convergent evolution - called analogy
a potential source of confusion in constructing a phylogeny is similarity between organisms that is due to convergent evolution - called analogy - rather than to shared ancestry. thus for mammals, the backbone is a shared ancestral character, a character that originated in an ancestor of the taxon
This is extremely vague, but assuming this is regarding concentration gradient in the nervous system, the Sodium-Potassium pump is responsible for transporting sodium and potassium.
