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Chapter 17: Organizing Life’s Diversity Section 1: The History of Classification Section 2: Modern Classification Section 3: Domains and Kingdoms 17.1 The History of Classification Main idea: Biologists use a system of classification to organize information about the diversity of living things. Objectives: Compare Aristotle’s and Linnaeus’s methods of classifying organisms. Explain how to write a scientific name using binomial nomenclature. Summarize the taxa in the biological classification 17.1 The History of Classification Review Vocabulary Morphology: the structure and form of an organism or one of its parts New Vocabulary: Classification Taxonomy Binomial nomenclature Taxon Genus Family Order Class Phylum Division Kingdom Domain Early Systems of Classification Biologists find it easier to communicate and retain information about organisms when the organisms are organized into groups. Classification is the grouping of objects or organisms based on a set of criteria. Biologists use a system of classification to organize information about the diversity of living things. Aristotle’s System More than 2000 years ago, Aristotle developed the first widely accepted system of biological classification. Aristotle classified organisms as either animals or plants. Animals were classified according to the presence or absence of “red blood.” Animals were further grouped according to their habitats and morphology. Plants were classified by average size and structure as trees, shrubs, or herbs. Aristotle’s System System useful for organizing but it had limitations. It did not account for evolutionary relationships. Many organisms did not fit easily into Aristotle’s system; such as birds that don’t fly or frogs that live on both land and water. Many centuries passed before Aristotle’s system was replaced by a new system that was better suited to the increased knowledge of the natural world. Linnaeus’s System In the 18th century, Carolus Linnaeus broadened Aristotle’s classification method and formalized it into a scientific system. Like Aristotle, he based his system on observational studies of the morphology and the behavior of organisms Linnaeus’s system of classification was the first formal system of taxonomy. Taxonomy is a discipline of biology primarily concerned with identifying, naming , and classifying species based on natural relationships. A branch of the larger branch of biology called systematics Systematics is the study of biological diversity with an emphasis on evolutionary history. Linnaeus’s System Linnaeus’s method of naming organisms, called binomial nomenclature, gives each species a scientific name with two parts. The first part is the genus name, and the second part is the specific epithet, or specific name, that identifies the species. Latin is the basis for binomial nomenclature. Biologists use scientific names for species because common names vary in their use. Binomial Nomenclature Common names that lead to confusion: Woodchuck or Groundhog Starfish are not fish Great Horned Owls do not have horns. Sea Cucumbers are not plants Scientific names eliminate confusion Instead of a redbird, cardinal or Northern cardinal having different names in different regions of the US, Linnaeus gave this bird its scientific name: Cardinalis cardinalis. Rules of Scientific Names The first letter of the genus name always is capitalized, but the rest of the genus name and all letters of the specific epithet are lowercase. If a scientific name is written in a printed book or magazine, it should be italicized. When a scientific name is written by hand, both parts of the name should be underlined. After the scientific name has been written completely, the genus name will be abbreviated to the first letter in later appearances (e.g., C. cardinalis). Modern Classification Systems Evolution added a new dimension to Linnaeus’s classification system. Organisms were no longer classified on the basis of morphological and behavioral characteristics alone. Evolutionary relationships are included in modern classification systems. Taxonomic Categories A nestedhierarchal system-each category is contained within another, and they are arranged from broadest to most specific. Species and Genus A named group of organisms is called a taxon (plural, taxa). A genus (plural, genera) is a group of species that are closely related and share a common ancestor. Example American black bear – Ursus americanus Asiatic black bear – Ursus thibetanus Family A family is the next higher taxon, consisting of similar, related genera. Example All bears, both living and extinct species, belong to the same family, Ursidae. All members of the bear family share certain characteristics: they all walk flatfooted and have forearms that can rotate to grasp prey closely. Higher Taxa An order contains related families (Carnivora). A class contains related orders (Mammalia). A phylum or division contains related classes. The term division is used instead of phylum for the classification of bacteria and plants. The taxon of related phyla or divisions is a kingdom. The domain is the broadest of all the taxa and contains one or more kingdoms. Systematic Applications Scientists who study classification provide detailed guides that help people identify organisms. Many times a field guide will contain a dichotomous key, which is a key based on a series of choices between alternate characteristics. 17.2 Modern Classification Main idea: Classification systems have changed over time as information has increased. Objectives: Review Vocabulary Compare and contrast species concepts Describe methods used to reveal phylogeny Explain how a cladogram is constructed Evolution: the historical development of a group of organisms New Vocabulary Phylogeny Character Molecular clock Cladistics cladogram Determining Species Typological species concept Aristotle and Linnaeus thought of each species as a distinctly different group of organisms based on physical similarities. The definition of species is called the typological species concept. Based on the idea that species are unchanging, distinct, and natural types. Biological Species Concept The biological species concept defines a species as a group of organisms that is able to interbreed and produce fertile offspring in a natural setting. Limitations: Wolves and dogs, as well as many plant species, are known to interbreed and produce fertile offspring even though they are classified as different species. Does not account for extinct species or species that reproduce asexually However, because the biological species concept works in most everyday experiences of classification, it is used often. Phylogenic Species Concept Phylogeny is the evolutionary history of a species. The phylogenic species concept defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent. Species Concepts Characters To classify a species, scientists construct patterns of descent by using characters. Characters are inherited features that vary among species. Characters can be morphological or biochemical. Morphological Characters Shared morphological characters suggest that species are related closely and evolved from a recent common ancestor. Analogous characters are those that have the same function but different underlying construction. These characters do not indicate a close evolutionary relationship. Homologous characters might perform different functions, but show an anatomical similarity inherited from a common ancestor. Birds & Dinosaurs Dinosaur fossils show that they share many features in common with birds. Hallow bones Theropods have leg, wrist, hip, and shoulder structures similar to birds. Some theropods may have had feathers The evidence provided by these morphological characters indicates that modern birds are related more closely to theropod dinosaurs than they are to other reptiles. Biochemical Characters Scientists use biochemical characters, such as amino acids and nucleotides, to help them determine evolutionary relationships among species. DNA and RNA analyses are powerful tools for reconstructing phylogenies. The similar appearance of chromosomes among chimpanzees, gorillas, and orangutans suggests a shared ancestry. Biochemical Characters Biochemical Characters Scientists use a variety of techniques to compare DNA sequences when assessing evolutionary relationships. Sequencing and compare whole genomes of different organisms Compare genome maps using restriction enzymes DNA-DNA hybridization during which single strands of DNA from different species are melted together Comparing the DNA sequences of different species is an objective, quantitative way to measure evolutionary relationships. Molecular Clocks Scientists use molecular clocks to compare the DNA sequences or amino acid sequences of genes that are shared by different species. The differences between the genes indicate the presence of mutations. The more mutations that have accumulated, the more time that has passed since divergence. The Rate of Mutation The rate of mutation is affected by many factors: Type of mutation Where the mutation is in the genome Type of protein that the mutation affects Population in which the mutation occurs Molecular clocks can be valuable tools for determining a relative time of divergence of a species. They are especially useful when used in conjunction with other data, such as the fossil record. Phylogenetic Reconstruction Cladistics is a method that classifies organisms according to the order that they diverge from a common ancestor. Cladistics reconstructs phylogenies based on shared characters. Scientists consider two main types of characters when doing cladistic analysis. An ancestral character is found within the entire line of descent of a group of organisms. (Birds & mammals – backbone). Derived characters are present members of one group of the line but not in the common ancestor. (Birds & mammals – feathers & hair). Cladograms Systematics use shared derived characters to make a cladogram. A cladogram is a branching diagram that represents the proposed phylogeny or evolutionary history of a species or group. A cladogram’s branches indicate phylogeny. The groups used in cladograms are called clades. A clade is one branch of the cladogram. Cladograms The greater the number of derived characters shared by groups, the more recently the groups share a common ancestor. 17.3 Domains and Kingdoms Main idea: The most widely used biological classification system has six kingdoms within three domains. Objectives: Review Vocabulary Compare major characteristics of the three domains Differentiate among the six kingdoms Classify organisms to the kingdom level Eukaryote: an organism composed of one or more cells containing a nucleus and membrane-bound organelles New Vocabulary Eubaceria Archaea Protist Fungus Grouping Species The broadest category in the classification used by most biologists is the domain. The most widely used biological classification system has six kingdoms and three domains. The three domains are Bacteria, Archaea, and Eukarya. Organisms are classified in domains according to cell type and structure. The six kingdoms are Bacteria, Archaea, Protists, Fungi, Plantae, and Animalia. Organisms are classified into kingdoms according to cell type, structure, and nutrition. Archaea are the only members of their own domain. Archaebacteria are unicellular prokaryotes Domain Bacteria Eubacteria, members of Domain Bacteria and Kingdom Eubacteria are prokaryotes whose cell walls contain peptidoglycan. Peptidoglycan is a polymer that contains two kinds of sugars that alternate in the chain. Eubacteria are a diverse group that can survive in many different environments. Aerobic (need oxygen) or anaerobic (die in oxygen). Autotrophic (produce their own food) or heterotrophic (get nutrition from other organisms). Domain Bacteria Domain Archaea Archaea are thought to be more ancient than bacteria and yet more closely related to our eukaryote ancestors. Their cell walls do not contain peptidoglycan. Archaea are diverse in shape and nutrition requirements. They are called extremophiles because they can live in extreme environments. Domain Eukarya All eukaryotes (cells with membrane-bound nucleus and other membrane-bound organelles) are classified in Domain Eukarya. Domain Eukarya contains Kingdom Protista, Kingdom Fungi, Kingdom Plantae, and Kingdom Animalia. Kingdom Protista Protists are eukaryotic organisms that can be unicellular, colonial, or multicellular. Protists are classified into three different groups—plantlike, animal-like, and funguslike. Plantlike are called algea; autotrophs that perform photosynthesis Animal-lke are called protozoans; heterotrophs Funguslike are slime molds and mildews Euglenoids are a type of protist that have plantlike and animal-like characteristics; usually grouped with plantlike because they have chloroplasts and can perform photosynthesis. Kingdom Protista Kingdom Fungi A fungus is a unicellular or multicellular eukaryote that absorbs nutrients from organic materials in its environment. Member of Kingdom Fungi are heterotrophic, lack mobility, and have cell walls. Their cell walls contain a substance called chitin, which is a rigid polymer that provides structural support. A fungus consists of a mass of threadlike filaments called hyphae. Hyphae are responsible for the fungus’s growth, feeding, and reproduction. Kingdom Fungi Mushrooms are heterotrophic organisms. Some fungi are parasites - grow and feed on other organisms and others are saprobes – get their nourishment from dead or decay organic matter. Fungi that live in a mutualistic relationship with algae are called lichens. Kingdom Plantae Members of Kingdom Plantae form the base of all terrestrial habitats. All plants are multicellular and have cell walls composed of cellulose. Most plants are autotrophs, but some are heterotrophic. Plants possess cells that are organized into tissues, and many plants also possess organs such as roots, stems, and leaves. Plants lack mobility, yet some plants have reproductive cells with flagella that propel them through the water. Kingdom Plantae Kingdom Animalia All animals are heterotrophic, multicellular eukaryotes. Animal cells do not have cell walls. Animal cells are organized into tissue, and most tissues are organized into organs. Animal organs often are organized into complex organ systems. Animals range in size. They live in the water, on land, and in the air. Most animals are motile, although some, such as coral, lack motility as adults. Kingdom Animalia Viruses - An Exception A virus is a nucleic acid surrounded by a protein coat. Viruses do not possess cells, nor are they cells, and are not considered to be living. Because they are nonliving, they usually are not placed in the biological classification system.