Do-NowGroup Discussion
• Discuss: • What is the equation for photosynthesis, and why is it a redox reaction?
• What are the steps of photosynthesis, and where does each occur?
• Briefly explain what happens at each step.
Turn in lab notebooks
Essen+alknowledgestandards• 2.A.1: All living systems require constant input of free energy
• 2.A.2: Organisms capture and store free energy for use in biological processes
FLT• I will be able to:
• describe the structure of a chloroplast
• describe the the role of ATP and NADPH in the Calvin Cycle
• compare and contrast oxidative phosphorylation and photophosphorylation in chloroplasts
• By completing Ch. 10 Lecture Notes
REVIEW1. The light dependent reactions
• Occur in the within and across the thylakoid membrane
• Chloroplasts split H2O into hydrogen and oxygen (photolysis)
• The electrons hold the free energy from the light • Through an ETC, light energy is transformed into ATP
and NADPH
• Generate ATP by photophosphorylation
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How a photosyste
m harvests light
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
STROMA
e–
Pigment molecules
Photon
Transfer of energy
Special pair of chlorophyll a molecules
Thyl
akoi
d m
embr
ane
Photosystem
Primary electron acceptor
Reaction-center complex
Light-harvesting complexes
Photosystems• Chlorophyllsinphotosystemsabsorbfreeenergyfromlight,andbooste-stoahigherenergylevel
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Heat
How a photosyste
m harvests light
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
STROMA
e–
Pigment molecules
Photon
Transfer of energy
Special pair of chlorophyll a molecules
Thyl
akoi
d m
embr
ane
Photosystem
Primary electron acceptor
Reaction-center complex
Light-harvesting complexes
Do-Now:GroupDiscussionPutthefollowingtermstogetherinacoherent
explana+on:• Photosynthesis • Cellular
Respiration • Plants • Animals • Oxidized • Reduced • Thylakoid • Stroma
• Calvin Cycle • Light Dependent
Reactions • NADPH • ATP • Excited electrons • Proton Motive
Force • ATP Synthase
Announcements• Clearmissingassignments!
• StudyforCh.10quiz&Ch.9-10testJ• Quarter1ends10/14• Ch.10Quiz?
CW/HW Assignments 9. Ch. 10 VCN
10. Photosynthesis Pre-Lab
1. Pre-labs due by Friday
2. Get stamps
3. Study!! Test Wednesday J
PLANNER
Essen+alknowledgestandards• 2.A.1: All living systems require constant input of free energy
• 2.A.2: Organisms capture and store free energy for use in biological processes
FLT• I will be able to:
• describe the structure of a chloroplast
• describe the the role of ATP and NADPH in the Calvin Cycle
• compare and contrast oxidative phosphorylation and photophosphorylation in chloroplasts
• By completing Ch. 10 Lecture Notes
Recall• Thethylakoidmembranesallowforanincreasedsurfaceareaforreac+onsoftheETCtotakeplace
• Therearetwotypesofphotosystemsembeddedinthethylakoidmembranes(ETC):
• PhotosystemII(PSII)
• PhotosystemI(PSI)
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Light-DependentReac+onsOverview• Photosystem II
Ø Goal: Produce ATP Ø Light energizes e-s and powers them
through the ETC Ø Photolysis: Light E helps split water
Ø H2O à ½ O2 + 2H+ + 2e- (provides H+ + e- !!!!!)
Ø e- s are energized and create a H+ gradient within the thylakoid membrane
Ø Chemiosmosis occurs (the PMF is used to synthesize ATP via ATP synthase)
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Light-DependentReac+onsOverview• Photosystem II
Ø Chemiosmosis occurs (the PMF is used to synthesize ATP via ATP synthase) § Note: this is different than cellular
respiration because… § Energy was originally harvested
from solar energy (thus its called photophosphorylation)
§ The proton gradient forms INSIDE the membrane instead of outside
§ Oxygen is not required 24
Light-DependentReac+onsOverview• Photosystem I
Ø Goal:MakeNADPH(e-carrier)
Ø e-sarereenergized&usedtoformNADPH
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Light-DependentReac+onsOverview• Overall:
• Webrokedownwater
• Waterprovideselectronsandprotons
• O2isreleasedaswaste
• TheETCandPMFhelpcreateATPandNADPH
• NADPHandATPcarrythecapturedenergyandwillbeusedintheCalvincycletocreatesugarsJ
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ElectronFlowintheLDR• Linear(non-cyclic)flow=normal
• PhotosystemII&IworktogethertomakeATPandNADPH
• CyclicelectronflowusesonlyPSII• ATPismadebutnotNADPH
• Sowhydoescyclicelectronflowoccur???• IfthereisashortageofATP,wecanproducemore
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Cyclic Electron Flow makes only ATP
ATP Photosystem II
Photosystem I
Primary acceptor
Pq
Cytochrome complex
Fd
Pc
Primary acceptor
Fd
NADP+ reductase
NADPH
NADP+ + H+
Light
Fd
Cytochrome complex
ADP +
i H+
ATP P
ATP synthase
To Calvin Cycle
STROMA (low H+ concentration)
Thylakoid membrane
THYLAKOID SPACE (high H+ concentration)
STROMA (low H+ concentration)
Photosystem II Photosystem I
4 H+
4 H+
Pq
Pc
Light NADP+ reductase
NADP+ + H+
NADPH
+2 H+
H2O O2
e– e– 1/2 1
2
3
Photochemical = Light Reactions
Pair-Share-Respond1. Wherecanyoufindphotosystems?
2. Iden5fythreeproductsproducedinthelightdependentreac5ons
3. WhatprovidestheelectronsforPSII?
4. ExplainhowATPisproducedinPSII.BeveryspecificJ
5. Iden5fytheroleofPhotosystemI
REVIEW2. The light independent reactions (Calvin Cycle)
• Takes place in the stroma • Forms C6H12O6 from CO2 using ATP and NADPH • The Calvin Cycle begins with carbon fixation,
which incorporates CO2 into organic molecules and then reduction produces sugar
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Details• TheCalvinCycleusesATPandNADPHtoconvertCO2tosugar
• TheCalvincycleregeneratesitsstar5ngmaterialaYermoleculesenterandleavethecycle
• TheCalvinCyclebuildssugarfromsmallermoleculesusingCO2,ATP,andNADPH
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CalvinCycle• The Calvin Cycle has three phases:
1. Carbon fixation (CO2 attaches to the 5-carbon RuBP catalyzed by Rubisco)
2. Reduction (sugar making) 3. Regeneration of RuBP (cycle)
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CalvinCycle• Carbon enters the cycle as CO2 and leaves as
a sugar named glyceraldehyde-3-phosphate (G3P), which will be used to create the C6H12O6
• Note: G3P is sometimes also called PGAL • Most G3Ps are used to regenerate RuBP • 3 turns of the cycle fixes 3 CO2 molecules
and creates 1 extra G3P • Glucose requires 6 turns of the cycle (2 extra
G3Ps)
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Pair-Share-Respond1. WhatisthepurposeoftheCalvin
cycle?
2. WhatarethethreestagesoftheCalvincycle?
3. CompareandcontrasttheCalvincyclewiththeKrebscycleJ
Whathappensinhot,aridclimates?• Onhot,drydays,plantsclosestomata,whichconservesH2O
butalsolimitsphotosynthesis
• Recall-stomata
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Whathappensinhot,aridclimates?• TheclosingofstomatareducesaccesstoCO2andcausesO2to
buildup
• Thesecondi+onsfavoraseeminglywastefulprocesscalledphotorespira+on
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Photorespira+on• Mostplants(~85%)areC3plants-stomataareopenduringtheday,andclosedatnight
• Whenstomataclose,thereisnogasexchangeàlowCO2causesthewastefulprocessofphotorespira+ontooccur
• O2isusedwithoutproducingenergymolecules
• Inphotorespira+on,rubiscobondswithandaddsO2insteadofCO2intheCalvincycle
• Photorespira+onconsumesO2andorganicfuelandreleasesCO2withoutproducingATPorsugar.WastefulL
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Photorespira+on• Photorespira+onmaybeanevolu+onaryrelicbecauserubiscofirstevolvedata+mewhentheatomospherehadfarlessO2andmoreCO2
• Photorespira+onlimitsdamagingproductsoflightreac+onsthatbuildupintheabsenceoftheCalvincycle
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C4Plants• C4plants=mostefficientatcarbonfixa+on
• Havethinnerleaves• Chloroplastsmaybelarger
• Foundinhighlightintensityenvironments
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C4Plants• C4plantsminimizethecostofphotorespira+onbyincorpora+ngCO2intofour-carboncompoundsinmesophyllcells
• ThissteprequirestheenzymePEPcarboxylase
• PEPcarboxylasehasahigheraffinityforCO2thanrubiscodoes;itcanfixCO2evenwhenCO2concentra+onsarelow
• Thesefour-carboncompoundsareexportedtobundle-sheathcells,wheretheyreleaseCO2thatisthenusedintheCalvinCycle
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C4 leaf anatomy
Mesophyll cell Photosynthetic cells of C4 plant leaf
Bundle- sheath cell
Vein (vascular tissue)
Stoma
The C4 pathway
Mesophyll cell CO2 PEP carboxylase
Oxaloacetate (4C)
Malate (4C)
PEP (3C) ADP
ATP
Pyruvate (3C)
CO2 Bundle- sheath cell
Calvin Cycle
Sugar
Vascular tissue
Carbon fixation occurs in Bundle Sheath, a region with low O2
CAMPlants• CAMplantsaretypicallysucculents(notalways)thatliveindesertoraridenvironments
• Theyhaveaninvertedstomatalcycle:stomatesopenatnight,andcloseduringtheday
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CAMPlants• Someplants,includingsucculents,usecrassulaceanacidmetabolism(CAM)forcarbonfixa+on
• CAMplantsopentheirstomataatnight,incorpora+ngCO2intoorganicacids
• Stomatacloseduringtheday,andCO2isreleasedfromorganicacidsandusedintheCalvinCycle
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CO2
Sugarcane
Mesophyll cell
CO2 C4
Bundle- sheath cell Organic acids
release CO2 to Calvin cycle
CO2 incorporated into four-carbon organic acids (carbon fixation)
Pineapple
Night
Day
CAM
Sugar Sugar
Calvin Cycle
Calvin Cycle
Organic acid Organic acid
(a) Spatial separation of steps (b) Temporal separation of steps
CO2 CO2
1
2
Review• Theenergyenteringchloroplastsassunlightgetsstoredaschemicalenergyinorganiccompounds
• Sugarmadeinthechloroplastssupplieschemicalenergyandcarbonskeletonstosynthesizetheorganicmoleculesofcells
• Plantsstoreexcesssugarasstarchinstructuressuchasroots,tubers,seeds,andfruits
• Inaddi+ontofoodproduc+on,photosynthesisproducestheO2inouratmosphere
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