Biology 0610Chapter 9 of 21

Transport in animals

Cambridge IGCSE Biology 0610 Topic 9 revision chapter covering transport in animals for the 2026-2028 syllabus, version 2, with Core and Supplement content separated statement by statement. Topic 9 has fourteen Core statements and fourteen Supplement statements, an unusually even split, and the dividing line is almost always the difference between a describing verb and an explaining one. The Core model is built first and stands on its own: the circulatory system is a system of blood vessels with a pump and valves that ensure one-way flow of blood; blood is pumped away from the heart in arteries and returns to the heart in veins; the eight named structures of the mammalian heart are identified on a full vertical section, with the valves named at Core only as one-way valves; the route from the vena cava to the aorta is traced chamber by chamber and valve by valve; the activity of the heart may be monitored by ECG, by pulse rate and by listening to the sounds of the valves closing; the effect of physical activity on heart rate is investigated with a full practical method, controlled variables, safety and stopping rules, and worked calculations for beats per minute, means, change from rest, percentage increase, gradient and recovery time; coronary heart disease is described in terms of the blockage of the coronary arteries, with the seven named risk factors of diet, lack of exercise, stress, smoking, genetic predisposition, age and sex, and the roles of diet and exercise in reducing the modifiable part of that risk; the structures of arteries, veins and capillaries are described strictly within the syllabus limit of relative thickness of wall, diameter of the lumen and the presence of valves in veins; the functions of capillaries are stated in both directions, as the exchange of oxygen and nutrients out of the blood and of carbon dioxide and wastes into it; the six named vessels to and from the heart, the lungs and the kidney are identified on a whole-body map; and the four components of blood are listed and identified from a photomicrograph, with the function of each, including the role of haemoglobin in red blood cells, phagocytosis and antibody production by white blood cells, and the two roles of blood clotting in preventing blood loss and preventing the entry of pathogens. The Supplement content is placed in clearly labelled blocks immediately after the Core material it extends, and never repeats it. It covers the single circulation of a fish, drawn as a figure in its own right and compared with the double circulation of a mammal; the two advantages of a double circulation, given as two separate arguments, one about re-pressurising the blood before it reaches the body and one about running the two circuits at different pressures; the identification of the atrioventricular and semilunar valves; the explanation of relative wall thickness for the left and right ventricles and for the atria compared with the ventricles, always through workload and pressure and never through oxygen content; the importance of the septum in separating oxygenated and deoxygenated blood; the functioning of the heart as a three-stage sequence of muscle contraction and valve action, in which every valve is moved by a pressure difference and none ever contracts; the explanation of the effect of physical activity on heart rate through increased respiration in the muscles; the relation of artery and vein structure to the pressure of the blood they transport and of capillary structure to their functions; the identification of the hepatic artery, the hepatic veins and the hepatic portal vein; the identification of lymphocytes and phagocytes and the matching of each to one function; and the description of clotting as the conversion of fibrinogen to fibrin to form a mesh. Throughout, red and blue are used strictly as diagrammatic oxygenation cues and never as literal blood colours, every figure carries a written label as well as a shade, and the boundaries of each statement - its limited to lists and its details are not required clauses - are reproduced and respected.Show more

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A summary of this Biology chapter — open a section to read it. The full notes, worked examples and practice questions are in the study modules above.

What is Transport in animals about?

The circulatory system is a system of blood vessels with a pump — the heart — and valves that ensure blood flows in one direction only. Blood is pumped away from the heart in arteries and returns to the heart in veins, and everything the body needs moving — oxygen, nutrients, carbon dioxide, urea, hormones and the blood cells themselves — travels in it.

Key ideas to remember

One sentence to hold the Core of this topic together: pressure creates flow, and valves give it direction. The third clause — structure follows pressure — is the thread that runs through the Supplement.
If you have five minutes and nothing else: say the route from the vena cava to the aorta out loud, naming every chamber and every valve. It touches the heart structures, the one-way valves and four of the six named vessels all at once.

What you need to be able to do

Core 9.1.1 Describe the circulatory system as a system of blood vessels with a pump and valves to ensure one-way flow of blood.
Core 9.2.2 State that blood is pumped away from the heart in arteries and returns to the heart in veins.
Core 9.2.1 Identify, in diagrams and images, the muscular wall, the septum, the left and right ventricles, the left and right atria, the one-way valves and the coronary arteries of a mammalian heart.
Core 9.2.3 State that the activity of the heart may be monitored by ECG, by pulse rate and by listening to the sounds of the valves closing.
Core 9.2.4 Investigate and describe the effect of physical activity on the heart rate, including the controls, repeats, safety rules and calculations that make the result trustworthy.
Core 9.2.5 Describe coronary heart disease in terms of the blockage of the coronary arteries, and state the possible risk factors: diet, lack of exercise, stress, smoking, genetic predisposition, age and sex.
Core 9.2.6 Discuss the roles of diet and exercise in reducing the risk of coronary heart disease.
Core 9.3.1 Describe the structure of arteries, veins and capillaries — limited to the relative thickness of the wall, the diameter of the lumen, and the presence of valves in veins.
Core 9.3.2 State the functions of capillaries.
Core 9.3.3 Identify, in diagrams and images, the main blood vessels to and from the heart (vena cava, aorta, pulmonary artery, pulmonary vein), the lungs (pulmonary artery, pulmonary vein) and the kidney (renal artery, renal vein).
Core 9.4.1 List the components of blood as red blood cells, white blood cells, platelets and plasma.
Core 9.4.2 Identify red and white blood cells in photomicrographs and diagrams.
Core 9.4.3 State the functions of red blood cells (transporting oxygen, including the role of haemoglobin), white blood cells (phagocytosis and antibody production), platelets (clotting) and plasma (transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide).
Core 9.4.4 State the roles of blood clotting as preventing blood loss and preventing the entry of pathogens.
Supplement 9.1.2 Describe the single circulation of a fish.
Supplement 9.1.3 Describe the double circulation of a mammal.
Supplement 9.1.4 Explain the advantages of a double circulation.
Supplement 9.2.7 Identify, in diagrams and images, the atrioventricular and semilunar valves of a mammalian heart.
Supplement 9.2.8 Explain the relative thickness of the muscle walls of the left and right ventricles, and of the atria compared with the ventricles.
Supplement 9.2.9 Explain the importance of the septum in separating oxygenated and deoxygenated blood.
Supplement 9.2.10 Describe the functioning of the heart in terms of the contraction of the muscles of the atria and ventricles and the action of the valves.
Supplement 9.2.11 Explain the effect of physical activity on the heart rate.
Supplement 9.3.4 Explain how the structure of arteries and veins is related to the pressure of the blood they transport.
Supplement 9.3.5 Explain how the structure of capillaries is related to their functions.
Supplement 9.3.6 Identify, in diagrams and images, the main blood vessels to and from the liver as the hepatic artery, the hepatic veins and the hepatic portal vein.
Supplement 9.4.5 Identify lymphocytes and phagocytes in photomicrographs and diagrams.
Supplement 9.4.6 State the functions of lymphocytes (antibody production) and of phagocytes (engulfing pathogens by phagocytosis).
Supplement 9.4.7 Describe the process of clotting as the conversion of fibrinogen to fibrin to form a mesh.

Common mistakes to avoid

“Arteries carry oxygenated blood; veins carry deoxygenated blood.” CorrectCore 9.2.2 Blood is pumped away from the heart in arteries and returns to the heart in veins. That is the whole definition. The pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood, and both are named correctly.
“The right side of the heart is on the right of the diagram.” CorrectCore 9.2.1 A heart diagram is drawn as if you are looking at the person from the front, so their anatomical right appears on your left. Find the aorta, which arches away from the left ventricle, before you label anything.
“An artery has a thick, muscular, elastic wall — that is the description.” CorrectCore 9.3.1 The Core description of a vessel is limited to three things: the relative thickness of the wall, the diameter of the lumen, and whether valves are present. Muscle and elastic tissue are useful background, but they are outside the three features the statement is limited to.
“Plasma carries heat around the body — that's one of its functions.” CorrectCore 9.4.3d The syllabus lists six things plasma transports: blood cells, ions, nutrients, urea, hormones and carbon dioxide. Heat distribution is true, and it is not on that list. Learn the six.
“Smoking causes coronary heart disease, so a smoker will get it.” CorrectCore 9.2.5 Smoking is a risk factor: it raises the probability of the disease across a population. It does not guarantee the disease in any individual, and people who have never smoked can develop it too.
“Double circulation means the blood goes round the body twice.” CorrectSupplement 9.1.3 Blood passes through the heart twice during one complete circuit of the body: once on the way to the lungs and once on the way to the rest of the body.
“The left ventricle wall is thick because it holds oxygenated blood.” CorrectSupplement 9.2.8 Wall thickness follows workload. The left ventricle generates the pressure needed to push blood all the way round the body, so its muscle is thickest. Oxygen content has nothing to do with it.
“The valves contract to push the blood along.” CorrectSupplement 9.2.10 Valves are passive flaps. They are pushed open and pushed shut by differences in pressure on their two sides. Only cardiac muscle contracts.
“Double circulation means the blood goes round the body twice.” Why wrongIt confuses the number of trips round the body with the number of visits to the pump. WriteSupplement 9.1.3 Blood passes through the heart twice during one complete circuit of the body: once on the pulmonary circuit and once on the systemic circuit.
“Arteries always carry oxygenated blood.” Why wrongIt takes a pattern that happens to hold in the systemic circuit and treats it as a definition. WriteCore 9.2.2 An artery carries blood away from the heart. The pulmonary artery carries deoxygenated blood to the lungs.
“Veins always carry deoxygenated blood.” Why wrongSame error, the other way round. WriteCore 9.2.2 A vein carries blood towards the heart. The pulmonary vein carries oxygenated blood from the lungs.
“The left side of the heart contains deoxygenated blood.” Why wrongIt usually comes from reading the diagram the wrong way round. WriteCore 9.2.1 The left side receives oxygenated blood from the lungs through the pulmonary veins and pumps it to the body.
“The right side of the heart is on the right of the diagram.” Why wrongA heart diagram is drawn as if you are facing the person, so their right is opposite your right. WriteCore 9.2.1 The anatomical right side appears on the viewer's left. Confirm it by finding the aorta, which arches away from the chamber below it: that chamber is the left ventricle, and the septum runs between it and the right ventricle beside it. Extended candidates have a second check — the thickest ventricle wall is always the left one (Supplement 9.2.8).
“The atria have thicker walls than the ventricles because they fill first.” Why wrongFilling requires no force; pumping does. WriteSupplement 9.2.8 The atria have the thinnest walls because they push blood only a short distance into the ventricles below them.
“The left ventricle wall is thick because of the oxygen in the blood.” Why wrongOxygen content has no mechanical effect on the muscle. WriteSupplement 9.2.8 The left ventricle pumps blood to the whole body, so it must generate the highest pressure, so it needs the thickest layer of cardiac muscle.
“The valves contract to push the blood along.” Why wrongValves are flaps of tissue, not muscle. WriteSupplement 9.2.10 Valves are opened and closed by differences in pressure on their two sides. Only the cardiac muscle contracts.
“Coronary arteries carry blood into the heart chambers.” Why wrongIt confuses supplying the muscle with filling the pump. WriteCore 9.2.5 Coronary arteries branch from the aorta and supply the cardiac muscle itself with oxygen and glucose. The chambers are filled by the vena cava and the pulmonary veins.
“The hepatic vein and the hepatic portal vein are the same vessel.” Why wrongThe similar names hide completely different routes. WriteSupplement 9.3.6 The hepatic vein carries blood from the liver to the vena cava. The hepatic portal vein carries blood from the gut to the liver.
“Veins have thick muscular walls because they have to push the blood back.” Why wrongVeins do no pushing; the heart and the skeletal muscles do. WriteCore 9.3.1 Veins have thin walls and a wide lumen because the blood in them is at low pressure, and valves stop it flowing backwards.
“Capillaries have no walls, so substances can just leak out.” Why wrong“Very thin” has been read as “absent”. WriteCore 9.3.1 A capillary wall is one cell thick, which gives a very short diffusion distance while still holding the blood cells and large proteins in.
“Platelets produce antibodies.” Why wrongPlatelets are cell fragments, and antibody production is a job for white blood cells. WriteCore 9.4.3b White blood cells produce antibodies; platelets are involved in clotting. Supplement 9.4.6 Extended candidates name the cell: it is the lymphocyte that produces antibodies.
“Lymphocytes engulf pathogens.” Why wrongEngulfing is the phagocyte’s job, and the two white blood cells are being swapped. WriteSupplement 9.4.6 Phagocytes engulf pathogens by phagocytosis; lymphocytes produce antibodies. At Core the answer is simply that white blood cells do both.
“An artery has a thick, muscular, elastic wall — that is the description.” Why wrongIt answers a question the syllabus did not ask. 9.3.1 is limited to three features. WriteCore 9.3.1 An artery has a thick wall, a relatively narrow lumen and no valves. Muscle and elastic tissue are not named anywhere in Topic 9, at either tier.
“Plasma is just water.” Why wrongIt is mostly water, but the dissolved substances are the entire reason the blood is worth circulating. WriteCore 9.4.3d Plasma is the liquid part of blood, and it transports blood cells, ions, nutrients, urea, hormones and carbon dioxide.
“Plasma carries oxygen, glucose, hormones, heat and vitamins.” Why wrongTwo of those five are not on the syllabus list, and one belongs to a different component. WriteCore 9.4.3d Plasma transports blood cells, ions, nutrients, urea, hormones and carbon dioxide. Oxygen is transported by the red blood cells; heat and vitamins are not in the named list.
“Smoking causes coronary heart disease, so every smoker gets it.” Why wrongIt treats a change in probability as a certainty for an individual. WriteCore 9.2.5 Smoking is a risk factor: it increases the probability of coronary heart disease. It does not guarantee it, and people who have never smoked can develop the disease too.

Examiner tips

Where the tiering bites in Topic 9 — and it bites in an unusual place. Topic 9 is split almost exactly down the middle: 14 Core statements and 14 Supplement. The dividing line is not "hard" versus "easy". It is almost always the difference between a describing verb and an explaining one. Describe the structure of an artery is Core 9.3.1; explain how that structure suits the pressure is Supplement 9.3.4. Describe the effect of exercise on heart rate is Core 9.2.4; explain it is Supplement 9.2.11. Read the command word before you decide how much to write.
The single most valuable habit in this topic, and where it belongs. Whenever you state a structural feature, ask whether the question wants you to go on and say what it does. At Core, “the wall of an artery is thick” is the answer — 9.3.1 asks you to describe the structure. At Supplement, “the wall of an artery is thick, so it withstands the high pressure of the blood leaving the heart without bursting” is the answer, because 9.3.4 asks you to explain. Writing the long version on a Core paper wastes time; writing the short version on an Extended paper loses marks.
Circulation is not respiration. Circulation moves substances around the body. Respiration is the chemical release of energy from glucose inside cells. The circulatory system delivers the raw materials for respiration and removes its waste — it does not carry out respiration, and it does not “produce energy”.
Two different arguments, not one said twice. Advantage 1 is about speed of delivery to the body; advantage 2 is about protecting the lungs. An answer that gives the pressure difference twice in different words has given one advantage. If the question says “advantages”, give both.
Orientation first, labels second. A heart diagram is drawn as if you are looking at the person from the front. Their anatomical right side therefore appears on your left. Before you write a single label, find the aorta — the single large vessel that arches over the top and away downwards — and follow it back into the chamber below it. That chamber is the left ventricle, and the septum runs between it and the right ventricle beside it. Everything else falls into place from there. Extended candidates have a second check: the thickest ventricle wall is always the left one. That is Supplement 9.2.8 and it is explained in section F.
Say what would happen without it. The quickest way to show you understand 9.2.9 is to give the consequence of failure: if the septum were incomplete, deoxygenated blood from the right ventricle would mix with oxygenated blood in the left ventricle, so the blood leaving in the aorta would carry less oxygen and less would reach the respiring tissues. That is worth more than repeating the word “separate” three times.
One rule, applied twice. Both halves of 9.2.8 are the same argument: how far does this chamber have to push the blood, and against how much resistance? Answer that, and the thickness follows. Never start from what is in the chamber.
Never write “the valve contracts”. Write “the valve is forced open” or “the valve is pushed shut”, and always say which pressure became the greater. Cardiac muscle contracts; valve flaps are pushed about by the blood.
Describe means say what the graph does, with numbers. “The heart rate goes up” is half a mark. “The heart rate rises from 72 to 138 beats per minute during the three minutes of exercise, then falls back to 72 over about six minutes after it stops” is the answer. Quote values and quote units.
Never stop at “the body needs more blood”. That is the observation, not the explanation. The marks are in the middle of the chain: respiration in the muscle cells increases, so more oxygen and glucose are needed and more carbon dioxide is produced.
Two words that must appear: oxygen and respiration. A great many answers say “the heart does not get enough blood” and stop. Say what the blood was carrying, and say what the muscle cells needed it for.
Two statements, two different lists. 9.2.5 asks you to state the seven risk factors. 9.2.6 asks you to discuss the roles of two things in reducing risk: diet and exercise. Do not answer the second question with the first list.
Discuss means both sides. A full 9.2.6 answer says what diet and exercise do — and then says what they do not do: they reduce the part of the risk that can be changed, and they leave age, sex and genetic predisposition exactly where they were. An answer that only lists healthy habits has discussed nothing.
Arteries do not push blood. The heart provides the push. An artery withstands the pressure and helps maintain it. Writing that the artery wall “squeezes each blood cell forward” loses the mark.
The valves are the one feature the statement names explicitly. Core 9.3.1 is limited to wall thickness, lumen diameter and the presence of valves in veins. That last phrase is there because valves are the single feature that identifies a vein beyond doubt: an artery has none, a capillary has none.
Exchange happens nowhere else. No substance is exchanged through the wall of an artery or a vein — both are far too thick. Every gram of glucose and every molecule of oxygen that ever reaches a body cell crosses a capillary wall to get there. If a question asks where exchange happens, the answer is always the capillaries.
Six vessels, not eight. The pulmonary artery and pulmonary vein appear twice in the syllabus list, once under the heart and once under the lungs, because they are the two vessels that join one to the other. They are the same two vessels both times. Read the list as: aorta, vena cava, pulmonary artery, pulmonary vein, renal artery, renal vein.
The naming rule. “Renal” means of the kidney; “pulmonary” means of the lung; and, for Extended candidates, “hepatic” means of the liver. Put those together with the Core 9.2.2 rule — artery away from the heart, vein towards it — and almost every name on your list builds itself. Only the hepatic portal vein has to be learned as a special case, and it is Supplement.
Colour is not evidence. In a stained photomicrograph the red blood cells often look pink and the white cells purple, but the stain is chosen by whoever prepared the slide. Shape and nucleus are the evidence. A question that shows you an unfamiliar micrograph is testing exactly that: it expects you to reason from what you can see, not to recognise a picture.
Two functions, one category. Core 9.4.3(b) attaches both functions to “white blood cells” without saying which cell does which. If a Core question asks what white blood cells do, give both and do not name either type — you cannot lose a mark for the names, but you can lose one for giving only half the function.
Two roles, and the second is the one that gets dropped. Almost every answer says a clot stops bleeding. Fewer say it keeps pathogens out — which is why 9.4.4 names it explicitly. The skin is a body defence, and a clot is what restores it while it heals.
Four words carry the statement. Fibrinogen, fibrin, soluble or insoluble, and mesh. Write all four and the description is complete. Nothing beyond them is required: 9.4.7 stops at the mesh, and the clotting factors and enzymes that drive the conversion are not part of it.
Learn the list as six items, in the syllabus’s own words. Plasma transports: blood cells, ions, nutrients, urea, hormones and carbon dioxide. Six. Note what is not on it: oxygen, which is carried by the red blood cells (9.4.3a), and heat, which plasma genuinely does distribute but which 9.4.3(d) does not name.
Never identify by colour. The colours in a photomicrograph come from the stain the technician chose. Shape, size and the presence or absence of a nucleus are the evidence, and they are the only evidence that transfers to a different slide.

How Transport in animals is examined

Transport in animals is the most heavily diagrammed topic in the syllabus. Almost every question begins with a picture — a heart in section, a vessel in cross-section, a blood smear, a map of vessels, or a graph of pulse rate against time — and asks you to read it before you explain anything.
Most Topic 9 items test one distinction: artery or vein, atrium or ventricle, red cell or white cell, renal artery or renal vein. Read the direction of the arrow before you read the label. Paper 1 is Core; Paper 2 is Core plus Supplement.
Structured questions ask for a labelled route, a matched comparison, or a linked explanation. Paper 3 is Core, so it asks you to state, describe and identify. Paper 4 adds Supplement, so it asks you to explain.
Both routes sit one of these. In this topic they mean two things: the pulse-and-exercise investigation (variables, repeats, means, graphs, anomalies), and reading, measuring and drawing a specimen — usually a blood smear or a vessel section.
Three Core statements and three Supplement ones use this exact verb. It means an unfamiliar drawing or photograph, not the one in your notes. Practise on pictures you have not seen before.
The single most valuable habit in this topic, and where it belongs. Whenever you state a structural feature, ask whether the question wants you to go on and say what it does. At Core, “the wall of an artery is thick” is the answer — 9.3.1 asks you to describe the structure. At Supplement, “the wall of an artery is thick, so it withstands the high pressure of the blood leaving the heart without bursting” is the answer, because 9.3.4 asks you to explain. Writing the long version on a Core paper wastes time; writing the short version on an Extended paper loses marks.

Frequently asked questions

What is the circulatory system?

Core 9.1.1 The circulatory system is a system of blood vessels with a pump — the heart — and valves that ensure blood flows in one direction only. The vessels are the arteries, capillaries and veins; the blood is what carries the oxygen, nutrients, carbon dioxide, urea, hormones and blood cells.

Do arteries always carry oxygenated blood?

Core 9.2.2 No. Blood is pumped away from the heart in arteries and returns to the heart in veins; that is the whole definition, and oxygen plays no part in it. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, and the pulmonary vein carries oxygenated blood from the lungs back to the heart.

What do the coronary arteries do?

Core 9.2.5 They branch from the aorta just above the aortic valve and supply the cardiac muscle itself with oxygen and glucose. They do not deliver blood into the heart's chambers. If one becomes narrowed or blocked, that region of muscle receives less oxygen and glucose, aerobic respiration in it is reduced, and the muscle may be damaged.

What can reduce the risk of coronary heart disease?

Core 9.2.6 A balanced diet and regular exercise. A diet that keeps blood lipid levels lower is associated with less fatty build-up inside the coronary artery walls; exercise strengthens the cardiac muscle and helps control body mass and blood lipid levels. Neither removes the risk: age, sex and genetic predisposition cannot be changed, so these measures reduce the modifiable part of the risk only.

What do capillaries do?

Core 9.3.2 They allow substances to be exchanged between the blood and the body cells: oxygen and nutrients pass out of the blood into the cells, and carbon dioxide and other wastes pass from the cells into the blood. No exchange happens through the wall of an artery or a vein.

Why are capillary walls only one cell thick?

Supplement 9.3.5 So that the distance substances must diffuse between the blood and the body cells is as short as possible. A shorter diffusion distance means a faster rate of diffusion, which is what allows oxygen and glucose to reach the cells, and carbon dioxide and wastes to leave them, quickly enough to keep up with respiration.

What does blood consist of, and what does each part do?

Core 9.4.1 Four components. Red blood cells transport oxygen, using haemoglobin. White blood cells carry out phagocytosis and antibody production. Platelets are involved in clotting. Plasma is the liquid the others are suspended in, and it transports blood cells, ions, nutrients, urea, hormones and carbon dioxide.

Which blood cell produces antibodies?

Supplement 9.4.6 The lymphocyte, a white blood cell with a large round nucleus and very little cytoplasm. The other white blood cell required at this level, the phagocyte, has a lobed nucleus and engulfs pathogens by phagocytosis rather than producing antibodies. At Core the answer is simply that white blood cells do both jobs; the split into two named cells is Supplement.

What is double circulation in a mammal?

Supplement 9.1.3 Double circulation means that blood passes through the heart twice during one complete circuit of the body: once through the right side on the pulmonary circuit to the lungs, and once through the left side on the systemic circuit to the rest of the body. It does not mean the blood travels round the body twice. This is Supplement content: a Core candidate is not examined on it.

Why is the wall of the left ventricle thicker than the wall of the right ventricle?

Supplement 9.2.8 Because the left ventricle pumps blood to the whole body, while the right ventricle pumps it only as far as the lungs. Reaching the whole body, against much more resistance, requires a much higher pressure, and a thicker layer of cardiac muscle contracts more forcefully to produce it. Oxygen content has nothing to do with it.

How do heart valves open and close?

Supplement 9.2.10 By differences in pressure. A valve is pushed open when the pressure behind it is greater than the pressure in front of it, and pushed shut when the pressure in front becomes greater. Valves are passive flaps of tissue and never contract; only the cardiac muscle does.

What is the difference between the hepatic vein and the hepatic portal vein?

Supplement 9.3.6 A hepatic vein carries blood away from the liver to the vena cava, and so back towards the heart. The hepatic portal vein carries blood from the gut into the liver, delivering most of the absorbed products of digestion for processing before they reach the rest of the body. It is the one vessel on your list that runs from one organ to another rather than back to the heart.

Is a risk factor the same as a cause?

Core 9.2.5 No. A risk factor increases the probability that a person will develop a disease; it does not guarantee it. A person with several risk factors for coronary heart disease may never develop it, and a person with none of the modifiable risk factors still may.

Syllabus reference and sources

Written against: Cambridge IGCSE Biology (0610), syllabus for examination in 2026, 2027 and 2028 (Version 2, published December 2025) — Subject Content, Topic 9: Transport in animals, subtopics 9.1 to 9.4.

Written by: Academiq Edu Instructor Panel

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