Types and Mechanisms of Transpiration
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Questions and Answers

What is the primary process involved in stomatal transpiration?

  • Translocation of sugars through phloem
  • Evaporation of water from soil
  • Osmotic diffusion of water from xylem to stomata (correct)
  • Active transport of nutrients into guard cells
  • During which condition is stomata likely to be open according to the starch-sugar interconversion hypothesis?

  • Night with low pH in guard cells
  • Daytime with high CO2 concentration
  • Daytime with alkaline medium in guard cells (correct)
  • High atmospheric humidity
  • Which of the following is an external factor that affects the rate of transpiration?

  • Internal water condition
  • Guard cell water condition
  • Available soil water (correct)
  • Rate of photosynthesis
  • What causes the guard cells to become turgid and open the stomata during the day?

    <p>Conversion of starch to sugar</p> Signup and view all the answers

    During the night, what occurs in the guard cells that contributes to stomatal closure?

    <p>Conversion of sugar back to starch</p> Signup and view all the answers

    Which transpiration type accounts for water loss through leaf surfaces not involved with stomata?

    <p>Cuticular transpiration</p> Signup and view all the answers

    What is a substance that acts as an antitranspirant to reduce transpiration rates?

    <p>Abscisic acid (ABA)</p> Signup and view all the answers

    Which mechanism is involved in the potassium ion transport within guard cells?

    <p>Selective permeability of the cell membrane</p> Signup and view all the answers

    Study Notes

    Transpiration

    • Types of Transpiration:
      • Stomatal transpiration: Water loss through stomata
      • Cuticular transpiration: Water loss through the cuticle
      • Lenticular transpiration: Water loss through lenticels
      • Stomatal Transpiration Mechanism:
        • Osmosis of water from xylem to intercellular spaces
        • Opening and closing of stomata
        • Diffusion of water vapor from intercellular spaces to the atmosphere
    • Opening and Closing of Stomata:
      • Starch-Sugar Interconversion Hypothesis:
        • Daytime: CO2 used for photosynthesis makes the guard cells alkaline, converting insoluble starch to soluble sugar, increasing osmotic pressure, causing the guard cells to swell and open stomata.
        • Nighttime: CO2 accumulates, making guard cells acidic, converting sugar back to starch, decreasing osmotic pressure, causing guard cells to lose water and close stomata.
      • K+ ion Transport Mechanism:
        • Potassium ions (K+) move into guard cells during the day due to active transport, increasing osmotic pressure, causing the guard cells to expand and open the stomata.
        • K+ ions move out of the guard cells at night, decreasing osmotic pressure, causing them to shrink and close the stomata.
      • Factors Affecting Rate of Transpiration:
        • External:
          • Atmospheric humidity
          • Temperature
          • Wind
          • Light
          • Available soil water
          • Carbon dioxide (C02) concentration
        • Internal:
          • Internal water condition
    • Plant Antitranspirants:
      • Substances reducing transpiration rate.
      • Examples: Abscisic acid (ABA), Phenyl Mercuric Acetate, increased C02 concentration.

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    Description

    Explore the different types of transpiration including stomatal, cuticular, and lenticular transpiration. Understand the mechanisms behind stomatal opening and closing, focusing on starch-sugar interconversion and potassium ion transport. This quiz delves into the essential processes of water loss in plants.

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