Cambridge IGCSE Biology 0610. Topic 9: Transport in animals

Transport in Humans: Heart, Blood & Vessels

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

The circulatory system transports substances around the body through the heart, blood vessels and blood. Questions commonly test the route of blood, vessel adaptations, blood components and coronary heart disease.

How Cambridge tests this topic

Transport questions reward students who can compare the three blood vessels as matched pairs and explain double circulation rather than just naming it. The big losses are getting oxygenated and deoxygenated sides of the heart the wrong way round, confusing arteries with veins, and listing blood components without their functions. Master the heart structure, the vessel comparison table and the 'why the left ventricle wall is thicker' reasoning and this becomes high-scoring.

Focused lessons

Break the topic into manageable skills

Use these guides when one concept, calculation or question pattern needs more attention than the full-topic overview.

Heart Structure and Blood Flow: Trace Every Chamber and Vessel

Core and Supplement · Cambridge 0610 Topic 9.1–9.2

Blood Components and Their Functions

Core and Supplement · Cambridge 0610 Topic 9.3

Arteries, Veins and Capillaries: Structure and Function

Core and Supplement · Cambridge 0610 Topic 9.2

Coronary Heart Disease: Causes, Risk Factors and Prevention

Core and Supplement · Cambridge 0610 Topic 9.4

Blood Clotting: Platelets, Fibrin and Wound Sealing

Core and Supplement · Cambridge 0610 Topic 9.3

The Lymphatic System and Tissue Fluid Formation

Supplement · Cambridge 0610 Topic 9.4

Double Circulation: Why Mammals Pump Blood Twice

Core and Supplement · Cambridge 0610 Topic 9.1

Pulse Rate, Heart Rate and the Effects of Exercise

Core and Supplement · Cambridge 0610 Topic 9.2

Double circulation: explain it, don't just name it

Humans have a double circulatory system: blood passes through the heart twice for each complete circuit of the body. One circuit (pulmonary) carries blood between the heart and the lungs; the other (systemic) carries blood between the heart and the rest of the body.

The exam mark is explaining the advantage: blood pressure is boosted again after passing through the lungs, so blood travels to the body at higher pressure and faster, delivering oxygen and glucose more efficiently. Contrast this with a single circulation (e.g. Fish) where pressure drops after the gills. A common error is describing the route without stating the advantage of higher pressure. Use 'oxygenated' and 'deoxygenated' carefully: the right side of the heart handles deoxygenated blood to the lungs; the left side handles oxygenated blood to the body.

Heart structure: the side that trips people up

Know the four chambers and which blood each holds:

Right atrium → right ventricle → pulmonary artery → lungs (deoxygenated blood).
Lungs → pulmonary vein → left atrium → left ventricle → aorta → body (oxygenated blood).

Two high-value marks: (1) the left ventricle wall is thicker/more muscular than the right because it must pump blood at higher pressure all the way around the whole body, whereas the right ventricle only pumps to the nearby lungs. (2) Valves (atrioventricular and semilunar) prevent the backflow of blood, ensuring one-way flow. The single most common slip is labelling the left and right sides as you look at the diagram. The heart's left is on the diagram's right. Remember the pulmonary artery is the one artery carrying deoxygenated blood, and the pulmonary vein the one vein carrying oxygenated blood.

Blood vessels: the comparison that scores

Compare arteries, veins and capillaries as matched features, each linked to function:

Feature	Artery	Vein	Capillary
Wall	Thick, muscular, elastic	Thinner	One cell thick
Lumen	Narrow	Wide	Very narrow
Valves	No	Yes (prevent backflow)	No
Blood pressure	High	Low	Falling

Link each to function: arteries have thick elastic walls to withstand high pressure from the heart; veins have valves because blood is at low pressure and could flow backwards; capillaries have one-cell-thick walls and narrow lumen giving a short diffusion distance for exchange of substances with tissues. State that arteries carry blood away from the heart and veins carry it towards the heart. Defined by direction, not oxygen content (remember the pulmonary exceptions).

Blood components: functions, not just names

Blood has four parts; examiners want function, not just identification:

Red blood cells: contain haemoglobin which binds oxygen to form oxyhaemoglobin in the lungs and releases it in respiring tissues; biconcave and no nucleus for more haemoglobin and surface area.
White blood cells: defence: phagocytes engulf pathogens; lymphocytes produce antibodies.
Platelets: involved in blood clotting, sealing wounds and preventing pathogen entry.
Plasma: liquid that transports blood cells, nutrients, carbon dioxide, urea, hormones and heat.

The phrase 'haemoglobin combines with oxygen to form oxyhaemoglobin' is a reliable mark, as is naming what plasma transports. Iron's role in making haemoglobin links to human nutrition. A common loss is saying white blood cells 'kill germs' without specifying engulfing (phagocytosis) or antibody production.

Coronary heart disease and exercise (application marks)

(Extended only and Core application) Coronary heart disease (CHD) is caused by the build-up of fatty material (containing cholesterol) in the coronary arteries, narrowing them and reducing blood/oxygen supply to the heart muscle. The exam asks for risk factors (diet high in saturated fat, smoking, lack of exercise, stress, obesity, genetic factors) and prevention (healthy diet, regular exercise, not smoking).

For exercise questions, explain that heart rate increases to deliver more oxygen and glucose to muscles for increased respiration, and to remove carbon dioxide faster. The mark-scheme link is 'more oxygen/glucose for respiration to release energy for muscle contraction'. Avoid saying exercise 'gives the muscles more energy' directly. Energy is released by respiration. To practise these applied answers with a specialist, take a trial class.

Key terms to connect with this topic

Use these definitions inside explanations and questions rather than memorising them as isolated sentences.

Artery: A blood vessel that carries blood away from the heart, usually oxygenated (except the pulmonary artery). Arteries have thick muscular walls, a narrow lumen relative to wall thickness, and elastic tissue that stretches and recoils to maintain blood pressure between heartbeats.
Capillary: The smallest type of blood vessel, with walls only one cell thick. Capillaries form dense networks in tissues, providing a large surface area and short diffusion distance for the exchange of substances (oxygen, glucose, carbon dioxide, urea) between blood and cells.
Coronary artery: A blood vessel that branches from the aorta and supplies the heart muscle with oxygenated blood and glucose for respiration. Blockage of a coronary artery by a blood clot or fatty deposits (atherosclerosis) can lead to a heart attack.
Double circulation: A circulatory system in which blood passes through the heart twice for each complete circuit of the body. Once in the pulmonary circuit (to the lungs) and once in the systemic circuit (to the rest of the body).
Haemoglobin: A red iron-containing protein found in red blood cells that reversibly binds with oxygen to form oxyhaemoglobin in the lungs. In tissues where oxygen concentration is low, oxyhaemoglobin releases its oxygen for use in aerobic respiration.
Heart: A muscular organ that pumps blood around the body through a double circulatory system. The right side pumps deoxygenated blood to the lungs (pulmonary circulation) and the left side pumps oxygenated blood to the rest of the body (systemic circulation). It has four chambers: two atria and two ventricles.
Plasma: The pale yellow liquid component of blood in which blood cells are suspended. Plasma transports dissolved substances including glucose, amino acids, urea, carbon dioxide, hormones, antibodies and heat energy around the body.
Platelet: A small cell fragment in the blood that plays a key role in blood clotting. When a blood vessel is damaged, platelets accumulate at the wound site and release chemicals that trigger the conversion of fibrinogen to fibrin, forming a mesh that traps blood cells and creates a clot.
Red blood cell: A biconcave disc-shaped blood cell that contains haemoglobin and transports oxygen from the lungs to body tissues. Red blood cells have no nucleus, which maximises space for haemoglobin, and their biconcave shape increases surface area for oxygen absorption.
Vein: A blood vessel that carries blood towards the heart, usually deoxygenated (except the pulmonary vein). Veins have thinner walls than arteries, a wider lumen, and contain valves to prevent backflow of blood.
White blood cell: A blood cell that is part of the immune system. There are two main types: phagocytes, which engulf and digest pathogens by phagocytosis, and lymphocytes, which produce antibodies. White blood cells have a nucleus and can change shape.

Browse the full IGCSE Biology glossary when a related term needs checking.

Apply the topic in practical work

These practical guides show how the Biology appears in methods, variables, measurements, graphs and evaluation.

Investigating the Effect of Exercise on Heart Rate: Exercise increases heart rate because muscles need more oxygen and glucose for increased aerobic respiration. Heart rate rises quickly during exercise and gradually returns to resting rate during recovery: fitter individuals recover faster.

Try a worked question (5 marks)

(a) Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. (b) Describe two ways in which the structure of a capillary is adapted for the exchange of substances between the blood and body tissues.

Show the answer and marking guidance

(a) the left ventricle pumps blood to the whole body / all body organs; this requires higher pressure than pumping to the lungs (which the right ventricle does); so a thicker/more muscular wall is needed to generate this pressure; (b) wall is one cell thick, giving a short diffusion distance; very narrow lumen / large surface area, allowing efficient exchange of substances (e.g. Oxygen, glucose, carbon dioxide);

Each semicolon separates a distinct answer point. This is original practice content, not an official Cambridge past-paper question.

Common mix-ups to avoid

Use these as a correction checklist after attempting a question.

Mixing up the left and right sides of the heart, or which side carries oxygenated blood.
Saying the pulmonary artery carries oxygenated blood. It is the exception that carries deoxygenated blood.
Defining arteries/veins by oxygen content rather than direction of flow (away from vs towards the heart).
Describing double circulation without stating the advantage of restored/higher pressure.
Listing blood components without their functions, e.g. Naming platelets but not their clotting role.
Saying exercise or food 'gives muscles energy' instead of releasing energy through respiration.

How to build the explanation step by step

For a 6-mark 'describe the path of blood through the heart and body' answer, follow the blood in order and state oxygenation at each step. Use stems like 'Deoxygenated blood enters the right atrium, passes to the right ventricle, and is pumped through the pulmonary artery to the lungs...' then 'Oxygenated blood returns via the pulmonary vein to the left atrium...'. Name every chamber, vessel and valve in sequence and state where gas exchange refreshes the blood. Examiners credit correct order and correct oxygenation labels, so accuracy of sequence is everything.

Review the full extended-response method →

Malaysia and syllabus context

Heart and circulation questions feature in nearly every May/June and Oct/Nov 0610 sitting, often with a labelled heart diagram. Malaysian students taking SPM Biology will recognise much of the circulatory content, but 0610 expects sharper double-circulation reasoning. CHD and diet questions resonate locally given Malaysia's dietary health discussions, making the applied marks easier to relate to.

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