Why do plant cells become turgid in fresh water and plasmolyze in salty water?

• A. In fresh water, water enters cells increasing turgor; in salt water, water exits, causing plasmolysis.
• B. In fresh water, water exits cells; in salt water, water enters cells.
• C. Turgor and plasmolysis are not affected by water salinity.
• D. Salt water increases turgor by drawing water into cells.

Answer: (A)

The main idea here is osmosis and how water moves in response to the surrounding solution’s tonicity. Plant cells have a rigid cell wall and a central vacuole that can swell with water, creating turgor pressure.

In fresh water, the solution outside the cell is hypotonic compared to the cell’s interior. Water potential is higher outside, so water moves into the cell by osmosis. The influx of water fills the vacuole, pushing the cell membrane against the cell wall and increasing turgor pressure, making the cell turgid or firm.

In salty water, the outside is hypertonic relative to the cell interior. Water moves out of the cell to balance solute concentrations, the vacuole shrinks, and the membrane pulls away from the cell wall—a process called plasmolysis. As water leaves, turgor pressure decreases and the cell becomes flaccid.

So, freshwater causes water entry and higher turgor; salty water causes water loss and plasmolysis.