SeetheDifference

Haveyoueverheldalizard?Howabouta snakeoraturtle?Ineachofthesecases,anendotherm(you)touchesanectotherm. Theectotherm’sbodytemperatureislikelylowerthanyours.Youcouldn’ttellthatjust bylookingattheanimal,andyouprobablywouldn’tbeabletofeeladifference,either.Butthedifferenceisstarkwhenyoulookatthermalinfraredimages.Theseimagesshowhowcoolorwarmanobjectisbymeasuringtheamountofheatitgives off.

hand

lizard

HOTTER

COLDER

Byfanningitsears,thiselephantbeginstocool down.

Thisspider’sbodyiscoolerthanits environment.

Lookatthethermalimage above
ofsomeoneholdingalizard.Asthescaleshows,thebrighterthecolor,thewarmerthetemperature.Thebrightredofthehandshowsthatthepersonmaintainsawarm,steadybodytemperature,eventhoughthesurroundingairis cooler.


Thelizardshowsupmostlyasshadesofblue.Beforebeingheld,itappearedasdarkblueorblack,justlikethebackground.Nosurprisethere—thelizard’sbodytemperaturewasthesameasthetemperatureofthesurrounding air.


Butwhathappensasthereptileandmammaltouch?Thereptileabsorbsheatfromtheperson’shand.Thelizard’stailstillappearsdarkbluebecauseitisn’tbeingtouched.Therestofthelizard’sbodyiswarmingnoticeably,withitsfeetandlegsshowingupasgreenandyellow.Howdoyouthinkthelizardwouldappearifthepersoncontinuedtohold it?

Thiscatgeneratesitsownbodyheat.
Itleavesbehindatrailofwarm pawprints.

Watchasapersonleaves
warmfootprintsonacold floor.

HOTTER

COLDER

COLDER

HOTTER

gharial

Asthisgharialsoaksupthesun’srays,itsbodytemperaturebeginsto rise.

Foodalsoprovidesenergy.Thebodyusesthatenergytomove.Energyfromfoodalsoproducesheat.Inthisway,ananimal’sbodyislikeafurnace,exceptinsteadofburningnaturalgasoroil,thebody“burns” food.


Thefasterananimal’smetabolism,the
moreenergytheanimalhasforkeepingwarmandmovingaround.Whichkindofanimal—ectothermorendotherm—doyouthinkhasthefaster metabolism?

ALivingFurnace

Whycansomeanimalsmaintainaconstantinternaltemperaturewhileotherscannot?Theanswercomesdowntooneword—metabolism.


Ananimal’smetabolismisallofthechemicalreactionsthattakeplaceintheanimal’sbody,andinyourbody,too.Tinymoleculesareconstantlycombiningandbreakingapartinbodycells,formingnewsubstances.Mostofthesechemicalreactionsinthebodyoccurasfoodbreaks down.


Youneedfoodtostayalive.Sodoeseveryotherlivingthing.Foodprovidesthematerialstogrowandtorepairdamagedcells.Forinstance,ifyoucutyourfinger,newcellsgrowoutfromeithersideofthecutandhealit.Thematerialsforthosenewcellscomefromthefoodyou eat.

HOTTER

COLDER

meerkats

Thesemeerkatsdon’tneedtowaitforthesun;theyregulatetheirownbodyheatandarealready warm.

flamingos

HOTTER

COLDER

Someoftheseflamingoshaveonelegthatishotterthantheother.Whenaflamingostandsononeleg,thatleglosesheat,whiletheotherlegistuckedupnexttoitsbodykeeping warm.

Youguessedit—endotherms.Themetabolismofbirdsandmammals,includinghumans,isfastenoughtogenerateconstantwarmth,allowingtheanimalstomaintainahighbodytemperature.Birdshavethefastestmetabolismandthehighestbodytemperature, 40o Cto 42o C (104o F to 108o F).Canyouthinkofareasonbirdswouldneedsuchafastmetabolism?Thinkabouthowbirdsmove.Thehighrateofmetabolismproducestheenergybirdsneedto fly.


Ontheotherhand,anectotherm’smetabolismisslow.Itcan’tgenerateenoughheattowarmtheanimal’sbody.Anectotherm’smetabolismdependsonthetemperatureof theenvironment.Whentheairwarmsup,anectotherm’smetabolism increases.