Science Fair Project Encyclopedia
Transpiration is a continuous process caused by the evaporation of water from leaves of plants and its corresponding uptake from roots in the soil. Transpiration cools plants down and enables mass flow of minerals to where it is needed in the plant. Mass flow is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved solutes travel with it through the xylem.
The rate of transpiration is directly related to whether the stomata are open or closed. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, wind speed, and water supply. A fully grown tree may lose several hundred gallons (a few m³) of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process.
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