Leaf stomata are basically pores that are typically on the back side of leaves. Which open and close that are controlled by these circular shaped cells called guard cells. Stomata when open allow carbon dioxide to enter the leaf and also allows water and oxygen to be released into the air. The more stomata stomata per area the more carbon dioxide can be absorbed into the leaf the more water is released.   Stomata is open during the day and closes at night, but stomata can close when the weather is too hot to prevent loss of water.