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How do stomata control gas exchange and water loss in plants?

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Tall baobab trees with thick, cylindrical trunks and broad canopies line a dirt road in Madagascar, surrounded by green vegetation under a blue sky. — Plant Grandidier's baobas (*Adansonia grandidieri*) in Madagascar.

Stomata are microscopic pores primarily located on the underside of leaves that facilitate gas exchange. They allow carbon dioxide to enter for photosynthesis and oxygen to exit.12

The opening and closing of these pores are regulated by two sausage-shaped guard cells. When these cells are filled with water and become turgid, the stomata enlarge, enabling gas exchange. Conversely, when the plant experiences water deficits, darkness, or high temperatures, the guard cells lose turgidity, causing the stomata to close.12

This mechanism is essential for balancing gas intake with the prevention of excessive transpiration—the loss of water vapor. While transpiration is often an unavoidable byproduct of gas exchange, plants can mitigate water loss by closing stomata during hot, dry, or windy conditions. Some species, such as those utilizing crassulacean acid metabolism (CAM), have evolved to open their stomata exclusively at night to further minimize water loss in arid environments.12