Should I Study the Concrete material before studying the more abstract things for the MCAT? PLEASE HELP!!

Please help!! I am planning on taking the MCAT in September 2021, but as I use the Khan Academy test prep, I realized that sections like the Biological and Biochemical Foundations of Living Systems Passages, Chemical and Physical Foundations of Biological Systems Passages, and Psychological, Social, and Biological Foundations of Behaviors Passages are much harder sections that require prior college-level knowledge. I am in need of a refresh so should I start with the other section such as biomolecules, cells etc. to build knowledge for the harder sections??