I thought it was pretty similar in difficulty and some questions are very close to the real thing. Other questions on the real DAT can be from out of nowhere. So just have a basic understanding of all the biology you can. I used shuams and it seemed to be very thorough, and a good resourse for this section.
Personally I thought biology section was easier on the DAT then it was in the destroyer, but I guess it depends on the version of test you get.
Good Luck!