OK, that's good as the Chemistry one seemed quite clear (I don't teach Chemistry, but I glanced at it as a comparator to mine).
So the grade descriptors says what skills you need to demonstrate in your written work for various grades. It's a bit vague, but should at least help students focus on what's needed: in my subject, for instance, it's that they should use a good level of detail in their chains of analysis and that they show strong awareness of alternate points of view, and that their arguments are balanced and supported by evidence.
Now none of that is rocket science but I have got students who persistently assert X leads to Y, without going through all the detailed steps to argue that. So if I were them I'd be practising paragraphs and seeing where I could add more detail of how and why.
So if as a student I noticed I'd had a lot of feedback saying my arguments lacked detail, I'd work on that, for instance, especially in topics that a) the school had said to revise and b) that have some kind of evaluative aspect to them.
I hope that is some help - I don't know Chemistry!