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A-Level Biology OCR A

Guard Cells Stomata Plants Water Change Shape Draw

Guard cells form stomata, regulating gas exchange and water loss. They change shape via turgor pressure, with a thicker inner wall causing asymmetric movement to open/close the stoma.

Guard cells form stomata, which regulate gas exchange and water loss; they change shape by altering turgor pressure, with a thicker cell wall on one side ensuring asymmetric movement to open or close the stoma.

Front Draw, label and annotate how guard cells are specialised for their function.
Back Guard cells:
  • They form small openings on surfaces of leaves - stomata
  • Stomata allow CO2 to enter plants but also allow water to exit plants
  • When the cells lose water, they become less swollen due to osmotic forces, change shape and stoma closes to prevent further water loss from plant
  • Cell wall is thicker on one side so the cell does not change shape symmetrically as volume changes

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