I dont think you need extra classes to do well on the Bio section. I started my bio (after intro bio) getting 8's. Then after reading the commercial MCAT review books, my BIO scores jumped to 12's and occasionally 13's. The only other bio classes I took was molecular bio which is NO help at all. I mean, who needs to know the holliday model for recombination or memorize all those transcription/translation factos hahaha
Physiology- never took it, just learned it from the MCAT prep books...you just need the basics, which were taught in my introductory bio courses
Microbiology- never took it, you just need to know the basic prokaryotic properties, which were also taught in my introductory bio courses
Biochemistry- took this, but didn't think it helped at all, cuz don't need to know useless info like the names and structures of glycolysis and krebs cycle intermediates, or the 20 essential amino acids for the MCAT
the stuff i didn't know i learned from the MCAT prep books and i thought that it worked for me...but taking more bio courses wouldn't hurt, but i'd say take easy classes whie studying for the MCAT. For example, don't take biochemistry while studying for the MCAT, rather take an easier class like microbio...you don't wanna sacrifice your GPA while studying for the MCAT unless you know you can own it.