dierences
as
of
the
make
acid
and
between
or
a
use
it
is
of
the
each
are
some
are
polar
base.
This
an
R-groups
amino
acid
has
little
R-groups that determine
R-groups
R-groups,
an
atom
R-groups
hydrophobic and some
and
broad
others
diversity
amazingly
wide
are
in
shown
in
range
become
of
of
R-groups
proteins.
Table 3.
O
Some
Of
c arbon
t
i
s
allows
(+
the
characteristics.
alpha
of
n
charged
of
the
y
hydrophilic.
to
y
on
attached
l
the
atom
5
2
P
aminoacids
hydrogen
eect
5
r
are
acids
2
at
2
are
Table 2.
amino
groups
that
5
e
When
in
acids
nature
only
s
s
The
H
Eleven R-groups are hydrophilic
with between zero and nine
y
r
e
Nine R-groups are hydrophobic
Seven R-groups can become charged
Four
v
hydrophilic
Four R-groups act as
Three R-groups act as
an acid by giving up a
a base by accepting a
R-groups are
Six R-groups
i
n
R-groups
do not contain
polar but never
contain rings
rings
charged
proton and becoming
o
Three
p
carbon atoms
proton and becoming
C
negatively charged
Table
In
c ases
contain
this
is
a
amino
due
synthesized.
contain
converted
to
blood
at
are
20
example
used
to
walls.
not
being
of
in
the
basic
repertoire
of
20.
modied aer a polypeptide
modic ation of amino acids
provide
tensile
Collagen
strength in tendons,
polypeptides
made
by
many positions, but at some of these positions it is
hydroxyproline,
which
makes
the
collagen
more
stable.
u
f
x
B1.2.7
an
vessel
proline
that
the
t
a
ribosomes
is
protein
of
i
and
acids
acids
one
r
o
skin
to
There
structural
ligaments,
amino
o
been
collagen,
of
d
in
proteins
most
has
Classic ation
n
Some
3
U
▴
positively charged
Impact of primary structure on the
l
O
The
structure
of
quaternary.
proteins
Primary
polypeptide.
by
E
The
backbone
of
a
atoms
into
and
and
any
C
there
adjacent
almost
four
structure
polypeptide
covalent bonds (
tetrahedral
has
v
and
a
conformation of proteins
C
c an
N
be
nitrogen
C
levels
of
is
linear
is
a
C
the
and
about
c arbon
three-dimensional
primary,
secondary, tertiary
sequence of amino acids in a
repeating
N
rotation
and
complexity:
so
sequence
on).
the
The
bonds
atoms.
This
of
atoms
bond
between
allows
linked
angles
the
are all
alpha
polypeptides
c arbon
to
fold
shape.
201
Form and function
LHA
▸
Figure
11
Rotation
about
bonds
H
O
in
a
R
polypeptide
C-α
N
s
s
N-terminus
C
C-α
N
C
e
C-α
C-terminus
H
r
O
peptide bond
rotation about
l
carbon bonds
conformation
The
the
arrangement
Most
determined
conformation
behaviour
of
of
by
This
naturally
a
freely
occurring
articial
predictions
protein
have
used
180,000
available
proteins.
on
amino
and
the
massive
structure.
and
and
is
or
protein
specic
of
their
R-groups.
through this
great
interest
procedures to determine
These
up
a
acids
have
resource.
speed
primary
into
functions
experimental
online
To
intelligence
based
polypeptide
conformation
proteins.
C
make
than
of
their
o
Bank,
conformations,
to
biologists
more
i
n
the
D ata
of
v
Protein
of
1970s,
sequence
why
a
y
the
structures
is
in
self-assemble
p
the
atoms
determines
r
e
tobiologists.
Since
the
proteins
cells.
of
polypeptides
O
conformation.
n
three-dimensional
its
t
i
s
is
y
The
This
been
is
working
will,
a
out
computing
This
deposited in the
only
for
small
of
fraction
protein
power
is
being
example,
used
allow all
protein conformations in the human proteome to be discovered relatively quickly.
n
U
B1.2.8
Pleating and coiling of secondary
o
regular
i
At
intervals
They
are
what
along
remains
of
a
polypeptide
c arboxyl
having
u
this
a
slight
polarity,
hydrogen
l
along
a
are
chain
amine
there
negative
hydrogen
bonds
are
polypeptide
strong
charge
bonds
to
allows
stabilize
the
c an
individually
chains
enough
and
weak,
many
H
hydrogen
form
distinctive
aer
are
a
between
the
of
are C=O and N
groups
they
polar,
slight
these
have
with
positive
H
the
to
form
Due
groups. Although
and
conformational
oxygen
charge.
frequency of C=O and N
them
groups.
been
H
groups
collectively they
structures within
proteinmolecules.
Two
E
•
commonly
The
The
β-pleated
in
types
of
polypeptide
structure
are
is
into
wound
stabilized
a
helic al
by
hydrogen bonding.
shape,
with
hydrogen
between adjacent turns of the helix.
parallel
run
occurring
α-helix — the
bonds
•
with
sheet — two
hydrogen
opposite
or
more
bonds
directions,
tetrahedral bond angles.
202
and
used to make peptide bonds. Both C =O and N
to
v
O
f
x
t
a
r
o
d
structure of proteins
sections
between
forming
a
of
them.
sheet
polypeptide
The
that
is
are
arranged in
sections of polypeptide
pleated
bec ause of the
y
P
(no rotation)
Molecules
structures
secondary
stabilized
structure
of
a
by
hydrogen
bonding
within
polypeptides
LHA
Regular
are the
protein.
alpha helix
H
C
s
s
N
H
beta-pleated sheet
C
C
O
O
N
H
O
H
O
O
H
O
C
C
C
N
C
N
H
C
C
C
N
C
N
C
C
C
C
N
N
C
e
C
H
C
N
C
C
H
N
H
O
N
C
H
O
H
O
▴
Figure
12
Beta
barrel
hydrogen
O
bond
H
membranes
O
H
C
C
C
curved
C
N
C N
C
N
C
C
C
N
O
O
O
H
C
H
C
C
c an
H
C
O
13
The
α-helix
(le)
and
the
β-pleated
sheet
(right)
are
r
e
Figure
examples
functions
of
p
i
n
o
v
Dependence of tertiary structure
on hydrogen bonds, ionic bonds, disulde
y
secondarystructures
B1.2.9
What
O
t
i
s
N
O
▴
cylinder.
n
H
a
O
C
C
form
in
sheets
perform?
y
H
they
proteins
β-pleated
C
O
C
N
to
N
N
C
large
l
N
have
O
C
H
N
O
O
y
H
P
H
O
C
r
O
C
Tertiary
stabilized
are
four
by
main
the
folding of a whole polypeptide
interactions
types
bonds
negatively
of
structure.
between
This
interaction.
between
charged
positively
R-groups.
There
charged and
Amine
groups
interaction
CH
H
CH
i
H
positively
3
charged
+
→ –COO
by
donating
Bec ause
(hydrogen
ions),
of
a
the
ionic
bonds
atom
between
forms
a
polar
link
a
O
hydrogen
groups
polypeptide
3
backbone
H
hydrogen
become
proton (
in
3
CH
bond
O
COOH
involvement of
bonds
sensitive to pH changes.
Hydrogen
A
).
C arboxyl
l
•
H
).
CH
CH
3
O
OH
C
CH
proteins
S
2
u
are
+
f
x
protons
+
→ –NH
t
a
+
r
o
+
2
NH
C
C
3
2
H
become positively charged by accepting a proton
(
hydrophobic
structure
R-groups.
o
Ionic
is
three-dimensional
d
•
a
n
is
structure
into
U
chain
C
covalent bonds and hydrophobic interactions
CH
2
2
disulfide bridge
R-groups.
between two
electronegative atoms such as O or N. It is
in
the
hydrogen
it
negative
a
one
to
O
of
them,
which
results
CH
a
the
slight
positive
charge,
CH
2
CH
2
NH
CH
2
other, which has a slight
2
3
O
2
ionic bond
charge.
Disulfide bonds
is
to
having
attractive
E
making
•
bonded
v
covalently
covalent
between
bond
and
the
pairs
of
cysteines. This
strongest of all the
interactions.
▴
•
Hydrophobic interactions
non-polar
between
Figure
14
R-group
interactions
contribute
to
tertiary
structure
any of the
R-groups.
203
Form and function
LHA
Tertiary
some
structure
c ases,
in
a
A
wide
a
correctly
folded
range
of
Within
and
as
fully
these
polypeptides
not
are
functional
tertiary
tertiary
do
not
described in
shapes
become
structure.
These
synthesized
this
process
by
to
the
ribosome. In
ensure
that
is
produced,
there
are
oen
most
parts
of
which
with
are
secondary
sheets.
folded
are
and
brous
instead
remain
proteins
and
elongated — they
have
Section B1.2.12
structural
Integrin
inside
extracellular
of
a
the
the
with
connects
to
so
the
components
helps
tissue
v
E
204
across
cell
matrix,
amino
of
a
cells
Channel
core
l
O
the
the
with
function
bind
the
a
that
This
be
proteins
the
outside
in
In
centre
channel
allows
core
region
addition,
the
with
amino
the
c arry out
non-polar
they
centre
of
acids
surface
the
in
and
are in contact
where
the
the
water is
protein
water
substances
bec ause
centre and
around
over some or
hydrophobic amino acids on parts of their
in
membranes
with
in
contact
both
have
hydroc arbon
are
membranes
hydrophobic
through
on
where
the
structure
region
remains
they
stabilizes
positioned
hydrophobic amino
core
is
a
of
the
belt,
membrane.
with
hydrophilic
aqueous solutions inside and
the
tertiary
correctly
in
structure of the
the
membrane
where
performed.
hydrophobic
position.
it
tertiary
in
hydrophobic
arrangement
that
bec ause
surface
between
non-polar
this
ensures
c an
the
proteins
and
cell.
have
their
o
in
membrane(grey).
of
each
hydrophobic
embedded
cytoskeleton
blue),
its
polypeptides
the
and
contact
water
clustered
the
acids
embedded
contact
on
C
of
protein
in
in
aqueous solution outside the cell. These
acids
amino
proteins
o
and
outside
u
acids
helix
f
x
alpha
inside
i
green
an
two
acids
interactions
routinely
proteins
they
an
stabilizes
between
Such
transmembrane
t
a
(shown
of
d
composed
r
o
protein
Integral
where
regions
transmembrane
are
surface.
soluble
in
amino
n
acids
a
i
n
proteins
their
surface.
In
bonding
c ategories:
hydrophilic.
be
or
protein.
U
all
hydrophobic
broad
y
arrangement
v
This
maximizes
to
amino
excluded.
Some
is
hydrophilic
hydrophobic
the
Integrin
need
cytoplasm
and
hydrogen
15
the
therefore
water
it
Figure
proteins
in
two
p
have
and
into
n
globular
function
proteins
with
charged
divided
hydrophobic
r
e
their
be
O
polar
c an
therefore
of
they
the
specic
of
allow
the
between,
have
a
hydrophilic
membrane.
which
tunnel
protein.
The
hydrophilic
holds
lined
width
ions
or
solutes
They
with
and
or
have
them
in
water to diuse
hydrophilic
a
regions
transmembrane
hydrophilic amino acids
charge distribution of this
molecules
to
pass
through.
y
l
y
•
proteins
and
t
i
s
non-polar
M any
▴
in
•
or
roles,
Eect of polar and non-polar amino
acids on tertiary structure of proteins
acids
results
P
B1.2.10
Amino
it
protein.
structures
β-pleated
is
with
r
which
have
helps
e
do
polypeptide
three-dimensional
structure — α-helices and/or
Some
a
protein
s
s
globular.
develops
chaperone
Molecules
LHA
B1.2.11
Quaternary structure of
non-conjugated and conjugated proteins
All
proteins
have
at
least
linked
components.
In
proteins
three-dimensional
a
the
by
form
of
proteins
their
four
The
inclusion
and
functional
of
their
consists
active
subunits.
the
To
beta
form
same types of
structure
with
8
on
of
page199).
Collagen is
three polypeptides wound
high
tensile
strength. It is
page207.
one
or
of
more non-polypeptide subunits in
For
example,
chains,
non-polypeptide
allowing
by
chain
the
The
protein
to
component
haem
with
increases
a
molecule
haem
the
group.
alpha
chemic al
group of haemoglobin
transport
that
haemoglobin
associated
components
proteins.
this
each
oxygen.
contributes
to
▴
chain
Figure
16
haem
The
quaternary
M any enzymes
the
c atalytic
site.
of
haemoglobin
polypeptide
β-chains)
in
adults
chains
chain
each
of
iron-containing
(two
which
haem
consists
α-chains
is
alpha chain
structure
bound
of
four
and
to
two
an
group
o
i
n
v
p
activity
It
have
non-polypeptide
linked
beta
y
oxygen,
a
protein.
polypeptides.
diversity
polypeptide, the
example, insulin has two polypeptides,
Figure
on
single
r
e
have
For
more
quaternarystructure.
polypeptide
are
in
polypeptide
of
only
or
O
to
are
two
t
i
s
addition
there
(shown
rope-like
19
a
the
of
more non-polypeptide
n
Conjugated
a
Figure
than
is
consist
y
in
more
subunits
polypeptides
structure.
bonds
of
or
l
to
illustrated
binds
tertiary
non-conjugated
together
consists
in
disulde
the
of
many
one
y
another
as
consist
but
have
P
linked
protein,
structure
some
r
interaction
that
and
arrangement
non-conjugated
quaternary
polypeptide,
e
In
one
together
s
s
polypeptides
During
the
process
of
development
from
Key
U
conception
through to six months aer birth, human
haemoglobin
changes
is
a
in
protein
composition.
Adult
gamma-globin
composed of two subunits
are
found during
gamma
globins.
Figure
17
i
and
polypeptides
dierent amounts: zeta, delta,
gestation and aer birth in a human.
which
two
subunits
are
early
gestation.
between the changes in
a
O
ofbeta
[1]
%
Distinguish
l
amounts
theamountof the gamma
v
3.
present in
thehighest
theamount
in
u
f
x
2.
State
nibolgomeah
the changes in haemoglobin composition during
1.
50
illustrates
t
a
r
o
epsilon
other
in
6
E
at
months
4.
State
the
5.
Suggest
of
reasons
composition
aer
birth.
of
30
20
10
[2]
0
10
weeks of gestation and
age.
source
40
globin with
globin.
Determine the composition of the
haemoglobinat10
for
weeks
[2]
oxygen
during
the
zeta-globin
epsilon-globin
o
Four
development
d
c alled globins. It has two alpha and two beta globin
beta-globin
delta-globin
alpha-globin
n
haemoglobin
subunits.
C
Data-based questions: Haemoglobin subunits during development
for
the
foetus.
[1]
▴
Figure
of
20
gestation
30
40
birth
2
4
month
6
of age
17
dierences in subunit
foetal
development and
[3]
205
Form and function
LHA
Experiments: Cryo-electron microscopy
A
haemoglobin
5nm.
This
is
far
for
Even
the
images
this
size
an
electron
microscopes
recently
fuzzy
blobs.
of
quaternary
be
determined
other
of
of
protein
molecules.
technology,
from
technology
carries out its task.
have
structures,
structures
interactions
discoveries
in
allows conformation changes to be revealed as a protein
were until
c an
now
between
As so oen with
this
has
research
led to a
labs
around
c ases,
proteins.
A
protein
grid
and
be
it.
thin
The
protein
of
using
been
ice
a
molecules
and
beam
developed
increase
the
images
of
for
are
c an
electrons.
processing
resolution.
At the
of
the
21st
century,
the
highest
i
n
▴
start
resolution
Figure
electron
was
about
cryo-EM
had
reduced
the
position
of
nanometre.
this
to
0.12
individual
By
2020,
nm.
This
atoms
in
a
image
of
the
protein
apoferritin
generated
by
cryo-
n
o
Relationship of form and function in
i
globular
The
function
considering
u
proteins
l
a
E
v
O
f
x
t
a
r
o
d
B1.2.12
of
and brous proteins
a
the
protein
consist
of
the
structures
such
as
by
together
linking
Collagen
bonds
is
an
polypeptides,
polypeptides
this
preventing
every
third
glycine
is
a
be
polypeptides
that
lack
helices.
of
a
repeating
in
brous
Their
proteins
quaternary
chains
brous
or
into
the
do
illustrated
proteins.
folding
not
structure
narrow
only
be
acid
a
triple
sequence
α-helix.
impossible
faces
amino
protein.
into
of
of
is
by
Fibrous
typic al tertiary
develop
secondary
developed
bres or laments, with
if
inwards
acid
with
The
The
they
The
which
has
winding
were
towards
an
quaternary
helix.
structure
primary
the
the
G
special
together
α-helices.
of
The
is
three
structure of the
three amino acids: P
hydroxyproline,
formation of an
would
hydrogenatom.
c an
globular
together
proline
amino
the
This
and
polypeptide
wound
is
form.
between the chains.
example
is
sequence
its
brous
polypeptides
alpha
on
between
elongated
Also,
hydrogen
depends
dierence
structure.
polypeptides
206
an
protein to be
discovered.
of
of
resolution
U
allows
1
Part
microscopy
C
possible
18
o
to
applied to a
v
has
images
is
many
plunged into liquid ethane
layer
obtained
Soware
the
a
sample
in
membrane
p
then
in
is
impossible
integral
y
ash-freeze
trapped
almost
with
r
e
sample
to
is
especially
O
t
i
s
(cryo-EM). It avoids the need to crystallize
n
The new technique is cryo-electron microscopy
proteins, which
l
y
the world.
X. The
P in
property
the
three
R-group of
centre of the triple helix and
R-group small enough to t: it is a single
y
wave
in
molecule
by
P
and
improvements
of
produced
e
tertiary
enables function to be investigated. The freezing technique
microscope to
r
imaging
so
proteins
light
Improvements
revolutionized
and
a
s
s
image.
small
produce
and
In addition to determining the form of proteins, cryo-EM
molecule has a diameter of about
too
Molecules
Figure
structure
wound
19
Collagen—the
consists
together
of
to
three
form
a
LHA
◂
quaternary
polypeptides
tough,
rope-like
protein
rope-like
high
X
tensile
faces
outwards
of
front
have
a
as
the
outer coat
white
rounded
of
shape,
the
of
eye).
formed
folding up of polypeptides. The shape is
intric ate
R-groups
of
is
the
together
examples
globular
of
the
by
to
the
precise
protein,
critic al
stabilized
amino
bonds
that
folding.
as
the
between
have
There
position
known
the
by
acids
of
been
are
many
each atom in
conformation,
protein’s function. The
site
of
receptors
show
this
relationship. Insulin is
example.
Only
an
insulin
Figure
20
molecule has
positioned
conformation
needed
to
bind
to
a
specic site
for
the
insulin
receptor.
sugar
allows
a
specic and
concentration is too high.
do
abiotic
factors
of
temperature
O utline
the
changes
in
pH
relationship
between
f
x
(C3.1.19)
What
the
relationship
the
mechanisms
(D2.2.2)
Outline
c.
Explain
the
E
b.
process
how
structure
between
a
Explain
v
O
a.
is
organism?
l
an
u
2.
of
a
of
enzyme
the
tertiary
the
behind
light
and
genome
the
receptor,
activity.
of
the
of
to
which
the
is
an
many
receptor
conveys
a
integral
body
(right)
signal
to
protein
cells.
It
there
the
that
is
has
a
is
conformational
a
interior
of
binding
site
thecell
proteins.
phytohormone
regulation
binds
of
(C1.1.8)
structure
and
(blue)
activity.
proteome of
transcription.
translation. (D1.2.5)
mutation
the
on
aect
molecules?
t
a
(B1.2.9)
c.
eect
of
o
why
form
i
the
Explain
the
d
Explain
b.
r
o
a.
inuence
the
insulin
receptor
membrane
n
How
in
U
Linking questions
1.
change
When
insulin
plasma
C
blood
This
to be sent to body cells when
i
n
unambiguous signal
insulin.
The
the
o
on
v
the
in
p
▴
another
y
active site of enzymes and the ligand-binding
r
e
being
and
O
brought
a
c artilage, basement
and the tough
y
proteins
many
for use in
t
i
s
the
the
allowing
produced
n
very
at
very
l
the
be
ligaments,
it
y
by
variable,
of epithelia
(visible
Globular
is
to
gives
R-group of amino acid
r
eye
collagen
P
the
and
collagen
tendons,
membranes
of
The
e
variations
skin,
structure
strength.
s
s
The
in
resulting
the
genome
polypeptide.
c an
lead to a change in the
(D1.2.11)
207
Form and function
TOK
What constraints are there on the pursuit
s
s
of knowledge?
born
tracts
(TPN).
For
that
it
the
would
This
is
as
skeleton
grown
in
have
fed
known
infant’s
have
be
poorly
nutrients
total
to
parenteral nutrition
grow
utero,
The
developed
through their
very
at
the
same
oen
enriched
in
a
to
be
dissolved
in
the
dierent
TPN
solution.
than
others.
The
question
is,
are
all
these
be
salt
end
up
determined?
bec ause
this
there
be
all
the
c alcium
bones
of
the
infant?
constraints
on
most
For
human
example,
it
is
removed
the
types
of
from
its
trials
model
How
for
c an this
investigation
c arried out.
must
be
preceded
by
argued that a piglet
before
it
is
weaned is a
p
o
C
n
Figure 2
been
prematurely born infants.
v
i
n
U
▴
has
mother
c alcium
from a highly
Investigating this question is a challenge
are
samples
y
c an
the
reason,
trials.
r
e
that
in
Does
or
Legitimately,
O
soluble
bioavailable?
isotope.
t
i
s
equally
radioisotopes
Dierent
concentrations, some
good
salts
of
stable
parents might nd mention of such investigations worrisome.
rate
that
higher
use
rare
n
to
particular
large quantities of
animal
dissolve
investigation of the metabolic fates of
l
salts
of
through
y
need
c alcium
standard
is
For
c alcium
gold
elements
A couple consults with a medic al professional.
Sucha consultation would normally occur in human trials of
nutrition through his blood vessels
infants
participation
attractive.
They
hopeful
that
in
the
human
committees
Informed
that
ensure
to
subjects
•
the
purposes
•
the
limits
on
of
the
beinvestigated.
208
also
restrictions
Ethics
boards
of
placed on the use of animals in
research
institutions
oen
have
guidelines that include:
•
providing
•
reducing
the
the
•
evidence
that
•
restrictions
•
providing
justic ation
for using animals
stress
might
medic al
total
number
of
individuals
used
seem
the
experiment
is
not
a
duplic ation of
experts
previous
are
Importantly,
governed
patient’
s
or
the
are
research.
research
treatment might be superior to
rights
by
are
investigations
their
require
in
the
details
protected.
transparent
guardians of:
experiment
ways
on
which
their
types
of
species
that
c an be chosen
research ethics
minimize pain.
procedures
E
disclosure
novel
to
There
is receiving
nancial
research
beholden
treatments.
subjects
consent
under
a
involving
feel
v
O
available
be
compensated
might
currently
may
l
or
unwell
u
and
of
f
x
Parents
o
The premature baby in an incubator
t
a
Figure 1
i
d
r
o
▴
medic al interventions
samples
c an
on
the
regimens
used to eliminate or
y
vessels.
oen
must
P
blood
infants
and
r
digestive
e
Prematurely
Molecules
End of chapter questions
1.
Migrating
flying.
A
of
must
study
refuel
was
migrating
along
the
conducted
birds
way to continue
among
four
3.
different
low-quality
food
samples
sites.
Birds
were
[3]
Cellulose
is
the
most
Describe
the
abundant
structure
organic polymer on
of
cellulose.
high
triglyceride
Compare
and
contrast
cis-fatty
acids
and
trans-fatty
concentration in blood
acids.
indic ates
concentration
in
fat
deposition
blood
plasma
whereas
high
butyrate
6.
indic ates fat utilization
Proteins
following
measured
for
triglyceride
the
same
of
Such
structural
and
was
LCC
proteins
were
0.8
HT
WS
W
and
The
diagram
below
LCC
protein
A
Witetroated sparro
W
D.J.
and
Source:
S
and
Biochemic al
Zoology,
78(1),
Butyrate
results
using
Site1
the
butyrate
Distinguish
the
and
triglyceride
Site2
differences
level
in
for
all
the
the
by similarities in primary
to
show family
shows
the
distribution
of
groups of
by kingdom.
plants
47
1
82
5
4
Schraegle, E
fatty
Meier,
birds.
17
BMC
Evolutionary
Biology, (2005),
5, p6
prokaryotes
[2]
a.
graph, the
triglyceride
presence of
Rose,
State
of
a
what
determines
the
primary
structure
protein.
[1]
[2]
b.
level and
Outline
of
the
concept
of
secondary
structure
proteins.
[2]
c.
State
how
many
groups
of
LCC
proteins
are
[2]
common
hypothesized
a
have
l
O
Scientists
levels
the
(LCC)
variety of
for the hermit thrush at Site1 and
Site2.
d.
between
u
Explain
acid.
triglycerides.
f
x
c.
at
fatty
i
Describe,
a
https://doi.
t
a
b.
is
and
r
o
acids
116–125.
o
a.
pp.
d
org/10.1086/425198.
wide
Stahlberg and
Eldermire, C. (2005)
I
Physiologic al
A
a
different kingdoms. The
analysed
304
n
Cerasale,
arbler
in
homology.
animals
Aerican robin
agnolia
then
sequences
C
Herit trus
WS
U
HT
grouped
were
relationships
species
ey
C.G.,
A
i
n
W
species
compare
from
o
0.0
involved
processes in cells.
to
p
0.2
0.2
out
species
each other into
coiled-coil
y
0.4
0.4
Guglielmo,
They
r
e
0.6
0.6
0.0
long
O
in
structure.
0.8
c arried
proteins
1.0
1.2
are
mechanic al
t
i
s
study
v
stinu yrartibra/noitartnecnoc
1.4
Source:
proteins
LCC
1.2
1.0
around
as
n
proteins.
A
1.4
A
known
birds.
1.6
WS
are
butyrate levels
1.8
HT
and
myosin consist of two or
levels and
groups
triglyceride levels
super-coil
and
winding
l
levels
summarizes
keratin
y
butyrate
data
as
helices
[2]
y
a
such
alpha
P
more
and fasting.
The
r
plasma
[3]
were taken at the two sites.
e
birds,
three named
c aptured and
5.
Among
specific functions of
known to stop at high-quality
E arth.
blood
the
proteins.
4.
and
O utline
s
s
species
birds
field
that
the
to
all
the
species
studied.
[1]
food quality is
d.
Deduce
the
found
all
signific ance
of
these
proteins being
better at Site1 than at Site2.
The
in
figure
this
E
2.
this
shows
v
Evaluate
hypothesis
a
using
the
data
L abel
one
peptide
bond
thespecies
studied.
[1]
C alculate
found
in
how
the
many
groups
prokaryote
of
LCC
proteins
are
kingdom.
[1]
molecule.
H
f.
O
H
O
O
C
C
N
C
C
C alculate
the
are
in
percentage
of
groups
analysed that
H
H
N
of
provided. [2]
e.
tripeptide.
in
N
C
g.
C
found
Deduce
that
the
animal
whether
plants
are
this
kingdom
data
only.
supports
moreclosely
the
[1]
hypothesis
related to animals than
OH
H
H
glycine
H
H
glycine
H
H
to
prokaryotes.
[2]
glycine
209
B
Fo r m
Cells
of
a
its
underlying
organisms
specialized
unique
structures
m i c ro s c o p e.
The
background
structure
a tt a c k i n g
as
its
prey
n
U
ejecting
its
as
t r i c h o c ys t s
well
and
ow n
as
are
not
observed
visible
using
m i c ro s c o p e,
is
s h ow i n g
Didinium
which
a tt a c h
ingests
cell
thus
u l t ra s t r u c t u r e .
image
o
a
t ox i n
ele ctron
Pa r a m e c i u m .
as
engulfs
seen
a
k n ow n
t ra n s m i t
an
k n ow n
C
i
n
organelles
of
is
composite
v
n as ut u m
of
a
be
to
y
level
p
u l t ra - m a g n i f i c a t i o n
this
r
e
the
c an
their
corresponds
within
These
within
in
n
the
light
s t r u c t u re.
Cells
O
a
and
specialized
structure
t
i
s
of
using
be
often
functions.
Some
then
are
shape
function.
l
Their
with
y
their
is
correlate d
y
multicellular
s t r u c t u re.
cell
often
P
are
e
form
Fo r m s
r
The
to
function
s
s
2
and
it.
to
h av e
the
The
t r i c h o c ys t s
to
Didinium
a tt a c k s
the
p r e y.
with
ability
Didinium
Pa r a m e c i u m
defend
i t s e l f.
c an
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
B2.1
Membranes and membrane transport
The
liquid
blobs
in
a
lava
lamp
are
a
s
s
How do molecules of lipid and protein assemble into biologic al membranes?
mixture of oils and
through
which
it.
Biologic al
membranes
separating
the
water-based
surfaces
for
of
What
lipids
the
be
water
outside.
Do
be
or
proteins
in
every
from
expect the
hydrophilic?
hydrophobic or
hydrophobic/hydrophilic
and
dye to
around
inside
you
hydrophobic
a
ever mixing?
frontier
cytoplasm
membrane
with
from
properties
are
membranes?
▴
Figure 1
O
t
i
s
needed
exible
environment
to
is
A lava lamp
n
the
a
water-based
membranes
hydrophilic?
form
fall
liquids
y
Will
of
and
two
l
interior
rise
the
y
the
blobs
prevents
P
cell,
the
What
r
colour
e
waxes, dissolved in a hydrophobic solvent. The other liquid,
y
p
r
e
What determines whether a substance c an pass through a biologic al membrane?
c an
and
How
bilayers
Simple
B2.1.4
Integral
B2.1.5
Movement
and
ions
needed
membrane
HL
of
do
by
this?
cell
B2.1.6
Channel
B2.1.7
Pump
across
water
proteins
B2.1.8
Selectivity
B2.1.9
Structure
proteins
in
for
Fluid
Cholesterol
B2.1.13
Membrane
across
membranes
by
model
of
and
G ated
Sodium–potassium
B2.1.16
membrane
membrane uidity in animal cells
B2.1.15
permeability
glycoproteins and
and
uidity
B2.1.14
exchange
of
fatty acid composition of
the
fusion
and
formation of
vesicles
transport
active
only
between
bilayers and their uidity
ion
channels
in
neurons
pumps
as
an
example of
transporters
Sodium-dependent
example
B2.1.17
mosaic
Relationships
B2.1.12
membranes
glycolipids
B2.1.10
B2.1.11
lipid
in
wearing a surgic al mask
AHL
facilitated diusion
function
Dentist
membranes
molecules
for
Figure 2
proteins
membrane
and
▴
membranes
role of aquaporins
E
the
a
basis
peripheral
of
easily?
barriers
diusion
and
Which
more
between ions such
allow
a
B2.1.3
as
particles.
l
Lipid
the
v
O
B2.1.2
as
very
u
f
x
SL
bilayers
and
only
could
are
t
a
enter.
exclude
between
membrane
discriminate
C
hydrophobic
a
pores in a
to
membranes
distinguish
through
and Cl
to
Lipid
osmosis
c an
What
dentist’s
n
and
largest
intended
+
, K
cell
B2.1.1
the
was
r
o
Na
the
it
a
i
+
as
if
through.
through
o
Membranes
should
pass
pass
Biologic al
and
pass
to
allow particles
to
d
will
and
size
able
be
particles?
sophistic ated
type
be
size
mask
hydrophilic
pore
U
virus
must
What
dentist’
s
porous
the
i
n
particles
mask?
are
than
o
masks
smaller
v
F ace
of
indirect
Adhesion
active
of
cells
glucose
cotransporters as an
transport
to
form
tissues
structure
211
Form and function
B2.1.1
Lipid bilayers as the basis of
cellmembranes
Membranes
border
cells
divide
the
membranes
despite
an
is
cells.
its
cytoplasm
into
compartments.
a
10
same.
A
The
plasma
Membranes
The
basic
membrane
inside
structure
forms
eukaryotic
of
all
biologic al
bilayer of phospholipids and other amphipathic
continuous
nanometres
their
environment.
sheet
or
that
less
arrangement
controls
across.
into
The
bilayers
is
the
passage of substances
structure of phospholipid
described in
Topic
B1.1.
r
and
of
and
forms
a
component
cell
the
being
molecules
essential
e
molecules
are
between
s
s
the
l
i
B2.1.2
u
The
tails
l
form
the
of
molecules
the
core
of
biologic al
a
to
charges
polar
There
and
are
E
solutions
are
in
all
usually
are
have
phospholipids
permeability
in
a
molecules
aqueous
continuous
particles,
such
so
“head”
hydrophobic
on
both
motion.
Due
to
and
and
this,
including
two
interact
the
ions
hydroc arbon
with
“tails”.
each other to
membrane
withpositive
core
or
has
low
negative
asglucose.
solutions
state,
random
phosphate
membranes.
hydrophilic
liquid
a
are
either
water
The
side
of
cell
molecules
solutes
nearest
membranes. These
and
to
hydrophilic solutes
the
membrane surface
might penetrate between the hydrophilic phosphate heads of the phospholipids,
but
to
if
they
the
reach
aqueous
chains
212
Lipid bilayers as barriers
Phospholipid
v
O
f
x
t
a
r
o
d
small compartments
n
vesicles and
cisternaethat divide the cytoplasm into
O
below
y
and
p
many membrane-bound
o
it
a nuclear
the top
o
In this image,
membrane is visible at
C
very clearly.
n
U
micrographs of cells show membranes
that
the
hydrophobic
solution
form
the
outside
core
of
the
core
the
of
the
membrane
membrane.
membrane
do
The
not
they
are
drawn back
hydrophobic
repel
hydroc arbon
hydrophilic solutes but
y
P
y
t
i
s
r
e
Freeze-fracture electron
v
Figure 3
i
n
▸
Cells
they
are
water
more
outside
Molecular
size
molecule,
are
only
also
the
slightly
than
each
inuences
lower
larger
large
to
other,
and
the
solutes
are
much
more
attracted to
membrane.
the
than
membrane
permeability.
single
molecules
such
permeability.
The
For
water
oxygen
as
atoms,
glycogen
hydrophobic
example,
or
pass
trend
is
that
the
larger
molecules which
through
membranes
s
s
the
easily
attracted
the
more
protein.
hydrophilic
phosphate
core
the
e
membrane
heads on
surface
of
the
r
membrane
l
n
O
y
v
p
Figure 4
y
P
y
t
i
s
r
e
◂
The hydrophobic core of the membrane has
low permeability to polar molecules such as glucose (blue)
cell
the
inside
cell
charged
c an be kept
particles such as chloride ions (green) so they
either in or out
U
C
the
i
n
outside
cytoplasm
o
and
aqueous solution
of a cell,
whereas small non-polar
molecules such as oxygen (red) c an pass through freely
Data-based questions: Membrane permeability
graph
in
Figure
5
Progesterone
shows
is
a
tails
v
0
E
75
substances
substances
heads
at
are
dierent
drugs.
distances
Free
energy
from
is
the
centre of a phospholipid
reduced
by
bond
formation.
water
ey
MM4
diaepam
Source:
Chem.
J.
B
Phys.
2017
, 121,
theophylline
20,
a
25
six
u
l
eerf
O
ygrene
f
x
lom Jk /
0
of
other
t
a
r
o
1
25
level
the
hydrophilic
50
50
2M
5228–5237 April
28, 2017
promaine
progesterone
1
distance
▴
and
i
hydroc arbon
75
energy
d
125
100
the
hormone
o
bilayer.
n
The
2
from
bilayer
3
centre
4
/ nm
Figure 5
213
Form and function
1.
Compare
and
contrast
a.
MMB4
and
b.
promazine
the
energy
levels of:
3.
2-PAM
Using
the
diagrams
hydroxyl (
[2]
OH)
and
groups
the
graph,
make
explain whether
molecules
more
or
less
hydrophilic.
and
progesterone
4.
Deduce
from
the
curves
in
the
Four
membrane
permeability
c ategories
have
been
graph, which of the
dened:
impermeable,
low,
medium, and high.
six substances is:
At
most
hydrophobic
[2]
b.
most
hydrophilic
[2]
least
one
Suggest
5.
Predict
of
one
the
the
drug
ve
for
drugs
each
permeability
is
in
each
c ategory.
c ategory.
c ategory
[4]
for
r
progesterone.
e
a.
s
s
2.
[2]
[2]
[1]
the
the
of
opposite
higher
to
the
easily.
through
the
centre
positive
and
easily
negative
o
phospholipids
pass
through
of
more
i
the cornea
is
diuse
easily
to
only
by
down
of
the
move
than
particles
move
from
concentration
particles
happen
if
passing
the
such
a
higher,
as
cell
is
between
phospholipid
oxygen
reduced
oxygen
will
bilayer
c an diuse
due
to
aerobic
pass into the cell
passive diusion.
over
so
Polar
their
membrane.
than
particles
energy to make diusion occur; it is
inside
is
More
concentration
movement
particles
outside
through.
charges
the
due
c an
hydrophobic,
n
c annot
is
use
concentration
membrane
membranes
charges
the
oxygen
It
net
movement
to
Non-polar
concentration
plasma
of
membranes
membrane.
particles.
the
the
have
a
lower
ions
surface,
Small
with
positive
molecules,
polar
c an
which
diuse
particles
at
or
negative
have partial
low
such
as
rates
between
urea or ethanol
large particles.
has no blood supply so its cells obtain
t
a
oxygen by simple diffusion from the air
high concentration
of oxygen in the air
u
air
high concentration
fluid (tears)
l
cell
Model of diusion
of oxygen in the tears
on outer
that coat the cornea
a
surface of the
with dots representing particles
cornea
v
E
oxygen passes through
the plasma
membrane by
simple diffusion
▴
214
d
r
o
f
x
O
Figure 6
U
The
If
and
not
C
respiration
the
i
n
through
to
the
therefore
motion.
of
o
permeable
across
in
do
area
p
diusion
is
random
an
concentration—a
organisms
v
is
There
to
y
process.
continuous
r
e
a
phospholipids
▴
lower
Living
Simple
in
concentration
direction.
gradient.
passive
are
higher
O
in
spreading out of particles in liquids and gases that happens
particles
area
n
the
y
bec ause
an
the
t
i
s
is
from
l
Simple diusion across membranes
Diusion
Figure 7
Passive diusion
lower concentration
of oxygen in the cornea
cells due to aerobic respiration
y
P
B2.1.3
Cells
Data-based questions: Diusion of oxygen in the cornea
Oxygen
concentrations
anesthetized
These
at
were
measured
dierent
measurements
in
distances
were
the
cornea of
1.
C alculate
from the outer
400
8
shows
humor
behind
the
cornea.
micrometres (400 µm)
the
diagram
of
measurements.
eye
structure
thick.
You
before
concentration
in
The
The
may
rabbit’
s
graph
in
a.
Describe
the
trend
inthe
cornea
in
oxygen
inner
surface.
[2]
need to look at a
b.
Suggest
reasons
a.
Compare
for
the
trend
air
is
20
in
the
the
oxygen
with
the
concentrations
the
data
in
a
data
method
fo
multicellular
10
5
the
400
U
varied
their
twogroups.
proteins
therefore
proteins
E
membrane.
this
to
the
to
the
with
on
them
often
them
of
wearing contact lenses
this
for
eect
each
data
measurements
showing
in
the
could
cornea.
be
point
minimized.
indic ate
[1]
[1]
how
varied. Explain the
range
bars
on
the
graph.
[2]
Figure 8
are
are
is
very
be
chains
in
diverse in
divided into
the
phospholipid
transmembrane
hydrophilic
on
are
c an
least part of their surface and
two
parts
centre of the
layers
or
extend
proteins—they
projecting
through the
side.
their
attached
reversible.
which
membrane
at
either
hydrophilic
of
is
on
They
hydroc arbon
proteins
heads
are
Most
attachment
attached
protein
one
proteins
membrane.
the
membrane,
phosphate
Peripheral
in
a
the
fit
in
integral
v
O
across
of
may
M any
membrane
the
hydrophobic
embedded
They
both.
regions
are
in
l
membrane.
functions,
position
u
f
x
Integral
chain
how
bars
of
[2]
n
in
i
these
t
a
and
and
◂
eect
large
o
d
of
structure
r
o
Bec ause
the
range
the
in
Integral and peripheral proteins in
membranes
extend
The
reasonfor
distance from outer surface of cornea/µm
across
Suggest
C
300
b.
much
substances
concentrations
o
i
n
200
6.
moving
[2]
evaluate diusion
y
Predict
graph,
p
r
e
a.
the
cornea to the
organisms.
onoxygen
v
n o it a rt n e c n o c
5.
of
in
the
[2]
deduce if
n
as
the
graph,
O
Using
y
4.
the
from
aqueoushumor.
t
i
s
aPk / negyxo
oxygendiuses
15
0
•
Using
y
humor
cornea.
l
b.
the
[2]
concentrations in the
P
in
are
oxygen
cornea.
kilopasc als
aqueous
•
in
answering the questions.
normal
20
B2.1.4
concentrations
from the outer to the
Figure
3.
100
cornea
cornea
(20 kPa).
0
rabbit
r
oxygen
the
[1]
concentration
The
of
e
is
thickness
continued into the
2.
aqueous
the
inmillimetres.
s
s
surface.
rabbits
surface,
to
Some
inserted
into
the
have
the
so
are
surface
a
not
of
single
embedded in
integral
proteins
hydroc arbon
membrane, anchoring the
surface.
215
Form and function
Membranes
oriented
so
proteins
in
pick
the
protein
content.
plasma
varies.
of
of
from
more
in
a
the
the
the
a
face,
cells
in
pump
very
plants
them
variable
membrane,
sheath
of
membrane
For
are
into
proteins
oriented so that they
the
higher
nerve
18%.
root cell.
is
its
protein
bres just act as
Most
are
example, pump
bec ause the function of
the
around
about
and
correctly.
plasma
membranes
protein content of about 50%. The highest
active
in
found
in
the
membranes
photosynthesis
and
of
r
75%—is
mitochondria,
are
root
a
content
have
outer
function
and
is
active
protein content—about
which
of
soil
myelin
protein
cell
an
their
membranes
The
have
and
out
e
and
face
c arry
membranes
ions
content
outside
inner
c an
Membranes
insulators
the
an
they
potassium
membranes
on
have
s
s
The
up
all
that
chloroplasts and
respiration.
l
n
molecules
Figure 9
The protein shown blue is a
receptor for the hormone EGF (epidermal
growth factor).
It
Water
c an
move
in
and
out
molecules
moving
in
and
out
most
more
molecules
move
isosmosis.
cells
also a protein but
binds to the exterior
as it
shown red, is
it
is
due
to
dierences
is a peripheral
(solutes).
Substances
rather than an integral protein.
of
that
water
These
regions
molecules
concentration.
lower
c an
cells
have
i
permeability
hair
At
cells
its
that
of
free
this,
small
to
in
all
channels
water.
absorb
cells
enough
movement
than
net
pass
is
of
regions
water
through
kidney
This
net
substances
the
higher
number
water
have
with
of
movement
dissolved in
bonds
a
with
water
lower
concentration
lower solute
water
from
regions
concentration. This
expended
to
make
it
occur.
molecules, despite being
the
phospholipid
which
cells
greatly
that
bilayer. Some
increase
reabsorb
membrane
water,
and
root
from the soil.
u
l
point
in
the
which
channel
therefore
prevent
pass
through
protons (H
a
E
v
O
f
x
molecules,
in
single
le.
Positive
+
this
water
At other
molecules. This
a
solute
of
movement.
intermolecular
directly
aquaporins,
are
of
the
net
other.
movement
with
energy
bec ause
Examples
the
no
concentration
move
is
is
narrowest point, the channel in an aquaporin is only slightly wider than
water
▴
forming
regions
to
c alled
water
by
there
no
or
concentration
solute
to
to
bec ause
happen
are
water
t
a
r
o
d
hydrophilic,
passive
the
higher
concentration
o
Osmosis
is
a
are
Bec ause
solute
movement
with
that
the
restrict
n
U
of
bonds
in
dissolve
Sometimes,
there
direction
C
means
i
n
molecules.
one
and
o
water
v
Osmosis
surface of the receptor,
in
freely.
same
p
EGF,
the
y
times,
bilayer (orange = hydrophobic region and
purple = hydrophilic).
is
r
e
bec ause it is embedded in the phospholipid
216
of
is an integral protein
O
of aquaporins
▴
t
i
s
acrossmembranes by osmosis and the role
Figure 10
Structure of an aquaporin
)
from
passing
through.
charges at
y
P
Movement of water
y
B2.1.5
Cells
(a)
B2.1.6
Channel proteins for
facilitated
diusion
Ions
and
polar
of
of
proteins
protein
cell.
that
acting
with
a
The
only
as
pore
that
type
of
easily
across
channels.
diameter
one
c annot
substances
A
of
a
pore
pass
the
and
protein
cytoplasm
the
passes
between phospholipids, but
membrane
channel
connects
particle
a
is
still
is
an
to
chemic al
possible with the help
integral,
the
properties
through—for
transmembrane
aqueous solution outside
of
its
sides
ensure
(b)
example, sodium ions or
the
is
by
c an
occur.
that
changed
when
these
in
on
to
the
the
does
the
a
energy
be
(the
more
require
required
for
is
through
side
of
stable)
to
energy.
active
is
against
channel
particle
the
the
two
c an
or
a
the
Most
dierent
(the
pump
the
allows
The
cell
is
site.
The structure of the protein
the channel ensures that only
magnesium
ions c an pass through the pore
is
already
membrane
whereas
one
always
direction,
protein
gradient,
down the
from one side of
The
ion
pump
or
stable),
protein
molecule to
protein
protein
use
making up
conformations. In
pump
proteins
Every
in
membrane.
channel viewed
from the outside of the
from channel
channel
pump
the
the
less
the
concentration
proteins
change
other
transport.
the
binding
which
to
ways
a
M agnesium
the side and
even though
in
transport,
through
enter
membrane.
used
inside
out
membrane
direction
chamber
Energy
active
passive
between
conformation,
three
Figure 11
from
in the centre
concentration
proteins
in
▴
temporarily
membranes:
out
across
either
the
substances
Pump
dier
across
c arry
particles
central
other
opposite
not
move
transported
reach
E
change
in
diffusion
conformation.
conformations
by the types
o
out
original
out
membrane. Some
c an
i
pass
and
concentration
t
a
changes
to
they
interconvertible
the
proteins
particles
move
usually
v
then
its
are
so
gradient.
conformation,
membrane
in
plasma
against
pump
outside.
proteins
move
c an
for the
between
active transport
the
absorbed
particles
a
the
proteins
Pump
l
one
O
Pump
tasks.
channel
facilitated
concentration
is
u
f
x
whereas
diuse
the
permeability
sometimes
energy
only
particles
proteins
cells
transport
use
through
proteins
whereas
pump
in
though
concentration
r
o
pump
•
they
proteins
diffusion
•
higher
transport
how
pump
so
d
•
a
even
substance
commonly,
already
proteins
required
p
out
The
energy
o
c arry
placed
closed,
substances,
outside.
Less
are
movement
necessary.
some
No
C
is
be
n
there
substances
and
U
gradient.
proteins
would
membrane
cytoplasm
There is
lower.
v
than
the
membrane.
hydrophilic
and
channel
here
Pump proteins for
absorb
higher
diusion
synthesized
opened
versa.
to
more
movement, so it is a type of diusion.
bec ause
the
vice
i
n
Cells
be
this
than
concentration
but
y
c an
in
higher
direction,
r
e
channels
B2.1.7
which
are
c ause
Simple
molecules
select
channel
to
diusion
concentration
the
either
O
of
cell
lower
from
in
t
i
s
to
phospholipid
Cells
the
facilitated
movement
the
through
n
expended
It
to
movement
pass
y
is
c alled
higher
net
to
l
a
particles
y
from
therefore
allow
P
pass
proteins
r
potassium ions, but not both.
Channel
e
the
molecules
these
s
s
diusion
returns to
from one of the
but
the
reverse
ATP to supply
produces
its
own
ATP
by
cellrespiration.
▴
Figure 12
Action of a pump
transports Vitamin B
into
protein that
Escherichia coli
12
217
Form and function
The
membranes
transfers
to
one
control
required
in
the
the
by
of
cells
specic
a
content
cell
to
contain
type
of
be
of
its
many
particle
dierent
across
cytoplasm
absorbed
pump
the
precisely.
even
when
proteins,
membrane.
It
also
they
are
allows
in
each of which
This
very
allows the cell
specic solutes
low
concentrations
environment.
s
s
Data-based questions: Phosphate absorption in barley roots
were
phosphate
in
the
used to
An
were
membrane
placed
experiment
air
was
bubbled
through.
phosphate.
concentration
was
the
in
as
percentages
air
bubbled
was
of
through.
measured.
/%
0.1
99.9
The
1
each
nitrogen
were
Phosphate
the
with
DNP
results.
blocks
respiration.
–1
g
of
the
a
used
oxygen
substance
13
by
the
roots to absorb
placed in the phosphate solution
production
Figure
absorption/
μ mol
21.0%
concentrations
rate of phosphate
shows
before,
was
were
bubbling
c alled
of
shows
ATP
the
through.
DNP
by
were
aerobic cell
results
of
the
0.4
–1
h
0.3
0.07
Varying
added.
experiment.
O
Nitrogen
/%
Table
same
and
Roots
t
i
s
Oxygen
oxygen
was done to test which method of
transport
n
absorption
and
and
Roots
y
varied
the
plants
l
but
barley
absorption.
solutions
phosphate
c ase,
from
phosphate
0.27
2.1
97
.1
0.32
21.0
79.0
0.33
absorption
/μmol
the
eect
of
below
reducing
21.0%
phosphateabsorption
Explain
the
eect
of
by
roots.
Table
1
answer,
the
absorb
mineral
oxygen
0.1% on phosphate
as
possible of
ions.
6
8
10
3
Eect of DNP concentration on phosphate absorption
Deduce,
with
a
reason,
whether
phosphate
by
the
roots
diusion
or
by
4.
Discuss
from
the
[2]
conclusions
thedata
in
the
that
c an
be
drawn
graph about the method of
membranetransport
used
by
the
roots to absorb
phosphate.
[2]
[3]
u
l
a
E
v
O
f
x
B2.1.8
Selectivity in membrane permeability
A semi-permeable membrane allows the passage of certain small solutes and is
freely permeable to the solvent. This describes articial membranes of the type that
are used for kidney dialysis, but it does not match the permeability properties of cell
membranes, which show more selectivity and have variable permeability to water.
A
selectively
not
others.
bec ause
A
channel
chloride
size
and
from
permeable
F acilitated
for
However,
polarity
passing
membrane
diusion
proteins
channel,
membrane.
218
4
activetransport.
you should use as
understanding
Figure 13
absorbedthe
[3]
t
a
r
o
howcells
to
▴
3.
answer.
i
21.0%
your
2
concentration / mmol dm
You should only
your
d
from
absorption.
muchbiologic al
in
reducing
concentration
In
oxygen
rate of
o
2.
from
the
the
0
DNP
n
useinformation
on
U
concentration
0
C
Describe
0.1
o
Table 1
0.2
1
h
v
1.
i
n
▴
1
g
y
0.15
99.1
p
99.7
0.9
r
e
0.3
of
and
cell
allows
active
pump
example,
simple
particles.
across
and
proteins
allows
diusion
Small
the
only
is
passage of particular particles, but
transport
not
are
selective
permeability
chloride
ions
to
diuse
across the
selective and depends only on the
hydrophobic
membranes.
allow
specic to particular particles.
particles
c annot
be
prevented
y
The
o
P
in
cut
phosphate
r
investigate
e
Roots
Cells
Bec ause
cell
membranes
permeable,
they
these
are
terms
are
partly
sometimes
widely
semi-permeable
described
as
and
partially
partly
selectively
permeable—all
three of
used.
s
s
B2.1.9
are
Structure and function of
glycoproteins and glycolipids
cells,
the
the
and
an
the
cell
layer
on
solution
The
preventing
the
in
outer
cells,
so
tissue
of
is
They
and
the
adjacent
or
chain
two
the
between
Glycolipids
attached
environment of the cell.
described in
help
the
Section B1.1.7.
immune
and
glycolipids
foreign
system to
tissue
together
c an
form a
membrane of animal cells,
c arbohydrates.
cells
of
hydroc arbon
membranes.
plasma
the
short
with
pathogens
between
of
of
cells,
recognition
face
gaps
core
a
one
extracellular
recognition.
glycoc alyx
the
the
Glycoproteins
the
contains
eukaryotic
into
non-self
destroyed.
glycoc alyx.
and
and
usually
c an
This
layer is
fuse, binding the cells
C
together
self
all
cell-to-cell
in
c arbohydrate
linked to lipids. The
or
i
n
c alled
aqueous
in
role
c arbohydrates
hydrophobic
outwards
membrane of
the
o
with
a
of
monosaccharide
part
of
and
v
c arbohydrate-rich
the
plasma
y
have
between
recognized
into
the
p
be
projecting
also
lipid
membranes
glycoproteins
Glycolipids
distinguish
t
single
The
of
membrane
r
e
of
naturally
plasma
c arbohydrate
role
units.
a
the
environment of the cell.
consisting
usually
in
y
sugar
which
in
is
exterior
c arbohydrate as the non-
O
occur
molecules
part
embedded
the
with
component
t
i
s
chains,
four
into
a
n
and
part
are
y
two
out
proteins
They
l
are
c arbohydrate
The
protein
projecting
Glycolipids
conjugated
P
part
with
are
component.
r
polypeptide
e
Glycoproteins
from falling apart.
n
U
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
◂
Figure 14
endothelium
The glycoc alyx of
cells in blood
projects into the lumen.
c apillaries
In this brain
c apillary the glycoc alyx is particularly dense
and
It
forms part
of the blood–brain barrier.
prevents plasma cells and
proteins from
circulating
binding to the c apillary wall,
which reduces the chance of inammation
and
blood
clotting.
219
Form and function
B2.1.10
Fluid mosaic model of membrane
structure
Several
In
this
models
is
now
model,
positions.
protruding
is
layers
bilayer
proteins
embedded
on
the
one
or
in
both
the
bilayer,
by
been
evidence
phospholipids
attached
to
phospholipid
sides.
The
molecules
the
have
proteins
the
proteins
are
to
c an
also
move.
This
surface.
Integral
the
tiles
in
in
a
mosaic.
each of the
n
the hydrophobic
core of the membrane
O
y
p
o
phospholipid
bilayer (about
8nm
o
d
integral proteins
peripheral proteins
i
attached to the
bilayer with a
membrane surface
transmembrane
protein on the left
u
f
x
t
a
r
o
embedded in the
mosaic model of membrane structure
l
a
E
v
O
LHA
B2.1.11
Relationships between fatty acid
composition of lipid bilayers and their uidity
S aturated
bilayers,
fatty
acids
giving
membrane
and
a
have
high
therefore
contrast,
unsaturated
chain,
they
uid,
so
exible
pack
and
straight
density
its
fatty
of
chains
exibility
acids
together
have
more
permeable.
and
therefore pack together tightly in
phospholipids.
This
reduces the uidity of the
and
permeability
one
or
loosely.
more
This
by simple diusion. In
kinks
makes
in
the
their
hydroc arbon
membranes
more
y
l
cholesterol
n
U
C
chains would
replaced.
embedded in
protein
r
e
i
n
(unsaturated
hydrocarbon
be
variety of
gives the model its
channel
v
hydrophobic tails
of phospholipids
to
to
a
c ases with parts
laterally
y
of a glycoprotein
head of
220
move
t
i
s
carbohydrate part
phospholipid
Fluid
outer
some
pore
phosphate
Figure 15
or
in
in
through
hydrophilic
▴
unlikely
mosaic model.
have kinks
have kinks)
is
likened
free
unsaturated chains
glycolipid
it
proteins
inner
are
straight chains whereas
carbohydrate
with
bilayer,
saturated hydrocarbon chains have
part of a
proposed but one particular
that
P
uid
of
are
the
phospholipid
of
name—the
a
structure
supported
r
two
there
Peripheral
are
Bec ause
membrane
strongly
e
proteins
of
so
s
s
model
Cells
the
amounts
membranes
strong
enough
to
too
porous.
the
temperatures
been
saturated
The
the
avoid
ideal
found
that
to
of
cell
have
sh
unsaturated
fatty
acids
are
properties.
They
must
remain uid but be
becoming
ratio
a
and
required
a
from
perforated.
saturated
to
experiences.
higher
For
must
example,
percentage
warmer
They
unsaturated
of
▴
A membrane containing only saturated
sh
from
unsaturated
Antarctic
waters
fatty acids in their
waters.
e
than
permeable but not
fatty acids depends on
r
membranes
be
regulated so that
s
s
have
of
have
LHA
Relative
fatty acids (right)
O
n
unsaturated
l
and
more
than a membrane
t
i
s
containing both saturated
fatty acids (le) is thicker,
a higher melting point
y
P
has a higher density of phospholipids and
y
Figure 16
viscous,
Data-based questions: Frost hardiness and double bonds in chickpeas
in
the
cells.
The
was
eectiveness
investigated.
leak out of
The
spraying
the
close
to
produced
treatments
treatments
by
keeping them at
freezing
of
by
the
preventing
were:
point
leaves
plants
in
for
with
two
response
weeks
to
2 weeks warm 
alied
o
i
Figure 17
–12
50
–10
that
shows
State
killed
the
the
3.
only
eects
of
Deduce
the
ABA
the
assessed
50%
of
leaf
membrane
(double bond
by nding the
cells.
The
graph in
between
LT
and
index.
data
in
the
eects
of
[1]
relationship.
on
of
the
are
have
raised
in
planting
them
whether
spraying
a
and
to
with
likely
plants.
ABA
or
be
2
[2]
o ” plants that
greenhouse
colder
to
[2]
unsaturated
“harden
warm
in
plants.
treatment on the
chickpea
outside
is
graph, outline the
cold
advised
in
[2]
chickpea
saturated
acclimatization
–8
unsaturated
treatments
results.
Gardeners
been
was
relationship
the
proportions
4.
and
the
50
Explain
Using
aer
hardiness
membranelipids
t
a
LT
a.
b.
alied
u
–14
a
–16
E
v
O
–18
l
1.8
f
x
elbuod
2.0
▴
d
2 weeks old 
r
o
xedni dnob
2 weeks old no 
2.2
Frost
17
saturated
doublebond
2.
2.8
2.4
1.
stress.
2 weeks warm no 
2.6
Figure
of
measured
temperature
n
3.0
index).
ABA, a
U
hormone
plants
outside
two
were
C
temperatures
of
of
The
proportions
lipids
o
acclimatization
•
to
i
n
•
cytoplasm
v
leakage
c ause
chickpea plants (Cicer arietinum). This kills
y
cells
p
temperatures
leaf
r
e
Freezing
before
conditions.
Discuss
weeks of cold
more
eective.
[3]
–6
(C)
221
Form and function
LHA
B2.1.12
Cholesterol and membrane uidity
in animal cells
Cholesterol
CH
3
CH
2
CH
CH
2
a
CH
glyceride.
2
Most
of
a
it
is
attracted
of
the
to
the
It
is
a
steroid
molecule
hydrophobic
membrane,
OH)
is
rather than
hydrophobic
but
one
hydroc arbon tails in the
end
heads
the
positioned
is
of
the
periphery.
between
group
between
hydrophilic.
molecule has a
This
Cholesterol
phospholipids
usually
saturated
facing
rather
in
is
the
outwards.
than
attracted to the
molecules
It
are
membrane,
preferentially
unsaturated
l
hydroc arbon chains.
The
uidity
of
too
The structure of cholesterol
what
inexible,
to
burst.
cell
Cell
substances
movement
pass
would
membranes
do
be
not
a
as
stiening
of
and
controlled. If
able
to
control
were too viscous and
the
exactly
of
cell
to
laterally.
would
any
of
be
the
more likely
three states of
sodium
Cholesterol helps to maintain
phospholipids.
temperatures,
fatty
less
ions
acid
and
tails
Cholesterol
maintaining
hydrogen
do
not
therefore
impermeability to
ions.
solidify
at
Cholesterol also
low
temperatures,
themembrane.
Membrane uidity and the fusion
n
is
cells
the
as
cell
sac
most
there
to
bec ause
small
and
i
of
a
o
vesicle
spheric al
is
a
membrane
the
to
membrane
cells
continuous
transport
of
of
eukaryotic
their
uidity
change
of
with
cycle
contents
of
and
membranes,
shape
and
a
droplet
contain
them.
making
then
of
uid
They
vesicles,
unmaking
which
allows
inside.
are
a
very
Vesicles
are
dynamic
feature
moving them within
them.
This
structures
c an happen
surrounded
by a
move.
u
membrane and is pinched o. Proteins in the membrane carry out this process,
l
a
E
v
O
f
x
t
a
r
o
d
A
To make a vesicle, a small region of a membrane is pulled from the rest of the
using energy from ATP
. If a vesicle is made from the plasma membrane by pinching
a small piece of it inwards, the vesicle will contain material that was outside the
cell. This is method of taking materials into the cell and is calledendocytosis.
Vesicles
Oen,
the
vesicle
made
they
plasma
blood,
cells
by
larger
membrane.
including
take
endocytosis
contain
in
large
contain
molecules
For
example,
antibodies,
are
undigested
organisms including
blood
take
cell
in
pathogens
in
the
absorbed
food
unicellular
water
and
needed
solutes
the
cell
placenta,
into
particles
the
from outside the cell.
that
c annot
proteins
foetus
kill
them.
This
is
part
of
the
body’
s
from
pass
the
across
mother ’s
by endocytosis. Some
by endocytosis. This happens in
Amoeba and
including
by
Paramecium. Some types of white
bacteria
and
viruses
by endocytosis and
Formation of a vesicle by
then
endocytosis
such
saturated
they
be
and formation of vesicles
exterior
Figure 19
higher
c arefully
liquid-ordered phase. The lipid molecules are
move
C
U
B2.1.13
to
If
o
preventing
ENDOCYTOSIS
cell interior
that
at
v
particles
ensure
i
n
so
to
free
arrangement
membranes
hydrophilic
helps
orderly
still
be
y
stabilizes
are
to
would
p
necessary
but
through.
restricted
r
e
the
densely
they
correspond
matter—they are in what is c alled a
packed
needs
uid,
O
Figure 18
membranes
were
t
i
s
membranes
n
hydrophobic
y
hydrophilic
response
to
infection.
y
hydroxyl
interc alates
HO
on
which
P
the
group
r
phosphate
3
with
222
eukaryotes.
e
centre
therefore
▴
of
cholesterol
3
hydroxyl (
▴
between 20% and 40% of the lipids in
3
CH
CH
up
membranes
CH
so
CH
plasma
s
s
the
CH
makes
3
Cells
c an
be
the
contents
the
membrane
vesicle
the
of
used
the
of
contents
rough
When
have
they
vesicle
the
membrane
Digestive
in
enzymes
a
and
for
useful
in
with
is
hormones
is
the
cells
for
In
this
are
a
rER.
Vesicles
apparatus.
target
plasma
membrane
membrane, the
exocytosis.
or
unwanted materials. An
of
unicellular
a
contractile
expulsion
Golgi
being
by ribosomes on
the
Golgi
with
c alled
c alled
the
exocytosis.
substance
protein
the
membrane
processed
fuse
the
proteins in
moving the
transferring all the contents of
products
from
sometimes
plasma
vesicles
bec ause
fuses
process
waste
water
vesicle,
been
This
expel
excess
the
vesicle
to
of
by
apparatus
c ase,
the
released,
secreted
in
vacuole,
exocytosis.
are
c arried to the
release
not
this
EXOCYTOSIS
organisms.
a
is
referred to
waste
product.
way.
the
v
E
rER
Vesicles
fuse
each
plasma
and
synthesize
bud
then
the
rER
increasing
the
area
method
is
membrane
inserted
membrane
o
same
mitochondria
y
of
the
membrane.
The
o
C
n
o
area
Ribosomes
it,
i
the
synthesized
with
t
a
cell,
are
amount.
Fusion of a vesicle with the
There
vacuoles in the cytoplasm of the cell
Phospholipids
on
Figure 20
membrane in exocytosis
u
growing
a
a
l
In
▴
The large vesicle in the centre of this Amoeba is a contractile vacuole.
are also many food
exterior
p
r
e
v
i
n
U
d
r
o
f
x
Figure 21
O
▴
vesicle
O
secretion,
a
vesicles
inside
c ases, it is
is
n
have
a
to
If
cell.
them
of
example
it
y
as
that
to
c arry
eect
some
t
i
s
plasma
into
moved
Polypeptides
of
and
the
In
c ases,
synthesized
accumulates
rER
has
is
An
and
destination,
This
moved.
Protein
cells.
other
y
loaded
then
the
the
used
cells.
(rER)
be
In
l
is
be
to
inside
moved.
P
also
removal
is
their
from
the
water
o
membrane.
expelled
c an
which
bud
around
be
need
secretory
process.
example
is
that
to
r
are
the
need
reticulum
reached
in
Exocytosis
The
in
proteins
across
contents
vesicle
occurs
materials
that
e
disappear
move
s
s
the
a
the
endoplasmic
containing
and
to
vesicle
LHA
Vesicles
used
and
of
to
proteins
move
the
needs
into
to
the
plasma
increase
the
the
to
rER
which
plasma
increase.
membrane.
are
membrane
size
of
added to the
membrane. They
by
a
very small
organelles such as
in the cytoplasm.
223
Form and function
LHA
vesicles bud off from
proteins are synthesized
vesicles bud off from
the Golgi
the Golgi
by ribosomes and then
the rER and carry the
apparatus
and carry the modified
apparatus
enter the rough
proteins to the Golgi
modifies the
proteins to the plasma
endoplasmic
apparatus
proteins
membrane
s
s
reticulum
EXOCYTOSIS
ENDOCYTOSIS
vesicles fuse
with the plasma
membrane
r
the contents of
a droplet of fluid becomes
vesicle is
pinched off
the vesicle are
expelled
l
the membrane
vesicles can then move
carrying their contents
Vesicle movements in a cell
channels
This
of
type
is
membrane
open
and
at
to
from
potassium
is
reversibly,
useful
in
pass
the
across
higher
neurons
channels
(nerve
along
synapses.
a
to
facilitated
allowing
C
and
channels
ions
transport
close
particularly
sodium
specic
movement
i
n
This
to
net
membrane
the
lower
diusion.
o
able
a
p
in
v
resulting
Gated ion channels in neurons
allow
diusion
cells)
nerve
y
Ion
r
e
B2.1.14
out again
O
Figure 22
then flattens
t
i
s
▴
n
y
through the cytoplasm
to
where
bres
in
either
Gated
be
ion
channels
switched
there
and
direction,
concentration of the ion.
are
on
and
are
o.
voltage-gated
neurotransmitter-gated
U
Voltage-gated sodium and potassium channels
a
nerve
impulse
neuron’s
involves
membrane.
potassium
across
the
i
membranes
positive
sodium
and
channels
u
rise
A
potassium
to
an
both
voltage
neuron
channels
than
remain
sodium
which
imbalance
negative
the
of
of
occur
of
by
and
are
voltage
positive
indic ates
inside.
closed.
If
If
potassium
facilitated
that
the
it
and
gated.
are
voltage
is
above
across
through
Voltages
negative
there
rises
ions
diusion
charges
relatively
below
more
−50 mV,
−50 mV sodium
+
open,
more.
allowing
When
it
sodium
reaches
ions
(Na
+40 mV,
)
to
diuse
potassium
in.
This
channels
c auses
open,
the
voltage
allowing
+
l
The
gating
a
reversible
open
extra
globular
E
c an
t
The
ball
state.
to
diuse
mechanism
with
position
amino
)
of
conformation
position
closed
of
due
outside
potassium ions (K
v
O
f
x
to
movements
movements
channels,
are
membrane.
charges
rapid
These
o
and
across
t
a
r
o
d
sodium
n
A
When
the
remains
There
may
open
in
a
the
sodium
with
pore
neuron.
and
potassium
subunits.
between
The
them
that
allows
The
potassium
channel
subunit
that
resembles
a
the
four
pore
subunits
and
until
similar
does
the
are
so
in
within
potassium
ball,
the
channels
subunits
pore.
place
be
both
of
changes
narrow
no
protein
acids.
inside
a
with
out
has
ions
pass or in a
by
a
exible chain
conformation, the ball
milliseconds
channel
to
four subunits and an
attached
open
involves
c an be in either an
returns
of
the
to
its
pore opening.
original
+
Sodium
and
potassium
closed
mechanism in the sodium channel.
channels
must
be
specic,
despite
Na
+
and K
ions
+
both
224
c arrying
a
single
positive
charge.
Sodium
channels
allow
Na
ions
to
pass
y
P
enclosed when a
e
part of the plasma
membrane is pulled inwards
Cells
but
Potassium
become
pass
ions
the
the
ion
in
a
pore.
To
a
become
associated
with
their
of
a
shell
amino
water
of
acids
through
water
in
the
bonds
broken
acids
when
This
in
this
bonds
molecules.
the
of
large to
potassium ion
part
temporarily
of
it
ions
the
pore.
c an again
are too small to
pore,
so
they
c annot
molecules.
2
+
+
+
+
+
outside
+
+
+
+
‒
+
+
+
‒
‒
‒
‒
‒
chain
ball
the axon and net positive
charge outside
+
K
p
+
+
charge
+
+
+
U
+
C
+
net positive
ions
o
v
channel closed by "ball and chain"
i
n
3
inside of axon
y
r
e
net negative charge inside
O
+ +
‒
+
+
+
t
i
s
+
+
‒
+
n
y
+
‒
net negative charge
channel briefly open
y
+
ions to
l
+
too
form
the
Na
narrowest.
dissolve, they
channel closed
+
its
pore,
Sodium
part
at
the
narrowest
of
allow
them
between
part
narrowest
they
makes
and
the
not
wide
P
1
shell
the
are
amino
passed
the
do
0.3 nm
but
molecules.
molecules
has
0.3 nm
is
r
shed
with
than
through,
of
channels
channel
e
ion
Potassium
water
pass
series
potassium
bonds
of
water
and
ions.
potassium
smaller
shell
Aerthe
form
a
slightly
to
surrounding
between
+
larger K
pore
are
bonded
through
the
the
The
s
s
and
not
through.
LHA
+
through
pass
+
n
of the membrane
hydrophilic outer
◂
Figure 23
Voltage-gating
parts of the membrane
f
x
t
a
r
o
i
o
d
hydrophobic core
of potassium channels
Nicotinic acetylcholine receptors
are
receptors
hence
receptors
binding
site
gated
into
the
in
many
both
of
nicotinic
the
which
charged
to
ions)
neuron,
open.
receptor,
a
the
subunits
for
pore
these
the
sodium
its
there
voltage
change
symmetric ally, with
Binding
ve
c an
acetylcholine
conformational
synapses,
receptors.
arranged
between
changing
of
At
acetylcholine bind to the
acetylcholine.
including
Binding
and
acetylcholine
subunits
opens
synapses.
nicotine
transmembrane
postsynaptic
channels
from
c alled
two
(positively
the
sodium
dissociates
ve
change,
E
c ations
diuses
have
are
between
conformational
which
they
But
a
a
neurotransmitter
acetylcholine.
l
These
the
v
O
receptors,
is
for
u
Acetylcholine
through
pass. Sodium
and
is
c auses a
subunits,
c ausing
reversible.
c aused
voltage-
When it
by binding is
▴
reversed
and
the
pore
in
the
receptor
is
Figure 24
Nicotinic acetylcholine
closed.
receptor with acetylcholine bound
(red) and
the c ation pore open
225
Form and function
LHA
Activity: Sketching the nicotinic acetylcholine receptor
Figure
24
on
the
previous
membrane.
expect
it
the
to
Month
have,
then
website
page
Sketch
this
check
shows
protein
whether
the
in
structure
side-view
your
sketch
of
a
nicotinic
within
the
matches
acetylcholine
membrane,
the
actual
to
receptor
show
structure
by
the
viewed
structure
going
online
from the outside of the
and
to
position
the
PDB
that
you
s
s
plasma
Molecule of
(molecule code number 2BG9).
Sodium–potassium pumps as an
r
example of exchange transporters
a
neuron
sodium
transport,
pump
dierent
in
being
to
supply
an
example
of
an
in
opposite
directions
a
one
result
ions
ATP
ions
generate
charge
across
the
three
pump
sodium
pumped
be
in.
protein.
ions
E ach
transporter
across
and
the
are
This
being
time
therefore
a
pump
In
by
follows a
pump
goes
it
round
transports
neurons, this helps
membrane potential, which is a
p
2
3
C
o
v
i
n
U
p
n
The pump is open
gradients
generated
pumped out of the
the
bec ause
membrane.
membrane.
1
concentration
These
energy.
exchange
imbalance
must
membrane.
y
voltage
that
potassium
uses
is
steps
there
the
sodium–potassium
r
e
to
of
a
impulse
across
O
This
it
using
ions
n
cycle
cycle
two
nerve
t
i
s
this
and
a
y
repeating
axon
convey
potassium
l
active
to
and
p
ATP
ADP
to the outside and
to the pump which
the Na
causes a conformational
exit, increasing the
sites, reducing the Na
change and closes
Na
concentration inside
the pump
outside the neuron
o
The pump opens
phosphate group
+
Na
+
ions can enter and
i
d
attach to their binding
+
ions can
+
5
concentration
6
u
l
a
E
v
O
f
x
4
t
a
r
o
ATP transfers a
to the inside, so three
p
p
+
Two K
+
Binding of K
The pump opens
outside enter and attach
ions from
causes release of the
to the inside and the
to their binding sites in
phosphate group,
K
the pump, reducing the
which causes a
increasing the K
conformational
concentration inside;
change and closes
more Na
the pump
then enter
+
ions can exit,
+
+
K
concentration outside
+
▸
226
Figure 25
The sodium–potassium pump
ions can
y
of
P
For
e
B2.1.15
Cells
LHA
B2.1.16
Sodium-dependent glucose
cotransporters as an example of indirect
active transport
molecule
c an
move
its
sodium
against
across
its
is
proteins
plasma
concentration
concentration
ion
a
greater
gradient.
than
the
it
being
lost
in
is
energy
by
to
cells
glucose
the
released
needed
used
reabsorb
cell.
that
by
move
in
the
has
The
glucose
sodium
the
the
wall
been
ion
molecule
is
moving
movement of the
glucose.
of
the
proximal tubule
ltered out the blood to
urine.
into
than
cells
inside.
depends
The
on
the
Na
concentration
ion
concentration being
gradient
is
maintained
by
transport
of
Na
ions
out
of
the
cell.
t
i
s
+
active
Sodium–potassium pumps in the
membrane
on
the
inner
(basal)
side
of
the
cell
transfer
Na
out of the
+
cell
towards
glucose
not
cotransport
typic al
cotransporter.
c apillaries
depends
on
active
transport
This
c alled
is
and
energy
bec ause
indirect
from
the
ATP,
energy
secondary
cytoplasm
in. Sodium-dependent
so
is
it
is
not
active
not
high
with
glucose
inner membrane
and
of cell with
low Na
concentrations
+
Na
protruding
the
CAMs
c ases,
the
is
a
some
same
in
domains
into
adjacent
group
cells
the
plasma
types
embedded
the
cells
in
dierent
extracellular
binding
type
of
CAM
cells
of
the
in
is
of
membranes of adjacent cells.
cell
the
junction.
environment.
together
CAMs
phospholipid
their
A
are
bilayer
junction
is
typic ally
and
others
formed
by
extracellular domains. In some
of
present in both cells and these bind together to
same
type.
In
other
c ases,
the
CAMs
are
Figure 27
asymmetric al
junction
is
formed.
This
is
useful
in
linking
If Hydra is broken up into
dierent and
single cells,
an
Glucose uptake into a cell
between
▴
build
Figure 26
by cotransport
by cell-to-cell junctions. These junctions depend on
(CAMs)
found
outwards
in
o
CAMs
with
linked
molecules
E
proteins
of
i
range
are
v
A
blood capillary
◂
Adhesion of cells to form tissues
tissue
cell-adhesion
t
a
a
fluid
u
in
tissue
of a
a
Cells
endothelium cells
forming the wall
l
f
x
O
B2.1.17
pumps
n
U
capillary
d
r
o
blood in
+
/ K
C
i
n
transporters
o
+
dependent glucose
by the
v
with Na
However,
directly
transport.
+
of cell
passive.
used
p
outer membrane
or
transfer K
y
is
blood
r
e
it
nearby
O
+
plasma
n
absorption
outside
l
greater
y
+
Glucose
y
prevent
These
a
r
cells
kidney.
The
into
bec ause
P
cotransport
in
the
gradient
energy
Sodium-dependent
transfer a sodium ion and a glucose
membrane
e
down
cotransporter
together
s
s
Sodium–glucose
the cells reaggregate into
dierent cell types to
tissues by cell-to-cell adhesion, with the
form
a
more
complex
structure.
tissues arranging to form
a new polyp
227
Form and function
LHA
plasma
plasma
membrane
of
Cell
cadherin
A
molecules
bonded
membrane
together
of
Cell
B
s
s
e
r
A
separated
and
spreading
substances
in
the
in
immune
migrating
to
a
form
Explain
the
Describe
i
loop
t
a
2.
What
are
of
on
active
active
organs.
It
types
junction
other
of
types
tumours,
it
is
needed
so
it
for
prevent
facilitate
prevents
tumours,
B
it.
cells
Cell
from
prevents
transport
transport
in
in
the
biologic al
generation
systems?
of
root
pressure
(B3.2.16)
gradients
c.
of
and
In
Cell
o
plants.
depend
role
role
o
d
r
o
of
of
auxin
eux
phytohormones.
how
active
c arriers
in
maintaining
concentration
(C3.1.20)
transport
plays
a
role
in
osmoregulation
by the
Henle. (D3.3.9)
the
roles
of
cell
membranes
in
the
interaction of a cell with its
environment?
u
l
f
x
a
E
v
O
228
in
the
C
b.
processes
Outline
n
U
a.
and
Some
secondary
(metastasis).
v
i
n
What
tissue
system.
Linking questions
1.
tissues
cells.
p
malignancy
of
roles
of
adjacent
y
becoming
major
architecture
of
O
movement
has
the
between
r
e
extracellular
adhesion
maintains
relationships
cytoplasm
fluid
Cell-to-cell adhesion
adhesion
functional
tissue
t
i
s
Cell
intercellular
with
n
Figure 28
space
l
▴
Cell
y
of
a.
Describe
helper
b.
the
Outline
one
recognition.
c.
role
of
the
T-lymphocytes.
Explain
the
example
cell
surface
inactivation
of
B-lymphocytes
(C3.2.8)
of
the
role
of
glycolipids in cell-to-cell
(B1.1.7)
process
of
tyrosine
kinase
activation.
(C2.1.11)
by
y
P
narrow
cytoplasm
B2.2
Organelles and compartmentalization
A
shoemaker
E ach
suited
to
who
tool
c arry
out
making
What
the
specic
task
such
of
specialization
a
what
cell
is
specialized
adapted
to
the
for a
function
by its
ways is the tool kit of a shoemaker
a
ways
is
cell?
How
similar
it
to
dierent
do
the
from the
tools
evolve? Is the
evolution
of
cells?
Shoemaker ’s tools
100,000 compartments
What
larvae
in
What
compartmentalized
dierence
a
into
and
discrete
cells?
constructed
of
eukaryotic
cells?
▴
the
Honeybees construct
or honey and
AHL
of
cells
that
are
separation of the nucleus and
Advantages of compartmentalization in the
B2.2.4
Adaptations
ATP
aerobic
by
wax comb with
are used
for storage of pollen
protection for worker larvae and pupae
HL
subunits
specic functions
of
Figure 2
hexagonal compartments that
separate compartments
cytoplasm of cells
What
by
u
l
E
B2.2.3
perform
Advantage
cytoplasm
as
v
to
comb
compartments
SL
Organelles
adapted
B2.2.2
the
f
x
O
B2.2.1
and
the
examples of
eukaryotic
t
a
honeybees
between
in
i
the
colony?
great benets
some
functions
r
o
is
are
bee
faeces, pollen,
o
cells.
the
compartments?
has
d
eukaryotic
also
to
storing
dierent
Compartmentalization
in
of
n
and
provide
advantages
U
honey
the
energy
advantages does
compartmentalization
are
of
o
the
colony.
quantities
C
construct
in
What
signic ant
large
to
bee
have
the
needed
a
must
justify
v
to
i
n
advantages
y
p
What are the advantages of compartmentalization in cells?
Compartmentalization
O
Figure 1
r
e
▴
n
what
tools
together.
tools?
t
i
s
of
is
in
y
in
within
eukaryotic
and
cutting
shoe
l
In
dierent
y
in
the
as
advantage
structure.
evolution
many
stitching
function
and
has
or
organelle
organelles
hand
holes,
particular
similar
by
structure that makes it well
P
E ach
is
a
a
r
leather,
works
has
e
tools.
s
s
How are organelles in cells adapted to their functions?
cell
of
the
only
mitochondrion
for
production of
respiration
B2.2.5
Adaptations
B2.2.6
Functional
of
the
chloroplast
benets
of
the
for
double
photosynthesis
membrane of the
nucleus
B2.2.7
rough
Structure
and
endoplasmic
function
of
free ribosomes and of the
reticulum
B2.2.8
Structure
and
function
of
the
B2.2.9
Structure
and
function
of
vesicles in cells
Golgi
apparatus
229
Form and function
B2.2.1
Organelles as discrete subunits of
cells that are adapted to perform specic
functions
more
vital
limited
In
range
their
some
Mitochondria
Chloroplasts
Amyloplasts
Chromoplasts
It
plasma
to
plasma
be
not
a
narrow
enough
membrane
discrete
protein
to
be
structure
are
all
organelles. Some
so
are
filaments
an
as
extracellular
spread
structures
through much of the
organelle
it
includes
many
different
structures
many functions.
have
smaller
may
of
membrane
organelles:
fewer
or
also
rapidly—for
organelles
bec ause
allow
they
functions
example,
than
eukaryotes.
concentrate
to
be
transcription
on
integrated
and
a
This
could
more
and
be
limited
therefore
bec ause
range of
c arried out
translation.
i
these
organelles
During
cell
division,
nucleus
Does
chloroplasts
plant
One
the
denition
plasma
the
to
denition
(a)
and
useful?
How
does
it
aect
your
(b)?
Another denition of the cytoplasm is the thick solution
that
lls
The
organelles
refers to the division of
refers to the division of the
ways
is
aect
each
this
your
Discuss
a
third
process?
cell
and
are
is
enclosed
by
the
cell
membrane.
embedded in the cytoplasm. In what
denition
answer
to
useful?
(a)
and
How does this denition
(b)?
cytokinesis?
cytoplasm
membrane
is
the
statement:
“The
criteria
for judgement we use
What happens to
aect
during
of
this
duplic ation of mitochondria and
constitute
vacuoles
the
mitosis
cytokinesis
E
cytoplasm.
and
is
chloroplasts
v
the
and
ways
answer
a
mitochondria
l
vacuoles in plant cells
b.
O
a.
are part of the cytoplasm
u
think
ornot?
everything
enclosed
excluding the nucleus. In what
the
truth
of
the
knowledge
claims
we
make.”
y
more
membrane
n
cells
are
t
a
r
o
you
f
x
Do
230
functions.
disperse
largely
Thinking skills: Applying criteria for judgement
ATL
by
cells
structure,
(Table 1).
Nuclei
y
on the fruits and
the seeds
the
o
feed
is
performs
coloration attracts
d
animals that
Red
solid
reticulum
p
pigments.
not
cytoplasm
their
by red
a
reticulum
o
ready
outside
discrete
are
the
organelles
consist
so
and
C
are mature and
Chlorophyll is replaced
is
apparatus
considered
cell
Prokaryotic
to be dispersed.
Section A2.2.10.
Double
vacuoles
endoplasmic
n
in the tomato fruit
are
than
not
cytoskeletons
and
organelle
t
i
s
walls
ribosomes
are
v
•
for a
structure
membrane encloses the uid
membrane-bound
endoplasmic
r
e
vesicles,
structures
give the fruit
chloroplasts when the seeds
described in
Their
Examples of organelles in eukaryotic cells
i
n
from
and
specialized
organelles.
l
Lysosomes
U
develop
the
not
perform one or
are
O
Nucleoli
•
is
many
are
to
they
P
Golgi
cell
have
double
it
adapted
y
Proteasomes
Table 1
are
bec ause
membrane
Smooth
Chromoplasts are
double membraned and contain DNA. They
Single
cells
c ases
and
Rough
Cells in ripe tomato fruits
colour.
other
RNA,
Microtubules
rather
red
In
or
Centrioles
•
a bright
or
that
micrographs
Vesicles
other
Figure 3
electron
membrane
organelle.
proteins
membrane
Nuclei,
contain chromoplasts that
an
of
in
single
cells
ecient
Eukaryotic
Ribosomes
▴
▴
functions.
in
are
r
of
a
structures
Organelles
appearance
composed
No
of
c ases
contents
discrete
e
and
are
functions.
s
s
Organelles
Cells
Experimental techniques: Dierential centrifugation
Separating
cells
fractionation.
types
of
organelle
is
c alled cell
sucrose
rst stage is to mix the cells with
extraction
buer.
The
cold
temperature
solution
Centrifugation
slows
chromoplasts
are
at
to
placed
high
in
speed
become
the
concentrated
−3
down
degeneration
c aused
to
gently
burst
the
in
a
cells
structures
buer,
sediment
c alled
supernatant,
is
disc arded.
mixture
is
then
organelles
separate
from
dierential
centrifugation.
of
the
tube
The
the
density
of
of
from
chosen
L arger
a
faster
c an
be
other
0.5 mol dm
the
This
required
is
c alled
and
varied
For
at
lower
organelles.
to
separate
example,
organelles
in
to
tomato
separate
cells,
three
−3
0.9 mol dm
and
progress in
newtechniques.
▴
Figure 4
Ultracentrifuge tubes are spun at
high revolutions
per minute by a rotor
1.45 mol dm
C
Advantage of the separation of
n
U
B2.2.2
that
−3
,
mixed
i
n
of
so
else.
rate
−3
layers
is
organelles sink to
smaller
density.
exampleof
of
o
chromoplasts
at
liquid
dierent
pellet
organelles.
v
organelles
The
the
everything
than
an
bottom of the
p
speeds
is
y
bottom
centrifugation
This
development
r
e
c arefully
rapid
investigating the functions
remaining liquid,
centrifuged again, with the
duration
the
the
The
resuspend
and
organelles.
following
Only
be
and
O
new
speed
individual
science
layers.
c anthere
t
i
s
This
of
determining
developed
n
“pellet”.
to
organelles. The
in
are
l
a
solution
progress
protocols
sucrose
y
form
the
food blender
such
1.45 mol dm
are denser than
to
tube
another
when
between the
−3
and
organelles. It is then
organelles
they
a
mixture is
remove whole cells
centrifuge
with
to
than
the
to
of
0.9 mol dm
y
extraction
larger
bec ause
version
release
ltered
The
problems
P
and
osmosis.
scientic
is
prevents
r
other
buer
and
and
homogenate
centrifuged
the
dierences
blitzed
open
resulting
and
pH
the
tube.
c auses the
e
then
by
and
centrifuge
(62,000 g)
s
s
ice-cold
into
The
the nucleus and cytoplasm into separate
compartments
together
transcription.
RNA
(mRNA)
In
membrane.
has
This
transcription
in
of
nucleus,
the
to
but
and
safeguards the DNA.
there is no nucleus, so DNA and
translation
translation
nucleus
be
nucleus
via
modied
before
it
is
c annot
the
c an
pores
aer
it
has
translated.
transcription
Topic D1.2
and
translation
are
happen
begin
in
The
until
the
been
immediately
messenger
nuclear
produced
process
modic ation and is described in more detail
both
a
and
out
mRNA
cells,
the
cells,
cytoplasm
l
O
transcriptional
passed
the
prokaryotic
the
eukaryotic
allows
inside
having the nucleus and cytoplasm as
u
f
x
aer
In
in
in
i
are
advantage
t
a
compartments.
ribosomes
D1.2.15,
chromosomes
another
r
o
separate
keeping
gain
o
eukaryotes,
Eukaryotes
d
In
is
by
c alled post-
(for HL only) inSection
described
(for SL and HL) in
E
v
◂
Figure 5
cell,
In this electron micrograph of part
of a prokaryotic
the arrow points to an RNA polymerase attached
DNA at
the point
spheric al structures are ribosomes.
produced
They are translating the mRNA
by a series of RNA polymerases that
along the DNA.
to a strand of
where transcription of a gene is initiated. The black
This image shows that
are moving to the right
translation c an begin before
transcription of a gene has been completed
in prokaryotes
0.5 µm
231
Form and function
B2.2.3
Advantages of compartmentalization
in the cytoplasm of cells
The
cytoplasm
of
eukaryotic
organelles.
There
cells
are
is
divided
several
into
compartments
advantages
of
being
by
membrane-
compartmentalized.
s
s
bound
food vacuoles
•
Enzymes
and
substrates
concentrated
Substances
membrane
could
an
membrane.
c ause
digest
as
pH
spread
damage
For
process
to
the
example,
cell,
c an
be
if
cell
the
and
kill
a
they
c an
be
maintained
c an be kept inside the
were
at
an
not
ideal
safely
may
be
different
from
the
levels
stored inside the
level
needed
for a particular
for
other
l
which
more
digestive enzymes of a
contractile
process,
much
throughout the cytoplasm.
processes
vacuoles
There
is
within
or
a
their
larger
area
contents
of
across
around within the cell.
for
processes that happen
avour
i
n
two other advantages of food
an
alliin
and
into
is
sulfur-containing
enzyme
a
to
c alled alliin in their
c alled alliinase in other parts of the cell.
compound
toxic
compound
p
converts
and
harmless
some
c alled
allicin,
o
smell
a
store
v
Alliinase
C an
store
They
y
cells
vacuoles.
This is only possible bec ause the
you suggest
available
r
e
Garlic
to provide optimum conditions
for the seriesofenzymes that digest the
vacuole is a separate compartment.
moved
Activity: Garlic cells and compartmentalization
inside drops below pH2 and later rises
food.
be
membrane
membranes.
food is
Aer formation of a vacuole, the
above pH7,
c an
n
•
with
feeds by endocytosis,
forming vacuoles in which ingested
pH
Organelles
Paramecium is a unicellular
eukaryote that
digested.
•
O
Figure 6
cell.
t
i
s
▴
y
in a
herbivores.
This
which
has
reaction
a
very
strong
occurs when
herbivores bite into garlic and damage cells, mixing the enzyme and its
substrate.
M any
cut,
not
U
or
or
cutting
humans
whole.
like
You
the
c an
avour
test
but
this
by
to
get
it,
smelling
garlic
a
must
whole
be
garlic
crushed
bulb, then
crushing it and smelling it again.
n
LHA
B2.2.4
Adaptations of the mitochondrion for
o
function
•
The
the
u
l
by
their
outer
rest
ATP
by
the
cell,
separates
creating
reactions
of
The
mitochondrial
It
inner
contains
of
the
aerobic
electron
a
proton
inner
aerobic
cell
respiration.
They
are
adapted to this
structure.
membrane
of
generate
a
E
v
O
f
x
•
produce
i
Mitochondria
t
a
r
o
d
production of ATP by aerobic cell respiration
a
the
contents
compartment
of
the
mitochondrion
specialized
for
the
from
biochemic al
respiration.
membrane
transport
gradient
membrane
that
chains
and
use
is
the
site
of
oxidative
and
ATP
it
produce
to
phosphorylation.
synthase which together
increase
the
surface
between
the
inner
ATP.
area
Cristae
available
are
for
projections
oxidative
phosphorylation.
•
The
intermembrane
space
and
outer
membranes
is
where
a high concentration of protons is generated by the electron transport chains.
The
volume
inner
•
of
this
membrane
space
builds
is
up
very
small,
so
a
concentration
gradient
across the
rapidly.
The matrix is the fluid filling the compartment inside the inner mitochondrial
membrane.
It
and
reaction.
the
volume
c an
232
used
C
vacuoles as separatecompartments?
be
link
of
the
contains
matrix,
performed
all
By
the
more
the
enzymes
and
concentrating
reactions
rapidly
of
than
substrates
enzymes
these
if
they
two
and
parts
were
for
the
Krebs
cycle
substrates in the small
of
aerobic
respiration
dispersed in the cytoplasm.
y
such
particular
r
could
lysosome
a
were
organelle.
lysosome
Conditions
for
they
P
•
that
of
if
e
•
than
Cells
matrix
separates the contents of the mitochondrion
contains enzymes of the
from the rest of the cell, creating a
Krebs cycle and link
compartment with ideal
LHA
outer mitochondrial membrane
cellular
conditions for
reaction
aerobic respiration
intermembrane
s
s
space into which
inner mitochondrial
protons are pumped
membrane
by the electron
contains electron
e
transport chain,
transport chains and
with a
r
ATP synthase
rapid
concentration
y
phosphorylation
diagram
of its structures
and their functions
n
Electron micrograph of mitochondrion with annotated
O
Figure 7
for expression of
t
i
s
▴
small volume
ribosomes and DNA
l
available for oxidative
y
inner membrane which increase
the surface area
buildup due to the
P
cristae are projections of the
y
r
e
Data-based questions: Structure and function in mitochondria
the
electron
micrographs
in
Figure 8 and then
wall
The
mitochondrial
n
o
i
c ardiac muscle,
(c) from
the
and
one
membrane
matrix
cytoplasm
ribosomes.
consistent
with
i.
Protein
ii.
Ribosomes
iii.
is
Which
this
contains
70S ribosomes,
of
eukaryotic cells contains
of
these
hypotheses is
observation?
[1]
synthesized in the mitochondrion.
in
mitochondria
have
evolved
from
Ribosomes
are
produced
by
aerobic cell
respiration.
u
a
The
the
l
1.
(b) from
membranes
One
A
(i) only
B
(ii) only
C
(i) and (ii)
D
(i), (ii) and (iii)
3.
Discuss the claim that the mitochondria in
4.
Predict,
mitochondria
produces
5.
Identify
other
8b
and
Figure
8c
are
spheric al.
[2]
(a) from a
with
reasons,
which
of
the
four types of
axolotl sperm,
most
ATP
per
unit
time.
[3]
batpancreas
E
(d) from
Two
D
Figure
Electron micrographs of mitochondria:
v
bean plant,
C
ribosomes in bacteria.
d)
Figure 8
membrane
whereas
t
a
r
o
f
x
▴
O
c)
wall
One
o
U
b)
One
B
80S
d
a)
2.
A
C
i
n
v
answer the questions.
p
Study
uid-lled
matrix.
cytoplasm
centre
What
of
the
separates
around
the
mitochondrion
the
matrix
is
these
structures
in
the
micrographs:
c alled
a.
to
the
right
of
the
mitochondria
b.
to
the
right
of
the
mitochondrion
in
Figure
8a
[1]
from the
mitochondrion?
in
Figure
8d.
[1]
[1]
233
Form and function
LHA
B2.2.5
Adaptations of the chloroplast for
photosynthesis
Chloroplasts
a
•
an
are
double
quite
extensive
intense
•
a
colourless
of
colour
fluid-filled
the
internal
due
spaces
fluid
structure
to
share
certain
chloroplast
membranes
c alled
features:
envelope
thylakoids,
the
the
thylakoids
thylakoids
c alled
stroma
that
contains
different enzymes.
chloroplasts
are
the
of
thylakoids,
then
there
c alled
may
be
grana.
starch
stroma.
thylakoid membranes
containing
O
naked DNA
y
o
membrane
chloroplast
starch grain
lipid droplet
o
Figure 9
i
▴
Chloroplast
structure
There is a clear relationship between the function of chloroplasts (described in
Topic C1.3) and their structure.
•
u
l
a
E
v
O
f
x
t
a
r
o
d
envelope
Chloroplasts absorb light.
in
the
thylakoid
membranes
c apacity.
The
that
are
of
are
illuminated
many
c arry
ensures
thylakoids
brightly
composed
•
Pigment
membranes,
thylakoid
that
often
light
the
chloroplast
have
which
arranged
absorption.
arranged
typic ally
thylakoids,
molecules,
out
in
has
stacks
more
light
is
needed.
The
This
volume
pumped
in,
been
of
a
develops
fluid
between
inside
proton
the
gradient
absorbed.
This
the
inside
thylakoids
develops
allows
ATP
is
and
very
after
small,
synthesis
to
area of
grana.
with
to
so
deep
be
A
outside
relatively
photosystems
large
large light-absorbing
c alled
chloroplasts
allow
a
in
The
Chloroplasts produce ATP by photophosphorylation.
have
234
C
membrane
n
outer
chloroplast
70S ribsomes and
p
r
e
v
i
n
U
inner
a
stroma
t
i
s
granum
If
grains or lipid
n
in
stacks
rapidly
y
droplets
there
photosynthesizing
many
l
been
are an
absorbed.
proton
of
Leaves
grana
the
when
gradient
thylakoids.
protons
are
few photons of light
begin.
y
most
has
P
In
which
chlorophyll
inside
around
but
outer
e
small
system
green
in
forming
r
•
variable
membrane
s
s
•
Cells
LHA
•
Chloroplasts c arry out the many chemic al reactions of the C alvin cycle.
The
for
stroma
the
This
is
a
C alvin
compartment
cycle
concentration
cycle.
ATP
the
of
the
the
plant
together
enzymes
reduced
bec ause
throughout
of
kept
NADP
and
are
thylakoids,
cell
with
in
their
substrates
needed
where
speeds
for
they
which
the
enzymes
substrates
the
are
up
C alvin
and
the
whole
cycle
produced,
needed
products.
and
are
C alvin
are
easily
s
s
available
and
are
distributed
stroma.
thylakoid
r
thylakoid
membrane
e
one
l
Pores
are
formed
c atastrophic
being
bathed
in
that
using
larger
would
avoid
integral
holes
to
a
be
drawn
water
edges
where
single
cell,
for
back
naturally
proteins,
through
damage
pure
in
that
the
hydrophobic
specic
only
when
such
core
membranes
core is
as
is
molecules
occur
red
of the pea
rapidly, closing the
shapes
hydrophobic
allowing
thylakoid
Drawing of part
to show the arrangement of the
by phospholipid
together
adopt
membranes
example
water.
the
perforated
i
but
they
membrane
is
bec ame
f
x
t
a
been
cisternae
bilayers
membrane
r
o
through,
apart,
of
a
o
attered
If
d
or
Areas
phospholipid
O
moving
perforation.
with
water.
n
molecules
to
C
principle
exposed
U
general
never
Figure 11
chloroplast
thylakoids
o
Functional benets of the double
membrane of the nucleus
A
v
i
n
B2.2.6
▴
of
y
Electron micrograph of pea chloroplast
granum—a stack
p
Figure 10
thylakoids
n
space
t
i
s
▴
r
e
of
y
P
y
thylakoid
to
when
blood
spheres
exposed.
cells
pass
there has
burst aer
Proteins synthesized by ribosomes in the cytoplasm are needed in the nucleus to
u
form part of the structure of chromosomes. They also regulate gene expression
by promoting or repressing gene transcription. These proteins must be able to
l
a
O
enter from the cytoplasm. Messenger RNA, transfer RNA (tRNA) and ribosomes
produced in the nucleus are exported to the cytoplasm. The RNA molecules are
large, and ribosomes are even larger because they are assemblages of ribosomal
v
RNAs (rRNAs) and proteins. This means there is a need for unusually large pores
through the nuclear membrane—larger than the pores through channel proteins in
E
membranes. A double membrane is used to make a larger pore, with the inner and
outer membrane connected to form a circular hole. The rims of these nuclearpores
are lined with proteins that can control whether or not a protein passes through.
235
Form and function
LHA
single-membraned
double-membraned
organelles such as vesicles,
organelles such as
vacuoles and lysosomes
chloroplasts
cisterna—a flattened
s
s
membrane sac such
as rough ER
e
double membrane
r
with pore, as in
nuclear membranes
l
a variety of shapes,
but
n
Membranes c an form
never begin or end
t
i
s
The double nuclear membrane has another functional benet. During both mitosis
O
and meiosis, the nuclear membrane breaks down to allow the chromosomes to be
moved to the poles of the cell. Nuclear membranes then reform around the new
groupings of chromosomes. This can easily be achieved with a double membrane.
r
e
y
Vesicles bud o, progressively breaking the whole nuclear membrane up into
vesicles, which are moved to the sides of the cell. Later, these vesicles can be used
p
to make new nuclear membranes by fusingtogether.
o
v
i
n
B2.2.7
Structure and function of free
C
ribosomes and of the rough endoplasmic
U
reticulum
Figure 13
Freeze-etched
electron
Ribosomes
micrograph of the double nuclear
have
membranes,
are
large
diameter
of
assemblages
nearly
with nuclear pores visible and
one
has
three
binding
peptide
synthesis
bonds
by
Ribosomes
free
u
l
a
E
v
O
f
x
as
The
i
of
small.
o
and
t
a
r
o
d
vesicles in the surrounding cytoplasm
236
a
n
▴
small
sites
and
that
are
and
typic al
contains
roles,
for
not
either
example
is
tRNA
exit
a
has
rRNA
a
attached
wide
to
the
proteins.
an
are
site
two
for
area
Eukaryote ribosomes
subunits,
mRNA.
that
synthesized
The
c atalyses
one
large
large subunit
the
formation
polypeptide.
Protein
Topic D1.2.
membranes
synthesized
by
in
the
them
cytoplasm
are
are
known
released into the
there or enter the nucleus. The cytoplasm of a
range
enzymes
binding
for
described in
remain
and
There
molecules,
tunnel
Polypeptides
cytoplasm
cell
for
ribosomes
ribosomes.
subunit
an
of
30nanometres.
that
of
proteins,
c atalyse
some
glycolysis,
c arrying
and
out
others
housekeeping
performing the
specialized functions of the cell.
If
a
ribosome
loc ation,
This
the
synthesizes
ribosome
organelle
single
consists
membrane.
transported
The
elsewhere
initial
destination
them
ultimately
for
a
polypeptide
becomes
of
that
attached
cisternae,
which
must
to
the
are
be
transported
rough
attened
to
a
endoplasmic
sacs
specic
reticulum.
bounded
by a
polypeptide
passes into the lumen of the rER and is then
in
a
the
these
secreted
cell
by
vesicle
polypeptides
from the cell.
is
that
the
buds
Golgi
o
from the rER. The usual
apparatus,
with
many of
y
P
Figure 12
y
▴
Cells
LHA
proteins synthesized by free
ribosomes are released into the
cytoplasm and remain there, or they
enter the nucleus, or are absorbed
by chloroplasts or mitochondria
s
s
proteins synthesized by
ribosomes on the rER pass into
the cisterna
of the ER via a
and
remain there or are transported
r
elsewhere in vesicles
e
translocaton channel
vesicles transport
mRNA
5’
’
mRNA
5’
the Golgi
’
apparatus or
membrane
O
o
Nobel
Visit
images of the
search
the
to
structure
structural
rst data about ribosome
the
for
PDB.
RCSB
their
loc ate
In
work
2009, they
on
the
structure of
protein data bank to obtain
Thermus thermophilus
function
E
view,
the
through
Prize
2000,
R amakrishnan, Thomas A. Steitz
made
a
a
ribosomes.
the
i
available
In
u
Yonath
three-dimensional
l
received
Venkatraman
E.
the
molecules.
v
O
subunits
regarding
biologic al
biologists
Ada
data
f
x
many
and
t
a
protein data bank (PDB) is a public database
containing
for
o
d
The
r
o
Applying technology
n
Figure 14
vesicles bud
off from the rER
C
i
n
U
▴
v
protein
y
reticulum
p
r
e
endoplasmic
n
y
t
i
s
lumen of
l
the plasma
y
P
proteins to lysosomes,
image
ribosome. Use the
1jgo.
Using
the
structure
rotate the image to visualize the small subunit and
large
mRNA
subunit,
the
associated
tRNA
molecules and
molecules.
▴
Figure 15
Key:
Molecular visualization of a functioning ribosome.
mRNA yellow;
tRNAs pink, purple and blue; rRNA white in
the small subunit
and
grey in the large subunit;
the small subunit
and
red
proteins violet in
in the large subunit
237
Form and function
LHA
B2.2.8
Structure and function of the
Golgiapparatus
The
Golgi
by
apparatus
the
transported
rough
from
polypeptide
in
of
proteins
the
the
rER
c an
by
be
its
of
a
is
the
For
plasma
This
proteins
pancreas
of
and
proteins
the
fuse
with
it
t
i
s
thecell.
Processing
protein
gradually
the
(the
in
moving
bringing
rER
cis
side)
been
carrying
Golgi
rER
to
According to the cisternal maturation
cisternae are formed
Currently,
many
d
When they reach the trans side they fragment
into vesicles
stack.
through
up
for
remain
reason
digestive
from to
enzymes
the
side).
with
each
side
nearest
Two models
move
cisternae
from
through the
do
not
move
in
Golgi
which
vesicles
on
cis
the
until
they
from the
side, which then
reach
the
trans
side,
intovesicles.
the
cisternal
about
for
move
between them.
cisternae
the
from
could
the
vacuole
the
the
maturation
functioning
cisternae
model
of
the
is
stronger, but
Golgi
apparatus,
needing to be kept together in a
i
Structure and function of vesicles
incells
u
inside it. They are typically small and dynamic structures that are continuously
l
made, moved and merged within cells. They are made by pinching o a small area of
a
membrane from a larger area. This happens in endocytosis in order to take in a small
droplet of uid from outside the cell. The protein clathrin helps with thisprocess.
Clathrin
E
inner
is
face
clathrin
a
three-legged
of
the
plasma
molecules
hexagons.
eventually
238
new
the
trans
food
example,
sequential,
(the
which
a
secreted, the
Vesicles are rounded sacs made of a single layer of membrane, and the material
v
O
f
x
t
a
r
o
B2.2.9
evidence
the
form
break
questions
including
the move through the stack.
move
they
o
coalescing vesicles and
on the cis side from
to
n
U
Figure 16
in
is
proteins
o
where
model,
proteins
C
i
n
coalesce
gradually
▴
transfer
For
cisternae
side
how
The cisternal maturation model
rER
structure
from the Golgi
or
vesicles
release
p
vesicles
membrane for
•
v
and
plasma
cisternae
opposite
explain
The vesicle transport model
proteins to the
secretion
the
to
cell.
when
apparatus.
processed
•
to
proposed
the
being
y
have
from the
are
apparatus
through
r
e
polypeptides
vesicles
Golgi
lysosome
O
membrane
SIDE
vesicles
quaternary
n
plasma
are
c an change the
c arbohydrate to make
The
transported
a
the
cells
TRANS
the
is
be
that
membrane
by
it
may
CIS
SIDE
adding
y
secreted
polypeptides
l
is
are
The
cisternae
groups.
completed,
vesicle.
endocytosis.
destination
enzymes
a
by
sulfate
the
assembling polypeptides and other subunits.
protein
in
inside
example,
or
(cisternae) in which polypeptides
processed.
This
to
bind
process
detach
to
protein
(Figure
membrane
to
each
helps
form
a
other
the
17)
when
to
of
that
becomes
vesicle
form
plasma
sphere
a
a
is
being
positioned on the
made.
Adjacent
lattice of pentagons and/or
membrane
membrane
to
become
with
a
indented and
clathrin
c age
around it.
y
by
by
are
Enzymes
phosphate
established
sacs
reticulum
vesicles.
destination
formed
attened
ways—for
adding
processing
to
in
numerous
or
of
P
apparatus
stack
r
When
a
e
glycoprotein
is
endoplasmic
s
s
made
Cells
LHA
s
s
e
r
for this.
•
In
be
some
c ases,
other
c ases,
the
of
a
the
rER
rER
and
organelles
in
of
the
the
the
a
Draw
What
Golgi
anatomy
of
their
structures
separation
E
a.
Outline
the
b.
Discuss
the
c.
role
l
2.
the
protein. (B2.2.8)
with
the
techniques
technique
of
Explain
separation
by
the
cellular
chromatography.
rER
as
c an
which
the
also
are
membrane.
also
become
move to the
area of the plasma
be
used
to
increase
lysosomes and mitochondria.
in
at
each
processing
reproductive
level of
used
by
secretion of
system and annotate
biologists?
electrophoresis.
between
and
(D3.1.4)
the
fractionation
and
rER
structure and function of
apparatus
gel
neuron is an
(B2.1.9)
female
are
a
growing cell,
the
correlations
the
a
and
increasing
method
functions.
of
relationship
techniques
the
moved. The
of
Phospholipids
proteins
off
such
between
glycolipids.
v
O
c.
Explain
and
u
b.
each
This
structure–function
relationship
be
general
o
the
glycoproteins
to
two
proteins in the
In
into
i
Outline
increase.
inserted
bud
organization?
f
x
a.
of
it,
the
t
a
examples
biologic al
to
d
are
r
o
What
with
or
movement.
membrane
cytoplasm
Linking questions
1.
vesicle
needs
amount.
the
the
Vesicles
fuse
small
of
vesicle
become
synthesize
They
very
need
membrane
are
n
size
by
membrane
membrane.
membrane.
membrane
the
the
the
for
U
plasma
on
to
reason
that
vesicles.
membrane
the
plasma
next
into
the
vesicle
presynaptic
There
C
Ribosomes
is
are
in
the
the
cells.
i
n
synthesized
inserted
it
that
materials
of
to
inside
o
of
contents
around
v
area
the
neurotransmitters
moving
membrane
the
is
materials
p
In
of
it
move
y
example
of
to
r
e
transport
•
used
O
c an
reasons
a vesicle
n
clathrin molecules bind
t
i
s
Vesicles
l
Three-legged
to each other forming a c age to support
y
P
Figure 17
y
▴
(D1.1.5)
denition
and
of
organelles and the
ultracentrifugation.
identic ation
of
(B2.2.1)
photosynthetic pigments
(C1.3.4)
239
B2.3
Cell specialization
Some
lizards
weeks
esc ape
that
from
follow,
a
a
tail
predator
c an
by
regrow.
shedding their tail. In
When
the
gecko’
s tail
e
the
s
s
What are the roles of stem cells in multicellular organisms?
regrows, it has skin, muscle and nerve bres, but the lost vertebrae
in
not
an
replaced.
accident,
do
give
rise
restricted
stem
cells
in
eight-cell
to
an
their
play
in
entire
a
person loses a nger
stage,
An
the
organism.
potential
these
If
re-grow?
to
early
cells
embryo
c an be
Gradually they
become all cell types.
▴
examples?
Figure 1
Gecko that has lost its tail
O
t
i
s
How are dierentiated cells adapted to their specialized functions?
Figure
2
cell?
the
the
ultrastructure
red
What
structures
dots
are
of
the
in
the
of
the
blue
a
hepatocyte
nerve
cell?
organelles?
organelles
related
C an
while
you
How
to
their
Figure
deduce
does
the
3
structure
functions?
What
the
neuron
neurons
HL
AHL
cells
following
cells
by
fertilization and
dierentiation
B2.3.7
Adaptations
volume
B2.3.8
pneumocytes
B2.3.4
Dierences
B2.3.9
size
between totipotent, pluripotent and
as
an
aspect
of
the
hepatocyte?
have
in
How
common?
specialization
ratios
and
constraints on cell size
to
of the brain
only
increase
surface
area-to-
Adaptations of type I and type II
in
alveoli
Adaptations
striated
area-to-volume
What is
ratios of cells
Loc ation and function of stem cell niches in adult humans
Surface
from
hepatocytes
Cells in the cerebellum
Properties of stem cells
Cell
neurons.
o
C
Figure 3
B2.3.3
B2.3.6
dier
and
B2.3.2
B2.3.5
several
n
▴
multipotent stem cells
240
of
do
of
o
specialized
i
E
v
unspecialized
into
ultrastructure
pre-synaptic cell and which is the post-
t
a
and
of
development
the
the
v
i
n
U
a
SL
is
u
l
Liver cells
Production
d
r
o
Figure 2
B2.3.1
their
f
x
O
▴
shows
which
p
the
of
y
synaptic
are
shows
identity
r
e
the
n
role
still
the
not
y
What
and
more
to
happen?
nger
l
become
Up
this
the
B2.3.10
muscle
of
c ardiac muscle cells and
bres
Adaptations
of
sperm
and
egg cells
y
repeatedly.
separated
does
does
P
divides
Why
why
r
are
Cells
B2.3.1
Production of unspecialized cells
following fertilization and their
development
into specialized cells by dierentiation
In
is
the
multicellular
many
an
cells
all
the
and
other
gene
product.
dierent
be
of
signalling
which
of
expression.
in
the
been
is
others.
gene
of
be
enough
gradients
in
in
cell
of
is
expressed. In
used to make
involves
switching
it
▴
each type and they
Figure 4
a uorescent
In this
Drosophila embryo,
marker shows cells that
are
needed. The position
dierentiates.
Gradients
expressing the genes for the two proteins
AbdA and
Exd.
These proteins form a
embryo and determine
chemic als
retinoic
it
dierent cell types.
are
the
being
in
dierentiation happens
they
how
These
of
is
cells
where
position
follows.
a
Cell
expressed
determine
forelimbs,
term
acid
are
guide
complex that
binds to DNA to regulate
regulators of
expression of specic genes. The marker
dierentiation of
shows that this is happening in some
pancreas,
lungs,
two
cells.
allowing
us
given
of
the
bec ause
therapeutic
In
u
lives,
potential
was
tissues
researched
repeatedly.
into
cell”
the
a
O
our
all
theory,
Stem
l
f
x
many
divide
split
“stem
bec ause
intensively
have
c an
c an
throughout
the
embryo
they
it
c alled
specialized
kidneys
and
other
organs.
segments of the embryo but
not
others
Properties of stem cells
century,
cell
is
highly
o
early
of
the
information
i
the
times
example,
not
body
cell’s
it
functions
dierent
to
to
the
t
a
of
a
that
the
d
19th
stem
indic ate
r
o
the
bec ause
For
must
the
say
development
but
therefore
dierentiation
development
In
have
must
chemic als
pathway
B2.3.2
cells
embryo
specic
n
cells
the
out
distinctively
and
genes
within
associated with its function. The
U
gene
in
The
there
positions
more eciently than if it
C
a
organism,
the
of
we
on
genes
sequence
grows, its
specic
structure, with the enzymes
i
n
cell
in
switched
particular
for
dierentiation.
cell,
is
embryo
way.
o
all
a
220
c arry
an
in
p
a
in
gene
of
of
used
the
multicellular
must
A
being
by
to
any
specialized
function
ideal
reactions
ways
are
its
the
identic al.
develop
could
As
embryo of
v
a
develop
expressing
bec ause
In
or
there
which
out
become
an
genetic ally
y
protein
on
is
chemic al
and
all
r
e
a
gene
terms,
c arry
develop
dierent
humans,
and
are
n
a
simple
of
to
genome
unspecialized.
pathways
c an
embryo
O
When
all
In
the
in
are
generate
an
t
i
s
types,
all
cells
cells
produce a single cell.
to
in
organism’
s
cell
cell
cells
to
y
dierentiation.
cell
out
of
each
The
the
gamete
repeatedly
y
c arry
the
female
divides
l
to
development
the
and
cell
that
dierent
allows
roles.
male
P
needed
in
embryo,
along
This
multiple
ensures
genes
early-stage
develop
functions.
had
Mitosis
a
this
r
In
have
of
e
They
cells.
fusion
organisms,
s
s
Fertilization
cells
adult
of
or
zygote and the cells
stem
their
role
from them. Stem
in
development and
regenerative uses.
there is no limit to the number
in
the
skin
divide
repeatedly
replace lost skin cells. Stem cells in the testes
also divide endlessly. This is the rst stage of gamete production and allows males
to
produce
produced
cells.
A
always
by
E
dierentiate
numbers
into
stem
cell
c apable
v
Cells
vast
a
division
specic
is
of
of
either
sperm
of
a
cell
throughout adulthood.
stem
type.
cell
If
might
they
undierentiated
dierentiating
along
remain as stem cells or
dierentiate,
or
partially
dierent
they
are no longer stem
dierentiated;
they
are
pathways.
241
Form and function
s
s
e
r
n
Tree trunks have a cylinder of stem
the layer of stem
into xylem;
on the outer side,
by dierent
methods.
they become phloem.
For this reason,
Xylem
and
phloem
they are dissimilar in structure.
is added
are both used
Xylem
tissue is the wood
to the trunk every year and
thousands of years in long-livedtrees
that
but
the new cells dierentiate
they transport
supports the tree.
itcontinues to widen throughout
dierent substances
Bec ause thestem cells
the tree’s life.
That
may be
p
o
v
B2.3.3
On the inner side,
for transport
y
more xylem
Unlike the layer of stem cells in human skin which
r
e
in the bark divide endlessly,
cells on the inner side of their bark.
cells in the trunk generates cells on both sides.
O
Figure 5
produces cells on one side,
t
i
s
▴
l
y
layer of stem
cells (cambium)
Loc ation and function of stem cell
i
n
niches in adult humans
stem
tissues,
cells
cells
bone
powers
within
a
proliferate
u
are
is
two
l
a
the
cell
body
stem
tissue
in
E
surgery.
a
vitro
cell
are
quantities
beef
without
of
burgers
the
there
need
in
and
to
stem
of
be
of
the
to
rear
cells
The
the
time,
cells
cell
in
give
precise
It
must
stem
cells
and
also
that
remain
for
many human
these
tissues
loc ation of
provide a
to
remain
them
to
inactive
proliferate
inactive
muscle
tissue.
and
Striated
hair
follicles
microenvironment
This
unless
c ause these cells
results
promotes
in
production of
growth.
type,
is,
bec ause
it
in
should
the
One
for
they
is,
be
c attle.
c an
be
possible
stem
possibility
(that
therefore
slaughter
if
be
laboratory)
uses
bres
may
the
then
marrow
dierentiation.
interest
that
Bone
where
and
niche
damaged
damage.
created.
and
present
niche.
stem
hair
muscle
future
for
stem
non-therapeutic
c an
cell
the
replace
cell
glass;
striated
repair.
needed
niches
in
stem
and
are
Stem
are
aer
cell
They
liver.
required.
research
in
also
microenvironments
large
cells
particular
are
the
proliferation
of
and
periods
Changes
stem
(literally,
There
when
dierentiate,
blood
niches
for
long
muscle,
of
body.
skin
c alled
regenerative
examples
replacement
Stem
and
is
over
injury.
highly
continuous
v
O
f
x
muscle
The
242
(skeletal)
muscle
adult
conditions
o
is
the
regeneration
dierentiate
t
a
striated
there
to
and
i
d
r
o
In
with
undierentiated
rapidly
of
tissue
microenvironment
and
in
marrow,
n
U
considerable
stem
remain
including
C
Some
and
cells
is
meat)
to
if
simulated outside
to
use
generate human
it
in
restorative
appropriate
use
them
to
produce
for human consumption.
produced
from stem cells,
y
P
phloem
xylem
Cells
Data-based questions: Adaptations of the Western spadefoot toad
The
by
Western
rain.
spadefoot toad (Scaphiopus hammondii)
When
the
egg
(a
shrinks
lack
due
persists,
the
a
how
thesurvival
of
the
was
drying.
develop
undergoing
form)
to
tadpoles
more
and
metamorphosis
lives
into
the
develop
grow
at
in
referred
develop
quickly
slowly
is
desert
to
large
before
in
in
C alifornia
tadpole
toad.
small
times
areas
the
adult
into
dierent
as
If
adult
the
stage.
pool
toads.
If
and
At
lays
some
where
there
the
is
its
eggs
sucient
group
was
it
in
pools
to
high
and
low
water
have
been laid
rain and the pool
levels helps
toad.
c arried
Tadpoles
out
to
were
determine
raised
in
a
what
hormones
constant
might
high-water
be
involved
environment.
in
They
triggering
transferred
to
a
tank
containing
10 dm
of
water — a
high-water
were
then
environment.
development
divided
The
formed
undergoes
developing into adult toads.
response
3
One
eggs
point,
into
other
in
[3]
response
two
group
groups.
was
to
a
tank
of
the
same
corticosterone
size
were
containing
measured
in
The
concentrations of
Figure6.
2.
Compare
and
O
3.
environment
environment
thyroxine
corticosterone in the
two
groups.
Suggest
[2]
how cellular
plays
a
role
in metamorphosis in the
spadefoot
toad.
[2]
C
o
low-water
of
and
dierentiation
high-water
contrast the
concentrations
p
0
n
U
B2.3.4
in
y
1
i
n
Figure 6
environment.
shown
t
i
s
environment
are
r
e
environment
low-water
results
v
low-water
2
g gn
high-water
water — a
The
1–
enoretsocitroc
g gn
enixoryht
1–
20
of
group.
3
yd ob
40
1 dm
4
ssam
yd ob
/ noitartnecnoc
ssam
/ noitartnecnoc
60
0
▴
only
each
n
and
y
thyroxine
l
3
transferred
y
pond
body
the
form
r
experiment
in
rain,
body
P
to
of
tadpoles
Suggest
An
change
its
e
1.
to
hatches,
s
s
metamorphosis
rst
Dierences between totipotent,
o
embryonic
stem
whole
one
stem
they
c an
to
cell
cells
c an
that
a
but
A
not
remain
into
series
in
the
cell
points
for
any
These
cell
example,
cells
type.
in
are
Totipotent
the
growth of
is
dierentiation
which
cells
still
a
cell
change
c apable
during
commits
of
embryo
to
develop
from being
dierentiating into a
type.
adult
body
types
stem
of
at
stem
cell
cells.
into
organs.
pathways
of
pluripotent
several
stem
useful,
other
Embryonic
every
Haematopoietic
generate
very
or
particular
another.
pluripotent.
types,
E
they
or
dierentiate
multipotent.
to
kidneys
of
dierentiate
potentially
a
The
of
pathway
composed
c an
l
range
they
involves
v
O
totipotent
are
hearts,
commit
This
entirely
that
u
gradually
development.
along
cells
replacement
f
x
Cells
are
means
i
This
t
a
embryos
totipotent.
r
o
E arly-stage
d
pluripotent and multipotent stem cells
of
cells
are
more
mature
in
bone
restricted in potential, but if
cell,
they
marrow
are
are
considered to be
multipotent
bec ause
dierent types of blood cell, but not other cell types.
243
Form and function
Social skills: Actively seeking and considering the perspective of others
ATL
represent
questions, individuals bring
will
dierent
stem
perspectives to the
conversation.
To
be
that
you
cell
view
does
possibilities.
Both
skin
not
they
It
also
cells
have
▴
and
regarding other
a
Embryonic
stem
cells
be
a
be
cultured
in
vitro.
are
totipotent
them
rules
that
govern their
of
equal
c ausing the destruction of
be
destruction
valuable
concern
culture
of
to
an
accident
epidermal
and
Hyperovulation
c an
the
of
ball
7
fertilized
of
shows
cells
egg.
for
a
production
medic ally
eggs
in
induced
women
to
be
to
increase
used in the
therapy
of
embryos.
What
diagram of
that
The
be
have unique
tools
c ausing
cells?
women
for
forms aer
concerns,
egg
if
orange cells
arise
from
y
r
e
B2.3.5
any,
donation?
O
a
a
n
Figure
uid-lled
of
of
y
treatments.
divisions
the
l
make
the
in
accident
t
i
s
several
c an
ethic al status or should
an
compensating
blastocyst,
embryos
same
dierence
Would
creation
medic al
and
the
considered.
2.
a
used in
Cell size as an aspect of
v
p
specialization
The size of a mature dierentiated cell is one way in which it is adapted to perform
o
its function. Evidence for this in humans is provided by the examples inTable 1.
50 µm
U
sperm
Adaptation
long,
extremely
any
which
cell.
and
is
so
by
longer
than
size
most
cells
have
one
of
Narrowness
and
small
allow
they
cell
sperm
to
swim
the
to
but
sperm
smallest
volume
the
egg
are
volumes
reduce
more
easily.
o
i
largest volume of any human cell. This allows large quantities of
food reserves to be stored in the cytoplasm. In birds, egg cells
are even larger, with huge amounts of stored food (yolk).
red blood
6 µm
cells
about
u
l
a
E
v
O
f
x
t
a
r
o
d
110 µm in diameter and spherical in shape, so egg cells have the
to
8 µm
1 µm
passage
in
diameter
thick
along
to-volume
in
the
narrow
ratio,
so
but
indented on both sides and only
middle.
The
c apillaries
loading
and
small
and
size
gives
unloading
a
of
and
shape
large
allow
surface
oxygen
is
area-
faster.
white blood
B-lymphocytes are only about 10 µm in diameter when inactive
cells
but enlarge to as much as 30 µm if they are activated and
become antibody-secreting plasma cells. The extra volume is
cytoplasm with rER and Golgi apparatuses for protein synthesis.
cerebellar
The
granule cells
for
cell
body
about
small
is
3 mm
volume
of
accommodate
244
function
narrow
human
resistance
egg
to
n
of
C
type
i
n
Cell
only
4.0 µm
(3,000 µm)
these
50
in
in
neurons
billion
of
diameter,
the
but
cerebellar
allows
the
them — 75%
twin
axons
cortex.
The
extend
very
cerebellum to
of
the
brain’s
neurons.
y
been
and
embryo that
are
P
have
that
the
that
willingness to suspend judgement until
facts
properties
of
cells
Figure 7
the
the
part
exhaust
embryos
all
the
these
r
curiosity
possibilities
is
requires a
use?
genuine
It
e
own
mass,
therapies.
there
the
cell
foetus.
recognize that
Do
your
inner
the
open-minded
1.
means
the
become
s
s
When considering debatable
Cells
motor
The cell body is about 20 µm in diameter
. This large size allows
neurons
enough proteins to be synthesized to maintain the immensely
long axon. It can extend for a metre or more (a million µm), so can
carry signals from the central nervous system to a distant muscle.
◂
Striated
muscle
muscle bres
diameter
100 mm
20 µm
to
are
100 µm
(100,000 µm).
greater
force
and
These
and
Table 1
Cell sizes
larger than normal cells, with a
lengths
that
dimensions
contract
by
a
c an
allow
exceed
the
bre to
greater length than
smaller muscle cells.
r
cerebellar
μm
◂
8
μm
30
μm
rate
waste
cell
cells
and
through
substances
the
cross
this
amounts
a
surface
to
removed.
at
the
and
the
the
its
=
volume (mm
accumulate
Surface
cell
bec ause
as
loss.
If
ratio
heat
is
faster
are
ratio
too
than
as
also
small,
it
they
is
are
produced
is
The
)
by
rate at which
expressed
be
For
absorbed
move into and out of
cell.
area-to-volumeratio
reactions
cell.
be
c an
C alculate
area
and
volume
1 mm,
the
the
volume and surface
then
the
surface
area-to-
ratio of cubes with sides
10 mm
and
100 mm.
What is
trend?
)
lost
more
may
over
unfolded
Also
rapidly
in
cell’s
waste
than
relation
overheat
the
same cube
cell. If it is too small, substances
required.
important
cells
v
a
produces
the
quickly
they
area-to-volume
O
and
the
u
enter
the
Effect of size on surface
3
l
f
x
not
the
of
must
reactions
these
area.
volume
area (mm
of
of
surface
Surface area-to-volume ratio is very important to a
will
volume
Substances
2
surface
rate
reactions
surface
on
The
These
t
a
ratio
in
depends
area
ratio:
area-to-volume
be
membrane
membrane
of
used
cell.
cells.
i
as
the
proportional
must
r
o
surface
products
plasma
is
of
of
o
relative
mathematic ally
cell)
substances
d
The
the
metabolism
cytoplasm
n
the
of
continue,
the
U
to
the
in
o
metabolic
metabolism
as
place
C
(the
collectively
take
Activity:
v
known
reactions
i
n
are
p
Surface area-to-volume ratios and
chemic al
μm
μm
y
100
μm
constraints on cell size
M any
cell 100
muscle fibre
plasma cell
r
e
25
B2.3.6
antibody-secreting
body
O
cell
even more widely in volume
human egg
striated
motor neuron
μm
Human cells
vary widely in diameter and
t
i
s
inactive
B-lymphocyte
10
Figure 8
n
y
cell
l
red blood
y
P
granule cell
5
e
exert
of
bres
s
s
striated
to
products will
they
c an
heat
production
be
excreted.
▴
Figure 9
bec ause the metabolism
surface.
Mathematic al models: Surface area-to-volume ratio
surface
are
lengths.
factors
operate
the
simplied
versions
area-to-volume
dierent
sc ale
E
Models
in
same
Although
operate
cells
as
the
ratio
of
in
more
the
of
of
the
c an
cubes
same
rounded
dimensions
complex
cells
way,
or
systems.
be
have
so
The
eect of size on the
modelled using cubes with sides of
a
the
irregular
simpler
trend
shape
than
real
organisms,
for the cubes will also
shape,
as
long
as
the
shape
stays
increase.
245
Form and function
LHA
B2.3.7
Adaptations to increase surface
area-to-volume ratios of cells
Some
cells
are
specialized
tubule
glomerular
ltrate,
from
the
lungs
to
and
that
for
in
red
and
increase
exchange
the
respiring
rapidly
adaptations
in
kidney
blood
cells
tissues.
out
reabsorb
Examples
useful
(erythrocytes)
These
across
their
processes.
that
cells
their
surface
must
plasma
which
be
able
to
r
distance
red
about
volume
from
blood
them
load
8 µm
than
any
in
a
part
cells
and
diameter
sphere
of
gives
unload
the
of
them
a
and
the
large
millions
their
of
surface
oxygen
biconc ave disc shape
same diameter and a smaller
cytoplasm
to
the
plasma
membrane.
O
t
i
s
Proximal convoluted tubule cells
Near
the
tubes,
outer
c alled
wall
of
the
blood
as
ion
the
through
required
by
remaining
therefore
of
numbers
tubules
in
the
useful
of
narrow,
receive
kidney.
the
They
substances
coiled
large
reabsorb
such
as
glucose.
the
a
also
both
the
ltrate.
large
the
The
ample
the
are
for
basal
membrane
in
these
basal
area.
the
and
the
membranes
membrane
The
membrane
ltrate to the blood, a
reabsorbed,
apic al
area.
outer
the
apic al
surface
space
the
from
proteins
body
surface
increase
have
and
with
has
waste
large
membrane
Both
channel
the
and
ensure
products
numbers of
has
apic al
pump
basal
infoldings
and
basal
proteins that
o
reabsorption.
i
Adaptations of type I and type II
pneumocytes in alveoli
u
The
lungs
total
l
a
E
v
O
f
x
t
a
r
o
d
selective
B2.3.8
in
provide
which
blood
ltrate
pump
n
U
which
the
reabsorbed
substances
membranes
contain
surface
epithelium.
•
Type
and
I
area
There
are
two
dioxide.
are
or
very
wide
widening
adjacent
c apillaries
the
thus
alveolus
The
very
and
small,
types
of
cell
This
is
are
also
where
consists
in
which
increasing
in
the
the
of
the
a
the
for
cells.
single
and
gas
diffusion
so
The
is
there
of
is
a
very
large
oxygen
little
need
for
thickness is only about
loc ated.
layer
alveolar
of
provide
volume of cytoplasm is small.
nucleus
oxygen
sacs
alveolar epithelium.
process,
thin
air
alveolus is one cell thick and is an
adapted
the
rate
These
the
and
extremely
blood
over
of
passive
organelles
but
the
a
alveoli.
wall
cells)
slightly
distance
of
The
(AT1
other
0.15 μm,
apart.
numbers
diusion.
pneumocytes
c arbon
These
huge
for
mitochondria
in
246
pass
be
and
(invaginations),
out
with
To
proteins
urea
of
large
These
convoluted tubules is only one cell thick, with the inner
contact
must
are
molecules
Channel
microvilli,
c arry
in
out
all
C
such
ltered
c apillaries.
i
n
or
membrane.
only
are
including
proximal
membrane
to
molecule
that
that
ltrate,
there
tubules.
o
close
uid
v
apic al
of
this
kidney
p
The
of
the
y
most
of
convoluted
r
e
volumes
surface
proximal
area-to-
molecules
n
maximum
Red and white blood cells
only
lower
of
y
Figure 10
are
a
size
helps
of
c apillaries
c arbon
The
wall of the
very thin cells. The air
are
less
than
0.5 μm
dioxide must diffuse is
exchange.
y
They
them
small
which
show
l
rapidly.
gives
▴
and
ratio,
all
ratio.
P
shape
volume
from
oxygen
transport
They
Red blood cells
The
proximal
transport
membrane.
area-to-volume
are
substances
e
substances
cells
s
s
convoluted
Cells
Type
II
pneumocytes
represent
alveolar
90%
surface
containing
L arge
and
some
cells)
are
more
cells)
but
they
area.
They
mitochondria,
amounts
lamellar
(AT2
alveolar
of
are
about
rough
phospholipid
bodies,
which
proteins.
The
are
numerous than type I cells (they
occupy only about 5% of the
10 µm
across with a dense cytoplasm
endoplasmic
are
vesicles
contents
reticulum
synthesized
of
in
containing
the
lamellar
the
and
lysosomes.
cytoplasm
many
and
stored
s
s
in
of
LHA
•
layers of phospholipid
bodies
are
secreted
byexocytosis.
membrane
microvilli
providing
r
a large surface area
adjacent cell in the tubule wall
of apical
e
lateral
separating the cell from an
membrane
large surface area of
area
from
is
a
the
in
the alveolus. Proteins
surfactant,
molecules.
lm
the
hydrophobic
layer
tension.
sides
the
of
moisture,
with
tails
the
alveolus to
also
single
type I pneumocyte
provides
cell
nucleus
layer of
hydrogen
hydrophilic
heads
outwards to the air
are dispersed
and
surfactant,
to
the
exhaled.
a
facing
phospholipids
due
be
form
lamellar bodies
Without
adhering
and
to
It
basement lamina
the
The
surface
the
air
the
spread
of
from
in
into
bodies
of
oxygen
c apillaries.
i
with
pass
allows
alveolar
and
secreted
molecules.
reducing
itself
surface
inwards
c an
lamellar
which
the
u
l
endothelium of capillary
between
air in alveolus
proteins acts as
the
blood plasma
alveolus might
red blood cell
bonding
between
1
▴
μm
Figure 12
Flattened
the alveolus and
blood
cells in the walls of
c apillary
a
E
v
O
f
x
t
a
water
on
the
r
o
collapse
dioxide
in
o
phospholipid
moisture,
blood
d
a
phospholipids
by
of
the
n
outer
of
the
to
c arbon
secreted
the
lm
U
on
by
diuse
which
Phospholipids
molecules
lined
then
C
an
and
invaginations
o
alveolus
dissolve
cell with microvilli and
i
n
The
basal membrane
Proximal convoluted
v
Figure 11
p
single layer of cells in the wall
y
infoldings providing a
glycoproteins that strengthens the
O
t
i
s
porous layer of
r
e
basement lamina—a
n
μm
active transport
▴
l
10
to provide ATP for
y
P
y
many mitochondria
◂
Figure 13
prominent
Type II pneumocyte with a
nucleus (blue). The cytoplasm
contains many organelles including lamellar
bodies (brown).
L ayers of phospholipid
visible in the lamellar bodies.
are
The irregular
surface of the cell is due to recent exocytosis
247
Form and function
LHA
B2.3.9
Adaptations of c ardiac muscle cells
and striated muscle bres
tissue
pulling
force
a
pulling
muscle,
The
the
bands.
In
structures
the
centre
of
Light
bands (green) and dark
in all the myobrils
within the muscle bre.
It
is this that
gives
f
x
the striatedappearance
u
C ardiac
muscle
a
E
v
O
l
myobrils,
with
appearance.
muscle
is
Where
the
junction
forms
the
the
light
However,
composed
of
wall
and
are
cells.
form
each
These
is
a
striated
many
These
a
light
muscle.
so
they
are
microscope,
Striated
structures
nuclei
known
present and
features
muscle
bres.
muscle
bre
there
are
bec ause
are
many
parallel,
have alternating light and dark
disc-shaped
explained in
much
shorter
c alled
an
interc alated
cell
interc alated
discs
connect
interc alated
disc,
there
adjacent
rapidly
heart
is
stimulated
structure,
referred to as
Topic B3.3
there
is
a
of
the
at
cell
to
contract,
of
muscle
cell.
the
If
both
cells,
one
so
of
of
cells
with
the
allowing
c ardiac
is
a
striated
c ardiac
have one nucleus.
there
are
are
has
muscle,
only
cell,
there
muscle
skeletal
which
muscle
ends
muscle,
c ardiac
another
between
stimulus
muscle
skeletal
bres
of
C ardiac
cell
in
most
end
connections
c ardiac
synchronization
heart.
cells,
the
disc.
each
As
aligned,
elongated
contacts
are
from
to
heart.
bands
the
one
of
the
unlike
of
cytoplasm
of
dark
end
propagated
248
bones,
t
a
blue.
to
band
to
using
cylindric al
p
i
r
o
with mitochondria between the myobrils
bands (red) are aligned
there
typic al
within
light
is
attached
o
of one striated muscle
bre is visible in this electron micrograph,
coloured
that
by another
n
Part
provided
contraction of one
o
Figure 16
d
▸
bre,
than
C
dark band
Structure of a myobril
usually
viewed
c alled
exerts a
parallel. Although a single plasma
v
i
n
Z-line
U
band
Figure 15
in
myobrils.
contraction
one sarcomere
light
also
is
unbranched
together
each
are
it
y
Muscle
nuclei visible
▴
they
muscle
reveal
c alled
body
structure
r
e
Z-line.
this,
long,
longer
muscle bres with stripes and multiple
the
the
their
arranged
fuse
this
n
micrograph of striated
cells
microscopes
cylindric al
Light
muscle
are
each
much
of
is
does
O
Electron
Figure 14
surrounds
move
many
This
it
return to its original length,
pairs — the
t
i
s
embryonic
of
muscle.
antagonistic
When
To
other.
When
Bec ause
which
are
to
the
length.
is
a
specialized
branched, so
several other cells. In an
plasma
membranes and
electric al signals to be
muscle
cell
in
the
wall of the
passed on to all the other cells, so
contraction
and
blood
is
pumped quickly out
y
bres,
the
used
muscles.
visible.
bres
of
on
in
in
movement.
y
muscle
are
work
shorten
c ause
l
muscle
exerted
muscles
composed
membrane
▴
that
to
r
is
be
c an
used
P
are
muscle
be
lengthening
skeletal
stripes
c an
must
many
muscles
c alled
as
force
so
contractile — it
e
c auses
is
that
s
s
Muscle
Cells
Figure 17
Light
micrograph of c ardiac
muscle tissue with short,
striations (pink).
LHA
◂
branched cells and
Interc alated
discs (purple)
are clearly visible where cells meet.
E ach
cell contains a single nucleus (purple)
s
s
e
r
l
a
much
larger
whereas
egg
Binding
for
that
layer
passively
embryo
enable
of
sperm
any
in
the
more
the
nucleus
•
Yolk — this
is
the
lipids
a
sperm
to
than
0.03 mm in length.
large
and
in
an
Centrioles — these
move
relatively
receive
actively and
slowly.
whereas
one
Egg cells
sperm
sperm
(and
have
no
little
more) in
of
but
from
which
later
c an
be
chemic ally
penetrating.
membrane which help it to fuse with the
the
sperm
enzymes
into
the
near
zona
nucleus
the
to
plasma
pellucida
and
has
entered
the
egg.
which
provide
the
resources
enter
the
egg.
membrane of the
make
it
needed
impenetrable
for
the
zygote
develop.
volume
other
Mitochondria — these
mitochondria
to
penetrate,
allowing
released
of
structures
embryo
E
of
have
are
v
also
the
Sperm
and
development
them
sperm
plasma
sperm,
a
which
the
cells
are
one.
glycoproteins containing ZP3 to which sperm
c an
l
O
cell
after
then
They
just
Beyond these similarities, male and
dierent.
u
of
egg
and
•
moved
granules — vesicles
Egg
•
a
proteins
Cortic al
stores
are
radic ally
fertilization.
prevent
membrane
•
than
n
to
less
i
which
f
x
•
as
pellucida — a
altered
are
needed
structures
known
and
debatable.
average length in humans of
mostly
t
a
bind
an
is
rather
each containing a haploid nucleus that
ospring.
food.
have
Zona
cells
gametes
to
r
o
•
are
parent
humans
reserves
process
cell
o
cells
from
d
the
with
are
a
p
rapidly
stored
cells,
cells
as
nuclei,
C
in
no
many
U
gametes
Egg
genes
cells
female
or
animal
human
classed
o
sperm
on
food
most
other
be
have
Adaptations of sperm and egg cells
passes
have
than
whereas
but
v
and
should
i
n
cells
bre
membrane,
y
30 mm,
B2.3.10
Egg
muscle
plasma
n
are
about
a
r
e
They
not
O
in
y
P
y
or
enclosed
t
i
s
Whether
produce
adult’
s
are
of
cytoplasm
inside
the
egg cell that contains
foods.
ATP
and
divide
repeatedly
to
generate all the
body.
needed
for mitosis.
249
Form and function
LHA
haploid
nucleus
cytoplasm (or yolk)
two centrioles
containing droplets of fat
s
s
first polar cell
e
r
diameter of egg
= 110 µm
l
layer of gel
(corona radiata)
composed
of glycoproteins
Figure 18
(zona
Structure of a human egg cell
cells
are
process — the
its
rst
role.
Tail — a
of
an
very
sperm
Sperm
long
Midpiece
that
so
u
l
a
E
v
O
f
x
Sperm
•
packed
resistance
also
have
Receptors
pellucida
the
haploid
oviduct
and
have
generates
the
the
at
the
base
needed
in
of
movement
the
that
plasma
from the testis of a male
female.
an
which
allow
needed
This
where
a
competitive
them
to
swim
rapidly.
arrangement of 9
for
+
2
forward motion with its
mitochondria
tail,
is
egg cell is the only one to
characteristic
force
the
a
they
are
c an
wound
supply
round
the
large
for the motion of the tail.
shape
structures
of
penetrate
structures
with
nucleus
and
is
very
and
the
narrow
due
volume
of
to
the
nucleus
cytoplasm
having
being
very small,
minimized.
they
use
membrane
to
insert
for
ZP3
their
nucleus
into
the
eggcell.
glycoproteins in the zona
to which the sperm binds.
sac
zona
of
enzymes
pellucida
so
that
the
digest
sperm
proteins
c an
reach
and
the
polysaccharides in the
plasma
membrane of
egg cell.
Binding
of
a
the
chromosomes
to
Acrosome — a
protective
•
in
reach
cells
Head — streamlined
tightly
•
ATP
i
•
of
in
mitochondria — multiple
o
quantities
the
cell,
the
250
with
microtubules
t
a
r
o
d
the
to
flagellum
beating action.
•
transfer
cell
n
U
microtubules
to
egg
C
achieve
•
adapted
cytoplasm
o
the
i
n
to
v
Sperm
pellucida)
p
▸
granules
y
r
e
layer of follicle cells
cortical
O
membrane
n
y
t
i
s
plasma
proteins
acrosome,
leading
egg.
to
in
the
inner
which
fusion
of
bind
the
acrosomal
to
membrane,
proteins
in
the
revealed
plasma
after
membrane
exocytosis
of
the
egg
membranes and entry of the sperm nucleus to
y
P
cell
Cells
LHA
haploid nucleus
acrosome
mid-piece
(7
head
(1.
thic, 
µm long, two-thirds of
it omitted from
this drawing)
μm
μm wide
s
s
and 4
tail (40
µm long)
μm long)
microtubules
in a
centriole
9+2 arrangement
Figure 19
helical
protein fibres to
mitochondria
strengthen the tail
r
▴
membrane
Structure of a human sperm cell
e
plasma
l
dierences
in
the
size
of
challenges
associated
cells
in
three
dierent kingdoms.
(A2.2.8)
b.
Explain
the
O utline
the
cells
that
lead
to
variation
become
the
role
of
methylation
speed
of
and
acetylation
of
expression.
process
of
cellular
spermatogenesis.
dierentiation
with
n
the
process
gene
between totipotent, pluripotent and multipotent cells.
U
Discuss
in
nerve
C
Distinguish
(B2.3.4)
c.
the
dierentiated?
(A2.2.13)
b.
in
o
do
Outline
factors
(C2.2.4)
i
n
a.
exchange as cells
v
How
gas
p
impulses.
with
(B3.1.1)
y
c.
larger.
r
e
become
O
the
t
i
s
Explain
n
What are the advantages of small size and large size in biological systems?
a.
2.
y
1.
y
P
Linking questions
respect to the
(D3.1.4)
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
251
Form and function
TOK
Should some knowledge not be sought
s
s
on ethic al grounds?
with
is
the
and
ac ademic study that looks into questions of
wrong.
situations
example,
methods
many
people
want
to
consider
ethic al
explore a topic
wrong or the
result in an outcome that some
wrong.
scientic
activities
from the 20th century
human
subjects
in
experiments that should
O
◂
involving
n
are
some
might
might
t
i
s
There
consider
they
confronted
raise
y
people
that
itself
sometimes
l
investigation
are
investigations
Figure 1
Henrietta L acks
standing outside her home several
not
have
been
c arried
out
on
ethic al
grounds. These
years before her death from
experiments include:
cervic al c ancer at the age of 31
to
debilitating
diseases (the
Tuskegee
Syphilis
•
deliberate
•
surgic al
•
tests with mind-altering substances.
had
no
experiment)
cells,
exposure
of
humans
to
radiation
cells
v
experiments
The
the
most
of
An
the
IRB
they
follow
subjects.
require
early
L acks
a
tissue
able
cells.
purpose
collection
and
use
today.
HeL a
practice
Today,
consent
to
cells
she
in
were
into
of
the
to
of
in
the
HeL a
her
reject
University in
c ancer cells
treatment
was sent
laboratory that the
cells
in
vitro. The cells
have
and
the
only
it
was
Public
was
discern
study
the
laboratory.
since
1952,
HeL a
HeL a
c arried
out
Health
the
from
1932
Service. The
natural
course
syphilis in black men. Of the 600male
about
men
400
had
needed
were
Participants
never
were
to
syphilis.
ensure
given
not
the
told
There
was none of
informed consent
option
their
of
leaving the
diagnosis
and
were
treated with placebos, although during the study
bec amewell
known
that
for
syphilis.
Based
on
the
lack
available,
the
Tuskegee
the
and
to
in
around the world.
Study
treatment
Of
research
States
transparency
study.
cervic al tumour that
multiply
a
Forty
original
further
wives
of
penicillin
opportunity
study
participants,
100
were
died
of
syphilis.
In
experiments,
to
was
28
was
get
and
died
19
an
as
eective
treatment when
“ethic ally
a
complic ations
infected
congenital
unjustied”.
result
of
children
the
of
syphilis
disease.
were born with
been highly
modern
rst
from
eective
without
her
permission.
access
L acks’
cells
in
than
the
if
a
placebo,
treatment
a
study
is
is
found
typic ally
to
be
more
stopped and
While
to
the
successful
treatment
is
provided.
research
1950s, it would not happen
be
their
required
use
for
human
c ancer.
biopsy
approve,
Hopkins
medic al
Henrietta
the
would
authorize
research
c arcinoma
E
legal
ensure
protect
cells
70years
range of phenomena, though they
this
a
sample
a
used
A
her
for
was
for
HeL a
a
Johns
discovered
were
studying
of
at
c ancerous
death.
was
to
the
proposals within the
l
for
a
v
were
It
research
patient
had
course
and
nicknamed
useful
the
lab.
survived
were
her
the
O
cells
to
authority
participants,
research
in
the
United
the
boards
to
to
of
untreated
used
c ancer
In
Syphilis
the
or
u
to
during
a
She
to
the
proposals
necessary
of
operates.
f
x
taken
led
it
was
1950s.
ultimately
has
review
university
objective
today
i
the
IRB
a
by
unethic al
t
a
Henrietta
which
research
principles
modic ations
in
within
r
o
institution
An
happen
o
or
reviews
ethic al
previous
to
institutional
committee
that
the
of
of
unlikely
d
human
a
be
been
Tuskegee
1972
n
organization
existence
is
examples
would
U
bec ause
(IRBs).
252
famous
practices
have
growing
thrived.
C
of
research
i
n
Some
to
success
however,
y
humans
p
of
o
exposure
r
e
•
The
her
any
cell
of
At
provide
informed
purpose.
line
source
cervix.
to
to
the
the
be
cultured
cells
was a
time, scientists
◂
Figure 2
Tuskegee
Syphilis Study participants
y
using
For
their
P
questions.
Scientists
where
r
right
e
Ethics
Cells
End of chapter questions
1.
The
table
shows
the
area
of
membranes
in
a
rat
liver cell.
3.
A
study
was
2
Membrane
component
through
Area/µm
the
plasma
endoplasmic
reticulum
30,400
inner
membrane
39,600
the
area
of
of
membranes in the
[2]
Low
your
total
area
0
membrane as a
of
membranes in the
working.
[3]
a.
Using
difference
mitochondrial
the
human
the
of
chloride
that
has
positively
ions
Water
been
thick
health
[2]
250
200
150
100
50
simple diffusion
0
71
61
51
41
31
21
01
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glucose / mmol dm
11
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of
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[1]
with
7
people
6
cells.
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5
cells
4
secretory
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by
300
2
secreted
facilitated diffusion
350
0
the
secretory
viscous.
through a
400
1
the
of
[1]
etar
fluid
and
associated
fo
the
thick
out
movement
450
l omm
is
of
a
why
fibrosis
out
by the
charged ions out of the
ions
its
500
mc
water
few
3–
move
too
e s o c u lg
chloride
secreted
with
cystic
and
processes that:
l
move
Explain
liquid
cells
v
O
b.
iii
The
viscous,
the
disease
malfunction
u
ii
of
positively
secretory
genetic
t
a
move
names
f
x
i
and
r
o
problems.
the
cells.
describe
into erythrocytes by simple diffusion and facilitated
rh sllec
becomes
the
alone,
diffusion.
i
cells
of
the
graph
through chloride
1–
out
In
channels
the
between the diameter of a
into cells. The graph shows the rate of uptake of glucose
pumped out,
from the cells into the liquid
d
move
State
moves
secreted.
chloride
ions
a.
also
passively
are
1.6
of passive protein channels on the movement of glucose
/ e k a tp u
the
follow
ions
and
in
1.2
diameter / nm
A second study was carried out to investigate the effect
example in the lung and
charged
information
membrane.
[2]
for
o
fibrosis,
cells,
molecule
n
channels.
[3]
table, suggest two of the main
U
and
the
livercells.
secretory
pancreas,
in
the
relationship
C
In
membranes.
data
From
the
area of the inner and outer
i
n
activities
2.
in
p
d.
the
0.8
molecular
o
Explain
v
c.
0.4
y
Show
the
plasma
r
e
cell.
movement
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n
area
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total
y
the
t
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s
evitaler
18,500
cell.
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the
l
100
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percentage
shows
High
280
lysosomes
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relationship
its
y
nucleus
b.
graph
the
and
r
mitochondrial
liver
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molecule
P
7,470
C alculate
determine
a
study.
enarbmem a hguorht
membrane
evom ot ytiliba
outer
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membrane.
to
of
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mitochondrial
other
a
out
diameter
e
rough
membrane
c arried
the
s
s
between
external
concentration
cystic
b.
Identify
the
rate
of
glucose
uptake
at
an
[4]
external
–3
glucose
concentration
E
i
simple
ii
facilitated
of
diffusion.
diffusion.
4 mmol dm
[1]
[1]
253
B
Fo r m
Organisms
of
its
forms
that
organs
adapted
per
ra t e ;
m i n u t e.
6be ats
per
the
at
of
to
When
surface
diving,
m i n u t e.
organisms
the
it
blue
he art
c an
h av e
whale
be ats
s l ow
are
adaptations
bec ause
to
referre d
structure
they
reproductive
animal
The
is
Ad a p t a t i o n s
These
to
organs
h av e
whose
functions.
to
referre d
organism
s ys t e m s
surviv al
largest
is
individual
g e n e ra t i o n
d i n o s a u rs .
the
an
functions.
o
s l ow
all
the
n
U
C
i
n
a
is
v
including
chances
their
its
y
whale
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p
the
The
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Multicellular
and
r
e
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functioning
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well
form
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often
The
the
t
i
s
is
and
and
organism
y
as
specialized
shape
an
n
to
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its
of
l
its
morphology
is
form
y
is
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o v e ra l l
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as
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The
e
form
s t r u c t u re.
r
The
function
s
s
3
and
lived,
he art
be ats
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d ow n
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ever
to
30
at
times
about
o
i
d
t
a
r
o
u
l
f
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a
E
v
O
B3.1
G as
exchange
How are multicellular organisms adapted to c arry out gas exchange?
organisms
their
need
to
gases
What
is
the
have
when
it
comes
of
water
but
the
to
c an
gas
freely
snorkeler
area-to-volume
multicellular
exchange?
exchange
needs
a
require
them?
ratio
organisms
How is it that the
gasses withthe
connection to the
atmosphere?
Figure 1
Snorkelers c an swim
O
t
i
s
▴
with sh but
with the air above
n
water
generate
surface
do
are the gases
processes
y
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What
Which
processes
challenges
in
from
l
sh
which
importance
What
need
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cells?
products.
exchanged?
and
they
P
for
waste
be
gasses
release other gases into the
r
these
as
the
and
e
environment
that
absorb
environment
s
s
All
still exchange gases
y
r
e
What are the similarities and dierences in gas exchange between a owering plant
beads
water
approximating
surface
in
plants.
making
the
surface
area
surfaces
of
to
mammals
what
ways
these
of
B3.1.3
M aintenance
of
Glass beads in water
HL
function
concentration
Adaptations
B3.1.5
Ventilation of the lungs
E
B3.1.4
of
B3.1.6
Measurement
B3.1.7
Adaptations
B3.1.8
Distribution
B3.1.9
Transpiration
a
markedly
dier?
AHL
in
all
organisms
of
of
lung
gas
as
a
lungs
for
Adaptations
at
exchange
gas
exchange
of
of
foetal
only
and
adult
haemoglobin
for the
oxygen
B3.1.12 Bohr shi
Oxygen
representing
dierent
dissociation
the
oxygen
anity
of
curves
as
a
haemoglobin
means of
for
oxygen at
concentrations
volumes
exchange
tissues
gradients
B3.1.13
mammalian
for
B3.1.11
transport
gas-exchange surfaces
v
surfaces in animals
and
vital
are
i
Properties
a
gas-exchange
plants
Figure 2
a
O
B3.1.2
as
generated.
the
u
SL
exchange
be
structures
▸
l
G as
owering
t
a
r
o
f
x
B3.1.1
c an
shape,
owering
do
and
o
In
and
in
shape.
very small, a huge
volume
similarity
have
any
provide the gas-
mammals
spheres
of
d
dierent.
is
spheres
both
relative
there
to
Spheres
ratio
n
Although
spheres.
U
exchange
By
are
area-to-volume
C
Shapes
in
surface
o
glass
smallest
i
n
the
v
The
p
and a mammal?
in
a
in
leaves
leaf
consequence
of
gas
exchange in
leaf
B3.1.10 Stomatal density
255
Form and function
B3.1.1
Gas exchange as a vital function in all
organisms
All
organisms
This
is
absorb
gas
photosynthesis
oxygen
for
cell
a
is
large
the
move
randomly,
across which the gases must
have
use
and
that
is
spongy
a
the
their
the
large
area-
surface
for gas
ratio is smaller and
exterior
much
surface
organism and the
outer
area-to-volume
organism
Terrestrial
exchange
rapid enough if it
of
required
or
only
sh
n
lungs
is
centre
is
greater. A
larger than the outer
mesophyll
in
a
leaf.
y
p
r
e
thin — the
surface
surface
is
area
is
covered
dioxide
large
by
a
in
They
c an
relation
film
of
are:
diffuse
to
across
the
freely
volume
of
moisture
in
terrestrial
distance,
in
most
the
organism
organisms so
dissolve
gases
n
U
c an
total
properties.
c arbon
C
moist — the
four
and
o
v
i
n
large — the
single
must
diffuse
only
a
short
c ases
through a
layers of cells.
o
i
d
r
o
total
this.
the
To
size
area
a
of
alveoli
in
tennis
court,
without
the
there
surface
are
in
area,
the
we
lungs
lungs
any
need
and
is
oen
said
evidence
to
know
•
for
their
you
and
mean
find
evidence-based
surface
area
of
values
human
for the number
alveoli?
how
•
what
C an
What
numbers
are
needed
to
c alculate an estimate
average
for
the
total
surface
area
of
an
axolotl’s
gills?
E
v
a
area is.
the
l
surface
of
estimate
alveoli
O
many
surface
u
be
f
x
The
t
a
axolotl gills
B3.1.3
M aintenance of concentration
gradients at exchange surfaces in animals
Diusion
of
example,
bec ause
in
256
share
•
•
in
an
is
molecules
the
therefore
as
Thinking skills: The reasonableness ofknowledge claims: The surface area of
ATL
to
surfaces
•
in Mexico
of
surface
produced.
such
organisms
surface
for use in
Properties of gas-exchange surfaces
permeable — oxygen
the water
Axolotls are critic ally endangered
centre
alveoli
•
gases
in their habitat
the
c an
the
the
distance
between
They
dioxide
animals
exchange
small
dioxide
O
between
example
total surface area with a distance of 10 µm
outside.
small.
surface,
for
the
and
other
organisms,
gas-exchange
The gill laments have a large
in c apillaries and
is
area
and
release another
process. Humans absorb
y
distance
larger
G as
distance
specialized
Axolotls develop lungs but
between blood
the
Bec ause
process.
the
c arbon
Aquatic
t
i
s
In
Gas-exchange
adulthood.
and
environment
B3.1.2
also retain their feathery external gills into
surface
the
air.
exchange.
slow
Unicellular
ratio
exchange.
the
a
short.
gas
the
in
and
c arbon
air.
gases
oxygen
the
only
oxygen
C arbon
happens
diuses
from
if
air
there
in
concentration
dioxide
diuses
from
are
the
of
concentration
alveoli
blood
the
in
blood
to
the
the
to
gradients.
adjacent
c apillaries
air
in
the
is
For
c apillaries
lower than
alveoli
bec ause
y
over
diuse
of
produced
release
with
absorb
l
occurs
basis
and
gases
relatively
oxygen
environment
trees
r
the
is
the
P
is
diusion
from
Redwood
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water.
exterior
Figure 3
respiration
gases
Diusion
gas
release
exchange
to-volume
▴
and
organisms
with
one
exchange.
s
s
one.
Organisms
there
is
a
lower
concentration
gases
must
to
continueto
be
maintained.
small,
aerobic ally
exchange,
it
is
cell
diuse
respiring
concentration
c arbon
dioxide
mammals,
organs
specialized
refer
to
by
too
low
to
in
the
fresh
water
through
flow
in
water
the
the
to
remains
from
air
to
dioxide
slits.
and
the
the
the
too
gradients.
out
of
the
This
lungs,
dioxide.
term
but
their
This
gills
alveoli
oxygen
was
it
blood
high.
by
exhaling
is
and
concentration
and
The
also
rate
now also
mouth
one-way
and
flow
ensures
remains
high
low.
the
ventilation
pump
of
then
from
prevents
of
concentration of the blood.
direction,
the
c arbon
across gills.
rising
through
gill
in
of
it
replace
dropping
c arbon
is
adjusted
over their gills and
water,
combined with
that
the
oxygen
concentration
and
the
c arbon
dioxide
C
i
n
concentration
the
opposite
adjacent
air
air
prevents
from
c arbon
of
respiration, this blood has a
o
the
from
aerobic
v
in
diffusion
expel
to
organisms such as sh
c apillary networks in the
concentration
concentration
water
This
Due
high
larger
dense
p
out
blood
air.
In
through
dioxide, so the
lower than outside and the
y
take
then
fresh
higher.
for gas
r
e
Fish
of
concentration
according
•
maintain
periodic ally
for
a
movement
movement
inhaling
dioxide
to
the
and
c arbon
remains
surface
gradients. This
O
it
exchange.
outer
concentration
For
gradients
t
i
s
M ammals
gas
concentration
n
to
helps
for
remains
continuously
oxygen
their
evens out
exchange.
l
used
also
used
for
of
use
Diusion
gas
y
originally
ows
air.
stop
surfaces,
produces
organism
the
y
concentration
Ventilation
•
concentration
blood
and
in
then
P
low
the
that
maintains
oxygen
within
exchange
organisms
that
and
r
or
uses
dioxide
slow
e
continuously
oxygen
c arbon
could
across
respiration
process
of
which
s
s
In
concentration
gradients,
Data-based questions: Concentration gradients
air
4
in
shows
the
the
typic al composition of atmospheric
alveoli
and
gases
dissolved
in
air
returning to
f
x
100
v
159
E
l a i t r ap
200
not
a.
as
why
high
the
oxygen
asinfresh
C alculate
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blood
concentration
air
that
difference
concentration
and
between
arriving
at
is
in
the
alveoli is
[2]
oxygen
air
the
in
inhaled.
in
the
alveolus
alveolus.
[1]
dioxide
570
b.
Deduce
concentration
dierence.
c.
i.
the
process
the
C alculate
565
ii.
a
300
u
570
400
2.
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c aused
by this
nitrogen
l
O
gH mm / erusserp
500
o
c arbon
59
600
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oxgen
t
a
700
e
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r
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the lungs in the pulmonary arteries.
n
air,
U
Figure
d.
dioxide
concentration
inhaled
and
Explain
this
Despite
in
air
the
in
air
the
to
air
the
in
c arbon
between air
exhaled.
[1]
dierence.
high
alveoli,
[1]
dierence
[2]
concentration
little
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or
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of
nitrogen
diuses
Suggest
from
reasons
forthis.
[2]
120
105
40
40
45
27
3
0
atmospheric
air in
blood
air that is
alveoli
travelling
inhaled
▴
to
air
exhaled
alveoli
Figure 4
257
Form and function
B3.1.4
trachea
Adaptations
of mammalian lungs
for
right bronchus
gas exchange
mammals
use
lungs
s
s
All
for gas
exchange, even marine species such
intercostal muscle
as
whales
the
and
lungs
dolphins.
through
Air
is
drawn
e
into
the
trachea
(windpipe) and then the le and
bronchi
each
lung,
(singular,
Alveolar
pulmonary
of
is
0.2 mm
a
which
Figure 5
Airways,
lungs and
associated
muscles in the human thorax
also
v
of
Structure of an alveolus
AT2 cell which
secretes surfactant
about
are
wall
by a dense
c apillary
wall
layer of cells. Air and
much
the
of
there
Some
of
elastic
The
surface
a
very short
c apillaries
of
the
cover
alveoli
are also some other cells.
these
strengthen
and
The
therefore
apart.
but
its
0.2 µm thick.
surrounded
network.
single
o
n
a
capillaries
258
o
i
0
0
2
u
l
E
v
O
f
x
t
a
m
0
0
only
distance
to
5
–
network of blood
Figure 6
C
i
n
U
d
r
o
phagocyte
a
but
extremely thin and consists
blood
exchange
(air-sacs).
alveolus has a diameter
0.5 mm,
y
is
which
alveoli
layer of cells, much of
are
c apillary
allows rapid gas
alveolar duct
is
Alveoli
p
r
e
thin AT1 cell
▴
single
to
six
O
t
i
s
A
ve
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n
or
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l
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branches
bronchioles.
branch
each
bronchioles
diaphragm
▴
ducts
bronchioles,
y
right lung
form
have
the
collagen
lung
bres
tissue and
bres to help limit inhalation
c ause
passiveexhalation.
y
to
ribs
bronchus). In
bronchus
P
the
repeatedly
r
right
Organisms
An
individual
bec ause
lungs — the
of
the
alveolus
there
are
total
body.
area
The
alveoli
Cells
the
wall
to
water
prevents
exhaled
from
a
of
as
lining
the
water
the
lungs.
in
the
tails
from
This
area
40
times
basket-like
as
pulmonary
hydrophobic
surface
about
the
large
phospholipids
moisture
the
large:
area
almost
secrete
of
the
is
small
for
gas
exchange, but
that
of
the
surfactant.
cell
greater than the outer surface
networks
Its
membranes.
alveoli,
facing
with
the
the
air.
c apillaries
molecules
have
They
a
form
heads facing the
the
prevent collapse of the lung.
the
alveoli
to
adhere when air is
alveolus
l
water
monolayer of
Pulmonary surfactant
molecules on the surface of the lm of
moisture lining the alveoli
air
conditions
that
are
Place
how
a
and
ruler
many
across
times
each
the
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such
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People
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COPD
COPD
right
side
forthis.
v
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▸
for
feel
often
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Figure 8
tissue from
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a
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3.
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obstructive
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o
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number
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b.
COPD
micrograph,
are
group
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each
results
a
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is
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Chronic
associated with smoking and
with
a
open
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Patients
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are
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U
become
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disease
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there
thin-walled
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pulmonary
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small
o
lung
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healthy
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y
p
r
e
Data-based questions: COPD and gas exchange
In
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Figure 7
t
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surface
surfactant
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structure
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air
a
monolayer on the
helps
to
of
blood
hydrophilic
This
sides
of
alveoli.
r
and
of
and
very
a
them — about 300 million in a pair of adult
e
surface
that
is
of
s
s
the
in
provides
many
surface
around
similar
so
draw
the
[3]
from
[3]
time.
[3]
enlarged and
Suggest
areason
[1]
Healthy lung tissue (top) and lung
a person with COPD (bottom)
259
Form and function
B3.1.5
The
airways
mouth,
in
their
walls
in
occupy
a
gas
to
is
the
and
ensure
walls,
the
compressed
it
will
the
involves
volume,
to
the
air
the
ow
open.
width
some
of
a
The
of
body
and
bronchioles
airways
physics.
the
gas
of
If
to
of
to
atmosphere
atmospheric,
stretched
helped
during
by
so
the
volume
260
Figure 9
allowing
push
it
contract, pulling
relax
inside
and
are
consequently
Muscle actions that
the
diaphragm
into
a
more
pulled
pressure
increases and
decreases, sucking air in
c ause inspiration and
expiration
in
abdominal
the
in
inside
lungs
lung
to
the
the
tissue
thorax to
atmosphere
that
become
the
so
abdomen
organs
during
The
external
into
their
The
internal
The
relaxes
it
c an
be
pushed
upwards
domed shape
only
ribc age
thorax
bres
The
forced
the
pressure
from
Expiration
Muscles
outwards
elongated state
v
▴
E
pressures
wall out
outwards
muscles
thorax to
y
The
muscles
Volume or
intercostal
the
drawn into the lungs
pressure has risen to atmospheric
p
their
inside
is
o
internal
into
a
The
relax
to
muscles
and
l
O
Internal
intercostal
intercostal
upwards
elastic
C
external
ribc age
wall
diaphragm
of
out
air
n
muscles
the
moves
o
The
abdomen
the
it
u
f
x
External
intercostal
the
from
so
abdomen
i
muscles
in
and
the
t
a
pressure
pushes
forced
recoil
lung
c ause
r
e
U
Muscles
wall
contracts
and
r
o
Abdomen
d
diaphragm
downwards
the
then
v
i
n
tnemevom mgarhpaid
ria
egacbir
tnemevom
tnemevom
The
is
inspiration.
Inspiration
Diaphragm
air
pressure
O
(expiration),
until
contractions
the
consequence,
n
above
(inspiration)
muscle
c ause
a
t
i
s
rise
Other
As
regions of
forced
and
wall
contract pushing the
diaphragm
upwards (but
expiration)
intercostal
muscles
relax
and
are
pulled
elongated state
intercostal
inward
and
muscles
contract, pulling the
downwards (but only during
expiration)
volume
inside
consequently
the
the
thorax
pressure
decreases and
increases,
forcing air out
y
the
pressure.
contractions
pressure.
spread out
Conversely,
l
from
muscle
atmospheric
nose,
c artilage
pressure rises. If gas is
pressure
y
below
gas
lower.
P
ventilation,
drop
the
have smooth muscle
lowerpressure.
During
of
have
vary.
particles
the
higher
consist
bronchi
becomes
volume,
regions
the
trachea
these
smaller
from
outside
The
basic
pressure
occupy
always
to
bronchioles.
remain
allowing
lungs
larger
move,
they
lungs
r
free
of
a
connect
bronchi
e
if
to
their
Ventilation
to
that
trachea,
s
s
bres
Ventilation of the lungs
Organisms
B3.1.6
•
Tidal
volume
stale
air
times
Vital
that
that
air
inhaled
after
after
•
is
not
meters.
through
to
use
dioxide
is
or
rate is the number of
the
the
total
total
volume
volume
of
of
air
air
that
that
c an be
c an be
exhalation.
volume
volume
is
the
amount
of
air
a
person
c an
inhale
forcefully
exhale
forcefully
inspiration.
volume
is
the
amount
of
air
a
person
c an
exhalation.
volumes
safe
c apacity)
inhalation
Ventilation
minute.
c an
be
Simple
the
this
measured
apparatus
delivery
tube
apparatus
for
using
is
either
shown
into
a
in
vessel
repeatedly
simple
Figure
and
the
inhaling
apparatus or
10.
One
volume
and
normal
is
breath
measured.
exhaling air as the
concentration will rise too high.
Figure 10
of
i
some
A oat
spirometer has an air reservoir oating on
Air in the reservoir c an be breathed
which
ow
volumes
c an
be
a tube with a mouthpiece on the end.
into the reservoir via alkali that
in and
out
through
air passes back
absorbs c arbon dioxide. This
repeated
breaths
rate into and out of the lungs
c an
used
Exhaled
prevents the concentration of c arbon dioxide from rising with
t
a
designs,
measure
lung
l
be
with
deduced.
data
There
logging
are
many
soware.
a
O
ATL
spirometers
measurements
Figure 11
water.
to measure volumes inhaled?
u
dierent
r
o
these
f
x
designed
and
be modied
o
it
Specially
from
▴
Simple apparatus for measuring the volume of air
How could
d
exhaled.
n
▴
U
pneumatic trough
C
i
n
delivery tube
o
graduations
y
p
r
e
jar with
v
bell
O
c arbon
per
n
It
inhaled and also the amount of
y
exhaled
is
t
i
s
is
that
y
lung
maximum
reserve
expelled
vital
maximum
tidal
normal
specialized
forced
or
air
ventilation.
l
These
a
a
in
fresh
each
P
after
(or
a
reserve
normal
Expiratory
drawn
of
with
r
after
volume
e
Inspiratory
the
exhaled
is
c apacity
exhaled
•
is
is
s
s
•
Measurement of lung volumes
Communic ation skills: Deciphering meanings by knowing etymology
is
the
study
E
biologic al
terms
v
Etymology
are
of
the
derived
•
pulmonarius
•
alveus
means
•
ventus
means “wind”
origin
from
of
words.
these
L atin
What
•
fundere
•
diffundere
means
“to
pour ”
words?
means
“to
pourapart”
means “lung”
“hollow
vessel”
Why
do
L atin
origins?
so
many
terms
in
biology
and
medicine
have
261
Form and function
B3.1.7
Adaptations for gas exchange inleaves
Chloroplasts
need
produced
of
moist
avoid
surface
surface
outer
waxy
close
it.
The
leaf
is
covered
waterproof
plants
and
is
layer
and
at
when
also
low
cells,
pore
oxygen
to
permeability
which
is
c an
dying
c alled
pass
a
is
the
stomata
if
a
to
stoma
through.
photosynthesis
close
from
not
upper epidermis
gases,
their
(plural,
The
is
on
for plants is to
adapted
secreted
cuticle.
the
but
upper
within
shape
the
either
stomata)
for both gas
by the
It
varies in
surface
of
and
epidermis
to
open
up
it
allows
pore
c arbon
and
gas
water
exchange
is
not
required.
stress and is in danger of
C
leaf vein
n
U
with rounded cells and
there
a
o
i
n
with tightly packed
spongy mesophyll
leaves
guard cells usually close the stomata
suering
v
palisade mesophyll
guard cell
o
i
lower epidermis
▴
Figure 13
fractured
u
The
Sc anning electron micrograph of a leaf of Prunus.
stomata
l
a
The
area
gas
dioxide
cells.
from
in
connect the air outside to a network of air spaces in the spongy
of
spaces.
for
the
leaf.
walls
of
exchange.
the
air
E
the
spongy
C arbon
the
air
outside
Bec ause
Inevitably,
there
mesophyll
cell
is
cells
of
the
then
loss
of
oxygen
and
are
then
in
c an
diuse
provide
a
diuse
in
through these air
very
permanently
generating
chloroplasts
through
a
large total surface
moist,
the
c arbon
mesophyll
concentration
mesophyll
cells.
gradient
Photosynthesis
chloroplasts, so it diuses to the surfaces of
into
water
diusion
cells
walls
dioxide,
oxygen
and
and
these
dissolve
to
and
mesophyll
c arbon
leaf
some
walls
c an
uses
the
concentration
mesophyll
dioxide
spongy
spaces
Photosynthesis
the
raises
The leaf was frozen and then
so the interior structure is visible
mesophyll
v
O
f
x
t
a
r
o
d
extensive air space
the
by
out
air
spaces
and
evaporation
through
the
out
of
the
leaf.
from the moist spongy
stomata.
There is also some
Veins in a leaf of Gunnera
use
of
water
in
photosynthesis.
Water
manicata
loc ated
262
wax,
waxy
p
wax visible on their surfaces
Figure 14
are
area
absorbed and
y
have sinuous edges, with ridges of thick
▴
of
the
thick
occurring
plant
dehydration.
leaf. The epidermis cells
cylindric al cells
layer
r
e
a lavender plant
a
c alled
change
open and the other is closed in this sc anning
electron micrograph of the outer surface of
in
is
particularly
One of the two stomata is
They
challenge
leaves
oxygen
large
O
dioxide
night
the
has
guard
be
A
n
to
A
c an
adapted to dry habitats.
cuticle
of
so
y
pairs
leaves.
surface,
The
removed.
in
the
leaf
veins
(Figure 14).
is
supplied
to
the
leaf
in
xylem
vessels,
y
The
the
dioxide
t
i
s
Figure 12
plants
by
the
be
l
in
from
c arbon
photosynthesis.
must
conservation.
This
between
which
provided
water
for
P
and
of
over
dioxide
photosynthesis
r
thickness
cells.
is
c arbon
of
e
The
of
water
of
process
required
loss
and
or
supply
excreted — this
excessive
epidermis
▴
is
exchange
are
a
the
s
s
oxygen
during
Organisms
B3.1.8
Plan
the
Distribution of tissues in a leaf
diagrams
junctions
show
the
between
areas
of
tissues,
but
not
individual
cells.
The
lines
indic ate
tissues.
upper
s
s
epidermis
palisade
xylem
e
mesophyll
r
spongy
mesophyll
Figure 15
An example of a tissue plan of
lower
trees
there
leaves
on
the
1.
Draw
that
diagrams
each of the
Compare
and
of
are
Prunus
contrast
which
b.
Discuss
reasons
sunand
shade
whichinthe
of
thickness of
the
[4]
grew in the sun and
shade.
for
the
dierences
[1]
between
leaves.
[3]
Micrographs of two leaves of Prunus caroliniana,
i
one that
grew in the shade. The
micrographs have the same magnic ation
t
a
r
o
grew in the sun and
B3.1.9
palisade
o
Figure 16
one that
structure of the two
thickness,
d
▸
[7]
mesophyll.
leaf
shaded.
n
Deduce
and
representative
U
a.
a
leaves.
structure
spongy
down
in
C
and
between
o
the
and
structure
i
n
waxycuticle
lower
tissues
the
overall
in
are in full sunlight and
the
leaves,including
mesophyll
3.
tree
that
v
2.
of
dierences
p
part
same
plan
are
branches
y
upper
r
e
on
O
t
i
s
many
leaves
n
transverse section
Data-based questions: Sun and shade leaves
On
with the leaf in
y
epidermis
l
a typic al dicotyledonous leaf,
y
◂
P
phloem
Transpiration as a consequence of
u
f
x
gas exchange in a leaf
of
air
is
already
molecules
in
this
from
is
and
state
so
the
c alled
is
water
If
and
number
air
is
E
molecules
very
number
be
no
net
air
c an
is
more
higher
loss
hold
humid
condensing,
from
when
energy
it
a
the
we
say
the
gas-exchange
is
saturated
available
to
join
of
air
is
a
become
The
to
with
a
gas.
water
Molecules
process is
evaporating
water
amount
bonds
of
become liquid.
temperature.
hydrogen
unless
individual
part
molecules
The
surface
of
opposite
others
saturated
with
eectively if the gas-
moist
separation
water
surface.
varies
break
the
vapour.
vapour
the
works
from
molecules
condensation — water
the
only
evaporates
Evaporation
water,
are
dioxide
Water
saturated.
liquid
separated
c arbon
moist.
a
the
oxygen
surface
v
O
exchange
l
Exchange
of
vapour.
water
This
between
is
is
equalto
There will
vapour that
bec ause
water
there
molecules at
temperatures.
263
Form and function
4.0%
1.0%
pressure between −60°C and
0.0%
lower air pressures,
–60
each
–40
–20
0
20
l
of
the
this
water
vapour.
leaf
as
is
high
vapour
water
air
kept
spaces
for
gas
already
exchange.
saturated with
water
their
open
The
mechanisms
to
in
outside,
outside
using
Guard
vapour will diuse out
of
guard
the
is
to
c alled
transpiration.
factors.
temperatures
air
do
c an
hold
cells
so
there
is
more
more
water
the
These
prevent
the
of
easing
due
the
of
the
diffusion.
water
are
of
air, the
night
in
in
pairs, one
stoma
all
There is
vapour.
found
the
nearly
stomata
rate
the
at
of
with
cells
and
c an
transpiration
when
there is no
daylight
is
photosynthesis
that
is
little
limited.
aperture of the stomata to be
concentration
concentrations
rate
aperture
routinely
humidity
between the air spaces
saturated
the
the
allow
relative
vapour
c an
closing
dioxide
widely,
is
cells.
this
the
lower
leaf
Plants
absorbed,
c arbon
less
so
water
control
plants
the
spaces
plants
warmer
higher
guard
cells
Most
be
higher
of
the
closed.
dioxide
stomata
the
fully
c an
the
c arbon
open
to
at
Also
gradient
disadvantage
dioxide
to
air
air
losses
stoma.
stomata.
according
atmospheric
the
the
of
air
p
u
l
to
inside
human
the
leaf.
activity
problem
of
water
unit
of
leaf
Rising
are
loss
a
allowing
little.
a
E
v
O
f
x
Control
plants
a
wide
c arbon
varied
o
closing
if
water
of
i
from
t
a
r
o
d
side
photosynthesis.
no
and
stems
the
saturated.
correlation):
n
U
leaf
minimize
either
adjust
the
of
environmental
correlation):
concentration
transpiration
and
evaporation.
becoming
(negative
by
humidity
moist
are
vapour in the air outside the
spaces,
o
before
leaves
aected
for
the
C
i
n
vapour
the
the
(positive
available
Plants
or
are
energy
Humidity
on
from
c auses
v
Temperature
no
by
rates
This
of
the
are
air
y
water
inside
B3.1.10
Stomatal
density,
and
a
264
in
leaf
walls. The
of
smaller
closed stomata
concentration
concentration
a
the
below the
•
Open and
the
inside
unless
drop
•
Figure 18
the
stomata.
Transpiration
▴
Unless
as
mesophyll
evaporate
saturation point, so more water evaporates from spongy mesophyll cell
loss
the
will
r
e
through
spongy
water
O
of
n
y
walls
Some
t
i
s
The
40
temperature / °C
temperature would be higher
Stomatal density
density
the
is
the
number
stomata
are
microscope.
too
of
number
of
stomata
stomata
in
a
small
to
be
per
known
seen
with
area
the
area
must
naked
be
surface.
counted.
eye
but
are
To nd the
Guard cells
easily visible with
y
At
the percentages at
P
+40°C.
e
sea-level
s
s
at
r
air c an hold
ni
that
percentage,
of water vapour
2.0%
ria
by mass,
egatnecrep
Graph showing
the maximum
noitarutas ta
Figure 17
tniop
retaw fo ssam yb
▸
3.0%
Organisms
Two
1.
techniques
A
sample
c an
of
break
be
all
on
Another
areas
a
nail
counts
should
leaf
should
be
the
be
c ast.
c an
Commelina
be
folded
and
across
if
the
c arried
epidermis
are
then
mounted in
leaf is non-hairy and smooth.
to
a
nail
The
cells
small
area of upper epidermis and
varnish
nail
is
peeled
varnish
forms
and
the
stomata
until
the
eld
number
out
of
examined.
the
on
moved
The
areas
and
a
of
of
stomata
mean
view
is
then
of
mounted on
c ast
clearly
c an
number
off,
a
of
the
leaf
visible.
lled
be
by the
counted.
stomata
c alculated. If
t
i
s
▴
meannumberofstomata
2
stomatal
density (mm
)
Figure 19
O
of the eld of view is determined, the stomatal density c an be c alculated.
The lower epidermis c an
usually be peeled
=
2
areaofeldofview(mm
)
n
Repeat
or
easy with
leaf
y
epidermis
dry,
of
is
The
lower epidermis and then the epidermis
are
examined.
margins
slide
peeled
and
Small
and
used
is
This
c an be torn in half obliquely which often
painted
it
the
leaf.
trying.
l
microscope
When
slide
the
be
is
the
y
with
from
leaf
slide
c an
varnish
off
worth
r
microscope
the area
apart
the
are
epidermis.
technique
epidermis.
surface,
The
of
peeled
P
a
or
microscope
Colourless
lower
tissues
off
is
species
e
2.
the
peeled
separates
water
Other
s
s
c an
used.
epidermis
Tradescantia.
to
be
more easily than the
upper epidermis
y
r
e
its
bubble
tap
c arry
below
out
the
new
consists
in
and
of
a
and
the
takes
along
travels
20
measure
shoot),
plant
move
Figure
the
c an
show
shows
water
leafy shoot in
a
graduated
c apillary tube
up
the
reservoir
xylem
that
water
through
c apillary
time
tube.
taken
are
allows the bubble
i
to
the
will
to
bubble
r
o
to
As
A
of
the
o
the
The
reset
(le
in
materials
tissues.
used
apparatus
point.
measured.
be
The
reservoir
bubble
distance
plant
(horizontal).
zero
the
to
device
d
The
tube
the
roots,
a
a
and
n
c apillary
marks
plants.
(right),
is
transport
C
in
This
water
U
tube
in
apparatus
structure
potometer.
uptake
a
in
using
i
n
similarities
a
involved
investigated
o
be
v
Mechanisms
p
Applying techniques: Using a potometer to measure rates of transpiration
measurements.
Figure 20
A potometer
u
l
O
f
x
t
a
▴
Measurement: Repeat measurements to improve reliability
is
standard
practice
should
be
plants
many
areas
of
number
will
be
not
be
of
as
the
correct.
the
as
The
but
variability
be
in
done
is
this
to
repeat
c ase,
samples
leaves on the plant and as
taken
if
In
possible.
should
stomata
same,
as
research
trials.
many
species
possible
of
scientic
replic ate
from
E
many
the
and
taken
in
v
measurements
a
It
For
each
leaf, as
Repeating
avoid
the
eect
on
it
allows
the
the
a
counts
danger
of
has
an
conclusions.
mean
to
be
several
outlier
It
the true stomatal
density than a
be.
the
c arefully,
natural
in
each count will
biologic al material.
also
allows
statistic ally.
more
The
reliable
less
the
disproportionate
reliability
bec ause
c alculated which will be closer to
each
It
a
increases
examined and a count
area. The counts
advantages. It helps
having
reliability
variation
single count is likely to
of
the
mean
between
the
to
be
assessed
repeats, the
mean.
265
Form and function
LHA
B3.1.11
Adaptations of foetal and adult
haemoglobin for
Haemoglobin
molecule
of
is
of
potentially
also
unloads
reduced
oxygen
for
for
this
as
Fully
the
oxygen
with
oxygen
10 kPa,
above which
ows
through
concentration of
oxygenated blood
where the partial
oxygen
diuses
c arried
into
the
by the
tissues of
very
it
of
changes
oxygen
readily
in
a
from fully
concentrations.
tissue
where
concentration. Without this
could
the
range
not
be
activity
kept
of
transport
described in
as
muscle
by
high
and
as
they
other
interacting
are in
tissues.
with
c arbon
Section B3.1.12
noitarutas
negyxo htiw
egatnecrep
E
v
a
nibolgomeah fo
u
l
f
x
O
this would be
the relationship
if oxygen
the actual
relationship
saturation was
between saturation and
directly
oxygen concentration is not
proportional
to
directly proportional with
concentration
most of the increase over a
narrow range of oxygen
concentrations. This is a
sigmoid curve
pressures in kilopascals)
266
no
pressures,
oxygen concentration (usually shown as partial
▴
with
blood
body,
groups.
oxygen rises,
oxygen
Instead,
oxygen
oxygen
are
an
and
of
Figure 22
oxygen
therefore fully
correlated
partial
reaches
the
narrow
oxygen
reducing
adapted
mechanisms
the
as
pressure
of
haem
are
the
saturation of haemoglobin is not
concentration.
relatively
other
oxygen binds
Oxygen dissociation curve
y
is
a
given
of
(separates)
molecules
dissociates,
unsaturated
lungs).
some
oxygen
Oxygen
n
The
or
have
organs
least
in
happens
healthy
four
increase
oxygen
molecule
pressure
This
to
O
binding,
oxygen
an
positively
partial
which
cells.
when
that
y
dioxide.
At
is
are
up
bec ause
p
i
Haemoglobin
other
dissociates
concentrations
tissues,
t
a
r
o
bec ause of the
oxygen binding c apacity of haemoglobin
respiring
normal
haemoglobin
has
alveoli,
all
over
As
partial
C
that
the
10 kPa.
o
adaptation,
to
(in
to
n
U
37°C, but
state),
o
therefore
of oxygen
3
blood c an hold over 200 cm
d
3
of water at
R
saturated.
the
13 kPa
below
respiration
units.
until
100%
unsaturated
ensures
aerobic
(the
so
c aused
anity
reduce
haemoglobin
haemoglobin
pressure
cooperative
to
are
that
concentrations
rises
c arried
proportional
saturated
This
is
usually
of
molecule,
when
bound
of
site,
Conversely,
a
blood
molecule.
t
i
s
directly
and
lungs
i
n
Bec ause
3
the
v
is
binding
changes
r
e
10 kPa
theorgan.
Less than 50 cm
as
level
oxygen
surrounding
haemoglobin
Figure 21
The
saturation
c apillaries
the
for
red
l
saturation
the
pressure
c an dissolve in 1 dm
oxygens
becomes
leaving
▴
changes
states
a
haemoglobin
haemoglobin
groups.
haemoglobin
between
as
by
four subunits in a haemoglobin
state).
kilopasc als
percentage
acts
c arried
the
P
four
per
of
y
oxygen
a
haem
probable
with
(theT
which
conformational
conformational
most
concentration.
with
in
protein
E ach
r
other
bound
group
cooperative
the
transport
transported
of
saturated
The
haem
be
group,
two
oxygen
haemoglobin.
haem
c auses
The
a
c an
the
to
e
one
anity
it
has
oxygen
Binding
to
is
reversibly
s
s
binds
the transport of oxygen
Organisms
birth,
a
months
with
for
produce
baby
for
cells
still
all
the
oxygen
than
red
red
c arrying
blood
adult
adult
is
a
of
haemoglobin
cells
cells
with
haemoglobin.
more
foetus
foetal
c arrying
haemoglobin.
therefore
pregnancy
types
blood
At
any
saturated
obtains
foetal
Foetal
and
aer
It
haemoglobin
haemoglobin
partial
with
oxygen
before
haemoglobin.
pressure
to
has
of
birth.
takes
be
a
At
several
replaced
stronger anity
oxygen,
foetal
s
s
haemoglobin
During
dierent
has
LHA
Humans
oxygen than adult haemoglobin.
via
the
placenta.
Oxygen
dissociates
from haemoglobin in maternal blood in the placenta and binds to haemoglobin
foetal
anity
blood.
for
This
c an
only
happen
bec ause
foetal
haemoglobin
has
stronger
of
c arbon
r
haemoglobin
haemoglobin.
C arbon
ions
for
Two
dioxide
and
active
in
oxygen
water
tissues
c arbon
and
mechanisms
and
hydrogen
in
Increases
are
results
dioxide
therefore
c ause
the
converted
in
greater
increase
decrease
in
release
concentration
red
dissociation
in
blood
cells
into
In
pH
the
of
the
lungs
O
→
H
+
HCO
2
3
blood,
where
which
the
reduces the affinity of haemoglobin
concentration
of
c arbon
dioxide
is
low,
y
H
p
oxygen.
hydrogen
o
v
for
the
oxygen
r
e
+
+
2
reduces
of
anity.
c arbonate ions.
CO
This
decrease the
n
1.
of
respiration
blood.
O
from
the
t
i
s
anity
into
l
dioxide
Bohr shi
aerobic
y
Increased
P
B3.1.12
y
a
oxygen than adult haemoglobin.
e
in
the pH is 7.4. In active muscle, there is a higher c arbon dioxide concentration
the
pH
active
E ach
respiring
of
group
the
to
four
subunits
at
the
converted
of
to
small
pH
in
c an
the
the
lungs
react
and
dissociation in
reversibly with
polypeptide. The amine
haemoglobin
becomes
o
4CO
of
difference is enough to
the
i
c arbaminohaemoglobin
2
affinity
of
concentration
t
a
to
the
and
d
converted
reduces
dioxide
haemoglobin
of
actively
c arbaminohaemoglobin,
u
f
x
is
c arbon
+
r
o
reaction
terminal
c arbamate
haemoglobin
high
This
haemoglobin
amino
c arbaminohaemoglobin.
This
7.2.
haemoglobin
tissues.
dioxide
is
about
n
c arbon
is
binding
U
2.
typic ally
oxygen
C
promote
i
n
and
for
oxygen.
respiring
promoting
Due to the
tissues, haemoglobin
release
of
oxygen.
C arbaminohaemoglobin changes back to haemoglobin in the lungs, due
to
the
low
c arbon
saturated
tissues
The
reduction
is
concentration.
c arried
in
red
consequence
each
remove
in
the
affinity
concentrations
ensure
oxygen
is
four
The
blood
of
this
c arbon
haemoglobin
cells
through
the
then
becomes
alveolar
mechanism is that haemoglobin
dioxide
molecules
from
respiring
transport them to the lungs.
E
to
Another
c an
and
dioxide
it
a
molecules
dioxide
v
O
c apillaries.
as
l
100%
that
respiring
is
of
haemoglobin
known
tissues
as
the
have
Bohr
enough
for
oxygen
shift
or
in
Bohr
oxygen
high
c arbon
effect. It helps
when
their
need
for
greatest.
267
Form and function
LHA
B3.1.13
Oxygen dissociation curves as
a means of representing the anity of
haemoglobin for
oxygen at dierent
s
s
oxygen concentrations
Oxygen
dissociation
is
101.3 kPa
oxygen
curves
21%
only
cover
air
a
curve
is
percentage
oxygen,
inside
the
range
from
for
adult
the
partial
alveoli
is
0 kPa
oxygen
Normal
pressure
lower,
to
so
15 kPa.
haemoglobin.
saturation of
atmospheric
of
oxygen
Figure
The
oxygen
cooperative binding.
shows the
form
of
the
l
O
that
is
the
displaced
haemoglobin
a
higher
dissociation
but
to
the
the
stronger
at
every
l
a
noitarutas
E
v
negyxo htiw
u
is
has
egatnecrep
A comparison of the oxygen
adult haemoglobin (HbA)
y
that
haemoglobin,
saturation
Figure 24
p
curve
o
adult
dissociation curves of foetal (HbF) and
268
C
shows
t
a
like
o
24
i
d
r
o
f
x
O
▸
Figure
n
y
t
i
s
r
e
bec ause of
the eects of cooperative binding
curve
n
The oxygen dissociation curve
haemoglobin is sigmoid
v
i
n
Figure 23
for adult
U
▸
21.2 kPa.
dissociation
23
sigmoid
pressure
is
curve
curve
le
is
indic ates
anity
partial
for
further
than
foetal haemoglobin is sigmoid,
to
the
increased
adult
pressure
of
le.
An
anity
haemoglobin,
oxygen.
100
HbF
HbA
50
0
0
partial
2
4
pressure
6
of
8
10
oxygen / kPa
oxygen
for
saturation
oxygen.
so
Foetal
percentage
y
dissociation
to
of
the
concentrations.
P
due
as
show
oxygen
concentration
usually
oxygen
is
and
curves
dierent
r
The
at
e
haemoglobin
Organisms
25
dierent
dioxide
of
shows
oxygen
concentration
haemoglobin
and
the
concentrations
results
a
for
is
This
release
of
is
curve
dioxide.
displaced
oxygen.
greater
dissociation
c arbon
to
the
right,
c alled
oxygen
The
the
for adult haemoglobin at two
curve
Bohr
from
3 kPa
(Pco
r
oxygen
in
gas
and
environment. (B2.3.6)
exchange.
exchange
between
produce
the
n
of
y
l
role
O
the
that
y
gases
p
processes
a
chain.
l
Explain
P
y
of
o
movement
C
gas
(C1.2.11)
area
their
volume and the
n
between
access to materials
system in the distribution of
t
a
relationship
of
o
circulatory
and
(B3.2.1)
in
metabolic
surface
cells
diusion
the
role
v
O
c.
problem
v
the
u
Outline
of
body.
between
between
of
cells?
body.
the
i
the
List
solve
i
n
Describe
the
the
r
o
in
is
organisms
materials
role
materials
15
oxygen / kPa
The Bohr shi
relationship
of
the
t
i
s
of
r
e
Figure 25
d
O utline
)
2
10
pressure
U
the
(Pco
0
(B3.1.1)
b.
same partial
25
cells?
f
x
a.
the
)
6 kPa
multicellular
their
Outline
What
in
at
2
50
egatnecrep
do
all
exchange
2.
Section B3.1.12)
75
noitarutas
How
c.
(see
100
Linking questions
b.
c arbon
e
negyxo htiw
▴
a.
higher
decreased anity
haemoglobin
5
for
shi
the
a
ofoxygen.
partial
1.
for
showing
s
s
pressure
in
of
LHA
Figure
(B2.1.3)
and
metabolic
c apillaries
c arbon
and
processes
alveoli.
dioxide in the human
mitochondrial
electron
transport
(C1.2.16)
E
269
B3.2
Transport
s
s
What are the dierences and similarities between transport in animals and plants?
Figure
1
shows
a
“nodding
oil
of
the
pressure
Are
one
up
a
well
bec ause
eventually a pump is
in
drawn?
phloem
like
mammalian
Why
To
like
system
like
extent
closed
C an
circulatory
uid,
what
the
mammals?
circulatory
is
is
two?
the
and
What
systems
or
sap,
or
are
necessary
movement of uid
circulatory
phloem
or
blood
system
found in
xylem be thought
is
the
role
of
pressure
▴
in
plant
and
animal
circulatory
Figure 1
A “nodding donkey”
systems?
O
t
i
s
dierences
for bringing oil to the surface
What adaptations facilitate transport of uids in animals and plants?
2
is
Lena
in
or
rivers?
all
What
that
plant
to
parts
quantities
of
Adaptations
a
the
the
B3.2.5
Adaptations
of
of
veins
C auses
and
Transport
of
B3.2.8
Adaptations
B3.2.9
Distribution
stem
of
a
B3.2.10
root
of
a
water
E
transpiration
they
require?
for
or
exchange of materials
external
environment
veins
the
rates
the
transport of blood
return of blood to
of
of
from
xylem
tissues
roots
vessels
in
a
to
leaves during
for
transport
transverse
of
water
section of the
dicotyledonous plant
Distribution
of
tissues
dicotyledonous plant
in
a
B3.2.12
cells
in
The delta
in Siberia
AHL
B3.2.11
Figure 2
for the Lena River
Release
and
Exchange
reuptake
of
only
of
tissue
substances
uid
between
in
c apillaries
tissue uid and
tissues
B3.2.13
Drainage
B3.2.14
Dierences
sh
the
and
B3.2.15
of
double
excess
tissue uid into lymph ducts
between
the
single
circulation
of
bony
circulation of mammals
Adaptations
of
the
mammalian
heart
for
delivering
pressurized blood to the arteries
consequences of occlusion of the
v
B3.2.7
◂
HL
for
for
exist
receive
a
O
heart
coronary arteries
270
pulse
that
there
have
mechanisms
l
Measurement
B3.2.6
and
Are
vessels
animal
heart
B3.2.4
the
and
arteries
vessel
u
from
of
or
materials
internal
arteries
that
animal
What
plant
c apillaries
the
f
x
away
of
and
ow?
of
reason
strengthened?
o
Structure
B3.2.3
pressure
t
a
B3.2.2
do
i
of
and
role
d
blood
What
the
r
o
Adaptations
between
is
structurally
SL
B3.2.1
leaf.
movement of uids in living
resistance
that
pattern of
n
ensure
a
reticulate
reminiscent of blood
U
reduce
to
in
is
C
features
to
delta
the
showing the delta of
The
i
n
in
in
typic ally
common
sucient
Lena
venation
play
and
are
the
image
Siberia.
o
gradients
in
v
c apillaries
walls
satellite
p
channels
things
a
River
y
the
r
e
Figure
n
as
drawing
y
organisms
of
pushed
materials?
and
but
for
ows
transverse
section of the
B3.2.16
Stages
B3.2.17
Generation
active
transport
in
of
the
root
cycle
pressure
in
xylem
vessels
by
mineral ions
B3.2.18
Adaptations
cells
transloc ation
for
c ardiac
of
of
of
phloem
sap
sieve tubes and companion
y
transport
rock,
tool
oil
bottom of the well to pull the oil out of the well.
only
sometimes
xylem
oil-bearing
Initially
l
in
the
donkey”—a
surface.
P
they
for
at
uids
the
r
needed
in
to
e
underground
Organisms
B 3 . 2 .1
Ad a p t a t i o n s
exc h a n g e
blood
of
and
of
c apillaries
materials
the
for
between
internal
or
ex t e r n a l
s
s
e nv i r o n m e n t
C apillaries
C apillaries
the
are
no
very
that
pass
the
Two
exceptions
transparent
so
there
to
uid
c alled
allow
very
except
are
large
useful
the
greater
be
not
uid
cells
fewer wider
increases
of
(see
particles
to
epithelium
the
blood
pass
cells,
through, but not
so
the
but
c apillary
not
the
red
identic al in composition to blood
The
oxygen, glucose and all other
molecules,
uid
substances
ows
and
which
of
very
c apillaries.
excrete
which
large
pores
Fenestrated
speeds
up
are
too
large
between the cells in a
c apillary network.
produced,
proteins which
membrane and it
plasma,
membrane.
protein
numbers
Figure 3 on the
brous
basement
contains
membrane.
fenestrated
to
part
but
Tissue
absorb
the
the
basement
similar
uid.
than
tissue
needs of the cells, but all
extracellular
medium-sized
the
greater
any
tissue cells. The density of
the
i
tissue
is
of
pores
through
the
on
is
in
endothelium
The
is
c alled
of
between
re-enters
there
and
pores
plasma
them
or
that
c apillary.
coating
gel
area
network
depends
layer
a
The
small
a
d
are
has
basement
then
tissues,
waste
in
the
c apillary
c apillaries
exchange
products.
allow
larger
between
tissue cells and the blood. The glomerulus (lter unit) of the kidney has
urine
c apillaries
production.
so
it
c an
produce
large
volumes
of
ltrate
in
the
rst stage
u
l
a
E
v
O
f
x
t
a
fenestrated
of
out
to
one
gel.
blood
are
tissue
blood
uid
of
out
of
r
o
the
in
These
volumes
allows
leaks
allowing
some
walls.
a
the
tissues
close
cells
surface
c apillary
o
In
of
There
c alled
through
tissue
body.
be
n
The
are
form
leak
total
U
tissue,
the
C
is
substances
to
to
that
It
in
must
o
uid
plasma.
almost
i
n
The
tissues
tissues
the
between
consists
layer
to
a
that
dierent
permeable.
cells,
all
eye — these
v
blood
10 μm. They
p
is
about
y
lter
in
body
wall
This
macromolecules.
wall
of
y
a
diameter
r
e
as
the
a
n
the
have
means
diusion
crosslinked
acts
of
with
c apillary network with a huge total length.
O
page).
through
a
l
in
c apillary
next
are
for
This
networks
cells
vessels
form
t
i
s
active
blood
cornea
c apillaries
vessels.
scope
the
to
vessels.
narrow
c apillary
The
and
blood
y
the
transport
lens
blood
blood
narrowest
repeatedly
P
M any
the
rejoin
r
are
are
and
e
branch
271
Form and function
red blood
blood
cell
plasma
basement
membrane –
a mesh of fibrous
that acts as a
gel
s
s
proteins forming a
filter
epithelium cells
e
forming the wall of
the capillary—very
r
thin except where the
nucleus of a
pore between
allowing fluid to
cell is
located
l
nucleus of
leak out through
y
membrane
10 µm
Structure of a c apillary
the
Bec ause
dierent
of
of
the
structure
Circular or
l
a
section
No inner surface
corrugated
corrugation
E
wall
v
Inner surface
Fibres visible in
Few
or
visible
no
▴
Figure 4
surrounded
the
these
two
heart
from
types
the
of
to
the
organs
organs to the
blood
vessel
(Figure 4).
An artery (upper le) and
by adipose (fat
1
lists
the
distinguishing
a vein (lower right) are
storage) tissue.
features
wall
distinguishable
272
the
The tissue below is muscle
bres
Table
in
function,
from
blood
u
Wider lumen
attened in
away
n
wall
f
x
O
section
in
walls
blood
low-pressure
o
Thinner
lumen
Circular in
the
i
Veins
wall
Narrower
their
of
t
a
Thicker
r
o
Arteries
veins
stream
C
i
n
Dierences in structure of the
walls of arteries and
a
dierence
to
U
Table 1
d
▾
high-pressure
c arry
o
a
Veins
v
heart.
body.
Structure of arteries and veins
pulses
p
of
c arry
y
Arteries
r
e
B3.2.2
O
Figure 3
cell
t
i
s
▸
n
the basement
epithelium
in
micrographs.
of
arteries
and
veins
that
are
easily
have
y
P
epithelium cells
Organisms
B3.2.3
Adaptations of arteries for the
transport of blood away from the heart
wall
•
tunic a
externa — a
•
tunic a
media — a
made
of
tunic a
intima — a
the
time
the
strong
bulging
outwards,
blood
in
the
in
In
that
with
and
the
way,
transporting
elastic
high
high
50%
bres
this
then
under
fibres.
high
declines
pressure
until
the
next
of
ow.
bres and tough collagen
stretch
tensile
and
or
the
and
variable
blood
dry
mass
artery
an
wall
stretching
the
wall.
of
the
each
the
to
bres
the
by
of
the
to
to
Peak
be
pushed
stretched, elastic
pressure in arteries
recoiling
help
organs
walls.
artery
When
heartbeat
energy
elastic
blood
Collagen
features make
pressures without
of
the
end
recoil.
These
of
c auses
return
then
strength.
bursting.
and
squeezing
reduce the amount of
the
body.
tunica media
thick layer of
coat of tough
smooth muscle
cells, elastic
and elastic
tissue and
i
u
l
tunica
tunica media
externa—
—thin layer of
relatively thick
elastic tissue and
tough outer
collagen fibres
coat
thicker wall in
arteries than
veins
a
E
v
O
f
x
t
a
r
o
collagen fibres
o
d
collagen fibres
n
outer
lumen
blood
elastic
U
tunica externa
tissue
of
pressure
blood
c an
aneurysm)
as
At
of
contain
pressure)
lumen
elastic
lumen.
expended
much
energy.
stretched
an
burst
of
C
energy
the
and
withstand
(systolic
potential
the
as
velocities
proteins
as
a
The
layer
i
n
the
up
artery
widening
store
and
to
pump,
them.
a
narrow lumens, which helps them to maintain
proteins
(known
includes
o
falls
thick
forming the lining of the artery;
also
v
bres
enough
heart
along
high
are
rope-like
make
an
fibres
fibres
p
in
collagen
elastic
y
bres
the
intima
relatively
and
bres
outwards
pressure
with
and
r
e
Elastic
tissue
muscle
n
arteries
of
ows
relatively
elastic
tough
smooth
O
are
are
containing
y
The
layers:
connective
t
i
s
walls
bres.
of
endothelium
tunic a
have
pressures
Artery
bres
and
Arteries
blood
several
l
high
smooth
the
ventricles
arteries
heartbeat.
layer
of
layer
protein elastin
arteries
the
thick
outer
y
enters
composed
tough
P
E ach
the
is
r
insome
artery
e
•
of
s
s
The
tunica intima
the space inside
the artery
an endothelium made of a
single layer of cells with
lumen—
through which
tunica
extra elastic tissue near
relatively
blood flows—
intima
the heart
wide
relatively narrow
▴
Figure 5
Tissue plan diagrams of artery and
vein in transverse section
273
Form and function
When
the
semilunar
c annot
Elastic
ow
even
the
help
inside
out
the
heart,
to
the
blood
and
pushing
ventricles
it
pump
artery
is
are
forced
blood
on
the
in
This
onwards
along
(diastolic
blood
closed.
artery, the
towards
arteries
pressure)
an
means that blood
from
the
and
organs.
prevent the
becoming
too
ow in the arteries.
lumen
is
artery
arteries
or
This
ow
hormone
to
c alled
is
and
tissues
in
so
the
increased.
each
smooth
they
smooth
This
signals
organ
is
muscle
cells
are
circular
contract, the diameter of the
vasoconstriction
When
neural
The
when
and
muscle
it
reduces
cells
ow of blood
relax, the lumen
vasodilation. The smooth muscle cells
and
enable
depending
the
on
body
to
availability
adjust
and
the
need.
diagram
is
a
drawing
that
shows the distribution of
join up lines
use a
in
an
line
the
organ.
It
does
not
show
individual
cells.
sharp pencil
E ach
represents
the
interface
hard lead to
r
e
drawing
draw lines freehand,
carefully to
with a
on
between
but use a ruler for
form continuous
y
draw single sharp
two
tissues.
The
low
power
objective
of
a
microscope
a
and
very
to
if
any
of
faintly.
the
c an
same
the
be
the
distribution
drawn.
areas
Everything
of
tissue
on
of
tissues, so
Unnecessary detail is
the
are
shaded, this
drawing should be
magnic ation.
274
then doubled
felt
as
There
a
is
Where
pulse.
one
heart
rate
The
wrist
felt.
Two
to
an
This
pulse
be
and
or
loc ated.
Counts c an be
artery
is
the
a
is
wave
close
bec ause
per
beat
deduced.
three
The
beats,
o
and
arteries.
the
i
to the windpipe.
done for a whole minute or for 30 seconds
bad
good
neck
are
under
body
artery
wall
the
heart,
so
two
are
should
blood
the
the
Pulse
ngertips
thumb
of
of
to
and
parts
heart
of
the
pressed
not
be
bad
pressure
this
becomes
good
are
body
of
counted
where
against
the
the
passes along the
pressure
stretched
measurement
lightly
used
high
surface,
rate
cell
plan diagrams
Measurement of pulse rates
time
t
a
a
groove next
bad
and
heart
u
l
v
E
There is a c arotid
Good
Every
c auseconfusion.
pulse on either side of your neck in the
good
Figure 6
cell
B3.2.4
is
The radial pulse is on the
side of the wrist.
bad
▴
n
U
d
r
o
Figure 7
thumb
f
x
O
▸
cells
C
i
n
shown
observe
o
done
to
diagram
v
avoided
is
used
plan
p
usually
that
labelling lines
structures such as
lines
is
O
plan
tissues
n
y
A
t
i
s
Communic ation skills: Drawing plan diagrams
ow
l
blood
is
arteriole.
blood
arterioles).
pulse
in
wave
and
rate
beats
pulse
skin
c an be
then
recoils.
allows
per
minute.
c an oen be
where the artery
bec ause it has a pulse which could
y
to
or
(c alled
longitudinal)
P
and
respond
of
of
radial
narrowed.
an
widens
ATL
low.
e
than
r
(rather
rate
of
walls also contain smooth muscle cells with a particularly high density in
branches
along
recoiling
towards
therefore
to
are
exit
s
s
the
the
pressure
help
Artery
bres
at
back
bres
minimum
They
elastic
valves
Organisms
It
is
are
also
possible
usually
light
through
through
of
the
blood
in
the
the
deduced
blood
a
of
and
the
tissues
The
meters
nger.
each
to
They
detectors
This
time
percentage
bec ause
absorbs
digital
ngertip.
nger
tissues
c alculated.
use
to
the
c alculate
have
to
enables
heart
blood
the
rate.
shine
how
of
Pulse
red
much
detection
beats,
of
pulse
that
measure
saturation
deoxygenated
LEDs
oximeters
and
of
the
and
from
this
with
oxygen
light
whereas
red
passes
variation in the amount
blood
absorbs
infrared
light
the
heart
rate
s
s
is
to
clipped
c an also be
oxygenated
infrared light.
traditional
Do
you
get
the
same
procedure
estimating
for
of
estimates
assessing
heart
using
for
the
a
rate
pulse
your
by
heart
reliability
measuring
pulse
rate and
oximeter.
rate?
and
accuracy
of
the
traditional
and modern methods.
•
Which
method
more
reliable?
the return of
pulse.
The
are
also
Blood
in
If
vein
blood
lower
To
starts
to
fill
flow
with
backwards,
blood
and
ow
tissues,
wider
veins
assisted
it
or
of
squeezes
even
the
is
skeletal
help bec ause
sitting
80%
valve
especially
so
towards
pocket
E
veins
in
flows
just
blood
allow
a
person
at
veins
rest
veins
the
are
to
the
heart.
or damaged. Blood can then ow backwards
in the vein and accumulate, causing swelling
there is no
wall
not
of
an
and enlargement. Varicose veins usually
artery.
develop in the legs because venous return to
used to adjust
so
the
problem
and
contain
wall does not
from
the
insucient
pocket
into
the
low blood
return of
valves. These
vein
in
the
direction
c aught in the flaps of the pocket
the
valve. This blocks the lumen of
and
and
by
blood
c an
pressures
flow
freely.
exerted
by adjacent
Contraction makes a muscle shorter and
vein
greatly
veins
opens
gravity
muscles.
dgeting
a
by
than
arteries,
projecting
gets
back
heart, it pushes the flaps to the sides of the
therefore
adjacent
they
in
vigorousexercise.
on
the
a
Blood
blood
The
v
O
vein.
l
When
it
close
it
means
Varicose veins develop in the
the heart is usually againstgravity
c apillaries
tissue
thevein.
•
the
u
f
x
which
of
in
This
bres
potential
circulation,
aps
convey
bec ause
than
The
towards
maintain
cells
pressure
and
elastic
body.
bursting.
cup-shaped
ow.
valve,
the
backow
heart.
three
parts
of
body
continuously.
fewer
muscle
prevent
is
far
smooth
much
to
the
o
•
blood
at
contains
of
veins
t
a
of
is
into
i
the
of
fewer
organs
d
blood
to
a
vein
all
r
o
in
a
dierent
thick
pressure
consist
of
far
to
veins
be
of
Figure 8
legs when pocket valves become weakened
n
ows
to
c apillaries
wall
blood
need
from
out
U
There
blood
C
drains
o
v
collect
Blood
i
n
Veins
▴
y
Adaptations of veins for
blood to the heart
p
r
e
B3.2.5
is
O
a
of
approach
t
i
s
Devise
method
modern
n
•
more
y
the
l
the
also
y
P
Traditional versus digital estimation of heart rate
Try
e
r
Assessing reliability and accuracy of tools:
like
to be
a
pump.
improves
is
in
The
squeezed
the
venous
veins,
relatively
into
a
atter
blood
but
this
is
ow.
thin
walls of
shape.
Walking,
Around
reduced during
▴
Figure 9
Discuss the pattern of venous
return that is occurring in the gymnast
during this manoeuvre
275
Form and function
Standing on your head
Pocket
valves
venous
Figure 10
to
as
headstands
at
an
vein
the
or
amusement
walls
heart.
become
Have
you
less
handstands,
or
park?
people
Young
ecient
ever
with
performed
experienced
c an
very
mostly
age,
c ausing poor
gymnastic
high
do
moves such
s
s
▾
and
return
g-forces on a ride
any of these activities
A normal artery (top) has a
easily
but
older
people
may
not
be
able
to.
What
is
the
explanation?
much wider lumen than an artery that is
e
occluded
by atheroma (bottom)
r
B3.2.6
C auses and consequences of
The
right
to
that
are
provide
of
of
wall
is
wall
and
of
wall,
clot
the
in
the
oen
as
a
totally
organs of
of
branches into two
the
wall
of
heart
the
blocked
the
restrict
of
branches
(plaque)
wall.
repeatedly
heart.
by
fatty
and
the
blockage
artery
and
contain
blood
pain
in
impregnated
surface
ow
the
to
the
chest
(angina)
it
c an
of
with
c alcium
salts,
rough. This tends to trigger
Hypertension
clots
depriving
heart
all
exercise.
inner
Blood
which
which
c ausing
become
the
or
to
regions
muscular
wall
They
(thrombosis).
heart,
known
the
of
atheroma
during
c an
make
thrombosis.
block
(high
the
oxygen
blood
pressure)
ow of blood to part
and
preventing normal
attack.
le and right
i
carotid arteries
(used for taking
vein (red indicates
a pulse)
oxygenated blood)
u
le coronary
right pulmonary
artery
l
deoxygenated blood)
a
E
v
O
f
x
t
a
r
o
d
o
This
he art
of
each
heart
from the aorta close to
coronary artery that supplies
artery,
o
blood
a
up
o
artery (blue indicates
le anterior
descending
right
coronary artery
coronary
(a
branch of the
artery
le coronary
artery)
▴
276
of
aorta
right pulmonary
artery
artery
risk
build
right
narrowed
c alled
especially
the
muscular
contractions.
the
parts
the
posterior
arteries,
all
of
branch
the
le
cholesterol.
n
the
the
are
side
coronary
C
formation
the
to
are
and
become
deposits
bre ath,
in
blood
c an
of
le
coronary
including
i
n
of
harden
increases
of
The
They
the
anterior
deposits
region
deposits
U
the
fatty
lipids
shortness
which
main
arteries
The
occlusion.
F atty
le
oxygenated
downstre am
or
three
and
le
y
an
variety
the
valve.
v
a
heart
the
arteries
p
is
supply
coronary
deposits.
the
by
Two
r
e
The
semilunar
of
thus
lungs.
O
There
the
pumped
the
t
i
s
arteries
at
side
blood
from
n
origin
the
c arries
apart
y
its
aorta
body
l
the
Figure 11
The coronary arteries are the rst
branches o the aorta
y
P
occlusion of the coronary arteries
Organisms
If a blockage persists there will be tissue death and therefore permanent damage
to the heart. Tissue death in heart muscle due to inadequate blood supply is called
a myocardial infarction. The conditions associated with narrowed or blocked
coronary arteries are collectively known as coronary heart disease(CHD).
heart
disease
epidemiologic al
the
study
•
of
nature
have
been
and
very
to
try
common
to
spread
and
identify
of
there
risk
diseases
have
factors
in
the
been
and
human
many
c auses. Epidemiology is
population.
Multiple risk
identied:
hypertension — raised
blood
pressure
increases the chance of blood
r
clotformation
pressure
•
obesity — associated
with
fat
bec ause
and
raised
nicotine
c auses
vasoconstriction
cholesterol — promotes
blood
pressure
and
high
plaque
blood
formation
cholesterol
high
salt
intake — a
large
quantity
of
sodium
chloride
in
the
diet
raises
bloodpressure
•
drinking
excessive
amounts
of
alcohol — associated
raised blood
sedentary
lifestyles — a
the
of
return
of
exercise
from
the
is
correlated
extremities
with
obesity
genes
increase
become
less
flexible.
of
is
followed
for
eect
the
aer
is
the
the
the
minimum
the
E
2.
and
Describe
the
anddiastolic
3.
C alculate
the
eects of
Evaluate
the
systolicand
impact
rate
blood
people
per
between
death
dat
44
rat /
37
36
35
1
10000 rsons yar
32
Diastolic
26
25
25
25
>160
17
13
13
12
21
systolic blood
and
140–159
10
159 mmHg
12
120–139
9
9
pressure
25
24
14
a
9
between
systolic
of
[1]
systolic
pressure
minimum
[3]
43
disas
reached in
contracted.
for
rate.
81
blood
0
1
>
0
–
0
9
on
the
9
9
–
0
8
pressure
difference
death
rate.
BP /
<120
9
8
–
5
7
mm
9
7
–
0
7
diastolic
the
on
coronary art
year.
79 mmHg.
blood
differences
pressure
relationship
pressure and the
pressure
140 mmHg
effect
of
diastolic
pressure in the arteries just
death
v
diastolic
75 mmHg
have
the
4.
heart
contract again.
pressurebetween
anda
10,000
a
Determine
shows
blood
maximum
ventricles
ventricles
12
l
O
1.
the
coronary
316,000 males
investigate
diastolic
per
for
than
u
arteries
is
to
Figure
rate
f
x
pressure
pressure
years
and
death
Systolic
before
12
factor
more
t
a
systolic
risk
study,
pressure.
between
on
major
i
blood
a
major
o
a
r
o
high
In
d
diseases.
prevents
hypertension
n
U
Hypertension
and
greater risk of
C
vessels
risk
i
n
age — blood
the
Data-based questions: Hypertension
were
a
o
predisposition — some
andthrombosis
old
to
formation
genetic
•
leading
v
•
lack
blood
p
clot
venous
r
e
•
y
with
pressure and obesity
O
t
i
s
•
n
concentrations
y
saturated
much
l
blood
eating
P
smoking — raises
•
y
•
too
e
factors
is
studies
s
s
Coronary
4
7
0
7
<
Hg
BP / mmHg
[2]
▴
between
Figure 12
The eect
of blood
pressure on coronary heart
disease
systolicand
diastolic
thedeathrate
is
blood
highest.
pressure
where
[1]
277
Form and function
Patterns and trends: Correlation coecients
level
between wingspan and body mass in blue jays (Cyanocitta
objective
cristata) or between average saturated fat intake per
the
person and CHD rate of dierent countries. Two variables
with
are positively correlated
points
if higher values of one variable
correlation
of
coecient
association
assessment
points
on
positive
lie
a
of
sc atter
a
numeric al
on
a
the
two
the
lie
straight
−1.
The variables are negatively correlated if higher values
the
correlation
0.
of one variable tend to correspond to lower values of
correlation
is
If
with
For
of
to
displayed
which
widely
the
variables
gradient
lie
there
correlation
to
close
is
a
to
a
weak
straight
per
correlation. If
line
with
a
line
with
taken
A
it
is
usually
a
and
strong
c ausal
link.
a
and
not
hard to
of
as
medic al
risk
in
unless
of
a
rst.
by
high
fatty acids
does
research
CHD.
nding
one
which
c an
between two
countries.
this
−1.
used in
saturated
dierent
such
are
coecients
association
mechanism
involved
in
of
intake
of
and
increased
invested
However,
is
not
prove
needed to
saturated fat
However, the time
such
a
mechanism would
correlation
had
been
U
C
o
v
i
n
B3.2.7
rate
correlation
biologic al
established
reach conclusions about the whole population.
mean
CHD
Scientic
expense
be
evidence
example
intake causes
sc atter
from the whole
sample
for
establish
negative
correlation.
signic ant
person
even
positive
correlation. If the
straight
small
factors,
correlated. If the points
is
negative
sample
a
provide
show the
p
with
a
positive
strong
shows
and
close
strong
very
only
population,
very
to
y
there
are
there
diagram
r
e
lie
gradient,
variables
sc attered,
is
variables
diagram
two
sc atter
relationships, the
O
fairly
a
t
i
s
are
in
gradient,
correlation,
n
extent
be
no
l
c an
straight line
between 1 and
correlation
y
D ata
High
a
Transport of water
from roots to
leaves during transpiration
is
the
roots
to
in
the
water,
height
be
water
If
is
maximum
and
water
dierent
from
plants
leaves
leaves.
the
a
in
from
i
reaches
tissue
lost
that
in
o
and
suction
is
ows
just
to
used
applied
eectively
height
is
to
of
the
pushed
10.4
top
m.
of
atmospheric
to
so
the
the
up
them,
Water
ow
of
is
absorbed
water
is
by
from the
of
an
air-lled tube with its base
tube
by
atmospheric
c an
so
water.
main
top
the
Trees
grow
the
to
pressure and
more than 10 times this
mechanism
used in plants must
pressure.
Xylem vessels are normally lled by xylem sap, which consists of water with
u
leaf, water is lost by evaporation from the cell walls of spongy mesophyll cells
l
and then diusion of water vapour out through the stomata. Cell walls contain a
a
mesh of cellulose molecules which are hydrophilic and form hydrogen bonds with
water. There is adhesion between the water and the cellulose of the cell walls. Loss
of water therefore causes water to be drawn through the interconnected leaf cell
walls in the pores between cellulose molecules. This process is a type of capillary
E
action and is similar to the way that water is drawn through lter paper (also mostly
composed of cellulose). The source of the water that is drawn through leaf cell
walls is a xylem vessel in the nearest vein.
278
transport
transpiration,
relatively low concentrations of potassium, chloride and other ions. In a transpiring
v
O
f
x
t
a
r
o
d
roots
n
Xylem
y
measures
hypotheses.
on
P
numeric al
is
most
somewhere
variables, they are uncorrelated or independent
testing
provides an
negative
there
the other variable. If there is no relationship between the
These
It
correlation. If
r
correlation coecient is
is
the
exactly
line
the
coecient
of
correlation coecient is 1. If the
tend to correspond to higher values of the other variable.
coecient
measure of the
variables.
strength
diagram
gradient,
exactly
is
between
e
A
variables. For example, we might expect a correlation
s
s
A correlation is an association between two numerical
Organisms
As the cell walls of leaf cells draw out water from xylem, they generate tensions
(pulling forces). As long as there is a continuous column of water in a xylem vessel,
these tensions are transmitted from the leaves down to the roots. This is called
transpiration pull and is strong enough to move water upwards, against the force
of gravity, to the top of the tallest tree. For the plant, it is a passive process; all the
s
s
energy needed comes from the thermal energy (heat) that causes transpiration.
The
pulling
very
water
upwards
water
low
pressures
in
c alled
c avitation
and
a
that
xylem
though
solid
it
vessels
does
water
length
of
is
vessels depends on the cohesion that
M any
liquids
would
be
unable
the
column
of
occ asionally
happen
even
a
and
liquid,
it
c an
transmit
liquid
to
resist the
would
with
pulling
break. This
water, but it is
forces
in
the
same
rope does.
l
lignified thickening
Key
of xylem vessel wall
cell walls
capillary
cell walls
llyhposem ygnops
evaporation
from cell walls
r
e
diffusion
spaces and
p
out through
n
Water movements in the leaf
o
cuticle
U
Figure 13
waxy
C
with stoma
v
i
n
lower
stomata
y
through air
epidermis
▴
O
t
i
s
action in
n
y
cellulose
y
Even
way
xylem
P
unusual.
in
molecules.
r
is
of
between
e
exists
o
d
Modelling water movement through cell walls
high
do
you
•
Do
you
expect
What
Test
your
does
movement
this
in
could
by
be
setting
a
How
factors
hypotheses
model
help
between the
tubes?
varied?
up
us
experiments.
to
understand
water
water
(to
which
◂
plants?
E
v
O
•
other
difference
unstoppered
strips of
paper towel
u
•
any
and
water to rise in the
l
f
x
stoppered
expect
t
a
papertowel?
i
How
r
o
•
dye
could
Figure 14
Tall tubes
be
with paper towel strips
added)
dipping into water, one
sealed and one open to
the air
279
Form and function
B3.2.8
Adaptations of xylem vessels for
transport of water
The structure of xylem vessels allows them to transport water inside plants very
s
s
eciently. They are formed from columns of cells, arranged end-to-end. The cell wall
material between adjacent cells in the column is largely removed and the plasma
membranes and contents of the cells break down. This creates long continuous
e
tubes, with minimal resistance to the ow of xylem sap. When mature, xylem vessels
are non-living, so the ow of water along them must be a passiveprocess.
vessel
atmospheric
Light
holes
plants,
passage.
c alled
pits
the
In
through
xylem
vessel
thickenings
plants,
which
the
water
wall
c an
water
and
in
vessel
but
exit.
rings
or
from collapsing.
there
In
the
are
are
always gaps
xylem
helices
thickenings
lower
pressure
more
pass.
vessels
with
large
extensive,
p
v
o
C
i
n
n
U
i
o
pits
t
a
wall
of xylem
u
l
a
and
E
with spiral bands of lignin.
vessel
continuous tubular
structure
brown.
▴
Figure 17
Structure of xylem
vessels
▴
Figure 18
Structure of xylem
vessels in
Xylem
in growing parts of the plant
such as roots
parts of the plant
that
are thickening such as
strengthened
Spiral bands
vessels to elongate and
growlengthwise and
280
v
vessels are coloured
exibility
xylem
much
(negative
Rheum rhaponticum. Cut
vessels are reinforced
allow xylem
usually
Longitudinal section through
a rhubarb stem,
xylem
d
r
o
f
x
O
Figure 16
to
are
with lignin
▴
the
enter
is
tension
wall
impregnated
supporting thickenings
c an
impregnated with a
y
thickenings of
or xylem of a
vessels with lignied
prevents
are
vessels
commonly
impermeable
water
wall
older
is
walls
are
which
micrograph of a vertic al
section of the primary wood
tree showing wood
young
water
the
thickenings
through
there
xylem
r
e
Figure 15
for
of
thickenings
inside
O
with
▴
by
and
the
t
i
s
formed
gaps
wall
thickening
pressure
strength
and
pressure
n
lignied
the
the
The
y
in
but
thickened,
l
potential)
The
are
lignin.
also retain their
andstems
the trunk or roots of a tree
y
than
walls
c alled
P
polymer
r
The
Organisms
B3.2.9
Distribution of tissues in a transverse
section of the stem of a dicotyledonous plant
The
outer
layer
of
near
the
epidermis.
and
of
a
vascular
of
stem
in
the
cells
centre
Dicots
other
bundle
and
between.
and
have
the
a
two
owering
The
cortex
of
young plant is the epidermis. The stems of
typic ally
on
tissues
transport
leaves
plants.
phloem
other
have
seed
The
the
and
in
vascular bundles
sunowers,
peas
xylem is usually on the inner side
outer
that
tissue
include
side,
usually
with
occur
c ambium consisting
in
a
dicot
stem
are pith
near the epidermis.
tissues and their functions
functions
water
in
Phloem
Transport
of
sugars
stems
from
epidermis
roots
from
to
leaves
leaves
to
roots
Production
of
more
Epidermis
Waterproong
Cortex
Support
Pith
Bulking out the stem
and
xylem and phloem
protection
pith
r
e
and
photosynthesis
▴
Figure 19
Tissue plan of a stem
p
all
plant
stems,
with
a
micrograph,
is
essential
microscope
many
as
that
while
in
variations
in
vascular
instead
bundle,
two
of
just
a
a
a
plan,
hollow
is
a
or
view a
centre to
c an
be
young
micrograph.
have
shown
sunower
in
each
phloem
(dark blue)
one. Some dicots such as
vascular
micrograph
phloem
by
These
drawing
showing
stem.
sclerenchyma
bundle.
u
this
structure
20
each
sclerenchyma
bres (crimson)
one
Draw
a
tissue
variations
tissue plans.
c ambium
vascular bundle in
(light
tissue
plan
blue)
based
E
v
a
on
to
of
l
of
O
part
f
x
adjacent
stem
same
structure. Some dicots
have
areas
sunowers (Helianthus annuus)
Figure
the
t
a
have
in
not
view a stem
instead of pith. Some dicots such as cucumber
(Cucumis sativa)
(bres)
20.
given in
is
i
stem
to
drawing
stem
r
o
the
either
Figure
such as elder (Sambucus nigra)
are
tissues
o
are
it
plans
of
d
There
so
such
tissue
arrangement
n
section
drawing
U
in
for
The
C
instructions
Section B3.1.8.
in a typic al dicotyledonous plant
o
v
Full
i
n
Applic ation of skills: Drawing stem tissue plans
bundle
phloem
y
C ambium
vascular
cambium
O
cortex
xylem
n
of
l
Transport
y
M ain
Xylem
t
i
s
Tissue
y
Plant
parts
P
Table 2
most
all
(dicots)
e
oaks
in
r
and
▾
cells
plants
s
s
dicotyledonous
xylem
(red)
▴
Figure 20
from
Light
micrograph of a section through a young stem
a sunower (Helianthus annuus),
showing one of the many
vascular bundles
281
Form and function
B3.2.10
Distribution of tissues in a transverse
section of the root of a dicotyledonous plant
The
distribution
the
vascular
shaped
be
area
the
root
may
smaller
epidermis,
the
vascular
roots
of
the
centre
between
the
points
large
cells
and
in
size,
be
in
stained
the
than
with
tissue
thick
root
small
red
are
xylem
and
walls
of
and
cells
root,
the
star.
microscope
thinner
that
and
walls.
may
epidermis
with
rounded
have
there
The
in
is
dierent.
outer
hairs
cortex,
vessels
stained
protruding.
with
relatively
22
shows
part
section.
the
a
in
root of
transverse
tissue plan to
tissues.
to the stem and
C
o
v
i
n
phloem
—transports
sucrose from
the leaves to
—an inner skin of cells that
cortex
water must pass through to
o
i
t
a
u
l
v
a
Figure 22
E
282
d
r
o
f
x
O
▴
—unspecialized cells
reach the xylem
▴
Figure 21
Tissue plan of a dicot
leaves
the roots
n
U
endodermis
water from
the roots up
p
identify
Draw
a
—transports
y
Allium tuberosum
of
r
e
Figure
n
O
xylem
narrow outgrowths (root hairs)
plans
that bulk out the root to
strengthen it and increase
its surface area
root
large
l
t
i
s
from the soil oen using long
Drawing root tissue
blue.
layer of cells
y
—absorbs water and mineral ions
c an
transverse
bec ause they
usually
The
root
is
xylem
images
are
plants
xylem in a star-
shape
thin-walled cells.
epidermi s
Applic ation of skills:
a
unlignied
with
the
in
dicotyledonous
of
y
and
is
are
stems
P
Between
walls
in
grouped
phloem
their
Other
cells
is
r
Phloem
by
Xylem
lignied.
tissues
e
are
in
and
identied
section.
of
tissue
s
s
All
Organisms
LHA
B3.2.11
Release and reuptake of tissue uid
in c apillaries
Plasma
such
are
is
the
many
as
uid
chloride
c arried
in
and
cells
sodium,
a
basement
c an
pass
to
tissue.
let
part
through
so
suspended.
structure
of
the
protein
the
are
glucose,
hormones
The
Most
membrane
out
cells
vitamins,
droplets.
adapted
in
blood
substances:
are
amino
and
of
are
of
water
mineral ions
proteins.
c apillary
plasma
molecules
consists
plasma
the
blood
It
acids,
wall
Lipids
(described
blood plasma
cerebrospinal
(7%)
fluid (1%)
leak out into spaces
too
large
to
pass
retained in the plasma, but other
c apillary
wall.
that
leaks
out
of
c apillaries
is
a
type
of
extracellular
uid,
c alled
(26%)
tissue
3
At
human,
of
tend
high
constitutes
release
to
and
release
pressure.
about
reuptake
tissue
Reuptake
of
of
20%
tissue
uid
tends
this
of
body
uid.
bec ause
to
tissue
mass.
in
blood
in
the
tissues of a
There is a continual
C apillaries
the
happen
uid
that
are close to an
supplied
c apillaries
that
by the arteriole
are close to a
▴
venule,
where
the
blood
pressure
is
much
lower.
Figure 23
human body
Exchange of substances between
uid
contains
large
ows
between
Oxygen
is
concentration
used
aerobic
in
C arbon
by
tissue
the
merge
C arbon
detoxied
a
the
liver
cell
it
form
is
or
to
by
venules,
by
by
the
c arry
lungs
wall.
bec ause the
Glucose, also
cotransporters.
As
tissue
uid
products.
The
ows
tissue
waste
other
products out of the
waste
products
are
kidneys.
u
f
x
l
reuptake of
tissue fluid
deoxygenated blood
exiting capillaries
a
E
v
O
by respiring cells
Figure 24
diusion
waste
the
and
oxygen absorption
▴
by
metabolism.
tissue fluid
entering capillaries
c apillary
becoming part of the blood plasma.
which
the
of
dissolved
release of
oxygenated blood
the
respiration.
transport.
products
network,
excreted
uid
aerobic
sodium–glucose
active
accumulates
excreted
through
respiration, diuses out of cells into the
waste
c apillary
to
dioxide
by
tissue
i
re-enters
c apillaries
tissue.
of
the
due
absorbed
by
other
from
pass
allowing the cells to absorb useful
t
a
The
then
cells
with
c annot
tissue,
lower
acids
r
o
uid
the
is
amino
produced
along
is
which
a
o
between
cells
respiration,
absorb
dioxide,
uid,
absorbed
in
in
d
tissue
cells
cells
n
Growing
the
U
oxygen
molecules,
C
substances.
oxygen, glucose and all other substances in blood plasma
protein
o
The
uid
from
i
n
apart
v
Tissue
p
tissue uid and cells in tissues
Distribution of water in the
y
r
e
B3.2.12
fluid (67%)
O
at
it
are about 14 dm
t
i
s
arteriole
so
there
n
process
is
time,
y
70 kg
any
l
uid.
intracellular
y
uid
P
tissue fluid
The
e
the
substances
is
the
r
through
the
which
dissolved
lipoprotein
inSection B3.2.1)
between
in
dierent
s
s
with
Exchange processes in respiring tissues
carbon dioxide excretion
from respiring cells
283
Form and function
LHA
B3.2.13
Drainage of excess tissue uid into
lymph ducts
Most
of
the
tissue
uid
released
by
c apillaries
returns to them, but some does
3
20 dm
of
tissue
uid
produced
per
day
3
17dm
would
c ause
into
to
c apillaries. If the other 3 dm
swelling,
vessels
of
c alled
the
oedema.
lymphatic
of lymphatic vessel
This
is
of
an
average
uid
prevented
stayed
adult’s
by
the
in
drainage
system.
composed
with large gaps
l
O
y
p
o
C
n
o
i
tissues,
there
uid
is
u
are
to
just
are
which
known
repeatedly
there
l
as
form
narrow
tissue
lymph
wider
two — the
veins.
Lymph
is
to
blood
returned
c ava
and
on
the
to
the
right
c an
rather
is
and
pass.
than
lymphatic
le
subclavian
blind-ended
uid
therefore
side
of
At
drained
in
the
with
narrow
end
of
the
from
this
These
all
permeable
lymphatic
The
ducts.
o
the
vessels
entering
uid.
lymphatic
Blood
the
tissue
vessels.
right
system.
lymphatic
Aer
drains
vessels,
vessels join up
system
of
vessels,
merge with the
tissues of the body and
subclavian
veins
ows
into
the
vena
heart.
a
E
v
O
f
x
t
a
the
through
n
y
t
i
s
r
e
v
i
n
all
walls
B3.2.14
Dierences between the single
circulation of bony sh and the double
circulation of mammals
There
284
lymph
anchoring filaments
Narrow ending of a lymph vessel into which excess tissue uid
In
tissue
are
valves
blood
circulates
to
lungs
the
to
in
mammalian
through
be
veins
arteries,
oxygenated.
and
heart
c apillaries
The
blood
that
and
must
ensure
veins.
be
at
a
one-way
ow, so
M ammals pump blood
relatively
low
pressure to
y
basement membrane
with pores between
U
r
o
d
Figure 25
of
P
of a single layer of endothelium cells
tissue cells
▴
body,
tissues it
r
wall
the
e
uid
in
3
return
s
s
not. Of the
Organisms
c apillaries
c apillaries,
organs
blood
of
the
much
and
the
the
le
side
blood
and
requires
pressure
With
of
right
a
the
returns
the
circulation,
The
dierent
and
with
heart
is
organs
that
a
ltration
few
the
side
of
pumps
relatively
heart
to
blood
the
ows
the
it
to
all
blood
blood,
so
through
c apillaries
deoxygenated
heart,
need
exceptions,
which
and
pumps
returned
blood
that
passing
The
from
their
circulations
pulmonary
the
systemic
been
water
c an
be
to
the
the
blood
heart
at
c arbon
high
and
organ
is
pressure
the
to
risk
of
the
through
▴
the
of
gills
bec ause the
c apillaries
bursting.
Figure 26
The double circulation of
mammals
moves in the opposite
body.
While
deoxygenated
re-pumping
to
the
passing
and
gills.
its
Fish
through
pressure
thus
have a
afferent arteries
u
l
a
v
O
f
x
t
a
r
o
i
o
d
heart
veins
ows
other
organs
oxygenated and still has enough
becomes
for
blood
over the gill laments and
dioxide
reduces
blood
singlecirculation.
The
pumped
C
return
pumped
another
the
is
blood;
support
gills,
to
organ,
the
oxygenated.
Water
n
must
the
directly
one
to
provides
through
be
by the
o
blood
to
heart
systemic circulation
circulation,
oxygenated
v
from
gills
laments.
are
circulation
p
gill
through the
delivering blood under
two
The
has
twice
y
to
water
ow
in
pulmonary
circulation
high
of
notable
heart
pump,
body.
circulations.
has
receives
the
double
of
systemic
blood
circulation
narrow
The
to
lungs
Oxygenated
deoxygenated blood being
i
n
it
out
lungs.
then
to
This
U
so
returns
circuit.
to
pulmonary
blood
in
owing
c apillaries
the
and
re-pumped.
circulation.
surrounding
falls,
full
diuses
pressure
It
double
deoxygenated
direction.
Aer
a
systemic
pump
oxygen
a
pressures
c apillaries
by
body
c arry
the
alveolar
r
e
Fish
the
pressure.
have
pulmonary
lungs.
than
the
separate le and right sides.
oxygenated
the
particular
pumped
with
through
ow on to other
O
receives
in
from
mix
be
to
lungs.
make
as
receives
not
has
to
owing
blood
t
i
s
known
heart
Aer
the
n
to
dierent
the
must
for
l
heart
to
heart
pressure
of
low
y
M ammals
the
apart
blood
the
lungs
so
kidneys
lower
to
the
too
y
at
returns
heart
blood
organ
it
bursting.
is
e
one
the
from
r
only
from
alveoli
pressure
P
in
so
lungs,
body
The
higher
oxygenated
blood
of
the
pressure.
much
body,
the
side
of
the
s
s
le
organs
to
in
residual
returning
pumped
The
the
LHA
prevent
gills
other organs
E
efferent arteries
▴
Figure 27
The single circulation of sh
285
Form and function
LHA
B3.2.15
Adaptations of the mammalian heart
for delivering pressurized blood to the arteries
The
mammalian
body
heart
has
continuously
evolved
to
throughout
pump
our
pressurized
lives.
It
is
well
blood
adapted
to
the
organs of
through
its
form to
s
s
the
c arry out this function.
•
Ventricles — chambers
•
pressure
Atria — chambers
and
blood
from
the
backflow
allow
blood
flow
C ardiac
it
is
they
from
possible
also
at
motor
when
contract.
the
A
ventricles.
c an
possible
collect
These
more
valves
the
atria
to
ventricles when the
and
the
wall
tissue
has
of
that
cells
the
in
These
the
contract
valves close
ventricles
The
cells
the
cells
that
relax and
This
connections
electric al signals to
enables
bec ause
contraction
itself.
wall of the
and
allow
body
contracts
of
forms
heart.
the
muscle
cell
group
artery.
when
branched
neurons.
the
the
ventricles
ventricles to the arteries when the
unique
the
the
ventricles
adjacent
in
it
from
muscle
is
so
the
muscle
the
the
from the
as
when
the
of
full
atria
from
generated
and
blood
as
The
and
therefore
is
it
coordinated
c an
c alled
membrane
this
contract
myogenic;
of
a
heart
activates adjacent
contracts almost
rate of the fastest.
o
i
arteries
aorta
vena
c ava
u
l
pulmonary
artery
right
atrium
le
atrium
a
E
v
O
f
x
t
a
r
o
d
c arotid
as
is
the
ventricle
to
muscle
depolarizes
simultaneously
atria
o
throughout
n
so
the
blood
to
C ardiac
that
collect
to
C
i
n
U
cells,
flow
membranes
stimulation
cell
empty
that
ventricle
y
atria.
plasma
means
muscle
wall
the
p
and
propagated
this
of
contract.
contractions.
without
between
v
between
be
to
the
blood
muscle — specialized
ventricles
as
r
e
C ardiac
is
so
n
valves
prevent
ventricles
•
of
relax.
to
to
between
blood
Semilunar
open
atrium
backflow
allow
generate high
O
•
muscular
ventricle,
t
i
s
ventricles
to
the
valves
prevent
open
the
y
and
to
c an
veins.
Atrioventricular
close
that
thinner
to
and
wall
l
•
contracts
muscular
▴
Figure 28
right
le
ventricle
ventricle
Exterior view of the heart
in its position in the thorax
y
it
on
strong
a
with
it
a
contracts, pumping blood out into the arteries.
P
when
pump
with
it
r
veins
286
when
e
blood
Organisms
Pacemaker — the
right
atrium
sinoatrial
initiates
each
node
in
the
heartbeat
semilunar valve
wall of the
LHA
•
aorta
by sending
pulmonary artery
an
electric al
between
signal
signals
into
the
atria.
determines
the
The
interval
rate
(pace) of
vena cavae
the
the
heart
beating.
of
the
The
but
wall
the
the
first to
heart
between the left
oxygenated blood in the left
from
in
heart
the
mixing
of
the
heart.
blood
deoxygenated
arteries
Coronary
and
veins
arteries
c arry
from the aorta to all parts of
oxygen
and
glucose.
right atrium
Coronary
heart
wall
collect
and
deoxygenated
blood
from
return it to the right atrium.
v
right ventricle
atrioventricular
valves
le
ventricle
o
septum
Figure 29
U
C
i
n
▴
p
the
veins
valve
y
supplying
r
e
wall,
with
side.
vessels — coronary
wall
heart
right
semilunar
between the left and right
prevents
oxygenated
the
the
the
Coronary
in
are
cycle.
O
•
cells
membranes.
heartbeat
t
i
s
blood
its
each
n
It
of
few
l
side
and
have
y
c ardiac
ventricles
node
y
atria.
of
each
of
pulmonary veins
spontaneous
extensive
initiate
membranes
in
region
contraction in other
have
c an
the
P
right
they
of
sinoatrial
c ause
node
Septum — the
and
the
rate
is
r
the
depolarize
of
that
fastest
node
e
cells,
sinoatrial
the
cells
sinoatrial
bec ause
•
with
proteins
muscle
The
The
s
s
of
heartbeat.
Structure of the heart
Structure and function of the heart
the
answers to these questions.
do
thinner
prevents
How
into
do
that
Aer
a
the
for
all
The
ventricles.
ventricles,
right
left
valve
wall?
side
of
the
heart
pump
oxygenated or
5.
Why
does
blood,
the
wall
brought
of
by
the
the
heart
need
coronary
its
own supply of
arteries?
from being
ventricle
ventricle
ventricle
repeating
initiates
in
the
c auses
of
delay
The
sequence
each
throughout
cells
signal
time-delay
ventricles.
a
node
spreads
electric al
the
the
left
6.
contracts?
Does
the
right
side
volume
of
blood
minute,
or
the
of
per
the
heart
minute,
a
pump
a
smaller
greater
volume per
wall being
same
volume per minute as the left?
u
the
follows
second
when
the
deoxygenated blood?
Stages in the c ardiac cycle
E
a
atrioventricular
explain
the
ventricles?
Does
a
sinoatrial
the
l
heart
The
of
atrium
v
O
The
of
you
than
B3.2.16
signal
the
the
f
x
thicker
walls
4.
walls of the atria being
t
a
pushed
3.
the
the
i
What
than
explain
r
o
2.
you
o
How
d
1.
n
Discuss
about
0.1
allows
stimulating
them
the
atria
the
atria
of
actions,
the
of
of
to
is
cycle
the
receive
seconds,
signal
to
of
walls
to
whole
the
electric al
turn
the
It
takes
signal.
le
the
as
the
sending
and
electric al
pump
then
atria.
the
both
known
by
This
right
blood
an
cycle.
electric al
less than a 10th
propagation of
atria
signal
propagated
c ardiac
out
that
is
to
contract.
conveyed to the
they
are holding into
throughout
the
walls of the
contract and pump blood out into the arteries.
287
Form and function
LHA
Stages
in
changes
heart.
of
a
the
c ardiac
during
Figure
a
30
heartbeat.
cycle
c an
heartbeat
shows
Vertic al
the
in
be
the
state
arrows
deduced
atrium,
of
heart
show
from
a
graph
showing
pressure
ventricle and artery on one side of the
chambers
and
valves during the stages
ows of blood.
3
atrium
3
25 cm
45 cm
atrium
3
25 cm
atrioventricular valve
closed
open
relaxing
contracting
ventricle
ventricle relaxing
3
0 cm
l
3
0
0.1
0.15
0.4
O
the body
0.45
Figure 30
Summary of stages of the c ardiac cycle with arrows to indic ate blood
ow between the vein,
v
atrium,
ventricle and
0.8
artery,
i
n
o
0.0–0.1 seconds: atrial systole
The atrium contracts causing a
p
including typic al volumes
y
r
e
time / s
▴
diastolic
n
y
systolic
t
i
s
diastolic
artery
tissues of
semilunar valve closed
80 cm
semilunar valve
rapid but relatively small
pressure increase, which pumps blood from the atrium to
C
the ventricle, through the open atrioventricular valve.
The semilunar valve is closed and blood pressure in the
U
artery gradually drops to its minimum as blood flow
n
continues along it and no blood is being pumped in from
the artery.
o
i
d
r
o
t
a
0.45–0.8 seconds: ventricular diastole
0.1–0.15 seconds: ventricular systole
Pressure in the ventricle drops below the
The ventricle contracts, with a
pressure in the atrium so the atrioventricular
up that causes the atrioventricular valve to close.
f
x
valve opens.
rapid pressure build-
u
The semilunar valve remains closed.
Blood from the vein drains into the atrium
and from there into the ventricle, causing a
l
slow increase in pressure.
a
E
v
O
0.4–0.45 seconds: ventricular diastole
▸
Figure
31
Timing of
actions in the
c ardiac cycle
288
0.15–0.4 seconds: ventricular systole
The ventricle stops contracting and
The pressure in the ventricle rises above the pressure
pressure inside it rapidly drops below the
in the artery so the semilunar valve opens and blood is
pressure in the artery, causing the semilunar
pumped from the ventricle into the artery, maximizing
valve to close.
the arterial
The atrioventricular valve remains closed.
Pressure slowly rises in the atrium as blood drains in
blood pressure.
from the vein and the atrium fills.
y
ventricle
P
ventricle
r
atrioventricular valve
atrioventricular valve
e
atrium relaxing
atrium relaxing
contracts
valve open
s
s
vein
Organisms
LHA
Data-based questions: Heart action and blood pressures
Figure
32
shows
artery
on
one
life
the
heart.
the
side
pressures
in
the
during
of
heart,
the
atrium,
one
ventricle and
second in the
ventricle
1.
Deduce
when
blood
is
being
pumped
s
s
120
of
from the
artery
100
atrium
ventricle.
The
the
atrioventricular
the
80
[1]
between
ventricle. State when the
valve
closes.
is
the
[1]
valve
between the
opens.
40
[1]
Deduce
when
the
semilunar
6.
Deduce
when
blood
is
valve
being
closes.
pumped
atrium
[1]
from the
0
ventricle
to
the
artery.
Give both the start and the
[2]
–20
Deduce
when
the
volume
of
blood
in
the
ventricle is:
maximum
[1]
minimum.
[1]
Figure 32
0.2
0.3
0.4
0.5
and
heart
rate of 75 beats per minute
0.6
0.7
0.8
time / s
Pressure changes in the atrium
heart
the aorta during a c ardiac cycle.
C
i
n
▴
and
ventricle of the
The timings assume a
n
U
B3.2.17
0.1
o
a
a
v
at
at
p
0
a.
b.
y
r
e
endtimes.
7
.
O
20
5.
n
artery. State when the semilunar
60
l
valve
the
valve
t
i
s
valve
and
the
contract.
y
semilunar
ventricle
is
to
y
and
valve
starts
P
atrium
atrioventricular
The
ventricle
r
3.
[2]
when
gH mm / erusserp
Deduce
4.
Give both the start and the
times.
2.
the
the
e
end
to
Generation of root pressure in xylem
o
d
vessels by active transport of mineralions
Water
has
tension
vessels,
expected
to
the
in
is
night,
air
most
some
c ases
down
to
opposite
be
for
to
before
lled
out
of
hypotonic
direction
root
to
enters
a
xylem
vessel. If
sap that is under tension.
cells
root
and
cells
into
and
xylem
water might
by osmosis. If the plant is not
pressure
c ause
it
with
rather
water
to
than
move
tension
into
in
xylem
the
sap
vessels
transpiration not occurring.
humidity
plants
water
positive
needed
spaces
allowing
the
is
cell
be
a
from
E
At
reasons
atmospheric
stomata
draw
sap
l
High
various
to
root
will
u
mechanism
to
one
vessels
xylem
the
likely
v
O
are
least
enough
move
is
at
xylem
root cells.
There
•
strong
though
there
another
from
•
is
even
transpiring,
and
through
f
x
be
pass
transpiring,
t
a
The
to
is
i
plant
r
o
the
may
inside
close
their
xylem
prevent
the
leaf
to
stomata,
vessels
to
diffusion
the
of
water
atmosphere
preventing
become
vapour
through
outside.
transpiration and in
air-filled
as
the
sap sinks back
roots.
▴
Figure 33
If grape vines are pruned
too late in winter when sap
•
In
deciduous
filled
but
started
trees
must
that
become
have
been
refilled
leafless
with
sap
in
winter,
before
new
xylem
leaves
vessels
have
has started
are airto rise due to root
pressure,
“bleeding”
from the cut ends of
there c an be
grown and
of sap
transpiring in spring.
thestems
289
Form and function
LHA
Root
water
transport of ions
movement by
rell
such as potassium
osmosis
air-lled.
sap
is
not
under
xylem
that
are impermeable to
water and ions so
vessels and pushes
force
pressure by active
water movement
by osmosis
uids
to
rise
by
of
gravity. Unlike
creating
a
vacuum
pressure is not dependent on
pressure
so
xylem
there is no limit to the
sapc anrise.
p
Generation of root
of ions and
vessel
n
U
C
Figure 34
transport
xylem
i
n
▴
moves
o
endodermis
cells
v
cortex
water
y
xylem vessels when
there is root pressure
so
by osmosis. This
the
r
e
prevent leakage from
transport
compared with
the
root
which
dead and
n
wall thickenings that
to
are
Active
O
height
membranes of
cells,
vessels
by
c arry out
inside
t
i
s
atmospheric
adjacent
vessels
that
against
c ause
them,
been
xylem
l
above
pressure
the
vessels
hypertonic
xylem
upwards,
plasma
xylem
y
pumps
the
the
Data-based questions: Modelling root pressure
of
from
lower
(Ψ
)
)
are
shows
by osmosis.
a
and
model
active
pressure potential (Ψ
/kPa
cells
a
290
Table 3
root
v
▴
sap
of
for
ions
P
E
xylem
Ψ
generating
and
water
C alculate
the
water potential of the soil and the
xylemsap.
[2]
water
2.
Deduce
the
direction
the
the
cytoplasm
soil,
sap.
Give
of
water
movement
between
Ψ
/kPa
s
−250
300
−650
3.
The
solute
dissolved
Ψ
for
of
root
your
cells
and
the
xylem
answer.
potentials
ions.
how
are
Deduce,
ions
are
due
[3]
almost
giving
moved
a
entirely to
reason
for
your
from the cytoplasm
/kPa
W
ofroot
4.
−750
reasons
root
movement
answer,
0
100
to
1.
Section D2.3.10
l
O
cytoplasm
of
)
P
scenario
transport
compartment
soil
water potential to
u
by
f
x
3
pressure
higher
described in
W
Table
of
t
a
(Ψ
s
potential
area
r
o
solute potential
an
water potential. The contributions of
o
moves
area
i
an
d
Water
State
what
zeroin
−350
5.
cells
the
Discuss
andthe
is
the
xylem
indic ated
sap.
by
a
[2]
pressure potential of
soil.
the
potential
to
[1]
reasons
between
xylem
sap.
for
the
the
difference
cytoplasm
of
in
pressure
the
root cells
[2]
y
the
sap
of
the
have
r
raises
to
the
into
proteins
membranes.
sap
used to
when
P
them
in
rise
ions
pump
The
plasma
cytoplasm
from
the
the
are
to
is
they
Root cells adjacent to
mineral
The
cells.
have
sap
that
when
e
not
makes
the
load
transport
sap
tension.
transport.
living
mechanism
with
c auses
active
do
ions into xylem vessels
also
vessels
these
for active transport of
the
xylem
active
membrane
with pump proteins
It
is
vessels
s
s
plasma
pressure
xylem
Organisms
Adaptations of phloem sieve tubes
and companion cells for
Sucrose
the
to
and
plant
where
unloaded
cell
starch
from
or
lipids
store.
or
are
cell
reactions
by
that
need
as
part
Leaves
a
are
photosynthesis.
sinks.
to
of
are
are
photosynthesis
be
supplied
growth
sources
Roots
from one part of a
Sources
or
bec ause
sinks
tissues of
or
are being
with
tissues
they
bec ause
substrates
where
produce
they
need
respiration.
is
that
the
tubes
transports
sieve
develop
connected
c arbon
tubes
by
that
from
large
compounds.
provide
columns
Of
channels
of
cells.
perforations
the
several cell types
through
which
transport
Adjacent cells in the
(holes)
in
the
end
walls, which
t
i
s
are then c alled sieve plates. Nearly all the contents of the cells break down during
including
sap,
solution
which
is
a
cell
to
ow
It
debatable
is
have
certainly
The
is
main
out
of
by
their
cells
own
have
the
sieve
through
than
the
by
without
the
withstand
particular,
the
thick
sieve
it
act
transport.
water
exits
by
cell
and
tube
are still cells, but
energy, so they
elements
at
companion
have
cells
producing
brace
the
the
bec ause
they
compounds
lowers
the
in
plant.
In
transport
hydrostatic
in
c an
conduct
As
an
morec arbon
sources
example,
then
in
the
that
addition
to
c an
through to
by
in
leaf
cell
walls
of
develop
pass
and
the
sinks
the
bulges
Figure 35
The holes in a c apsule used in
a coee-making machine are reminiscent of
other
ATP
,
sources.
for
sieve tube
sieve tube
transport. In
or
bursts.
cell
respiration.
tissue
are
in
sieve tubes, so
the
drops.
drives
either
in
during
substrates
by
tubes
▴
pressure. This could
maintained
pressure
and
sap
sieve
the
preventing
opposite
compounds
is
concentration
the
and
of
hydrostatic
need
sap
tubes
tubes
that
connections
the pores in a sieve plate
the
active
required
solute
supply.
pass. These plasmodesmata
cellulose
tube,
a
c an
the
pressures
for
ATP
sieve
and
Sieve
leaf
high
sucrose,
few or no
cytoplasmic
by
phloem
once).
growing
in
rather than
unloading
elements
for the
ne
membrane
xylem,
sinks
osmosis
sink.
directions
as
This
E
to
plates
sinks,
between
in
the
a
other
as
easier
and
the
increasing
l
and
plasma
v
O
generally
active
a
Sieve
u
as
f
x
not
c an
into
loading
elsewhere
develop
osmosis,
elements
source
those
tube
i
in
Although
pressure
is
sieve
adjacent
which
companion
concentrations
water
happen
roots
c alled
tubes
requiring
o
solute
elements.
In
make
tube.
draws
Roots
on
sieve
t
a
not
rely
of
processes
mitochondria
r
o
This
into
for
process
d
High
diameter
loaded
walls
n
larger
end
U
have
subunits
ATP
transport.
and
many
plasmodesmata,
a
use
sometimes
active
c alled
sucrose
remaining
and
are
the
C
Companion
They
of
by phloem
transported. The
tube.
energy-requiring
c arried
mitochondria
the
membrane
alive.
perforations
replaced
being
i
n
which
whether
a
the
sieve
are
o
cells.
the
contents
compounds
v
are
do
and
through
cell
other
p
they
contents
The
and
y
of
sap
nucleus.
sucrose
r
e
loss
the
of
O
dierentiation,
n
become
produced
tissues
stored.
transported
to
l
column
Sieve
by
be
y
occur.
are
anabolic
being
tissue
it
Sinks
are
c an
sources
y
the
phloem,
from
r
is
for
is
P
Phloem
c an
a
compounds
transport
compounds
compounds
substrates
within
the
respiration
c arbon
c arbon
The
e
for
other
another.
transloc ation of sap
s
s
plant
LHA
B3.2.18
The
the
unloaded
by
dierence in
ow
of
sap
from
direction (but not both
transport
direction
c arbon compounds
out
photosynthesis
of
the
than
it
leaf when it is
is
using
in
growth
andrespiration.
291
Form and function
LHA
phloem
sap
s
s
e
phloem sieve tube
element with
companion cell
r
plasma
membrane
with nucleus,
(purple) but few or
and
no organelles
other organelles
l
which phloem sap can flow
Structure of a sieve tube element and adjacent companion cell
a.
do
pressure
Describe
o
d
Explain
i
t
a
r
o
f
x
Explain
active
2.
u
l
a
E
v
O
292
the
away
the
c apillaries.
c.
What
a.
dierences
contribute
to
the
movement ofmaterials in
of
for
high
organism?
blood
b.
o
an
adaptations
from
role
the
of
arteries
pressure
transport of
heart. (B3.2.3)
pressure
ltration
in
the
formation
of
tissue uid in
(B3.2.10)
role
of
the
transport
the
of
mineral
processes
Compare
of a
n
U
How
Freeze–fracture electron
sievetube
C
i
n
Linking questions
1.
p
Figure 36
Figure 37
micrograph showing cell walls in a
v
▴
▴
y
sieve plate with pores through
r
e
cell walls to form a
cytoplasmic connection
O
membrane crossing the
n
y
t
i
s
plasmodesmata
— tubes of plasma
happen
and
generation
in
contrast
ions.
cycles
at
cellular
of
root
pressure
in
xylem
vessels
each
level
of
reproduction
biologic al
with
the
organization?
lysogenic
virus. (A2.3.4)
b.
O utline
c.
Using
the
stages
examples,
biologic al
of
the
explain
systems.
c ardiac
cycle.
the
of
(B1.1.4)
by
(B3.2.16)
role
(B3.2.15)
oxidation
and
reduction in
cycle
y
P
mitochondria
B3.3
Muscle
and
motility
The
rowers
the
through
the
direction
water.
1
m
will
is
for use
pulled
rowlock, which is
3.7m
what
racing
ways
is
oar. In which
rowing a
mechanism within muscles that
generation
shorten
is
In
a
oar
the
itself
relative
of
force?
and
role
exert
of
Muscle
a
actin
tissue
pulling
and
force
myosin in
contraction?
p
v
orb-weaving spider (Nephila clavipes)
c aught
neurotoxin
tremble
to
and
its
web.
then
Insects that
move
increasingly
o
become
silk
potent
C
a
i
n
golden
applies
y
Figure 1
What are the benets to animals of having muscle tissue?
The
O
t
i
s
r
e
▸
y
What
on
a
muscles
the
n
muscle
so.
of
of
l
does
rests
end
move?
and
c an
powerful
blade
y
it
oar
the
the
the
P
for
develop
The
boat
contraction
contractile—it
as
1
when
from
this
analogy
c auses
is
Figure
stroke,
r
positioned
good
in
power
e
in
s
s
How do muscles contract and c ause movement?
U
slowly before becoming paralysed. The spider injects
exoskeleton.
survival
chances
of
muscle
in
of
animals
or
muscle?
the
prey’s
lack
How
systems?
metabolic ally
contraction?
What
as
a
▴
AHL
universal
of
lament
model
B3.3.3
Role
the
v
titin
B3.3.4
Structure and function of motor units in skeletal muscle
B3.3.5
Roles
B3.3.6
Movement
B3.3.7
R ange of motion of a joint
B3.3.8
Internal
E
of
skeletons
at
and
a
as
and
The golden silk orb-weaving spider (Nephila clavipes)
organisms
contraction
antagonistic
anchorage
Figure 2
only
living
Sliding
protein
muscle
feature
B3.3.2
of
of
What is the
expensive is
u
movement
a
for
l
Adaptations
muscle?
organs of mammals such
circulatory
f
x
O
B3.3.1
group
play
systems
skeletal
the
i
muscle
digestive
role
muscle,
t
a
as
taxonomic
does
working
are nil.
r
o
role
digested contents out of the
d
Which
the
Without
o
insect’
s
n
enzymes and later sucks
for
muscles
muscles
and
in
as
muscle
relaxation
levers
synovial joint
external
intercostal
muscles
as
example of antagonistic muscle action to facilitate internal body
movements
B3.3.9
Reasons
B3.3.10
for locomotion
Adaptations
for
swimming in marine mammals
293
Form and function
LHA
B3.3.1
Adaptations for
movement as a
universal feature of living organisms
Movement
is
one
of
the
functions
of
life.
Two
types
of
movement
c an be
•
movements
within
the
body
of
s
s
distinguished:
an
organism such as peristalsis in the gut or
ventilation of the lungs
locomotion,
which
is
the
movement
of
an
organism
e
•
from one place
toanother.
happens
in
all
living
the
organisms.
cytoplasm.
The
Even
latter
a
unicellular
in
organism
butnot all.
some
there
organisms
generating li and
organism
that
moves
from
place
to
place
is
motile.
h
around
while
double
An
10,400km
their
organism
animals,
a
into
particularly
of
sessile
themselves.
are
in
a
polyps.
In
lter-feeding,
move
much
greater
is
the
sessile.
are
habitats.
in
Most
motile.
For
7–8days. They
journey.
plants
There
example,
are
are
a
sessile,
some
sessile
coral consists
corals, the polyps construct a rigid skeleton
them
but
Zealand
before
animals
marine
hard
allows
New
position
Most
or
to
reserves
xed
soil.
aquatic
This
Siberia
fat
animals
move
bar-tailed godwits (Limosa lapponica)
they
to
extend
c annot
to
their
tentacles
move
to
a
into
new
the
water
loc ation.
n
U
C
i
n
o
they
in
with
the
v
when
remains
growing
colony
around
eastern
weight
example,
M any
animals
p
of
that
from
For
Some
y
roots
body
migrate.
territory.
r
e
with
they
their
O
migrate
when
within
t
i
s
distances
feeding
n
y
An
–1
to 90 km
l
their wings,
velocities of up
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
▴
Figure 4
Adult
barnacles remain attached
to a solid
larval stages in the barnacle life cycle which swim,
goose barnacles (Lepas anatifera).
required
294
in
happens
for motility
surface,
so they are sessile.
so they are motile.
There are
This photo shows adult
They are lter-feeding using modied
legs that
are not
y
within
Bar-tailed godwits (Limosa
lapponica) have ight muscles that they
use to beat
former
movements
P
are
Figure 3
r
The
▴
Organisms
LHA
B3.3.2
Sliding lament model of muscle
contraction
Muscle
bres
contain
sarcomeres
of
a
are
linked
sarcomere
further
dark
parallel
a
dark
band
the
light
bands
bands
and
light
myobrils.
at
in
Z-discs.
the
are
bands
centre.
wider
are
E ach
There
In
and
visible
myobril consists of a series
are light bands at either end
relaxed
overall
in
muscle,
the
electron
the
Z-discs
sarcomere
is
longer.
micrographs.
r
relaxed sarcomere
e
Zlines,
and
apart,
many
end-to-end
s
s
of
l
muscle
contracted
laments
The
contraction
At
of
heads
myosin
a
the
and
in
There
muscle.
So
the
are
a
they
of
that
a
precise
and
Z-disc
at
interlock
is
one
like
a
surrounded
laments
form
The
myosin
by six actin
dark band
at
the
the
laments
c ause
Z-line
light
band
light band
Z-line
cross-bridges
force,
towards
swivel,
end.
ngers with the
same
myosin
using
energy
centre of the
overlap
exerting
actin
more.
force which
light band shortens,
dark band remains
distance
(8–10
nm)
towards the
indicating actin
the same length
heads
then
detach,
then
swivel back
slides along myosin
mechanism.
at
the
sites
same
sarcomeres,
therefore
very
in
Bec ause
on
the
time.
And
many
large
although
each
myosin
they
exert
very
of
actin,
are
myobrils,
exerts
regular spacing
many
there
numbers
head
the
of
in
heads along a
many
myosin
only
a
myosin
many muscle
heads in
small
sarcomere contracts
force,
▴
collectively
regular
muscle, is due to
spaced
exert
myosin
bind,
short
The
c an
lament
and
binding
bind
many
to
sarcomeres
next binding site on the actin. This is sometimes
ratchet
E
bres.
to
lament
laments,
heads
laments
sarcomere.
as
a
Myosin
laments,
actin
actin
therefore
u
the
to
to
and
lament
“heads”
a
reattach
referred
of
the
and
l
and
of
myosin
laments.
have
actin
the
the
myosin
actin
they
v
O
centre
the
the
attached
sarcomere
cross-bridges
pushes
making
due
i
This
myosin
along
The
f
x
time
pushes
and
sites
is
t
a
ATP
.
E ach
sarcomeres,
intervals
intervals.
sarcomere,
E ach
of
are
the
sarcomere
cross-bridges with them.
r
o
from
to
ends.
form
actin
regular
binding
regular
both
of
a
lament — thin actin laments and thick
o
sliding
this.
by
at
c an
laments
centre
in
d
the
and
bands
protein
Electron micrographs of
contracted
n
laments
Actin
the
of
U
actin
occupy
dark
types
and
o
laments.
laments
and
two
Figure 5
relaxed
C
myosin
light
of
v
of
i
n
pattern
arrangement
◂
y
contracted sarcomere
p
r
e
muscle
O
Z-disc
t
i
s
dark band
n
light band
Z-disc
The
y
light band
y
P
relaxed
c an
powerful
Figure 6
Diagram
of a sarcomere in relaxed muscle
forces.
(above) and
contracted
muscle (below)
295
Form and function
LHA

myosin filaments have heads hich
form cross-bridges hen they are
ATP binds to the myosin heads
2
attached to binding sites on actin
and causes them to break the
filaments
cross-bridges by detaching
s
s
from the binding sites
movement
+
P
r
released and the heads push the
ATP is hydrolysed to ADP
and phosphate, causing
this is called the poer stroke
+
P
the sarcomere than the previous sites
The cycle of stages in the ratchet
mechanism
that
c auses an actin lament
position as they are
storing potential
energy
from ATP
y
Figure 7
r
e
▴
“cocked” in their ne
O
actin that are further from the centre of
change their angle. The
heads are said to be
t
i
s
the heads attach to binding sites on

P
n
y
ADP
+
l
the myosin heads to
ADP
to slide over myosin lament
p
v
Data-based questions: Transverse sections of striated muscle
in
of
muscle
an
in
Figure
electron
8
show
small
micrograph
of
parts
a
of
a
myobril,
transverse
1.
Explain
section
tissue.
2.
difference
alongitudinal
section
Deduce
part
U
bythe
what
drawings
n
3.
the
C
seen
o
drawings
as
i
n
The
Compare
the
of
as
between
of
the
small
pattern
of
a
transverse and
muscle.
[2]
myofibril
is
represented
dots.
dots
[2]
in
the
three
diagrams.
i
o
Explain
[3]
the
thepattern
◂
u
B3.3.3
l
a
E
v
O
f
x
t
a
r
o
d
4.
Figure 8
differences
of
between
the
diagrams in
dots.
[3]
Patterns seen in transverse sections of myobrils
Role of the protein titin and
antagonistic muscles in muscle relaxation
Titin
is
the
34,350
Titin
is
is
elastic
stretched
myosin
•
largest
amino
It
and
and
but
acts
in
like
releasing
laments
holds
polypeptide
acids,
to
each
the
a
far
it
is
discovered. In humans, it is a chain of
even longer with 35,213 amino acids.
molecular
this
Z-disc
myosin
so
mice
energy
and
filament
has
in
spring,
when
it
storing
recoils.
potential
Titin
energy when it
connects the end of
several functions.
the
correct
position
in
the
centre of six
as
recoils.
parallel actin filaments.
296
•
It
prevents
•
It
adds
to
overstretching
the
force
of
of
the
sarcomere.
contraction
by
releasing
energy
it
y

the centre of the sarcomere-
P
actin filament inards toards
e
ATP
ADP
the ADP and phosphate are

Organisms
of
is
needed
muscles
to
contract,
so
has
to
provided
the
name,
a
an
muscle
in
of
by
the
the
titin
they
c annot
pair
other
and
pair
it
Muscles
the
muscle
of
that
the
to
is
lengthen
c an
energy
muscles
providing
as
therefore
relax.
supply
another
antagonistic
member
molecules
when
it
only
a
muscle. Lengthening
exert
needs
to
force when they
lengthen.
The
energy
known as the antagonist. Despite
work
energy
together,
needed
with
the
contraction of
s
s
each
be
stretch
happens
LHA
Energy
for lengthening the titin
relaxes.
dark
light
band
band
r
e
light
band
l
that
unit
it
muscle
in
a
than
bres
in
bres
respond
of
via
a
These
from
the
group
but
passes
along
the
to
the
at
the
contraction
multiple
of
same
the
a
single
muscle
in
unit.
main
by
These
axon
of
neuron
muscle
together
There
bres
muscle
motor
skeletal
dierent
are
bres
with
are
of
not
other
neuron and then
bres in the motor unit, all of the
contracting.
with
typic al
junctions.
with
a
a
stimulate
motor
mingled
muscle
time
that
neuromuscular
are
contract when
neuron to the
acetylcholine. These
neurons
branches
motor
single
E
v
coordinated
impulse
branches
motor
has
consists
stimulates
a
muscle
the
bres.
passed
neurotransmitter
neuron
l
nerve
all
is
u
f
x
a
O
along
n
of
bres
motor
motor
bres
together
the
motorunits.
When
O
muscle
each
One
muscle
stimulus
neuromuscular junctions.
more
hundreds
clumped
y
usually
o
bres.
muscle
using
striated
i
the
many
bec ause
of
The
t
a
all
synapse,
c alled
r
o
muscle
a
neuron.
o
are
muscle,
composed
d
There
at
are
are
motor
n
bre
synapses
a
U
muscle
by
C
muscles
stimulated
v
Structure and function of motor units
in skeletal muscle
Skeletal
titin
Structure of a sarcomere showing titin laments
i
n
B3.3.4
myosin
(thick filaments)
p
Figure 9
actin
(thin filaments)
y
P
y
t
i
s
▴
r
e
Z-disc
as
few
This
motor
helps
to
achieve a
neurons
as
possible.
▴
at
Figure 10
Motor end
plates (boutons)
the ends of branches of a motor neuron
forming synapses with muscle bres
297
Form and function
LHA
B3.3.5
for
A
Roles of skeletons as an anchorage
muscles and as levers
skeleton
is
a
internal.
of
Skeletons
spiders,
of
chitin
the
is
is
a
insertion,
and
insertion
on
the
moves
by
is
of
is
the
so
have
body
exoskeletons
surface.
for muscles and
contraction
muscle
which
not
the
is
part
xed
does
not
is
on
the
of
the
c auses
c ause
movement.
movement.
jawbone
skull.
(mandible)
Contraction
cheek bone enabling biting
O
t
i
s
y
p
C
o
r
f
f
t
o
e
n
t
n
l
a
t
u
s
e
c
r
e
r
i
o
o
f
▴
Figure 12
The eort
than the resultant
is further from
the fulcrum
force so this lever increases the
t
a
(mandible)
size of the force but
decreases the distance moved.
Bec ause the forces are on opposite sides of the
Contraction of the masseter muscle c auses the jawbone
fulcrum,
the direction of the force is reversed
u
By acting as levers, bones c an change the size and direction of a force (Figure12).
l
a
E
v
O
f
x
to move upwards, closing the mouth
298
muscle
v
i
n
U
d
Figure 11
r
o
▴
jawbone
insects
the
anchorage
r
e
of
the skull
muscle
an
contraction
masseter
bone,
jawbone,
the skull)
jawbone and
of
body.
are
attached to two parts of the skeleton.
where
xed,
cheek
the
providing
muscle
(zygomatic
joint
and
most
animal’
s
n
muscle
the
origin
the
origin
movement
cheek bone
masseter
cover
an
endoskeletons
A
lever
has
applied
is
to
exerted
further
the
force,
at
from
force,
nearer
a
to
xed
the
a
but
but
is
c alled
the
position
the
the
point
lever
on
fulcrum
increases
the
than
the
the
than
decreases
fulcrum
the
eort.
fulcrum,
When
other
the
side
which
eort
the
force,
moved.
is
is
the
pivot
applied,
fulcrum.
force,
moved.
resultant
distance
of
resultant
distance
the
the
the
If
lever
the
lever
point.
The
resultant
eort
is
force
force
applied
increases the size of
Conversely,
a
a
if
the
eort
is
applied
decreases the size of the
y
is
between the
protects
crustaceans
that
andspeech.
bone — part
and
whereas
l
this
as
Typic ally,
attachment
the
such
plates
body
y
of
facilitate
example,
and
supports
the
have endoskeletons consisting of bones.
levers.
other
of
r
For
as
tough
that
outside
P
The
the
e
Vertebrates
One
framework
on
Arthropods
consisting
acting
hard
are
s
s
Exoskeletons
Organisms
LHA
For a bone acting as a lever, the fulcrum is the joint where the bone meets another
bone. The eort is applied to the bone by one or more muscles, viatendons.
s
s
e
r
have
provide
the
an
anchorage
bones
guide
the
for
muscles
types
of
to
fluid
ends
the
of
fills
of
friction
bone
shocks
a
the
that
that
c avity
that
It
by
the
in
relation
similar
By
to
each
structure
c an
covers bone at the
cartilage
(pale blue)
capsular
ligament
synovial
fluid
(dark blue)
preventing contact
otherwise
c ause
joint
bones
rub
to
between
ligament
together.
between pelvis
pelvis
fracture.
the
and femur
c artilages
lubric ates the joint, helping to
would
occur
if
the
c artilages
were dry
u
f
x
and touching.
•
that
might
might
in
bones.
friction
tissue
that
i
the
prevent
prevent
regions
absorbs
smooth
ligaments.
a
n
helps
Synovial
on
tough,
and
movement
t
a
•
also
is
r
o
It
move
have
o
It
between
joints
following components.
d
joint.
to
synovial joints.
shape,
C artilage
between bones of the skull,
bones
articulated
occur at a joint.
•
sutures
n
Most
the
allow
U
their
articulation.
as
joints
C
Bones
such
Most
i
n
joints
joints,
l
c alled
c alled
Synovial
•
is
Fixed
movement.
y
are
joints.
any
o
and
bones for
fast running
v
other — this
for digging
Movement at a synovial joint
at
allow
Skeleton of cheetah (Acinonyx
p
not
Figure 14
jubatus) with long narrow limb
r
e
do
meet
wide forelimb
O
are used
B3.3.6
Bones
with short,
t
i
s
bones that
▴
Skeleton of European mole
y
P
Figure 13
(Talpa europaea),
y
▴
Ligaments are tough cords of tissue containing large quantities
synovial
femur
l
of the protein collagen. They prevent aberrant movements
a
O
membrane
that would dislocate or damage the joint. The joint capsule is
(brown)
a tough ligamentous covering to the joint. It seals the joint and
v
holds in the synovial fluid and it helps to prevent dislocation.
Muscles
provide
•
Tendons
attach
are
E
•
composed
the
forces
muscle
of
living
extracellular
collagen,
tendons
are
long
over
distance
the
the
tendon
and
to
that
c ause
bone.
tissue,
which
Figure 15
The hip joint
movement at the joint.
Like ligaments they
with
has
cord-like
▴
large quantities of
high
so
tensile
forces
c an
strength. Some
be
transmitted
between the muscle and the bone to which
attaches it.
299
Form and function
LHA
Poultry wing dissection
The
2.
anatomy of a poultry wing such as a chicken or turkey
wing
homologous
on
the
to
the
human
arm.
In
this
Cut
the
skin
pointing
dissection,
along
the
the
scissors
entire length of the wing,
up
so
as
not
to
cut
the
tissues
s
s
focus
is
underneath.
elbow joint of the poultry wing.
3.
1st digit
Remove
2nd digit
under
tissue
below it.
Use
blunt
a
from
Pull
on
that
results.
each
of
to
by
placing
at
the
your finger
connective
separate the individual muscles
without
the
wing
tearing
tearing them.
muscles
and
note
humerus
ulna
Determine
pairs
of
the
muscles
movement
that
are
l
antagonistic.
a
muscle
to
where
C arefully
the
▴
Figure 16
dry
it
Bird wing bones
the
wing
with
a
under
paper
running
towel
water
bec ause
and
the
surface
the
Note
to
is
a
it
o
the
are
including
the
range
hinge
extension
joints
the
surface
of
the
c artilage.
allowing
protract
joint.
and
It
a
joint
are
c apsule and the
possible.
movements
The
has
retract,
that
hip
joint,
greater
abduct
and
in
one
The
elbow joint
plane:
exion
between the pelvis and
range
of
adduct,
movement than the
and
rotate.
t
a
The hip
of
ligamentous
(straightening).
ball-and-socket
c an
the
movements
outward rotation
a
v
E
300
Figure 17
c artilage.
synovial fluid.
abduction
adduction
▴
radius and the ulna.
o
joint,
joint
and
joint:
due
the
texture
C
knee
femur,
a
determines
(bending)
elbow
is
of
oily
expose
u
l
O
retraction
of
i
d
r
o
f
x
protraction
the
This
n
and
to
R ange of motion of a joint
structure
ligaments,
tendons
appearance.
10.
v
i
n
U
The
in
Separate the bones at the joint and note the
the
the
and
Identify
may be
humerus,
white
9.
bacteria.
B3.3.7
muscles
are
p
Salmonella
the
which
8.
thoroughly
appearance
contaminated with
connects to the bones.
y
Rinse
remove
ligaments
r
e
1.
it
appearance of the tendons.
O
7
.
the
t
i
s
Note
n
Follow
y
6.
scapula
is a ball-and-socket
joint
that
allows movements in all three planes
inward rotation
y
5.
probe
other
the
lightly
P
3rd digit
each
from
and
r
4.
skin
skin
e
radius
the
the
Organisms
range
The
simplest
a
of
protractor
are
also
movements
method
(Figure
computer
is
at
to
18).
a
joint
use
a
Digital
programs
c an
be
investigated
goniometer
goniometers
that
analyse
by
consisting
are
of
available
images
to
LHA
The
measuring joint angles.
two
as
obtain
rulers
phone
connected to
apps.
There
measurements of
jointangles.
s
s
Making c areful measurements: Using a goniometer
joint.
stretching
There
persist
different
terms
of
the
Do
types
of
increases
joints
range
does
between
range of motion
stretching
regime
they
in
allow
the
differ
range of
the
and
of
range
boys
types
motion
of
of
motion
after
motion
see an
stretching?
at
hip
joints
compare
andgirls?
p
o
A goniometer
C
i
n
v
Figure 18
Internal and external intercostal
n
U
B3.3.8
▴
y
How
the
day later?
r
e
•
research questions.
on
joint?
different
increased
stretching
O
motion of a
•
possible
stretching
one
of
y
the
some
of
types
stretching and isometric
t
i
s
in
are
effect
range of motion at a
n
Do
joint
dynamic
the
dierent
y
•
a
of
l
of
Here
the
increase
P
Does
c an
number
including
stretching.
•
a
r
regime
are
e
Muscle
muscles as an example of antagonistic muscle
action to facilitate internal body movements
are
of
the
titin
muscles.
potential
E
stores
in
and
allowing
intercostals
pink = internal
intercostal muscles. This
in
internal
relaxed
stretching of the
stretching
the
muscles contracted and internal intercostals
blue = external
a
internal
intercostal
rib
ribc age
intercostal muscles
ribc age
and
the
Contraction
v
O
the
contraction of
moves
directions.
external
inhalation
dierently. This
u
opposite
layers
vertebra
Ribcage up and out with external
sternum
l
in
bres in these
alternating
dierent
expands
muscle
orientated
that
are
external and internal
the
f
x
means
the
of
They
i
and
are the
ribs.
t
a
up
layers
the
r
o
made
layers
muscles
between
o
intercostal
muscles
d
The
the
During
internal
muscles.
the
Ribcage down and in with internal
intercostal
muscles contracted and external intercostal
exhalation, the
intercostal
stretch
intercostals
energy
intercostal
muscles relaxed
muscles
external
contract
intercostal
▴
Figure 19
The internal and external intercostal muscles are antagonistic. They form
continuous layers of striated muscle between the ribs. In this diagram, pairs of ribs are viewed
from the side, with muscle bres shown at intervals
301
Form and function
LHA
B3.3.9
Reasons for locomotion
Locomotion requires expenditure of energy, so will only occur if there are benets
for
the
animal.
There
are
multiple
food
Herbivores
to
move
searching
to
the
nd
Predators
best
nd
for
the
nectar
pastures.
move
to
c atch
plant
and
foods
pollen.
Frugivores
and
kill
that
they
Grazing
move
their
moving
to
from
need.
animals
nd
place
Bees
y
move
abundant
sources
move
own
species.
(Propithecus diadema) eating wild
esc ape
from
is
potential
therefore
predators
strong
or
selective
from
stamina.
M any
animals
have
a
roosting
site
they
roosts
are
with
inactive.
many
Jackdaws (Corvus monedula),
individuals,
oen
in
dispersed
an
avoiding
inbreeding.
their
will
attempt
females.
for
the
Arctic
They sometimes jump
repeatedly
North
of up
to 2 m — a behaviour
lifetime
known as “pronking”.
in
chasing them
mate.
leaving its home
and
their
dominant
both
poles
snow
the
to
so
the
and
avoid
for
When
they
summer
Some
food
and
coast
species
breeding
of
the
such
grounds,
as
with
US,
leave the
a
new
migrate
sc arcities
back
pride,
of
towards
between
winter.
the
migrate
equator
between
breeding in the north and
salmon,
the
nd
c an mate with all the
autumn.
the
example,
they
geese (Anser caerulescens)
Atlantic
Some
pride.
male
spring
for
By
c arry out a once-in-a-
young
inhabited
migrating back to
by the adults.
i
u
l
a
v
E
M ale Americ an moon moths
(Actias luna) have huge antennae that
detect
a
t
a
r
o
f
x
O
Figure 22
to
nd
dawn.
o
d
region
the
south.
This may alert other
the
to
in
another
hemispheres
example,
the
migration
springbok to dangers or confuse predators
▴
closer
For
Americ a
overwintering
to a height
migrate
southern
nd
the
n
.
migrate
winter.
U
speeds of over
–1
bird
to
at
unrelated individual to mate with thus
o
Others
of
and
travel
an
C
cheetahs and other
northern
to
v
(Antidorcas marsupialis) in southern Afric a
species
i
n
M any
the
travel
displace
Migration
must
nd
example, gather at dusk
disperse
Young male lions (Panthera leo),
and
to
c an
for
and
p
adult
birth
animal
treetops,
y
of
individual
r
e
they
Springbok antelope
populations
territory,
pride
80 km h
movement
return to during times
O
Animals
in
t
i
s
Searching for a mate
predators by running at
they
members of their
rapid
n
in
c an esc ape from
that
y
when
Figure 21
for
eastern
M adagasc ar
▴
hostile
pressure
fruit.
l
in M antadia National Park,
There
guava
and/or
fruit
to
ripe
c an
pheromones given o by unmated
females hundreds of metres away. This
allows them
to y in the direction of a female
▴
Figure 23
S almon migrate from
the oceans to their spawning grounds in the headwaters
in order to mate with her
of rivers.
302
Young salmon remain in the river for up
to three years and
then migrate out
to sea
y
Prey
of
prey.
sifaka
ower to
grassland
r
A diademed
from
P
Figure 20
place.
across
Esc aping from danger
▴
to
e
ower
for
s
s
Foraging for
reasons
Organisms
Adaptations for
LHA
B3.3.10
swimming in
marine mammals
E arly
mammals
for
much
more
those
needed
all
life
water.
in
viscous.
for
terrestrial,
Swimming
locomotion
Streamlining — marine
resistance
to
motion
but
Water
is
therefore
on
land
mammals
by
about
about
these
or
are
a
50
million
years
ago
some
evolved
thousand times denser than air and
requires
alo
in
dierent
the
adaptations
from
air.
•
shaped to minimize
Airways
shaped
to
rear,
near
which
the
front and tapering
c auses
less
–
flukes
in
fin
with
transverse
an
no
connection
avoid
elongated
section which
dorsal fin
reduces
surface
blubber
–
without
smooth
absence
hair,
due
of
reducing
for locomotion:
–
which
ear flaps
for
steering, in place of
legs
flukes
on
the
increase
tail,
which
thrust
are lobes to left and right
when
the
tail
is
moved up and
–
dorsal
fin
to
preventing
blubber,
water
which
to
by
provides
cease
surface,
for
buoyancy,
moving
and
example
float
when
it
flukes
allowing a
just
is
blowhole
below the
sleeping.
Figure 24
flipper
Streamlining of a dolphin viewed
(upper drawing) and
from
from the side
above (lower drawing) with transverse
sections through the ipper,
dorsal n and uke
i
u
l
a
E
v
O
f
x
t
a
r
o
d
o
▴
n
dolphin
stability
U
–
provide
rolling
C
i
n
down
o
that
used
and
v
–
are
limbs
friction.
p
front
even distribution of
y
Adaptations
flippers,
to
hind
r
e
•
skin
and
O
body
drag
t
i
s
–
between the mouth and lungs to
water entering thelungs.
n
profile
dorsal
through which marine
breathe
y
teardrop
and
from the larynx to the upper
head,
l
flippers,
the
of
mammals
drag than
other shapes
–
surface
y
the
widest
ventilation of the lungs:
leading
P
towards
be
allow
blowhole
r
–
–
to
features:
e
•
were
s
s
adaptations
▴
Figure 25
Internal anatomy of dolphins
303
Form and function
LHA
Data-based questions: Relationship between movement and food sources
Basking sharks (Cetorhinus maximus)
(small
coastal
M arine
paths
coast
seas.
taken
of
by
two
Plymouth
oating
marine
biologists
basking
(UK).
At
recorded
sharks
the
lter
feed on
animals)
about
same
in
the
1.
Using
temperate
the
sc ale
given,
c alculate the
straightline distance:
s
s
zooplankton
swimming
a.
from
point
A
to
point
B
b.
from
point
C
to
point
D
[1]
8 km o the
[1]
time, the densities of
−3
(in
g m
)
were
recorded
within
2.
3 m of the
Distinguish
behaviour
swimming path of the sharks.
Using
the
data
for
1
the
and
swimming
shark
2.
[1]
given, suggest
the
difference in the
swimmingbehaviour of the two
sharks.
which
t
i
s
of
the
advantages
and
[2]
O
are
sharks.
disadvantages
of
dispersal
of
ospring
from
parents?
examples
b.
Distinguish
o
List
of
intraspecic
between
seed
competition.
(C4.1.10)
dispersal and pollination in plants.
(D3.1.12)
i
c.
Outline
2.
What
are
reasons
the
biologic al
u
l
a
E
v
O
f
x
t
a
r
o
d
a.
n
U
their
p
What
C
1.
food
o
v
i
n
Linking questions
than
affect the distribution
basking
Paths taken by two basking sharks with densities of zooplankton along
the paths
304
may
[3]
other
y
Figure 26
r
e
▴
the
factors
n
two
l
State
y
4.
for locomotion in living things. (B3.3.9)
relative
advantages
of
versatility
and
specialization in
mechanisms?
a.
Distinguish
b.
Explain
c.
Compare
between
how
specic
and
stem
cells
immunity
contrast
and
dierentiated cells. (B2.3.2)
develops.
fundamental
and
(C3.2.8)
realized
niche.
(D4.2.12)
y
P
reasons
shark
r
3.
between
of
e
zooplankton
Organisms
TOK
What counts as a good justic ation for
s
s
aclaim?
need
even
observation
to empirical evidence. In other words, they are justied by
example,
an
observations. Repeated observations lead to hypotheses
of
showing
that can be tested by experimentation. A hypothesis is a
then
form of generalization. What makes a good generalization?
In
other
One requirement of good generalization is the number of
of
an
times the phenomenon is observed under similar conditions.
inclusion
The reliability of quantitative data is increased by repeating
quantitative
the
10.0
500
4.5
1,000
M argin of error is reduced
by increased
sample size
and
whose
of
through
stomata
microhabitats
vary
the
within
vary?
stomata
of
likely
leaves. Does
the
samples.
this
that
theory
are
it
come
from
water
plants,
of
comes
stomata.
the
that
is
a
there
is
is
a
In
lead
to
be
in
to
the
be
sample.
biased
unworthy of
remedied
by
outliers.
surprising.
It
is
having a
possible,
observed on either side of a
this
a
in
as
found
c ase,
the
the
it
is
not
reasonable
to
technique
used to
“coherence
have
theory.
predictive
test”.
power
Sometimes,
supplements
justifying
it
us
species without stomata. It
aw
of
it
be
very
are
known
are
c an
c an
is
few stomata. They might
including
deem
new
reasonable
to
too
rejecting
establishment
when
of
o
number
occurs
d
the
exchange
of
that
that
to
for
stomata
Generalizations
(plants
Gas
number
no
This
lead
we
This
generalization
stomata.
n
Table 1
3.2
U
▴
more
detect
that
set.
p
100
a
so
o
14.1
in
or
without
expectations
data
that
C
50
is
our
v
31.6
22.4
i
n
10
20
a
conclude
For
n
to
bec ause
problems.
l
error/ %
mind
O
of
open
associated
y
M argin
many
t
i
s
r
e
leaf
size/N
too
outlier
standard
unlikely,
an
has
y
the
Sometimes
S ample
an
observation
number of respondents in a survey reduces the margin of error
.
but
as
words,
measurements. For example, Table 1 shows that increasing the
have
observer might consider that a particular eld
it
in
to
y
is
reject
of
P
view
act
e
Experimenters
them. In biology, knowledge claims are justied by reference
r
Knowledge claims require justication for others to accept
knowledge
to
c an
reason
observation
claims.
Plants that
extreme habitats, such as desert plants and
are
In
expected
what
live
in
ways
to
do
medium
theory
of
evolution
explanations
of
the
have unique distributions
they
water
by
dier
from
mesophytes
environments)?
natural
selection
Knowledge
leads to
members of a population
i
for
gas
unique
adaptations
found
in
dierent
exchange.
t
a
r
o
plants
Repeated counts of the number of stomata visible in the eld
of view at high power illustrate the variability of biological
material and the need to replicate trials from the same plant.
u
f
x
Good generalizations apply in a variety of circumstances. In
the case of this experiment, it would be important to observe
O
l
many dierent individual plants under the same conditions as
well as making replicate observations from each individual.
a
v
E
▴
Figure 2
M arram
xerophyte (a plant
grass (Ammophila arenaria) is a
adapted
to dry conditions). It has
unique adaptations such as rolled
▴
Figure 1
of a tulip
Light
micrograph of the epidermis (the upper cell layer)
isolated
leaves with stomata
within folds of the rolledleaves
leaf
305
Form and function
End of chapter questions
1.
European
robins (Erithacus rubecula)
2.
migrate south in
The
graph
a
their
tidal
direction
they
upper
beak.
of
flight
detect
The
of
when
birds
the
to
birds
green
investigated.
circles
while
the
the
light,
the
red light and
figure, triangles
mean
arrows
migrate.
direction
indic ate
the
70
flown
overall
60
2.0
50
direction
own
[1]
30
Journal
of
Experimental
Biology, 211 (20),
b.
Distinguish
between
on
the
f
x
the
reason,
at
the
eect
in
the
European
night.
deactivate
this
E
inredlight.
Distinguish
c.
Distinguish
d.
State
the
Dupler,
e.
C alculate
T
.
The
threshold
process
effects
and
of
between
–1
tidal volume
of
respiratory
pulmonary
muscle
function.
training
JEPonline 2002
ventilation.
[3]
ventilation
and
respiration
the
external and internal
processes.
intercostal
tidal
[2]
between
muscles
in
role
of
the
apparatus
ventilation.
used
to
[2]
measure the
volume.
[1]
the
total
volume
of
air
inhaled in 1 minute
red light on the
during
the
highest
velocity
of
the
treadmill in this
[1]
test,
giving
the
units.
[2]
deduce, with a
robins
f.
Compare
and
contrast
the
eect
of
increasing
migrate during the
treadmill
the
the
would
volume
beaks
of
some
speed
in
this
on
the
ventilation
rate and tidal
runner.
[2]
robins
3.
The
body
mass
index
(BMI)
is
defined as the body
magnetoreceptors.
mass
divided
by
the
square of the body height, and
aect their orientation
−2
is
expressed
in
units
of
k gm
(resulting
from
mass in
[1]
kilograms
followed
for
and
and
divided
metres). A long-term study
apparently
disease
adulthood.
are
in
40,000
heart
adolescence
BMIs
height
nearly
coronary
through
306
18
km h
[2]
a
to
of
diagram,
anesthetized
Predicthow
experiments,
l
Scientists
inorder
data
or
Outline
b.
as
15
speed /
[2]
robins.
v
O
e.
of
whether
daytime
these
robins in spring
u
Using
of
the
a.
1.2
possible conclusion that could be
regarding
behaviour
d.
results
of
t
a
suggestone
drawn
behaviour
red light and
i
Based
the
(fall).
r
o
c.
on
autumn
of
and
theventilatory
29-35
o
and
eect
d
greenlight
the
p
The
W.
o
al,
max,
C
et
Amonette,
2
12
ventilation rate
n
Wiltschko
v
i
n
R
3344-3350 2008
VO
5(2):
U
Source:
on
9
treadmill
e
1.4
1.0
y
r
e
20
Source:
1.6
ladit
robins.
1.8
emulov
northerly
/
strongest
n
the
40
O
resultin
2.2
t
i
s
season and light conditions which
noitalitnev
the
2.6
2.4
y
direction of flight.
2.8
md
birds
indic ate
In
normally
Identify
bythe
moved in and out
80
etar
a.
being
3
individual
the
was
of
air
breath.
y
by
mean
edge
c aptive
of
volume of
treadmill. The
htaerb
the
a
volume
tidal
a
l
on
in
the
each
on
studied in spring and autumn, which
year
of
birds
is
in
and
P
darkness
the
lungs
rate
exercise
1–
response
total
of
volume
the
nim shtaerb /
The
times
of
ventilation
during
r
are
loc al magnetic field,
1–
was
the
magnetoreceptors in the
orientation
environment
the
using
through
the
runner
e
which
shows
well-trained
s
s
the autumn (fall) and north in the spring. They orient
The
(CHD)
results
adulthood
into
five
healthy
show
affect
groups
young men
from adolescence
how
the
risk
the
of
BMI at
CHD. The
(quintiles), Q1 being
Organisms
the
lowest
BMI and Q5 the
highest. A
or
less
is
ii
Explain
iii
C alculate
Determine
the
of
long
rises
each
in
saturation.
rising
Estimate
the
saturation
minimum
takes.
[2]
oxygen
saturation that the
person with height
1.85 mand
s
s
patient
of
experienced during the night, and when it
mass
occurred.
of
100 kg.
the
Deduce
the
a
the
adolescence
5.
is
In
one
research
trained
more
trace
to
take
off,
fly
35metres
and
land
on
a
perch.
[2]
below.
contracting
a
downward
take
apnea.
One
possible
c ause
is
the
blockage of
fast
sleep
palate
during
sleep.
This
is
c alled
apnea. It has some potentially harmful
including
an
increased risk of accidents
p
consequences,
soft
TB
the
shows
due
the
during
severe
obstructive
percentage
a
night
sleep
of
sleep
oxygen
and
tiredness.
saturation of
sleep in a patient with
apnea.
a.
U
b.
n
o
e.
c auses
in
phases
from
how
TB
the
Another
is
meant
by
the
the
number
whole
of
downstrokes
ight.
of
the
the
data
muscle
muscle,
to
ight.
[1]
is
the
the
in
[3]
the
electromyograph
used.
the
produced
for
pattern
the
35-m
[1]
supracoracoideus, is
SB
muscle. State the
by
a
contraction of
supracoracoideus.
Predict
the
falls
what
[3]
deduce
during
Deduce
the
to
example,
Compare the activity of the SB muscle during the
trace
due
an
muscles.
data,
movement
f.
pattern
of
wing
antagonistic
g.
typic al
(%).
i
t
a
the
saturation
d.
a
Explain
a
the
of
the
400 ms
using
Using
three
u
l
v
i
shows
E
apnea.
d
r
o
f
x
O
8
sleep
Outline,
antagonistic
c.
Hour
C
blood
disrupted
i
n
arterial
to
landing
o
figure
daytime
v
during
flight
y
the
traces
Contraction of the SB muscle
off
r
e
obstructive
by
The
electric al activity
movement of the wing.
SB
airways
show
O
Tirosh et al NEJM 2011 364, 1315
ventilation of the lungs stops. This is
thoracobrachialis (TB),
spikes
muscles.
t
i
s
Source:
the
The
increases therisk
[1]
the
electromyography.
n
that
shown
c auses
c alled
and
y
BMI,
CHD.
Sometimes
(SB)
using
l
monitored
factor, other
y
adulthood.
one
were
P
in
in
a.
[2]
sternobrachialis
of
The
taken.
BMI
State
than
the
was
pigeons (Columba livia)
During the flight, the activity of two muscles, the
are
4.
the
project,
dangerous than ahigh
was
c.
when
hypothesis
highBMI in
r
that
patterns of the patient during
graph,
thenight
discuss
sleep
e
Using
[2]
[1]
c.
b.
[2]
cycle of falling
BMI of
b.
a
c auses
how
desirable.
and
a.
the
risk factor of 2
of
[1]
the
electromyograph
supracoracoideus muscle during
ight.
role
[2]
Explain
the
muscle
contraction.
of
ATP
in
vertebrate skeletal
obstructive
[4]
oxygen
[2]
307
B
Fo r m
structure
refers
to
relationships,
an
to
average
annual
The
rate
in
of
relatively
structure
is
of
higher
forest,
the
levels
of
much
in
the
levels
a
taiga
is
In
than
from
the
tropic al
and
of
rainfall
levels
and
to
oen
lead
sparse
desert.
is
a
the
the
contribute
moderate
inuenced
forest
precipitation
higher
nutrients
than
also
ecosystem
of
Taiga
temperatures.
litter
ow
of
rainfall.
high
n
U
nutrients
a
development
and
by
of
and
interact
relationships
High
grassland
C
i
n
characterized
a
present
Organisms
factors
p
community
temperature
the
of
o
by
leads
v
The
development
are
consist
community
y
development
Abiotic
ecosystem.
r
e
in
to
rainfall
the
of
that
them.
Ecosystems
biotic
O
form
form.
The
mutualistic
relationships.
result
the
organisms
between
t
i
s
overall
its
n
feeding
is
components.
the
interactions
competitive
the
ecosystem
l
in
of
an
y
web
of
abiotic
y
and
e
structure
biotic
P
of
Ecosystems
r
The
function
s
s
4
and
taiga,
in
biome
and
the
tropic al
biomass
cold
storage
to
ecosystem.
of
rainforests.
the
litter
is
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
B4.1
Adaptation
to
environment
The
thick
coat
tissue
in
the
desert
that
stem
make
an
related
suited
to
adaptations
the
infrequent
rainfall
characteristics such as these
its
adaptations
is
to
low
storage
of
habitat
come
to
are
organisms
reason
that
we
c alled
exist?
to
What
are
extreme
avoid implying
Musk ox (Ovibos moschatus) during the autumn,
Norway
O
Dovreell National Park,
n
adaptation?
y
do
What
an
is
the
water
l
Figure 1
c actus
biology,
with
The
t
i
s
▸
to
a
In
correlated
habitats.
y
purpose
of
is
P
examples
ox
northerly
individual
How
environments?
a
musk
of
habitats.
adaptations.
other
a
its
r
in
of
of
e
temperatures
s
s
How are the adaptations and habitats of species related?
r
e
What c auses the similarities between ecosystems within a terrestrial biome?
in
line
proximity.
have
between
species
similar
Islands
to
the
environments
east and west
but
very
dierent
species of plant and animal. Islands to the west of the
have
Asian
Australasian
this
phenomenon?
separation,
same
this
terrestrial
needed
thrive.
in
same
that
to
place
B4.1.3
Abiotic
B4.1.4
R ange
B4.1.5
Conditions
B4.1.6
Abiotic
factors
B4.1.7
Biomes
as
E
Adaptations
of
despite
▴
geographic
Figure 2
island
The Wallace line runs between Borneo and
the K-shaped
of Sulawesi
forms of plant and animal tend to
ecosystems.
this
a
the
any particular type of
world,
similar
leads
B4.1.2
in
What is the
convergence?
SL
which
organisms
variables
of
mechanism that
for plants and animals to
the
v
O
as
the
u
the
therefore
Habitat
is
l
f
x
occurs
evolve
mechanism
What
Wherever
separation,
and
geographic
environment poses challenges and
are
environment
despite
t
a
and
have
forms of plant and animal tend
convergence?
adaptations
east
explanation
i
Every
the
any particular type of
world,
r
o
to
B4.1.1
the
independently.
leads
survive
Wherever
in
to
possible
o
evolve
the
a
d
to
occurs
islands
is
n
environment
and
What
U
for
species
species.
C
line
o
line
division
i
n
the
a
environments despite their
v
geographic al
of
marks
similar
y
Wallace
present
p
The
aecting
to
a
community,
the
abiotic
species,
and
HL
population
or
organism
lives
environment of their habitat
species distribution
tolerance of a limiting factor
required
as
for
the
groups
of
coral
reef
formation
determinants
of
terrestrial biome distribution
ecosystems
with
hot
and
similar
communities
due
to
similar
abiotic
conditions
and
convergent
evolution
B4.1.8
Adaptations
to
life
in
deserts
tropic al
rainforest
309
Form and function
B4.1.1
Habitat as the place in which
a community, species, population or
organismlives
where
in
the
means
an
world.
As
an
other
and
where
means
the
type
is
in
little
on
competition
that
from
it
means the place
loc ation — where
inhabited:
the
the
is
at
are
very high altitude in the
snow-covered
other
c an apply
plants.
These
through the
sites
have a
grows on acidic soils that
O
t
i
s
y
p
r
e
o
C
n
o
i
Glacier crowfoot (R. glacialis) growing at
u
B4.1.2
l
a
E
v
O
f
x
t
a
Figure 3
over 2,400m
altitude on a northeast
facing slope of limestone rock on the M assif des Diablerets in the Alps
Adaptations of organisms to the
abiotic environment of their habitat
The
environment
other
living
Living
communities
example,
This
is
are
factors.
more
an
of
to
as
factors
or
seen
in
in
swamps.
everything
biotic
All
plants
factors
in
example,
habitats
organisms
that
live
that
materials
dominate
extreme
taiga.
is
non-living
organisms — for
inuence
clearly
organism
and
referred
Biotic
desert
mangrove
of
organisms
things
abiotic
have
310
It
community.
R. glacialis
drained.
v
i
n
U
d
r
o
▴
physic al
ecosystem.
n
well
or
glacialis
sites
season with intense sunlight.
also
place
within
species
Ranunculus
Europe,
of
where
population,
biology,
y
but
there
and
In
geographic al
l
growing
moist
mountains
L atin.
the
ecosystem
whole
in
be
in
is
such
and
around it. This includes
as
ecosystems
in
tropic al
where
are
water
as
c alled
Abiotic
abiotic
such
rock.
are dense
densities
their
habitats
are
there
rainforests.
to
and
things
where
population
adapted
extreme
air,
non-living
are
factors
low — for
environment.
sand dunes and
y
winter
are
a
it
lives”
could
example, the habitat of
and
short
or
of
“she
This
usually,
type
organism
or
P
Alps
More
the
lives.
r
one
lives”
e
conditions,
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organism
s
s
Habitat
Ecosystems
Adaptations of grasses to sand dunes
S and
and
dunes
at
the
are
top
conservation
retains
(which
high
salt
and
little
helps
to
water
store
adaptations
types
aer
water
are
of
of
high
required
wind-blown
plants
on
initially
sand
water
die
growth.
for
dunes
Also,
hinders
would
for
from
concentrations
and
soils).
which
form
salt
rainfall
in
plant
that
challenges
of
on
by
are
the
dunes
little
dunes
water
sand
dominant
organic
matter
c an contain
osmosis.
on
are
sand accumulation.
contain
dehydration
Grasses
and
beach
uptake
sand in deserts
beach
For these
dunes,
plant
so
on
special
beach
▴
in
many
parts
of
the
world.
Lyme
grass (Leymus mollis)
occurs
where
Figure 4
Dunes,
accumulating
the
seaward
edge
of
dunes
in
North
cuticle
on
leaves
indentations
to
reduce
(furrows)
transpiration
where
humid
air
c an
remain
even in windy
that
reducing
•
rhizomes
sclerenchyma
extend
to
into
of
stems)
dune
to
that
and
during
grow
upwards
as
sand accumulates and
water
known
thus
droughts
as
fructans
water
in
root
uptake.
and
leaf cells to
i
n
Adaptations of trees to mangrove swamps
C
o
potential
wilting
obtain
c arbohydrates
osmotic
creating a humid chamber and
p
accumulation
the
droughts,
exposed to wind
prevent
(underground
deep
increase
during
area
v
•
up
y
tough
roll
surface
r
e
•
c an
the
O
leaves
t
i
s
conditions
n
in
y
waxy
l
stomata
C alifornia
y
thick
•
Bay,
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grass has these adaptations:
•
•
Humboldt
P
Lyme
at
Lyme grass on the M a-le’l
sand is
r
dunes
e
most
sand
The
tolerance
concentrations
reasons,
of
beaches.
s
s
S and
mounds
of
Mangrove swamps develop on the coast in the tropics and subtropics where
there are sheltered conditions and mud accumulates. These swamps are ooded
U
with seawater at high tide. The dominant species are trees. The environmental
n
challenges are waterlogged anaerobic soils and high salt concentrations. The salt
concentration of the mud can be twice as high as that of seawater. This is due to the
o
M angrove
trees
have
would
secretion
•
root
of
epidermis
up
into
•
large
trunk
of
as
root
very
and
to
the
out
are
and
in
a
the
that
(cork)
them
▴
to
Figure 5
Part
of a lyme grass leaf
thrive in a
showing tough sclerenchyma (pink) and
in
the
furrows (visible on the le side in this
which
micrograph) with stomata at their base
leaf
reduces
excessive absorption
soil
vertic al
c an
allow
surface
root
absorb
downward
where
there
branches
oxygen
arch
for usein
from the
tree in the soft mud
c an
be
c arried
by
the
ocean to
shores
of
mineral
mannitol,
saline
air
buttress
seeds
muddy
accumulation
such
grow
to
buoyant
distant
•
that
E
roots
which
v
roots
central
prevents
that
species:
glands
suberin
close
the
most
u
growing
pneumatophores,
stilt
and
oxygen
thatgrow
•
salt
in
salt
a
O
•
roots
most
to
from
adaptations
for
l
is
salt
coated
f
x
c able
following
intolerable
excess
permeability
•
the
t
a
•
be
i
that
r
o
habitat
d
daily ooding with seawater and evaporation concentrating the salt in themud.
leaf
which
cells,
ions
and
c arbon compounds
increases the osmotic potential
allowing
water
absorption
from the
▴
Figure 6
The mud
in mangrove swamps is decient
M angrove trees have evolved
vertic al roots c alled
in oxygen.
pneumatophores
which they use to obtain oxygen from the air
environment.
311
Form and function
B4.1.3
Abiotic variables aecting species
distribution
The
distribution
map.
factors.
The
a
range
grow
chemic als
the
have
in
these
factors.
This
northern
their
cells
adaptations
of
for
excessively,
and
their
method
of
hightemperatures.
distributions
large
aected
of
in
hot
heat
loss
to
in
For
by
minimize
Arctic
whereas
habitats.
example,
some
water
loss.
for
spawning.
The
and
u
some
more
of
to
the
factors.
survive
frosts
and
prevent
frost
the
tropics.
would
factors
such
They
would
transpire
be
very inecient at
as
water
availability
special adaptations. The
many
ranges
l
a
R anges
and
of
between
species
plant
full
of
for
by
required
substrates
5.5
abiotic
small
adaptations
by
aquatic
requirements
freshwater
between
each
relatively
have
ears,
for
life
have longer loops of Henle in their
limited
gravel
of
have
species
sunlight
tolerance
tolerance
of
pH
rats
have
animals
streams
with
and
factor,
no
particle
8.0.
animals
are
for one stage in the
more
size
than
3 m
between
deep
10 mm
As with plants, animals
based on their adaptations.
and
for
ranges
will
of
only
others
tolerance
grow
only
variables
in
grow
such
as
for
soils
in
salt
abiotic
within
shade.
a
variables.
specic
Animal
For
pH
range;
species also
concentration in aquatic
temperature.
the
Taiwan
water
is
bears
adaptations
owing
have
polar
R ange of tolerance of a limiting factor
animal
require
habitats
must
tolerance
i
t
a
B4.1.4
a
fast
o
of
distribution
require
They
and
range
example,
v
312
100 mm
a
animal
S almon
n
U
cycle.
in
or
c an
be
distribution
the
of
mosquito,
investigated
a
species
experimentally,
and
abiotic
Aedes aegypti found
or
variables.
it
by
nding
For
correlations
example, a study
requires a minimum night-time
temperature of13.8°C.
Ecologists surveying on a
extending from
woodland
Tasmania
d
r
o
burned
E
Figure 8
transect
f
x
O
▴
c ases,
life
have
species
means that a plant
antifreeze
require
Some
desert
verydierent.
Plant
abiotic
temperature
C
i
n
kidneys
have
in
intensity,
plant
However, the northern plant
o
conditions.
climates,
v
arid
and
growth
physic al
from these northern
p
heat
minimizing
In
like
crystals.
light
Every
adapted
Plants
some
earsof elephants with their dense networks of surface blood help to
dissipate
in
are
Extremes
act
one
not
in
y
temperature.
that
r
e
and
regions.
ice
for
are
photosynthesis
of the range in red
Animal
range
shown on
O
the centre of gravity
its
be
especially abiotic
availability,
nutrients.
tropics
c an
living
mineral
the
formation
for
of
outside
from
in
of
them
water
it
n
not
are
survive
c ausedby
do
that
species
temperature,
availability
each
suit
so
species,
at
unburned to
Backhouse Tarn,
Correlations
be
between
investigated
example
using
by
the
distribution
mapping
quadrats,
or
the
by
of
entire
a
species
species
sampling
along
and
range,
an
by
abiotic
random
transect lines.
variable
c an
sampling
for
y
have
not
for
animals
world,
aect
l
species
areas
plant
would
damage
The species range
in
example,
they
tolerance
by
the
P
is shown in green and
of
the
and
in
that
r
has
and
lives
e
aected
salinity,
it
factors
t
i
s
glacialis in Sc andinavia.
Ranunculus
plants
are
soil
the
y
Distribution of
of
distributions
regions
Figure 7
where
others.
c annot
▴
is
reect
not
pH,
so
species
maps
but
soil
For
a
adaptations
environments
Plant
of
Distribution
s
s
a
Ecosystems
Transects
Transects
of
c an
species
to
be
should
interest.
For
peat
distribution
of
investigate
dierent
a
bog
line
the
levels
of
used
the
down
reveal
species
tolerance
transect
taken
might
plant
A
a
Belt
in
variables of
slope
from
correlations
and
•
ranges
for this
and
soil
pH.
These
and
measured
often
0.5
assessed
using
quadrats
using
There
are
electronic
several
abiotic
Observational
defined
Line
two
are
defined
observer
pace
and
sensors and portable
of
target
species.
This
and
all
investigate
ranges
of
tolerance
changes
in
organisms that
and
population
recorded.
of
interest
that
are
in
records
now
the
available
ecologic al
level
for
a
parameter.
many
of
parameters
research. A log is a
•
c an
take
•
c an
be
repeated
left
to
take
measurements
measurements
long periods
electronic
an
have
been
or
the
pH
taken
storage
of
an
data.
such
internal
These
as
expensive
to
loggers
than
many
be
data
analysis
measuring
and
Bec ause
portable
hundreds
of
used,
of
both
such as:
their
for
c an
or
be
transferred
long-term
for
time.
very
rapidly
automatic ally
over
easily to a computer
storage.
advantages,
ecologic al
used
data
loggers
are widely
research and other purposes
many
•
and
with
easy to
•
medic al
C are
diagnostics — in
Units
to
remote
industries
such
example,
monitoring
as
all
areas
food
and
of
settings
far
from
Intensive
from hospitals
drink
production — for
fermentation in wineries
battery
i
for
parameters
designs
over
be
used
•
flight
recorders
on
aircraft.
different
u
l
f
x
t
a
available
compact
r
o
•
for
record and
have
o
to
power
older
d
designed
stored
temperature, light
memory
data
operate
•
•
n
less
regular
measurements
designed with a sensor to monitor
advantages:
•
at
Compact, portable data
condition
and
digital
digital
U
store
is
sensors.
environmental
intensity
measurements
C
loggers
of
logging
i
n
from
record
D ata
o
intervals.
v
permanent
y
are
device
p
that
a
sensors
c an
also
O
t
i
s
is
r
e
sensor
Electronic
is
size
Observations: Making observations with sensors
A
walks along
records
method
dierent methods of
poles
intervals
n
line
regular
fixed
c an be
l
the
a
sampling — a tape is laid along the
between
at
y
touch
at
transect.
intercept
ground
estimated
a
Abundance
placed
transects — the
route
monitoring
•
m.
is
by
y
a
1.0
species
P
using
or
of
separated
variables
to
sampling
m
lines
temperature, light
other
sightings
loggers.
two
r
be
data
abundance
between
distance,
a
c an
area
alongthe belt.
between
•
intensity
transects — the
the
e
the
span
example,
to
to
variables.
s
s
purpose
woodland
used
abiotic
kite
diagram
common
Lifeboat
in
intertidal
Station
on
a
The
Figure
v
O
Data-based questions: Intertidal zonation
9
illustrates the distribution of
of
the
shaded
species
300 m south of Bembridge
was
the
of
(ACFORis
Isle
Wight,
UK.
The
thickness
region
abundant,
a
indic ates
common,
sc ale
of
whether
frequent,
the
organism
occ asional
or
rare
abundance).
E
313
Form and function
large shallow rock pool
shingle
height above
edge of ledge
sand
chart
datum / m
4
s
s
1
Enteromorpha sp.
Fucus spiralis
Arenicola marina
Fucus serratus
Littorina mariae
r
Anemonia viridis
Littorina littorea
e
Sargassum muticum
Patella vulgata
S.balanoides
l
Laminaria digitata
shore distance
abundance scale
=
ACFOR
Examine
State
the
Using
large
5.
[3]
species that is most abundant in the
area.
the
sc ale
bar, determine the length of the
rock
pool.
species
shingle
of
them
being
b.
Using
adapted to:
sand
c.
rock
species
that
near
the
Suggest
7
.
pools.
[3]
Suggest
in
are
one
research
[3]
the
kite
adapted
diagram,
to
the
predict two
same abiotic
way
[2]
in
could
which
have
the
been
objectivity of
improved.
about
algae. The pH of the
24-hour
concentration
pH 7
values
a
of
the
are
during
day.
maxima
andminima?
cycle, due to changes
in
the
water.
The
lowest
found during the night and
about
sunlight
have
seashores that contain
a
dioxide
in
Ecologists
pH 10
What
are
when
the
there is bright
reasons
for these
▴
Figure 10
for
from the upper parts of the
o
i
loggers.
on
lower
reasons
t
a
falls
E
314
data
pools
photosynthesizing
and
highest
using
rock
v
the
of
in
l
c arbon
values
pH
and
rises
O
in
absent
data
found
zone.
u
monitored
water
only
natural pools or in articial aquatic mesocosms
monitored
animals
are
intertidal
environment.
d
r
o
in
f
x
pH
be
the
[2]
pH changes in rock pools
c an
the
intertidalzone.
6.
the
The
species
edge
n
one
Several
[1]
shallow
Deduce
a.
explain the methods
U
4.
and
data.
C
3.
diagram
the
i
n
survey
kite
collect
spring tide high water mark (the highest
o
to
water)
v
2.
the
used
by salt
p
1.
Species abundance as a function of distance from
normally reached
5 m
y
Figure 9
point
r
e
▴
O
t
i
s
Nucella lapillus
n
y
Gibbula cineraria
Laurencia pinnatifida
Rock pool at
Limerick Point,
Ireland
[1]
y
P
Chondrus crispus
Ecosystems
Data-based questions: D ata-logging pH in an aquarium
Figure
11
shows the pH and light intensity in an aquarium
containing
a
varied
newts
and
other
of
1.
Explain the changes in light intensity during
2.
Determine
3.
a.
Deduce
b.
Explain
a.
Deduce
b.
Explain
organisms including
animals.
The
data
the
experiment.
[2]
s
s
pondweeds,
community
was
how
many
days the data
obtained by data logging using a pH electrode and a light
logging
meter.
The
bya
cycle
of
was
light
illuminated
and
dark
using
articially
a
lamp
to
covers.
[2]
give a
the
trend
in
pH
in
controlled
this
trend.
the
trend
in
pH
in
trend.
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biodiverse
marine
suitable
hard
of
Hard
reef.
corals
These
pH — above
•
S alinity — between
50m
to
depth
allow
32
problems.
conditions
of
and
42
parts
They
only
develop
form
the
zooxanthellae,
which
where
rocky
need
structure
light
for
required.
water,
deposition
c an
skeletons
of
so
enough
c alcium
per
light
penetrates.
c arbonate in the skeleton.
thousand
of
dissolved
ions
to
avoid
a
O
•
the
mutualistic
l
osmotic
•
than
7.8
are
whose
u
Depth — less
•
f
x
•
contain
ecosystems.
corals,
t
a
photosynthesis.
r
o
the
for
i
are
are
o
d
reefs
conditions
C
formation
coral reef
n
Conditions required for
o
intensity in an aquarium
U
B4.1.5
Changes in pH and light
i
n
Figure 11
v
day / hours: minutes
p
0/14:02
y
0
7.25
r
e
10
t h i 
20
n
30
7.30
O
40
y
50
7.35
t
i
s
60
yrartira / ytisnetni
70
7.40
l
80
stinu
90
y
100
pH
7.45
[1]
[2]
P
iht intensity
7.50
[1]
[2]
darkness.
(pH)
this
r
4.
Coral
light.
timer.
pH sensor
▴
the
e
24-hour
aquarium
Clarity — turbidity would prevent penetration of light so the water must beclear
.
T
emperature — 23–29°C so both the coral and its zooxanthellae remain healthy.
v
E
315
Form and function
s
s
e
r
l
n
o
i
t
a
the reef and
provide a habitat
for many other species.
The blue-green sh on this Pacic reef are
n
C
o
v
i
n
U
u
corals build
a
316
l
Hard
v
E
Figure 13
Chromis viridis
d
r
o
f
x
O
▴
O
35° south of the Equator
y
between 35° north and
p
Coral reefs c an develop
y
P
y
t
i
s
Figure 12
r
e
▴
Ecosystems
B4.1.6
Abiotic factors as the determinants
ofterrestrial biome distribution
With
any
combination
develop.
the
The
geographic al
similar.
loc ation,
ecosystems
abiotic
E arth:
factors
on
a
but
the
one
the
particular
adaptations
specic
type
are
type
ecosystem
a
of
the
will
of
ecosystem is likely
vary depending on
species
are likely to be
biome.
and
these
one
rainfall.
factors
axis
The
c an
and
most
be
mean
likely
shown
annual
ecosystem
using
a
given
graph,
temperature
with
on
the
any particular
r
precipitation
of
of
mean annual
other.
l
rainforest
tropical
200
temperate
taiga
o
o
d
la
w
0
10
0
la
b
d
n
hot
la
ss
gra
te
ra
pe
savanna
/
d
nd
desert
n
m
te
U
tundra
u
r
h
s
n
C
i
n
100
forest
o
seasonal forest
v
seasonal
y
rainforest
p
r
e
temperate
O
t
i
s
mc / noitatipicerp launna
tropical
300
n
y
400
y
P
of
factors,
are the principal determinants of biome distribution on
temperature
combination
abiotic
composition
e
Two
All
of
species
s
s
to
sert
de
cold
20
10
30
o
d
average annual temperature / °C
Relationship
between temperature,
Biomes as groups of ecosystems with
u
similar
Gymnocalycium baldianum
rainfall and biomes
t
a
f
x
B4.1.7
i
Figure 14
r
o
▴
10 mm
communities due to similar abiotic
l
O
Euphorbia obesa
are
may
widely
be
abiotic
the
solutions.
similar
when
For
and
that
world.
and
This
is
related
resemble
The
animals
an
other,
even though they
swollen stem
evolving similar adaptations in
example
species
each
resemblance is due to the similar
that
of
convergent
face
the
same
evolution.
By
problems nd the
5 mm
example,
storage.
produce
the
plants
distantly
adaptations,
they
in
conditions.
selection,
conservation
ecosystems
with
E
same
to
of
separated
conditions,
response
natural
groups
v
Biomes
a
conditions and convergent evolution
plants
C acti
in
in
deserts
Americ a
develop
and
despite
not
being
closely
owers
that
these
desert
adaptations
euphorbias
related.
plants
In
c an
in
some
be
for
Afric a
water
have
very
c ases, it is only
distinguished.
▴
Figure 15
Gymnocalycium baldianum
(a c actus) and Euphorbia obesa
(a euphorbia),
both viewed
from
above
317
Form and function
Temperature
Tropic al
Temperate
Taiga
forest
forest
forest)
(boreal
high
medium
low
Hot
desert
high
Tundra
high/medium
very
low
high
high/medium
high/medium
very
medium
medium/low
high
medium
medium/low
high
high/medium
low
Seasonal
minimal
warm
short summers;
minimal
variation with a
very short
variation
rainforests
long, cold
variation
dry
summer;
summers
winters
winters
E ach of the major biomes is characterized
season
by particular climatic conditions
o
C
montane
n
bamboo
i
o
lower
ecosystems are visible.
bamboo forest
(light
brown),
green),
The summit
is snow
heathland/chaparral
lower montane forest
colours) outside the boundary of the protected
area
n
O
y
p
heathland / chapparal
upper
t
a
dierent
y
l
y
t
i
s
r
e
v
i
n
U
Kenya,
(dark green),
a
E
318
l
(mixed
v
O
land
afro-alpine
(dark
forest
forest
montane
farmed land
the ecosystems are afro-alpine (light
upper montane forest
green) with farmed
u
In this satellite image of Mount
Descending eastwards,
(grey-green),
d
r
o
Figure 16
covered.
f
x
▴
very
cold winter
r
Table 1
cold
P
▴
season or
e
colder
s
s
Precipitation
Light intensity
in
low
Grassland
forest
Ecosystems
B4.1.8
Adaptations to life in hot deserts and
tropic al rainforest
Hot
deserts
without
matter
are
nights.
any
of
characterized
R ainfall
totals
precipitation.
soil
organisms.
by
per
Soil
The
very
year
high
are
daytime
very
development
saguaro
and
low
is
temperatures and much
and
very
fennec
there
limited,
fox
are
c an be long periods
with
little
examples
s
s
colder
organic
of
organisms
The
saguaro
is
a
species
that
root
system
to
is
adapted
to
life in hot deserts. It has the
•
pleated
•
vertic al
tap
stems
roots
with
that
collect
storage
stems
that
allow
orientation
of
water
tissue
to
from
shrinkage
stems
to
up
conserve
in
to
1 m
to
30m
from the stem
down in the subsoil
water
after
infrequent
droughts
and
swelling
reduce
interception
of
desert
after
sunlight
at
rains
rains
midday and
▴
maximize
it
at
cooler
times
ofday
Figure 17
n
fat
up
l
deep
•
water
O
•
collect
P
wide-spreading
y
a
t
i
s
•
y
c actus
r
of
following adaptations:
e
adapted to these conditions.
S aguaro (Carnegiea
gigantea) in hot desert in Arizona
leaves
thick
waxy
prevent
CAM
day,
fennec
fox
is
reduce
it
•
long
builds
hot
slow-growing
species
of
transpiration.
mammal
that
it
adapted
underground
to
covering
hot
den
provide
temperatures
where
heat
it
c an
insulation
stay
both
life in hot deserts. It has
during
cool
daylight
during
large
•
a
pale-coloured
ears
to
are
heat
rate
feet
and
that
help
c an
heat
The
provide
yellow
keep
be
loss
characterized
intensity.
to
day
▴
Figure 18
insulation
when
Farafra oasis,
Fennec fox (Vulpes zerda) at
Egypt
walking on
reflects sunlight (a darker coat would absorb it)
c ause
by
by
body
temperature
increased
to
more
down
than
600
breaths per
high
precipitation
evaporation.
high
meranti
temperatures,
and
the
monkey
are
that
adapted
to
examples
a
spider
adapted to these conditions.
meranti (Shorea
rainforests.
E
grow
to
competition
trunk
of
wind
stress
hard
v
O
organisms
c an
the
u
(panting)
light
that
radiate
rainforests
high
of
l
Tropic al
that
coat
ventilation
f
x
variable
minute
pads
i
•
the
sand
the
hours
for the cold nights and
t
a
a
it
highest
r
o
•
tropic al
the
to
o
very
The
avoids
hair
transpiration and
c actus
days
hairs
and
an
thick
it
transpiration
for
allowing stomata to open at night and close during the
reducing
d
•
so
area
n
•
•
the
to
surface
U
nocturnal
•
eating
the
following adaptations:
•
of
a
epidermis
reduce
o
the
from
stem
to
C
the
metabolism
the
i
n
The
herbivores
of
on
spines,
v
heat
to
p
•
cuticle
reduced
y
a
•
r
e
•
faguetiana)
It
has
over
the
is
a
species
of
tree
is
life in
following adaptations:
100m
high,
overtopping
other
trees
and
avoiding
for light
dense
wood
to
provide
support
especially against the
▴
Figure 19
Yellow meranti (Shorea
faguetiana) near the Kinabatangan River in
Borneo
319
Form and function
•
trunk
is
buttressed
rainforest
soils
smooth
•
broad
trunk
•
evergreen
oval
to
leaves
flowers
and
none
other
in
of
rainwater
with
pointed
which
take
throughout
photosynthesis
seed
to
the
to
in
deter
large
species
feet
be
that
used
that
c an
without
grip
and
reaching
from
thumbs
hands,
mammal
for
tree
that
grasping
year
in
five, with
that
is
adapted
fruit
c an
to
tree
grasp
branches
to
life
branches and lianas and
and
allowing the arms to
at
any
flowers,
active
judged
time
of
insects
a
wide
rainforest
in
the
daytime when vision is most acute and
between
year
as
range of sounds to be made to
c anopy
o
breeding
dense
and
be
branches and act like a fifthhand
allowing
branches.
there
is
a
constant
supply
of
fruit,
nuts,
seeds,
andeggs.
n
U
C
c an
onto
larynx
the
night
distances
buds,
extra
v
Spider monkey (Ateles
at
in
i
n
Figure 20
georoyi) in Belize
like
developed
sleeping
of
one
seeds.
y
tail
species
the
feeding or other purposes
communic ate
▴
hands
act
eat
temperatures as high as 35°C
about
p
highly
c an
for
a
tolerate
that
swinging
r
e
long
•
•
climbing
fruit
•
•
for
allowing
for
O
•
hook-like
is
to
quantities
following adaptations:
legs
rapidly
conditions
Linking questions
are
i
a.
o
What
the
Explain
properties
the
regulating
b.
Discuss
c.
Outline
heart
a
2.
Is
light
a.
root
and
the
statement:
the
role
components
between
shoot
the
rate.
auxin
growth.
of
biologic al
and
cytokinin
systems?
as
a
means of
(C3.1.22)
“integration
results
in
emergent
properties”.
Explain
b.
Explain
for
why
a
of
feedback
control
in
the
regulation of the human
(C3.1.14)
essential
through
life?
the
food
how
energy
chain.
content
of
each
trophic
level
decreases
(C4.2.14)
photosynthesis
results
in
an
increase
in
biomass.
(C4.2.15)
c.
Outline
how
ecosystems
320
of
interactions
(C3.1.2)
u
l
E
v
O
f
x
t
a
r
o
d
1.
chemosynthesis
are
dependent
represents
on
light
as
a
an
exception to the rule that
source
of
energy. (B4.2.6)
y
large
and
shoulders
rainwater
ideal
n
•
pick
arms
of
l
flexible
the
shed
y
long
•
has
bec ause
year
adapted
produced
years
that
advantage
t
i
s
•
It
support
P
rainforests.
increased
rapidly
tips
The spider monkey (Atelesgeoroyi)
in
provide
e
enzymes
•
base
r
•
the
shed
leaves
photosynthesis
at
shallow
s
s
•
are
B4.2
Ecologic al
niches
When
Charles
predicted
same
that
21years
mouthparts
use.
They
the
are
to
aer
like
tube.
a
as
the
a
long
tubular
death
300 mm
star
300 mm
orchid’s
D arwin’s
party
On
has
equally
act
indeed
unroll
nectar
with
M adagasc ar
long
orchid
long
pollinator.
and
and
nectar
mouthparts
The
named
have
to
tube, he
must
moth
Xanthopan
be
exist in
was nally
praedicta.
coiled up when not
blower when the moth is about to insert them
what
do
you
think
D arwin
based
his
l
into
moth
a
which
prediction?
O
Figure 1
n
y
t
i
s
▴
y
in
sent
P
Its
a
ecosystem
discovered
was
r
the
D arwin
sesquipedale),
e
(Angraecum
s
s
What are the advantages of specialized modes of nutrition to living organisms?
Xanthopan praedicta
y
p
r
e
How are the adaptations of a species related to its niche in an ecosystem?
the
so
deeper
the
concentration
main
challenge
dierent
structural
at
pond?
the
water,
in
in
shallow
Which
would
as
penetrates
of
near
the
the
plants
role
of
a
species
mode
of
that
thus
would
SL
an
obligate
in
plants,
O
S aprotrophic nutrition in some fungi and bacteria
B4.2.7
Diversity
B4.2.8
Relationship
v
B4.2.9
E
Hominidae
nutrition
Adaptations
B4.2.10
B4.2.11
a
Mixotrophic
B4.2.6
in
between
of
Adaptations
Adaptations
of
Fundamental
B4.2.13
Competitive
and
and
Figure 2
Kettlehole pond
HL
anaerobes,
algae
and
facultative
several
anaerobes
groups
of
and
obligate
photosynthetic
aerobes
prokaryotes
archaea
predators
plant
centre of
protists
dentition
herbivores
of
B4.2.12
some
species
the
ecosystem
Holozoic nutrition in animals
of
in
▴
B4.2.5
in
lower the
dierent
thrive
B4.2.4
nutrition
the
margins of the pond,
in
are
nutrition
glaciers.
Drying in summer
theedges?
organisms
the
and
pond.
benecial,
of
retreating
o
the
between
by
dierent depths in the
i
Photosynthesis
at
t
a
Dierences
B4.2.3
as
at
seen
light
are
types
thrive
created
base
water
l
B4.2.2
less
the
u
niche
at
be
d
Ecologic al
the
mud
r
o
f
x
B4.2.1
c an
adaptations
edges.
Which
features
plants
n
dominate
the
landsc ape
U
is
ll
dierent
o
The
oxygen
of
C
pond.
ponds
zones
i
n
Circular
v
Kettlehole
form
and
the
diet
of
omnivorous
for
feeding
on
for
nding,
c atching
plants
for
harvesting light
and
and
of
and
plants
killing
herbivorous
for
prey
resisting
and
of
representative
members of the family
herbivory
prey
animals
for
resisting
predation
realized niches
exclusion
and
the
uniqueness
of
ecologic al niches
321
Form and function
B4.2.1
Ecologic al niche as the role
of a species in an ecosystem
One
of
a
the
central
unique
hypotheses
role,
c alled
its
of
ecology
ecologic al
is
that
niche.
every
species
Ecologic al
in
niches
an
ecosystem
have both biotic
s
s
fulls
and abiotic elements.
•
Zones
of
tolerance
•
Food
is
abiotic
specialize.
To
compete
nutrition
by
other
that
variables determine the habitat of a
ecosystem.
synthesis
organisms.
effectively,
is
their
using
To
light,
water
minimize
they
must
and
c arbon
competition,
develop
specialism.
dioxide or
species must
adaptations
for the
l
Other species are utilized to provide a diverse range of services — for example,
n
y
the supply of mineral elements by recycling, pollination of flowers or dispersal
of seeds; the support provided by the trunks and branches of trees.
niche
ecosystem,
a
of
a
Unless
species
will
species
all
the
not
is
made
up
dimensions
be
able
to
of
of
survive,
10
12
14
l
O
Two aspects of the niche of the blue-gray
a
gnatc atcher (Polioptila caerulea) are prey size and
foraging height.
according to these two variables in oak woodland,
in C alifornia.
There are many other aspects of this bird’s
E
ecologic al niche
322
The graph shows the percentage of the
v
diet
▸
Figure 4
P
. caerulea eating a gnat
or
factors — it is
are
satised in an
reproduce.
y
8
length / mm
o
6
u
f
x
4
prey
Figure 3
C
0.5
2
n
t
a
r
o
t hg i e h
1
0
▴
i
e v ob a
5
10
grow
p
r
e
2
4
many
niche
o
20
v
i
n
U
3
d
 / d n u o rg
30
very
the
O
ecologic al
multidimensional.
t
i
s
The
y
from
the
P
in
of
in
either
it
mode
•
obtained
taking
for
lives
r
by
it
e
species — where
Ecosystems
B4.2.2
Dierences between organisms
Activity: Winogradsky
that are obligate anaerobes, facultative
columns
anaerobes and obligate aerobes
To
and
organisms
the
total
plants
do
not
require
have
absence
of
oxygen
this
for
aerobic
requirement.
molecular
oxygen
cell
Some
(O
)
respiration, but some other
microorganisms
including
some
c an
only
make
mud
live in
is
species of bacteria,
a
and
Winogradsky column,
water
placed
in
measuring
a
from a pond
large
bottle or
cylinder,
with
a
2
and
protozoa.
water-logged
soil
or
Anoxic
muds,
(lack
of
intestinal
oxygen)
tracts
conditions
(guts)
of
occur
animals
and
in
swamps,
range
e
archaea
s
s
Animals
of other materials. The column
deep in lakes
is
sealed
and
placed in the light.
Concentration
r
orseas.
gradients
for
P
oxygen and other substances
organisms
c an
be
placed
in
three
c ategories
according
to
their
oxygen
develop in the column, with
requirements
(Table 1).
obligate
require
aerobes
supply
Examples
the
t
i
s
Requirements
and
due
to
archaea
so
only
live
in
oxygen
All
oxic
Micrococcus luteus
environments
oxygen
or
so
killed
only
by
live
in
Clostridium tetani
anoxic
oxic
or
archaea
available
anoxic
so
live
Escherichia coli
environments
bacterium),
(a
gut
Saccharomyces
i
n
(yeast)
Table 1
Oxygen requirements of organisms
B4.2.3
n
U
C
▴
p
in
if
o
anaerobes
oxygen
v
use
(tetanus
bacterium), methanogenic
environments
facultative
skin
y
inhibited
anaerobes
(a
bacterium)
r
e
obligate
animals and plants;
O
continuous
growing
concentrations suit
them.
a
groups
n
where
C ategory
bands
bacteria
y
of
l
coloured
y
Living
Photosynthesis as the mode of
o
d
nutrition in plants, algae and several groups
c arbon
compounds
from
on
energy
it
to
which
eukaryotic
including
algae
life
is
based.
mosses,
O
unicellular algae such as
several
groups
of
bacteria
Photosynthesis
bacteria,
therefore
E
and
v
purple bacteria.
but
not
in
are
conifers
seaweeds
for
xing
acids
three
and
that
and
c arbon
the
groups
dioxide and
many
of
other
c arbon
photosynthesizers:
flowering plants
grow
on
rocky
shores and
including
occurs
in
two
▴
Figure 5
Winogradsky column in a
glass bottle
Chlorella
a
•
used
amino
There
ferns,
including
is
sugars,
u
plants,
•
sunlight
produce
l
f
x
•
from
i
photosynthesis,
using
t
a
In
r
o
of photosynthetic prokaryotes
cyanobacteria
of
the
three
(blue–green bacteria) and
domains
of
life:
in
eukaryotes
archaea.
323
Form and function
B4.2.4
Animals
Holozoic nutrition in animals
obtain
supplies
compounds
by
compounds
come
proteins
animals
must
happens
nutrition,
c arbohydrates,
from
be
other
that
They
are
organisms.
digested
internally,
meaning
food.
before
aer
the
they
stages
in
of
and
c an
has
be
are
as
c arbon
ingested.
swallowed
the
Digestion in most
This
is
holozoic
before being fully
digested.
the
sequence
2.
digestion — breaking
3.
absorption — transport
They
absorb
the
u
including
l
of
c arbon
organisms.
of
their
own
dioxide.
a
E
v
c arries
detritus
Obligate
out
or
Some
c arbon
unicellular
that
are
F acultative
mixotrophs
In
them
way
modes
supplies
synthesize.
this
not
holozoic.
Spiders,
for
gut
anus
them
other
by
c annot
by
grow
with
c ases,
a
autotrophic
be
entirely
there
is
sucient
endocytosis,
unless
This
c arbon
be
so
compounds
or
from
heterotrophic
autotrophic,
consuming
algae.
It
does
uses
the
it
utilize
light,
is
a
not
that
have
entirely
it
c an
they
and
have
c annot
own
to
feed
food that they
themselves
chloroplasts
“klepto-chloroplasts”
degrade
also
mixotroph.
autotrophic and
the
its
but
facultative
both
bec ause
compound
that
they
they
may
protist
until
c arbon
Euglena gracilis, for example, has chloroplasts
a
photosynthesis
c an
from simple substances
their
(protists) use both methods
exclusively
when
nutrition.
obtain
eukaryotes
not
organisms
of
compounds
mixotrophs
photosynthesis
smaller
heterotrophic
obtains
are
prey and suck out the liquids
egestion
Heterotrophs
heterotrophic, or use both modes.
on
they
their
products of digestion in their gut and then
epidermis
Organisms
mixotrophic.
and
tissues
Mixotrophic nutrition in someprotists
make
nutrition.
are
body’
s
o
gut
i
t
a
r
o
O
f
x
Autotrophs
consume
324
of
B4.2.5
other
proteins and other
the
n
Holozoic nutrition
of
from the end of the gut.
so
into
membrane of
assimilation
o
Figure 6
externally
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plasma
absorption
U
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lumen
d
mouth
part
material
C
i
n
ingestion
food
synthesize
them
v
assimilatethem.
digestion
their
digestive
to
the
molecules
tissues of the body
p
produced.
digest
inject
foods
making
undigested
across
and
smaller
n
animals
example,
thus
food
blood
into
y
for
the
r
e
Some
molecules
digested
into
digested
and
egestion — voiding
food
O
5.
of
thus
assimilation — using
macromolecules
large
P
and
holozoic nutrition:
food into the gut
t
i
s
4.
cells
the
y
epidermis
of
be
obtained in
replaced.
y
ingestion — taking
l
is
1.
r
This
c arbon
polysaccharides
absorbed.
been
food
such
other
bec ause
e
pieces
acids
Molecules
food
whole
amino
heterotrophic,
s
s
and
of
consuming
Ecosystems
s
s
e
r
Figure 8
Humming birds are heterotrophic;
which they obtain nectar are autotrophic
Figure 10
Ochromonas sp. c an make their own food
photosynthesis,
nutrients and
y
p
either Protista
o
c alled
▴
n
in another kingdom,
Organisms such as
or animal kingdoms so are placed
C
into the plant
O
t
i
s
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e
t
v
Euglena — a facultative mixotroph.
i
n
Figure 9
Euglena do not
U
▴
the plants from
n
▴
molecular
l
Arabidopsis thaliana — the autotroph that
y
P
Figure 7
biologists use as a model plant
y
▴
but
c an also uptake both dissolved
through
organic
particulate organic matter, including intact cells
o
d
Data-based questions: Mixotrophy in golden algae
the
2951).
light
of
0.8
Taiwan
light
but
no
mixotrophic growth
prey
(heterotrophic) and both
The
prey
obligate
a
with
contrast
supplied to the
growth
rates
for the
atotrophic growth
0.6
heterotrophic growth
0.4
0.2
[4]
0.0
reasons,
mixotroph,
the
Key
measured in
ht w o rg
and
E
Deduce,
not
no
east
1.0
Jersey
Vibriobacteria.
Compare
or
but
were
New
Ocean
were
conditions:
(mixotrophic).
twoisolates.
2.
rates
a
were
Pacic
l
algae
light
of
v
O
and
prey
the
growth
of
d / et a r
combinations
(autotrophic),
prey
from
Their
east
1–
three
and
Ochromonas
Ocean
u
1393)
(isolate
f
x
(isolate
Atlantic
i
from
t
a
strains of the golden alga
isolated,
1.
r
o
Two
a
whether
isolate
facultative
1393 is an
–0.2
mixotroph,
mixotroph.
[3]
1393
3.
Discuss
the
nutrition
of
isolate
2951.
[3]
2951
isolate
▴
Figure 11
Growth rates of two isolates of the alga
Ochromonas
325
Form and function
B4.2.6
S aprotrophic nutrition in some fungi
and bacteria
S aprotrophs
externally.
and
fungi
break
are
down
as
digestive
then
absorb
saprotrophic.
c arbon
nitrogen
enzymes
the
They
compounds
into
the
into
products
are
in
also
dead
ecosystem,
the
of
dead
known
as
organic
allowing
organic
digestion.
matter and digest
M any types of bacteria
decomposers
matter
them
to
and
be
bec ause they
release elements
used
again
by
otherorganisms.
r
of
of
organisms,
of
simple
possible
presented
pairs
but
of
not
in
to
deduce
Figure
choices.
for
questions
The
parasites
Figure 12
S aprotrophic fungi growing
leaves and
an
killed organisms
=
tapeworms
or
p
o
v
Eiter ingests organic matter y endocytosis no cell
u
l
a
E
v
O
f
x
t
a
Enzymes not
reires simle
dead organic matter
SAPROTROPHS
Figure 13
=
ETRTORES
secreted Only
its environment to digest
▴
organic matter
alls or y taking it into
alls resent No ingestion o organic matter No gt
Secretes enzymes into
=
c ause
o
i
d
r
o
Cell
that
n
U
START HERE
326
C
i
n
its gt
fungi
Feeds on dead
CONSUMERS
enzymes
key, which consists
for unicellular and multicellular
Feeds on living or recently
by secreting digestive
group it is in. The
dichotomous
works
as
organism’s mode of
trophic
y
decomposing them
a
r
e
over the surfaces of dead
as
key
such
diseases in plants.
▴
13
about
what
O
are
series
series
t
i
s
questions
a
a
usually
n
is
y
it
l
answering
nutrition
A dichotomous key
ions and
comonds sc
as CO

=
AUTOTROPHS
y
P
Activity: Determining trophic level
By
e
such
secrete
They
s
s
it
Ecosystems
Data-based questions: Fishing down marine food webs
Trophic
the
levels
position
the
a
be
represented
species
within
producers
an
by
a
number
ecosystem.
rst
3.
indic ating
Explain
with
By
occupy
the
trophic
so
have
a
TL
of
1.
For
primary
consumers, TL = 2, and
in
Deduce
the
theperiod
so
on. The
higher
between
Sun’
s
energy.
than
one
level
more
Fish
oen
levels
and
are
not
other
have
always
animals
estimated
5.
that
mean
Explain
change
in
age
of
c aptured
feed
at
trophic
two
advantages
fish
at
a
of
lower
humans
mean
more
Key
3.5
levels.
the
of
higher
increased
animals
trophic
“shing
that
tendency
feed
levels
down marine
at
for marine
lower
trophic
(Figure 14).
Suggest
a
method
thetrophic
level
that
of
a
might
fish
be
once
it
used
is
to
3.2
3.1
3.0
2.9
2.8
2.7
deduce
2.6
c aptured.
2.5
[2]
Compare
of
changes
fish
from
since
Suggest
why
mean
marine
and
trophic
freshwater
1970.
there
a
dierence in the
1995
2000
How the mean trophic level of landed sh has
over a 30-year period
C
adapted
the
are
other
diverse
in
are
to
of
extreme
dicult
to
domains
the
c ategories:
eukaryotes.
The
archaea
environments such as hot springs,
energy
light
culture
of
sources
energy
in
the
laboratory,
so
they
are
life.
by
used
for
ATP
production.
pigments — but pigments other
used
chemotrophic — oxidation
v
+
and
eukaryotes.
M any
a
O
chlorophyll
3
bacteria
u
main
ionstoFe
heterotrophic — oxidation
E
•
to
phototrophic — absorption
than
•
than
extremely
three
archaea,
l
•
are
are
lakes.
researched
are
closer
archaea
f
x
There
are
soda
life:
n
well
of
and
of
t
a
less
1990
year
have no nucleus, which is a similarity with bacteria. In other
i
types
lakes
1985
o
archaea
salt
Archaea
domains
and
r
o
Some
i
n
unicellular
respects
1980
Diversity of nutrition in archaea
three
d
are
are
Figure 14
changed
1975
[2]
U
There
▴
[3]
is
twotrends.
B4.2.7
level
o
fisheries
in
v
b.
landed
the
y
a.
p
r
e
1970
2.
marine
y
consist
at
3.3
[4]
n
to
to
feed
phrase
reduction
O
levels
refers
that
The
the
level.
fresh water
t
i
s
landings
sh
sh).
is
c atching and
trophic
y
webs”
of
over-shing
over
l
number
long-lived
food
1.
commercial
fish
[2]
P
the
(i.e.
of
increase
shown.
consuming
stated as
level cihport naem
in
eect
might
[2]
3.4
One
level
fish.
energy-transfer
organism and the initial xing of the
Trophic
numbers.
the
trophic
r
whole
the
number,
mean
individual
e
steps
the
the
an
level (TL)
4.
and
why
age
s
s
denition,
c an
of
2
of
of
inorganic
c arbon
chemic als,
compounds
for
example
obtained
+
Fe
from other
organisms.
327
Form and function
B4.2.8
Relationship between dentition
and the diet of omnivorous and herbivorous
representative members of the family
s
s
Hominidae
The
family
Hominidae
includes
the
genera that contain humans (Homo),
members
Hominidae
show
by
to
to
tougher
tear
the
extinct
grind
like
in
the
the
jaw
fossilized
in
Figure
jaw
17
is
and
from
teeth of an individual of
a
female
What,
if
anything,
c an
be
Humans
and
and
at
have
sharper
c an
have
be
grind
types
at
down
of
brous plant
teeth
to
break
down
molars in the back of their
and
been
incisors
than
herbivores
established, the diet
from
their
dentition — for
Paranthropus robustus
Australopithecus anamensis,
who
lived
more
who
than
t
a
Figure 17
to
inferred
a
▴
c an be
eSkeletons.org, a database
c anines
u
l
v
Jaw of Australopithecus anamensis
at
dierent
o
i
d
r
o
E
328
Figure 16
and
of
relationships
Homo neanderthalensis
deduced about their diet?
f
x
O
▴
found
n
the last glaciation).
food,
This
natural history museums or digital
p
The
diet.
large
mix
others
members of
o
shows
a
and
Austin.
C
16
ago.
U
years
be
at
v
Figure
to
Homo oresiensis
i
n
Activity: Deducing diet
those
Hominidae
larger c anines than humans
example, in
as
meat.
structure–function
species
dentition.
in
diet
Living
y
of
and
food,
and
skulls
Texas
have
their
diet
between
of
r
e
Once
crush
in
to
diet.
n
mouth
tend
tend
plants
of
the
O
and
such
in
included
y
herbivores
Omnivores
meat
online
University
herbivorous
is
t
i
s
both
of
the
relationship
collections
chimpanzees (Pan). Some
Jaw of Homo neanderthalensis
lived
110,000
about
years
4.1 million
ago
(before
y
available
sponsored
prey
and
exclusively
l
collections
teeth
a
physic al
animal
an
P
using
have
r
the
tissues.
Chimpanzees have much
Hominidae
omnivorous — some
The
Figure 15
the
are
studied
▴
of
e
orang-utans (Pongo), gorillas (Gorilla),
Ecosystems
Theories: Making deductions about diet from fragmentary evidence
A
theory
widely
in
science
applic able.
a
general
Predictions
c an
be
prediction.
explanation that is
c an
be
based
generated
on
they
observed
are
by
made
dentition
of
deductive
in
reasoning.
animals
c arnivores
developed
about
and
with
observations
teeth.
These
living
omnivores,
theories
and
then
structure–function
theories
animals
c an
from
be
the
about
of
extinct
to
verify
tested
these
diet
of
by
of
their
hominid
was.
What
are
found
in
this
increase the certainty?
if
other
herbivores.
been
are
the
vicinity
of
the
extinct
resisting
derived
by
herbivores.
with
jaw-like
with
tubes
tubular
and
Insects
mouthparts
on
the
for
for
structural
great
evolution
mouthparts
feed
have
show
groups:
insects
sieve
They
mouthparts
leaf
such
predictions
that
diversity,
from
the
feed
on
biting
off,
piercing
of
fossil
same
leaves
c an
prey
species
hominid?
C an
chewing and
leaves or stems
sap.
n
o
i
d
t
a
r
o
u
l
f
x
a
v
Figure 18
are
Insect
U
phloem
have
insects
insects
of
diet.
Are
n
and
reach
other
pieces
possible
sure what
o
and
broad
plants
be
skeletons
teeth
C
aphids
two
Most
infer the diet
not
l
on
their
to
is
O
to
it
y
into
beetles
O
▴
extinct
p
mouthparts.
divided
to
them
homologous — they
ingesting
•
c annot
predicting the
characteristics
i
n
•
an
non-scientic?
v
be
exclusively
used
y
adapt
be
however,
t
i
s
feed
that
ancestral
also
predictions — we
therefore
r
e
that
features
all
c an
hominid;
c an be
herbivory
are
of
relationships
feeding on plants and of plants for
but
dentition
species
Adaptations of herbivores for
Animals
show that
are
checking whether the actual diet matches the
B4.2.9
or
y
of
theories
P
diet
the
rejected.
r
of
be
known diets, including
the
the
corroborate
should
e
herbivores,
If
may
and
from these
Theories
theories
This
false
s
s
patterns.
is
Theories
Frog beetle (Sagra buqueti) has chewing
E
mouthparts for feeding on leaves
▴
Figure 19
Rose aphids (Macrosiphum rosae) have piercing
mouthparts
329
Form and function
Plants
show
tough
sharp-pointed
have
stings
to
herbivores.
are
a
variety
c ause
These
substances
be
stored
herbivores
pain.
so
are
any
bec ause
part
part
of
of
of
their
a
for
deterring
herbivores
M any
substances
that
in
adaptations
spines,
plants
risk
herbivore
injury
synthesize
when
attacks.
eating
substances
that
Some
it.
have
Others
are
toxic to
are
secondary metabolites. (Primary metabolites
the
basic
plant,
high
metabolic
particularly
pathways of a cell.) They
seeds,
concentrations
of
which
protein
are
and
s
s
may
of
attractive to
starch or oil.
e
r
l
n
y
c ases,
herbivores
plant–herbivore
have
responded
adaptations
specicity,
with
U
C
metabolic
o
some
developing
p
r
e
Stings on the tree nettle (Urtica ferox) which is endemic to New Zealand
i
n
In
Figure 21
v
▴
O
Spines on a leaf stalk of the
fan palm (Saribus rotundifolius)
for
only
to
toxic
detoxifying
a
few
compounds
them.
species
of
This
in
has
herbivore
plants
by
resulted in
adapted
to
feed
on a particular plant.
n
o
t
a
only tolerates these
also makes itself toxic to
predators by accumulating them
E
330
may
be
u
it
a
glycosides,
l
aphid (Aphis nerii) not
the milkweed
v
O
but
Predators
are
killed
Prey
adaptations
tuberosa) synthesize toxic glycosides
to deter herbivores,
animals for
system.
Milkweed plants (Asclepias
Adaptations of predators for
nding, c atching and killing prey and of prey
i
d
r
o
Figure 22
f
x
▴
B4.2.10
may
be
resisting predation
adapted
to
before
is
species
are
it
are
shown
structural,
nd
suitable
ingested,
adapted
in
Table
chemic al
or
2,
or
to
prey
it
resist
but
and
may
die
then
c atch
inside
predation.
there
behavioural.
are
many
the
and
kill
it.
predator ’s
Selected
The
prey
digestive
examples of
others. These adaptations
y
P
y
Figure 20
t
i
s
▴
Ecosystems

Table 2
Some adaptations of prey and
Type
predators
Predators
Prey
Physic al
s
s
e
r
Bu-tip moths (Phalera bucephala)
no molars, but
giving them
when roosting during daylight
relatively large incisors and
c anines on their upper jaw
and
razor-sharp.
These are used
to pierce
most
so the vampire c an feed on the blood
Chemic al
This is the time when the night-ying moths are
vulnerable to predation
o
d
paralyzes prey when injected via poison fangs.
The snake c an then swallow the prey without
C aterpillars of the cinnabar moth (Tyria
alkaloids from it. Their black and yellow stripes are warning
coloration which deters predators. Adults are day-ying,
with red and black warning coloration, indicating that they
i
retain toxins obtained when the larvae fed on ragwort
u
l
f
x
a
E
v
O
▴
resisting
Figure 26
jacobaeae) feed on ragwort and accumulate toxic
t
a
r
o
Behavioural
it
▴
y
containing a mixture of neurotoxins,
including an inhibitor of the enzyme acetylcholinesterase.
The venom
o
C
n
Black mambas (Dendroaspis polylepis)
produce venom
p
r
e
v
i
n
Figure 25
U
▴
O
are pointed
prey,
c amouage
hours on twigs or on the
t
i
s
ground.
that
n
resemble broken birch twigs,
with small premolars and
l
Figure 24
Vampire bats (Desmodus rotundus) have
unique dentition,
y
P
▴
Figure 23
y
▴
Figure 27
Grizzly bears (Ursus arctos) learn ambush
▴
Figure 28
strategies for catching migrating salmon either by trial
swim
and error or copying others. Some bears wait at the top
direction.
of waterfalls for a sh to jump out of the water. Others put
of predation,
their heads underwater and watch for a sh swimming past
detected
Blue-striped
in a tight
This “schooling”
and
snappers (Lutjanus kasmira)
group, oen with sudden changes of
behaviour reduces the chance
bec ause threats are more likely to be
it
is dicult
for a predator to c atch any one
individual in the bewildering shoal
331
Form and function
Behavioural
blue
This
tits
behaviour
when
research
seed-eating
on
start
to
longer
change
changes.
new
enzymes
take
millions
to
be
with
develop
nches
size
Chemic al
may
of
in
across
milk
and
on
the
or
new
but
there
the
of
the
be
Islands
of
the
as
shows
slowest
to
change,
and
bec ause
this
may
obtaining
in
such
light,
is
enough
water
photosynthesis,
environments.
so
for
abundant
show
great
plants
Plants
diversity
use
of
plant
compete
a
for
variety
of
form.
growth and
light.
Forest
strategies in
y
forest canopy
including
emergents
which are the
o
C
i
n
v
p
r
e
trees in the
tallest
individuals
n
o
i
d
t
a
r
o
l
u
f
x
a
v
O
strangler
shade-tolerant
Tropic al rainforest
E
is characterized
by great
epiphyte
shrubs and
diversity
herbs
•
•
Trees
have
reach
the
Lianas
do
a
climb
not
dominant
forest
need
through
to
leading
c anopy
where
other
produce
as
shoot
they
that
are
grows
rapidly
unshaded
trees,
using
them
much
xylem
for
tissue
by
to
great height to
other
support.
(wood)
as
trees.
This
means lianas
free-standing
trees.
y
develop
for
n
there
suitable
U
epiphytes
beaks
l
where
are
O
for
their
P
forests
of plantform
that
Adaptations of plant form for
t
i
s
ecosystems
Figure 30
Structural
change, but
years.
environments
temperatures
1920s
available on an
enzymes
y
In
the
rapidly
genetic
aer pecking through the
lianas
in
doorsteps.
1990s.
seeds
regulating
harvesting light
332
to
of a milk bottle
B4.2.11
▸
in
must
size
usually
ways
example,
disappeared
Galápagos
when
are
For
delivered
diminished
bec ause
shape
quickly.
bottles
Europe,
cream
adaptations
needed
milk
e
foil c ap
rapidly
bottled
relatively
from
r
feeding on cream
of
change
cream
s
s
Blue tit (Cyanistes caeruleus)
spread
deliveries
c an
on
take
island
Figure 29
feeding
adaptations
soon
▴
adaptations
started
Ecosystems
•
Epiphytes
•
grow
light
intensity
their
roots.
Strangler
their
leaving
Shade-tolerant
of
out
trees
the
so
but
they
there
receive higher
is
minimal
soil
for
encircling them and
leaves
of
the
tree.
Eventually the
epiphyte.
and
herbs
absorb
light
reaching
the
forest
floor.
the
tolerate
not
a
allow
range of biotic and abiotic conditions, but their
them
fundamental
is
niche
would
competition
of
the
outside
species.
occupy
and
this
the
If
the
entire
typic ally
a
range.
The
species
is
niche
niche.
excluded
In
natural
from parts
▴
its
fundamental
niche
by
competitors.
The
actual
extent
of
the
potential
Figure 31
A realized niche is a subset
range
O
of
niche
were living
fundamental
species
realized
fundamental
range of
t
i
s
there
it
survive
of a fundamental niche.
that
a
species
occupies
is
its
realized
niche.
n
competitors,
to
y
do
ecosystems,
trunks
shade
trees,
l
is
any
floor,
y
without
shrubs
of
forest
e
tolerance
the
the
to
branches
the
Fundamental and realized niches
organisms
adaptations
up
on
P
Living
climb
branches,
only
and
grew
r
B4.2.12
trunks
they
s
s
•
dies
the
if
epiphytes
outgrowing
tree
on
than
The reductions are
due to overlaps with the niches of other
competitor species
Competitive exclusion and the
fundamental
the
and
experimentally
with
the
and
humidity,
T.
Table
3,
T.
blue
was
usually
more
segments
castaneum
and
is
expected
was
Tribolium castaneum
dierent combinations of
excluded
indic ate
orange
the
T.
confusum
percentage
segments
of
indic ate
T. confusum at
i
l
in some
trials
the
where
converse.
various temperatures
Humidity
30%
70%
a
E
v
O
29
This
u
f
x
24
at
t
a
r
o
Temperature/°C
species
successful in other combinations. In
Competition between T. castaneum and
humidity levels
one
competition.
beetles
together
castaneum
confusum
excluded
our
by
o
and
T.
reared
overlap,
range
d

Table 3
in
When
its
n
charts
species
of
U
pie
confusum
two
part
combinations but
T.
of
that
Tribolium confusum.
temperature
the
niches
from
C
demonstrated
other
o
the
exclude
i
n
to
v
Where
p
uniqueness of ecologic al niches
y
r
e
B4.2.13
34
333
Form and function
If
two
one
species
species
in
outcompeted
excluded
an
species
from
the
must
have
species
if
to
is
does
whole
a
the
overlapping fundamental niches and
in
not
have
in
an
niche
all
a
ecosystem.
realized
survive
have
other
parts
of
realized
According
that
diers
the
fundamental
niche
to
from
and
will
be
ecologic al
the
niche, the
competitively
theory,
every
realized niches of all other
s
s
species
it
ecosystem
outcompetes
ecosystem.
e
Data-based questions: Competitive exclusion in
r
c at-tails
margins
biomass
depth
contrast
of
the
between
Analyse
the
realized
niches.
from
data
the
two
the
ecosystem.
species
growing
growth of
growth of
T. latifolia.
in
natural
out
of
plant
The
when
the
without
T. latifolia
any
in the
[4]
with and without
[2]
[4]
o
T. latifolia
T. angustifolia
C
i
n
v
Key
n
y rd
o
g / s s am
U
e e rf - h s a
i
u
l
a
E
v
O
f
x
t
a
r
o
d
0
‒20
20
60
100
60
100
80
40
0
‒20
20
water
▴
each
graph
graphs using the concepts offundamental and
1,600
800
lower
grown
grow on
of
water.
T. angustifolia and
T. angustifolia
that
y
3.
the
of
production
p
Distinguish
species
primary
r
e
2.
a
means
competition.
competition
334
in
two
shows
O
and
of
together
transplants
Negative
Compare
absence
of
graph
t
i
s
1.
growing
upper
n
the
competition.
The
y
shows
when
Typha angustifolia are
lakes.
l
species
of
Figure 32
depth / cm
Competition in c at-tails
y
the
P
Typha latifolia and
Ecosystems
Linking questions
1.
What
are
the
relative
advantages
O utline
the
role
of
specicity
b.
Explain
the
evidence
for
of
specicity
in
enzyme
evolution
and
versatility?
function.
provided
by
(C1.1.7)
the
pentadactyl
s
s
a.
limb.
(A4.1.4)
Explain
each
what
form
of
is
meant
by
nutrition,
the
what
universality
are
the
of
unique
the
genetic
inputs,
code.
(A2.1.7)
processes and
outputs?
Distinguish
meant
between
O utline
one
the
holozoic nutrition. (B4.2.4)
mechanisms
of
digestion
of
detritus
feeders
(C4.2.12)
example
of
mixotrophy. (B4.2.5)
O
t
i
s
n
saprotrophs.
by
y
c.
is
y
b.
and
what
l
Explain
P
a.
e
c.
For
r
2.
y
p
r
e
C
o
v
i
n
n
U
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
335
Form and function
TOK
Are some types of knowledge less open
s
s
to interpretation than others?
everyday
than
language,
one
competing
is
explanations
fragmentary
is
more
to
verify
the
and
the
it
the
interpretation.
structure
interpretation.
consensus
is
possible
methods
of
view
to
the
situations,
It
is
of
a
about
obtain
exploring
skeletal
subject
there
is
muscle
straightforward
their
further
cellular
greater
However,
bres
matter
structure. This is
samples
to
examine,
ultrastructure
▴
are
Figure 2
O
bec ause
as
one
bec ause
such
t
i
s
to
open
In
H. oresiensis skull (le) next to computer
artwork of a human (H. sapiens) skull (right)
reliable.
example
of
an
area
where
y
r
e
An
n
such
is
than
c an be
y
knowledge
not
evidence
uncontrollable.
for
there
for a phenomenon, particularly
l
tolerance
“interpretation” implies
biology,
disagreements due to
dierent interpretations persist is in the phylogeny of the red
very
bring
of
from
other
the
14
bones
ever
of
while
suggest
others
in
a
336
that
at
been
Indonesia.
found,
more
found.
species
not
to
whether
red
Eorts to
have
depended
not
The
the
the
worth
and
US
nancial
Fish
red
present
very
preserving.
and
wolf
as
resources
Wildlife
an
endangered
protected status. The International
Conservation
endangered
recognized
or
is
expensive
recognizes
grants
the
are
sc arce.
coyotes.
from other populations.
wolves
in
the
of
Nature
species.
species.
One
CITES
interpretation
distinct
species
of
ancestry
their
whereas
to
is
the
historic
has
listed
However,
appendices
that
the
modern
red
it
is
been
have
a
is
with
the
not
skulls
This
is
of
the
the
red wolf
red wolf
endangered
a
historic al
red
wolves
other
wolves
and
coyotes
has
red wolf is a
wolves
but
trace some
hybridization
continued,
distinctiveness of the population.
possible
from the
the
c ase
discovered on
one
skull
bones
from this
and
uncovered.
been
to
more
teeth
Tools
found along with
more
primitive
modern
H. oresiensis
underwent
it
fragments. Some of the skeletal
relationship
suggest
Only
though
have
skeletal
interpretation is that
erectus
looking
individuals
prey
However,
Homo oresiensis
been
H. oresiensis
features
bone.
has
E
has
by
one
Flores
species
and
study
only
a
a
if
such
short-statured
island
is
for
critic ally
as
of
with
extinction
natural world. Scientists would participate
of
v
the
n
the
O
the
and
o
analysis
population
of
i
expand
currently
from
animals
are
species
back
of
eorts
conservation
a
hybridized
uncovers a skull, it is an
l
to
dier
population
Service
as
t
a
the
the
introduction
Conservation
for
C. lupus rufus). The modern population
population
Viewpoints
small
or
has
C
i
n
U
of
in
the
Union
u
artefact
palaeoanthropologist
f
x
a
the
and
The structure of skeletal muscle bres is clearly visible
through microscopy
When
d
Figure 1
r
o
▴
on
small
o
v
is
p
wolf (Canis rufus
process
is a
species
species.
One
descendant of
known
as
island
H.
dwarsm.
▴
Figure 3
A modern red wolf
threatening
y
there
material
word
In
P
if
the
possibility.
r
more
e
In
Ecosystems
End of chapter questions
1.
One
method
the
conditions
used
they
thermophiles,
high
for
survival.
species
The
graph
minimum
species
of
pH
Both
that
groups include
are
adapted
to
live
shows the optimum
required
for
New
are
Eubacteria is the
technologies
being
used
such
help
lived.
This
technique
teeth
over
a
types
of
lifetime
food
were
as
surfaces
Archaea and thermophilic
of
examined
allows
to
be
in
were
groups
Teeth
of
were
teeth.
hard,
brittle
Flat
from
early humans and
compared. The upper
analysed
for
stages
similar
results.
teeth
are
wear of
The
slope.
lower
best
of
the
suited
to
The
slope, the
crushing
110
elastic
foods
100
3
4
5
6
7
8
the
highest
recorded
State
the
for
the
Archaea
the
not
data,
always
between
f
x
suggest
be
a
possible
1
2
3
wear stages
habitat
i
State
what
changes
occurred
to
all
teeth
ii
Compare
thoseof
b.
for
Using
the
[1]
the
teeth
of
early Hominids with
A.afarensis
data,
Hominids and
[2]
suggest
how
A.afarensis
the
diets
of
early
diered.
[2]
Archaea and thermophilic
c.
Suggest what other evidence would help
[2]
scientiststo
for methanogenic
determine
earlyHominids.
what
food
was
eaten
by
[2]
[1]
a
E
v
O
l
Archaea.
0
A. afarensis
withwear.
for
why this
suitable
u
State
those
a.
[2]
Eubacteria.
e.
with
n
distinguishing
[1]
Eubacteria.
to
5
0
growth
i
would
optimum
t
a
reference
method
10
[1]
o
results
thermophilic
With
Eubacteria.
Archaea.
r
o
d.
the
temperature
suited
between minimum pH
and
d
Compare
for
Microbiology, 5, p316
growth
thermophilic
growth
temperature
the
optimum
relationship
supporting
c.
the
Reviews
U
b.
for
Nature
15
C
State
(2007),
25
20
meat.
better
o
Valentine
n a em
DL
i
n
Source:
30
are
y
2
e c af r u s
1
as
early Hominids
p
50
v
m u m i tp o
60
0
35
r
e
ht w o rg
70
40
such
teeth
O
Key
80
minimum pH supporting growth
a.
t
i
s
90
shaped
n
eating
More
y
to
foods.
teeth
wear to
l
the
seerged / epols
C° / erutarepmet
flatter
of
revealing what
of
thermophiic uacteria
Archaea
pattern
analysis
early Hominids
y
consistency
the
how
analysed,
eaten.
teeth
topographic
P
ensure
the
were
dental
understand
Australopithecus afarensis
growth
Eubacteria.
e
to
r
selected
and
and
are
temperatures.
temperature
by
need
which
2.
microbiologists to distinguish
e
at
by
Archaea
s
s
between
337
I n t e ra c t i o n
and
C
s
s
interdependence
e
r
1
Molecules
n
Molecules are particles of matter that
into smaller parts without
The elements that
are most
c annot
losing their chemical
y
r
e
identity.
each level of biologic al
O
t
i
s
be divided
interdependence
Systems result in the
emergence of new properties at
organization.
l
integration of components.
y
P
and
on interactions,
y
Systems are based
useful to organisms
are those whose atoms interact
to form
molecules, usually
by covalent
p
is an example of
bonding.
bond
each of the atoms contributes one of
electrons in the bond.
C
i
n
the shared
o
v
interdependence:
A covalent
The properties of the
molecules are oen quite dierent
of which they are composed.
U
interact
n
molecules are emergent
from the elements
Thus the properties of
properties.
Molecules c an
with each other to produce emergent
properties.
o
vaporization are emergent
properties.
i
secretions of a hippopotamus.
u
l
a
E
v
O
f
x
t
a
r
o
d
For example the wetness of water or its high heat of
Consider the skin
As the hippo spends most
of the day in the water yet
is also very sensitive to both
drying out
secretes molecules that
and
sunburn,
it
diverse functions such as skin moisturizer,
and
antibiotic.
The secretion also serves to regulate the
hippo’s temperature on land.
thermoregulation and
properties that
serve
water repellent
result
Self-defence against
disease,
moisture regulation are all emergent
from
the properties of molecules and
their interaction with other molecules.
C1.1
Enzymes and metabolism
In what ways do enzymes interact with other molecules?
interact
competitive
cellular
able
reaction
in
to
(family
to
reduce
of
genes
the
light
abdomen.
control
end
products of
inhibitors. The build-up
as
How
responsible
concentration of the
L ampyridae)
produce
their
as
expression
enzymes,
Fireies
are
the
act
Cells
The
a
are
a
group
of
species
result of an enzyme-
does
the
rey
regulate
▴
an
down
includes
growth,
and
repair
combined
in
Blue
metabolic
shows
low
activity.
of
activity,
Suggest
and
healthy
in
the
green
why
of
HL
c atalysts
ATP
.
toxins
complex network of
emission
a
activity
a
of
Processes such as
tomography (PET) and
human
body’s
shows
part
of
body
internal
(Figure 2)
organs such
intermediate activity
the
leg
is
▴
AHL
C1.1.11
Intracellular
u
C1.1.2
Role of enzymes in metabolism
reactions
C1.1.3
Anabolic
C1.1.12
and
c atabolic
reactions
l
O
Interactions
between
Role
C1.1.7
in
molecular
E
collisions
of
v
induced-t binding
C1.1.6
enzyme
Relationships
enzyme–substrate
a
C1.1.5
substrate
motion
and
and
active
site
to
allow
substrate–active site
specicity
the
and
structure
of
the
active
Generation
of
C1.1.13
Cyclic al
C1.1.14
Allosteric
C1.1.15
Competitive
inhibitor
C1.1.16
c atalysis
between
and
only
extracellular
heat
energy
site,
denaturation
and
binding
linear
sites
reversibly
Regulation
of
to
as
an
metabolic
a
of
in
enzyme-c atalysed
enzymes
on
activation
consequence of an
pathways
by
feedback
inhibition
C1.1.17
Mechanism-based
chemic al
changes
to
inhibition
irreversible binding of aninhibitor
Eect
reactions of
active site
on the rate of enzymeactivity
Measurements
the
non-competitive inhibition
inhibition
of
C1.1.10
by
pathways in metabolism
and
C1.1.8 Eects of temperature, pH and substrate concentration
C1.1.9
enzyme-c atalysed
metabolism
C1.1.4 Enzymes as globular proteins with an active site for
catalysis
Figure 2
green.
t
a
as
f
x
Enzymes
on
form
breakdown
i
high
SL
C1.1.1
depend
sc an
The
metabolism.
positron
(CT)
r
o
shows
of
the
n
3D
tomography
brain.
molecules.
part
chemic alreactions.
variations
red
new
also
in
reactions
involved in
o
the
and
is
U
as
make
energy
are
yield
to
usable
chemic al
reactions
macromolecules into their subunits and
d
shows
chemic al
to
maintenance
coloured
interdependent
of
products
computed
the
these
molecules
interdependent
The
of
of
breakdown
re-assembly
waste
all
C
and
the
of
Some
i
n
their
sum
o
It
the
v
breaking
is
organism.
p
within
y
Metabolism
Figure 1 A rey
r
e
What are the interdependent components of metabolism?
O
t
i
s
emission of light?
n
c atalysed
that
oen
activity.
substrates,
molecules
y
again.
beetles
the
increase
and
membranes.
enzyme
reactions
new
as
including
inhibitors,
y
of
molecules
l
substrate
such
regulating
c an
generating
of
P
substrate
for
range
structures
by
enzyme-c atalysed
of
a
r
metabolism
with
non-competitive
e
within
and
s
s
Enzymes
the
active
as
site
a
consequence
c aused
by the
reactions
energy
339
Interaction
and
interdependence
C1.1.1
A
c atalyst
Enzymes as c atalysts
is
a
substance
changed
by
reactions
many
quantity
Platinum
is
of
an
example
to
in
of
an
vehicles
only
exhaust
inorganic
with
of
are
small
a
gases
to
equation
for
an
is
dioxide
are
made
and
by
enzymes
in
to
the
help
c atalytic
convert
water.
living
cells
convert
enzyme-c atalysed
to
did
not
make
enzymes,
slowly
digestion,
at
the
chemic al
ambient
growth
and
reactions
temperatures.
movement
C
i
n
o
respiration,
very
v
happen
unburned
speed up
substrates into
reaction is:
y
cells
would
p
r
e
photograph shows one day’s supply for a
If
c atalyse
relation to
n
a person
their food. The
person with cystic brosis
in
l
much slower than normal. Pills containing
with cystic brosis to digest
c an
O
reaching
Digestion is therefore
a mixture of enzymes c an help
used
t
i
s
by the pancreas from
they
needed
on
Life
would
all
which
life
is
based
processes such as
be
very
slow.
Data-based questions: The eectiveness of
U
enzymes
enzymes
comparing
with
i
been
o
eectiveness
reactions
and
c alculated
of
reactions
reaction
with
of
dierent
enzymes.
without
for
rates
of
the
an
rst
and
enzyme.
by
without
Table
The
dierent
an
1
ratio
amounts.
enzyme
shows
the
between
R atios
allow comparison
rates
these
of
four
rates has
reaction.
–1
Reaction
u
l
a
E
v
O
f
x
Without
rate /s
With
enzyme
Enzyme
R atio
enzyme
C arbonic
−1
1.3 × 10
6
1.0 × 10
Ketosteroid
–7
1.7 × 10
4
6.4 × 10
isomerase
–13
Nuclease
1.7 × 10
6
9.5 × 10
OMP
–16
2.8 × 10
dec arboxylase
Table 1
6
7
.7 × 10
anhydrase
▴
340
the
increase
rate
t
a
r
o
d
of
the
n
Dierent
8
3.9 × 10
y
general
They
reactions,
It
to become blocked with
the small intestine.
reaction but is not
r
c atalysts.
In
c arbon
This prevents digestive enzymes
produced
up,
are
engines,
enzyme
mucus.
used
P
biologic al
reactions.
these
c atalyst.
Cystic brosis c auses the
pancreatic duct
chemic al
not
amounts
combustion
are
A
rate
y
Figure 3
means
biochemic al
products.
▴
This
the
c atalysts
reactants.
tted
hydroc arbons
Enzymes
times.
increases
Bec ause
e
converters
that
reaction.
s
s
the
the
Molecules
State
which
the
reaction
has
the
slowest
3.
State
which
reaction
has
the
fastest
4.
C alculate
5.
Discuss
which
6.
Explain
how
enzyme
term
the
for
“rate
ratios
the
of
reaction”.
between
second,
of
the
the
the
third
enzymes
is
rate
rates
and
enzymes
[2]
rate
with
of
fourth
the
increase
without
enzyme.
[1]
enzyme.
[1]
reaction with and without an
reactions.
most
the
an
an
eective
rate
of
the
[2]
c atalyst.
[2]
reactions they
r
c atalyse.
[2]
e
Dene
2.
s
s
1.
there
foods
in
There
are
thousands
Most
extracellular
of
these
reactions,
for
and
interacting
a
are
cycle
are
of
metabolic
transformed
is
very
chains
shown
example, digestion of
of
in
reactions.
into
reactions
Figure
complex.
They
They
another
4.
are
form
pathways in which one
by a series of small steps. Most
but
there
M aps
are
also
showing
available
on
all
the
phosphate
n
U
carbamoyl
ornithine
and
is
their
group
numbers
Bec ause
of
reactions
specicity.
of
non-biologic al
reactions.
a
enzymes
specic
v
metabolic
E
a
l
O
of
all
reactions.
c atalysts
of
dierent
fumarate
◂
This cycle of metabolic
cells. There are ve reactions, so ve dierent
enzyme 4
enzymes are required. Can you nd out what
argininosuccinate
are
c atalysed
E ach
enzyme
by
a
such
signic ant
as
platinum,
specicity,
Even
a
an
relatively
one
c an
of
the
properties
reaction, or
between enzymes
c atalyse
organisms
simple
One
specic
dierence
which
living
these enzymes are?
enzyme.
c atalyses
is
enzymes.
Figure 4
reactions is used to synthesize urea in liver
This
enzyme
arginine
u
f
x
aspartate
enzyme 3
o
citrulline
urea
enzyme 5
t
a
r
o
i
d
enzyme 2
example in
o
3
for
C
NH
enzyme 1
cycles. An
pathways of
internet,
i
n
+
2
some
the
Encyclopedia of Genes and Genomes.
CO
Almost
chemic al
reactions happen inside
v
Kyoto
interdependent
p
of
metabolism
the
is
pathways
example
some
of
organisms.
intestine.
molecule
these
also
network
living
y
of
of
are
in
r
e
type
the
complex
O
but
the
occurs
t
i
s
cells
that
n
is
reactions
l
Metabolism
y
P
Role of enzymes in metabolism
y
C1.1.2
have
to
many
make
dierent
large
prokaryotic cell makes
341
Interaction
and
interdependence
hundreds
of
liver
make
cells,
Enzyme
If
a
cell
specicity
happen
cells
temporarily
while.
c an
extremely
control
and
it
c an
rate
It
more
allows
drive
slowly
the
particular
summary,
metabolism
with
benets.
enzyme,
stopping
In
many
Cells
complic ated metabolism, such as
dierent enzymes.
or
of
a
not
enzymes
give
over
organisms
particular
at
all.
reaction.
enzymes
therefore
a
from
living
their
By
making
There
are
working
if
organisms
activities
to
control metabolism.
reaction that would
more
also
a
or
less of an
mechanisms
reaction
is
considerable
and
not
control
r
has
using
molecules
In
energy
product.
example
anabolic
from
are
of
synthesis
of
combined
They
are
anabolic
and
c atabolism.
ones.
anabolism,
reactions,
ATP.
Examples
larger
to
These
bec ause
produce
c arbon
larger
macromolecules
condensation
Anabolic
reactions
are
molecules,
produced
reactions
energy.
dioxide,
water and
using
from
bec ause
reactions include:
energy
monomers,
water
is
a
by-
•
DNA
•
synthesis of complex carbohydrates including starch, cellulose and glycogen.
(replic ation)
the
i
n
to
synthesis
break
c ases,
of
ATP,
down
this
larger
energy
which
c an
of
be
C
digestion
molecules
c aptured
then
reactions include:
•
is
p
some
o
reactions
energy.
v
C atabolic
In
by ribosomes
by
used
in
y
protein
r
e
•
synthesis
(translation)
reactions
require
O
light.
an
into
t
i
s
from
small
is
anabolism
n
other
parts:
molecules
y
Photosynthesis
two
l
smaller
into
smaller
coupling
the
cell.
ones,
the
releasing
c atabolic
Examples
of
reaction
c atabolic
food—in humans this happens in the mouth, stomach and
U
smallintestine
Figure 5
An easy way to remember that
•
anabolic reactions build
cell
respiration—in
c arbon
dioxide
are sometimes misused to
organic
of
glucose
or
lipids
are
oxidized to
complex
c arbon
compounds—decomposers
do
this
with
dead
matter.
u
l
a
342
v
E
Figure 6
the right
digestion
respiration,
water
t
a
r
o
f
x
O
▴
•
i
promote “body building”
and
o
d
steroids that
aerobic
smaller molecules
into larger ones is to think of the anabolic
n
▴
Anabolic reactions in trees c an lead
was recently blown over in a storm
and
to a huge accumulation of biomass,
c atabolic reactions,
mainly c arried
as in the Moor Park Oak in Shropshire (le).
out
by fungi,
The tree on
are now breaking down its macromolecules
y
Metabolism
P
Anabolic and c atabolic reactions
up
over
chemic al composition.
C1.1.3
build
for
required
e
a
their
has
an
of
s
s
enzyme,
enzymes.
thousands
produces
otherwise
for
dierent
Molecules
C1.1.4
Enzymes as globular
active site for
are
chemic al
properties
to
be
the
globular
c atalysed,
surface
allows
the
are
is
as
must
the
site
active
site
the
and
the
enzyme
bound
then
three-dimensional
function
to
the
rele ased,
c atalysts.
bind
(see
to
active
site,
le aving
the
7).
it
is
region
and
other.
This
substances
converted
active
on
shape
e ach
other
and
re action
The
match
most
a
special
Figure
substrate
while
a
structure
For
site
free
into
to
re action.
▴
sites
vary
in
size,
depending
on
the
size
of
the
substrates.
Figure 7
Computer-generated
Typic ally,
l
Active
y
another
with
to
substrates
active
substrate
products
or
c alled
bind
precise
r
the
The
of
to
with
them
P
c atalyse
substrate
substrate
While
products.
allow
enzyme
properties
the
c annot.
the
the
proteins,
that
e
chemic al
of
c atalysis
s
s
Enzymes
proteins with an
image of the enzyme hexokinase (blue),
a
few
amino
acids
at
the
active
site
are
essential
to
create
the
chemic al
n
y
just
with a molecule of its substrate glucose
conditions
that
change
the
substrates
enough
to
convert
them
into
products.
(yellow) bound
the
amino
acids
that
form
the
active
site
are
not
next
to
t
i
s
Oen
substrate,
of
the
that
make
polypeptides.
is
site
change
may
crucial.
any
part
enzyme.
reason
of
the
the
They
are
overall
enzyme
is
brought
together
by
the
folding
three-dimensionalstructure of the
altered,
the
structure
c atalysis is unlikely tohappen.
of
the
site
Again,
allow
it
substrate
to
the
This
model
is
surface
active
used
to
be
attract
the
substrate
▴
compared with a key
inappropriate
site
enzyme, the
bec ause
interactions
c ause both to change: bond angles
the
site.
three-dimensional
This
the
active
numbers show where each amino acid
comes in the sequence of the polypeptide.
acid
is
c alled
site
Twelve amino acids form
For example,
molecular
LEU-233 shows that the amino
leucine is 233rd
in the sequence.
induced-fit binding.
Are any of the 12 amino acids that
approaches and binds to another part of the
and
Figure 8
the active site of sucrase isomaltase. The
c ause
changes
in
each
the active site next
form
to each other in the
polypeptide?
(Figure 9).
a
vac ant
near
are the basis
When it is close enough to
enzyme
changing
l
site
the
site.
active
the
substrate,
binding
the
is
enzyme
n
site.
to
second
and
it
an
o
a
that
the
altered,
substrate
of
Until
random.
t
a
is
are
and
is
of
y
p
active
site.
active
However,
2.
E
v
O
Active
the
the
site.
u
other
of
to
substrate
lengths
active
active
r
o
there
active
lock.
the
movement
properties
the
binds
f
x
If
a
the
bond
shapes
▴
the
i
into
between
and
chemic al
towards
substrate
fitting
of
d
The
approaches
direction
the
molecule
1.
and
the two substrates are linked to
o
substrate
interact,
•
substrate
C
A
substrate’s
•
the
c atalysis.
U
•
between
i
n
of
A second
binds to the active
make glucose phosphate
Interactions between substrate and
active site to allow induced-t binding
Interactions
site and
active
v
C1.1.5
If
and
the
that
r
e
enzyme
up
For
phosphate,
O
polypeptides
to the active site.
each other in the
First
substrate
Product
bound
released
3.
so
Second
active
site
substrate
becomes
bound
4.
Substrates
converted
to
product
vac ant
Figure 9
343
Interaction
and
interdependence
•
Changes
break
•
The
to
and
substrate
new
products
interacting
c an
with
empty
be
detach
it,
and
to
form,
from
the
the
active
enzyme’s
available
for
make
it
easier
converting
site.
active
more
for bonds within them to
substrates
Without
site
returns
substrates
to
into
products.
substrates
to
its
bind,
or
products
original
state. It is
so
the
c atalytic
cycle
s
s
now
molecules
bonds
repeated.
e
C1.1.6
Role of molecular motion and substrate–
r
active site collisions in enzyme catalysis
an
it.
active
it
think
a
The
liquid,
come
not
like
road.
about
the
direction
of )
collision
so
substrate
occurs,
work
molecule
are
is
some
M any
over
is
c ases,
part of
If random
Enzyme–substrate collisions.
movements bring any of the
substrate molecules close to the active site
orientation,
•
When
will
happen
site
in
are
both
however,
site
the
the
be
they
at
or
will
if
if
any
substrate
between
the
to
chemic al
orientation.
so
they
only
to
the
molecular
reactions
dissolved
substrate
is
motion
in
water,
a
smaller
of
in
so
free
to
move.
more (a higher
the
increases,
active
site
are
properties
site.
aligned,
that
However,
draw
the
forces
promote binding when a
active
happen
are
active
have
close
are
temperature
angle
and
occur, we
occ asionally come
there
their
distances
moves
random. If the liquid
or
adjust
it
substrate
collisions
they
at
enzymes
very
the
may
which
but
and
increase
molecules
if
a
site.
substrates and enzymes:
the
are
cytoplasm.
free
to
Substrate
move. In most
molecule than the enzyme so it
Some
substrates
enzyme
has
to
are
move
very
in
large
and
relation
do
not
move
to
the
substrate.
in
membranes
much.
In
Enzymes
these
that
c ases, the
replic ate or
transcribe DNA do this.
Some
enzymes
are
embedded
and
c annot
move—they
are
the substrate
to theactive site
E
v
a
c an bind
l
O
with the correct
•
u
Figure 10
f
x
▴
enzyme
movesmore.
enzyme
active site
enzyme
in
short
already
variation
t
a
r
o
and
enzyme
Some
enzyme-c atalysed
i
substrates
c an
together
molecules,
happens
substrate
active
o
d
•
the
ones
place.
the
water
There
an
substrate–active site collision.
repeatedly
molecular motion.
take
molecules
or
closely
changes
enzyme
this
substrate
towards
only
packed
n
U
involved
c an
and
which
collisions
binding
substrates
are
molecule
C
Successful
a
that
substrate–active
o
When
a
faster
how
v
to
at
i
n
leading
as
impacts
of
motion.
p
concentration
known
is
site
molecular
molecular motion in liquids.
each
rate
active
this
velocity
understand
substrate
The
the
of
y
both
together.
with
result
r
e
contains
high
molecules
of
a
together,
the
To
bind
as
O
need
In
a
only
t
i
s
on
to
site
is
vehicles
c an
happens
n
However,
This
l
and
molecule
to
y
close
immobilized.
C1.1.7
In
these
c ases,
the
substrate
has
to
do
all
the
movement.
Relationships between the structure
of the active site, enzyme–substrate
specicity and denaturation
The
shape
molecules
specicity.
344
and
to
chemic al
bind,
but
properties
not
other
of
an
enzyme’s
substances.
This
active
is
site
c alled
allow
substrate
enzyme–substrate
y
substrate
very
P
A
Molecules
Some
enzymes
example,
are
glucose
absolutely
is
glucokinase.
Other
with
of
any
one
specicity,
any
so
a
amino
structure.
between
amino
enzymes
to
the
too
c an
For
example,
also
hexokinase
have
broad
c an bind
substrate
between them digest polypeptides
a
precise
structure
altered.
the
site
result,
great
to
the
are
protein,
aected
Even
if
c an
be
on
are
factors
prevent
enzyme
to
binding
will
reversed,
no
the
at
aect
of
weak
as
a
heat
active
work
is
as
or
a
an
and
and
distance
the
substrates,
longer
enzyme
and
intric ate
interactions
hydrophobic
such
happen
likely
shape
relatively
including
by
changes
enzyme
the
three-dimensional
depends
hydrogen
acidity, so
from
site.
the
active
Even small
prevent
c atalysis
c atalyst. If the
denatured.
O
t
i
s
Data-based questions: Biosynthesis of glycogen
In 1947
, the Nobel Prize in Physiology or Medicine was
4.
Curve
5.
glycogen. Glycogen is a polysaccharide. It is composed of
a.
Describe
b.
Explain
noisrevnoc %
n
this.
not
12
been
the
the
was
the
obtained
shape
was
of
using
curve
heat-treated
A.
[2]
obtained using enzymes
heat-treated.
shape
shape
of
of
curve
curve
B.
[1]
B.
[2]
B
60
40
20
are
glucose
[1]
needed
A
for the
phosphate.
[2]
10
20
30
40
50
time / min
increases
molecules
c an
the
rate at
be
linked
▴
Figure 12
Graph showing the percentage conversion of
glucose phosphate to glycogen by the two groups of enzymes,
molecule. Explain the
over a 50-minute period
[2]
Eects of temperature, pH and substrate
E
C1.1.8
for
12
glycogen is
a
reason
phosphate
glycogen
o
glucose
growing
enzymes
from
l
a
of
reason.
side-branches
v
O
to
of
a
i
which
dierent
glycogen
formation
Give
u
The
two
f
x
3.
of
production
Figure
had
C
i
n
why
synthesis
the
anabolic.
t
a
Explain
or
in
that
80
U
whether
c atabolic
2.
d
Deduce
r
o
1.
Bonding in glycogen
B
Figure
Explain
o
1,4 and 1,6 bonds (see Figure 11).
Curve
v
glucose molecules bonded together in two ways, called
Figure 11
in
y
two enzymes that convert glucose phosphate into
▴
A
enzymes.
p
r
e
won by Gerty Cori and her husband C arl. They isolated
n
are
For
Proteases
substrate.
y
changes
a
protease
within
within
active
As
specic.
sugars.
same
active site of the enzyme
l
binding.
with
This
acids
easily
less
the
the
y
changes
aer
are
of
interactions
interactions
are
hexose
bind
to
P
site,
binds
sequence.
proteins
These
always
that
r
bonds.
and
e
are
chemic al
of
types
acid
Enzymes
specic
substrate
enzymes
group
few
only
s
s
with
a
the
concentration on the rate of enzyme activity
1. Eects of temperature
Enzyme
In
activity
liquids,
the
the
particles
is
aected
particles
gain
are
kinetic
by
in
temperature
continual
energy.
As
a
in
two
random
result,
ways.
motion.
enzyme
When
and
a
liquid
substrate
is
heated,
molecules
345
Interaction
and
interdependence
rate at which reaction
move
decreases owing to
molecule
denaturation of
optimum temperature,
enzyme molecules
which
is
not
always
around
more
colliding
increased.
quickly
with
Enzyme
and
the
activity
the
chance
of
a
substrate
active site of the enzyme is
therefore
increases.
40 °
and can be much higher
When
and
enzymes
the
are
chance
of
heated,
these
bonds
bonds
in
the
enzyme
breaking
is
vibrate
increased.
more
s
s
in the enzymes of organisms
When
adapted to high ambient
bonds
in
the
enzyme
break,
the
enzyme
structure changes.
temperatures
Changes
to
the
active
site
will
mean
it
c an no longer bind with
rate at which
e
substrate molecules: the enzyme is denatured. Dierent enzyme
reaction increases
denature
temperature
at
in
a
rises,
slightly
more
dierent
and
more
temperatures.
enzyme
substrate and
solution
molecules
will
molecules
will
be
denatured
rises,
enzyme
temperature
on
are
reasons
Figure
13
a
for
both
shows
0
10
20
30
40
50
Enzymes
60
Temperature and
to
rate of
hydrogen
ion
sc ale
solution
is
slightly
hydrogen
10
is
ion
logarithmic.
times
acidic;
more
pH
5
is
the
by
This
means
A
times
how
acidic
and
that
solution
more
chemic al
ions
a
and
acidic
pH
7
than
is
alkaline
is.
acidity.
therefore
reducing
at
or
the
it
is.
Acidity
(protons). The higher
solution
therefore
eect
environment. In
acidic
hydrogen
concentrations
acidic.
10
of
more
concentration
U
C
a
ion
their
o
pH
higher
i
n
The
hydrogen
v
indic ate
of
to
aected
presence
concentration,
enzymeactivity
measure
the
are
p
the
they
y
Figure 13
due
sensitive
r
e
is
▴
are
particular
temperature  °
overall
typic alenzyme.
2. Eects of pH
reaction
increases and
the
O
rate of
there
activity.
c atalysis
n
in
and
l
temperature
t
i
s
of
denatured and enzyme activity will fall.
completely.
decreases
actual
be
enzyme
y
As
stop
will
all
However,
molecules
P
Eventually,
enzyme
r
as
kinetic energy of
The
pH
Lower
sc ale is a
pH
values
greateracidity.
pH
by one unit makes
neutral. A solution at pH 6
pH6,
pH
4
is
100
times
more
acidic than pH 6, and so on.
Most enzymes have an optimum pH at which their activity is highest. If pH
stomach
increases or decreases from the optimum, ionic bonds between the amino acids
acidic hot
in the enzyme are altered. This changes the structure of the enzyme, including its
active site. As a result, the active site will no longer bind substrates or convert them
decaying plant
i
r
o
3
to products. Beyond a certain pH, the enzyme will be irreversibly denatured.
matter
t
a
large intestine
4
optimum pH at which enzyme
small intestine
optimum for most enzymes)
as pH increases or decreases
from the optimum, enzyme
ytivitca
a
activity is reduced. This is because
the shape of the active
emyzne
E
10
v
9
l
8
O
7
activity is fastest (pH 7 is
alkaline lakes
u
6
f
x
5
o
d
springs
2
n
Key
1
fit so well. Most enzymes are
denatured by very hih or low
pH, so the enzyme no loner
catalyses the reaction.
▴
Figure 14
pH
346
pH
variation in
enzymeenvironments
site is
altered so the substrate does not
▴
Figure 15
pH and enzyme activity
y
noitcaer fo etar
molecules
owing to increased
Molecules
Not all enzymes have the same optimum pH—in fact, there is a wide range.
This reects the varied environments in which enzymes work. For example, the
protease secreted by Bacillus licheniformis has a pH optimum between 9 and
10. This bacterium is cultured to produce its alkaline-tolerant protease for use in
biological laundry detergents, which are alkaline.
s
s
3. Eects of substrate concentration
Enzymes
c annot
of
molecules
in
graph,
a
between
distinctive
and
and
is
the
is
rate
been
formed
of
greater
the
the
is
increased,
rate at which
as
reaction.
(Figure
16):
substrate
and
released.
in
sites
of
the
are
As the
occupied at
substrate–active site
rate at which enzymes
concentration rises.
and
the
a
unavailable to other
active
substrate
Once
and
proportion
increases
concentration
seen
of
occupied
more
smaller
substrate
curve
site
reason,
and
the
enzyme
graph
activity
rises
less
is
and
less
▴
maximum.
214amino
which
a
acids.
phosphate
It
is
c atalyses
→
2ADP
the
The eect
of substrate
wild
type
form
a.
the
optimum
b.
the
temperature
of
the
enzyme, identify:
temperature
[1]
between
n
ATP + AMP
For
reversible
transferred
nucleotides:
1.
C
in
of
U
reactions
adenylate kinase consists of a single
Figure 16
concentration on enzyme activity
o
v
enzyme
polypeptide
i
n
Data-based questions: Adenylate kinase
The
substrate concentration
plotted
p
steeply as substrate concentration increases, but never quite reaches a
n
a
smaller
and
site.
O
on
relationship
this
molecules
frequently
active
movements
y
the
get
greater
the
r
e
If
reactions
a
For
aects
have
more
with
random
increase.
active
products
rises,
Therefore,
blocked.
that
substrate
more
to
t
i
s
c atalyse
are
until
will
of
binds
due
l
concentration
the
occur
occur
y
molecules
moment.
trend
site,
substrate
collisions
reaction
another
active
substrate
any
concentration
will
substrate
sites
y
is
an
its
the
r
to
the
collisions
c atalyses
there
bound
If
until
active
P
has
site
and
emyzne
However,
reaction
ytivitca
enzyme
a
substrates
liquids.
substrate–active
the
c atalyse
between
e
Collisions
o
d
The graph in Figure 17 shows the eect of temperature on
2.
fully
a.
the activity of ve forms of adenylate kinase. WT is the wild
denatured.
State
the
enzyme
i
r
o
type form. The other forms are mutants in which one amino
above which the enzyme is
25°C,
[1]
activity
at
each
35°C
of
of
and
the
wild
these
type
form of the
temperatures: 15°C,
45°C.
[2]
t
a
acid (either valine or alanine) has been changed to glycine.
V142G
600
f
x
V135G
A55G
A37G
l
300
10
E
0
v
150
20
rise
3.
Explain
wild
a
O
s / ytivitca
450
Using
4.
a.
15
50
the
with
reasons
form
and
and
Compare
evaluate
doubles
hypothesis that
every 10°C
temperature.
the
type
b.
30
40
50
60
5.
Using
the
changing
from
Figure 17
in
data,
activity
of
[2]
for the change in activity of the
the
enzyme
between:
45°C
[2]
55°C.
and
[2]
contrast
the
curves
for WT and
V135G.
temperature / °C
▴
this
enzyme
u
1–
WT
b.
[3]
data
the
alanine
in
the
55th
to
graph,
amino
glycine.
describe
acid
in
the
eect of
adenylate kinase
[2]
Source: S aavedra, H.G., Wrabl, J.O., Anderson, J.A. et al. Dynamic
allostery can drive cold adaptation in enzymes. Nature 558,
324–328 (2018). https://doi.org/10.1038/s41586-018-0183-2
347
Interaction
and
interdependence
Models: Use of graphs to show relationships between variables
A
graph
is
variables.
used
Two
to
show
axes
across
the
goes
up
graph.
the
the
x-axis
the
goes
across
independent
x-axis
and
from
An
le
e asy
to
to
way
bec ause
v ariable
the
relationship
in
between
this.
right
to
the
an
dependent
do
The
and
two
x-axis
the
this
letter
cross!
x
is
experiment
v ariable
is
a
is
is
on
step
in
the
A
two
scientic
hypothesis
variables,
it
This
of
graph.
type
the
results
graph,
performed
and
predictions
based
an
experiment
of
data
variable
enzyme
point
at
one
graph
shows
on
the
particular
the
added
the
it
results
are
is
as
look
at
between
level of the
This
If
c an
be
used
to
they
do
not,
then
relationship
It
line
is
is
c alled
usually
a
a
through
of
a
are
them
graph
this
shown
all.
and
will
a
“line
line
of
may be
best
be
a
in
the
useful
relationship
skill
Figure 18.
There is no relationship
between between
x and
y
y
x
to
x
x
0
y
is inversely
proportional
to
As
x
t” that
You should be able to
deduce
below
p
y is
new
curve, whether
o
i
y and
a
between the
variables,
x
y
evaluate
results match the model
possible to the data points but does not
variables;
x and
t
a
Figure 18
levels of the
u
E
▴
Figure17
0
x
a
v
x and
correlation between
other
x
0
directly proportional
348
y
There is a positive correlation
between
pass
y
l
f
x
O
0
as
There is a negative
and
overall
y
o
d
r
o
y
x
graph?
straight.
examples
n
positive
correlation between
at
in
needed. If the data points on the
this.
C
i
n
U
There is a
0
results
actual
independent
v
y
an
shape
the
been
y
Some
x
or
close
the
be
and
show
necessarily
plotted
y
to
curved
goes
hypothesis.
level of the
0
suggest
To test the
the
sketch
may
dependent
model—a simple
complex.
the
r
e
dependent
each
more
a
experimental
hypothesis
shown using a
is
in
have
as
variable.
hypothesis—do
shown
formulate
relationship
straight
indic ates that it is uncertain
would
lines,
result, or a
made. Oen the
n
a
is
to
were
O
on
be
is
expected
individual
This
y
experiment
When
something
with
an
of
an
with
page.
t
i
s
hypothesis,
an
is
graph
of
compared
investigation
c an
representation
are
graph
be
l
sketch
any
the
joined
values
may
x
increases there is
an exponential increase in
y
in
science.
y
between
If
the
It
measurements
r
rst
are
previous
independent
the
hypothesis.
points
if
P
a
result
the
what
on
y-axis.
The
repeat
on
that
plotted
plotted
variable.
mean
data
y-axis
remember
independent
e
The
graph
the
needed
s
s
goes
are
Molecules
C1.1.9
Measurements in enzyme-c atalysed
reactions
experiments
reliable.
Reliability
the
•
results
are
deliberately
to
enzyme
factors
that
could
change.
affect
control
In
a
Often
free
must
to
of
analyse.
what
levels
variable is commonly
concentration or pH.
be
kept
should
properly
designed
enzyme
experiment:
there is just one
easy
choice
variables
a
an
constant
be
to
monitored
enzyme
ensure the
regularly
experiment,
activity—apart
from the independent
variables.
variables—these
are
the
results
of
the
O
Dependent
not
has
enzyme
that
is.
in
are
showing that
investigated, so
experiment
independent
factors
Control
being
results
experiment. In an enzyme
n
all
do
test”.
variable
the
and
l
they
the
of
are
effect
the
researcher
concentration,
are
the
from
ensure
y
ensure
“fair
what
that
to
experiment
t
i
s
to
variable—are
•
a
the
types
factors
data
an
y
substrate
is
see
experiments,
variables—these
experiment
if
dierent
are
making
independent
repeating
P
Control
are
to
measurements,
by
r
are
temperature,
•
varied
variable,
Variables
In
There
variables—these
independent
use.
accurate
e
are
require
demonstrated
consistent.
Independent
they
is
s
s
Enzyme
experiment, the dependent variable is the quantity that is measured to calculate
of
your
of
reaction
own
to
products,
rates
experiment
else.
so
Reaction
the
units
to
variable.
is
or
an
is
the
independent
rate
important
secondary
rate
are
the
This
the
in
often
skill,
data
speed
change
is
whether
from
at
the
variable
c alled
an
which
should
you do this using data
experiment
substrates
amount
of
affect the
enzymeactivity.
c arried out
are
chemic al
converted
divided
for
nding
the
Allow
reaction
the
with
until
all
concentration
known
amount
substrate
the
happen
for
product
has
a
fixed
formed.
time
The
There
and
time
are
be
remains high.
of
substrate
been
and
converted
allow
to
the
approaches to
relatively short, so
reaction to continue
products.
reaction to go to completion.
two
measure the amount of
should
i
for
to
or
t
a
r
o
taken
a
the
up
).
o
Start
(mmol s
d
2.
substrate
second
rate:
reaction
used
per
n
substrate
the
millimoles
U
1.
example,
by
C
−1
time,
o
someone
changes
i
n
by
Only
v
from
rate.
dependent
p
C alculation
the
y
reaction
level
r
e
the
Measure the time
With both approaches, the quantity of product or substrate is divided by thetime.
With
enzymes,
starch
in
or
other
grams
per
cubic
c an
expressed
macromolecules,
decimetre
3
per
100 cm
starch
solution
volume
mass
of
or
reagents
solutions
E
molar
measured
enzyme
gram
a
of
1
as
of
a
concentration
concentration
100 cm
example,
of
solution.
100 cm
Grams
of 1%
Method
grams
(g)
or
milligrams
(mg)
decimetre
(dm
of
measurement
electronic balance
3
cubic
3
)
or
cubic
centimetre
(cm
)
pipettes
or
syringes;
measuring
cylinders
−3
moles
per
cubic
decimetre
(mol dm
grams
per
cubic
decimetre
(g dm
)
indirect
measurement
of
mass
and
volume
indirect
measurement
of
mass
and
volume
−3
acidity
pH
light
percentage
Table 2
For
Units
Celsius
▴
3
per
3
percentage.
temperature
absorbance
concentration is usually
grams
starch.
l
mass
contains
v
O
Q uantity
be
or
u
f
x
measured
(°C)
)
thermometer;
pH
absorbance(%)
meter;
digital
universal
temperature
probe
indic ator
colorimeter
Possible ways of measuring or determining the level of variables in enzyme experiments
349
Interaction
and
interdependence
The
following
example
enzyme-c atalysed
measuring
describes
reaction.
reaction
one
experiment
However,
there
are
to
investigate
many
other
the
rate of an
enzymes
and
ways of
rate.
s
s
Collecting and processing data: Measuring
c atalase activity
of
apparatus
c atalase.
the
test
one
could
These
before
of
be
a
the
toxic
most
used
sources
being
(for
reaction.
by-product
of
example,
have
to
to
be
with
c atalyses
metabolism,
enzymes
liver
investigate the activity
mixed
C atalase
widespread
would
used
Yeast
tissue,
and
into
other
kidney
macerated
injected.
and
oxygen.
mixed with
O
measuring
cylinder
water
water
peroxide
n
o
Figure 19
Apparatus for measuring c atalase activity
i
T
o investigate the eect of substrate concentration, you could measure the
reaction rate repeatedly using the same concentration of yeast but dierent
hydrogen peroxide concentrations. Alternatively, you could investigate the
eect of varying catalase concentration.
1.
u
l
a
E
v
O
f
x
t
a
r
o
d
▴
and
sources of the
then
y
C
U
hydrogen
water
o
v
i
n
3
0.8 mol dm
injected
oxygen
p
three-way tap
is
conversion of
tissue or germinating
t
i
s
r
e
yeast
water
the
n
water
peroxide,
is
the
be
y
seeds).
start
c an
How
in
c an
the
activity
Figure
19?
Include
of
c atalase
suitable
be
SI
measured
units
for
the
using
the
reaction
apparatus
shown
rate.
2.
What factors should be kept constant if investigating the eect of substrate
3.
How
concentration?
−3
c an
the
0.8 mol dm
hydrogen
peroxide
solution
be
diluted to
−3
make
4.
Why
concentrations
is
before
it
necessary
measuring
to
of
0.2,
0.4
macerate
c atalase
and
0.6 mol dm
other
activity
in
c atalase
?
sources
such
as
liver
tissue
them?
S afety goggles must be worn if this experiment is performed. C are
should be taken not to get hydrogen peroxide on the skin.
350
l
enzyme
to
19
c atalase.
y
C atalase
tube
Figure
contain
P
hydrogen
in
cells
r
into
shown
Yeast
e
The
Molecules
Data-based questions: C alculating rates of reaction
3
1.
3
10 cm
0.1%
1%
starch
40°C.
using
A
test
iodine
starch
was
solution
solution.
for
The
starch
solution.
was
was
The
mixed
reaction
done
rst
test
with
1 cm
mixture
every
that
of
2.
Ten drops of a commercial catalase solution were
was kept
30
added to four reaction vessels containing a 1.5%
seconds,
s
s
at
of
amylase
hydrogen peroxide solution. Each of the solutions had
showed no
been kept at a dierent temperature. The % oxygenin
present aer 8 minutes.
the reaction vessel was determined using a data
C alculate
mixture
in
the
mass
of
starch
in
the
reaction
grams.
[2]
a.
Explain
b.
Convert
the
to
mass
milligrams.
of
starch
Use
the
c.
Plot
d.
Discuss
graph
this
the
rate
at
each
reaction
from
“per
a
graph
of
“per
reaction
minute”
second”.
[1]
whether
should
51°C
22.0
v
a
linear
sc ale.
[2]
C
n
10
20
30
40
50
60
70
time / s
o
Percentage of oxygen concentration over time at
various
temperatures aer adding c atalase to a 1.5% hydrogen peroxide solution
i
t
a
r
o
d
Figure 21
of
o
i
n
18.0
0
▴
p
% / n e g yx o
19.5
18.5
instead
[3]
for the
Thinking skills: Choosing a method to determine reaction rate
ATL
processing
is
easier
in
rate
of
amount
these
reaction
Paper
discs
dierent
reaction
of
reactant
enzyme
c an
be
data
into
a
form
b.
per
describe
Lipase
fatty
measured as
product
experiments,
c atalyses
acids
reaction
second.
the
breakdown
andwater.
as
the
F atty
of
acids
triglycerides to
aect the pH of the
reactionproceeds.
how the
c.
Gelatin
cubes
in
the
protease
enzyme
c atalase
are
of
hydrogen
that
are
c an
digested
be
by papain, which is a
extracted
from
papaya
fruits.
added
d.
concentrations
produces
or
is
determined:
soaked
E
to
the
of
raw
rate
a
each
converting
Reaction
l
For
involves
interpret.
v
O
change
to
u
that
f
x
D ata
a.
Figure 20
used
sc ale
34°C
20.0
U
▴
21°C
19.0
logarithmic
y
21.0
20.5
be
a
[4]
rate against
4°C
r
e
21.5
[1]
rate of
O
t
i
s
y-axis
the
temperature.
[1]
temperature.
to
determine
digested
amylase.
of
to
n
b.
percentage
l
Convert
by
oxygen
y
d.
minute
in
[1]
reaction
per
variation
y
C alculate
mass
the
zero.
P
c.
this
time
r
at
e
logger in a set-up similar to Figure 20.
a.
The
enzyme
c atechol
oxidase
c an
be
to
yellow pigment in
extracted
from
peroxide. The
bananas.
It
converts
c atechol
a
oxygen bubbles.
cut
air
fruit.
to
The
turn
yellow
pigment
reacts
with
oxygen in the
brown.
351
Interaction
and
interdependence
Mathematics: Using logarithmic sc ales
Most graphs have linear scales on the axes. This means that
Logs
the intervals between values on the axes are
number
are
exponents.
for
the
Usually
10
is
used as the base
exponent.
100
=
10
, so log 100
equally. Sometimes a logarithmic scale is more useful.
=
s
s
2
equal—for example, the values 0, 1, 2, 3 are spaced
2
3
1,000
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To
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logarithmic.
2.5465
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a
v ariable
example, 352
=
10
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r
Logarithmic
c an
Example
the
very
wide
range
of
v alues
and
it
is
dicult
to
The
small
v alues
or
se e
the
dierences
enzyme
question
them
on
a
graph.
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are
also
useful
for
inc re ase
or
de c re ase
a
line ar
in
a
sc ale,
v ariable
the
at
a
graph,
In
a
log-linear
is
linear.
for
at
35°C
a
plot,
it
be
a
straight
line.
one
sc ale is logarithmic and the other
is
sc ales
available
c an be logarithmic.
you
c an
plot
logarithmic
45°C.
Is
with
there
rising
an
the
values
exponential
temperatures?
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Plot the log values on a graph with temperature on the
for enzyme activity to base 10logs.
x-axis and the log values for enzyme activity on the
are logarithmic.
with
at
activity
2.
y-axis. You can use an axis break at the origin.
for both types of plot.
graphs
enzyme
1.
3.
Alternatively,
in
y
paper
both
sc ales
data-based
for enzyme
temperatures: 68 at 15°C, 123 at 25°C,
536
with
or
plot,
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described
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n
With
351
y
exponential.
page
l
the
243
truly
on
testing
activity
whether
experiment
betwe en
Is it possible to draw a straight line through (or close to)
sc ales
p
all the points? If so, what conclusions can you draw?
by
converting
the
data
to
logarithms
(logs).
o
v
i
n
Data-based questions: Interactions between temperature and enzyme activity
1
C
Changes to the amino acid sequence of enzymes
U
(isopropylmalate dehydrogenase) from six dierent
in hot conditions. The graph shows the relationship
enzyme activity at 25°C. The graph is a log-linear plot.
is
sc ale
for the
a.
the
Which
at
Using
microbe
c atalyses
25°C?
trend
the
problems
does
data
that
graph?
the
enzyme?
E
4.
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this
has
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has
the
the
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heat-stable
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a
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of
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l
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advantage of using a logarithmic
microbe
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em y z n e
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x
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molecules have denatured due to unfolding, and
a
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Bs
ta
i
r
o
between the temperature at which half of the enzyme
10
o
d
species of microbe, three of which are adapted to live
lomµ / C°52
in Figure22 shows data for the same enzyme
Sc
n
they convert substrates to products. The graph
nim
can aect how heat-stable they are and how quickly
30
form of the enzyme
40
50
60
denaturation
Saccharomyces cerevisiae
graph
show?
[2]
Bacillus subtilis
(Bs)
Bacillus cereus
(Bc)
(Sc)
Methanothermobacter
thermautotrophicus
Sulfolobus tokodaii
the
graph,
would
Bacillus subtilis
a
hot
Sulfolobus tokodaii
in
(Mt)
by:
▴
Figure 22
Source:
Akanuma,
spring
at
80°C
or
higher
the
human
intestine
at
of
S.,
Bessho,
M.,
mesophilic-like
Kimura, H. et al.
c atalytic
properties
[2]
a
thermophilic
37°C.
stability.
enzyme
Sci
Rep
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9,
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(2019).
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org/10.1038/s41598-019-45560-x
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beexperienced
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Thermus thermophilus
thermal
352
90
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reaction most quickly
Establishment
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https://doi.
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Molecules
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Suggest
why
there
are two
state.
The right-hand graph in Figure 23 shows energy changes for the same reaction
peaks
rather than one in the
graph
for
t
a
by
when it is catalysed by an enzyme. The net amount of energy released is unchanged
an
a
reaction
c atalysed
enzyme.
but the activation energy is smaller
. This is because the bonds in the substrate are
4.
Explain
how
lowering the
weakened as it binds to the active site, so less energy is needed to break them. As a
activation
energy
increases the
f
x
transition state
rate
of
the
enzyme-controlled
reaction.
a
activation
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energy
E
ygrene
v
O
l
u
result, the rate of the reaction increases—typically by a factor of a million or more.
transition state
activation
energy
substrate
substrate
◂
product
product
Figure 23
Graphs showing
activation energy without an
enzyme (le) and with an enzyme
progress of reaction
progress of reaction
(right)
353
and
interdependence
LHA
Interaction
C1.1.11
Intracellular
and extracellular
enzyme-c atalysed reactions
Enzymes
are
synthesized
by
are
ribosomes
use
inside
in
reaction
is
the
the
by
and
digestive
system,
where
the
other
enzyme
matrix.
of
One
of
food
is
of
larger
the
by
glycolysis. The
group to the glucose
example, enzymes of the
the
to
Krebs
cycle enzymes is
malate.
macromolecules. The
plasma
organisms,
digested
as
for
hexokinase in the cytoplasm.
fumarate
through
multicellular
solid
such
phosphate
organelles—or
breakdown
pass
synthesized
enzymes,
membrane and enter
this
process
O
humans
the
inside
a
t
i
s
For
pathways
of
conversion
then
known as
are
n
c an
(also
They
Intracellular
y
c atalyse
produced
work
mitochondrial
c atalyses
exoenzymes
addition
c atalysed
reticulum.
it.
free ribosomes in the cytoplasm.
metabolic
the
enzymes
in
by
enzymes
outside
l
which
monomers
cells.
work
endoplasmic
work
occurs in the
extracellular enzymes.
Unicellular heterotrophic archaea, bacteria and fungi cannot take in
r
e
y
macromolecules because their cell walls form a barrier so they cannot perform
endocytosis. To feed on macromolecules, these microorganisms secrete
p
exoenzymes. These enzymes work outside the cell to convert the macromolecules
o
2.
Suggest what the dark blue organelles are in the image.
n
U
1.
Suggest
a
vesicles,
3.
are
Suggest
for
of
storing
digestive enzymes in
secreting
them
immediately aer
produced.
reasons
for
the
variation
in
size
of
the
vesicles
i
in these cells.
◂
Figure 24
False-colour sc anning electron micrograph of
enzyme-secreting cells in the pancreas, with the cytoplasm
coloured
u
l
pale blue.
Before secretion,
inside membrane-bound
sacs c alled
the enzymes are stored
vesicles (coloured
yellow).
The enzymes are secreted into the small intestine via the
a
E
v
O
f
x
t
a
r
o
d
o
they
reason
instead
pancreatic duct
c arbohydrates,
C1.1.12
and
aer activation they help the digestion of
fats and
proteins
Generation of heat energy by the
reactions of metabolism
The
conversion
example,
reactants.
354
C
i
n
Questions
v
into monomers, which can then be absorbed across the plasmamembrane.
in
of
energy
metabolic
The
from
one
reactions,
additional
energy
form
the
is
to
another
products
ultimately
is
never
contain
less
converted
to
100%
ecient.
energy than the
heat.
For
y
cycle
is
Extracellular
and
P
Krebs
M any
c atalyse
cell
r
This
intracellular
the
the
synthesized
glycolysis
Some
fumarase,
are
enzymes
reaction
molecule.
cell,
to
ribosomes.
from
e
Intracellular
rst
attached
the
by
released
s
s
exoenzymes)
Molecules
a
and
body
mammals
use
temperature
metabolism
example,
releases
during
the
more
exercise,
cooling
In
conditions,
very
mammals
does
not
of
the
raise
rele ase
overall
contracting
metabolic
temperature
known
as
is
falling
shivering.
by
rate
do
together
their
when
this
will
purpose.
in
is
an
in
groups
neighbours.
bas al
several
experience
This
For
sweat and uses
heat.
huddle
rele ase d
c an
this
to
Birds
metabolism
w ays.
A
involuntary
adaptation
to
produce
▴
by
the
muscles
to
raise
the
core
temperature.
this
tissue
Figure 25
M any
compost
mammals
have
brown
fat
tissue.
Cells
in
have
large
numbers
Decomposing manure or
c an become very hot, as this
of
that
c arry
out
uncouple d
respiration.
This
allows
them
shows.
What
organisms
l
steaming heap
mitochondria
to
y
contractions
he at
metabolic
penguins
They
for
produces
P
muscle
body
he at
environment. Sometimes
r
core
by metabolism to maintain
their
needed
excess
emperor
he at.
of
is
human
metabolic
their
whose
the
than
dissipate
enough
human
heat
that
e
and
cold
adv antage
to
generated
than
s
s
evaporative
take
heat
greater
LHA
Birds
he at
by
oxidizing
substrates
without
producing
ATP.
n
generate
y
are responsible for this metabolic heat
generation?
The
electron
false
to
colour,
see.
micrograph
to
What
make
would
pathway
nine
cells
for
to
one
In
all
molecule
tissue than adults.
Suggest
when
that
Figure 26
having
brown
a
relatively
adipocytes
of
the
In
will
more
be
brown
active in
Electron micrograph of part
of a heat-generating
brown adipose cell with many mitochondria (dark green) in the
cytoplasm
(pale green) and
droplets of fat
(pale yellow).
The cell’s
nucleus (purple) is partly visible (lower right)
initial
and
have
enzyme-c atalysed
small
in
substrate
intermediates
thousands of
reactions
c ause
transformations happen not in
steps.
Figure
chain
into
nine
Glycolysis
one
droplets in the
pathways
reactions
chemic al
of
glucose
product.
given
easier
BREAD
Most
game
involves
been
BLEED
this.
involve
has
hibernate.
Together,
these
steps
form a
BLEND
BLIND
BLINK
27
is
an
reactions.
dierent
means
reactions,
the
of
pyruvate
other
(see
product
analogy.
▴
but
of
why
adipose
large
end
convert
enzymes.
forms
Suggest
animals
infants
26
structures
natural colour of this cell
TREAD
chemic al
L arge
word
pathways
to
fat
Figure
BREED
of
sequence
The
glycolysis
dierent
respiration.
a
C
by
in
pathway.
metabolic
used
do
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n
is
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but
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Most
in
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v
O
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v
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n
3.
U
u
Cyclic al and linear
in metabolism
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why
cytoplasm.
4.
d
r
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x
C1.1.13
Explain
the
p
havebeen?
2.
the
y
r
e
1.
O
t
i
s
Questions
For
example,
Figure 27
glycolysis
Figure 28). The metabolic
chemic al
reactions,
c atalysed
by
“glucose-splitting” and is part of cell
one
molecule
reaction,
a
of
substrate
is
converted
six-c arbon sugar is split
355
and
interdependence
LHA
Interaction
s
s
Figure 28
Glycolysis
two
dierent
molecule
twice
the
chain.
This
and
a
cycle,
is
every
in
another
the
reaction.
next
two
Two
CO
is
the
pathways.
a
product
of

p
+


2
glycerate phosphate
i
n
6
C alvin

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
6 P
U
6 P
cycles
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be
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Krebs
cycle.
group C
2
res
cycle
C
compound
6
+

+

+
+

+

CO
2
C
5
compound
o
i
glucose and
CO
2
u
C1.1.14
Allosteric sites and non-
competitiveinhibition
l
a
E
v
O
f
x
t
a
other compounds
Every
have
enzyme
a
unbind.
second
enzyme
Binding
sites
to
be
and
allosteric
binding
inhibit
and
site
on
an
active
site
c alled
enzymes
properties
site
of
c atalysis
by
to
an
a
which
c ause
the
an
evolved
binding
substrates,
so
enzyme’
s
the
to
enzyme
bec ause
the
active
it
will
is
to
change
known
they
two
M any enzymes
c an bind and
shape, so the
site.
In
some
c atalyse
site
as
allow the activity of an
alternative
reversibly
allosteric
are
binds.
substance
site.
enzyme
the
they
so
substrate
specic
between
enzyme
and
the
allosteric
have
the
dierent
Switching
activates
enzyme
with
site,
where
unbinding
is
regulated.
prevents
compete
an
active
binding
Allosteric
the
has
second
structure
356
are
reaction and a
+
d
r
o
1 TP
substrate

+
6 TP
output:
second

n
5 TP
and
compound
C
6 P
cycle
TP
C
3 P
3
o
3
v
3 RuBP
a
the
unusual
one
which
cycle
acetyl
+
More
of
cycles,
C alvin
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
2
is
latter stages of the chain happen
y
3
are
r
e
C1.3.17 and C1.2.12
input:
the
examples
chapters,
cycles are described in detail in Sections
into
which
O
of
converted
very common and metabolism as a whole is
intermediate
versions of the
fully
means
interdependent
the Krebs cycle. These
more
is
n
pathways
In
these
l
metabolic
interlinked
reactions.
of
y
of
of
network
One
molecule.
a
substrate
C alvin cycle and
glucose
in
sugars.
(glyceraldehyde-3-phosphate),
t
i
s
Simplied
per
reaction
sugar
Branching
of
Figure 29
next
three-c arbon
other
a
states
reaction.
inhibited.
rather
than
alters the
c ases, binding to
the
non-competitive
In
other
c ases,
Substances that
active site do not
inhibitors.
y
the
the
P
for
of
r
into
▾
e
▴
Molecules
LHA
substrate
competitive
inhibitor
non-
s
s
competitive
inhibitor
while a
inhibitor changes the
inhibitor remains bound
bind to the active
active site so substrates
to the active site,
site of the enzyme
cannot bind
substrates cannot bind
Figure 30
c annot
c atalyse
substrate
the
the
site
active
inhibitor
will
if
the
the
enzyme
With
many
“winner ”
of
vac ant,
in
is
this
more
always
will
substrate
arrive
and
at
the
bec ause
inhibitor
As
long
structurally
remain
enzyme
similar
unlike
bound
to
the
for
substrate or an inhibitor
rst
and
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extent of inhibition
the
competitive
low
and
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the
until
molecules
active
site
increases
from
a
the
than
rst.
in
inhibitor
substrate
the
inhibitor
is
substrate
binding
to
the
not
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concentration
enzyme
This
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is
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concentration
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c annot
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f
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and
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so
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non-competitive
of
relatively
inhibition
inhibitors,
graph.
is
molecule
concentration
extent
almost
a
products
are
site.
t
a
on
be
an
Whichever
r
o
shown
of
concentration
the
non-competitive
a
active
an
o
substrates
inhibitors
s ame
into
d
uninhibited.
converte d
the
of
bind
n
increased,
to
site
c annot
U
the
is
prevent
site
bind.
greater
If
Competitive
bind
active
C
could
not
the
substrate.
active
molecule
becomes
are
the
c an
to
substrate
i
n
When
they
than
re action.
they
the
o
longer
its
so
bind
bound,
v
substrate,
inhibitors
remains
p
the
enzyme
inhibitor
y
the
r
e
as
O
t
i
s
reversibly to an active site
n
Competitive inhibition as a
consequence of an inhibitor binding
Competitive
l
y
C1.1.15
y
P
▴
competitive
e
a non-competitive
the substrate can
r
no inhibitor so
no inhibitor
of reaction
l
a
noitcaer fo etar
E
v
O
competitive inhibitor
non-competitive inhibitor
substrate concentration
▴
Figure 31
Eect
of substrate concentration on the rate of an enzyme-c atalysed
with no inhibitor (orange) and
with a xed
reaction
low concentration of a competitive inhibitor (red)
or non-competitive inhibitor(blue)
357
LHA
Interaction
and
interdependence
Statins—an example of a competitive inhibitor
Statins
are
medicines
that
work
by
competitive enzyme
H
They
are
used
which
contribute
to
treat
high
blood
cholesterol,
HO
HO
COOH
c an
to
heart
COOH
disease. Statins bind to
s
s
inhibition.
O
OH
the
active
site
of
the
enzyme
HMG-CoA
reductase. The
H
O
SCoA
full
name
of
this
enzyme
is
3-hydroxy-3-methyl-glutarylO
H
A
reductase.
It
c atalyses
one
of
the
reactions
e
coenzyme
HMG-CoA
the
in
liver
metabolic
cells.
pathway
This
used
reaction
is
to
the
synthesize
cholesterol
r
in
rate-limiting step in the
lovastatin
pathway,
so
if
statins
lower
the
rate,
less
cholesterol
produced
by
the
body.
A
Structural similarities between HMG-CoA (the
person with high-blood
substrate of HMG-CoA reductase) and
must
receive
cholesterol
levels
the
to the active site and act as a
reduced enough but not too much.
O
t
i
s
Thinking skills: Evaluating and defending ethic al positions
ATL
Chemic al
weapons
of
the
For
enzyme
would
example,
not
production
exist without the activities
sarin
is
a
essential
and
some
scientists
acetylcholinesterase
has
a
critic al
role
chemist
used
be
Haber
work
in
as
“the
received
banned
21st
father
the
by
century.
1918
of
and
used
several
Does
a
treaties,
Schrader
Prize
in
during
chemic al
Chemistry
during
have
the
First
use
been
of
World
time
the
instrumental
peacetime
war
he
a
award
in
chlorine
War.
fertilizers
scientist
have
However,
ceremony
gas
as
is
a
bec ause
his
chemic al
quoted
belongs
to
yields.
encouraging and
Haber
belongs
recognized
science?
for
developing the chemistry behind the industrial
to
as
the
country”.
weapon
saying:
World, but
Should
Haber
for important contributions to
o
Regulation of metabolic pathways by
i
feedback inhibition
The
complex
ensure
they
u
pathways
product
l
a
E
v
O
f
x
t
a
r
o
d
C1.1.16
the
“During
sarin
deserve
nerve agents”?
Nobel
developing
developed as
as
Such
agricultural
n
his
described
being
the
was
U
Fritz
in
it
boycotted
been
C
Despite
has
Schrader
however,
i
n
weapon.
been
Gerhard
L ater
fertilizer.
increasing
o
insecticide.
had
in
p
Haber
v
German
an
ammonia
been
in the functioning of the nervous system. It was discovered
by
of
competitive inhibitor
y
scientists.
r
e
of
n
y
competitiveinhibitor
to
statins (such as lovastatin
correct dose of statins, so
shown here) allow statins to bind
are
l
cholesterol
are
of
network
produce
controlled
the
last
reaction.
The
enzyme
that
This
binding
changes
as
the
inhibition
will
o
end
and
the
whole
of
the
metabolic
This
is
a
a
will
ecient
has
an
be
open
method
If
enzyme
will
of
cell
but
This
too
in
is
regulating
a
In
which
these
the
the
more
end
more
of
the
metabolic
of
end
product binds.
c atalysis
of
end
This
inhibition
M any
systems, the
product—inhibits the
example
of
regulated to
much.
preventing
an
of
be
too
end
pathway.
minimal
produce
the
to
much
the
must
not
system.
site,
synthesis
be
to
site
active
bound.
prevents
there
a
inhibition
allosteric
the
feedback.
rst
in
substance,
pathway—c alled
of
remains
and
pathways
each
the
shape
the
product,
of
feedback
in
negative
inhibit
pathway
very
the
pathway
end
by
inhibited
product
also
increasingly
little
is
metabolic
reaction
rst
long
of
enough
for as
non-competitive
product
is
eectively
product.
the
end
rst
If
made, it
switches
there is too
enzyme. The
product.
pathway.
Bec ause the
rst enzyme is inhibited, the products of the intermediate steps in the pathway—
358
y
is
Figure 32
P
▴
Molecules
are
only
used
not
accumulate
The
metabolic
in
a
as
steps
cell
if
pathway
threonine
into
by
product.
in
the
in
isoleucine
cells
is
making
end
an
the
product
that
end
is
product—do
not
being
initial
of
substrate
substrate does not fit the
used.
(threonine)
active site when the end
converts the amino acid
example
LHA
which
threonine
product is bond
feedback inhibition
in active site
an
end
s
s
enzyme 1
Through
a
series
of
ve
reactions,
the
amino
acid
threonine
enzyme
(threonine
is
converted
to
isoleucine.
As
the
concentration of isoleucine
activated if
deaminase)
up,
it
binds
to
the
allosteric
site
of
the
rst enzyme in
inhibitor
the
chain,
threonine
deaminase.
As
a
result, it acts as a non-
unbinds
e
builds
intermediate A
r
competitive
inhibitor.
enzyme 2
enzyme 3
inhibits the first
intermediate C
enzyme 
O
t
i
s
enzyme in the
chemic al changes to the active site
pathway by
c aused by the irreversible binding
intermediate 
binding to its
enzyme 
allosteric site
ofaninhibitor
of
reversible.
metals
of
to
–SH
enter
body
Some
heavy
target
specic
one
converted
the
formation
complex
cysteine
these
pollutants
inhibitor,
so
they
to
a
of
that
a
c an
of
to
never
the
as
toxic if they
environment.
Such
rele ased,
This
a
Figure 33
occurs in the
very
inhibitors
enzyme’s
active
le aving
a
again.
end product
(isoleucine)
are
site.
the
bound
produces
c atalyst
i
inhibition.
it
are
permanently
bond.
work
the
and
becomes
cov alent
wherever
metals
enzyme.
bind
product
however,
r
o
mechanism-based
acid
dangerous
The
inhibitor–enzyme
amino
reason,
substrate,
▴
non-specic
bec ause they bind
n
by
be
are
have all
o
site
are
the
the
this
inhibitors
to
lead
far
irreversible.
U
active
they
would
siteopen.
in
For
and
enzymes
d
the
and
similar
substrate
active
groups
enzyme.
irreversible
structurally
The
an
of
so
be
C
of
mercury
range
also
i
n
structure
the
as
wide
c an
o
irreversibly
such
a
described
inhibition
v
inhibitors
inhibition
p
Heavy
enzyme
However,
y
examples
been
r
e
The
n
inhibition as a consequence of
y
end product
l
Mechanism-based
y
P
intermediate B
C1.1.17
to
stable
This
is
c alled
t
a
Mechanism-based inhibitors c ause harm to an organism, bec ause every molecule
of
inhibitor
an
c an
organism
based
the
kill
ever
P
the
Some
order
to
one
enzyme
inhibited
living
kill
gram-positive
a
substances
E
C
3
in
mechanism-based
O
H
inhibitor.
of
l
to
inactivate
function
organisms
another
bacteria.
enzyme
molecule.
enzyme
is
vital
synthesize
organism—for
In
addition,
inhibitors
The
and
and
may
a
mechanism-
example, penicillin
some
they
inhibitor
there is a lethal
chemic al
are some of the most
discovered.
v
O
are
the
inhibitor
method
weapons
toxic
of
enzyme
this
if
u
concentration
uses
permanently
f
x
kill
O
N
N
◂
N
N
Figure 34
Novichok agents are
mechanism-based
inhibitors of the enzyme
F
F
acetylcholinesterase.
They are lethal in
minute quantities and
Novichock
A-230
have been implic ated
Novichok A-234
in some high-prole attacks on individuals
359
LHA
Interaction
and
interdependence
Penicillin—an example of mechanism-based inhibition
bursting (lysis). Penicillium can then monopolize the food
low external solute concentrations cause water to enter by
source. The fungus only does this when food supplies are
osmosis and hydrostatic pressures inside the cell become
limited, because resources are needed for the synthesis
very high. The enzyme transpeptidase is very important
and secretion of penicillin.
s
s
The cell walls of bacteria prevent them from bursting when
in the process of cell wall formation, because it
fungus
growing on the
peptidoglycan molecule that forms the entire
r
e
Penicillium
cross-links strands of carbohydrate into one huge
surface of the agar
cell wall. When bacteria grow, one enzyme
gel
breaks these links, allowing the wall to expand.
and
releasing
a
S aprotrophic bacteria and fungi compete for
few small colonies
of
bacteria
diffused
from the fungus
in dead matter and then absorb the products
produces a chemical known as penicillin,
which is a mechanism-based inhibitor. It binds
to the active site of transpeptidase in the cell
large colonies of
of the enzyme from binding. Penicillin forms
where
p
bacteria
a permanent covalent bond with a particular
v
penicillin has not
amino acid in the active site, binding irreversibly
▴
work to reform these links. As a result, the cell
killed
Figure 35 Alexander Fleming’s petri dish which rst
of bacterial growth by penicillin from
showed the inhibition
a mycelium ofPenicillium
n
U
wall is weakened and the bacteria are killed by
being
C
working but the transpeptidase enzyme cannot
not
i
n
are
cross-links in the bacterial cell wall continues
o
reached so bacteria
with the enzyme. The enzyme that breaks
y
r
e
walls of bacteria and prevents the substrate
O
t
i
s
through the agar gel
of digestion. The fungus Penicillium notatum
n
extracellular digestion of carbon compounds
where
has
y
penicillin
l
food because they both secrete enzymes for
Linking questions
are
o
What
examples
of
structure–function
relationships
in
biologic al
i
macromolecules?
a.
Explain
the
enzyme
b.
u
l
a
E
v
O
f
x
t
a
r
o
d
1.
Explain
relationship
activity.
the
role
played
semi-conservative
c.
O utline
the
structure.
2.
What
between allosteric enzyme shape and
(C1.1.14)
by complementary base pairing in
replic ation.
structure
of
(D1.1.2)
phospholipids
and
their
role
in
membrane
(B2.1.1)
biologic al
processes
depend
on
dierences or changes in
concentration?
a.
Outline
the
a
is
nerve
concentration
returned
to
changes
resting
that
potential.
must
occur
when
the
axon of
(C2.2.2)
+
b.
Explain
of
c.
ATP
.
how H
Explain
how
the
concentration
360
concentration
c an
be
used
to
power
the
production
(C1.2.15)
homeostatic
c an
be
regulation of blood glucose
achieved. (D3.3.3)
y
P
penicillin into it
Transpeptidase then remakes the links.
C1.2
Cell respiration
In
living
systems,
while
reaction.
out
Bacteria
source.
from
the
In
oor.
loc ations
As
Figure
a
1,
on
result,
the
a
of
energy-releasing
energy-absorbing
seabed,
food
white
of
oxidize methane as an
the
a
type
type
chain
substrate
methane
c an
is
frozen
methane.
The ice worms (Sirsoemethanicola) consume the bacteria
on
the
that
methane.
2 O
4
CO
2
energy
2 H
+
2
at
O
2
glucose
is
FAD.
in
powering
parenchyma
cell
starch
is
leading
molecules
the
surrounded
grains.
M any
by
an
usable
of
electrons
ATP.
In
organelle
are
use
to
the
c alled
also
an
C1.2.7
Role
of
NAD
cell
C1.2.2
processes within cells
C1.2.8
Conversion
f
x
Energy
transfers during
interconversions
respiration
producing
using
energy
released
E
Dierences
anaerobic
as
a
system
ATP within the cell
compounds
C1.2.5
a
for
Cell
ATP and
l
C1.2.4
between
v
O
ADP
net
withenergy
and
from
c arbon
cell
respiration
aecting
C1.2.10
C1.2.11
reduced NAD
transport
▴
Figure 2 A parenchyma cell from a
voodoo lily
AHL only
as
a
c arrier
of
hydrogen
and
oxidation
by
removal
of
hydrogen
respiration
ATP
cell
of
and
Conversion
glucose
to
pyruvate
by
stepwise
reactions
in
glycolysis with a
means
regenerating NAD in
reduced NAD
of
pyruvate
to
lactate
as
a
of
respiration
Anaerobic
Oxidation
cell
and
respiration
in
yeast
dec arboxylation
of
and
its
use
pyruvate
in
as
a
brewing andbaking
link
reaction
in
aerobic cell
respiration
C1.2.12
of
Oxidation
ATP
and
Transfer
and
dec arboxylation
of
acetyl
groups
in
the
Krebs
cycle with a
reduced NAD
of
energy
by
reduced
NAD
to
the
electron
transport chain in the
mitochondrion
C1.2.14
the
of
anaerobic
C1.2.13
between
aerobic cell
Variables
C1.2.9
yield
respiration in humans
C1.2.6
yield
u
C1.2.3
supplies
molecules
amyloplast, which
during
Life
and
electron
visible.
energy withincells
ATP
energy
molecules such as
ATP
distributes
that
of
storage
Figure 2, the nucleus of the
i
molecule that
form
in
energy-rich
production
their
more
a
later
t
a
the
of
of
d
as
the
mitochondria
r
o
ATP
to
transfer
production
SL and HL
C1.2.1
breakdown
for
o
contains
stages,
Reduced
The
into
stored
n
chain,
done
starch.
be
U
and
or
converted
y
glycogen
be
c an
o
as
to
they
C
such
need
Alternatively,
i
n
ATP
.
v
molecules
as
in the Gulf of Mexico
p
How is energy distributed and used inside cells?
such
Figure 1 These ice worms (Sirsoe methanicola) are
a depth of 800 m
r
e
becomes reduced
O
t
i
s
▴
CH
n
y
becomes oxidized
Energy-rich
l
grow
seeps
emerge in the
y
oflight.
a
methanophiles
certain
ocean
are
are
P
absence
c alled
At
reactions
reactions
r
energy
oxidation
reduction
e
reaction
s
s
What are the roles of hydrogen and oxygen in the release of energy in cells?
rate of
Generation
of
a
proton
gradient
by
ow
of
electrons
along
the
electron
transport chain
C1.2.15
Chemiosmosis
and
C1.2.16
Role
as
of
oxygen
the
synthesis
terminal
of
electron
ATP in the mitochondrion
acceptor
in
aerobic
cellrespiration
C1.2.17 Dierences between lipids and carbohydrates as respiratorysubstrates
361
Interaction
and
interdependence
C1.2.1 ATP as the molecule that distributes
energy within cells
adenine
phosphate
Nucleotides
grops
•
a
five-c arbon sugar
•
one
ATP
is
nucleotide
are
a
ATP
is
oen
for
chain
described
temporary
it
consists
three
and
as
base
adenine,
the
of
them
energy
of
is
parts
of
it
suitable
for
thisrole:
nitrogen blue and
ATP
is
and
other
is
ATP
c annot
stable
at
c annot
bound
organelles
energy.
was
conversion
to
is
to
cell.
freely
of
ADP
and
there
for
would
bec ause it is
transfer
The
between
properties
of
ATP
through the cytoplasm
neutral (as in cytoplasm).
phospholipid
cell
and
be
ATP
its
bilayer
movement
of
membranes. This
between
membrane-
controlled.
c an
easily
be
removed
and
reattached
by
reactions:
ADP
phosphate
many
often
+
phosphate
releases
processes
be
an
a
energy
relatively small amount
within
excess.
+
This
the
cell.
would
If
be
more
energy
wasted
by
Life processes within cells that ATP
supplies with energy
Cells
need
energy
for
three
main
types
of
activity.
u
1. Synthesizing macromolecules
Anabolic
l
a
E
v
O
f
x
t
a
r
o
i
C1.2.2
cell,
o
d
using ATP to supply energy for a process?
group
enough
heat.
move
the
c an
O
are the dierences
between using c ash to buy something and
to
a
2
ATP
This
released,
cells
n
U
of
H
c an
o
Hydrolysing
of
condensation
+
it
C
ATP
out
within
v
i
n
and
close
through
diffuse
phosphate
hydrolysis
so
p
it
third
levels
freely
means
The
•
pH
pass
water
the
y
ATP
•
in
the
of
energy
aqueous solutions in the cell.
r
e
•
soluble
for
charged.
O
•
ve-
n
dierent
oxygen
•
What
between
negatively
and
the
groups. The phosphate
currency
energy
t
i
s
hydrogen white,
and
the
phosphate
each
storage
of
three parts:
l
Black atoms are c arbon,
Figure 4
in
of
be
to
re actions
endothermic
conversion
time
a
replic ation,
from
of
monomer
RNA
that
link
monomers
and
therefore
ATP
to
is
in
ADP.
linked
to
unlikely
One
the
transcription
or
together
to
more
growing
and
into
happen
ATP
molecules
polymer.
proteins
large
without
in
polymers
coupling
is
used
Synthesis
translation
of
all
would
them
every
DNA
during
require
energy
ATP.
2. Active transport
Pumping of ions or other particles across a membrane against the concentration
gradient requires energy from ATP
. The energy is used to cause reversible changes
in the conformation (shape) of the pump protein. When the pump is in one
362
y
groups
and
consist
r
ribose
They
groups.
bec ause
sugar
DNA.
Adenosine triphosphate
phosphorus yellow
▴
phosphate
c arbon
make
red,
more
and
e
a
or
processes
(ATP).
RNA
y
Figure 3
subunits
nitrogen-containing base
used
▴
the
a
P
ribose
are
•
s
s
three
Molecules
conformation, the particle can enter it from one side of the membrane. When
the pump is in the other conformation, the particle can exit on the other side of
the membrane. One of the two shapes is more stable than the other. ATP is used
to cause the change from the more stable to the less stable conformation. The
change back to the more stable conformation happens without the need for
s
s
energy.
3. Movements
for
require
energy
example,
to
transport
when
of
human
across
from
place
system
large
each
to
other.
of
The
change
during
move
arrays
amounts
to
apart
during
to
the
cells
moved—
vesicles
shape
of
a
cell,
Some
of
and
infection.
myosin
for
these
use
example,
Muscle
laments,
cells
which
movements
is
contains
more
rele ase d
is
some
protein
the
in
a
small,
the
membrane
in
the
pump
from
a
and
sucient
or
this
a
is
for
many
ADP.
Therefore,
The
processes
to
another
substrate
in
a
mole cule,
chemic al
than
phosphate.
linke d
mole cule—for
or
energy
ADP
group
membrane
detaches
change
but
phosphate
to
change
a
that
within
is
rele ase d.
a
to
convert
ADP
respiration,
in
proteins
in
•
chemosynthesis,
energy
which
in
light
which
is
released
energy
is
by
to
energy
is
released
ATP.
oxidizing
converted
u
photosynthesis,
f
x
•
which
back
i
or
phosphate
t
a
cell
and
o
required
from:
r
o
•
is
d
come
by
to
This
cell.
as
a
When
energy
change
substrate
product.
Energy
This
is
energy
such
re action.
conformational
converts
of
the
mole cule,
metabolic
energy
example,
energy
amount
n
a
pump
the
potential
converte d
U
in
relatively
c ases,
phosphate
c auses
is
C
In
chemic al
ATP
o
when
i
n
rele ase d
v
ATP
p
interconversions between ATP and ADP
y
r
e
Energy transfers during
O
ATP.
C1.2.3
for
cells
(locomotion)—for
sites
energy
are
and
energy—and
cytokinesis.
place
actin
of
of
mitosis
n
sliding
blood
using
L arger
needed
pinches
movement
powerfully
by
by
for
cell
poles
t
i
s
force
provided
molecules—are
dividing
the
cells.
Components
the
l
in
contract
exert
a
within
to
y
c an
ATP
shape
phagocytes
materials
movement.
moved
y
more
example,
for
are
P
therefore
changes
ATP
r
move
from
chromosomes
e
Cells
into
energy
a
c an
c arbohydrates, fats
chemic al
energy
cell respiration or photosynthesis
oxidizing
inorganic substances such as sulfides.
of
system
within
a
require
are
v
nervous
ATP
that
a
quantity
processes
l
up,
O
The
unable
cell
at
to
any
time
is
very
small;
if
it
is
all
used
ADP +
energy
stop.
For
example,
neurons in the
ATP
phosphate
convey impulses and muscle cells stop
contracting, c ausing cramp. Without ATP, cells start to degrade within
This
E
minutes.
damage
is
soon
However,
this
is
from
and
phosphate.
ADP
normally
irreparable,
prevented
by
leading
continual
to
cell
death.
regeneration
of
ATP
active
▴
Energy
transfers
during
interconversions
between
ATP
and
ADP
Figure 5
100%
ecient,
so
some
of
the
energy
is
transformed
into
processes
ATP is converted to ADP + phosphate and
are
back again by dierent
not
cell
cell processes
heat.
363
Interaction
and
interdependence
Activity: C alculating the rate of conversion between
ATP and ADP
s
s
e
r
l
n
At
any moment,
there is only about
How many times per day is an average ATP molecule
back again?
U
C
i
n
to ADP and
Humans are typic ally much more
o
120 moles of ATP per day.
0.2 moles of ATP in the body.
C1.2.4
O
conserving ATP while waiting for prey.
using about
converted
y
This six-eyed spider (Pholcus phalangioides) c an remain motionless on a
v
active,
p
Figure 6
wall for days,
Cell respiration as a system for
n
producing ATP within the cell using energy
o
Cell
respiration
is
i
respiration,
is
use d
to
cells.
u
l
In
In
humans,
many
cells,
a
while,
at
ATP.
the
for
known
one-for-one
swapping
E
across
exchange
and
bec ause
dioxide
there
inside
continue
the
cell
would
bec ause
respiration
of
cre ate
the
the
gas
is
the
oxygen
to
membrane
be
a
Without
of
are
lack
cell
cell
and
c arbon
the
be
energy
use d
ones
do
in
as
many
Plants
not
gas
a
they
harmful
which
of
not
are
could
c arbon
c ause
the
diusion.
continue
excess
exchange
direct
and
simple
could
is
these
involve
by
but
It
membrane
dioxide
processes
and
dioxide.
plasma
c arbon
production
gradients
In
this
substrates.
Together
they
respiration
oxygen
cells.
and
c an
main
independently,
dierent
of
the
respiratory
cells.
both
respiration,
oxygen
concentration
the
although
Instead
living
energy
photosynthesis.
through
exits
exchange,
are
produces
cells
all
compounds
of
by
by
rele ase
acids
source
and
dioxide
to
c arbon
made
enter
respiration
gas
performe d
fatty
exchange,
plasma
use
of
and
molecules.
soon
cell.
range
e at
is
oxidize d
previously
c arbon
Without
the
we
uses
as
that
are
glucose
oxygen
time,
are
G as
but
respiration
same
life
wide
lipids
movements
oxygenmove
A
food
or
necessary
of
compounds
the
c arbohydrates
therefore
function
substrates,
interdependent.
364
a
c arbon
produce
respiratory
use
v
O
f
x
t
a
r
o
d
released from c arbon compounds
of
c arbon
not
dioxide
gases
in
todiuse.
y
P
y
t
i
s
r
e
▴
Molecules
Data-based questions: Energy in respiratory substrates
s
s
e
r
l
syrup
label,
energy
The
in
the
the
oil
per
oil
the
is
of
100 g
Deduce
source
answer to
of
of
only
sugar.
whether
of
the
energy.
energy
sugar
contains
C alculate
fats
or
when
the
signic ant
energy content
[2]
c arbohydrates
used
as
a
are a richer
respiratory
substrate.
[1]
c anola
C alculate
c anola
0.93 g per cubic
[2]
energy and fat content
100 g.
[2]
o
i
d
r
o
C1.2.5
your
syrup,
n
of
giving
U
centimetre.
kiloc alorie,
place.
of
5.
c alculate the number of kilojoules
one
decimal
density
are joules. Using the data on
the
C
one
3.
energy
i
n
of
for
n
the
units
O
SI
In
amounts
[3]
p
The
4.
contrast the nutritional content of the
(right) as shown on food labels
o
foods.
v
2.
and
two
syrup
y
Compare
of c anola (rapeseed) oil (le) and
y
P
y
Nutritional content
r
e
1.
Figure 7
t
i
s
▴
Dierences between anaerobic and
t
a
aerobic cell respiration in humans
Cell
respiration
Some
be
oxygen
needed).
using
are
Simple
glucose
as
a
using
aerobic
word
a
variety
(they
use
equations
of
alternative metabolic
oxygen).
Others
summarize
are
anaerobic
dierent types of cell
substrate:
a
O
l
respiration
is
performed
pathways
u
(no
c an
f
x
pathways.
Aerobic respiration in humans and
glucose
+
c arbon
oxygen
dioxide
+
water
v
many other animals and plants
ADP
E
Anaerobic respiration in humans,
ATP
glucose
lactate
other animals and some bacteria
Anaerobic
respiration
ADP
in
yeast and
ATP
glucose
ethanol
+
c arbon
dioxide
other fungi
ADP
ATP
365
Interaction
and
interdependence
The
features
Aerobic
Oxygen
cell
is
aerobic
anaerobic
respiration
respiration
used
oxidation
and
as
an
electron acceptor
Oxygen
is
cell
not
substances
in
such
compared
Anaerobic
reactions
C arbohydrates
are
as
glucose, lipids
Only
Table 1.
respiration
used—other
act
oxidation
in
as
oxygen
acceptors
reactions
c arbohydrates
c an
be
deamination
dioxide
c an
and
be
used
water
are
C arbon
or
reactions
All
o
runners
•
long-distance
runners,
i
f
x
t
a
r
o
d
short-distance
is
a
(lactic
limit
how
to
much
u
timesc ale
c an
only
l
E
v
a
O
Aer
acid)
the
anaerobic
over
which
sprint
vigorous
for
to
down
of
a
from
muscle
a
of
most
It
is
organs of the
however,
anaerobic
period.
anaerobic cell
respiration is that it
used
contractions
predator
occur
used
a
all
It
in
during
power
the
c an
of
to
and
or
our
will
c atching
lives
training
when
we
need to
today.
or
have
been
needed
prey during times of
Instead
sport—for
anaerobic
example,
by:
several
of
lactate.
The
respiration
is
anaerobic
human
be
the
metres
rowers during a sprint finish.
distance—not
take
400
body
done.
muscle
contractions,
c an
anaerobic
up
product
that
respiration
short
the
races
cyclists
waste
the
muscle
oxygen.
period
is
in
concentration
requires
break
to
lifters during a lift
•
L actate
time
oxygen
ATP
contractions.
rarely
be
2
are not
O
to
short
y
events
likely
a
lower—only
mitochondria
Sometimes,
advantage
powerful
esc ape
n
U
weight
These
more
over
supply
respiration.
The
muscle
maximally
allowing
shortage.
is
of
system
C
by
rapidly
power
ancestors,
survival
muscles.
is
reactions happen in the
p
very
blood
aerobic
ATP
o
the
in
i
n
our
used
for
r
e
ATP
supply
and
v
c an
•
366
lungs
enough
is
respiration
anaerobic cell
the
rapidly
respiration
food
respiration
of
t
i
s
Table 1
for
bursts of intense exercise
yield
products;
per glucose
are in the cytoplasm, but
oxygen
humans,
In
Short
The
required
of
maximize
by ATP from
higher—more
use
body
Figure 8
much
cytoplasm;
In
are fuelled
is
molecules per glucose
more occur in mitochondria including
▴
▴
ATP
waste
n
Initial
of
ATP
the
produced
y
30
are
not
l
yield
than
is
than
lactate
minutes
c alled
This
is
for
the
for
the
400
must
in
tolerate
contractions
more
demand
respiration
c an
be
enough
reason
c an
be
muscles.
and
this
There
restricts
for the short
maximized.
We
metres.
broken
oxygen
down. This
to
be
absorbed
oxygen that builds up during a
oxygen debt.
y
water
The
dioxide plus either lactate
ethanol
P
wasteproducts
r
C arbon
used
e
including fats and oils and amino acids
aer
s
s
in
of
Molecules
Data-based questions: Oxygen consumption in tobacco hornworms
Tobacco
sexta.
hornworms
L arvae
moths.
instars.
E ach
one
shedding
by
The
its
oxygen
in
a
simple
data
to
larval
stages
changes
and
includes
c alled
into
the
developing
the
a
Details
next
the
new
tracheal tubes
thetissues.
9
show
3rd,
4th
5th
instar
the
body
mass and
to
the
of
Body
rate
of
one
is
This
larvae, made
paper
is
are
c arried
C allier
freely
low
to
into
results
younger
intermediate
have
For
The
0.10
mass
results
are
0.06
0.04
Predict, using the data
the
graphs,
how the
0.02
rate
of
a
larva
in
larvae
critic al weight.
reasons
dierence
in
the
for the
trends
between the periods
and
critic al
weight.
[2]
O
l
researchers
reduced
oxygen content. They
at
larvae
with
20%
lower
6
7
8
9
10
11
12
13
0.032
0.030
0.010
0.024
0.022
0.020
0.005
0.018
0
.
2
0
.
3
0
.
4
0
.
5
0
.
6
0
.
7
0
.
8
0
.
9
1.0
1.1
1.2
1.3
1.4
3rd instar
0.009
0.006
0.008
0.005
0.007
0.004
0.006
0.003
0.005
larvae
0.002
body
mass
0.004
0.001
0.003
0.000
oxygen.
6
4
2
.
0
.
0
.
0
2
2
2
8
1
.
0
.
0
2
6
1
0
.
0
.
0
1
4
1
content.
.
0
reared
weiht / 
with
2
0
.
0
.
0
0
1
0
.
earlier
0
6
4
for
larvae
.
0
reason
in
0
a
moulting
air
0.12
reared in normal air
Suggest
in
0.14
0.026
8
3.
instar
E
than
a
v
moulted
the
a
hornworms in air with
that
weiht
reared some
tobacco
found
14664–14669.
0.007
above the
u
f
x
The
below
0.015
t
a
Suggest
r
o
b.
Pp
0.028
i
[2]
5
o
the
rate
d
above
trends in
n o i t a r ip s e r
respiration
“Control
0.08
n
the
[2]
4
4th instar
0.020
mc / etar
described.
Discuss
108.
0.16
0.10
C
you
3
U
that
3
rate
0.025
O
a.
[1]
2
have
2.
nim
critical weight.
Explain the change in
2
i
n
1
moulting until it reaches the
respiration
2011.
Reveals Size-Dependent
aer critical
o
1
will change as it grows from
b.
v
respiration
Vol.
p
in
F
by
reference
y
a.
mass.
H
published
The
available on the internet at
r
e
1.
body
Nijhout
paper
research.
Mechanisms of Molting and
5th instar
0.08
high
the
and
weiht
been
larvae with
body
mass is
http://www.pnas.org/content/108/35/14664.full.pdf+html.
and older larvae with intermediate
to
in
the
graphs
larva.
body
O
divided
the
given
out
Supply
PNAS.
t
i
s
instar,
V
Oxygen
0.12
each
intermediate
n
respiration
who
by
The
y
the
methods
research
Size
graphs.
critic alweight.
Size-Independent
before critical
shows
the
the
l
on
of
as
Metamorphosis.”
respirometer.
point
separate
to
biologists
and
measurements of the
and
on
referred
y
E ach
exoskeleton
Figure
of
of
then
plotted
Manduca
by the adult
P
using
and
laid
r
supply
graphs
eggs
series
exoskeleton
The
rate
a
grows
that
respiration
is
larvae of the moth
the
e
one.
There
instar
the
from
s
s
female
larger
are
emerge
reduced
weiht / 
oxygen
[2]
▴
Figure 9
Respiration rates of tobacco hornworms (C allier and Nijhout, 2011)
367
Interaction
and
interdependence
C1.2.6 Exploring and designing: Variables aecting the rate of cell respiration
The
rate
types
of
of
cell
respiration
c an
be
determined
from
simple
several
oxygen uptake
•
c arbon
•
consumption
the
diameter
of
the
space
inside
the
tube
is
s
s
•
if
known.
measurement:
C alculating rates
dioxide
production
A rate is an amount per unit time. Therefore, to nd the
respiration rate, the volume of oxygen used must be
glucose
or
other
respiratory
e
of
3
divided by the time. For example, if 50 mm
of oxygen was
substrates.
3
used in ten minutes, the rate would be 5 mm
uptake
is
usually
used
to
determine
the
oxygen per
r
Oxygen
rate of
minute. This calculated rate is the dependent variable in an
respiration.
It
c annot
be
measured
by
nding
how
experiment using arespirometer
.
much
air
gases
other
than
breath
is
into
oxygen
the
lungs
and
only
absorbed
by
the
bec ause air contains
a
small
Control of variables
proportion of air
body.
Respirometers
to
c an
give
control
accurate
variables
Measuring oxygen uptake
are
many
possible
designs
of
apparatus,
all
known
be
as
respirometers.
They
controlled.
have these parts:
temperature
•
a
sealed
glass or plastic container in which the
tissue
is
placed
with
enough
air
for it to
inside
healthy
a
a
thermostatic ally
•
a
c apillary
tube
containing
fluid
connected to the
of
oxygen
respirometer.
C arbon
in
dioxide
the
so
production
atmosphere
respirometer,
base,
any
changes
all
as
c arbon
volume
in
normally
oxygen
dioxide
changes
the
adds
intake
is
to
the
be
the
in
changes
c apillary
recorded
tube
are
due
by
Respirometers
which
one
others
are
is
c alled
oxygen
movement
in
uid
millimetres
ide ally
be
or
in
the
other
converted
to
c apillary
units
units
measure of
of
tube
of
air
generated
temperature
the
air
will
increase.
of
water
changes,
bath.
the
respirometer
If
air
uid
will
pressure
in
move
the
c apillary
without
any
c an
be
variable
is
used
to
perform
deliberately
experiments in
changed, while all
volume.
the
constant.
The
independent
experiments
organisms
•
kept
the
used.
For
respiration
but
variable
variable.
they
that
There
must
not
is
changed
are
many
c ause
harm
to
any
example:
rate
of
different
organisms could be
compared
•
the
effect
of
temperature
on
respiration
rate could be
is
distance,
investigated
it
This
•
is
respiration
inactive
rates
could
be
compared
in
active and
organisms.
a
O
l
u
should
the
f
x
me asured
of
a
t
a
r
o
the
movements
therefore
Converting measurements to volumes
If
of
volume and
heat
Experimental investigation of variables
by the
to
i
oxygen consumption.
types
uptake.
volume
o
Volume
uid
the
d
alone.
of
if
the
volume
controlled
respirometer
some
possible
intake
increases
particular,
reduces it. In
absorbed
should
the
volume of air
n
a
air
measure
U
of
the
pressure,
example,
the
In
respirometer must
temperature should be kept constant using
C
to
inside
i
n
container
the
o
v
tube
For
respirometer,
possible,
outside
carbon dioxide produced during respiration
bec ause
organisms
If
a base (alkali) such as potassium hydroxide to absorb
is
interact.
p
•
or
respiring
This
inside
y
remain
by
pressure
r
e
organism
and
O
There
t
i
s
temperature
results but it is
c arefully.
n
essential
l
each
breathed
y
in
is
Data-based questions: Respirometers
1:
Experimental
possible
Figure
10.
E
One
design
of
3.
design
respirometer
is
Explain the need for a base inside the respirometer.
2.
Deduce, giving a reason, the direction in which
4.
[2]
with
oxygen
inside
Explain
the
a.
move in the right-hand side of the
c apillarytube.
Predict,
a
reason, the change in the amount of
the
tube
during
the
experiment.
[2]
shown in
1.
the uidwill
368
v
Part
how
the
reliability
putting
of
the
controlled
[2]
following
results
test
from
tube
water
changes
in
bath
the
a
would
improve
experiment:
thermostatic ally
[2]
y
P
aerobic
Molecules
7
.
Plot
8.
Using
a
graph
your
of
the
graph,
mean
volumes.
deduce
temperature
and
the
germinating
pea
seeds.
the
[3]
relationship
respiration
between
rate of the
3
graduated 1 cm
[2]
s
s
syringe
Part
3:
Anaerobic
respiration
in
yeast
The apparatus in Figure 11 was used to monitor mass
e
changes during the brewing of wine. The ask was placed
wire basket containing a
on an electronic balance which was connected to a
filter paper rolled
computer for data logging. Results are shown in Figure12.
r
living organism or tissue
wick
tube
airlock to
potassium hydroxide
prevent
solution
Respirometer with a manometer for measuring
of
oxygen
oxygen uptake
side
of
another
the
test
c apillary
tube
tube,
to
that
the
is
le-hand
identic al
connected
to
to a
logging
yeast in a
the
right-hand
tube
but
does
not
contain
computer
solution of
tissue.
[2]
r
e
respiring
data-
O
attaching
balance
t
i
s
b.
n
y
Figure 10
l
electronic
entry
▴
y
to form a
P
capillary
sugar and
y
nutrients
Part
2:
Using
shows
seeds
was
the
results
temperature
on
of
an
experiment in which the
respiration
in
germinating
pea
investigated.
of
uid
▴
Figure 11
in
560
−1
respirometer / mm min
3.5
▴
6.0
6.5
8.0
7.5
11.5
11.0
9.5
whether
close
the
enough
to
arereliable.
diameter
E
b.
The
v
a.
at
indic ate
that
inside
of
movement
at
of
oxygen
2
3
4
5
6
7
8
9
10
11
12
13
time / days
Figure 12
9.
a.
Monitoring anaerobic cell respiration in yeast
C alculate
the
total
loss
theexperiment
and
of
Explain
of
the
mass during
mean
daily
loss.
[2]
theresults
b.
the
loss
mass.
[3]
[1]
the
Suggest
each
two
reasons
for
the
increasing
rate
ofmass
c apillary tube of the
2 mm.
mean
1
temperature
from
the
start
of
the
experiment
untilday
6.
[2]
Convert the distances
temperature
to
used.
temperature.
0
loss
was
the
550
545
▴
e ach
data-logging apparatus
555
10.
respirometer
C alculate
repe ats
a
are
6.
5.0
l
D iscuss
4.0
5.5
Table 2
O
5.
4.0
u
f
x
30
3.0
t
a
r
o
25
2.0
o
15
1.5
2.5
i
2.0
2.5
d
5
Yeast
n
3rd
reading
g / ssam
2nd
reading
10
20
U
1st
reading
555.00
C
Movement
i
n
Temperature /°C
p
of
o
2
eect
data
v
Table
secondary
volumes
11.
[2]
volume
for
each
from
12.
[2]
Suggest
two
day
11
reasons
Suggest
how
from
data.
the
for
the
mass
remaining constant
onwards.
the
rate
[2]
of
respiration
c an
be
c alculated
[1]
369
Interaction
ATL
To
and
interdependence
Thinking skills: Designing questions for experimental investigation
plan
an
research
investigation
question.
involving
1.
Which
2.
Which
foods
biology
are
some
you
cellrespiration
c an
yeast
use
in
need
a
examples
in
Consider
focused
of
research
1.
The
yeast.
these
criteria
for a good IA inquiry question:
answer
should
not
Answering
the
be
question
known
must
before starting.
depend
on
you
c arrying
out
the
The
phrasing of the question should suggest the
anaerobic cell
investigation.
respiration?
2.
anaerobic
is
method
yeast able to use in
out
anaerobic
cellular
The
variables
that
are
directly
measured should be
stated in thequestion.
respiration
faster at 0°C or100°C?
4.
oxygen
is
The
of
What
the
strengths
criteria
be
a
and
limitations
think
should
be
of
5.
each
met
Consider
an
for an
area
the
that
alternative
goodone?
include
signic ance
interests
fuel
you.
sources,
reference to
C1.2.7
of
your
Are
investigation to
you
interested in
enzymesor
baking
bread?
y
r
e
LHA
to
you
not
O
question
do
should
experiment with the statement of thequestion.
cellularrespiration?
some
question
signic ance. Students oen muddle the intent of the
aerobic or
t
i
s
inquiry
use
n
are
question?
yeast
l
What
does
y
anaerobic
available,
Role of NAD as a c arrier
of hydrogen
p
and oxidation by removal of hydrogen
v
during cell respiration
gain
is
the
for
example
certain
to
help
types
of
molecule
a
The
o
l
Structure of NAD
changes
c arriers
oen
link
is
is
ions
green
Copper
respiration
v
E
Figure 13
or
molecules
Electron
u
f
x
O
▴
that
electrons.
They
ribose sugar
copper
blue
i
reaction
phosphates
nicotinamide base
a
t
a
r
o
d
containing
sugar
loss
these
atoms
substance
laboratory
and
is
and
in
the
reduction is the
Benedict’s test—a
of
two
ions
that
to
and
bec ause
form
adenine
in
of
a
have
accept
reductions
(Cu
2+
). Cu
molecules
atoms
they
c an
positive
Sugar
red
and
cells.
copper
lost
or
a
reduction
by giving them
orange
precipitate. The
electrons.
lose
The
ions oen
c ause
electrons
main
dinucleotide).
reversibly.
electron
The
c arrier in
structure of the NAD
Figure 13.
shows
are
a
the
+
basic
2
little
reaction.
electrons
more
→
reduced NAD
complic ated.
NAD
initially
has
one
positive
+
charge
and
exists as NAD
.
Substances
are
oxidized
in
respiration
by
removing
+
two
hydrogen
accepts
two
NADH.
The
atoms.
E ach
electrons
and
hydrogen
one
consists
proton
from
of
the
an
electron
hydrogen
and
atoms,
+
other
proton (H
+
NAD
370
together.
in
solutions.
(nicotinamide
details
a
occur
from one substance to
involves the use of copper sulfate solution,
insoluble
substances
below
always
this
charge
to
are
in
from
the
that
electrons
test
copper
are
oxidations
of
2+
a
colour
oxidized,
shown
chemic al
The
are
NAD
equation
with
processes
transfer
electrons
visualize
NAD
The
of
sugar.
ribose sugar
impart
chemic al
involve
n
useful
test
Oxidation
are
they
electrons.
U
A
of
reduction
bec ause
o
another.
adenine base
and
happens
C
This
i
n
Oxidation
)
is
released:
+
2
+
+
2H
+
electrons (2e
)
→
NADH
+
H
a
proton. NAD
becoming
y
If
c arry
r
4.
yeast
P
Does
befollowed.
cellrespiration?
3.
3.
to
e
monosaccharides
s
s
questions
in
Here
Molecules
LHA
s
s
e
r
l
y
P
O
n
y
t
i
s
y
p
r
e
C
o
v
i
n
n
U
o
i
d
t
a
r
o
u
l
f
x
a
E
v
O
371
and
interdependence
LHA
Interaction
Then
there
is
a
second
phosphorylation:
fructose-1,6-bisphosphate
fructose-6-phosphate
ATP ADP
s
s
Stage 2: Lysis
Fructose
bisphosphate
is
now
split
to
form
two
→
2 triose phosphate
r
Stage 3: Oxidation
of
these
triose
hy d r o g e n
phosphates
atoms
are
is
ox i d i z e d
remove d,
not
by
removing
hy d r o g e n
ions.
If
+
remove d
an
organic
group
3C)
the
ele ctrons
not
becomes
acid.
and
no
In
this
organic
rele ase d
by
the
become
a tt a c h e d ,
c ase
acid
the
the
is
of
sugar
triose
product
is
ADP.
U
phosphates.
2 reduced NAD
acid,
NAD
the
end
of
twice
the
glycolysis,
bec ause
glycerate
product
of
yields
two
nal
reactions
The
overall
ATPs.
phosphate
phosphate
of
Energy
group
ra t h e r
to
than
bisphosphoglycerate
is
by
transfer of phosphate
bisphosphoglycerate has two
converted
to
another
organic
pyruvate
molecules
Four
accepted
glycolysis.
ADP
bisphosphoglycerate
them
t
a
r
o
ATPs
are
are
ATP
ADP
produced
therefore
ATP
per
glucose
and
each of
produced per glucose in these
glycolysis.
outcomes
of
the
four
stages
of
glycolysis
per
glucose
molecule
are
u
asfollows:
ADP
•
One
glucose
l
each
containing
containing
a
•
Two
•
There
NAD
three
molecules
six
c arbon
atoms
is
converted
into
two
pyruvates
c arbon atoms.
are
converted
to
reduced
NAD.
ATP
v
O
f
x
ATP
Two
reactions,
is
o
ADP
reactions
happen
is
produces
phosphates.
bisphosphoglycerate
i
d
2NAD
these
This
nal
c an
sugar
reduced NAD
phosphate
the
one
two
second
a
n
2ADP
In
pyruvate.
in
This
of
triose
y
to
a
the
o
produced
with
c arrying
by
hy d r o g e n
b i s p h o s p h o g l y c e ra t e
C
is
groups
triose
lost
The
Oxidation
a l l ows
v
i
n
ATP
is
g l y c e ra t e
Stage 4: ATP formation
2ATP
been
p
+
2ADP
h av e
ox i d i z e d .
N A D.
r
e
p h o s p h o g l y c e ra t e .
2ATP
triose phosphate
would
been
re duce d
ox i d a t i o n
so
h av e
n
×
which
),
would
O
(2
N A D,
(H
it
t
i
s
2 pyruvate
by
so
y
phosphate
Note
ions
l
were
hy d r o g e n .
hy d r o g e n
is
stageof
a
net
yield
glycolysis
of
two
and
ATP s.
four
are
This
is
be c ause
produce d
in
two
the
are
final
use d
stage,
in
so
the
the
first
net
glucose
372
Figure 14
E
▴
yield
is
does
not
4
−
2
=
2
per
glucose.
Although
this
is
a
relatively
small
yield,
it
(6C)
An overview of glycolysis
re quire
islimite d.
the
use
of
oxygen
so
is
useful
when
the
supply
of
oxygen
y
that
P
E ach
e
fructose-1,6-bisphosphate
molecules of triose phosphate:
Molecules
LHA
C1.2.9
Conversion of pyruvate to lactate as
a means of regenerating NAD in anaerobic
cellrespiration
summary
ADP
and
equation
NAD
must
be
for
glycolysis
replenished
(Figure
for
the
14)
shows
that
supplies
of
glucose,
process to continue in a cell.
H
•
Glucose
should
from
run
out
as
long
as
there
are
will
only
is
need
run
out
if
all
of
it
has
been
converted
to
ATP,
in
which
c ase
C
C
r
ADP
there
H
will
run
c arry
out
out
glycolysis.
unless
it
is
O
regenerated
by
oxidation
of
reduced
NAD.
▴
are
several
methods
of
regenerating
NAD.
In
each
c ase,
two
Figure 15
+
gives up
bacterial
it
cells,
into
two
electrons)
are
transferred
to
another
molecule,
atom
hydrogen
is
transferred
from
reduced
NAD
to
shown on the right-hand
keeping the electron from
pyruvate,
is then pyruvate,
pyruvic acid.
pyruvate
lactate
Two
reduced
For
and
this
cell
bec ause
the
pH
lactic
an
and
concentrations
in
this
respiration
accumulation
way
by
fermentation.
of
is
used
lactic
(for
c attle)
are
of
that
rise
able
them
was
c an
used
too
to
used
to
normally exist in their
so are referred to with the
‘–ate’ name rather than the ‘–ic acid’ name
glycolysis to
be
in
high,
convert
glycolysis is
methods
foods
or
made
of
pyruvate to lactate
food
fungi.
by
indenitely.
of
dissociates
bacteria
anaerobic cell
continue
conversion
some
(which
by
all
not
be
with
in
acid
decomposition
silage
do
should
glycolysis
It
to
preservation,
form
lactate)
lowers
Yoghurt, kimchi,
lactic
fermentation.
i
t
a
r
o
C1.2.10
each
NAD
state,
o
and
and
the
d
sauerkraut
out
prevents
all
by
n
c alled
so
converted
C
Anaerobic
produced
NAD,
is
U
c arried
are
glucose
lactic acid
reason, cells should not run out of NAD: as long as glucose
lactate
respiration
is
to
each
i
n
available
back
as
a proton to become
Organic acids such as pyruvic
o
regenerated.
is
pyruvates
NAD
reduced NAD
used
v
a
are
side,
the hydrogen. It
y
pyruvate.
molecules
and
dissociated
p
NAD
r
e
NAD
Two
acid
readily
with one negative charge.
Pyruvate c an accept
lactate. This happens in the cytoplasm of cells.
It
the hydrogen
O
converting
and
NAD. In some human cells and also some other animal
t
i
s
and
protons
reduced
) from
n
(two
oxidizing
a proton (H
y
atoms
This is pyruvic acid.
hydrogen
l
There
y
NAD
to
P
•
no
H
O
elsewhere.
H
•
C
stores in a cell or it is
e
transported
not
s
s
O
The
▴
Figure 16
Kimchi was traditionally made
Anaerobic cell respiration in yeast
from
and its use in brewing and baking
South Korea,
u
f
x
It
NAD used in glycolysis can be regenerated by conversion of pyruvate to ethanol
and carbon dioxide instead of lactate. This is a two-stage process. In the rst
l
stage, carbon dioxide is removed from the pyruvate in a decarboxylation reaction.
a
O
The product is ethanal. In the second stage, two hydrogens are transferred
from reduced NAD to ethanal, converting it to ethanol. The number of NADs
c abbage and
provided
other vegetables in
using large underground pots.
food
for the winter when fresh
vegetables were not
available. The cool
anaerobic conditions in the pots encourage
Lactobacillus and
out
other bacteria to c arry
lactic fermentation,
eventually killing
themselves with low pH
and
preserving
v
thevegetables
regenerated is the same as the number used per glucose in glycolysis, so this
process allows production of ATP by anaerobic respiration to continue indenitely,
E
as long as glucose is available and ethanol concentrations do not rise too high.
ethanal
CO
2
reduced
NAD
NAD
▴
Figure 17
Conversion of pyruvate to ethanol
373
and
interdependence
LHA
Interaction
Anaerobic
cell
dioxide
is
in
used
where
Figure 18
the
by
baking
dough
stretches out
to
is
once
kept
all
warm,
the
the
it
to
of
a
that
Yeast
as
c arries out the
naturally in habitats
surface
of
fruits.
aerobic ally
or
anaerobic ally.
the
oen
the
yeast
in
the
will
grow
dough
and
has
something
used
respire.
been
used
for
must
this
Initially
it
up,
yeast
the
juice,
barley
grains,
c annot
tanks,
so
rapidly
starch
use
up
of
any
ethanol as a waste
ethanol
fermentation
As
concentration
a
well
as
brewing
using
yeast.
state
are
the
all
mixed
Any
into
is
with
of
in
a
is
is
of
c arried
limited.
been
also
be
matter
sugar
large
fuel
in
The
used
used
c ane
be
to
uporwhen
volume).
produce
corn
fermenters.
vehicles,
the
start,
utilized
and
large
ethanol
to
the
15%by
c an
in
ye asts
bubbles
(about
but
bec ause
out
at
from
starch
The
present
from
made
amylase,
dioxide
has
however,
made
amounts
sugar
c an
from
is
Beer
using
is
Here,
Wine
beer
ye ast
plant
as
forms bubbles
anaerobic ally.
sugar
the
ethanol
used
or
tank
c arbon
the
to
produced
Bioethanol
sugar
the
fermentation
source.
is
to
amount
toxic
it
respire
“rise”. Ethanol is
wine.
large
respire
the
and
dioxide.
wine
in
then
of
when
ethanol
energy
sometimes
i
C1.2.11
on
converted
distillation.
and
either
bioethanol
o
pure
Sugars
by
The
as
a
(maize),
ethanol
sometimes
in
a
gasoline(petrol).
Oxidation and dec arboxylation
u
of pyruvate as a link reaction in aerobic
cellrespiration
l
a
E
v
O
f
x
t
a
r
o
d
puried
most
and
most
becomes
drinks,
renewable
but
but
n
feedstock,
is
ends
ethanol
bioethanol,
present
beer
contain
of
liquid
or
concentration.
converted
the
Depending
U
the
grains
Brewing
into
as
Instead,
swell,
to
dioxide
evaporates during baking.
c arbon
sugar
C
of anaerobic cellrespiration?
The
starch.
oxygen
esc apes.
high
be
such
than
o
and
rst
dissolved
i
n
surface
must
oxygen
remains
a
water.
metabolize
diusion
produced
with
drinks
rather
has
it
p
ye asts
naturally
mixed
This
brewing
ethanol
but
to
y
sugar.
which
respiration
esc ape.
dough
c arbon
If
oxygen
This
the
a
available,
much
reactions
pyruvate
link
is
gives
are
from
between
pyruvate
higher
part
of
glycolysis
glycolysis
yield
the
a
be
ATP
Krebs
into
and
c an
of
oxidized
than
cycle,
but
two-c arbon
the
Krebs
to
c arbon
anaerobic
an
initial
acetyl
cycle,
so
is
cell
dioxide
reaction
group.
and
water.
respiration. Most of
This
referred
to
is
conversion of
conversion
as
the
link
forms a
reaction.
Bioethanol is currently an
alternative to fossil fuels.
In
the
link
reaction
a
complex
of
three
enzymes
c arries
out
these
processes:
What is the best
•
dec arboxylation
by
removal
of
c arbon
dioxide,
to
change
three-c arbon
energy source for cars in a zero-carbon future?
pyruvate
•
into
oxidation
by
converting
374
it
a
two-c arbon
removal
to
of
molecule
two
electrons;
reduced NAD
these
electrons
are
accepted
by
NAD,
y
grape
when
the
the
n
produce
to
c annot
c ause
(sticky),
l
used
is
cell
viscous
added
aerobic ally
starts
O
also
very
respiration
bubbles
anaerobic
does the release of heat
by the ame tell us about
respires
P
is
aim
by
is
be
purpose. If the
y
produced
cell
These
v
What
anaerobic
dough
t
i
s
is burned on
the
the
Yeast is a
mixture to make dough
texture,
is
fermentation. It
that
occurs
the
either
kneading
lighter
gas.
organism
such
respire
our,
bread
the
fungus
available,
c an
r
e
Brandy that
puddings in some countries is distilled
Figure 20
water
bubbles
Bec ause
by
little
▴
are
means
give
oxygen
dough.
the
product
To
create
within
Ye ast
wine.
sugars
adding
it.
produced
also
from
other
c ases,
pyruvate to ethanol and
alcoholic
dough more elastic
anaerobic ally.
Figure 19
unicellular
a
both
or
gluten bres,
but
fruit
Yeast
is
converts
r
dough
▴
In
anaerobe—this
made
which
fermentation
brewing.
yeast.
or
glycolysis
ethanol
Kneading mixes the
ingredients and
making bread
and
by
as
e
to
is
then
known
s
s
and
is
glucose
faculative
Bread
is
baking
fermentation
▴
respiration
c arbon
Molecules
binding
a
of
the
complex
acetyl
c arrier
group
(produced
molecule
c alled
by
the
coenzyme
previous
A.
The
two
LHA
•
process) to
product
is
acetyl
coenzyme A.
O
CoA
s
s
CoA
inner
outer
membrane
CH
3
3
CO
NAD+
reduced NAD
2
by
glycolysis
in
the
cytoplasm,
but
both
the
link
reaction
matrix
the
Krebs
in
the
outer
take
place
in
membrane
the
of
the
of
the
mitochondrion.
mitochondrion
moves
A
transporter
pyruvate
from the
matrix.
▴
inter-
membrane
Figure 22
O
cytoplasm into the mitochondrial
matrix
t
i
s
protein
cycle
n
and
y
produced
l
is
The link reaction
y
Pyruvate
Figure 21
P
▴
e
r
CH
membrane
space
Membranes and
compartments of a mitochondrion
Oxidation and dec arboxylation of
acetyl groups in the Krebs cycle with a yield
happens
but
fe d
the
the
organic
into
in
which
by
in
the
or
fat
Krebs
is
a
of
of
dioxide.
c arbon
removed
cycle
or
waste
the
product
is
removed
held
in
transferred
molecules
accept
the
E
energy
in
energy.
by
the
as
protons,
Krebs
A
discovery.
to
of
cycle
honour
of
Acety l
oxaloacetate,
and
back
cycle
has
the
groups
producing
into
acetyl
CoA
citrate
oxaloacetate
6C
4C
reduced NAD
atoms
is
NAD
re actions,
6C
removed,
aerobic
4C
cell
CO
re action.
NAD
Krebs cycle
H
reduced NAD
O
2
C arbon
4C
most
cells
and
5C
is
CO
cycle
of
2
such
are
the
2
oxidations
reduced FAD
Much
NAD
4C
rele ased
4C
FAD
the
electrons
to
NAD
c arriers
so
its
in
a
This
dec arboxylation
in
oxidations.
either
act
for
coenzyme
substrates
by
in
a
re actions
rele ase
are
In
in
link
v
and
c arbon
oxygen
excreted.
Four
Prize
cycle”
enzyme-c atalysed
l
O
dioxide
the
is
converted
“Krebs
u
sugar
all
atoms
dec arboxylation
and
f
x
as
two
c arbon
respiration,
is
series
number
c arbon
producing
from
oxidize d
t
a
decre ased
Nobel
are
mitochondrion.
i
The
a
c arbon
r
o
re actions.
four
Citrate
by
a
transfer
the
citrate.
has
six.
by
c alle d
the
o
has
oxaloacetate
aw arde d
of
d
citrate
w as
cycle
acid
Oxaloacetate
commonly
re action
n
who
are
link
matrix
U
biochemist
is
the
the
C
names
by
in
i
n
several
produce d
that
p
groups
re actions
o
Acety l
v
of ATP and reduced NAD
y
r
e
C1.2.12
they
that
These
or
of
are
to
reduced NAD
are
electrons
FAD.
Both
electrons;
hydrogen
are
ATP
ADP
these
they
also
▴
Figure 23
The Krebs cycle
c arriers
375
and
interdependence
LHA
Interaction
as
well.
When
NAD
the
NAD
FAD
and
was
or
described
NAD
reduced
electron
accept
FAD
transport
eects
of
•
three
•
two
molecules
•
one
ADP
acetyl
one
turn
group
NADs
is
are
transfer
chain
is
in
of
electrons
the
the
inner
Krebs
topic.
and
FAD
they
the
functions
become
energy
mitochondrial
cycle
they
c arbon
converted
to
to
reduced
dioxide
are
NAD
and
one
FAD
ATP.
with
your
into
2.
Linoleic
classmates:
the
are
The
diagram
released
in
is
Figure
Krebs
by
used
24
cycle.
in
into
How
Krebs
you
two-c arbon
many
represents
dioxide
glucose?
sunflower oil. It has
9
aerobic
C an
c arbon
each
acid
the
in
for
acetyl
molecules
cycle when a
respiration?
the
route
of
c arbon
i
n
the
fatty
c atabolized
respiration.
acid
many
cycle
explain it?
C
U
▴
FAD
CO
2
2
Figure 24
n
of energy by reduced
o
Transfer
CO
NAD to the electron transport chain in
i
themitochondrion
In
the
inner
electron
u
l
a
E
v
O
f
x
t
a
r
o
d
C1.2.13
mitochondrial
c arriers
25).
Together,
The
rst
the
reduced
NAD
by
this
c arrier
changes
in
membrane,
accepting
sequence
the
c arrier
chain
from
back
to
and
of
c arriers
accepts
an
a
oxidized
NAD.
there
then
The
are
passing
forms
pair
of
state
c arrier
groups
on
the
to
a
proteins that act as
of
electron
electrons
gains
of
pairs
electrons
transport
from
reduced
chemic al
(see
Figure
chain
(ETC).
reduced
state
and
energy
NAD. This
converts the
by
this
transfer of
electrons.
Reduced
NAD
Oxidation
FAD,
is
produced
reactions
tra