# Explain how the structure of a red blood cell (erythrocyte) is adapted to maximise oxygen transport in mammals.

> IB DP Biology Higher Level (2023 syllabus) — B3.2 Transport · Explain · 4 marks

## Mark scheme (4 marks)

1. Biconcave disc shape increases surface area to volume ratio, allowing faster diffusion of oxygen into and out of the cell
2. Absence of a nucleus (and other organelles) creates more space for haemoglobin, increasing oxygen-carrying capacity
3. High haemoglobin concentration enables binding of up to four oxygen molecules per haemoglobin molecule (cooperative binding), loading oxygen efficiently at the lungs
4. Flexible plasma membrane allows the cell to deform and squeeze through narrow capillaries, maintaining continuous oxygen delivery to tissues

## Key terms

- [erythrocyte](https://www.gradenine.co.uk/glossary/erythrocyte)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-a-edb03ab5) · Published by Druglandscape Ltd.