Question

Question 16
The shape of the guard cell changes due to changes in the

(a) protein composition of cells
(b) temperature of cells
(c) amount of water in the cells
(d) position of nucleus in the cells

Answer 1

(c) amount of water in the cells

Guard cells are able to control the stomata by changing shape. When the guard cells take in potassium ions, water diffuses into the cells by osmosis. Osmosis is the movement of water from an area of high concentration of solute (dissolved substance) to an area of low concentration of solute. When the water enters the cells, they swell and become bow shaped. This causes the guard cells to bend away from each other, thereby opening the stomata. Conversely, when guard cells lose potassium ions, water diffuses out of the cells by osmosis. As water leaves the cells they become flaccid and less bowed, which closes the stomata between them.