The pre-reqs will usually take you four semesters from start to finish. 1  Semester one – Chemistry – Chemistry is a requirement in order to take the actual pre-requisites classes.  Semester two – Microbiology – Microbiology is often seen as one of the more enjoyable classes in the nursing pre-reqs. This class is difficult, but enjoyable at the same time. You could take this class at the same time as Anatomy and Physiology Part One, just remember that you need an “A”.