Question

explain why do multicellular organisms need a trnsportation system for carrying food and oxygen ?

Answer 1

Large multicellular organisms have small surface area to volume ratio. They cannot carry out simple exchange of nutrient and wastes. If there is no transport system, cells in the inner part of the organism would starve or be poisoned by their own wastes. So, multicellular organisms need series of tubes through which all materials can be transported.