As you may be aware, the biology section covers a massive amount of information; so much, that it is impractical for you to know it all. You have to understand and be comfortable with the fact that you will not know everything on test day. Trust me, you will get some questions which you have never even reviewed.
Fortunately, the test is multiple-choice and there is no penalty for guessing. Therefore, the process of elimination is your best friend. When I came across a question on a topic I had never heard of before, I could still answer correctly by eliminating answer choices I knew were bogus.
There was a great post on the Student Doctor Network forums about how someone had a biology question on the function of metanephridia in worms. I had never heard of this structure, let alone studied worms much at all. But, you can still answer the question if you reviewed the function of kidneys. In kidneys, there are things called nephrons, and their function is to filter the blood and excrete metabolic waste. If you recognize that metanephridia has the root word "nephr" in there, you could deduce that metanephridia have a similar function to nephrons in worms. Indeed, the correct answer choice referred to the metabolic excretion organ in worms.
Spend time studying basic biology you find in AP review books. There is no need to read through 1000+ pages of Campbell Biology. Then, train your mind using the Bootcamp.com to extrapolate your knowledge to questions you're not familiar with. With practice, it'll become second nature. You'll fly through your exam answering questions on anything the test throws at you.