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

What happens to an animal cell when placed in a hypotonic solution?

1. It remains unaffected

2. It expands and potentially bursts

3. It shrinks and loses water

4. It becomes turgid and firm

The correct answer is: It expands and potentially bursts

When an animal cell is placed in a hypotonic solution, the concentration of solutes outside the cell is lower than that inside the cell. This creates a concentration gradient that leads to water moving into the cell through osmosis, as water naturally moves from an area of lower solute concentration to an area of higher solute concentration. As water continues to enter the cell, the internal pressure increases. Since animal cells do not have a rigid cell wall to counteract this pressure, they can expand significantly. If too much water enters, the cell may not be able to withstand the increased internal pressure and can burst, a process known as lysis. This phenomenon is specific to animal cells because they lack the structural support provided by cell walls in plant cells, which would contain the expansion and prevent bursting. In summary, in a hypotonic solution, the influx of water causes the animal cell to expand and potentially burst due to the pressure buildup.