The apparatus used to measure the transpiration rate of plants is known as a potometer.

A potometer is a straightforward device utilized by both scientists and students to quantify the rate of transpiration in plants. Transpiration refers to the process by which water is lost from a plant, primarily through tiny openings in the leaves called stomata. This process is essential for the plant’s survival, as it facilitates the transport of nutrients from the roots to other parts of the plant.

The functioning of a potometer is based on measuring the volume of water absorbed by a plant over a specific duration. The basic configuration includes a plant stem inserted into a tube filled with water. As the plant transpires, it draws water from the tube, and the rate of this water uptake is recorded. This data is then used to estimate the transpiration rate.

There are various types of potometers, but the bubble potometer is the most commonly used model in educational settings. This particular design features a water reservoir and an air bubble within a capillary tube. As the plant transpires, water is drawn up, causing the air bubble to move. The distance that the bubble travels over a predetermined time period provides an estimate of the transpiration rate.

It is crucial to understand that the potometer does not measure transpiration directly. Instead, it assesses water uptake, which serves as an indirect estimate of transpiration. This is because not all the water absorbed by a plant is lost through transpiration; some is utilized in processes such as photosynthesis or growth, while other water may be lost through different mechanisms. Nevertheless, under controlled conditions, the potometer can yield a reliable estimate of the transpiration rate.