Kingdom

The term kingdom is one of the seven major classification groups that biologists use to identify and categorize living things. These seven groups are hierarchical or range in order of size. The kingdom group is the first and largest group. The classification scheme for all living things is: kingdom, phylum, class, order, family, genus, and species.

As the broadest of all classification groups, kingdom is made up of phyla (singular, phylum). From the time of Greek philosopher and scientist Aristotle (384–322 b.c.) to the mid-twentieth century, only two kingdoms were recognized—Animalia (animal) and Plantae (plant). However, with increasingly modern and sophisticated techniques, biologists eventually came to recognize a five kingdom approach. These additional kingdoms were necessary in order to include other forms of life that did not belong in either the plant or animal kingdom. Today, the five kingdoms are monerans, protists, fungi, plants, and animals.

Monera, the smallest kingdom (with only about 4,000 species), includes the prokaryotic bacteria (single cells that do not have a nucleus) and certain types of algae. Bacteria play an important role as decomposers, and some monerans can make their own food through photosynthesis. Organisms in the kingdom Protista are eukaryotic (their cells contain a nucleus) but are both plantlike and animal-like. Some algae and protozoans are protists. The kingdom Fungi consists of molds, yeasts, and mushrooms. These are all multicelled organisms that live by absorbing food. Although these organisms look like plants, they do not make their own food. Members of the kingdom Plantae make their own food and often grow flowers and form seeds. The kingdom Animalia includes multicelled organisms that live by taking in food. Animalia is made up of vertebrates (animals with a backbone) and invertebrates (animals without a backbone). This is the largest kingdom, containing more than 2,000,000 species.

[See alsoClass; Classification; Family; Genus; Phylum; Species ]