Transpiration

Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves. It is a vital process in the Water cycle.

Process

Transpiration occurs in the stomata of leaves. These are small openings on the leaf surface that are surrounded by guard cells. The guard cells control the opening and closing of the stomata, thereby regulating the process of transpiration.

The process begins when water is absorbed by the roots from the soil. This water is then transported upwards through the xylem vessels to the leaves. In the leaves, some of the water is used for photosynthesis while the rest is evaporated into the atmosphere through the stomata.

Factors affecting transpiration

Several factors affect the rate of transpiration. These include:

• Temperature: Higher temperatures cause the plant cells which carry water to the stomata to heat up and change more of the water inside them into vapor.
• Humidity: When the surrounding air is dry, transpiration rates increase.
• Wind and air movement: Increased movement of the air around a plant will result in a higher transpiration rate.
• Light: Plants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata.

Importance of transpiration

Transpiration has several important functions:

• It helps transport water and nutrients from the roots to different parts of the plant.
• It cools the plant and keeps its temperature stable.
• It allows plants to have access to carbon dioxide, which is necessary for photosynthesis.

See also

• Evapotranspiration
• Stomata
• Xylem
• Photosynthesis

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