Incorrect Statement on Xylem Water Transport Steps:

• Apply cohesion-tension theory: transpiration lowers water potential in leaves, creating a gradient that pulls water from roots.
• Note water potential decreases gradually along the entire xylem pathway from roots to leaves.
• Recognize xylem vessel elements are short segments (0.1–1 mm); resistance within each is low, so potential is nearly uniform inside one.
• Identify D as incorrect: it wrongly suggests significant potential change within individual elements, not the overall path.

Why D is correct:

• Water potential gradient occurs over the whole xylem length (meters), not detectably within short vessel elements, where flow resistance causes negligible drop (per Poiseuille's law on minimal pressure loss in low-resistance conduits).

Why the others are wrong:

• A: Adhesion of water to cellulose xylem walls supports the continuous column against gravity.
• B: Transpiration tension makes hydrostatic pressure less negative (higher) in roots than leaves.
• C: Hydrogen bonds create cohesion, enabling the entire water column to move as a unit via mass flow.

Final answer: D