Transpiration Rate

Transpiration is the process by which water is lost from a plant mainly through its leaves.
It occurs in the stomata, small openings on the surfaces of leaves.
Water evaporates into air spaces in the leaf before diffusing out of the stomata into the environment.
Transpiration also plays a significant role in transporting minerals from the soil to all parts of the plant.

The movement of water from the roots of the plant through the xylem vessels and out through the stomata is known as the transpiration stream.
This also carries vital nutrients around the plant.

The rate of transpiration can be affected by several environmental factors.
An increase in light intensity speeds up transpiration rate as stomata open wider to allow for more photosynthesis.
A higher temperature can also increase transpiration rate, as evaporation and diffusion are faster at higher temperatures.
Higher wind speed results in faster transpiration, as the moving air carries away water vapour, maintaining a high concentration gradient.
Lower humidity, i.e., drier air, means a higher rate of transpiration as the concentration gradient is steeper.

Many plants have adaptations to reduce water loss and manage their transpiration rates.
Small or narrow leaves, thick waxy cuticles, leaf rolling, and presence of hairs on leaves are some adaptations that help restrict water loss.
Additionally, in some plants, the stomata are sunken in pits or are only present on lower leaf surfaces, reducing exposure to wind and direct sunlight.

The rate of transpiration can be measured using a laboratory apparatus called a potometer.
The potometer measures the rate at which a plant takes up water, which very closely approximates the rate of transpiration.
However, not all water taken up is transpired, as some is used in photosynthesis or growth