Cohesion-tension theory drives water ascent

Steps:

• Identify key processes: transpiration (1) evaporates water from leaves, creating tension; cohesion-adhesion (2) forms water columns in xylem; root pressure (3) pushes water upward from roots.
• Explain gradient: transpiration lowers water potential at leaves, pulling water up via cohesion; root pressure maintains base pressure.
• Link to height: combined processes sustain gradient against gravity for tall plants.
• Confirm all three contribute to overall mechanism.

Why A is correct:

• All three processes (transpiration pull, cohesion-adhesion, root pressure) collectively maintain the water potential gradient per the cohesion-tension theory.

Why the others are wrong:

• B omits root pressure, which aids initial flow and gradient in low-transpiration conditions.
• C excludes cohesion-adhesion, essential for continuous water column without breakage.
• D ignores transpiration, the primary driver of upward pull in most plants.

Not enough information on exact processes 1-3, but assuming standard ones, A fits.

Final answer: A