Hi there, I achieved A* in Biology last year so I hope that my tips can help.
I also struggled a lot when doing 5 or 6 marker questions, especially the ones that asked to compare and evaluate data. I would rarely get full marks or marks as high as those. I am not sure if this is a general rule for all the 6 markers, but for some mark schemes, they allow the examiner to award marks if they think that your point is relevant even if it isn't stated in the mark scheme itself. Keep in mind that you're probably a harsh maker (which is better than the alternative!) but from my experience, the examiners were more lenient in the real exams.
You said that you are practising exam questions which is great! Do you do them only once? If so, after a few days come back to the question and try again. Keep re-doing them until you get it right.
If it is a general 5/6 marker question based on knowledge, I recommend writing the exam questions that you struggled with on a flashcard and the mark scheme on the other side. Use those flash cards to remember what the mark scheme says.
If it is a question asking you to compare or evaluate data, grab a couple of exam questions and look over the mark schemes: is there anything common that they're looking for? e.g. positive/negative trend, specifying changes in data using values from the x and y axes, possible explanations as to why, etc.
I understand that sometimes the mark schemes are worded differently between papers. My teacher told me that if the concept is the same and they understand what you are saying, the examiners will give you the mark. Sometimes the mark schemes would use different key words needed for the mark. Whenever this happened, I would make a flashcard of the question and mark scheme and include both key words until I memorised them. When I sat my exams, I would write "keyword1/keyword2" into my answers. You will get the mark.
The most important advice I give for anyone studying STEM subjects is to do practice questions and exam papers. If you forget something, you can go back to your notes but I would highly recommend making a flashcards out of information. You will remember it better and for longer. You can also use active recall by grabbing a blank sheet of paper and trying to write down everything you remember about a sub-topic (for me, the topics were too big to recall in one session). Trying to remember information forces your brain to make new and longer-lasting connections than re-reading notes or writing them out again. Active recall helped me achieve an A*.
From my experience, the examiners tend to be more lenient when awarding marks than your teachers or yourself. Do as many exam questions as you can, learn from them, take a break, then try again.
- Re-do the exam questions you struggled with
- Make flashcards of those exam questions
- Try to memorise the keywords used in the mark schemes
- Active recall > re-reading or re-writing notes
P.S. I always doubted myself and thought getting A*s was an impossible dream but it happened somehow. You're clearly working hard. I wish you the best.
Hope this helps!