Problem 38 - Objective Biology for NEET

Question

Cell wall is (a) Permeable (b) Impermeable (c) Semi-permeable (d) Selectively permeable

Step-by-Step Solution

Answer

The cell wall is (a) Permeable

Step 1: Understand the terms

Permeable refers to a material or membrane allowing liquids or gases to pass through it. Impermeable, on the other hand, does not allow substances to pass through. Semi-permeable allows certain substances to pass through but not all, while selectively permeable allows only specific types to pass through based on factors such as molecule size or solubility.

Step 2: Understanding properties of the cell wall

The cell wall is a rigid layer surrounding the cells of plants, fungi, and bacteria. It is not present in animal cells. The cell wall provides strength and protection to the cell and allows certain substances to pass through, thus it is permeable.

Step 3: Conclusion

Based on the understanding of both the cell-wall properties and the concepts of permeability, one can conclude that the cell wall is permeable.

Key Concepts

Cell Wall Structure

The cell wall is an essential part of plant cells and other organisms like fungi and some bacteria. It acts like a sturdy shield around the cell. Think of it as a protective barrier. However, unlike plants, animal cells lack this outer layer.
The cell wall is primarily made of cellulose in plants, which is a tough carbohydrate. This cellulose forms a strong network of fibers, giving the wall the strength it needs. In fungi, the cell wall is usually made of chitin, while in bacteria, it often consists of peptidoglycan.

• Cellulose: Main component in plant cell walls.
• Chitin: Found in fungal cell walls.
• Peptidoglycan: Common in bacterial cell walls.

These building blocks not only provide structural support but also prevent the cell from bursting due to pressure changes from the inside and outside.

Permeability Types

Understanding permeability is key to knowing how substances move in and out of cells. There are several types to consider:

• Permeable: Allows most substances to pass through. Think of it like an open door.
• Impermeable: Blocks substances entirely, like a solid brick wall.
• Semi-permeable: Lets certain small molecules pass but blocks others, similar to a sieve.
• Selectively permeable: Chooses specific molecules to pass based on characteristics like size or solubility. It's like a bouncer at a door allowing only certain people inside.

The cell wall is generally considered permeable because it allows many substances to move through it, though it primarily supports the cell mechanically rather than controlling traffic.

Plant Cell Wall Properties

Plant cell walls have distinct properties essential for plant life. They are not just a barrier; they perform numerous functions. Here are some key features:

• Rigid Structure: Provides shape and prevents over-expansion when water enters the cell, maintaining cell integrity.
• Permeability: Although primarily for structure, it allows water, gases, and some nutrients to pass freely. This makes it generally permeable.
• Protection: Shields against pathogens and mechanical damage.
• Support: Helps plants stand upright, especially important for non-woody plants that lack other supportive structures.

These properties are vital for plant survival and growth, facilitating processes like photosynthesis by allowing gas exchange and maintaining cell turgor pressure.