The six kingdoms of living organisms are Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia. Each organism is placed into one of these six kingdoms based on specific characteristics, such as cell type, metabolic processes and mode of reproduction.
Organisms in each kingdom share certain traits. For example, Archaebacteria are the most primitive of living things, and are all single-celled organisms that tend to live in extreme environments, such as in hot springs and thermal vents. Archaebacteria are prokaryotic organisms, and reproduce by budding or through binary fission. Eubacteria are slightly more complex than Archaebacteria. They are still single-celled, but their cells are eukaryotic, which means that each cell has a nucleus and formed organelles. Eubacteria also reproduce through binary fission.
Organisms in the kingdom Protista may be multicellular or unicellular. Some protists produce their own food, while others obtain nutrition through ingestion or absorption. Fungi, which include unicellular yeasts as well as multicellular mushrooms and molds, obtain their food through absorption. Organisms in the kingdom Plantae are capable of producing their own food through photosynthesis. This kingdom includes more than 25,000 species of plants. Kindgom Animalia, however, is the largest kingdom, with more than 1 million known species. Animals are all heterotrophs, which means that they obtain their food by ingesting other organisms or parts of organisms.