Stomata
Biology: Cambridge International GCSE Supplement, topic 6.2.2
Guard Cells and Stomata
Stomata are pores in the lower epidermis of leaves that facilitate (make easier) the diffusion of gases, including evaporated water, in and out of the leaf. Guard cells can open and close the stomata:
Opening the stomata
- The guard cells can open the stomata by taking up lots of water, swelling and becoming turgid.
- Guard cells will open the stomata when:
- There is the presence of light, for photosynthesis.
- There is high humidity, which reduces water loss, allowing stomata to remain open.
Closing the stomata
- To close the stomata, the guard cells lose water and return to a flaccid state.
- Guard cells will close the stomata when:
- It is dark, as photosynthesis slows, and stomata close to conserve water.
- There is low water availability, to reduce water loss.
- There are high temperatures to prevent evaporation and preserve water.
Gases
- Carbon dioxide (CO₂): Enters the plant for photosynthesis.
- Oxygen (O₂): Leaves the plant as a byproduct of photosynthesis.
- Water vapour: Also moves out during transpiration.