How would you explain the difference between diffusion and facilitated diffusion?
The main difference is that diffusion does not involve particular structures while facilitated diffusion does.
Diffusion refers to the movement of molecules along concentration gradient(i.e. from higher concentration to lower concentration). e.g. movement of small molecules like water across cell membrane.
However, unlike water, larger molecules cannot simply diffuse in and out of cell through plasma membrane and require specific structure to help them move. These are transport proteins also called carrier proteins.