From my point of view, I am doing my GCSE's this year but I take an AS course in General Science by OCR, and to be honest it's detail, and a bit of further knowledge.
I had my AS exam yesterday, revised 2 hours before it, and 3 hours the night before and I'm hoping for an A.
They are not that hard, and I understand I do a mixed science subject so it is nowhere near as specific as the separate sciences, but I still get the general idea that the answers require more detail, and when you look at past papers, simple stuff such as defining respiration will get you 2 marks, but you need to give a more insightful answer then what you would at GCSE.
As for A-Level maths, all the people at school say its either impossible and they are going to fail, or they are going to get an A..