Read this passage from the lesson and answer the questions that follow.DomainsThe six-kingdom system didn't show that all four eukaryote kingdoms are more closely related to eachother than to the two bacteria kingdoms. It also didn't show that the two bacteria kingdoms are asdifferent from each other as they are from the eukaryote kingdoms. To show these similarities anddifferences, a new taxon, called the domain, was introduced. It was defined as a taxon higher than thekingdom.The Three-Domain SystemIn 1990, a new classification system was introduced that contained three domains: Bacteria, Archaea,and Eukarya. The Bacteria domain was formerly the Eubacteria kingdom, and the Archaea domain wasformerly the Archaebacteria kingdom. The Eukarya domain includes all four eukaryote kingdoms: plants,animals, protists, and fungi. The three-domain system emphasizes the similarities among eukaryotes andthe differences among eukaryotes, bacteria, and archaea. By using domains, these relationships could beshown without replacing the popular six-kingdom system. Archaea were first found in extremeenvironments. For example, they were found in the hot water geysers in Yellowstone National park.Archaea have since been found in all of Earth's habitats. They are now known to be present everywherein high numbers. They may contribute as much 20 percent to Earth's total biomass. The three-domainsystem was quickly adopted by many other biologists. There were some critics, however, who arguedthat the system put too much emphasis on the uniqueness of Archaea. Later studies confirmed howdifferent Archaea are from other organisms. For example, organisms belonging to Archaea were found todiffer from both Eukarya and Bacteria in the composition of their cell membranes and the system theyuse for DNA replication. These differences convinced most critics that the three-domain system wasjustified. After its introduction in 1990, the three-domain system became increasingly popular. Within adecade of its introduction, it had largely replaced earlier classifications.How Are the Three Domains Related?Comparisons of ribosomal RNA base sequences showed that organisms belonging to Eukarya are moresimilar to Archaea than they are to Bacteria. This suggested the hypothesis that Archaea and Eukaryashared a more recent common ancestor with each other than with Bacteria. However, the results of astudy published in 2007 seem to conflict with this hypothesis. Comparing DNA base sequences, the 2007study suggested that the domain Archaea may be older than either Bacteria or Eukarya. That wouldmake Archaea the most ancient group of organisms on Earth. Which, if either, hypothesis is correct is notyet known. Scientists need to learn more about Archaea and their relationships with other organisms toresolve these questions.Questions1. Where does the domain fit into Linnaean taxonomy?2. Why was there a need for the domain?3. List the domains of the three-domain system.4. What kingdoms are included in each of the three domains?5. State two current hypotheses about how the three domains are related.

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Domain system in biology is a classification system developed by Carl Woese in the 1970s to organize…

Questions 1. Where does the domain fit into Linnaean taxonomy? 2. Why was there a need for the domain? 3. List the domains of the three-domain system. 4. What kingdoms are included in each of the three domains? 5. State two current hypotheses about how the three domains are related.