The structure and function of bloodSpec 8.6
In short
Blood is a tissue made of plasma with red blood cells, white blood cells and platelets suspended in it. Red blood cells are biconcave discs with no nucleus, full of haemoglobin, which binds to oxygen. Phagocytes engulf pathogens and lymphocytes make antibodies. Plasma carries dissolved substances, and platelets help the blood clot at a wound.
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 (what this means)
Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels meanStandard 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
Do not say red blood cells ‘carry haemoglobin’ as their job. They carry oxygen. Haemoglobin is the substance inside them that binds to oxygen.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026