Q.Name the condition in which protoplast of the plant cell shrinks.

Plasmolysis: When a Plant Cell Loses Its Turgor

Imagine a balloon stuffed inside a rigid cardboard box. The balloon is fully inflated, pressing firmly against every wall of the box. Now, let a little air out. The balloon shrinks and pulls away from the cardboard, leaving empty space between them. That is the core picture of plasmolysis — except the balloon is the living protoplasm of a plant cell, and the cardboard box is the cell wall.

The Intuition: Water Wants Balance

A plant cell normally sits in a watery environment. Inside the cell, the fluid (cytoplasm and vacuolar sap) contains dissolved salts, sugars, and other solutes. Outside the cell, the surrounding solution may have a different concentration of solutes. Water always moves from where it is more abundant (dilute solution) to where it is less abundant (concentrated solution) — this is osmosis.

When the outside solution has a higher concentration of solutes than the inside of the cell, we call it a hypertonic solution. The water inside the cell is now "more abundant" relative to the outside. So water moves out of the cell, across the selectively permeable plasma membrane, into the external solution.

As water leaves, the protoplast (the living part — plasma membrane and cytoplasm) shrinks. But the cell wall is rigid and does not shrink. So the protoplast pulls away from the cell wall, leaving a gap. That gap fills with the external hypertonic solution. This is plasmolysis.

The Precise Statement

Plasmolysis is the shrinkage of the protoplast away from the cell wall due to the exosmosis of water when a living plant cell is placed in a hypertonic solution.

Key points to remember:

• Protoplast = the entire living part of the cell (plasma membrane + cytoplasm + nucleus + vacuole). It is the part that shrinks.
• Cell wall = the rigid, non-living outer covering. It does not shrink.
• Exosmosis = outward movement of water.
• Hypertonic solution = external solution with higher solute concentration than the cell sap.

The Reversal: Deplasmolysis

If you take a plasmolyzed cell and put it back into pure water (or a hypotonic solution), water will re-enter the cell by endosmosis. The protoplast swells and gradually presses back against the cell wall, restoring the original turgid state. This reversal is called deplasmolysis.

Why Does This Matter?

Plasmolysis is not just a textbook curiosity. It has real applications:

• Salt stress in crops: When soil becomes too salty (hypertonic to root cells), water is drawn out of roots, causing wilting. This is plasmolysis in action.
• Preserving food with salt/sugar: Salt on meat or sugar on fruit creates a hypertonic environment. Microbes (bacteria, fungi) on the food undergo plasmolysis and die, preserving the food.
• Testing cell viability: Biologists use plasmolysis to check if plant cells are alive. Only living cells will plasmolyse and deplasmolyse.

Visual Summary

Final answer: Plasmolysis is the shrinkage of the protoplast away from the cell wall due to water loss when a living plant cell is placed in a hypertonic solution. It is reversible by deplasmolysis.

Plasmolysis is taught as part of Transport in Plants in the Class 11 NCERT Biology textbook, which is why students often look up "Plasmolysis important questions class 11" or "Plasmolysis short notes" while preparing for CBSE boards and NEET Botany.