All individual papers will have their own mark schemes that examines have to adhere to.
The exact make up of the mark scheme will depend on the paper. There will be common elements between questions set from paper to paper but it will not be possible to say, "Each question such-and-such will look for these elements, from paper to paper"
I understand (but could be wrong) that it is possible to buy mark schemes to help with marking past papers.
Basically, though, I think most papers can be marked using 'common sense' i.e. a question worth 10 marks with 5 parts will be worth 2 marks per section. That is how I mark grade 5 past papers.
Steve