The process that brings about the shrinking of a spirogyra cell when placed in a strong solution is ?

Step 1: Analyze the question The question asks for the process that makes a Spirogyra cell shrink when it is placed in a strong (concentrated) solution. Spirogyra is a green alga with cells that have a cell wall, a cell membrane, and a large central vacuole.

Step 2: Explain the concept

• Osmosis is the movement of water from a region of high water potential to one of low water potential through a semi-permeable membrane. It is the underlying mechanism, but it is not the name for the shrinking itself.
• Plasmolysis is the shrinking of the protoplasm (cytoplasm and vacuole) away from the cell wall. It happens when a plant cell loses water by osmosis in a hypertonic (strong) solution.
• Autolysis is the self-digestion of cells by their own enzymes, usually after cell death.
• Diffusion is the movement of particles from high to low concentration. It does not specifically describe cell shrinkage.

Step 3: Solve

1. The Spirogyra cell is placed in a strong solution, which is hypertonic to the cell sap.
2. Water leaves the vacuole and cytoplasm by osmosis.
3. The protoplasm shrinks and pulls away from the cell wall.
4. This shrinking of the protoplasm is called plasmolysis.

Step 4: Answer The correct option is C. plasmolysis.

Tip: Remember "Plasmo-lysis = protoplasm pulls away." Osmosis is the cause (water movement), while plasmolysis is the visible effect in plant cells. If you see the words "shrinking of the cell" with a plant cell in a strong solution, think plasmolysis. The opposite, in which a cell swells and becomes firm in a dilute solution, is called turgidity.