mass flow

Mass flow in plant physiology refers to the movement of substances through the plant's vascular tissues, primarily phloem and xylem.12

Phloem Transport:
* Photosynthesis products, mainly sugars, move through the phloem from leaves to growing tissues and storage organs.1
* This movement is metabolically controlled and can occur in various directions.1
* The rate of transport is measured by velocity or mass transfer (dry weight transported per unit time).1
* The pressure-flow hypothesis suggests a pressure gradient drives this movement.1

Xylem Transport:
* Xylem primarily transports water and dissolved minerals from the roots to the rest of the plant.2
* This movement is generally upward and driven by transpiration pull, where water is pulled up due to evaporation from leaves.34
* In some cases, root pressure can push water upward.4
* The cohesion theory explains how water columns are pulled up through the xylem without breaking.4

While phloem transport involves the movement of sugars, xylem transport focuses on water and minerals, with different mechanisms driving their flow.142