A Level Biology Practice Exam

What does water potential (Ψ) measure in plants?

1. The number of water molecules in the soil

2. The readiness of water to move from one area to another

3. The pressure exerted by soil moisture

4. The total amount of water in plant tissue

The correct answer is: The readiness of water to move from one area to another

Water potential (Ψ) is a measure of the potential energy in water and its tendency to move from one area to another. In the context of plants, it reflects how readily water can move through the plant system and the surrounding environment. This movement is influenced by factors such as solute concentration and pressure, making it essential for understanding water dynamics within plant physiology. The correct answer emphasizes the importance of water's movement, as it is crucial for processes like osmosis, nutrient transport, and maintaining turgor pressure in plant cells. This definition aligns with the concept of water potential, which combines osmotic potential (the effect of solutes) and pressure potential (the physical pressure of water). While the other options touch on aspects related to water and plants, they do not accurately capture the essence of what water potential specifically measures. For instance, just counting water molecules or assessing soil moisture without considering the movement dynamics wouldn't provide a complete understanding of the role water potential plays in plant health and function.