short answer: yes.
honestly, i feel that for bio no matter how much u study...it will never be enough. im sure people who have gotten high 20s might disagree, and no offense, but you prolly either got lucky or you studied wayy wayy too hard. bio is soo random that ANYTHING is fair game. agreed that its the same for gc and oc...but with these subjects, if you have the basic concepts down pretty well...you can do any problem. however, bio doesnt really work that way because there is a LOT more focus on how much you can memorize rather than how much you can reason out if you know a certain amount. and since memorizing the human organ systems has NO relation to memorizing plant systems...u gotta do it seperately. although they won't have more than 3-4 questions about plants...you can't just rule out studying for plants completely because those four questions might be the difference between a 21 or a 26. but in the end...it also depends on what kind of a score you are aiming for...and how much time you have that you can allocate to a particular subject. id say ACE gc and oc...because thats doable...and once ur pretty confident with those...move on to bio and do as much as you can fit in your brain, cuz no matter how much you fit...it will never be enough. hope this helps, gluck!