The structure and function of bloodSpec 8.6
Blood is a tissue made of plasma with red blood cells, white blood cells and platelets suspended in it.
| Component | Structure | Function |
|---|---|---|
| Red blood cells (erythrocytes) | Biconcave disc shape, no nucleus, full of haemoglobin | Carry oxygen from the lungs to the cells. Haemoglobin combines with oxygen to form oxyhaemoglobin |
| White blood cells: phagocytes | Flexible, so they can change shape to surround a pathogen | Engulf (take in) pathogens and digest them. This is phagocytosis |
| White blood cells: lymphocytes | Make and release antibodies into the blood | Antibodies attach to specific pathogens and help to destroy them |
| Plasma | Pale yellow liquid | Transports blood cells and dissolved substances: carbon dioxide, urea, digested food molecules, mineral ions and hormones |
| Platelets | Small fragments of cells, with no nucleus | Help the blood to clot at a wound |
Red blood cells
- The biconcave disc shape gives a large surface area for oxygen to be absorbed.
- Haemoglobin binds to oxygen, so the cell can carry a lot of oxygen.
- There is no nucleus, which leaves more room for haemoglobin.
White blood cells
Phagocytes can change shape, so they can surround and engulf pathogens and then digest them. Lymphocytes make antibodies that attach to specific pathogens and help to destroy them.
Plasma and platelets
Plasma is the liquid part of blood and carries many dissolved substances around the body. Platelets make the blood clot where there is a cut. This stops blood loss and stops pathogens entering the body.
Higher tier
Standard form with blood cell counts
A sample of blood has 5 × 10⁶ red blood cells in each mm³. How many red blood cells are there in 2 mm³? Give your answer in standard form.
- Multiply: 2 × 5 × 10⁶ = 10 × 10⁶ = 10 000 000.
- Write as a number between 1 and 10 multiplied by a power of ten: 1 × 10⁷.
Answer: 1 × 10⁷ red blood cells