I would suggest you to read few books on “Memory Improvements” for improving you’re remembering power.” My favorite book on memory improvement is written by Harry Lorene and the book name is ‘The Memory Book’. And how about developing a strong passion for studying biology? Both, an improved memory and a strong passion for Biology will definitely help you to get better marks in your biology exam.
Additionally, you can also practice few previous year questions and get it checked by someone [your mentor or teacher] to get an overview on your style of writing and you can also know by this whether your answers are mark fetching or not. And you can follow their instructional according.
I would also suggest you to include diagrams in your answer, if needed. And always try to directly answer the question to the point. So to sum up, we can work on improving our memory and then we must develop a strong passion for studying biology and then we must study biology deeply from all directions. And then the last thing we probably need is nothing but calmness of mind. A clam mind would act as a catalyst for getting better and highest marks in biology examination.