For the PS and BS you can usually answer the questions without reading the passage if you have a good understanding of the topic.
This was a question I did on my last practice exam, "what is a start codon?" You should know that it is, AUG. The passage will not tell you what the each codon stand for, but it does give you a background on DNA sequences and Codons.....
That said, it's very important to read the passages because most of the time they have the answers in them. Don't bother reading the questions then reading the passages; you'll just be wasting time.