EE BIOL 162 Study Guide - Final Guide: Stoma, Photoperiodism, Succinic Acid

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plumwildebeest506

8 Jun 2018

School

UCLA

Department

Ecology and Evolutionary Biology

Course

EE BIOL 162

Professor

Sack

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Class7:DiversityinPhotosynthesis

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1. PleaseexplainC4photosynthesis,usingthefollowingterms:HCO3,PEPCarboxylase,

mesophyll,Kranzanatomy,plasmodesmata,malate,separationofpathwaysinspace,water

useefficiency

 C4foundinmanymonocots(grassesandsedges)aswellaseudicots(shrubs)

 C4photosynthesisreducesphotosynthesisbyconcentratingCO2nearrubisco

Firstreactionsoccursinmesophyllcells;CO2→HCO3,whichisfixedto3carbon

Phosphoenolpyruvate(PEP),bytheenzymePEPcarboxylase;thisreactionproduces

a4carboncompound(malate)

Themalatewilldiffusepassivelyviaplasmodesmatatothebundlesheathcells

 BundlesheathcellshavemanychloroplastswhichruntheCalvincycle

Malateisdecarboxylateddownto3carbonpyruvate(whichissentbackto

mesophyllcells),andCO2(releasedtothebundlesheathchloroplasts)itenters

thefullC3Calvincyclereactionsinthebundlesheaths

C4plantshaveKranzanatomyenlargedbundlesheath,withlotsofchloroplasts;there

aremanyplasmodesmataconnectingtothemesophylls

 SomeC4plantsdonothave“Kranzanatomy”

 ShowntoseparateC4photosynthesiswithinsinglecells,byseparatingthe

PEPcarboxylasereactionsfromtheCalvincyclereactionwithinthecell



2. WhydoesC4photosynthesishaveacost?Pleasedescribeindirectanddirectcosts.

 RegenerationofPEPconsumes2ATP

 Alsousesenzymes

 IfO2waslowandphotorespirationdidnotoccur,theC4plantswouldrequiremore

quantaoflightperCO2thanC3plantsforthesameCO2fixation

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3. WhatthreepossibleenvironmentalconditionsmightpromotetheevolutionoftheC4

photosyntheticpathway?Why?

C4plantstendtooriginateinaridregions,implicatingheat,droughtand/orsalinityas

importantconditionspromotingC4evolution

 Whentemperatureishigher,C3plantsneedtoincreasephotorespiration(bctheRubisco

reactsquickerwithO2andbecauseO2becomesmoresolubleathighertemps)

 ThereforemoreadvantagetobeingC4

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4. UnderwhatconditionswouldC4plantshaveanadvantageoverC3plants?Underwhat

conditionswouldC3plantshaveanadvantageoverC4plants?Pleaseexplainwhy?

 C4plantsarebetterindriersoils

 TheyareabletoopenstomatalessforthesameamountofCO2fixationunder

highirradiancethushavebetterwateruseefficiency(=CO2fixedperwater

loss):aboutdoublethatofC3plants

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 C4plantsloselesswater,andsokeeptheirleafwaterpotentialshigher

duringtranspiration,somoreeffectiveatdriersoils

 C3plantsfavoredwhenCO2levelsrise

 HowevernotcleariftemperaturesarealsoincreasingalongwithCO2,soitis

notclearifphotorespirationwouldreallybeloweroverallintheC3plants



5. PleaseexplainCAMphotosynthesisusingthefollowingterms:stomata,Rubisco,malate,

PEPcarboxylase,wateruseefficiency

CAMislikeC4inthePEPcarboxylasefixesHCO3,andthenreleasesCO2toC3

ButCAMallowsincreasedCO2concentrationbyfixingHCO3withPEP

carboxylaseatnight(whenthestomataopeninCAMplants)

Malatestoredinthevacuole

 PEPisgeneratedbythebreakdownofstarchfromchloroplast

Duringtheday(whenstomataareclosed),themalateisreleasedfromvacuole,

andbreaksdowntopyruvateandCO2inthechloroplast,andthelightreactions

andC3calvincyclerun

CAMleadstohugewateruseefficiency(upto10xhigherthanC3plants)bcstomata

openonlyatnightwhenCAMoperates.CAMalsohavewaterresistantcuticles



Class8:EcologyofPhotosynthesis:ResponsetoCO2andLight



●CO2limitation=limitationtoRubiscoactivity;lightlimitation=limitationtoRuBPregeneration

1. Whyarepalisadeandspongytissuesbetterforrespectivelycapturingdirectanddiffuse

light?Whydoesthecombinationmaximizetotallightcapture?

 Palisadecellsallowpenetrationoflightviavacuolesandintercellularairspaces:light

channeling

 Efficientfordirectionandcaptureofdirectlight

 Lightpassesbetweenchloroplasts:sieveeffect

 Spongymesophyll:honeycombedairspacesreflectandrefractlight:lightscattering

 Veryefficientfordirectionandcaptureofdiffuselight

 Palisadesarelongerandcolumnarsochloroplastsinasenselineup

 Shadeleavesaremorespongy



2. HowareleavesspecializedforinternalCO2uptake?Pleasegivetwoways

 Sunleavearethicker,withmorelayersofpalisademesophylltoallowdirectlightto

penetrateintotheleaf.IntracellularareaismaximizedforCO2capture

 CO2diffusesinthroughthestomata:ratedependsonstomatalresistance,intercellular

airspaceresistance,andliquidphaseresistance

 Theinternalresistancesarereducedbyhavingamajorpartoftheleafas

airspace,andbyhavinglargerinternalcellsurfaceareasforCO2uptake,thus

keepingdiffusiondistancefromstomatatochloroplastsmall

 LightabsorbedandCO2fixedrightintothecenteroftheleaf



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3. Whatarethefivetypicalparametersofaphotosyntheticlightresponsecurve?Howwould

thesevarybetweentheleavesofasunadaptedversusashadeadaptedspecies?

 MeasuringnetCO2fixationasafunctionoflightgivesthelightresponsecurve

 Fiveparameters

1. Saturationirradiance

a. Wherecurvesaturatesorflattensoff

2. Lightsaturatedassimilationrate(Amax)

a. Highestphotosyntheticrateathighlight

3. Darkrespirationrate(yintercept)

4. Quantumyield(slopeoflefthandportion)

a. Howresponsiveplantistolight

5. Lightcompensationpoint(xintercept):photosynthesisJUSTequalsdark

respiration,sonetphotosynthesis=0

 Sunleaveshavehighersaturationirradiance,higherAmax,higherdarkrespirationrates

(morenegativenumberyintercept),andhigherlightcompensationpointsthanshade

leaves

 Sunandshadeleaveshavesimilarquantumyields



4. Whatisphotoinhibition?

 Photoinhibition:reactioncenterofPSIIisinactivatedand/ordamaged

 Dynamicphotoinhibition:occursundermoderateexcesslightandisreversible

 Chronicphotoinhibition:indicatedirreversibledamagetothephotosynthetic

apparatus

 aggravatedwhenlargeamountsoftheexcesslightenergycannotbe

usedinphotosynthesis

 Whenplantsfaceadditionalstress,lowtemps,drought,flooding



5. Howcanplantsadapttoreducephotoinhibition?

 Leavesmayhavespecializedanatomytodealwithexcesslight:haris,saltglands,

specializedwaxesincreasereflection

 Excessheatisgivenoffbyemissionoflongwaveradiation,sensibleheatloss,

evaporativecooling

 Leafmovement:leavesconductsolartracking,suchthatlaminaisalwaysperpendicular

tosun

 Pulvinusbetweenlaminaandpetiolecontainsmotorcellswhichgenerate

mechanicalforcesbychangingturgor

 Leavesangledtowardsunincoolerhoursofthedayandsometimesangleaway

duringhotpartsoftheday

 Sunleaveshavehighernitrogenandrubiscoconcentrationsandalargerpoolof

xanthophyllcyclecomponentstodissipateexcesslightenergy

 Underhighlightviaolaxanthinisconvertedtoantheraxanthinandthento

zeaxanthin

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EE BIOL 162 Study Guide - Final Guide: Stoma, Photoperiodism, Succinic Acid

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