Plasmolysis
- ICSE Class 10, Unit 2 Plant Physiology
Plasmolysis is the shrinking of a plant cell's contents away from its cell wall when the cell loses water to a stronger solution outside it.
A solution stronger than the cell sap is called hypertonic. A weaker one is hypotonic, and an equal one is isotonic. Put a plant cell in a hypertonic solution and water leaves it by osmosis. The vacuole shrinks. The cytoplasm and its plasma membrane pull away from the wall. The wall keeps its shape, because it is rigid.
Put the cell back in plain water soon enough, and water flows in again. The cell swells back. This is deplasmolysis.
A small example
Place a strip of coloured onion peel in strong salt water and look at it under a microscope. The coloured contents shrink into a ball in the middle of each cell. The gap between that ball and the wall fills with the salt solution, since the wall lets it through.
Where marks go
The 2025 ICSE Biology paper gave a diagram of a plasmolysed root cell for 3 marks. It asked for labels on the cytoplasm, the hypertonic solution and the plasma membrane. CISCE's report on the 2025 ICSE Biology paper says the diagram was copied well but labels were misplaced. The report names three label errors. Under step marking, each correct part of an answer can earn credit:
- The nucleus was labelled as the cytoplasm.
- The cell sap in the vacuole was marked as the hypertonic solution. The solution is the liquid in the gap outside the shrunken contents.
- The cell wall was marked as the plasma membrane.
Sources
Facts last checked against these sources on 30 September 2026.
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