Immersed in a solution with more dilute solutes than the cytoplasm, water enters the cell, causing the cytoplasm and vacuole to swell. The cytoplasm is forced against cell wall. The cell wall is rigid and provides backwards pressure which stops any further increase in volume, so no further uptake of water can occur. The force of the cytoplasm pushing against the cell wall introduces mechanical stress which makes the cell hard or turgid
Immersed in a solution isotonic with the cytoplasm, water enters and leaves the cell at equal rates, and the cell is at equilibrium.
The cell is not under mechanical stress, so is soft and flaccid.
Immersed in a solution with more concentrated solutes than the cytoplasm, water leaves the cell, causing the cytoplasm and vacuole to shrink. The cytoplasm is pulled away from the cell wall. This effect is called plasmolysis