Movement of substances in xylem is unidirection while in phloem it is bidirectional. Explain

Explanation

Xylem is involved in the one way transport of water and minerals from soil to root `rarr` stem `rarr` leaves. Serveral forces act in this mechanism like imbibition, root pressure and finally transpiration pull. There is continuous loss of water at the body surface of plants. Thus, it is a unidirectional process.
Phloem's main function is to transport food from source to sink where source implies with the part of plant responsible for synthesising food and sink to those parts and organs that needs or consumes food for their growth and development. These source and sink parts of a plants may vary in different phases of its growth, thus the food need to travel in both upwards and downward direction. So, phloem shows bidirectional movement of substances.