Bio104 Laboratory ? Student?s Guide John Jay College, C.U.N.Y Lab #4 ? Page 1 Lab #4: Use of the Microscope; Bacteria and Protists I. The Domains of Life A. There are three major branches, or Domains, on the tree of life: Archaea, Bacteria, and Eukarya. B. It turns out that most of the living things on earth, comprising most of the biomass, are microscopic single-celled species! Today we will look at unicellular examples of two different domains: Bacteria and Eukarya. C. Protists are eukaryotes and most (but not all) are single-celled. However, some of the single-celled protest species can exist in colonies that resemble a multicellular organism, but this is not true