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