PLASMOLYSIS AND PRESSURE POTENTIAL

Plasmolysis Plasmolysis can be defined as the shrinkage of protoplast due to exosmosis of water. Plasmolysed Cell When a living cell is placed in a solution having lower water potential than that of the cell, plasmolysis takes place and the cell is called plasmolysed.

Deplasmolysed.

If this plasmolysed cell is placed in distilled water (which has highest water potential) the water molecules would move from distilled water through differentially permeable cell membrane into the cell, and the cell would become deplasmolysed.

Incipient of plasmolysis.

The point at which plasmolysis is just about to happen is called incipient plasmolysis. At incipient plasmolysis the protoplast has just ceased to exert any pressure against the cell wall, so the cell is flaccid.

Pressure potential.

If a plasmolysed cell is placed in distilled water, the one having higher water potential than the contents of the cell, water enters the cell by endosmosis, volume of protoplast increases, and it begins to exert pressure against the cell wall of plant cell. The cell wall is rigid – so the pressure exerted by the protoplast against the cell wall is called pressure potential.

Full turgidity.

As the pressure potential of the cell increases due to endosmosis, the cell becomes turgid. Full turgidity i.e. maximum pressure potential is achieved when a cell is placed in pure water or distilled water.

Osmoregulation in Animals.

The animal cells cannot withstand higher pressure potential as there is no cell wall around protoplast. Thus the turgid cells burst in a solution of higher water potential.