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GCSE Biology · key term
One of a pair of cells surrounding a stoma that changes shape to open or close the pore.
Used by AQA, Edexcel and OCR
Specification 4.2.3.1 · Paper 1
One of a pair of cells surrounding a stoma that controls whether the pore is open or closed.
Revise: Plant TissuesEach stoma is bordered by two guard cells. By changing shape, these cells open or close the pore, helping the leaf balance gas exchange against water loss.
Specification 6.9, 6.14B · Paper 2
A specialised cell that changes shape to open or close a stoma, controlling gas exchange and water loss.
Revise: TranspirationEach pore is surrounded by two specialised guard cells. Many stomata are on the lower surface of a leaf, where conditions tend to be cooler and more shaded, helping to limit unnecessary water loss.
One of a pair of specialised cells that controls the opening and closing of a stoma.
Specification B2.2g · Paper 1 (Foundation), Paper 3 (Higher)
Revise: Transpiration and translocationA stoma is a pore in the leaf surface surrounded by two guard cells. Carbon dioxide can diffuse in through an open stoma for photosynthesis, while oxygen and water vapour can diffuse out. Opening the pore helps gas exchange, but it also allows more water to escape.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
One of a pair of cells surrounding a stoma that change shape to open or close the pore.
Revise: Stomata: Structure, Function and MicroscopyEach pore is bordered by a pair of guard cells. The guard cells change shape to open or close it.
A stoma is a pore; guard cells are the cells around it that control its opening.
Link guard-cell condition to the pore: turgid guard cells open the stoma; flaccid guard cells close it and reduce water loss.
Label the opening as the stoma and the two surrounding cells as guard cells; do not use the terms interchangeably.
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