Plasmolysis:-If a plant cell is placed in a highly concentrated sugar or salt solution (i.e., hypertonic solution), water from the cell sap flows out due to exosmosis through the plasma membrane out side the cell. The loss of water from the cell sap causes contraction or shrinkage of the protoplast. Since the cell wall is firm and less elastic, it cannot keep pace with the contraction of plasma membranes. ultimately the protoplasm separates from the cell wall and assumes spherical shape This condition is called plasmolysis.
The stage of plasmolysis at which the first sign of shrinkage of cell contents from cell wall becomes detectable is called ‘incipient plasmolysis’. The stage when the cell wall has reached its limit of contraction and cytoplasm has detached from cell wall attaining spherical shape is called ‘evident plasmolysis’. If a plasmolysed cell is placed in pure water or hypotonic solution, endosmosis takes place, the protoplasm, as well as the cell as a whole, attains its original shape and size respectively. The phenomenon is known as deplasmolysis
Importance
1. it is the characteristic feature of living plant cells. All living plant cells plasmo-lyse when kept in a hypertonic solution.
2. Pickels, meat and fish are preserved by salting. Similarly, jams and jellies are preserved by sweetening with sugars. Salting and sweetening create hypertonic condition in which the fungi and bacteria get killed by plasmolysis.
3. Salting kills the weeds of lawns by inducing plasmolysis in their cells.
4. Plasmolytic method is applied for the determination of osmotic pressure of a cell in the laboratory.
| plasmolysis | deplasmolysis |
|---|---|
| 1. It is the contraction or shrinkage of protoplast from cell wall. | 1. It is the stage when the plasmolysed plant cell attains its original shape and size. |
| .2. It occurs in plant cells when they are placed in hypertonic solution. | .2. It occurs in plasmolysed plant cells when they are placed in hypotonic solution. |
| 3 it occurs as a result of exosmosis | 3. it occurs as a result of endosmosis. |
Expt. To demonstrate the phenomenon of plasmolysis and deplasmolysis
Requirements.
Fresh Spirogyra filaments or peelings of lower epidermis of Rhoeo discolor leaves, 5% salt solution, water, slide, cover slip, watch glass, microscope.
Method.
Peel off the lower epidermis of the f leaf of Rhoeo discolor and cut into small pieces. Observe single strip under the microscope and see that all the cells are uniformly coloured. Immerse another strip into 5% salt solution in a watch glass y for few minutes. Mount the strip in the same solu- tion and examine under the microscope. The cells become plasmolysed. Wash the plasmolysed strip with pure water and mount in a drop of water. Examine under the microscope.
Observation and conclusions.
The cells of strip immersed in 5% salt solution show shrinkage of their protoplasm. The cellular contents shrink and move away from the cell-wall. This phenomenon is called plasmolysis. The plasmolysed cells, when washed and mounted in water, regain their original size. The protoplast swells up and comes in contact with the cell wall. This is called deplasmoly-sis
Explanation.
5% salt solution is much concentrated and strong as compared to cell sap. It acts as hypertonic solution. The cell sap loses water to external medium due to exosmosis with the result the protoplasm contracts. The cell wall, being rigid, firm and less elastic, fails to keep pace with the protoplasmic contraction. Ultimately protoplasm separates from the cell wall and assumes sphereshape. It is called plasmolysis. read more
