Explain how the structure of a red blood cell is adapted for its function of carrying oxygen.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Red blood cells are biconcave discs, which increases their surface area relative to volume and facilitates rapid diffusion of oxygen.
They lack a nucleus, freeing up space for haemoglobin, the oxygen‑binding protein.
The larger haemoglobin content allows each cell to carry more oxygen.
The disc shape also reduces cell density, helping them to move easily through capillaries.
They lack a nucleus, freeing up space for haemoglobin, the oxygen‑binding protein.
The larger haemoglobin content allows each cell to carry more oxygen.
The disc shape also reduces cell density, helping them to move easily through capillaries.
Examiner tips
- Use the word ‘biconcave disc’ and link it to increased surface area. Mention the absence of a nucleus and the resulting extra space for haemoglobin. Show how more haemoglobin means more oxygen transport.
- Include the key terms ‘surface area’, ‘haemoglobin’ and ‘oxygen transport’ to match the mark scheme.
Common mistakes
- Writing that the disc shape is for flexibility only, ignoring surface area. Forgetting to mention the lack of a nucleus. Using ‘nucleus’ instead of ‘nuclei’ or ‘nucleus’ incorrectly in plural.
Mark scheme (4 marks)
- Red blood cells have a biconcave disc shape
- This increases the surface area for absorption / diffusion of oxygen
- Red blood cells have no nucleus
- This leaves more space / room for haemoglobin, which carries oxygen
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →