When a cell is kept in water or in a solution less saturated than the cell sap, water enters the cell. This increases the volume of the ell and the protoplasm exerts pressure against the cell wall. As a result of this the cell wall becomes stretched. This state of the cell is termed turgid condition.
Turgidity is the fully expanded condition of a cell with its wall stretched due to excessive accumulation of water. The outward pressure exerted by the cell fluid on the cell wall is called turgor pressure. The inward pressure exerted on the cell contents by the stretched cell wall is called wall pressure.
Normally these two pressures counterbalance each other and a state of equilibrium is maintained between them. Three factors influence the turgidity of a living cell. These are: (a) formation of osmotically active substances inside the cell, (b) an adequate supply of water, and (c) a semi-permeable membrane.
Importance of Turgidity
(a) It helps in the movement of nutrient solutions from cell to cell. This is because of the difference in the concentration of the cell sap between one cell and the other.
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(b) It is necessary for the growth of different organs.