Kingdoms of Life



Living organisms are incredibly diverse, making their classification a challenge. Modern categorization schemes focus on grouping organisms based on shared evolutionary history. The current system categorizes all life into three domains: Bacteria, Archaea, and Eukarya. Below the domain level, there are six kingdoms of life: Eubacteria, Archaebacteria, Protista, Plantae, Animalia, and Fungi. The two prokaryotic kingdoms include diverse single-celled organisms. The protist kingdom is a grouping of diverse organisms that do not fit into any of the other kingdoms of Eukarya. In fact, these organisms are so diverse that the concept of a Protista kingdom has largely been abandoned by science, and the term is used only for convenience. Fungi are heterotrophs that gain nutrients through absorption. Plants and animals are multicellular eukaryotes. Plants are organisms that can make their own food through photosynthesis, but all animals consume other organisms for food.

At A Glance

  • The tree of life illustrates evolutionary relationships among all organisms as they are currently understood.
  • The modern system for classifying life sorts all organisms into one of three domains and one of six kingdoms.
  • The two prokaryotic domains, Bacteria and Archaea, contain diverse single-celled organisms that exhibit a wide variety of metabolic abilities.
  • Bacteria are small unicellular organisms that obtain food through a variety of processes.
  • Gram staining is a method used to identify, based on cell wall structure, members of the different types of bacteria, such as Proteobacteria, Spirochetes, and Cyanobacteria.
  • Archaea are prokaryotic organisms with a variety of structural and metabolic characteristics that distinguish them from bacteria.
  • Protists are eukaryotic organisms that are not plants, fungi, or animals.
  • Fungi are heterotrophic organisms that have wide-ranging functions as ecological decomposers, sources of nutrition, and the basis of antibiotic medications.
  • Plants are multicellular eukaryotes that are able to photosynthesize.
  • Animals are multicellular eukaryotes that consume other organisms for energy.
  • There are three multicellular kingdoms: Plants, Fungi, and Animals.
  • Viruses are nonliving structures with a genome that infect cells and use their cellular machinery to replicate.