General Science • BiologyHard
What is the primary evolutionary significance of the Casparian strip located in the endodermal cell walls of vascular plant roots?
A. It facilitates active transport of sugars downward from leaves to roots through sieve tubes
B. It forms a suberized waterproof barrier that prevents apoplastic movement of water and solutes, forcing them through the symplast to ensure selective uptake✓ Correct Answer
C. It provides mechanical rigidity to prevent roots from collapsing under high soil compaction
D. It secretes digestive enzymes into the surrounding soil to break down complex organic minerals
💡 Solution & Explanation
The Casparian strip is a band of hydrophobic suberin impregnating the radial and transverse walls of root endodermal cells, which blocks the passive apoplastic flow of water through cell walls and forces substances to cross the selectively permeable plasma membrane into the symplast. This regulation allows plant roots to selectively absorb mineral nutrients while excluding toxic ions. Distractors confuse endodermal functions with phloem translocation or mechanical support tissues like sclerenchyma. Water transport in xylem relies heavily on transpirational pull generated in leaves.
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