[Campbell Biology P.852] According to the cohesion-tension hypothesis, what is the primary d... | Practice Question

According to the cohesion-tension hypothesis, what is the primary driving force for the upward movement of xylem sap in tall plants?

  • A: Active pumping of water into the xylem by root cells.
  • B: The positive pressure generated by root pressure.
  • C: Negative pressure (tension) generated by the evaporation of water from leaves.
  • D: Osmotic uptake of water into xylem vessels.

Explanation

The cohesion-tension hypothesis states that the movement of xylem sap is driven by a water potential difference created by the evaporation of water from leaf cells. This evaporation lowers the water potential, generating negative pressure tension that pulls water up the xylem.