tough practice questions for a level science

hey, does anyone know where to find , preferably free, challenging and hard practice questions on A Level bio chem and physics?
my teachers compose papers of the worst questions imaginable and we are always told to look for difficult questions. I plan on going through AS papers but i dont want to waste whole A Level practice papers.... exam board isn't that important since they mix it anyway, but i do OCR A for bio and chem and Edexcel for physics

For physics A level - the maths and physics tutor website has grouped up lots of questions from past papers according to their difficulty. The Gold papers are the hardest and the Bronze papers are the easiest.

Thank you! But did you mean Maths? I can only find those for maths not physics ?