Problem 174 - Objective Biology for NEET

Question

Assertion: Endodermis is impervious to water Reason: Endodermis contain band of suberised matrix called casparian strip.

Step-by-Step Solution

Answer

The endodermis in a plant is indeed impervious to water due to the presence of the casparian strip, a band of suberised matrix. Thus, the assertion is correct and the reason is the correct explanation of the assertion.

Step 1: Understanding the Assertion

The assertion states that the endodermis is impervious to water. This needs to be validated. Endodermis is the innermost layer of cells in the cortex of a plant root, and it separates the vascular tissue from the cortex. It is indeed impervious to water because of a structure known as casparian strip.

Step 2: Understanding the Reason

The reason explains that the endodermis contains bands of suberised matrix called the casparian strip. The casparian strip is a thin band of waterproof material (suberin) deposited on the radial and transverse walls of the endodermis. It effectively blocks water and solutes from entering the vascular tissue via the cell walls of the endodermis.

Step 3: Verifying the Truthfulness of Assertion and Reason

Now that you have understood the roles of the endodermis and the casparian strip, check if the reasons given and the assertion made are true. Both are indeed correct based on their biological functions.

Step 4: Checking the Relationship Between Assertion and Reason

The last step involves coordinating the assertion and reason. The reason accurately explains why the assertion holds true, therefore, there is a direct link between the assertion and reason.

Key Concepts

Casparian strip

The Casparian strip is a crucial component of plant root anatomy that plays an essential role in regulating water and nutrient uptake. This thin band of waxy material is found in the cell walls of the endodermis, forming a barrier that ensures selective permeability. Its primary function is to block the passive flow of substances via the apoplast—the network of cell walls in a plant root that allows free movement.

The Casparian strip is composed of suberin, a hydrophobic substance that effectively prevents water and solutes from seeping uncontrolled into the vascular tissue. This regulation is critical for maintaining homeostasis within the plant. Without this control, harmful substances or excessive water could disrupt cellular processes within the plant's inner transport systems. By ensuring that anything entering the vascular system passes through a selectively permeable cell membrane, the Casparian strip helps keep the plant healthy and functioning properly.

Suberin

Suberin is an important lipid biopolymer found in certain plant tissues. It functions as a barrier to water and solutes, crucial for plant survival, especially in heterogeneous soil environments.

This biopolymer is primarily found in the cell walls of the endodermis and the outer protective tissues of plants such as bark. Its waxy and hydrophobic nature makes it extremely effective at repelling water, contributing to the function of the Casparian strip.

In addition to providing a waterproof barrier, suberin also acts as a defense mechanism against pathogens. By restricting entry through the cell wall, it helps prevent infection, making it an indispensable part of the plant's defense system. Furthermore, suberin's presence regulates root pressure and ensures that the plant efficiently utilizes its resources.

Vascular tissue

Vascular tissue is the plant's internal transport system responsible for moving water, nutrients, and sugars throughout the plant. It consists of two main components: xylem and phloem.

The xylem is tasked with transporting water and dissolved minerals from the roots upward through the plant, reaching leaves and other parts. Meanwhile, the phloem is responsible for distributing sugars produced during photosynthesis from the leaves to other areas of the plant needing energy.

This complex system of "pipelines" allows plants to support their various functions and growth. The vascular tissue's integration with other plant systems, including the endodermis and Casparian strip, facilitates efficient transport and contributes to the plant’s overall health and stability. It ensures that nutrients reach their target destinations and that waste products are removed efficiently.

Plant root anatomy

Plant root anatomy is intricate and specialized to perform several crucial functions, including nutrient uptake, water absorption, and providing structural support. At the core of these functions lies the endodermis, a critical inner layer that plays a role in regulating water and nutrient flow.

The endodermis surrounds the vascular tissue, forming a protective and selective barrier aided by the Casparian strip. Root anatomy also features epidermis, cortex, and pericycle layers, each contributing to the root's overall functionality.

The epidermis acts as the first line of defense and is involved in nutrient absorption. The cortex stores carbohydrates and transports nutrients inward to the endodermis, while the pericycle is key in secondary root growth.

By understanding plant root anatomy, we gain insights into how plants efficiently manage resource acquisition and distribution, which is vital for their growth and survival in varying environments.