Transpiration Pull Drives Water Upward

Steps:

• Recall that water transport in plants occurs via xylem tissue in the stem.
• Identify the main force: evaporation from leaves creates tension, pulling water upward.
• Evaluate options against the cohesion-tension theory.
• Select the option matching evaporation-driven movement.

Why A is correct:

• Transpiration, the evaporation of water from leaves, generates negative pressure (tension) in xylem, pulling water up the stem via cohesion-tension theory.

Why the others are wrong:

• B: Root pressure pushes water but is minor compared to transpiration pull and insufficient for tall plants.
• C: Photosynthesis uses water in leaves but does not drive its upward movement through the stem.
• D: Osmosis occurs at roots for entry but not for bulk upward flow in the stem.

Final answer: A