Hello Praveen,

Xylem flow is an unidirectional process and  phloem  flow is  a bidirectional one.  This is because xylem transports water from soil to leaves and  phloem  transfers the food synthesized in leaves to all the parts of plants wherever it is necessary.

During the growth of a plant, the leaves act as the source of food as they carry out photosynthesis.

Hope this helps you. We wish you the best for your future endeavours!

Regards