I was interested to learn this morning that biologists no longer divide all life into two cellular kingdoms; they divide life into three kingdoms. When I took college biology as recently as the mid-1990s, teachers and textbooks were still stating that all life could be divided into the prokaryotic and eukaryotic cellular kingdoms (we belong to the eukaryotic kingdom because our cells have nuclei among other internal structures that bacteria in the prokaryotic kingdom do not).
The new kingdom was discovered in the late-1970s when research revealed some microorganisms that resembled bacteria but were as different from bacteria as we are. These organisms are the Archaea, and include the interesting little critters of the world that live in the most hostile environments such as hot springs in Yellowstone National Park. The current three kingdom theory of life is only now beginning to show up in textbooks and is not generally taught in schools. I discovered this information on the great The Phylogeny of Life website published by the University of California Berkeley.