The Three Domains Of Life

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Until as recent as the nineteenth century, biologists have categorized organisms into two different kingdoms, Animalia and Plantae. With supporting evidence, researchers have concluded that there are three distinct domains, Domain Bacteria, Domain Archaea, and Domain Eukarya. Bacteria and Archaea are classified as Prokaryotes and Domain Eukarya are classified as Eukaryote. As stated earlier, Domain Bacteria are prokaryotes, and they are the most common of all living organisms. Many are classified as decomposers, and live almost everywhere. Although bacteria is associated with causing human and animal disease, the opposite it true. Many species of bacteria can be beneficial by helping to digest food. By their presence in the lower intestine of most animals and humans, their enzymes contribute to the break down of food. Also many species of bacteria aid in the development of antibiotics, such as penicillin, and many aid in keeping away harmful bacteria by competitive exclusion. Domain Archaea are also prokaryotes and were once grouped with domain bacteria, but in the late 1970s, researchers had sufficient evidence to conclude that they were two distinctly different groups. Archaea are known to inhabit some of the most wildly extreme environments such as natural hot springs, and the digestive tracts of cows, where they produce methane. These organisms are also extremely resistant to antibiotics that affect bacteria, but are susceptible to antibiotics that affect the eukaryote. The third domain, Domain Eukarya, contains the four kingdoms, Protista, Plantae, Fungi, and Animalia, all of which are eukaryotes. All kingdoms in domain eukaryote are multicellular, contain a nucleus, where their DNA (deoxyribonucleic acid) is stored, and they have a complex cell structure, complete with organelles. Protists are mostly single celled organisms that include algae,
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