Transpiration

Transpiration is the process in which a plant gives off water as water vapor. Most of this water vapor is lost through the stomata (plural of stoma). Stomata are openings in the lower epidermis of a leaf. Transpiration is also known as the evaporation of water from the parts of the plant above ground and occurs mostly through the leaves. The process of transpiration is water is taken into plants through their roots and then moves up the stem into the leaves. This movement is called transpiration stream. Transpiration increases when the roots have enough water, the temperate is neither high nor very low, there is a slight breeze, and there is bright sunlight.

You can show that a plant transpires by putting a potted plant inside a closed plastic bag. After a while the bag will steam up and eventually drops of water will form on the inside. Remember to water the plant after. To make plants transpire more rapidly you need light. Plants transpire more rapidly in the light than in the dark. This is largely because light stimulating the opening of the stomata (mechanism). Light also speeds up transpiration by warming the leaf. Plants also need high temperatures to transpire more rapidly because water evaporates more rapidly as the temperate rises. For example, at 30 degrees Celsius, a leaf may transpire three times as fast as it does 20 degrees Celsius. Plants also need humidity to transpire more rapidly because the rate of diffusion of any substance increases as the difference in concentration of the substances in the two regions increases. When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly. Plants also need soil water to transpire more rapidly because a plant cannot continue to transpire rapidly if its water loss is not made up by replacement from soil. When absorption of water by roots fails to keep up with the rate of transpiration, loss of turger occurs, and the stomata close. This immediately reduces the rate of transpiration as well as of photosynthesis. If loss of turger occurs, the plant wilts.

Plants need wind to transpire less rapidly because