guard cells
control the opening and closing of stomata
Guard cells are specialized cells found in the epidermis of plant leaves that regulate gas exchange and water loss by controlling the opening and closing of stomata.
Stomata are small pores on the surface of leaves that allow for gas exchange between the plant and the atmosphere. Carbon dioxide from the atmosphere diffuses into the leaf through open stomata, while oxygen and water vapor diffuse out. The regulation of stomatal opening and closing is essential for plant survival, as it balances the uptake of carbon dioxide with the loss of water.
Guard cells are shaped like a kidney or a dumbbell. They are one of the few epidermal cells that contain chloroplasts, which allow them to produce ATP and support photosynthesis. When enough light and water are available, guard cells take up potassium ions and other solutes from neighboring cells in the leaf. As the concentration of solutes increases within the guard cells, water also flows in, causing them to swell and spread apart.
This swelling and separation of guard cells cause the stomata to open, allowing for gas exchange to occur. Conversely, when it gets dark, or the plant is dehydrated, guard cells lose potassium ions and other solutes, which causes water to flow out of them. As the guard cells shrink and come closer together, the stomata close, reducing the loss of water and preventing the plant from drying out.
In summary, guard cells are specialized cells found in plant leaves that regulate gas exchange and water loss. They open and close stomata in response to changes in light and water availability by changing their shape and the amount of solutes they contain.
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