Exam paper content/ writing style

I have once seen (from a different learning resource) a response to a question which did not necessarily cite cases or state what the cases entailed; instead the answer just simply superimposed the implied cases with X and Y references by way of explanation.
The question was, What is Past Consideration? Instantly I had began to write down the meaning of past consideration and was already stating the case of Re McArdle – a couple whose claim against other family members was dismissed on the basis of past consideration.

But When I read the answer from the material; whilst it was rich and convincingly good, I was a little unsure and would be interested to know whether one could, in an exam, get away with just saying things like “if X performs an act or service before Y promises X something in return, that consideration is in the past and bla bla bla” without actually citing the related case as a basis for explanation.

I’m not even sure now if I’ve asked this question as clearly as I should, but hey let’s hope I have 🙂