A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

A potometer is primarily used to measure the rate at which a plant takes up water, which directly corresponds to its transpiration rate. When a plant loses water through transpiration, it creates a negative pressure that pulls more water from the soil through the roots. Although the main focus of a potometer is measuring water uptake, it's important to note that this water uptake is closely connected to the plant's transpiration. By assessing how quickly a bubble or water level changes in the potometer tube, one can infer the plant's water absorption rate.

Other options, such as the rate of photosynthesis or growth, are not directly measured with a potometer. While transpiration plays a role in photosynthesis, the potometer itself does not quantify the photosynthetic rate. The growth rate of a plant also cannot be determined using a potometer, as it requires different metrics such as plant height or biomass over time.