Blood and the immune system — Edexcel International GCSE Science (Double Award)
The components of blood, what plasma transports, how red blood cells carry oxygen, and how phagocytes and lymphocytes defend the body.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Blood is a tissue made of plasma, red blood cells, white blood cells and platelets. Plasma transports carbon dioxide, digested food, urea, hormones and heat energy. Red blood cells transport oxygen: their biconcave disc shape gives a large surface area, they contain haemoglobin that combines with oxygen to form oxyhaemoglobin, and they have no nucleus.
The immune response is the defence of the body against pathogens by white blood cells. Phagocytes ingest pathogens and destroy them, a process called phagocytosis. Lymphocytes recognise the antigens on a pathogen's surface and release antibodies. Each antibody is specific: its shape fits the antigens on one pathogen only, and it helps to destroy that pathogen.
Exam questions
5 exam-style questions (14 marks), each with its mark scheme.
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9 cards: flip them, mark what you knew, and practise the rest.
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The whole of structure and functions in living organisms on one page, so you can see where this subtopic fits.
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Quick check questions
Name the four components of blood.
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Red blood cells, white blood cells, platelets and plasma.
Give three adaptations of a red blood cell for carrying oxygen.
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Biconcave shape, no nucleus, contains haemoglobin.
How do phagocytes destroy pathogens?
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They ingest (engulf) them.
What do lymphocytes release?
Show answer
Antibodies that are specific to the pathogen.
Frequently asked questions
How are red blood cells adapted to carry oxygen?
Red blood cells are adapted to carry oxygen in three ways. Their biconcave disc shape gives a large surface area for oxygen to diffuse in and out quickly. They contain haemoglobin, which combines with oxygen in the lungs to form oxyhaemoglobin and releases it in the tissues. They have no nucleus, leaving more room for haemoglobin.
How do white blood cells fight infection?
White blood cells fight infection in two ways. Phagocytes surround pathogens and ingest them, then destroy them inside the cell, which is called phagocytosis. Lymphocytes recognise the antigens on a pathogen's surface and release antibodies that are specific to that pathogen. The antibodies attach to the pathogen and help to destroy it.
Why are antibodies specific?
Antibodies are specific because each antibody has a shape that fits the antigens on one particular pathogen only. Antigens are molecules on the surface of a pathogen that the immune system recognises as foreign. A different pathogen has different antigens, so lymphocytes must release a different antibody to help destroy it.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026