Answer: roots to leaves.
- A roots to leaves
- B leaves to roots
- C only sideways
- D downward
Correct answer: A. roots to leaves
Explanation: Xylem carries water upward from the roots to the leaves.
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.