Absolutely study on a rotating basis. Most prep courses and books are unwisely formatted in that they cover Physics 1 or Biology 1 in an early chapter and then NEVER return to those topics. On exam day you could be months and months distant from when you covered those topics. Also, think about your exam day. You are going to be tested on ALL of the topics, not just a chapter or subject area. In fact, on MCAT-2015 the subjects are so cross-disciplinary you will be doing biochem on both BB and CP, doing biology on 3 of the 4 sections, facing a physical science question mixed into a biological passage, and so forth. Train your brain now to learn the way you'll be tested by moving somewhat randomly between topics and regularly reviewing ALL topics. Evidence strongly suggests that you need spaced repetition to get info into long-term memory--or reviews of the same material with time spaced in between. Finally, ALWAYS worth saying...don't get caught up in content! This is a critical thinking exam for which most students spend 80-95% of their time studying content!