Describe the role of red blood cells in transporting oxygen around the body.

Pearson Edexcel International GCSE Biology (4BI1) — 2.11 Transport: humans · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Red blood cells contain haemoglobin, which binds oxygen in the lungs to form oxyhaemoglobin.
Oxyhaemoglobin then releases oxygen when it reaches tissues.
The biconcave shape of red blood cells gives a large surface‑area‑to‑volume ratio, which maximises oxygen uptake and diffusion.
Thus red blood cells transport oxygen efficiently around the body.

Examiner tips

  • Use the exact terms haemoglobin, oxyhaemoglobin, biconcave, surface‑area‑to‑volume ratio.
  • Show the sequence: binding in lungs, transport, release in tissues.
  • Keep the answer concise – one sentence per point.
  • Mention the shape to justify the large surface area.

Common mistakes

  • Confusing haemoglobin with myoglobin or not naming the oxygen‑binding protein.
  • Omitting the biconcave shape or the surface‑area‑to‑volume ratio.
  • Writing a long paragraph instead of clear, separate points.

Mark scheme (4 marks)

  1. Red blood cells contain haemoglobin
  2. Haemoglobin combines with / binds to oxygen (in the lungs) to form oxyhaemoglobin
  3. Oxyhaemoglobin releases / dissociates to release oxygen at the tissues / body cells
  4. Red blood cells are biconcave / have a large surface area (to volume ratio) to maximise oxygen uptake / diffusion of oxygen

Key terms in this question

red blood cells

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