How did I not see that before I took the MCAT??? Oh well. Are you asking about a prompt bank, or a bank of topics to have in mind for answering the prompt. If the latter, you are way better off developing your own bank of examples, since they will be personally meaningful to you. It could be the economic downturn, the origin of calculus, stem cell research, just 2 or 3 areas that you find interesting. Then flesh them out and practice using them as examples for various prompts.