Plasmolysis
If a plant cell is placed in a hypertonic solution, the plant cell loses water and hence turgor pressure, making the plant cell flaccid. Plants with cells in this condition wilt. Further water loss causes plasmolysis: pressure decreases to the point where the protoplasm of the cell peels away from the cell wall, leaving gaps between the cell wall and the membrane. Eventually cytorrhysis – the complete collapse of the cell wall – can occur. There are some mechanisms in plants to prevent excess water loss in the same way as excess water gain, but plasmolysis can be reversed if the cell is placed in a weaker solution (hypotonic solution). Stomata help keep water in the plant so it does not dry out. Wax also keeps water in the plant. The equivalent process in animal cells is called crenation.
The liquid content of the cell leaks out due to diffusion. The cell collapse and cell membrane pulls away from the cell wall (in plants). Most animal cells consist of only a phospholipid bilayer and not a cell wall, therefore shrinking up under such conditions.
Plasmolysis only occurs in extreme conditions and rarely happens in nature. It is induced in the laboratory by immersing cells in strong saline or sugar (sucrose) solutions to cause exosmosis, often using Elodea plants or onion epidermal cells, which have colored cell sap so that the process is clearly visible. Methylene blue can be used to stain plant cells.
Plasmolysis can be of two types. It can be either concave plasmolysis or convex plasmolysis. Convex plasmolysis is always irreversible while concave plasmolysis is usually reversible.
Read more about this topic: Plasmolysis