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Structure, Functions, Types & Mechanism of Stomata MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET
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Mechanism of Stomatal Opening
- Stomatal opening and closing is a physiological function dependent on the light.
- They open in light and close in the dark. Such stomata are called photoactive.
- In succulents plants, the stomata are scotoactive. They open at night and close during the day time.
- Stomata open and close as a result of osmosis.
- Under hot and dry conditions, when water loss due to evaporation is high, stomata must close to prevent dehydration.
- Guard cells actively pump potassium ions (K +) out of the guard cells and into surrounding cells.
- This causes water in the enlarged guard cells to move osmotically from an area of low solute concentration (guard cells) to an area of high solute concentration (surrounding cells).
- The loss of water in the guard cells causes them to shrink. This shrinkage closes the stomatal pore.
- When conditions change such that stomata need to open, potassium ions are actively pumped back into the guard cells from the surrounding cells.
- Water moves osmotically into guard cells causing them to swell and curve.
- The outer wall of guard cells bend outwards because it is thin and elastic.
- The inner wall does not bend as it is thick and inelastic.
- This bending of outer wall causes opening of stomatal pore.
- The opening of the stoma is also aided due to the orientation of the microfibrils in the cell walls of the guard cells.
- Cellulose microfibrils are oriented radially rather than longitudinally making it easier for the stoma to open.
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