Blood — Cambridge IGCSE Biology
The components of blood and their functions, white blood cell types, and how blood clots.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Blood is made of red blood cells, white blood cells, platelets and plasma. Red blood cells have no nucleus and contain haemoglobin, which combines with oxygen to transport it. White blood cells defend against pathogens by phagocytosis and antibody production. Platelets help blood to clot, and plasma transports cells, ions, nutrients, urea, hormones and carbon dioxide.
Blood clotting prevents blood loss and stops pathogens entering a wound. Clotting is the conversion of soluble fibrinogen to insoluble fibrin, which forms a mesh that traps red blood cells and dries into a scab. The two types of white blood cell are lymphocytes, which produce antibodies, and phagocytes, which engulf pathogens by phagocytosis.
Exam questions
7 exam-style questions (19 marks), each with its mark scheme.
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Quick check questions
List the four components of blood.
Show answer
Red blood cells, white blood cells, platelets and plasma.
What is the function of haemoglobin?
Show answer
To transport oxygen in the red blood cells.
State two roles of blood clotting.
Show answer
Prevents blood loss and prevents entry of pathogens.
Supplement What does a phagocyte do?
Show answer
Engulfs pathogens by phagocytosis.
Supplement Name the protein converted to fibrin during clotting.
Show answer
Fibrinogen.
Frequently asked questions
What are the four components of blood and their functions?
Blood is made of red blood cells, white blood cells, platelets and plasma. Red blood cells transport oxygen using haemoglobin. White blood cells defend against pathogens by phagocytosis and antibody production. Platelets help blood to clot. Plasma, the liquid part, transports blood cells, ions, nutrients, urea, hormones and carbon dioxide.
How do red blood cells carry oxygen?
Red blood cells carry oxygen using haemoglobin, a red pigment that combines with oxygen. Red blood cells are small, round and pale in the middle, with no nucleus. In an exam, saying 'red blood cells carry oxygen' is not enough: say that the oxygen is carried by haemoglobin.
How do white blood cells fight infection?
Supplement White blood cells defend the body against pathogens in two ways. Phagocytes, which have a lobed nucleus, engulf pathogens by phagocytosis. Lymphocytes, which have a large round nucleus filling most of the cell, produce antibodies. Antibodies bind to antigens on pathogens, which leads to their destruction.
How does blood clot?
Supplement When a blood vessel is damaged, soluble fibrinogen in the plasma is converted to insoluble fibrin. Fibrin forms a mesh of fibres across the wound, which traps red blood cells to form a clot. The clot dries into a scab. Clotting prevents blood loss and stops pathogens entering the body.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026