Answer: The membrane's permeability.
- A The root pressure
- B The membrane's permeability
- C The number of stomata
- D The length of xylem
Correct answer: B. The membrane's permeability
Explanation: Diffusion across a membrane is faster with a steeper gradient, higher temperature and greater membrane permeability to that substance.
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.