Cambridge IGCSE Biology 0610: Transport in animals – Study Guide

This study guide teaches topic 9, Transport in animals, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. It covers syllabus sections 9.1 Circulatory systems, 9.2 Heart, 9.3 Blood vessels and 9.4 Blood. Core content is examined on Papers 1 and 3; Supplement content, marked Extended only below, is added for Extended candidates on Papers 2 and 4. The heart-rate investigation in 9.2 also suits the practical papers (5 and 6).

Course pages: Cambridge IGCSE Biology hub and the printable 0610 checklist. When you have worked through this guide, use the revision notes and then the practice questions.

What this unit covers

Section	What you must be able to do	Tier
9.1	Describe the circulatory system: vessels, a pump and valves for one-way flow	Core
9.1	Describe single circulation (fish) and double circulation (mammal); explain the advantages of double circulation	Extended only
9.2	Identify heart structures; arteries carry blood away, veins return it; monitoring the heart; heart rate and activity; coronary heart disease	Core
9.2	Identify atrioventricular and semilunar valves; explain wall thickness; importance of the septum; how the heart works; explain the effect of activity on heart rate	Extended only
9.3	Structure of arteries, veins and capillaries; functions of capillaries; main vessels of the heart, lungs and kidney	Core
9.3	Link vessel structure to blood pressure and function; vessels of the liver	Extended only
9.4	Components of blood and their functions; identify red and white cells; roles of clotting	Core
9.4	Identify lymphocytes and phagocytes; their functions; fibrinogen to fibrin	Extended only

9.1 Circulatory systems

A circulatory system is a system of blood vessels with a pump (the heart) and valves that make sure blood flows in one direction only. That one sentence is the whole Core outcome. Learn all three parts: vessels, pump, valves.

Single and double circulation (Extended only)

In a fish, blood follows a single circulation. The heart pumps blood to the gills, where it picks up oxygen. From the gills the blood goes straight on to the rest of the body and then back to the heart. Blood passes through the heart once for each complete circuit of the body.

In a mammal, blood follows a double circulation. Blood passes through the heart twice for each complete circuit:

• pulmonary circulation: right side of heart → lungs → left side of heart
• systemic circulation: left side of heart → body organs → right side of heart

Advantages of a double circulation:

• Blood returning from the lungs goes back to the heart and is pumped again, so blood reaches the body at high pressure. It flows faster, so oxygen and glucose reach respiring tissues more quickly.
• Blood can be sent to the lungs at a lower pressure, which avoids damage to the delicate lung capillaries and gives time for gas exchange.
• Oxygenated and deoxygenated blood are kept separate, so blood going to the body carries as much oxygen as possible.

In a fish, blood loses much of its pressure passing through the gill capillaries, so it flows more slowly to the body.

9.2 The heart

Structures you must identify

Core: muscular wall, septum, left and right atria, left and right ventricles, one-way valves and coronary arteries. Remember that diagrams show the heart as if you are facing the person, so the left side of the heart is on the right of the page.

Extended only: name the valves. The atrioventricular valves lie between each atrium and its ventricle. The semilunar valves lie at the base of the aorta and the pulmonary artery.

The coronary arteries run over the outside of the heart. They supply the heart muscle itself with oxygen and glucose.

Arteries and veins

Blood is pumped away from the heart in arteries and returns to the heart in veins. This is the definition, and it holds even for the pulmonary artery (deoxygenated blood) and pulmonary vein (oxygenated blood).

Monitoring the heart

The activity of the heart can be monitored by:

• an ECG (electrocardiogram), which records the electrical activity of the heart
• the pulse rate, counted at the wrist or neck
• listening to the sounds of the valves closing, using a stethoscope

Wall thickness (Extended only)

• Left ventricle wall thicker than right ventricle wall: the left ventricle pumps blood all round the body, so it must produce a higher pressure. The right ventricle pumps blood only to the nearby lungs, at lower pressure.
• Atria walls thinner than ventricle walls: the atria only pump blood a short distance, into the ventricles below them. The ventricles pump blood out of the heart into the arteries.

The septum (Extended only)

The septum separates the left and right sides of the heart. It stops oxygenated blood (left side) mixing with deoxygenated blood (right side). Without it, blood pumped to the body would carry less oxygen, and less oxygen would reach respiring cells.

How the heart pumps (Extended only)

1. Blood enters the atria from the veins (vena cava on the right, pulmonary vein on the left).
2. The atria contract. Blood is pushed through the open atrioventricular valves into the ventricles.
3. The ventricles contract. Pressure in the ventricles rises. The atrioventricular valves close, which stops blood flowing back into the atria.
4. The semilunar valves open and blood is forced into the aorta and pulmonary artery.
5. The ventricles relax. The semilunar valves close, which stops blood flowing back from the arteries into the ventricles.

The heart sounds you hear through a stethoscope are the valves closing.

Physical activity and heart rate

During physical activity, heart rate increases. After activity it gradually falls back to the resting rate.

Explanation (Extended only): active muscles contract more, so their cells respire faster. They need a faster supply of oxygen and glucose, and faster removal of carbon dioxide. A higher heart rate pumps blood round the body faster, delivering these substances and removing waste at a greater rate.

Worked example: investigating heart rate

A student counted her pulse for 30 seconds, three times at rest and three times immediately after two minutes of step-ups.

Condition	Count 1	Count 2	Count 3
At rest (beats in 30 s)	36	38	37
After exercise (beats in 30 s)	58	60	59

(a) Calculate the mean heart rate at rest, in beats per minute.

mean count at rest = (36 + 38 + 37) ÷ 3 = 37 beats in 30 s
heart rate = 37 × 2 = 74 beats per minute

(b) Calculate the percentage increase in heart rate after exercise.

mean count after exercise = (58 + 60 + 59) ÷ 3 = 59 beats in 30 s
heart rate = 59 × 2 = 118 beats per minute
percentage increase = (118 − 74) ÷ 74 × 100 = 59.46...% ≈ 59%

(c) Suggest one variable she should keep constant. The type and duration of exercise (for example, the same step height and rate for two minutes).

Repeating each count and taking a mean makes the result more reliable. Divide the change by the starting value, not the final one.

Coronary heart disease

Coronary heart disease (CHD) happens when the coronary arteries become blocked, for example by fatty deposits in the artery wall. Less blood reaches the heart muscle, so it gets less oxygen and glucose. The muscle cannot respire properly and may die, which can cause a heart attack.

Possible risk factors: diet, lack of exercise, stress, smoking, genetic predisposition, age and sex.

Reducing the risk: diet and exercise. A diet lower in saturated (animal) fat and cholesterol reduces fatty deposits in arteries. Eating less salt helps keep blood pressure down. Regular exercise strengthens the heart, helps control body mass and helps keep blood pressure down. Both help, but they cannot remove risk factors such as age, sex or genetic predisposition. In a “discuss” question, give both roles and a limitation.

9.3 Blood vessels

Structure (Core)

Feature	Artery	Vein	Capillary
Wall	Thick, muscular and elastic	Thin	One cell thick
Lumen	Narrow	Wide	Very narrow
Valves	No	Yes	No

Functions of capillaries: they carry blood through the tissues, close to every cell, so that substances are exchanged between the blood and the cells. Oxygen and glucose pass out to the cells; carbon dioxide and other wastes pass into the blood.

Structure and pressure (Extended only)

• Arteries carry blood at high pressure straight from the heart. The thick wall withstands this pressure without bursting. The elastic tissue stretches as each surge of blood arrives and recoils between beats, which keeps blood moving and evens out the flow.
• Veins carry blood at low pressure. They do not need a thick wall. The wide lumen gives little resistance to flow, and the valves prevent backflow.
• Capillaries: the wall is one cell thick, so there is a short diffusion distance. Their narrow lumen brings blood very close to cells. There are very many of them, so the total surface area for exchange is large, and every cell is close to a capillary.

Main blood vessels to identify

Organ	Vessel in	Vessel out
Heart (Core)	Vena cava (right atrium), pulmonary vein (left atrium)	Pulmonary artery (right ventricle), aorta (left ventricle)
Lungs (Core)	Pulmonary artery	Pulmonary vein
Kidney (Core)	Renal artery	Renal vein
Liver (Extended only)	Hepatic artery; hepatic portal vein (from the gut)	Hepatic veins

Extended only: the hepatic portal vein is unusual: it carries blood from the gut to the liver, not back to the heart. This blood contains absorbed nutrients.

9.4 Blood

Blood is made of red blood cells, white blood cells, platelets and plasma.

Component	Function
Red blood cells	Transport oxygen. They contain haemoglobin, which combines with oxygen in the lungs and releases it in respiring tissues
White blood cells	Phagocytosis and antibody production
Platelets	Clotting (details not required at Core)
Plasma	Transports blood cells, ions, nutrients, urea, hormones and carbon dioxide

Identifying cells in photomicrographs. Red blood cells are the most numerous cells, have no nucleus and look paler in the centre. White blood cells are larger, fewer, and each has a nucleus. Platelets appear as small fragments.

Extended only. A lymphocyte has a large round nucleus that fills most of the cell, with little cytoplasm. A phagocyte has a lobed nucleus and more cytoplasm. Lymphocytes produce antibodies; phagocytes engulf pathogens by phagocytosis.

Clotting

Clotting prevents blood loss and prevents the entry of pathogens through a wound.

Extended only: when a vessel is damaged, the soluble plasma protein fibrinogen is converted into insoluble fibrin. Fibrin forms a mesh of fibres that traps blood cells and forms a clot.

Common errors

• Defining arteries as vessels that carry oxygenated blood. The definition is direction: away from the heart.
• Saying the left ventricle is thicker “to pump more blood”. Both ventricles pump the same volume; the left pumps at higher pressure over a longer distance.
• Placing atrioventricular valves at the exits of the ventricles. They sit between atria and ventricles; semilunar valves guard the arteries.
• Saying capillary walls are “thin” without saying one cell thick.
• Writing that veins have valves “to pump blood”. Valves only prevent backflow.
• Saying plasma carries oxygen. Oxygen travels in red blood cells, bound to haemoglobin.
• In CHD answers, saying the heart “runs out of blood”. Say the heart muscle gets less oxygen and glucose, so it cannot respire.

Next steps

• Condense this into the transport in animals revision notes.
• Test yourself with the transport in animals practice questions.
• Take the free 0610 Core diagnostic or 0610 Extended diagnostic.
• White blood cells lead on to topic 10: diseases and immunity study guide.

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.