SECTION NUMBER

Knowing and quoting the section numbers with subsection and clause are always good. But at the same time quoting a wrong section or subsection may irritate the examiner and result in disaster.
No hard and fast rule that you've to compulsorily quote subsection and clause, unless the question asks you to do so. So only write the section or subsection if and only if you precisely know it. Else it would be advisable to not quote it.
Hence to answer your question, the examiner won't cut the whole answer and all, for merely not writing subsection and clause. If the answer is correct, even if you've not written the section numbers, appropriate marks will be awarded.