# Explain how guard cells control the opening and closing of stomata in a plant leaf.

> WJEC GCSE Biology (Wales) — 1.5.1 Plant structure and function · Explain · 4 marks

## Mark scheme (4 marks)

1. When the plant has plenty of water, guard cells take up water by osmosis
2. Guard cells become turgid / swell up
3. The uneven/thickened inner wall causes the guard cells to curve / bow outward, opening the stoma
4. When water is scarce / in dry conditions, guard cells lose water / become flaccid and the stoma closes

## Key terms

- [guard cells](https://www.gradenine.co.uk/glossary/guard-cells)
- [stomata](https://www.gradenine.co.uk/glossary/stomata)

## Related

- [Revision notes for WJEC GCSE 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/explain-how-guard-cells-control-the-33b33c8d) · Published by Druglandscape Ltd.