Q. 9 Movement of substances in xylem is unidirectional while in phloem it is Explain bidirectional.

xylem is involved in the one way transport of water and minerals from soil to root stem leaves. several forces act in this mechanism like imbibition, root pressure and fanally transpiration pull. there continuous loss of water at the body surface of plant. thus, it is a unidiriectional process.
phloems 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 very in diffrerent phases of its growth, thus the food need to travel in both upwords and downward direction. so, phloem shows bidirectional movement of substances.