Terri Ann Science Center

Did you know that plants 'sweat?' Transpiration is both an important and costly process for plants, and it requires that a delicate balance between it and other necessary cellular processes be maintained.
Definition of Transpiration
Imagine yourself on a hot summer day. When you get thirsty, you drink water to rehydrate. But where does this water go? Some of it goes to bodily processes, but, on a hot day, you are likely sweating. Sweating, or evaporative cooling, is how your body prevents overheating. Water comes out through sweat glands and evaporates as it hits the air, leaving your skin feeling cooler.

Plants also 'sweat,' but this process is called transpiration. Plants use their roots in the ground to draw up water and nutrients. Plants also use much of this water for cellular processes, but some of it leaves the plant and goes into the air.

Transpiration Process
Similar to the sweat glands on your skin, plants have openings on their leaves that allow water to escape, called stomata (singular: stoma). Stomata are usually found on the underside of a leaf to reduce excess water loss, and they're surrounded by guard cells that open and close the pores.

Though stomata release water, their main purpose is to exchange gases. Plants need to 'breathe' carbon dioxide from the atmosphere in order to photosynthesize, or change sunlight into usable chemical energy. They also need to release oxygen back into the atmosphere as a waste product of cellular processes. This gas exchange occurs through the stomata, and, while this happens, some water is lost from the plant.