Unit 3: Cells

Chapter 8: Photosynthesis

8-3: The Reactions of Photosynthesis

Ms. PetrucciBiology

PhotosynthesiPhotosynthesiss

8-3 The Reactions of Photosynthesis

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The Biochemical The Biochemical ReactionsReactions

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It Begins with Sunlight!It Begins with Sunlight!

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Photoautotrophs Absorb Light Photoautotrophs Absorb Light EnergyEnergy

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Inside A ChloroplastInside A Chloroplast

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Structure of the ChloroplastStructure of the Chloroplast

• Double membraneDouble membrane organelle organelle• Outer membrane Outer membrane smoothsmooth• Inner membraneInner membrane forms stacks of forms stacks of connected sacs called connected sacs called thylakoidsthylakoids

• Thylakoid stack is called the Thylakoid stack is called the granumgranum (grana-plural) (grana-plural)

• Gel-like material around grana Gel-like material around grana called called stromastroma

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Thylakoid membranesThylakoid membranes

• Light DependentLight Dependent reactions occur reactions occur herehere

• Photosystems are made up of Photosystems are made up of clusters of chlorophyll moleculesclusters of chlorophyll molecules

• Photosystems are Photosystems are embedded in embedded in the thylakoid membranesthe thylakoid membranes

• The two photosystems are:The two photosystems are:– Photosytem IPhotosytem I– Photosystem IIPhotosystem II

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Function of the StromaFunction of the Stroma

• Light IndependentLight Independent reactions reactions occur hereoccur here

• ATP usedATP used to make to make carbohydrates like carbohydrates like glucoseglucose

• Location of the Location of the Calvin CycleCalvin Cycle

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Photosynthesis OverviewPhotosynthesis Overview

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Energy CarriersEnergy Carriers• Nicotinamide Adenine Dinucleotide Nicotinamide Adenine Dinucleotide

Phosphate Phosphate (NADP(NADP++))• Picks Up Picks Up 2 high-energy 2 high-energy electrons and Helectrons and H++ from the Light from the Light Reaction to form NADPHReaction to form NADPH

• NADPHNADPH carries energy to be carries energy to be passed on to another moleculepassed on to another molecule

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NADPHNADPH

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• Occurs across the Occurs across the thylakoid thylakoid membranesmembranes

• Uses light energyUses light energy• Produce Produce OxygenOxygen from water from water• Convert Convert ADP to ATPADP to ATP• Also convert Also convert NADPNADP++ into into the energy carrier the energy carrier NADPHNADPH

Light Dependent ReactionsLight Dependent Reactions

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Light Dependent ReactionLight Dependent Reaction

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Light Dependent ReactionLight Dependent Reaction

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Photosystem IPhotosystem I

•Discovered Discovered FirstFirst•Active in the final stage of the Active in the final stage of the Light Dependent ReactionLight Dependent Reaction•Made of 300 molecules of Made of 300 molecules of ChlorophyllChlorophyll•Almost completely chlorophyll aAlmost completely chlorophyll a

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Photosystem IIPhotosystem II

•Discovered Discovered SecondSecond•Active in the beginning stage Of Active in the beginning stage Of the Light Dependent Reactionthe Light Dependent Reaction•Contains about Contains about equal amounts of equal amounts of chlorophyll a and chlorophyll bchlorophyll a and chlorophyll b

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Photosynthesis BeginsPhotosynthesis BeginsPhotosystem Photosystem II absorbs light II absorbs light energyenergy

Electrons are energizedElectrons are energized and passed and passed to the to the Electron Transport ChainElectron Transport Chain

Lost electrons are replaced from Lost electrons are replaced from the splitting of waterthe splitting of water into 2H into 2H+, +,

free electrons, and Oxygenfree electrons, and Oxygen2H2H+ + pumped across thylakoid pumped across thylakoid membranemembrane

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Photosystem IPhotosystem IHigh-energy electronsHigh-energy electrons are are moved to Photosystem I moved to Photosystem I through the Electron through the Electron Transport ChainTransport Chain

Energy is used to Energy is used to transport Htransport H++ from stroma to inner from stroma to inner thylakoid membranethylakoid membrane

NADP+ converted to NADPHNADP+ converted to NADPH when it picks up 2 electrons & when it picks up 2 electrons & H+H+

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PhosphorylationPhosphorylation

Enzyme in thylakoid Enzyme in thylakoid membrane called membrane called ATP ATP SynthetaseSynthetase

As H+ ions passed through As H+ ions passed through thylakoid membrane, thylakoid membrane, enzyme binds them to ADPenzyme binds them to ADP

Forms Forms ATPATP for cellular for cellular

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Light Reaction SummaryLight Reaction SummaryReactants:Reactants:• HH22OO• Light EnergyLight EnergyEnergy Products:Energy Products:• ATPATP• NADPHNADPHOther Product:Other Product:• OxygenOxygen

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Light Independent ReactionLight Independent Reaction

• ATP & NADPHATP & NADPH from light from light reactions used as energyreactions used as energy

• Atmospheric Atmospheric C0C022 is used is used to to make make sugarssugars like glucose and fructose like glucose and fructose

• Six-carbon Sugars made during Six-carbon Sugars made during the the Calvin CycleCalvin Cycle

• Occurs in theOccurs in the stroma stroma

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The Calvin CycleThe Calvin Cycle

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The Calvin CycleThe Calvin Cycle

• Two turnsTwo turns of the Calvin Cycle are of the Calvin Cycle are required to make one molecule of required to make one molecule of glucoseglucose

• 3-CO3-CO22 molecules enter the cycle to molecules enter the cycle to form several form several intermediate compounds intermediate compounds (PGA)(PGA)

• A 3-carbon molecule called A 3-carbon molecule called Ribulose Ribulose BiphosphateBiphosphate (RuBP) is used to (RuBP) is used to regenerate the Calvin cycleregenerate the Calvin cycle

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Factors Affecting the Rate Factors Affecting the Rate of Photosynthesisof Photosynthesis

• Amount of Amount of available wateravailable water

• TemperatureTemperature• Amount of Amount of available light available light energyenergy