Advanced Placement (AP) Biology Practice Exam

Which structure protects plant cells from bursting when placed in a hypotonic environment?

1. Cell membrane

2. Cell wall

3. Nucleus

4. Cytoskeleton

The correct answer is: Cell wall

The cell wall is the structure that provides protection to plant cells in a hypotonic environment. When plant cells are placed in such an environment, there is a higher concentration of solutes inside the cell than outside. This causes water to flow into the cell through osmosis. As the cell fills with water, it swells; however, the rigid cell wall prevents the cell from bursting under the pressure of the increasing internal volume. The cell wall is primarily composed of cellulose, which gives it strength and the ability to withstand osmotic pressure. While the cell membrane does play a role in controlling the movement of substances in and out of the cell, it is not strong enough on its own to prevent the cell from bursting in a hypotonic situation. The nucleus is involved in cellular regulation and genetic material storage but does not contribute to structural integrity in the way that the cell wall does. The cytoskeleton provides support and shape to the cell, but it cannot prevent bursting either. Overall, the robust nature of the cell wall is crucial for maintaining the integrity of plant cells in varying osmotic conditions.