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Plant cells thrive when the solution outside the cell has a lower solute concentration than the cytoplasm inside the cell.

This is a hypotonic condition, in which water enters the cell through osmosis. As water enters, the vacuole expands and pushes the cytoplasm outward against the rigid cell wall. This pressure, called turgor pressure, stiffens the cell and keeps the plant upright.

If the solute concentration outside the cell is higher than that inside the cell, the environment is hypertonic, causing water to flow out of the cells. As a result, the cytoplasm shrinks, and the plasma membrane detaches from the cell wall. This process, called plasmolysis, explains why plants lose turgor pressure and wilt.