The shape of guard cells changes due to changes in the
(a) protein composition of cells
(b) temperature of cells
(c) amount of water in cells
(d) position of the nucleus in the cells
Explanation: Stomata is a pore-like structure present on the epidermis of the leaves. It is guarded by the guard cells that help to regulate the rate of transpiration by opening and closing the stomata. If the guard cells are turgid or swollen, the stomatal opening is large. This turgidity is caused by the accumulation of K+ ions in the guard cells. As K+ levels increase in the guard cells the water potential of the guard cells drops and water enters the guard cells. In the second case, 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. Hence, (c) is the correct option.