Question

Why is the flow of water multi directional in phloem, but uniform directional in xylem?

Answer 1

it is due to process of translocation and formation of adh energy in phloem which not happen in xylem

Answer 2

Movement of water through the xylem is caused by root pressure, capillary action and mainly via transpirational pull. All these factors results in a net upward movement of water molecules through the xylem vessel.

In the phloem, movement is multidirectional because of the presence of companion cells. These companion cells have many mitochondria that can carry out aerobic respiration to provide sufficient energy for active transport of substances in the desired direction.

The xylem vessel has no protoplasm, hence water cannot move due to active transport — hence it can only go upwards.