BiologyFromWikipedia,thefreeencyclopedia

Biologydealswiththestudyofthemanylivingorganisms.(top:E.colibacteriaandgazelle)(bottom:Goliathbeetleandtreefern)

Biologyisanaturalscienceconcernedwiththestudyoflifeandlivingorganisms,includingtheirstructure,function,growth,evolution,distribution,andtaxonomy.[1]Modernbiologyisavastandeclecticfield,composedofmanybranchesandsubdisciplines.However,despitethebroadscopeofbiology,therearecertaingeneralandunifyingconceptswithinitthatgovernallstudyandresearch,consolidatingitintosingle,coherentfields.Ingeneral,biologyrecognizesthecellasthebasicunitoflife,genesasthebasicunitofheredity,andevolutionastheenginethatpropelsthesynthesisandcreationofnewspecies.Itisalsounderstoodtodaythatallorganismssurvivebyconsumingandtransformingenergyandbyregulatingtheirinternalenvironmenttomaintainastableandvitalcondition.

Subdisciplinesofbiologyaredefinedbythescaleatwhichorganismsarestudied,thekindsoforganismsstudied,andthemethodsusedtostudythem:biochemistryexaminestherudimentarychemistryoflifemolecularbiologystudiesthecomplexinteractionsamongbiologicalmoleculesbotanystudiesthebiologyofplantscellularbiologyexaminesthebasicbuildingblockofalllife,thecellphysiologyexaminesthephysicalandchemicalfunctionsoftissues,organs,andorgansystemsofanorganismevolutionarybiologyexaminestheprocessesthatproducedthediversityoflifeandecologyexamineshoworganismsinteractintheirenvironment.[2]

Contents

1History2Foundationsofmodernbiology

2.1Celltheory2.2Evolution

2.3Genetics

ErnstHaeckel'sTreeofLife(1879)

2.3Genetics2.4Homeostasis2.5Energy

3Studyandresearch3.1Structural3.2Physiological3.3Evolutionary3.4Systematic3.5Ecologicalandenvironmental

4Basicunresolvedproblemsinbiology5Branches6Seealso7References8Furtherreading9Externallinks

History

ThetermbiologyisderivedfromtheGreekword,bios,"life"andthesuffix,logia,"studyof."[3][4]TheLatinformofthetermfirstappearedin1736whenSwedishscientistCarlLinnaeus(CarlvonLinn)usedbiologiinhisBibliothecabotanica.Itwasusedagainin1766inaworkentitledPhilosophiaenaturalissivephysicae:tomusIII,continensgeologian,biologian,phytologiangeneralis,byMichaelChristophHanov,adiscipleofChristianWolff.ThefirstGermanuse,Biologie,wasusedina1771translationofLinnaeus'work.In1797,TheodorGeorgAugustRooseusedtheterminabook,GrundzgederLehrevanderLebenskraft,inthepreface.KarlFriedrichBurdachusedthetermin1800inamorerestrictedsenseofthestudyofhumanbeingsfromamorphological,physiologicalandpsychologicalperspective(PropdeutikzumStudiendergesammtenHeilkunst).ThetermcameintoitsmodernusagewiththesixvolumetreatiseBiologie,oderPhilosophiederlebendenNatur(180222)byGottfriedReinholdTreviranus,whoannounced:[5]

Theobjectsofourresearchwillbethedifferentformsandmanifestationsoflife,theconditionsandlawsunderwhichthesephenomenaoccur,andthecausesthroughwhichtheyhavebeeneffected.Thesciencethatconcernsitselfwiththeseobjectswewillindicatebythenamebiology[Biologie]orthedoctrineoflife[Lebenslehre].

Althoughmodernbiologyisarelativelyrecentdevelopment,sciencesrelatedtoandincludedwithinithavebeenstudiedsinceancienttimes.NaturalphilosophywasstudiedasearlyastheancientcivilizationsofMesopotamia,Egypt,theIndiansubcontinent,andChina.However,theoriginsofmodernbiologyanditsapproachtothestudyofnaturearemostoftentracedbacktoancientGreece.[6]WhiletheformalstudyofmedicinedatesbacktoHippocrates(ca.460BCca.370BC),itwasAristotle(384BC322BC)whocontributedmostextensivelytothedevelopmentofbiology.EspeciallyimportantarehisHistoryofAnimalsandotherworkswhereheshowednaturalistleanings,

andlatermoreempiricalworksthatfocusedonbiologicalcausationandthediversityoflife.Aristotle'ssuccessorattheLyceum,Theophrastus,wroteaseriesofbooksonbotanythatsurvivedasthemostimportantcontributionofantiquitytotheplantsciences,evenintotheMiddleAges.[7]

ScholarsofthemedievalIslamicworldwhowroteonbiologyincludedalJahiz(781869),AlDinawari(828896),whowroteonbotany,[8]andRhazes(865925)whowroteonanatomyandphysiology.MedicinewasespeciallywellstudiedbyIslamicscholarsworkinginGreekphilosophertraditions,whilenaturalhistorydrewheavilyonAristotelianthought,especiallyinupholdingafixedhierarchyoflife.

BiologybegantoquicklydevelopandgrowwithAntonvanLeeuwenhoek'sdramaticimprovementofthemicroscope.Itwasthenthatscholarsdiscoveredspermatozoa,bacteria,infusoriaandthediversityofmicroscopiclife.InvestigationsbyJanSwammerdamledtonewinterestinentomologyandhelpedtodevelopthebasictechniquesofmicroscopicdissectionandstaining.[9]

Advancesinmicroscopyalsohadaprofoundimpactonbiologicalthinking.Intheearly19thcentury,anumberofbiologistspointedtothecentralimportanceofthecell.Then,in1838,SchleidenandSchwannbeganpromotingthenowuniversalideasthat(1)thebasicunitoforganismsisthecelland(2)thatindividualcellshaveallthecharacteristicsoflife,althoughtheyopposedtheideathat(3)allcellscomefromthedivisionofothercells.ThankstotheworkofRobertRemakandRudolfVirchow,however,bythe1860smostbiologistsacceptedallthreetenetsofwhatcametobeknownascelltheory.[10][11]

Meanwhile,taxonomyandclassificationbecamethefocusofnaturalhistorians.CarlLinnaeuspublishedabasictaxonomyforthenaturalworldin1735(variationsofwhichhavebeeninuseeversince),andinthe1750sintroducedscientificnamesforallhisspecies.[12]GeorgesLouisLeclerc,ComtedeBuffon,treatedspeciesasartificialcategoriesandlivingformsasmalleableevensuggestingthepossibilityofcommondescent.Thoughhewasopposedtoevolution,BuffonisakeyfigureinthehistoryofevolutionarythoughthisworkinfluencedtheevolutionarytheoriesofbothLamarckandDarwin.[13]

SeriousevolutionarythinkingoriginatedwiththeworksofJeanBaptisteLamarck,whowasthefirsttopresentacoherenttheoryofevolution.[14]Hepositedthatevolutionwastheresultofenvironmentalstressonpropertiesofanimals,meaningthatthemorefrequentlyandrigorouslyanorganwasused,themorecomplexandefficientitwouldbecome,thusadaptingtheanimaltoitsenvironment.Lamarckbelievedthattheseacquiredtraitscouldthenbepassedontotheanimal'soffspring,whowouldfurtherdevelopandperfectthem.[15]However,itwastheBritishnaturalistCharlesDarwin,combiningthebiogeographicalapproachofHumboldt,theuniformitariangeologyofLyell,Malthus'swritingsonpopulationgrowth,andhisownmorphologicalexpertiseandextensivenaturalobservations,whoforgedamoresuccessfulevolutionarytheorybasedonnaturalselectionsimilarreasoningandevidenceledAlfredRusselWallacetoindependentlyreachthesameconclusions.[16][17]Althoughitwasthesubjectofcontroversy(whichcontinuestothisday),Darwin'stheoryquicklyspreadthroughthescientificcommunityandsoonbecameacentralaxiomoftherapidlydevelopingscienceofbiology.

Thediscoveryofthephysicalrepresentationofhereditycamealongwithevolutionaryprinciplesandpopulationgenetics.Inthe1940sandearly1950s,experimentspointedtoDNAasthecomponentofchromosomesthatheldthetraitcarryingunitsthathadbecomeknownasgenes.Afocusonnewkindsofmodelorganismssuchasvirusesandbacteria,alongwiththediscoveryofthedoublehelicalstructureofDNAin1953,markedthetransitiontotheeraofmoleculargenetics.Fromthe1950stopresenttimes,biologyhasbeenvastlyextendedinthemoleculardomain.ThegeneticcodewascrackedbyHarGobindKhorana,RobertW.HolleyandMarshallWarrenNirenbergafterDNAwasunderstoodtocontaincodons.Finally,theHumanGenomeProjectwaslaunchedin1990withthegoalofmappingthegeneral

Humancancercellswithnuclei(specificallytheDNA)stainedblue.Thecentralandrightmostcellareininterphase,sotheentirenucleiarelabeled.ThecellontheleftisgoingthroughmitosisanditsDNAhascondensed.

Naturalselectionofapopulationfordarkcoloration.

humangenome.Thisprojectwasessentiallycompletedin2003,[18]withfurtheranalysisstillbeingpublished.TheHumanGenomeProjectwasthefirststepinaglobalizedefforttoincorporateaccumulatedknowledgeofbiologyintoafunctional,moleculardefinitionofthehumanbodyandthebodiesofotherorganisms.

Foundationsofmodernbiology

Celltheory

Celltheorystatesthatthecellisthefundamentalunitoflife,andthatalllivingthingsarecomposedofoneormorecellsorthesecretedproductsofthosecells(e.g.shells,hairsandnailsetc.).Allcellsarisefromothercellsthroughcelldivision.Inmulticellularorganisms,everycellintheorganism'sbodyderivesultimatelyfromasinglecellinafertilizedegg.Thecellisalsoconsideredtobethebasicunitinmanypathologicalprocesses.[19]Inaddition,thephenomenonofenergyflowoccursincellsinprocessesthatarepartofthefunctionknownasmetabolism.Finally,cellscontainhereditaryinformation(DNA),whichispassedfromcelltocellduringcelldivision.

Evolution

Acentralorganizingconceptinbiologyisthatlifechangesanddevelopsthroughevolution,andthatalllifeformsknownhaveacommonorigin.ThetheoryofevolutionpostulatesthatallorganismsontheEarth,bothlivingandextinct,havedescendedfromacommonancestororanancestralgenepool.Thislastuniversalcommonancestorofallorganismsisbelievedtohaveappearedabout3.5billionyearsago.[20]Biologistsgenerallyregardtheuniversalityandubiquityofthegeneticcodeasdefinitiveevidenceinfavorofthetheoryofuniversalcommondescentforallbacteria,archaea,andeukaryotes(see:originoflife).[21]

IntroducedintothescientificlexiconbyJeanBaptistedeLamarckin1809,[22]evolutionwasestablishedbyCharlesDarwinfiftyyearslaterasaviablescientificmodelwhenhearticulateditsdrivingforce:naturalselection.[23][24][25](AlfredRusselWallaceisrecognizedasthecodiscovererofthisconceptashehelpedresearchandexperimentwiththeconceptofevolution.)[26]EvolutionisnowusedtoexplainthegreatvariationsoflifefoundonEarth.

Darwintheorizedthatspeciesandbreedsdevelopedthroughtheprocessesofnaturalselectionandartificialselectionorselectivebreeding.[27]Geneticdriftwasembracedasanadditionalmechanismofevolutionarydevelopmentinthemodernsynthesisofthetheory.[28]

APunnettsquaredepictingacrossbetweentwopeaplantsheterozygousforpurple(B)andwhite(b)blossoms

Theevolutionaryhistoryofthespecieswhichdescribesthecharacteristicsofthevariousspeciesfromwhichitdescendedtogetherwithitsgenealogicalrelationshiptoeveryotherspeciesisknownasitsphylogeny.Widelyvariedapproachestobiologygenerateinformationaboutphylogeny.TheseincludethecomparisonsofDNAsequencesconductedwithinmolecularbiologyorgenomics,andcomparisonsoffossilsorotherrecordsofancientorganismsinpaleontology.[29]Biologistsorganizeandanalyzeevolutionaryrelationshipsthroughvariousmethods,includingphylogenetics,phenetics,andcladistics.(Forasummaryofmajoreventsintheevolutionoflifeascurrentlyunderstoodbybiologists,seeevolutionarytimeline.)

Genetics

Genesaretheprimaryunitsofinheritanceinallorganisms.AgeneisaunitofheredityandcorrespondstoaregionofDNAthatinfluencestheformorfunctionofanorganisminspecificways.Allorganisms,frombacteriatoanimals,sharethesamebasicmachinerythatcopiesandtranslatesDNAintoproteins.CellstranscribeaDNAgeneintoanRNAversionofthegene,andaribosomethentranslatestheRNAintoaprotein,asequenceofaminoacids.ThetranslationcodefromRNAcodontoaminoacidisthesameformostorganisms,butslightlydifferentforsome.Forexample,asequenceofDNAthatcodesforinsulininhumansalsocodesforinsulinwheninsertedintootherorganisms,suchasplants.[30]

DNAusuallyoccursaslinearchromosomesineukaryotes,andcircularchromosomesinprokaryotes.AchromosomeisanorganizedstructureconsistingofDNAandhistones.Thesetofchromosomesinacellandanyotherhereditaryinformationfoundinthemitochondria,chloroplasts,orotherlocationsiscollectivelyknownasitsgenome.Ineukaryotes,genomicDNAislocatedinthecellnucleus,alongwithsmallamountsinmitochondriaandchloroplasts.Inprokaryotes,theDNAisheldwithinanirregularlyshapedbodyinthecytoplasmcalledthenucleoid.[31]Thegeneticinformationinagenomeisheldwithingenes,andthecompleteassemblageofthisinformationinanorganismiscalleditsgenotype.[32]

Homeostasis

Homeostasisistheabilityofanopensystemtoregulateitsinternalenvironmenttomaintainstableconditionsbymeansofmultipledynamicequilibriumadjustmentscontrolledbyinterrelatedregulationmechanisms.Alllivingorganisms,whetherunicellularormulticellular,exhibithomeostasis.[34]

Tomaintaindynamicequilibriumandeffectivelycarryoutcertainfunctions,asystemmustdetectandrespondtoperturbations.Afterthedetectionofaperturbation,abiologicalsystemnormallyrespondsthroughnegativefeedback.Thismeansstabilizingconditionsbyeitherreducingorincreasingtheactivityofanorganorsystem.Oneexampleisthereleaseofglucagonwhensugarlevelsaretoolow.

Energy

ThehypothalamussecretesCRH,whichdirectsthepituitaryglandtosecreteACTH.Inturn,ACTHdirectstheadrenalcortextosecreteglucocorticoids,suchascortisol.TheGCsthenreducetherateofsecretionbythehypothalamusandthepituitaryglandonceasufficientamountofGCshasbeenreleased.[33]

Basicoverviewofenergyandhumanlife.

Schematicoftypicalanimalcelldepictingthevariousorganellesandstructures.

Thesurvivalofalivingorganismdependsonthecontinuousinputofenergy.Chemicalreactionsthatareresponsibleforitsstructureandfunctionaretunedtoextractenergyfromsubstancesthatactasitsfoodandtransformthemtohelpformnewcellsandsustainthem.Inthisprocess,moleculesofchemicalsubstancesthatconstitutefoodplaytworolesfirst,theycontainenergythatcanbetransformedforbiologicalchemicalreactionssecond,theydevelopnewmolecularstructuresmadeupofbiomolecules.

Theorganismsresponsiblefortheintroductionofenergyintoanecosystemareknownasproducersorautotrophs.Nearlyalloftheseorganismsoriginallydrawenergyfromthesun.[35]Plantsandotherphototrophsusesolarenergyviaaprocessknownasphotosynthesistoconvertrawmaterialsintoorganicmolecules,suchasATP,whosebondscanbebrokentoreleaseenergy.[36]Afewecosystems,however,dependentirelyonenergyextractedbychemotrophsfrommethane,sulfides,orothernon

luminalenergysources.[37]

Someofthecapturedenergyisusedtoproducebiomasstosustainlifeandprovideenergyforgrowthanddevelopment.Themajorityoftherestofthisenergyislostasheatandwastemolecules.Themostimportantprocesses

forconvertingtheenergytrappedinchemicalsubstancesintoenergyusefultosustainlifearemetabolism[38]andcellularrespiration.[39]

Studyandresearch

Structural

Molecularbiologyisthestudyofbiologyatamolecularlevel.[40]Thisfieldoverlapswithotherareasofbiology,particularlywithgeneticsandbiochemistry.Molecularbiologychieflyconcernsitselfwithunderstandingtheinteractionsbetweenthevarioussystemsofacell,includingtheinterrelationshipofDNA,RNA,andproteinsynthesisandlearninghowtheseinteractionsareregulated.

Cellbiologystudiesthestructuralandphysiologicalpropertiesofcells,includingtheirbehaviors,interactions,andenvironment.Thisisdoneonboththemicroscopicandmolecularlevels,forunicellular

organismssuchasbacteria,aswellasthespecializedcellsinmulticellularorganismssuchashumans.Understandingthestructureandfunctionofcellsisfundamentaltoallofthebiologicalsciences.Thesimilaritiesanddifferencesbetweencelltypesareparticularlyrelevanttomolecularbiology.

Anatomyconsiderstheformsofmacroscopicstructuressuchasorgansandorgansystems.[41]

Geneticsisthescienceofgenes,heredity,andthevariationoforganisms.[42][43]Genesencodetheinformationnecessaryforsynthesizingproteins,whichinturnplayacentralroleininfluencingthefinalphenotypeoftheorganism.Inmodernresearch,geneticsprovidesimportanttoolsintheinvestigationofthefunctionofaparticulargene,ortheanalysisofgeneticinteractions.Withinorganisms,geneticinformationgenerallyiscarriedinchromosomes,whereitisrepresentedinthechemicalstructureofparticularDNAmolecules.

Developmentalbiologystudiestheprocessbywhichorganismsgrowanddevelop.Originatinginembryology,moderndevelopmentalbiologystudiesthegeneticcontrolofcellgrowth,differentiation,and"morphogenesis,"whichistheprocessthatprogressivelygivesrisetotissues,organs,andanatomy.ModelorganismsfordevelopmentalbiologyincludetheroundwormCaenorhabditiselegans,[44]thefruitflyDrosophilamelanogaster,[45]thezebrafishDaniorerio,[46]themouseMusmusculus,[47]andtheweedArabidopsisthaliana.[48][49](Amodelorganismisaspeciesthatisextensivelystudiedtounderstandparticularbiologicalphenomena,withtheexpectationthatdiscoveriesmadeinthatorganismprovideinsightintotheworkingsofotherorganisms.)[50]

Physiological

Physiologystudiesthemechanical,physical,andbiochemicalprocessesoflivingorganismsbyattemptingtounderstandhowallofthestructuresfunctionasawhole.Thethemeof"structuretofunction"iscentraltobiology.Physiologicalstudieshavetraditionallybeendividedintoplantphysiologyandanimalphysiology,butsomeprinciplesofphysiologyareuniversal,nomatterwhatparticularorganismisbeingstudied.Forexample,whatislearnedaboutthephysiologyofyeastcellscanalsoapplytohumancells.Thefieldofanimalphysiologyextendsthetoolsandmethodsofhumanphysiologytononhumanspecies.Plantphysiologyborrowstechniquesfrombothresearchfields.

Physiologystudieshowforexamplenervous,immune,endocrine,respiratory,andcirculatorysystems,functionandinteract.Thestudyofthesesystemsissharedwithmedicallyorienteddisciplinessuchasneurologyandimmunology.

Evolutionary

Evolutionaryresearchisconcernedwiththeoriginanddescentofspecies,aswellastheirchangeovertime,andincludesscientistsfrommanytaxonomicallyorienteddisciplines.Forexample,itgenerallyinvolvesscientistswhohavespecialtraininginparticularorganismssuchasmammalogy,ornithology,botany,orherpetology,butusethoseorganismsassystemstoanswergeneralquestionsaboutevolution.

Evolutionarybiologyispartlybasedonpaleontology,whichusesthefossilrecordtoanswerquestionsaboutthemodeandtempoofevolution,[51]andpartlyonthedevelopmentsinareassuchaspopulationgenetics.[52]Inthe1980s,developmentalbiologyreenteredevolutionarybiologyfromitsinitialexclusionfromthemodernsynthesisthroughthestudyofevolutionarydevelopmentalbiology.[53]Relatedfieldsoftenconsideredpartofevolutionarybiologyarephylogenetics,systematics,andtaxonomy.

Aphylogenetictreeofalllivingthings,basedonrRNAgenedata,showingtheseparationofthethreedomainsbacteria,archaea,andeukaryotesasdescribedinitiallybyCarlWoese.Treesconstructedwithothergenesaregenerallysimilar,althoughtheymayplacesomeearlybranchinggroupsverydifferently,presumablyowingtorapidrRNAevolution.Theexactrelationshipsofthethreedomainsarestillbeingdebated.

Systematic

Multiplespeciationeventscreateatreestructuredsystemofrelationshipsbetweenspecies.Theroleofsystematicsistostudytheserelationshipsandthusthedifferencesandsimilaritiesbetweenspeciesandgroupsofspecies.[54]However,systematicswasanactivefieldofresearchlongbeforeevolutionarythinkingwascommon.[55]

Traditionally,livingthingshavebeendividedintofivekingdoms:MoneraProtistaFungiPlantaeAnimalia.[56]However,manyscientistsnowconsiderthisfivekingdomsystemoutdated.Modernalternativeclassificationsystemsgenerallybeginwiththethreedomainsystem:Archaea(originallyArchaebacteria)Bacteria(originallyEubacteria)andEukaryota(includingprotists,fungi,plants,andanimals)[57]Thesedomainsreflectwhetherthecellshavenucleiornot,aswellasdifferencesinthechemicalcompositionofkeybiomoleculessuchasribosomes.[57]

Further,eachkingdomisbrokendownrecursivelyuntileachspeciesisseparatelyclassified.Theorderis:DomainKingdomPhylumClassOrderFamilyGenusSpecies.

Outsideofthesecategories,thereareobligateintracellularparasitesthatare"ontheedgeoflife"[58]intermsofmetabolicactivity,meaningthatmanyscientistsdonotactuallyclassifythesestructuresasalive,duetotheirlackofatleastoneormoreofthefundamentalfunctionsorcharacteristicsthatdefinelife.Theyareclassifiedasviruses,viroids,prions,orsatellites.

Thescientificnameofanorganismisgeneratedfromitsgenusandspecies.Forexample,humansarelistedasHomosapiens.Homoisthegenus,andsapiensthespecies.Whenwritingthescientificnameofanorganism,itispropertocapitalizethefirstletterinthegenusandputallofthespeciesinlowercase.[59]Additionally,theentiretermmaybeitalicizedorunderlined.[60]

ThedominantclassificationsystemiscalledtheLinnaeantaxonomy.Itincludesranksandbinomialnomenclature.HoworganismsarenamedisgovernedbyinternationalagreementssuchastheInternationalCodeofNomenclatureforalgae,fungi,andplants(ICN),theInternationalCodeofZoologicalNomenclature(ICZN),andtheInternationalCodeofNomenclatureofBacteria(ICNB).Theclassificationofviruses,viroids,prions,andallothersubviralagentsthatdemonstratebiological

MutualsymbiosisbetweenclownfishofthegenusAmphiprionthatdwellamongthetentaclesoftropicalseaanemones.Theterritorialfishprotectstheanemonefromanemoneeatingfish,andinturnthestingingtentaclesoftheanemoneprotectstheclownfishfromitspredators.

characteristicsisconductedbytheInternationalCommitteeonTaxonomyofViruses(ICTV)andisknownastheInternationalCodeofViralClassificationandNomenclature(ICVCN).[61][62][63][64]However,severalotherviralclassificationsystemsdoexist.

Amergingdraft,BioCode,waspublishedin1997inanattempttostandardizenomenclatureinthesethreeareas,buthasyettobeformallyadopted.[65]TheBioCodedrafthasreceivedlittleattentionsince1997itsoriginallyplannedimplementationdateofJanuary1,2000,haspassedunnoticed.ArevisedBioCodethat,insteadofreplacingtheexistingcodes,wouldprovideaunifiedcontextforthem,wasproposedin2011.[66][67][68]However,theInternationalBotanicalCongressof2011declinedtoconsidertheBioCodeproposal.TheICVCNremainsoutsidetheBioCode,whichdoesnotincludeviralclassification.

Ecologicalandenvironmental

Ecologystudiesthedistributionandabundanceoflivingorganisms,andtheinteractionsbetweenorganismsandtheirenvironment.[69]Thehabitatofanorganismcanbedescribedasthelocalabioticfactorssuchasclimateandecology,inadditiontotheotherorganismsandbioticfactorsthatshareitsenvironment.[70]Onereasonthatbiologicalsystemscanbedifficulttostudyisthatsomanydifferentinteractionswithotherorganismsandtheenvironmentarepossible,evenonsmallscales.AmicroscopicbacteriuminalocalsugargradientisrespondingtoitsenvironmentasmuchasalionsearchingforfoodintheAfricansavanna.Foranyspecies,behaviorscanbecooperative,competitive,parasitic,orsymbiotic.Mattersbecomemorecomplexwhentwoormorespeciesinteractinanecosystem.

Ecologicalsystemsarestudiedatseveraldifferentlevels,fromindividualsandpopulationstoecosystemsandthebiosphere.Thetermpopulationbiologyisoftenusedinterchangeablywithpopulationecology,althoughpopulationbiologyismorefrequentlyusedwhenstudyingdiseases,viruses,andmicrobes,whilepopulationecologyismorecommonlyusedwhenstudyingplantsandanimals.Ecologydrawsonmanysubdisciplines.

Ethologystudiesanimalbehavior(particularlythatofsocialanimalssuchasprimatesandcanids),andissometimesconsideredabranchofzoology.Ethologistshavebeenparticularlyconcernedwiththeevolutionofbehaviorandtheunderstandingofbehaviorintermsofthetheoryofnaturalselection.Inonesense,thefirstmodern

Thehierarchyofbiologicalclassification'seightmajortaxonomicranks.Intermediateminorrankingsarenotshown.Thisdiagramusesa3Domains/6Kingdomsformat

ethologistwasCharlesDarwin,whosebook,TheExpressionoftheEmotionsinManandAnimals,influencedmanyethologiststocome.[71]

BiogeographystudiesthespatialdistributionoforganismsontheEarth,focusingontopicslikeplatetectonics,climatechange,dispersalandmigration,andcladistics.

Basicunresolvedproblemsinbiology

Despitetheprofoundadvancesmadeoverrecentdecadesinourunderstandingoflife'sfundamentalprocesses,somebasicproblemshaveremainedunresolved.Forexample,oneofthemajorunresolvedproblemsinbiologyistheprimaryadaptivefunctionofsex,andparticularlyitskeyprocessesineukaryotes,meiosisandhomologousrecombination.Oneviewisthatsexevolvedprimarilyasanadaptationforincreasinggeneticdiversity(seereferencese.g.[72][73]).AnalternativeviewisthatsexisanadaptationforpromotingaccurateDNArepairingermlineDNA,andthatincreasedgeneticdiversityisprimarilyabyproductthatmaybeusefulinthelongrun.[74][75](SeealsoEvolutionofsexualreproduction).

Anotherbasicunresolvedprobleminbiologyisthebiologicbasisofaging.Atpresent,thereisnoconsensusviewontheunderlyingcauseofaging.VariouscompetingtheoriesareoutlinedinAgeingTheories.

Branches

Thesearethemainbranchesofbiology:[76][77]

AerobiologythestudyofairborneorganicparticlesAgriculturethestudyofproducingcropsandraisinglivestock,withanemphasisonpracticalapplicationsAnatomythestudyofformandfunction,inplants,animals,andotherorganisms,orspecificallyinhumans

Histologythestudyofcellsandtissues,amicroscopicbranchofanatomyAstrobiology(alsoknownasexobiology,exopaleontology,andbioastronomy)thestudyofevolution,distribution,andfutureoflifeintheuniverseBiochemistrythestudyofthechemicalreactionsrequiredforlifetoexistandfunction,usuallyafocusonthecellularlevelBioengineeringthestudyofbiologythroughthemeansofengineeringwithanemphasisonappliedknowledgeandespeciallyrelatedtobiotechnologyBiogeographythestudyofthedistributionofspeciesspatiallyandtemporallyBioinformaticstheuseofinformationtechnologyforthestudy,collection,andstorageofgenomicandotherbiologicaldataBiomathematics(orMathematicalbiology)thequantitativeormathematicalstudyofbiologicalprocesses,withanemphasisonmodelingBiomechanicsoftenconsideredabranchofmedicine,thestudyofthemechanicsoflivingbeings,withanemphasisonappliedusethroughprostheticsororthoticsBiomedicalresearchthestudyofhealthanddisease

Pharmacologythestudyandpracticalapplicationofpreparation,use,andeffectsofdrugsandsyntheticmedicines

Biomusicologythestudyofmusicfromabiologicalpointofview.Biophysicsthestudyofbiologicalprocessesthroughphysics,byapplyingthetheoriesand

methodstraditionallyusedinthephysicalsciencesBiosemioticsthestudyofbiologicalprocessesthroughsemiotics,byapplyingthemodelsofmeaningmakingandcommunicationBiotechnologythestudyofthemanipulationoflivingmatter,includinggeneticmodificationandsyntheticbiology

Syntheticbiologyresearchintegratingbiologyandengineeringconstructionofbiologicalfunctionsnotfoundinnature

BuildingbiologythestudyoftheindoorlivingenvironmentBotanythestudyofplantsCellbiologythestudyofthecellasacompleteunit,andthemolecularandchemicalinteractionsthatoccurwithinalivingcellCognitivebiologythestudyofcognitionasabiologicalfunctionConservationbiologythestudyofthepreservation,protection,orrestorationofthenaturalenvironment,naturalecosystems,vegetation,andwildlifeCryobiologythestudyoftheeffectsoflowerthannormallypreferredtemperaturesonlivingbeingsDevelopmentalbiologythestudyoftheprocessesthroughwhichanorganismforms,fromzygotetofullstructure

Embryologythestudyofthedevelopmentofembryo(fromfecundationtobirth)EcologythestudyoftheinteractionsoflivingorganismswithoneanotherandwiththenonlivingelementsoftheirenvironmentEnvironmentalbiologythestudyofthenaturalworld,asawholeorinaparticulararea,especiallyasaffectedbyhumanactivityEpidemiologyamajorcomponentofpublichealthresearch,studyingfactorsaffectingthehealthofpopulationsEvolutionarybiologythestudyoftheoriginanddescentofspeciesovertimeGeneticsthestudyofgenesandheredity.

EpigeneticsthestudyofheritablechangesingeneexpressionorcellularphenotypecausedbymechanismsotherthanchangesintheunderlyingDNAsequence

Hematology(alsoknownasHaematology)thestudyofbloodandbloodformingorgans.IntegrativebiologythestudyofwholeorganismsLimnologythestudyofinlandwatersMarinebiology(orBiologicaloceanography)thestudyofoceanecosystems,plants,animals,andotherlivingbeingsMicrobiologythestudyofmicroscopicorganisms(microorganisms)andtheirinteractionswithotherlivingthings

ParasitologythestudyofparasitesandparasitismVirologythestudyofvirusesandsomeotherviruslikeagents

Molecularbiologythestudyofbiologyandbiologicalfunctionsatthemolecularlevel,somecrossoverwithbiochemistryMycologythestudyoffungiNeurobiologythestudyofthenervoussystem,includinganatomy,physiologyandpathologyPopulationbiologythestudyofgroupsofconspecificorganisms,including

PopulationecologythestudyofhowpopulationdynamicsandextinctionPopulationgeneticsthestudyofchangesingenefrequenciesinpopulationsoforganisms

PaleontologythestudyoffossilsandsometimesgeographicevidenceofprehistoriclifePathobiologyorpathologythestudyofdiseases,andthecauses,processes,nature,anddevelopmentofdiseasePhysiologythestudyofthefunctioningoflivingorganismsandtheorgansandpartsoflivingorganismsPhytopathologythestudyofplantdiseases(alsocalledPlantPathology)PsychobiologythestudyofthebiologicalbasesofpsychologyQuantumbiologythestudyofQuantummechanicstobiologicalobjectsandproblems.Sociobiologythestudyofthebiologicalbasesofsociology

Structuralbiologyabranchofmolecularbiology,biochemistry,andbiophysicsconcernedwiththemolecularstructureofbiologicalmacromoleculesZoologythestudyofanimals,includingclassification,physiology,development,andbehavior,including:

EthologythestudyofanimalbehaviorEntomologythestudyofinsectsHerpetologythestudyofreptilesandamphibiansIchthyologythestudyoffishMammalogythestudyofmammalsOrnithologythestudyofbirds

Seealso

GlossaryofbiologyListofbiologicalwebsitesListofbiologistsListofbiologytopicsListofomicstopicsinbiologyListofbiologyjournalsOutlineofbiologyReproductionTerminologyofbiologyPeriodictableoflifesciencesinTinbergen'sfourquestions

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71. Black,J(2002)."Darwinintheworldofemotions"(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1279921).JournaloftheRoyalSocietyofMedicine95(6):3113.doi:10.1258/jrsm.95.6.311(https://dx.doi.org/10.1258%2Fjrsm.95.6.311).PMC1279921(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1279921).PMID12042386(https://www.ncbi.nlm.nih.gov/pubmed/12042386).

72. Gerstein,A.C.Otto,S.P.(2006)."Whyhavesex?Thepopulationgeneticsofsexandrecombination".BiochemicalSocietyTransactions34(4):519522.doi:10.1042/BST0340519(https://dx.doi.org/10.1042%2FBST0340519).PMID16856849(https://www.ncbi.nlm.nih.gov/pubmed/16856849).

73. Agrawal,A.F.(2006)."EvolutionofSex:WhyDoOrganismsShuffleTheirGenotypes?".CurrentBiology

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FurtherreadingAlberts,BruceJohnson,A,Lewis,J,Raff,M,Roberts,K&Walter,P(2002).MolecularBiologyoftheCell(4thed.).Garland.ISBN9780815332183.OCLC145080076481227615702365169932405(https://www.worldcat.org/oclc/145080076+48122761+57023651+69932405).Begon,MichaelTownsend,CR&Harper,JL(2005).Ecology:FromIndividualstoEcosystems(4thed.).BlackwellPublishingLimited.ISBN9781405111171.OCLC576398965767585562131207(https://www.worldcat.org/oclc/57639896+57675855+62131207).Campbell,Neil(2004).Biology(7thed.).BenjaminCummingsPublishingCompany.ISBN080537146X.OCLC71890442(https://www.worldcat.org/oclc/71890442).Colinvaux,Paul(1979).WhyBigFierceAnimalsareRare:AnEcologist'sPerspective(reissueed.).PrincetonUniversityPress.ISBN0691023646.OCLC1008173824132192(https://www.worldcat.org/oclc/10081738+24132192).Mayr,Ernst(1982).TheGrowthofBiologicalThought:Diversity,Evolution,andInheritance(http://books.google.com/books?id=pHThtE2R0UQC).HarvardUniversityPress.ISBN9780674364462.Hoagland,Mahlon(2001).TheWayLifeWorks(reprinted.).JonesandBartlettPublishersinc.ISBN076371688X.OCLC22309010545487537(https://www.worldcat.org/oclc/223090105+45487537).Janovy,JohnJr.(2004).OnBecomingaBiologist(2nded.).BisonBooks.ISBN0803276206.OCLC5513857156964280(https://www.worldcat.org/oclc/55138571+56964280).Johnson,GeorgeB.(2005).Biology,VisualizingLife.Holt,Rinehart,andWinston.ISBN003016723X.OCLC36306648(https://www.worldcat.org/oclc/36306648).Tobin,AllanDusheck,Jennie(2005).AskingAboutLife(3rded.).Belmont,CA:Wadsworth.ISBN053440653X.

ExternallinksBiology(https://www.dmoz.org/Science/Biology)atDMOZOSU'sPhylocode(http://www.ohio.edu/phylocode/index.html)BiologyOnlineWikiDictionary(http://www.biologyonline.org/dictionary/Main_Page)MITvideolectureseriesonbiology(http://ocw.mit.edu/courses/biology/7012introductiontobiologyfall2004/)BiologyandBioethics(http://www.bioeticaunbosque.edu.co/english/).BiologicalSystems(https://inlportal.inl.gov/portal/server.pt?

73. Agrawal,A.F.(2006)."EvolutionofSex:WhyDoOrganismsShuffleTheirGenotypes?".CurrentBiology16(17):R696R704.doi:10.1016/j.cub.2006.07.063(https://dx.doi.org/10.1016%2Fj.cub.2006.07.063).PMID16950096(https://www.ncbi.nlm.nih.gov/pubmed/16950096).

74. Bernstein,HarrisBernstein,CarolandMichod,RichardE.(2011)."MeiosisasanEvolutionaryAdaptationforDNARepair"(http://www.intechopen.com/books/dnarepair/meiosisasanevolutionaryadaptationfordnarepair).Chapter19inDNARepair.InnaKrumaneditor.InTechOpenPublisher.doi:10.5772/25117(https://dx.doi.org/10.5772%2F25117)

75. Hrandl,Elvira(2013).MeiosisandtheParadoxofSexinNature(http://www.intechopen.com/books/meiosis/meiosisandtheparadoxofsexinnature),Meiosis,Dr.CarolBernstein(Ed.),ISBN9789535111979,InTech,doi:10.5772/56542(https://dx.doi.org/10.5772%2F56542).

76. "BranchesofBiology"(http://www.biologyonline.org/dictionary/Branches_of_biology).Biologyonline.org.Retrieved20131002.

77. "Biologyon"(http://www.bellaonline.com/articles/art28786.asp).Bellaonline.com.Retrieved20131002.

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open=514&objID=2622&parentname=CommunityPage&parentid=7&mode=2&in_hi_userid=200&cached=true)IdahoNationalLaboratoryTheTreeofLife(http://tolweb.org/tree/phylogeny.html):Amultiauthored,distributedInternetprojectcontaininginformationaboutphylogenyandbiodiversity.TheStudyofBiology(http://logiclaw.com/index.php?title=The_Study_of_Biology)UsingtheBiologicalLiteratureWebResources(http://www.library.illinois.edu/bix/biologicalliterature/)

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