Question

Describe briefly the mechanism of stomatal opening and closing.

Answer 1

As K+ levels increase in the guard cells, the water potential of the guard cells drops, and water enters the guard cells. In figure B, the guard cells have lost water, which causes the cells to become flaccid and the stomatal opening to close. This may occur when the plant has lost an excessive amount of water.

• The opening and closing of the stomata is controlled by the guard cells.

• In light, guard cells take up water by osmosis and become turgid. Because their inner walls are rigid they are pulled apart, opening the pore. In darkness water is lost and the inner walls move together closing the pore.