What causes the opening and closing of guard cells of stomata during transpiration?
The opening and closing of stomata depend upon the turgid or flaccid state of the guard cells. The inner wall of guard cells (towards pore) is thick and outer wall (towards other epidermal cells) is thin. When the turgor pressure of the guard cells in increased the outer thinner wall of the guard cell is pushed out (towards the periphery) thus pulling the inner thicker wall leading to the opening of stomatal pore. When the guard cells are in a flaccid state the outer thinner wall of guard cells returns to original position (moves towards pore) due to which tension on the inner wall is released and stomatal aperture gets closed.
