Question

Xylem tube transport sap upwards only where as pholem transport food in both the direction why do you think their is difference

Answer 1

There is difference as
1. Water is only to be transported in upward direction as there source is down the ground.
3.whereas food source or they are transported in leaves and food are needed all through out the plant body that is why pholem are bi directional.

Answer 2

A tissue called Xylem acts as a pipeline and take water and minerals from the roots up the stem, and to the leaves for photosynthesis. So xylem transports water and minerals in upward direction only. Special types of tissues called phloem carry the prepared food which has to be transported in all directions. So phloem transports prepared food in all directions.