[Campbell Biology P.842] Which statement best describes the mechanism of root pressure, as e... | Practice Question

Which statement best describes the mechanism of root pressure, as explained in the text?

  • A: It is primarily driven by the evaporation of water from leaves during the day, creating a pulling force.
  • B: It involves the active pumping of mineral ions into the xylem of the vascular cylinder, which lowers water potential and draws water into the stele.
  • C: It is the sole mechanism responsible for transporting water to the tops of the tallest trees.
  • D: It causes water to move from the vascular cylinder back into the root cortex.

Explanation

The section 'Pushing Xylem Sap: Root Pressure' states: 'At night, when there is almost no transpiration, root cells continue actively pumping mineral ions into the xylem of the vascular cylinder. Meanwhile, the Casparian strip of the endodermis prevents the ions from leaking back out into the cortex and soil. The resulting accumulation of minerals lowers the water potential within the vascular cylinder. Water flows in from the root cortex, generating root pressure, a push of xylem sap.'