Based on what we have learned so far in microbiology from Module 1: Introduction to Microbes & Tools to Study Them, Module 2: Prokaryotes, Module 3: Eukaryotes, Module 4: Viruses, Module 5: Microbial Nutrition, so for, which concept did you struggle the most with? After your post review your classmate's "challenging concepts" and pick one to respond to. Also need citation of concept.