My knowledge of biology is good but I never seem to get all the marks on a question - how can I get as many marks as possible?

This is a really common problem of knowing all the knowledge behind the question but still not getting the most marks you can. The best way to manage this is to simply learn the mark scheme; the questions the examiners ask are very similar year on year. Print off a past paper and the mark scheme and write in the mark scheme to the blank past paper. Highlight every sentence or key word which gives you a mark. This will help you to get full marks on all the common questions whilst also helping you to develop your exam technique and see what sort of words and phrases to use to get the most marks overall.