Which main physical principle is responsible for driving water absorbed by roots upward through xylem vessels in plants?

Correct answer: Transpiration pull and cohesion-tension theory

Answer: B, the transpiration-pull or cohesion-tension theory. Water evaporates from moist leaf surfaces through stomata. This evaporation lowers water potential in the leaf and creates tension, or negative pressure, in the continuous xylem water column. Cohesion between water molecules helps keep that column unbroken, while adhesion to xylem walls supports its movement. Root pressure can contribute in some situations, but it is not the main force for the normal upward movement of water in tall plants. A is incorrect because simple diffusion cannot explain long-distance transport through xylem. C is incorrect because atmospheric pressure alone does not pull water to the top of a tree. D describes movement of cytoplasm inside cells, not xylem transport. Memory cue: transpiration pulls; cohesion holds.