I cannot answer those questions with certainty and precision (brains and drugs are my thing). As for what to do after you do exams, i used to do this. I would do exams and note down the questions i got wrong, i would divide them into categories (plants, nervous system, experimental design) and make a tally. It looked a little like this - Plants: II, Nervous System: IIIIIII, Experimental Design: II.
I would use that as a guide to what i needed to learn. I would go back and learn this area in detail again, preferably from multiple sources. This worked because i wasn't the best student and i didn't learn everything by that point. It was more of a time saving measure given urgency to show what i most needed to learn. It will be useful for most students. If you are at the top and only make a few errors, it will not narrow things down as much unless you can work out a concept or area you just plain dont understand. If you're at this top level i guess just try practice as much as you can, answer peoples questions in other threads too for practice.