Should I take the AP Biology exam or take bio in college as a prerequisite for nursing school?

If you do not feel you are prepared for more advanced classes in biology, then whether you take AP exams or not, you take the intro biology courses in college.

If you can pass the AP class with a B or higher, take it.  The more knowledge you have the better prepared you will be for university level classes.

You are no obligation, you can still take the first level bio class at the university 

Your college will allow you to place into a higher level class if you pass the test, but won't require you to do so. You can still choose to take the lower level class if that's what feels right to you.

My recommendation would be to take the test now so that you have more options later. If you do pass, you will also transfer in those credits, which might spare you having to take a different class that you aren't interested in.

Often there is a nursing  pre-reg designated level bio class, just one is required. Take it in college, you get good grades and it will help your chances to get into the nursing program.

i would do what you think will work better