At WikiPremed taxonomy and photosynthesis are listed as optional . Those topics aren't central to the course. There won't be any questions on the MCAT that depend on prior factual knowledge. However, I still think these major scientific topics are useful to browse over if you are not too pressed for time. While you don't need the animal phyla for the MCAT, taking a no-pressure look through them will help flesh out your understanding of things like animal tissues and embryological development. With photosynthesis, while you don't need to stress out about the Calvin cycle, reading through as a test of comprehension is good practice for biochemistry passages where prior knowledge is often not the issue but what is important is your ability to put unfamiliar knowledge into the context of deeper principles. Of course, looking at photosynthesis will also deepend your understanding of oxidative metabolism.
You have to make judgement calls. The deeper you go and the more articulated your knowledge base the better, but you don't want to neglect Solution Chemistry for Taxonomy.
