Shoe Box Lab: PhotosynthesisShoe Box Lab: Photosynthesis Essential Question : How do you design an...
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AP Biology: Unit 4: Energy Pod 2: Energy Exchange Adapted from D. Knuffke, L. Ferguson, & B Williamson 1 Shoe Box Lab: Photosynthesis Essential Question: How do you design an experiment to quantify the effect of an environmental variable (ex. pH, temperature, light intensity, age of leaves, etc.) on the rate of photosynthesis. Background: Photosynthesis is an anabolic process used by all photoautotrophs to capture light energy and convert it to the chemical energy in carbohydrates. It can be measured in a variety of ways. Although numerous intermediary reactions are involved, the overall photosynthetic reaction is simple: carbon dioxide combines with the hydrogen from water producing a carbohydrate– the six-carbon sugar glucose –and oxygen gas. 6CO 2 + 6H 2 O + sunlight → C 6 H 12 O 6 +6O 2 The photosynthetic production of oxygen and knowledge of leaf anatomy will allow for the construction of a simple system that can be used to experimentally investigate many of the photosynthetic variables. Many extracellular spaces exist within plant leaves that are normally filled with air for purposes of gas exchange. This is why leaves will float on the surface of bodies of water. But would you happen if all the air is forced out of the air spaces in the leaf? What will the leaf do then? If basic requirements for photosynthesis are supplied, the oxygen the leaf produces will form gas bubbles and the leaf would re-float. In essence, this is the experimental method, however, small disks cut from leaves will be used instead of whole leaves to perform the floating leaf disk assay (FLDA). This assay of photosynthesis may be used to answer many questions, including: How do changes in light intensity, wavelength, or CO 2 concentration affect the rate of photosynthesis? One problem in measuring a rate of photosynthesis is that there is a competing process occurring at the same time, cellular respiration, a process that uses oxygen. The FLDA actually measures the rate of photosynthetic oxygen production minus the rate of respiratory oxygen use during the same period. The FLDA measures the net rate of photosynthesis, the energetic “profit” made by the plant. Actual photosynthetic activity is greater than this and is called the gross rate of photosynthesis. If cellular respiration can be measured separately, a simple calculation can determine gross photosynthesis. Materials: • Sodium bicarbonate (Baking soda) • Liquid Soap • Plastic syringe (10 cc or larger)—remove any needle! • Leaf material • Hole punch • Plastic cups • Timer • Group specific materials as needed • Light source Safety and Housekeeping: The primary safety issues in this lab have to do with solutions NEAR electric lights. Take CAUTION to observe proper care with solutions near lights. If you will be working in close proximity to exposed lightbulbs, make sure to wear EYE PROTECTION in the form of safety glasses. Moreover, some high-intensity light sources get extremely HOT. If you are using these, be ADVISE not to drip water on them (shatter hazard) or to lean against a light (burn hazard).
Transcript of Shoe Box Lab: PhotosynthesisShoe Box Lab: Photosynthesis Essential Question : How do you design an...
AP Biology: Unit 4: Energy Pod 2: Energy Exchange
Adapted from D. Knuffke, L. Ferguson, & B Williamson
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ShoeBoxLab:Photosynthesis EssentialQuestion: How do you designanexperimenttoquantifytheeffectofanenvironmentalvariable(ex.pH,temperature,lightintensity,ageofleaves,etc.)ontherateofphotosynthesis.Background:Photosynthesisisananabolicprocessusedbyallphotoautotrophstocapturelightenergyandconvertittothechemicalenergyincarbohydrates.Itcanbemeasuredinavarietyofways.Althoughnumerousintermediaryreactionsareinvolved,theoverallphotosyntheticreactionissimple:carbondioxidecombineswiththehydrogenfromwaterproducingacarbohydrate–thesix-carbonsugarglucose–andoxygengas.
6CO2+6H2O+sunlight→C6H12O6+6O2Thephotosyntheticproductionofoxygenandknowledgeofleafanatomywillallowfortheconstructionofasimplesystemthatcanbeusedtoexperimentallyinvestigatemanyofthephotosyntheticvariables.Manyextracellularspacesexistwithinplantleavesthatarenormallyfilledwithairforpurposesofgasexchange.Thisiswhyleaveswillfloatonthesurfaceofbodiesofwater.Butwouldyouhappenifalltheairisforcedoutoftheairspacesintheleaf?Whatwilltheleafdothen?Ifbasicrequirementsforphotosynthesisaresupplied,theoxygentheleafproduceswillformgasbubblesandtheleafwouldre-float.Inessence,thisistheexperimentalmethod,however,smalldiskscutfromleaveswillbeusedinsteadofwholeleavestoperformthefloatingleafdiskassay(FLDA).Thisassayofphotosynthesismaybeusedtoanswermanyquestions,including:Howdochangesinlightintensity,wavelength,orCO2concentrationaffecttherateofphotosynthesis?Oneprobleminmeasuringarateofphotosynthesisisthatthereisacompetingprocessoccurringatthesametime,cellularrespiration,aprocessthatusesoxygen.TheFLDAactuallymeasurestherateofphotosyntheticoxygenproductionminustherateofrespiratoryoxygenuseduringthesameperiod.TheFLDAmeasuresthenetrateofphotosynthesis,theenergetic“profit”madebytheplant.Actualphotosyntheticactivityisgreaterthanthisandiscalledthegrossrateofphotosynthesis.Ifcellularrespirationcanbemeasuredseparately,asimplecalculationcandeterminegrossphotosynthesis.Materials:
• Sodiumbicarbonate(Bakingsoda)• LiquidSoap• Plasticsyringe(10ccorlarger)—removeanyneedle!• Leafmaterial• Holepunch
• Plasticcups• Timer• Groupspecificmaterialsasneeded• Lightsource
SafetyandHousekeeping:TheprimarysafetyissuesinthislabhavetodowithsolutionsNEARelectriclights.TakeCAUTIONtoobservepropercarewithsolutionsnearlights.Ifyouwillbeworkingincloseproximitytoexposedlightbulbs,makesuretowearEYEPROTECTIONintheformofsafetyglasses.Moreover,somehigh-intensitylightsourcesgetextremelyHOT.Ifyouareusingthese,beADVISEnottodripwateronthem(shatterhazard)ortoleanagainstalight(burnhazard).
AP Biology: Unit 4: Energy Pod 2: Energy Exchange
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TheFloatingLeafDiskAssayforPhotosyntheticActivity:Forthisexperiment,youwillusethe“FloatingLeafDiskAssay”forphotosyntheticactivity.Adetailedprotocolforthisprocedureisattached.Essentially,theassayfollowsthefollowingsteps:
1. Smalldisksectionsofleaftissuearepunchedfromaleaf.2. Thedisksareinfiltratedwithabicarbonatesolution.Theinfiltrationservestwomajorpurposes:
a. Itincreasesthedensityoftheleafdiskssothattheysinkb. Itsuppliesthediskswithacarbonsource(thebicarbonateion)forthepurposeofphotosynthesis.
3. Afterinfiltration,thedisksareplacedatthebottomofacontainer(wewillusepetridishes)ofthebicarbonatesolution.
4. Whenexposedtolight,thediskswillproduceOxygengas,decreasingtheirdensitytothepointthattheywillfloattothetopofthecontainer.
5. Thetimeittakesfordiskstofloatisdirectlyrelatedtotherateofphotosyntheticactivitytakingplaceintheleafdisks.
ProceduralConstraints&Suggestions:TheNeedforAControl:
• Youwouldn’twanttorunanexperimentwithout(atleastonecontrol).DeterminationoftherateofPhotosynthesisANDtheRateofRespiration:
• TherateofrespirationneedstobedeterminedinordertocalculatetherateofgrossphotosynthesisStepstocompletebeforebeginningyourexperiment:
• Developadetailedprotocol&clearexperimentalplanforyourexperiment.• Reviewthesafetyandhousekeepingitemsfortheexperiment.• Developadatatableforyourexperiment&Determineanycalculationsthatwillbenecessaryforyourdata.• Thinkabouthowyouwillgraphyourresults(atleastonegraphisrequiredforthislab).
Stepstocompleteduringyourexperiment:
• Recordthetimeittakesfortheleafdiskstofloat.• Takeapictureofyourexperiment.Makesuretocaptureoneofyouandyourpartner!• Recordanythingthattakesplacethatcapturesyourattentionduringtheexperiment
Stepstocompleteafteryourexperiment:
• Usinggoogleslides,produceawriteupthatincludesthefollowing:o ExperimentalDesignandProtocol.Makesuretoincludepicturesofyouconductingtheexpiremento Claim,Evidence(DataTable,Graph&Calculations),Reasoning(OneSlideEach)o Analysisquestions:
§ Whywasthesoapneededintheprotocol?§ ExplainthespecificpurposeoftheBicarbonateIonsintheleafdiskphotosynthesis(inother
words,whatmoleculeisBicarbonatestandinginfor).§ Whatisthesourceofelectronsfortheleafdiskphotosynthesis?§ Proposetwootherwaysofmeasuringtherateofphotosynthesisinaphotoautotroph(any
organismyouwant).§ Whyisitimportanttousetheaveragerateofphotosynthesis(orrespiration)?§ Whatistheimportanceofestablishingacontrolforthisexperiment?§ Whymustweconsiderrespirationwhenperformingthisactivity?§ Whyisitimportanttostudyphotosyntheticrateofplants?
• SubmittheGoogleSlidesviaGoogleClassroomandprintacopyforyourBILL
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TheFloatingLeafDiskAssayforInvestigatingPhotosynthesis
Introduction:Tryingtofindagood,quantitativeprocedurethatstudentscanuseforexploringphotosynthesisisachallenge.Thestandardproceduressuchascountingoxygenbubblesgeneratedbyanelodeastemtendtonotbe“student”prooforreliable.Thisisaparticularproblemifyourlaboratoryinstructionemphasizesstudent-generatedquestions.Overtheyears,Ihavefoundthefloatingleafdiskassaytechniquetobereliableandunderstandabletostudents.Oncethestudentsarefamiliarwiththetechniquetheycanreadilydesignexperimentstoanswertheirownquestionsaboutphotosynthesis. Thebiologybehindtheprocedure:Leafdisksfloat,normally.Whentheairspacesareinfiltratedwithsolutiontheoveralldensityoftheleafdiskincreasesandthedisksinks.TheinfiltrationsolutionincludesasmallamountofSodiumbicarbonate.Bicarbonateionservesasthecarbonsourceforphotosynthesis.Asphotosynthesisproceedsoxygenisreleasedintotheinterioroftheleafwhichchangesthebuoyancy--causingthediskstorise.Sincecellularrespirationistakingplaceatthesametime,consumingoxygen,theratethatthedisksriseisanindirectmeasurementofthenetrateofphotosynthesis.
Procedure:
1. Thebicarbonateservesasanalternatedissolvedsourceofcarbondioxideforphotosynthesis.Preparea0.2%solution.(Thisisnotverymuchitisonlyabout1/8ofateaspoonofbakingsodain300mlofwater.)
2. Add1dropofdiluteliquidsoaptothissolution.The
soapwetsthehydrophobicsurfaceoftheleafallowingthesolutiontobedrawnintotheleaf.It’sdifficulttoquantifythissinceliquidsoapsvaryinconcentration.Avoidsuds.Ifyoursolutiongeneratessudsthendiluteitwithmorebicarbonatesolution.
AP Biology: Unit 4: Energy Pod 2: Energy Exchange
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3. Cut10ormoreuniformleafdisksforeachtrial.Singleholepunchesworkwellforthisbutstoutplasticstrawswillworkaswell.
4. Choiceoftheleafmaterialisperhapsthemostcriticalaspectof
thisprocedure.Theleafsurfaceshouldbesmoothandnottoothick.Avoidplantswithhairyleaves.Ivy,freshspinach,WisconsinFastPlantcotyledons--allworkwell.Ivyseemstoprovideveryconsistentresults.Manydifferentplantleavesworkforthislab.Myclasseshavefoundthatinthespring,Pokeweedmaybethebestchoice.Avoidmajorveins.
5. Infiltratetheleafdiskswithsodiumbicarbonatesolution.a. Removethepistonorplungerandplacetheleafdisks
intothesyringebarrel.b. Replacetheplungerbeingcarefulnottocrushtheleaf
disks.Pushontheplungeruntilonlyasmallvolumeofairandleafdiskremaininthebarrel(<10%).
c. Pullasmallvolumeofsodiumbicarbonatesolutionintothesyringe.Tapthesyringetosuspendtheleafdisksinthesolution
e. Holdingafingeroverthesyringe-opening,drawbackontheplungertocreateavacuum.Holdthisvacuumforabout10seconds.Whileholdingthevacuum,swirltheleafdiskstosuspendtheminthesolution.
f. Letoffthevacuum.Thebicarbonatesolutionwillinfiltratetheairspacesintheleafcausingthediskstosink.
g. Youwillprobablyhavetorepeatthisprocedure2-3timesinordertogetthediskstosink.Ifyouhavedifficultygettingyourdiskstosinkafterabout3evacuations,itisusuallybecausethereisnotenoughsoapinthesolution.Addafewmoredropsofsoap.
7. Pourthedisksandsolutionintoaclearplasticcup.Addbicarbonatesolutiontoadepthofabout3centimeters.Usethesamedepthforeachtrial.Shallowerdepthsworkjustaswell.
8. Foracontrolinfiltrateleafdiskswithasolutionofonlywaterwithadropofsoap--nobicarbonate.
9. Placeunderthelightsourceandstartthetimer.Attheendof
eachminute,recordthenumberoffloatingdisks.Thenswirlthediskstodislodgeanythatarestuckagainstthesidesofthecups.Continueuntilallofthedisksarefloating.
