OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is water potential a measure of?

1. The stability of plant cell walls

2. The likelihood of water molecules to move

3. The concentration of solutes in water

4. The rate of photosynthesis in plants

The correct answer is: The likelihood of water molecules to move

Water potential is a measure of the likelihood of water molecules to move from one area to another, typically expressed in terms of pressure and solute concentration. It provides a quantitative understanding of how the movement of water is influenced by solutes and pressure within a given environment. In plants, water potential is crucial because it determines the movement of water into and out of cells, which is essential for maintaining turgor pressure, nutrient transport, and overall physiological functions. A higher (more positive) water potential indicates a greater tendency for water to move into that area, while a lower (more negative) water potential indicates a tendency for water to move out. The other options address related concepts but do not accurately define water potential. For example, while the concentration of solutes can affect water potential, it is not synonymous with it. The stability of plant cell walls and the rate of photosynthesis may relate to plant health and water movement but do not directly define what water potential measures.