How can osmosis cause cell turgidity or plasmolysis?

Osmosis can cause cell turgidity by water influx into the cell, or plasmolysis by water efflux due to concentration differences.

Osmosis is a fundamental biological process where water molecules move from an area of lower solute concentration to an area of higher solute concentration, across a semi-permeable membrane. This movement aims to equalise the solute concentration on both sides of the membrane. In the context of cells, this semi-permeable membrane is the cell membrane.

When a cell is placed in a hypotonic solution (a solution with lower solute concentration than the cell's cytoplasm), water molecules move into the cell via osmosis. This influx of water causes the cell to swell and become turgid. Turgidity is crucial in plant cells as it helps maintain the plant's structure. The cell wall of plant cells prevents them from bursting due to the increased internal pressure.

On the other hand, when a cell is in a hypertonic solution (a solution with higher solute concentration than the cell's cytoplasm), water molecules move out of the cell, again via osmosis. This efflux of water causes the cell to shrink, a process known as plasmolysis. In severe cases, the cell membrane can pull away from the cell wall (in plant cells) or the cell can shrivel up (in animal cells). This can be detrimental to the cell's function and survival.

In summary, osmosis can cause cell turgidity or plasmolysis depending on the solute concentration of the solution the cell is in. This highlights the importance of maintaining a balanced internal and external cellular environment.