Transpiration is when water move through a plant and its evaporation from aerial parts; leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5% is lost by transpiration and guttation. Leaf surfaces have things called stomata. The stomata are bordered by guard cells that open and close the pore. Transpiration happens at the stomata. The opening of the stomata is to allow the diffusion of carbon dioxide from the air for photosynthesis. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots. Water is absorbed at the roots by osmosis and any dissolved mineral nutrients travel with it through the xylem.

As water is cohesive the leaves are able to pull water through to the xylem. It is also adhesive which is how it sticks to the leaves. When the water evaporates it pulls other water to create a continuous flow of water within the plant.