It depends entirely on the question. If it says "acording to Item A" then, if you don't refer to the Item, you won't get the marks. However, this tends to be small mark questions so you won't miss many marks.
If it says "with reference to Item A and other sources" then as long as you made some reference to the Item you'll be fine (and even if you didn't you won't lose anything of any consequence). For higher mark questions students who stick to the Item/s don't generally score highly.
My advice is that it's always easy to worry after an exam that you didn't do what others did - personally I think it's wrong for teachers / students to go over an exam before the marks are known; there's no point and it just creates unnecessary worries. The time to worry is if the result is bad, not whether you should have written something but didn't.