# Explain how the structure of the alveoli is adapted to maximise the rate of gas exchange in the lungs.

> IB DP Biology Standard Level (2023 syllabus) — B3.1 Gas exchange · Explain · 4 marks

## Mark scheme (4 marks)

1. Alveoli have a very large total surface area, increasing the area available for diffusion of oxygen and carbon dioxide.
2. The alveolar walls are one cell thick (squamous epithelium), giving a very short diffusion distance/pathway for gases.
3. Alveoli are surrounded by a dense network of capillaries, maintaining a steep concentration gradient by continuously removing oxygen and delivering carbon dioxide.
4. The moist lining of the alveoli allows gases to dissolve, enabling diffusion across the membrane.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard 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-the-d0d46972) · Published by Druglandscape Ltd.