Red blood cells are specialised cells that carry oxygen around the body. Explain how the structure of red blood cells is adapted to carry out this function efficiently.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Red blood cells are biconcave, which increases their surface‑area‑to‑volume ratio and allows rapid oxygen diffusion.
They contain haemoglobin, a protein that binds oxygen.
The cells lack a nucleus, freeing cytoplasmic space for haemoglobin and therefore increasing oxygen capacity.
They contain haemoglobin, a protein that binds oxygen.
The cells lack a nucleus, freeing cytoplasmic space for haemoglobin and therefore increasing oxygen capacity.
Examiner tips
- Use the term "biconcave" and link it to surface area. Mention haemoglobin and its oxygen‑binding role. Explain the advantage of no nucleus for oxygen transport.
- common_mistakes
- :
- Forgetting to mention the biconcave shape. Failing to state that haemoglobin binds oxygen. Not explaining why the absence of a nucleus is beneficial.
Mark scheme (5 marks)
- Red blood cells have a biconcave shape
- The biconcave shape increases the surface area for gaseous exchange / oxygen uptake
- Red blood cells contain haemoglobin which binds to / carries oxygen
- Red blood cells have no nucleus
- Having no nucleus leaves more space / room for haemoglobin, so more oxygen can be carried
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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