CK-12 FOUNDATION I. Linnaean Taxonomy Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) Brainard SHUMOCK To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook mate- rials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2011 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®”, and “FlexBook Platform®”, (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution/Non-Commercial/Share Alike 3.0 Un- ported (CC-by-NC-SA) License (http://creativecommons.org/licenses/by-nc-sa/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: August 21, 2011 Authors Jean Brainard, ELISABETH SHUMOCK Contributors Barbara Akre, ELISABETH SHUMOCK i www.ck12.org Contents 1 I. Linnaean Taxonomy 1 1.1 Classification ............................................ 1 www.ck12.org ii Chapter 1 I. Linnaean Taxonomy Figure 1.1 Why classify? To study the great diversity of organisms, biologists must give each organism a name. Biologists must also attempt to organize living things into groups that have biological meaning. The discipline known as taxonomy allows scientisits to classify an assign each organism on Earth a universally accepted name. By using scientific names for organisms scientists can ensure that everyone is discussing the same organism. Taxonomists classify organisms into biologically significant groupings based upon their unique characteristics and evolutionary history. The pictures above show a vast variety of organisms giving them common names and their taxonomic names or scientific names. Earth Forms and Life Begins 1.1 Classification Lesson Objectives • Explain how living things are organized for study. • Describe and define binomial nomenclature. • Explain Linnaeus’ system of classification and how it differs from phylogenetic classification. • Be apply to classify organisms using a dichotomous key. Vocabulary • binomial nomenclature • clade 1 www.ck12.org • class • derived characteristics • dichotomous key • domain • family • genus • kingdom • Linnaean classification system • order • phylogenetic tree • phylogeny • phylum • species • taxa • taxonomy Introduction The evolution of life on Earth over the past 4 billion years has resulted in a huge variety of species. For more than 2,000 years, humans have been trying to classify the great diversity of life. The science of classifying organisms is called taxonomy. Classification is an important step in understanding the present diversity and past evolutionary history of life on Earth. Linnaean Classification All modern classification systems have their roots in the Linnaean classification system. It was de- veloped by Swedish botanist Carolus Linnaeus in the 1700s. He tried to classify all living things that were known at his time. He grouped together organisms that shared obvious physical traits, such as number of legs or shape of leaves. For his contribution, Linnaeus is known as the ‘‘father of taxonomy.” You can learn more about Linnaeus and his system of classification by watching the video at this link: http://teachertube.com/viewVideo.php?video_id=169889http://teachertube.com/viewVideo.php?video_- id=169889. The Linnaean system of classification consists of a hierarchy of groupings, called taxa (singular, taxon). There are seven taxa in the Linnaean system ranging from the species to the kingdom (see Figure 1.2). The species is the smallest and most exclusive grouping. It consists of organisms that are similar enough to produce fertile offspring together. Closely related species are grouped together in a genus. Groups of genus that share many of the same characteristics are grouped togethr into a family. Groups of similar families make up an order. Orders that share a great deal of similarites are grouped into a class. Groups of very closely related classes are placed into a phylum. The kingdom is the largest and most inclusive grouping in the Linnaean system of classification. It consists of organisms that share just a few basic similarities. Examples are the plant and animal kingdoms. Binomial Nomenclature Perhaps the single greatest contribution Linnaeus made to science was his method of naming species. This method, called binomial nomenclature, gives each species a unique, two-word Latin name consisting of the genus name and the species name. The scientific name is always written in italics. The first word is capitialized, and the second word is lowercased. An example is Homo sapiens, the two-word Latin name for humans. It literally means ‘‘wise human.” This is a reference to our big brains. Why is having two www.ck12.org 2 Figure 1.2: Linnaean Classification System: Classification of the Human Species. This chart shows the taxa of the Linnaean classification system. Each taxon is a subdivision of the taxon below it in the chart. For example, a species is a subdivision of a genus. The classification of humans is given in the chart as an example. 3 www.ck12.org names so important? It is similar to people having a first and a last name. You may know several people with the first name Michael, but adding Michael’s last name usually pins down exactly whom you mean. In the same way, having two names uniquely identifies a species. Revisions in Linnaean Classification: The Three Domain System Linnaeus published his classification system in the 1700s. Since then, many new species have been discov- ered. The biochemistry of organisms has also become known. Eventually, scientists realized that Linnaeus’s system of classification needed revision. A major change to the Linnaean system was the addition of a new taxon called the domain. A domain is a taxon that is larger and more inclusive than the kingdom. Most biologists agree there are three domains of life on Earth: Bacteria, Archaea, and Eukarya (see Figure 1.3). Both Bacteria and Archaea consist of single-celled prokaryotes. Domain Bacteria contains the kingdom of Eubacteria; domain Archaea contians the kingdom of Archaebacteria. Eukarya consists of all eukaryotes, from single-celled protists to humans. This domain includes the kingdoms of Animalia (animals), Plantae (plants), Fungi (fungi), and Protista (protists). Table 1.1 below summarizes the key evidence used in classifying organisms into these major taxonomic groups. Figure 1.3: Three-Domain Classification. This diagram shows the three domains of organisms that cur- rently live on Earth. www.ck12.org 4 Table 1.1: Table 1.1: Classification of Living Things DOMAIN Bacteria Archaea Eukarya KINGDOM Eubacteria ArchaebacteriaProtista Fungi Plantae Animalia CELL Prokaryote Prokaryote Eukaryote Eukaryote Eukaryote Eukaryote TYPE CELL Cell walls Cell walls Cell walls of Cell walls of Cell walls No cell STRUC- with pepti- without cellulose in chitin of cellulose; walls or TURES doglycan peptidogly- some; some chloroplasts chloroplasts can have chloro- plasts NUMBER Unicellular Unicellular Most uni- Most mul- Multicellular Multicellular OF CELLS cellular; ticellular; some colo- some unicel- nial; some lular multicellular MODE OF Autotroph Autotroph Autotroph Heterotroph Autotroph Heterotroph NUTRI- or het- or het- or het- TION erotroph erotroph erotroph EXAMPLES Streptococcus, Methanogens; Amoeba, Mushrooms, Mosses, Sponges, Escherichia halophiles Parame- yeasts ferns, flow- worms, in- coli cium, slime ering plants sects, fishes, molds, giant mammals kelp Phylogenetic Classification Linnaeus classified organisms based on obvious physical traits. Basically, organisms were grouped together if they looked alike. After Darwin published his theory of evolution in the 1800s (discussed in one of the following chapters), scientists looked for a way to classify organisms that showed phylogeny. Phylogeny is the evolutionary history of a group of related organisms. It is represented by a phylogenetic tree, like the one in Figure 1.4. One way of classifying organisms that shows phylogeny is by using the clade. A clade is a group of organisms that includes an ancestor and all of its descendants. Clades are based on cladistics. This is a method of comparing traits in related species to determine ancestor-descendant relationships through a cladistic analysis that identifies and considers only characteristics of organisms that are evolutionary innovations. Characteristics that appear in recent parts of a lineage but not in its older members are called derived characteristics. Clades of derived charcteristics are represented by cladograms, like the one in Figure 1.5. This cladogram represents the mammal and reptile clades. The reptile clade includes birds. It shows that birds evolved from reptiles. Linnaeus classified mammals, reptiles, and birds in separate classes. This masks their evolutionary relationships. Using Dichotomous Keys What tools are available to help people identify unfamiliar organisms? One is a field guide, a book with illustrations that highlight differences between similar-looking organisms. Another tool used to identify organisms is a dichotomous key. A dichotomous key is a series of paired statements that describe physical 5 www.ck12.org Figure 1.4: Phylogenetic Tree. This phylogenetic tree shows how three hypothetical species are related to each other through common ancestors.