Answer with Explanation:
The "guard cells" have an important function regarding the regulation of gas exchange in the plant's leaves. They surround the so-called "stoma" or pore that can be found on the leaves' epidermal layer. These pores open and close under the control of the guard cells.
The guard cells open and close a pore in response to "turgor pressure." This pressure is responsible for pushing the plasma membrane, which goes against the cell wall. When two guard cells are under such pressure, they bend outward. This opens the stomata. On the contrary, when there is loss of turgor such as loss of water due to osmosis, the stomata closes.
The turgor of the guard cells is dependent on many factors such as: humidity, the intensity of light, [tex]CO_{2}[/tex] concentrations and so on.
