Lignin impregnates xylem walls for water impermeability

Steps:

• Recall xylem vessels transport water in plants and require impermeable walls to prevent leakage.
• Identify key substances in plant cell walls: cellulose for structure, lignin for strengthening and waterproofing.
• Eliminate non-plant or irrelevant options like collagen.
• Confirm lignin's role in secondary cell wall deposition for vascular tissues.

Why B is correct:

• Lignin is a hydrophobic polymer that deposits in xylem vessel walls, creating a barrier impermeable to water as defined in plant anatomy.

Why the others are wrong:

• A. Cellulose forms permeable microfibrils in primary cell walls, allowing water passage.
• C. Suberin provides impermeability in cork cells but not in xylem vessels.
• D. Collagen is a protein in animal connective tissues, absent in plants.

Final answer: B