Problem 21 - Objective Biology for NEET

Question

On what basis we classify sclerenchyma into fibres or sclereids? (a) Structure (b) Origin (c) Development (d) All of these

Step-by-Step Solution

Answer

The classification of sclerenchyma into fibres or sclereids is based on their Structure.

Step 1: Understanding Sclerenchyma

Understand that sclerenchyma is a type of plant tissue composed of cells that are thickened and hardened. It provides strength and support to the plant.

Step 2: Understanding Fibres and Sclereids

Fibres are long, slender cells that are heavily lignified and dead. They provide mechanical strength to the plant. On the other hand, sclereids are shorter cells with extremely thickened, lignified walls. They are found in seed coats and nutshells.

Step 3: Knowledge Application

Applying the knowledge of fibres and sclereids to the options given, it can be seen that the basic difference between fibres and sclereids lies in their structural forms.

Key Concepts

Sclerenchyma

Sclerenchyma is an essential plant tissue known for its function in providing structural support. This plant tissue is characterized by its cells, which have thickened and hardened walls resulting from lignin deposition. This process strengthens the cell walls, making them more rigid and durable. Sclerenchyma cells are usually non-living at maturity because their thick walls limit their cellular activities. However, this very characteristic makes them excellent at providing mechanical strength to various parts of the plant, such as stems and roots.
Sclerenchyma can be distinguished from other plant tissues by:

• Thick, lignified cell walls
• Primarily non-living cells at maturity
• Serving a supportive role in the plant

By forming a protective and supportive layer, sclerenchyma ensures that plants can withstand various environmental challenges.

Fibres

Fibres are one of the two main types of sclerenchyma cells. They play a crucial role in providing tensile strength, enabling plants to withstand pulling and bending forces. These cells are elongated and slender, often found in bundles or strands that run longitudinally along the plant's body parts like stems and leaves.
The main features of fibres include:

• Long and thin cell structure
• Highly lignified cell walls, contributing to their hardness and strength
• Predominantly non-living cells, as they lose a large part of their protoplasm as they mature

Fibres are primarily involved in mechanical support, and their durability is utilized in manufacturing materials like ropes and textiles, owing to their resilience and strength.

Sclereids

Sclereids, another type of sclerenchyma cell, differ from fibres in several significant ways. They are typically shorter and vary substantially in shape, often appearing as star-shaped, roughly spherical, or irregular. Their thick, lignified cell walls are mainly responsible for their ability to provide support and protection within certain plant tissues.
**Distinctive characteristics of sclereids include:**

• Shorter length compared to fibres
• A variety of shapes and a more random distribution within the plant tissues
• Presence in specific plant parts like seed coats, fruit walls, and nutshells, contributing to their toughness

Despite their small size, sclereids significantly influence the plant's rigidity and protection. Due to their presence, they can impact certain textures, making pears gritty and creating the hard layers in nuts.