Structure, Functions, Types & Mechanism of Stomata MCQ

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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.