Question

The additional apoplastic route of water that allows direct access to xylem and phloem is along the margins of ________ .

• A. primary root
• B. secondary root
• C. root hair
• D. casperian strips

Hint:

Casparian strip = checkpoint of water entry into vascular tissue.

Answer 1

The Correct Option is D

Concept:
Water movement in roots occurs through two pathways:
• Apoplastic pathway (through cell walls)
• Symplastic pathway (through cytoplasm)

Step 1: Understand Casparian strip. Casparian strips are bands of suberin present in the endodermis of roots. They:
• Block the apoplastic pathway
• Force water to enter the symplast (cytoplasm)

Step 2: Additional apoplastic route. Water can bypass partially along the margins of Casparian strips to gain regulated access toward vascular tissues (xylem and phloem).

Step 3: Analyze options.
• (A) Primary root → General structure $\times$
• (B) Secondary root → Not specific $\times$
• (C) Root hair → Absorption site $\times$
• (D) Casparian strips → Controls apoplastic flow \checkmark

Step 4: Conclusion. \[ \text{Apoplastic route is regulated along Casparian strips} \]