Question

in single celled organisms diffusion in sufficient to meet all the requirements of food exchanges of gases of removed of waste but it is not in case of multicellular organism​

Answer 1

Diffusion is a very slow process. If multicellular organisms used diffusion to meet all requirements of food, exchange of gases or removal of wastes it would take too much of time for carrying even a single particle in the body of the organism and hence diffusion is a process only for unicellular organisms.