Cohesion-Tension Theory Drives Xylem Water Transport

Steps:

• Identify key mechanisms: transpiration pull, cohesion of water molecules, and adhesion to xylem walls enable upward flow.
• Recall that root pressure aids but is minor; capillary action contributes minimally in tall plants.
• Evaluate options: all three (transpiration, cohesion, adhesion) are primary contributors per standard plant physiology.
• Confirm A includes all essential factors without excluding valid ones.

Why A is correct:

• A encompasses transpiration pull (1), cohesion (2), and adhesion (3), aligning with the cohesion-tension theory where evaporative loss creates negative pressure pulling water upward via cohesive forces.

Why the others are wrong:

• B omits adhesion, essential for water's attachment to vessel walls during ascent.
• C excludes cohesion, the force binding water molecules into a continuous column.
• D ignores transpiration pull, the main driver generating tension for bulk flow.

Not enough information on exact statements for 1, 2, 3, but based on standard factors, A fits.

Final answer: A