photosynthesis | Definition, Formula, Process, Diagram ...

photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. photosynthesis TableofContents photosynthesis Introduction&TopQuestionsGeneralcharacteristicsDevelopmentoftheideaOverallreactionofphotosynthesisBasicproductsofphotosynthesisEvolutionoftheprocessFactorsthatinfluencetherateofphotosynthesisLightintensityandtemperatureCarbondioxideWaterMineralsInternalfactorsEnergyefficiencyofphotosynthesisChloroplasts,thephotosyntheticunitsofgreenplantsStructuralfeaturesChemicalcompositionoflamellaeLipidsProteinsQuinonesTheprocessofphotosynthesis:thelightreactionsLightabsorptionandenergytransferThepathwayofelectronsEvidenceoftwolightreactionsPhotosystemsIandIIQuantumrequirementsTheprocessofphotosynthesis:theconversionoflightenergytoATPTheprocessofphotosynthesis:carbonfixationandreductionElucidationofthecarbonpathwayTheCalvin-BensoncycleCarboxylationReductionIsomerization/condensation/dismutationPhosphorylationRegulationofthecycleProductsofcarbonreductionPhotorespirationCarbonfixationinC4plantsCarbonfixationviacrassulaceanacidmetabolism(CAM)DifferencesincarbonfixationpathwaysThemolecularbiologyofphotosynthesis FastFacts 2-MinSummary TopQuestions Whyisphotosynthesisimportant? Whatisthebasicformulaforphotosynthesis? Whichorganismscanphotosynthesize? RelatedContent Quizzes Media Videos Images More MoreArticlesOnThisTopic AdditionalReading Contributors ArticleHistory Home Health&Medicine Anatomy&Physiology photosynthesis biology Actions Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/photosynthesis GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites NationalCenterforBiotechnologyInformation-ChloroplastsandPhotosynthesis BiologyLibreTexts-Photosynthesis BritannicaWebsites ArticlesfromBritannicaEncyclopediasforelementaryandhighschoolstudents. photosynthesis-Children'sEncyclopedia(Ages8-11) photosynthesis-StudentEncyclopedia(Ages11andup) Print print Print Pleaseselectwhichsectionsyouwouldliketoprint: TableOfContents Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/photosynthesis Feedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites NationalCenterforBiotechnologyInformation-ChloroplastsandPhotosynthesis BiologyLibreTexts-Photosynthesis BritannicaWebsites ArticlesfromBritannicaEncyclopediasforelementaryandhighschoolstudents. photosynthesis-Children'sEncyclopedia(Ages8-11) photosynthesis-StudentEncyclopedia(Ages11andup) By JamesAlanBassham SeeAll • LastUpdated: Aug13,2022 • EditHistory TableofContents photosynthesis Seeallmedia KeyPeople: JosephPriestley MelvinCalvin JanIngenhousz JeanSenebier RobertHuber ...(Showmore) RelatedTopics: chlorophyll photolysis pheophytin CrassulaceanAcidMetabolism photorespiration ...(Showmore) Seeallrelatedcontent→ TopQuestionsWhyisphotosynthesisimportant?PhotosynthesisiscriticalfortheexistenceofthevastmajorityoflifeonEarth.Itisthewayinwhichvirtuallyallenergyinthebiospherebecomesavailabletolivingthings.Asprimaryproducers,photosyntheticorganismsformthebaseofEarth’sfoodwebsandareconsumeddirectlyorindirectlybyallhigherlife-forms.Additionally,almostalltheoxygenintheatmosphereisduetotheprocessofphotosynthesis.Ifphotosynthesisceased,therewouldsoonbelittlefoodorotherorganicmatteronEarth,mostorganismswoulddisappear,andEarth’satmospherewouldeventuallybecomenearlydevoidofgaseousoxygen.Whatisthebasicformulaforphotosynthesis?Theprocessofphotosynthesisiscommonlywrittenas:6CO2+6H2O→C6H12O6+6O2.Thismeansthatthereactants,sixcarbondioxidemoleculesandsixwatermolecules,areconvertedbylightenergycapturedbychlorophyll(impliedbythearrow)intoasugarmoleculeandsixoxygenmolecules,theproducts.Thesugarisusedbytheorganism,andtheoxygenisreleasedasaby-product. Readmorebelow: Generalcharacteristics:OverallreactionofphotosynthesischlorophyllLearnmoreaboutchlorophyll.Whichorganismscanphotosynthesize?Theabilitytophotosynthesizeisfoundinbotheukaryoticandprokaryoticorganisms.Themostwell-knownexamplesareplants,asallbutaveryfewparasiticormycoheterotrophicspeciescontainchlorophyllandproducetheirownfood.Algaearetheotherdominantgroupofeukaryoticphotosyntheticorganisms.Allalgae,whichincludemassivekelpsandmicroscopicdiatoms,areimportantprimaryproducers. Cyanobacteriaandcertainsulfurbacteriaarephotosyntheticprokaryotes,inwhomphotosynthesisevolved.Noanimalsarethoughttobeindependentlycapableofphotosynthesis,thoughtheemeraldgreenseaslugcantemporarilyincorporatealgaechloroplastsinitsbodyforfoodproduction.eukaryoteLearnmoreabouteukaryotes.prokaryoteLearnmoreaboutprokaryotes.Summary Readabriefsummaryofthistopic photosynthesis,theprocessbywhichgreenplantsandcertainotherorganismstransformlightenergyintochemicalenergy.Duringphotosynthesisingreenplants,lightenergyiscapturedandusedtoconvertwater,carbondioxide,andmineralsintooxygenandenergy-richorganiccompounds.ItwouldbeimpossibletooverestimatetheimportanceofphotosynthesisinthemaintenanceoflifeonEarth.Ifphotosynthesisceased,therewouldsoonbelittlefoodorotherorganicmatteronEarth.Mostorganismswoulddisappear,andintimeEarth’satmospherewouldbecomenearlydevoidofgaseousoxygen.Theonlyorganismsabletoexistundersuchconditionswouldbethechemosyntheticbacteria,whichcanutilizethechemicalenergyofcertaininorganiccompoundsandthusarenotdependentontheconversionoflightenergy.Energyproducedbyphotosynthesiscarriedoutbyplantsmillionsofyearsagoisresponsibleforthefossilfuels(i.e.,coal,oil,andgas)thatpowerindustrialsociety.Inpastages,greenplantsandsmallorganismsthatfedonplantsincreasedfasterthantheywereconsumed,andtheirremainsweredepositedinEarth’scrustbysedimentationandothergeologicalprocesses.There,protectedfromoxidation,theseorganicremainswereslowlyconvertedtofossilfuels.Thesefuelsnotonlyprovidemuchoftheenergyusedinfactories,homes,andtransportationbutalsoserveastherawmaterialforplasticsandothersyntheticproducts.Unfortunately,moderncivilizationisusingupinafewcenturiestheexcessofphotosyntheticproductionaccumulatedovermillionsofyears.Consequently,thecarbondioxidethathasbeenremovedfromtheairtomakecarbohydratesinphotosynthesisovermillionsofyearsisbeingreturnedatanincrediblyrapidrate.ThecarbondioxideconcentrationinEarth’satmosphereisrisingthefastestiteverhasinEarth’shistory,andthisphenomenonisexpectedtohavemajorimplicationsonEarth’sclimate.Requirementsforfood,materials,andenergyinaworldwherehumanpopulationisrapidlygrowinghavecreatedaneedtoincreaseboththeamountofphotosynthesisandtheefficiencyofconvertingphotosyntheticoutputintoproductsusefultopeople.Oneresponsetothoseneeds—theso-calledGreenRevolution,beguninthemid-20thcentury—achievedenormousimprovementsinagriculturalyieldthroughtheuseofchemicalfertilizers,pestandplant-diseasecontrol,plantbreeding,andmechanizedtilling,harvesting,andcropprocessing.Thiseffortlimitedseverefaminestoafewareasoftheworlddespiterapidpopulationgrowth,butitdidnoteliminatewidespreadmalnutrition.Moreover,beginningintheearly1990s,therateatwhichyieldsofmajorcropsincreasedbegantodecline.ThiswasespeciallytrueforriceinAsia.Risingcostsassociatedwithsustaininghighratesofagriculturalproduction,whichrequiredever-increasinginputsoffertilizersandpesticidesandconstantdevelopmentofnewplantvarieties,alsobecameproblematicforfarmersinmanycountries. BritannicaQuiz BiologyBonanza Whatdoestheword"migration"mean?Howmanysetsoflegsdoesashrimphave?Frompoisonousfishtobiodiversity,learnmoreaboutthestudyoflivingthingsinthisquiz. Asecondagriculturalrevolution,basedonplantgeneticengineering,wasforecasttoleadtoincreasesinplantproductivityandtherebypartiallyalleviatemalnutrition.Sincethe1970s,molecularbiologistshavepossessedthemeanstoalteraplant’sgeneticmaterial(deoxyribonucleicacid,orDNA)withtheaimofachievingimprovementsindiseaseanddroughtresistance,productyieldandquality,frosthardiness,andotherdesirableproperties.However,suchtraitsareinherentlycomplex,andtheprocessofmakingchangestocropplantsthroughgeneticengineeringhasturnedouttobemorecomplicatedthananticipated.Inthefuturesuchgeneticengineeringmayresultinimprovementsintheprocessofphotosynthesis,butbythefirstdecadesofthe21stcentury,ithadyettodemonstratethatitcoulddramaticallyincreasecropyields.Anotherintriguingareainthestudyofphotosynthesishasbeenthediscoverythatcertainanimalsareabletoconvertlightenergyintochemicalenergy.Theemeraldgreenseaslug(Elysiachlorotica),forexample,acquiresgenesandchloroplastsfromVaucherialitorea,analgaitconsumes,givingitalimitedabilitytoproducechlorophyll.Whenenoughchloroplastsareassimilated,theslugmayforgotheingestionoffood.Thepeaaphid(Acyrthosiphonpisum)canharnesslighttomanufacturetheenergy-richcompoundadenosinetriphosphate(ATP);thisabilityhasbeenlinkedtotheaphid’smanufactureofcarotenoidpigments. 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SubscribeNow GeneralcharacteristicsDevelopmentoftheideaThestudyofphotosynthesisbeganin1771withobservationsmadebytheEnglishclergymanandscientistJosephPriestley.Priestleyhadburnedacandleinaclosedcontaineruntiltheairwithinthecontainercouldnolongersupportcombustion.Hethenplacedasprigofmintplantinthecontaineranddiscoveredthatafterseveraldaystheminthadproducedsomesubstance(laterrecognizedasoxygen)thatenabledtheconfinedairtoagainsupportcombustion.In1779theDutchphysicianJanIngenhouszexpandeduponPriestley’swork,showingthattheplanthadtobeexposedtolightifthecombustiblesubstance(i.e.,oxygen)wastoberestored.Healsodemonstratedthatthisprocessrequiredthepresenceofthegreentissuesoftheplant.In1782itwasdemonstratedthatthecombustion-supportinggas(oxygen)wasformedattheexpenseofanothergas,or“fixedair,”whichhadbeenidentifiedtheyearbeforeascarbondioxide.Gas-exchangeexperimentsin1804showedthatthegaininweightofaplantgrowninacarefullyweighedpotresultedfromtheuptakeofcarbon,whichcameentirelyfromabsorbedcarbondioxide,andwatertakenupbyplantroots;thebalanceisoxygen,releasedbacktotheatmosphere.Almosthalfacenturypassedbeforetheconceptofchemicalenergyhaddevelopedsufficientlytopermitthediscovery(in1845)thatlightenergyfromthesunisstoredaschemicalenergyinproductsformedduringphotosynthesis.OverallreactionofphotosynthesisInchemicalterms,photosynthesisisalight-energizedoxidation–reductionprocess.(Oxidationreferstotheremovalofelectronsfromamolecule;reductionreferstothegainofelectronsbyamolecule.)Inplantphotosynthesis,theenergyoflightisusedtodrivetheoxidationofwater(H2O),producingoxygengas(O2),hydrogenions(H+),andelectrons.Mostoftheremovedelectronsandhydrogenionsultimatelyaretransferredtocarbondioxide(CO2),whichisreducedtoorganicproducts.Otherelectronsandhydrogenionsareusedtoreducenitrateandsulfatetoaminoandsulfhydrylgroupsinaminoacids,whicharethebuildingblocksofproteins.Inmostgreencells,carbohydrates—especiallystarchandthesugarsucrose—arethemajordirectorganicproductsofphotosynthesis.Theoverallreactioninwhichcarbohydrates—representedbythegeneralformula(CH2O)—areformedduringplantphotosynthesiscanbeindicatedbythefollowingequation:Thisequationismerelyasummarystatement,fortheprocessofphotosynthesisactuallyinvolvesnumerousreactionscatalyzedbyenzymes(organiccatalysts).Thesereactionsoccurintwostages:the“light”stage,consistingofphotochemical(i.e.,light-capturing)reactions;andthe“dark”stage,comprisingchemicalreactionscontrolledbyenzymes.Duringthefirststage,theenergyoflightisabsorbedandusedtodriveaseriesofelectrontransfers,resultinginthesynthesisofATPandtheelectron-donor-reducednicotineadeninedinucleotidephosphate(NADPH).Duringthedarkstage,theATPandNADPHformedinthelight-capturingreactionsareusedtoreducecarbondioxidetoorganiccarboncompounds.Thisassimilationofinorganiccarbonintoorganiccompoundsiscalledcarbonfixation.Duringthe20thcentury,comparisonsbetweenphotosyntheticprocessesingreenplantsandincertainphotosyntheticsulfurbacteriaprovidedimportantinformationaboutthephotosyntheticmechanism.Sulfurbacteriausehydrogensulfide(H2S)asasourceofhydrogenatomsandproducesulfurinsteadofoxygenduringphotosynthesis.TheoverallreactionisInthe1930sDutchbiologistCornelisvanNielrecognizedthattheutilizationofcarbondioxidetoformorganiccompoundswassimilarinthetwotypesofphotosyntheticorganisms.Suggestingthatdifferencesexistedinthelight-dependentstageandinthenatureofthecompoundsusedasasourceofhydrogenatoms,heproposedthathydrogenwastransferredfromhydrogensulfide(inbacteria)orwater(ingreenplants)toanunknownacceptor(calledA),whichwasreducedtoH2A.Duringthedarkreactions,whicharesimilarinbothbacteriaandgreenplants,thereducedacceptor(H2A)reactedwithcarbondioxide(CO2)toformcarbohydrate(CH2O)andtooxidizetheunknownacceptortoA.Thisputativereactioncanberepresentedas:VanNiel’sproposalwasimportantbecausethepopular(butincorrect)theoryhadbeenthatoxygenwasremovedfromcarbondioxide(ratherthanhydrogenfromwater,releasingoxygen)andthatcarbonthencombinedwithwatertoformcarbohydrate(ratherthanthehydrogenfromwatercombiningwithCO2toformCH2O). By1940chemistswereusingheavyisotopestofollowthereactionsofphotosynthesis.Watermarkedwithanisotopeofoxygen(18O)wasusedinearlyexperiments.PlantsthatphotosynthesizedinthepresenceofwatercontainingH218Oproducedoxygengascontaining18O;thosethatphotosynthesizedinthepresenceofnormalwaterproducednormaloxygengas.TheseresultsprovideddefinitivesupportforvanNiel’stheorythattheoxygengasproducedduringphotosynthesisisderivedfromwater.