You have to read every chapter, except the lab stuff in the back. The animal form and function chapter is a little weak on the details, so I recommend supplementing with something else like Feralis notes, for example.
Like Ari Said, don't skip anything except lab topics and yes supplement with Feralis. I took the DAT and Bio is very random and detailed...if you skip you may hurt your score because you may see 10 questions on the same topic!