What causes the opening and closing of guard cells of stomata during transpiration?

Explanation

During transpiration, the movement of (Potassium) ions, in and out of the guard cells, causes the opening and closing of stomate. When the water moves inside the guard cells, causing them swell up and become turgid, making the stomata open. When guard cells cause water to move out of the cell, make guard cells shrunk, and the stomata pore closes.