Question

Selective permeability is the characteristic feature of:

• A. Cell wall
• B. Root Hair
• C. Plasma membrane
• D. Pseudo-stem

Hint:

The plant cell wall is fully permeable, whereas the plasma membrane is selectively permeable, regulating solute transport to maintain homeostasis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cellular boundaries differ in their permeability to water, ions, and organic molecules.
Selective permeability is a functional property that allows a barrier to regulate the passage of specific substances.

Step 2: Detailed Explanation:
Let us evaluate the physical properties of the structures listed:
1. Cell wall (A): The plant cell wall is a rigid, porous outer layer composed primarily of cellulose, hemicellulose, and pectin.
It is fully permeable to water and dissolved solutes, providing structural support rather than selective transport regulation.
2. Root Hair (B): Root hairs are cellular extensions of root epidermal cells.
While they absorb water and nutrients, they are complex cellular structures containing both a cell wall and a plasma membrane, rather than a single semi-permeable boundary.
3. Plasma membrane (C): The plasma membrane (and the tonoplast vacuolar membrane) is a selectively permeable phospholipid bilayer containing transport proteins.
It allows water and small, uncharged molecules to pass through while regulating the transport of larger polar molecules and charged ions via active or passive mechanisms.
This selective transport is a key characteristic of the plasma membrane.
4. Pseudo-stem (D): This is a macro-anatomical plant structure (such as in bananas) composed of overlapping leaf sheaths, with no primary role in selective permeability.

Step 3: Final Answer:
Therefore, selective permeability is the characteristic feature of the plasma membrane.