Transpiration is the process by which plants release water vapor into the air through tiny openings in their leaves. These microscopic pores, called stomata, open to let carbon dioxide in for photosynthesis, and when they do, water escapes as vapor, much like how you breathe out moisture on a cold day and can see your breath.

This might sound wasteful, but transpiration actually serves crucial purposes. As water evaporates from the leaves, it pulls more water up from the roots through the plant's stem, like sucking liquid through a straw. This upward flow delivers nutrients dissolved in the water to every part of the plant. Transpiration also cools the plant down on hot days, the same way sweating cools your body.

A large oak tree can transpire over 100 gallons of water per day during summer. Forests release so much water through transpiration that they affect local weather patterns and help create clouds. When you walk through a forest on a hot day and feel the air is cooler and more humid than in an open field, you're experiencing the effects of transpiration.

Scientists measure transpiration rates to understand plant health and the water cycle in ecosystems.