What did you write for the separation of powers? I remember I lost a mark for it in a weekly practice question because I forgot to mention that there shouldn't be any interference between any of the powers, even though I described the overlap. Make sure you say that the judicial power is entirely separate, too.
For responsible government (along with what Jezza said), you have to say that the ministers are accountable for the actions of their department as well as their own, and any difficulties that arise within those departments are their responsibility. You'd also need to say something about how ministers have to act with propriety and integrity, or resign.
Oh, I almost forgot - ministers are questioned in parliament to ensure that they are running their departments properly.