Biology a level AQA

It is to do with the 25 mark essays.

I have to do a 25 mark essay on the importance of H+ ions in organisms. I was wondering if anyone could help me out with some ideas please?

easy , photosynthesis ETC, aerobic respiration nadh,Ph effect so homeostasis,also ph in haemoglobin and any other enzymes / proteins that's what I could think top of my head right now you can make an essay out of that probably get you 18 20 marks because it was too focused on ph but they cover two different topics