The key concepts in Part 1 are briefly reviewed. Organisms in the Protista Kingdom are virtually all single-celled. Most are heterotrophic, some are autotrophic like algae, a few like euglena are both. Most reproduce asexually, but occasionally some also sexually which produces genetic variation and long term evolutionary benefits. All cells, whether as single-celled Protistans, or in multi-cellular Plants, Animals and Fungi, have nuclear and other internal structures with basic similarities.
Bacteria in the Eubacteria and Archaebacteria Kingdoms, however, have very different nuclear and internal structures, each in their own way, from the cells in the other 4 Kingdoms.
Eubacteria vary considerably in shape and structure. Some are autotrophic like cyanobacteria, others heterotrophic. Reproduction is usually by mitosis.
Recent research has found that archaebacteria are so different structurally and bio-chemically from Eubacteria, that they warrant a separate Kingdom. Archaebacteria live in the kind of extreme environmental conditions that existed in primeval Earth, and can convert inorganic chemicals into energy.
New DNA sequencing reveals three quite distinct evolutionary lineages for all life forms which now leads to another broader classification of three Domains: all life forms with eukaryotic cells, those in the Plant, Animal, Fungi, and Protista Kingdoms, are placed in the Domain Eukarya; those in the Eubacteria Kingdom which all have prokaryotic cells belong in the Domain Bacteria; and those organisms in the Archaebacteria Kingdom which all have prokaryotic cells are placed in the Domain Archae.
Finally, the hierarchical classification from Kingdom to Species, is briefly presented. Because viruses do not have the capability of an independent cellular life, they are included in neither the Kingdom nor Domain classifications.