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The movement of water into or out of a cell depends on the concentration of water surrounding it.

Animal cells

When water moves into an animal cell (e.g. a red blood cell), the cell membrane stretches and the cell gets bigger.

If this continues, the cell membrane will burst – this is called lysis.

Turgidity in plant cells

When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall.

The force of this increases the turgor pressure within the cell making it firm or turgid.

The pressure created by the cell wall stops too much water entering and prevents cell lysis.

If plants do not receive enough water the cells cannot remain turgid and the plant wilts.

Cells that are not turgid are flaccid.

Plasmolysis

When too much water moves out of a plant cell, the cell contents shrink.

This pulls the cell membrane away from the cell wall.

A plasmolysed cell is unlikely to survive.