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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.

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.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
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Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
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Read this passage from the lesson and answer the questions that follow. Domains The six-kingdom system didn't show that all four eukaryote kingdoms are more closely related to each other than to the two bacteria kingdoms. It also didn't show that the two bacteria kingdoms are as different from each other as they are from the eukaryote kingdoms. To show these similarities and differences, a new taxon, called the domain, was introduced. It was defined as a taxon higher than the kingdom. The Three-Domain System In 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 was formerly 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 and the differences among eukaryotes, bacteria, and archaea. By using domains, these relationships could be shown without replacing the popular six-kingdom system. Archaea were first found in extreme environments. 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 everywhere in high numbers. They may contribute as much 20 percent to Earth's total biomass. The three-domain system was quickly adopted by many other biologists. There were some critics, however, who argued that the system put too much emphasis on the uniqueness of Archaea. Later studies confirmed how different Archaea are from other organisms. For example, organisms belonging to Archaea were found to differ from both Eukarya and Bacteria in the composition of their cell membranes and the system they use for DNA replication. These differences convinced most critics that the three-domain system was justified. After its introduction in 1990, the three-domain system became increasingly popular. Within a decade 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 more similar to Archaea than they are to Bacteria. This suggested the hypothesis that Archaea and Eukarya shared a more recent common ancestor with each other than with Bacteria. However, the results of a study published in 2007 seem to conflict with this hypothesis. Comparing DNA base sequences, the 2007 study suggested that the domain Archaea may be older than either Bacteria or Eukarya. That would make Archaea the most ancient group of organisms on Earth. Which, if either, hypothesis is correct is not yet known. Scientists need to learn more about Archaea and their relationships with other organisms to resolve these questions. 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.
Transcribed Image Text:Read this passage from the lesson and answer the questions that follow. Domains The six-kingdom system didn't show that all four eukaryote kingdoms are more closely related to each other than to the two bacteria kingdoms. It also didn't show that the two bacteria kingdoms are as different from each other as they are from the eukaryote kingdoms. To show these similarities and differences, a new taxon, called the domain, was introduced. It was defined as a taxon higher than the kingdom. The Three-Domain System In 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 was formerly 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 and the differences among eukaryotes, bacteria, and archaea. By using domains, these relationships could be shown without replacing the popular six-kingdom system. Archaea were first found in extreme environments. 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 everywhere in high numbers. They may contribute as much 20 percent to Earth's total biomass. The three-domain system was quickly adopted by many other biologists. There were some critics, however, who argued that the system put too much emphasis on the uniqueness of Archaea. Later studies confirmed how different Archaea are from other organisms. For example, organisms belonging to Archaea were found to differ from both Eukarya and Bacteria in the composition of their cell membranes and the system they use for DNA replication. These differences convinced most critics that the three-domain system was justified. After its introduction in 1990, the three-domain system became increasingly popular. Within a decade 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 more similar to Archaea than they are to Bacteria. This suggested the hypothesis that Archaea and Eukarya shared a more recent common ancestor with each other than with Bacteria. However, the results of a study published in 2007 seem to conflict with this hypothesis. Comparing DNA base sequences, the 2007 study suggested that the domain Archaea may be older than either Bacteria or Eukarya. That would make Archaea the most ancient group of organisms on Earth. Which, if either, hypothesis is correct is not yet known. Scientists need to learn more about Archaea and their relationships with other organisms to resolve these questions. 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.
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