Problem 145 - Objective Biology for NEET

Question

The waxy substance associated with cell walls of cork cells are impervious to water because of the presence of which gets deposited on cork cells (a) Cutin (b) Suberin (c) Lignin (d) Hemicellulose

Step-by-Step Solution

Answer

The answer is (b) Suberin. It is the substance that gets deposited onto cork cells and makes them impervious to water.

Step 1: Understand the question

The problem is asking about the characteristics of cork cell walls and the substance that contributes to their water-resistant nature. The exercise also provides four choices which are all substances found in plant cells: Cutin, Suberin, Lignin, and Hemicellulose.

Step 2: Analyze the options

Cutin is a waxy substance present on the epidermal cell surface of the plant which helps in preventing excessive water loss, but it's not the one found in cork cells. Lignin is a complex polymer deposited within the cell wall of some cells, providing strength and rigidity. It's found in woods and barks, but not the one in cork cells. Hemicellulose is a type of polysaccharide found in plant cell walls and helps with cell structure, but it's not responsible for the water-resistant nature of cork cells.

Step 3: Find the right answer

Suberin is a waxy, fatty substance found in higher plants. It's deposited in the cell walls of cork cells, making them more impervious to water. This substance is responsible for the characteristic 'corkiness' and waterproofing property of the layer.

Key Concepts

Cork cells

Cork cells are specialized plant cells that form the outer protective layer of stems and roots. When you think of cork, you might picture a wine bottle stopper or a bulletin board. This cork is harvested from the bark of cork oak trees, where these specialized cells are prevalent. Cork cells are unique in that they contain a substance known as suberin, which imparts them with their water-resistant property. This functionality is crucial for plants as it helps to reduce water loss and protect against environmental stressors. Cork cells are dead at maturity, meaning they serve a structural and protective role rather than a live one. The structure of cork cells is characterized by:

• A thick cell wall that protects the plant's inner tissues.
• Air-filled cavities that contribute to the cell's insulation properties.
• An exterior that is robust and can resist external damage.

Water resistance in plants

Water resistance in plants is a vital property that helps them survive in various environmental conditions. This resistance is mainly achieved through substances like suberin and cutin. Suberin in cork cells is essential because it forms a barrier to water and solutes, thus reducing water loss through evaporation. This barrier is vital in dry climates, where water conservation is imperative for plant survival. Suberin provides:

• A waterproof layer that protects other plant tissues from losing moisture.
• Defense against pathogens that thrive in moist environments.

Besides suberin, cutin, found on the surface of leaves and young shoots, also contributes to water resistance. Even though cutin is not the primary substance in cork cells, it functions similarly by creating a protective, water-repellent film.

Plant cell wall composition

Plant cell walls are complex structures composed of various substances, each serving specific functions in growth, protection, and support. A typical plant cell wall comprises:

• Cellulose: A strong, fibrous molecule that provides structural support.
• Hemicellulose: A heterogeneous group of polysaccharides working alongside cellulose.
• Pectin: A gel-like substance that aids in cell adhesion.
• Lignin: Found in some cells, it adds rigidity and waterproofing, especially in wood and bark.

Suberin finds its place mainly in specific cells, like cork cells, adding to the impermeable properties of these walls. The deposition of these substances varies according to the function and location of the cell within the plant. Thus, cork cells, with their suberin-rich walls, are distinct for their unique role in preventing water loss and providing mechanical protection.