Stomata are small pores found on the surface of leaves. They allow for the exchange of gases between the environment and the air spaces inside the leaf. Stomata are regulated by guard cells, which are specialised parenchyma cells that control the opening and closing of the stomatal pore.

When the guard cells are turgid, the stomatal pore opens, allowing for the exchange of gases. When the guard cells are flaccid, the stomatal pore closes, preventing the loss of water vapour from the leaf.

The opening and closing of stomata is controlled by a number of factors, including light intensity, temperature, and humidity. Stomata open in response to light and close in response to darkness. Stomata also open in response to high temperatures and low humidity, and close in response to low temperatures and high humidity.