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PhotosynthesisPhotosynthesis
Converting Light Energy to Converting Light Energy to Chemical Energy Chemical Energy
Photosynthesis Is an Endergonic ReactionPhotosynthesis Is an Endergonic Reaction
++
glucoseglucose(C(C66HH1212OO66))
+ 6 O+ 6 O22
OHO
OCH2OH
O O
++
6 CO6 CO22
+ 6 H+ 6 H22OO
O OC
OHH
EnergySupplied
+ energy =+ energy =
Photosynthesis Occurs in Chloroplasts Photosynthesis Occurs in Chloroplasts of Leaf Mesophyll Cellsof Leaf Mesophyll Cells
Leaf StructureLeaf Structure
MesophyllMesophyllCellsCells
MesophyllMesophyllCellsCells
Upper EpidermisUpper EpidermisUpper EpidermisUpper Epidermis
LowerLowerEpidermisEpidermis
LowerLowerEpidermisEpidermisVeinVeinVeinVein StomaStomaStomaStoma
Chloroplast Chloroplast StructureStructure
Inner & OuterInner & OuterMembranesMembranes
ThylakoidsThylakoids(contain pigments)(contain pigments)
GranumGranum(stack of thylakoids)(stack of thylakoids)
StromaStroma(interior matrix)(interior matrix)
Light, Chloroplast Pigments, & Light, Chloroplast Pigments, & PhotosynthesisPhotosynthesis
Gamma RaysGamma Rays X-RaysX-Rays UVUV InfraredInfrared Micro-Micro-waveswaves
RadioRadioWavesWaves
Visible LightVisible Light
400400 450450 500500 550550 600600 650650 70007000 750750Wavelength (nanometers)Wavelength (nanometers)
00
2020
4040
6060
8080
100100
% L
ight
Abs
orpt
ion
% L
ight
Abs
orpt
ion
400400 450450 500500 550550 600600 650650 700700 750750Wavelength (nanometers)Wavelength (nanometers)
400400 450450 500500 550550 600600 650650 700700 750750
Visible LightVisible Light
ChlorophyllChlorophyll
CarotenoidsCarotenoids
PhycocyaninPhycocyanin
CollectivelyCollectively
Chapter 7 8Light, ChloroplastLight, ChloroplastPigments & PhotosynthesisPigments & Photosynthesis
Gamma RaysGamma Rays XX-- RaysRays UVUV InfraredInfrared MicroMicro--waveswaves
RadioRadioWavesWaves
Visible LightVisible Light
400400 400400 400400 400400 400400 400400 400400 400400Wavelength (nanometers)Wavelength (nanometers)
Photosynthetic PigmentsPhotosynthetic Pigments• Chlorophyll Chlorophyll
– major photosynthetic pigmentmajor photosynthetic pigment– absorbs violet, blue, red wavelengths, reflects absorbs violet, blue, red wavelengths, reflects
greengreen
• Accessory PigmentsAccessory Pigments– CarotenoidsCarotenoids
• absorb blue and green,absorb blue and green,reflect yellowreflect yellow
– PhycocyaninsPhycocyanins• absorb green and yellow,absorb green and yellow,
reflect bluereflect blue
GlucoseGlucose
OO22
Photosynthesis Involves Photosynthesis Involves Two Sets of ReactionsTwo Sets of Reactions
Light-DependentLight-DependentReactionsReactions
(in thylakoids)(in thylakoids)
Light-IndependentLight-IndependentReactionsReactions
(in stroma)(in stroma)
DepletedDepletedCarriersCarriers
(ADP, NADP(ADP, NADP++))
DepletedDepletedCarriersCarriers
(ADP, NADP(ADP, NADP++))
EnergizedEnergizedCarriersCarriers
(ATP, NADPH)(ATP, NADPH)
HH22OO
COCO22+H+H22OO
Light-Dependent ReactionsLight-Dependent Reactions
• Energy from light is used to formEnergy from light is used to form– ATP: energy carrierATP: energy carrier– NADPH: electron carrierNADPH: electron carrier
• Occur in photosystems located in Occur in photosystems located in thylakoid membranesthylakoid membranes– organized array of pigment moleculesorganized array of pigment molecules– each photosystem containseach photosystem contains
• light-harvesting complex, with reaction centerlight-harvesting complex, with reaction center• electron transport system electron transport system
Absorbs light energy and transfers it toAbsorbs light energy and transfers it to
Reach electron carriers
Electrons absorb energy
PhotosystemsII and I
Electron Flow in Light-dependent
Reactions
Summary of Summary of Light-DependentLight-Dependent Reactions Reactions
ReactantsReactants ProductsProducts
WaterWaterelectron supplierelectron supplier
½ O½ O22
Protons (2HProtons (2H++))
Electrons (2eElectrons (2e-- ) )
ADPADPenergy carrierenergy carrier
+ energy + PO+ energy + PO44 ATPATP
NADP+NADP+electron carrierelectron carrier
+ 2e+ 2e-- + H + H+ + NADPHNADPH
Applying Your KnowledgeApplying Your Knowledge
A.A. Where is ATP produced?Where is ATP produced?
B.B. Which one contains an electronWhich one contains an electrontransport system?transport system?
C.C. Where is NADPH produced?Where is NADPH produced?
1.1. Photosystem IPhotosystem I
2.2. Photosystem IIPhotosystem II
3.3. Both PS I and PS IIBoth PS I and PS II
4.4. Neither PS I nor PS IINeither PS I nor PS II
Chemiosmosis Produces ATPChemiosmosis Produces ATP
Chemiosmosis Chemiosmosis Produces ATPProduces ATP
ATP is Produced by ATP is Produced by ChemiosmosisChemiosmosis
• Diffusion of hydrogen ions (HDiffusion of hydrogen ions (H++ ) through ) through a differentially permeable membrane, a differentially permeable membrane, resulting in ATP productionresulting in ATP production– energy from electron transport pumps Henergy from electron transport pumps H++
to interior of thylakoidto interior of thylakoid– HH++ diffuses to exterior through pores of diffuses to exterior through pores of
ATP-synthesizing enzymeATP-synthesizing enzyme– movement of Hmovement of H++ provides energy for ATP provides energy for ATP
synthesissynthesis
Light-Independent ReactionsLight-Independent Reactions(C3 Photosynthesis Cycle)(C3 Photosynthesis Cycle)
• Produce Glucose (CProduce Glucose (C66 H H1212OO66) using CO) using CO22 as a carbon source as a carbon source
• Occur in stroma of chloroplastOccur in stroma of chloroplast
• Use ATP and NADPH from Light-Use ATP and NADPH from Light-Dependent ReactionsDependent Reactions
• Six turns of the cycle produce one Six turns of the cycle produce one glucose moleculeglucose molecule
The CThe C33
Cycle of Cycle of Carbon Carbon FixationFixation
6-Carbon Compoundsform briefly
Cycle is named for 3-Carbon Compounds
C3 Photosynthesis CycleC3 Photosynthesis Cycle
C C C C C C
6-Carbon Intermediates X 66-Carbon Intermediates X 6
C C C C C C
3-Carbon Intermediates X 123-Carbon Intermediates X 12
C C C C C C
Modified 3-Carbon Modified 3-Carbon Intermediates X 12Intermediates X 12
12 ATP12 ATP
12 NADPH12 NADPH
CCarbon DioxideCarbon DioxideX 6X 6
12 ADP12 ADP
12 NADP12 NADP++
GlucoseGlucose6-Carbon Product6-Carbon Product
C C C C C C
Rearrangements Rearrangements to reform 5C reactantsto reform 5C reactants
6 ATP6 ATP6 ADP6 ADP
3-Carbon X 2 3-Carbon X 2
3-Carbon X 10 3-Carbon X 10
C C C C C
5-Carbon Reactants X 65-Carbon Reactants X 6RUBISCORUBISCO
Summary of Summary of Light-IndependentLight-Independent Reactions Reactions
ReactantsReactants ProductsProducts
6 CO6 CO22 Glucose (CGlucose (C66 H H1212OO66))
ATPATPenergy carrierenergy carrier
ADP + POADP + PO44
+ energy + energy (in bonds of glucose) (in bonds of glucose)
NADPHNADPHelectron carrierelectron carrier
NADPNADP+ +
++ 2e2e-- + H + H+ + (used in C3 reactions)(used in C3 reactions)
OHO
OCH2OH
A Summary of PhotosynthesisA Summary of Photosynthesis
Light-dependent Light-dependent reactions occur reactions occur
in thylakoidsin thylakoids Light-Light-independent independent reactions (creactions (c33
cycle) occur in cycle) occur in stromastroma
Applying Your KnowledgeApplying Your Knowledge
A.A. Which reactions produce glucose?Which reactions produce glucose?
B.B. Which reactions use water?Which reactions use water?
C.C. Which reactions release oxygen?Which reactions release oxygen?
D.D. Which reactions use energy from ATP?Which reactions use energy from ATP?
1.1. Light-Dependent ReactionsLight-Dependent Reactions
2.2. Light-Independent ReactionsLight-Independent Reactions
3.3. Neither choice 1 nor 2Neither choice 1 nor 2
4.4. Both choices 1 and 2Both choices 1 and 2
22
4411
22
Adaptations to Adaptations to Hot and Dry Hot and Dry ConditionsConditions
• Plants close leaf pores (stoma) to avoid losing Plants close leaf pores (stoma) to avoid losing water at high temperatures water at high temperatures
• Closed stoma prevent diffusion of COClosed stoma prevent diffusion of CO2 2 into into
leaf and diffusion of Oleaf and diffusion of O22 out of leaf out of leaf
• Excess OExcess O2 2 leads to photorespiration, leads to photorespiration,
interferes with photosynthesisinterferes with photosynthesis
• C4 Pathway is used to continue COC4 Pathway is used to continue CO2 2
collection collection
CC33 Plants & the C Plants & the C33 Pathway Pathway
CC33 plants use the C plants use the C33 pathwaypathway
In a CIn a C33 plant, most plant, most chloroplasts are in chloroplasts are in
mesophyll cells.mesophyll cells.
CC33 Plants & the C Plants & the C33 Pathway Pathway
RUBISCO combines RUBISCO combines with Owith O22 instead of CO instead of CO22
Much photorespiration Much photorespiration occurs under hot, dry occurs under hot, dry
conditionsconditions
RUBISCORUBISCO
CC44 Plants & the C Plants & the C4 4 PathwayPathway
CC44 plants use the C plants use the C44 pathwaypathway
In a CIn a C44 plant, both plant, both mesophyll & bundle-mesophyll & bundle-sheath cells contain sheath cells contain
chloroplasts.chloroplasts.
CC44 Plants & Plants &
the Cthe C4 4
PathwayPathwayAlmost no Almost no
photorespiration photorespiration occurs under hot, occurs under hot,
dry conditions.dry conditions.
COCO22 is captured is captured with a highly with a highly
specific enzyme.specific enzyme.
Much glucose Much glucose synthesis occurs.synthesis occurs.
Mesophyll cell in a CMesophyll cell in a C44 plant plant
Bundle-sheath cell in a CBundle-sheath cell in a C44 plant plant
4C 4C
3C 3C
RUBISCORUBISCO
Interconnections:Interconnections:Photosynthesis & RespirationPhotosynthesis & Respiration