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This lesson covers the components of blood and the structure and function of the three types of blood vessel — arteries, veins and capillaries — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to describe each blood component, explain how blood vessels are adapted for their function and interpret data on blood composition.
Blood is a tissue made up of four main components:
| Component | Description | Function |
|---|---|---|
| Plasma | Straw-coloured liquid that makes up about 55 % of blood volume | Transports dissolved substances: glucose, amino acids, CO₂, urea, hormones, antibodies, heat |
| Red blood cells (erythrocytes) | Biconcave disc shape; no nucleus; packed with haemoglobin | Transport oxygen from lungs to body tissues |
| White blood cells (leucocytes) | Larger than red blood cells; have a nucleus; several types | Defend the body against pathogens (part of the immune system) |
| Platelets | Small cell fragments; no nucleus | Help blood clot at wound sites to prevent blood loss and entry of pathogens |
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