18.3 Kingdom & Domains I. Updating Classification Systems A. From 2 to 5 Kingdoms 1. only Plantae & Animalia to start 2. by 1950 Monera, Protista, & Fungi added B. 6 kingdoms 1. In 1990’s Kingdom Monera questioned 2. Then split into Eubacteria & Archaebacteria
II. The Three Domain System A. Major Characteristics 1. Cell Type: prokaryotic or eukaryotic 2. Cell Walls: absent or present 3. Body Type: unicellular or multicellular 4. Nutrition: autotroph or heterotroph B. Domain Bacteria 1. equivalent to Kingdom Eubacteria 2. prokaryotes that have a strong exterior wall & a unique genetic system
3. All similar in structure, with no internal compartments. 4. Most abundant organisms on Earth & found in every environment. C. Domain Archaea 1. equivalent to Kingdom Archaebacteria. 2. chemically unique cell wall & membranes, & a unique genetic system 3. evolved in a separate lineage from bacteria early in Earth’s history 4. some archaea eventually gave rise to eukaryotes.
5. Were first found in extreme environments a. ex. - salt lakes, the deep ocean, or hot springs that exceeded 100°C. b. These are called extremophiles 6. Methanogens live in oxygen-free environments. D. Domain Eukarya 1. Made up of Kingdoms Protista, Fungi, Plantae, and Animalia. 2. complex inner structure allowed cells to become larger than earliest cells.
3. Utilize true multicellularity & sexual reproduction 4. Plantae a. autotrophs that use photosynthesis b. cell wall is made of cellulose c. More than 350,000 known species 5. Animalia a. multicellular heterotrophs. b. lack a rigid cell wall. c. More than 1 million known species
6. Fungi a. heterotrophs, mostly multicellular. b. cell wall is rigid material called chitin. c. more closely related to animals than to any other kingdom. d. More than 70,000 known species 7. Protista a. a “leftover” taxon, so it is a diverse group. b. did not descend from a single common ancestor. c. More recently, biologists have proposed to replace Protista with several new kingdoms.