chapter 30: fishes and amphibiansblogs.polson.k12.mt.us/dobrien/files/2011/01/chap30.pdf · ihk...

VertebratesVertebratesBears, salmon, gulls—and humans—belong to the group of animals known as vertebrates, animals with backbones.Their ability to survive the rigors ofchanging environments, such as theAlaskan tundra, and engage in complexbehaviors, such as migration, are just a few of the characteristics that dis-tinguish vertebrates from other members of the animal kingdom.

814

3030

3131

3232

3333

UNIT CONTENTSUNIT CONTENTS

Fishes and Amphibians

Reptiles and Birds

Mammals

Animal Behavior

Unit 9Unit 9

VertebratesBIODIGESTBIODIGEST

UNIT PROJECTUNIT PROJECT

Use the Glencoe Science Web site for more project

activities that are connected to this unit.science.glencoe.com

BIOLOGY

http://science.glencoe.com

ChapterChapter

Fishes and Amphibians

What You’ll Learn■ You will compare and

contrast the adaptations of the different groups offishes and amphibians.

■ You will relate the move to land to the evolution offishes and amphibians.

Why It’s ImportantFishes are the most diverse andsuccessful vertebrate group.Amphibians are adapted to live both in water and on land.The development of a bonyendoskeleton in fishes andlungs in amphibians weremajor steps in animal evolu-tion—steps that eventually ledto human evolution.

Look through the vocabularywords, noting the familiarwords. As you read the chapter,note how the words might beused differently in the study ofbiology. Write down the defini-tions to any new terms.

To find out more about fishesand amphibians, visit theGlencoe Science Web site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

30

Leopard frog eggshatch into wigglingtadpoles. A fewmonths later, theybecome four-legged, jumping,croaking animals.

BIOLOGY

816 FISHES AND AMPHIBIANS


Section

What Is a Fish?Fishes, like all vertebrates, are clas-

sified in the phylum Chordata. Thisphylum includes three subphyla:Urochordata, the tunicates; Cephalo-chordata, the lancelets; and Verte-brata, the vertebrates. Fishes belongto the subphylum Vertebrata. Inaddition to fishes, subphylumVertebrata includes amphibians, rep-tiles, birds, and mammals. Recallfrom the previous chapter that allchordates have four traits in com-mon—a notochord, gill slits, muscleblocks, and a dorsal hollow nervecord. In vertebrates, the notochordof the embryo becomes a backbone

in adult animals. All vertebrates arebilaterally symmetrical, coelomateanimals that have endoskeletons,closed circulatory systems, nervoussystems with complex brains andsense organs, and efficient respira-tory systems.

Three classes of fishesFishes comprise three classes of

the subphylum Vertebrata: ClassAgnatha (AG nuh thuh), with jawlessfishes, lampreys and hagfishes; ClassChondrichthyes (kahn DRIHK theez),with cartilaginous fishes, sharks andrays; and Class Osteichthyes (ahs teeIHK theez), with bony fishes. Anexample of each class is shown in

30.1 FISHES 817

Have you ever visited an aquarium to seethe amazing diversity

of fishes? As you pass tankafter tank, you can see fishesof all shapes, sizes, and colors.What’s interesting is thateven though fishes share acommon environment, theyhave evolved a variety of different adaptations.Although fishes may showconsiderable variety instructure and behavior,they all share commoncharacteristics.

SECTION PREVIEW

ObjectivesRelate the structuraladaptations of fishes totheir environments.Compare and contrastthe adaptations of thedifferent groups offishes.Interpret the phylog-eny of fishes.

Vocabularyspawningfinlateral line systemscaleswim bladdercartilage

30.1 Fishes

Saltwater aquarium(above) and a bluetang (inset)

Figure 30.1. More than 20 000species of fishes exist. In fact, thereare more fish species than all otherkinds of vertebrates added together.

Fishes inhabit nearly every type ofaquatic environment on Earth. Theyare adapted to living in shallow, warmwater and deeper cold and sunlesswater. They are found in freshwaterand salt water, and some fishes evensurvive in heavily polluted water.

Fishes breathe using gillsAgnathans, like all fishes, have gills

made up of feathery gill filaments thatcontain tiny blood vessels. Gills arean important adaptation for fishes andother vertebrates that live in water.As a fish takes water in through itsmouth, water passes over the gillsand then out through slits at the sideof the fish. Oxygen and carbon diox-ide are exchanged through the capil-laries in the gill filaments. You canfind out more about respiration infishes in the MiniLab on this page.

Fishes have two-chambered hearts

All fishes have two-chamberedhearts, as shown in Figure 30.2. Onechamber receives deoxygenated bloodfrom the body tissues, and the secondchamber pumps blood directly to thecapillaries of the gills, where oxygenis picked up and carbon dioxidereleased. Oxygenated blood is carriedfrom the gills to body tissues. Bloodflow through the body of a fish is rel-atively slow because most of theheart’s pumping action is used topush blood through the gills.

Fishes reproduce sexuallyAll fishes have separate sexes.

Fertilization is external in mostfishes, with eggs and sperm depositedin protected areas, such as on floatingaquatic plants or in shallow nests of

Measuring Breathing Rate in Fishes Fishes are able toextract oxygen from water as it flows over their gills. Theirrate of breathing is related to the availability of oxygen inthe water. More oxygenresults in a slower breath-ing rate. The breathingrate of a fish can be esti-mated by counting thenumber of times perminute its gill covers opento allow water to flowacross its gills.

Procedure! Make a hypothesis about how the breathing rate of a

fish may be influenced by a change in temperature of the water in which it is swimming. Record your hypothesis.

@ Fill a beaker with non-chlorinated water. Let the beakersit until the water reaches room temperature (about20°C). Measure the temperature with a thermometer and record it in a data table.

# Add a small goldfish. CAUTION: Handle animals with care.Wait 5 minutes for the fish to acclimatize to the watertemperature.

$ Count the number of times the goldfish’s gill covers openin one minute. This is a measure of the rate at which thefish is breathing. Record your result in a data table.

% Repeat step 4 four more times. Find an average for yourtrials and record these data in your table.

^ Remove the goldfish from the beaker. Add one ice cube made from non-chlorinated water to the beaker.

& When the ice cube has melted, record the water’s temperature.

* Repeat steps 3-5. Remove goldfish from the beaker, and add another ice cube to the beaker. Repeat step 7.

( Repeat steps 3-5. CAUTION: Wash your hands after working with animals.

Analysis1. How does water temperature influence the rate at which

breathing occurs in a goldfish?2. Do your data support your hypothesis? Explain.3. Was the breathing rate faster or slower in colder water

compared with warmer water?4. How might the amount of oxygen in cold water compare

with that in warm water? Explain your answer.5. Sequence the events associated with a fish obtaining

oxygen. Start with a molecule of oxygen in water and besure to include the capillaries located in the fish’s gills.

MiniLab 30-1MiniLab 30-1 Experimenting

Gill cover


gravel on stream bottoms. Althoughmost fishes produce large numbers ofeggs at one time, agnathans calledhagfishes produce small numbers oflarge eggs. Some cartilaginous fisheshave internal fertilization. For exam-ple, some female sharks and rays pro-duce as few as 20 eggs and keep theminside their bodies until they havehatched and developed to about 40cm in length. These young, whenreleased, behave like miniatureadults, and many survive.

Most bony fishes have external fer-tilization. Reproduction in fishes andsome other animals is called spawn-ing. During spawning, some femalebony fishes, such as cod, produce asmany as 9 million eggs, of which onlya small percentage survive. In somebony fishes, such as guppies, mollies,and swordtails, fertilization is inter-nal and young fishes develop withinthe mother’s body. These species areknown as live-bearers because theiroffspring are born fully developed.Most fishes that produce millions of

eggs provide no care for their off-spring after spawning; in thesespecies, only a few of the young sur-vive to adulthood. But some, such asthe mouth-brooding cichlids, staywith their young after hatching.When their young are threatened bypredators, the parent fish scoop theminto their mouths for protection.

30.1 FISHES 819

Figure 30.1The three classes of fishesinclude jawless fishes, cartilagi-nous fishes, and bony fishes.

Circulation in a Fish

Aorta

Heart

Gills Bodycells

AV

Figure 30.2In a fish’s heart,deoxygenated bloodflows from the firstchamber to the sec-ond chamber, thenon to the gills whereit picks up oxygen.Blood in a fish flowsin a one-way circuitthroughout the body.

Jawless fishes called lampreyshave long, tubular bodies with-out paired fins, and no scales.

AA

Cartilaginous fishes calledskates have a flattened bodyshape with large paired finsthat enable them to “fly”over the ocean bottom asthey search for food.

CC

Most fishes youare familiar withare bony fishes,such as thisswordfish.

BB


Problem-Solving Lab 30-1Problem-Solving Lab 30-1 Cause and Effect

In the Problem-Solving Lab on thispage, find out some other reasonswhy the numbers of some species offreshwater fishes are declining.

Most fishes have paired finsFishes in the classes Chondrich-

thyes and Osteichthyes have pairedfins. Fins are fan-shaped membranesthat are used for balance, swimming,and steering. Fins are attached to andsupported by the endoskeleton andare important in locomotion. Thepaired fins of fishes, illustrated inFigure 30.3, foreshadowed thedevelopment of limbs for movementon land and ultimately of wings forflying.

Fishes have developed sensory systems

All fishes have highly developedsensory systems. Cartilaginous andbony fishes have an adaptation calledthe lateral line system that enablesthem to sense their environment.The lateral line system is a line offluid-filled canals running along thesides of a fish that enable it to detectmovement and vibrations in thewater.

Some fishes also have an extremelysensitive sense of smell and candetect small amounts of chemicals inthe water. Sharks can follow a trail of

Figure 30.3The paired fins of a fish include the pec-toral fins and the pelvic fins. Fins foundon the dorsal and ventral surfaces caninclude the dorsal fins and anal fin.

AA

BB

Total number of species

< 100100 – 199200 +

Percent ofspecies at risk

< 1010 – 29.930 +

Dorsal fin

Caudalfin Pelvic

fins

Pectoralfins

Why are fish species numbers declining? There are threemajor threats to the survival of freshwater fishes. These are:agricultural runoff; dams and water diversion; and competi-tion from introduced non-native species. All of these threatsexist in the southern United States.

AnalysisThe two maps that appear here (A and B) illustrate the

problem described in the introduction.

Thinking Critically1. Sequence the general areas of the United States that have

the highest to lowest number of fish species and percent-age of species at risk.

2. Do the two patterns tend to agree? Explain why.3. Compare the approximate number of species at risk to the

total number of fish species present in: California, Texas,Hawaii, North Carolina, Florida, Illinois, and North Dakota.

4. Explain why or how the following may be a problem tofish survival: agricultural runoff; dams and water diver-sion; introduction of non-native fish species.

5. Explain how the three problems associated with decliningfish populations might be caused by humans.

30.1 FISHES 821

Gill arches

Gill arches

Gill slitsSkull JawsJawless, filter-feeding fish

Beginning of jaw formation Fish with jaws

blood through the water for severalkilometers. This ability helps themlocate their prey.

Most fishes have scalesCartilaginous and bony fishes have

skin covered by intermittent or over-lapping rows of scales. Scales are thinbony plates formed from the skin.Scales, shown in Figure 30.4, can betoothlike, diamond-shaped, cone-shaped, or round. Shark scales aresimilar to teeth found in other verte-brates. The age of some species offishes can be estimated by countingannual growth rings in their scales.

Jaws evolved in fishesPerhaps one of the most important

events in vertebrate evolution was theevolution of jaws in ancestral fishes.The advantage of a jaw is that itenables an animal to grasp and crushits prey with great force. Sharks areable to eat large chunks of food.This, among other factors, explainswhy some early fishes were able toreach such great size. Figure 30.5shows the evolution of jaws in fishes.

When you think of a shark, do youimagine gaping jaws and rows ofrazor-sharp teeth? Sharks have six to20 rows of teeth that are continuallyreplaced. The teeth point backwards,preventing prey from escaping once

caught. Sharks are among the moststreamlined of all fishes and are welladapted for life as predators.

Most fishes have bony skeletonsThe majority of the world’s fishes

belong to the class Osteichthyes, thebony fishes. Bony fishes, a successfuland widely distributed class, differgreatly in habitat, size, feedingbehavior, and shape, as Figure 30.6shows. All bony fishes have skeletonsmade of bone rather than the carti-laginous skeletons found in other

Figure 30.4Fishes can be classified by the typeof scales present. Diamond-shapedscales are common to bony fishes,such as gars (a). Bony fishes suchas chinook salmon have eithercone-shaped or round scales (b).Tooth-shaped scales are character-istic of the sharks (c).

Figure 30.5You can see how jawsevolved from the car-tilaginous gill archesof early jawless fishesin this series of illus-trations. Teethevolved from skin.

OriginWORDWORD

scaleFrom the OldEnglish word sceala,meaning “shell” or“husk.” A scale is athin, bony plate onthe skin of a fish.

a

b

c

el

classes of fishes. Bone is the hard,mineralized, living tissue that makesup the endoskeleton of most verte-brates. The appearance of bone wasimportant for the evolution of fishesand vertebrates in general because itallowed fishes to adapt to a variety ofaquatic environments, and finallyeven to land.

Bony fishes have separate vertebrae that provide flexibility

The evolution of a backbone com-posed of separate, hard segmentscalled vertebrae was significant in pro-viding the major support structure ofthe vertebrate skeleton. Separate ver-tebrae provide great flexibility. This isespecially important for fish locomo-tion, which involves continuous flex-ing of the backbone. You can see howmodern bony fishes propel themselvesin water in Figure 30.7. Some fishesare effective predators, in part becauseof the fast speeds they can attain as aresult of having a flexible skeleton.

Bony fishes evolved swim bladders

Another key to the evolutionarysuccess of bony fishes was the evolu-tion of the swim bladder. A swimbladder is a thin-walled, internal sacfound just below the backbone inbony fishes; it can be filled withmostly oxygen or nitrogen gases thatdiffuse out of a fish’s blood. Fish witha swim bladder control their depth byregulating the amount of gas in the


Figure 30.6Bony fishes vary in appearance,behavior, and way of life.

Figure 30.7Most bony fishes swim in one of three possible ways.

An eel moves itsentire body in anS-shaped pattern.

AA

A mackerel flexes the posterior end of its body to accen-tuate the tail-fin movement.

BB

A tuna keeps its body rigid, movingonly its powerful tail.Fishes that use thismethod move fasterthan all others.

CC

Predatory bony fishes, such asthis pike, have sleek bodieswith powerful muscles and tailfins for fast swimming.

CC

Sea horses move slowlythrough the underwaterforests of seaweed wherethey live. They are unusual in that the males brood theiryoung in stomach pouches.

BB

Eels are long andsnakelike and canwriggle through mudand crevices in searchof food.

AA

bladder. The gas works like the gas ina blimp that adjusts the height of theblimp above the ground.

Fishes that live in oxygen-poorwater or in ponds or rivers that dryup in the hot season often have otherways to get oxygen. The Africanlungfish, for example, has a structurethat allows it to obtain oxygen bygulping air. This structure is a modi-fied swim bladder. The modifiedswim bladder is connected to thefish’s mouth by a tube.

Diversity of FishesFishes range in size from the tiny

dwarf goby that is less than 1 cmlong, to the huge whale shark thatcan reach a length of 15 m—thelength of two school buses.

Agnathans are jawless fishesLampreys and hagfishes belong to

the class Agnatha. Though they donot have jaws, they are voraciousfeeders. Hagfishes, Figure 30.8, havea slitlike, toothed mouth and feed ondead or dying fish by drilling a holeand sucking the blood and insidesfrom the animal. Parasitic lampreysattack other fishes and attach them-

selves by their suckerlike mouths.They use their sharp teeth to scrapeaway the flesh and then suck out theprey’s blood. The skeletons ofagnathans, as well as of sharks andtheir relatives, are made of a tough,flexible material called cartilage.

Sharks and rays are cartilaginous fishes

Sharks, skates, and rays, likeagnathans, possess skeletons com-posed entirely of cartilage. Sharks,skates, and rays belong to the classChondrichthyes, illustrated in Figure30.9. Because living sharks, skates,and rays are classified in the samegenera as species that swam the seasmore than 100 000 years ago, theyare considered living fossils. Sharksare perhaps the most well-known

30.1 FISHES 823

Figure 30.8When touched, ahagfish’s skin givesoff a tremendousamount of mucus,thus allowing thefish to slither awaywithout becoming ameal.

Figure 30.9Cartilaginous fishes includesharks, skates, and rays.

The hammerhead shark is a large sharkfound in warm ocean water. It has eyes atthe ends of its flattened, extended skull.

AA

Most rays are ocean bottomdwellers, but the Atlantic mantaray prefers to glide along justunder the water’s surface.

BB

predators of the oceans. Like sharks,most rays are predators and feed onor near the ocean floor. Rays haveflat bodies and broad pectoral fins ontheir sides. By slowly flapping theirfins up and down, rays can glide,searching for mollusks and crus-taceans, along the ocean floor. Somespecies of rays have sharp spines withpoison glands for defense on theirlong tails. Other species have organsthat generate electricity to kill bothprey and predators.

Three subclasses of bony fishesScientists recognize three sub-

classes of bony fishes—the lung-fishes, the lobe-finned fishes, and theray-finned fishes. Figure 30.10shows examples of each subclass.Lungfishes have both gills and lungs.The lobe-finned fishes are repre-sented by only one living species. Inthe ray-finned fishes, fins are fan-

shaped membranes supported by stiffspines called rays. Ray-finnedfishes—such as catfish, perch,salmon, and cod—are more familiarto humans because most of the fisheswe consume belong to this subclass.You can see the parts of a ray-finnedfish in the Inside Story.

Origins of FishesScientists have identified fossils of

fishes that existed during the earlyOrdovician period, 500 million yearsago. For 50 million years, ostraco-derms (oh STRAHK oh durmz), earlyjawless fishes, were the only verte-brates on Earth. Although mostostracoderms became extinct at theend of the Devonian period, 400 mil-lion years ago, present-day agnathansappear to be their direct descendants.

Weighed down by heavy, bonyexternal armor, ostracoderms, shown


Figure 30.10Lungfishes, lobe-finned fishes,and ray-finned fishes are thesubclasses of the bony fishes.

Lungfishes representan ancient subclassthat arose nearly 400million years ago.Lungfishes such asthis African lungfishhave both gills andlungs.

AA

Lobe-finned fishes, such asthis coelacanth, appeared inthe fossil record about 395million years ago. Longthought to be extinct, livingexamples of coelacanthswere caught off the coast ofAfrica beginning in 1938.

BB

You can easily see therays that support thepectoral fins of thisflying fish, an exampleof a ray-finned fish.

CC

INSIDESSTORTORYY

INSIDE

11

22

33

55

30.1 FISHES 825

A Bony Fish

The bony fishes, class Osteichthyes, includesome of the world’s most familiar fishes, such

as the bluegill, trout, minnow, bass, swordfish, andtuna. Though diverse in general appearance and behav-ior, bony fishes share some common adaptations withother fish classes.

Critical Thinking Compare the ideal shapes for fishesthat swim in rocky crevices and those that swim inopen water.

Lateral line system When fishes swim past obsta-cles, pressure changes occur in the water. Fishes candetect these changes with their lateral line systems,which enable them to swim in the dark and in complexcoral reefs.

Swim bladder The mass of a fish’s tissue isgreater than that of water; therefore, withouta swim bladder, a fish would not be able tofloat. Gas pressure in the swim bladder altersthe specific gravity of the whole body,enabling the fish to float at any depth.

Gills Gills are thin, blood vessel-richtissues where gases are exchanged.

Scales Scales are covered with slipperymucus, allowing a fish to move throughwater with minimalfriction. Fins The structure and

arrangement of fins arerelated to a particulartype of locomotion.Tropical fishes that liveamong coral reefs tendto have small fins capa-ble of maneuvering inthis complex, three-dimensional environ-ment, whereas a tunahas large, broad fins formoving quicklythrough open water.

Rainbow trout,Salmo gairdneri

KidneyUrinary bladder

Reproductive organ

StomachIntestine

LiverHeart

44

in Figure 30.11, were fearsome-looking animals that swam sluggishlyover the murky seafloor. Although allostracoderms had cartilaginous skele-tons, they also had shields of bonecovering their heads and necks. Thedevelopment of bone in these ani-mals was an important evolutionarystep because bone provides a placefor muscle attachment, whichimproves locomotion. In ancestralfishes, bone that formed into platesprovided protection as well.

Lobe-finned fishes, the coelacanths(SEE luh kanthz), are another ancient

group, appearing in the fossil recordabout 395 million years ago. They arecharacterized by lobelike, fleshy fins,and live at great depths where they aredifficult to find. The limblike skeletalstructure of fleshy fins is thought to bean ancestral condition of all tetrapods(animals with four limbs). The earli-est tetrapods discovered also had gillsand therefore were still aquatic.

Scientists hypothesize that the jaw-less ostracoderms were the commonancestors of all fishes. Modern carti-laginous and bony fishes evolved dur-ing the mid-Devonian period.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. List three characteristics of fishes.2. Compare how jawless fishes and cartilaginous

fishes feed.3. Why was the evolution of a swim bladder

important to fishes?4. How does a flexible skeleton aid swimming in

fishes?

Thinking Critically5. Why was the development of jaws an important

step in the evolution of fishes?

6. Making and Using Tables Construct a table tocompare the characteristics of the jawless, carti-laginous, and bony fishes. For more help, refer toOrganizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Figure 30.11Ostracoderms, theearliest vertebratefossils found, werecharacterized bybony, external platescovering the bodyand a jawless mouth.Lacking jaws, ostra-coderms obtainedfood by sucking upbottom sedimentsand sorting out thenutrients.

Anaspid

Cephalaspid

Heterostracan


Section

What Is an Amphibian?The striking transition from a

completely aquatic larva to an air-breathing, semiterrestrial adult givesthe class Amphibia (am FIHB ee uh)its name, which means “double life.”The class Amphibia includes threeorders: Caudata (kaw DAHT uh), withsalamanders and newts; Anura (uhNUHR uh), with frogs and toads; andApoda (uh POH duh), with leglesscaecilians, as shown in Figure 30.12.Amphibians have thin, moist skin andfour legs. They have no claws ontheir toes. Although most adultamphibians are capable of a terrestrialexistence, nearly all of them rely onwater for reproduction. Fertilizationin most amphibians is external, andwater is needed as a medium fortransporting sperm. Amphibian eggs

lack protective membranes and shellsand must be laid in water to staymoist. How do frogs capture theirfood? Find out by reading the InsideStory on the next page.

Amphibians are ectothermsAmphibians are more common in

regions that have warm temperaturesall year because they are ectotherms.

If an alien visitor to our planetwere to watch our television programs and read our children’s

literature, it might return home with wondrous stories of how frogs on Earth can talk and change by the touch of a kiss into princes. Frogsand toads don’t talk, but they dochange—from fishlike tadpolesto four-legged animals withbulging eyes, long tongues,loud songs, and remark-able jumping ability.

SECTION PREVIEW

ObjectivesRelate the demands of a terrestrial environ-ment to the adaptationsof amphibians.Relate the evolution of the three-chamberedheart to the amphibianlifestyle.

Vocabularyectothermvocal cords

30.2 Amphibians

Figure 30.12Caecilians, orderApoda, are long,limbless amphibians.They look like wormsbut have eyes thatare covered by skin.

Pickerel frog (above)and tadpoles (inset)

827

Liver

Intestine

Fat bodies

Backbone

Heart

Vocalcords


A Frog

Many species of frogs look similar. As adults, theyhave short, bulbous bodies with no tails. This

adaptation allows them to jump more easily.

Critical Thinking How does a three-chambered heartbenefit a frog?

Green frog, Rana clamitans

INSIDESSTORTORYY

INSIDE

Tympanic membrane Vibrationsfrom water or air are picked up bythe tympanic membrane and trans-mitted to the inner ear and then tothe brain. The tympanic membranealso amplifies the sounds frogs make.

22

Eyes Some frogs’ eyes protrude from thetops of their heads—an adaptation thatenables them to stay submerged in the waterwith only their eyes above the surface.

11

Tongue A frog’stongue is long, sticky,and fastened to thefront of the mouth.These adaptationsallow frogs to snaretheir prey, such asflies, with amazingaccuracy.

33

Lungs Lungs enableadult amphibians tobreathe air.

44

Calls Male frogsuse sound to attractfemales. Femaleshave distinct calls toindicate whether ornot they are willingto mate.

55

Legs The hind legs of afrog are muscular. If youhave ever tried to catch afrog, you can appreciate thepower in these leg muscles.

66

Adult frog

Young frog with stucturesneeded for life on land.

Tadpoles with legs feedon plants in the water.

Fertilized eggs

Young leglesstadpoles liveoff yolk storedin their bodies

An ectotherm (EK tuh thurm) is ananimal in which the body tempera-ture changes with the temperature ofits surroundings. Because many bio-logical processes require particulartemperature ranges in order to func-tion, amphibians become dormant inregions that are too hot or cold forpart of the year. During such times,many amphibians burrow into themud and stay there until suitableconditions return.

Amphibians undergo metamorphosis

Unlike fishes, most amphibians gothrough the process of metamorpho-sis. Fertilized eggs hatch into tadpoles,the aquatic stage of most amphibians.You can compare tadpoles with adultfrogs in the MiniLab on the nextpage. Tadpoles possess fins, gills, anda two-chambered heart as seen infishes. As tadpoles grow into adult

frogs and toads, they develop legs,lungs, and a three-chambered heart.Figure 30.13 shows this life cycle.You can observe the development offrog eggs in the Investigate BioLab atthe end of this chapter.

Young salamanders resemble adults,but they have gills and usually have atail fin. Most adult salamanders lackgills and fins. Instead, they breathethrough their moist skin or with lungs.Up to one-fourth of all salamandershave no lungs and breathe onlythrough their skin. Most salamandershave four legs for moving about, buta few have only two front legs.

Walking requires more energyThe laborious walking of early

amphibians required a great deal ofenergy from food and large amountsof oxygen for aerobic respiration.The evolution of the three-cham-bered heart in amphibians ensured

30.2 AMPHIBIANS 829

Figure 30.13The amphibian life cycle includesan aquatic tadpole stage and aterrestrial adult stage.

Looking at Frog and Tadpole AdaptationsAn adult frog and its larval stage are adapted to dif-ferent habitats. How are the structures of a frog and a tadpole adapted to their environments?

Procedure! Copy the data table.@ Examine a living or preserved adult frog and larval

(tadpole) stage. CAUTION: Wear disposable latex glovesand use a forceps when handling preserved specimens.

# Observe the first seven traits listed. Complete your datatable for these observations.

$ Use references to fill in the information for the last threetraits listed.

Analysis1. Explain how hind leg musculature aids in adult frog survival. 2. Correlate the type of respiratory organ in an adult and a

tadpole with their differing habitats. 3. Correlate the type of appendages (arm, leg, tail) in an

adult and a tadpole with their differing habitats.4. Correlate mouth size in an adult and a tadpole with their

differing diet.5. Explain how eyes may aid in the survival of both stages.6. Explain why the tympanic membrane may not be essential

to the survival of a tadpole.7. Predict how skin color and texture aids in adult frog

survival. CAUTION: Wash your hands after working withlive or preserved animals.

MiniLab 30-2MiniLab 30-2 Comparing and Contrastingthat cells received the proper amountof oxygen. This heart was an impor-tant evolutionary transition from thesimple circulatory system of fishes.

In the three-chambered heartof amphibians, one chamberreceives oxygen-rich bloodfrom the lungs and skin, andanother chamber receives oxygen-poor blood from thebody tissues. Blood from bothchambers then moves to thethird chamber, which pumps

oxygen-rich blood to body tissuesand oxygen-poor blood back to thelungs and skin so it can pick up moreoxygen. This results in some mixingof oxygen-rich and oxygen-poorblood in the amphibian heart and inblood vessels leading away from theheart. Thus, in amphibians, the skinis much more important than thelungs as an organ for gas exchange.

Because the skin of an amphibianmust stay moist to exchange gases,most amphibians are limited to lifeon the water’s edge. However, somenewts and salamanders remain totallyaquatic. Amphibians such as toadshave thicker skin, and although theylive primarily on land, they still mustreturn to water to reproduce.

Diversity of AmphibiansBecause amphibians still complete

part of their life cycle in water, theyare limited to the edges of ponds,lakes, streams, and rivers or to areasthat remain damp during part of theyear. Although they are not easilyseen, amphibian species are numer-ous worldwide.

Frogs and toads belong to the order Anura

Frogs and toads are amphibianswith no tails. Frogs have long hindlegs and smooth, moist skin. Toads


Trait or information AdultTadpole

Limbs present?

Eyes present?

Tympanic membrane present?

Tail present?

Mouth present?

Nature of skin (color and texture)

General size

Respiratory organ type

Diet

Habitat

Data Table

Rana temporaria

have short legs and bumpy, dry skin.Like fishes, frogs and toads have jawsand teeth. All adult frogs and toadseat insects. Many species of frogs andtoads secrete chemicals through theirskin as a defense against predators.Some frogs and toads produce toxinsthat can kill predators, such as dogs,quickly. You can find out more aboutpoisonous frogs in the ChemistryConnection at the end of this chapter.

Frogs and toads also have vocalcords that are capable of producing awide range of sounds. Vocal cordsare sound-producing bands of tissuein the throat. As air moves over thevocal cords, they vibrate and causemolecules in the air to vibrate. Inmany male frogs, air passes over thevocal cords, then passes into a pair ofvocal sacs lying underneath thethroat, illustrated in Figure 30.14.

Frogs and toads, like all amphib-ians, spend part of their life cycle inwater and part on land. They breathethrough lungs or through their thinskins. As a result, frogs and toadsoften are among the first organismsto be exposed to pollutants in the air,on land, or in the water. Decliningnumbers of frog species, or deformi-ties in local frogs, sometimes indicatethat the environment is no longerhealthy.

Salamanders belong to the order Caudata

Unlike a frog or toad, a salaman-der has a long, slender body with aneck and tail. Salamanders resemblelizards, but have smooth, moist skinand lack claws. Some salamanders aretotally aquatic, and others live indamp places on land. They range insize from a few centimeters in lengthup to 1.5 m. Newts are salamandersthat live entirely in water. The youngthat hatch from salamander eggs looklike small adults and are carnivorous.

Caecilians are limbless amphibians

Caecilians are amphibians thathave no limbs, with a short, or no,tail. Caecilians are primarily tropicalanimals with small eyes that are oftenblind. They eat earthworms andother invertebrates found in the soil.

Origins of AmphibiansImagine a time 350 million years

ago when the inland, freshwater seaswere filled with carnivorous fishes.One type of tetrapod had evolvedthat retained gills for breathing and afinned tail for swimming. In later fos-sils, the four limbs are found furtherbelow the body to lift it off theground. Any animal that could moveover land from the mud of a dryingstream to another water source mightsurvive. Most likely, amphibiansarose as their ability to breathe airthrough well-developed lungsevolved. The success of inhabitingthe land depended on adaptationsthat would provide support, protectmembranes involved in respiration,and provide efficient circulation.

30.2 AMPHIBIANS 831

Figure 30.14Most male frogs havethroat pouches that,along with the tym-panic membrane,increase the volumeof their calls.

Challenges of life on landLife on land held many advantages

for early amphibians. There was alarge food supply, shelter, and nopredators. In addition, there wasmuch more oxygen in air than inwater. However, land life also heldmany dangers. Unlike the tempera-ture of water, which remains fairlyconstant, air temperatures vary a great

deal. In addition, without the supportof water, the body was clumsy andheavy. Some of the efforts to moveon land by early amphibians probablywere like movements of modern-daysalamanders. The legs of salamandersare set at right angles to the body.You can see in Figure 30.15 why thebellies of these animals may havedragged on the ground.

Amphibians first appeared about360 million years ago. Amphibiansprobably evolved from an aquatictetrapod, as shown in Figure 30.16,around the middle of the PaleozoicEra. At that time, the climate onEarth is known to have become warmand wet, ideally suited for an adaptiveradiation of amphibians. Able tobreathe through their lungs, gills, orskin, amphibians became, for a time,the dominant vertebrates on land.


Figure 30.16Transitional fossils with four limbsfrom the Devonian period showthat they had amphibian charac-teristics, but they also retainedsome fishlike features.

Figure 30.15Adaptation to life onland involves thepositioning of limbs.The evolution oftetrapods led to thediversification of landvertebrates.

Reptiles such asthis crocodile havelegs on the sidesof their bodies,like amphibians,but the limbs havejoints that enablethem to bend andhold the body upoff the ground.

BB

Like reptiles, mammal bodies are raisedabove the ground, but the limbs arepositioned underneath the body. Thisposition allows greater speed of locomo-tion, making mammals such as this chee-tah the fastest-moving land animals.

CC

The salamander, anamphibian, has legsthat extend at rightangles to its body.

AA

Recall that early vertebratesevolved from mud-sucking, swim-ming fishes to aquatic tetrapods.Scientists have found fossil evidencethat supports the hypothesis thatlimbs first evolved in aquatic animals.Some of these aquatic vertebratesevolved into air-gulping animals that

crawled from one pond to another,and finally to fully developedamphibians that lived mainly on land.Although the fossil record for fishesand amphibians is incomplete, mostscientists agree that the relationshipsshown in Figure 30.17 represent thebest fit for the available evidence.

30.2 AMPHIBIANS 833

Frogs and Toads3700 species

Salamanders400 species

Lungfishes6 species

Placoderms

Lobe-finnedfishes

1 species Ray-Finned Fishes18 000 species

Sharksand Rays850 species

Ostracoderms

Earlytetrapod

Reptiles

Lampreys

63 species

Hagfishes

Osteichthyes

Agnatha

Amphibians

Chondrichthyes

PRESENTCENOZOICPALEOZOICPRECAMBRIAN MESOZOIC

Section AssessmentSection AssessmentUnderstanding Main Ideas1. Describe the events that may have led early ani-

mals to move to land.2. List three characteristics of amphibians.3. Name two ways that amphibians depend on

water.4. How does metamorphosis through two different

forms benefit amphibians?

Thinking Critically5. How does a three-chambered heart enable

amphibians to obtain the energy needed formovement on land?

6. Sequencing Trace the evolutionary develop-ment of amphibians from lungfishes. For morehelp, refer to Organizing Information in the SkillHandbook.

SKILL REVIEWSKILL REVIEW

Figure 30.17The radiation of classes of fishesand orders of amphibians on theGeologic Time Scale shows theirrelationships.

ANIMALS


Development of Frog Eggs

Most frogs breed in water. The male releases sperm over the female’seggs as she lays them. Some frogs lay up to a thousand eggs. A jel-

lylike casing protects the eggs as they grow into embryos. When the em-bryos hatch, they develop into aquatic larvae commonly called tadpoles.Tadpoles feed by scooping algae from the water or by scraping algae fromwater plants with small, toothlike projections in their mouths.

During metamorphosis, tadpoles lose their tails and develop legs.Many internal changes take place as well. Gills are reabsorbed by thebody, and lungs form. Development and metamorphosis to the adult frogtake from three weeks up to several years, depending upon the species.

INVESTIGATEINVESTIGATE

ProblemHow does temperature affect the

development of frog eggs?

ObjectivesIn this BioLab, you will:■ Compare develop-

ment of frog eggs atvarying tempera-tures.

■ Distinguish amongvarious stages ofdevelopment.

MaterialsRinger’s solution4 culture disheslight bulbs with source of electricitythermometerbinocular microscopefrog eggs, Xenopus laevisflashlight

Safety PrecautionsAlways wear goggles in the lab.

Wash hands before and after eachobservation.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

1. Obtain four culture dishes ofRinger’s solution and fertilizedfrog eggs.

2. Make a data table similar to theone shown for sketching of stagesof development of the eggs.

3. Observe your eggs and determinetheir stage of development. Atroom temperature, you shouldsee the two-cell stage about 1.5hours after fertilization, theeight-cell stage at 2.25 hours, the

PROCEDUREPROCEDURE

32-cell stage at 3 hours, the lategastrula stage at 9 hours, and avisible head area between 18 and20 hours. Hatching will occur atabout 50 hours (about two days).

4. Set up the appropriate numbers of light bulbs of different wattagesover the water to keep the temperatures at 20°, 25°, and30°C.

5. Place a dish of eggs in the refrig-erator. Measure the temperatureof your refrigerator. Keep a flash-light on in the refrigerator at alltimes so that you have only onevariable, the temperature.

6. Make a hypothesis about howtemperature will affect develop-ment of the eggs.

7. Set up a time schedule for obser-vations and making sketchesbased on what stage you areobserving. Make observationsuntil the eggs hatch. Record yourobservations in a journal.

8. Observe your eggs under themicroscope according to the sched-ule you have made. Draw sketchesof your eggs in the data table.

30.2 AMPHIBIANS 835

30° C

25° C

20° C

refrigerator

Day 2Day 1Temperature Day 3

Data Table

Going FurtherGoing Further

Make a Hypothesis Make a hypothesisabout what other environmental factorswould affect the development of frog eggs.Explain your reasoning.

To find out more about metamorphosis, visit the

Glencoe Science Web site.science.glencoe.com

1. Interpreting ObservationsWhich eggs develop the fastest?The slowest? Explain.

2. Interpreting Observations Didyour data support your hypothesis?Explain.

3. Drawing Conclusions Whatadvantage is it for frogs to haveeggs that develop at differentrates that correspond to differenttemperatures?

4. Thinking Critically What wouldhappen if frog eggs developed

when the weather was still cold inthe spring?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

BIOLOGY


The most colorful frogs in the world are found inSouth and Central America. These poisonous

frogs, including 130 species of the Dendrobatidaefamily, range in size from 1 to 5 cm. Although

all frogs have glands that produce secretions, thesefrogs secrete toxic chemicals through their skin. Apredator will usually drop the foul-tasting frogwhen it feels the numbing or burning effects of

the poison in its mouth. The frogs advertise theirpoisonous personalities by bright coloration; theymay be red or blue, solid colored, marked withstripes or spots, or have a mottled appearance.

The poison secreted by these frogs is used by nativepeoples to coat the tips of the darts they use in

their blow guns for hunting. Thus, these frogs areknown as poison-arrow frogs.

The secretions of the poison-arrow frogs ofthe frog family Dendrobatidae are alkaloid

toxins. An alkaloid toxin is a compound thatincludes a ring consisting of five carbon atomsand one nitrogen atom. The toxins secreted bypoisonous frogs act on an ion channel betweennerve and muscle cells. Normally, the channel isopen to allow movement of sodium, potassium,and calcium ions. The toxins can block the flowof potassium and stop or prolong nerve impulsetransmission and muscle contraction. One groupof alkaloids affects the transport of calcium ions,which are responsible for muscle contraction.Current research indicates that these alkaloidsmay have clinical applications for muscle diseasesand as pain killers.

Frog poison eases pain Recent research showsthat a drug derived from the extract from thepoison-arrow frog, Epipedobates tricolor, works as apowerful pain killer. The drug ABT-594 mayhave the same benefits as morphine, but not theside effects. Morphine is the primary drug usedto treat the severe and unrelenting pain caused by

cancer and serious injuries. Side effects of mor-phine include suppressed breathing and addic-tion. The “frog drug” does not interfere withbreathing and does not appear to be addictive ininitial testing. Another benefit of ABT-594 isthat as it blocks pain, it does not block other sen-sations, such as touch or mild heat. One day painyou experience might be eased by a frog!


ConnectionChemistryChemistry

Connection Killer Frogs

Research on newly discovered organisms such aspoisonous frogs may result in drugs to treat spe-cific disorders in human patients. Find out whathuman diseases are caused by problems in thetransmission of nerve impulses and write an essayidentifying the disorders that might be treated bytoxins from poisonous frogs.

To find out more about poisonous frogs, visit the

Glencoe Science Web site.science.glencoe.com

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

Cl

O

N

N

H

Poison-arrow frog, Epipedobates tricolor

BIOLOGY


Chapter 30 AssessmentChapter 30 Assessment

SUMMARYSUMMARY

Section 30.1

Section 30.2

Main Ideas■ Fishes are vertebrates with backbones and nerve

cords that have expanded into brains.■ Fishes belong to three groups: the jawless lam-

preys and hagfishes, the cartilaginous sharks andrays, and the bony fishes. Bony fishes are madeup of three groups: the lobe-finned fishes, thelung-fishes, and the ray-finned fishes.

■ Jawless, cartilaginous, and bony fishes may haveevolved from ancient ostracoderms.

Vocabularycartilage (p. 823)fin (p. 820)lateral line system

(p. 820)scale (p. 821)spawning (p. 819)swim bladder (p. 822)

Fishes

Main Ideas■ Adult amphibians have three-chambered hearts

that provide oxygen to body tissues, but mostgas exchange takes place through the skin.

■ Land animals face problems of dehydration, gasexchange in the air, and support for heavy bod-ies. Amphibians possess adaptations well-suitedfor life on land.

■ Amphibians probably evolved from ancientaquatic tetrapods.

Vocabularyectotherm (p. 829)vocal cords (p. 831)Amphibians

CHAPTER 30 ASSESSMENT 837

1. An animal with gill slits, a dorsal hollownerve cord, and a backbone is a(n) ________.a. invertebrateb. invertebrate chordatec. vertebrated. echinoderm

2. In addition to fishes, the subphylum Verte-brata includes ________.a. amphibians, reptiles, birds, and mammalsb. echinoderms, reptiles, birds, and mammalsc. tunicates, lancelets, reptiles, and birdsd. tunicates, reptiles, birds, and mammals

3. Scientists hypothesize that the commonancestors to all fishes are the ________.a. amphibians c. ostracodermsb. echinoderms d. lancelets

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 4. How do jawless fishes obtain food?a. by injecting prey with poison from their

hooklike fangsb. by using their round mouths like vacuum

cleaners to suck up organic matterc. by drilling a hole and sucking out blood

and insides of a prey animald. by using their sharp teeth to grab and

swallow smaller fishes5. Which of the following is NOT a character-

istic of most fishes?a. have scalesb. have a two-chambered heartc. breathe using gillsd. exchange gases through thin, moist skin

6. ________ use fins like the stabilizers of boats.a. Frogs c. Sea starsb. Fishes d. Lancelets


7. The lateral line system enables a ________ todetect movement and vibrations in the water.a. frog c. toadb. salamander d. fish

8. The class Amphibia is well-named becauseamphibians ________.a. spend part of their lives on land and

part in waterb. lay shelled eggs on land but develop

in waterc. spend part of their lives in the air and

part on landd. use swim bladders for breathing in water

but use lungs on land9. Reptiles have legs on the sides of their

bodies, but the limbs are flexed. Salamandershave legs that ________.a. extend straight out from the body

and do not bendb. extend at right angles from the sides

of the body c. are missing some of the key bones

of reptilesd. evolved from shark’s fins

10. The evolution of a three-chambered heart inamphibians ensured that cells receive theproper amount of ________.a. oxygen c. bloodb. carbon dioxide d. heat

11. The skeletons of lampreys, hagfishes, sharks,and their relatives are made of ________.

12. In all fishes, gas exchange takes place in the________.

13. The ________-chambered heart pictured to the right belongs to a(n) ________.

14. A fish that has a niche similar to a leech isa(n) ________.

15. Fishes control their depth in the water byaltering the amount of ________ in their________.

16. The ________ enables a fish to navigate inthe dark.

17. Fossil evidence shows that early tetrapodshad ________ like fishes and ________ likeamphibians.

18. Both hagfishes and sharks have ________skeletons.

19. Fishes and amphibians are ________because their body temperature reflects thetemperature of their surroundings.

20. The ________ in the diagram below has legsthat show an earlier evolutionary origin thanthe other animals pictured.

21. What accounts for the different body shapesof fishes?

22. What are the advantages and disadvantagesof internal fertilization?

23. Describe the importance of the evolution of bone in fishes to the evolution of verte-brates.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

838 CHAPTER 30 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Skip Around, if You Can Just because the questions are in order doesn’tmean that you have to answer them that way. Youmay want to skip over hard questions and comeback to them later, after you’ve answered all theeasier questions that will guarantee you morepoints toward your score.

a.

c.

b.


CHAPTER 30 ASSESSMENT 839

24. A male sea horse incubates fertilized eggs in abrood pouch. A codfish lays its eggs in theopen sea. Which of these two types of fisheswould need to lay more eggs? Why?

25. Using a Graph The following graph showsthe number of leopard frogs in a wetland on afarm. One year, there was a prolongeddrought in the farmer’s area. What year didthe drought occur? Explain.

26. Concept Mapping Complete the conceptmap by using the following vocabulary terms:lateral line system, scales, swim bladder.

THINKING CRITICALLYTHINKING CRITICALLY

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

Amphibian populations are declining inmany parts of the world. To reintroducenative amphibians into your state, assumeyou have a grant to breed frogs on a farm.To find out what temperature you need foroptimum hatching of frog eggs, you testeggs at four different temperatures.

Interpreting Data Answer the followingquestions based on the graph.1. How many eggs hatched at 25°C?

a. 150 c. 110b. 70 d. 15

2. At which temperature did the fewesteggs hatch?a. 15°C c. 25°Cb. 20°C d. 30°C

3. Based on the results of your experiment,what temperature will you use for opti-mum hatching of eggs?a. 15°C c. 25°Cb. 20°C d. 30°C

4. Designing an Experiment You are trying to find out the optimum pH forhatching frog eggs. Design a controlledexperiment that would give you quantitative data.

Num

ber o

f fro

gs h

atch

ing

15°C 20°CTemperature

25°C 30°C

180

150

120

90

60

30

Number of Frogs Hatching at VariousTemperatures in 5 Days

Num

ber o

f fro

gs

1995 1996

Year

1997 1998

Number of Frogs in a Wetland

Fishes

are vertebrates that

two-chamberedheart

1. 2.

3.

have a

sense vibrations

with a

have a

protect skin with

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

CD-ROM


chapter 30: fishes and amphibiansblogs.polson.k12.mt.us/dobrien/files/2011/01/chap30.pdf · ihk...

Documents