The stomata on plant leaves ____.

A) are only open at night
B) are open when guard cells are swollen with water
C) close when the osmotic pressure of guard cells increases
D) are covered by the cuticle to reduce water loss
E) open and close in response to sunlight only

Stomata on plant leaves are surrounded by two guard cells. When the guard cells are swollen with water, the stomata are open, allowing for gas exchange between the plant and the environment. When the guard cells lose water and become flaccid, the stomata close to prevent excessive water loss from the plant. The opening and closing of stomata are also regulated by factors such as light intensity, carbon dioxide concentration, and plant hormones.