Q.Explain, in one line, why an amino acid is described as amphoteric, and name the dipolar ionic form it takes at physiological pH.

[!TLDR]

An amino acid is amphoteric because it carries both an acidic carboxyl group and a basic amino group; at physiological pH it exists as a zwitterion.

[!ANSWER]

An amino acid is amphoteric because it carries both a basic amino group and an acidic carboxyl group on the same molecule, so it can act as either an acid or a base; at physiological pH it exists as a dipolar ion called a zwitterion.

An amino acid is described as amphoteric because it possesses both a basic functional group (the amino group, -NH2) and an acidic functional group (the carboxyl group, -COOH) within the same molecule, allowing it to react as either an acid or a base depending on the surrounding pH. At physiological pH, both groups are ionised at once -- the amino group gains a proton to become positively charged and the carboxyl group loses a proton to become negatively charged -- so the molecule as a whole carries no net charge and is called a zwitterion (dipolar ion).

[!ANSWER]

An amino acid is amphoteric because it carries both a basic amino group and an acidic carboxyl group on the same molecule, so it can act as either an acid or a base; at physiological pH it exists as a dipolar ion called a zwitterion.

Recall that "amphoteric" means able to act as both acid and base, then connect this directly to the amino acid's two opposing functional groups and the resulting zwitterion form.

Forgetting to name the resulting dipolar form (zwitterion) after explaining why the amino acid is amphoteric.