Problem 48 - Objective Biology for NEET

Question

In terms of permeability, the cell wall and plasmalemma are (a) Permeable and differentially permeable respectively (b) Both semi-permeable (c) Scmi-permeablc and differentially permeable (d) Both differentially permeable

Step-by-Step Solution

Answer

(a) Permeable and differentially permeable respectively

Step 1: Understanding Cell Wall and Plasmalemma

The cell wall is a rigid layer present outside the cell membrane in plant cells, fungi and bacteria. It provides mechanical support, protection, and rigidity to the cells. The plasmalemma, also known as cell membrane or plasma membrane, is a semi-permeable layer that surrounds the cytoplasm of all cells. It controls the movement of substances into and out of cells

Step 2: Understanding Permeability

Permeable refers to a membrane that allows all types of substances to pass through it freely. Semi-permeable or selectively permeable refers to a membrane that only allows certain types of substances to pass through it. Differentially permeable refers to allowing different rates of diffusion for different substances, depending upon their needs in the cell.

Step 3: Matching with given options

The cell wall does not selectively allow certain substances to pass through it; it is permeable to most substances. Thus, the cell wall is defined as permeable. The plasmalemma, on the other hand, selectively allows the passage of certain molecules; hence, it is differentially permeable. Now, matching these definitions to the given options, we can conclude that option (a) is the correct answer.

Key Concepts

Cell Wall

The cell wall is a fascinating structure that is primarily found in plant cells, fungi, and some bacteria. It is a stiff layer located outside the cell membrane, providing significant roles in the life of a cell.
The cell wall offers mechanical support, giving the cell a defined shape and protecting it from external pressures. This rigid structure helps maintain the integrity and stability of the cell.
It is crucial to understand that the cell wall is not selective. It does not differentiate when it comes to substances passing through it, categorizing it as permeable.

• Composed mainly of cellulose in plants, adds durability and strength.
• In fungi, made up of chitin, while in bacteria, it consists of peptidoglycan.
• Allows water, gases, and small molecules to pass freely.

Understanding the cell wall's permeability is vital, as it contrasts significantly with other parts of the cell, such as the plasmalemma.

Plasmalemma

Also known as the cell membrane or plasma membrane, the plasmalemma is an essential component of all living cells. It acts as the boundary between the cell's internal environment and the outside world.
The plasmalemma is described as differentially permeable, which means it can regulate what enters and exits the cell with precision.
This selectivity maintains balance within the cell and allows it to function efficiently.

• Makes sure vital nutrients enter the cell while waste products are removed.
• Contains proteins that act as gates or channels to control the passage of specific molecules.
• Maintains cell’s homeostasis, ensuring a stable internal condition.

The varied permeability of the plasmalemma makes it a crucial player in cellular activity, continuously adjusting to the cell’s needs and protecting it from harmful substances.

Differential Permeability

Differential permeability, also known as selective permeability, describes the ability of a membrane to allow certain substances to pass through more readily than others.
This ability can vary depending on the particular needs of the cell at any given time, making it a smart and adaptive process.
Various factors influence this type of permeability, making it a sophisticated biological feature.

• Size and charge of molecules: Smaller, nonpolar molecules often pass more easily.
• Presence of specific transport proteins: These proteins facilitate the movement of larger molecules.
• Concentration gradients: The difference in concentration between the inside and outside of the cell can drive the movement.

Differential permeability is a key concept in understanding how cells interact with their environments and efficiently manage resources, ultimately ensuring their survival and optimal functioning.