The ascent of sap in tall trees primarily occurs due to transpiration pull, cohesion, and adhesion forces rather than root pressure alone. 

Xylem transports water and dissolved minerals mainly in an upward direction, while phloem can transport food both upward and downward. 

Phloem transport requires metabolic energy, whereas xylem transport is largely a passive process. 

Minerals absorbed by roots move through phloem vessels to reach the leaves where they are utilized for photosynthesis.