Blood
Section: Biology | Syllabus: Cambridge IGCSE Combined Science (0653)
Components of Blood
Blood is a liquid tissue made up of four main components:
| Component | Description | Functions |
|---|---|---|
| Red blood cells | Biconcave disc shape; no nucleus when mature; contain haemoglobin | Transport oxygen from the lungs to body cells |
| White blood cells | Larger than red blood cells; have a nucleus; fewer in number; several types | Defence against disease, by phagocytosis and antibody production |
| Platelets | Tiny cell fragments; no nucleus; irregular shape | Involved in blood clotting |
| Plasma | Pale yellow liquid, mainly water | Transports blood cells, dissolved ions, nutrients, urea, hormones and carbon dioxide |
Red blood cells, white blood cells and platelets can each be identified in a blood smear
Red Blood Cells and Haemoglobin
- Biconcave disc shape - increases surface area relative to volume, for faster diffusion of oxygen
- No nucleus - leaves more space for haemoglobin, maximising oxygen-carrying capacity
- Contains haemoglobin - a red, iron-containing protein that binds oxygen
haemoglobin + oxygen ⇌ oxyhaemoglobin
In the lungs, this reaction goes to the right, and haemoglobin binds oxygen. In body tissues, the reaction goes to the left, and oxygen is released.
Blood Clotting
- Prevents blood loss - seals damaged blood vessels to stop bleeding
- Prevents the entry of pathogens - the clot acts as a physical barrier, blocking microorganisms from entering through the wound
White Blood Cells: Phagocytes and Lymphocytes (Supplement)
| Type | Appearance | Function |
|---|---|---|
| Phagocytes | Irregular, multi-lobed nucleus; granular cytoplasm | Engulf and destroy pathogens by phagocytosis |
| Lymphocytes | Large, round nucleus taking up most of the cell; little cytoplasm | Produce antibodies |
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