- A Osmotic carrying of sucrose molecules along with water uptake under normal conditions
- B Bulk flow of sucrose straight from xylem vessels into phloem in most reference accounts
- C Active co-transport of sucrose with protons, driven by an H+-ATPase gradient
- D Passive diffusion of sucrose with little carrier protein involvement as frequently documented
Correct answer: C. Active co-transport of sucrose with protons, driven by an H+-ATPase gradient
Explanation: Sucrose is actively loaded into the phloem against its concentration gradient using a proton-sucrose co-transport mechanism, powered by H+-ATPase pumps in the plasma membrane.
Concept context
Water and mineral absorption, the ascent of sap, transpiration, and phloem transport via the pressure flow hypothesis.