ThermoregulationMammalsandbirdsgenerallymaintainbodytemperaturewithinanarrowrange(36-38~Cformostmammalsand39-42℃formostbirds)thatisusuallyconsiderablywarmerthantheenvironment.Becauseheatalwaysflowsfromawarmobjecttocoolersurroundings,birdsandmammalsmustcounteracttheconstantheatloss.Thismaintenanceofwarmbodytemperaturedependsonseveralkeyadaptations.Themostbasicmechanismisthehighmetabolicrateofendothermyitself.Endothermscanproducelargeamountsofmetabolicheatthatreplacetheflowofheattotheenvironment,andtheycanvaryheatproductiontomatchchangingratesofheatloss.Heatproductionisincreasedbysuchmuscleactivityasmovingorshivering.Insomemammals,certainhormonescancausemitochondriatoincreasetheirmetabolicactivityandproduceheatinsteadofATP.Thisnonshiveringthermogenesis(NST)takesplacethroughoutthebody,butsomemammalsalsohaveatissuecalledbrownfatintheneckandbetweentheshouldersthatisspecializedforrapidheatproduction.ThroughshiveringandNST,mammalsandbirdsincoldenvironmentscanincreasetheirmetabolicheatproductionbyasmuchas5to10timesabovetheminimallevelsthatoccurinwarmconditions.Anothermajorthermoregulatoryadaptationthatevolvedinmammalsandbirdsisinsulation(hair,feathers,andfatlayers),whichreducestheflowofheatandlowerstheenergycostofkeepingwarm.Mostlandmammalsandbirdsreacttocoldbyraisingtheirfurorfeathers,therebytrappingathickerlayerofair.Humansrelymoreonalayeroffatjustbeneaththeskinasinsulation;goosebumpsareavestigeofhair-raisingleftoverfromourfurryancestors.Vasodilationandvasoconstrictionalsoregulateheatexchangeandmaycontributetoregionaltemperaturedifferenceswithintheanimal.Forexample,heatlossfromahumanisreducedwhenarmsandlegscoo]toseveraldegreesbelowthetemperatureofthebodycore,wheremostvitalorgansarelocated.Hairlosesmostofitsinsulatingpowerwhenwet.Marinemammalssuchaswhalesandsealshaveaverythicklayerofinsulationfatcalledblubber,justundertheskin.Marinemammalsswiminwatercolderthantheirbodycoretemperature,andmanyspeciesspendatleastpartoftheyearinnearlyfreezingpolarseas.Thelossofheattowateroccurs50to100timesmorerapidlythanheatlosstoair,andtheskintemperatureofamarinemammalisclosetowatertemperature.Evenso,theblubberinsulationissoeffectivethatmarinemammalsmaintainbodycoretemperaturesofabout36-38℃withmetabolicratesaboutthesameasthoseoflandmammalsofsimilarsize.Theflippersortailofawhaleorseallackinsulatingblubber,butcountercurrentheatexchangersgreatlyreduceheatlossintheseextremities,astheydointhelegsofmanybirds.Throughmetabolicheatproduction,insulation,andvascularadjustments,birdsandmammalsarecapableofastonishingfeatsofthermoregulation.Forexample,smallbirdscalledchickadees,whichweighonly20grams,canremainactiveandholdbodytemperaturenearlyconstantat40℃inenvironmentaltemperaturesaslowas-40℃--aslongastheyhaveenoughfoodtosupplythelargeamountofenergynecessaryforheatproduction.Manymammalsandbirdsliveinplaceswherethermoregulationrequirescoolingoffaswellaswarming.Forexample,whenamarinemammalmovesintowarmseas,asmanywhalesdowhentheyreproduce,excessmetabolicheatisremovedbyvasodilationofnumerousbloodvesselsintheouterlayeroftheskin.Inhotclimatesorwhenvigorousexerciseaddslargeamountsofmetabolicheattothebody,manyterrestrialmammalsandbirdsmayallowbodytemperaturetorisebyseveraldegrees,whichenhancesheatlossbyincreasingthetemperaturegradientbetweenthebodyandawarmenvironment.Evaporativecoolingoftenplaysakeyroleindissipatingthebodyheat.Ifenvironmentaltemperatureisabovebodytemperature,animalsgainheatfromtheenvironmentaswellasfrommetabolism,andevaporationistheonlywaytokeepbodytemperaturefromrisingrapidly.Pantingisimportantinbirdsandmanymammals.Somebirdshaveapouchrichlysuppliedwithbloodvesselsinthefloorofthemouth;flutteringthepouchincreasesevaporation.Pigeonscanuseevaporativecoolingtokeepbodytemperaturecloseto40℃inairtemperaturesashighas60℃,aslongastheyhavesufficientwater.Manyterrestrialmammalshavesweatglandscontrolledbythenervoussystem.Othermechanismsthatpromoteevaporativecoolingincludespreadingsalivaonbodysurfaces,anadaptationofsomekangaroosandrodentsforcombatingsevereheatstress.Somebatsusebothsalivaandurinetoenhanceevaporativecooling.Glossary:mitochondria:amembraneofATPATP:energythatdrivescertainreactionsincells

New-AgeTransportItlooksasifitcamestraightfromthesetofStarWars.Ithasfour-wheeldriveandrisesaboverockysurfaces.Itlowersandraisesitsnosewhengoingupanddownhills.Andwhenitcomestoariver,itturnsamphibious:twohydrojetpoweritalongbyblastingwaterunderitsbody.Thereisroomfortwopassengersandadriver,whositinsideaglassbubbleoperatingelectronic,aircraft-typecontrols.Avehiclesodaringonlandandwaterneedswindscreenwipers--butitdoesn'thaveany.Watermoleculesaredisintegratedonthescreen'ssurfacebyultrasonicsensors.ThisunusualvehicleistheRacoon.ItisaninventionnotofHollywoodbutofRenault,aratherconservativeFrenchstate-ownedcar-maker,betterknownforitsfamilyhatchbacks.RenaultbuilttheRacoontoexplorenewfreedomsfordesignersandengineerscreatedbyadvancesinmaterialsandmanufacturingprocesses.Renaultisthinkingaboutstartlinglydifferentcars;otherproducershaveradicalnewideasfortrains,boatsandaeroplanes.Thefirstofthenewfreedomsisindesign.Powerfulcomputer-aideddesign(CAD)systemscanreplacewithaclickofacomputermousehoursoflaboriousworkdoneonthousandsofdrawingboards.Sonewproducts,nomatterhowcomplicated,canbedevelopedmuchfaster.Forthefirsttime,Boeingwillnothavetobuildagiantreplicaofitsnewairliner,the777,tomakesureallthebitsfittogether.ItsCADsystemwilltakecareofthat.ButRenaultistakingCADfurther.ItclaimstheRacoonistheworld'sfirstvehicletobedesignedwithinthedigitisedworldofvirtualreality.Complexprogramswereusedtosimulatethevehicleandtheterrainthatitwasexpectedtocross.ThisallowedateamledbyPatrickG.M.LeQuément,Renault'sindustrial-designdirector,to"drive"itlongbeforeaprototypeexisted.Renaultisnotaloneinthinkingthatvirtualrealitywilltransformautomotivedesign.InDetroit,Fordisalsoinvestigatingitspotential.JackTurner,thefirm'sheadofdesign,wouldlikedesignersindifferentpartsoftheworldtoworkmorecloselytogether,linkedbycomputers.Theywoulddomorethanstylecars.Virtualrealitywillallowengineerstopeerinsidetheworkingpartofavehicle.Designerswillwatchbeatingsmove,oilflow,gearsmeshandhydraulicspump.Asthesetechniquescatchon,evenstrangervehiclesarelikelytocomealong.Transformingthesecreationsfromvirtualrealitytoactualrealitywillalsobecomeeasier,especiallywithadvancesinmaterials.Firmsthatoncebashedeverythingoutofsteelnowfindthatnewalloysorcompositematerials(whichcanbemadefrommixturesofplastic,resin,ceramicsandmetals,reinforcedwithfibressuchasglassorcarbon)arechangingtherulesofmanufacturing.Atthesametime,oldmaterialskeepgettingbetter,astheirproducerstrytosecuretheirplaceinthefactoryofthefuture.Thiscompetitionisincreasingthepaceofdevelopmentofallmaterials.OnecompanyinthisfieldisScaledComposites.Itwasstartedin1982byBurrRutan,anaviatorwhohasdevisedmanyunusualaircraft.IthasalsoworkedoncompositesailsfortheAmerica'sCupyachtraceandonGeneralMotors'Ultralite,a100-milesper-gallonexperimentalfamilycarbuiltfromcarbonfibre.Again,theRacoonreflectsthisracebetweentheoldandthenew.ItusesconventionalsteelandwhatRenaultdescribesasanew"high-limitelasticsteel"initschassis.Thissteelis30%lighterthantheusualkind.TheRacoonalsohaspartsmadefromcomposites.Renaultplanstoreplacethepetrolenginewithasmallgasturbine,whichcouldbemadefromheat-resistingceramics,anduseittorunageneratorthatwouldprovidepowerforelectricmotorsateachwheel.Withcompositesitispossibletobuildmanydifferentpartsintoasinglecomponent.Fiat,Italy'sbiggestcarmaker,hasworkedoutthatitcouldreducethenumberofcomponentsneededinoneofitscarbodiesfrom150to16byusingacompositeshellratherthanonemadeofsteel.Aircraftandcarsmayincreasinglybeassembledasiftheywereplastickits.Advancesinenginetechnologyalsomakecarslighter.TheUltralite,whichScaledCompositeshelpedtodesignforGeneralMotors,usesatwo-strokeengineina"powerpod"attherearofthevehicle.TheenginehasbeendevelopedfromanEastGermandesignandweighs40%lessthanaconventionalenginebutproducesasmuchpower.Itisexpectedtoruncleanlyenoughtoqualifyasanultra-lowemissionsvehicleunderCalifornia'stoughnewrules.

GENERAL SYSTEMS THEORY 1 The Greek word "systema" means union, and scientists use the word "system" to describe a collection of several components that are linked to one another by functional relationships. Everything outside the system is known as the surroundings. Most scientific literature is a description of the components of a system, their relationships with one another, and their relationships with other systems. Although each science has its own systems with their own subject matter and networks of relationships, the formal characteristics of systems are similar for all sciences. The scientific discipline called general systems theory formulates principles that are valid for systems in general, no matter the elements involved and the relations or forces among them. 2 Systems can be divided into two types: closed systems and open systems. A closed system receives no supply of energy from outside and transfers no energy outwards. An open system receives energy from its surroundings and transfers it out again. 3 A closed system is isolated fiom its surroundings. The energy supply of a closed system is limited and is progressively used up by the processes operating within the system. The ability of the system to function decreases as the available energy is exhausted. Without any additional energy supplied from the outside, the system's processes stop altogether and no further change is possible in the system. A mill wheel supplied with water from a non-refillable container is a closed system. Once the container of water is empty, the wheel no longer turns because there is no water to turn it. In a truly closed system, the water would have to be collected below the mill wheel in a second container to ensure that the system did not supply any energy to the outside. 4 Some scientists argue that there are few truly closed systems in nature, and many define closed systems more broadly as those allowing energy but not mass to cross the system boundary. By this definition, the Earth system as a whole is a closed system. The boundary of the Earth system is the outer edge of the atmosphere, and except for the occasional meteorite, virtually no mass is exchanged between the Earth system and the rest of the universe. However, energy in the form of solar radiation passes from the sun, through the atmosphere to the Earth's surface, which in turn radiates energy back out to space across the system boundary. Hence, energy passes across the Earth's system boundary, but mass does not, making it a closed system. 5 In an open system, energy and mass can be transferred between the system and its surroundings. Living organisms are open systems. They absorb light energy or chemical energy in the form of organic molecules and release heat and metabolic waste products, such as carbon dioxide, to the surroundings. Generally, relationships exist between the components of a system and its surroundings, that is, other systems. Each open system is part of a larger system that receives and gives off energy. In an open system, the energy is continually resupplied from sources outside the system. In the example of the mill wheel, if the non-refillable water container is replaced by a reservoir fed continuously by a stream, it becomes an open system because the energy supply is renewed from the outside. 6 The natural environment is made up of open systems. These can behave as closed systems temporarily if the energy supply is halted for a period. If, for example, the stream to the reservoir supplying the mill dries up for a long period, the energy consumption of the mill wheel cannot be balanced by new energy supply. The water in the reservoir is used up, and if the dry period is long enough, the mill wheel stops turning. Eventually, the stream may flow again, filling the reservoir and turning the mill wheel again. This occurs because the stream-reservoir-mill system is itself a part of the Earth's much larger systems of water circulation and water budget, which include condensation, precipitation, run-off, and evaporation. The water systems receive their energy supply from the Earth's heat budget, which in turn receives its energy supply from the sun's radiation.

TOEFLReadingPassage2InnovationsinMedievalEuropeanAgriculture1.Intheyear1,000CE,Europe'ssocietieswereorganizedunderasystemknownasManorialism.Thebasicunitwasthemanor,avillageorvillagesincludinglargeareasoffarmlandandruledoverbyalord,whoprovidedmilitaryprotectionforthelocalpeasantpopulationinreturnfortheirlaborandashareoftheirharvestedcrops.Unfortunately,theagriculturaltechniquesinpracticeatthetimewereratherundeveloped.Farmershadtoworkarduouslyeverydaytoproducejustenoughfoodtosurvive.Butthen,intheeleventhcentury,severalchangestookplacethatallowedforasignificantincreaseincropyields.2.Severalfactorsmayhaveplayedaroleinthistransformation.Thereisevidence,forexample,thattheglobalclimatebegantowarmslightlyintheninthcentury.Historiansalsonotethatthefrequencyofviolentinvasionsbyneighboringpeopleshaddecreasedbytheyear1,000.Yet,evenmoreimportantwereseveralspecifictechnologicalinnovations,someofwhichwereintroducedfromotherpartsoftheworld,Europeanfarmershad,tosomeextent,alreadybeeninfluencedbyoutsiders;thewaterwheelsandwindmillsusedduringManorialismoriginatedintheMuslimworld,forinstance.Itwasthetoolsandtechniquesthatmadetheirwayontothecontinentafter1,000CE,however,thatdrasticallychangedthecourseofEuropeanagriculture.3.Priortotheeleventhcentury,mostfarmerspracticedtheoldRomantwo-fieldsystemofcroprotation.Aplotoflandwouldbedividedintotwohalves.Thetwohalveswerethenrotatedeverysixmonths,withonebeingplantedandtheothergoingunused.ThissystemworkedintheMediterraneanregion,wheresoilqualitywasgenerallylower.However,firstinGermany,thenelsewhereinEurope,farmersfinallyfiguredoutthatthelocalconditionscouldsupportmorecrops,andtheybegantoimplementathree-fieldsystem.Eachparceloflandwasnowdividedintothirds,withtwogrowingcropsandonelyingfallowatanygiventime.Thissimplemodificationyielded33%morefoodwhilerequiringlesslaborandalsoencouragedtheplantingofagreatervarietyofcrops.Asdietsimprovedandpeasantsacquiredmorefreetime,theywereabletoundertaketheclearingoflandbycuttingtreesanddrainingmarshes,thuscreatingmorefarmlandandfurtherincreasingfoodproduction.4.Anothershifttowardgreateragriculturalefficiencycameastheresultofanewtool.Upuntilthistime,mostpeasantsusedasimplewoodenplowtocutfurrowsinthefields.LikelyintroducedbytheSlavsofEasternEurope,theheavyplowmadethisjobmucheasier.Itfeaturedalargeironbladetoslicethroughthethicksoilandotherfeaturesthatreducedtheamountoftimeittooktodigadequatefurrows.Duetoitsweight,ateamofeightoxenwasneededtopulltheheavyplow,and,becausemostpeasantswereluckytoownoneox,theirnewtoolledtogreatercollaborationamongfarmers.Single-familyfieldswerecombinedtocreatelargecommunalplots,andcooperationboostedefficiency.Anotherchangewasthat,sinceateamofeightoxenwasverydifficulttoturn,longverticalstripsoffarmlandtooktheplaceofthestandardsquarefield.5.Astimewenton,theuseofoxeninplowteamswasabandonedinfavorofthehorse.Thisresultedfromboththeinventionofthehorseshoearound900CE,whichenabledhorsestoworkwithoutdamagingtheirhooves,andtheintroductionofthehorsecollar,givingtheanimalstheabilitytopulltheplowwiththeirchests.Replacingthetraditionalyokeharness,whichhadrequiredthattheypullfromtheneck,thehorsecollarexpandedasinglehorse'spullingpowerfrom1,000to5,000pounds.Ateamofhorsesstillcouldnotpullmoreweightthanateamofoxen,butthehorsesweretwiceasfastandcouldworklongerintotheday.AlongwiththeotherdevelopmentsoccurringinEuropeanagriculturearoundthistime,thesubstitutionofhorsesforoxenhelpedincreasetheaveragecropyieldofmostmanors.Surplusfoodstoreswereaccumulated,whichservedasthefoundationsofthegreatcivilizationsthataroseduringthenextcenturies.

TheGreatDepressionEconomistsagreethattheWallStreetcrashofOctober1929heraldedtheGreatDepressionandbyitsdramaticeffectsonbusiness,banking,andconsumerconfidenceplayedamajorroleinworseningit.Butmanyothersagreethatthecrashwasnottherealcauseoftheeconomicturmoil.TheseverityoftheGreatDepressioncanbetraced,atleastontheAmericandomesticfront,totheimpressivestrengthoftheinvestmentboomofthe1920sandtothevastlyincreasedproductivityoftheagriculturalsectorintheaftermathofWorldWarⅠ.Inthelate1920stherewasarapidriseincapitalinvestmentintheUnitedStates--bothinproductiveindustryandintheformofhousebuilding.Theoutputofcapitalgoods,thatis,machineryandequipmentusedintheproductionprocess,rosebynearlyaquarterbetween1927and1929,andagreathouse-buildingexplosionwhichhadbegunin1921continuedsteadilyupwardsthroughoutthedecade.Fueledatfirstbyprofitsandthenbypurespeculation,thestockmarketreachedunsustainably-highlevels.Worriedbythespeculativenatureoftheupwardspiralingstockprice,theFederalReserveBankdecidedtocooltheeconomybyraisinginterestrates,andthistight-moneypolicyledtocutbacksinindustrialproduction.Thedownturnininvestmentoccurredinthemiddleof1929--severalmonthsbeforethestockmarketcollapsed.Atthesametimetherewasreducedproductionofconsumerproductsduetosaturationofmiddleclassdemand,andthisinturncausedtheneedforcapitalgoodstofallevenmoreprecipitouslyduetowhateconomistscalltheacceleratorprinciple.Thisprinciplestatesthatasmallfallintheoutputofconsumergoodsresultsinamuchlargerfallintheoutputofcapitalgoods.Itwasthecapitalgoodsindustrieswhichwereworsthit,andby1932theoutputofcapitalgoodswasonlyaboutaquarterofwhatithadbeenin1929.Thefallintheoutputofconsumergoods,thoughmuchlesssharpthanthis,wasstillharsh,andthenetresultwasthatin1932totalindustrialproductionwasnomorethanhalfwhatithadbeenthreeyearsbefore.Thisfallinproductionwasaccompaniedbyasteepriseinunemployment,whichfurtherreducedconsumerspendingpower.By1932morethan12millionAmericanswereunemployed.Theothermainreasonwhytheeconomicdownturnwassoseverelayintheagriculturalsector.TheproductivityofAmericanfarmshadrisenenormouslyunderthestimulusofworldwidefood:shortagesbroughtonbyWorldWarⅠ;anditcontinuedtoriseduringthe1920safterprewarsourcesoffoodandagriculturalrawmaterialshadbeenrestored.Surplusesleadtolowerprices,andfarmersfacedwithlowerpricesfortheirproductstriedtoincreasetheiroutputinthehopethatgreatersalescouldoffsetlowerpricesandhelpmaintainincome.Buttheconsequenceofmillionsoffarmerstryingtoincreasetheiroutputledtoafurtherfallinpricesandfarmincomes.Sotherewasaviciousspiral,inwhichfarmpricesandfarmincomeschasedeachotherdownward.Whentheover-supplyoffarmproducts,whichalreadyexistedinthelate1920s,wasaccentuatedbythefallindemandforfoodandrawmaterialsthatfollowedthedownturninindustrialinvestmentin1928and1929,thesituationbecameevenmoresevere.Thepricesoffarmproductsfellbymorethanhalfinthethreeyearsafter1929,andAmericanfarmincomesufferedaccordingly;andthisfallinfarmincomeitselfledtoafurtherdeclineinconsumptionandhence,incapitalinvestmentaswell.Onceittookhold,theslumpquicklyspreadtoEuropeandotherpartsoftheworldduetothecomplexnatureofinternationalfinancialdealingsandtheattemptsbygovernmentstoprotecttheircurrenciesbyimposingprotectionisttariffsonforeignimports.TheseverityoftheDepressionwassuchthatfullemploymentandproductionwerenotseenagainuntilthelate1930s.Glossary:slump:asuddenfallinprice,amount,orvalue

{{B}}Set 6 Biology Cardiac Muscle{{/B}}

Directions: Read the passage. Then answer the questions. Give yourself 20 minutes to complete this practice set. WILLIAM SMITH In 1769 in a little town in Oxfordshire, England, a child with the very ordinary name of William Smith was born into the poor family of a village blacksmith. He received rudimentary village schooling, but mostly he roamed his uncle's farm collecting the fossils that were so abundant in the rocks of the Cotswold hills. When he grew older, William Smith taught himself surveying from books he bought with his small savings, and at the age of eighteen he was apprenticed to a surveyor of the local parish. He then proceeded to teach himself geology, and when he was twenty-four, he went to work for the company that was excavating the Somerset Coal Canal in the south of England. This was before the steam locomotive, and canal building was at its height. The companies building the canals to transport coal needed surveyors to help them find the coal deposits worth mining as well as to determine the best courses for the canals. This job gave Smith an opportunity to study the fresh rock outcrops created by the newly dug canal. He later worked on similar jobs across the length and breadth of England, all the while studying the newly revealed strata and collecting all the fossils he could find. Smith used mail coaches to travel as much as 10,000 miles per year. In 1815 he published the first modern geological map, "A Map of the Strata of England and Wales with a Part of Scotland," a map so meticulously researched that it can still be used today. In 1831 when Smith was finally recognized by the Geological Society of London as the "father of English geology," it was not only for his maps but also for something even more important. Ever since people had begun to catalog the strata in particular outcrops, there had been the hope that these could somehow be used to calculate geological time. But as more and more accumulations of strata were cataloged in more and more places, it became clear that the sequences of rocks sometimes differed from region to region and that no rock type was ever going to become a reliable time marker throughout the world. Even without the problem of regional differences, rocks present a difficulty as unique time markers. Quartz is quartz—a silicon ion surrounded by four oxygen ions—there's no difference at all between two-million-year-old Pleistocene quartz and Cambrian quartz created over 500 million years ago. As he collected fossils from strata throughout England, Smith began to see that the fossils told a different story from the rocks. Particularly in the younger strata, the rocks were often so similar that he had trouble distinguishing the strata, but he never had trouble telling the fossils apart. While rock between two consistent strata might in one place be shale and in another sandstone, the fossils in that shale or sandstone were always the same. Some fossils endured through so many millions of years that they appear in many strata, but others occur only in a few strata, and a few species had their births and extinctions within one particular stratum. Fossils are thus identifying markers for particular periods in Earth's history. Not only could Smith identify rock strata by the fossils they contained, he could also see a pattern emerging: certain fossils always appear in more ancient sediments, while others begin to be seen as the strata become more recent. By following the fossils, Smith was able to put all the strata of England's earth into relative temporal sequence. About the same time, Georges Cuvier made the same discovery while studying the rocks around Paris. Soon it was realized that this principal of faunal (animal) succession was valid not only in England or France but virtually everywhere. It was actually a principle of floral succession as well, because plants showed the same transformation through time as did fauna. Limestone may be found in the Cambrian or—300 million years later—in the Jurassic strata, but a trilobite—the ubiquitous marine arthropod that had its birth in the Cambrian—will never be found in Jurassic strata, nor a dinosaur in the Cambrian.

Reading4"TheDigitalDivide"TheChallengeofTechnologyandEquityInformationtechnologyisinfluencingthewaymanyofusliveandworktoday.WeusetheIntemettolookandapplyforjobs,shop,conductresearch,makeairlinereservations,andexploreareasofinterest.Weusee-mailandtheInternettocommunicateinstantaneouslywithfriendsandbusinessassociatesaroundtheworld.Computersarecommonplaceinhomesandtheworkplace.→Althoughthenumberoftnternetusersisgrowingexponentiallyeachyear,mostoftheworld'spopulationdoesnothaveaccesstocomputersorthelnternet.Only6percentofthepopulationindevelopingcountriesareconnectedtotelephones.Althoughmorethan94percentofU.S.householdshaveatelephone,only42percenthavepersonalcomputersathomeand26percenthaveIntemetaccess.Thelackofwhatmostofuswouldconsiderabasiccommunicationsnecessity—thetelephone—doesnotoccurjustindevelopingnations.OnsomeNativeAmericanreservationsonly60percentoftheresidentshaveatelephone.Themovetowirelessconnectionsmayeliminatetheneedfortelephonelines,butitdoesnotremovethebarriertoequipmentcosts.→WhohasInternetaccess?Fiftypercentofthechildreninurbanhouseholdswithanincomeover$75,000haveInternetaccess,comparedwith2percentofthechildreninlow-income,ruralhouseholds.Nearlyhalfofcollege-educatedpeoplehaveInternetaccess,comparedto6percentofthosewithonlysomehighschooleducation.Fortypercentofhouseholdswithtwoparentshaveaccess;15percentoffemale,single-parenthouseholdsdo.Thirtypercentofwhitehouseholds,11percentofblackhouseholds,and13percentofHispanichouseholdshaveaccess.Teensandchildrenarethetwofastest-growingsegmentsofInternetusers.ThedigitaldividebetweenthepopulationswhohaveaccesstotheInternetandinformationtechnologytoolsisbasedonincome,race,education,householdtype,andgeographiclocation.Only16percentoftheruralpoor,ruralandcentralcityminorities,younghouseholders,andsingleparentfemalehouseholdsareconnected.→AnotherproblemthatexacerbatesthesedisparitiesisthatAfrican-Americans,Hispanics,andNativeAmericansholdfewofthejobsininformationtechnology.Womenholdabout20percentofthesejobsandarereceivingfewerthan30percentofthecomputersciencedegrees.Theresultisthatwomenandmembersofthemostoppressedethnicgroupsarenoteligibleforthejobswiththehighestsalariesatgraduation.Baccalaureatecandidateswithdegreesincomputersciencewereofferedthehighestsalariesofallnewcollegegraduatesin1998at$44,949.Dosimilardisparitiesexistinschools?Morethan90percentofallschoolsinthecountryarewiredwithatleastoneInternetconnection.ThenumberofclassroomswithInternetconnectionsdiffersbytheincomelevelofstudents.Usingthepercentageofstudentswhoareeligibleforfreelunchesataschooltodetermineincomelevel,weseethatnearlytwiceasmanyoftheschoolswithmoreaffluentstudentshavewiredclassroomsasthosewithhighconcentrationsoflow-incomestudents.→AccesstocomputersandtheInternetwillbeimportantinreducingdisparitiesbetweengroups.Itwillrequiregreaterequalityacrossdiversegroupswhosemembersdevelopknowledgeandskillsincomputerandinformationtechnologies.IfcomputersandtheInternetaretobeusedtopromoteequality,theywillhavetobecomeaccessibletopopulationsthatcannotcurrentlyaffordtheequipmentwhichneedstobeupdatedeverythreeyearsorso.However,accessaloneisnotenough.Studentswillhavetobeinteractingwiththetechnologyinauthenticsettings.Astechnologybecomesatoolforlearninginalmostallcoursestakenbystudents,itwillbeseenasameanstoanendratherthananendinitself.Ifitisusedinculturallyrelevantways,allstudentscanbenefitfromitspower.

TheEvolutionofBirdsBirdsBeganasFeatheredReptilesBirdsevolvedduringthegreatreptilianradiationoftheMesozoicera.Amnioticeggsandscalesonthelegsarejusttwoofthereptilianfeaturesweseeinbirds.Butmodernbirdslookquitedifferentfrommodernreptilesbecauseoftheirfeathersandotherdistinctiveflightequipment.CharacteristicsofBirdsAlmosteverypartofatypicalbird'sanatomyismodifiedinsomewaythatenhancesflight.Theboneshaveaninternalstructurethatishoneycombed,makingthemstrongbutlight.Theskeletonofafrigatebird,forinstance,hasawingspanofmorethan2metersbutweighsonlyabout113grams.Anotheradaptationreducingtheweightofbirdsistheabsenceofsomeorgans.Females,forinstance,haveonlyoneovary.Also,modernbirdsaretoothless,anadaptationthattrimstheweightofthehead.Foodisnotchewedinthemouthbutgroundinthegizzard,adigestiveorgannearthestomach.(Crocodilesalsohavegizzards,asdidsomedinosaurs.)Thebird'sbeak,madeofkeratin,hasproventobeveryadaptableduringavianevolution,takingonagreatvarietyofshapessuitablefordifferentdiets.Flyingrequiresagreatexpenditureofenergyfromanactivemetabolism.Birdsareendothermic;theyusetheirownmetabolicheattomaintainawarm,constantbodytemperature.Feathersand,insomespecies,layersoffatprovideinsulationthatenablesbirdstoretaintheirmetabolicallygeneratedheat.Anefficientrespiratorysystemandacirculatorysystemwithafour-chamberedheartkeeptissueswellsuppliedwithoxygenandnutrients,supportingahighrateofmetabolism.Thelungshavetinytubesleadingtoandfromelasticairsacsthathelpdissipateheatandreducethedensityofthebody.Forsafeflight,senses,especiallyvision,mustbeacute.Birdshaveexcellenteyes,perhapsthebestofallthevertebrates.Thevisualareasofthebrainsarewelldeveloped,asarethemotorareas;flightalsorequiresexcellentcoordination.Withbrainsproportionatelylargerthanthoseofreptilesandamphibians,birdsgenerallydisplayverycomplexbehavior.Avianbehaviorisparticularlyintricateduringbreedingseason,whenbirdsengageinelaborateritualsofcourtship.Becauseeggsareshelledwhenlaid,fertilizationmustbeinternal.Copulationinvolvescontactbetweenthemates'vents,theopeningstotheircloacae.Aftereggsarelaid,theavianembryomustbekeptwarmthroughbroodingbythemother,father,orboth,dependingonthespecies.Abird'smostobviousadaptationforflightisitswings.Birds'wingsareairfoilsthatillustratethesameprinciplesofaerodynamicsasthewingsofanairplane.Providingpowerforflight,birdsflaptheirwingsbycontractionsoflargepectoral(breast)musclesanchoredtoakeelonthesternum(breastbone).Somebirds,suchaseaglesandhawks,havewingsadaptedforsoaringonaircurrentsandflaptheirwingsonlyoccasionally;otherbirds,includinghummingbirds,mustflapcontinuouslytostayaloft.Ineithercase,itistheshapeandarrangementofthefeathersthatformthewingsintoanairfoil.Thefastestbirdsaretheappropriatelynamedswifts,whichcanfly170km/hr.Inbeingbothextremelylightandstrong,feathersareamongthemostremarkableofvertebrateadaptations.Feathersaremadeofkeratin,thesameproteinthatformsourhairandfingernailsandthescalesofreptiles.Feathersmayhavefunctionedfirstasinsulationduringtheevolutionofendothermy,onlylaterbeingco-optedasflightequipment.Theevolutionofflightrequiresradicalalterationinbodyform,butflightprovidesmanybenefits.Itenhanceshuntingandscavenging:manybirdsexploitflyinginsects,anabundant,highlynutritiousfoodresource.Flightalsoprovidesreadyescapefromearthboundpredatorsandenablessomebirdstomigrategreatdistancestoutilizedifferentfoodresourcesandseasonalbreedingareas.Thebirdthattravelsfarthestinitsannualmigrationisthearctictern,whichfliesround-tripbetweentheNorthPoleandSouthPoleeachyear.Analysesoffossilizedskeletonssupportthehypothesisthattheclosestreptilianrelativesofbirdswerethetheropods,agroupofrelativelysmall,bipedalcarnivorousdinosaurs.Mostresearchersagreethattheancestorofbirdswasafeatheredtheropod.However,somescientistsplacetheoriginofbirdsmuchearlier,fromanancestorcommontobothbirdsanddinosaurs.Theintensecurrentinterestintheoriginofbirdswillundoubtedlybringusclosertounderstandinghowthesemastersoftheskyevolvedfromnonflyingreptiles.Glossary:cloacae:theopeningtothereproductiveandintestinaltractbrooding:tohatcheggsbysittingonthenest

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{{B}}Set5{{/B}}{{B}}PresidentHoover'sPoliticsDuringtheGreatDepression{{/B}}Atfirsteverythingseemedfineanddandy.Americawasenjoyingoneofthebiggesteconomicsurgesinthenation'shistory.However,eventhoughAmericabenefitedfromtheeconomicboomofthesocalled"RoaringTwenties",theimbalancebetweentherichandthepoorcombinedwiththeproductionofmoreandmoregoodsandrisingpersonaldebtcausedoneofthebiggestrecessionsinhistory.OnBlackTuesday,October29,1929,thestockmarketcrashed,triggeringtheGreatDepression,whichwastheworsteconomiccollapseinthehistoryofthemodem,industrialworld.ItspreadfromtheUnitedStatesandrippledouttotherestoftheworld,withbanksfailingandbusinessesgoingbustforoveraspanofadecade,leavingmorethanaquarteroftheworkingforceinAmericawithoutjobs.PresidentHerbertHoover,underestimatingtheseriousnessofthecrisis,calledit"apassingincidentinournationallives,"andassuredAmericansthatitwouldbeoverwithintwomonths.Hooverdidnotthinkthatthefederalgovernmentshouldofferrelieftothepoverty-strickenpopulationbecausehefirmlybelievedinindividualism.Focusingoneconomicprogramstohelpfinancebusinessesandbanks,Hoovermetwithresistancefrombusinessexecutiveswhopreferredtolayoffworkers.BlamedbymanyfortheGreatDepression,Hooverwaswidelyridiculed.Hoover'seconomywasputtothetestwiththeonsetoftheGreatDepressionin1929.Itwashisvocalstanceonnon-interventionthatledtoDemocraticcriticismthatHooverwasa"sittingduck"president;ontheotherhand,hismorepro-freemarketopponentsalsodeniedhewasalaissez-fairepresidentandcondemnedhimforbeinganinterventionist.Hoovertriedtorestoreconfidencewithaseriesofspeechesbuthisweakspeakingstylehamperedtheseefforts.Thebiggestproblemwasthathispredictionsofanupturnjustaroundthecomernevermaterialized.Hispromiseswerenotdeliveredandhelostalotofthepublic'sconfidence.Together,thegovernmentandbusinessesactuallyspentmoreinthefirsthalfof1930thanthepreviousyear;yetfrightenedconsumerscutbacktheirexpendituresbytenpercent.Aseveredroughtravagedtheagriculturalheartlandbeginninginthesummerof1930,whileforeignbanksdeclaredbankruptcy,drainingU.S.wealthanddestroyingworldtrade.Thecombinationofthesefactorscausedadownwardspiral:asearningfell,domesticbankscollapsed,andmortgageswerecalledin.Hoover'shold-the-linepolicyinwageslastedlittlemorethanayear.Unemploymentsoaredfromfivemillionin1930tooverelevenmillionin1931,causingthissharprecessiontobecometheGreatDepression.In1930,HooverreluctantlysignedtheSmoot-HawleyTariffAct,whichraisedtariffsonover20,000dutiableitems.TheTariff,combinedwiththe1932RevenueAct,whichhikedtaxesandfeesacrosstheboard,isoftenblamedfordeepeningtheeconomicdepression,andisconsideredbysometobeHoover'sbiggestpoliticalmistakes.Moreover,theFederalReserveSystem'stighteningofthemoneysupplyisalsoregardedbymostmodemeconomistsasamistakentactic,underthecircumstances.Inordertocovertheexpensesofthesegovernmentprograms,HooveragreedtooneofthelargesttaxincreasesinAmericanhistory.TheRevenueActof1932raisedtaxesonthehighestincomesfrom25%to63%,whiletheestatetaxwasdoubled,andcorporatetaxeswereraisedbyalmost15%.Also,a"checktax"wasincludedthatplaceda2-centtaxonallbankchecks.Duringthe1932elections,Hoover'sopponentsblastedtheRepublicanincumbentforspendingandtaxingtoomuch,increasingnationaldebt,raisingtariffs,andblockingtrade,aswellasplacingmillionsonthedoleofthegovernment.RooseveltattackedHooverfor"recklessandextravagant"spending,andofleading"thegreatestspendingadministrationinpeacetimeinallofhistory."Unemploymentroseto24.9%bytheendofHoover'spresidencyin1933,ayearthatisconsideredtobethedepthoftheGreatDepression.

SocialReadjustmentScalesHolmesandRahe(1967)developedtheSocialReadjustmentRatingScale(SRRS)tomeasurelifechangeasaformofstress.Thescaleassignsnumericalvaluesto43majorlifeeventsthataresupposedtoreflectthemagnitudeofthereadjustmentrequiredbyeachchange.Inrespondingtothescale,respondentsareaskedtoindicatehowoftentheyexperiencedanyofthese43eventsduringacertaintimeperiod(typically,thepastyear).Thepersonthenaddsupthenumbersassociatedwitheacheventchecked.TheSRRSandsimilarscaleshavebeenusedinthousandsofstudiesbyresearchersallovertheworld.Overall,thesestudieshaveshownthatpeoplewithhigherscoresontheSRRStendtobemorevulnerabletomanykindsofphysicalillness--andmanytypesofpsychologicalproblemsaswell(DerogatisGruen,1993;Scully,TosiMonroeWashington,2000).First,theassumptionthattheSRRSmeasureschangeexclusivelyhasbeenshowntobeinaccurate.Wenowhaveampleevidencethatthedesirabilityofeventsaffectsadaptationaloutcomesmorethantheamountofchangethattheyrequire(TurnerWheaton,1994).Fifth,thecorrelationbetweenSRRSscoresandhealthoutcomesmaybeinflatedbecausesubjects'neuroticismaffectsboththeirresponsestostressscalesandtheirself-reportsofhealthproblems.Neuroticindividualshaveatendencytorecallmorestressthanothersandtorecallmoresymptomsofillnessthanothers(Watson,DavidDenisoffMalefo,2000).TheLESrevisesandbuildsontheSRRSsurveyinavarietyofwaysthatcorrect,atleastinpart,mostoftheproblemsjustdiscussed.Specifically,theLESrecognizesthatstressinvolvesmorethanmerechangeandasksrespondentstoindicatewhethereventshadapositiveornegativeimpactonthem.Thisstrategypermitsthecomputationofpositivechange,negativechange,andtotalchangescores,whichhelpsresearchersgainmuchmoreinsightintowhichfacetsofstressaremostcrucial.TheLESalsotakesintoconsiderationdifferencesamongpeopleintheirappraisalofstress,bydroppingthenormativeweightsandreplacingthemwithpersonallyassignedweightingsoftheimpactofrelevantevents.Ambiguityinitemsisdecreasedbyprovidingmoreelaboratedescriptionsofmanyitemstoclarifytheirmeaning.TheLESdealswiththefailureoftheSRRStosamplethefulldomainofstressfuleventsinseveralways.First,somesignificantomissionsfromtheSRRShavebeenaddedtotheLES.Second,theLESallowstherespondentstowriteinpersonallyimportanteventsthatarenotincludedonthescale.Third,theLEShasanextrasectionjustforstudents.Sarasonetal.(1978)suggestthatspecial,tailoredsectionsofthissortbeaddedforspecificpopulationswheneveritisuseful.

Directions : Read the passage. Then answer the questions. Give yourself 20 minutes to complete this practice set. BEGGING BY NESTLINGS Many signals that animals make seem to impose on the signalers costs that are overly damaging. A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. These loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, resulting in the death of the defenseless nestlings. In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that "noisy" nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials. Further evidence for the costs of begging comes from a study of differences in the begging calls of warbler species that nest on the ground versus those that nest in the relative safety of trees. The young of ground-nesting warblers produce begging cheeps of higher frequencies than do their tree-nesting relatives. These higher-frequency sounds do not travel as far, and so may better conceal the individuals producing them, who are especially vulnerable to predators in their ground nests. David Haskell created artificial nests with clay eggs and placed them on the ground beside a tape recorder that played the begging calls of either tree-nesting or of ground-nesting warblers. The eggs "advertised" by the tree-nesters" begging calls were found bitten significantly more often than the eggs associated with the ground-nesters" calls. The hypothesis that begging calls have evolved properties that reduce their potential for attracting predators yields a prediction: baby birds of species that experience high rates of nest predation should produce softer begging signals of higher frequency than nestlings of other species less often victimized by nest predators. This prediction was supported by data collected in one survey of 24 species from an Arizona forest, more evidence that predator pressure favors the evolution of begging calls that are hard to detect and pinpoint. Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where several other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds. If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging, then parents should make food delivery decisions on the basis of their offspring"s calls. Indeed, if you take baby tree swallows out of a nest for an hour, feeding half the set and starving the other half, when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than those who beg less vigorously. As these experiments show, begging apparently provides a signal of need that parents use to make judgments about which offspring can benefit most from a feeding. But the question arises, why don"t nestlings beg loudly when they aren"t all that hungry? By doing so, they could possibly secure more food, which should result in more rapid growth or larger size, either of which is advantageous. The answer lies apparently not in the increased energy costs of exaggerated begging—such energy costs are small relative to the potential gain in calories—but rather in the damage that any successful cheater would do to its siblings, which share genes with one another. An individual"s success in propagating his or her genes can be affected by more than just his or her own personal reproductive success. Because close relatives have many of the same genes, animals that harm their close relatives may in effect be destroying some of their own genes. Therefore, a begging nestling that secures food at the expense of its siblings might actually leave behind fewer copies of its genes overall than it might otherwise.

Select the appropriate sentences from the answer choices and match them to the period before or after the five-even shift．TWO of the answer choices will NOT be used．This question is worth 3 points． Answer Choices A．The child's brain waves have rhythms similar to those of adults． B．The child's cognitive development cannot be measured scientifically． C．The child learns in simple ways and can focus on only one quality at a time． D．The child knows that the quantity stays the same when objects are rearranged． E．The child cannot distinguish between right and wrong． F．The child can quickly solve problems involving conservation． G．The child is not able to understand the conservation of quantity．

Global Developments Sociologists tell us there is a link between private lives and social forces. An outstanding example of such a link is the contrast in life chances between people in developed and in less developed countries. A child born in, say, the United States or Switzerland is not a better or more deserving person than one born in Ethiopia or Brazil. Yet because of social forces beyond individual control, each child faces the prospect of living out a lifetime under utterly different material conditions. Why should this be? What can account for the fact that some societies have become heavily industrialized and economically advanced, while others are changing so much more slowly? Social scientists have offered two different explanations. One emphasizes a universal but uneven process of modernization and economic growth; the other focuses on a worldwide system of political and economic inequality. Some social scientists view development in terms of modernization, a process of economic, social and cultural change that facilitates the transition from pre-industrial to industrial society. Modernization theorists claim that the various countries of the world are converging on a basically similar social type, the modern industrialized society. Some 250 years ago, the developed countries of today also had rudimentary, pre-industrial economies, but because they modernized relatively quickly, they now have productive economies that offer high living standards. During the same period, however, the poor countries have been slow to modernize. Differences in development, therefore, are largely the result of uneven modernization; but as "modern" features spread from the developed to the less developed countries, they too will follow the path to industrialization and affluence. What kinds of change does modernization entail? Some modernization theorists emphasize a change in individual psychology. They claim that people in the developed societies are more likely to have a work ethic, a desire for achievement, a willingness to defer gratification, a sense of control over their destiny, a strong sense of individualism. In contrast, a lack of ambition, an orientation toward the present, a fatalistic outlook, and a weak sense of individualism are said to be typical of people in more traditional societies.A. [■] Other modernization theorists emphasize sweeping structural changes in society.B. [■] Traditional societies are more likely to have an extended family system, in which kinship obligations encourage people to remain, physically and socially, where they started. C. [■] Similarly, modernization involves such features as heavy urbanization, extensive schooling, advanced technology, low population growth, a legal-rational political system, and a range of sophisticated services such as efficient transport, banking and communications.D. [■] On the whole, these features are lacking or inadequate in less developed countries, where government is usually authoritarian, the population is predominately rural and ill educated, and the necessary services are not in place. Other social scientists view development in the context of the world system, a network of unequal economical and political relationships among the developed and the less developed countries. This international system consists of a "core" of highly industrialized countries, and a "periphery" of less developed countries that are dependent on and exploited by those at the core. World-system theorists point out that the peoples of the third world were quite capable of providing for themselves before "modern" ideas and technologies began to "diffuse" from the colonial powers. In fact, they claim, development and underdevelopment proceeded simultaneously over a period of more than two centuries as the richer countries financed their own industrial expansion by draining the surplus resources of the poorer ones. The colonial system finally broke down when the last of the colonies won their formal independence around the middle of the twentieth century. But by then a new international relationship had been established: neocolonialism, the informal political and economic domination of some societies by others, such that the former are able to exploit the labor and resources of the latter for their own purposes. In essence, the world system is a form of international stratification, with a wealthy minority enjoying a disproportionate share of the planet's resources and using various means—political, economic, and sometimes military—to maintain their position.

{{B}}Set4{{/B}}{{B}}Lichens{{/B}}Tobecertain,alichenisnotthemostconspicuousofplants.Lichensgrowinunassumingfashiononrocks,logsandotherexposedsurfacesinawiderangeofhabitatsaroundtheworld.Totheuntrainedeyetheylooklikelittlemorethancrustypatchesthat,atfirstglance,mighteasilybemistakenforadiscolorationofthesurface.Eveniftheaveragepersonshouldhappentonoticethelichen'spresenceandcorrectlyidentifyitassomeformoflife,heisunlikelytogomuchfurtherincontemplatingit.Thoughalmosttotallyignoredbythelayperson,forthebotanist,lichensareoneofthemostfascinatingofallplants,andoneofthemostintenselystudied.Theyarethesubjectofsomuchscientificscrutinyprimarilybecausealichenisnotjustoneplant.Itis,infact,acompositeorganismmadeupoffungusandalgaelivingtogetherinacloseassociationthatis,presumably,beneficialtoboth.Whenthesetwoverydifferentplantscombine,theresultisauniqueandverylong-livedcompositeorganismthatappears,atleastonamacroscopicscale,tobeaunitaryplant.Itisanorganismthatbearsnoresemblancetoeitherofitsconstituentswhentheyareobservedindividually.Theseparatefungalandalga)elementscanberecognizedonlywhenthebodyoftheplant,calledathallusbecausetherearenostemsorroots,issectionedandexaminedunderamicroscope.Whenviewedthisway,thefunguscomponentdominatesthepicture,asitaccountsforninetenthsofthetotalbodymassofthelichen.But,entrappedwithinit,clearlyvisibleasdarkspots,arethealgaecells.Essentially,nothingisknownofhowanamorphousmassoffungiandalgaecometogethertoformahighlydifferentiated,structurallystablebody.Despiteallthescientificscrutinylichenshavereceived,itisstillnotentirelycertainwhateachmembergainsfromtheassociation.Someresearchershavespeculatedthatthefungijoinintherelationshipbecausetheyareabletoconsumethealgaecellsastheydieandthereforeareguaranteedafoodsupply.Itiswell-knownthatthechlorophyll-containingalgaecellsproducefoodbymeansofphotosynthesis.Theremaybesomemechanism,stillunknowntous,throughwhichthisenergysourceisutilizedbythefungus.Funguspossessesnochlorophyllofitsown.Howorevenwhetherthealgaebenefitfromthisassociationisstilllesscertain,thoughwecaneasilyimaginethattheygainmechanicalprotectionfromtheelementsbybeingtightlyenvelopedinthestructuralfibersofthefungusbody.Theyshouldalsobenefitfromretentionofwaterbetweenthefibers.Thehardinessoflichenshasmadethemwhatbotaniststerm"pioneerplants".Thisreferstotheirabilitytocolonizehabitatswhereotherplantsdonotexist.Theyarecommononbarrenrockysurfaces,wherethelackofsoilprecludestheestablishmentofmostotherkindsofplantlife.TheycanevenbefoundinplacesashostileandextremeastheinterioroftheAntarcticcontinent.Althoughtheyaremostoftenassociatedwithfarnorthernorsouthernenvironments,theyhavebeenfoundlivinginsunbakeddesertsoilsthatareotherwisedevoidoflife.ThemosthighlyspecializedlichensaretheendolithicspeciesoftheAntarctic,whichasthenameindicates,liveinsiderocks,formingmoreorlesscontinuoustissuestructuresbetweentherockcrystals.Asremarkableintheirrobustnessaslichensare,thereisonekindofanenvironmentwhichtheyaregenerallyunabletotolerate.Habitatsthatareheavilyaffectedbypollutionaxenoticeablydevoidoflichens.Theseorganismsareespeciallysusceptibletosulfurdioxidepoisoningandtheyabsorbandaccumulateothertoxinsaswell;bothairandwaterborne.Thisheightenedsensitivityarisesfromthefactthatlichenshavenomeansofriddingtheirtissuesofthesesubstances.Itisthoughtthatthepollutantsaccumulateanddestroythechlorophyllinthealgaecells,thusdisruptingtherelationshipwiththefungus.Thisparticularcharacteristicmakeslichensanespeciallygoodindicatorofenvironmentalhealth.Surveyscurrentlyindicatethatlichensarecompletelyabsentfromurbancenterswithpopulationsof100,000ormore.