Transpiration is the evaporation of water / loss of water from those parts of plants that are outside the earth, especially leaves but also stems, flowers and fruits. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, wind speed, and soil water supply.

It happens because the plant needs to open its pores in order to obtain carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables the flow of mineral nutrients from roots to shoots. This mass flow is caused by the lower (hydrostatic) water pressure in the upper parts of the plants.

The reason for this low pressure is that water gets out of the leaves into the atmosphere. Water gets into the plant at the roots by osmosis, and it transports dissolved mineral nutrients to the upper parts of the plant through the xylem.

Evapotranspiration (ET) is a term used to describe the sum of evaporation and plant transpiration from the earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves. Evapotranspiration is an important part of the water cycle. An element (such as a tree) that contributes to evapotranspiration can be called an evapotranspirator

For More Information: Plant Transpiration - K-12 Experiments & Background Information

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