Question 1
Paper 4 short-answer style1 markName the component of blood that transports oxygen. (1 mark)
Model answer
Red blood cells.
Why this scores
One mark for 'red blood cells'.
Launching your learning experience…
Detailed notes on Transport in Animals for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
A liquid tissue with four jobs: oxygen transport, defence, clotting, and carrying everything else dissolved.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Tiny biconcave discs packed with haemoglobin. No nucleus. Made in bone marrow.
Structure.
Adaptations:
| Feature | Why |
|---|---|
| Biconcave disc | Large surface area for O₂ uptake; more flexible. |
| No nucleus | More space for haemoglobin = more O₂. |
| Packed with haemoglobin | Each Hb molecule binds 4 O₂. |
| Small + flexible | Can squeeze single-file through capillaries. |
How haemoglobin works.
Lifespan.
Worked qualitative. Why are people with sickle-cell anaemia anaemic?
Cambridge tip. Always include 'no nucleus → more space for haemoglobin' in adaptation answers. Cambridge marks the explanation, not just the feature.
Phagocytes engulf pathogens. Lymphocytes make antibodies. Both bigger than red cells, with nuclei.
Two main types of white blood cell, both bigger than red cells, both with nuclei.
1. Phagocytes.
2. Lymphocytes.
Where they're made.
Worked qualitative. Why does an infection often make lymph nodes SWELL?
Cambridge tip. Distinguish phagocytes (eat) and lymphocytes (make antibodies). Don't lump them as 'white blood cells fight infection'.
Platelets trigger; fibrinogen → fibrin mesh; red cells trapped → clot/scab.
Step 1. Blood vessel is damaged → platelets gather at the wound.
Step 2. Platelets release CHEMICAL FACTORS that trigger a chain of reactions.
Step 3. Soluble FIBRINOGEN (in plasma) is converted to insoluble FIBRIN.
fibrinogen (soluble)→fibrin (insoluble)
Step 4. Fibrin forms a MESH of fine strands across the wound.
Step 5. Red blood cells get TRAPPED in the mesh → forms a CLOT (jelly-like plug).
Step 6. Clot dries → SCAB. Skin underneath repairs.
Why it matters:
Things that go wrong.
Worked qualitative. Why is haemophilia much more common in MALES than females?
Cambridge tip. Memorise the chain: PLATELETS → FIBRINOGEN → FIBRIN → CLOT. Don't say 'blood thickens' — that's vague.
Pale yellow, ~90% water. Carries everything dissolved.
Composition.
Functions.
Plasma vs serum.
Worked qualitative. Why does dehydration make blood 'thicker' (harder to flow)?
Cambridge tip. Cambridge often asks 'what does plasma transport?' List THREE: glucose, urea, hormones (or antibodies). Three keeps the marks safe.
Verbatim phrases and definitions Cambridge mark schemes credit.
Blood appears every Paper 4 (5-10 marks). Common formats: name + function of components, RBC adaptations, clotting steps. Examiner reports flag students saying RBCs have a nucleus, calling platelets 'cells' (they're fragments), and confusing plasma with whole blood.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (9.4); 0610/42 Oct/Nov 2024 — Q8 (blood); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on blood, written exactly the way a tutor would explain them at the board.
Question
Name the four main components of blood and state the function of each.
Step-by-step solution
Step 1
Red blood cells: carry oxygen (and some carbon dioxide) using haemoglobin.
Step 2
White blood cells: defend against pathogens — phagocytes engulf them, lymphocytes make antibodies.
Step 3
Platelets: cell fragments that help the blood to clot at wounds.
Step 4
Plasma: a pale yellow liquid (mostly water) that carries dissolved substances — nutrients, hormones, urea, carbon dioxide and antibodies.
Answer
Red cells (carry oxygen), white cells (defence), platelets (clotting), plasma (transports dissolved substances).
Question
Name the component of blood that: (a) transports oxygen; (b) helps the blood to clot; (c) engulfs and digests pathogens; (d) transports dissolved glucose, urea and hormones.
Step-by-step solution
Step 1
(a) Transports oxygen → red blood cell.
Step 2
(b) Helps the blood to clot → platelets.
Step 3
(c) Engulfs and digests pathogens → phagocyte (a white blood cell).
Step 4
(d) Transports dissolved substances → plasma.
Answer
(a) Red blood cell; (b) platelets; (c) phagocyte (white blood cell); (d) plasma.
Examiner tip
Plasma is the LIQUID that transports dissolved substances — the cells are suspended in it but are not 'plasma'.
Question
Describe how red blood cells are adapted for the transport of oxygen.
Step-by-step solution
Step 1
Biconcave disc shape → a large surface area for absorbing oxygen.
Step 2
No nucleus → more room inside the cell for haemoglobin, so more oxygen can be carried.
Step 3
Full of haemoglobin → the iron-containing protein that binds oxygen reversibly.
Step 4
Small and flexible → can squeeze through narrow capillaries to reach the tissues.
Answer
Biconcave (large surface area), no nucleus (more haemoglobin), packed with haemoglobin (binds oxygen), small and flexible (fit through capillaries).
Examiner tip
State 'haemoglobin' and 'no nucleus, so more room for haemoglobin' explicitly — both are marking points.
Question
Outline the roles of platelets and fibrinogen in the clotting of blood at a wound.
Step-by-step solution
Step 1
When a blood vessel is cut, platelets collect at the wound and release chemicals.
Step 2
These chemicals cause the soluble protein fibrinogen (in the plasma) to be converted into insoluble fibrin.
Step 3
The fibrin forms a mesh of fibres across the wound.
Step 4
Red blood cells become trapped in the mesh, forming a clot that seals the wound; this dries to form a scab, which keeps out pathogens while new skin grows.
Answer
Platelets gather and trigger the change of fibrinogen into fibrin, which forms a mesh that traps red blood cells to make a clot (then a scab).
Question
Describe how haemoglobin picks up oxygen at the lungs and releases it at the body cells.
Step-by-step solution
Step 1
At the lungs, the oxygen concentration is high, so haemoglobin combines with oxygen to form oxyhaemoglobin (bright red).
haemoglobin+oxygen→oxyhaemoglobin
Step 2
The oxygenated blood is carried to the body tissues.
Step 3
At the body cells, the oxygen concentration is low (the cells are using it in respiration), so the oxyhaemoglobin breaks down, releasing oxygen to the cells.
oxyhaemoglobin→haemoglobin+oxygen
Step 4
The reaction is reversible: haemoglobin loads oxygen where it is plentiful (lungs) and unloads it where it is scarce (tissues).
Answer
At the lungs (high oxygen) haemoglobin + oxygen → oxyhaemoglobin; at the tissues (low oxygen) oxyhaemoglobin → haemoglobin + oxygen. The binding is reversible.
Examiner tip
The reversible reaction with oxyhaemoglobin, driven by the oxygen concentration being high at the lungs and low at the tissues, is the key idea.
Question
Describe how the two main types of white blood cell — phagocytes and lymphocytes — defend the body against pathogens.
Step-by-step solution
Step 1
Phagocytes move towards pathogens, then engulf and digest them (phagocytosis), destroying them.
Step 2
Lymphocytes produce antibodies — proteins with a shape specific to a particular pathogen.
Step 3
The antibodies attach to the pathogens and destroy them, or clump them together so phagocytes can engulf them more easily (some also neutralise toxins).
Step 4
After infection, some lymphocytes remain as memory cells, so the body can respond faster if the same pathogen returns.
Answer
Phagocytes engulf and digest pathogens; lymphocytes make specific antibodies that destroy or clump pathogens (and produce memory cells for faster future responses).
Examiner tip
Two distinct mechanisms: phagocytosis (engulfing) and antibody production (specific to the pathogen).
High-scoring sample answers for blood on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
Name the component of blood that transports oxygen. (1 mark)
Model answer
Red blood cells.
Why this scores
One mark for 'red blood cells'.
State the function of (a) platelets and (b) plasma. (2 marks)
Model answer
(a) Platelets help the blood to clot at a wound. (b) Plasma transports dissolved substances such as glucose, amino acids, urea, hormones and carbon dioxide around the body.
Why this scores
One mark each: platelets → clotting; plasma → transports dissolved substances.
Explain how a red blood cell is adapted to carry oxygen. (3 marks)
Model answer
A red blood cell is packed with haemoglobin, the protein that combines with oxygen. It has no nucleus, leaving more room for haemoglobin so it can carry more oxygen. Its biconcave shape gives a large surface area for oxygen to diffuse in and out quickly.
Why this scores
Three marks: contains haemoglobin; no nucleus → more room for haemoglobin; biconcave shape → large surface area. Each feature linked to oxygen transport.
Describe how the blood forms a clot at a cut in the skin. (4 marks)
Model answer
When the skin is cut, platelets gather at the wound and release chemicals. These cause the soluble protein fibrinogen in the plasma to be converted into insoluble fibrin. The fibrin forms a mesh of fibres across the wound, and red blood cells become trapped in the mesh, forming a clot that seals the cut (and dries to a scab).
Why this scores
Four marks: platelets gather/release chemicals; fibrinogen → fibrin; fibrin forms a mesh; red cells trapped to form a clot.
Describe how haemoglobin transports oxygen from the lungs to the body cells. (5 marks)
Model answer
In the lungs, where the oxygen concentration is high, the haemoglobin in the red blood cells combines with oxygen to form oxyhaemoglobin. The blood then carries the oxyhaemoglobin to the body tissues. At the tissues, where the oxygen concentration is low because the cells are using oxygen in respiration, the oxyhaemoglobin breaks down, releasing oxygen to the cells. This works because the reaction between haemoglobin and oxygen is reversible — haemoglobin picks up oxygen where there is plenty (the lungs) and releases it where there is little (the tissues).
Why this scores
Five marks: at the lungs high oxygen; haemoglobin + oxygen → oxyhaemoglobin; carried to tissues; at tissues low oxygen; oxyhaemoglobin breaks down/releases oxygen (reversible reaction).
Describe how white blood cells defend the body against disease-causing organisms (pathogens). (6 marks)
Model answer
There are two main types of white blood cell, and they defend the body in different ways. Phagocytes move towards a pathogen and engulf it, then digest it with enzymes, destroying it — this is called phagocytosis. Lymphocytes produce antibodies, which are proteins with a shape specific to a particular pathogen's surface. The antibodies attach to the pathogens, and either destroy them, clump them together so that phagocytes can engulf them more easily, or neutralise the toxins the pathogens produce. After the infection, some lymphocytes remain in the blood as memory cells; if the same pathogen enters again, these cells produce the correct antibodies much more quickly, so the person is immune and does not become ill. In these ways the white blood cells both destroy pathogens directly and provide long-term protection.
Why this scores
Up to 6 marks: phagocytes engulf and digest pathogens; lymphocytes make antibodies; antibodies are specific to the pathogen; antibodies destroy/clump pathogens or neutralise toxins; memory cells remain; faster response on re-infection (immunity).
Definitions to memorise and the exact keywords mark schemes credit for blood answers — sharpened from recent examiner reports for the 2026 0610 sitting.
Biconcave disc-shaped cell containing haemoglobin. Carries oxygen from the lungs to the tissues.
Iron-containing protein in red blood cells that binds oxygen reversibly. Forms oxyhaemoglobin in the lungs; releases oxygen at the tissues.
Cell of the immune system. Two main types: phagocytes (engulf pathogens) and lymphocytes (make antibodies).
Type of white blood cell that engulfs and digests pathogens (phagocytosis).
Type of white blood cell that produces antibodies against pathogens.
Small cell fragment that helps the blood to clot at wounds, triggering the change of fibrinogen into fibrin.
Pale yellow liquid part of the blood (mostly water). Transports dissolved substances: glucose, amino acids, urea, hormones, carbon dioxide and antibodies.
Insoluble protein formed during clotting. Creates a mesh that traps red blood cells to form a clot.
The traps other students keep falling into on blood questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Most cells have a nucleus.
How to avoid it
Mature human red blood cells LOSE their nucleus, which leaves more room for haemoglobin (more oxygen-carrying capacity).
Why it happens
They start the process.
How to avoid it
Platelets TRIGGER the clot; the clot itself is the FIBRIN mesh with trapped red blood cells. Platelets are the signal, not the structure.
Why it happens
Both are in the blood.
How to avoid it
PLASMA is the LIQUID part only — water plus dissolved substances. The cells are suspended in plasma but are not plasma.
The things students keep getting wrong in this sub-topic, answered.