Predict what would happen to an onion epidermal cell placed in a hypertonic solution.

• A. The cell would swell and become turgid.
• B. The cell would remain unchanged.
• C. The cell would plasmolyse as water exits and the membrane pulls away from the cell wall.
• D. The cell would immediately lyse due to water influx.

Answer: (C)

Hypertonic environments make water move out of plant cells by osmosis, since the outside solution has a higher solute concentration and lower water potential. In an onion epidermal cell, the rigid cell wall prevents bursting, so as water exits, the central vacuole and cytoplasm shrink and the plasma membrane pulls away from the cell wall. This separation of membrane from wall is plasmolysis. The onion cell overall loses turgor and becomes flaccid, which is the opposite of swelling in a hypotonic solution or remaining unchanged in an isotonic one, and it won’t lyse because water influx isn’t driving the cell to burst in a hypertonic environment.