question_answer 37)

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

Answer:

                  Xylem is involved in the one way transport of water and minerals from soil to root  stemleaves. Several forces act in this mechanism like imbibitions, root pressure and finallytranspiration pull. There is continuous loss of water at the body surface of plants. Thus, it isa unidirectional process. Phloem's main function is to transport food from source to sink where source implies withthe part of plant responsible for synthesising food and sink to those parts and organs thatneeds or consumes food for their growth and development. These source and sink parts ofa plants may vary in different phases of its growth, thus the food need to travel in bothupwards and downward direction. So, phloem shows bidirectional movement ofsubstances.