Cambridge IGCSE Biology 0610: Transport in animals – Revision Notes

For full explanations and a worked heart-rate investigation, use the transport in animals study guide. These notes condense topic 9 of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028: sections 9.1 Circulatory systems, 9.2 Heart, 9.3 Blood vessels and 9.4 Blood. Core statements are tested on Papers 1 and 3. Lines marked Extended only are Supplement content, tested on Papers 2 and 4.

Links: Cambridge IGCSE Biology hub, printable checklist, practice questions for this topic, 0610 Core diagnostic and 0610 Extended diagnostic.

Key definitions

Term	Definition to learn
Circulatory system	A system of blood vessels with a pump and valves to ensure one-way flow of blood
Artery	Vessel carrying blood away from the heart
Vein	Vessel carrying blood back to the heart
Capillary	Narrow vessel, wall one cell thick, where substances are exchanged with cells
Single circulation (Extended only)	Blood passes through the heart once per complete circuit (fish)
Double circulation (Extended only)	Blood passes through the heart twice per complete circuit (mammal)
Coronary heart disease	Blockage of the coronary arteries, so heart muscle gets less oxygen and glucose

9.1 Circulatory systems

• Core: vessels + pump + valves → one-way flow.
• Extended only. Fish: heart → gills → body → heart. Mammal: heart → lungs → heart → body → heart.
• Extended only. Advantages of double circulation, one point each:
  • blood returns to the heart after the lungs and is pumped again, so it reaches the body at high pressure and flows faster
  • blood goes to the lungs at lower pressure, protecting lung capillaries
  • oxygenated and deoxygenated blood are kept separate

9.2 Heart

Structures (Core): muscular wall, septum, left and right atria, left and right ventricles, one-way valves, coronary arteries. Extended only: atrioventricular valves (between atria and ventricles) and semilunar valves (at the bases of the aorta and pulmonary artery).

Monitoring (Core): ECG, pulse rate, listening to the sounds of valves closing.

Route of blood through the heart

vena cava → right atrium → right ventricle → pulmonary artery → LUNGS
pulmonary vein → left atrium → left ventricle → aorta → BODY

Method in steps: one heartbeat (Extended only)

1. Atria contract → blood pushed through atrioventricular valves into ventricles.
2. Ventricles contract → atrioventricular valves close (no backflow into atria).
3. Semilunar valves open → blood enters aorta and pulmonary artery.
4. Ventricles relax → semilunar valves close (no backflow into ventricles).

Wall thickness and septum (Extended only)

Comparison	Reason
Left ventricle thicker than right	Pumps blood round the whole body at higher pressure; right pumps only to the lungs
Atria thinner than ventricles	Atria pump only into the ventricles; ventricles pump out of the heart
Septum present	Stops oxygenated and deoxygenated blood mixing, so body receives fully oxygenated blood

Heart rate and activity

• Core: heart rate rises during physical activity and falls back to resting afterwards. Investigate by counting the pulse for a fixed time before and after activity; repeat and take a mean.
• Extended only: muscles respire faster → need more oxygen and glucose and must lose more carbon dioxide → faster heart rate delivers blood faster.

Coronary heart disease (Core)

• Coronary arteries blocked → less oxygen and glucose to heart muscle → muscle cannot respire → may die (heart attack).
• Risk factors (the syllabus list): diet, lack of exercise, stress, smoking, genetic predisposition, age, sex.
• Diet: less saturated fat and cholesterol, less salt. Exercise: strengthens heart, controls body mass, lowers blood pressure. Neither changes age, sex or genetic predisposition.

9.3 Blood vessels

Feature	Artery	Vein	Capillary
Wall thickness	Thick, muscular, elastic	Thin	One cell thick
Lumen	Narrow	Wide	Very narrow
Valves	None	Present	None
Blood pressure (Extended only)	High	Low	Falling

Function of capillaries (Core): exchange of substances between blood and cells.

Structure–function links (Extended only):

• artery: thick wall withstands high pressure; elastic tissue stretches and recoils to keep blood flowing
• vein: low pressure so thin wall is enough; wide lumen means low resistance; valves stop backflow
• capillary: one-cell-thick wall gives a short diffusion distance; many capillaries give a large surface area and bring blood close to every cell

Vessels to name

Organ	In	Out
Heart	Vena cava, pulmonary vein	Aorta, pulmonary artery
Lungs	Pulmonary artery	Pulmonary vein
Kidney	Renal artery	Renal vein
Liver (Extended only)	Hepatic artery, hepatic portal vein	Hepatic veins

Extended only: the hepatic portal vein runs from the gut to the liver, carrying absorbed nutrients.

9.4 Blood

Component	Function
Red blood cells	Transport oxygen; haemoglobin combines with oxygen
White blood cells	Phagocytosis; antibody production
Platelets	Clotting
Plasma	Transports blood cells, ions, nutrients, urea, hormones, carbon dioxide

• Identify (Core): red cells have no nucleus and are most numerous; white cells are larger and have a nucleus.
• Extended only: lymphocyte = large round nucleus, little cytoplasm → antibody production. Phagocyte = lobed nucleus, more cytoplasm → engulfs pathogens by phagocytosis.
• Clotting (Core): prevents blood loss and entry of pathogens.
• Extended only: fibrinogen (soluble) → fibrin (insoluble) → mesh traps blood cells → clot.

Worked reminders

Heart rate from a timed count. Scale the count up to one minute.

24 beats in 20 s → 24 × (60 ÷ 20) = 24 × 3 = 72 beats per minute

Heart rate from an ECG. Divide 60 by the time between two peaks (in seconds). If the peaks are 0.5 s apart, the rate is 60 ÷ 0.5 = 120 beats per minute.

Percentage change. Subtract the starting value from the new value, divide by the starting value, then multiply by 100. Round to the precision the question asks for.

Reading a heart diagram. Find the thickest ventricle wall first: that is the left ventricle, and the aorta leaves it. Then work outwards. The vessel leaving the other ventricle is the pulmonary artery. The large vein entering the atrium on that same side is the vena cava.

Reading a vessel cross-section. A round outline with a thick wall and small lumen is an artery. A flattened or irregular outline with a thin wall and large lumen is a vein. A vessel only one cell wide is a capillary.

Must-know distinctions

• Artery vs vein: defined by direction of flow, not by oxygen. The pulmonary artery carries deoxygenated blood.
• Atrioventricular vs semilunar valves (Extended only): between chambers vs at the exits to the arteries.
• Lymphocyte vs phagocyte (Extended only): makes antibodies vs engulfs pathogens.
• Fibrinogen vs fibrin (Extended only): soluble protein in plasma vs insoluble fibres of the clot.
• Pressure vs volume (Extended only): the left ventricle generates a higher pressure; it does not pump a bigger volume.

Quick self-test

1. State the three parts of a circulatory system that ensure one-way flow.
2. Name the blood vessel that carries blood from the right ventricle.
3. A pulse is counted as 17 beats in 15 seconds. Calculate the heart rate in beats per minute.
4. On an ECG trace, one heartbeat peak occurs every 0.75 s. Calculate the heart rate.
5. State three ways of monitoring the activity of the heart.
6. Give four risk factors for coronary heart disease.
7. State one structural difference between an artery and a vein that you could see in a cross-section.
8. Name the vessel that carries blood from the kidney.
9. State the function of haemoglobin.
10. (Extended) Explain why the atrioventricular valves close when the ventricles contract.
11. (Extended) Name the vessel carrying blood from the small intestine to the liver.
12. (Extended) State the role of fibrin in clotting.

Answers

1. Blood vessels, a pump (the heart) and valves.
2. Pulmonary artery.
3. 17 × 4 = 68 beats per minute.
4. 60 ÷ 0.75 = 80 beats per minute.
5. ECG, pulse rate, listening to the sounds of the valves closing.
6. Any four of: diet, lack of exercise, stress, smoking, genetic predisposition, age, sex.
7. Artery has a thicker wall (or narrower lumen); vein has valves.
8. Renal vein.
9. It combines with oxygen in the lungs and releases it in respiring tissues, so red blood cells can transport oxygen.
10. Pressure in the ventricles rises above that in the atria; the valves close to prevent backflow of blood into the atria.
11. Hepatic portal vein.
12. Fibrin forms a mesh of fibres that traps blood cells to form a clot.

Where marks are usually lost

• Writing “arteries carry oxygenated blood” as a definition instead of “carry blood away from the heart”.
• Mixing up the pulmonary artery and pulmonary vein, or the vena cava and aorta, on heart diagrams.
• Forgetting the diagram is drawn as if facing the person, so labelling left and right the wrong way round.
• Saying the left ventricle is thicker “to pump more blood” rather than “to pump at higher pressure round the whole body”.
• Describing capillary walls as just “thin” instead of one cell thick.
• Saying valves in veins “push blood” instead of “prevent backflow”.
• Explaining raised heart rate without naming both oxygen and glucose delivery, or the removal of carbon dioxide.
• In heart-rate calculations, forgetting to scale a 15 s or 30 s count to one minute, or dividing a percentage change by the final value.
• Stating that plasma transports oxygen.
• Describing clotting with “fibrin turns into fibrinogen” (the conversion is the other way).

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), section 9 Transport in animals. Published by Cambridge University Press & Assessment.