Explain why xylem transport is unidirectional and phloem transport bidirectional.
The plant part which synthesise the food, i.e. leaf known as source and part that needs or stores the food called as sink. Food, primarily sucrose, is transported by vasculai tissue phloem, from a source to a sink. But depending on season or plants need, the source sink may be reversed. Sugar stored in roots may be mobilised to become a source of food source in early spring when buds of trees require energy for their growth and development and act as sink. Since the source – sink relationship is bidirection in phloem while in xylem it is unidirection.
