How do you explain the amphoteric behaviour of animo acids?

Explanation

Amino acids exist as zwitterion. In acid medium `-COO^(Θ)` group of the zwitterion accepts a proton to form a cationic species while in the basic medium, `-overset(oplus)(N)H_(3)` group loses a proton to form an anionic species.

Thus `-overset(oplus)(N)H_(3)` group acts as the acidic group, while `-COO^(Θ)` group acts as the basic group thereby justifying that amino acids exhibit amphoteric behavious.