Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

18-1 Finding Order in Diversity Photo credit: ©Gary Randall/Visuals Unlimited Copyright Pearson Prentice Hall

18-1 Finding Order in Diversity Natural selection and other processes have led to a staggering diversity of organisms. Biologists have identified and named about 1.5 million species so far. They estimate that 2–100 million additional species have yet to be discovered. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Why Classify? In the discipline of taxonomy, scientists classify organisms and assign each organism a universally accepted name. When taxonomists classify organisms, they organize them into groups that have biological significance. Copyright Pearson Prentice Hall

Assigning Scientific Names Common names of organisms vary, so scientists assign one name for each species. Because 18th century scientists understood Latin and Greek, they used those languages for scientific names. This practice is still followed in naming new species. Copyright Pearson Prentice Hall

Assigning Scientific Names Early Efforts at Naming Organisms The first attempts at standard scientific names described the physical characteristics of a species in great detail. These names were not standardized because different scientists described different characteristics. Copyright Pearson Prentice Hall

Assigning Scientific Names Carolus Linneaus developed a naming system called binomial nomenclature. In binomial nomenclature, each species is assigned a two-part scientific name. The scientific name is italicized. Copyright Pearson Prentice Hall

Assigning Scientific Names The first part of the name is the genus to which the organism belongs. A genus is a group of closely related species. The genus name is capitalized. The second part of the name is unique to each species within the genus. This part of the name often describes an important trait or where the organism lives. The species name is lowercased. Copyright Pearson Prentice Hall

Linnaeus’s System of Classification Linnaeus not only named species, he also grouped them into categories. What is Linneaus’s system of classification? Copyright Pearson Prentice Hall

Linnaeus's System of Classification   Linnaeus's seven levels of classification are—from smallest to largest— species genus family order class phylum kingdom Copyright Pearson Prentice Hall

Linnaeus's System of Classification  Each level is called a taxon, or taxonomic category. Species and genus are the two smallest categories. Grizzly bear Black bear Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Linnaeus's System of Classification Genera that share many characteristics are grouped in a larger category, the family. Grizzly bear Black bear Giant panda Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Linnaeus's System of Classification An order is a broad category composed of similar families. Grizzly bear Black bear Giant panda Red fox Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Linnaeus's System of Classification The next larger category, the class, is composed of similar orders. Grizzly bear Black bear Giant panda Red fox Abert squirrel Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Class Mammalia Copyright Pearson Prentice Hall

Linnaeus's System of Classification Several different classes make up a phylum. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake PHYLUM Chordata Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Linnaeus's System of Classification The kingdom is the largest and most inclusive of Linnaeus's taxonomic categories. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake Sea star KINGDOM Animalia Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

Linnaeus's System of Classification Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake Sea star Linnaeus’s hierarchical system of classification uses seven taxonomic categories. This illustration shows how a grizzly bear, Ursus arctos, is grouped within each taxonomic category. Only some representative species are illustrated for each category above the species level. Copyright Pearson Prentice Hall

18-2 Modern Evolutionary Classification Copyright Pearson Prentice Hall

Evolutionary Classification Which Similarities Are Most Important? Linnaeus grouped species into larger taxa mainly according to visible similarities and differences. How are evolutionary relationships important in classification? Copyright Pearson Prentice Hall

Evolutionary Classification Phylogeny is the study of evolutionary relationships among organisms. Copyright Pearson Prentice Hall

Evolutionary Classification Biologists currently group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. The strategy of grouping organisms is based on evolutionary history and is called evolutionary classification. Copyright Pearson Prentice Hall

Evolutionary Classification The higher the level of the taxon, the further back in time is the common ancestor of all the organisms in the taxon. Organisms that appear very similar may not share a recent common ancestor. Copyright Pearson Prentice Hall

Evolutionary Classification Different Methods of Classification Crustaceans Mollusk Appendages Conical Shells Crab Barnacle Limpet Crab Barnacle Limpet Molted external skeleton Early systems of classification grouped organisms together based on visible similarities. That approach might result in classifying limpets and barnacles together (left). Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. Crabs and barnacles are now grouped together (right) because they share several characteristics that indicate that they are more closely related to each other than either is to limpets. These characteristics include segmented bodies, jointed limbs, and an external skeleton that is shed during growth. Tiny free-swimming larva Segmentation CLASSIFICATION BASED ON VISIBLE SIMILARITY CLADOGRAM Copyright Pearson Prentice Hall

Evolutionary Classification Superficial similarities once led barnacles and limpets to be grouped together. Appendages Conical Shells Crab Barnacle Limpet Early systems of classification grouped organisms together based on visible similarities. That approach might result in classifying limpets and barnacles together. Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. Crabs and barnacles are now grouped together because they share several characteristics that indicate that they are more closely related to each other than either is to limpets. These characteristics include segmented bodies, jointed limbs, and an external skeleton that is shed during growth. Copyright Pearson Prentice Hall

Evolutionary Classification However, barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share. Barnacles and crabs are classified as crustaceans, and limpets are mollusks. Copyright Pearson Prentice Hall

Classification Using Cladograms Many biologists now use a method called cladistic analysis. Cladistic analysis identifies and considers only new characteristics that arise as lineages evolve. Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters. Copyright Pearson Prentice Hall

Classification Using Cladograms Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. Cladograms help scientists understand how one lineage branched from another in the course of evolution. Copyright Pearson Prentice Hall

Classification Using Cladograms A cladogram shows the evolutionary relationships between crabs, barnacles, and limpets. Crustaceans Mollusk Crab Barnacle Limpet Early systems of classification grouped organisms together based on visible similarities. That approach might result in classifying limpets and barnacles together. Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. Crabs and barnacles are now grouped together because they share several characteristics that indicate that they are more closely related to each other than either is to limpets. These characteristics include segmented bodies, jointed limbs, and an external skeleton that is shed during growth. Molted external skeleton Segmentation Tiny free-swimming larva Copyright Pearson Prentice Hall

Similarities in DNA and RNA How can DNA and RNA help scientists determine evolutionary relationships? Copyright Pearson Prentice Hall

Similarities in DNA and RNA The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships. Copyright Pearson Prentice Hall

Similarities in DNA and RNA DNA Evidence DNA evidence shows evolutionary relationships of species. The more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms. The more two species have diverged from each other, the less similar their DNA will be. Copyright Pearson Prentice Hall

Molecular Clocks Molecular Clocks Comparisons of DNA are used to mark the passage of evolutionary time. A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently. Copyright Pearson Prentice Hall

Molecular Clock Molecular Clocks A gene in an ancestral species 2 mutations 2 mutations new mutation new mutation new mutation By comparing the DNA sequences of two or more species, biologists estimate how long the species have been separated. Species Species Species A B C Copyright Pearson Prentice Hall

A molecular clock relies on mutations to mark time. Molecular Clocks A molecular clock relies on mutations to mark time. Simple mutations in DNA structure occur often. Neutral mutations accumulate in different species at about the same rate. Comparing sequences in two species shows how dissimilar the genes are, and shows when they shared a common ancestor. Copyright Pearson Prentice Hall

18-3 Kingdoms and Domains Photo credit: ©Gary Randall/Visuals Unlimited Copyright Pearson Prentice Hall

The Tree of Life Evolves Systems of classification adapt to new discoveries. Linnaeus classified organisms into two kingdoms—animals and plants. The only known differences among living things were the fundamental traits that separated animals from plants. Copyright Pearson Prentice Hall

The Tree of Life Evolves Five Kingdoms Scientists realized there were enough differences among organisms to make 5 kingdoms: Monera Protista Fungi Plantae Animalia Copyright Pearson Prentice Hall

The Tree of Life Evolves Six Kingdoms Recently, biologists recognized that Monera were composed of two distinct groups: Eubacteria and Archaebacteria. Copyright Pearson Prentice Hall

The Tree of Life Evolves The six-kingdom system of classification includes: Eubacteria Archaebacteria Protista Fungi Plantae Animalia Copyright Pearson Prentice Hall

The Tree of Life Evolves Changing Number of Kingdoms Introduced Names of Kingdoms 1700’s Plantae Animalia Late 1800’s Protista Plantae Animalia 1950’s Monera Protista Fungi Plantae Animalia This diagram shows some of the ways organisms have been classified into kingdoms over the years. The six-kingdom system includes the following kingdoms: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia. Archae-bacteria 1990’s Eubacteria Protista Fungi Plantae Animalia Copyright Pearson Prentice Hall

The Three-Domain System Molecular analyses have given rise to a new taxonomic category that is now recognized by many scientists. The domain is a more inclusive category than any other—larger than a kingdom. Copyright Pearson Prentice Hall

The Three-Domain System The three domains are: Eukarya, which is composed of protists, fungi, plants, and animals. Bacteria, which corresponds to the kingdom Eubacteria. Archaea, which corresponds to the kingdom Archaebacteria. Copyright Pearson Prentice Hall

The Three-Domain System Modern classification is a rapidly changing science. As new information is gained about organisms in the domains Bacteria and Archaea, they may be subdivided into additional kingdoms. Copyright Pearson Prentice Hall

Domain Bacteria Domain Bacteria Members of the domain Bacteria are unicellular prokaryotes. Their cells have thick, rigid cell walls that surround a cell membrane. Their cell walls contain peptidoglycan. Copyright Pearson Prentice Hall

The domain Bacteria corresponds to the kingdom Eubacteria. Copyright Pearson Prentice Hall

Domain Archaea Domain Archaea Members of the domain Archaea are unicellular prokaryotes. They live in extreme environments. Their cell walls lack peptidoglycan, and their cell membranes contain unusual lipids not found in any other organism. Copyright Pearson Prentice Hall

The domain Archaea corresponds to the kingdom Archaebacteria. Copyright Pearson Prentice Hall

Domain Eukarya Domain Eukarya The domain Eukarya consists of organisms that have a nucleus. This domain is organized into four kingdoms: Protista Fungi Plantae Animalia Copyright Pearson Prentice Hall

Domain Eukarya Copyright Pearson Prentice Hall

Its members display the greatest variety. Domain Eukarya Protista  The kingdom Protista is composed of eukaryotic organisms that cannot be classified as animals, plants, or fungi. Its members display the greatest variety. They can be unicellular or multicellular; photosynthetic or heterotrophic; and can share characteristics with plants, fungi, or animals. Copyright Pearson Prentice Hall

Members of the kingdom Fungi are heterotrophs. Domain Eukarya Fungi  Members of the kingdom Fungi are heterotrophs. Most fungi feed on dead or decaying organic matter by secreting digestive enzymes into it and absorbing small food molecules into their bodies. They can be either multicellular (mushrooms) or unicellular (yeasts). Copyright Pearson Prentice Hall

Plants are nonmotile—they cannot move from place to place. Domain Eukarya Plantae  Members of the kingdom Plantae are multicellular, photosynthetic autotrophs. Plants are nonmotile—they cannot move from place to place. Plants have cell walls that contain cellulose. The plant kingdom includes cone-bearing and flowering plants as well as mosses and ferns. Copyright Pearson Prentice Hall