Actually all the exams that I have taken, bio score has been the lowest. Its funny because bio has always been my strong point and chemistry, both general and orgo, always killed me. So far 5 AAMC exams and in all bio is killing me.
Its seems the tiny details get me. I know the material, but the analysis part gets tricky, and every once in a while there will be a question which was not covered in the book, as rare as it may be, it has happened.
The things you own end up owning you.