Facilitated diffusion therefore allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.
What I know is that amino acid has side chain, amine groupe ,and groupe of carboxyl so what make them difference is side group where the is 20 different R-group which give each individual characteristics