okay,
take this advice with a grain of salt: when I was taking Kaplan courses, my MCAT prof knew I was shooting for at least 10's. I asked her how many I should get right in each section, and she told me that if you get above 75% in each section, then you're in very good shape. I found that advice to be very true, because after about a month of practise, I noticed that as long as I got anywhere close to a 75% of questions right, my score usually turned out to be at least a 10.
Not sure if this will work on AAMC and other tests too.
Also, don't forget that tests are scored on a curve. A harsh biology curve is only to be expected because MOST people that apply to med school are bio majors and excellent in their own field. My own mCAT had a harsh curve for Bio. Sci and I expect others may attest to this also. Anybody else with conflicting opinions?