Chapter 10PhotosynthesisSlide 3Chloroplasts: The Sites of Photosynthesis in PlantsTracking Atoms Through Photosynthesis: Scientific InquiryThe Splitting of WaterSlide 7Slide 8Photosynthetic Pigments: The Light ReceptorsSlide 10Slide 11Slide 12Chlorophyll aExcitation of Chlorophyll by LightSlide 15Noncyclic electron flowSlide 17Slide 18Slide 19Slide 20The Calvin cycleThe Importance of Photosynthesis: A ReviewYou should now be able to:Slide 24PowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 10Chapter 10PhotosynthesisPhotosynthesis–Occurs in plants, algae, certain other protists, and some prokaryotesThese organisms use light energy to drive the synthesis of organic molecules from carbon dioxideand (in most cases) water. They feed not onlythemselves, but the entire living world. (a) Onland, plants are the predominant producers offood. In aquatic environments, photosyntheticorganisms include (b) multicellular algae, suchas this kelp; (c) some unicellular protists, suchas Euglena; (d) the prokaryotes calledcyanobacteria; and (e) other photosyntheticprokaryotes, such as these purple sulfurbacteria, which produce sulfur (sphericalglobules) (c, d, e: LMs).(a) Plants(b) Multicellular algae(c) Unicellular protist10 m40 m(d) Cyanobacteria1.5 m(e) Pruple sulfurbacteriaFigure 10.2•The leaves of plants–Are the major sites of photosynthesisVeinLeaf cross sectionFigure 10.3MesophyllCO2O2StomataChloroplastMesophyll5 µmOutermembraneIntermembranespaceInnermembraneThylakoidspaceThylakoidGranumStroma1 µmChloroplasts: The Sites of Photosynthesis in PlantsTracking Atoms Through Photosynthesis: Scientific Inquiry•Photosynthesis is summarized as6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O •Photosynthesis is a redox process–Water is oxidized, carbon dioxide is reducedThe Splitting of Water•Chloroplasts split water into–Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules6 CO212 H2OReactants:Products:C6H12O66 H2O 6 O2Figure 10.4•An overview of photosynthesisH2OCO2LightLIGHT REACTIONSCALVINCYCLEChloroplast[CH2O](sugar)NADPHNADP ADP+ PO2Figure 10.5ATP•The electromagnetic spectrum–Is the entire range of electromagnetic energy, or radiationGammaraysX-rays UV InfraredMicro-wavesRadiowaves10–5 nm10–3 nm1 nm103 nm106 nm1 m106 nm103 m380 450 500 550 600 650 700 750 nmVisible lightShorter wavelengthHigher energyLonger wavelengthLower energyFigure 10.6–The colors that we see are wavelengths of light that are reflected (or not absorbed)LightReflectedLight ChloroplastAbsorbedlight GranumTransmittedlight Figure 10.7Photosynthetic Pigments: The Light Receptors•Pigments– Are substances that absorb visible light•The absorption spectra of three types of pigments in chloroplasts Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below.EXPERIMENTRESULTSAbsorption of light bychloroplast pigmentsChlorophyll a(a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments.Wavelength of light (nm)Chlorophyll bCarotenoidsFigure 10.9•The action spectrum of a pigment–Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesisRate of photosynthesis(measured by O2 release)Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.(b)•The action spectrum for photosynthesis–Was first demonstrated by Theodor W. Engelmann400500 600 700Aerobic bacteriaFilamentof algaEngelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most.Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b.(c) Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis.CONCLUSIONChlorophyll aCCHCH2CCCCCCNNCH3CCCCCCCCCNCCCCNMgHH3CHCCH2CH3HCH3CHHCH2CH2CH2HCH3COOOOOCH3CH3CHOin chlorophyll ain chlorophyll bPorphyrin ring:Light-absorbing“head” of moleculenote magnesiumatom at centerHydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts: H atoms notshownFigure 10.10Excitation of Chlorophyll by Light• When a pigment absorbs light–It goes from a ground state to an excited state, which is unstableExcitedstateEnergy of electionHeatPhoton(fluorescence)ChlorophyllmoleculeGroundstatePhotone–Figure 10.11 A•If an isolated solution of chlorophyll is illuminated–It will fluoresce, giving off light and heatFigure 10.11 BPrimary electionacceptorPhotonThylakoidLight-harvestingcomplexesReactioncenterPhotosystemSTROMAThylakoid membraneTransferof energySpecialchlorophyll amoleculesPigmentmoleculesTHYLAKOID SPACE(INTERIOR OF THYLAKOID)Figure 10.12e–Noncyclic electron flow•Produces NADPH, ATP, and oxygenFigure 10.13Photosystem II(PS II)Photosystem-I(PS I)ATPNADPHNADP+ADPCALVINCYCLECO2H2OO2[CH2O] (sugar)LIGHTREACTIONSLightPrimaryacceptorPqCytochromecomplexPCeP680e–e–O2+H2O2 H+LightATPPrimaryacceptorFdee–NADP+reductaseElectronTransportchainElectron transport chainP700LightNADPHNADP++ 2 H++ H+15723468•A mechanical analogy for the light reactionsMillmakesATPATPe–e–e–e–e–PhotonPhotosystem IIPhotosystem Ie–e–NADPHPhotonFigure 10.14PrimaryacceptorPqFdCytochromecomplexPcPrimaryacceptorFdNADP+reductaseNADPHATPFigure 10.15Photosystem IIPhotosystem INADP+•The spatial organization of chemiosmosis–Differs in chloroplasts and mitochondriaKeyHigher [H+]Lower [H+]MitochondrionChloroplastMITOCHONDRIONSTRUCTUREIntermembrancespaceMembranceMatrixElectrontransportchainH+DiffusionThylakoidspaceStromaATPH+PADP+ATPSynthaseCHLOROPLASTSTRUCTUREFigure 10.16•The light reactions and chemiosmosis: the
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