Regarding the DAT bio section, LG2DS described it best as an Olympic sized swimming pool that is 1 foot deep.
A lot of random facts to memorize, but it's very broad and not detailed.
On my version of the DAT, out of 40 questions, around 35 were gimmes. Pretty straight forward. But 5 of the questions were insanely detailed that I wouldn't have known them if I studied for another month, some of which were not covered in Cliffs or Kaplan.
So if you are struggling with biology right now, I would skip the C4/CAM metabolism cycle and concentrate on understanding the other biology concepts (and there are many of them!). But if you have a firm grasp on biology and want to score 22+, then you would have to put an exponentially increased amount of effort to memorize all of these things in detail.
The general strategy I've seen on this forum is that they concentrate more energy on the 2 chems, because the scores are easier to be raised, and it'll inflate your Academic Average with lesser effort.