I think it was really valuable to have Destroyer for BIO, but if you don't have the money for it then DEFINITELY get the 5 practice test book from Cliff's AP bio. You can get it for like $10 on Amazon kindle. I also really liked DAT qVault for Bio. I got a 25 and these were the only sources I used, I never read Kaplan or Barron's or Campbell's. However, I did really well in bio in school and had also taken micro and physio.