# Explain why the lungs contain a large number of alveoli rather than a single large air sac.

> Eduqas GCSE Biology — 1.2.2 The respiratory system · Explain · 4 marks

## Mark scheme (4 marks)

1. A large number of alveoli provides a much greater total surface area
2. A greater surface area allows more gas exchange to occur at the same time
3. A single large air sac would have a much smaller surface area to volume ratio
4. This means the rate of diffusion of oxygen into the blood (and carbon dioxide out) would be too slow to meet the body's needs

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Biology](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-lungs-contain-a-f3fddf67) · Published by Druglandscape Ltd.