Question

Plasmolysis in a plant cell is defined as
(a) break down (lysis ) of plasma membrane in hypotonic medium
(b) shrinkage of cytoplasm in hypertonic medium
(c) shrinkage of nucleoplasm
(d) none of them

Answer 1

Answer:

Plasmolysis in a plant cell is defined as (b) shrinkage of cytoplasm in hypertonic medium.

Explanation:

Plasmolysis is the process in which plant cell will lose the water and turgor pressure after being placed in hypertonic solution. During plasmolysis loss of turgor pressure can force the detachment of protoplast from the cell wall which will result into shrinking of protoplast. Plasmolysis is driven by vacuole. Plasmolysis is a reversible process and addition of hypotonic solution can lead the expansion of protoplast and reinstatement of original turgor pressure. During the plasmolysis majority of osmotic water flows into the central vacuole and drastic changes in protoplast size and shape can affect the subcellular architecture of the plant cell.

Answer 2

Answer:

Option (b) shrinkage of cytoplasm in hypertonic medium

Explanation:

Concept Introduction:

• Solutions can be of the following three types of cell sap.

[I] Hypertonic solution (hyper = more than)

• A solution with a concentration more than that of the cell sap is known as hypertonic.

• If a cell is placed in such a solution, water will move out of it (exosmosis) and the protoplasm will contract/shrink.

[II] Hypotonic solution (hypo= less than)

• When the concentration of a solution is less than that of the cell sap, it is known as hypotonic.

• When a cell is immersed in a hypotonic solution, water will diffuse into the cell (endosmosis) and it will increase in size.

[III] Isotonic solution (iso = the same)

• A solution with a concentration equal to that of the cell sap is known as isotonic.

• When a cell is kept in an isotonic solution there would be no diffusion of solvent.

• As a result, there is no change in the volume and weight of the cell.

• For example: If the osmotic concentration of the cell sap is 0.5 M, then 0.5 M solution is isotonic to it.

• Solutions of 0.6 M or more concentration are hypertonic and those of less than 0.5 M concentration are hypotonic.

• When a plant cell is kept in a hypertonic solution, the plasma membrane breaks down. 
• As a result of this concentration gradient, the cell loses water because the concentration of water outside the cell is low and the cell shrinks because of exosmosis.
• The protoplasm including cytoplasm and nucleus starts shrinking which is called plasmolysis.

Thus option b) is correct.

• In a hypotonic solution medium, the water(solvent) molecules move into the cell, which is called osmosis. 

• As the water molecules continue to move in the cell (endosmosis), it swells and eventually break down. Thus, lysis of plasma membranes takes place. This is called cytolysis or lysis of cells.

So, this option a) is incorrect.

• It is the shrinkage of cells, not the shrinkage of nucleoplasm is termed plasmolysis.

Thus, option c) is incorrect.

• Since we have got the most appropriate correct answer, option d) is incorrect.

Therefore Plasmolysis in a plant cell is defined as the vital process causing the shrinkage of the cell cytoplasm to contract away in the hypertonic medium.

#SPJ6