1• Photosynthesis is the process by whichautotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESISCarbondioxideWater Glucose OxygengasPHOTOSYNTHESISDo you remember how photosynthesis works?Do you remember the formula?L12S1• Photosynthesis is the process by whichautotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESISCarbondioxideWater Glucose OxygengasPHOTOSYNTHESISDo you remember the formula?L12S1• Photosynthesis is the process by whichautotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESISCarbondioxideWater Glucose OxygengasPHOTOSYNTHESISDo you remember the formula?Do you remember the formula?L12 S1• Photosynthesis is the process by whichautotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESISCarbondioxideWater Glucose OxygengasPHOTOSYNTHESISL12S1• The location and structure of chloroplastsFigure 7.2LEAF CROSS SECTIONMESOPHYLL CELLLEAFChloroplastMesophyllCHLOROPLASTIntermembrane spaceOutermembraneInnermembraneThylakoidcompartmentThylakoidStromaGranumStromaGranaWhere does photosynthesis take place?L12S2• The location and structure of chloroplastsFigure 7.2LEAF CROSS SECTIONMESOPHYLL CELLLEAFChloroplastMesophyllCHLOROPLASTIntermembrane spaceOutermembraneInnermembraneThylakoidcompartmentThylakoidStromaGranumStromaGranaWhere does photosynthesis take place?L12S22• The location and structure of chloroplastsFigure 7.2LEAF CROSS SECTIONMESOPHYLL CELLLEAFChloroplastMesophyllCHLOROPLASTIntermembrane spaceOutermembraneInnermembraneThylakoidcompartmentThylakoidStromaGranumStromaGranaWhere does photosynthesis take place?L12S2• The Calvin cycle occurs in the chloroplast’s stroma– This is where carbon fixation takes place and sugar is manufacturedATP and NADPH power sugar synthesis in the Calvin cycleTHE CALVIN CYCLE: CONVERTING CO2TO SUGARSINPUTFigure 7.10AOUTPUT:CALVINCYCLEINPUT: CO2+ ATP + NADPHOutput: G3P Sugars The enzymatic process bywhich CO2 is incorporatedinto organic compounds sothat some can be exportedand while still regeneratingthe compounds of the cycle.L12S3You do not need to know the details of this diagram,but you do need to understand why there is a cycleImportantReactionL12 S4What Environmental FactorsControl the Rate of Photosynthesis?LightCarbon dioxide concentrationTemperature because it affects all enzyme reactionsand because it affects humidityWater supply and humidityL12S5The supply of CO2 can limit the rate of photosynthesisPC-C-C-C-C C-C-C + C-C-CP PPRibulose 1, 5-biphosphate 3-phosphoglycerateCO2RuBisCOEnzymeL12S6Infra-red Gas Analyzer measures theconcentration of CO2 in the air streambefore and after it flows across the leaf inthe chamberThe chamber is enclosedover the leaf. Light andtemperature are measuredwhile photosynthesis isbeing measured.Photosynthesis rate calculated from gas flowrate and CO2 concentration differenceL12S73Basics of foliage photosynthesis00Saturation level.sometimes calledphotosyntheticcapacity.Compensation pointThe irradiance at which CO uptake is zero2Photosynthetic efficiency:Increase in photosynthesisper increase in irradianceAny questions?Increasing CO2concentration in theatmosphere canincrease themaximum rate ofphotosynthesisLight ReactionLimitingDark ReactionLimitingL12S8Species differences in leaf photosynthesisA has the highestphotosynthetic rate at lightsaturationB has the highestphotosynthetic efficiencyand the lowestcompensation point.Another important measure is called Water Use Efficiency:the ratio of photosynthesis achieved per unit of water lost.Units: mmol/mol milli mols of CO per mol of water transpired 2Units: µmol/m /smicro mols of CO persquare meter foliage persecond22milli [m] 0.001 (a thousandth) micro [µ] 0.000 001 (a millionth)Any questions?L12S9More at: http://faculty.washington.edu/edford/research/research_home.htmlWind River CanopyCrane Research FacilityL12S10Thuja plicataAbies grandisPseudotsugamenziesiiTsuga heterophyllaOld-growth species:Douglas-firPseudotsugaWestern hemlockTsugaUpper Canopy Lower CanopyPhot. Cap.13.19.0µmol/m /s2Water Use Eff.6.24.9mmol/molPhot. Cap.8.83.2Water Use Eff.3.54.8Notice thedifference inbranch structurebetween the speciesL12S11Plant of the dayThe problem of photorespiration andthe evolution of photosynthesisWhen the enzyme Rubisco uses oxygen to breakdowncarbohydrate to CO2 rather than using CO2 to synthesizecarbohydrateHow some grasses have evolved a C4 metabolic processand some desert plants have evolved Crassulacean AcidMetabolismL12S124Although Rubisco acts like a ca rboxylase in photosynthesis, it canalso act as an oxygenase when O2 is available.O2 and CO2 compete for the same active site!This is called Photorespiration3-phosphoglycerate2-phosphoglycerateThis becomes a problem (or an advantage?) when photosynthesisrates are high, i.e. photosystem II produces lots of O2 .PPPPC-C-C-C-C C-C-C + C-C RuBisCORibulose 1, 5-biphosphateEnzymeO2CO2L12S13It is believed that photorespiration in plants has increased overgeologic time due to increasing atmospheric O2 concentration -the product of photosynthetic organisms themselves.In the presence of higher O2 levels,photosynthesis rates are lower.The inhibition ofphotosynthesis by O2 was firstnoticed by the German plantphysiologist, Otto Warburg,in 1920, and called the"Warburg effect".275 ppm CO273 ppm CO2L12S14Decarboxylation of malate (CO2 release)creates a higher concentration of CO2 inbundle sheath cells than found inphotosynthetic cells of C3 plants.The first product of CO2 fixation ismalate (C4) in mesophyll cells, notPGA as it is in C3 plants. This istransported to bundle sheath cellsCO2 is released from malate in bundlesheath cells, where it is fixed again byRubisco and the Calvin cycle proceeds.PEP is recycled back to mesophyll cells.This enables C4 plants to sustain higherrates of photosynthesis. And, becausethe concentration of CO2 relative to O2 inbundle sheath cells is higher,photorespiration rates are lower.L12S15XylemBundle sheath cellsfilled withchloroplasts.CALVINREACTION SITEPhloemParenchyma filledwith chloroplastsC4 acids synthesized in the parenchymamove to the bundle sheathCarbon skeletoncompoundsreturn toparenchymaAnatomical separation of theC4