I have a strong (not necessarily correct) opinion on this subject, so take it for what its worth to you.
Biology can be a biootch, or it can be a blessing.
First of all, they can pretty much ask you about anything on earth, so get as many practice questions in as you can. I actually read texts from anatomy, physiology, microbiology, cell bio, zoology, genetics, botany, evolution etc.. Like I said they have a wide array of questions that can be asked a million different ways.
Second, pray that you don't get a wierd version of the DAT. I have two pals that had about ten questions on plants on their DAT. They never had any botany classes or anything like that. They came out with a 15 and 16. I had one, but a ton of evolution and taxonomy questions with systems and evolutionary histories, cladograms, etc. So mine was more animal based, with a mix of anatomy and physiology. I came out with a 21, which I figured was missing about 5-8 questions.
Third, you can be guaranteed to get a handful of questions on cellular respiration, so know it inside and out, don't just memorize!
I hope that helps, good luck, apply early next year!