Question

Give reason: If you sprinkle some common salt on grass growing on a lawn, it is killed at that spot.

Answer 1

A hypertonic solution is that type of solution that has high concentration of solutes on the outer side of the cell as compared to the inside of the cell. Recall the term plasmolysis where cells lose water when they are in a hypertonic environment. This process further causes damage to cell membrane and as a result of that, it collapses.

Complete answer:
- When a plant cell is placed in a hypertonic solution, the water which is inside the cell’s cytoplasm diffuses out of it and as a result of that, the plant cell becomes flaccid.
- In a flaccid plant cell, the plasma membrane is not tightly pressed to the cell wall. Then, owing to the plasmolysis phenomena, the plant cell loses water and thus the turgor pressure decreases at that extent that the protoplasm of the cell goes away from the cell wall. This causes gaps to form between the membrane and the cell wall and therefore the plant cell completely shrinks and crumps.

This is why when we can say that sprinkling the salt on the growing grass disturbs the osmotic balance of the grass cell and the water rushes out of the cell to maintain equilibrium on both sides thereby resulting in shrinking of cell and killing it at that spot.

Note: A plasmolysed cell can be revived back to its original state by the phenomenon called deplasmolysis where the plasmolysed cell is recovered when it is placed in the water. Thus, the protoplasm of the cell again swells up because the water is again retained. In this phenomena the cell becomes turgid rather than flaccid (which happens in plasmolysis). When the cell becomes turgid, it has no place for accumulation of more water and thus it becomes fully swollen up.