stomata

What are stomata?

Stomata are small openings found all over the the lower surface of a leaf to allow carbon dioxide to diffuse into the leaf. The rest of the leaf is covered by an impermeable layer called the waxy cuticle.

When the stomata are open, there is a steady loss of water from the leaf cells as it evaporates into the internal air space and then diffuses out through the stomata. The plant needs to open the stomata during the day to allow carbon dioxide to enter for photosynthesis but closes them at night ( or in extreme conditions) to reduce water loss from the leaf.

The opening and closing of the stomata is controlled by guard cells.

Simply, the stomata’s purpose is to let carbon dioxide in and oxygen out. This means the stomata must be open, which has the unfortunate side effect of losing water. The plant needs carbon dioxide for photosynthesis - which can only happen when there is light. So, during the night when there is no light all the stomata close as any carbon dioxide absorbed would not be able to be used anyway.