When you get to the stage where you are able to do past papers, you'll gradually gain an understanding of what the bio marking guidelines are like. It is literally like a checklist, it is super formulaic (so it is easy to lose marks doing silly things like not defining key words). In the HSC I always answered in dot points. They were still full, fleshed-out sentences, but I used a dot point for each 'point' of my answer. Basically a dot point for everything I thought would be worth a mark. This strategy made me answer the questions much more directly, clearly, and concisely, you don't need to waffle on and worry about the flow of your sentences so much. I never used any extra space, and my handwriting was pretty large! You don't need to be writing essays. For super long questions, use subheadings too! Make it easy for the marker to go straight off of their checklist.