Problem 164 - Objective Biology for NEET

Question

The cell layer located at the periphery in the cross-section of the root is called (a) Endodermis (b) Epiblema (c) Pericycle (d) Xylem

Step-by-Step Solution

Answer

(b) Epiblema

Step 1: Identify cell biology concept

This involves cell structure and function.

Step 2: Recall relevant principles

Review organelle structure and function.

Step 3: Apply knowledge

Analyze the scenario.

Step 4: State the answer

The answer is: (b) Epiblema

Key Concepts

Epiblema

The epiblema, also known as the rhizodermis or root epidermis, is the outermost layer of cells in the root of a plant and plays a vital role in the absorption of water and minerals from the soil. Unlike other epidermal layers in the plant, the epiblema is unique to roots. It is characterized by being a single layer of cells without any cuticle, making it permeable to water. This layer contains root hairs, which are extensions of the epiblemal cells that greatly increase the surface area for absorption.

Additionally, the epiblema serves as the plant root's protective layer against soil pathogens and helps anchor the plant firmly in place. The presence of root hairs is critical because they are the main site for nutrient uptake due to their close contact with the soil solution.

Endodermis

The endodermis is the innermost layer of the root cortex, functioning as a selective barrier between the outer cortex and the vascular cylinder. One of the most distinctive features of the endodermal cells is the presence of a Casparian strip—a band of suberin that wraps around each cell, blocking uncontrolled passage of substances into the vascular cylinder.

The endodermis regulates the flow of water and solutes into the xylem, ensuring that only the necessary nutrients reach the vascular tissues while harmful substances are excluded. Its selective permeability is crucial for the maintenance of water balance and nutrient uptake within the plant.

Pericycle

Surrounding the vascular tissues and located just inside the endodermis is the pericycle, a layer of cells that is known for its ability to give rise to lateral roots. This layer is important for the overall growth and development of the plant's root system. The pericycle is also involved in the secondary growth of roots, which leads to an increase in thickness and supports the plant as it matures.

The cells of the pericycle retain the capability to divide, differentiating into the various cell types needed to form new root branches. This allows the plant to explore further into the soil for resources and helps stabilize the plant more firmly in the ground.

Xylem

Xylem tissue functions as the plant's water transport system, conducting water and dissolved minerals from the roots to the rest of the plant. This vascular tissue also provides structural support due to the lignin present in the xylem cell walls, which strengthens the cells and enables them to withstand the force of water transport under tension.

The structure of xylem can be complex, often consisting of tracheids and vessels in flowering plants. Tracheids are long, thin cells that transport water through pits in their walls, while vessels are larger tubes that allow for more efficient water flow. Through capillary action and the transpiration pull, water moves upwards within the xylem, allowing plants to grow tall and survive in a range of habitats.