What is microorganisms 4 Microorganisms are creatures that are not directly visible to the unaided eye, with dramatical biologic diversity. Viruses, bacteria, fungi, protozoa and some algae are all in this category All with the exception of plants and animalsWhat is Microorganisms  Microorganisms are creatures that are not directly visible to the unaided eye, with dramatical biologic diversity.  Viruses , bacteria, fungi, protozoa and some algae are all in this category  All with the exception of plants and animals