Question

Plasmolysis is due to
A. Exosmosis
B. Endosmosis
C. Osmosis
D. Adsorption

Answer 1

Hint: Plasmolysis-shrinkage of the protoplast of a cell from its cell wall under the influence of a hypertonic solution is called plasmolysis. Hypertonic solution gains water by osmosis across a semipermeable membrane from some other specified solution.

Complete Answer:
- The phenomenon of plasmolysis can be understood by a simple experiment. Take a plant cell and solution (either salt solution or sugar solution).
- Place the plant cell in a highly concentrated salt or sugar solution (this is a hypertonic solution), there will be withdrawal of water from the cytoplasm and central vacuole of the cell, thus the size of protoplast reduces. Since the cell wall is firm and less elastic, it cannot keep pace with the contraction of plasma membranes. Ultimately protoplasm separates from the cell wall and assumes spherical shape. This is called plasmolysis.
- The first stage of plasmolysis is called limiting plasmolysis. The extra hypertonic solution continues to withdraw water from the cell by exosmosis and causes incipient plasmolysis. Due to continued exosmosis protoplast shrinks further known as evident plasmolysis.
- The swelling up of a plasmolysed protoplast under the influence of a hypotonic solution is called de-plasmolysis. It is possible only immediately after the plasmolysis and shows endosmosis.
- Osmosis is the diffusion of water molecules from high concentration to low concentration by semi-permeable membranes.
- Endosmosis: It is the osmotic entry of water into the cell.
- Exosmosis: It is the osmotic withdrawal of water from the cell. As during plasmolysis, exosmosis takes place.

Hence, the correct option is (A).

Note: Pickles, meat and fish are preserved by salting. Jams and Jellies are preserved by sweetening with sugars. Salting and sweetening creates hypertonic conditions in which the fungi and bacteria get killed by plasmolysis. The phenomenon of plasmolysis is used to study osmotic pressure.