In all honesty, I wasn't very good at bio. I found it tough to memorise all of the content as I didn't enjoy most of mod 5 and 6. From what I have learned in other sciences, however, the long responses need time. Spending just a few minutes planning a response for a 7-9 mark question is extremely helpful. If you are running out of time, it is probably best not to do this as relevant information will usually get you a few marks, say 3/9, which is better than 0. As far as the rest of the exam, I don't really have any advice other than to be specific in your responses and to read questions carefully so you don't miss out on anything.