I've found this is true for humanities as well, not just sciences. Ive always had a bad memory compared to others and so needed to be concise and precise in what I learnt ( which I actually think helped me in the long run )
Just make sure that you have knowledge that specifically links to each syllabus point, but you have to be prepared to express it differently or link between different ideas. The only good ways I've found to improve this is just lots of past papers and mindmaps. I know that there were often people who knew far more knowledge than me but I still way outperformed them by being more adept at answering specific questions on exam days, because I had a core of key ideas and knew how to make them relevant to any question.
Regularly hand stuff in to your teachers and if they are good follow the feedback religiously, which will help to get an idea of what that relevant knowledge is.
