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Unit Projects

Unit ProjectsUnit ProjectsUnit Projects

Unit 8Unit 8Advance PlanningChapter 25■ Order slides for the Quick

Demo and Alternative Lab.■ Purchase rotifers and vinegar

eels for the two MiniLabs.■ Order Daphnia for the Project.■ Collect earthworms and pla-

narians for the Reinforcement.Chapter 26■ Order slides for the Quick

Demo and Biology Journal.■ Order live hydra for the Mini-

Lab and Close.■ Order sponges and cnidarians

for the Reinforcement.■ Order a live vinegar eel culture

for the Quick Demo.Chapter 27NoneChapter 28■ Obtain arthropods for the

Quick Demo.■ Obtain bess beetles for the

Alternative Lab.■ Obtain preserved crayfish for

the MiniLab.■ Obtain live crayfish and a but-

terfly chrysalis for the QuickDemos and MiniLab.

Chapter 29■ Purchase a slide of sea star

pedicellariae for the MiniLab.■ Obtain sea stars for Quick

Demos.■ Purchase echinoderm fossils

for the Portfolio.■ Purchase slides of a lancelet

and sea urchin developmentfor the Alternative Lab.

■ Purchase Branchiostoma cali-forniense for the MiniLab.

■ Obtain live sea urchins for theBioLab.

DisplayVisual-Spatial Have students makea poster showing a plan for devel-

opment of a butterfly garden that wouldattract local butterflies.

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Make a MapVisual-Spatial Have students mapthe migration of monarch butter-

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Final ReportHave student groups make a poster thatillustrates their observations of the meta-morphosis of a butterfly.

InvertebratesInvertebratesAlmost all animals on Earth—95 percent—are invertebrates, animals without backbones. Tidal pools and the oceans thatsustain them are home to many of theworld’s invertebrates. The enormous diver-sity in form and function of invertebrates is the result of a long evolutionary history.As you study invertebrates, you will discover adaptations that are evolutionarymilestones.

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UNIT CONTENTSUNIT CONTENTS

What Is an Animal?

Sponges, Cnidarians,Flatworms, and Roundworms

Mollusks and SegmentedWorms

Arthropods

Echinoderms and InvertebrateChordates

UNIT PROJECTUNIT PROJECT

Use the Glencoe Science Web Site for more project

activities that are connected to this unit.www.glencoe.com/sec/science

Unit 8Unit 8

InvertebratesBIODIGESTBIODIGEST

Unit ProjectsUnit ProjectsUnit Projects

Unit Projects

Unit 8Unit 8

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Invertebrates

Unit OverviewIn this unit, students becomefamiliar with invertebrates.Chapter 25 introduces the gen-eral characteristics of animals aswell as their body plans.

In Chapter 26, students begintheir examination of specificinvertebrate groups through thestudy of the structure, adapta-tions, ecology, and phylogeny ofsponges, cnidarians, flatworms,and roundworms. In Chapter 27,students examine the characteris-tics, ecology, and phylogeny ofmollusks and segmented worms.

Chapter 28 allows students toexplore the largest group of ani-mals—the arthropods. In thischapter, the diversity of arthro-pods is examined, while featuresthat enabled many arthropods tobecome land dwellers are ex-plained.

The unit concludes in Chapter29 with a presentation of echino-derms and invertebrate chor-dates.

Introducing the UnitAsk students to examine the photoof the tidal pool. Ask them toidentify several of the organismsshown in the photo. Have theclass brainstorm to create lists ofhow these organisms are alikeand how they are different. Tryto lead students to include char-acteristics of each organism thatshow its adaptation to its envi-ronment. L2

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The Life Cycle of a ButterflyHave students do one of the projects forthis unit as described on the GlencoeScience Web Site. As an alternative, stu-dents can do one of the projects describedon these two pages.

Use the LibraryIntrapersonal Ask students to re-search information about butterfly

metamorphosis. L2

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Design and BuildKinesthetic Have students obtainthe materials and develop an enclo-

sure to observe butterfly metamorphosis.

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Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations. Teacher Classroom Resources

Assessment Resources Additional Resources

Products Available FromGlencoeTo order the following products,call Glencoe at 1-800-334-7344:CD-ROMMammals: A MultimediaEncyclopediaVideodiscSTV: Animals

Products Available FromNational Geographic SocietyTo order the following products,call National Geographic Societyat 1-800-368-2728:BookNational Geographic Book ofMammalsVideosPredators of North AmericaStrange Creatures of the Night

Tigers of the SnowWhite WolfWild Survivors: Camouflage andMimicry

Index to NationalGeographic MagazineThe following articles may beused for research relating to thischapter:“Poison-Dart Frogs: Lurid andLethal,” by Mark W. Moffet,May 1995.“Animals at Play,” by Stuart L.Brown, December 1994.“The Amazing Frog-Eating Bat,”by Merlin D. Tuttle, January1982.

Teacher’s Corner

692B

What Is an Animal?What Is an Animal?

TransparenciesReproducible MastersSection

Typical AnimalCharacteristics

Body Plans andAdaptations

Section 25.1

Section 25.2

Teacher Classroom Resources

Reinforcement and Study Guide, pp. 111-112Critical Thinking/Problem Solving, p. 25BioLab and MiniLab Worksheets, p. 113Laboratory Manual, pp. 179-182Content Mastery, pp. 125-126, 128

Reinforcement and Study Guide, pp. 113-114Concept Mapping, p. 25BioLab and MiniLab Worksheets, pp. 114-116Laboratory Manual, pp. 183-186Content Mastery, pp. 125, 127-128 L1

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Section Focus Transparency 61Basic Concepts Transparency 44Reteaching Skills Transparency 38

Section Focus Transparency 62Basic Concepts Transparency 44

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LSAssessment Resources Additional Resources

Spanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

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Chapter Assessment, pp. 145-150MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 25 quiz

Chapter 25 OrganizerChapter 25 Organizer

Activities/FeaturesObjectivesSection

Typical AnimalCharacteristicsNational Science EducationStandards UCP.1, UCP.2,UCP.5; A.1, A.2; C.1, C.5,C.6; G.1-3 (1 session, 1/2block)

Body Plans andAdaptationsNational Science EducationStandards UCP.1, UCP.2,UCP.4, UCP.5; A.1, A.2; C.3,C.5; E.1, E.2; F.4, F.5, F.6;G.1-3 (2 sessions, 11/2 blocks)

1. Describe the characteristics of animals.2. Sequence the development of a typical

animal

3. Compare and contrast radial and bilateral symmetry with asymmetry.

4. Trace the phylogeny of animal bodyplans.

5. Compare body plans of acoelomate,pseudocoelomate, and coelomate animals.

Careers in Biology: Marine Biologist, p. 694MiniLab 25-1: Observing AnimalCharacteristics, p. 695Problem-Solving Lab 25-1: p. 696Inside Story: Early Animal Development, p. 698Internet BioLab: Zebra Fish Development, p. 706Biology & Society: Protecting EndangeredSpecies, p. 708

Problem-Solving Lab 25-2: p. 702MiniLab 25-2: Check Out a Vinegar Eel, p. 703

Section 25.2

Section 25.1

MATERIALS LIST

BioLabp. 706 aquarium, zebra fish, turkeybaster, beaker, dropper, petri dish,stereomicroscope, wax pencil or labels

MiniLabsp. 695 microscope, microscope slide,coverslip, toothbrush bristles, rotiferculture, dropper, waterp. 703 microscope, microscope slide,coverslip, dropper, vinegar eel culture

Alternative Labp. 702 microscope, prepared slides ofcross sections of hydra, planarian,nematode, and earthworm

Quick Demosp. 694 microscope, prepared slides ofnerve, muscle, blood, and stomach cellsp. 701 kitchen bowls, vases, andspoons; dried marine sponge, pre-served jellyfish, live goldfish

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

692A

Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Animation: Embryo DevelopmentVideo: Fetal DevelopmentExploration: Symmetry

Videodisc ProgramEmbryo Development

The Infinite VoyageThe Geometry of Life

The Secret of Life SeriesDividing Cells, Early EmbryoSex and the Single Gene: Cell DevelopmentEvolution of SymmetryFlatworm Cross SectionDeveloping Zebra Fish

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Section

Characteristics ofAnimals

All animals have several character-istics in common. Animals areeukaryotic, multicellular organismsthat have ways of moving that helpthem reproduce, obtain food, andprotect themselves. Animals also havespecialized cells that form tissues andorgans—such as nerves and muscles.Unlike plants, animals are composedof cells that do not have cell walls.Most adult animals are fixed in sizeand shape; they do not continue togrow throughout their lives.

Methods for obtaining food varyExamine the animals shown in

Figure 25.1. One characteristic common to all animals is that they

are heterotrophic, meaning theymust consume food to obtain energyand nutrients. All animals dependeither directly or indirectly onautotrophs for food.

What do you think of when you hear theword animal? Many people envisionan organism with hair or fur and a

bony skeleton. Yet more than 95 percent of the1.5 million species of animals that have beendescribed have neither bones nor hair.

If you saw the organism in the inset photograph for the first time, wouldyou classify it as an animal? Thisorganism is a sponge, an animalthat remains attached to rocksor coral reefs in the ocean forall of its adult life. It doesn’thave a bony skeleton or hair,yet it is still an animal.

SECTION PREVIEW

ObjectivesDescribe the character-istics of animals.Sequence the development of a typical animal.

Vocabularysessileblastulagastrulaectodermendodermmesodermprotostomedeuterostome

25.1 Typical AnimalCharacteristics

Figure 25.1The barnacle andlizard each get theirfood in differentways.

Coral polyps (above) andred sponges(left)

A lizard captures flieswith its long,sticky tongue.

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A barnacle extendsbristles from itsshell to catchsmall organismsas they drift byin the water.

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Section 25.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 25,Section 25.1

Which of these organisms do you think are animals?

On what characteristics did you base your answer?

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Jellyfish

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Spider

Porcupine

Sea star

Transparency Typical AnimalCharacteristics61

PrepareKey ConceptsStudents will study typical animalcharacteristics and the develop-ment of animals from eggs. Theywill compare and contrast animalfeatures and the differences intypes of development.

Planning■ Gather live animals for theGetting Started Demo.■ Buy zebra fish for the BioLab.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 61 on the overhead pro-jector and have students answerthe accompanying questions.

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Assessment PlannerAssessment PlannerPortfolio Assessment

Portfolio, TWE, pp. 697, 704MiniLab, TWE, p. 703Alternative Lab, TWE, p. 703BioLab, TWE, p. 707

Performance AssessmentAlternative Lab, TWE, p. 703BioLab, SE, p. 707MiniLabs, SE, pp. 695, 703Problem-Solving Lab, TWE, p. 696

Knowledge AssessmentMiniLab, TWE, p. 695Section Assessment, SE, pp. 699, 705Chapter Assessment, SE, pp. 709-711

Skill AssessmentProblem-Solving Lab, TWE, p. 702

692 WHAT IS AN ANIMAL?

What Is an Animal?

What You’ll Learn■ You will distinguish animal

characteristics from those ofother life forms.

■ You will identify the stages ofearly animal development.

■ You will interpret body plansof animals.

Why It’s ImportantThe animal kingdom includesorganisms as diverse assponges, earthworms, clams,crickets, and birds. Humans arealso animals. An understandingof animals will provide a betterunderstanding of ourselves.

Comparing Animals Examine two different animals.Make a list of four similaritiesand four differences betweenthese animals. What traits iden-tify an organism as an animal?

To find outmore about

animals, visit the GlencoeScience Web Site. www.glencoe.com/sec/science

25

GETTING STARTEDGETTING STARTED

ChapterChapter

You know that the bat and jellyfish are animals,but can you name the characteristics they share?There are millions of speciesof animals, but they all haveseveral features in common.

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Theme DevelopmentThis chapter stresses the themesof unity within diversity andevolution. Students will gain theunderstanding that within thetremendous variety of animals,there are common threads orshared features. They will alsolearn how animal characteristicsand adaptations have evolved.

Chapter 25Chapter 25

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Project, p. 694;Building a Model, p. 697;

Reteach, p. 697; Meeting IndividualNeeds, p. 698

Visual-Spatial Display, p. 694;Quick Demo, p. 694; Biology

Journal, p. 700; Reteach, p. 704;Extension, p. 704

Intrapersonal Check for Under-standing, p. 697 Linguistic Tech Prep, p. 697;Portfolio, pp. 697, 704Naturalist Biology Journal, p. 696; Check for Understand-

ing, p. 704

GETTING STARTED DEMOGETTING STARTED DEMO

Naturalist Ask studentsto observe two of the

following animals in clear plas-tic containers: a hamster, anearthworm, a cricket, or agrasshopper. Ask them to listways in which these animalsare both alike and different.Remind students to treat liveanimals gently.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of the unitas an overview.

Resource ManagerResource Manager

Section Focus Transparency 61and Master

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Digestive tract

Anus

Observing Animal Characteristics Animals come in a variety of sizes and shapes, and can be found living in a number of different habitats.

Procedure! Copy the data table.@ Add a few bristles from an old toothbrush to a glass

slide. Add a drop of water containing rotifers to yourslide. The drop should cover the bristles. Add a coverslip.CAUTION: Use caution when working with a microscope,slides, and coverslips.

# Observe your rotifers under low-power magnification.$ Use the data table to record the characteristics that you

were able to see. Describe the evidence for each trait.

Analysis1. Are these organisms autotrophs or heterotrophs?2. Were you able to see evidence of feeding? Explain.3. Are rotifers multicellular? Explain.

MiniLab 25-1MiniLab 25-1 Observing and Inferringdigestion is carried out within indi-vidual cells; in other animals, diges-tion takes place in an internal cavity.Some of the food an animal con-sumes and digests is stored as fat orglycogen and used when food is notavailable. Recall that glycogen is apolysaccharide, like starch, that isused for food storage.

Examine digestive tracts of a flat-worm and earthworm in Figure25.3. Notice that there is only oneopening to the flatworm’s digestivetract, a mouth. An earthworm has adigestive tract with two openings,with a mouth at one end and an anusat the other.

Animal cell adaptationsMost animal cells are adapted to

carry out different functions. Animalshave specialized cells that enablethem to sense and seek out food andmates, and allow them to identify andprotect themselves from predators. Inthe human body, nerve cells conductinformation and red blood cells trans-port oxygen. Observe the tiny animalsin the MiniLab. Can you identify anyspecialized cells in these animals?

25.1 TYPICAL ANIMAL CHARACTERISTICS 695

Figure 25.3In animals such as planariansand earthworms, food isdigested in a digestive tract.

Planarians feed on small, live organismsor on the dead bodies of larger animals.The planarian’s digestive tract has onlyone opening through which food entersand wastes exit.

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Earthworms ingest soil anddigest the organic mattercontained in it. Food entersthe mouth and travels alongthe digestive tract in onedirection. Indigestible wasteis eliminated at the anus.

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Animal Characteristic

Observed? (Yes or No) Evidence

Multicellular

Feeding

Movement

Size in mm

Data Table

Extendedpharynx

Digestivetract

Mouth

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Purpose Students will observe animaltraits in rotifers.

Process Skillsclassify, observe and infer, collectdata, draw conclusions

Teaching Strategies■ Rotifers are available frombiological supply houses.■ Rotifers are classified in theanimal phylum Rotifera. Theseanimals are used as representativeanimals because students areunfamiliar with this phylum.■ Review the technique used formeasuring organisms under themicroscope.■ Remind students to treat liveanimals gently.

Expected ResultsStudents will observe movementand feeding. They will find a sizerange from about 0.04 to 2.0 mmin length. Students will infer thatthese animals are multicellular.

Analysis1. They are not green, thus are

probably not autotrophs.2. Student answers will vary.

Most rotifers will be activelyfeeding on bacteria; thewheel-like action of ciliaimplies that these animals arepulling water and food intotheir bodies.

3. Students won’t see individualcells, so they infer that therotifers are multicellular.

Knowledge Ask studentsto find references regarding theclassification and anatomy ofrotifers and to write a report ontheir classification. Use thePerformance Task AssessmentList for Writing in Science inPASC, p. 87. L2

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MiniLab 25-1MiniLab 25-1CAREERS IN BIOLOGY

Marine Biologist

Would you enjoy spending your days studying the organisms

found in the oceans? Perhaps you should become a marine biologist!

Skills for the JobMany marine biologists do go

SCUBA diving in the oceans to find speci-mens, but they also spend time examining those organisms in labs and do library research. They focus ontopics such as the effect of temperature changes and pollu-tion on ocean inhabitants. Many marine biologists work forgovernment agencies, such as the National Oceanic andAtmospheric Administration (NOAA), and the EnvironmentalProtection Agency (EPA). Some work for private industries,such as fisheries and environmental consulting firms. Mostmarine biologists have a master’s degree or a doctorate, plusskill in analyzing data and solving problems.

For more careers in related fields, be sureto check the Glencoe Science Web Site.

www.glencoe.com/sec/science

Animals such as lizards and birdscan move from place to place in anactive search for food. Other animals,such as barnacles, remain stationaryand are adapted to capture food fromthe water in which they live.

Whether an animal moves quicklyor slowly depends partly on its envi-ronment. Scientists hypothesize that

animals first evolved in water. Wateris more dense and contains less oxy-gen than air, but water contains moresuspended food. In the water, station-ary animals don’t expend muchenergy to obtain food. But there islittle suspended food in the air; thus,land animals use more oxygen andexpend more energy to find food.

The osprey and sidewinder snakein Figure 25.2 are examples of verte-brates, animals with backbones,whereas the sea star is an inverte-brate. Yet all these animals moveabout in their environments. Find outhow an animal’s environment affectsits survival in the Biology & Society atthe end of this chapter.

Some aquatic animals, such assponges and corals, move about onlyduring the early stages of their lives.They hatch from eggs into free-swim-ming larval forms; as adults, mostattach themselves to rocks or otherobjects. Organisms that don’t movefrom place to place are known as sessile (SES ul) organisms. They rely onwater currents to carry food to them.

Animals must digest foodAnimals are heterotrophs that

ingest their food; after ingestion,theymust digest it. In some animals,

694 WHAT IS AN ANIMAL?

The soaring osprey dives to snatch a fish from the waters of a lake or stream.

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A sidewinder rattlesnake barelytouches the groundas it follows thetrail of a mouse.

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A sea star moves usinga unique system oftube feet.

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Figure 25.2Animals move in aremarkable variety of ways.

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2 TeachDisplay

Visual-Spatial Make a bul-letin board display of a vari-

ety of vertebrate and invertebrateanimals. Calendars and catalogsfrom biological supply companiesmay have animals such as thehydra and planaria mentioned inthis chapter. Ask students tobring in photographs to displaythat they may have taken of ani-mals other than pets.

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Career PathCourses in high school:biology, botany, chemistry,

math, computersCollege: at least bachelor’s andmaster’s degrees in marine biolo-gy or other specialized areas

Career IssueThe citizens of the United Stateslive on land, not in the ocean. Askstudents why our federal govern-ment should spend our tax moneyon marine biologists.

For More InformationFor more information on marinebiology, students can write to:

American Society of Limnology and Oceanography

Virginia Institute of MarineScience

College of William and Mary Route 1208Gloucester Point, VA 23062

Quick DemoQuick Demo

Visual-Spatial Ask stu-dents to examine a pre-

pared slide of animal cellssuch as nerve, muscle, blood,and cells lining the stomach.Ask them to make a labeledsketch of these cells in theirjournals.

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CAREERS IN BIOLOGY

P R O J E C TWhat do Daphnia eat?

Kinesthetic Ask students to maintainDaphnia cultures for two weeks. Each

culture should have ten Daphnia. Have stu-dents choose different food materials to test.For example, one group might use cookedegg white, another might use wheat grain,and a third might use live protozoans. At theend of the two-week period, students should

determine which cultures seem to be themost healthy (as measured by activity). Askthem to write a report of their experimentaldesigns, observations, and conclusions andinclude this report in their portfolios.Daphnia should be released underwater. Ifpoured from the container, air becomestrapped under their exoskeletons and theydie.

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Cultural Diversity

Animals in a Cross-CulturalPerspectiveDiscuss the diverse views different societiesand cultures have about the place of animalsin nature. Begin your discussion by askingstudents how animals are viewed and usedin the United States. Next, point out that not

all cultures view animals in this way. Forexample, Native American traditions oftenportray animals as important as or evenmore important than humans. Obtain booksabout the legends and myths of differentcultures, and discuss with students the roleof animals in these stories.

illustrated in Figure 25.4. First, theclay is formed into a solid ball. Then,the potter presses in on the top of theball to form a cavity that becomes theinterior of the bowl. In the same way,the cells at one end of the blastulafold inward, forming a cavity linedwith a second layer of cells. The layerof cells on the outer surface of thegastrula is called the ectoderm.Thelayer of cells lining the inner surfaceis called the endoderm.The ecto-derm cells of the gastrula continue togrow and divide, and eventually theydevelop into the skin and nervous tis-sue of the animal. The endodermcells develop into the lining of theanimal’s digestive tract and intoorgans associated with digestion.

Formation of mesodermIn some animals, the development

of the gastrula progresses until alayer of cells called the mesoderm isformed. Mesoderm is found in themiddle of the embryo; the term mesomeans “middle.” The mesoderm(MEZ uh durm) is the third cell layerfound in the developing embryobetween the ectoderm and the endo-derm. The mesoderm cells developinto the muscles, circulatory system,excretory system, and, in some ani-mals, the respiratory system. Howdoes the mesoderm form? You canfind out by reading the Inside Storyon the next page.

In some classes of animals, theopening of the indented space in thegastrula becomes the mouth. Theseanimals, which include earthwormsand insects, are called protostomes. Aprotostome (PROHT uh stohm) is ananimal with a mouth that developsfrom the opening in the gastrula.

In other animals, such as fishes,birds, and humans, the opening ofthe gastrula does not develop into amouth. A deuterostome (DEW tihr

uh stohm) is an animal in which themouth develops from cells elsewhereon the blastula.

Scientists hypothesize that proto-stome animals were the first toappear in evolutionary history, andthat deuterostomes followed at a latertime. Biologists today often classifyan unknown organism by identifyingits phylogeny. Recall that phylogenyis the evolutionary history of anorganism. Determining whether ananimal is a protostome or deuteros-tome can help biologists identify itsgroup. Even though sea urchins, forexample, are invertebrates and fishesare vertebrates, both are deuteros-tomes and are, therefore, moreclosely related than you might con-clude from comparing their adultbody structures.

25.1 TYPICAL ANIMAL CHARACTERISTICS 697

Figure 25.4You can thinkof a blastula asa hollow ballof cells. Bypushing in onone side, a gas-trula is formed.

OriginWORDWORD

protostomeFrom the Greekwords proto, mean-ing “before,” andstoma, meaning“mouth.”

deuterostome From the Greekwords deutero,meaning “sec-ondary,” and stoma,meaning “mouth.”

A protostome and a deuterostome differ in the loca-tion of the cells thatbecome the organ-ism’s mouth.

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Building a ModelKinesthetic Give studentssalt dough that you have

prepared (one part salt, one partflour, one part water). Have themcover a space on their desktopswith a few paper towels and diptheir fingers into flour so that thedough will not stick to them. Askstudents to make models of a fer-tilized egg, a blastula, and a gas-trula. They should make crosssections of the stages in sequence,with one stage turning into thenext stage, rather than lining upall three stages at once. They willhave to add more dough to showthat the fertilized egg becomeslarger; but after that time, doughshould not be added because thetotal amount of cytoplasm doesnot increase as the early embryodevelops.

3 AssessCheck for Understanding

Intrapersonal Give studentsa live insect. Ask them to list

the characteristics that show that theinsect is an animal. Remind themto treat live animals gently.

ReteachKinesthetic Make clay mod-els of stages of development.

Ask students working in groupsto place the models in sequenceand describe what happens ineach stage.

ExtensionEncourage students to visit a sci-ence museum that has displaysabout development. Have themmake a photo essay of the exhibitthat can be displayed in class.Have students include captionsfor the photos.

Portfolio Have studentssummarize the development of asea urchin egg from fertilizationto the planula stage. Have theminclude this summary in theirportfolios. PP

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How important isthe first cell division in frogdevelopment?During development,a fertilized egg celldivides into two cellsby the process ofmitosis. The first divi-sion of a cell some-times results in twocells with an unequalamount of cytoplasm.Does the amount ofcytoplasm in each cellafter the first divisionhave any impact onthe development ofan organism? It does in frogs.

AnalysisIn a frog cell, a small section of colored cytoplasm forms

just after fertilization. This area is called the gray crescent.Note its appearance in the diagram. Follow the changes indevelopment as the first division of cytoplasm occurs equallythrough the gray crescent and unequally through the graycrescent.

Thinking Critically 1. Explain how each set of diagrams illustrates the role of

the gray crescent in early frog development. 2. Answer the question posed at the beginning of this lab.3. Predict the effect on frog development if the first division

occurred on the horizontal plane rather than on the vertical plane.

Problem-Solving Lab 25-1Problem-Solving Lab 25-1 Interpreting ScientificDiagrams

Development of Animals

Most animals develop from a sin-gle, fertilized egg cell called a zygote.But how does a zygote develop intothe many different kinds of cells thatmake up a snail, a fish, or a human?After fertilization, the zygotes of dif-ferent species of animals all have sim-ilar stages of development.

FertilizationMost animals reproduce sexually.

Male animals produce sperm andfemale animals produce eggs.Fertilization occurs when a spermpenetrates the egg, forming a unicel-lular zygote. In animals, fertilizationmay be internal or external.

Cell divisionThe unicellular zygote divides by

mitosis to form two new cells in aprocess called cleavage. Find out howimportant this first cell division is infrog development by studying theProblem-Solving Lab. Once cell divisionhas begun, the organism is known asan embryo. Recall that an embryo isan organism at an early stage ofgrowth and development. The twocells that result from cleavage thendivide to form four cells and so on,until a hollow ball of cells called ablastula (BLAS chuh luh) is formed.In some animals, such as a lancelet,the blastula is a single layer of cellssurrounding a fluid-filled space. Inother animals, such as frogs, theremay be several layers of cells sur-rounding the space. The blastula isformed early in the development ofan animal embryo. In sea urchindevelopment, for example, the for-mation of a blastula is completeabout ten hours after fertilization. Inhumans, the blastula forms about fivedays after fertilization.

GastrulationAfter blastula formation, cell divi-

sion continues. The cells on one sideof the blastula then fold inward toform a gastrula. The gastrula (GAS

truh luh) is a structure made up oftwo layers of cells with an opening atone end. Gastrula formation can becompared to the way a potter createsa cup or bowl from a lump of clay,

696 WHAT IS AN ANIMAL?

Graycrescent

1stcleavage

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Purpose Students will determine thatcytoplasm differences can influ-ence development in frogs.

Process Skillsinterpret scientific diagrams,compare and contrast, draw a con-clusion, think critically, predict

Teaching Strategies■ Explain to students that thenormal pattern for cell divisionoccurs as shown on the left in thediagram. The last phase shown inboth diagrams shows the larvalstage of frog development.

Thinking Critically

1. When the gray crescent ispresent, normal developmentoccurs. If the gray crescent isnot present, developmentdoes not occur.

2. The first cell division indevelopment is critical fornormal embryo development.

3. Neither cell would continueto develop into an embryo.

Performance Have stu-dents use a stereomicroscope orhand lens to examine preservedfrog eggs. Have them diagramwhat they observe and label thegray crescent. (Note: Preservedfrog eggs are available from bio-logical supply houses.) Use thePerformance Task AssessmentList for Scientific Drawing inPASC, p. 55.

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Demonstrating DevelopmentNaturalist Provide students with dia-grams of the human body showing

bone, muscle, spinal cord, brain, kidneys,liver, lungs, and pancreas. Give them coloredpencils and have them shade parts of thebody that develop from ectoderm yellow,parts that develop from endoderm green,

and parts that develop from mesoderm red.Provide them the following information:ectoderm produces brain, spinal cord, nerves,outer skin, eye lens, nose, and ears. Endo-derm produces pancreas, liver, lungs, and lining of the digestive system. Mesoderm produces skeleton, muscles, excretory system,inner skin.

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Spina BifidaLinguistic Ask students to interviewa doctor about spina bifida. Ask stu-

dents to write a report of their findingsand to prepare diagrams that show normaland abnormal stages of development.

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Linguistic Have students work inpairs to look up words in the dictio-

nary that begin with the prefixes ecto-and endo-. Ask students to make a list ofthe words. Have students exchange listsand write their own definitions of thewords. Then ask each student to compareactual definitions with their own defini-tions.

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Resource ManagerResource Manager

BioLab and MiniLab Work-sheets, p. 113

Basic Concepts Transparency44 and Master

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Figure 25.5Free-swimming larvae developfrom fertilized sea urchin eggs in just 48 hours (a). The larvae will develop into adult sea

urchins over the next few months (b).

Continued growth and development

Cells in developing embryos con-tinue to change shape and becomespecialized to perform different func-tions. Most animal embryos continueto develop over time, becoming juve-niles that look like smaller versions ofthe adult animal. In some animals,such as insects and echinoderms, theembryo develops into an intermedi-ate stage called a larva (pl. larvae)that often bears little resemblance tothe adult animal. In these animals thelarva is still surrounded by a mem-brane formed right after fertilization.When the larva hatches, it breaks

through this fertilization membrane.Animals that are generally sessile asadults, such as sea urchins, often havea free-swimming larval stage, shownin Figure 25.5. You can observedevelopment in fishes in the BioLabat the end of this chapter.

Forming an adult animalOnce the juvenile or larval stage has

passed, most animals continue to growand develop into adults. This growthand development may take just a fewdays in some insects, or up to fourteenyears in some mammals. Eventuallythe adult animals reach sexual matu-rity, mate, and the cycle begins again.

25.1 TYPICAL ANIMAL CHARACTERISTICS 699

Section AssessmentSection Assessment

Understanding Main Ideas1. Describe the characteristics that make a

mouse an animal.2. Explain why movement is an important

characteristic of animals. 3. Explain the difference between a protostome

and a deuterostome.4. Compare and contrast planarian and earthworm

digestive tracts.

Thinking Critically5. Name a land animal that is sessile. Why would

being sessile be a disadvantage to an animal thatlives on land?

6. Sequencing Place the following words insequence, beginning with the earliest stage: gastrula, larva, adult, fertilized egg, blastula. For more help, refer to Organizing Informationin the Skill Handbook.

SKILL REVIEWSKILL REVIEW

a

bMagnification: 1200�

View an ani-mation of embryodevelopment in thePresentation Builderof the InteractiveCD-ROM.

CD-ROM

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Linguistic Ask students towrite a note to a friend

explaining what they do and donot understand about develop-ment. Have them exchange notesand help each other with areas ofdifficulty. L1

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Ectoderm Mesoderm

Endoderm

698 WHAT IS AN ANIMAL?

Early Animal Development

The fertilized eggs of most animals follow a similar pattern of early development. From a single cell, many

divisions occur until a hollow ball of cells forms. The hollow ball folds inward and continues to develop.

Critical Thinking How do cells change as an embryo develops?

Magnification: 258�

Sea urchin blastula

INSIDESSTORTORYY

INSIDE

Fertilization A zygote is formed when an egg is fertilized by a sperm.

11

First cell divisionThe zygote divides by mitosis to form two cells. From thispoint, the developing organism is called anembryo.

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Formation of a blastulaContinuous cell division results in a fluid-filled ball of cells, theblastula. Notice that during theseearly developmental stages, thetotal amount of cytoplasm hasnot increased.

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Gastrulation As the embryo continuesto grow, some of the cells of the blastulafold inward, forming the gastrula. Allanimal embryos except sponges passthrough this gastrula stage.

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Further celldivisionCell divisioncontinues. Theeight-cell stageis shown here.

Formation of mesoderm In proto-stomes, the mesoderm forms fromcells that break away from the endoderm near the opening of the gastrula. In deuterostomes, the mesoderm forms from pouches of endoderm cells on the inside of the gastrula. After the formation of mesoderm, development continues with each cell layer forming specialized tissues.

698

IINSIDENSIDESSTORTORYY

INSIDE

MMEETING EETING IINDIVIDUAL NDIVIDUAL NNEEDS EEDS MEETING INDIVIDUAL NEEDS

Visually Impaired Kinesthetic Obtain several old tennisballs or other type of hollow rubber

balls. Have visually impaired students handlethe balls and explain that the blastulaappears just like the hollow balls. Then havethese students hold the ball in one hand

while pushing in on one side of the ball withtheir thumbs. Explain that now the balls rep-resent the gastrula stage. Ask students to usetheir free hand to point to the parts of theball that represent ectoderm and endoderm.P

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VIDEODISCBiology: The Dynamicsof Life

Disc 1, Side 2, 1 min. 10 sec.Embryo Development (Ch. 30)

CD-ROMBiology: The Dynamicsof Life

Animation: EmbryoDevelopment Disc 4

!:,Å"

VIDEODISCThe Secret of LifeDividing cells, early

embryo

!7PT'n$E"

CD-ROMBiology: The Dynamicsof Life

Video Selections: FetalDevelopment Disc 5

VIDEODISCThe Infinite VoyageThe Geometry of Life

Development of the Egg afterFertilization (Ch. 3)

3 min. 30 sec.!7ALD"

Purpose Students study the stages of earlyembryonic development.

Teaching Strategies■ Ask students to study the dia-grams, then write a numbered listdescribing the developmentalstages shown. They can use thelist as a study guide.

Visual LearningHave students describe thechanges in appearance at eachstage of development.

Critical ThinkingCells continue to divide, becom-ing smaller and smaller with eachcell division.

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The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INTERNETINTERNET

Section AssessmentSection AssessmentSection Assessment1. It is a multicellular heterotroph that

uses food for energy. It moves to getfood and its cells do not have cell walls.

2. Animals do not make their own food,but depend upon other organisms forfood. They must search for food, somovement is necessary for survival.

3. In protostomes the mouth developsfrom the opening in the gastrula. In

deuterostomes, the mouth developselsewhere on the gastrula.

4. In planarians, food is sucked in throughthe pharynx and ground up by move-ment; digestion occurs by phagocytosisin individual cells. In an earthworm,food is taken in by the mouth, groundup in the gizzard, and moves throughthe rest of the digestive system. Food is

carried to all body cells by the circula-tory system, and wastes are expelledthrough the anus.

5. Students will probably not be able toname a land animal that is sessile. Allanimals on land must move to obtainfood.

6. fertilized egg, blastula, gastrula, larva,adult 699

Resource ManagerResource Manager

Reinforcement and StudyGuide, pp. 111-112

Reteaching Skills Trans-parency 38 and Master

Critical Thinking/ProblemSolving, p. 25

Content Mastery, p. 126 L1

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about once they have reached theadult stage.

The bodies of most sponges con-sist of two layers of cells. Unlike allother animals, a sponge’s embryonicdevelopment does not include theformation of an endoderm and meso-derm, or a gastrula stage. Fossilsponges first appeared in rocks datingback to more than 700 million yearsago. They represent one of the oldestgroups of animals on Earth—evidencethat their two-layer body plan makesthem well adapted for life in aquaticenvironments.

Radial symmetry in a hydraA hydra, a tiny predator pictured

in Figure 25.7B, feeds on small ani-mals it snares with its tentacles. Ahydra has radial symmetry. Its tenta-cles radiate out from around its

mouth. As you can see, animals withradial symmetry (RAYD ee uhl) canbe divided along any plane, through acentral axis, into roughly equalhalves. Radial symmetry is an adapta-tion in hydra that enables the animalto detect and capture prey comingtoward it from any direction.

Have you ever had your groceriesdouble bagged at the store? The bodyplan of a hydra can be compared to asack within a sack. These sacks arecell layers organized into tissues withdistinct functions. A hydra developsfrom just two embryonic cell layers—ectoderm and endoderm.

Bilateral symmetryThe butterfly in Figure 25.7C has

bilateral symmetry. An organism withbilateral symmetry (bi LAT uh rul)can be divided down its length into

25.2 BODY PLANS AND ADAPTATIONS 701

Figure 25.7All animals have akind of symmetrythat enables themto survive in theirsurroundings.

This irregularly shaped spongeis an example of an animal withan asymmetrical body plan.

AA An example of an animal withradial symmetry, a hydra feedson tiny animals it immobilizeswith venomous stinging cellsfound along its tentacles.

BB In bilaterally symmetricalanimals, such as butterflies,sensory tissue is commonlyconcentrated in the head, oranterior, end.

CC

Anterior

Dorsal

Ventral

Posterior

701

Section

What Is Symmetry?Look at the animals shown in

Figure 25.6. You know that all ani-mals share certain characteristics, butthese animals don’t look like they havemuch in common. The sponge seemsto have no particular shape, whereasthe fish has a head, body, and severalpairs of fins. The jellyfish doesn’t havea head or tail, and is circular in form.Each animal can be described in termsof symmetry according to its shape.Symmetry (SIH muh tree) refers to abalance in proportions of an object or

Objects made by a potter can be manydifferent shapes and sizes. There is a plan for making each type

of pottery. One plan results in a bowl, another in a vase, and still another in a flat plate. Each piece of pottery is suited for a particular function. Animals’ bodies also have plans—body shapes that are suitedto a particular way of life. In this section,you will study a variety of animal bodyplans and see how a specific body structure isadapted to life in a particular environment.

SECTION PREVIEW

ObjectivesCompare and contrast radial andbilateral symmetry withasymmetry.Trace the phylogeny of animal body plans.Compare body plans of acoelomate, pseudocoelomate, andcoelomate animals.

Vocabularysymmetryradial symmetrybilateral symmetryanteriorposteriordorsalventralacoelomatepseudocoelomcoelomexoskeletonendoskeleton invertebratevertebrate

25.2 Body Plans andAdaptations

Figure 25.6A sponge (a), a fish(b), and a jellyfish (c)all exhibit differentkinds of symmetry.

organism. All animals have some kindof symmetry. Different kinds of sym-metry enable animals to move aboutin different ways.

Asymmetry in a spongeMany sponges have an irregularly

shaped body, as seen in Figure 25.7A.An animal that is irregular in shapehas an asymmetrical body plan.Animals with no symmetry often aresessile organisms that do not movefrom place to place.Most spongesdo not move

a b c

700

Section 25.2

PrepareKey ConceptsStudents compare and contrasttypes of symmetry and studybasic body plans of animals.

Planning■ Collect a variety of kitchen

items that display differenttypes of symmetry for theQuick Demo.

■ Gather dried marine sponges,a preserved jellyfish, and livegoldfish in clear plastic con-tainers for the Quick Demo.

1 FocusBellringer Before presenting this lesson, display Section Focus Trans-parency 62 on the overhead pro-jector and have students answerthe accompanying questions.

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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 25,Section 25.2

How are shapes of the organisms in each group similar?

How is the shape of each organism suited to the environmentin which it lives?

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SECTION FOCUS

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Transparency Body Plansand Adaptations62

Group A

Group B

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Symmetry in Objects Visual-Spatial Divide the class intogroups. Have each group list in their

journals as many items with radial symme-try as they can find in the classroom withina given time period. Repeat the activitywith asymmetrical and bilaterally symmet-rical objects.

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Quick DemoQuick Demo

Bring in kitchen items such asbowls, vases, and a variety ofspoons. Explain that each itemis suited to a particular func-tion. For example, the bowlshold soft or liquid foods, thespoons pick up or stir soft orliquid foods, and the vases holdflowers for display. Explainthat, in a similar way, animalshave structures that are suitedto specific functions such aslocomotion, food-getting, andcirculating materials through-out their bodies.

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Pass around the dried bodies ofmarine sponges, a live goldfishin a clear plastic container, anda large preserved jellyfish. Askstudents to describe the shapesof the animals and explain ifone side of the animal isequally balanced by the other.marine sponge, no; live gold-fish, yes; preserved jellyfish, yes.Explain to students that thequality they have just observedis called symmetry.

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Note Internet addresses that you find useful in the spacebelow for quick reference.

2 Teach

VIDEODISCThe Secret of LifeEvolution of symmetry

CD-ROMBiology: The Dynamicsof Life

Exploration: Symmetry Disc 4

!7;EVE"

Resource ManagerResource ManagerConcept Mapping, p. 25Section Focus Transparency 62 and

Master

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700

Check Out a Vinegar Eel Vinegareels are roundworms with pseudo-coeloms. They exhibit an interestingpattern of locomotion because theyhave only longitudinal (lengthwise)muscles.

Procedure! Prepare a wet mount of vinegar eels. CAUTION: Use

caution when working with a microscope and slides. @ Observe them under low-power magnification. # Note their pattern of locomotion. Prepare a

series of diagrams that illustrate their pattern of movement.

$ Time how fast they move by timing in seconds how long ittakes for one roundworm to move across the center of yourfield of view. Find out the diameter of your low-power fieldin mm. Calculate vinegar eel speed in mm/sec. You maywant to time several animals and average their speed.

Analysis1. Name the type of symmetry present in vinegar eels. 2. Describe the pattern of locomotion for vinegar eels.3. How does the pseudocoelom aid vinegar eels in

locomotion?4. What is the speed of locomotion for a vinegar eel? Based

on the speed of your vinegar eel, predict the speed inmm/sec for a flatworm. Explain your answer.

MiniLab 25-2MiniLab 25-2 Observing and Inferring

Pseudocoelomates have a body cavity

A roundworm is another animalthat has bilateral symmetry. However,unlike the solid body of a flatworm,the body of a roundworm has a bodycavity that develops between theendoderm and mesoderm. This bodycavity is called a pseudocoelom. Apseudocoelom (SEWD uh see lum) isa fluid-filled body cavity partly linedwith mesoderm.

The pseudocoelom enables ani-mals, such as roundworms, to movequickly. How does this work? Thinkabout the way your muscles work.The muscles in your arm lift yourhand by pulling against your armbones. If there were no rigid bones inyour arms, your muscles would notbe able to do any work. Although theroundworm has no bones, it doeshave a rigid, fluid-filled space, thepseudocoelom, which is partly sur-rounded by mesoderm. Its musclesattach to the mesoderm and braceagainst the pseudocoelom. You canobserve movement in a pseudo-coelomate animal in the MiniLab onthis page.

25.2 BODY PLANS AND ADAPTATIONS 703

Vinegar eel

Figure 25.8Animals with acoelo-mate bodies usuallyhave a thin, some-what flattened shape(a). Pseudocoelomateanimals are largerand thicker in bodyshape than theiracoelomate ancestors(b). The coelom provides a space for complex internal organs (c).

AcoelomateFlatworm

PseudocoelomateRoundworm

CoelomateSegmented Worm

Coelom

EndodermEctoderm Mesoderm Body cavity Digestive tract

Pseudocoelom

a b c

Magnification: 292�

Purpose Students observe the pattern andspeed of locomotion of vinegareels and relate these patterns to apseudocoelomate body plan.

Process Skillscollect data, observe and infer,predict

Teaching Strategies■ Vinegar eels, Turbatrix aceti,are classified as roundworms,phylum Nematoda.■ Use depression slides whenmaking wet mounts or add a fewbristles from an old toothbrushto a regular slide to preventcrushing the roundworms.■ Review the meaning of “fieldof view.” Remind students that inorder to correctly judge speed ofthese worms, they must time theanimal as it moves across thediameter of their field of view.■ Remind students to treat liveanimals gently.

Expected ResultsStudents will observe the move-ment of vinegar eels as a series ofjerking contractions. The speedof these animals will be in therange of 2 to 5 mm/second.

Analysis1. bilateral symmetry2. series of jerky contractions3. The body cavity is filled with

fluid. Body muscles can braceand contract against this fluid.

4. The speed will range between2 and 5 mm/sec. The speedof a flatworm will be slowerdue to the fact that flatwormshave no body cavity. Apseudocoelom allows moreefficient muscle contraction.

Portfolio Have studentsstudy vinegar eels under low- andhigh-power magnification. Havethem diagram and label bodystructures they observe. Use thePerformance Task AssessmentList for Scientific Drawing inPASC, p. 55. PP

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3. If you were to observe these animals’movements, predict what you mightsee. Explain in terms of their bodyplans. Students’ descriptions shouldmatch those given in the chapter.

Portfolio Ask students to sum-marize what they have learned aboutbody plans in this lab. Have them con-sider the survival value of each type ofbody plan. Instruct them to put theirsummaries in their portfolios. Use thePerformance Task Assessment List forWriting in Science in PASC, p. 87. L2

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703

similar right and left halves that formmirror images of one another.Bilaterally symmetrical animals canbe divided only along one plane to form equal halves, in contrast toradially symmetrical animals that canbe divided along any plane. In bilat-eral animals, the anterior, or headend, often has sensory organs. Theposterior of these animals is the tailend. The dorsal (DOR sul), or backsurface, also looks different from theventral (VEN trul), or belly surface.

Animals with bilateral symmetry can find food and mates and avoidpredators because they have sensoryorgans and good muscular control.Test your ability to identify animalsymmetry in the Problem-Solving Lab.

Bilateral Symmetry and Body Plans

Animals that are bilaterally sym-metrical also share other importantcharacteristics. All bilaterally symmet-rical animals developed from threeembryonic cell layers—ectoderm,endoderm, and mesoderm. Somebilaterally symmetrical animals alsohave fluid-filled spaces called bodycavities inside their bodies in whichinternal organs are found. The devel-opment of body cavities made it pos-sible for animals to grow larger andto develop organs and organ systems,such as digestive systems.

Acoelomate flatworms have nobody cavities

Flatworms are bilaterally symmet-rical animals with solid, compactbodies, as shown in Figure 25.8.Animals that have three cell layers—ectoderm, endoderm, and meso-derm—but no body cavities arecalled acoelomate (ay SEE lum ate)animals. Acoelomate animals mayhave been the first group of animalsin which organs evolved from cells ofthe mesoderm. Like other acoelo-mate animals, the organs of flat-worms are embedded in the solidtissues of their bodies. Althoughacoelomate animals have no bodycavities, they do have a digestive tractthat extends throughout the body. Aflattened body and a digestive tractallow for the diffusion of nutrients,water, and oxygen to supply all bodycells and to eliminate wastes.

702 WHAT IS AN ANIMAL?

Is symmetry associated with other animal traits?Animals show different patterns in their symmetry. Symmetrypatterns are often associated with certain other characteris-tics or traits found in the animal.

AnalysisStudy these three animal diagrams. Determine the type

of symmetry being shown.

Thinking Critically1. Animal A shows what type of symmetry? Explain your

answer.2. Describe other traits associated with animal A.3. Name some objects other than animals that show the

A pattern of symmetry.4. Animal B shows what type of symmetry? Explain your

answer.5. Describe other traits associated with animal B.6. Name some objects other than animals that show the

B pattern of symmetry.7. Animal C shows what type of symmetry? Explain your

answer.8. Describe other traits associated with animal C.9. Name some objects other than animals that show the

C pattern of symmetry.

Problem-Solving Lab 25-2Problem-Solving Lab 25-2 Classifying

AA BB CC

Purpose Students identify the type ofsymmetry in three animals.

Process Skillsclassify, observe and infer, com-pare and contrast, think critically

Teaching Strategies■ Review the three types of sym-metry present in animals.

Thinking Critically

1. bilateral—body can bedivided along its length intotwo equal halves

2. head and tail regions present,body cavity present, goodmuscular control

3. pencil, pen, doll4. asymmetry—body is irregular 5. does not move about, body

consists of two cell layers6. blob of clay, cottage cheese7. radial—body can be divided

along any plane through acentral axis into equal halves

8. tentacles radiate from mouth,tissues present

9. wheel with spokes, openumbrella, apple corer

Skill Have students pre-pare a concept map that uses thefollowing terms: sponge, hydra,flatworm, roundworm, earth-worm, radial symmetry, bilateralsymmetry, asymmetry, pseudo-coelomate, coelomate, acoelo-mate. Use the PerformanceTask Assessment List for ConceptMap in PASC, p. 89. L2

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Alternative LabBody Plans

Purpose Students examine prepared slides of crosssections of a hydra, flatworm, roundworm,and earthworm to determine if the animalsare acoelomate, pseudocoelomate, orcoelomate.

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Materialsmicroscope, prepared slides of cross sec-tions of hydra, planarian, nematode, earth-wormProcedureGive students the following directions.

1. Examine the cross-section slides.2. Sketch and label each cross section

with the following labels: animal withtwo cell layers, pseudocoelomate ani-mal, acoelomate animal, coelomate

animal. Also label the drawings withthe names of organisms.

Analysis1. Order the animals’ body plans from

least to most complex. hydra, pla-narian, nematode, earthworm

2. In what way is each animal’s body planan adaptation to its environment?Hydra and planarians are adapted tomovement in water. Nematodes andearthworms are adapted to life in soil.702

Problem-Solving Lab 25-2Problem-Solving Lab 25-2 MiniLab 25-2MiniLab 25-2

A vertebrate(VURT uh brayt) isan animal with abackbone. All verte-brates are bilaterallysymmetrical animals thathave endoskeletons. Examplesof vertebrates include fishes, birds,reptiles, amphibians, and mammals,including humans. Figure 25.10shows examples of invertebrate andvertebrate animals.

Origins of AnimalsWhere did animals come from?

Most biologists agree that the animalkingdom probably evolved from colo-nial protists. Scientists trace this evo-lution back in time to the beginning

of the Cambrian period.Although it may seem thatbilaterally symmetricalanimals appeared muchlater, all the major animalbody plans that exist todaywere already in existence545 million years ago.Since then, many newspecies have evolved. Allnew species appear to be variationson the animal body plans that devel-oped during the Cambrian period.

25.2 BODY PLANS AND ADAPTATIONS 705

Section AssessmentSection Assessment

Understanding Main Ideas1. Explain the difference between radial and

bilateral symmetry in animals, and give an example of each type.

2. Compare the body plans of acoelomate andcoelomate animals. Give an example of an animal with each type of body plan.

3. Explain how an adaptation such as an exoskele-ton could be an advantage to land animals.

4. Compare movement in acoelomate and coelomate animals.

Thinking Critically5. Explain how having a coelom enables an animal

to have complex organ systems.

6. Making and Using Tables Construct a tablethat compares the body plans of the sponge,hydra, flatworm, roundworm, and earthworm.For more help, refer to Organizing Informationin the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Figure 25.10Invertebrate animals such as an octopus(a) and a sea slug (b) have no backbones.Vertebrates with backbones include amonkey (c) and a flamingo (d).

a

b

c

d

Portfolio Ask studentsto each remember from child-hood their favorite stuffed animal.Have them make a sketch of it,describe its symmetry, and itsbasic body plan. They shouldinclude this report in their portfo-lios.

4 CloseDiscussionHave students examine the phy-logenetic diagram in Chapter 14.Ask them to discuss the evolu-tionary trends of symmetry, celllayers, and patterns of develop-ment of the animal groups shownon the diagram.

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Pseudocoelomate animals have acomplete, one-way digestive tractwith organs that have specific func-tions. The mouth takes in food, themiddle section breaks it down andabsorbs nutrients, and the anus expelswastes.

The coelom provides space for internal organs

The body cavity of an earthwormdevelops from a coelom (SEE lum), afluid-filled space that is completelysurrounded by mesoderm.

Humans, insects, fishes, and manyother animals have a coelomate bodyplan. The greatest diversity of ani-mals is found among the coelomates.

The coelom provides space for thedevelopment of specialized organsand organ systems. In coelomate ani-mals, the digestive tract and otherinternal organs are attached by dou-ble layers of mesoderm and are sus-pended within the coelom. Like thepseudocoelom, the coelom cushionsand protects the internal organs andprovides room for them to grow andmove independently within an ani-mal’s body.

Animal Protection and Support

During the course of evolution, asdevelopment of body cavities resultedin a greater diversity of animal species,many animals became adapted to lifein different environments. Some ani-mals, such as mollusks, evolved hardshells that protected their soft bodies.Other animals, such as sponges,evolved hardened spicules betweentheir cells that provided support.Some phyla of animals developedexoskeletons. An exoskeleton is ahard, waxy covering on the outside ofthe body that provides a frameworkfor support, shown in Figure 25.9.Exoskeletons also protect soft bodytissues, prevent water loss, and pro-vide protection. Exoskeletons aresecreted by the epidermis and extendinto the body, where they provide aplace for muscle attachment.

Other phyla of animals haveevolved different structures for sup-port and protection. Sea urchins andsea stars, for example, have an inter-nal skeleton that is covered by layersof cells. An endoskeleton is an internal skeleton that provides sup-port inside an animal’s body. Anendoskeleton may be made of cal-cium carbonate, as in echinoderms;cartilage, as in sharks; or bone. Bonyfishes, amphibians, reptiles, birds,and mammals all have endoskeletonsmade of bone. The endoskeletonprotects internal organs and providesan internal brace for muscles to pullagainst.

Exoskeletons are often found ininvertebrates. An invertebrate is ananimal that does not have a back-bone. Many invertebrates, such ascrabs, spiders, grasshoppers, dragon-flies, and beetles, have exoskeletons.Echinoderms are examples of inver-tebrates that have endoskeletons.

704 WHAT IS AN ANIMAL?

Figure 25.9The exoskeleton ofthis crab has beenshed in order forthe crab to grow. A new exoskeletonforms in a fewhours to provideprotection again.

OriginWORDWORD

coelom From the Greekword koiloma,meaning “cavity.” A coelom is a bodycavity completelysurrounded bymesoderm.

704

Reinforcement Show students a live planarian ina deep-well projection slide(available from biological supplycompanies). Fill the well withpond or stream water. Use anoverhead projector to project theswimming planarian onto ascreen. Next, place a small earth-worm in a wet petri dish with afew small pebbles. Project it withyour overhead projector. Ask stu-dents to relate the movements ofboth animals to their body plans.P

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Coelom Development Linguistic Have students write anaccount of the evolutionary devel-

opment of the coelom. They should firstdetermine the time period, explain howthe coelom developed, identify animalswith coeloms, and explain how thecoelom has survival value.

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VIDEODISCThe Secret of LifeFlatworm cross section

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3 AssessCheck for Understanding

Naturalist Ask students tomake a table describing the

features of the three basic bodyplans.

ReteachVisual-Spatial Give studentsa variety of kitchen utensils

and ask them to describe whattype of symmetry each has.

ExtensionVisual-Spatial Ask a group ofstudents to collect speci-

mens from a freshwater pond.Have them make drawings of thespecimens and demonstrate theirbody plans and symmetry to theclass.

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Section AssessmentSection AssessmentSection Assessment1. Animals with radial symmetry, such as

the hydra, can be divided along anyplane into equal halves. Animals withbilateral symmetry, such as the flat-worm, can be divided only along oneplane to form two equal halves.

2. Animals with acoelomate bodies, suchas a flatworm, have three cell layerswith a digestive tract but no body

cavity. Animals with coelomate bod-ies, such as an earthworm, have acoelom in which internal organs aresuspended within the coelom.

3. An exoskeleton prevents water lossfrom body organs and supports ananimal’s body on land.

4. Acoelomate animals have no bodycavity, whereas coelomate animals

can brace their muscles against thecoelom, thereby giving them morepowerful movements.

5. The coelom provides space for special-ized organs and organ systems.

6. Make sure students’ tables indicatecell layers, and presence of a coelom,a pseudocoelom, or no body cavity.

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7. Go to the Glencoe Science WebSite as shown in the Sharing YourData box below to post your data.

8. Continue to observe your embryosdaily for a minimum of one week.Note the appearance of new organsand when movement is first seen.If you wish to continue watchingdevelopmental changes, consultwith your teacher for directions.CAUTION: Wash your handswith soap and water immediatelyafter completing observations.

25.2 BODY PLANS AND ADAPTATIONS 707

1. Communicating Explain whyzebra fish are ideal animals forstudying embryonic development.

2. Thinking Critically Explain whyyou may not have been able to seestages such as a blastula or gastrula.

3. Thinking Critically Suggest howyou could change the experi-ment’s design to allow for observ-ing these stages.

4. Using the Internet Visit theGlencoe Science Web Site for linksto Internet sites that will help youcomplete sequences of the majorchanges during development ofzebra fish.a. between 1 and 10 hpf. Include

labeled diagrams of thesechanges.

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Date hpf Diagram Observations

Data Table

b. between 10 and 28 hpf. Includelabeled diagrams.

c. between 28 and 72 hpf. Includelabeled diagrams.

Sharing Your DataSharing Your Data

Find this BioLab as well as links to sites with

diagrams of zebra fish development on the Glencoe Science Web Site at www.glencoe.com/sec/ science. Post yourdata in the data table provided for this activ-ity. Use the additional data from other stu-dents to answer the questions for this lab.Were there large variations in data posted byother students? What might have causedthese differences?

INTERNETINTERNET

1. They are inexpensive, easy tocare for, form many embryos,and show rapid development.

2. The early stages occurrapidly after fertilization.

3. Students could reset thetimer, or use embryos thatwere collected and preservedby an earlier class.

4. For questions a-c, studentanswers should agree with theinformation in Data andObservations. Encourage stu-dents to print out Internetdiagrams and include them intheir answers to this question.

Portfolio Ask students toprepare a report of their findingsusing their own data and diagramsas well as the diagrams availablefrom their Internet sources. Usethe Performance Task AssessmentList for Writing in Science inPASC, p. 87. PP

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ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

707

■ Use binocular microscopes to view thedevelopment of embryos.■ Use this Internet address if you havetrouble with breeding these fish:http://weber.u.washington.edu/~fishscop/

Data and ObservationsBetween 1-2 hpf: dividing cells will appearabove yolk sac.

Between 2-5 hpf: blastula formation.Between 5-10 hpf: gastrulation formation is complete with appearance of somites.

Between 10-28 hpf: tissues and organs form.Between 28-72 hpf: fins, gills, mouth form.

Sharing Your DataSharing Your Data

To navigateto the

Internet BioLabs, choose theBiology: The Dynamics of Lifeicon at the Glencoe ScienceWeb Site. Click on the studenticon, then the BioLabs icon. Theadvantage to having largenumbers of trials in an experi-ment is that the results will bemore accurate.

706 WHAT IS AN ANIMAL?

Zebra FishDevelopment

T he zebra fish (Danio rerio) is a common fresh-water fish sold in pet shops. They are ideal

animals for study because they undergo developmentalchanges quickly and major stages can be observed withinhours after fertilization.

INTERNETINTERNET

PREPARATIONPREPARATION

1. Copy the data table. 2. Using the turkey baster, draw

up water containing zebra fishembryos from the bottom of theaquarium.

3. Release the water into a beakerand allow the embryos to settle to the bottom.

4. Label a petri dish with your name and class period. Fill thebottom of the dish with aquariumwater. Using a dropper, place several embryos in your dish.

5. Your teacher will advise you as to the approximate time that fertilization took place. Allages should be reported in yourdata table as hpf (hours past fertilization).

6. Using a binocular microscope,observe the embryos. Make a diagram in your data table of the embryos’ appearances and indicate the age of theembryos in hpf.

PROCEDUREPROCEDURE

Materialsaquarium zebra fishturkey basterbeakerdropperpetri dishbinocular

microscopewax pencil or labels

Safety PrecautionsAlways wear safety goggles in the

lab. Use caution when working with abinocular microscope and glassware.

Problem What do the developmental stages

of the zebra fish look like?

ObjectivesIn this BioLab, you will: ■ Observe stages of zebra fish devel-

opment. ■ Record all observations in a data

table.■ Use the Internet to collect and com-

pare data from other students.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

INTERNETINTERNET

706

PROCEDUREPROCEDURE

Teaching Strategies■ Use the baster to remove excess debrisfrom the bottom of the tank on the eveningprior to spawning.■ Females will release eggs about 30 min-utes after the light comes on. Time this lightpattern to correspond with your first morn-ing class. Students may be able to see malesfollowing females along the bottom of the

tank as eggs are released. Fertilization isexternal.■ Classes that occur later in the day maynot be able to find early stages of embryonicdevelopment because fertilization has takenplace in the morning. Embryonic develop-ment is rapid.■ Feeding is not necessary for the firstweek. Later, feed the young live paramecia.

VIDEODISCThe Secret of LifeDeveloping zebra fish

Developing zebra fish, close-up

!7qg+2~I"

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Time Allotment 30 minutes on day 1, 15 minuteson days 2 through 5

Process Skillsinterpret scientific illustrations,observe and infer, organize data,sequence, experiment

■ Zebra fish are available frompet shops or biological supplyhouses. Purchase six of eachsex. Fish must be young(between 6 and 24 monthsold). Remind students to treatlive animals gently.

■ Prepare an aquarium with fil-ter, lights, timer, and heater.Marbles should be placedalong the bottom. Embryoswill fall between the marbles.

■ Set timer and lights as follows:14 hours light to 10 hoursdark. Set the heater at 28.5ºC.

■ Feed fish flakes in the morningand brine shrimp or live bloodworms in the afternoon.

PREPARATIONPREPARATION

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SUMMARYSUMMARY

Section 25.1

Section 25.2

Main Ideas■ Animals are heterotrophs, digest their food

inside the body, typically have a type of locomo-tion, and are multicellular. Animal cells have nocell walls.

■ Embryonic development from a fertilized egg issimilar in many animal phyla. The sequenceafter division of the fertilized egg is: the forma-tion of a blastula with one layer of cells; a gas-trula with two layers of cells, ectoderm andendoderm; and finally a gastrula with meso-derm, a layer of cells between the ectoderm andendoderm.

Vocabularyblastula (p. 696)deuterostome (p. 697)ectoderm (p. 697)endoderm (p. 697)gastrula (p. 696)mesoderm (p. 697)protostome (p. 697)sessile (p. 694)

Typical AnimalCharacteristics

Body Plans andAdaptations

CHAPTER 25 ASSESSMENT 709

1. Which of these organs forms from the ectoderm?a. stomach c. intestinesb. skin d. liver

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. Which animal pair shares the most characteristics?a. earthworm—sea starb. earthworm—insectc. earthworm—leechd. earthworm—clam

Main Ideas■ Animals have a variety of body plans and types

of symmetry that are adaptations.■ Animals may be asymmetrical, radially symmet-

rical, or bilaterally symmetrical.■ A coelom is a fluid-filled body cavity that sup-

ports internal organs. ■ Flatworms and other acoelomate animals have

flattened, solid bodies with no body cavities.■ Animals such as roundworms have a pseudo-

coelom, a body cavity that develops between theendoderm and mesoderm.

■ Coelomate animals such as humans and insectshave internal organs suspended in a body cavitythat is completely surrounded by mesoderm.

■ Exoskeletons provide a framework of supporton the outside of the body, whereas endoskeletons provide internal support.

■ Animals probably evolved from colonial protists in the Cambrian period.

Vocabularyacoelomate (p. 702)anterior (p. 702)bilateral symmetry

(p. 701)coelom (p. 704)dorsal (p. 702)endoskeleton (p. 704)exoskeleton (p. 704)invertebrate (p. 704)posterior (p. 702)pseudocoelom (p. 703)radial symmetry (p. 701)symmetry (p. 700)ventral (p. 702)vertebrate (p. 705)

709

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web Site:www.glencoe.com/sec/science

Chapter 25 AssessmentChapter 25 Assessment

All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.

In 1973, the United States government passed alaw, the Endangered Species Act, to help pre-

vent the extinction of threatened or endangeredspecies, and to preserve the habitats needed fortheir survival. An endangered species is onewhose numbers have fallen so low that it couldbecome extinct in the near future. A threatenedspecies is one that would soon become endan-gered if steps are not taken to protect it. In 1998,about 965 species in the United States werelisted as endangered or threatened.

Preserving or restoring habitat Under theterms of the Endangered Species Act, it is illegalto kill or harm protected species. Protectionunder the act also means that efforts must bemade to preserve or restore the species’ habitat.A recovery plan written for each species outlinessteps to be taken to help reestablish it. Periodi-cally, the status of each species is reviewed, and itmay be reclassified.

Different ViewpointsHow far should we go to protect endangered

species? Some people argue that the EndangeredSpecies Act places too much importance onplants and animals at the expense of humanneeds. The recovery plan for the peregrine fal-con included protecting any known nesting sitesfrom disturbance by humans. For example, if fal-cons were found nesting in a forest that was to belogged, logging had to be delayed until after theyoung falcons left the nest. Loggers sometimesdisagree with regulations like this because theyfear losing their ability to make a living. Butactions called for by the Endangered Species Act,including nest protection, elimination of DDTuse, and introduction of captive-bred birds intothe wild, have given the falcon a second chance.

Successful reintroduction An introductionprogram that began in the 1980s in New YorkCity has been a particular success. By 1998, therewere 12 breeding pairs of falcons nesting on citybuildings and bridges. By the end of the twenti-eth century, falcons were on their way off theendangered species list.

708 WHAT IS AN ANIMAL?

Analyzing the Issue Use your research skills to find out the current status of peregrine falconpopulations in the United States. Prepare a briefreport that describes the results of reintroductionefforts to date.

To find out more about endangered species, visit

the Glencoe Science Web Site.www.glencoe.com/sec/science

INVESTIGATING THE ISSUEINVESTIGATING THE ISSUE

Protecting Endangered SpeciesThe American peregrine falcon is a fast-flying, streamlined hawk thatfeeds primarily on birds it catches in the air. During the mid-1900s, thefalcon’s ability to reproduce was seriously weakened by the insecticideDDT. In 1972, DDT was banned in the United States. Banning the use of DDT gave peregrine falcons a chance to recover.

Peregrinefalcon

Purpose Students explore ways in whichhuman actions can affect the sur-vival of other species. They areexposed to differing opinionsabout the level of effort expendedto rescue endangered and threat-ened species.

BackgroundThe Endangered Species Act re-quires the preservation of habitat,often the primary source of dis-agreements about the law. Landuse issues may be especially diffi-cult to resolve when the speciesin question is small and unfamil-iar, such as a wildflower, butterfly,or small fish.

Teaching Strategies■ Encourage students to doInternet or library research tofind out whether the EndangeredSpecies Act has been altered bylegislation.■ Have students obtain currentinformation about local or statelaws that deal with protection ofspecies that are endangered orthreatened.

Investigating the IssueStudents should discover thatcaptive breeding and reintroduc-tion efforts, plus the banning ofthe pesticide DDT, are having apositive impact on the status ofperegrine falcon populations inthe United States.

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Going FurtherGoing FurtherGoing Further

Several species listed as threatened orendangered at one time have begun tomake a comeback. Invite students to findout about the current status of the baldeagle, red wolf, California sea otter,Louisiana black bear, or the American alli-gator. What controversies surrounded therecovery efforts for these species? L2

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quiz

VIDEODISCSTV: BiodiversityPreserving Diversity

Unit 2, Side 1, 4 min. 45 sec.The Peregrine Falcon

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UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

708

VIDEOTAPEMindJogger Videoquizzes

Chapter 25: What is an animal?Have students work in groups as they playthe videoquiz game to review key chapterconcepts.

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.www.glencoe.com/sec/science

CD-ROM

during the stage5.

to a

Animals develop from a

zygote

stage in which these tissues form

1.

3.

which forms the

4.

2.

Chapter 25 AssessmentChapter 25 Assessment

CHAPTER 25 ASSESSMENT 711

22. How are body plans of animals related to theenvironment in which they live? Give twoexamples.

23. Why are asymmetrical organisms often sessile? Explain.

24. How is obtaining food different in animalsand fungi?

25. Under a microscope, you observe an unfamiliarorganism from a tide pool. When you offerlive invertebrate food, the organism seems to pursue and consume this prey. How couldyou tell whether the organism is a protist or an animal?

26. Observing and Inferring You are looking ata preserved specimen of an unidentified ani-mal. It is easy to see that it has radial symme-try. What would you predict about its direc-tion of movement when alive? Explain.

27. Observing and Inferring Explain why thedevelopment of a body cavity enabled ani-mals to move and feed more efficiently.

28. Concept Mapping Complete the conceptmap by using the following vocabulary terms:blastula, ectoderm, gastrula, endoderm,mesoderm.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The following diagrams represent three different animal body plans.

Interpreting Scientific IllustrationsUse the diagram to answer the followingquestions.1. Which body plan would be capable of

more complex and powerful movement?a. 1 c. 3b. 2 d. all of these

2. Which type of body plan belongs toacoelomate animals such as flatworms?a. 1 c. 3b. 2 d. none of these

3. Which type of body plan belongs to pseudocoelomate animals such asroundworms?a. 1 c. 3b. 2 d. none of these

4. Which type of body plan is more likelyto be seen in animals that inhabit landenvironments?a. 1 c. 3b. 2 d. all of these

5. Making a Table Make a table that compares the three body plans. For each body plan, indicate an example ofan animal with that type; whether or nota body cavity is present, and if so, whichtype; and how the animal’s body planaffects its locomotion.

1

2

31

2

3

711

22. Fishes have coeloms that theirmuscles can push against asleverage in swimming motions.Acoelomate flatworms havethin bodies that aid diffusionthrough the cell layers.

23. Asymmetrical organisms haveno front or back end; thus, theyhave little direction to theirmovement and cannot pursuefood. They often wait for foodto come to them—which worksfor a sessile animal.

24. Most animals move to get foodor cause food to be drawntoward them. Most animalsdigest their food inside theirbodies. Fungi usually live on orin their food source and do notmove to find food. Fungisecrete chemicals that dissolvefood outside their bodiesbefore they take it in.

25. If it is multicellular, it is an ani-mal.

26. Radially symmetrical animalsdon’t have an anterior or poste-rior end; they don’t move for-ward or backward as easily asbilaterally symmetrical animals.

27. Animals with no body cavitiesdepend upon diffusion to movefood into and wastes out ofcells; animals with body cavitieshave space to develop organsystems that deliver food andtake away wastes. Movement inacoelomate animals dependsupon structures such as cilia,whereas coelomate animalshave structures that muscles canwork against for locomotion.

28. 1. Blastula; 2. Endoderm; 3. Ectoderm; 4. Mesoderm; 5. Gastrula

THINKING CRITICALLYTHINKING CRITICALLY

Chapter 25 AssessmentChapter 25 AssessmentChapter 25 AssessmentChapter 25 Assessment

3. All animals must search for food because theyare ________.a. autotrophic c. sessileb. heterotrophic d. photosynthetic

4. A(n) ________ is an example of an animal thatis sessile as an adult.a. osprey c. coralb. flatworm d. sea star

5. Which of the following is NOT a character-istic of animals?a. cells with cell wallsb. multicellular organismsc. are consumersd. break down food

6. When do mesoderm cells begin to form fromthe endoderm?a. during the blastula stageb. during the gastrula stagec. before the blastula staged. after the gastrula stage

7. Which animal shown in the diagram below isan example of an animal with radial symmetry?

a. c.

b. d.

8. Fishes have one fin along their backs.Because fishes are ________ symmetrical, this fin is called the ________ fin.a. radially, anterior c. bilaterally, posteriorb. radially, ventral d. bilaterally, dorsal

9. Which animal obtains food by filtering it outof water?a. clam c. sidewinderb. sea star d. flatworm

10. Of these, which is NOT an example of avetebrate animal?a. nurse shark c. coral snakeb. black bear d. garden spider

11. The ________ shown in the diagram belowhas only one opening in its digestive system.

12. A(n) ________ body plan enables muscles tobrace against a rigid structure, therebyenabling faster movement.

13. A cat has an endoskeleton, whereas a dragonfly has a(n) ________ for protectionand support.

14. Your pet hamster has a(n) ________ body plan.15. A butterfly’s mouth develops from the

opening of the indented space in the________ of the developing embryo.

16. The muscles in the legs of a horse developfrom the embryonic tissue called ________.

17. A swordfish is a ________ because its mouthdid not develop from the opening in thegastrula.

18. A saddle is placed on the ________ surface ofa horse.

19. Sponge larvae are free-swimming, whereasmost adult sponges are ________.

20. An adult sea star has ________ symmetry.

21. During the development of an embryo, ablastula forms first, followed by formation ofa gastrula. The mouth of the embryo devel-ops from the opening in the gastrula. Couldthe embryo develop into a bird? Explain.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

710 CHAPTER 25 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Make Yourself ComfortableWhen you take a test, try to make yourself as com-fortable as possible. You will then be able to focusall your attention on the test.

710

3. b4. c5. a6. b7. b8. d9. a

10. d11. planarian12. coelomate13. exoskeleton14. coelomate15. gastrula16. mesoderm17. deuterostome18. dorsal19. sessile20. radial

21. No, because this pattern is thatof a protostome. A bird is adeuterostome.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

Chapter 25 AssessmentChapter 25 Assessment

Body Plan Example Coelom

Acoelomate

Pseudocoelomate

Coelomate

Comparison of Three Body Plans

Flatworm

Roundworm

Fish

Relative Speed

none

fluid-filled, partly lined with mesoderm

fluid-filled, lined with mesoderm

slow

faster

faster

1. c2. a3. b4. c

5.