Life is divided into five kingdoms
An old model or guideline was retired in favor of a new one.
TaughtAll living things belong to one of five kingdoms: Animalia, Plantae, Fungi, Protista, and Monera.
NowCarl Woese's three-domain system, proposed in 1977 and formalized in 1990, puts Bacteria, Archaea, and Eukarya at the top level. Archaea turned out to be as different from bacteria as you are.
What actually happened
Robert Whittaker's five-kingdom scheme from 1969 organized life by what organisms look like and how they feed. It was intuitive and it dominated school biology for decades.
Carl Woese did something different: he compared ribosomal RNA sequences, reading the molecular record instead of the anatomy. He found that the organisms lumped together as "Monera" contain two lineages that diverged so long ago they are less related to each other than either is to us. Archaea are now recognized as a separate domain, and eukaryotes appear to have emerged from within them. The old five-kingdom chart also collapsed for another reason: Protista is not a real group, just a bucket of everything left over. If your textbook had a neat five-branch diagram, it has been replaced by a bushy tree with a far stranger shape.
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Who was taught this
Still standard through 1998, so anyone who finished school between 1950 and 1990 learned the earlier version.