Answer: Active uptake by root hair cells, then movement via symplast or apoplast to the xylem.
- A Bulk flow driven by transpirational pull, bypassing active transport in typical laboratory settings
- B Diffusion down a concentration gradient, with little active uptake as generally observed
- C Active uptake by root hair cells, then movement via symplast or apoplast to the xylem
- D Osmosis of dissolved minerals along the water potential gradient under usual circumstances
Correct answer: C. Active uptake by root hair cells, then movement via symplast or apoplast to the xylem
Explanation: Minerals are actively absorbed (often against a concentration gradient) by root hair cells using energy-dependent transporters, then move radially through the symplast or apoplast (interrupted by the Casparian strip) into the xylem.
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.