Gas exchange in plants
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Questions and Answers

What is the main purpose of stomata in plants?

  • To regulate temperature in the plant
  • To exchange gases, primarily taking in carbon dioxide and releasing oxygen (correct)
  • To release water vapor into the atmosphere
  • To release oxygen into the atmosphere

    • What is the function of guard cells in relation to stomata?

  • To regulate the rate of respiration
  • To regulate the rate of transpiration (correct)
  • To regulate the rate of photosynthesis
  • To regulate the rate of cellular division

    • What is the reason why guard cells tend to close stomata at night?

  • Because there is too much sunlight
  • Because the plant is in a state of dormancy
  • Because photosynthesis is not occurring (correct)
  • Because the air is too humid

    • What is the function of the palisade mesophyll in the leaf?

    <p>To synthesize glucose during photosynthesis</p> Signup and view all the answers

    Why do guard cells curve when they swell with water?

    <p>Because the cell wall is thicker on the stomatal side</p> Signup and view all the answers

    What triggers the movement of potassium ions into guard cells?

    <p>Light</p> Signup and view all the answers

    What is the role of abscisic acid (ABA) in regulating guard cell function?

    <p>It is involved in regulating the process of opening and closing stomata</p> Signup and view all the answers

    What is the result of guard cells becoming flaccid?

    <p>The stomata close</p> Signup and view all the answers

    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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