Transpiration Pull Drives Water Upward in Plants

Steps:

• Identify the process: Water transport in plants occurs via xylem from roots to leaves.
• Recall the mechanism: Cohesion-tension theory explains upward movement due to evaporation.
• Evaluate options: Match each to known plant physiology principles.
• Select best: Choose the one aligning with transpiration's role.

Why A is correct:

• Transpiration is the evaporation of water from leaves, creating negative pressure that pulls water up the stem via cohesion-tension (as per the cohesion-tension theory).

Why the others are wrong:

• B: Root pressure pushes water but is minor and insufficient for tall plants; transpiration dominates.
• C: Photosynthesis uses water in leaves, but this doesn't drive upward movement—it's a sink, not the force.
• D: Osmosis moves water into roots, but bulk flow up the stem relies on transpiration, not osmosis alone.

Final answer: A