Since only some plants need sodium and those in small quantities, a completely plant-based diet will generally be very low in sodium. This requires some herbivores to obtain their sodium from salt licks and other mineral sources. The animal need for sodium is probably the reason for the highly conserved ability to taste the sodium ion as "salty." Receptors for the pure salty taste respond best to sodium; otherwise, the receptors respond only to a few other small monovalent cations (,  and somewhat to ). The calcium ion (Ca) also tastes salty and sometimes bitter to some people but, like potassium, can trigger other tastes.
Sodium ions play a diverse and important role in many physiological processes, acting to regulate blood volume, blood pressure, osmotic equilibrium and pH.