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Questions and Answers
What is the main purpose of stomata in plants?
What is the function of guard cells in relation to stomata?
What is the reason why guard cells tend to close stomata at night?
What is the function of the palisade mesophyll in the leaf?
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Why do guard cells curve when they swell with water?
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What triggers the movement of potassium ions into guard cells?
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What is the role of abscisic acid (ABA) in regulating guard cell function?
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What is the result of guard cells becoming flaccid?
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Study Notes
Gas Exchange in Plants
- Plants need to 'breathe' carbon dioxide from the atmosphere to photosynthesise and release oxygen as a waste product.
- Gas exchange occurs through the stoma (plural stomata) and involves the release of water from the plant.
- Stomata are regulated by guard cells, which surround each stoma and control the rate of transpiration.
Structure and Function of Guard Cells
- Guard cells are a pair of cells that surround each stoma.
- They have an uneven thickness of the cell wall, thicker on the side next to the stomatal opening and thinner on the opposite side.
- When guard cells are turgid, they curve, opening the stomata, and when they are flaccid, they straighten, closing the stomata.
Photosynthesis and Stomatal Opening
- In daylight, photosynthesis occurs in the palisade mesophyll and guard cells, producing glucose.
- Light triggers the movement of potassium ions into the guard cells, which breaks down starch into malate.
- The presence of glucose and malate decreases the water potential of the guard cells, drawing water in from surrounding epidermal cells by osmosis.
- The guard cells swell and become turgid, opening the stomata.
Stomatal Closure
- In the dark, potassium leaves the guard cells, and malate is converted back into starch.
- The water potential of the guard cells increases, causing water to leave the cells, making them flaccid and closing the stomata.
- The hormone abscisic acid (ABA) is involved in regulating this process.
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