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This paper covers the whole of Topic 9. Like a real Cambridge paper it ranges across every sub-topic — 9.1 circulatory systems, 9.2 the heart, 9.3 blood vessels and 9.4 blood — and it mixes them inside single questions. All three Topic 9 papers do; they differ in the angle they come at it from, not in what they cover.
Question 1 — The Pump in Section: Why Every Wall Is the Thickness It Is
Total: 12 marks
Fig. 1.1 is a vertical section through a mammalian heart. Study it carefully before you begin — nothing on it is named, and no colour code has been used.
(a)[4]
Name the structures labelled A, B, C and D on Fig. 1.1.
Model Answer — 1(a)
A — the septum [1]
B — the muscular wall of the left ventricle (accept left ventricle wall) [1]
C — an atrioventricular valve (the right atrioventricular valve) [1]
D — a semilunar valve, at the base of the aorta [1]
⚠ If you missed marks here: The two kinds of valve are named for where they sit, not for what they do — an atrioventricular valve lies between an atrium and a ventricle, a semilunar valve lies at the base of an artery leaving the heart. Writing “valve” or “flap” for both C and D throws away one mark, and calling C a “bicuspid valve” loses it too because C is on the side of the heart that has three cusps, not two.
(b)[2]
State which side of Fig. 1.1, the left or the right of the page, shows the left ventricle. Explain how you can tell.
Model Answer — 1(b)
the left ventricle is drawn on the right of the page [1]
because the section is of a person facing you, so their left side appears on your right — and it is confirmed by that chamber having by far the thicker muscular wall [1]
⚠ If you missed marks here: This is the single most reliable way to lose marks in a heart question — assuming the left of the diagram is the left of the heart. Cambridge draws the heart as though the person is standing in front of you, so left and right are reversed. Get into the habit of finding the thick-walled ventricle first: that is always the left one, whichever way round the diagram has been printed.
(c)[3]
The wall labelled B is about three times as thick as the equivalent wall on the other side of the heart. Explain why.
Model Answer — 1(c)
the left ventricle pumps blood to the whole body, whereas the right ventricle pumps only to the lungs, which are close by [1]
so the left ventricle must generate a much higher pressure to push blood all the way round the body and back [1]
a thicker wall contains more muscle, so it contracts more powerfully; it does not hold more blood — both ventricles pump the same volume with each beat [1]
⚠ If you missed marks here: The favourite wrong answer is that the left ventricle is bigger because it pumps more blood. It cannot: the two sides are in series, so whatever the left side pumps out must come back through the right side. What differs is pressure, not volume. If the right ventricle pumped at the same pressure as the left, the delicate capillaries in the lungs would be damaged.
(d)[3]
Explain why the walls of the atria are much thinner than the walls of the ventricles, and explain the importance of the structure labelled A.
Model Answer — 1(d)
an atrium only has to push blood a short distance, into the ventricle immediately below it [1]
so only a small force and a low pressure are needed, and little muscle is required [1]
the septum completely separates oxygenated blood on the left from deoxygenated blood on the right, so the blood leaving for the body carries as much oxygen as possible [1]
⚠ If you missed marks here: Notice the vocabulary the mark scheme uses: oxygenated and deoxygenated. “Pure” and “impure” blood earn nothing at all. Also, the septum is a wall, not a valve — nothing is meant to pass through it in either direction, which is exactly why a baby born with a hole in it becomes breathless: mixed blood reaching the body is short of oxygen.
Question 2 — One Beat, Two Sounds
Total: 12 marks
A heart beats roughly seventy times a minute for a lifetime, and every one of those beats is the same short sequence of events. This question is about that sequence, and about how a doctor can find out what it is doing without ever seeing it.
(a)[4]
Describe the events of one complete heartbeat, from the moment the atria begin to contract. In your answer refer to the muscle that contracts and to the valves that open and close at each stage.
Model Answer — 2(a)
the muscle of the atria contracts, pushing blood through the open atrioventricular valves into the ventricles [1]
the muscle of the ventricles then contracts, raising the pressure inside them [1]
this closes the atrioventricular valves (preventing backflow into the atria) and forces the semilunar valves open, so blood is pushed into the aorta and the pulmonary artery [1]
the muscle of the whole heart then relaxes; the semilunar valves close, preventing blood returning from the arteries, and the atria fill again from the veins [1]
⚠ If you missed marks here: A very common answer has the two sides of the heart beating one after the other — left then right. They do not: both atria contract together and both ventricles contract together, so the two circuits are driven by the same beat. Also watch the order of the valves. The atrioventricular valves shut before the semilunar valves open, and if you reverse that the blood has nowhere to go.
(b)[3]
A student writes: “The heart tells the valves when to open and when to shut.” Explain why this statement is wrong, and describe what actually opens and closes a valve.
Model Answer — 2(b)
valves have no muscle and no nerve supply of their own — nothing sends them an instruction [1]
a valve is pushed open by the blood when the pressure behind it is higher than the pressure in front of it [1]
and it is pushed shut when the pressure in front becomes higher than the pressure behind, so blood starting to flow backwards fills the valve and seals it — the result is one-way flow [1]
⚠ If you missed marks here: Valves are purely mechanical, and that idea is worth learning once because it answers half a dozen exam questions. It explains why the same design works in a vein, where there is no muscle at all; it explains why a leaking valve cannot simply be told to try harder; and it explains why the heart sounds happen at fixed points in the beat rather than whenever the body chooses.
(c)[2]
A doctor listening to a chest hears two sounds in each beat, often written as “lub” and “dup”. State what makes each of these two sounds.
Model Answer — 2(c)
the first sound (“lub”) is the atrioventricular valves closing as the ventricles contract [1]
the second sound (“dup”) is the semilunar valves closing as the ventricles relax [1]
⚠ If you missed marks here: Both sounds are valves closing, never opening — an opening valve moves aside quietly, a closing one is slammed by a column of blood. Answers that say “the heart beating” or “blood rushing through” describe the right moment but not the structure, and Cambridge is asking for the structure.
(d)[3]
State three ways in which the activity of the heart may be monitored, and for one of them describe what is actually being measured.
Model Answer — 2(d)
an ECG (electrocardiogram) [1]
measuring the pulse rate [1]
listening to the sounds of the valves closing, using a stethoscope [1]
description, any one, e.g. the pulse is the stretching of an artery wall each time the left ventricle forces a surge of blood into it, so counting pulses counts beats per minute; or an ECG records the electrical activity of the heart muscle
⚠ If you missed marks here: A pulse is not blood arriving; it is the artery wall being stretched and recoiling. That is why you can only feel a pulse over an artery and never over a vein — by the time blood reaches a vein the surges have been smoothed out completely.
Question 3 — Three Kinds of Plumbing for Three Kinds of Pressure
Total: 12 marks
Table 3.1 gives measurements taken from three different kinds of blood vessel in a mammal. The three vessels are labelled P, Q and R.
vessel
mean thickness of wall / mm
mean diameter of lumen / mm
mean blood pressure / kPa
P
0.50
5.000
1.5
Q
0.001
0.007
4.0
R
1.00
4.000
13.0
(a)[3]
Identify each of P, Q and R, giving one piece of evidence from Table 3.1 for each.
Model Answer — 3(a)
P is a vein — the widest lumen, a thin wall, and the lowest pressure of the three [1]
Q is a capillary — a wall of 0.001 mm, that is 1 µm, which is a single flattened cell, and a lumen of only 7 µm, just wide enough for one red blood cell [1]
R is an artery — the thickest wall and by far the highest pressure, with a lumen narrower than the vein [1]
⚠ If you missed marks here: Read the pressure column before the size columns. Many candidates pick the vessel with the widest lumen as the artery because they think “big vessel, big job”, but it is the vein that has the wider lumen — low pressure needs little resistance to flow. Notice too that the capillary is not at the lowest pressure: pressure falls all the way from artery to capillary to vein, so a capillary sits between the two.
(b)[3]
Explain how the structure of vessel R is related to the pressure of the blood it carries.
Model Answer — 3(b)
the wall is thick and contains muscle and elastic fibres, so it can withstand the high pressure without bursting [1]
the elastic tissue stretches as each surge of blood arrives and recoils afterwards, which keeps the blood moving between beats and smooths out the surges [1]
the narrow lumen helps to maintain the high pressure as blood is carried away from the heart [1]
⚠ If you missed marks here: “Thick wall” on its own is a description, not an explanation — the mark comes from joining it to withstanding the pressure. And do not confuse the two jobs of the artery wall: muscle and thickness resist bursting, while the elastic recoil is what keeps blood flowing when the heart is relaxed. Without recoil, flow to your tissues would stop between every beat.
(c)[3]
State the function of vessel Q, and explain two ways in which its structure suits it to that function.
Model Answer — 3(c)
function: exchange of substances between the blood and the body cells — oxygen and nutrients out of the blood, carbon dioxide and other waste into it [1]
the wall is only one cell thick, giving a very short diffusion distance, so substances diffuse quickly [1]
capillaries are extremely numerous and highly branched, giving a very large surface area for diffusion; the lumen is so narrow that blood flows slowly, allowing more time for exchange (accept: walls are permeable / leaky) [1]
⚠ If you missed marks here: Every one of these features is a way of speeding up diffusion, exactly as the villus and the root hair do — short distance, large surface area, steep concentration gradient. If you can see that a capillary is just another exchange surface, you have already learnt most of this answer. One thing capillaries definitely do not have is valves; a vessel one cell thick has nothing to build a valve out of.
(d)[3]
Vessel P contains valves along its length. Vessel R contains none. Explain both of these observations.
Model Answer — 3(d)
the blood in P is at very low pressure, because the pressure has been lost as the blood was forced through the narrow capillaries [1]
so there is little to push it forward and it would flow backwards, especially when travelling upwards against gravity; the valves shut to prevent this, ensuring one-way flow towards the heart (blood is squeezed along by the skeletal muscles around the vein) [1]
in R the pressure behind the blood is high, so blood cannot flow backwards and no valves are needed — except the semilunar valves at the very start, where the heart relaxes [1]
⚠ If you missed marks here: The pressure in a vein is not low because the heart “used it up” or because the blood is tired — it was lost as friction while the blood squeezed through millions of capillaries. Another trap is to say veins have thick walls “because the blood has further to travel”. They have thin walls; there is no pressure to resist, and a thin, easily squashed wall is what lets the surrounding muscles massage the blood along.
Question 4 — Named Vessels, and the One That Breaks the Pattern
Total: 12 marks
Cambridge names nine blood vessels in this topic. Every one of them is named after where it goes, not after what it carries — and that single fact is enough to answer most of this question.
(a)[4]
Name the blood vessel that carries blood: (i) from the heart to the lungs; (ii) from the lungs to the heart; (iii) from the heart to a kidney; (iv) from the body back to the heart.
Model Answer — 4(a)
(i) pulmonary artery [1]
(ii) pulmonary vein [1]
(iii) renal artery [1]
(iv) vena cava [1]
⚠ If you missed marks here: Two habits fix all four of these. The first word tells you the organ: pulmonary is lungs, renal is kidney, hepatic is liver. The second word tells you the direction: artery means away from the heart, vein means back to it. The only vessel that does not follow the pattern is the vena cava, which has no organ in its name because it collects from everywhere.
(b)[2]
The pulmonary artery carries deoxygenated blood. Explain why it is still correctly called an artery.
Model Answer — 4(b)
an artery is defined as a vessel that carries blood away from the heart — not by the oxygen the blood contains [1]
the pulmonary artery carries blood away from the right ventricle to the lungs, and it also has the structure of an artery: a thick muscular wall, a narrow lumen and no valves along its length [1]
⚠ If you missed marks here: Textbook diagrams colour arteries red and veins blue, and that habit costs marks every year. There are exactly two exceptions in the whole body and they are the two pulmonary vessels: the pulmonary artery carries deoxygenated blood, the pulmonary vein carries oxygenated blood. Their existence is the proof that the definition is about direction.
(c)[3]
The hepatic portal vein does not follow the usual pattern for a blood vessel. Describe what is unusual about it, state what it carries, and explain why the liver also needs a hepatic artery.
Model Answer — 4(c)
it runs from one organ directly to another — from the small intestine to the liver — instead of returning to the heart, so it begins in capillaries and ends in capillaries [1]
it carries blood loaded with the products of digestion just absorbed from the small intestine, mainly glucose and amino acids, at a concentration that can be very high after a meal [1]
that blood is deoxygenated, having already passed through the capillaries of the gut, so the liver cells need the hepatic artery to bring them oxygenated blood for respiration [1]
⚠ If you missed marks here: Three vessels have “hepatic” in the name and they are easy to blur together. The hepatic artery brings oxygen in; the hepatic vein takes blood out to the vena cava; the hepatic portal vein brings absorbed food in from the gut. And note the word absorbed: the hepatic portal vein carries nutrients that are already dissolved in the blood, not food travelling through the gut.
(d)[3]
A molecule of glucose is absorbed through the wall of the small intestine. Name, in order, the blood vessels and heart chambers it passes through on its way to a kidney. Begin with the vessel that carries it away from the small intestine.
right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein [1]
left atrium → left ventricle → aorta → renal artery [1]
⚠ If you missed marks here: The trap in every route question is trying to get from the right side of the heart to the left side directly. You cannot — the septum is solid, so the only way across is the whole trip through the lungs. Routes that jump from the right ventricle to the aorta score nothing beyond the first mark, however tidy they look.
Question 5 — One Circuit or Two
Total: 10 marks
A fish and a mammal both have a muscular heart, blood vessels and valves. The difference lies entirely in how the circuit is laid out.
(a)[3]
Describe the single circulation of a fish.
Model Answer — 5(a)
the blood passes through the heart once for each complete circuit of the body [1]
the heart pumps deoxygenated blood to the gills, where it is oxygenated [1]
from the gills the blood travels straight on to the rest of the body without returning to the heart first, and only then comes back to the heart [1]
⚠ If you missed marks here: The word “single” counts how many times the blood goes through the heart in one lap, not how many hearts or how many vessels there are. A fish heart has one atrium and one ventricle, so the whole of the blood is at one stage of the journey at any moment.
(b)[2]
Describe the double circulation of a mammal.
Model Answer — 5(b)
the blood passes through the heart twice for each complete circuit of the body [1]
there are two separate circuits: the right side pumps deoxygenated blood to the lungs and back, and the left side pumps oxygenated blood to the rest of the body and back [1]
⚠ If you missed marks here: Double circulation does not mean two hearts, and it does not mean two sets of blood vessels running side by side round the body. It means one heart doing two jobs at once: every drop of blood is pumped twice in each lap, once to the lungs and once to everything else.
(c)[3]
Explain the advantages of a double circulation over a single circulation.
Model Answer — 5(c)
in a single circulation the blood loses most of its pressure squeezing through the narrow capillaries of the gills, so it reaches the body slowly [1]
in a double circulation the blood returns to the heart and is re-pressurised after leaving the lungs, so it is delivered to the body at high pressure and flows faster [1]
so oxygen and nutrients are delivered, and carbon dioxide removed, more quickly, supporting the high rate of respiration and metabolism that a mammal needs to stay warm and active [1]
⚠ If you missed marks here: The advantage is about pressure and speed of delivery, not about the amount of oxygen the blood picks up. A fish oxygenates its blood perfectly well at the gills; what it cannot do is deliver that blood quickly. If you write only “it carries more oxygen”, you have missed the whole mechanism.
(d)[2]
A double circulation can only work if one structure inside the heart is completely intact. Name that structure and explain what would happen to the oxygen supply to the body if it were incomplete.
Model Answer — 5(d)
the septum [1]
oxygenated and deoxygenated blood would mix, so the blood pumped out to the body would carry less oxygen, and less oxygen would reach the respiring cells — leaving the person breathless and tired on very little effort [1]
⚠ If you missed marks here: The second mark needs the consequence spelt out as far as the cells. “The blood would mix” is only half an answer; the examiner wants to see that you know why mixing matters, which is that the tissues then receive blood carrying less oxygen than it should.
Question 6 — What Is Actually Flowing Through the Pipes
Total: 12 marks
Fig. 6.1 shows four structures drawn from a stained blood smear seen under a light microscope. They are drawn to the same scale as one another.
(a)[4]
Name the structures labelled W, X, Y and Z on Fig. 6.1.
Model Answer — 6(a)
W — a red blood cell (no nucleus; the pale centre is the dip in the biconcave disc) [1]
X — a lymphocyte (a white blood cell with a very large round nucleus and only a thin rim of cytoplasm) [1]
Y — a phagocyte (a white blood cell with a lobed nucleus and an irregular shape) [1]
Z — platelets [1]
⚠ If you missed marks here: The first thing to look for is always the nucleus. A human red blood cell has none, so anything with a stained nucleus is a white blood cell; and platelets are fragments of cells, far smaller than any of the others and with no nucleus either. Calling Z “white blood cells” is the standard error — platelets are not cells at all, which is why they cannot carry out phagocytosis.
(b)[3]
Describe two features of the structure of W and explain how each one helps it to carry out its function. Name the compound that is formed when it does so.
Model Answer — 6(b)
it is a biconcave disc, which gives a large surface area for the diffusion of oxygen in and out, and means no part of the cell is far from the surface [1]
it has no nucleus, leaving more room inside for haemoglobin, so each cell carries more oxygen (accept: flexible, so it can squeeze through a capillary) [1]
in the lungs the haemoglobin combines with oxygen to form oxyhaemoglobin, which breaks down again to release the oxygen where it is needed [1]
⚠ If you missed marks here: Oxyhaemoglobin is one word and it is a compound, not a mixture — writing “haemoglobin with oxygen in it” will not do. Notice also that the reaction has to be reversible: a molecule that grabbed oxygen and never let go would be useless, and that is precisely what carbon monoxide does to haemoglobin.
(c)[3]
The structures in Fig. 6.1 make up less than half of the volume of blood. State what makes up the rest, and describe what it transports.
Model Answer — 6(c)
plasma — the straw-coloured liquid part of the blood, which is mostly water [1]
it transports the blood cells and platelets themselves [1]
and, dissolved in it, ions, nutrients such as glucose and amino acids, urea, hormones and carbon dioxide [1]
⚠ If you missed marks here: Plasma transports the cells as well as the dissolved substances, and that mark is missed more often than any other in this list. Be careful with oxygen too: the plasma carries carbon dioxide, but oxygen is carried by the haemoglobin inside the red blood cells, not dissolved in the plasma.
(d)[2]
State the function of X and the function of Y.
Model Answer — 6(d)
X (lymphocyte) — antibody production [1]
Y (phagocyte) — phagocytosis, engulfing and digesting pathogens [1]
⚠ If you missed marks here: Both are white blood cells, so “fights disease” describes both and distinguishes neither — it earns nothing. Cambridge wants the two precise words: phagocytosis for one and antibody production for the other. Note the shapes make sense of the jobs: the phagocyte has a lobed nucleus and flexible cytoplasm so it can change shape to flow around a bacterium, while the lymphocyte barely moves at all.
Question 7 — Sealing a Leak, and Blocking a Supply Pipe
Total: 10 marks
A system of pipes under pressure has two obvious weaknesses: it can spring a leak, and it can become blocked. The body has an elegant answer to the first. It has no answer at all to the second.
(a)[3]
Describe how a clot forms at a cut in the skin, naming the two proteins involved and describing what the clot is made of.
Model Answer — 7(a)
damaged tissue and platelets release substances that start the process, but only at the wound [1]
the soluble plasma protein fibrinogen is converted into the insoluble protein fibrin [1]
the fibrin forms a mesh of threads across the wound that traps red blood cells, forming the clot, which dries to a scab [1]
⚠ If you missed marks here: Fibrinogen and fibrin are one letter apart and easily swapped, so fix the direction in your head: fibrinogen is the soluble one already dissolved in your plasma right now, and it turns into insoluble fibrin only where there is damage. If it happened everywhere your blood would set solid inside its own vessels.
(b)[2]
State the two roles of blood clotting.
Model Answer — 7(b)
it prevents further loss of blood from the damaged vessel [1]
it prevents the entry of pathogens through the break in the skin [1]
⚠ If you missed marks here: Almost every candidate gives the first role and stops. Cambridge lists two, and the second one — sealing the skin against pathogens — is worth a mark on its own. If the question says “the two roles”, that is a promise there are exactly two things to write.
(c)[2]
The heart is full of blood, yet its muscle has its own arteries. State what those arteries are called and explain why the heart cannot simply take what it needs from the blood inside its chambers.
Model Answer — 7(c)
the coronary arteries [1]
the wall of the heart is thick muscle and substances would have to diffuse too far to reach the cells in the middle of it; every muscle cell needs its own capillary supply of oxygen and glucose for respiration, which only a network of vessels can provide [1]
⚠ If you missed marks here: This is the same principle that forces every large organism to have a transport system at all: diffusion is quick over a few micrometres and hopeless over a few millimetres. Note also that half the blood inside the heart is deoxygenated anyway, so even the outer cells could not rely on it.
(d)[3]
Describe coronary heart disease and its consequences for the heart muscle. State two risk factors other than diet and lack of exercise, and describe how diet and exercise can each reduce the risk.
Model Answer — 7(d)
fatty material builds up in the walls of the coronary arteries, narrowing or blocking the lumen, so less blood, and therefore less oxygen and glucose, reaches the heart muscle; the muscle cannot respire aerobically, which causes pain and, if the vessel is completely blocked, the death of that part of the muscle [1]
any two other risk factors: smoking, stress, genetic predisposition, increasing age, sex (males are at higher risk) [1]
diet — eating less saturated fat, cholesterol and salt and keeping to a healthy body mass slows the build-up of fatty deposits and lowers blood pressure; exercise — regular exercise strengthens the heart muscle, lowers blood pressure and helps maintain a healthy body mass [1]
⚠ If you missed marks here: Be precise about which vessels block. It is the coronary arteries, the ones supplying the heart muscle itself — not the aorta and not the vessels inside the chambers. And “exercise is good for you” is not an explanation: the mark needs a mechanism, such as a stronger heart muscle or a lower blood pressure.
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