Technically speaking I think they can ask something like that - although I think it would definitely be a curveball if they did.
With regards to representative government I guess a weakness could be something along the lines of political influence influencing Parliament and MPs being scared to pass controversial but necessary laws out of fear of being voted out of office.
With responsible government, it's a bit more tricky - but you could similarly argue that due to public scrutiny, MPs can be reluctant to pass controversial but necessary laws. You might also be able to suggest that public scrutiny makes it more difficult for Parliament to 'get things done', and that things like question time take time away from the law-making function of Parliament.
Regarding the separation of powers, you could argue that since there is some crossover, there could be a conflict of interest.
Like I said, it would surely trip a lot of people up, but fingers crossed they don't ask it!