I often understand the question and think I have answered it correctly, but I don't get all the marks for my answer. What am I doing wrong?

One of the things that you need to remember about Biology A Level is that you have to memorise the key points of the mark scheme. Something that I consistently struggled with when I was doing past papers is that I would write loads for the 4 to 5 mark questions, and yet only get two marks for my technically correct answer because I had missed the key points. I overcame this in two ways. The first was practice, practice, practice. The more past papers I did, the more I started recognising certain styles of questions on each topic, and the easier it was to remember what I answered the last time and, more importantly, what aspects of that answer were on the mark scheme. The second was to take these key points and memorise them. I found that repeatedly writing notes on lined paper worked really well for me, but there are a lot of different ways to do this such as making flash cards and practicing them out loud, or writing on sticky notes and placing these around your bedroom (or house if your parents are okay with that). Now, pick a topic you think this happens often with and let's find a past paper online, then we can work through some questions and I'll help you tailor them to the mark scheme points.