section 1 the reptilian body - jourdanton isd · section 1 the reptilian body ... reptiles have a...

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. In this section, studentswill learn how reptiles are well-adapted to life on land. Terrestrialadaptations include a strong skeleton, watertight skin coveredwith scales, watertight eggs, largerlungs with greater surface area,internal fertilization, and a partiallydivided heart.

Ask students to design a survivalcapsule for themselves. The capsulecan only be 1.5 m high by 1 m wide.The capsule will not be opened forthree weeks. Nothing, other thangasses, can pass through the wall ofthe capsule. What should the capsulecontain? Ask students to comparetheir capsule with the amniotic eggdescribed in this section.

ActivityFavorite Reptile Have each stu-dent draw a picture of his or herfavorite reptile. Have volunteersshare their drawings with the classand tell why they chose their par-ticular reptile. Lead a discussion ofhow reptiles are viewed in popularculture. Visual Bio 3FLS

MotivateMotivate

TAKS 1 Bio/IPC 2C, 2D

Bellringer

FocusFocus

Section 1

772 Chapter 34 • Reptiles and Birds

• Reading Organizers• Reading Strategies• Basic Skills Worksheets

Reading a ThermometerTemperature Conversions

Planner CD-ROM

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Data Lab• Data Sheet for Quick Lab GENERAL

GENERAL

GENERAL

GENERAL

Chapter Resource File

Section 1 The Reptilian Body

Key Characteristics of ReptilesMany people react with fear or repulsion when they see a snakeslither across a yard or field. But snakes and their reptile relativesare important members of most ecosystems, and they kill largenumbers of insect pests and small rodents. It’s true that some rep-tiles—venomous snakes and crocodilians (crocodiles and alligators)—are dangerous. Most reptiles, however, live quietly and go abouttheir business, preferring to avoid humans.

Members of class Reptilia live throughout the world in a wide vari-ety of habitats, except in the coldest regions, where it is impossiblefor ectotherms to survive. Reptiles share certain fundamental char-acteristics, features they retain from the time when reptiles replacedamphibians as the dominant terrestrial vertebrates. Figure 1 summa-rizes these key features.

Reptiles have a strong, bony skeleton, and most have two pairs oflimbs, although snakes and some lizards are legless. The legs of rep-tiles are positioned more directly under their body than are thelimbs of amphibians. Thus, reptiles can move more easily on landthan amphibians can. Unlike amphibians, reptiles have toes withclaws, which are used for climbing and digging. Claws also enablereptiles to get a good grip on the ground, allowing many reptiles torun quickly for short distances.

The nervous system of a reptile is very similar to that of anamphibian. Like their dinosaur ancestors, modern reptiles have abrain that is small in relation to their body. For example, an alligatorabout 2.5 m (8 ft) long has a brain that is about the size of a walnut.Despite this small brain size, reptiles are capable of complex behav-iors, including elaborate courtship.

Objectives● Describe the key character-

istics of reptiles.

● Relate a reptile’s ectothermicmetabolism to its activitylevel.

● Summarize the adaptationsthat enable reptiles to live on land.

Key Terms

amniotic eggoviparousovoviviparous

www.scilinks.orgTopic: Characteristics

of ReptilesKeyword: HX4038

Figure 1 Characteristicsof living reptiles. This maleanole is extending his dewlap,a display used during court-ship and when defendingterritory.

• Strong, bony skeleton and toes withclaws

• Ectothermic metabolism• Dry, scaly skin, almost

watertight• Amniotic eggs, almost

watertight• Respiration through well-developed

lungs• Ventricle of heart partly divided by a

septum• Internal fertilization

Key Features of Reptiles

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7B

7B 11A

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Student Edition TAKS Obj 1 Bio/IPC 2C TAKS Obj 2 Bio 4B TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 4B, 7B, 8C, 10A, 11ATEKS Bio/IPC 2C

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 3 Bio 7B TEKS Bio 3F, 7B, 11ATEKS Bio/IPC 2C, 2D

pp. 772–773

TAKS 3

TAKS 3

Interactive Reading AssignChapter 34 of the Holt BiologyGuided Audio CD Program to helpstudents achieve greater success inreading the chapter.

Using the FigureHave students draw a graph thatdepicts the changes in human bodytemperature for a 24-hour period.(The graph should show that thehuman body remains at about 37˚Cfor the entire day.) Then ask them tocompare their graphs to the one forthe lizard’s body temperature inFigure 2. Ask: Why are the graphsdifferent? (The lizard depends onexternal sources for heat, so its bodytemperature tracks the temperatureof the environment. Humans producetheir own heat, so body temperatureis not dependent on environmentaltemperature changes.) VisualTAKS 1 Bio/IPC 2C, 2D; TAKS 3 Bio 7B

LS

GENERALSKILLBUILDER

READINGREADING

TeachTeach

Chapter 34 • Reptiles and Birds 773

IdentifyingEctothermsSkills AcquiredAnalyzing data,interpreting graphs,predicting patterns

Teacher’s Notes Remind students that ecto- refersto “outside,” endo- refers to“within,” and therm refers to“heat.” Hence, ectotherm means“outside heat” and endothermmeans “heat within.”

Answers to Analysis1. Species A (yellow curve)

probably is an ectotherm. Itstemperature increases duringthe day, when the air tempera-ture increases.

2. around 12 A.M.3. around 12 P.M.4. It has been exposed to

sunlight-warmed air since early in the morning.

5. It would decline steadily fromits value at 6 P.M. to its valueat 12 A.M.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

MISCONCEPTION ALERT

Cold-blooded Emphasize that the termsectothermic and coldblooded are not syn-onyms, although they are often mistakenlyused that way. Many reptiles experiencebody temperatures as high as or higher than human body temperature. For exam-ple, the body temperature of the desertiguana in western North America regularlyreaches 42°C (108°F), which would be fatalfor a human. TAKS 1 Bio/IPC 2D

Transparencies

TT BellringerTT Key Features of ReptilesTT Changes in Lizard Body

TemperatureTT Reptilian Heart Structure

Ectothermic MetabolismReptiles’ ectothermic metabolism is too slow to generate enoughheat to warm their bodies, so they must absorb heat from their sur-roundings. As a result, a reptile’s body temperature is largely deter-mined by the temperature of its environment. Many reptiles regulatetheir temperature behaviorally, by basking in the sun to warm up orseeking shade to cool down. Figure 2 shows that a lizard can main-tain a relatively constant body temperature throughout the day bymoving between sunlight and shade. At very low temperatures, mostreptiles become sluggish and unable to function. Intolerance of coldgenerally limits their geographical range and, in temperate climates,forces them to remain inactive through the winter.

Figure 2 Body temperature in a lizard. Alizard may regulate its bodytemperature by moving repeat-edly between sun and shade.

Tem

pera

ture

(°C

)

5 6 7 8 94 11 12 1 2 310 5 6 7 840

10

20

30

40

5

15

25

35

Time of daySunrise Noon Sunset

Changes in Lizard Body Temperature

Emergesfromden

Basking Activity Returns

to denResting in

shade

Lizard's bodytemperature

Air temperature

Analysis

1. Analyze the data and deter-mine which animal species, A or B, is most likely an ecto-therm. Explain your reasoning.

2. Identify the time of day theanimal you identified as anectotherm reaches its lowestbody temperature.

3. Identify the time of day the animal you identified as an ectothermreaches its highest body temperature.

4. Propose a reason why theectotherm’s body temperatureis highest at this time.

5. Predict what the endo-therm’s graph line would looklike if it were extended to show body temperaturebetween 6 P.M. and midnight.

Identifying EctothermsBackground

The body temperature of all animalschanges during the course of a day. How itchanges can help you identify an animal asan ectotherm or an endotherm.

010001011001110101000100100010011100100100010000010100100111010101001000101010010010

Tem

pera

ture

(°C

)

10

20

30

40

6 A.M.12 A.M. 12 P.M. 6 P.M.

Time of day

Body Temperatures of Two Animals

Species A Species B Air

2C 11A

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TAKS 1 TAKS 1 Bio/IPC 2C; Bio 11A

Teach, continuedTeach, continued


ModelingWatertight SkinSkills AcquiredCalculating, analyzingdata, inferring conclusions

Teacher’s Notes Be sure to have students wipethe pan of the scale cleanbetween weighings. Place anincandescent lamp on eachtable to simulate a desert environment.

Answers to Analysis1. The mass of the skinless grape

should decrease. The mass ofthe intact grape should stay the same.

2. The skin prevents water fromevaporating from an intactgrape, so the grape’s weightdoes not change. Without itsskin, a grape loses water andbecomes lighter.

3. The skinless grape representsan amphibian’s skin. Theintact grape represents a reptile’s skin.

4. Watertight skin, as in theintact grape, prevents waterloss. This allows an animal tosurvive in dry environments.Most amphibians, like theskinless grape, would dry up if out of water or moist envi-ronment for an extendedperiod of time.

did you know?Introduced Species Cause Problems In thewestern United States, the tansy ragwort plantis poisonous to cattle. The cinnabar moth,whose larvae eat the tansy ragwort, was intro-duced into the region to control this plant.However, the larvae accumulate toxins that killthe northern alligator lizards that prey on thelarvae. Populations of these lizards may be atrisk in certain areas of the west.TAKS 3 Bio 12B; Bio/IPC 3C; Bio 3F

Water RetentionAmphibians such as frogs cannot be considered fully terrestrialbecause they lose too much water through their skin. Amphibians muststay moist to avoid dehydration, and their method of reproductionrequires a moist environment. Reptiles have evolutionary adap-tations that free them from the water requirements of amphibians.

Watertight SkinTerrestrial animals face a serious problem of water loss as waterevaporates through their skin. Modern reptiles have evolved a skinmade of light, flexible scales. These scales overlap and form a pro-tective, almost watertight skin that minimizes water loss, as shownin Figure 3.

Reviewing InformationReread the bulleted list ofkey features of reptiles inFigure 1. Then write themdown on a separate piece of paper, leaving room towrite notes about eachcharacteristic. As you read,summarize how the informa-tion relates to a particularcharacteristic.

Figure 3 Reptilian scales.The scales of a reptile’s skin form a tight seal thatretains moisture within thereptile’s body.

Modeling Watertight Skin Scales make a reptile’s skin almost watertight. This is one of reptiles’ adaptations to terrestrial life. You can use grapes to model and compare water loss in different types of skin.

Materials

forceps, 2 grapes, balance, Petri dish

Procedure

1. Find the mass of one grape,and record it in a data table.Then place the grape in anopen Petri dish.

2. Using forceps, peel the skin from the second grape.Find and record the mass ofthe peeled grape. Then placeit in the same Petri dish, butdo not let the two grapestouch.

3. Wait 15 minutes, and thenfind and record the mass ofeach grape again.

Analysis

1. Calculate the differencebetween the original and finalmasses of each grape.

2. Propose an explanation forany changes in mass youobserved.

3. Determine which graperepresents an amphibian’sskin and which represents areptile’s skin.

4. Describe how a watertightskin is an adaptation to ter-restrial life. Include informa-tion you have learned in thislab in your explanation.

2B 2C 2D 7B

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TAKS 1 BioIPC 2B, 2C, 2D; TAKS 3 Bio 7B

Student Edition TAKS Obj 1 Bio/IPC 2B, 2C, 2D TAKS Obj 3 Bio 7B TAKS 3 Bio 12ETEKS Bio 7B, 12C, 12ETEKS Bio/IPC 2B, 2C, 2D

Teacher Edition TAKS Obj 1 Bio/IPC 2B, 2C, 2D TAKS Obj 3 Bio 7B, 12B, 12ETAKS Obj 5 IPC 6BTEKS Bio 3F, 7B, 12B, 12C, 12ETEKS Bio/IPC 2B, 2C, 2D, 3CTEKS IPC 6B

pp. 774–775

IPC Benchmark Review

To prepare students for the TAKS and accompany thediscussion of thermoregulation in reptiles, have stu-dents review Convection, Conduction, and Radiation,TAKS 5 IPC 6B on p. 1063 of the IPC Refresher in theTexas Assessment Appendix of this book.

TAKS 1, TAKS 3

Green Turtles Tour the Atlantic Green turtles migrate more than 2,000 km (1,250 mi)from the waters off Brazil to the beaches ofAscension Island in the central Atlantic Ocean.A female green turtle will lay her eggs on thesame beach where she hatched. Scientists donot yet know for certain how she finds herbirthplace. Bio 12C

ActivityComparing Eggs Using fieldguides, books, and Internetresources, have students researchthe eggs of birds, reptiles, andamphibians. Ask each student tomake life-size, full-color drawingsof several types of eggs on smallpieces of paper. When students arefinished, assemble the drawingsinto three large posters forcomparison: The Eggs ofAmphibians, The Eggs of Reptiles,and The Eggs of Birds.

InterpersonalTAKS 1 Bio/IPC 2C, 2D; TAKS 3 Bio 7BLS


Trouble for Turtles inTexasTeaching Strategies• Show students a map of Texas

and trace the flow of theGuadalupe River. Ask stu-dents to locate cities that arenear the river. Then havestudents locate Canyon Lake.

• Tell students that in Cagle’smap turtle, a turtle’s sex isdetermined by the tempera-ture during which it was incu-bated. When temperatures arehigher than 30.5ºC, femaleturtles are produced; when itis lower than 28ºC, maleturtles are produced.

Discussion• How do humans affect the

habitat of the Cagle’s mapturtle? (Humans disrupt turtlehabitat by drawing water fromthe river, using the river forrecreation, building dams, anddeveloping areas along the river.)

• Even though they spend mostof their life in the water,Cagle’s map turtles lay theireggs on land. Why don’t theireggs dry out? (Turtles layamniotic eggs. Amniotic eggshave a food and water supplyso that they don’t dry out.)

• Male and female turtles eatdifferent things. What do youthink would be a benefit ofthis strategy? (It mightdecrease competition for food.)

Watertight EggsFor a reptile living on dry land, reproduction presents another seri-ous water-loss problem. Without a watery environment, both spermand eggs will dry out. A reptile’s fertilized eggs need a moist envi-ronment in which to develop. As you will read later in this chapter,the first problem is overcome by internal fertilization.

The nature of a reptile’s amniotic (am nee AHT ic) egg solves thesecond problem. An contains both a water supply anda food supply and is key to a reptile’s success as a terrestrial animal.Because the egg’s tough shell makes it essentially watertight, it doesnot dry out, even in very dry habitats. Most reptiles, all birds, andthree species of mammals reproduce by means of amniotic eggs withshells. (Other mammals produce amniotic eggs, but the embryodevelops within the female’s uterus rather than within a shell. Youwill learn about the development of these eggs in a later chapter.) Theformation of amniotic eggs with shells suggests that these threegroups of animals evolved from a common ancestor.

amniotic egg

The Guadalupe River in south-ern Texas is home to several

threatened and endangeredspecies. Another may soon beadded to the list: Cagle’s mapturtle, Graptemys caglei. Firstdiscovered in 1974, this reptile atone time had a larger range thanit does today. It is now thought toexist only in the Guadalupe River.Although the turtle is not yetconsidered threatened or endan-gered, it has been listed as aprotected species in Texas.

Cagle’s map turtles rarely leavethe water except to lay eggs. Thefemales eat clams and aquaticsnails. The males eat insect larvae,which are usually found in poolsand in rocky areas with riffles.

A Changing EnvironmentThe Guadalupe River windsthrough a part of Texas that has arapidly growing human populationwith an increasing demand forwater. Some parts of the riverattract so many recreational visi-

tors that water quality and shore-line habitat are being degraded.Clearing of forests along the riverfor building construction couldfurther lower the river’s waterquality and change its flow.Numerous dams already interruptthe flow of the river, and two addi-tional dams have been proposed.Dams cause riffles to disappearand allow silt to cover rocks, mak-ing it harder for turtles to find food.

Monitoring the SituationResearchers at West Texas A&MUniversity in Canyon have beenstudying the ecology of Cagle’smap turtle for more than 20 years.The data they have collectedshow how the turtle is faring indifferent areas. For example, tur-tle populations now are greatlyreduced in Canyon Lake, a reser-voir in the upper portion of theriver.

Further work by the researcherswill focus on the turtles’ waterflow requirements and habitat

characteristics. Knowing whatwater flows the turtles need mayallow scientists to recommendwhen and how much watershould be released from thedams. Learning more about theturtles’ preferred habitat, such asthe size of rocks they use most,will help people identify sectionsof the river that may have to bepreserved. Changes such asthese, the researchers believe,are needed to keep Cagle’s mapturtle from becoming a threat-ened species.

www.scilinks.orgTopic: Texas ReptilesKeyword: HXX4023

Trouble for Turtles in Texas

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TAKS 3 Bio 12E; Bio 12C

TAKS 3

Teaching TipSurface Area Ask students whichmelts faster—multiple cubes of iceor a single block of ice of the sameweight? Lead students into a dis-cussion of the importance of sur-face area in living things. Relate thecubes of ice to alveoli in the lungs.

Verbal

Math Skills Ask students to findthe surface area of an 8 mL cube andthe combined surface area of eight 1mL cubes. Remind students that thesurface area of a cube is found by l � w � 6 (where l � length, w �width, and 6 � the number of sides).Point out that an 8-mL cube hastwo-centimeter sides and a 1-mLcube has one-centimeter sides.(Although the overall volume is thesame, the 8-mL cube has a surface areaof 24 cm2 and eight 1-mL cubes have acombined surface area of 48 cm2.)

Logical

Group ActivityLocal Snakes Use a field guide todetermine what kinds of snakesare found in your area. Havegroups research these snakes andreport to the class on the snakes’habitat, range, reproduction,behavior, feeding habits, and anyother relevant information.

Verbal

TAKS 1 Bio/IPC 2C, 2D; Bio 8B

Co-op LearningLS

LS

GENERALBUILDERSKILL

TAKS 4 IPC 9DLS



Snakes in Literature Throughout history,many cultures have used snakes in literary,cultural, and religious settings, such as TheBible, and in stories such as the Greek mythof Medusa. Even children’s stories likeAladdin and The Jungle Book include snakes.Snakes are often portrayed as evil, cold-blooded animals. Have students research thisphenomenon in literature and write an essayon whether the reputation of the snake isdeserved. TAKS 1 Bio/IPC 2D

SOCIAL STUDIESSOCIAL STUDIESCONNECTIONCONNECTION

Respiration Because most reptiles are far more active than amphibians, theyhave greater metabolic requirements for oxygen. Their bodies meetthis demand in several ways.

LungsA reptile’s scaly skin does not permit gas exchange, so reptiles can-not use their skin as an additional respiratory surface, as manyamphibians can. However, the lungs of most reptiles have manyinternal folds, as shown in Figure 4. These folds greatly increase therespiratory surface area of a reptile’s lungs. In addition, reptileshave strong muscles attached to their rib cage. The action of thesemuscles helps to move air into and out of the lungs, increasing thelungs’ efficiency.

HeartRecall that the ventricle of the amphibian heart is not divided by aseptum. Oxygen-poor blood and oxygen-rich blood mix somewhatin the amphibian’s ventricle. In most reptiles, however, the septumextends into the ventricle, partly dividing it into right and lefthalves, as shown in Figure 5. The septum enables a much better, butstill incomplete, separation of oxygen-rich and oxygen-poor blood.As a result, oxygen is delivered to the body cells more efficientlythan in amphibians.

Unlike most reptiles, crocodilians have a heart with a com-pletely divided ventricle that consists of two pumping chambers.This arrangement fully separates the lung circulation from thebody circulation. Thus, the delivery of oxygen throughout thebody is further improved in these animals.

Figure 4 Reptilian lungs.The lungs of reptiles containnumerous internal folds.

Figure 5 Reptilian heart.In most reptiles, the ventricleof the heart is partly divided bya septum.

Reptilian Heart Structure

Rightatrium

From body To body

To body

Righthalf of

ventricle Lefthalf of

ventricle

Leftatrium

Fromlungs

To lungs

Incompleteseptum

Oxygen-poor blood from the bodyenters the right atrium. Oxygen-rich

blood from the lungs enters the left atrium.

1

An incomplete septum partlydivides the ventricle. Thus,

there is less mixing of oxygen-richand oxygen-poor blood than there isin the amphibian heart.

2

Arteries carry oxygen-richblood from the left half of

the ventricle to the body andoxygen-poor blood from the righthalf of the ventricle to the lungs.

3

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Student Edition TAKS Obj 1 Bio/IPC 2C TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A, 11ATEKS Bio/IPC 2C

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TAKS Obj 4 IPC 9D TEKS Bio 7B, 8B, 8C, 10A, 11ATEKS Bio/IPC 2C, 2DTEKS IPC 9D

pp. 776–777

Answers to Section Review

1. strong, bony skeletons, and toes with claws;ectothermic metabolism; dry scaly skin, almostwatertight; amniotic eggs; well-developedlungs; partly or completely divided ventricle;internal fertilization

2. Because they are ectotherms, reptiles must thermoregulate behaviorally. They can be physically active and hunt for food only whentheir body temperature is within a certain critical range.

3. The almost watertight skin and amniotic eggsof reptiles minimize water loss on land.TAKS 3 Bio 7B

Bio 11A

TAKS 2 Bio 8C

ReteachingHave students pair up and list eachof the seven key features of reptiles,which are given in Figure 1, onindividual index cards. On the backof each card, have them write aone-word clue to identify the char-acteristic on the front of the card.Ask students to shuffle the cardsand turn them so only the cluewords are showing. Have one stu-dent choose a card at random andread the clue word. His or her part-ner should respond with the keycharacteristic. If the studentanswers correctly, his or her part-ner should set the card aside.Students should continue the gameuntil all of the cards are set aside.Students should then switch rolesand repeat the process.

Interpersonal

QuizTrue or False:

1. As in most amphibians, fertiliza-tion in reptiles is external. (False.Fertilization is internal, an adapta-tion to life on land.)

2.The heart of most reptiles onlypartially separates blood fromthe lungs and blood from thebody. (True. Except in crocodil-ians, freshly oxygenated bloodmixes in the heart with oxygen-depleted blood.)

AlternativeAssessmentHave teams of students write briefdescriptions of what they think arethe five most important things theyhave learned about reptiles. Haveteams present their descriptions tothe class, with each team memberparticipating in the presentation.

Verbal

TAKS 2 Bio 8C

Co-op LearningLS

GENERAL

TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B

TAKS 2 Bio 8C

GENERAL

TAKS 2 Bio 8C

Co-op LearningLS

CloseClose


ReproductionUnlike the eggs of most amphibians, reptilian eggs are fertilizedwithin the female, a process called internal fertilization. The malereptile introduces his semen directly into the female’s body. Thesemen contains sperm and fluid secretions. Internal fertilizationprotects the gametes from drying out, even though the adult ani-mals are fully terrestrial.

Many reptiles are (oh VIHP urh uhs), meaning theyoung hatch from eggs, as shown in Figure 6. In most cases, theeggs are not protected by the parents. Most snakes and lizards, allturtles and tortoises, and all crocodilians are oviparous. All birdsand three species of mammals are also oviparous.

Some species of snakes and lizards are , whichmeans the female retains the eggs within her body until shortlybefore hatching, or the eggs may hatch within the female’s body.Although the embryos receive water and oxygen from the female,their nourishment comes from the yolk sac. The offspring of a snake,shown in Figure 6, are born able to fend for themselves. In ovovivip-arous reptiles, the eggs are less vulnerable to predators.

ovoviviparous

oviparous

Figure 6 Reproduction.Sea turtles hatch from eggsburied on sandy beaches. The eggs of some species ofsnakes are incubated withinthe female’s body, and theyoung are born live.

Sea turtles Hatchling snakes

Section 1 Review

Identify seven characteristics of reptiles. 8C

Describe how the ectothermic nature of reptilesinfluences their physical activity and feeding habits.

Summarize the skin and egg adaptations thatallow reptiles to live on land. 7B

Critical Thinking Forming ReasonedOpinions Data show that an animal’s tempera-ture changes over the course of a day. A studentasserts that this proves the animal is an ecto-therm. What must the student consider beforemaking such a claim? 2C 11A

Describe how reptiles meet their need for moreoxygen than amphibians require. 10A

If a lizard’s internal temperature sensors detect a decrease in bodytemperature, the lizard can maintain homeostasis by 11A

A speeding up its metabolism.B slowing its metabolism.C basking in the sunshine. D resting in the shade.

TAKS Test PrepTAKS Test Prep

The term ovoviviparouscomes from three differentLatin words: ovum, meaning“egg,” vivus, meaning“alive,” and parere, mean-ing “to bring forth or bear.”

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4. The student would need to compare theanimal’s temperature changes to changes in theenvironmental temperature.

5. In contrast to amphibians, reptiles have well-developed lungs with alveoli, as well as strongrib muscles.

6. A. Incorrect. Ectotherms cannotalter their metabolism to maintain homeostasis. B. Incorrect. A slower metabolism would not increase body temperature. C. Correct.Ectotherms maintain body temperature bybasking. D. Incorrect. Resting in the shadewould not increase body temperature. Bio 11A

Bio 11A

TAKS 1 Bio/IPC 2C; Bio 11A

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. In this section, students areintroduced to the orders of the rep-tiles, one of the most diverse classesof terrestrial vertebrates. Studentswill also learn the distinguishingcharacteristics of all the orders.

Ask students to list as manyreptiles as they can. Then, havethem indicate which reptiles ontheir list are closely related. Afterreading the section, have studentsmake corrections and add anymissing groups of reptiles to theirlists. (Students should indicate thatsnakes and lizards are related, turtlesand tortoises are related, and thatcrocodiles and alligators are related.Students are probably unfamiliar withthe tuataras.)

DemonstrationObtain a picture of a skink, andcover its body so that only its headshows. Ask students if the animal isa lizard or a snake. Then reveal therest of the animal, pointing outhow similar some lizards are tosnakes. Ask students how to tell alizard from a snake. (Most lizardshave legs and external ears, a pec-toral girdle, and many have movableeyelids. Snakes lack these features.)

Visual TAKS 2 Bio 8C; Bio 8BLS

GENERAL

MotivateMotivate

TAKS 2 Bio 8C; Bio 8B

Bellringer

FocusFocus

Section 2


• Lesson Plans• Directed Reading• Active Reading GENERAL

GENERAL

Chapter Resource File• Reading Organizers• Reading Strategies• Occupational Application Worksheet:

Emergency MedicalTechnician GENERAL

Planner CD-ROM

Transparencies

TT BellringerTT External Structures of SnakesTT Internal Structures of SnakesTT Orders of Living ReptilesTT Orders of Extinct Reptiles

Section 2 Today’s Reptiles

Lizards and Snakes You’ve probably walked by a snake or lizard without even knowingit was there. Most are quiet, and their coloration often concealsthem from view. Even if you visited the jungles of South America,you might not notice an anaconda unless it moved. What’s an ana-conda? It’s the world’s largest snake, frequently reaching 5 m (about16 ft) in length. The largest anaconda ever found was twice thatlong. Very large anacondas have been known to prey on jaguars.After such a meal, the anaconda may not eat again for up to a year.

Snakes and lizards belong to order Squamata. A distinguishingcharacteristic of this order is a lower jaw that is only loosely con-nected to the skull. This allows the mouth to open wide enough toaccommodate large prey and explains how an anaconda can swal-low a jaguar. This ability is a contributing factor to the success ofsnakes and most lizards as predators.

LizardsCommon lizards include iguanas, chameleons, geckos, anoles, andhorned lizards (often mistakenly called “horny toads”). A few speciesof lizards are herbivores, but most are carnivores. Most lizards aresmall, measuring less than 30 cm (1 ft) in length, but lizards thatbelong to the monitor family can be quite large. The Komodo dragonof Indonesia, shown in Figure 7, is the largest monitor lizard. It canbe up to 3 m (10 ft) in length and weigh up to 125 kg (275 lb). Thetail of some species of lizards, such as the gecko shown in Figure 7,breaks off easily when seized by a predator, allowing the lizard toescape. Lizards can regenerate a new tail, but it does not have anyvertebrae in it.

Objectives● Compare the four living

orders of reptiles.

● Describe the timber rattle-snake’s adaptations forlocating and capturing prey.

● Compare the parental careof crocodilians with that ofother reptiles.

Key Terms

carapaceplastron

Figure 7 Lizards. Geckosare small reptiles, rarelyexceeding 24 cm (10 in.) inlength. The Komodo dragon isthe world’s largest lizard.

Komodo dragon

Gecko

8C

8B

7B

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TEKS Bio 7B, 8C, 12B

Teacher Edition TAKS Obj 2 Bio 8CTAKS Obj 3 Bio 12BTEKS Bio 8B, 8C, 12BTEKS Bio/IPC 3C

pp. 778–779

TAKS 2

TAKS 3

Teaching TipDangerous Snakes Ask studentswhat venomous snake is the mostdangerous in the world. Recordtheir responses. (examples: kingcobra, sea snake, coral snake, andAustralian tiger snake) Ask why aparticular species is consideredmore dangerous than others. Tellthem that many different venomoussnakes are touted as the “most dan-gerous snake alive,” or the “mostpoisonous snake on Earth.” Pointout that several factors determinehow “dangerous” a snake is.Among these factors are the toxic-ity of its venom, the type of venom(hemolytic or neurotoxic), and theamount of venom a bite victimreceives. In India, there are about900,000 snakebites each year,resulting in about 9,000 deaths.Many of these bites are deliveredby the aggressive king cobra, whichis frequently encountered by India’slarge human population. VerbalBio/IPC 3C

LS

TeachTeach


Answer

People who have other pets thatmight harass a gecko, such as acat or a dog, should not try touse geckos for pest control.

TAKS 3 Bio 12B

Real Life

MEDICINEMEDICINECONNECTIONCONNECTION

Medical professionals are nearly unanimous intheir views of what not to do for snakebite:

• No ice or any other type of cooling on the bite

• No tourniquets

• No electric shock

• No incisions in the wound Bio/IPC 3C

The American Red Cross recommends the following first-aid treatment for snakebite:

• Wash the bite with soap and water.

• Immobilize the area and keep it lower thanthe heart.

• Get medical help.

SnakesSnakes probably evolved from lizards during the Cretaceous period.The close relationship between lizards and snakes is reflected intheir many similarities. In fact, it is often difficult to distinguish thelegless species of lizards from snakes. Snakes lack movable eyelidsand external ears, as do several species of lizards. Also, both snakesand lizards molt periodically, shedding their outer layers of skin.

Body Structure The skeleton of snakes is unique. Most snakes haveno trace of a pectoral girdle (the supporting bones for the bones ofthe forelimbs), which is found even in legless lizards. The snake’sjaw is very flexible because it has five points of movement. (Yourjaw, in contrast, has only one movement point.) One of these pointsis the chin, where the halves of the lower jaw are connected by anelastic ligament. This ligament permits the lower jaw to spreadapart when a large meal is being swallowed. The African egg-eatingsnake, shown in Figure 8, can swallow eggs that are much largerthan its head in a process that can take an hour or more.

Feeding While many snakes simply seize their prey and swallow itwhole, some snakes use other methods to subdue their prey. Manyvery large snakes, such as anacondas, boas, and pythons, are con-strictors, as are some smaller species, such as king snakes.Constrictors wrap their body around their prey, gradually squeezingtighter and tighter until the prey suffocates. The snakes then swal-low their prey whole, even if the prey is very large. Like all snakes,constrictors have no teeth that are suited for cutting and chewing.

Some snakes kill their prey with venom (poison). Of the 13 fami-lies of snakes, only four are venomous: (1) cobras, kraits, and coralsnakes; (2) sea snakes; (3) adders and vipers; and (4) rattlesnakes,water moccasins, and copperheads. In most venomous snakes,modified salivary glands produce a venom that is injected into thevictim through grooved or hollow teeth. The African boomslangand twig snakes produce venom but do not inject it. Instead, theybite their prey with fangs located at the back of their mouth.Grooved teeth direct the venom into their victim’s wound. You canread more about the biology of snakes in Up Close: Timber Rattle-snake, on the following pages.

Real LifeNeed a lizard? Instead of calling anexterminator to rid theirhomes of unwanted pests,some adventuresomehomeowners keep a Tokaygecko. This gecko preysvoraciously on mice andinsects and is very efficientat ridding a home of these pests. Finding Information Investigate the pros andcons of using geckos forpest control. Who shouldtry this method and whoshould avoid it?

Figure 8 Snake feeding.Snakes have flexible jaws thatallow them to swallow preymuch larger than their head.

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TAKS 3


MISCONCEPTION ALERT

Slimy Snakes Contact a local nature center,zoo, or herpetological society to arrange for alive, non-poisonous snake and handler tovisit the class. Have students make a list ofsome of their preconceptions about snakes.For instance, many students believe that asnake’s skin is slimy, like that of a frog.Another misconception is that the tongue of

a snake is poisonous, and that snakes willattack people for no reason. Show the class alive snake, and allow students to touch andexamine the snake. Help to dispel misconcep-tions by discussing possible origins for suchfears. Remain sensitive to the fact that manypeople will continue to fear snakes.TAKS 1 Bio/IPC 2D

GENERAL

Timber Rattlesnake

Teaching Strategies Help students understand therattlesnake’s ability to sense itsprey in the dark by using awarm object such as a heatingpad. Place the heating pad on atable and allow it to warm thesurface. Remove the heatingpad and have students movetheir hands above the tabletopwithout touching the tableitself. They should be able tofeel the heat radiating from thewarmed spot. Have studentsdetermine how close theirhands must be to detect theheat. Inform them that a rat-tlesnake can locate warm preyfrom a distance of 1 m (39 in.).These snakes, however, senseheat with their pit organs, notthrough their skin.On a sheet of paper, have stu-dents list each major headingin the Up Close feature. Afterthey read each section, havethem hypothesize how thatparticular feature of the timberrattlesnake is an adaptation forsurvival. Then have studentsexchange papers with a partnerand read their partner’s paper,noting how their partner mayhave identified a different survival value for some of the features.

TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B; Bio 12C

Up Close

External Structures

Up CloseTimber Rattlesnake

Scientific name: Crotalus horridus

Size: Typically 90–150 cm (36–60 in.) long; maximum 189 cm (74 in.)

Range: Eastern and central United States, from northern New York to northern Florida and west, to central Texas

Habitat: Prefers thick brush, dense woodland, or swamp

Diet: Primarily small mammals

●

●

●

●

●

Rattle The rattle typically consists of 5 to 7 interlocking rings

made of keratin, a protein. When shaken, it produces a rattling

sound that serves as a warning. Contrary to popular belief, the

snake does not add a rattle each year. Instead, each time the

snake sheds its skin during molting, a new ring is added

to the base of the rattle. The more rapidly the snake

grows, the more rattles it accumulates during a

given time. This is why the number of rattles

a snake has increases with the size

of the snake.

Pit organ Between each eye and nostril of the rattlesnake is an organ

that can detect infrared radiation. The snake can locate a warm-bodied

animal in a cool, nighttime environment by detecting the difference in

infrared radiation emitted by the animal and the cooler background. Thus,

a rattlesnake can hunt in total darkness.

Rattle

Pit organ ▼

▲

Eye

Nostril

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TAKS 2, TAKS 3

Student Edition TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A, 12C

Teacher Edition TAKS Obj 1 Bio/IPC 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A, 12CTEKS Bio/IPC 2D, 3C

pp. 780–781

Venomous Snakes About 99 percent ofvenomous snakebites in the United States arefrom pit vipers. About 8,000 snakebitesoccur in the United States each year, andaround 9 to 15 victims die. Every stateexcept Maine, Alaska, and Hawaii is hometo at least one poisonous snake species.Bio /IPC 3C


Timber RattlesnakeDiscussion • Explain why it would be eas-

ier for a timber rattlesnake tokill a mouse than a lizard atnight. (The mouse is anendotherm and the pit viper’sheat-sensitive pits can detectits body heat. The lizard is anectotherm and would not nec-essarily be warmer than itssurroundings.)

• What is the advantage to arattlesnake of announcing itspresence to other animals byrattling? (Answers may varybut may include that by rat-tling the snake keeps largemammals, such as cattle, fromstepping on it.)

• How is an ovoviviparoussnake, such as the timber rat-tlesnake, different from aviviparous snake in the waydeveloping embryos are sus-tained? (Ovoviviparous mothers supply no nutrients to the developing young, whileviviparous mothers do.)

Up Close

did you know?Triple-jointed Jaws The tiny snakes calledthreadsnakes have triple-jointed jaws. When athreadsnake burrows into the nests of ants orother social insects, parts of its lower jaw rotatelike a pair of swinging doors. It is thought thatthis action helps the snake to eat quickly andescape injury or death from ant stings.TAKS 3 Bio 7B; Bio 12C

Internal Structures

Venom glands The timber rattle-

snake has hollow upper front teeth,

or fangs. When the rattlesnake

strikes, these hinged fangs swing

forward from the roof of the mouth

and inject venom deep into the prey.

The venom contains hemotoxins,

proteins that attack the circulatory

system, destroying red blood

cells and causing internal

hemorrhaging. Modified salivary

glands in the upper jaw produce

the venom.

Jacobson’s organs Flicking its

forked tongue into the air, the rattle-

snake takes in chemical samples

from the environment. These chemi-

cals are transferred to two depres-

sions in the roof of the mouth called

Jacobson’s organs, which detect

the odor of the chemicals. The

snake uses these organs to follow

the scent trail of prey.

Reproductive structures This male rattlesnake

produces sperm in his testes. Female timber rattlesnakes

are ovoviviparous. A female carries her fertilized eggs in her

body while they develop. Each egg has a thin membrane

through which water and oxygen pass from the mother to

the embryo. All nourishment is provided by the egg’s yolk.

After the eggs hatch in the mother’s body, the live young

are ejected and must fend for themselves.

Spine The rattlesnake’s spine is

made up of several hundred ver-

tebrae, each with its own pair of

attached ribs. It provides the frame-

work for thousands of muscles that

manipulate not only the skeleton but

also the snake’s skin, causing the

overlapping scales to extend or lie flat.

Internal anatomyThe internal organs are

elongated, matching the

snake’s body shape. The

left lung is nonfunctional.

Jacobson’s organs ▼

Fang

Tongue

TracheaEsophagus

Venomgland

▼Heart

Cloaca

Left lung

Right lung

Stomach

Small intestine

Large intestine

Kidneys

Liver

Gallbladder

Pancreas

▼ Testes ▼ Spine

781

Using the FigurePoint out in Figure 10 that a turtle’sshoulders lie within its rib cage.Students should recognize that theirown shoulders are outside of theirribs. Tell students that a turtle isattached to its shell and cannotcrawl out of it, as cartoon turtlesoften do. Visual

Writing Skills Have studentsimagine that they are the first per-son from their country to see aturtle. Ask students to write adescription of a turtle, for an audi-ence that has never seen a turtlebefore. Encourage them to be bothdescriptive and accurate. Verbal

Teaching TipEndangered Crocodilians Tellstudents that although crocodiliansare fierce predators, many of the 25species of crocodilians are endan-gered or threatened. Overhuntingof crocodilians for their hides,which are used to make leathergoods, is the primary cause of theirdecline. TAKS 3 Bio 12B; Bio/IPC 3C

TAKS 1 Bio/IPC 2DLS

BUILDERSKILL

TAKS 3 Bio 7BLS

GENERAL



did you know?Alligators’ Sounds Alligators are unusualamong reptiles in being able to make definitevocalizations. The male alligator bellowsloudly during mating season. Vocal sacs oneach side of his throat inflate when he calls.When alligators hatch from their buried eggs,they make a sound that is almost like a bark.The sound signals their mother that it is timeto open the nest. Hatchlings also have a dis-tress call they use to alert their mother if theyfeel threatened. TAKS 3 Bio 7B; Bio 12C

CulturalAwarenessCulturalAwareness

Turtle Myths The turtle appears as a cen-tral character in mythologies from aroundthe world. An ancient Chinese mythdescribes how the turtle Kwei created theuniverse. The Chinese Book of Rites namesthe turtle as one of the four benevolentspirit animals. Hindu myths from Indiadescribe the world as being supported byfour elephants standing on a turtle’s back.And in North America, several native cul-tures imagined the world as an island on theback of a great turtle. Bio/IPC 3C

Other Orders of Reptiles The remaining orders of living reptiles contain far fewer species thanthe order Squamata does. There are about 250 species of turtles(which generally live in water) and tortoises (which live on land), allclassified in the order Chelonia. The order Crocodilia is composed of25 species of large, aquatic reptiles. The order Rhynchocephalia(RING koh seh FAY lee uh) contains only two species of tuataras.

Turtles and TortoisesTurtles and tortoises, shown in Figure 9, differ from other reptilesin that their bodies are encased within a hard, bony, protectiveshell. Many of them can pull their head and legs into the shell foreffective protection from predators. While most tortoises have adome-shaped shell, water-dwelling turtles have a streamlined, disk-shaped shell that permits rapid maneuvering in water. Turtles andtortoises lack teeth but have jaws covered by sharp plates, whichform powerful beaks. Many are herbivores but some, such as thesnapping turtle, are aggressive carnivores.

Today’s turtles and tortoises differ little from the earliest knownturtle fossils, which date to more than 200 million years ago. Thisevolutionary stability may reflect the adaptive aspects of their basicshell-covered body structure. The shell is made of fused plates ofbone covered with horny shields or tough, leathery skin. In eithercase, the shell consists of two basic parts. The is the dor-sal (top) part of the shell, and the is the ventral (bottom)portion. The vertebrae and ribs of most species are fused to theinside of the carapace, as shown in Figure 10. The shell provides thesupport for all muscle attachments in the torso.

Crocodiles and AlligatorsOf all the living reptiles, the crocodilians are mostclosely related to the dinosaurs. In addition tocrocodiles and alligators, shown in Figure 11, theorder Crocodilia includes the alligator-likecaimans and the long-snouted gavial. Crocodiliansare aggressive carnivores. Some are quite large.American alligators can reach 5.5 m (18 ft) inlength, and Nile crocodiles can reach 6 m (20 ft) inlength and weigh 750 kg (1,650 lb). Crocodiliansgenerally capture prey by stealth, often floating

just beneath the water’s surface near the shore. When an animalcomes to the water to drink, the crocodilian explodes out of the waterand seizes its prey. The crocodilian then hauls the prey back into thewater to be drowned and eaten. The bodies of crocodilians are welladapted for this form of hunting. Their eyes are high on the sides ofthe head, and their nostrils are on top of the snout. As a result, theycan see and breathe while lying nearly submerged in the water. Croc-odilians have a very strong neck and an enormous mouth studded

plastroncarapace

Figure 9 Turtle andtortoise. Like other seaturtles, this green sea turtle(top) spends virtually its entirelife in the sea. The Galápagostortoise (bottom) spends its lifeon land.

Figure 10 Turtle interior.In this ventral view, a turtle’splastron has been removed toshow the relationship of thevertebral column, ribs, pelvis,and pectoral girdle to the carapace.

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TAKS Obj 3 Bio 12B TEKS Bio 7B, 8B, 8C, 10A, 11B, 12B

Teacher Edition TAKS Obj 1 Bio/IPC 2D TAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 7B, 12B TEKS Bio 7B, 8B, 8C, 10A, 11B,12B, 12CTEKS Bio/IPC 2D, 3C

pp. 782–783


1. Snakes and lizards both have scaly skin andmolt periodically. Their lower jaw is looselyconnected to the skull.

2. Jacobson’s organs, located in the roof of themouth, detect microscopic airborne particles,which the brain interprets as scent. Pit vipersuse their pit organs to detect heat.

3. Their bodies are encased in a protective shell,and they lack teeth.

4. Alligators and other crocodilians are the onlyreptiles to care for their young. Some alligatorsbuild nests for their young and care for themfor up to a year after they hatch. Bio 8B

TAKS 2 Bio 10A; Bio 8B, 11B

TAKS 3 Bio 7B

TAKS 2 Bio 8C

5. The crocodile is able to keep most of its bodysubmerged and hidden while still being able tobreathe and look for prey.

6. A. Incorrect. The Jacobson’sorgans in the roof of the mouth are sensitive toairborne chemicals. B. Incorrect. Snakes lackears and do not hear faint sounds. C. Incorrect.Snakes can feel ground vibrations throughtheir bodies, not the pit organs. D. Correct.Using pit organs, warm-blooded animals canbe found even in the dark. Bio 11B

Bio 11B

ReteachingWrite the following words orphrases on the board: lizards andsnakes, turtles and tortoises, croco-diles and alligators, and tuataras.Have students copy them, leavingspace for additional information.Have students write distinguishingtraits of each group in the appro-priate spaces without using theirtextbooks. (lizards and snakes-lowerjaw has loose connection to skull, nopectoral girdle in snakes, molt peri-odically, may lack eyelids; turtles andtortoises-hard shell, lack teeth, jawshave a powerful beak; crocodiles andalligators-long snout, eyes high onhead, nostrils on top of head, largemouth with sharp teeth; tuataras-lizardlike, active at night) When thestudents have finished their work,have them share their results with apartner, recording any characteris-tics they omitted but their partneridentified. Verbal

Quiz1. The reptiles that share the most

characteristics with snakes arethe ________ (lizards)

2.Unlike other reptiles, ________care for their young after theyhatch. (crocodilians)

3. The shells of turtles and tortoisesconsist of a plastron on theunderside and a ________, whichfuses with the rib cage. (carapace)

AlternativeAssessmentAssign students to work in groupsof three. Each group will researchthe reptiles of an assigned conti-nent. For each reptile, include thefollowing: order, appearance(drawing), size, diet, habitat, range,and status (common, rare, threat-ened, or endangered). When groupshave finished their research anddrawings, the entire collection canbe assembled on a large mural ofthe continents. Ask a local elemen-tary school to display the mural.

Interpersonal

TAKS 2 Bio 8C

Co-op LearningLS

TAKS 3 Bio 7B

TAKS 2 Bio 8C

TAKS 2 Bio 8C

GENERAL

Co-op LearningLS

CloseClose


with sharp teeth. A valve in the back of the mouth pre-vents water from entering the lungs when crocodiliansfeed underwater.

Unlike other living reptiles, crocodilians care fortheir young after hatching. For instance, a femaleAmerican alligator builds a nest of rotting vegetationfor her eggs. After the eggs hatch, the mother may tearopen the nest to free the hatchlings. The young alliga-tors remain under her protection for up to a year.

TuatarasThe two living species of tuataras are members of thegenus Sphenodon and are native to New Zealand.Sphenodon punctatus, the more common species, isshown in Figure 12. Tuataras are lizardlike reptiles upto 70 cm (2 ft) long. Unlike most reptiles, tuataras aremost active at low temperatures. They burrow or baskin the sun during the day and feed on insects, worms,and other small animals at night. Tuataras are some-times called living fossils because they have survivedalmost unchanged for 150 million years. Since thearrival of humans in New Zealand about 1,000 yearsago, the tuatara’s range has diminished, and theirnumbers are declining.

Figure 11 Crocodilians. In general, thesnouts of alligators are shorter and broaderthan those of crocodiles.

American alligator

Australian crocodiles

Figure 12 Tuatara. Tuataras live on only a few small islands in New Zealand.

Section 2 Review

Describe the characteristics shared by lizardsand snakes. 8C

Describe the function of two different organsthat help snakes locate their prey. 7B

Summarize the ways turtles and tortoises differfrom other reptiles. 8B 10A 11B

Compare the parental care shown by alligatorswith that shown by most other reptiles. 8B

Critical Thinking Recognizing RelationshipsHow does the position of a crocodile’s nostrils andeyes relate to its method of hunting? 11B

The pit organ of a rattle-snake is sensitive to A airborne chemicals.B faint sounds.C ground vibrations.D infrared radiation.

TAKS Test PrepTAKS Test Prep11B

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TAKS 2 Bio 8C; TAKS 3 Bio 7B; Bio/IPC 2D; Bio 8B

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. In this section, students willsummarize the key features of birds.These include several reptile-likecharacteristics, such as amniotic eggs and scale-covered feet and legs.Unique adaptations include feathersfor flight and insulation, a strong yetvery lightweight skeleton, a highlyefficient respiratory system and completely divided heart. These fea-tures allow flight for nearly all birds.Students will also examine the highlyvariable beaks and feet of birds,which allow different species tomake use of a range of diets andhabitats.

Ask students to list the unique adap-tations of birds that allow them tofly.

DemonstrationBring a feather to class and askstudents what kind of animal it isfrom. When students answer “abird,” ask them to think of anybird that does not have feathers.(There are none.) Ask them if theycan think of any living animals thathave feathers but are not consid-ered birds. (no) Emphasize thathaving feathers is a unique classifi-cation characteristic for the classAves. Visual TAKS 2 Bio 8C; Bio 8BLS

MotivateMotivate

TAKS 3 Bio 7B

Bellringer

FocusFocus

Section 3


• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Math Lab GENERAL

GENERAL

GENERAL


• Reading Organizers• Reading Strategies • Supplemental Reading Guide

Through a Window

Planner CD-ROM

Transparencies

TT BellringerTT Characteristics of BirdsTT Contour Feather StructureTT Avian SkeletonTT Avian Heart StructureTT Avian Lung Structure

Section 3 Characteristics andDiversity of Birds

Key Characteristics of BirdsWhy do people use the expression “free as a bird”? Most likely itcomes from a bird’s ability to fly seemingly wherever it wishes.Through human history, the gift of flight has been celebrated in sto-ries, poetry, and songs. But there is more to birds than flight; infact, some species of birds can’t fly.

The birds you see today are the modern members of class Aves.Unlike their reptilian relatives, birds lack teeth and have a tail thatis greatly reduced in length. But they do retain some reptiliancharacteristics. For instance, birds lay amniotic eggs that are verysimilar to those of reptiles, and the feet and legs of birds arecovered with scales. Other characteristics unique to birds distin-guish them from all other animals. The most obvious is thepresence of feathers and the modification of the forelimbs intowings. Figure 13 lists some distinguishing features of birds. Tolearn more about the anatomy and habits of one bird, see UpClose: Bald Eagle later in this section.

FeathersFeathers are modified reptilian scales that develop from tiny pits,called follicles, in the skin. Just as snakes and lizards replace theirskin by molting, birds molt and replace their feathers. However, fewbirds shed all of their feathers at one time.

Birds have two main types of feathers: contour feathers anddown feathers. cover the bird’s body and giveadult birds their shape. Specialized contour feathers, called flightfeathers, are found on a bird’s wings and tail. These feathers helpprovide lift for flight. As shown in Figure 14, a contour feather hasmany branches called barbs. Each barb has many projections, called

Contour feathers

Objectives● Summarize the key charac-

teristics of birds.

● Describe how a bird’sfeathers and bone structureaid flight.

● Summarize how a bird’slungs and heart are adaptedfor high efficiency.

● Relate the structure of abird’s feet and beak to itshabits and diet.

Key Terms

contour featherpreen glanddown feather

www.scilinks.orgTopic: Characteristics

of BirdsKeyword: HX4036

Figure 13 Characteristicsof birds. Like most birds, thistern is well adapted to flight.

• Forelimbs modified into wings• Body covered with feathers• Lightweight bones• Endothermic metabolism• Super-efficient respiratory

system• Heart with completely

divided ventricle

Characteristics of Birds

8C

7B

7B 10A

7B 11B

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Student Edition TAKS Obj 2 Bio 8C TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A, 11B

Teacher Edition TAKS Obj 1 Bio/IPC 2D TAKS Obj 2 Bio 8CTAKS Obj 3 Bio 7B, 12B TEKS Bio 3D, 7B, 8B, 8CTEKS Bio/IPC 2D

pp. 784–785

TAKS 2

TAKS 3

TAKS 3

TAKS 2,TAKS 3

Paired Summarizing Afterstudents have read silently aboutbirds, have pairs of students sum-marize what they have read withoutlooking at the textbook. One studentshould listen without interruptingbut should be prepared to point outany inaccuracies in the summary, andto add any ideas that were left out.Students may refer to the textbookduring this clarification process. You may want to pair ELL stu-dents with native English speakers.

Teaching TipPreening Birds often sit and preentheir feathers. Students have proba-bly observed this behavior. Havestudents hypothesize about thefunction of preening and the reasonthat birds spend so much time doingit. After a period of discussion,point out that when birds preen,they smooth out and clean theirfeathers, making them more aerody-namic. Also note that birds spreadoil from a gland near the base oftheir tail to waterproof the feathersand make them more resistant tobreakage, much the way hair condi-tioner works. Logical

DemonstrationBring cooked, cleaned chickenbones to class for students to exam-ine. Cut a few bones in half so stu-dents can see the hollow structure.If you have a wishbone, allow stu-dents to pull it gently to note itsflexibility. The cartilage keel on thebreast of a chicken is also interest-ing to examine because it providesan attachment surface for flightmuscles. Visual TAKS 3 Bio 7BLS

GENERAL

TAKS 1 Bio/IPC 2D; TAKS 3 Bio 7BLS

GENERAL

TAKS 2 Bio 8C; Bio 8B

SKILLBUILDER

READINGREADING

TeachTeach


MISCONCEPTION ALERT

Bird Nests Children who find bird nestsare often warned not to touch them. Thechildren are told, “the mother won’t returnto the nest if you touch it.” In reality, mostbirds have a very poor sense of smell andprobably would not know if their nest hadbeen touched by a human (exceptions areflightless birds, ducks, and vultures). Tocompensate, many birds have keen visionand hearing. Interpersonal TAKS 3 Bio 7BLS

English Language Learners

CareerCareerVeterinarian When most people think of aveterinarian, they think of a “dog or cat doctor.” Many students will know that veteri-narians also treat livestock. However, mostpeople probably do not know that veterinari-ans also treat birds and reptiles. Have studentsinvestigate the training required to become aveterinarian, and have them find out where vet schools are located in your region of the country. Verbal Bio 3DLS

Shaft

Vane

Barb Barbule Hook

barbules, that are equipped with microscopic hooks. These hooks linkthe barbs to one another, giving the feather a continuous surface anda sturdy but flexible shape. With use, the connections becomeundone. When you see a bird pulling its feathers through its beak, it is relinking these connections. This process is called preening.Preening also serves another function. Most birds have a gland calleda which secretes oil. When a bird preens, it spreads theoil over its feathers, cleaning and waterproofing them.

cover the body of young birds and are foundbeneath the contour feathers of adults. Their soft, fluffy structureprovides good insulation for the bird, helping the bird conserve body heat.

Feathers are important for other reasons too. Their colorationmay be protective (as camouflage) or may be important in the selec-tion of a mate. For example, the feathers of some birds allow themto blend in with their surroundings. In other species, the malesdevelop special plumage during the breeding season.

Strong, Lightweight SkeletonIf you have ever picked up a bird, such as a para-keet, you may have been surprised at how light itwas compared to a mammal of a similar size. Thisis because the bones of birds are thin and hollow.Many of the bones are fused, making a bird’s skel-eton more rigid than a reptile’s. The fused sectionsform a sturdy frame that anchors muscles duringflight. The power for flight (or for swimmingunderwater in the case of some birds, like pen-guins) comes from large breast muscles that canmake up 30 percent of a bird’s body weight. Thesemuscles stretch from the wing to the breastbone.The breastbone is greatly enlarged and bears aprominent keel for muscle attachment, as illus-trated in Figure 15. Muscles also attach to the fusedcollarbones (wishbone). No other living vertebrateshave a keeled breastbone or fused collarbones.

Down feathers

preen gland

The structure of a contour feather helps create a smooth, aerodynamic surface, aiding flight.

Figure 14 Contour feather

Fused collarbones

Keeled breastbone

Figure 15 Avian skeleton.A bird’s large, keeled attach-ment point for flight muscles,while its fused collarbones(wishbone) help absorb thestresses of flight.

785

Teaching TipHeat Source The high tempera-ture of birds is a by-product oftheir rapid metabolism. You maywish to use the analogy of a carengine for metabolism. If theengine is running, heat is produced.The faster the engine is running,the more heat is produced.Ectothermic reptiles are like carswhose engines run very slowly allthe time, producing little heat. Incontrast, birds (and mammals)keep their engines running at highspeed all of the time, producingmuch heat. TAKS 3 Bio 7B



CulturalAwarenessCulturalAwareness

Eagle Feathers The only people in NorthAmerica who can legally own eagle feathersare Native Americans. The eagle is so highlyvalued by tribes throughout the United Statesthat its feathers must be earned through per-sonal sacrifice, and then they may be used onlyin special ceremonies. For instance, if a

Winnebago pow-wow dancer accidentallydrops an eagle feather during a performance,the dance is stopped until the feather is purifiedby an elder and then reclaimed by the dancer,who is not allowed to dance again for a year.Bio/IPC 3C

From body

From body

To body

To lungsFromlungs

Leftatrium

Leftventricle

Rightventricle

Rightatrium

Completeseptum

Oxygen-rich blood from thelungs enters the left atrium,

which pumps it to the left ventricle.

3

The left ventricle pumps the oxygen-rich blood to

the body.

4The right ventricle pumps theoxygen-poor blood to the lungs.2

Oxygen-poor blood from the body entersthe right atrium. The right atrium pumps

this blood to the right ventricle.

1

Avian Heart Structure

Endothermic MetabolismBirds are endotherms; that is, they generate enough heat throughmetabolism to maintain a high body temperature. Birds maintainbody temperatures ranging from 40°C to 42°C (104°F to 108°F),which is significantly higher than the body temperature of mostmammals. For comparison, your body temperature is 37°C (98°F).These high temperatures are due to a high rate of metabolism,which satisfies the increased energy requirements of flight.

Completely Divided VentricleAs in crocodilians, the ventricle of birds is completely divided by aseptum, as shown in Figure 16. Oxygen-rich and oxygen-poor bloodare kept separate, meaning that oxygen is delivered to the body cellsmore efficiently. The sinus venosus, which is a prominent part ofthe fish heart, is not a separate chamber of the heart in birds (ormammals). However, a small amount of tissue from it remains inthe wall of the right atrium. This tissue is the point of origin of theheartbeat and is known as the heart’s pacemaker.

Highly Efficient LungsBirds such as the geese shown in Figure 17 use a considerableamount of energy when they fly. Since birds often fly for long pe-riods of time, their cellular demand for energy exceeds that of eventhe most active mammals. How do birds get the energy they need?

Recall that reptiles meet their increased need for oxygen withlungs that have a larger surface area than the lungs of amphibians.But there is a limit to how much the efficiency of a lung can beimproved just by increasing its surface area. Another way to

Interpreting GraphicsAfter studying Figure 18, useyour own words to summa-rize how one breath of aircirculates through a bird’slungs. Remember to includeboth the inhalation and theexhalation cycle.

Figure 16 Avian heart.A bird’s heart has a complete septum.

www.scilinks.orgTopic: Texas SongbirdsKeyword: HXX4021

786

IPC BenchmarkMini-Lesson

Biology/IPC Skills TAKS 5 IPC 4BInvestigate and describe applications of Newton's laws.Newton’s second law states that theamount of force acting on an object isequal to the object’s mass multiplied byits acceleration. Furthermore, anobject’s momentum is the product of itsmass and velocity. This helps explainone of the principles of flight. Bird’swings have a special shape called anairfoil and airplane wings mimic thisshape. As a mass of air passes over awing it’s path is bent downward,thereby changing its momentum.Changes in the momentum of the airresult in changes on the forces actingon the wing. The amount of lift on awing depends on the amount andvelocity of the air being diverteddownward. For more lift, the wing caneither divert more air—the mass—orincrease the downward velocity of theair. Activity: Have students build paperairplanes that have airfoil wings. Thentest them outside to see if their designswere successful.

Student Edition TAKS Obj 2 Bio 10A TAKS Obj 3 Bio 7B TEKS Bio 7B,10A

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 3 Bio 7A, 7B TAKS Obj 5 IPC 4BTEKS Bio 7A, 7B, 12CTEKS Bio/IPC 2C, 2D, 3CTEKS IPC 4B

pp. 786–787

the eggs of the incubating species. Therefore, thecowbird nestlings are fed first and get a headstart in their development over the other chicksin the nest. Cowbird nestlings may even ejectthe nestlings of the incubating species, therebyeliminating competition for food.TAKS 3 Bio 7B; Bio 12C

Teaching TipWhite or Dark Meat? The darkcolor of some chicken meat is partlydue to the presence of myoglobin, ahemoglobin-related molecule thathelps provide oxygen to musclesthat must contract vigorously andrepeatedly. Ask students why aduck has dark breast meat but achicken has white breast meat. (Theduck flies long distances, but thechicken does not.) Ask what chick-ens usually use for locomotion andwhat color that meat is. (They usu-ally use their legs to walk, and thelegs contain dark meat.)

Activity Origin of Birds Ask students toidentify the living reptiles that aremost closely related to birds. (crocodilians) Have them name twocharacteristics that crocodiliansand birds share. (a heart with com-pletely divided ventricle, parentalcare of young, amniotic eggs, andvocalization) Have studentsresearch recent fossil discoveriesthat have changed views on theorigin of birds. VerbalTAKS 1 Bio/IPC 2C, 2D; TAKS 3 Bio 7A(grade 11 only), 7B

LS

TAKS 3 Bio 7B; Bio 12C

GENERAL


did you know?Brood Parasites The brown-headed cowbirdis a brood parasite. A female brown-headedcowbird will fly to a nest full of eggs, roll one ortwo eggs out, and lay the same number as thenumber she has displaced. When the owner ofthe nest returns, it will incubate all the eggs,including the cowbird’s. The cowbird eggs oftenhave a shorter incubation time and hatch before

increase the efficiency of a lung is to have airpass over its respiratory surface in one direc-tion only, just as water flows over a fish’s gills inone direction. This is what happens in birds.One-way air flow is possible in birds becausethey have air sacs connected to their lungs, asshown in Figure 18. There is no gas exchange inthe air sacs. They simply act as holding tanks.

There are two important advantages to one-way air flow. First, the lungs are exposed only toair that is almost fully oxygenated, increasingthe amount of oxygen transported to the bodycells. Second, the flow of blood in the lungsruns in a different direction than the flow of air does. Unlike theflow of water and blood in fish gills, the flow of air and blood in birdlungs are not completely opposite (countercurrent). Nevertheless,the difference in direction does increase oxygen absorption.

These three characteristics—endothermic metabolism, a com-pletely divided ventricle, and highly efficient lungs—provide theenergy a bird needs for takeoff and sustained flight. They enable ahummingbird to flap its wings rapidly (20–80 beats per second) as ithovers by a flower. They also permit migrating birds to fly thou-sands of kilometers without stopping. One species of shorebirdscalled the lesser yellowlegs flies across the open ocean from Massa-chusetts to Martinique in the West Indies. Incredibly, some of thesebirds cover this distance of 3,220 km (about 2,000 mi) in less than 6 days. Note, however, that many birds, such as gulls and vultures,remain aloft for long periods of time using little energy. These birdstake advantage of upward air movements that lift them.

Avian Lung Structure

During inhalation, most of the fresh air (yellow) inhaled is pulled into the posterior air sacs.At the same time, stale air (green) from the previous inhalation is pulled into the anterior air sacs.

1

During exhalation, fresh air (yellow) from the posterior air sacs enters the lungs. At the same time, stale air (green) from the previous inhalation moves from the anterior air sacs out of the body.

2

Inhalation

Exhalation

Right lung

Trachea

Posterior air sacs Anterior air sacs

Figure 18 Avianrespiration. A single breathof air stays in a bird’s respi-ratory system for two cyclesof inhalation and exhalation.

Figure 17 Flight. Thesebarnacle geese expend anenormous amount of energyduring take off and flight.

787


Bald EagleTeaching Strategies• The largest bald eagle nests

in North America werefound in Vermillion, Ohio—3.7 m (12 ft) deep, 2.6 m(8.5 ft) in diameter, andweighing 1,800 kg (2 tons)-and in Florida—6.1 m (20 ft)deep and 2.9 m (9.5 ft)across. An eagle nest is calledan aerie.

• After World War II, the num-bers of bald eagles in thelower 48 states fell drasticallybecause of the widespread useof the pesticide DDT. BecauseDDT breaks down veryslowly, it accumulates in thefood chain and causes theeggshells of bald eagles andmany other birds to becomethin and fragile. Affected eggsbreak when a parent attemptsto incubate them. In 1972,the use of DDT was bannedin the United States. By 1978,fewer than 500 breeding pairsof bald eagles remained in theUnited States outside Alaska.A slow recovery of the eaglesbegan, and by the summer of1999, six states had removedbald eagles from the endan-gered species list.

• Show students a picture of alarge but immature baldeagle and ask them whatkind of bird it is. Point outthat the bald eagle does notget its white head and tailuntil its fourth or fifth yearof life.

Up Close

Transparencies

TT External Structures of BirdsTT Internal Structures of BirdsTT Avian AdaptationsTT Major Orders of Birds

External Structures

Up CloseBald Eagle

Scientific name: Haliaeetus leucocephalus

Size: Wingspan is typically over 2 m (6.5 ft), and bodyweight often exceeds 7 kg (15 lb)

Range: Nearly all of North America, from Florida to northern Alaska

Habitat: Forested areas near water that have tall trees for perching and nesting

Diet: Fish, small mammals, birds, carrion

●

●

●

●

●

Eyes Vision is a bald

eagle’s most important

sense. The bird’s keen

eyesight allows it to see

prey at great distances.

Its visual acuity is 3–4

times higher than ours.

Feathers The body of

the bald eagle is covered

with feathers everywhere

except the feet and the

beak, which are bare.

Both sexes develop the

characteristic white head

and neck at maturity.

Grasping feet The bald eagle

has large feet and talons—the hind

talon may be 5 cm (2 in.) long. The

talons are used to snatch fish from

the water while the eagle is flying.

When the muscles of the legs

contract, the tendons in the lower

legs are pulled, and the talons

lock together around the fish.

Beak The beak is mas-

sive, with an elongated,

sharp, downward-curving

tip. Because they have no

teeth, bald eagles do not

chew their food. Instead,

they use their beak to tear

their prey into portions

that they swallow whole.

Grasping feet

▼ Feathers

▲

▼ Beak

▲ Eye

Nostril

Talon

788

TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7B, 12B; Bio 3F

Student Edition TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B, 12B TEKS Bio 3F, 7B, 8C, 10A, 12B

Teacher Edition TAKS Obj 1 Bio/IPC 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B, 12B TEKS Bio 3F, 7B, 8C, 10A, 12BTEKS Bio/IPC 2D

pp. 788–789

TAKS 2, TAKS 3

ActivityEagle Eyes Eagles have much better vision than humans do. Tosimulate how much better, tape aworksheet on the wall and havestudents stand about 3 m away andtry to read it. Then have themmove 1 m away and read the work-sheet. Tell them that an eagle couldsee the paper at 3 m as well ashumans can at 1 m.TAKS 1 Bio/IPC 2D; TAKS 3 Bio 7B

GENERAL


Bald EagleDiscussion• Identify three differences

between the internal struc-tures of the timber rattlesnakeand the bald eagle. (The rat-tlesnake has one functionallung, lacks air sacs, has neithera crop nor a gizzard, hasvenom-producing glands, anddoes not have hollow bones.)

• Would the heat-sensitive pitsof the timber rattlesnake bean effective way of sensingprey for a bald eagle? (No, therattlesnake’s pits are sensitiveonly to nearby heat sources,and the bald eagle spots itsprey from great distances.)

• Why might it be a disadvan-tage for an eagle to have aurinary bladder? (Urine con-tains a greater amount ofwater, which is heavy. Theextra weight would be a disad-vantage in flight.)

• Why might teeth be a disad-vantage to a bird? (Teeth areheavy and require heavy jaws.)

VisualLS

Up CloseInternal Structures

Brain In the ratio of brain size to body size, birds rank

second among vertebrates, behind only mammals. The

large cerebellum receives and integrates information from

the muscles, eyes, and inner ears. This makes possible the

precise control of movement and balance necessary for flight.

The optic lobe is large because it processes input from the

eagle’s most important sense organs—the eyes. The

cerebrum performs many functions, including evaluation of

sensory information, control of behavior, and learning.

Excretory system The excretory system is

efficient and lightweight. It does not store waste

liquids in a bladder. Instead, the bald eagle

(and other birds) converts its nitrogenous

wastes to uric acid, which is concen-

trated into a harmless white paste.

The uric acid travels to the

cloaca and is eliminated.

Cloaca The cloaca is a common

collecting chamber for the excretory,

digestive, and reproductive systems.

As fertilized eggs travel down the

female eagle’s oviduct, egg white,

membranes, and the shell are added.

The completed egg then passes

into the cloaca and out of the

female’s body.

Digestive system Large

meals are temporarily stored in

the crop, the expandable

lower portion of the esophagus.

The food then passes into a

two-chamber stomach. In the

first chamber, stomach acids

begin breaking down the food.

The partially digested food is

then passed to the second

chamber, the gizzard, where

it is ground and crushed.

Undigested material is

eliminated through the cloaca.

Medulla oblongata Optic lobe

Cerebellum Cerebrum

Liver

▼ Gizzard

Crop

Esophagus

Small intestine

Large intestine

▼ Kidney

Left ovary

▼ Cloaca

Pancreas

Left lung

▲ Brain

Trachea

Air sac

Heart

789

Teaching TipReptiles and Birds Have studentsmake a three-column chart like theone in the Graphic Organizershown at the bottom of this page.They should use the information onbirds in Section 3 and the materialon reptiles in Sections 1 and 2.Students should use the followingcharacteristics for both reptiles andbirds: type of body covering, typeof heart, mode of reproduction,type of metabolism, and parentalcare of offspring. Visual

Teaching TipIntroduced Pests House spar-rows and European starlings aretwo common birds that may befamiliar to students. Inform stu-dents that these two species wereintroduced into the United Statesfrom Europe. Both species havebecome serious pests. These exoticspecies out compete native song-birds for food and nesting sites. Infact, they are thought to be at leastpartly responsible for the decline inthe numbers of bluebirds. Bio/IPC 3C

TAKS 2 Bio 8C, 10A; TAKS 3 Bio 7BLS

GENERAL



Graphic Organizer

Use this graphic organizer with Teaching Tip: Reptiles and Birds.

Characteristic Reptiles Birds

Body covering Scaly skin Feathers

Type of heart Partially or completely Completely divided divided ventricle ventricle

Reproduction Oviparous or ovoviviparous Oviparous

Metabolism Ectothermic Endothermic

Parental care Little or none Until offspring can fly

Adaptations of Birds While there is great diversity among the 28 orders of birds,60 percent of all bird species belong to order Passeriformes.These birds, also know as the songbirds, number approxi-mately 5,300 species and are by far the largest group of ter-restrial vertebrates. Birds are adapted for different ways oflife, and you can tell a great deal about the habits and diet ofa bird by examining its beak (bill), legs, and feet. Carnivorousbirds such as hawks have curved talons for seizing prey anda sharp beak for tearing apart their meal. The beaks of ducksare flat for shoveling through water or mud, and theirwebbed feet enable them to swim. Finches are seed eaters,and their short, thick beak is adapted for crushing seedswhile their curved toes enable them to cling to branches.Other birds, such the penguins shown in Figure 19, are flight-less, and their wings and feet are modified for swimming.

During the evolutionary history of birds, their beaks, legs,and feet have been adapted to the particular environment thebirds live in, as shown in Table 1. Some birds are more highlyspecialized than others, and many birds are highly flexible intheir eating habits. The song sparrow, for example, has astrong bill that it uses in winter to crack hard seeds. In sum-mer, the sparrow uses its bill to catch soft-bodied insects.

Figure 19 Penguin. Thepenguin’s wings are adaptedfor swimming rather than flying.

Type of bird Beak adaptations Foot adaptations

Songbirds (e.g., cardinal, robin)Seed-cracking:Short, thick,strong beak

Insect-catching:Long, slenderbeak for probing

Hovering: Legs so small the bird cannot walk on the ground;tiny feet

Perching: Toes can cling tobranches; one toe points backward

Probing: Thin, slightly curved beakfor inserting into flowers to sip nectar

Hummingbirds

Table 1 Avian Adaptations

790

Student Edition TAKS Obj 2 Bio 8C TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 2 Bio 8C, 10A TAKS Obj 3 Bio 7B TEKS Bio 7B, 8C, 10A, 12CTEKS Bio/IPC 2C, 2D, 3C

pp. 790–791

Trends in OrnithologyResearchers around the country have beenmonitoring bird populations each year todetermine long-term trends. One apparenttrend: of the 42 bird species that are listed asthreatened or endangered, 22 are associatedwith wetlands. The trend holds true for otheranimals as well. Have students research thethreatened and endangered birds in your area.In their reports, students should discuss theprobable causes of decline, as well as plans forspecies recovery. Bio/IPC 3C

Using the TableHave students pair up. Instruct thestudents to cover the two columnson the right side of Table 1 with asheet of paper. Have one studentuncover the Beak adaptations col-umn, choose one, and read thedescription. The other studentshould try to identify the type ofbird whose beak is described. Thisprocess should continue until thesecond student has correctly identi-fied each bird. The students shouldthen switch roles and repeat theprocess using the Foot adaptationscolumn. Verbal

DemonstrationShow students pictures of severaldifferent types of birds. Be sureto include some with distinctlydifferent beaks and feet. A typicalassortment would be: woodpecker,heron, pelican, grosbeak, chick-adee, goose, and hummingbird.Ask students to examine the differ-ent types of beaks and feet and tohypothesize about each bird’s habi-tat and diet. Visual

Group Activity Avian Adaptations Divide theclass into small groups, and assigneach group a particular feedingstrategy and bird habitat. Have eachgroup use a field guide to identifyfive species of birds that share theassigned feeding strategy andhabitat. Students should then usedrawings or written descriptions todemonstrate the similarities in beaks,feet, and behavior among birds withsimilar lifestyles. Have each groupshare its findings with the entireclass. Visual

TAKS 3 Bio 7B; Bio 12CTAKS 1 Bio/IPC 2C, 2D;

Co-op LearningLS

TAKS 3 Bio 7B; Bio 12CLS

TAKS 2 Bio/IPC 2C, 2D; TAKS 3 Bio 7BLS


Birding (once called birdwatching) has beendescribed as the second-favorite outdooractivity in the United States, after gardening.Invite a local naturalist or member of anearby chapter of the Audubon Society tovisit your classroom and discuss tips on howto attract and identify backyard birds. Makea list of local birds and show slides of eachbird to your class. Slides can be purchasedfrom many sources, including the CornellUniversity Laboratory of Ornithology.Bio/IPC 3C; Bio 8C

REAL WORLDREAL WORLDCONNECTIONCONNECTION

Type of bird Beak adaptations Foot adaptations

Sieving: Long, flattened, rounded bill Swimming: Three toes linked bywebs for improved swimming

Woodpeckers Drilling: Strong, chisel-like beak Grasping: Feet with two toespointing forward and two pointingbackward

Parrots Cracking, tearing: Short, stout,hooked beak used to crack seedsand nuts and to tear vegetation

Climbing/grasping: Strong toes,two pointing forward, two pointingbackward; adapted for perching,climbing, and holding food

Grasping: Powerful, curved talonsfor seizing and gripping prey

Tearing: Curved, pointed beak forpulling apart prey

Birds of prey

Ducks

Long-legged waders Fishing: Long, slender, spear-shapedbeak for fishing

Wading: Longlegs; toesspread out overa large area tosupport bird onsoft surfaces

791

ReteachingHave each student develop tenquestions for this section, and usethe questions in a review game.

Interpersonal

QuizTrue or False:

1. Birds are ectotherms. (False. Birdsare endotherms.)

2.Birds have a two-way airflow dur-ing respiration. (False. Birds have aone-way airflow.) TAKS 3 Bio 7B; Bio 8B, 12C

TAKS 3 Bio 7B; Bio 8B, 12C

GENERAL

TAKS 1 Bio/IPC 2C, 2DLS

CloseClose


1. forelimbs modified as wings; feathers; stream-lined shape; lightweight bones, endothermicmetabolism; highly efficient lungs; heart withcompletely divided ventricle

2. An endothermic body and a rapid metabolismprovide the energy necessary for flight.

3. The bald eagle has strong feet with sharp talonsfor grabbing prey, and a massive, hooked beakfor tearing prey into pieces it can eat.

4. The small, pointed beak indicates that it is nota seedeater because seedeaters have thick beaksfor crushing seeds. The foot structure, however,

TAKS 3 Bio 7B; Bio 11B

TAKS 2 Bio 10A; TAKS 3 Bio 7B

TAKS 3 Bio 7B

is consistent with the songbird anatomy.

5. A. Incorrect. The kidneys playan important excretory role in birds, but arenot closely associated with the other systems.B. Correct. The cloaca is an opening thatallows wastes to leave the body. In females, italso allows sperm to enter the body and fertil-ized eggs to leave the body. C. Incorrect. Thegizzard is the second part of the stomach thathelps to grind food; it is not part of the excre-tory or reproductive systems. D. Incorrect. Theovary is a reproductive organ; it is not part ofthe digestive or excretory systems.TAKS 2 Bio 10B (grade 11 only)

TAKS 1 IPC 3A; TAKS 3 Bio 7B; Bio 3A


CalculatingAverage BoneDensitySkills AcquiredAnalyzing data,calculating

Teacher’s Notes After students read the explana-tory paragraph, have themglance at the data and predictwhich animal has the higheraverage bone density.

Answers to Analysis1. Animal 1: 1.3 g/cm3;

Animal 2: 2.0 g/cm3

2. A certain amount of variationis normal in biological systems.

3. Animal 1

<x + 6x - 7 - 02

18

49376

0

52

Other AdaptationsThere are many groups of birds, each of which is adapted to its par-ticular living conditions. For example, gulls and terns have stream-lined bodies that are adapted for flying over the water in search offish. Owls’ excellent low-light vision enables them to survive as noc-turnal hunters. For a list of the orders of birds, see “Classificationin Kingdoms and Domains” in the Appendix.

Analysis

1. Calculate the average bonedensity for each of the twoanimals in the data table.Express your answer in gramsper cubic centimeter.

2. Critical ThinkingEvaluating MethodsWhy is it important to analyzeseveral samples and obtainthe average of your data?

3. Critical Thinking DrawingConclusions Based on youranswer to item 1, which of thetwo animals is more likely tobe a bird?

Calculating Average Bone DensityBackground

Density is the ratio of the mass of an object to its volume. Several teams of studentsdetermined the density of bones from two different animals. You can use their data to practice calculating average bone density.

<x + 6x - 7 - 02

8

493 0

52

DATA TABLE

Bone type Team 1 Team 2 Team 3 Team 4

Animal 1 1.6 g/cm3 1.0 g/cm3 1.2 g/cm3 1.4 g/cm3

Animal 2 2.3 g/cm3 1.8 g/cm3 1.8 g/cm3 2.1 g/cm3

1. Add the densities of one bone type. For example, if three bone samples have densities of 3.0, 3.1, and 2.9 g/cm3, their sum would be 9.0 g/cm3.

2. Divide the sum of the densities by the number of samples.

Average density � � � 3.0 g/cm39.0 g/cm3

3sum of the densitiesnumber of samples

Identify the adaptations of birds for flight. 7B

Summarize how birds obtain the energynecessary for flight. 7B 10A

Relate the bald eagle’s methods of hunting andfeeding to its external body features. 7B 11B

Critical Thinking Evaluating HypothesesA student examines a bird that has delicate,perching feet with long, slender toes. Its beak issmall but slightly long and pointed. The studentconcludes that the bird is a seed-eating songbird.Do you agree? Explain your reasoning. 3A 7B

Which structure is part of theexcretory, digestive, and reproductive systems of a bird? 10B

A kidney C gizzardB cloaca D ovary


Section 3 Review

2C 2D 7B

792

TAKS 1 Bio/IPC 2C, 2D;TAKS 3 Bio 7B

Student Edition TAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 1 IPC 3ATAKS Obj 2 Bio 10A, 10B TAKS Obj 3 Bio 7B Math TAKS Obj 10, 8.14A, 8.15A,8.16BTEKS Bio 3A, 7B, 10A, 10B, 11BTEKS Bio/IPC 2C, 2DTEKS IPC 3A

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D TAKS Obj 1 IPC 3ATAKS Obj 2 Bio 8C, 10A, 10B TAKS Obj 3 Bio 7BTEKS Bio 3A, 7B, 8B, 8C, 10A, 10B,11B, 12CTEKS Bio/IPC 2C, 2DTEKS IPC 3A

pp. 792–793

TAKS 1, TAKS 3

MATH TAKS Obj 10, 8.14A, 8.15A, 8.16B

AlternativeAssessmentHave each student use the red andblue subheadings in this chapter tocreate questions based on each sub-heading, and then correctly answerit. For example, “Reptiles ShareSeveral Key Characteristics,” couldbecome “What key characteristicsdo reptiles share?” Verbal

TAKS 3 Bio 7B; Bio 12CTAKS 1 Bio/IPC 2C, 2D; TAKS 2 Bio 8C;

LS

GENERAL


• Science Skills Worksheet• Critical Thinking Worksheet• Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


which have a

Lizards

ectotherms

Reptiles

3-chambered heart 4-chambered heart

Tuataras

endotherms

TurtlesSnakes Crocodilians

which have a

Ovoviviparous Oviparous

Scales

and have

areare which areare

and have

Feathers

and have a

such as

birds

Answer to Concept MapThe following is one possible answer to Performance Zone item 15 on the following page.

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONEKey Terms

Section 1amniotic egg (775)oviparous (777)ovoviviparous (777)

Section 2carapace (782)plastron (782)

Section 3contour feather (784)preen gland (785)down feather (785)

The Reptilian Body

● Reptiles have a strong, bony skeleton. ● Reptiles are ectothermic.● Reptiles have nearly watertight skin and eggs, both of which

enable them to be terrestrial animals.● Reptiles have paired lungs that have a greater surface area

for gas exchange than the lungs of amphibians.● Reptiles have a double-loop circulatory system. Most have

a ventricle that is partly divided into right and left halves,resulting in incomplete separation of oxygen-rich and oxygen-poor blood.

● Reptilian fertilization is internal.

Today’s Reptiles

● Snakes and lizards (order Squamata) share many character-istics, such as periodic molting, but snakes have no legs.

● The shells of turtles and tortoises (order Chelonia) are made of fused plates of bone covered with horny shields orleathery skin.

● Unlike other reptiles, crocodilians (order Crocodilia), care for their young after hatching. They also have a completelydivided ventricle.

● There are only two species of tuataras (order Rhynchocephalia).

Characteristics and Diversity of Birds

● Birds are endotherms. Their high rate of metabolism helpsthem meet the large energy requirements for flight.

● A bird’s contour feathers give the bird its shape and aidflight. Its down feathers provide insulation.

● The bones of birds are thin and hollow, and many of themare fused; all are adaptations for flight.

● One-way airflow through the lungs provides the largeamounts of oxygen birds need for flight.

● The ventricle of the bird heart is completely divided by a septum.

3

2

1

793

ANSWERS

Using Key Terms

1. b2. a3. a4. a5. a. Oviparous animals lay eggs. In

ovoviviparous animals,embryos develop within eggsinside the mother’s body.These eggs hatch within themother, giving the appearanceof live birth.

b. Contour feathers are large andallow the bird to fly. Downfeathers are small and fluffy;they are found under the con-tour feathers and functiononly to insulate.

Understanding Key Ideas

6. b7. b8. a9. c

10. a11. d12. d13. d14. The dams cause riffles, which

contain insects that male turtlesfeed on, to disappear. Thus, tur-tles may not be able to find adequate food to survive indammed areas.

15. One possible answer to the con-cept map is found at the bottomof the Study Zone page. Bio 3E

TAKS 3 Bio 7B

TAKS 3 Bio 7BTAKS 3 Bio 7BTAKS 2 Bio 8C; Bio 8BTAKS 2 Bio 10ATAKS 3 Bio 7BTAKS 2 Bio 10ATAKS 2 Bio 10ATAKS 3 Bio 7B

TAKS 3 Bio 7BTAKS 3 Bio 7BTAKS 3 Bio 7BBio 8B

Section Questions1 3, 5a, 6–8, 14, 19, 222 1–3, 9–11, 14–16, 193 3, 4, 5b, 11, 12–15, 17, 18, 20, 21

Assignment Guide


CHAPTER 34

Using Key Terms1. All of the following reptiles belong to the

order Crocodilia, except a. alligators. c. crocodiles.b. tuataras. d. gavials.

2. The two basic parts of a turtle’s shell are thea. carapace and plastron.b. septum and amnion.c. chorion and allantois.d. keratin and cloaca.

3. The eggs of reptiles and birds aredescribed as a. amniotic.b. oviparous.c. ovoviviparous.d. externally fertilized.

4. The preen gland a. secretes oil.b. senses chemicals.c. stimulates egg production.d. causes a change in body temperature.

5. For each pair of terms, explain thedifferences in their meanings.a. oviparous, ovoviviparousb. contour feather, down feather

Understanding Key Ideas6. Which is not an adaptation of reptiles

for life on land? a. watertight skinb. external fertilizationc. amniotic eggd. kidneys

7. The heart of most reptiles has a. no septum.b. a partly divided ventricle.c. a fully divided ventricle.d. two pumping chambers.

8. In reptiles, fertilization a. is internal.b. is external.c. always occurs in water.d. does not occur.

9. Snakes differ from lizards in that snakesdo not have a. lungs. c. a pectoral girdle.b. kidneys. d. a flexible jaw.

10. Jacobson’s organs are involved in the sense of a. smell. c. sight.b. hearing. d. touch.

11. Which group of living reptiles is mostclosely related to birds? a. snakes c. rhynchocephaliansb. turtles d. crocodilians

12. The feathers of most birds are well adapted for a. swimming and repelling water.b. expelling heat and feeding.c. flying and conducting heat.d. flying and insulating.

13. The foot illustrated below is most likely ofa bird adapted for a. wading. c. perching.b. grasping. d. swimming.

14. In what ways might the damming of the Guadalupe River affect the ability of Cage’s map turtle tofind food?

15. Concept Mapping Construct a con-cept map that describes the characteristicsof both reptiles and birds. Include the fol-lowing terms in your map: ectotherm,endotherm, oviparous, ovoviviparous,scales, feathers, three-chambered heart, andfour-chambered heart.

PerformanceZONE

CHAPTER REVIEW

8B

7B

7B

7B

7B

10A

8B 8C

7B

7B

7B

3E

7B

10A

10A

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Review and AssessTAKS Obj 1 Bio/IPC 2A, 2B, 2C, 2DTAKS Obj 2 Bio 8C, 10ATAKS Obj 3 Bio 7B TEKS Bio 3E, 7B, 8B, 8C, 10A, 12CTEKS Bio/IPC 2A, 2B, 2C, 2D

pp. 794–795

Critical Thinking

16. Because the young are carriedinside the body, they receive someheat as a result of the mother’smuscular movements and baskingbehavior.

17. Because it mixes oxygen-rich andoxygen-poor blood, a three-chambered heart would notdistribute enough oxygen to thehummingbird’s muscles to sustainflight.

18. Animals that invest a long periodof parental care typically havefewer offspring than animals withlittle or no parental care, but theoffspring that are cared for aremore likely to live to adulthood.In both cases, only a small number of offspring survive tobreeding age.

19. Predators are distracted by thewiggling tail part, which gives thelizard time to escape.

Alternative Assessment

20. Students should research bothseeds and feeder types to predictwhich birds will be attracted.

21. Answers will vary depending onbirds chosen. Students shouldacknowledge their sources andinclude an illustration of eachbird.

22. Students should research whattype of food and habitat isappropriate for the lizard theychoose and set up their terrariumaccordingly.

1. A.Incorrect.Crocodilians are not tolerant ofthe low temperatures sometimesfound in deserts. B. Correct.Turtles, lizards, and snakes areable to tolerate both the low andhigh temperatures often found indeserts. C. Incorrect. Tuataras arenot able to tolerate the high heatof the desert. D. Incorrect.Tuataras are not able to toleratethe high heat of the desert, andcrocodilians are not tolerant of thelow temperatures sometimes foundin deserts. TAKS 1 Bio/IPC 2C

TAKS 1 Bio/IPC 2A, 2B, 2C, 2D

TAKS 1 Bio/IPC 2A, 2B, 2D

TAKS 1 Bio/IPC 2C; TAKS 3 Bio 7B

TAKS 2 Bio 10A

TAKS 2 Bio 10A

TAKS 1 Bio/IPC 2A; TAKS 3 Bio 7B

2. F. Correct. Although birds are endothermswith a very small temperature range, theirrange overlaps with lizards, the only reptilewith temperatures above 40ºC. G. Incorrect.Tuataras do not have body temperatures aswarm as birds, which have temperatures of40ºC–42ºC. H. Incorrect. Crocodilians do nothave body temperatures as warm as birds.J. Incorrect. Turtles do not have body tem-peratures as warm as birds. Bio 12C

3. A. Incorrect. While crocodilians have agreater body temperature than tuataras, theranges of body temperatures are about thesame for both. B. Correct. According to thisdata, turtles and snakes have a body tempera-ture range of about 9ºC–38ºC. C. Incorrect.Lizards often have a higher body temperaturethan tuataras but their temperature rangesoverlap. D. Incorrect. The lowest body tem-perature for a crocodilian is higher than thehighest body temperature for a tuatara.TAKS 1 Bio/IPC 2C


Test

Critical Thinking16. Forming Hypotheses Many viviparous

snakes and lizards live in cold climates.Why might viviparity be advantageous insuch environments?

17. Predicting Outcomes How might having a three-chambered heart, like that of most reptiles, affect a hummingbird in flight?

18. Recognizing Logical Connections Howmight a long period of parental care berelated to the number of offspring ananimal produces?

19. Forming a Hypothesis When a piece of a lizard’s tail breaks off, the separatedportion may wiggle about forcefully. Howmight this adaptation be an advantage forthe lizard?

Alternative Assessment20. Applying Information Design and build a

bird feeder. Place the feeder where it can beeasily observed. Keep a journal of your obser-vations to share with your class.

21. Being a Team Member and CommunicatingWork with two or three of your classmatesto find out what kinds of birds are commonin your area. Select at least six birds toexplore in depth and research the following:its habitat, its food, its beak and foot adap-tations, and where it winters. Present theinformation you gathered in an illustratedguide. Make copies of your guide availablefor interested students.

22. Organizing Information Create a habitat ina terrarium for a small lizard, and observethe lizard’s behavior. Make a labeled draw-ing of the environment you create, andkeep a journal of your observations.


The chart below shows the normal ranges ofbody temperature in five groups of reptiles.Use the chart and your knowledge of science toanswer questions 1–3.

1. Which groups could probably best tolerate the temperature extremes found in deserts? A Turtles, snakes, and crocodiliansB Turtles, lizards, and snakes C Tuataras, turtles, and snakesD Tuataras and crocodilians

2. If a bar showing the body temperature range of birds were added to this chart, thebar for birds would partially overlap with the bar for F lizards. H crocodilians.G tuataras. J turtles.

3. Which of these statements is supported bythe data in the chart? A Crocodilians have a greater body

temperature range than tuataras.B Turtles and snakes have similar body

temperature ranges. C Lizards always have a higher body

temperature than tuataras.D Some tuataras can have a higher body

temperature than some crocodilians.

20 30 40 5010 0

TuatarasTurtlesLizardsSnakes

Crocodilians

Body temperature (°C)

10A

10A

2C

12C

2C

2A 7B

2C 7B

When a question refers to a graph, study the dataplotted on the graph to determine any trends oranomalies before you try to answer the question.

2A 2B 2D

2A 2B 2C 2D

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section 1 the reptilian body - jourdanton isd · section 1 the reptilian body ... reptiles have a...

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