h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Recently (not sure when) there became 6 kingdoms: Animalia, Plantae, Fungi, Protista, Bacteria, and Archaea. Both bacteria and archaea are prokaryotic, unicellular organisms but there are which I could not tell you because I am only in high school biology but just incase someone wanted to look in depth into this. The archaea are a kind of bacteria that survive in extremes such as hot springs, or springs with high acidity.

Nearly bit archae (of old called archaebacteria) are not a kind of bacteria at all, that's why they're now in a different kingdom
They just seem like bacteria as they are single celled prokaryotes, their cellular make up is quite different though. Also, although some do live in extreme temperatures, there are plenty that don't also.