ANA SAYFA


STOMATAL OPENING AND CLOSING MECHANISM
 
 
 
Stomatal structure:
 
 
 
 
 
The inner wall of the guard cell is thicker than the outer wall.
 
→This causes to become turgid when a guard cell take in water from epidermal cells.
 
 
 
 
 
*Stomatal opening and closing mechanism 1:
 
 
During the day:
 
→The guard cells produce glucose by photosynthesis.
 
→Thus, the rate of glucose increases.
 
 
 
 
→Then, the osmotic pressure increases.
 
→The guard cells, take up water from the epidermal cells by osmosis.
 
 
 
 
→ The turgor pressure increases and then, the stoma opens.
 
 
 
 
During the night:
 
 →Within the guard cells: the glucoses turn to starch.
 
     n (Glucose) ----------> Starch + (n-1) H2O
 
 
→Thus, the rate of glucose decreases.
 
 
 
 
→The osmotic pressure decreases.
 
→The guard cells lose water by osmosis.
 
 
 
 
 
→The turgor pressure decreases and then, stoma closes.
 
 
 
 
 
 
 
*Stomatal opening and closing mechanism 2:
 
 
During the day:
 
→The guard cells take in Kfrom epidermal cells.
 
 
 
 
→This causes to increase osmotic pressure within the guard cells.
 
→Then, the guard cells take in water by osmosis from the epidermal cells.
 
 
 
 
→This causes to increase turgor pressure within the guard cells.
 
→Thus, the guard cells become turgid and stoma opens.
 
 
 
 
During the night:
 
→The epidermal cells take in K+ from guard cells.
 
 
 
 
→This causes to increase osmotic pressure within the epidermal cells.
 
→Then, the epidermal cells take in water by osmosis from the guard cells.
 
 
 
 
→This causes to decrease turgor pressure within the guard cells and stoma closes.
 
 
 
 
 
 
 
 
 
 
 
 
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