Problem 82 - Objective Biology for NEET

Question

Movement of water is correctly represented by (a) Cortex \(\rightarrow\) Root hair (Epidermis) \(\rightarrow\) Xylem \(\rightarrow\) Endodermis \(\rightarrow\) Pericycle (b) Root hair (Epidermis) \(\rightarrow\) Endodermis \(\rightarrow\) Xylem \(\rightarrow\) Pericycle \(\rightarrow\) Cortex (c) Root hair (Epidermis) \(\rightarrow\) Cortex \(\rightarrow\) Endodermis \(\rightarrow\) Pericycle \(\rightarrow\) Xylem (d) Xylem \(\rightarrow\) Cortex \(\rightarrow\) Endodermis \(\rightarrow\) Pericycle \(\rightarrow\) Root hair (Epidermis)

Step-by-Step Solution

Answer

The correct pathway of water transport in the plant is represented by option (c): Root hair (Epidermis) \(\rightarrow\) Cortex \(\rightarrow\) Endodermis \(\rightarrow\) Pericycle \(\rightarrow\) Xylem.

Step 1: Identifying the correct pathway

Water in plants generally moves from areas of higher concentration to areas of lower concentration. The movement of water within a plant typically starts at the root hairs, which absorb the water from the surrounding soil. From there, the water is moved to the cortex, which surrounds the vascular bundle at the inner part of the root. After the cortex, water moves towards the endodermis, a thin layer of cells that acts as a barrier and controls the passage of substances to the xylem and phloem. Endodermis is surrounded by the pericycle, an area from which lateral roots may originate. And finally, water reaches the xylem, the vital tissue responsible for translocation of water and minerals in a plant.

Step 2: Answer Check

Looking at the options, we have to identify the correct sequence matching the one outlined in the previous step, starting with the root hairs and ending at the xylem. The correct pathway of water transport is: Root hair (Epidermis) \(\rightarrow\) Cortex \(\rightarrow\) Endodermis \(\rightarrow\) Pericycle \(\rightarrow\) Xylem. This pathway matches the option (c).

Key Concepts

Root Hair Absorption

Plants absorb water from the soil primarily through microscopic structures called root hairs. These are thin-walled extensions of epidermal cells in the root, which dramatically increase the surface area available for water intake. The process of water absorption is largely driven by osmosis, where water moves from an area of higher water potential (the soil) to an area of lower water potential (the root hair cells).

Inside the root hairs, water contains nutrients collected from the soil, which are essential for plant growth. A concentration gradient between the soil and the plant's internal environment facilitates this passive movement of water. Once inside the root hairs, the water begins its journey through the plant, heading next to the root cortex.

Plant Vascular System

The plant vascular system is akin to a network of highways that facilitates the transport of water, minerals, and food throughout the plant. This system consists of two major types of conduits - the xylem and the phloem. While the xylem is primarily responsible for the upward movement of water and dissolved minerals from the roots to the rest of the plant, the phloem distributes organic nutrients made in the leaves to all parts of the plant.

Both xylem and phloem are interconnected and extend from the roots to the leaves through the stems and branches. The efficient distribution of these vital elements supports various plant functions, including photosynthesis, growth, and reproduction. The seamless integration of these vascular pathways is central to the plant's survival and adaptability.

Xylem Function

The xylem is the plant's principal water-conducting tissue, performing the critical function of transporting water and nutrients from the roots to the leaves, where photosynthesis occurs. Xylem is composed of dead, hollow cells that stack end-to-end to form long tubes extending throughout the plant. Due to this structure, xylem vessels can efficiently conduct water upward, supported by capillary action, water's cohesive properties, and transpiration pull.

Functionally, the xylem not only delivers vital water and solutes but also provides structural support to the plant. The rigidity of the xylem vessels contributes to the plant's ability to stand upright and reach towards sunlight, maximizing its photosynthesis potential.

Endodermis in Roots

The endodermis is a critical layer of cells in the plant's roots that serves as a selective barrier, regulating the flow of water and solutes into the plant's vascular system. This single layer of cells is tightly packed, with a characteristic feature called the Casparian strip. The Casparian strip is a band of waxy, suberized material that wraps around each cell and prevents the passive movement of substances between cells. As a result, all materials must pass through the cells to get into the xylem.

By controlling what enters the vascular system, the endodermis ensures that harmful substances are kept out, and only essential water and minerals reach the xylem. The precision of this regulation is key to maintaining the plant's internal chemical balance and overall health.