Explain how the structure of red blood cells makes them well adapted for carrying oxygen around the body.

OCR GCSE Biology A: Gateway Science (J247) — B2.1 Supplying the cell · Explain · 4 marks · View as Markdown

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

Red blood cells are produced in the bone marrow and travel through blood vessels to deliver oxygen to cells throughout the body.

Model answer (4 marks)

Red blood cells have a biconcave shape, which increases their surface area relative to volume and allows more efficient gas exchange.
The increased surface area also facilitates rapid diffusion of oxygen into the cell.
Red blood cells lack a nucleus, freeing up internal space.
The absence of a nucleus allows more haemoglobin to be packed inside, so each cell can carry more oxygen.

Examiner tips

Use the word ‘biconcave’ and link it to surface area. Explain how more surface area improves diffusion. Mention the nucleus absence and the resulting extra space for haemoglobin. Show the causal chain: shape → area → diffusion; nucleus → space → haemoglobin → oxygen capacity.

Common mistakes

Writing ‘round’ instead of ‘biconcave’. Failing to connect increased surface area to faster diffusion. Forgetting to mention the nucleus or the extra haemoglobin. Using vague terms like ‘good shape’ without specifying biconcave.

Mark scheme (4 marks)

Red blood cells have a biconcave shape
The biconcave shape increases the surface area of the red blood cell
Red blood cells have no nucleus
Having no nucleus leaves more space / room for haemoglobin, so more oxygen can be carried

Key terms in this question

red blood cells