Whaaaaat, Russ, as if you didn't do VCE Biol.
I know you'll be like 'what input could mavisgibbons possibly have on the matter', but a few of my good friends didn't do VCE Biol and then attempted Biology in Uni. I think that as long as you have realistic expectations of the workload and the effort you need to put in, you will be fine. For example, one friend worked very hard all of last semester and got herself a H1, by preparing for the exam and pracs properly and seeking help when she didn't understand concepts, utilising the textbook and putting in a bit of extra work.
Another friend took Biology as her breadth and had completely unrealistic expectations about how to pass the course. She didn't show up to the majority of lectures, claiming she could make them up by listening to the recordings and reading over the slides later. She slept through two pracs, or rather, she just forgot about that week when both groups A and B do their prac together and was just slack the other time. She didn't purchase the textbook or spend time revising concepts she had learnt in class, and she didn't attend her tutorials. But she was convinced she would be fine, because she understood Genetics.
By Week 8, as I had been saying (behind her back of course, I am lovely!) the entire semester, she became completely overwhelmed and gave up. Despite sitting her MST and going to enough pracs to potentially not fail, she didn't even attempt the examination and has now wasted her 400 and whatever dollars, and will have to take another subject at another time and it's likely her Bachelor will now take more than three years!
So there's a horror story, but yes, it depends completely on how well you can manage doing the course. If you are able to recognise that, without background knowledge, you need to go the extra mile then I don't think you will have a problem keeping up with the workload. But I do remember sitting in my lectures and thinking (for some of the course, not all) 'if I hadn't done VCE Biology, this course would be so hard'. So I genuinely do marvel at those who are able to attempt the course and do well! They must work hard.