Question

why are xylem and phloem called complex tissues? how are they different from one other?

Answer 1

They are because they have more than one type of cells.
Xylem transport water and minerals
phloem transport food

Answer 2

Xylem and phloem are the main components which fulfill the plants requirements like Water and minerals , and food for the plant.
Xylem -Water and minerals
Phloem - food for the plant.