Download OCR Biology A: Exchange and transport

WORKBOOK ANSWERS
OCR AS/A-level Biology A
Exchange and transport 
Biodiversity, evolution and disease
This Answers document provides suggestions for some of the possible answers that might be
given for the questions asked in the workbook. They are not exhaustive and other answers
may be acceptable, but they are intended as a guide to give teachers and students feedback.
Module 3
Exchange and transport
Topic 1 Exchange surfaces
The need for specialised exchange
surfaces
1 Anaerobic respiration. It allows a supply of energy when oxygen is in short supply, e.g. for
strenuous exercise when not enough oxygen can be taken in.
2 It is enough for smaller organisms because the diffusion pathway is small and the
concentration gradients are favourable. In larger organisms the diffusion pathway is too
long and the concentration gradients are too small, so it is inefficient. (This is a
comparative question so both parts are needed.)
3 Surface area to volume ratio; impermeable (or reduced permeable) body surface; need to
maintain concentration gradients of the two gases so gas will continue to move in the
correct direction down the concentration gradient.
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Philip Allan for Hodder Education
1
4
Feature
Problem
Adaptation
Concentration
gradient
Gases must diffuse down a
concentration gradient
Mechanisms such as breathing to
keep gases moving on to the surface
and outwards away from the surface
Permeability of
surface
External surface is impermeable
to the gases
Permeable surface inside the body
allows diffusion through the surface
into or out of the body
Moist surface
Organisms living on land live in
a dry atmosphere, making
diffusion difficult
Moist surface inside the body allows
gases to dissolve first
Surface area to
volume ratio
Larger organisms have a
reduced surface area to volume
ratio and so less gas can diffuse
across the surface
Large internal surface area provided
to ensure efficient diffusion across the
surface
Gas exchange and ventilation in
mammals
1
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2 In the medulla oblongata (in the brain), the inspiratory centre sends nerve impulses down
the nerves to the diaphragm and intercostal muscles. (A2: sympathetic and
parasympathetic pathways are involved.)
3 A = bronchus, B = internal intercostal muscles, C = external intercostal muscles,
D = lung, E = diaphragm, F = bronchioles, G = pleural cavity, H = pleural membranes,
I = trachea, J = larynx.
4 Alveoli are small swellings on the air sac that enlarge the total surface area greatly and
provide a thin surface for exchange.
5
Feature
Requirement
Adaptation
Surface
area
Large surface area
In humans, the alveoli
increase the surface area to
approximately 70–100 m2
Thickness
of the
surface
Small diffusion pathway
The alveolar wall is just one
cell thick and the cells are
flattened (squamous)
epithelial cells
Blood
supply
An efficient transport medium to bring
waste carbon dioxide from the body
cells to the surface and remove the
oxygen as soon as it has diffused in
The blood system provides
an efficient transport
medium. It transports oxygen
away from the surface
quickly and brings carbon
dioxide to the surface. This
maintains the diffusion
gradient for both oxygen and
carbon dioxide
Ventilation
mechanism
A method of delivering fresh oxygen
and removing waste carbon dioxide is
needed to maintain the diffusion
gradient
A flow of fresh gases into the
gas exchange site brings in
fresh oxygen and the
removal of waste carbon
dioxide to the outside
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6
Tissue
Structure found in
Function
Cartilage
C-shaped rings in trachea; complete
rings in bronchi and larger bronchioles
of airway
Strength and support of the airway
Ciliated
epithelium
The walls of the trachea, bronchi and
larger bronchioles
Cilia move mucus, which contains trapped
dust and bacteria that enter the airway,
and moves it back to the top of the
trachea
Goblet cells
Between ciliated cells lining the walls
of the trachea, bronchi and larger
bronchioles
Produce mucus
Smooth
muscle
The walls of the trachea, bronchi and
larger bronchioles
Allows airway to expand during exercise
and maintains the tone of the airways
Elastic fibres
Walls of the trachea, bronchi and all
bronchioles and alveoli
Allows elasticity of the airways and lung
for expansion during inhaling and passive
recoil during exhaling
Squamous
epithelial cells
Alveoli only
Provide a thin, flexible layer for an
efficient and large gas exchange site.
Secrete surfactant to prevent the walls
sticking together
7 1.5 × 20 × 1/100 = 0.3 litres of oxygen per breath, so over 1 minute (20 breaths) = 6.0
litres. The volume of oxygen per kg mass is 6.0/60 = 1/10 = 100 cm3/kg.
8 The breathing rate increases as carbon dioxide levels rise. This is because the breathing
rate is largely controlled by carbon dioxide levels detected by carbon dioxide sensors and
received by the breathing centre in the brain. Nerve impulses from here send signals to
the intercostal muscles and the diaphragm.
9 Tidal volume is the volume of air that is normally breathed in or out when at rest, whereas
vital capacity is the maximum volume of air that can be breathed in or out in a single
breath.
10 A small volume of air is always retained within the lung because otherwise the lung would
collapse completely. This volume is called the residual volume and it cannot be measured.
Residual volume together with vital capacity gives the total lung capacity.
11
a
Mean tidal volume = 0.56
Mean breathing rate = 21.33
b
An increase in carbon dioxide within the chamber of air of the spirometer.
Reject ‘exercise’ as this is unlikely when using a spirometer unless the set-up is more complex,
which is not stated in the question.
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Gas exchange and ventilation in bony
fish and insects
1 The floor of the buccal cavity lowers; increases volume of the cavity; pressure is now lower
than water outside; draws water in through the mouth; mouth closes; floor of buccal cavity
is raised; pressure increases so water is forced into the gill cavity; pressure in the gill
cavity rises; forces open the operculum; water is forced out; the cycle is repeated.
2 As the water flows into the gill cavity and across the gills at the start of every ventilation
cycle, it ensures a continual supply of water with high % of dissolved oxygen. The carbon
dioxide produced is removed at the end of the ventilation cycle when the operculum opens
and the water leaves.
Exam-style questions
1
a
Organism D.
b
It will have a limited ability to take in any molecules such as oxygen by diffusion, so
it cannot supply the needs of the cell.
a
A large surface area provided by the tracheae and tracheoles; moist surface and
thin surface.
b
There is no connection to the blood transport system as the trachea form a network
of tracheoles across the whole body and so oxygen-containing air is delivered
straight to the tissues via the tracheae and tracheoles.
c
Advantage: direct delivery of oxygen to the tissues and direct removal of carbon
dioxide.
2
Disadvantage: the system limits the size of the organism as the tracheoles can only
successfully deliver enough oxygen if the diffusion distance is short and the
pumping mechanism of the abdomen keeps the air flowing. This can only occur over
a relatively short distance.
Topic 2 Transport in animals
Transport systems in multicellular
animals
1 Living cells need a supply of oxygen and nutrients and to remove waste products; larger
organisms have an unfavourable diffusion gradient/the diffusion distance is larger and so
inefficient/too slow; there is a decreasing surface area to volume ratio as the organism
gets larger, so demand for oxygen and nutrients is greater than the possible supply; as
activity levels increase, the amounts of oxygen and nutrients needed also increase (as do
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the waste products), and are too great to be supplied to all parts/cells of the body by
diffusion alone; on land, the surface area is too dry for efficient diffusion, which needs a
moist surface.
Circulatory systems
1 A = lung capillaries, B = right atrium, C = right ventricle, D = systemic capillaries, E = left
ventricle, F = left atrium, G = pulmonary circuit, H = systemic circuit.
2 The blood can maintain a relatively high pressure and speed because it only flows through
a capillary network once before returning to the heart. In a single circulation, it has to flow
through two capillary networks in each circuit so it loses a lot of pressure and slows
considerably. Higher pressure and speed mean concentration gradients are retained more
efficiently, so exchange is more efficient.
3 Fish are ectotherms and do not need to supply energy to maintain a constant body
temperature; they live in water, which has a relatively stable temperature and so they have
a low metabolic rate; a single circulatory system is efficient in this situation.
4 The blood (haemolymph) in insects does not carry oxygen to the tissues or collect waste
carbon dioxide because the system of tracheae and tracheoles carries out this function.
Therefore, there is no need for a highly efficient circulatory system. In other animals, the
blood must deliver oxygen efficiently to the tissues and carry away waste carbon dioxide.
Blood vessels
1
Type of vessel
Structure
Role in transport
Arteries
Thick wall of collagen (tunica
adventitia), thick muscle and
elastic tissue (tunica media)
and narrow lumen lined with
endothelium
Carry blood under high
pressure away from the heart
Arterioles
Small vessels, wall of muscle
and elastic
Connect arteries to capillaries,
so pressure lower
Capillaries
Large number of very small
vessels, wall of single
squamous cells and a narrow
lumen
Exchange site as they form a
very thin layer; slow down
blood flow and reduce blood
pressure to make exchange
more likely
Venules
Small vessels, little muscle
and elastic
Connect capillaries to veins,
so very low pressure
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Type of vessel
Structure
Role in transport
Veins
Thin wall with very little muscle
and elastic tissue (tunica
media) and large lumen lined
with endothelium and valves
along length
Carry blood under very low
pressure back to the heart;
valves maintain a one-way
flow
Blood, tissue fluid and lymph
1
Feature
Blood
Tissue fluid
Lymph
Cells
Red and white cells,
platelets
Only a few white
cells, but no red
cells or platelets
Many white cells, but
no red cells or
platelets
Fluid
Plasma
Plasma
As plasma
Dissolved
solutes
Amino acids, sugars,
fatty acids, carbon
dioxide
Amino acids,
sugars, fatty acids,
carbon dioxide
Amino acids, sugars,
fatty acids, carbon
dioxide
Proteins
Clotting factors,
hormones, plasma
proteins,
immunoglobulins
No large protein
molecules
Immunoglobulins,
antibodies
Location
In blood vessels
Bathing the cells of
the tissues
In lymphatic vessels
2 They contain macrophages and many white cells, which help to fight infection.
3
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The mammalian heart and the cardiac
cycle
1 A = superior vena cava, B = semilunar valves, C = right atrium, D = atrioventricular
(tricuspid) valve, E = inferior vena cava, F = right ventricle, G = septum, H = left ventricle, I
= tendons (chordae tendineae), J = atrioventricular (biscupid) valve, K = left atrium, L =
pulmonary vein, M = pulmonary artery, N = aorta.
2
a
The atria have thinner walls — they receive blood with lower pressure and have
only a short distance to pump the blood (into the ventricles). The ventricles have to
contract strongly to pump high pressure blood around either the pulmonary circuit
(right ventricle) or the whole body (systemic circuit) in the case of the left ventricle.
b
The left ventricle wall must be much thicker than the right ventricle wall in order to
pump blood around the whole body. It must also have more muscle than the right
ventricle wall.
3 The atrioventricular valves are between the atria and the ventricles and the semilunar
valves are between the ventricles and the two major arteries. They prevent the backflow of
blood and ensure the blood continues to flow back to the heart. (The large lumen ensures
that enough blood is returned to the heart even though the flow is much slower than in
arteries. The output of blood from the heart must be the same as the inflow of blood to the
heart. Tendons attach the atrioventricular valves to the ventricle wall to help withstand the
high pressure as the heart muscle contracts, preventing the valves turning inside out.)
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4
5 60/0.8 = 75 beats/s. (Award 1 mark for the working out and 1 mark for the correct answer.)
6
a
The artery walls stretch when high pressure blood from the heart enters the arteries.
b
When the heart relaxes, the blood flow slows so the elastic tissue recoils, exerting
extra pressure on the blood and helping to even out the flow between heart
contractions. This is not the same as a contraction.
7 Myogenic (the muscle beats without any stimulation at all).
8
a
Sympathetic and parasympathetic.
b
Sympathetic: speeds up the heart rate so the heart beats faster. Parasympathetic:
slows down the heart rate so it beats more slowly.
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9
Name of structure
Position
Role
Sinoatrial node (SAN)
Pacemaker set in the wall
of the right atrium
Generates electrical
impulses and sets off a
wave of electrical activity
across the heart muscle of
the atria
Non-conductive septum
Between the atria and
ventricles
Prevents the impulse
travelling from the atria to
the ventricles, so the atria
contract first
Atrioventricular node (AVN)
Conductive node at the
base of the atria in the
septum
Delays the electrical signal
for long enough for the atria
to contract and then allows
the signal to travel across
the septum
Bundle of His
Specialised muscle fibres in
the central septum of the
heart
Carry the impulse to the
heart apex (at the bottom)
so the contraction of the
ventricles starts at the apex
and squeezes the blood out
of the ventricles into the
arteries
Purkyne tissue
Specialised muscle fibres in
the outer walls of the heart
Carry the impulses back up
the outer walls of the
ventricles, causing
contraction of the ventricles
10
ai
Depolarisation of the atria, causing them to contract.
a ii
Depolarisation of the ventricles, causing them to contract.
a iii
Repolarisation of the ventricles, causing them to relax.
b
The number of beats per minute (or how close together or how far apart are the
peaks). A fast beat is tachycardia and a slow beat is bradycardia.
c
Irregular beat; the heart muscle is responding incorrectly to the electrical signals or
the signals are not regular; the doctor would conclude that the ECG indicates either
damage to the heart muscle or an enlarged heart.
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Haemoglobin
1
a
Quaternary structure as there are four protein globular chains (two α and two β);
each has an iron-containing haem group attached.
b
The haem allows oxygen to bind to the molecule — one oxygen per haem group, so
four oxygen molecules per haemoglobin (4O2 or 8O).
2 The steep increase is due to the increasing ease of taking up oxygen once the initial
oxygen molecule is taken up. This initial oxygen distorts the haemoglobin molecule so it
becomes easier for the remaining oxygen molecules to be taken up.
3 The partial pressure of carbon dioxide influences the uptake of oxygen. The Bohr effect is:
as carbon dioxide partial pressure increases, the affinity of haemoglobin for oxygen
reduces (the curve moves to the right). This means that as carbon dioxide levels rise,
oxygen is more readily released from the haemoglobin. It is caused by the rise in pH that
results from the carbon dioxide increase.
4 The fetal curve is to the left of the adult curve, meaning that the affinity for oxygen is
greater than in adult haemoglobin. This is important because the fetus must remove
oxygen from the maternal haemoglobin.
5
(1)
Dissolved carbon dioxide in the plasma as it is readily soluble.
(2)
As bicarbonate ions, which are formed by dissociation of carbonic acid in the red
blood cells. Carbonic acid forms when carbon dioxide dissolves in water. The
bicarbonate ions are then transported into the plasma by the chloride shift —
chloride diffuses into the cell from the plasma.
(3)
By forming carbaminohaemoglobin, a compound formed when carbon dioxide
bonds to the haemoglobin molecule. The H+ ions released combine with
haemoglobin to form haemoglobonic acid. To do so the oxygen must first be
released from oxyhaemoglobin. The advantage is that when carbon dioxide levels
are high oxygen is more readily released and the H+ ions are buffered to prevent an
increase in acidity.
Exam-style questions
1
a
Open circulatory system
Closed circulatory system
Single circulatory system
Double circulatory system
b

Highest = systole; lowest = diastole.
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c
Systole/contraction causes increased pressure; of the left ventricle wall/muscle;
diastole/relaxation so decreasing pressure.
d
Pressure from behind as the blood pushes onwards; the valves along the length of
the veins; prevent backflow; skeletal muscles place pressure on the vessels to force
blood onwards.
e
The capillary wall is thin/only one cell thick; high pressure would damage/burst the
capillary; this reduces the chance of tissue fluid build-up/oedema; allows the
exchange of materials at the capillaries.
2 Haemoglobin is a pigment found in red blood cells. These cells are also known as
erythrocytes. Haemoglobin has a high affinity for oxygen. In the lungs the haemoglobin
associates with oxygen to form oxyhaemoglobin. In respiring tissues the oxygen is
released by dissociation. In very active tissues the amount of oxygen released can be
increased by the presence of more carbon dioxide. This is called the Bohr effect.
3 Initiated in sinoatrial node; no stimulus required; spreads across muscle of both atria;
which contract; a short lull as detected by atrioventricular node; travels through bundle of
His and Purkyne tissue to heart apex, where ventricular contraction begins; coordination
by sympathetic and parasympathetic nerves from the cardiac centre in the brain;
sympathetic: speeds up heart rate so the heart beats faster; parasympathetic: slows down
heart rate so a slower beat.
Topic 3 Transport in plants
Transport systems in multicellular plants
1 Plants have a highly branching body that gives a very large surface area to volume ratio in
all plants; the metabolic rate of plant tissue is low and so oxygen demand is low; the
leaves and stems produce oxygen during photosynthesis in the chloroplasts, reducing
further the need for oxygen from outside.
2 Aligned end to end to form a continuous tube; end walls broken down; the walls are
lignified so the cells are dead — no cell contents to impede water flow; the lignin
strengthens the walls against the high pressure exerted by the flow of water and supports;
gaps in the side walls (pits) allow the lateral movement of water.
3 Tracheids and sclerenchyma cells.
Both needed for the mark.
4
a
Provides strength as well as being a rigid support.
b
Allows flexibility, e.g. in the stem, which may be important in conditions where the
wind provides a sideways force on the plant.
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The vascular system
1 Aligned end to end to form a continuous tube; end walls are perforated to form sieve
plates; have no nucleus and few cell organelles so can more easily transport assimilates;
each sieve tube has a companion cell with which it shares many of the life-supporting
processes carried out by the organelles; connect to the companion cells via
plasmodesmata.
2 Xylem — dead cells and walls thickened with lignin; phloem — living cells with no wall
thickening; xylem — no end walls; phloem — has sieve plates for end walls; xylem —
exists as a continuous tube or individual cells; phloem — needs the support of a
companion cell to share a nucleus and organelles and sustain cell life.
3
Method of water
transport
Details of route
Function
Apoplast
Through the permeable cell
walls, which offer little
resistance
Most of the water uses this
route; it is efficient as water
moves rapidly as if through
filter paper
Symplast
Through the cytoplasm of
one cell to another using the
plasmodesmata in side walls
A continuous flow from one
cell’s cytoplasm to another;
slower route
Vacuolar
From one cell vacuole to the
next, so passes through cell
membrane and tonoplast
Allows some control of
which molecules pass
through
4 It is a band of waterproof (suberin) waxy material that blocks the apoplast route at the
endodermis; this prevents flow into the xylem by this route; the symplast route must be
taken, so a selection of what enters (water, dissolved ions) can occur. Protein carriers in
the endodermis also regulate uptake by active transport.
Transpiration
1
a
The transpiration stream.
b
The cohesion of water molecules to each other (they are polar molecules); as water
molecules are pulled from above, they pull other water molecules with them;
because they are under cohesive forces (stick to each other); the theory is called
the cohesion-tension theory because there is tension on the water from above as
water evaporates from the leaf.
2 The water molecules must be close together to allow cohesion; a continuous column or
stream of water is needed; no air locks can occur; sideways movement to avoid air
blockages provided by the pits in the side walls; adhesion of the water molecules to the
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walls of the xylem to ensure water remains in place even when no transpiration is
occurring (this avoids gravity causing the column to fall); stomatal pores in the leaves
allow both gas exchange and water to leave by evaporation.
3 Because the stomatal pores must be open to allow gas exchange.
4
Factor
Requirement
Effect on transpiration rate
Temperature
Needs a water potential gradient
from inside leaf air spaces to
outside the leaf; the stomata must
be open — high temperatures
cause stomatal closure which stops
transpiration
Increasing temperature increases
kinetic energy of the water
molecules, so they move more
rapidly and diffusion increases
Movement of
air
The water potential gradient must
be higher inside leaf than outside to
allow water to move down the
gradient; the stomata must be open
Increasing air movement increases
transpiration as the concentration
gradient is maintained, but a
maximum level is quickly met
Humidity
The diffusion gradient between air
outside leaf and the air in the leaf air
spaces must be high so that water
can diffuse out; the stomata must be
open
Increasing humidity reduces the
water potential gradient, so the
transpiration rate falls
Light
The stomata must be open — in the
dark they are closed but open as
light increases
Increasing light intensity is only
effective on rate until all the
stomatal pores are open
5
a
That the same amount of water is taken up as is lost by transpiration.
b
Some water is taken up and used by the plant in metabolic processes such as
photosynthesis and some water may be produced by the plant’s metabolic
processes.
6 No air must get into the apparatus; it must be set up under water to avoid an air lock in the
xylem vessels; it must be airtight to stop water loss from the apparatus and prevent air
from entering, or water movement will be halted; the leaves of the plant must be dry to
prevent a humid atmosphere around the leaves; the apparatus must be allowed to
stabilise before taking readings.
7
a
20°C = 28.33 mm/min; 30°C = 55.33 mm/min; 40°C = 27.00 mm/min.
b
As the temperature increases, the mean distance moved by the bubble increases;
up to 30°C/a positive correlation between temperature rise to 30°C and bubble
distance moved.
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c
At 20°C the reading at 3 minutes is incorrectly recorded to whole numbers. All the
data must be recorded to the same number of decimal places, in this case to 1
decimal place, so the reading should be 30.0
d
As temperatures rise above 35°C/higher temperatures the stomatal pores close
(and so slow transpiration).
e
Calculate standard error or calculate the distance of each reading from the mean for
that temperature and calculate the percentage distance. If greater than 10%, the
result may be considered to be anomalous.
8 Calculate the cross-section of the capillary:
πr2 = 3.142 × 0.6 × 0.6 = 1.131
Multiply by the distance moved in 30 s = 25.0, so 1.131 × 25 = 28.278
Multiply by 2 for water uptake per minute = 56.6 mm 3 min–1
Adaptations of plants to the availability of
water
1 A waxy cuticle over the leaves and stem; stomata restricted to the lower surface of the
leaves to reduce diffusion; stomata close at night when carbon dioxide uptake is not
needed; overlapping leaf canopy further reduces diffusion.
2 Any four from: reduction in stomatal number; stomatal pores protected to reduce the
diffusion gradient and so water loss, e.g. sunk in pits; in grooves; surrounded by hairs or
leaf rolled up with stomata on the inside; leaves reduced in size to small needles or spines
so the surface area of the leaf is reduced; deep, wide roots to increase water uptake.
3 Any four from: stomata on upper surface; large air spaces; thin, flat leaves or feathery
leaves for buoyancy; thin waxy cuticle; reduced veins in leaves; reduced root system.
Translocation
1 The meristems or growing points in roots, stems and leaves; storage organs; buds of
flowers.
2 It has not been proven or disproven by experimentation.
3
a
Active transport into phloem; ATP supplied by companion cells; passive movement
through the cytoplasm and plasmodesmata.
b
Actively pumped out of the phloem at the sink; (as a result) decrease in water
potential in the phloem; water leaves the phloem by osmosis (some enters the
xylem); creates a reduction in pressure in phloem; pressure gradient from source
(high pressure) to sink (low pressure).
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4 Transport in phloem — radioactive tracers and ringing experiments support this. Mass flow
— supported by modelling experiments/not supported so far in living plants. Loading and
unloading — supported by the use of ATP and active transport, and mitochondria in
companion cells and living phloem tubes; metabolic poisons halt translocation. Source to
sink movement — pressure gradient high at source and low at sink supported by pressure
evidence when the phloem is cut as the sap leaves faster at source than at the sink.
(Award no marks for giving a counter-argument as the question does not ask for this.)
Exam-style questions
1
a
Cut the end under water and immediately transfer it to the potometer under water.
b
The water used/retained by the plant can be calculated; the calculated transpiration
loss will be more accurate.
ci
Water loss = 376.8 – 375.8 = 1.0 g per 20 minutes, so 3.0 g per hour.
Water uptake = 10.00 – 9.40 = 0.60 cm per 20 minutes, so 1.8 cm per hour.
c ii
The assumption is that the water loss from the plant is the same as water taken up.
However, some water is retained by the plant and some is used by the plant, e.g. for
photosynthesis.
c iii
Both mass and volume of water in the tube are reaching a point of stability, i.e. there
is little or no further loss in value for both.
c iv
The stomatal pores close, which may reduce further water loss and prevent the
plant from dying.
2 Active transport/uptake. (Allow facilitated diffusion, but award no credit for osmosis.) Cells
have hairs/extensions; thin cell wall; large/increased surface area; many/more
mitochondria; (many) carrier proteins/transport proteins/protein pumps in cell-surface
membrane.
3 D: thick waxy cuticle; E: waxy layer prevents water loss from that surface.
D: leaf curled/folded; E: reduces surface that is exposed; creates high water (vapour)
potential (outside stomata); reduces water (vapour) potential gradient.
D: hairs; E: reduces evaporation/diffusion through the leaf surface; trap water vapour;
creates high water (vapour) potential (outside stomata); reduces water (vapour) potential
gradient.
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Module 4 Biodiversity,
evolution and disease
Topic 4 Communicable diseases,
disease prevention and the immune
system
Pathogens
1 They prevent harmful organisms growing on the body; some may assist in the digestion of
complex foods; some produce vitamins that we do not obtain from our food.
2 It lives on or in the host body and obtains all of its needs, such as energy, nutrients,
moisture and protection, without any benefit to the host; some cause harm to the host.
3 A communicable disease is any disease caused by a pathogen. A non-communicable
disease is a disease not caused by a pathogen but it may be caused by genetic or
environmental factors, such as diet or pollution.
4 Any three from: transmission through water; contaminated food; airborne pathogens;
droplet infection; direct skin contact; use of a vector such as the mosquito.
5 Failure to vaccinate in many countries, owing to misunderstanding/fear of the process.
Overuse of antibiotics/poor use of antibiotics forming resistant strains; mutations; reduction
in inoculations because of religious or other reasons.
6 It is an intercellular bacteria — it infects the space between the cells, especially in the
meninges of the brain.
7 They feed on the dead and decaying tissue before re-infecting new hosts.
8 They infect cells and then use the host cell replication procedures to make more viruses;
they do not need to carry out any functions normally associated with living cells because
the host cell carries it all out for them, including reproduction.
9 Similarities: they both consist of a viral protein forming a coat (capsid) around a central
RNA core; surrounded by a phospholipid bilayer formed from the cell-surface membrane
of the host cell; glycoproteins in the bilayer allow them to re-infect new host cells.
Difference: HIV is a retrovirus with an enzyme (reverse transcriptase) that copies the viral
RNA into host DNA so it becomes a permanent part of the host cell DNA (a provirus).
Allow 2 marks for similarities; 1 mark for a difference.
10
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17
a
Plasmodium species.
b
There are a number of different Plasmodium species that infect humans.
Plasmodium falciparum is the most dangerous as it may cause death. The method
of infection is by a vector (the female mosquito), where the parasite lives part of its
life cycle and reproduces before infecting a new human host.
11 Cell walls of chitin, not cellulose; oil is the food storage material, not starch; the body is
made up of long thin threads (or filaments) called hyphae; often with multiple nuclei per
cell; reproductive structures are spores.
12 The immune system of animals often prevents fungal attack; the microbiome (bacterial
organisms naturally growing on or in animal cells) makes the host inhospitable to fungi.
13 Plant: potato or tomato blight (Phytophthora infestans); black sigatoka in bananas
(Mycosphaerella fijiensis). Animal: ringworm (Trichophyton verrucosum); athlete’s foot
(Trichophyton rubrum); infections of the mouth and reproductive tracts (Candida albicans).
14 It has cell walls of cellulose, not chitin, and stores starch. Both of these are plant
characteristics, although it also has fungal hyphae and spores.
15
Pathogen
Bacterial
Viral
Disease
Transmission
Animal
TB — Mycobacterium tuberculosis and
M. bovis
Droplets in the air
Plant
Ring rot — Clavibacter michiganensis
subsp. sependonicus
Contact with infected plant
material
Animal
Influenza — influenza A, B or C (from
family Orthomyxoviridae)
Droplets in the air
Plant
Tobacco mosaic virus — TMV
Contact with infected plant
material or indirectly through
aphids carrying the virus from one
plant to another
Peach blight and potato leaf roll
Indirect transfer through aphids
such as Myzus persicae
Malaria — Plasmodium species (e.g. P.
falciparum)
Indirect transfer via the female
Anopheles mosquito species
Animal
Ringworm — Trichophyton verrucosum
or athlete’s foot — Trichophyton rubrum
Contact such as via
towels/footwear
Plant
Black sigatoka — Mycosphaerella
fijiensis
Spores dispersed through the air
Potato blight — Phytophthora infestans
Spores dispersed through the air;
swimming spores in water film
Protoctistan
Fungal
Fungal-like
16
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a
From one host to another, so it needs contact or droplets spread from one host to
the next.
b
Via an intermediary or secondary host, such as a vector that transmits the pathogen
in its own body. Frequently some of the life cycle of the pathogen occurs in this
secondary host.
17 A disease that could not normally survive in a host, but it takes advantage of a weakened
host. This is typical of the symptoms of AIDS that occur once HIV begins to attack the
host’s lymphocytes.
18 Any three from: check the procedure to ensure no contamination; repeat using all four TB
drugs together to test the development of resistant strains; repeat using other
combinations of the four drugs; repeat all stages of the investigations at least three times
to ensure the conclusions are reliable and valid; carry out statistical tests to check the
results are valid.
Factors affecting transmission
1 Resistance is an inherited condition that confers protection against catching a specific
disease. Immunity is where an initial encounter of the disease-causing organism results in
the development of future protection because the immune system develops the necessary
antibodies to help fight the disease so a subsequent encounter will not result in any
symptoms.
2
Type of transmission
Type of disease
Factors that affect transmission
Direct
Influenza
Proximity of hosts, so spread is more
rapid in schools and hospitals or poor
housing
TMV in plants
Monoculture farming methods
Indirect
Transmission by
vectors
Climate and weather; a breeding
ground such as stagnant water
Human diseases
H1N1 influenza strain
or SARS
Increased travel
Cholera, typhoid or
polio
Contaminated water supply such as
in poor areas; poor sanitation; poor
hygiene and untreated sewage
Smallpox
Travel to areas with no resistance
and no immunity
HIV
Human behaviour can increase the
risk of spread
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Plant defences
1 They all prevent the infection entering the plant.
2 Any three from:
secretion of chemicals that encourage microbes that compete with the pathogen
secretion of chemicals that are toxic to pathogen
secretion of inhibitors of enzymes that pathogens rely on to gain entry to the plant cells,
such as cellulose
enzymes assist pathogen by breaking down the cell wall and inhibitors disrupt this process
production of resin that prevents the spread of pathogens
3 Any one from:
production of calluses around the pathogen-infected site
cell death around the pathogen
tyloses in the vascular tissue block the vessels and prevent the spread of pathogens
cell signalling stimulates the production of defence chemicals such as phytoalexins that
disrupt the pathogen either by affecting its reproduction or its metabolism or by disrupting
its cell-surface membrane
salicylic acid travels to other parts of the plant, giving them protection against infection
ethylene stimulates other parts of the same plant when under attack
4 A long-term response to pathogens and infections caused by cell-signalling molecules.
The primary non-specific defences in
animals
1
Category of defence
mechanism
Method
Example
Cellular
Cells signal the body about
an invasion of pathogens;
produce substances that
protect; ingest pathogens
Secretion of cytokines,
interleukins and histamines;
goblet cells throughout the gut
and airways produce a sticky
mucus of glycoproteins to trap
bacteria and particles
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Category of defence
mechanism
Method
Example
Chemical
The body secretes
substances that change the
environment to become
hostile to the pathogen;
causes pathogens to burst;
stops pathogens reproducing
or growing; prevents entry
into the cells
The enzyme lysozyme is an
antibacterial agent that is
produced in tears; fatty acids in
sebum have antibacterial
properties; hydrochloric acid
produced by the stomach lining
destroys bacteria; histamines;
cytokines
Physical
Tissues act as a barrier
Skin and mucus membranes of
the gut; the gas exchange
system; reproductive system
Microbiome (our own
bacterial flora living on
and within us)
Compete with pathogens and
prevent them developing and
growing
Bacteria in the reproductive
tract prevent growth and
development of the fungus
Candida albicans; E. coli in the
gut compete successfully with
pathogens and prevent them
developing
2
a
Barrier: keratin in the outer layer is a tough dead layer that prevents entry.
Chemical: secretions such as sebum make the skin acidic; sweat evaporates and
leaves salts and little moisture; all prevent growth of microbes.
b
A sudden expulsion of air (a sneeze or cough) that removes pathogens from the
airways, caused by irritation of airway’s lining; it also increases the spread of
pathogen.
3 The gut flora (part of the microbiome) is also destroyed and so other infections may
develop, such as Candida albicans.
4
a
Blood clotting — seals the wound to stop blood loss and prevents entry of
pathogens.
Inflammation — vasodilation increases blood flow to the site, leaky capillaries allow
fluid into the tissues, phagocytes leave the blood for the affected tissue to attack
pathogens
Cytokines — promote inflammation, release phase proteins that attach to pathogens
to encourage attack by phagocytes and signal to the rest of the body.
Wound repair — respond to growth factors from platelets, stem cells divide and form
new tissue, wound contraction.
Phagocytes — engulf pathogens and foreign proteins, neutrophils engulf and
destroy bacteria, monocytes form macrophages in the tissues (such as liver, lungs,
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kidney, brain, spleen and lymph nodes) and are long-lasting, also present foreign
antigens on their surface, dendritic cells interact with the pathogens and
lymphocytes.
b
It responds in the same way whatever the type of pathogen; it is very rapid but not
completely effective.
5 A specific defence response to a particular pathogen involving lymphocytes producing
antibodies that recognise different pathogens by their antigens.
The primary and secondary immune
responses
1 B lymphocytes originate in the bone marrow and differentiate there; they become plasma
cells and are found in the plasma and in the lymphatic system; they produce antibodies
and memory cells.
T lymphocytes originate in the bone marrow but move to the thymus to mature and
differentiate; they do not make antibodies but work in a number of other ways; they
secrete chemicals such as cytokines and interleukins that stimulate mitotic divisions,
stimulating B lymphocytes and coordinating the response.
2
3 Similarities: both have receptor proteins on the surface of the cells; the first stage is
antigen presentation; occurs on macrophages and stimulates the cell response in both;
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clonal selection and expansion by mitosis occur in both; cytokines produced and
coordinated.
Differences: macrophage releases cytokine, interleukin 1 (IL-1) to stimulate T helper cells
to divide; B cells ‘display’ to T helper cells to activate those correct ones with
complementary fit; T helper cells release the cytokine, interleukin 2 (IL-2); IL-2 stimulates
B cells to divide and differentiate into plasma cells and also memory cells; B plasma cells
produce antibodies by protein synthesis; IL-2 coordinates the activity of the other aspects
of the immune response including lymphocytes and macrophages; it stimulates T helper
cells to produce another cytokine, interferon (IFN), to stimulate macrophage activity; T
cells produce a number of different types of T cells at the start of the immune response; B
cells respond by specific antibody production; T cells respond by T helper cells producing
cytokines to coordinate the immune response and by T killer cells that attack and destroy
infected cells (e.g. a cell infected with a virus); T regulator cells shut down the immune
response and prevent uninfected cells from being attacked.
Award a maximum of 2 marks for similarities and 4 marks for differences.
4
a
The memory cells remain present in the blood and lymph and are activated as soon
as the same antigen is detected; they produce complementary plasma cells without
the need for clonal selection and activation; as more clones are already present.
b
The response is faster and the number of plasma cells and antibodies are very
much greater in the secondary response; there are no symptoms or evidence of the
disease in the individual because the pathogen is destroyed more quickly.
a
Primary response: 18 days; secondary response: 6 days.
b
Primary response: 2.5 au; secondary response: 7 au.
5
Antibodies
1 Antibodies are formed of more than two polypeptide chains held into a Y shape by
disulfide bonds (which are strong bonds).
2
a
This is the same for all antibodies of a particular type; it binds to the receptors on
phagocyte surfaces.
b
This is the antigen-binding site — each antibody variable region has a different
antigen-binding site; it binds to specific antigens of a pathogen or foreign protein
that carry the complementary shape; this region is different for each type of
antigen/complementary to a specific antigen.
3 Antitoxins: make toxins produced by pathogens harmless by combining with them.
Agglutinins: bind two antigens from different pathogens together making them clump.
Opsonins: coat pathogens to mark them for destruction by phagocytes.
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Types of immunity
1
Type of
immunity
Active
Passive
Natural
Immunity following an infection
Immunity conferred by antibodies
from an immune individual
crossing to a non-immune
individual
e.g. chicken pox virus
e.g. crossing the placenta during
pregnancy and in the mother’s
milk during breast-feeding
Immunity following a vaccination
containing disease antigens
Immunity following an injection of
antibodies from another source to
give immediate immunity
e.g. mumps or whooping cough
e.g. tetanus, rabies or diphtheria
Artificial
2 Day 3 = 90 au; day 7 = 50 au.
Autoimmune diseases
1
a
Where the immune response attacks the body’s own cells, often against one organ
but it may be against the whole body such as in Crohn’s disease, lupus or
rheumatoid arthritis.
b
The immune system attacks self-antigens using mostly T helper cells and T killer
cells. It may be the result of a genetic predisposition caused by an inherited gene,
but environmental issues also play a part.
Immunisation and vaccination
1 Vaccination is the active process of immunising people using live, attenuated or killed
pathogens. Immunisation is artificial active immunity by the use of vaccination and artificial
passive immunity.
2
a
Vulnerable adults such as those with a chronic illness (weakened immune systems),
pregnant women (the fetus has not developed an immune system) or health
workers (increased risk as close contact with sufferers).
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b
The individuals are especially susceptible and as the virus mutates frequently, it
forms new strains at regular intervals and it would be difficult to keep everyone in
the population fully vaccinated.
3 Ring: vaccination of those around or living near infected individuals — limits but does not
stop the spread of the disease.
Herd: vaccination of as many individuals as possible in a population — 95–100% needed
and the disease and its spread are stopped.
4
Organism
Problem for vaccine development
Plasmodium
A eukaryotic organism that produces many antigens on its surface
and different ones at different stages in development
Viruses
Viruses infect the cells and take over the host cell replication
mechanism; antigens are ‘hidden’ or different strains cross breed
to form new ones
Mutated viruses
Antigenic drift — small changes in the antigens; antigenic shift —
large changes in the antigens for the same virus strain
New diseases
No effective drugs have yet been developed
Possible sources of medicines
1 Compounds produced by fungi and actinobacteria and other plants and animals; possible
genes that may produce suitable drugs; develop molecules that will fit into receptor
proteins on membranes such as those for hormones or neurotransmitters; modification of
existing drugs; traditional plant remedies that offer potential medicines; personalising
medicines for the individual; synthesising medicine using produced genomes that can suit
an individual or a small group of people.
Antibiotics
1 They are ‘anti-biotic’ (i.e. anti-bacterial) and work by damaging the bacterial cell walls, by
inhibiting bacterial enzymes or by preventing bacterial reproduction; none of these are
effective against other organisms such as viruses or protoctistans.
2 Mutations leading to antibiotic-resistant strains; prescription misuse of antibiotics for viral
infections; patient misuse by halting treatment too early; overuse of antibiotics; use of
antibiotics in farming.
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Exam-style questions
1
a
Short term: group 2 had an immediate benefit, since the antibody concentration
immediately rose to 23 au on injection. In group 1 it took 10 days to reach an
antibody concentration of 24 au.
b
Long term: group 1 had longer-term benefits, since the antibody concentration took
8- days to fall to 3 au, whereas in group 2 the antibody concentration fell to 2 au
within 15 days. The antibody concentration in group 2 fell quickly to the level at 15
days, whereas in group 1 there was a slower, steadier fall over 80 days.
2
Type of nonspecific defence
Action
Blood-clotting
Rapid response; platelets release a compound; chain reaction or
cascade; large number of plasma proteins; fibrin produced; traps
blood cells; clot forms
Inflammation
Histamines secreted; site of infection inflamed by interleukins
promoting inflammation; increase in blood flow due to
vasodilation; leaky capillaries allow fluid to leave the capillary for
tissues; allow plasma proteins to leave; secretion of cytokines
that stimulate and signal to whole body
Wound repair
Stem cells at the site divide and begin repair; platelets secrete
growth factors; new blood vessels; collagen produced; formation
of new tissue; contractile cells contract wound and close it up;
destruction of unwanted cells
Phagocytes
Neutrophils spread rapidly to the site and destroy pathogens,
but then die and form pus; monocytes enter tissues and form
macrophages; these are important in the specific response;
dendritic cells have a large surface area to interact and trap
pathogens; take them to lymph nodes
3
a
Transmission is by droplet infection, so coughing and sneezing of an infected
person spreads the infection in the air, which is then inhaled by another person.
b
In 1920 it was 78 000 and in 2005 it was 5000 individuals, so the difference is
73 000.
c
There was a steady drop from about 1915 of 90 000 cases to 50 000 cases in 1950,
with an increase in about 1925 and again in 1940.
From 1950 to 1968 the fall was very steep (50 000 to about 14 000) and from 1968
to 1990 the fall slowed to 5000 where it remained at almost a plateau with just a
very slight rise at 2005.
Allow 1 mark for correct data quotations (two sets, i.e. year and number of cases ×2).
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4
a
b
Polypeptide chains that are held together by disulfide bonds.
5 Introduction of attenuated or killed pathogen; carries the antigen; activates the patient’s
immune response; build-up of antibodies and memory cells.
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Topic 5 Biodiversity
Levels of biodiversity
1 A group of organisms with observable similarities that can interbreed to produce fertile
offspring.
2 The variety of different species found in a particular place.
3 Species richness is the number of different species present. Species evenness is the
abundance of organisms/number of different organisms within a species.
4 The unique combination of genes in different individuals and the different forms of those
genes present (alleles).
5 All the alleles of all the genes within a species.
6 Separation of different allozymes within an individual; sequencing the DNA: studying the
nucleotide sequences of the allozymes; allowing comparisons between individuals after
sequencing.
7
Assessment
What this means
Method
Proportion of gene loci with
two or more alleles
The proportion showing
polymorphism
Determine the genotypes in
a sample of the population
and calculate the % of
alleles
Proportion of heterozygotes
in population
Those with different alleles
for a feature, e.g. Hh
Cross-breeding or
interbreeding (not
inbreeding)
The number of different
alleles for a gene
Polyallelic or allele richness
Determine differences in
protein structure, e.g. blood
proteins in dogs show the
number of alleles varies
between 2 and 11
8
a
P = 9/39 = 0.23
b
95%
9 The number of different habitats available and for different species; may be determined by
assessing the number of niches — the more niches present in a habitat, the greater the
habitat diversity.
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Sampling
1 Random sampling using quadrats.
2 Sampling plants across zones; to demonstrate zonation.
3 Two from: pooters; sweep nets; pond nets; pitfall traps; beating trays.
Simpson’s Index of Diversity
1
a
Species
Total number of
each species (n)
n/N
(n/N)2
Dandelion
27
0.69
0.4761
Clover
7
0.18
0.0324
Trefoil
1
0.02
0.0004
Plantain
1
0.02
0.0004
Groundsel
3
0.07
0.0049
Total
N = 39
∑(n/N)2 = 0.5142
Award 1 mark for N = 39, 1 mark for all n/N2 values calculated correctly and 1 mark for a value of
∑(n/N)2 = 0.5142 or 0.51.)
b
D = 1 – 0.5142 = 0.4858 (or 0.49)
c
When the index is close to 0, there is low diversity. When the index is close to 1,
there is high diversity. A value of 0.49 is a 49% probability of different species, so it
is close to the average.
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Factors affecting biodiversity
1
Factors
affecting
biodiversity
Causes
Effects
Loss of habitats:
Deforestation
Clearing for: industry or housing
Destruction of
coral reefs
Farming, fishing and leisure
Destruction of the
sea bed
Dragnets scrape the sea bed
Exploitation
Removal of timber for industry or
furniture; overfishing so fish stock
falls
Reduction in the number of species
and loss of habitat
Over-hunting
Removal of wild animals as ‘bush
meat’
Species at risk of extinction
Agriculture
Monoculture of one type of crop or
livestock
Reduction in the number of a
particular species
Pollution from
agriculture
Waste products; use of fertilisers
and pesticides
Loss of biodiversity as some
species thrive with additional
fertilisers and others are destroyed;
runoff pollutes streams and pond
water
Climate change
Modification of weather patterns
such as drought and floods affects
species distribution
Distribution of species changes;
lack of food for some species
causes decline
Loss of species and loss of
resources to rebuild number of
species; loss of habitat
Maintaining biodiversity
1 Biological: imbalance in natural communities; high diversity gives greater stability; ability to
withstand environmental changes; importance of keystone species; loss of top predators;
loss of control of the rest of food chain/web.
Economic: provision of ecosystem services such as oxygen input/carbon dioxide uptake;
water vapour; soil fertility; protection from erosion; reduce impact of flooding; insect
pollinators, e.g. bees; provide natural materials for drugs; for enzymes used in
biotechnology, e.g. DNA polymerase; house-building/furniture/flooring.
Maximum 2 marks each for biological and economic.
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2 Any three from: control of land management; conserve species/re-establish species;
restore damaged ecosystems; create new/re-establish old habitats; maintain habitats by
controlling invading species (e.g. Himalayan honeysuckle).
3 Any two from: botanic gardens; seed banks; zoos; protected game reserves.
Exam-style questions
1
a
The number of different species present (in a habitat).
b
Idea of random/unbiased sampling; repeated many times; mean calculated;
sampling at different times of the year; method suggested for sampling, e.g. random
quadrats and a grid set-up/random pinframes using grid set-up/line transect
described and selected line justified.
c
It measures abundance/numbers in each species; is more quantitative then species
richness; a higher species evenness indicates higher biodiversity (or the counterargument); can calculate Simpson’s Index of Diversity.
d
Student A on site A gained a higher value, which shows greater diversity than at site
B (or the higher value shows a greater number of species present than at site B).
a
Nymphaea.
b
Natural habitat lost/destroyed/damaged; number of species in population is (too)
low; (sexual) reproduction in the wild is difficult with low numbers; the ability to
maintain the gene pool ex situ; protection against
competition/grazers/pathogens/disease.
c
Any two from: collected without damage to the ecosystem; stored in little space;
cheaper to store/transport; viable for longer than adult plants; the ability to store
greater genetic/allelic diversity; protection against pollination by undesired
strains/against diseases.
d
Random sampling; set up a grid using measuring tapes at right angles; quadrat
coordinates random; use a key (identification); method to determine abundance,
e.g. ACFOR; sampling repeated many times; repeated throughout the year/at
different times of the year. (Or an answer that describes the use of a transect.)
a
Catch in 1968 = 3 900 000
2
3
Catch in 1970 = 3 100 000
Difference = 800 000, so rate = 800 000/2 = 400 000 tonnes per year
Catch in 1997 = 1 400 000
Catch in 1998 – 1 200 000
Difference = 200 000 tonnes per year
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Rate of decline is slower in 1998.
b
This indicates a decline in fish stocks and a decline in other species within the
related food web; biodiversity must be lower.
c
Fish stocks are slowly improving due to a reduction in fishing and better control on
fishing of young fish/there is an increase in line-caught fish popular in restaurants
and fish counters, so less damage is caused by dragnets.
There is no change in the basic level of fish stocks but simply a natural fluctuation in
numbers; the rise is no larger than previous increases seen over the past 60 years.
The increase is due to an increase in fishing as some controls are relaxed.
4
a
Any two from: hair; skin/tissue samples; blood; elephant dung; saliva; urine; bone;
sexual fluids.
b
Little mixing of populations; geographically isolated; family groups stay together;
little migration.
c
The Convention on International Trade in Endangered Species.
d
Any three from: ban on the sale of ivory; international markets fall so price
falls/below level of desired price; allows populations to recover; ban on hunting;
education/increase awareness; economic advantage to host country as it attracts
funds; (increased) cooperation between countries.
a
Fertilisers promote growth of a few species only; others are out-competed; disrupted
food chains; reduction in soil humus/quality so plants cannot grow.
b
Loss of genetic diversity/variation; changes in environment/agricultural needs; lost
alleles/genes that would have been useful; fewer pollinators; loss of predators.
c
Runoff/rainfall; affects rivers and streams; riverside species affected; flooding
spreads fertilisers further on to low-lying land.
5
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Topic 6 Classification and evolution
The biological classification of species
1 Domain, kingdom, phylum, class, order, family, genus, species.
Allow the reverse order, but not an incorrect order.
2 Mammalia.
3 Eukaryota, Animalia, Chordata, Mammalia, Artiodactyla, Giraffidae, Giraffa, G. jumae.
The species name can be underlined (instead of being italicised). The word ‘jumae’ must have a
lower-case j.
The binomial system
1
a
Mimus
b
Mimus macdonaldi or M. macdonaldi. The genus is always given a capital letter and
the species a lower case letter to differentiate between the two.
The five kingdoms
1 Prokaryotes, Protoctista; Fungi; Plantae; Animalia. All organisms (except viruses) are
grouped into five separate large groups on the basis of some distinctive shared
characteristics.
2
Features
Kingdoms
Prokaryotae
Protoctista
Fungi
Plantae
Animalia
Body type
Mostly
unicellular
Unicellular
and
multicellular
Mycelium
of hyphae
(except
yeasts)
Multicellular
Multicellular
and compact
Nucleus
Absent
Present
Present
Present
Present
Cell walls
Wall of
peptidoglycan
Wall
present in
some
Wall of
chitin
Wall of
cellulose
Absent
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Features
Kingdoms
Prokaryotae
Protoctista
Fungi
Plantae
Animalia
Cell
vacuoles
Only in a few
Some (e.g.
algae):
large,
permanent
vacuole.
Protozoans:
small,
temporary
vacuole
Large
permanent
vacuoles
Large
permanent
vacuoles
Small
temporary
vacuoles
Organelles
Absent
Present
Present
Present
Present
Motility
Some have
flagella
Some have
undulipodia
or cilia
Absent
Some
gametes
have
undulipodia
Muscular
system
Nervous
coordination
Absent
Absent
Absent
Absent
Present
Examples
(give two of
each group)
Bacteria,
cyanobacteria
Algae,
amoeba,
slime
moulds
Yeast,
mould
fungi
Liverworts
and
mosses,
ferns,
conifers and
flowering
plants
Coral,
worms,
insects,
molluscs,
echinoderms,
vertebrates
3
a
Prokaryotae: single-celled or filaments of single cells or colonies of single cells;
smaller than eukaryotes; no linear chromosomes; divide by binary fission; no
nuclear membrane; no membrane-bound organelles.
b
Protoctista: diverse group; all are eukaryotes; true nucleus with nuclear membrane;
membrane-bound organelles.
c
Fungi: all are heterotrophic; feed on dead, decaying matter; mycelium of threads
called hyphae; cell wall of chitin; store oil and may be multinucleated; reproduce by
spores; may be sexual or asexual, except yeasts, which reproduce by budding.
d
Plantae: multicellular; photosynthetic; complex bodies; frequently highly branched;
some specialised cells; immobile; usually reproduce sexually; cellulose cell wall;
mostly store starch.
e
Animalia: multicellular; heterotrophic nutrition, although some have a symbiotic
relationship with an autotrophic organism; complex and compact bodies; possess a
nervous system; no cell walls.
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New classification systems
1 Three domains: bacteria/eubacteria, archea/archebacteria and eukaryotes/eukarya
Five kingdoms: prokaryotae/prokaryotes, protoctista, fungi, plantae/plants and
animalia/animals. In the kingdom-based system, eukaryotes are subdivided into different
kingdoms/eukaryotes are all in same domain; prokaryotes are all in same
kingdom/prokaryotes are split into different domains; domain classification based on
rRNA/ribosomes/RNA polymerase/protein synthesis/enzymes/membrane
structure/flagella.
2
a
Antibodies: using antibodies to detect similarities and differences between complex
molecules and compounds; relies on the specific shape of the variable region of
antibodies.
b
Protein sequencing: sequencing amino acids in a protein; identifying similarities and
differences in proteins of different species; by comparing the primary structure of the
proteins (e.g. cytochrome C on the mitochondrial membrane); usually uses the one
letter code for amino acids to read the sequence; also uses the R groups of different
proteins.
c
DNA hybridisation: identification of DNA similarities between species; DNA is cut
into small pieces and the H bonds between each half of each section by high
temperatures (of 90°C); mixing the strands with similar treated DNA of other
species; bonding between the DNA half strands of different species occurs;
differences occur as the DNA match is not correct; imperfect matches have weaker
H bonds; small amounts of heat separate these whereas much more heat is
required to separate perfect matches.
d
DNA sequencing: sequencing DNA bases is easier than sequencing the amino
acids of a protein due to the degenerate nature of the DNA code; allows significant
differences between codes to be identified; allows mutations to be identified; much
more accurate differences to be seen.
Classification and phylogeny
1 The evolutionary history of a specific taxon; a group of organisms at any level or rank in
the hierarchical classification system, for example a named species or any group such as
plants or mammals.
Evidence for the theory of evolution
1 Any three from: collect resources (such as food, water, a space to live); survive predation;
survive diseases; mate and produce offspring (to pass on their genes).
2
© Jenny Wakefield-Warren 2015
Philip Allan for Hodder Education
35
a
Morphology: similarities of the external form of organisms, e.g. birds have feathers,
wings and a beak.
b
Anatomy: a comparative study of the limbs in all tetrapods (amphibians, reptiles,
birds and mammals) shows striking similarities.
c
Fossils: mineralised remains of an organism or faeces or other evidence. The Rift
valley in Africa has a wealth of fossils that can be dated according to the rock layer
they are found in/carbon dating/argon dating.
d
Biochemistry: similarities in proteins and amino acids; the similarity of the genetic
code: DNA; ATP is the universal energy currency; similarities in enzymes, e.g. DNA
polymerase; comparative studies of DNA and proteins show remarkable similarities
in closely related forms.
e
Classification: the study of classification and phylogeny.
Variation
1 Genetic variation is the variation in the genotype within a species. Phenotypic variation is
the differences that are detectable within a species, e.g. the external appearance or the
biochemistry of organisms within the species.
2 Interspecific variation is the differences between the species. Intraspecific variation is the
differences within the same species.
3
Type of variation
Continuous
Discontinuous
Discrete categories
No
Yes
Intermediates
Yes
No
Continuous with no
categories
Yes — a range of
values/measurements
No
Type of data
Quantitative
Qualitative
Genes controlled by
Many genes with two or more
alleles
One or two genes, each with
only two or a few alleles
Environmental effect
Large effect
Little or no effect
Examples
Height of animals, plant leaf
width, coat colour
Human blood groups
© Jenny Wakefield-Warren 2015
Philip Allan for Hodder Education
36
4
a
Holly leaf type
Replicates of spine
numbers
Mean number of spines
Ilex aquifolium
12
14
9
11.66
Ilex verticillata
3
2
4
3
b
Errors: there is an incorrect number of decimal places for Ilex aquifolium as the data
are in whole numbers, but the mean is recorded to 2 decimal places. It should be to
the same number of decimal places or one more decimal place for any calculated
data — one value recorded to 2 decimal places and the other to a whole number.
c
Validity of conclusion: It is valid because it is based on 50 leaves and replicated
three times; not valid because it is a small sample size/no statistical test has been
carried out on the data; the environmental effect has not been considered; any
suitable named environmental effect.
The implications of evolution for humans
1 Antibiotic drug resistance over time is as a result of use of overuse/misuse of antibiotics;
change in the genes/mutation in the genes. Pesticide resistance over time is as a result of
overuse/misuse. Both are selective agents; both types of resistance result from mutations;
both are adaptations to a hostile environment; pesticides are manufactured
chemicals/antibiotics were originally naturally produced by organisms such as fungi.
Exam-style questions
1
a
It assists in deciding which group/taxon/organisms or species (or named example)
belong to; compare DNA/genes/sequence of bases/proportion of different bases;
the idea that the more similar the DNA/genes, the closer the relationship.
b
Fossils/fossil records; anatomy; physiology; behaviour; embryology.
a
On mitochondrial membranes or thylakoids in green plants.
b
Between cartilaginous and bony fish; between birds and reptiles.
2
© Jenny Wakefield-Warren 2015
Philip Allan for Hodder Education
37