How can transpiration be measured experimentally?

Transpiration can be measured experimentally using a potometer, which measures the rate of water uptake by a plant.

A potometer is a simple device that can be used to measure the rate of transpiration in plants. It works on the principle that the rate of water uptake by a plant is directly proportional to the rate of transpiration. The potometer consists of a graduated tube filled with water, a reservoir, and a capillary tube with a plant shoot attached to it.

To measure transpiration, the plant shoot is first cut under water to prevent air from entering the xylem vessels. The shoot is then attached to the potometer, ensuring that the apparatus is completely filled with water and free from air bubbles. The potometer is then placed in a controlled environment, and the initial water level in the capillary tube is recorded.

As the plant transpires, it draws up water from the potometer, causing the water level in the capillary tube to drop. By measuring the drop in water level over a certain period of time, the rate of water uptake, and hence the rate of transpiration, can be calculated.

It's important to note that the potometer measures the rate of water uptake, not the actual rate of transpiration. This is because some of the water taken up by the plant is used for photosynthesis and not lost through transpiration. However, under normal conditions, the majority of the water taken up by a plant is lost through transpiration, so the potometer provides a good estimate of the transpiration rate.

Other factors that can affect the rate of transpiration, such as light intensity, temperature, humidity, and wind speed, can also be investigated using a potometer. By controlling these factors, the effect of each on the rate of transpiration can be studied.