Well PROBABLY but it isn't guaranteed. From my experience it isn't easy to get a band 6 in biology, you have to really know your stuff. I remember doing every past paper multiple choice and getting 18 + in everyone, then in the actual hsc I got 13 because our exam was nothing like the past papers and just tested things in a weird way. So there's no real way of knowing, just do your best x
I didn't take HSC Biology but I have studied it at uni and I tutor several students who study it, with one taking Science Extension this year. You can memorise the syllabus and do your practice papers but this won't guarantee a band 6, as has been said elsewhere in the thread. What is necessary is that you can visualise the processes that are being discussed (particularly in the genetics components, which are more biochemistry than biology if I'm honest) because this will help you actually address the questions asked of you. NESA knows that people think biology is just a 'memory' subject so they throw curve-ball questions quite frequently; imo, more than any of the other science subjects.