How do Unicellular organisms get and get rid of substances in order to live?

Why can multicellular organisms not get and get rid of substances via diffusion?

What do the xylem tubes transport?

How do xylem tubes transport water and mineral salts?

What do phloem tubes transport?

What is the movement of food substances around a plant called?

How are root hairs adapted to take in water?

Water is taken in to the root hairs by which process?