Answer: Cohesion between water molecules and tension from transpiration pulling water up.
- A Root pressure alone pushing water up through xylem vessels at all times
- B Osmotic gradients generated by living stem parenchyma cells along the trunk
- C Cohesion between water molecules and tension from transpiration pulling water up
- D Active ATP-driven pumping of water molecules through xylem conduits
Correct answer: C. Cohesion between water molecules and tension from transpiration pulling water up
Explanation: Cohesion-tension theory: water molecules stick together (cohesion) and to xylem walls (adhesion). Transpiration creates tension, pulling a continuous water column up.
Water can travel through cell walls (apoplast) or cell-to-cell through the cytoplasm (symplast) - but the Casparian strip at the endodermis blocks the apoplast route entirely, forcing everything through a selectively permeable membrane (symplast) before it can enter the xylem.
Concept context
Water and mineral absorption, the ascent of sap, transpiration, and phloem transport via the pressure flow hypothesis.