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Order From Chaos

When you need a new pair of shoes, what do you do? You probably walk confidently into a shoe store, past the tens or hundreds of pairs of shoes you don’t want and straight to the kind you do want. How do you find them? Shoes are organized in the store in categories. People organize objects by grouping similar objects together.

Section 18-1

Interest Grabber

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1. Consider the task facing early biologists who attempted to organize living things. How might they have begun?

2. Suppose that you have been given a green plant, stringy brown seaweed, a rabbit, a mushroom, a worm, and a grasshopper. You’ve been asked to organize these things into categories that make sense. How would you do it?

3. Decide on your categories and write each on a sheet of paper. Next to each category, write the defining characteristics of that category. Then, write in the organisms that fall into each category.

Section 18-1

Interest Grabber continued

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18–1 Finding Order in DiversityA. Why Classify?

B. Assigning Scientific Names

1. Early Efforts at Naming Organisms

2. Binomial Nomenclature

C. Linnaeus’s System of Classification

Section 18-1

Section Outline

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Section 18-1

Flowchart

Linnaeus’s System of Classification

Kingdom

Phylum

Class

Order

Family

Genus

Species

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Grizzly bear Black bear Giant panda

Red fox Abert squirrel

Coral snake

Sea star

KINGDOM Animalia

PHYLUM Chordata

CLASS Mammalia

ORDER Carnivora

FAMILY Ursidae

GENUS Ursus

SPECIES Ursus arctos

Section 18-1

Figure 18-5 Classification of Ursus arctos

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One Big Family?

How can you determine if one organism is closely related to another? It may seem easy, but it isn’t, and looks are often deceiving. For example, roses and orchids are both flowering plants, but roses grow on bushes or vines and have thorns. Many orchids don’t even grow in soil—they can grow in trees! Rose and orchid blossoms look very different, and roses and orchids cannot produce hybrids, or offspring of crosses between parents with different traits.

Section 18-2

Interest Grabber

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1. Do you think roses and orchids are closely related? Explain your answer.

2. Now, apply the same logic to dogs. Different breeds of dogs—such as a Labrador retriever and a collie—can breed and produce offspring. So what is the difference between the rose-orchid combination and the Lab-collie combination?

3. What defines a species? Is appearance important? What other factors might be considered?

Section 18-2

Interest Grabber continued

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18–2 Modern Evolutionary ClassificationA. Which Similarities Are Most Important?

B. Evolutionary Classification

C. Classification Using Cladograms

D. Similarities in DNA and RNA

E. Molecular Clocks

Section 18-2

Section Outline

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CLADOGRAM

Appendages Conical Shells

Crab Barnacle Limpet Crab Barnacle Limpet

Crustaceans Gastropod

Molted exoskeleton

Segmentation

Tiny free-swimming larva

Section 18-2

Traditional Classification Versus Cladogram

CLASSIFICATION BASED ON VISIBLE

SIMILARITIES

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CLASSIFICATION BASED ON VISIBLE

SIMILARITIES

CLADOGRAM

Appendages Conical Shells

Crab Barnacle Limpet Crab Barnacle Limpet

Crustaceans Gastropod

Molted exoskeleton

Segmentation

Tiny free-swimming larva

Section 18-2

Traditional Classification Versus Cladogram

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My Way or the Highway

Categories that are used to organize an assortment of things should be valid. That is, they should be based on real information. However, categories should be useful, too. Suppose that you are taking a survey of traffic. You sit at the side of a busy intersection and record the vehicles you see in one hour.

Section 18-3

Interest Grabber

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1. What categories could you use to organize your count of vehicles?

2. Look at your list of categories. Are all of them equally useful?

3. Is there more than one valid and useful way to organize living things?

Section 18-3

Interest Grabber continued

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18–3 Kingdoms and DomainsA. The Tree of Life Evolves

B. The Three-Domain System

C. Domain Bacteria

D. Domain Archaea

E. Domain Eukarya

1. Protista

2. Fungi

3. Plantae

4. Animalia

Section 18-3

Section Outline

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Section 18-3

Concept Map

are characterized by

such as

and differing which place them in

which coincides withwhich coincides with

which place them in which is subdivided into

Living Things

Kingdom Eubacteria

Kingdom Archaebacteria

Eukaryotic cellsProkaryotic cells

Important characteristics

Cell wall structures

Domain Eukarya

Domain Bacteria

Domain Archaea

Kingdom Plantae

Kingdom Protista

Kingdom Fungi

Kingdom Animalia

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DOMAIN

KINGDOM

CELL TYPE

CELL STRUCTURES

NUMBER OF CELLS

MODE OF NUTRITION

EXAMPLES

Bacteria

Eubacteria

Prokaryote

Cell walls with peptidoglycan

Unicellular

Autotroph or heterotroph

Streptococcus, Escherichia coli

Archaea

Archaebacteria

Prokaryote

Cell walls without peptidoglycan

Unicellular

Autotroph or heterotroph

Methanogens, halophiles

Protista

Eukaryote

Cell walls of cellulose in some; some have chloroplasts

Most unicellular; some colonial; some multicellular

Autotroph or heterotroph

Amoeba, Paramecium, slime molds, giant kelp

Fungi

Eukaryote

Cell walls of chitin

Most multicellular; some unicellular

Heterotroph

Mushrooms, yeasts

Plantae

Eukaryote

Cell walls of cellulose; chloroplasts

Multicellular

Autotroph

Mosses, ferns, flowering plants

Animalia

Eukaryote

No cell walls or chloroplasts

Multicellular

Heterotroph

Sponges, worms, insects, fishes, mammals

Eukarya

Classification of Living Things

Section 18-3

Figure 18-12 Key Characteristics of Kingdoms and Domains

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KingdomsEubacteria

Archaebacteria

Protista

Plantae

Fungi

Animalia

DOMAIN EUKARYA

DOMAIN ARCHAEA

DOMAIN BACTERIA

Section 18-3

Figure 18-13 Cladogram of Six Kingdoms and Three Domains

Videos

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Panthera leo?, Part 1

Panthera leo?, Part 2

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Video 1

Panthera leo?, Part 1

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Video 2

Panthera leo?, Part 2

Links from the authors on the search for new species

Interactive test

For links on classification, go to www.SciLinks.org and enter the Web Code as follows: cbn-5181.

For links on domains of life, go to www.SciLinks.org and enter the Web Code as follows: cbn-5183.

Go Online

Interest Grabber Answers

1. Consider the task facing early biologists who attempted to organize living things. How might they have begun?

Students may say that early biologists attempted to formulate logical systems for organizing the diversity of life.

2. Suppose that you have been given a green plant, stringy brown seaweed, a rabbit, a mushroom, a worm, and a grasshopper. You’ve been asked to organize these things into categories that make sense. How would you do it?

Students may group the plantlike, sessile organisms (the plant, seaweed, and mushroom) together, grouping the others as animals.

3. Decide on your categories and write each on a sheet of paper. Next to each category, write the defining characteristics of that category. Then, write in the organisms that fall into each category.

Remind students that organizational systems are human-made, and there are no right or wrong ones. Some, however, are more useful than others.

Interest Grabber Answers

1. Do you think roses and orchids are closely related? Explain your answer.

Students may say that their different growth habits and inability to hybridize indicate that they are not closely related.

2. Now, apply the same logic to dogs. Different breeds of dogs—such as a Labrador retriever and a collie—can breed and produce offspring. So what is the difference between the rose-orchid combination and the Lab-collie combination?

Students may know that all domestic dogs are a single species.

3. What defines a species? Is appearance important? What other factors might be considered?

Students may suggest that a species is defined by its members’ ability to interbreed, regardless of appearance.

Interest Grabber Answers

1. What categories could you use to organize your count of vehicles?

Students’ answers may include, type of vehicle, color, age, or manufacturer.

2. Look at your list of categories. Are all of them equally useful?

Students may suggest that the usefulness of the criteria depends on the intent of the study.

3. Is there more than one valid and useful way to organize living things?

Students should conclude that the same set of living things could be categorized in several ways, depending upon the criteria used.

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