Answer: active transport (energy).
- A active transport (energy)
- B only simple diffusion
- C plain osmosis
- D the force of gravity
Correct answer: A. active transport (energy)
Explanation: Moving ions against a gradient requires energy (active transport).
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.