Plants and Photosynthesis: Transpiration

Transpiration is the process in which water moves through plants from roots to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere.
It is essentially evaporation of water from plant leaves.
Transpiration is influenced by several external factors: light, temperature, humidity, and wind.
More light leads to more transpiration because it opens the stomata (pores) on the plant.
Higher temperatures increase rates of evaporation and photosynthesis which in turn increases transpiration.
Wind and low humidity can increase transpiration as they both reduce the external water vapor thus increasing the water potential gradient.
The process of transpiration is important for plant health. It helps transport vital nutrients from the soil around the plant system.
Transpiration is also used to cool the plant.
Transpiration and cohesion facilitate the movement of water through the xylem up against the force of gravity. This is known as the transpiration-cohesion-tension mechanism.
The rate of transpiration can be measured using a potometer.
The factors affecting transpiration in plants are key part of practical investigations.
During transpiration, water from the soil is taken in by the plant’s roots and released out into the atmosphere from the leaves.
Transpiration provides the force or ‘pull’ to draw water up from the roots, via the xylem in a continuous stream to the leaves.
To investigate the rate of transpiration, one can measure the uptake of water in a plant. When a shoot is enclosed in a bag, the humidity increases and transpiration decreases.
Transpiration rates can be affected by several things including humidity, light, temperature, and the volume of air movement. For example, a plant will transpire more quickly in hot, dry, windy weather compared with cool, humid, still conditions.
Effects of various conditions on the rate of transpiration can be tested through practical investigations using a potometer.