Having had those undergraduate courses prior to matriculation may help you a bit, especially for FOM. It's nice to have some sort of baseline knowledge so you can more easily, or readily, make sense of the massive amount of information being thrown at you at the beginning of medical school. As such, you could potentially have a bit of a jump at the gate and feel somewhat more at ease.
However, that said, I really wouldn't overestimate their value either. At first, I was sort of regretting that I didn't have any micro, etc., because the learning curve was a bit steeper for me relative to those who had taken some undergraduate micro, but now, I've basically caught up with everyone else. Additionally, my observation is that what little advantange that folks may have from having had taken these undergraduate classes prior may become leveled by the apparent clinical focus of the material covered, or the minutiae of the material tested (whether you have baseline knowledge or not, you still have to do significant work to go over the minutiae).
The bottomline is that everyone has to study hard and it is this that essentially defines how you do in medical school. Success in medical school is multifactorial, but a great deal of it relies on your study habits, in my opinion, and prior knowledge, such as your aforementioned classes, present a pretty minor factor. If you hadn't taken those aforementioned courses yet, I wouldn't rush to take them now. The relevant material you could cover in each undergraduate class would likely be covered in a single 1-hr lecture in medical school. Your time may be better spent on relaxing and enjoying yourself prior to matriculation, since non-study time is a bit scarce when school starts.
