Blood is a tissue
Blood contains plasma, with red blood cells, white blood cells and platelets suspended in it. The components work together in transport, defence and clotting.
Lesson 2.8 · AQA Combined Science
Blood and its components
Red blood cells carry oxygen
Red blood cells contain haemoglobin, which binds oxygen. Their biconcave disc shape provides a large surface area and a short diffusion path. They have no nucleus, leaving more space for haemoglobin, and are flexible enough to pass through narrow capillaries.
Defend and repair
White blood cells defend against pathogens. Some engulf them; others produce antibodies or antitoxins. They have a nucleus. Platelets are small cell fragments that help blood clot. Clots reduce blood loss and entry of pathogens.
Plasma transports dissolved substances
| Plasma carries | Examples |
|---|---|
| Products of digestion | Glucose and amino acids |
| Waste products | Carbon dioxide to lungs; urea to kidneys |
| Other substances | Hormones; blood cells and platelets are suspended in plasma |
Plasma is the liquid component. Most oxygen is carried by haemoglobin inside red cells.
Remember
Red cells: oxygen. White cells: defence. Platelets: clotting. Plasma: transport.
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