ChapterChapter 17 Diversity Organizing...

452 ORGANIZING LIFE’S DIVERSITY

What You’ll Learn■ You will both identify and

compare various methods of classification.

■ You will distinguish amongsix kingdoms of organisms.

Why It’s ImportantBiologists use a system of classification to organize living things. Understandingclassification helps you studyorganisms and their evolution-ary relationships.

Look through some of thephotos and illustrations inthe chapter. Make a list ofsome of the obvious differ-ences used to classifyorganisms. As you read thetext, compare this list tothe classification systemsdescribed in the reading.

To find out more about classifi-cation and taxonomy, visit theGlencoe Science Web site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

Biologists have classifiedall the organisms you seein these photos as well asmillions of others.

BIOLOGY

ChapterChapter

Organizing Life’sDiversity17

http://science.glencoe.com

Section

How ClassificationBegan

Organizing items can help youunderstand them better and findthem more easily. For example, youprobably order your clothes drawersand your CD collection. Biologistswant to better understand organismsso they organize them into groups.One tool that they use to do this isclassification—the grouping ofobjects or information based on simi-larities. Taxonomy (tak SAHN uhmee) is the branch of biology thatgroups and names organisms basedon studies of their different charac-teristics. Biologists who study taxon-omy are called taxonomists.

Aristotle’s systemThe Greek philosopher Aristotle

(384–322 B.C.) developed the firstwidely accepted system of biologicalclassification. He classified all theorganisms he knew into two groups:plants and animals. He subdividedplants into the three groups, herbs,shrubs, and trees, depending on thesize and structure of a plant. Hegrouped animals according to wherethey lived or spent a great deal oftime: on land, in the air, or in water.

The basis for Aristotle’s groupswas useful but did not group organ-isms according to their evolutionaryhistory. According to his system,birds, bats, and flying insects are clas-sified together even though they have

17.1 CLASSIFICATION 453

Every day you see items that aregrouped, and you group itemsyourself. In a supermarket, you

find all the fresh produce in one area,baked goods in another, and dairyproducts in still another. In a musicstore, the type of music is the basis forshelving a CD. When you put awaythe dishes, you probably place the din-ner plates on one shelf and the glasseson another. You group similar articlesso often that you probably never thinkabout why you do it. However, group-ing things creates order, and ordersaves time and energy when you lookfor an item.

SECTION PREVIEW

ObjectivesEvaluate the history,purpose, and methodsof taxonomy.Explain the meaning of a scientific name.Describe the organiza-tion of taxa in a biologi-cal classification system.

Vocabularyclassificationtaxonomybinomial nomenclaturegenusfamilyorderclassphylumkingdomdivision

17.1 Classification

A display of fruit for sale

OriginWORDWORD

taxonomyFrom the Greekwords taxo, meaningto “arrange,” andnomy, meaning“ordered knowl-edge.” Taxonomy is the science of classification.

little in common besides the abilityto fly. As time passed, more organ-isms were discovered and some didnot fit easily into Aristotle’s groups,but many centuries passed beforeAristotle’s system was replaced.

Linnaeus’s systemIn the late eighteenth century, a

Swedish botanist, Carolus Linnaeus(1707–1778), developed a method ofgrouping organisms that was moreuseful than Aristotle’s. Linnaeus’s sys-tem was based on physical and struc-tural similarities of organisms. Forexample, he might use the similaritiesin flower parts as a basis for classify-ing flowering plants, Figure 17.1. Asa result, the groupings revealed therelationships of the organisms.

Eventually, some biologists pro-posed that structural similaritiesreflect the evolutionary relationshipsof species. For example, althoughbats fly like birds, they also have hairand produce milk for their young.Therefore, bats are classified as

mammals rather than as birds, reflect-ing the evolutionary history that batsshare with other mammals. This wayof organizing organisms is the basisof modern classification systems.

Two names for a species Modern classification systems use

a two-word naming system calledbinomial nomenclature thatLinnaeus developed to identifyspecies. In this system, the first wordidentifies the genus of the organism.A genus (JEE nus) (plural, genera)consists of a group of similar species.The second word, which oftendescribes a characteristic of theorganism, immediately follows thegenus name. Thus, the scientificname for each species is a combina-tion of the genus and descriptivenames. For example, the scientificname of modern humans is Homosapiens. Modern humans are in thegenus Homo, and one of their charac-teristics is intelligence. The Latinword sapiens means “wise.”


Figure 17.1Linnaeus classifiedflowering plantsaccording to their flower structures.

OriginWORDWORD

binomial nomenclatureFrom the Latinwords bi, meaning“two,” nomen, mean-ing “name,” andcalatus, meaning“list.” The systemof binomial nomen-clature assigns twowords to the nameof each species.

Latin is the language of scientificnames. Taxonomists are required togive each newly discovered species aLatin scientific name. They use Latinbecause the language is no longerused in conversation and, therefore,does not change. Scientific namesshould be italicized in print andunderlined when handwritten. Thefirst letter of the genus name isuppercase, but the first letter of thedescriptive name is lowercase.

Although a scientific name givesinformation about the relationships ofan organism and how it is classified,many organisms have common namesjust like you and your friends mighthave nicknames. However, a commonname can be misleading. For example,a sea horse is a fish, not a horse. Inaddition, it is confusing when aspecies has more than one commonname. The bird in Figure 17.2 livesnot only in the United States but alsoin several countries in Europe. Ineach country it has a different com-mon name. Therefore, if an Englishscientist publishes an article about thebird’s behavior and uses the bird’sEnglish common name, a Spanish sci-entist looking for information mightnot recognize the bird as the samespecies also living in Spain.

Biological ClassificationExpanding on Linnaeus’s work,

today’s taxonomists try to identify theunderlying natural relationships oforganisms and use the information asa basis for classification. They com-pare the external and internal struc-tures of organisms, as well as theirgeographical distribution and chemi-cal makeup to reveal their probableevolutionary relationships. Groupingorganisms on the basis of their evolu-tionary relationships makes it easierto understand biological diversity.

Taxonomy: A frameworkJust as similar food items in a

supermarket are stacked together,taxonomists group similar organisms,both living and extinct. Classificationprovides a framework in which tostudy the relationships among livingand extinct species.

For example, biologists study therelationship between birds anddinosaurs within the framework ofclassification. Are dinosaurs moreclosely related to birds or reptiles?The bones of some dinosaurs havelarge internal spaces like those inbirds. Some paleontologists whostudy dinosaur fossils propose thatsome dinosaurs may have beenendothermic—able to maintain aconstant body temperature—which isa characteristic of all birds. Becauseof such evidence, they suggest thatdinosaurs are more closely related toostriches, which are birds, than tolizards, which are reptiles.

Taxonomy: A useful toolClassifying organisms is a useful

tool for scientists who work in agri-culture, forestry, and medicine. For


Figure 17.2In the United Statesand England, thisbird is called thehouse sparrow, inSpain the gorrion, inHolland the musch,and in Sweden thehussparf. However,the bird has only onescientific name,Passer domesticus.

Using a Dichotomous Key Howcould you identify a tree growingin front of your school? You mightask a local expert, or you could usea manual or field guide that con-tains descriptive information andkeys about trees. A key is a set ofdescriptive sentences that is sub-divided into steps. A dichotomouskey has two descriptions at eachstep. You follow the steps until thekey reveals the name of the tree.

Procedure! Using a few leaves from local trees and a dichotomous key

for trees of your area, identify the tree from which eachleaf came. To use the key, study one leaf. Then choose theone statement from the first pair that most accuratelydescribes the leaf. Continue following the key until youidentify the leaf’s tree. Repeat the process for each leaf.

@ Glue each leaf on a separate sheet of paper. For each leaf,record the tree’s name.

Analysis1. What is the function of a dichotomous key?2. List three different characteristics used in your key.3. As you used the key, did the characteristics become more

general or more specific?

MiniLab 17-1MiniLab 17-1


Figure 17.3Taxonomists can easily distinguishamong this poison ivy (a) and otherplants, such as Virginia creeper,with which it is often confused. The red berries produced by a holly bush are poisonous to humans (b).

example, suppose a child eats berriesfrom the holly plant that you see inFigure 17.3. The child’s parentswould probably rush the child andsome of the plant and its berries tothe nearest hospital. Someone workingat a poison control center could iden-tify the plant, and the physicians wouldthen know how to treat the child.

Anyone can learn to identify manyorganisms. The MiniLab on this pagewill guide you through a way of iden-tifying some organisms in your ownneighborhood. Then try the BioLabat the end of this chapter.

Taxonomy and the economyIt often happens that the discovery

of new sources of lumber, medicines,and energy results from the work oftaxonomists. The characteristics of afamiliar species are frequently similarto those found in a new, relatedspecies. For example, if a taxonomistknows that a certain species of pinetree contains chemicals that makegood disinfectants, it’s likely thatanother pine species will also containthese useful substances.

Classifying

a

b

Is the red wolf a separate species? The work of taxono-mists results in changing views of species. This is due to boththe discovery of new species and the development of newtechniques for studying classification.

AnalysisA. The red wolf (Canis rufus) can breed and produce off-

spring with both the coyote (Canus latrans) and the graywolf (Canis lupus). Despite this fact, the three animaltypes have been classified as separate species.

B. A biologist measured their skulls and concluded that insize and structure the red wolf’s measurements fell mid-way between gray wolves and coyotes.

C. Based on these data, the biologist concluded that they areseparate species.

D. Geneticists, attempting to determine if the three animaltypes were separate species, found that the nucleotidesequences from the red wolf’s DNA were not distinctivelydifferent from those of gray wolves or coyotes.

E. The geneticists concluded that the red wolf is a hybrid ofthe gray wolf and coyote.

Thinking Critically1. A species can be defined as a group of animals that can

mate with one another to produce fertile offspring butcannot mate successfully with members of a differentgroup. Does statement (A) support or reject this defini-tion? Explain your answer.

2. What type of evidence was the biologist using (B)? Thegeneticists (D)? Explain your answer.

3. A hybrid is the offspring from two species. Which sentence,beside (D) and (E), supports hybrid evidence? Explain.

4. If you supported the biologist’s work, would you use thethree different scientific names for coyotes, gray wolves,and red wolves? Explain your answer.

5. If you supported the geneticists’ conclusions, would you usethe three different scientific names? Explain your answer.

6. How does this example support the idea that the work ofscientists results in changing views of species?

Problem-Solving Lab 17-1Problem-Solving Lab 17-1 Drawing aConclusion

How Living Things Are Classified

In any classification system, itemsare categorized, making them easierto find and discuss. For example, in anewspaper’s classified advertisements,you’ll find a section listing autos forsale. This section frequently subdi-vides the many ads into two smallergroups—domestic autos and importedautos. In turn, these two groups aresubdivided by more specific criteria,such as different car manufacturersand the year and model of the auto.Although biologists group organisms,not cars, they subdivide the groupson the basis of more specific criteria.Any group of organisms is called ataxon (plural, taxa).

Taxonomic rankingsOrganisms are ranked in arbitrary

taxa that range from having verybroad characteristics to very specificones. The broader a taxon, the moregeneral its characteristics, the morespecies it contains. You can think ofthe taxa as fitting together like nestedboxes of increasing sizes. You alreadyknow about two taxa. The smallesttaxon is that of species. Organismsthat look alike and successfully inter-breed belong to the same species. Thenext largest taxon is a genus—a groupof similar species that have similarfeatures and are closely related.

It is not always easy to determinethe species of an organism. For exam-ple, over many years, taxonomistshave debated how to classify the redwolf, the coyote, and the gray wolf.Some biologists wanted to classifythem as separate species, and otherswanted to classify them as a singlespecies. Use the Problem-Solving Labon this page to explore the evidencefor and against classifying these threeorganisms as separate species.


Red wolf Coyote Gray wolf


Figure 17.4Mountain lions (a) are not classified in thesame genus as lynxes (b) and bobcats (c).

CAREERS IN BIOLOGY

Biology Teacher

A re you intrigued by the actionsand interactions of plants,

animals, and other organisms?Would you like to share this inter-est with others? Maybe you shouldbecome a biology teacher.

Skills for the JobBiology teachers help students

learn about organisms through discussionsand activities both inside and outside the classroom. As a biol-ogy teacher, you might also teach general science and health.To become a biology teacher, you must earn a bachelor’s de-gree in science, biology, or a closely related field. You some-times have to spend several months student teaching. Manypositions require a master’s degree. In addition, you have topass a national test for teachers in many states. This nationaltest includes a test in biology or in a combination of biologyand general science. After all this education, testing, andwork, you will be ready to teach others!

To find out more about careers in related fields, be sure to check the Glencoe Science Web site.science.glencoe.com

a

b

c

In Figure 17.4, you can comparethe appearance of a lynx, Lynx rufus, abobcat, Lynx canadensis, and a moun-tain lion, Panthera concolor. The scien-tific names of the lynx and bobcat tellyou that they belong to the samegenus, Lynx. All species in the genusLynx share the characteristic of havinga jaw that contains 28 teeth. Mountainlions and other lions, which are simi-lar to bobcats and lynxes, are notclassified in the Lynx genus becausetheir jaws contain 30 teeth.

Bobcats, lynxes, lions, and moun-tain lions belong to the same familycalled Felidae. Family, the nextlarger taxon in the biological classifi-cation system, consists of a group ofsimilar genera. In addition to domes-ticated cats, bobcats, lynxes, and lionsbelong to the family Felidae. Allmembers of the cat family share cer-tain characteristics. They have shortfaces, small ears, forelimbs with fivetoes, and hindlimbs with four toes.Most can retract their claws.

BIOLOGY


Kingdom

Phylum

Bobcat Lynx

Class

Order

Family

Genus

Species

Animalia Animalia

Chordata Chordata

Mammalia Mammalia

Carnivora Carnivora

Felidae Felidae

Lynx Lynx

Lynxrufus

Lynxcanadensis

The larger taxaThere are four larger taxa. An order

is a taxon of similar families. A class isa taxon of similar orders. A phylum(FI lum) (plural, phyla) is a taxon ofsimilar classes. Plant taxonomists usethe taxon division instead of phylum.A kingdom is a taxon of similar phyla ordivisions. The six kingdoms aredescribed in the Focus on beginning onthe next page.

Figure 17.5A lynx, called Lynxcanadensis, has botha short tail with blackfur circling its tip andhighly visible tufts ofhair on its ears. Abobcat, Lynx rufus,has a short tail withblack fur only on thetop of its tail’s tipand inconspicuoustufts of ear hair.However, thesespecies share manycharacteristics.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. For what reasons are biological classification

systems needed?2. Give two reasons why binomial nomenclature

is useful.3. What did Linnaeus contribute to the field of

taxonomy?4. What are the taxa used in biological classifica-

tion? Which taxon contains the largest numberof species? Which taxon contains the fewestnumber of species?

Thinking Critically5. Use categories that parallel the taxa of a biologi-

cal classification system to organize the itemsyou can borrow from a library.

6. Classifying Make a list of all the furniture ineither your classroom or your room at home.Classify it into groups based on function. Formore help, refer to Organizing Information inthe Skill Handbook.

SKILL REVIEWSKILL REVIEW


As shown in Figure 17.5, bobcatsand lynxes belong to the order,Carnivora. Carnivores have similararrangements of teeth and belong tothe class, Mammalia. Mammals havehair or fur covering their bodies andproduce milk for their young. Thephylum Chordata, to which mam-mals belong, includes mostly animalswith backbones. Kingdom Animaliaincludes all phyla of animals.

ARISTOTLE RECOGNIZESPLANTS AND ANIMALS

Taxonomy, as the science ofbiological classification is

called, began with theGreek philosopherAristotle (384–322 B.C.).A keen observer ofnature, Aristotle sepa-rated all living thingsinto two major groups:

plants and animals. Hegrouped plants into herbs,

shrubs, and trees, and classi-fied animals on the basis of size,

where they lived—on the land orin the water, and how they moved.Although Aristotle’s system ofclassification did little to revealnatural relationships among livingthings, it was widely accepted andused, with few modifications, intothe Middle Ages.

PUFFIN

OAK TREE

CONEFLOWER

DROMEDARY

The great diversity of life onEarth–estimated at 3 to 10 mil-lion species and counting–can beoverwhelming. To make sense ofthis bewildering array of livingthings, biologists use classifica-tion systems to grouporganisms in ways thathighlight their similari-ties, differences, andrelationships. The sys-tematic grouping of liv-ing things originated inthe 4th century B.C. Butbiological classificationhas changed a greatdeal over the years,as new tools andtechnologies have made it possi-ble to examine organisms inincreasing detail and trace theircomplex evolutionary pathwaysthrough time.

MOTH COLLECTION

FOCUS ONKingdomsof

RHODODENDRON460

Life

LINNAEUS IDENTIFIES TWO KINGDOMSModern classification began with the work of John Ray (1627–1705), an English naturalist who outlined the idea of species. In the mid-1700s, Swedish botanist Carolus Linnaeus (1707–1778) picked up on this idea and developed a clas-sification scheme that formed the basis of the system we use today. Linnaeus divided all living things between two kingdoms—plants and animals. But he subdivided these kingdoms into a hierarchy of smaller and more specific groups: classes, orders, genera, and species. Linnaeus placed organ-isms in these groups primarily on the basis of their physical similarities and differences.

PROTISTS: THE THIRD KINGDOMLinnaeus’ classification system revolutionized taxonomy, but from the startthere were problems. Organisms such as mushrooms and sponges resembleplants but do not make their own food. To whichkingdom did they belong? As light microscopesimproved, the situation became much more com-plex as biologists discovered a vast assortment ofminute, primarily one-celled organisms. In 1866,German zoologist Ernst Haeckel (1834–1919) pro-posed giving these unicellular organisms—namedprotists—a kingdom of their own.

PROKARYOTES AND FOUR KINGDOMSThe three-kingdom classification system persisted, however,until the middle of the 20th century when the electron micro-scope and advances in biochemistry made it possible to studyliving things at the subcellular level. These new tools revealedthat there are two fundamentally different kinds of cells in the liv-ing world—prokaryotes and eukaryotes. Prokaryotes, such as thebacterium Salmonella (below left), lack the membrane-bound nuclei and most of theorganelles characteristic of eukaryotic cells. All prokaryotes were then recognized asa separate kingdom that contained all the bacteria.

SALMONELLA (PROKARYOTE)Magnification: 34 300 X

KELP (EUKARYOTE)

VOLVOX (EUKARYOTE) Magnification: 15 x

QUEEN ANGELFISH

FLY AGARIC MUSHROOMS

BARREL SPONGE WITH CRINOIDS

461

462

PLANTSANIMALSFUNGI

PROKARYOTES

MONERANS

EVOLUTIONARY RELATIONSHIPSWith the five-kingdom system in place,many taxonomists focused their research onreclassifying living things in terms of theirevolutionary relationships rather than ontheir structural similarities. Present-dayorganisms, such as the millipede (below),were compared with extinct forms pre-served in the fossil record, such as thetrilobite (below right). New biochemical

techniques made it possible tocompare nucleotide sequencesin genes and amino-acidsequences in proteins fromdifferent organisms to deter-mine how closely those organ-isms were related.

THE FIVE-KINGDOM SYSTEMA flurry of ideas for new classification sys-tems followed close on the heels of the dis-covery of prokaryotes. In 1959, Americanbiologist R.H. Whittaker (1924–1980) pro-posed a five-kingdom system (right) thatsoon became universally accepted. The fivekingdoms were Monera (bacteria), Protista(algae and other protists), Fungi (mushrooms,molds, and lichens), Plantae (mosses, ferns,and cone-bearing and flowering plants), andAnimalia (invertebrate and vertebrate ani-mals). The kingdom Monera included all theprokaryotes; the other four kingdoms consist-ed of eukaryotes. Fungi, plants, and animalswere easily distinguished by their modes ofnutrition. But the kingdom Protista was agrab bag, a diverse assortment of livingthings—some plantlike, some animal-like,some funguslike—that did not fit clearly intoany of the other eukaryotic kingdoms.

TRILOBITE

MILLIPEDE

PROTISTS

WHITTAKER’S SYSTEM

EUKARYOTES

DOMAINS AND SUPERKINGDOMSThe discovery of the nature of Archaea led C. R. Woese and his colleagues at theUniversity of Illinois to propose a new classifi-cation scheme (left) made up of threedomains. The domain Bacteria has one king-dom, Eubacteria (true bacteria). The domainArchaea contains two kingdoms. The domainEukarya consists of the kingdoms Fungi,Plantae, and Animalia. Woese recognized thatthere were unresolved questions regardingwhere to place protists in Eukarya.

Recent efforts to establish the most naturalgroupings of organisms that show evolutionaryrelationships use molecular genetics. Genbankis a federal agency that gathers genetic datafor all of Earth’s organisms. Genbank’s sys-tem (below left) recognizes three superking-doms: Archaea, Eubacteria, and Eukaryota.The eukaryotes are not grouped into king-doms because the six kingdoms we are nowfamiliar with show many different origins.

EXPANDING Your View

THE SIXTH KINGDOMIn the 1970s, genetic tests showedthat members of the kingdomMonera were far more diverse thananyone had suspected. One groupof bacteria, originally called archae-bacteria (ancient bacteria), seemedespecially unusual. Archaebacteria,or archaeans, as most biologists nowrefer to them, often live in extremeenvironments—very hot or saltyplaces—such as the Grand Pris-matic Spring (left) in Yellowstone National Park. In 1996, researchers sequencedthe archaean genome and discovered that thesetiny cells are as different from bacteria as youare. A sixth kingdom was formed.

1 THINKING CRITICALLY How have technological advances, suchas improved microscopes and new biochemical tests, changed bio-logical classification?

2 JOURNAL WRITING The kingdom Protista contains very diverseorganisms—from unicellular “animallike” amebas to multicellular“plantlike” giant kelp. In your journal, predict what might happento the protist kingdom in the next few years as biologists study itsmembers in more detail at biochemical and genetic levels.

ARCHAEA Magnification: 29 000�

GRAND PRISMATIC SPRING, YELLOWSTONE NATIONAL PARK

WOESE’S SYSTEM

GENBANK‘S SYSTEM

DOMAIN DOMAIN DOMAIN

Bacteria Archaea Eukarya

KINGDOM KINGDOMS KINGDOMSEubacteria Euryarchaeota Animalia

(Methanogens)Plantae

Crenarchaeota Fungi(Thermophiles)

Protista?

SUPERKINGDOM SUPERKINGDOM

Archaea Eubacteria

SUPERKINGDOM

Eukaryota

Section


How Are EvolutionaryRelationshipsDetermined?

Evolutionary relationships aredetermined on the basis of similari-ties in structure, breeding behavior,geographical distribution, chromo-somes, and biochemistry. Becausethese characteristics provide the cluesabout how species evolved, they alsoreveal the probable evolutionary rela-tionships of species.

Structural similaritiesStructural similarities among

species reveal relationships. Forexample, the presence of manyshared physical structures impliesthat species are closely related and

may have evolved from a commonancestor. For example, because lynxesand bobcats have structures more sim-ilar to each other than to members ofany other groups, taxonomists suggestthat they share a common ancestor.Likewise, plant taxonomists use struc-tural evidence to classify dandelionsand sunflowers in the same family,Asteraceae, because they have similarflower and fruit structures.

If you observe an unidentified ani-mal that can retract its claws, you caninfer that it belongs to the cat family.You can then assume that the animalhas other characteristics in commonwith cats. Taxonomists observe andcompare features among members ofdifferent taxa and use this informationto infer their evolutionary history.

S uppose you entered a roomfull of strangers and wereasked to identify two related

people. What clues would you lookfor? You might listen for similar-sounding voices. You might look for similar hair, eye, and skin coloration. You might watch forshared behaviors and mannerismsamong individuals. Whentaxonomists want toidentify evolutionaryrelationships amongspecies, they exam-ine certain charac-teristics of species.

SECTION PREVIEW

ObjectivesDescribe how evolu-tionary relationships are determined.Explain how cladisticsreveals phylogeneticrelationships.Compare the six king-doms of organisms.

Vocabularyphylogenycladisticscladogrameubacteriaprotistfungus

17.2 The Six Kingdoms

Western sword fern(Polystichum munitum)(above) and Northernholly fern (Polystichumlonchitis) (inset)

Breeding behaviorSometimes, breeding behavior

provides important clues to relation-ships among species. For example,two species of frogs, Hyla versicolorand H. chrysoscelis, live in the samearea and look similar. During thebreeding season, however, there is anobvious difference in their matingbehavior. The males of each speciesmake different sounds to attractfemales, and therefore attract andmate only with members of their owngroup. Scientists concluded that thefrogs were two separate species.

Geographical distributionThe location of species on Earth

helps biologists determine their rela-tionships with other species. Forexample, many different species offinches live on the Galapagos Islandsoff the coast of South America.Biologists propose that in the pastsome members of a finchlike birdspecies that lived in South Americareached the Galapagos Islands, wherethey became isolated. These finchesprobably spread into different nicheson the volcanic islands and evolvedover time into many distinct species.The fact that they share a commonancestry is supported by their geo-graphical distribution in addition totheir genetic similarities.

Chromosome comparisonsBoth the number and structure of

chromosomes, as seen during mitosisand meiosis, provide evidence aboutrelationships among species. Forexample, cauliflower, cabbage, kale,and broccoli look different but havechromosomes that are almost identi-cal in structure. Therefore, biologistspropose that these plants are related.Likewise, the similar appearance ofchromosomes among chimpanzees,gorillas, and humans suggest a com-mon ancestry.

BiochemistryPowerful evidence about relation-

ships among species comes from bio-chemical analyses of organisms.Closely related species have similarDNA sequences and, therefore, simi-lar proteins. In general, the moreinherited nucleotide sequences thattwo species share, the more closelyrelated they are. For example, theDNA sequences in giant pandas andred pandas differ. They differ so muchthat many scientists suggest that giantpandas are more closely related tobears than to red pandas such as theone shown in Figure 17.6. Read theBioTechnology feature at the end of thischapter to learn more about howchemical similarities can reveal evolu-tionary relationships.

17.2 THE SIX KINGDOMS 465

Figure 17.6DNA sequences in redpandas (a) and giantpandas (b) suggestthat red pandas arerelated to raccoonsand giant pandas arerelated to bears.

ab

PhylogeneticClassification: Models

Species that share a commonancestor also share an evolutionaryhistory. The evolutionary history of a species is called its phylogeny(fy LOH juh nee). A classification system that shows the evolutionaryhistory of species is a phylogeneticclassification and reveals the evolu-tionary relationships of species.

Early classification systems did notreflect the phylogenetic relationshipsamong organisms. As scientists learnedmore about geologic time, they mod-ified the early classification schemesto reflect the phylogeny of species.

CladisticsOne biological system of classifica-

tion that is based on phylogeny iscladistics (kla DIHS tiks). Scientistswho use cladistics assume that asgroups of organisms diverge andevolve from a common ancestralgroup, they retain some unique

inherited characteristics that taxono-mists call derived traits. Biologistsidentify a group’s derived traits anduse them to make a branching dia-gram called a cladogram (KLAD ehgram). A cladogram is a model of thephylogeny of a species, and modelsare important tools for understand-ing scientific concepts.

Cladograms are similar to the pedi-grees, or family trees, you studied inan earlier chapter. Branches on bothpedigrees and cladograms show pro-posed ancestry. In a cladogram, twogroups on diverging branches proba-bly share a more recent ancestor thanthose groups farther away. If twoorganisms are near each other on apedigree’s branch, they also share anancestor. However, an important dif-ference between cladograms and pedi-grees is that, whereas pedigrees showthe direct ancestry of an organismfrom two parents, cladograms show aprobable phylogeny of a group oforganisms from ancestral groups.

In Figure 17.7, you see the clado-gram for modern birds, such asrobins. How was the cladogram devel-oped? First, taxonomists identified thederived traits of modern birds—flightfeathers, light bones, a wishbone,down feathers, and feathers with


Figure 17.7This cladogram uses the derived traits of a modern bird, such asthe robin, to model its phylogeny. Groups that are closer togetheron the cladogram probably share a more recent common ancestor.

OriginWORDWORD

phylogenyFrom the Greekwords phylon, mean-ing “related group,”and geny, meaning“origin.” Organismsare classified basedon their phylogeny.

cladisticsFrom the Greekword klados, mean-ing “sprout” or“branch.” Cladisticsis based on phy-logeny.

Light bones3-toed foot;wishbone

Downfeathers

Feathers withshaft, veins,and barbs

Flight feathers;arms as longas legs

Sinornis

Allosaurus

Theropods

Velociraptor

Archaeopteryx

Robin

Using a Cladogram to Show Relationships Cladogramswere developed by Willie Hennig. They use derived character-istics to illustrate evolutionary relationships.

Procedure! The following table shows the presence or absence of six

derived traits in the seven dinosaurs that are labeled A-G.@ Use the information listed in Table 17.1 to answer the

questions below.

Analysis1. Copy the partially completed cladogram. Complete the

missing information on the right side.

2. How many traits does dinosaur F share with dinosaur C,with dinosaur D, and with dinosaur E?

3. Dinosaurs A and B form a grouping called a clade. Thedinosaurs A, B, and C form another clade. What derivedtrait is shared only by the A and B clade? By the A, B, andC clade? By the D, E, F, and G clade?

4. Traits that evolved very early, such as the hole in the hipsocket, are called primitive traits. The traits that evolved later, such as a grasping hand, are called derived traits.Are primitive traits typical of broader or smaller clades?Are derived traits typical of broader or smaller clades?Give an example in each case.

MiniLab 17-2MiniLab 17-2 Classifyingshafts. Next, they identified ancestralspecies that have at least some ofthese traits. Most biologists agree thatthe ancestors of birds are a group ofdinosaurs called theropods. Some ofthese theropods are Allosaurus,Archaeopteryx, Velociraptor, Sinornis,and Protoarchaeopteryx. Each of theseancestors has a different number ofderived traits. Some groups sharemore derived traits than others.

Finally, taxonomists constructedthe robin’s cladogram from thisinformation. They assume that ifgroups share many derived traits,they share common ancestry. Thus,Archaeopteryx and the robin, whichshare four derived traits, are on adja-cent branches, indicating a recentcommon ancestor. Use the MiniLabon this page to construct a cladogramfor another species.

Another type of modelIn this book, you will see clado-

grams and other types of models thatprovide information about the phylo-genetic relationships among species.One type of model resembles a fan.Unlike a cladogram, a fanlike modelmay communicate the time organ-isms became extinct or the relativenumber of species in a group. A fan-like diagram incorporates fossil infor-mation and the knowledge gainedfrom anatomical, embryological,genetic, and cladistic studies.

In Figure 17.8 on the next page,you can see a fanlike model of thesix-kingdom classification system.For easy reference, the same diagramis located inside the back cover ofthis textbook. This model includesboth Earth’s geologic time and theprobable evolution of organisms dur-ing that timespan. In addition, thisfanlike diagram helps you to findrelationships between modern andextinct species.


Dinosaur trait D E F GCBA

Hole in hip socket

Extension of pubis bone

Unequal enamel on teeth

Skull has “shelf” in back

Grasping hand

Three-toed hind foot

yes

yes

no

no

no

no

yes

yes

yes

no

no

no

yes

no

no

no

yes

no

yes

yes

yes

yes

no

no

yes

yes

yes

yes

no

no

yes

no

no

no

yes

yes

yes

no

no

no

yes

yes

Table 17.1 Derived traits of dinosaurs

11

22

33

44

55

66

A B C D E F G

Three-toedhind foot

Grasping hand

EUBACTERIA

ARCHAEBACTERIA

PROTISTS

FUNGI

Mosses

Ferns

CENOZOIC PALEOZOIC PRECAMBRIANMESOZOIC

544 million years ago




PLANTS

Conifers

Flowering Plants

Mammals


LIFE’S SIX KINGDOMS

LIFE’S SIX KINGDOMS

ANIMALS

Amphibians and Fishes

Starfishes

Arthropods

Mollusks and Worms

Jellyfishesand Sponges

Birds and Reptiles

CENOZOICMESOZOICPALEOZOIC




Figure 17.8In this phylogenetic diagram, six colors representthe six kingdoms of living things. The phylogeny of organisms is represented by a fanlike structureperched on the Geologic Time Scale. The fan’s baserepresents the origin of life during the Precambrian.The fan’s rays represent the probable evolution ofspecies from the common origin. The major groupsof modern organisms occupy the fan’s outer edge,which represents present time.

How many species are there in each kingdom? You may not realize it, but you probably already have seen more than 1000 different species since you were born. How close might you be to having seen all the different species that exist?

AnalysisThe circle graph above shows Earth’s six kingdoms.

Thinking Critically1. List the approximate number of species for each of the

six kingdoms. Each degree of the circle graph is equal to10 000 species. Archaebacteria represent 1/20 of a degree,and Eubacteria represent 1 degree.

2. What is the approximate total number of species for alllife forms on Earth?

3. What approximate percent of the total life forms on Earthare in each kingdom?

4. Why do all questions refer to the number of species as“approximate?”

Problem-Solving Lab 17-2Problem-Solving Lab 17-2 Using Graphs

Groups of organisms that arecloser in the same colored ray sharemore inherited characteristics andare probably more closely relatedthan groups that are farther apart.For example, find the jellyfishes, thefishes, and the reptiles on the model.Notice that fishes and reptiles arecloser to each other than they are tothe jellyfishes, indicating that theyare more closely related to each otherthan they are to jellyfishes.

The Six Kingdoms of Organisms

As you saw in Figure 17.8, the sixkingdoms of organisms are archae-bacteria, eubacteria, protists, fungi,plants, and animals. In general, dif-ferences in cellular structures andmethods of obtaining energy are thetwo main characteristics that distin-guish among the members of the sixkingdoms. The six kingdoms reflectevolutionary history. Learn moreabout the number of species in eachkingdom in the Problem-Solving Labon this page.

ProkaryotesThe prokaryotes, organisms with

cells that lack distinct nuclei boundedby a membrane, are microscopic andunicellular. Some are heterotrophs andsome are autotrophs. In turn, someprokaryotic autotrophs are chemosyn-thetic, whereas others are photosyn-thetic. Prokaryotes are classified intwo kingdoms: Archaebacteria andEubacteria. The oldest prokaryoticfossils are about 3.5 billion years old.

There are a few hundred species ofarchaebacteria and most of them livein extreme environments such asswamps, deep-ocean hydrothermalvents, and seawater evaporatingponds, Figure 17.9. Most of theseenvironments are oxygen-free. The

Animals

Plants Protista

Fungi

Eubacteria

Archaebacteria

470

Figure 17.9Most archaebacteria,such as these salt-lovingHalococcus (a) live inextreme environments,such as seawater evapo-rating ponds (b).

a

b

lipids in the cell membranes ofarchaebacteria, the composition oftheir cell walls, and the sequence ofnucleic acids in their ribosomal RNAdiffer considerably from those ofother prokaryotes. However, theirgenes have a similar structure tothose in eukaryotes.

All of the other prokaryotes, morethan 10 000 species of bacteria, areclassified in Kingdom Eubacteria.Eubacteria, such as the ones you seein Figure 17.10, have very strongcell walls and a less complex genetic


Figure 17.10Eubacteria are adiverse kingdom ofprokaryotes. Both theircellular structure andthe way they obtainfood vary widely.

makeup than found in archaebacteriaor eukaryotes. They live in mosthabitats except the extreme oneswhere the archaebacteria live.Although some eubacteria cause dis-eases, such as strep throat and pneu-monia, most bacteria are harmlessand many are actually helpful.

Protists: A diverse groupKingdom Protista contains diverse

species as you can see in Figure 17.11,but protists do share some character-istics. A protist is a eukaryote that

OriginWORDWORD

eubacteriaFrom the Greekwords eu, meaning“true,” and bakte-rion, meaning“small rod.”Eubacteria areprokaryotes.

protistFrom the Greekword protistos,meaning “very first”or “superlative.”The first eukaryotecells were protists.

The bacteria thatcause strep throatare heterotrophscalled Streptococcus.

AA

Cyanobacteria, suchas Oscillatoria, live infreshwater and arephotosynthetic.

BB

Magnification: 40 000�Magnification:

100�

Figure 17.11Although these three protists lookdifferent, they are all eukaryotesand live in moist environments.

Funguslike slime molds oftencreep through damp forests,feeding on microorganisms.

AAThe paramecium is ananimal-like protist thatmoves through water.

BB

These kelps are multicellularplantlike protists. Althoughthey look like plants, they donot have organs or organsystems.

CC

Magnification: 150�

lacks complex organ systems and livesin moist environments. Fossils ofplantlike protists show that protistsexisted on Earth up to two billionyears ago. Although some protists areunicellular, others are multicellular.Some are plantlike autotrophs, someare animal-like heterotrophs, andothers are funguslike heterotrophsthat produce reproductive structureslike those of fungi.

Fungi: Earth’s decomposersOrganisms in Kingdom Fungi are

heterotrophs that do not move fromplace to place. A fungus is either aunicellular or multicellular eukaryotethat absorbs nutrients from organicmaterials in the environment. Fungifirst appeared in the fossil recordabout 400 million years ago. Thereare more than 100 000 known speciesof fungi, including the one you see inFigure 17.12.

Plants: Multicellular oxygen producers

All of the organisms in KingdomPlantae are multicellular, photosyn-thetic eukaryotes. None moves fromplace to place. A plant’s cells usuallycontain chloroplasts and have cellwalls composed of cellulose. Plantcells are organized into tissues that,in turn, are organized into organsand organ systems. You can see twoof the many diverse types of plants inFigure 17.13.

The oldest plant fossils are a littlemore than 400 million years old.


Figure 17.12Morels are edible fungithat grow for only afew days in only a fewplaces.

Figure 17.13A Hibiscus is just onekind of flowering plant(a). Tropical tree ferns donot produce flowers (b).

a

b

Figure 17.14Many animals have well-developednervous and muscular systems.

However, some scientists proposethat plants existed on Earth’s landmasses much earlier than these fossilsindicate. Plants do not fossilize asoften as organisms that contain hardstructures, such as bones, which morereadily fossilize than soft tissues.

There are more than 500 000known species of plants. Althoughyou may be most familiar with flow-ering plants, there are many othertypes of plants, including mosses,ferns, and evergreens.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. How do members of the different kingdoms

obtain nutrients?2. Make a list of the characteristics that archaebac-

teria and eubacteria share. Then make a list oftheir differences.

3. For what reasons is a fanlike diagram a usefulmodel for phylogenetic classification? Explaineach of your reasons.

4. How do cladograms and fanlike diagrams differ?

Thinking Critically5. Why is phylogenetic classification more natural

than a system based on characteristics such asmedical usefulness, or the shapes, sizes, and colors of body structures?

6. Making and Using Tables Make a table thatcompares the characteristics of members of eachof the six kingdoms. For more help, refer toOrganizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW


Animals: Multicellular consumersAnimals are multicellular het-

erotrophs. Nearly all are able tomove from place to place. Animalcells do not have cell walls. Theircells are organized into tissues that,in turn, are organized into organsand complex organ systems. Someorgan systems in animals are the ner-vous, circulatory, and muscular sys-tems, Figure 17.14. Animals firstappeared in the fossil record 600 mil-lion years ago.

The luna moth’s antennae aresense organs, which are part ofits nervous system. The moth’santennae detect tiny quantitiesof chemicals in the air.

AA

The cheetah uses many of its organ systems,especially its nervous and muscular systems,to speed through the grasslands, perhapschasing prey.

BB


INVESTIGATEINVESTIGATE

ProblemHow is a dichotomous key made?

ObjectivesIn this BioLab, you will:■ Classify organisms on the basis of

structural characteristics.■ Develop a dichotomous key.

Materialssample keys from guidebooksmetric ruler

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

1. Study the drawings of beetles.2. Choose one characteristic of the

beetles and classify the beetlesinto two groups based on thatcharacteristic. Take measure-ments if you wish.

3. Record the chosen characteristicin a diagram like the one shown.Write the numbers of the beetlesin each group on your diagram.

4. Continue to form subgroupswithin your two groups based ondifferent characteristics. Recordthe characteristics and numbers

of the beetles in your diagramuntil you have only one beetle ineach group.

5. Using the diagram you have justmade, make a dichotomous keyfor the beetles. Remember thateach numbered step should con-tain two choices for classification.Begin with 1A and 1B. For help,examine sample keys provided byyour teacher.

6. Exchange dichotomous keys withanother team. Use their key toidentify the beetles.

PROCEDUREPROCEDURE

Making a Dichotomous Key

Do you remember the first time you saw a beetle? You may haveasked someone nearby, “What is it?” You may still be naturally

curious and want to know the names of insects you find. To help identifyorganisms, taxonomists have developed dichotomous keys. A dichotomouskey is a set of paired statements that can be used to identify organisms.When you use a dichotomous key, you choose one statement from eachpair that best describes the organism. At the end of each statement youchose, you are directed to the next set of statements to use. Finally, youwill read a statement that contains at the end the name of the organismor the group to which it belongs.

Scarab beetle

Longhornedwoodboringbeetle

Bark beetle


1. Comparing and Contrasting Wasthe dichotomous key you con-structed exactly like those of otherstudents? Explain your answer.

2. Analyzing Data What characteris-tics were most useful for making aclassification key for beetles? Whatcharacteristics were not useful?

3. Thinking Critically Why do keystypically offer only two choices andnot more?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Beetles

Group 1

Group 2

1

Variegated mud-loving beetle

2 3 4 5 6

Mycetaeid beetle Apricot borer Water tiger Predaceous divingbeetle

Crawling waterbeetle

7

Flathead apple beetle

8 9 10 11 12

Red-neckedcane beetle

Cucumber snoutbeetle

13

Red flour beetle

14 15

Blind ant-beetle

False wirewormbeetle

16

White-markedspider beetle

17 18

Monterey cyprusbeetle

Drug store beetle

Whirligig beetle

Ironclad beetle

Broad-hornedflour beetle

Going FurtherGoing Further

Application Using the same procedurethat you just used to make a beetle key,make a dichotomous key to identify the students in your class.

To find out more about identifying organisms,

visit the Glencoe Science Web site.science.glencoe.com

BIOLOGY


A ccumulated molecular differences in theDNA of two species can indicate how long

they have been separate species. Comparing both the DNA base sequences and the amino acidsequence of a specific protein of two species canindicate the closeness of their relationship.

Comparing DNA One way to compare DNA isto measure how strongly the single strands ofDNA from two species will bond. This method isknown as DNA-DNA hybridization. Double-stranded DNA from each species is heated toseparate the complementary strands. Then thesingle strands of DNA from each species aremixed and allowed to cool. As the DNA cools,the single strands from the two species bond, orhybridize. If the species are closely related, moreof their DNA base pairs will match, and theirDNA strands will bond strongly.

Another method of comparing the DNA ofspecies is called DNA sequencing. Biologistsselect a gene that species have in common andcompare the genes’ bases. Counting how manybase pairs differ can indicate approximately howlong ago each species became distinct. Estimatesobtained by DNA sequencing show that many ofthe animal phyla began to appear on Earth about1.2 billion years ago.

Protein Clocks A specific protein is assumed toevolve at about the same rate in all species thatcontain the protein. Comparing the amino acidsequences of the protein in several species canshow about how long ago the species diverged.For example, cytochrome c is a protein in thecells of aerobic organisms. Both human andchimpanzee cytochrome c has the same aminoacid sequence. The cytochrome c of other pri-mates has a different amino acid sequence.


Molecular Clocks

How long ago did animals first appear on Earth? Did the giant panda evolve along the same family line as bears or raccoons? To help answer questions like these,

biologists have learned how to use DNA, proteins, and other biological molecules as “clocks” that reveal details about evolutionary relationships.

TechnologyTechnologyBIOBIO

Analyzing Information The cytochrome cfound in humans and chimpanzees differs fromthat found in dogs by 13 amino acids, in tuna by31 amino acids, and in rattlesnakes by 20 aminoacids. What assumptions can you make based onthis information?

To find out more aboutmolecular clocks, visit the

Glencoe Science Web site.science.glencoe.com

INVESTIGATING THE TECHNOLOGYINVESTIGATING THE TECHNOLOGY

Application for the FutureDNA-DNA hybridization has shown that

flamingoes are more closely related to storksthan they are to geese. Protein clock data suggestthat humans and chimpanzees became distinctspecies recently in the history of Earth. Thesebiotechnological methods are useful in determin-ing phylogenetic relationships.

Flamingoes andstorks are closelyrelated.

BIOLOGY


Chapter 17 Assessment

SUMMARYSUMMARY

Section 17.1

Section 17.2

Main Ideas■ Although Aristotle developed the first classifica-

tion system, Linnaeus laid the foundation formodern classification systems by using structuralsimilarities to organize species and by develop-ing a binomial naming system for species.

■ Scientists use a two-word system called binomialnomenclature to give species scientific names.

■ Classification provides an orderly framework inwhich to study the relationships among livingand extinct species.

■ Organisms are classified in a hierarchy of taxa:kingdom, phylum or division, class, order, fam-ily, genus, and species.

Vocabularybinomial nomenclature

(p. 454)class (p. 459)classification (p. 453)division (p. 459)family (p. 458)genus (p. 454)kingdom (p. 459)order (p. 459)phylum (p. 459)taxonomy (p. 453)

Classification

Main Ideas■ Biologists use similarities in body structures,

breeding behavior, geographic distribution,chromosomes, and biochemistry to determineevolutionary relationships.

■ Modern classification systems are based on phy-logeny. Both cladograms and the fanlike modelsinclude information about phylogeny.

■ Taxonomists organize organisms into six king-doms. Kingdoms Archaebacteria and Eubacteriacontain only unicellular prokaryotes that differchemically from each other. Kingdom Protistacontains eukaryotes that lack complex organsystems. Kingdom Fungi includes heterotrophiceukaryotes that absorb their nutrients. KingdomPlantae includes multicellular eukaryotes thatare photosynthetic. Kingdom Animalia includesmulticellular, eukaryotic heterotrophs with cellsthat lack cell walls.

Vocabularycladistics (p. 466)cladogram (p. 466)eubacteria (p. 471)fungus (p. 472)phylogeny (p. 466)protist (p. 471)

The SixKingdoms

CHAPTER 17 ASSESSMENT 477

1. Which of the following is a scientific name ofa species?a. bison bison c. homo Sapiensb. Mimus Polyglottis d. Quercus alba

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. Which of the following would be a usefulcharacteristic to use in cladistics?a. derived characteristicb. similar habitatc. mutationsd. random differences

Chapter 17 Assessment

Chapter 17 AssessmentChapter 17 Assessment

3. Which taxon contains the others?a. family c. orderb. species d. phylum

4. Unlike a pedigree, a cladogram ________.a. shows ancestryb. shows hypothesized phylogenyc. indicates ancestry from two parentsd. explains relationships

5. Which of the following pairs of terms aremost closely related?a. Linnaeus—DNA analysisb. Aristotle—binomial nomenclaturec. protist—prokaryoted. taxonomy—classification

6. Linnaeus based most of his classification system on ________.a. cell organellesb. biochemical comparisonsc. structural comparisonsd. embryology

7. A group of prokaryotes that often live inextreme environments is the ________.a. archaebacteria c. eubacteriab. protists d. fungi

8. Based on the structures of the organisms yousee, which of the following is most closelyrelated to a domestic cat?

9. A flaw in Aristotle’s classification system wasthat ________.a. it included too many organismsb. it did not show natural relationshipsc. large organisms were not includedd. it was based on Greek instead of Latin

10. Which of the following describes the organism shown to the right?a. unicellular

consumerb. unicellular producerc. multicellular

consumerd. multicellular

producer

11. The evolutionary history of a species is its________, but ________ is the science thatgroups and names species.

12. A diverse group of eukaryotes that lack com-plex organ systems and live in moist places isthe ________.

13. A group of related classes in the plant king-dom is a ________, but in the animal king-dom it is called a ________.

14. From their scientific names, Quercus alba andQuercus rubrum, you know that these speciesof oak trees are in the same ________.

15. ________ is the name given to the taxon thatcontains all the families of carnivores, such asbears and cats.

16. Modern classification systems are based on________.

17. A multicellular heterotrophic eukaryote thatabsorbs nutrients would be classified inKingdom ________.

18. Linnaeus devised a two-word naming systemfor organisms that is called ________.

19. The process of grouping similar objects orinformation is called ________.

20. All genera of dogs are classified in the taxoncalled a ________.

478 CHAPTER 17 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

You Are Smarter Than You Think Nothing on these tests is rocket science. You canlearn to master any of it. When you admit that,you’re 90 percent of the way home. Just keeppracticing.

a. c.

b. d.

Chapter 17 AssessmentChapter 17 Assessment

CHAPTER 17 ASSESSMENT 479

21. Explain why Linnaeus’s system of classifica-tion is more useful than Aristotle’s.

22. You find an unusual organism growing on thebark of a dying tree. Under a microscope,you observe that its cells are eukaryotic, have cell walls, and do not contain chloroplasts. Into what kingdom would you classify thisorganism? Explain your decision.

23. Observing and Inferring In what way doesthe work of Linnaeus illustrate the nature of science?

24. Classifying Make a list of a minimum of five physical features you could use to classifytrees.

25. Comparing and Contrasting Compare theclassification system of your school librarywith that of organisms.

26. Concept Mapping Complete the conceptmap by using the following vocabulary terms:divisions, taxonomy, kingdoms, binomialnomenclature, phyla.

THINKING CRITICALLYTHINKING CRITICALLY

APPLYING MAIN IDEASAPPLYING MAIN IDEAS ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

Identify the organisms in these photographs.

Key1A Front and hind wings similar in size andshape, and folded parallel to the body when at rest..............................................damselflies

1B Hind wings wider than front wings nearbase, and extended on either side of the bodywhen at rest...................................dragonflies

Classifying Study the dichotomous key andanswer the following questions.1. Interpreting Data The insect in the

photo on the right is a damselfly becauseit has ________.a. wings that are opaqueb. wings folded at restc. smaller eyesd. wings not similar in size

2. The insect in the photo on the left is adragonfly because it has ________.a. wings that are opaqueb. wings folded at restc. larger eyesd. wings not similar in size

3. Classifying From the key and the pho-tographs above, identify traits that indi-cate dragonflies and damselflies mayhave evolved from a common ancestor.

2.

4. 5.

that are subdivided into

for plants

1.

3.

uses a naming system called

classifies organisms into

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web site.science.glencoe.com

CD-ROM


Geologic Time ScaleThe four eras of the Geologic Time Scale span

about 4.6 billion years of Earth’s history.

The Precambrian EraThe Precambrian era encompasses approxi-

mately the first four billion years of the scale.Prokaryotic cells appear in rocks dated 3.6 billionyears old. By the end of the Precambrian, the firsteukaryotic cells had evolved.

The Paleozoic EraThe following 300 million years make up the

Paleozoic era. Many plant groups such as fernsand conifers appeared. Animal groups such asworms, insects, fishes, and reptiles evolved.

The Mesozoic EraFrom 245 million years ago to 66 million years

ago, the Mesozoic era, reptiles diversified, andmammals and flowering plants evolved. TheMesozoic, the Age of Dinosaurs, ended with arapid extinction of the dinosaurs.

The Cenozoic EraThe current Cenozoic era, which has encom-

passed the previous 66 million years, is oftenreferred to as the Age of Mammals. Primates,including humans, evolved during this era.

Change Through TimeScientists propose that about five billion years ago Earth

was extremely hot. As Earth slowly cooled, water vapor in its atmosphere fell as rain, forming today’s oceans. Life hadappeared in these oceans by 3.6 billion years ago. Since then,millions of species have evolved and then become extinct.

For a preview of the change through time unit, study this BioDigest before you read thechapters. After you have studied the change through time chapters, you can use the

BioDigest to review the unit.

BIODIGESTBIODIGEST

Precambrian era

Paleozoic era

Mesozoic era

Cenozoic era

I billionyears ago

2.6 billionyears ago

3 billionyears ago

5 billion years ago

The Geologic Time Scale illustrates majorevents that have occurred during Earth’s4.6-billion-year history. Each era is subdi-vided into smaller time spans called periods.

480

FOCUS ON HISTORYFOCUS ON HISTORY

Two scientists, Stanley Miller andHarold Urey, pioneered work about

the origin of Earth’s life. Their experi-ments showed that small molecules canform complex organic materials underconditions that may have existed onearly Earth. Other scientists demon-strated how these complex chemicalscould form protocells, which are large,organized structures that carry out

some activities associated with life, suchas growth and division.

The American biologist LynnMargulis proposed the endosymbionttheory. This theory suggests that cellorganelles, such as mitochondria andchloroplasts, may have evolved whensmall prokaryotes entered larger pro-karyotes and began to live symbioticallyinside these larger cells.

Pioneers

Origin of Life TheoriesPeople once thought that life was able to

arise spontaneously from nonliving material. Two scientists, Francesco Redi and Louis Pasteur,designed controlled experiments to try to dis-prove spontaneous generation. Their exper-iments convinced scientists to accept the theoryof biogenesis—that life comes only from preexist-ing life.

Modern Ideas About the Origin of Life

Most scientists agree that small organic mole-cules formed from substances present in Earth’searly atmosphere and oceans. At some point,nucleic acids must have formed. Then, clusters oforganic molecules might have formed protocellsthat may have evolved into the first true cells.

Heterotrophic, anaerobic prokaryotes wereprobably the earliest organisms to live on Earth.Chemosynthetic prokaryotes evolved over time,followed by oxygen-producing photosyntheticprokaryotes. As the amount of oxygen in theatmosphere increased, aerobically respiring euka-ryotes probably evolved.

Change Through Time

481

BIODIGESTBIODIGEST

Lynn Margulis

Eukaryotic cells, like this Euglena, contain organelles, such as mitochon-dria and chloro-plasts, that probably evolved over time from a symbiotic associ-ation of prokaryotes.

A heterotrophic prokaryote

Louis Pasteur dis-proved the idea ofspontaneous genera-tion by conductingexperiments usingbroth in swan-neckedflasks like this one.

Magnification: 37 500�

Magnification:2250�

Change Through Time

482

BIODIGESTBIODIGEST

Evidence of EvolutionCharles Darwin and Alfred Wallace proposed

the idea of natural selection as a mechanism ofevolution. Natural selection occurs because allorganisms, which produce many more youngthan can survive, compete for mates, food, space,and other resources. Such competition favors thesurvival of individuals with variations that helpthem compete successfully in a specific environ-ment. Individuals that survive to reproduce canpass their traits to the next generation.

FossilsThe fossil record contains evidence for evolu-

tion and provides a record of life on Earth. Fossilscome in many forms, such as imprints, the burrowof a worm, or an actual bone. By studying fossils,scientists learn how organisms changed over time.

Scientists use relative and radiometric datingmethods to determine the age of fossils. Relativedating assumes that in undisturbed layers of rock,the deepest rock layers contain the oldest fossils.Radiometric dating analysis compares the knownhalf-lives of radioactive isotopes to a ratio of theamount of radioactive isotope originally in a rockor fossil with the amount of isotope in the rock orfossil today.

VITAL STATISTICSVITAL STATISTICS

Half-Lives of Radioactive IsotopesRadium226—1620 yearsCarbon14—5710 (± 30) yearsPotassium40—1.3 billion yearsRubidium87—4.7 billion yearsUranium235—710 million yearsUranium238—4.5 billion years

Fossils of dinosaurs similar to this Tyran-nosaurus rex have been found in Northand South America, and also in China.

The members of relatedspecies have variationssuch as those you see inthe shells of these snails.

FOCUS ON ADAPTATIONSFOCUS ON ADAPTATIONS

The finches in the Galapagos Islands are an example of the rapid development of a species. It has been

proposed that the 13 species of Galapagos finches evolvedfrom just a few ancestral species of finches that arrivedfrom South America and colonized the newly formedhabitats of these volcanic islands.

The adaptive radiation of finch speciesoccurred as the original finch populationadapted to the different niches found inthe islands. The pressures of natural selec-tion produced different species, each withtheir own feeding and habitat adaptations.

Additional EvidenceSimilar anatomical structures, called homolo-

gous structures, in different organisms might indi-cate possible shared ancestry. For example, bothvertebrate limbs and developmental stages showhow vertebrates might be related. In addition,similarities among the nucleic acid sequences ofspecies provide evidence for evolution. Direct evi-dence for evolution has been observed in the lab-oratory among species of bacteria that havedeveloped resistance to antibiotics.

Mechanics of EvolutionEvolution occurs when a population’s genetic

equilibrium changes. Mutations, genetic drift, andmigration may slightly disrupt the genetic equilib-rium of large populations, but they will greatlyalter that of small populations. Natural selectionaffects the genetic equilibrium of all populations.

Three Patterns of EvolutionThree patterns of natural selection lead to

speciation. Stabilizing selection favors the sur-vival of a population’s average individuals for a feature. Directional selection naturally selectsfor an extreme feature. Disruptive selection,which usually occurs when a physical barrierdivides one population into two, eventually produces two populations, each with one of a feature’s extreme characteristics.

Change Through Time

483

BIODIGESTBIODIGEST

In California, there areseven subspecies ofreproductively isolatedsalamanders, Ensatinaeschscholtzi.

The bones that makeup a penguin’s wingsare homologous tothose that form thewings of an alba-tross. The forelimbbones of four-leggedvertebrates are alsohomologous.

Tool-using

Adaptive Radiation in Galapagos Finches

Cactusground

Largeground

Insectivorous

Warbler

Vegetarian

Primate EvolutionPrimates are a grouping of mammals with

adaptations such as binocular vision, opposablethumbs, and mobile skeletal joints. These adapta-tions help arboreal animals survive in forest trees,where all primates may have originally lived andwhere most primates still live.

There are two categories of primates: the prosimians,including lemurs and tarsiers,and the anthropoids, includinghumans, apes, and monkeys.Monkeys are subdivided furtherinto two groups that are calledOld World monkeys and NewWorld monkeys.

Primates first appear in thefossil record in the Cenozoic era.Fossils indicate that increasingbrain size and bipedal locomo-tion are the two major trends inprimate evolution.

Unlike most Old World monkeys, New World monkeys, such as this howler monkey, have prehensile tails that are used as a fifth limb.

Human AncestryFossils of the possible human ancestors,

called Australopithecines, were discovered inAfrica and date from 5 to 8 million years ago.They show that these ancestors were bipedaland climbed trees.

After examining more recently discoveredhominid fossils, paleoanthropologists suggestthat the increasing efficiency of bipedal loco-motion and the decreasing size of jaws andteeth were two directions of human evolution.

The appearance of both the genus Homoand stone tools coincides in the fossil recordabout 2 million years ago. The use of fire, tools,language, and ceremonies developed in laterspecies of Homo.

Organizing Life’s Diversity

Biologists use a classification system to studyand communicate about both the three to tenmillion species living on Earth today and the manyextinct species represented by fossils. AlthoughAristotle produced the first system of classifica-tion, Linnaeus developed the basic structure ofthe modern-day classification system. Linnaeusalso developed a naming system, termed bino-mial nomenclature, that is still used today.

Today’s phylogenetic classification uses a hier-archy of taxa to classify organisms. From largestto smallest, this hierarchy is kingdom, phylum ordivision, class, order, family, genus, and species.The most useful systems of classification showevolutionary relationships among species.

Change Through Time

484

BIODIGESTBIODIGEST

VITAL STATISTICSVITAL STATISTICS

HominidsCranial Capacity of HominidsAustralopithecus—range of 375–550 ccHomo habilis—range of 500–800 ccHomo erectus—range of 750–1225 ccHomo sapiens (archaic)—average of 1200 ccHomo neanderthalensis—average of 1450 ccHomo sapiens (modern)—average of 1350 cc

Kingdom

Phylum

Bobcat

Class

Order

Family

Genus

Species

Animalia

Chordata

Mammalia

Carnivora

Felidae

Lynx

Lynx rufus

Taxonomists classifythe bobcat within ahierarchy of taxa.

Six Kingdoms of ClassificationSpecies are classified into one of six kingdoms.

Prokaryotes belong to Kingdom Archaebacteriaor Kingdom Eubacteria depending on their RNAsequences. Kingdom Protista contains the eukary-otes that lack complex organ systems and live inmoist environments. The kingdom Fungi includesheterotrophic eukaryotes that absorb nutrients.Multicellular autotrophs with complex organ sys-tems are placed in Kingdom Plantae. KingdomAnimalia includes multicellular heterotrophs.

Criteria for ClassificationBiologists use criteria such as body structure,

breeding behavior, and geographic distributionto classify organisms. Biochemistry and chromo-some analysis are also important for explainingthe relationships among organisms.

Change Through Time

485

BIODIGESTBIODIGEST

The phylogenetic relationship of the six kingdoms can be represented by a fanlike diagram.

EUBACTERIA

ARCHAEBACTERIA

PROTISTS

FUNGI

PLANTS ANIMALS

BIODIGEST ASSESSMENTBIODIGEST ASSESSMENT

Understanding Main Ideas1. The Geologic Time Scale’s longest era was

the ________.a. Precambrian c. Mesozoicb. Paleozoic d. Cenozoic

2. When did humans and primates evolve?a. the Precambrian c. the Mesozoicb. the Paleozoic d. the Cenozoic

3. Who disproved spontaneous generation?a. Louis Pasteur c. Charles Darwinb. Lynn Margulis d. Miller and Urey

4. Which scientist proposed the endosymbiont theory?a. Francesco Redi c. Harold Ureyb. Lynn Margulis d. Stanley Miller

5. Direct evidence of evolution includes________.a. fossilsb. anatomical similaritiesc. bacterial antibiotic resistanced. embryo

6. Which dating method relies on the positionof rock layers?a. radiometric c. absolute b. relative d. morphology

7. Which of the following was proposed byCharles Darwin?a. endosymbiont hypothesisb. biogenesisc. natural selectiond. experimentation

8. ________ is one of the two major groupsof primates.a. Old World monkey c. apesb. New World monkey d. prosimians

9. Binomial nomenclature is a biological sys-tem of ________.a. naming species c. evolutionb. phylogeny d. bipedalism

10. Multicellular heterotrophs are placed inKingdom ________.a. Protista c. Plantaeb. Fungi d. Animalia

Thinking Critically1. Describe the types of organisms that

existed in the Mesozoic. In the Cenozoic.

2. Explain how natural selection might be amechanism of evolution.

3. Why do biologists classify organisms?

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