# Explain how the process of diffusion allows oxygen to move from the alveoli into the blood in the lungs, and describe two features of the alveoli that make this process efficient.

> AQA A-Level Biology (7402) — 3.2.3 Transport Across Membranes · Explain · 5 marks

## Mark scheme (5 marks)

1. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration
2. Oxygen concentration is higher in the alveoli than in the blood / there is a concentration gradient between the alveoli and the blood
3. Alveoli have a large surface area (to allow more diffusion to occur)
4. Alveoli walls are one cell thick / have a thin membrane / short diffusion distance
5. Alveoli have a good blood supply / rich capillary network that maintains the concentration gradient

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-process-of-diffusion-8de1e262) · Published by Druglandscape Ltd.