w. sean chamberlin, phd professor, earth sciences ... · professor, earth sciences, fullerton...
TRANSCRIPT
1
TheAlgae-in-a-BottleExperiment:
AHigh-ImpactLearningActivity
W.SeanChamberlin,PhD
Professor,EarthSciences,FullertonCollege
2
TableofContents
Summary........................................................................................................................................................................... 4StudentLearningOutcome ......................................................................................................................................... 4LessonPlan....................................................................................................................................................................... 4Whystudyalgae?........................................................................................................................................................................... 5Introducesomebasicfactsaboutmicroalgae. ........................................................................................................................ 5Introducephotosynthesis............................................................................................................................................................ 5Introducechlorophylla................................................................................................................................................................ 6Introducerespiration. .................................................................................................................................................................. 6Emphasizethatphotosynthesisplusrespirationmakealgaegrow. .................................................................................. 7Introducelimitingfactors. ........................................................................................................................................................... 7Askscientificquestions................................................................................................................................................................ 8Discusscarbondioxide................................................................................................................................................................. 8Discussandaddsalts. ................................................................................................................................................................... 9Discussandaddnutrients. .......................................................................................................................................................... 9Discusslightandremovethelabelonthebottle..................................................................................................................10(Optional)Discusslightandnutrientsandmaximumbiomass. .......................................................................................11Don’tforgettomakenotes:thescientificnotebook. ...........................................................................................................11Takepictures!Learngoodscientifichousekeeping. ............................................................................................................11Addalgae.Observe.Taketimezeromeasurements. ...........................................................................................................12Letthealgaeincubate! ...............................................................................................................................................................12Makeobservationsormeasurementsperiodically. .............................................................................................................12Framethosephotos! ...................................................................................................................................................................13Compileresultsandgraphthem. .............................................................................................................................................13Shareandinterprettheresults. ...............................................................................................................................................13
BackgroundandExplanationofApproach..........................................................................................................14TheSlowApproach ..................................................................................................................................................................14TheBasics........................................................................................................................................................................................................ 14TheScientificNotebook ............................................................................................................................................................................ 14Pre-Tests .......................................................................................................................................................................................................... 15DissolvedGases............................................................................................................................................................................................. 15WaterChemistry .......................................................................................................................................................................................... 15BiologicallyImportantNutrients(akafertilizers)......................................................................................................................... 16LimitingFactors-Nutrients: ..................................................................................................................................................................... 16LightIntensity ............................................................................................................................................................................................... 17TheLight-DarkCycle .................................................................................................................................................................................. 17Chlorophylla .................................................................................................................................................................................................. 18Photoadaptation ........................................................................................................................................................................................... 18LightSources.................................................................................................................................................................................................. 19LightintheBottle......................................................................................................................................................................................... 20ScientificQuestions&Predictions........................................................................................................................................................ 20TheSeasonalApproach ............................................................................................................................................................................. 21
TheFastApproach....................................................................................................................................................................21ScientificQuestions&Predictions........................................................................................................................................................ 21PicturesandNotebooks ............................................................................................................................................................................ 22LabelingBottles ............................................................................................................................................................................................ 23ConducttheExperiment ........................................................................................................................................................................... 23KeepTakingPicturesandMakingObservations............................................................................................................................ 23ASimpleObservationActivity................................................................................................................................................................ 24AssessAttitudesandUnderstanding................................................................................................................................................... 24
3
MaterialsandOptionalEquipment........................................................................................................................25BottledWater.............................................................................................................................................................................25Saltwater......................................................................................................................................................................................25SourcesofAlgae ........................................................................................................................................................................25SourcesofNutrientMedia .....................................................................................................................................................25LightSources ..............................................................................................................................................................................26BulbFixturesandBulbs ............................................................................................................................................................................ 26FluorescentLights ....................................................................................................................................................................................... 26AquariumLEDFixtures ............................................................................................................................................................................. 26MobileLightingSystems ........................................................................................................................................................................... 26
ScientificEquipment................................................................................................................................................................27HelpfulResources ........................................................................................................................................................27
4
Summary
TheAlgae-in-a-BottleExperimentprovidesanengagingandflexiblehigh-impactteachingtoolfor
helpingstudentstoknow,understand,andapplyanumberofconceptsrelatedtothebiologyandecology
ofaquaticplantsandtheirenvironments.Itisalsorelevanttomethodsbeingdevelopedfortheuseof
algaeasanalternativeenergysource,thatis,biofuels.Theprotocolsinthisexperimentcanbeadapted
useasademonstrationactivityinoneortwoclasssessions,orasanatureofscience,inquiry-based
activityoverafewtoseveralweeks.Theeasy-to-obtainandinexpensivematerialsusedinthe
experimentmakeitaccessibletoinstitutionswhereresourcesandspacearelimited,aslongassunlight
orartificiallightareavailabletocarryouttheexperiment.Preliminaryresultswithnon-majorsenrolled
inintroductorygeneraleducationoceanographycoursesinacommunitycollegeindicateincreased
engagementandahighlevelofenthusiasmfortheexperiments,andsuggestabetterknowledgeand
understandingoftheeffectsoflightandnutrientsonphotosynthesis,andgreaterappreciationforthe
natureofscience.WebelievethattheAlgae-in-a-BottleExperimentoffersaneffectivemeansfor
improvingscienceliteracyandforintroducingscientificresearchtodiverselearnersfrommiddleschool
tocollege.
StudentLearningOutcome
Uponsuccessfulcompletionofthisexperiment,studentswillbeabletowritetheequationof
photosynthesisandexplainhowvaryingconditionsoflightandnutrientswillaffectthegrowthratesof
microalgaeandtheproductivityoffoodwebsthatdependonthem.
LessonPlan
Thetopicsandstepsoutlinedbelowrepresentasequenceofdiscussionsandactivitiesthatintroduce
theprocessofphotosynthesisandthefactorsthataffectthegrowthofalgaeinaquaticenvironments.The
lessonplanisapplicabletostudentsenrolledinintroductorybiology,botany,plantphysiology,algology,
marinebiology,environmentalbiology,ecology,andoceanographywhereageneralunderstandingof
photosynthesis,primaryproduction,theglobalcarboncycle,andaquaticfoodwebsisdesired.
Thelevelofcomplexityofeachstepandactivitycanbetailoredaccordingtothegoalsofinstruction,
orbackgroundoftheinstructor.Thesequencemaybesimplified,expanded,accelerated,orsloweddown
dependingonthetimeandresourcesavailabletotheinstructor.Theentiresequencemaybecompleted
asademonstrationactivityinthetimeframeofasingle-class,oritmaybecarriedoutasaninquiry
5
activityoveranumberofclasses.Inthelongertimeframe,eachsteporactivitymaybeinterwovenwitha
lectureorotheractivity,assomestepscanbecompletedin10-15minutes.Thelongertimeframe,akind
ofWhatAboutBob?baby-stepsapproach,offersthegreatestopportunitytoachievethehighestlevelsof
contentmasteryandconceptualunderstanding.Forexample,theinstructormaychoosetogivestudents
bottlesofwaterthatalreadycontainalgae,andaskstudentstoobservethechangesincolorthatappear
overthecourseofafewdaysorweeks.Studentsmayeventakethebottleshometomakethese
observations.Alternatively,theinstructormaychoosetocoveronly1-2stepsinthelessonplaneach
class,permittinggreatertimeforintroductionanddiscussionofconcepts,andallowingstudentstocarry
outindividualinvestigationsintheformofaninquiryorresearchactivity.
Themaingoalhereistoprovideinstructorswithafairlysimpleactivity(inpractice)thatisfunand
engagingforstudents,andthatallowsstudentsandinstructorstoexploreandlearnaboutfundamental
processesofglobalimportance.Studentslearnbestbydoing,andit’sinthatspiritthatthisactivityis
presented.
Whystudyalgae?
Tellthemtheyaregoingtocreateahomeforamostmarvelousorganism,onethatservesasthebaseof
thefoodweb,and,indoingso,providesfishandshellfishtomuchoftheworld;onethatregulatescarbon
dioxide,and,assuch,controlsthetemperatureofourplanet,andonethatmayonedayprovidefuel,what
hasbecomeknownasbiofuels,fortransportation.Thisorganismbelongstoagroupoforganismsknown
asthealgae,orbecausetheyaretiny,themicroalgae.Intheocean,werefertomicroalgaeas
phytoplankton,thealgaedrifters.
Introducesomebasicfactsaboutmicroalgae.
Microalgaearesingle-celled,microscopic,photosyntheticorganisms,relatedtoseaweeds,thatinhabit
thelightedregions(i.e.,thephoticzone)ofallaquaticenvironments,freshwaterandsaltwater,including
yourcatordog’swaterdish,yourAuntMary’sbirdbath,andyourkidbrother’sgoldfishbowl.Theclass
willgrowaspeciesofmarinemicroalgae.Distribute8-ozbottledwatertoindividualorteamsofstudents.
Asktheclasstoexaminetheirbottles.Whatwouldbetheidealenvironmentfortheiralgaeinabottle?
Whatareessentialingredientsoftheirnewhome?Writetheirresponsesontheboard.
Introducephotosynthesis.
Writeontheboardabasicequationforphotosynthesis:CO2+H20!sugars+O2.Discuss.Whatdothe
symbolsinthisequationmean?Simplyput,plantsandalgaeusecarbondioxideandwatertoproduce
sugars,akindofenergymolecule,andintheprocess,produceoxygenasabyproduct.What’smissing?
6
Algae,likeplants,needlighttogrow.Addlight:CO2+H20+light!sugars+O2.Whatelsedoplantsneed
togrow?Theyalsoneedfertilizers.Inthealgaebusiness,wecallthembiologicallyimportantnutrients,
orsimply,nutrients.Examplesofcommonlawnandgardenfertilizersmaybeshown.Onthefrontofthe
packagearetheletters,N,P,andK.Whatdothesesymbolsstandfor?Thesearethebasicmacronutrients
requiredbyallplantsandalgae.Addnutrients:CO2+H20+light+nutrients!sugars+O2.(Atthispoint,
moreadvancedcoursesmaydevelopfurtherdetailsofphotosynthesis,suchasthelightanddark
reactions,andthewater-splittingreactions,whichhelpsexplainhowsolarenergyistransformedinto
chemicalenergywhichisthenusedasanenergysourcetomanufacturecellularmaterials,andhelps
explainthattheO2producedbyplantsandalgaecomesfromthesplittingofwater,notthesplittingof
carbondioxide.)
Introducechlorophylla.
Thecentralplayerinphotosynthesisisamoleculecalledchlorophylla.Thismoleculeistheprimarylight-
absorbingmoleculeofallplantsandalgaeandphotosyntheticbacteria.Askstudentsiftheyhaveever
seenchlorophyll?Ifawindowisnear,askthemtolookoutsideatatree.Cantheyseechlorophyll?
Explainthatthegreencolorofplantsandalgaecomesfromchlorophyll.Thismoleculeabsorbssunlight
andtransferstheenergyfromsunlightintoasystemthattransformsthesolarenergyintoaformof
chemicalenergythatcanbeusedbytheplant.Theindividualcellsofalgaearetoosmalltosee,butwhen
thealgaeareabundant,theirchlorophyllisvisible.Askstudentsiftheyhaveevernoticedchangesinthe
coloroftheoceanfromwintertospringtosummertofall.Inwinterandsummer,theoceanmaybeblue
andmostlytransparent.Inthespringandfall,theoceanmaybegreenandopaque.Thedifferenceincolor
andthechangeincolorfrombluetogreencomesfromthepresenceofphytoplankton.Whentheoceanis
blue,therearefewphytoplanktoninthewater.Whentheyoceanisgreen,phytoplanktonareabundant.
Intheexperiment,thecolorinsidethebottleprovidesanindicationoftheamountofalgae.Changesin
thecolorinsidethebottleoveraperiodofdaysindicatehowfastthealgaearegrowing.Itwillbe
importanttoobserveanddocumentthesechanges.
Introducerespiration.
Askstudentswhathappenstoplantswhentheydon’tgetenoughlight?Studentswillgenerallyanswer
thattheplantswilldie,buttheinstructormaycounterbyaskingifplantsdieatnight?Whydon’tplants
dieatnight?Plantsandalgaestoreenergyinthesamemannerashumansdo.Whenlight(orfood)isnot
available,plants(andhumans)usetheirstoredenergy.Plants,algae,andhumansstoreenergyasfatty
acids,whichwemaythinkofasenergymolecules,justlikesugars.Whenplants,algae,andhumansneed
energy,theybreakdownthesefattyacidsinaprocesscalledcellularrespiration.Here’stheequation:
7
fattyacids+O2!CO2+H20.Doesthisequationlookfamiliar?Infact,respirationresembles
photosynthesisintheoppositedirection.Organismsuseoxygentobreakdownenergymolecules(sugars
andfats)and,indoingso,producecarbondioxideandwater.Whyisthisimportant?Becauseplantsand
algaeusesomeoftheenergytheyproduce,andtheyuseoxygentobreakdownthatenergy.Simplyput,
plantsandalgaecarryoutrespirationandrequireoxygen.Repeat:plantsandalgaerequireoxygen.
Fortunatelyforus,plantsandalgaeproducemoreenergymoleculesandmoreoxygenthantheyneed.
Otherwise,wemightonlyfindplantsonPlanetEarth!
Emphasizethatphotosynthesisplusrespirationmakealgaegrow.
Photosynthesisturnssolarenergyintochemicalenergy,andrespirationtakesthatchemicalenergyand
usesittobuildallofthethingsthatmakeupaplantoralgalcell,includingthemolecularmachinerythat
letsplantsandalgaephotosynthesize.Photosynthesisandrespirationworktogether.Growthinplants
andalgaeoccursviacellulardivision:onecelldividesintotwocells,twocellsdivideintofourcells,andso
onandsoforth.Becausealgaeareunicellular,wecanmeasurehowfasttheyaregrowingbycountingthe
increaseincellnumbersoveraperiodoftime.Alternatively,wecanmeasurechangesinthe
concentrationofchlorophyll,eithervisuallyaschangesincolor,orquantitatively,usingscientific
instrumentsdesignedtodetectchlorophyll(e.g.,colorimeters,spectrophotometers,fluorometers,etc.)If
wewanttoconductexperimentsonwhatmakesalgaegrow,thentrackingtheirgrowthratewillbe
important.Theinstructormaywanttoholduptwodifferentbottlesofalgaewithdifferent
concentrationsofchlorophylltoemphasizethispoint,orprojectamicroscopicimageofmicroalgae.
(Advancedclassesmaybeintroducedtogrowthcurvesandgrowthequations,ifdesired.)
Introducelimitingfactors.
Innature,somethingalwayslimitshowfastplantsoralgaecangrow.Ifit’snotlight,thenitmightbe
nutrients.Ifit’snotlightandnutrients,thenitmightbewater(forplants)orsomeotherfactor(for
algae).Theideathatsomethingalwayslimitshowfastplantsoralgaecangrowprovestobeanimportant
one,especiallyinagriculture.Ifyouwanttogrowmorecropsfaster,youneedtoidentifythefactorthatis
limitingthegrowthofthecrops.Inthemid-1800s,JustinvonLiebig,auselesschemistrystudent(inthe
eyesofhisprofessors)cameupwiththeideaofalimitingfactor,theonefactorrequiredforthegrowthof
aplantthatisintheleastsupply.Itmightbelight,itmightbenutrients,oritmightbesomethingelse.
ThuswasbornLiebig’sLawoftheMinimum.Anillustrationofawoodenbucketwithdifferentlengthsof
planksservesasausefulanalogy:thelengthoftheshortestplankdeterminestheamountofwaterheld
bythebucket.Analogously,thelimitingfactordeterminesthegrowthrateoftheplantoralgae.This“law”
hasimportantimplicationsforunderstandingthegrowthofalgaeinabottle,andinnature.Inadditionto
8
agriculture,Liebig’sLawoftheMinimumhasbeenappliedtounderstandingthebiologyandecologyof
phytoplanktongrowthintheocean.
Askscientificquestions.
TheAlgae-in-a-BottleExperimentmaybeconductedasademonstrationactivity,wherestudentsoptimize
waterlevels,preparesaltwater,addnutrients,findsuitablelight,addalgae,andwatchthealgaegrow,or
itmaybepresentedasaninquiryactivity,wherestudentscomeupwith(oraregiven)scientific
questionstoexplore,formulatehypothesesandpredictions,setupexperimentalconditions,carryoutthe
experiments,andanalyzeandcommunicatetheresults.Ineitherapproach,it’susefultoaskstudentsto
workinpairsorteamstocomeupwithafewscientificquestionsconcerningthegrowthoftheiralgaeat
differentlightlevelsanddifferentnutrientconcentrations.Whathypothesesmighttheytest?Whatdo
theypredictwillhappen?Alternatively,theinstructormaywriteafewquestions,hypotheses,and
predictionsontheboard.Toavoidconfusion,startwithlightasalimitingfactorfirst.Forexample,how
fastwillalgaegrowinhighlight?Howfastwilltheygrowunderlowlight?Howfastwillalgaeathigh
lightgrowwithshortdaysandlongnights,suchasfoundinwinterintemperatezones?Howfastwill
theygrowwithlongdaysandshortnights,resemblingsummerintemperatezones?Thereareanumber
ofvariationshere,butitcanbeusefultoallowstudentstoexplorethepossibilities,justasascientist
might.Similarquestion-generatingcanbecarriedoutwithnutrients,butwithoneimportantextension:
theconcentrationofnutrientsinthebottlewilldeterminethemaximumbiomassofthealgaeinthe
bottle.Lowernutrientconcentrationswillproducelowerbiomass,andhighernutrientconcentrations
willproducehigherbiomass.
Discusscarbondioxide.
Holdupapieceofwood.Whatkindofatomsdoesitcontain?Carbon.Fromwheredoesthecarboninthe
woodcome?Carbondioxide.Howdoplantsobtaincarbondioxide?Fromtheatmosphere.Howdoalgae
obtaincarbondioxide?Fromcarbondioxidedissolvedinthewater.(It’snotnecessarytointroducethe
formsofdissolvedcarbondioxideinseawater,i.e.,thecarbonatebufferingsystem,asthistendsto
overcomplicatethematter.)Howdoescarbondioxidegetintothewater?Acrosstheair-waterinterface.
Holdupabottleandask,ifalgaeusethecarbondioxideinthewater,howwilltheygetmore?Itmight
takesomepromptingtogetstudentstorealizeit,butthecapwillhavetoberemovedfromthebottleto
periodicallyrefreshtheairinthebottle.Thebottlemayneedtobeshaken.Whatelsecanbedonebesides
removingthecap?(Moreprompting.)Createaheadspace.Atthispoint,studentsmaydrinkorpourouta
portionofthewatersothatthewaterlevelisevenwiththeshoulderofthebottle,rightwhereitbeginsto
taper.
9
Discussandaddsalts.
Iftheclassisgrowingmarinealgae,whatmusttheydotothewaterinthebottle?Addsalts.(Depending
onthelevelofcomplexitydesired,theinstructormayintroducethepropertiesofwater,thenatureof
dissolving,anionsandcations,themajorconstituentsofseawater,thePrincipleofConstantProportions,
salinity,andmeasuringsalinityusingconductivity,buttheseconceptsarenotessentialformeetingthe
learningoutcomesfortheexperiment.)Whatkindsofsaltsmakeupseawater?Mostly,wefindsodium
chlorideinseawater,butwealsofindnineothermajorelements,themajorconstituents,andmorethan
80traceelements,theminorconstituents.Fortunately,wecanbuysaltsforsaltwateraquariums,and
that’swhatwewilluseforouralgae.(Atthispoint,theinstructormayinstructthestudentstoadda
teaspoonofseasaltstotheirbottle,orletstudentscalculatetheamountneededaccordingtothe
directions,forexample,ahalfcupofsaltspergallonofwater.Theproportionalitycalculationisagood
exerciseforstudents.Studentswillneedtomeasuretheamountoffreshwaterintheirbottle,nowthat
theyhavereduceditsvolumetolessthan8ounces.)
Discussandaddnutrients.
Whatelsedoalgaeneedintheirseawatertogrow?Ifstudentswerepayingattentionearlier,theywill
answernutrients.Buttheinstructormayneedtoreferthembacktotheequationofphotosynthesis
writtenontheboard.Whatwouldhappenifnonutrientswereadded?Whereisaplaceonlandwithlow
nutrients?Deserts.Whereisaplaceintheoceanwithlownutrients?Thetropicalocean.There’svery
littleplantgrowthindesertsbecauseofwaterandlownutrients,andverylittlephytoplanktongrowthin
thetropicaloceanbecauseoflownutrients.Soifnonutrientswereadded,therewouldbelittletono
growthofalgae.Whatiflotsofnutrientswereadded?Domorenutrientsnecessarilymeanhigher
growth?Itcanbeusefultoshowagraphofgrowthrateversusnutrientconcentrationforlimiting
concentrationsofnutrients.Atsomepoint,asaturatingconcentrationofnutrientsisreached,beyond
whichadditionalincreasesintheconcentrationdonotproducefastergrowth.Instructorsmayalsowant
toreferbacktothediscussionoflimitingfactorstoexplainthatathighnutrientconcentrations,nutrients
maynolongerbelimiting,and,asaresult,someotherfactormightlimittheirrateofgrowth.What
happenswhenthenutrientsrunout?Thealgaestopgrowing,andthecolorinsidethebottleremains
constant.(Ultimately,theamountofnutrientsinsidethebottledeterminesthefinalbiomasswithinthe
bottle.Soonesimpleexperimentsimplyinvolvescomparingthecoloroftwobottles—onewithlow
nutrientsandonewithhighnutrients—attheendofagivenperiodoftime.Ifnutrientconcentrationsare
saturating,andthetwobottlesheldatthesamelightintensities,theymaybothgrowatthesamerate,but
thebottlewiththehighernutrientconcentrationwillpermitgreatergrowthandahigherfinal
10
concentrationofalgae.Thisisapointthattheinstructormaychoosetoexplainwhentheexperiments
havebeencompletedtoallowstudentstoderivethisconclusionontheirown.)Aswithseasalts,algae
nutrientsareavailableforpurchase,albeitinahighlyconcentratedform.Theinstructorwillwantto
prepareasolutionofnutrientsaheadoftimefromwhichstudentscanpipetteagivenamount.The
amountdispensedtostudentswilldependonthetypeofexperimentthattheinstructororstudentshave
chosentocarryout.Inthesimplestapproach,somestudentswilladdafewdropsandotherswilladd
doubleortriplethenumberofdrops.Intheabsenceofinstrumentationtomeasuretheconcentrationsof
nutrientsinthebottles,there’sabitofguessworkhere.Experimentwithit.That’sscience!
Discusslightandremovethelabelonthebottle.
Fortunately,discussionsoflightinvolvemorefamiliarterritory.Studentsgenerallyunderstandhighlight
andlowlight.Theymaybelessfamiliarwithlight:dark(L:D)cycles,thoughsomepromptingand
questioningaboutlengthofdaysinsummerversuswinter,timeitgetsdarkatnight,timeitgetslightin
themorning,etc.,helpsstudentsgrasptheidea.Keytothisstepisadiscussionofthelightenvironment
insidethebottle.Holdingupabottle,theinstructormightaskwhatpropertiesofthebottleitselfmay
impedethequantityoflightthatthealgaereceiveinsidethebottle.Somestudentswillimmediately
recognizethatthecapblockslight.Adiscussionoftheorientationofthebottlewithrespecttothelight
sourcecanbehelpful.Whichisbetter,illuminationfromaboveorilluminationfromtheside?Whatare
thepotentialadvantagesanddisadvantagesofeitherapproach?Savvystudentswillalsorecognizethat
thebottle’slabelwillblocklight.Theclassshouldremovethelabelsfromtheirbottleatthispoint.Ifthe
instructorhasalreadychosenthelightintensityorlightintensitiesfortheexperiment,thenheorshe
maywanttoaskstudentstoworkinpairsorteamstopredictgrowthratesunderthatlightintensity(or
rangeoflightintensities),assumingthatnutrientsarenotlimiting.Ifnaturalsunlightistobeused,the
instructormightaskhowgrowthrateswillvarythroughtheday,andatnight(!)AdiscussionofL:D
cycles,whichofferanotherexperimentalvariable,maybecarriedoutamongstudentsorasaclass.Inthe
end,itwillbeimportantforstudentstoknowortohavedecidedthelightintensity(low,medium,or
high)andthelightregime(12:12,16:8,8:16)fortheirparticularexperiments.(Adventurousinstructors
maywanttointroduceBeer’sLaw,theexponentialdiminishmentoflightasitpassesthroughaliquid.
Thiscanbeusefulfordiscussionsofself-shadingofalgaewithinthebottle,orasanexplanationfor
differencesingrowthratesthatmayoccurinshallowerordeeperbottles.Opportunitiesalsoexistto
coverelectromagneticradiation,theseasonalcycle,theabsorptionpropertiesofwater,theabsorption
spectraofphotosyntheticpigments,whytheoceanisblue,andsatelliteoceanography,amongothers.)
11
(Optional)Discusslightandnutrientsandmaximumbiomass.
Asmentionedearlier,theconcentrationofnutrientswilldeterminethemaximumbiomassofalgaethat
willgrowwithinthebottle.However,thespeedwithwhichthemaximumbiomassisachievedwill
dependonlightintensity.Foragivennutrientconcentration,ahighlightintensitywillpromotefaster
growthandaquickeruseofnutrientsthanalowlightintensity.Asaresult,underhighlight,the
maximumbiomassmaybereachedinamatterofafewdays,whereasunderlowlight,themaximum
biomassmaynotbereachedforseveraldays.Instructorsmaywanttopromptstudentstothinkabout
whatishappeninginsidethebottleasthealgaegrow.Forexample,whatishappeningtothenutrient
concentrationoftheseawaterinthebottle?It’sdecreasing.Whatishappeningtothebiomass?It’s
increasing.Whathappenstothelightintensityinsidethebottleasthebiomassofthealgaeincreases?
Thelightisdiminishedbecausethealgaeareabsorbingit.Wheretimepermits,discussionofthese
interactionscanreallyhelptosolidifystudentsunderstandingoftheconcepts.Studentsmaybeaskedto
createamatrixofpossibleoutcomes,ortheymaybeaskedtocreateconceptmaps.Shortanswerand
essayquestionsonthetopicscoveredtothispointwillhelpinstructorsidentifymisconceptions,andwill
helpensurethatstudentsaremakingthelinkbetweenthetheoreticalconceptsandtheactual
experiment.Dostudentsgraspwhatisgoingonwithinthebottle?Dotheyhavetheconceptual
understandingtosupportandexplainwhateverresultstheyachieve?
Don’tforgettomakenotes:thescientificnotebook.
Dependingonthetypeofcourseandtheexperiencelevelofthestudents,itmaybenecessaryto
introduceappropriatemethodsfordocumentingtheexperimentalmethods,observations,anddataina
scientificnotebook.
Takepictures!Learngoodscientifichousekeeping.
Oncestudentshavepreparedtheirseawaterandnutrientsolution,andhaveaclearideaofthelight
protocolthattheywillobserve,it’sagoodtimeforstudentstotakepicturesoftheirbottles(usingtheir
smartphonesorotherdevices),andevenselfieswiththeirbottle.Wehighlyrecommendthatinstructors
simplyinstructstudentstotakepictureswithoutsupplyinganyadditionaldetails.Studentsshouldbe
askedtosharetheirphotoswitheachother,evenpostthemonFacebookorInstagram.Ifpossible,
studentsshouldaskstudentstoemailtheirphotostotheinstructorsothatheorshecanprojectthemon
theclassroomprojectionscreen.Twoorthreephotosfromdifferentstudentsworksideallytomakethe
followingpoints:1)Howwillstudentsbeabletoidentifytheirbottlesamongaclassroomofbottles?2)
Howwilltheybeabletotellfromapictureiftheirbottleshaveturnedgreener?and3)Whymightitbe
importanttoreproduceexactlythewayinwhichthephotographwastaken?Thefirstpointmaybe
12
addressedbyassigninguniqueidentifierstoeachstudent.Theinstructormightaskifitmatterswhere
studentsplacetheirlabels.(Thebestapproachistouseapermanentmarkerandlabeltheplasticcapon
thebottle.)Thesecondpointmaybeaddressedbysuggestingthatstudentstaketheirpicturesagainsta
whitebackground.Awhiteboardworksgreatforpicturetaking.Thethirdpointreferstocreatingatime
sequenceofphotographsthatareidenticalineveryrespect:samedistancefromthecamera,same
lighting,sameangle.Reproducingthephotographicconditionsasexactlyaspossibleensuresthatany
changesobservedareduetothegrowthofthealgae,notthewaythepicturewastaken.
Addalgae.Observe.Taketimezeromeasurements.
It’sfinallytimetoaddalgae.Theinstructorwillprovideaflaskorcontainerofstockculturefromwhich
studentsmaypipetteasmallamount(~1ml),ortheinstructormayaddthealgae.Tothedegreepossible,
identicalamountsshouldbeaddedtoeachbottletoensureconsistencyandreproducibilityintheresults.
Followingtheadditionofalgae,studentsshouldcaptheirbottle,andgentlyshakeit.Theymaythentake
pictures(usingthepicture-takingcriteriaestablishedinthepreviousstep).Ifquantitativemeasurements
aretobetaken,thestudentsshouldbeinstructedtotakethesemeasurementsatthistime.Students
shouldmakevisualobservationsoftheiralgae,andwritethoseobservations,alongwiththetimeand
date,intheirnotebooksorontheirworksheet.Theinstructormaywanttoremindstudentstobesure
thattheyhaveproperlylabeledtheirbottles.
Letthealgaeincubate!
Studentscannowplacetheirbottlesinthelocationchosenfortheexperiment(awindowsill,atabletop
withalightsource,aplantgrowthcart,etc.).Theywillwanttonotetheorientationofthebottlewith
respecttothelightsourceassmallperturbationsinthebottle,bottlecaps,labelresidue,mayslightly
changethelightregime.Studentswillwanttomaintainthesameorientationthroughouttheexperiment.
Makeobservationsormeasurementsperiodically.
Followingtheinitialadditionofalgae,thetimetableformakingfurtherobservationsormeasurements
willdependontheclassschedule.Ifstudentsaretakingpictures,observationsmaybecompletedina
shortamountoftimeatthebeginningofclassoveraperiodofaweekorafewweeks.Iftheyaremaking
measurementsofchlorophyll,itmaytakelonger,butwithenoughresourcesandproperorganization,
thesemeasurementsshouldn’ttakelongeither.Anaturalendpointfortheexperimentisthepointwhere
nofurtherchangesincolor(orchlorophyll)areobserved(ormeasured),themaximumbiomasspoint,or
ashortertimeperiod,dependingontheinitialquestionsbeinginvestigated.
13
Framethosephotos!
Theavailabilityofappsthatpermituserstocreatecollagesofphotosprovesveryusefulforillustrating
before-and-afterphotosofthealgaeinthebottle.Atimesequenceofseveralphotosmayalsobecreated.
Studentsgenerallyknowtheseappswell,andwillrequirelittledirectionforcreatingacollageoftheir
experiment.
Compileresultsandgraphthem.
InclassroomswhereiPadsorcomputersareavailable,studentsmayenterdataintoaspreadsheetas
theycollectit.Otherwise,theymaycreatetablesandgraphsofdatainacomputerlaboronacomputerat
home.Barchartsillustratingchangesincolor(measuredbyacolorimeterorspectrophotometer)or
chlorophyll(measuredinafluorometer)helpillustratechangesandratesofchangeinalgalgrowth.
Shareandinterprettheresults.
Weencourageinstructorstoallowstudentstoshareandinterprettheirresultswiththerestoftheclass.
Theonlineavailabilityoffreepresentationsoftware(e.g.,GoogleSlides)makesiteasyforstudentsto
prepareafewshortslidesoftheirresults,andmakesiteasyforstudentstoprojecttheirslidesona
classroomprojectionsystemconnectedtotheInternet.Alternatively,studentsmaypreparePowerPoint
presentations,andsubmitthemonaUSBdrive,ortheymaywriteuptheirexperimentsinalaboratory
reportorscientificpaper.Weencourageinstructorstofocusonthepresentationandinterpretationof
theresultsversusaproperaccountingofmethods,thoughthisisimportant.Fartoooftenstudentsfeel
liketheresultsoftheirexperimentsarenotvalid,thattheydidsomethingwrong,orthatsome
experimentalerrorgavethemtheresultsthattheyachieved.Onthecontrary,it’simportanttocomeup
withpossibleexplanationsforanyresultsthestudentsfind.Algaemaygrowornotgrowforavarietyof
reasons,includingtemperaturefluctuations(unaccountedforinourexperiments),bacterial
contamination,differencesinbottlesthatinducedifferencesintheinternallightintensity,accidental
differencesintheamountofsalts,nutrients,oralgaeadded.Studentsshouldbeencouragedtocompare
theirresultswiththoseoftheirteammembers.Ifthetreatmentswereidentical,shouldn’ttheresultsbe
identical?Alivelydiscussionofresultsdemonstratesthatstudentswereengagedintheprocess,thatthey
wereinvestedintheexperiments,andthattheyunderstandtheconceptualunderpinningsofthe
experiments.Thisisthemostrewardingpartoftheexperimentforstudentsandinstructors.
14
BackgroundandExplanationofApproach
Theideaforaclassroomexperienceingrowingalgaeemergedfromanundergraduateresearchprojectin
algaebiofuelsatFullertonCollege,alargecommunitycollegeinSouthernCalifornia.Lackingspaceand
resourcesforsophisticatedbioreactors,studentsgrewan“off-the-shelf,”euryhaline(tolerantofawide
rangeofsalinity),marinealgalspecies,Tetraselmis,ina120-gallonaquariumequippedwithLED
aquariumlights.Successfulpropagationofthealgae(i.e.,theydidn’tkillit)ledtotheideaofhavinga
classroomofstudentsgrowthealgaein8-ozwaterbottles.(Smallerwaterbottleswereusedtoreduce
theexpense,but11-or12-ozbottlesshouldworkequallyaswell.)
TheSlowApproach
TheBasics
Inthesimplestversionoftheexperiment,studentsareintroducedtothebasicsofphotosynthesis,
includingthelimitingeffectsoflightandnutrientsonmarinealgalgrowth.Studentsarethengivenan8-
ozbottleofwaterpurchasedatagroceryorsuperstore,andaskedtodiscusswhatarethenecessary
“conditions”toturntheirbottledwaterintoasuitablehomefortheirmarinealgae.Studentsgenerally
understandthatlightisnecessaryforalgalgrowth,buttheyarelesscertainwhatwillhappenunderlow
lightconditions,orunderconditionswithvaryinglight-darkcycles.Similarly,studentsgenerally
understandthatsomekindof“fertilizers”(i.e.,biologicallyimportantelements)areimportanttomake
algaegrow,butlackthesophisticationtopredictwhatmighthappenatdifferentconcentrationsof
nutrients.Nonetheless,studentsareontherighttrackinknowingthattheiralgaewillrequirelightand
nutrients.
TheScientificNotebook
Followingageneralintroductiontotheexperiment,andinpreparationforcarryingouttheexperiment,
it’sagoodideatointroducestudentstotheimportanceofdocumentingeverystepalongtheway.If
scientificnotebooksandscientificnotetakinghavenotbeenintroducedtotheclass,thennowwouldbea
goodtime.Theinstructormayaskstudentstotakenotesindividuallyintheirownnotebooks,orthey
mayprovidecompositionnotebookstotheteamsofstudentswhowillworktogetherontheexperiments.
Introductiontothescientificmethod,posingquestions,formulatinghypotheses,makingpredictions,
carefullydocumentingobservationsandmeasurements,anddatarecordingcanbeintroduced.
Otherwise,iftimeisrestricted,theinstructormaywishtopresentacommonquestionorquestionstothe
15
class,andguidestudentsthroughapre-chosensetofhypothesesandpredictionsforagivensetof
experimentalconditions.
Pre-Tests
Instructorsmayalsowishtoadministerpre-testsdevelopedforthealgae-in-a-bottleexperiment.(See
Appendix.)Studentattitudestowardsscienceandstudentknowledgeofphotosynthesisandalgal(or
plant)growthmaybeassessedtogaugelevelsofenthusiasmandlevelsofknowledgepriortothe
activity.Followingtheexperiment,asetofpost-testscanbeadministeredtodetermineimprovementsin
attitudesandunderstanding,andasatoolforimprovingthewayinwhichtheexperimentiscarriedout.
DissolvedGases
Followingtheintroduction,theinstructormayprovideeachstudentwithabottleofwater.Thefirst
discussionwithstudents,bottleinhand,mayconcernthepresenceofdissolvedgases,andspecificallythe
deliverofcarbondioxide,toalgaeinthebottle.Theinstructormaywanttointroducetheconceptof
respiration,andevengasexchangeacrossanair-waterinterface,ifdesired.Anystudentwhohasowneda
goldfishshouldbefamiliarwiththeimportanceofaerationforoxygenation.Algae,too,needoxygen,
exceptthisisnotusuallyaproblembecausetheyproducetheirown,apointthatcanbereinforcedby
referringtoasimpleequationforphotosynthesis.However,algaealsoneeddissolvedcarbondioxideto
grow.Studentsmaybeaskedhowtheiralgaewillobtaincarbondioxideinabottlethatisfilledtothe
brimandcapped.Anumberofsolutionscanbeexplored—removingthecap,addinganairpump,shaking
thebottleregularly—allofwhichservethepurpose.Themostelegant(andeasiesttoimplement)
solutionistosimplypourwateroutofthebottle.Werecommendreducingthewaterleveltothe
shoulderofthebottle.Heretheinstructormayintroducetheconceptofheadspaceinabottletoallowfor
anappropriateexchangeofgases.Ademonstrationofheadspaceinasodabottleforpreventing
explosionscanbehelpful.Foradvancedclasses,theinverserelationshipbetweenthesaturation
concentrationofagasandwatertemperaturemayalsobeexplored.
WaterChemistry
Furtherdiscussioncanbeelicitedregardingtherequirementsformarine-versus-freshwateralgae.
Invariably,someonementionssaltwater,andadiscussionensuesregardingthechemicalcompositionof
saltwater,andhowtoreproducethatformulainabottleofwater.Anumberofimportantwater
chemistryconcepts,suchasthenatureofdissolving,cationsandanions,thePrincipleofConstant
Proportions,etc,canbeintroducedhere,buttheconversationcanbeshortenedbytellingstudentsabout
“instantocean”saltsmanufacturedforthesaltwaterandreefaquariumhobbyist.Onevariantofthe
16
experimentasksstudentstocalculatetheamountofsaltsthatshouldbeaddedtobottleofwaterbased
onthemanufacturer’sdirectionsfortheamountofsaltstoproduceagallonofsaltwater.Studentsmust
grapplewithunitconversionsandratiostocomeupwiththecorrectamountofsalts.Theyalsowillneed
tomeasurethevolumeofwaterintheirbottleaftertheyhaveremovedsomewatertoallowforgas
exchange(asmentionedabove).Instructorsmayextendthispartoftheexperimenttoincludelessonsin
measurement,methodsprotocols,andrecordkeepinginascientificnotebook.Oncestudentshave
preparedtheirsaltwatersolution,theymaycheckthesalinityinsidetheirbottleusingarefractometeror
salinometer(ifavailable).Otherwise,theinstructormaysimplyprovideananswer,allowstudentstoadd
apre-determinedamountofsalt(usuallyateaspoon),andcontinuewiththeexperiment.
BiologicallyImportantNutrients(akafertilizers)
Onceanunderstandingofidealwaterconditionsisestablished,andstudentshavepreparedtheir
seawatersolution,thenextstepistointroducetheneedforbiologicallyimportantnutrients,andthe
conceptofalimitingfactor.Anexpandedversionoftheequationofphotosynthesismaybepresented,or
anintroductionto“fertilizers”andtheimportanceofnitrogen(N),phosphorus(P),andpotassium(K)
maybepresented.TheinstructormayintroducestudentstoJustinvonLiebig,aworthlesschemistry
student,accordingtohisprofessors,buttheoriginatoroftheideathatoneelement(orfactor)aboveall
limitsthegrowthofplants(ormicroalgae),thatis,Liebig’sLawoftheMinimum.Formarinealgae,
nitrogenintheformofnitrateisgenerallylimitingintheocean,butthisfactmayovercomplicatestudent
understandingatthispoint.Wegenerallyaskwhatmighthappenifalgaeweresimplyintroducedtotheir
bottlesatthisstage.Somepromptingofanswersusinghouseholdplantsasexamplesmaybeappropriate.
Wegenerallyaskhowmanystudentshavegrownplants,orhelpedtofertilizealawn.Fordemonstration,
weshowdifferentbagsoffertilizerwiththeirdifferingratiosofN,P,andK.Where’sthesoilinthe
aquaticalgaehome?What’sthepurposeofsoil?Whydowefertilizeplants?Whathappensifwedon’t?
ThestandardnutrientenrichmentmediumforgrowingaquaticalgaeisGuillard’sf/2,thoughother
mixtureshavebeguntoreplacethisone.Afulldescriptionofthesemediaisbeyondthescopeofthistext,
butlinkstousefulresourcesonthistopiccanbefoundintheAppendix.Forthepurposesofthe
experimentshere,wepurchaseliquidf/2fromanaquaculturevendor.
LimitingFactors-Nutrients:
Thecriticaldecisionhereishowmuchnutrientenrichmentmediatoadd.Theinstructormaywishto
showstudentsagraphoftherelationshipbetweennutrientconcentrationandgrowthrate.When
concentrationsarelimiting(thelinearpartofthegraph),algalgrowthwillberegulatedbythenutrient
concentration.Whereconcentrationsaresaturating(thehorizontalpartofthegraph),nutrient
17
concentrationswillbesaturatingandsomeotherfactorwilllimitthegrowthofthealgae,ortheywill
growattheirmaximalrate.Asanextensiontotheexperiment,studentsmaybeaskedtohypothesize
whatwillhappenunderconditionsoflimitingandsaturatingnutrients.Whichbottlewillturngreen
faster?Theymayalsobeaskedtoconsidertheendresult(i.e.,thefinalconcentrationofalgaeintheir
bottle,i.e.,themaximumbiomass)undereachoftheseconditions.Whichbottlewillturngreenest?Iftime
islimited,orthecomplexityofthistopicisonethatinstructorsdonotwishtointroduce,studentsmaybe
instructedtoaddapre-setamountofsaturatingnutrients,ortosimplygiveanyamountatry.Inour
experience,studentstendtowanttoaddplentifulnutrients,sotheinstructormaywanttogivestudentsa
morenarrowchoice,2,4,or6drops.Tothoseeagertoaddlotsofnutrients,theinstructormightaskif
it’spossibletoaddtoomuch?(Yes.)Whathappenswhenyouoverfertilizealawn?(Itdies.)What
happenstothesalinityifyouaddtoomuchnutrientmedia?(Thesalinityislowered.)
LightIntensity
Oncenutrientshavebeenadded,it’stimetoconsiderthelightintensityunderwhichthealgaewillbe
grown.Studentsshouldbeaskedtopredictratesofgrowthversusdifferentlightintensities.The
instructormayaskiftherecanbetoomuchlight,ortoolittle.Agraphofgrowthrateversuslight
intensitymaybeshowntostudentsfollowingdiscussionoftheirpredictions.Weretheirprediction
accurate?Theinstructorwillwanttopointoutkeyconceptssuchasthecompensationlightintensity,the
minimumlightintensityneededtomeetthemetabolicdemandsofthealgae(orplant)itself.Belowthis
lightintensity,thealgaewill“starve.”Thesaturationlightintensity,thelightintensityatwhichgrowth
rateismaximal,shouldremindstudentsofthesaturatingnutrientconcentration.Abovethislight
intensity,thegrowthrateofthealgaewillnolongerincrease;thegrowthrateismaximal.However,light
intensitycanbecometoohigh,andtheconceptofphotoinhibitionmaybeintroduced.Studentsmaybe
askedtonameafewcommonplantsthatpreferthesun,andonesthatprefertheshade.Whathappensto
shadeplantswhenyouplacetheminbrightlight?(Theywitheranddie.)Algaereducetheirgrowthrate
atextremelyhighlightintensities.
TheLight-DarkCycle
Inadditiontolightintensity,thelight-dark(L:D)cycleplaysanimportantroleinthegrowthofthealgae.
It’sinstructivetoprobestudentunderstandingoftheL:Dcycleandhowitchangesthroughtheseasonal
cycle.Whenarenightsthelongestanddaystheshortest?Whenaredaysthelongestandnightsthe
shortest?Howlongisdaylightduringthesummer?Howaboutduringthewinter?CommonL:Dcyclesare
16:8hours(summer),12:12hours(spring/fall),and8:16hours(winter).Iftheclassisusingnatural
light,studentscanlookuptheL:DcycleontheUSNavalObservatorywebsite
18
(http://aa.usno.navy.mil/data/docs/Dur_OneYear.php).Withartificiallight,theL:Dcyclecanbe
controlledwithasimpletimer(suchasthosefoundinahardwarestore).Studentsmaybeaskedhowthe
L:Dcyclemightaffecttheirexperiments.WillthealgaegrowfasterunderalongerL:Dcycle,orwillthey
simplygrowforalongerperiodoftime?Why?HowwilltheL:Dcycleaffectthetimeneededtoreachthe
maximumbiomassinthebottle?
Chlorophylla
Atsomepoint,instructorswillwanttomentionthepresenceofchlorophylla(hereafter,simplycalled
chlorophyll).Chlorophyllisthemajorlightabsorbingpigmentofallphotosyntheticorganisms(including
cyanobacteria,algae,andhigherplants)thatproduceoxygen.(Thislatterdistinctionmayormaynotbe
importanttointroduce:somebacteriacarryoutformsofnon-oxygenicphotosynthesisthatdonotuse
chlorophyll,andwe’llleaveitatthat).Thegreenthatstudentsobserveintheleavesofatree,oranalgae-
filledpond,comesfromchlorophyll.Whileit’snotnecessarytointroducebiochemicalmechanismsby
whichplantscaptureandprocesslightenergy(i.e.,theZ-scheme),itisimportanttopointoutthat
chlorophylltakesenergyfromthesun(orartificiallights)andturnsitintochemicalenergy(i.e.,ATPand
NADPH)thattheplantcanusetogrow.Theterm,chlorophyllantenna,iscommonlyusedinthe
literature,butweprefertothinkofchlorophyllasakindofcatcher’smittthat’susedtocapturebaseballs
(i.e.,photons)oflight.Ultimately,studentswillusechangesintheconcentrationofchlorophyllasan
approximationforgrowthrate.Usingphotography(smartphonesortabletsworkgreat),colorchart
comparison(e.g.,Fore-ulescale),acolorimeter(homebuiltorpurchased),orafluorometer(e.g.,Turner
DesignsAquafluor),studentswilltrackchangesinthegrowthofthealgaeintheirbottles.Studentsmay
beaskedtopredictwhatwillhappentochlorophyllconcentrationsintheirbottlesasthealgaegrow.
Photoadaptation
Dependingontimeandthelevelofcomplexitythattheinstructorwishestointroduce,theconceptof
photoadaptationmaybeintroduced.Thephysiologyofalgae(andplants)permitsthemtotunetheir
photosyntheticmachinerytoavailablelightconditions(nutrientconditions,too,butthat’sanother
topic!).Whilewemaynormallyconsiderthattheamountofchlorophyllperalgalcellisconstant,in
reality,thisratiochangeswithlightconditions.Whenlightintensityislow,individualalgalcellsproduce
greateramountsofchlorophyll.Why?Morecatchers’mitts(i.e.,morechlorophyllantennae)enablethe
algalcelltocapturemorephotonsoflight.(Technicallyspeaking,morechlorophyllincreasesthe
probabilityoflightcapture.Algaemayincreasethesizeoftheirantennae,ortheymaymakemore
antennae,dependingonthespecies.)Thus,underlowlightconditions,individualalgalcellswillbecome
19
greener.Attheotherendofthespectrum,underhighlightconditions,algaewillreducetheir
concentrationsofchlorophyllpercell(toavoidphotoinhibitionandtoconserveenergy).Assuch,under
highlightintensities,individualalgalcellswillappearlessgreen.Theinstructormaywanttoaskstudents
toexaminetheleavesofshadeandsunplantsandcomparetheircolor.Typically,shadeplantswill
appearadarkergreenbecauseoftheirhighchlorophyllpercellratio,ascomparedtosunplants,witha
lightergreencolor,thatis,alowerchlorophyllpercellratio.It’spossibleatthispointtointroduce
studentstootherphotosyntheticpigments,suchotherformsofchlorophyll(e.g.,chlorophyllb,
chlorophyllc)andaccessorypigments(e.g.,fucoxanthins)thathelpcapturelight(especially,wavelengths
oflightthatchlorophylladoesnotcapture),orphotoprotectivepigments(e.g.,carotenoids)thatprotect
thephotosyntheticmachinerymuchinthesamewaythatsunglassesprotectoureyes.Theseother
pigmentsbecomevisibleinclimateswheretheleaveschangecolor:absorptionofchlorophyllduringfall
makesthesepigmentsapparentastheyellows,oranges,andredsoffallleaves.Differentspeciesofplants
(andalgae)makedifferentkindsofaccessoryandprotectivepigments,and,assuch,areresponsiblefor
impartingvisiblecolordifferencesinthekindsofplantsthatweseeinnature.Additionaltopicsthatmay
beintroducedhereincludethecharacteristicsofvisiblelight(i.e.,colorsandtheirwavelengths),whywe
seecolor(pigmentsinmaterialsabsorbdifferentcolorsandthecolorweseeisthecolornotabsorbed),
theabsorptionpropertiesofdifferentalgalpigments(chlorophyllprimarilyabsorbsanarrowrangeof
bluelight,~430nm,andotherchlorophyllsandotherpigmentsdifferinthecolorstheyabsorb),algal
andplanttaxonomy(which,tosomeextent,isbasedonthepresenceofparticularpigments),andthe
evolutionofalgaeandhigherplants(thepresenceofchlorophyllbinhighplantssuggeststhatthey
evolvedfromchlorophytes,agroupingofalgaethatcontainchlorophyllb).
LightSources
Thedecisionoflightintensitiesatwhichtogrowthealgaeinabottledependsmainlyontheavailability
ofartificiallightsandspace.Thoughsomelightsourcesarebettersuitedtoalgalgrowththanothers,just
aboutanylightsourcecanbeused,evenatungstenlightbulb.Highandlowlightintensitiesmaybe
simulatedbyplacingthebottlesofalgaeclosertoorfurtherfromthelightsource,respectively.
Alternatively,householdwindowscreenmaybecutandwrappedaroundindividualbottlestoreduce
lightintensity.Ifspaceandalightsourcearelimited,thebottlesofalgaemaybesimplyplaceina
windowsillforstudentstoobserveoverthecourseofafewdaysorweeks.Thereareanumberof
differentoptionshere.SeetheAppendixforpossiblelightsourcesandwheretobuythem.
20
LightintheBottle
Followingadiscussionoflight,studentsshouldbeaskedtolookattheirbottles,anddetermineif
anythingaboutthebottlemightblockthepathoflightfromthelightsourceintothebottle.Some
studentsmaysuggestthatthecapmayblocklight,acorrectassertion.Butit’stypicaltogetsmilesand
laughterwhenoneormorestudentssuggestthattheyremovethelabelsfromtheirbottles.(The
importanceofthisstepcannotbeoverstated:thedegreetowhichstudentsunderstandtheroleoflightin
algalgrowthwillbeexpressedintheirconfidencethatremovingthelabelisano-brainer.)Atthispoint,
weletthemremovethelabelanddisposeofitproperly.Theinstructorshouldnowaskhowthebottles
shouldbeorientedinrelationtothelightsource.Shouldthebottlesbelitfromthetoportheside?Would
itbebettertolaythebottlesontheirsideforalightsourceabovethebottles?Iftimepermits,a
discussionofBeer’sLawcanbeintroducedhere,theexponentialdecreaseinlightintensityaslight
passesthroughwater.Thoughit’snotnecessarytointroduceabsorptionandscattering,theinstructor
canprovidetheseprocessesasanexplanationforthereductioninlightintensitywithdepthinacolumn
ofwater.Agraphofthisrelationshipcanbeuseful,especiallyasBeer’sLawhelpsstudentstounderstand
howconcentrationsofchlorophyllcanbedeterminedusinganinstrumentthatmeasuresreductionsin
lightasitpassesthroughatesttubeofchlorophyllsolution,i.e.,acolorimeterorspectrophotometer.
Beer’sLawmayalsobeappliedtounderstandingwhytheoceanisblue,asbluelightisthecolorleast
absorbedbyseawater.Beer’sLawhasanumberofapplicationsinchemistry,andtheinterested
instructormayfinditusefultoexplorethisliterature,andintroduceadditionalconcepts,dependingon
theemphasisandcomplexityofthecourse.Thekeypointhereisthatlightintensitywillbereducedfrom
thelightedsideofthebottletotheoppositesideofthebottleasaresultofabsorptionandscatteringby
water(astrongabsorberandscatterer),bythealgaesuspendedinthewater(specifically,chlorophyll
andotherpigments),and,possibly,theplasticofthebottle
ScientificQuestions&Predictions
Afterstudentshaveremovedtheirlabelsanddecidedontheorientationandplacementoftheirbottlesin
thelightpath,theinstructormayaskstudentstopredictthegrowthrateforthelightintensitythatthey
choseorthat’savailabletothem.Studentsmaybeaskedhowfastwilltheirbottlesturngreen?Howlong
willittakebeforethebottlesstopturninggreen?Whatwillcausegrowthtostopinthebottle,if
anything?Willalgaegrowninhighlightreachtheirpeak“greenness”fasterorslowerthanalgaegrown
inlowlight?Whatroledonutrientsplayinallofthis?Themannerinwhichthesequestionsareexplored
andthetimedevotedtotheirdiscussionwilldependonthedegreetowhichthisexperimentservesasan
inquiry-basedactivityorademonstrationactivity.Thealgaeinabottleexperimentisadaptabletoa
21
numberofpedagogicalapproacheswithsimplificationsorexpandeddiscussionspossibleatanyofthe
stepsleadinguptointroductionofthealgaeintothebottle.
TheSeasonalApproach
Onewaytoconnecttheexperimentswithecosystemprocessesistotakeaseasonalapproachwhereby
teamsofstudents“duplicate”conditionsoflightandnutrientsthatarepresentduringeachofthefour
seasonsintemperatezonewaters.Typically,lightintensityislowestinwinter,butdissolvednutrient
concentrationsarehighest.Conversely,lightintensityreachesitsmaximuminsummer,butnutrients
maybeundetectableinsurfacewaters.Springandfall,timeswhenalgaebloomsarecommoninlakes
andintheocean,providesufficientlightandplentifulnutrients.L:Dcyclesandwatertemperaturesdiffer,
too.Thefollowingcombinationsmaybeexploredforexploringtheseasonalcycleofproductivityin
aquaticecosystems:
• Winter:lowlighthighnutrients,8:16L:Dcycle,coldesttemperatures
• Spring:mediumlight,highnutrients,12:12L:Dcycle,warmertemperatures
• Summer:highlight,lownutrients,16:8L:Dcycle,warmesttemperatures
• Fall:mediumlight,mediumnutrients,12:12L:Dcycle,coldertemperatures
Studentsshouldbeaskedtopredictgrowthratesandtimetoreachmaximumbiomassforeachofthe
“seasons.”Inpresentingtheirresults,studentsmaybeaskedtocomparewhathappenedintheirbottles
tothetypicalseasonalresponseofalgae“inthewild.”Weretheresultsasexpected?Ifnot,why?
TheFastApproach
Foregoingmostofthedetaileddiscussionoutlinedabove,allofthestepstothispointcaneasilybe
accomplishedinasingleclasssessionprovidedtheinstructorhasthematerialsreadyandhasprepareda
placeforthebottlestobeplacedaheadoftime.Studentscaneasilyremovesomeofthewaterinthe
bottle,addateaspoonofseasalts,addonetoseveralsquirtsofnutrients,andremovethelabelonthe
bottleinthespaceoflessthananhour.However,instructorswillwanttogathertheclassandslowdown
thepacetoaddressacouplequestionsofmethodologythatwillmaximizetheeducationalbenefitsofthe
experiment,andthatwillensurethemostreliableresults.
ScientificQuestions&Predictions
First,instructorswillwanttoaskstudentswhatisthestartingpointfortheexperiment.Isitthebottleof
preparedwaterwithoutalgae,orisitthebottleofwaterplusthealgae?Whatarethedifferences
22
betweenthebottlewithoutalgaeandthebottlewithalgae?Howcanweobserveandmeasurethose
differences?Themostappropriatestartingpointforobservingormeasuringthegrowthofalgae,thetime
zero,asitwere,couldbetheobservationormeasurementthatoccursoncetheinitialaliquotofalgaehas
beenadded.However,ifquantitativemeasuresaregoingtobeused,suchasfluorometry,itwillbe
importanttoobtainablank.Whatdoestheinstrumentreadwithoutanyalgae?Wethinkitcanbeuseful
andimportanttointroducetheconceptoftheinstrumentorobservationalblank.Studentsshouldbe
madeawareofthestateofthebottleanditswaterpriortointroductionofthealgae(theblank)aswellas
thetimezero,thestateofthebottleoncethealgaehavebeenintroduced.Quantitativedeterminationof
theconcentrationofalgaeinthebottlerequiresablank,themeasurementobtainedpriortointroduction
ofthealgaetoaccountforinstrumenteffectsonthemeasurement.Thedegreetowhichthisis
emphasizeddependsonthemethodsthatwillbeusedtodocumentchangesinalgalgrowth.But,inany
case,wethinkit’simportanttomakeobservationsormeasurementspriortointroductionofthealgaeto
theirnewhomes.
PicturesandNotebooks
Second,studentsmaybeaskedhowtheyaregoingtodocumentthestartoftheexperiment.Willthey
takepictures?Willtheymakeobservationsonthecolorinsidethebottleoncethealgaehavebeen
introduced?Willtheypickacoloronacolorchart?Regardlessofthemethodschosen,westrongly
recommendthatstudentstakepictures,butthere’salessonhere.Doesitmakeadifferencehowtheytake
thepicture?Attheoutset,weletstudentstakepictureswithoutanydiscussionofhowtheydoit.
Followingthepicturetaking,includingtimeforstudentstotakeselfieswiththeirbottlesofalgae,weask
studentstosharetheirphotoswitheachother.Dotheynoticeanything?Instructorsmayaskafew
studentstoemailtheirphotostotheinstructor’semailaddresssothattheinstructorcanprojectthemon
aclassroomLCDprojector,ifavailable.Typically,studentsplacetheirbottlesontheirdesksoratableand
takepicturesfromanyangleandanydistancewithoutanythoughtofwhethertheycanseecolorinside
theirbottles,ortakethesameshotatafuturedate,oncethealgaehavegrown.Atthispoint,instructors
shouldemphasizetheimportanceofreproducibilityinmakingobservationsormeasurements.Ask
studentstocommentoneachother’sphotoswithregardtothevisibilityandcolorofthecontentsinside
thebottle.Cantheyimproveonthepicture?Doesitmatter?Moststudentswillrealizethattheirpictures
arenotideal.Adiscussionoftheidealphotoshouldfollow.Intheend,instructorswillwanttoemphasize
thatitisimportanttotakethepicturewiththesamecamerainthesameposition(withrespecttothe
bottle),anditwillbeimportantthatthebottleisinaplacewiththesamelightingandagainsta
backgroundwherethecolorinsidethebottlecanbeeasilydiscerned.Wehavefoundthatplacingthe
bottlesontheledgeofawhiteboardworksverywell,aslongasstudentstaketheirpicturessothatthe
23
entirebottleiscaptured,sothatthebottlefillstheframeofthecamera,andsothatthecameraisheld
perpendiculartothebottle.
LabelingBottles
Third,andthisisapointthatinstructorscanwaittointroduce,howwillstudentsbeabletoidentifytheir
bottleofalgae?Howwilltheytellonebottlefromtheother?Thiscanbeafunlessonifstudentsareleftto
theirowndevicesattheoutset.Iftheinstructorhasaskedforafewphotosviaemail,heorshecanshow
thephotoandasktheclasstowhomitbelongs.Inmostcases,studentswillhaveneglectedtolabelthe
bottlesoridentifyownershipofthebottleinawaythat’svisibleintheirpictures.Oncestudentsrealize
thisshortcoming,theygetit!Wefindthatit’susefultodiscussandcomeupwithasetofidentifiers
uniquetotheclass(ifdifferentsectionsarecarryingouttheexperiment),theteam(ifstudentsare
workinginteams),andtheindividual(thepersonresponsibleforaparticularbottle).Wealsofindthat
it’susefultoaskstudentswheretheyshouldplacetheirlabels.Ifstudentshavelearnedthelessonsof
lightpenetration,theywillsuggestthatthebottlecapistheappropriateplacebecauseplacingalabelor
writingonthebottlewillreducelightinsidethebottle.Atthispoint,weaskstudentstoproceedwith
labelingoftheirbottles,andtoretakepicturesusinganow-well-definedprotocol.
ConducttheExperiment
Finally,it’stimetoaddalgae.Werecommendaconsistentandpre-determinednumberofdropsforall
students;typically1-3dropsareideal,moreifthestockculturedensityislow.Obviously,thestarting
concentrationwillinfluencethenumberofdaysuntilpeakalgaldensityisreached.Instructorsmaywish
toruntheexperimentaheadoftimewithanumberofdifferentstartingconcentrationstofindthe
concentrationthatbestfitsthetimetabledevotedtotheexperiment.Theimportantconsiderationisto
allowachangetobeobservableordetectablefortheconditionsoflightandnutrientsunderwhichthe
experimentisconducted.Bottleswithhighlightintensitiesandhighnutrientconcentrationswillshow
visiblechangesinashorterperiodoftimethanbottlesgrownatlimitingnutrientconcentrationsunder
lowlight.Intruth,withoutquantitativemeasurementsoflightintensitiesandnutrientconcentrations,it’s
goingtobedifficulttopredictwithanycertaintythedailyrateofchangeingrowth.Butthat’sthefunof
it!Instructorsmaywanttoletsomestudentsstartwithmoredrops.It’sanexperiment.Aslongasallof
thevariablesarecarefullydocumented,thenthere’sknowledgetobegainedinanyapproach.
KeepTakingPicturesandMakingObservations
Followingadditionofalgae,studentswillwanttotakeanotherroundofpictures.Inclassroomswhere
quantitativemeasurementsarebeingcarriedout,thefirstsetofmeasurementsshouldbetakenatthis
24
pointtoestablishtheinitialconcentrationofalgaeineachbottle.Verylikely,despitecarefulattentionto
waterbottlevolumesandtheamountofnutrientsandalgaeadded,therewillbeslightdifferencesamong
students.Anystudentswhosemeasurementsdifferwidelyfromotherstudentsshouldbequeriedasto
theprocedurestheyfollowed.Wetypicallyrequirestudentstoworkinteamsof3or4andcarryout
identicaltreatments.Thus,agiventeamofstudentsperformstheexperimentintriplicateor
quadruplicate,andresultswithineachteamshouldbesimilar.Dependingonthedegreetowhichtheir
initialmeasurementsdifferfromtheexpected,andtimeavailability,instructorsmaychoosetomakethe
studentorstudentstostartover,ortheymayallowtheteamtoproceedwiththeirexperimentsasis.
ASimpleObservationActivity
Forsomeinstructors,thealgae-in-a-bottleexperimentmayconsistsimplyofanactivitywherestudents
prepareabottleofalgae,andwatchitgrow,eitherintheclassroomorathome.Forothers,classsessions
followingthetimezeromeasurementswillrequiretimeforcontinuingtodocumentgrowthusing
photographandothermeasures.Datamaybecompiledfortheclassasawholeastheexperiment
proceeds,orattheendoftheexperiment.Instructorsmayaskstudentstocreateapicturecollageoftheir
bottles,prepareatableofobservations,createbarorlinechartsofanyquantitativemeasures,and/or
writeuptheresultsoftheirexperimentusingalaboratoryreportformat.Wheresufficientquantitative
measuresareavailable,studentsmaycalculatetherateofchangeinchlorophyllconcentrationby
subtractingpreviousvaluesfromsubsequentones,orbysimplysubtractingthetimezeroconcentration
fromthefinalone.Resultscanbepresentedorallyinfrontoftheclass,ortheinstructormaychooseto
compileandpresentselectresultstoillustratekeyfindings.Studentsmaybeaskedtoexplainany
differencesintheirresultsfromtheoutcomestheyexpected,orhowtheymightimproveupontheir
experiments.Therearenumerouspossibilitiesforexploringanddiscussingthephysical,chemical,and
biologicalprocessesthatoccurintheiralgaehomes.
AssessAttitudesandUnderstanding
Followingtheexperiments,instructorsmaywanttoassesschangesinattitudestowardstheexperiments
(i.e.,theaffectivedomain)andchangesinconceptualunderstanding(i.e.,theeffectivedomain)usingthe
post-testsprovidedintheAppendix.Theresultsofthepre-postassessmentscanprovidevaluable
informationontheeffectivenessofeachstepoftheactivity,andpointoutwaysthatdeliveryofthe
experiment,i.e.,thelessonplan,canbemodifiedandimproved.Aboveall,wehopethatimplementation
oftheexperimentreapsbenefitsforhelpingstudentstounderstandthenatureofscience,andfor
bringingtostudentsadeeperconceptualunderstandingofthefactorsthatgovernthegrowthofplants
andalgaeinthenaturalworld.
25
MaterialsandOptionalEquipment
TheAlgae-in-a-BottleExperimentreliesprimarilyoneasy-to-find,inexpensive-to-purchasematerials
availableinlocalgroceryorboxstores,oronline.Instructorswishingtoadoptmorerigorous,research-
basedprotocolsmay,too,findmaterialseasilyavailable,albeitatgreaterexpense.
BottledWater
Bottlesof8-ounce,springwaterworkbestandaretheleastexpensive.
Saltwater
Mortonorotherbrandsofseasalts.
Professionalgradeseasalts:$75,Oceanic81050NaturalSeaSaltMix,makes200gallons
http://www.amazon.com/Oceanic-81050-Natural-200-Gallon-Bucket/dp/B000256EWG
InstantOcean,Coralife,andothersmaybesuitable.
SourcesofAlgae
Liquidmicroalgaecultures:$10-$30,FloridaAquaFarms
http://florida-aqua-farms.com/shop/liquid-microalgae-cultures/
Research-grademicroalgaecultures,$175,NationalCenterforMarineAlgaeandMicrobiota
https://ncma.bigelow.org
SourcesofNutrientMedia
MiracleGro,$9,Amazon
http://www.amazon.com/Miracle-Gro-1001233-Purpose-Plant-Food/dp/B000P6QYJK
MicroalgaeGrowMassPack,$20+,FloridaAquaFarms
http://florida-aqua-farms.com/product-category/store/micro-macro-nutrients/
Researchgradef/2media,$85,NationalCenterforMarineAlgaeandMicrobiota
https://ncma.bigelow.org
26
LightSources
Aninfinitevarietyoflightfixturesarepossible,rangingfromsimplebulbandfluorescentlightfixturesto
LEDaquariumfixtures.Thetypeyouchoosewilldependonbudgetandspaceconsiderations.Forbest
growth,choosebulbsdesignedspecificallyforplants(thatis,bulbsthatemitasmuchbluelightas
possible,thecolormostabsorbedbychlorophylla)
BulbFixturesandBulbs
Bulbfixturescangeneratelotsofheat,buttheyareinexpensive,andanumberofbulbsdesigned
specificallyforplants,includingcompactfluorescentbulbsandLEDbulbs,arenowavailable.Type
“growbulb”inAmazonorclickbelow.
http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-
keywords=grow+bulb
FluorescentLights
Fluorescentfixturesarecooler,andoffertheadvantagethatyoucanstandthemonedgeandplace
alotofbottlesinfrontofthem.Choosefullspectrumorplantgrowbulbsforthebestresults.Type
“growbulbsfluorescent”inAmazonorclickbelow:
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-
keywords=grow+bulbs+fluorescent&rh=i%3Aaps%2Ck%3Agrow+bulbs+fluorescent
AquariumLEDFixtures
Designedfortrue(hardorstony)corals,whichcontainalgalsymbionts,aquariumLEDfixtures
offerthemostadvancedlightingsystemsforgrowingalgae.Theyarenotinexpensive,buttheir
wavelengthsofemissionareidealforalgae,andmostLEDfixturespermityoutovarythelight
intensity.WeusetheTaoTronics165WDimmableLEDAquariumLights,buttheyarenot
availableatthetimeofthiswriting.Type“LEDreefaquariumlighting”inAmazon.Wesuggestthat
youreadthereviewsandmakeyourowndecisionbasedonyourbudgetandspace
considerations.
http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-
keywords=led+reef+aquarium+lighting&rh=i%3Aaps%2Ck%3Aled+reef+aquarium+lighting
MobileLightingSystems
Amobilesystemisidealforuseinmulti-useclassrooms(e.g.,mostcollegeclassrooms)wherethe
experimentalsetupcannotbeleftinplace.Mobilelightcartscanbewheeledinandoutofa
27
classroom,andstoredsafelyinaclosetorotherlocationwhereelectricaloutletsareavailable.
Pricesrangefromthefewtoseveralhundredsofdollars.Weusemobile,4-shelf,plantgrowcarts
withfluorescentlamps,purchasedfor$782.50atCarolinaBiologicalSupply.Type“plantgrow
cart”inGoogleforotheroptions.
ScientificEquipment
Measuringcups,teaspoons,andtablespoons,availableatyourlocalgroceryorboxstore
Plastictransferpipettes,$4.39,packof100
http://www.amazon.com/Plastic-Transfer-Pipettes-Gradulated-
Pack/dp/B005IQTSE0/ref=sr_1_1?ie=UTF8&qid=1428780519&sr=8-1&keywords=pipettes%27
Refractometerformeasuringsalinity,$49.99,MarineDepot
http://www.marinedepot.com/ps_viewitem.aspx?idproduct=MD2101&child=MD2101&utm_sour
ce=adwordsfroogle&utm_medium=cse&utm_campaign=adwordsfroogle&utm_content=MD2101&
gclid=CjwKEAjwjKOpBRChjsTyicbFy3QSJADP1gTNYxtayxnYdL87VtARFk9DOuffxNO8mH_wVOCO
elk-wBoCLGfw_wcB
EducationalColorimeterKit,formeasuringcolorchanges,$145.00,IORodeo
http://www.iorodeo.com
AquaFluorHandheldfluorometerformeasuringchlorophyll,~$3000,TurnerDesigns
http://www.amazon.com/Plastic-Transfer-Pipettes-Gradulated-
Pack/dp/B005IQTSE0/ref=sr_1_1?ie=UTF8&qid=1428780519&sr=8-1&keywords=pipettes%27
HelpfulResources
CulturingMethodsandInformation,NationalCenterforMarineAlgaeandMicrobiota
https://ncma.bigelow.org/culturing-methods
HowtoGrowAlgae,Wiki-How
http://www.wikihow.com/Grow-Algae
MeasuringSalinitywithaRefractometer
http://reefkeeping.com/issues/2006-12/rhf/
TheBasicsofPhotosynthesis,SimpleEnglishWikipedia