2.14 understand the importance in plants of turgid cells as a means of support

Turgidity

When a plant has taken in water by osmosis and it's plump and swollen it's said to be turgid. 

The cells contents push up against the wall of the cell and exert a pressure on the cell wall - this is called turgor pressure! This results in a rigid plant.

When there is no/ little water available for the cell it cannot draw in water by osmosis so cannot retain the turgor pressure. Because of this the plant starts to wilt and the cells in this state are known as flaccid.