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

If the water potentials of the cell and tissue fluid are equal, what is the likely outcome?

1. The cell will burst

2. The cell will swell

3. The cell will stay the same

4. The cell will shrink

The correct answer is: The cell will stay the same

When the water potentials of the cell and the surrounding tissue fluid are equal, the process known as osmosis results in no net movement of water into or out of the cell. Water potential is a measure that combines the effects of solute concentration and pressure, and when two environments have equal water potentials, it indicates that the concentration of solutes within the cell and the tissue fluid are balanced. In this scenario, since there is no gradient to drive water movement, the volume and shape of the cell remain stable. This dynamic state is referred to as being in isotonic conditions, where the cell neither gains nor loses water, leading to the conclusion that the cell will stay the same in size and internal pressure. In contrast, if the cell were in a situation where the water potential of the tissue fluid was lower (hypertonic environment), the cell would shrink as water moved out to balance the potentials. Alternatively, if the water potential of the tissue fluid was higher (hypotonic environment), the cell would swell as water moved in. Understanding these concepts of osmotic balance is crucial in discussions about cell health and function in biological systems.