# The spongy mesophyll layer is an important part of a leaf. Explain how the features of the spongy mesophyll layer and the stomata work together to allow efficient gas exchange in a leaf.

> WJEC A-Level Biology (Wales) — 2.2 Adaptations for gas exchange · Explain · 5 marks

> Plants require carbon dioxide for photosynthesis and must be able to exchange gases efficiently across their internal surfaces.

## Mark scheme (5 marks)

1. The spongy mesophyll has air spaces between its loosely packed cells
2. The air spaces create a large surface area for gas exchange / diffusion
3. Gases dissolve in the moist surface of the spongy mesophyll cells before diffusing across the cell membrane
4. Stomata are pores in the lower epidermis that allow carbon dioxide to diffuse into the leaf and oxygen / water vapour to diffuse out
5. A concentration gradient is maintained because carbon dioxide is used up in photosynthesis, keeping its concentration inside the leaf low

## Key terms

- [spongy mesophyll](https://www.gradenine.co.uk/glossary/spongy-mesophyll)
- [stomata](https://www.gradenine.co.uk/glossary/stomata)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](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/the-spongy-mesophyll-layer-is-an-d2a8e383) · Published by Druglandscape Ltd.