A Level Biology Practice Exam

What causes the water potential in a plant to change?

1. The movement of nutrients from soil to roots

2. The concentration of solutes and pressure from water molecules

3. The overall amount of light exposure the plant receives

4. The temperature fluctuations in the environment

The correct answer is: The concentration of solutes and pressure from water molecules

The correct answer focuses on the concentration of solutes and the pressure from water molecules as the primary factors that influence water potential in plants. Water potential is a measure that determines the direction of water movement within the plant and is affected by solute potential (the concentration of dissolved substances, or solutes) and pressure potential (the physical pressure exerted by water in the cells). When solute concentration increases in the plant cells due to the uptake of nutrients or water loss, the solute potential becomes more negative, resulting in a lower overall water potential. Conversely, pressure potential can increase when the plant cells become turgid due to water intake, raising the water potential. Therefore, both solute concentration and the physical pressure exerted by water molecules play crucial roles in determining how water moves into, through, and out of a plant system. In contrast, while nutrients moving from soil to roots can indirectly influence water uptake, they do not directly cause changes in water potential. Factors such as light exposure can affect photosynthesis and transpiration rates, but they do not have a direct impact on water potential itself. Temperature fluctuations can influence water movement and transpiration rates, but again, these are not direct causes of changes in water potential in the same