Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Water and mineral uptake by root hairs from the soil occurs through apoplast until it reaches endodermis.
Reason (R): Casparian strips in endodermis are suberized.
In light of the above statements, choose the correct answer from the options given below.
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The Casparian strip acts as a cellular checkpoint, forcing all water and solutes to pass through a selectively permeable cell membrane (symplast) before entering the vascular system. This allows the plant to regulate nutrient intake and prevent backflow.
Both Assertion & Reason are true and the Reason is the correct explanation of the Assertion.
Both Assertion & Reason are true but the Reason is not the correct explanation of the Assertion.
Assertion is true statement but Reason is false.
Both Assertion and Reason are false statements.
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Concept:
Water moves through root tissues toward the vascular cylinder (xylem) via three pathways: apoplastic (through non-living cell walls), symplastic (through interconnected cytoplasm via plasmodesmata), and transmembrane pathways. Step 2: Detailed Explanation:
Let us analyze both statements and their biological relationship:
Assertion (A): Water and dissolved minerals absorbed by root hairs move freely through the apoplastic pathway (cell walls and intercellular spaces) across the root cortex.
However, this movement continues unchecked only until it reaches the endodermal layer of the root. At the endodermis, the apoplastic flow is blocked, forcing water to enter the symplastic pathway. Thus, Assertion (A) istrue.
Reason (R): The radial and transverse walls of the endodermal cells contain a band of hydrophobic, waxy material called suberin, which forms theCasparian strip.
This suberized band is completely impermeable to water and solutes.
Therefore, water moving through the apoplast cannot cross this barrier and must cross the selectively permeable plasma membrane of the endodermal cells, entering the symplast. Thus, Reason (R) istrue.
Connection: The presence of the impermeable, suberized Casparian strip in the endodermis (Reason) is the exact biological explanation for why apoplastic water flow is blocked at the endodermis, forcing it into the symplast (Assertion).
Thus, both statements are true and R is the correct explanation of A. Step 2: Final Answer:
The correct option is (A).
