Advanced Placement (AP) Biology Practice Exam

What occurs to a plant cell when it is placed in a hypotonic solution?

1. It shrinks

2. It becomes flaccid

3. It becomes turgid

4. It bursts

The correct answer is: It becomes turgid

When a plant cell is placed in a hypotonic solution, water moves into the cell through osmosis. This is because the concentration of solutes is lower in the hypotonic solution compared to the concentration of solutes inside the plant cell. As water enters the cell, the cell swells, and the central vacuole fills with water, creating increased pressure against the cell wall. This pressure is known as turgor pressure. As a result, the plant cell becomes turgid, which is essential for maintaining the structural integrity and support of the plant. A turgid cell helps keep the plant upright and firm. Therefore, the process of being placed in a hypotonic solution, resulting in water influx and turgor pressure build-up, effectively leads to the plant cell becoming turgid. While there are scenarios where a cell could burst (known as lysis in animal cells, for instance), plant cells typically do not rupture due to the presence of a sturdy cell wall that provides resistance against over-expansion.