Control of Stomata
Transpiration is important in bringing water and its dissolved mineral ions to upper parts of the plant. However, if too much water escapes, a plant will die. An adaptation involving guard cells and stomata prevents excess water loss.
During the day, carbon dioxide enters a leaf, so the stomata must be open. Guard cells have chlorophyll and undergo photosynthesis when light is available. As photosynthesis occurs, guard cells swell, their shape changes, and the size of the space (the stoma) between them is increased. Carbon dioxide can then enter the leaf. However, water also escapes from the stomata during the day. Transpiration is this loss of water from stomata.
At night, because light is not present, no photosynthesis occurs in the guard cells. The guard cells collapse, their shape changes, and they move together, reducing the size of the stomata between them. As stomata become smaller, loss of water is decreased. In summary, this adaptation prevents excess water loss, Some water escapes during the day when the stomata are fully open. However, at night the openings become smaller, so less water escapes.
แหล่งข้อมูล: BIOLOGY living system. Page 456.
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