A vacuole is a fluid-filled sac that is present in all plant cells. Only some types of animal cells have vacuoles.
Plant cells use the vacuole
- to store food or waste material and
- to maintain turgidity (stiffness).
The vacuole is primarily filled with water with dissolved ions. In addition, it can contain food or waste for storage.
By filling the vacuole with water, the cell can have a bigger volume (without changing the concentration of chemicals in the cell's main body). As a result of this increase in volume, its membrane is pressed against the cell wall providing structural stability to the cell and the plant as a whole.
Animal cells cannot maintain turgidity as they have no cell wall to stop them from bursting!