AQA GCSE Answers Key [ For teachers ]

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B4 Organising animals and plantsStudent Book answers
B4.1 The blood
Question
number
Answer Marks Guidance
1 Any three from:
 transport of blood cells,
 transport of dissolved gases,
 transport of food,
 transport of hormones,
 removal of waste products,
 defence against infection,
 preventing blood loss through clotting.
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2 a Blood is made up of plasma (dissolved substances in yellow liquid)
in which red blood cells are suspended.
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2 b red blood cells 1
2 c Any three from:
 transports waste products to kidneys as urea,
 transports soluble products of digestion to cells,
 transports waste carbon dioxide to lungs,
 transports oxygen around body in red blood cells.
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3 white blood cells:
 relatively large blood cells with nuclei,
 protect against invasion of harmful microorganisms,
 some (lymphocytes) form antibodies or antitoxins,
 some (phagocytes) actively engulf and digest bacteria and
viruses
platelets:
 fragments of larger cells with no nuclei,
 help with clotting to keep microorganisms out.
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B4 Organising animals and plantsStudent Book answers
B4.2 The blood vessels
Question
number
Answer Marks Guidance
1 a carry blood away from the heart,
thick wall of muscle (to contain blood under pressure)
and elastic fibres (to allow stretch as blood is forced through by
heartbeat as pulse)
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1 b carry blood towards the heart,
relatively thin walls (blood not under pressure),
have valves (to keep blood flowing towards heart)
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1 c link arteries and veins,
very thin walls (to promote diffusion of substances in and out)
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2 a Arteries carry blood from heart to organs, veins return blood to heart,
capillaries link arteries and veins.
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2 b Oxygen and dissolved food substances diffuse from blood into cell
and waste products such as carbon dioxide diffuse out of cell into blood.
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3 In fish blood leaves the capillaries of the gas exchange organ slowly, at
low pressure, and without a pulse.
Active land mammals require lots of food and oxygen to supply muscles
and organs for movement and warmth. They also produce a lot of waste
materials such as carbon dioxide that must be removed.
Single circulation system would not be able to supply tissues or remove
waste fast enough as blood would travel around body too slowly.
Double circulation system much more efficient because blood is
pumped to gas exchange organ, then returns to heart and is pumped
around body quickly at pressure.
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B4 Organising animals and plantsStudent Book answers
B4.3 The heart
Question
number
Answer Marks Guidance
1 flow chart should include:
deoxygenated blood from body enters right atrium through vena cava →
oxygenated blood from lungs enters left atrium through pulmonary vein
→ atria contract together and force blood down into ventricles (lower
chambers) → right ventricle sends deoxygenated blood to lungs
through pulmonary artery → left ventricle pumps oxygenated blood
around the body through aorta
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2 a prevent blood flowing backwards,
making heart more efficient
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2 b supply heart muscle cells with oxygenated blood
for aerobic respiration and efficient contraction
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2 c allows heart to pump blood around body very efficiently,
enables blood to leave heart at high pressure,
right ventricle only has to send blood to the lungs (where high pressure
would be damaging)
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3 Pulmonary artery carries blood away from heart.
Blood carried from heart to lungs is deoxygenated blood from the body,
which is dark red until it picks up oxygen in the lungs.
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4 a metal mesh placed in artery and opened up by inflation of tiny balloon
to hold narrowed blood vessel open so blood can flow freely
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4 b Advantages:
Stent: no anaesthetic required, relatively cheap, effective
Bypass surgery: very effective against severe blockages
Disadvantages:
Stent: ineffective against severely blocked or narrowed arteries
Bypass surgery: general anaesthetic required, expensive
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B4 Organising animals and plantsStudent Book answers
B4.4 Helping the heart
Question
number
Answer Marks Guidance
1 group of cells in right atrium of heart
producing regular electrical signal that spreads through heart and
makes it contract
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2 electrical device implanted into chest producing regular electrical
signals to stimulate heart to contract and beat,
often inactive if heart beating normally and activated by change in heart
rhythm
may measure additional demands increase heart rate during exercise
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3 a Valves prevent backflow of blood in heart.
Leaky valve can allow blood to flow backwards,
which means full amount of blood does not leave heart
and blood coming into heart chamber mixes with blood that hasn’t left,
making heart less efficient.
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3 b i advantage: lasts a long time
disadvantage: lifetime medication required to prevent clotting
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3 b ii advantage: no medication needed
disadvantage: limited lifespan (12–15 years)
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4 Can be used to keep patient alive until suitable heart for transplant
becomes available.
Can be used in some cases to rest patient’s own heart and allow it to
recover.
May be used to replace the natural heart in the long term.
Very expensive,
not effective over long periods,
could be overtaken by organs grown from stem cells.
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Any other valid evidence-based argument.

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B4 Organising animals and plantsStudent Book answers
B4.5 Breathing and gas exchange
Question
number
Answer Marks Guidance
1 Intercostal muscles between ribs and diaphragm contract and relax,
changing chest volume and pressure
and forcing air in or out.
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2 a exchange of oxygen and carbon dioxide gases in lungs 1
2 b Oxygen needed by cells for cellular respiration to provide energy,
carbon dioxide poisonous waste product that must be removed.
Gaseous exchange supplies oxygen to blood and removes carbon
dioxide.
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3 a Award marks for well‑drawn bar chart correctly labelled. 3
3 b Bar chart shows we breathe in air containing mainly nitrogen with
oxygen and a tiny bit of carbon dioxide, and breathe out air
containing mainly nitrogen but with less oxygen and more carbon
dioxide.
We take oxygen from air breathed in and pass carbon dioxide into
air breathed out, but we breathe in and breathe out air.
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3 c ventilation and rich blood supply for steep concentration gradient,
clusters of alveoli/spherical alveolus shape for large surface area,
thin alveolus walls to minimise diffusion distances
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B4 Organising animals and plantsStudent Book answers
B4.6 Tissues and organs in plants
Question
number
Answer Marks Guidance
1 a cover surfaces and protect them, may secrete waxy substance for
waterproofing
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1 b contains lots of chloroplasts for photosynthesis 1
1 c contains some chloroplasts for photosynthesis 1
2 Tightly packed palisade mesophyll cells at top of leaf contain many
chloroplasts for photosynthesis
and are protected by epidermis.
Spongy mesophyll cells also photosynthesise and have large air spaces
and surface area to maximise gas exchange.
Xylem supply water for photosynthesis,
phloem transport food from photosynthesis around plant.
Stomata can be opened or closed by guard cells to let gases in and out.
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B4 Organising animals and plantsStudent Book answers
B4.7 Transport systems in plants
Question
number
Answer Marks Guidance
1 transport of food made in leaves and water and mineral ions taken from
soil to rest of plant
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2 Mature xylem cells are dead, phloem cells are living.
Xylem transport water and mineral ions from soil, phloem transport
dissolved sugars from photosynthesis.
Xylem found on inside of vascular bundles, phloem on outside.
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3 Phloem in trees found in a ring just underneath bark.
Soft bark of young trees vulnerable to damage by animals.
If complete ring of bark is eaten, transport of water from roots and
sugars from leaves stops and young tree will die.
Plastic covers protect young bark from animals.
Covers can be removed once trees are more mature and bark is harder.
If covers aren’t used, most of young trees are likely to be destroyed and
woodland will eventually die as old, mature trees are not replaced.
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B4 Organising animals and plantsStudent Book answers
B4.8 Evaporation and transpiration
Question
number
Answer Marks Guidance
1 a small openings all over leaf surface surrounded by guard cells 1
1 b Stomata open to allow air into the leaves to provide carbon dioxide for
photosynthesis,
and close to control loss of water.
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2 Water vapour evaporates from cells lining air spaces
and diffuses out of leaf through stomata
down a concentration gradient.
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3 As water evaporates from leaf surface, more water is pulled up through
xylem to replace it.
Water moves into roots by osmosis to replace water moving up xylem.
Transpiration stream is constant movement of water molecules through
xylem from roots to leaves.
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4 sum of readings = 1 855
divide by number of readings =
mean number of stomata = 265 per mm2
of leaf
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B4 Organising animals and plantsStudent Book answers
B4.9 Factors affecting transpiration
Question
number
Answer Marks Guidance
1 a waxy cuticle
guard cells
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1 b Rate of transpiration would increase because rapid air movement
across leaf would remove water vapour from near leaf surface and
increase concentration gradient for diffusion of water out of the leaf,
which would increase rate of evaporation from leaf cells,
increasing water uptake.
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2 a rate of transpiration slightly reduced 1
2 b rate of transpiration greatly reduced 1
2 c Petroleum jelly on top surface has little effect as few stomata covered.
Most stomata are found on underside of leaves and would be
unaffected.
Petroleum jelly on bottom surface greatly reduces transpiration as most
of stomata would be covered, allowing little diffusion to take place.
Rate of evaporation from cell surfaces would be reduced as
surrounding air would become saturated with water vapour (decreasing
concentration gradient).
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3 a Stomata on underside would be under water and water could not be lost
through them.
Stomata on top surface enable effective gas exchange for
photosynthesis through direct exposure to sunlight.
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3 b Excess transpiration not a risk as plants live in water.
No shortage of water to bring up from roots to replace that lost in
transpiration.
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