Guard Cell
Contents
Key Stage 3
Meaning
The two guard cells can be seen at the top of this leaf.
A guard cell is a specialised cell in a plant leaf which can change shape to allow or stop gases from getting into the leaf.
Adaptations of the Guard Cell
- Guard cells can change shape to open and close a hole called a stoma.
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| The under side of a leaf showing guard cells and stomata. |
About Guard Cells
- Guard cells are shaped with a gap between them called a stoma.
- There are more guard cells found on the bottom of the leaf than the top.
- Photosynthesis needs water, so guard cells are there to make sure the leaves don't use up too much water and die of dehydration.
- Guard cells fill with water to become turgid, making the stomata larger. This allows carbon dioxide into the leaf for photosynthesis.
- When the leaf gets dehydrated the guard cells become flaccid making the stomata smaller. This stops carbon dioxide from getting into the leaf and prevents photosynthesis
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| Turgid guard cells are full of water and have a hole called a stoma between them to allow air in and out. | Flaccid guard cells are dehydrated and the stoma is blocked stopping air form getting in or out of the leaf. |
Key Stage 4
Meaning
A guard cell is a specialised cell in a plant leaf which can change shape to open or close a hold in the leaf called a stoma allowing or preventing gas exchange.
Adaptations of the Guard Cell
- Guard cells can change shape to open and close a hole called a stoma.
About Guard Cells
- Guard Cells are essential to control the rate of photosynthesis and transpiration.
- When guard cells become flaccid, due to dehydration, the stomata close and water vapour can no longer escape the leaf. This stops transpiration, preventing further water loss. The closed stomata also prevent Carbon Dioxide from entering the leaf, stopping photosynthesis and conserving water (which is needed for photosynthesis.
- There are more guard cells found on the bottom of the leaf than the top.
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| Turgid guard cells are full of water and have a hole called a stoma between them to allow air in and out. | Flaccid guard cells are dehydrated and the stoma is blocked stopping air form getting in or out of the leaf. |
References
AQA
- Guard cell, pages 60-1, 68, 70-71, GCSE Biology; Student Book, Collins, AQA
- Guard cells, page 44, GCSE Biology; The Revision Guide, CGP, AQA
- Guard cells, page 66, GCSE Biology; Third Edition, Oxford University Press, AQA
- Guard cells, pages 38, 40, GCSE Combined Science; The Revision Guide, CGP, AQA
- Guard cells, pages 60, 88, GCSE Combined Science Trilogy; Biology, CGP, AQA
- Guard cells, pages 66, 94, GCSE Biology, CGP, AQA
Edexcel
- Guard cells page 87, GCSE Combined Science, Pearson Edexcel
- Guard cells, page 125, GCSE Biology, Pearson, Edexcel
- Guard cells, pages 211, 212, GCSE Biology, CGP, Edexcel