Systematics is a dynamic science in which new data continuously change how scientists classify organisms. The Greeks classified organisms into two kingdoms: Plantae and Animalia. In 1866, a German biologist proposed a third kingdom, Protista, for bacteria and microorganisms. In 1937, a French marine biologist coined French versions of our terms "prokaryote" ("before nucleus") for bacteria and "eukaryote" ("with nucleus") for all other organisms. A more recent classification system was proposed in 1969 by an American plant ecologist. This system consisted of five kingdoms, with fungi in their own kingdom and bacteria in the kingdom Prokaryotae. Modern molecular biology and sequence analysis of ribosomal RNA resulted in the current classification system, which comprises three domains and six kingdoms. Today, scientists group the bacteria into two groups: the Archaebacteria and the Eubacteria.

Click the button below to explore the content of the tutorial. Be sure to click the buttons along the top of the interactive diagram to see the other screens. When you've finished your exploration, simply close the pop-up window and proceed by clicking the 'next' or 'back' buttons.