Answer: More negative (lower).
- A Higher than the xylem
- B Equal to the air
- C Exactly zero always
- D More negative (lower)
Correct answer: D. More negative (lower)
Explanation: Loading sugar lowers (makes more negative) the sieve-tube water potential, so water enters from the xylem and builds the pressure that drives flow.
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.