Seriously? Anyway, probably not a good idea to start if you haven't learned most the science materials you need to know for the DAT. You can start to practice for gchem after you are done with your Gchem series. For Bio, you probably won't get to touch every single topics until your late sophomore or junior year. Biology contains so much materials to study and anything that is somewhat bio related is a fair game. It includes general bio, physiology, some basic anatomy, biochem, plant bio, microbiology, immunology, genetics etc....But don't freak out, you are actually studying for the DAT when you are taking these courses. You just have to review and practice before taking the DAT. For now, you should just focus on doing well in school.