What is plasmolysis?
Contraction of the protoplasm of the plant cell due to removal of water is called plasmolysis.
If the plant cell is present in a solution having a higher concentration as compared to the cell, the external solution is said to be a hypertonic solution. Since the concentration inside the cell is low, the water from inside the cell tends to move through the semipermeable membrane to move out of the cell. This is responsible for bringing the cell to a state of equilibrium concentration.
Due to the movement of water out of the cell the protoplasm of the cell shrinks, resulting in plasmolysis.