I felt like I totally wasted my time memorizing all the hormones. I don't think there was even one hormone question on the August exam, and if there was . . . it was only one, and I should have studied other "concepts" more thoroughly. The biology portion of the test was extremelly heavy in interpreting data. I don't know that there's any one concept that would definitely be on the test, or not on the test. You need the basic science information, then you have to be able to interpret information from the passage that will include some information you already know, and a ton of information that you have to extrapolate from the passage. It's really hard to study for. I think if you find yourself memorizing alot, and not understand concepts so much, then you're headed down the wrong path. You need to understand concepts of all the areas included in any MCAT study guide. Obviously there will be a certain amount of memorizing, but make sure you fully understand the concept behind what you're memorizing.