托福考试阅读模拟冲刺题_1.docx

托福考试阅读模拟冲刺题托福考试2017阅读模拟冲刺题Thefailuresandreverseswhichawaitmen-andoneafteranothersaddenthebrowofyouth-addadignitytotheprospectofhumanlife,whichnoArcadiansuccesswoulddo.以下是小编为大家搜索整理的托福考试2017阅读模拟冲刺题，希望能给大家带来帮助!更多精彩内容请及时关注我们应届毕业生考试网!Pheromonesaresubstancesthatserveaschemicalsignalsbetweenmembersofthesamespecies.Theyaresecretedtotheoutsideofthebodyandcauseotherindividualsofthespeciestohavespecificreactions.Pheromones,whicharesometimescalled"socialhormones,"affectagroupofindividualssomewhatlikehormonesdoanindividualanimal.Pheromonesarethepredominantmediumofcommunicationamonginsects(butrarelythesolemethod).Somespecieshavesimplepheromonesystemsandproduceonlyafewpheromones,butothersproducemanywithvariousfunctions.Pheromonesystemsarethemostcomplexinsomeoftheso-calledsocialinsects,insectsthatliveinorganizedgroups.Chemicalcommunicationdiffersfromthatbysightorsoundinseveralways.Transmissionisrelativelyslow(thechemicalsignalsareusuallyairborne),butthesignalcanbepersistent,dependinguponthevolatilityofthechemical,andissometimeseffectiveoveraverylongrange.Localizationofthesignalisgenerallypoorerthanlocalizationofasoundorvisualstimulusandisusuallyeffectedbytheanimal'smovingupwindinresponsetothestimulus.Theabilitytomodulateachemicalsignalislimited,comparedwithcommunicationbyvisualoracousticmeans,butsomepheromonesmayconveydifferentmeaningsandconsequentlyresultindifferentbehavioralorphysiologicalresponses,dependingontheirconcentrationorwhenpresentedincombination.Themodulationofchemicalsignalsoccursviatheelaborationofthenumberofexocrineglandsthatproducepheromones.Somespecies,suchasants,seemtobeveryarticulatecreatures,buttheirmediumofcommunicationisdifficultforhumanstostudyandappreciatebecauseofourownolfactory,insensitivityandthetechnologicaldifficultiesindetectingandanalyzingthesepheromones.Pheromonesplaynumerousrolesintheactivitiesofinsects.Theymayactasalarmsubstances,playaroleinindividualandgrouprecognition,serveasattractantsbetweensexes,mediatetheformationofaggregations,identifyforagi