Although I think you should take biochem anyways because it's a good class, some medical schools will allow you substitute biochem for the second semester of orgo. I'm not sure if this will help you in anways, but if you find yourself in squeeze for time, this might prove to be of some use.
Do you mean Plant Diversity? Regardless, it's not a prerequisite that I've seen or heard of. Perhaps it may be at your school, so verify with either advisor (be careful though, some of them don't know anything) or your course catalog. Unless you're on a quarter system, and yo're referring to the Plant quarter of the 1-year biology sequence. If that's the case, you have to take it because it a required prerequisite for med-schools.