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Structure, Functions, Types & Mechanism of Stomata - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET

Concepts Covered - 0

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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