Answer: Facilitated diffusion.
- A Facilitated diffusion
- B Active transport
- C Simple imbibition
- D Bulk mass flow
Correct answer: A. Facilitated diffusion
Explanation: Facilitated diffusion uses a membrane transport protein but still moves substances down their gradient, needing no ATP.
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.