senior science is similar to the sciences you did in yr7-10. That is, each term, you do a different topic so it pretty much has an overview of science. Unlike Bio or chem, senior science is more general and focuses more on the practical components of science, relating it to what you would see in real life. Eg. in lifestyle chemistry you would look at soaps, rather than at atoms. In Medical Biotechnology, you would look at joints etc.
BTW, prelim bio is a very very dry, and boring. It gets much better in HSC biology, much more interesting, but it does require you to memorise alot of the course. But most sciences require you to memorise alot.
Hope that helped =)
