thushan is right. start reading stuff now, so as to familiarise yourself to the content. biology is a very difficult subject, with a lot of content as well as the content itself being somewhat difficult to understand. also, it is a subject about precision and being concise, in which your answers need to be as specific and accurate as possible (this only comes with intensive effort and large scale reading). tsfx and jacaranda are great, but you should also get biozone and have a flick through it before sacs and exams. i was expecting a 70+/75 on the midyear exam, but got only a 67.5/75 because of tonnes of half marks being lost throughout the exam, because my answers werent specific enough, and my wording was too englishy. i had done about 45 prac exams before hand and had completely finished all questions in the jacaranda, heinemman and tsfx books before the exam, as well as corresponding biozone pages. i just wanted to illustrate how difficult this subject really is (i personally find chem only slightly harder than bio mind you).
just dont underestimate the subject, study hard,
DONT STRESS, learn to be specific and concise and you all should pull a 40+, if not a 45+