The way you learn is not by reading information; you learn by retrieving it and producing it. This builds neural pathways (memories). The more you retrieve the memory, the more you will remember it. Here are some ideas;
1. Make some flashcards by writing key points from the pages you need to learn and ask a friend/relative to test you on what's on them, e.g. "Topic" is the question, "Bacteria etc." is the answer, or have a key phrase written on the front and the explanation on the back; the friend holds up the card so you can see the front and they can see the back, thus testing your memory
2. Visualise an image that is tailored to the thing you need to remember, e.g. a painting of a certain chemical reaction that you have made in your mind. Whenever you look back at that memory, you'll remember the reaction.
3. Talk through the material with a friend; talking helps evoke memories that you may have forgotten, and you will have digested the information and remembered without realising you've done it! Therefore, talking about it and teaching it to a friend can help you remember it also
SP