Practice some lines and try to say them as passionate as possible like if they might ask you about your subject selection
"The subject I'm most passionate about is physics. In particular the conflict between the wave and particle model. It really interests me how de Broglie showed that everything, even humans have a wavelength. Interesting fact he has the same birthday as me."
Maybe a bit thick, but it would show your interests in the subject.
Be aware of what to answer to the question "Tell me 3 of your weaknesses".
Nothing is more impressive than being able to admit weaknesses and mistakes while being under pressure.
In year 7 I won a science competition in chemistry, the end of the speach of the judges at the ceremony was "Even under the high pressure of the interview he was able to admit a mistake he made "Oh I missed a pi" " - (We had to write a 15 pages report on our project and I had a formula of some volume stuff (can't remember) they asked me something on the same page as the formula and I said that sentence)
I did a practice run of answering a few questions from
Studential and I stuttered too many times or just thought too long on answering the question..
Subject selection is drilled into me (Asian Five) so that'll be a good thing for me to use

As for 3 weaknesses? I can admit list a few off the top of my head but that's a good question actually

Just show them that you're passionate in science (which you clearly are) but don't overdo it, and don't talk too much 
I didn't even mention anything related to science besides which fields I enjoyed most, and what I wanted to do in uni. To this very day I still wonder how I got in after that terrible interview.... guess my portfolio saved me 
Also they might ask you to describe a scenario in which you achieved/did something, what sacrifices you would make by coming to this school and of course the typical "Why do you want to go to JMSS" question
Phew.. luckily AN has helped me become more educated in how to reach my goals and stuff at uni

Though this year is really different to other years since my year there were 1000+ people trying out and it's really competitive..
For the sacrifice question.. would I be able to say I rejected MHS because of financial situation and then lead to answering the question?
If you get asked what your greatest weakness is, if you make an "off the cuff" remark about how you struggle in interviews, it's a great opener
Wow this is good stuff :DD
I guess I can use this and just hope that I don't freak out on the day :S