AP Biology Day 22 Monday, October 10, 2016

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

Ch.10:Photosynthesis

Now…•  Let’saddali9ledetailaboutphotosynthesisJ

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LightDependentReac+ons

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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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Photosystems•  Photosystem=reac5on-centercomplexmadeupofmany

pigmentsthatcancollectlight-energy

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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

Photosystems•  Energyfromthesunpowersthetransferofanelectronfrom

chlorophyllatoanelectronacceptor

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AP Biology Day 23 Wednesday, October 12, 2016

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

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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

Stage2:TheCalvinCycle

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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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Photorespira+on•  Solu+ons?

•  C4&CAMPlants

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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

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Review•  Theenergyenteringchloroplastsassunlightgetsstoredaschemicalenergyinorganiccompounds

•  Sugarmadeinthechloroplastssupplieschemicalenergyandcarbonskeletonstosynthesizetheorganicmoleculesofcells

•  Plantsstoreexcesssugarasstarchinstructuressuchasroots,tubers,seeds,andfruits

•  Inaddi+ontofoodproduc+on,photosynthesisproducestheO2inouratmosphere

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CW/HW•  PhotosynthesisPre-LabJ

•  Ch.10Quiz???

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