Micro Organismsa) Classification, characteristics,(Structure, size, method and rate ofreproduction)b) Normal flora of the body.c) Pathogenesis & common diseases.d) Methods for study of microbes,culture & isolation of microbes. Micro Organisms An organism that is so small that it can only be seen under a microscope (not with the naked eye). Thus, microorganisms are very microscopic, unicellular living organisms. They are not only microscopic but each microorganism has its own distinct existence.