It's v. its

This is simple enough. Do you write  That is hi’s car? Of course not. His has no apostrophe, neither does hers, my, yours or any of the possessive pronouns. Therefore  its as a possessive pronoun (The dog is biting its own tail) has no apostrophe either.

It’s means it is. The apostrophe stands for to the missing “i” from "is" just as in “don’t” the apostrophe stands for the missing “o” from "not".