Question

With the help of well-labelled diagrams, describe the process of plasmolysis in plants, giving appropriate examples.

Answer 1

Plasmolysis can be defined as the shrinkage of the cytoplasm of a plant cell, away from its cell wall and toward the centre. It occurs because of the movement of water from the intracellular space to the outer-cellular space. This happens when the plant cell is placed in a hypertonic solution (i.e., a solution having more solute concentration than the cell cytoplasm). This causes the water to move out of the cell and toward the solution. The cytoplasm of the cell shrinks and the cell is said to be plasmolysed. This process can be observed in an onion peel kept in a highly concentrated salt solution.



(b) When a plant cell is placed in a hypertonic solution or a solution having higher water potential, the water diffuses into the cell (i.e., movement is observed from higher to lower water pressure region). The entry of water in the plant cell exerts pressure on the rigid cell wall. This is called turgor pressure. As a result of its rigid cell wall, the plant cell does not burst.

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Answer 2

The process of plasmolysis can be best understood by its stages :

1. Limiting plasmolysis

This is the 1st stage where water loss happens or takes place in a gradual manner. The TP gets reduced to zero. Vacuole size and the size of cell gets reduced because of exosmosis.

2. Incipient plasmolysis

The exosmosis that happens even after the limiting plasmolysis reduces the size of protoplast further. It is contracted so much that the protoplasts gets withdrawn from the wall of cell.

3. Evident plasmolysis

In this last stage, the cells turns into round structure because of contraction of protoplast continuously.