Advanced Placement (AP) Biology Practice Exam

What is the effect on a red blood cell when it is placed in a hypotonic solution?

1. The cell shrinks due to water loss

2. The cell swells and may burst

3. The cell remains unchanged in size

4. The cell undergoes plasmolysis

The correct answer is: The cell swells and may burst

When a red blood cell is placed in a hypotonic solution, the concentration of solutes outside the cell is lower than that inside the cell. This gradient causes water to move into the cell through osmosis in an attempt to balance the concentrations on both sides of the cell membrane. As water enters the cell, it swells. If enough water continues to flow into the cell, it can lead to the cell membrane stretching to its limit and possibly bursting, a process known as lysis. This behavior is a fundamental concept in understanding osmosis and cellular environments, as it demonstrates how cells interact with their surroundings based on solute concentrations. In contrast, cells in hypertonic solutions would lose water and shrink, while isotonic solutions would maintain the cell's size. Thus, the correct answer highlights the crucial effect that a hypotonic environment has on the physical integrity of the cell.