Problem 177 - Objective Biology for NEET

Question

Sclerenchymatous sheath is present in vascular bundles of (a) Monocot root (b) Dicot root (c) Dicot stem (d) Monocot stem

Step-by-Step Solution

Answer

The sclerenchymatous sheath is present in the vascular bundles of a Monocot stem.

Step 1: Identify the characteristics of a sclerenchymatous sheath

A sclerenchymatous sheath is a type of tissue in plants that is made up of sclerenchymatous cells. These cells are characterized by their thick, hard walls, which are usually lignified. This makes them ideal for providing structural support and protection to vascular bundles.

Step 2: Understand the difference in the structure of monocots and dicots

Both monocot and dicot have vascular bundles, but they are arranged differently. In monocots, the vascular bundles are scattered, while in dicots, they are arranged in a ring. Dicot roots have an xylem in the center with elongations separated by phloem, and monocot roots have a pith in the center, with strands of xylem and phloem surrounding it.

Step 3: Associate the characteristics with the plant structure.

Combining these facts leads to the conclusion that a monocot stem, which contains scattered vascular bundles requiring extra support and protection, is the structure likely to have a sclerenchymatous sheath. The monocot stem (option d) is therefore the answer.

Key Concepts

Monocot vs Dicot

Understanding the difference between monocots and dicots is vital in studying plant biology, as they represent two major types of flowering plants. Structurally, one can distinguish between them by looking at various characteristics such as leaf venation, flower parts, and most notably, the structure of their vascular bundles.

Monocots, short for monocotyledons, have a single seed leaf called a cotyledon, which emerges when a seed germinates. The vascular bundles in monocots are scattered throughout the stem without a specific arrangement. In contrast, dicots, or dicotyledons, have two cotyledons and exhibit a ring-like pattern in the arrangement of their vascular bundles.

In terms of root structure, monocots typically have a fibrous root system, while dicots often present a taproot system. The structural differences in roots also influence the arrangement of vascular bundles, with dicots having a central xylem core in the root, while monocots showcase a pith surrounded by xylem and phloem.

Sclerenchymatous Sheath

The sclerenchymatous sheath is a layer of cells known for providing strong structural support and protection, primarily due to the presence of lignin, a polymer that gives the cells rigidity. The cells comprising this sheath, called sclerenchyma cells, have significantly thickened cell walls and are typically dead at maturity, leaving behind a robust structure.

Sclerenchyma cells play an essential role in supporting plants in various ways. They can be found in different parts including stems, leaves, and around vascular bundles. In monocots, the need for additional support around vascular bundles is imperative because the bundles are spread throughout the plant’s stem, hence the presence of a sclerenchymatous sheath enveloping them. This arrangement contrasts with dicots, where the ring formation of vascular bundles lends a different type of mechanical strength.

Plant Structural Support

In the plant kingdom, structural support is fundamental for maintaining shape, resisting against forces like wind and gravity, and ensuring the flow of nutrients and water. This support system is complex and multifaceted, consisting of various tissues and cells that evolve to meet these challenges.

Key players in plant support include cellulose, hemicellulose, and pectin, which are found in the primary walls of plant cells. Together, they provide tensile strength and resistance. However, it is the secondary cell wall containing lignin that makes cells like sclerenchyma ideal for support. This is why sclerenchymatous sheaths are so important as they reinforce vascular bundles in plants, especially in high-stress areas such as the scattered vascular bundles of monocot stems.

Other support systems include turgor pressure within cells, allowing non-woody parts of the plant to stand erect, and specialized structures such as tendrils and thorns. Overall, different plants have evolved an array of structural support mechanisms adapting to their environments and growth habits.