Biology – 3.2 Osmosis | e-Consult

When a plant cell is placed in a hypotonic solution (a solution with a lower concentration of solutes than the cell's cytoplasm), water moves into the cell by osmosis. This influx of water increases the volume of the cell and pushes the cell membrane against the cell wall. This results in the cell becoming turgid. Turgor pressure is the pressure exerted by the cell contents against the cell wall, and it's what gives plant tissues their rigidity.

Conversely, if a plant cell is placed in a hypertonic solution (a solution with a higher concentration of solutes than the cell's cytoplasm), water moves out of the cell by osmosis. This causes the cell to lose water and shrink. The cell membrane pulls away from the cell wall, resulting in plasmolysis. The cell becomes flaccid as the turgor pressure decreases.

If a plant cell is placed in an isotonic solution (a solution with the same concentration of solutes as the cell's cytoplasm), there is no net movement of water. The cell remains turgid, with a normal level of turgor pressure.