Problem 54 - Objective Biology for NEET

Question

A cell is plasmolysed after being kept in a hypertonic solution. What will be present between the cell wall and plasmalemma? (a) Isotonic solution (b) Hypertonic solution (c) Air (d) Hypotonic solution

Step-by-Step Solution

Answer

After a cell is plasmolysed due to a hypertonic solution, the space between the cell wall and the plasmalemma will contain Air.

Step 1: Understanding Key Terms

First, understand the key terms - hypertonic solution, isotonic solution, and hypotonic solution. A hypertonic solution has a higher solute concentration, an isotonic solution has an equal concentration, while a hypotonic solution has a lower concentration of solute compared to another solution.

Step 2: Understanding Plasmolysis

Next, understand the process of plasmolysis, which is the shrinking of the cytoplasm as a result of water loss when a cell is placed in a hypertonic solution. In this case, the water inside the cell exits in order to balance the concentration of water inside and outside the cell, causing the protoplasm (the living substance inside the cell) to shrink away from the cell wall.

Step 3: Determining What Is Between the Cell Wall and Plasmalemma

Lastly, determine the substance that exists in the space between the cell wall and the plasmalemma after plasmolysis. Since cell plasmolysis is often accompanied by the creation of a large vacuum within the cell, the correct answer is (c) Air.

Key Concepts

Hypertonic Solution

A hypertonic solution is pivotal in understanding water movement in plant cells.
To put it simply, a hypertonic solution has a higher solute concentration than another solution, particularly the fluid inside a plant cell. If a plant cell is placed in a hypertonic solution, an interesting process occurs due to osmosis, which is the movement of water across a semi-permeable membrane.

Imagine sipping through a very narrow straw; water would move from the glass (just like from inside the cell) into your mouth, which is like the hypertonic solution with 'thirst' for water. The cell wall, being rigid, stays intact, but the interior parts of the cell, including the plasmalemma, shrink away due to water leaving. This phenomenon leaves a gap between the plasmalemma and the cell wall, and understandably, this gap is not filled with fluid but air.

Plasmalemma

The term plasmalemma might sound complex, but it's simply the scientific term for the plant cell's plasma membrane. It is the thin, flexible boundary between the inner parts of the cell and its external environment. Think of it as the skin of the cell, protecting its contents.

Now, when we talk about plasmolysis in plant cells, the plasmalemma plays a central role. It’s the barrier that decides which substances enter and leave the cell. During plasmolysis, this membrane detaches from the cell wall due to the outward flow of water. This detachment in a hypertonic environment is a bit like a balloon deflating within a box; the balloon's rubber represents the plasmalemma and the box, the cell wall. The air that remains between the two is the same as the air that fills the space when plasmolysis occurs in plant cells.

Solute Concentration

The concept of solute concentration can be a tad abstract, but let's demystify it with a pinch of salt in water. If we pour salt into a glass of water, the salt dissolves and becomes the solute. The water is the solvent, and together, they form a solution.

In the scenario of plant cells and surrounding solutions, the solute concentration is a game-changer. If the surrounding solution has more dissolved substances (a higher solute concentration) than the cell's interior, it's called hypertonic. Just like humans moving from overcrowded places to more peaceful areas, water inside the plant cell moves outwards to where it’s less crowded with solutes, attempting to balance things out. This movement is driven by osmosis and results in the shrinking of the plant cell's contents. Hence, knowing the solute concentration helps in predicting the direction of water movement and the outcome for the cell—in this case, plasmolysis.