Problem 65 - Objective Biology for NEET

Question

During plasmolysis (a) Cell membrane of a plant cell shrinks away from its cell wall (b) Water first lost from the cytoplasm and then from the vacuoles (c) Area between cell wall and shrunken protoplast is occupied by outer solution (d) All the above

Step-by-Step Solution

Answer

The suitable answer for this exercise is option (d) - All the above.

Step 1 Analysis of Statement (a)

In plasmolysis, the cell membrane of a plant cell does shrink away from its cell wall due to water loss. Hence, this statement is true.

Step 2 Analysis of Statement (b)

During plasmolysis, water is indeed first lost from the cytoplasm and then from the vacuole as it is a progressive process. Therefore, statement (b) is also correct.

Step 3 Analysis of Statement (c)

The area between the cell wall and the protoplast gets occupied by the external solution, as a result of the water moving out of the cell. This makes statement (c) accurate.

Step 4 Selection of the Correct Option

Upon careful evaluation and cross-verification, all the statements (a, b, and c) are correct. That makes option (d) 'All of the above' the suitable answer for this exercise.

Key Concepts

Cell Membrane Shrinkage

When a plant cell undergoes plasmolysis, a prominent occurrence is the shrinking of the cell membrane. This phenomenon happens when the cell is exposed to a hypertonic solution—essentially, a liquid that has a higher solute concentration compared to the inside of the cell. Due to osmosis, water molecules move from an area of lower solute concentration within the cell to a higher solute concentration in the outside environment. As water leaves the cell, the cell membrane pulls away from the rigid cell wall. This process highlights the flexibility and semi-permeability of the cell membrane, as it can adjust shape without disintegrating while selectively allowing substances to pass through.

Visualizing this, imagine a balloon (the cell membrane) within a cardboard box (the cell wall). As air (water) escapes from the balloon, it deflates and detaches from the box's interior, but does not break. This adaptive quality of the cell membrane is crucial for the survival of the cell under various environmental conditions.

Cytoplasm Water Loss

Cytoplasm water loss is the initial stage of plasmolysis, marking the beginning of dehydration within the plant cell. The cytoplasm, a gel-like substance filling most of the cell's interior, is where most cellular activities occur. When the external solution is hypertonic, water is drawn out of the cytoplasm before any other cellular components. The osmotic gradient motivates water molecules to exit the cell, through the plasma membrane, into the external solution. As a result, cellular processes can be affected due to the changed solute concentration and volume of the cytoplasm. If the water loss is severe, it can halt many cellular functions and can ultimately be detrimental to cell viability.

In simpler terms, the cytoplasm's water loss can be compared to draining a pool. As you remove water, the pool's surface area decreases, affecting anything that was previously submerged (analogous to the enzymes and organelles in the cytoplasm). This stage is crucial to understand as it sets the stage for subsequent effects of plasmolysis.

Vacuoles in Plasmolysis

The vacuole is a central, large compartment within plant cells that stores water and various substances. In plasmolysis, after the cytoplasm loses water, the vacuoles are the next to be affected. As the process advances, water exits the vacuoles, causing them to shrink. This diminishes the turgor pressure within the cell, which is the pressure of the cell contents against the cell wall. Typically, turgor pressure is responsible for maintaining the plant's structure and rigidity.

In the context of a relatable scenario, imagine a water balloon that is fully inflated inside a box. If the water balloon starts to leak, it gradually loses its full shape and the box's shape might be visibly changed due to the lack of internal pressure. Similarly, as vacuoles lose water, the plant cell loses its firmness and can lead to wilting. Understanding the role of vacuoles in plasmolysis is significant because these structures help maintain cellular homeostasis and support the plant’s upright position.