A Level Biology Practice Exam

What process describes the shrinkage of a plant cell's protoplast due to water loss?

1. Osmosis

2. Plasmolysis

3. Diffusion

4. Hydrolysis

The correct answer is: Plasmolysis

The correct answer is plasmolysis, which refers specifically to the process where the protoplast, the living part of a plant cell, shrinks away from the cell wall due to the loss of water. This typically occurs when a plant cell is placed in a hypertonic solution—where the concentration of solutes outside the cell is higher than inside. As water moves out of the cell by osmosis, the protoplast shrinks and pulls away from the rigid cell wall, leading to wilting or reduced turgor pressure. Osmosis is the overall process of water movement across a semipermeable membrane but does not specifically refer to the shrinkage effect in plant cells. Diffusion involves the movement of solutes rather than water and is not what describes the cell's response to water loss. Hydrolysis is a chemical reaction involving the breaking down of compounds by the addition of water and is not related to the shrinkage of protoplasts in plant cells. Therefore, plasmolysis accurately describes the phenomenon in question.