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Home , Binomial nomenclature, Domain (biology), Linnaean taxonomy

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I. Linnaean

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Printed: August 21, 2011 Authors Jean Brainard, ELISABETH SHUMOCK

Contributors Barbara Akre, ELISABETH SHUMOCK

i www.ck12.org Contents

1 I. 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 , must give each a . 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 Begins

1.1 Classification Lesson Objectives

• Explain how living things are organized for study. • Describe and define binomial . • Explain Linnaeus’ system of classification and how it differs from phylogenetic classification. • Be apply to classify organisms using a dichotomous key.

Vocabulary

• •

1 www.ck12.org • • derived characteristics • dichotomous key • • • • • Linnaean classification system • • • phylogeny • • • taxa • taxonomy

Introduction

The of life on Earth over the past 4 billion years has resulted in a huge variety of species. For more than 2,000 years, 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 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 of groupings, called taxa (singular, ). 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 and 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 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 sapiens, the two-word Latin name for humans. It literally means ‘‘wise .” 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 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: , , and Eukarya (see Figure 1.3). Both Bacteria and Archaea consist of single-celled . Domain Bacteria contains the kingdom of Eubacteria; domain Archaea contians the kingdom of Archaebacteria. Eukarya consists of all , from single-celled to humans. This domain includes the kingdoms of Animalia (), Plantae (), 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 Prokaryote Eukaryote Eukaryote Eukaryote 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 , ; , Mushrooms, , , Escherichia Parame- yeasts , 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. are based on . 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 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 clades. The reptile clade includes . It shows that birds evolved from . 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. Do you see why Species 1 and 2 are more closely related to each other than either is to Species 3?

Figure 1.5: Mammal and Reptile Clades. This cladogram classifies mammals, reptiles, and birds in clades based on their evolutionary relationships.

www.ck12.org 6 characteristics of different organisms. In the Figure 1.6 you can see an example of a dichotomous key. If you were given a round, chewy piece of wrapped in white paper, could you follow this key to find its scientific name? It really quite simple, you always begin at number 1. 1a applies the candy is chewy, this is followed by a number 2 which is telling us to look at item 2 and find the characteristic that applies. 2a states that the candy is wrapped and refers us to number 3. 3a has a listing for round candy and refers us to number 4. 4a states that the wrapper is all white and gives us the scientific name of Saltus taffinia.

Figure 1.6: This key could be used to classify a variety of pieces of candy.

Lesson Summary

• Classification is an important step in understanding life on Earth. All modern classification systems have their roots in the Linnaean classification system. The Linnaean system is based on similarities in obvious physical traits. It consists of a hierarchy of taxa, from the kingdom to the species. Each species is given a unique two-word Latin name. The recently added domain is a larger and more inclusive taxon than the kingdom. • Phylogeny is the evolutionary history of group of related organisms. It is represented by a phylogenetic tree that shows how species are related to each other through common ancestors. A clade is a group of organisms that includes an ancestor and all of its descendants. It is a phylogenetic classification, based on evolutionary relationships. • A dichotomous key is a tool that can be used to help us identify unfamililar organisms.

Lesson Review Questions

Recall

1. What is taxonomy? 2. Define taxon and give an example. 3. What is binomial nomenclature? Why is it important? 4. What is a domain? What are the three domains of life on Earth?

7 www.ck12.org 5. What is cladistics, and what is it used for?

Apply Concepts

6. Create a taxonomy, modeled on the Linnaean classification system, for a set of common objects, such as motor vehicles, tools, or office supplies. Identify the groupings that correspond to the different taxa in the Linnaean system. 7. and are more closely related to each other than either is to . Draw a phylogenetic tree to show these relationships. 8. Using the Dichotomous key presented in this chapter, find the scientific name for a piece of candy that has the characteristics listed below. Be sure to write the name in the proper scientific name when you find it.

• You are given a ball-shaped piece of hard candy that is not wrapped.

Think Critically

8. Compare and contrast a Linnaean taxon, such as the family or genus, with the clade. 9. Explain why reptiles and birds are placed in the same clade.

Points to Consider

This chapter gives you a glimpse of 4 billion years of evolution on Earth. In the next chapter, you will read about the forces that bring about evolution. Natural selection is one of these forces. It generally results in a population or species becoming better adapted to its environment over time.

• How does natural selection work? How does it bring about evolutionary change? • What might be the other forces of evolution?

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