If its random, its random. You can't help it, you can just hope for the best and put in all your effort. Bio is random, but that shouldn't shake your confidence...besides worst case scenario you'll get 2 points lower in Bio than you might on a good day so it shouldn't make too much of a difference.
When people say its random, they just mean its a vast subject. There are any number of nuanced questions that the DAT writers can pull from any corner of biology. Just off the top of my head they could ask something like
Which of these has cristae?
a) Chloroplasts
b) Mitochondria
c) Rotifers
d) Rough Endroplasmic Reticulum
e) Small intestine
Cristae aren't important, but you could be asked some question about it. That is what people mean when they say its random. Fortunately, even the WORST bio test will only have 3-5 of such bizarre questions. Like I said, if you prepared well, you'll do well! Be confident and try your best.
