Reading Essentials for Biology Glencoe (794133), страница 84
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Thedevelopment of bone in early vertebrates was important becausebone provides a place for muscles to attach. This enabled thefishes to move more quickly and efficiently.Ostracoderms may have been the common ancestor of allfishes. Modern cartilaginous and bony fishes evolved during theDevonian Period. Lobe-finned fishes, such as the coelacanths, areanother ancient group. They appear in the fossil record about 395million years ago. They had lobelike, fleshy fins, and they livedin deep places in the ocean. This makes them hard to find. Theskeletal structure of fleshy fins is believed to be an ancestral traitof all animals that have four limbs, called tetrapods. The earliesttetrapods had gills and were aquatic.7.
When did most ostracoderms become extinct?________________________________________________________________________◗ After You ReadMini Glossarycartilage: a tough, flexible material that formsthe skeletons of two classes of fishesfin: fan-shaped membrane used for balance,swimming, and steeringlateral line system: a line of fluid-filled canalsthat run along the sides of a fish that enablethe fish to detect movement and vibrationsin the waterscale: thin bony plates formed from the skin offishesREADING ESSENTIALSspawning: external reproduction in some speciesof fishes; fishes that spawn may produce asmany as 9 million eggs, and provide no carefor their young after spawningswim bladder: a thin-walled internal sac locatedjust below the backbone in most bonyfishes; the swim bladder can be filled withmostly oxygen or nitrogenous gases thatdiffuse out of a fish’s bloodChapter 30369NameDateClassSection30.1Fishes, continued1. Read the terms and definitions in the Mini Glossary on page 369.
In the space below createa drawing of a shark or skate and label the parts, using at least five of the terms listed above.2. Use the diagram below to describe the parts of a fish. Describe the parts listed in each oval.HeartFishesSkeletonFinsSensory systemVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about fishes.370Chapter 30READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.GillsNameDateClassSection30.2 AmphibiansSC.F.1.4.2 The student knows that body structures are uniquely designed and adapted for their function. SC.G.1.4.1 Thestudent knows of the great diversity and interdependence of living things.
Also covers SC.F.1.4.7◗ Before You ReadYou may have heard frogs croak or seen toads hopping near creeks or ponds. Frogs and toads aremembers of the same order and have a number of characteristics in common. On the lines below,explain what you have observed about frogs and toads.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is an amphibian?Amphibia (am FIHB ee uh) means double life.
Animals thatbelong to the class Amphibia change from aquatic to semiterrestrial during their life cycles. This is how they got the nameamphibian. As larvae, almost all of these animals are completelyaquatic. When most amphibians reach the adult stage, theybreathe air.
Amphibians can be found on land, but they mustlive near water or other moist areas. Therefore, these animalsare called semiterrestrial. There are three orders in the classAmphibia. Salamanders and newts belong to the order Caudata(kaw DAH tuh). Frogs and toads belong to the order Anura(uh NUHR uh). Caecilians, amphibians that do not have legs,belong to the order Apoda (uh POH duh).Amphibians have thin, moist skin.
Most amphibians have fourlegs. Most adult amphibians can exist on land, but nearly all ofthem need water for reproduction. Fertilization in most amphibians is external, and water is needed to carry the sperm to theeggs. The eggs do not have a membrane or a shell to protectthem. They must be laid in water or in other damp areas.What is an ectotherm?CompareHighlight each question inthis section about amphibians.Use these questions and theinformation in the text towrite a comparison ofamphibians and fishes.1.
Why do amphibians laytheir eggs in water?________________________________________________________________________An ectotherm (EK tuh thurm) is an animal that has a variable,or changing, body temperature. Amphibians cannot regulate theirown body temperature or maintain their temperature at a stableREADING ESSENTIALSChapter 30371NameDateClassSection30.2Amphibians, continuedlevel as humans do. An ectotherm gets its heat from externalsources.
Amphibians are more common in areas that have warmtemperatures all year round because they are ectotherms. Manybiological processes require certain temperature ranges. Becauseof this, amphibians are dormant, or completely inactive, whenthey live in areas that are too hot or too cold for them duringcertain parts of the year. During these hot and cold times, manyamphibians burrow into the mud and stay buried in the mud untilthe temperature changes.2. What changes occurwithin the tadpole’s bodyas it becomes an adultfrog or toad?________________________________________________________________________Most amphibians go through metamorphosis.
Fertilized frogand toad eggs hatch into tadpoles. This is the totally aquaticstage. Tadpoles have fins, gills, and a two-chambered heart likefishes. As tadpoles grow into adult frogs and toads, they developlegs, lungs, and a three-chambered heart.Young salamanders resemble adult salamanders. Most salamander larvae also are aquatic. In this stage they have gills, and theyusually have a tail fin. Most adult salamanders do not have gills orfins.
They breathe through their skin or with their lungs. Somesalamanders do not have lungs. They can only breathe throughtheir moist skin. Salamanders that live completely on land do nothave a larval stage. When these young salamanders hatch, theylook like small adults. Most salamanders have four legs, but somehave only two front legs.What kind of hearts do amphibians have?Amphibians have a three-chambered heart. When early amphibians began to walk, walking required a great deal of energy fromfood.
It also required a large amount of oxygen for respiration.The evolution to a three-chambered heart helped to ensure thatthe amphibian’s cells would receive enough oxygen. The changefrom a two- to a three-chambered heart was an important evolutionary change.In the three-chambered heart, one chamber receives oxygenrich blood from the lungs and the skin. Another chamber receivesoxygen-poor blood from the body tissues. Blood from both ofthese two chambers goes into the third chamber of the heart.This third chamber pumps oxygen-rich blood into the body tissues.
It also pumps oxygen-poor blood back to the lungs and theskin. This blood then picks up oxygen. The three-chamberedheart mixes some oxygen-rich and some oxygen-poor blood.372Chapter 30READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How does an amphibian change duringmetamorphosis?NameDateClassSection30.2Amphibians, continuedOxygen-rich and oxygen-poor blood also are mixed in bloodvessels that lead away from the heart.
This is why the skin inamphibians is more important than the lungs for gas exchange.The skin of an amphibian must stay moist to exchange gases.This means that most amphibians have to live on the water’s edgeor in other, very moist areas. Some newts and some salamandersspend their entire lives in the water. Toads, which have a thickerskin, live primarily on land. They return to water to reproduce.Amphibian DiversityBecause most amphibians depend on water to reproduce, theymust live on the edges of ponds, streams, and rivers, or in areasthat remain damp during parts of the year.
Amphibian species arefound worldwide.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How are frogs and toads different fromother amphibians?Frogs and toads are members of the order Anura. Frogs andtoads do not have tails. Frogs have long back legs and smooth,moist skin. Toads have short legs and bumpy, dry skin. Frogs andtoads have jaws and teeth. They are predators. They eat insectsand worms.
To defend themselves from predators, many frogs andtoads secrete chemicals through their skin.Frogs and toads have vocal cords. Vocal cords are bands of tissue located in the throat. As air passes over the vocal cords, theyvibrate. This makes molecules in the air vibrate, and a wide rangeof sounds is produced. In many male frogs, air passes over thevocal cords, and then goes into a pair of vocal sacs that are underneath the throat.
This enlarges these sacs, making them look likesmall balloons.Most frogs and toads spend part of their lives in water and partof their lives on land. They breathe through lungs or throughtheir skins. Because they breathe through their skins, they areexposed to pollutants in the air, on land, or in the water.3. Name two differencesbetween frogs and toads.________________________________________________How are salamanders different from otheramphibians?Salamanders belong to the order Caudata. Salamanders havelong, slender bodies. They have necks and tails. Salamanders looklike lizards, but they have smooth, moist skin.
They do not haveclaws. Some salamanders spend their entire life cycle in water.READING ESSENTIALSChapter 30373NameDateClassSection30.2Amphibians, continuedOthers live on land in damp places. Salamanders can be small, afew centimeters long, or they can be up to 1.5 m long. Whenyoung salamanders hatch from eggs, they look like small adults.Salamanders are carnivores, or meat-eaters.________________________________________________________________________Caecilians belong to the order Apoda. They do not have limbs.Caecilians are burrowing amphibians.
Some have short tails; others have no tail at all. They have small eyes, but are often blind.Caecilians eat earthworms and other invertebrates that live in thesoil. All caecilians have internal fertilization. They live primarilyin tropical areas.Origins of AmphibiansTetrapods, animals with four legs, evolved over 360 millionyears ago. One type of tetrapod developed gills for breathing anda finned tail for swimming. These tetrapods may have used theirlimbs to move along the bottom of marshlands. Later fossils showthe four limbs located further below the body. These limbs couldlift the body off the ground.
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