For chemistry: www.chemguide.co.uk This is primarily aimed at A Level chemistry but there will be bits in there that may come up on your GCSE chemistry, for example titrations.
If i think of any more I'll PM you
And don't be afraid to go and see other science teachers if you're stuck, they are there to help!
I agree with matt_copas, but to add to it, try getting your hands on some decent science books of your own (if that kind of thing interests you and if you think that it would help your studies). I also do separate sciences and I find that this really helps to ease the frustration of being told "you don't need to know that theory" or "you don't need to know about circulation until A level"!
These books have information on cell and DNA structure (etc.), mitosis and other biological processes as well as information on human anatomy and physiology.