Microbiology (from Greek μῑκρος, mīkros, “small”; βίος, bios, “life”; and -λογία, -logia) is the study of microscopic organisms, which are defined as any living organism that is either a single cell (unicellular), a cell cluster, or has no cells at all (acellular). This includeseukaryotes, such as fungi and protists, and prokaryotes. Viruses and prions, though not strictly classed as living organisms, are also studied. Microbiology typically includes the study of the immune system, or Immunology. Generally, immune systems interact withpathogenic microbes; these two disciplines often intersect which is why many colleges offer a paired degree such as “Microbiology and Immunology”.