4Fig. 10-3Leaf cross sectionVeinMesophyllStomataCO2O2ChloroplastMesophyll cellOutermembraneFigure 10.3 Zooming in on the location of photosynthesis in a plantThylakoidIntermembranespace5 µmStromaGranumThylakoidspaceInnermembrane1 µm
5Fig. 10-3a Leaf cross section Vein Mesophyll Stomata CO2 O2 ChloroplastMesophyll cellFigure 10.3 Zooming in on the location of photosynthesis in a plant5 µm
6Fig. 10-3b Chloroplast Outer membrane Thylakoid Intermembrane space StromaGranumThylakoidspaceInnermembraneFigure 10.3 Zooming in on the location of photosynthesis in a plant1 µm
7Photosynthesis Photosynthesis- Converting solar energy into the usable energy of carbohydrates.Photosynthesis requires:Light EnergyCarbon DioxideWaterChlorophyllPutting together with light
8The light reactions (in the thylakoids): Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules.Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)The light reactions (in the thylakoids):Split H2ORelease O2Reduce NADP+ to NADPHGenerate ATP from ADP by photophosphorylation
9Light Energy Photon- packets of Energy Light travels in waves and is a type of radiationShort wave length radiation has high energy photonsLong wave length radiation has lower energy photons
10Light EnergyPhotons of visible light have enough energy to raise electrons to higher levels of energy which is needed for photosynthesis.Visible light energy is absorbed by plants to produce sugar. (C6H12O6)Chlorophyll is the substance that absorbs light energy.
11Pop Quiz 1. In your own words, define photosynthesis 2. In your own words, define cellular respiration.3. What is ATP4. How is ATP generated or made?5. Which bond in ATP is loaded with energy?
12Chlorophyll (borophyll) Two Types of ChlorophyllChlorophyll AChlorophyll BCarotenoidsOther pigments that are yellow-orange in plants which absorb violets, blues, and greens.As chlorophyll A and B breakdown they become more noticeable, especially during the fall.Both absorb violet, blue, and red light. Because green is only minimally absorbed, the leaf appears green. The green light is reflected off of the leaf.}
13Photosynthesis- the formula 6 CO2 + 6 H2O C6H12O6 + 6 O2LIGHTCHLOROPHYLL
14i Light NADP+ ADP Light Reactions Chloroplast H2O + P Fig. 10-5-1 Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleChloroplast
15i Light NADP+ ADP Light Reactions ATP NADPH Chloroplast O2 H2O + P FigH2OLightNADP+ADP+PiLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplastO2
16i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH FigH2OCO2LightNADP+ADP+PiCalvinCycleLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplastO2
17Chloroplasts – contain chlorophyll Chloroplasts are double membrane organelles. (See figure in book)Note the granum, stroma, thylakoid, and thylakoid spaceChlorophyll is found within the membranes of the thylakoids
18Photosynthesis has two reactions Light dependent Reactions (light RXN)Light capturing reactionabsorbs solar energyOccurs in the thylakoid membraneLight independent Reactions (dark RXN) Now called the Calvin CycleSynthesis reactionProduces glucoseOccurs in the stroma
19Light Dependent Reactions Takes place in the thylakoid membraneRequires two light gathering systemsPhotosystems- systems used to gather solar energy which contain chlorophyll A,B, and carotenoids.The photosystems were named in the order that they were discovered, not the order in which they occur.Photosystem I (PSI) The molecules of Chlorophyll a & b which make up the photosystems Photosystem II (PSII) act like antennas gathering solar energy and focus it to a particular spot.}
20i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH FigH2OCO2LightNADP+ADP+PiCalvinCycleLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplast[CH2O](sugar)O2
21PSI and PSIIBasically, the function of the photosystems is to convert energy so that glucose can be produced. This is accomplished by generating electron flow.Sometimes PSI occurs exclusively called the cyclic electron pathway.When both PSI and PSII occur PSII occurs first and then PSI. This process is the non-cyclic electron pathway.
22Generating electron flow Energy is directed onto a particular molecule of chlorophyll A . The electrons of this molecule are so excited that they escape their orbitals and move through a series of electron acceptors.Reaction center- The molecule of chlorophyll A that loses an electron.
23(INTERIOR OF THYLAKOID) FigPhotosystemSTROMAPhotonPrimaryelectronacceptorLight-harvestingcomplexesReaction-centercomplexe–Thylakoid membraneFigure How a photosystem harvests lightPigmentmoleculesTransferof energySpecial pair ofchlorophyll amoleculesTHYLAKOID SPACE(INTERIOR OF THYLAKOID)
24Cyclic Electron Pathway (PS1) (not play station 1) An electron leaves the RXN center but eventually returns to it.As the electron is passed from acceptor to acceptor Energy for ATP is released.Occurs when:CO2 levels are extremely lowby photosynthetic bacteria
25Cyclic pathway – PS1 (cont.) Does not produce NADPHProduces ONLY ATPProbably first to evolve,Because CO2 levels are low no glucose is produced and the organism must survive on the small amount of ATP that is generated
26Non-cyclic Pathway (PS 2) (not play station 2) Water is split and an electron enters PSIICauses the reaction center to lose an electron and travel through a series of electron acceptors.As the electron is passed along ATP is generated. This ATP will be used in the Light independent reactionsThe electron then enters PSI which during the non-cyclic pathway produces the molecule NADPH instead of ATP.
27Non-cyclic (cont.)The products of the non-cyclic pathway, NADPH and ATP, enter the StromaNADP is one of several biological molecules that act as an electron carrier.In the stroma, the light independent reactions occur.The splitting of water results in a H ion (which is basically an electron) and O which is released from the leaf as a waste product.
28Electron transport chain FigElectrontransportchainPrimaryacceptorPrimaryacceptor47Electron transport chainFdPqe–2e–8e–H2Oe–NADP++ H+Cytochromecomplex2 H+NADP+reductase+31/2O2NADPHPce–e–P7005P680Light1Light66ATPFigure How linear electron flow during the light reactions generates ATP and NADPHPigmentmoleculesPhotosystem I(PS I)Photosystem II(PS II)
29Electron transport chain FigH2OCO2LightNADP+ADP+PiLightReactions:Photosystem IIElectron transport chainPhotosystem IRuBP3-PhosphoglycerateCalvinCycleATPG3PFigure A review of photosynthesisStarch(storage)NADPHChloroplastO2Sucrose (export)
30Photophosphorylation Occurs when ATP is generated using photosynthesis.Photophosphorylation occurs because of severe differences in the concentration of H+ ions inside the thylakoid space compared to the stroma.The movement of ions allows for a phosphate to be added to ADP.
31Diagram of the Light Dependent Reactions and ATP Synthase
32Quiz1. How is the cyclic pathway different than the non-cyclic pathway?2. In the non-cyclic pathway, what produces ATP?3. In the non-cyclic pathway, what produces NADPH?4. What is the role of NADPH?
33Light Independent Reactions AKA- Calvin Cycle (The Dark RXN) The products of the light dependent reactions are NADPH and ATP.Both are used in the light independent reactions.The actual process of producing glucose during the light independent RXN is called the Calvin Cycle.
34A Comparison of Chemiosmosis in Chloroplasts and Mitochondria Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energyMitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATPSpatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities
35In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrixIn chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
36H+ Diffusion Electron transport chain ADP + P FigMitochondrionChloroplastMITOCHONDRIONSTRUCTURECHLOROPLASTSTRUCTUREH+DiffusionIntermembranespaceThylakoidspaceElectrontransportchainInnermembraneThylakoidmembraneFigure Comparison of chemiosmosis in mitochondria and chloroplastsATPsynthaseMatrixStromaKeyADP + PiATPHigher [H+]H+Lower [H+]
38The Calvin Cycle (light independent reactions) Has three steps/parts (see fig)1. CO2 fixation2. CO2 reduction3. Regeneration of RuBPRuBP is a 5 carbon compound that will combine with CO2 to form a 6 Carbon Compound.Remember, glucose is a 6 C compound
39Step 1- CO2 FixationRefers to the attachment of CO2 to an organic compound.3 CO2 bind with 3 RuBP molecules.Results in 3 six Carbon compoundswhich change to 6 three carbon compoundsThe three Carbon compound is called PGAThe Calvin Cycle is sometimes called the C-3 cycle because of PGA.
40Phase 1: Carbon fixation Ribulose bisphosphate FigInput3(Entering oneat a time)CO2Phase 1: Carbon fixationRubisco3PPShort-livedintermediate3PP6PRibulose bisphosphate(RuBP)3-PhosphoglycerateFigure The Calvin cycle
41Step 2 - CO2 Reduction Requires ATP and NADPH (from light RXN) PGA gets converted to G3P (PGAL) using ATP and NADPH.ATP ADP + PNADPH NADPPGA G3P (PGAL)The reduction of CO2 to CH2O results in 6 total PGAL molecules.5 molecules of G3P (PGAL) will be used to regenerate RuBP.It takes 3 turns of the Calvin Cycle to have a net gain of 1 G3P (PGAL)
42Fig. 10-18-2 Figure 10.18 The Calvin cycle Input 3 (Entering one at a time)CO2Phase 1: Carbon fixationRubisco3PPShort-livedintermediate3PP6PRibulose bisphosphate(RuBP)3-Phosphoglycerate6ATP6 ADPCalvinCycle6PP1,3-Bisphosphoglycerate6NADPH6 NADP+6PiFigure The Calvin cycle6PGlyceraldehyde-3-phosphate(G3P)Phase 2:Reduction1PGlucose andother organiccompoundsOutputG3P(a sugar)
43G3P (PGAL) Glucose Glucose is used to produce ATP Plants need several other organic compounds.G3P (PGAL) can be converted to many other compounds such as: fatty acids, Amino Acids, and of course Glucose.Technically, the Calvin cycle ends with the production of G3P (PGAL)
44Step 3 - RuBP Regeneration 5 (PGAL) G3P 3 RuBP3 ATP 3 ADP + PATP comes from the light dependent reactions
45Fig. 10-18-3 Figure 10.18 The Calvin cycle Input 3 (Entering one at a time)CO2Phase 1: Carbon fixationRubisco3PPShort-livedintermediate3PP6PRibulose bisphosphate(RuBP)3-Phosphoglycerate6ATP6 ADP3 ADPCalvinCycle63PPATP1,3-Bisphosphoglycerate6NADPHPhase 3:Regeneration ofthe CO2 acceptor(RuBP)6 NADP+6PiFigure The Calvin cycle5PG3P6PGlyceraldehyde-3-phosphate(G3P)Phase 2:Reduction1PGlucose andother organiccompoundsOutputG3P(a sugar)
46Electron transport chain FigH2OCO2LightNADP+ADP+PiLightReactions:Photosystem IIElectron transport chainPhotosystem IRuBP3-PhosphoglycerateCalvinCycleATPG3PFigure A review of photosynthesisStarch(storage)NADPHChloroplastO2Sucrose (export)
47Variations in Photosynthesis The C-3 Pathway –CO2 is fixed during the Calvin cycle, and the first detectable molecule is a 3 Carbon compound (PGA).The C-4 Pathway –CO2 is fixed to a 3 C compound (forming a 4 C compound) prior to the Calvin Cycle.CAM Plant Pathway –Similar to the C- 4 Pathway, but at a slightly different time.
48C-3 Pathway Occurs in the mesophyll of the leaf RuBP PGA P3G (PGAL) See Figure
49C-4 PathwayCO2 is attached to a 3 C compound called PEP with an enzyme called PEP-carboxylase.This process forms oxaloacetate and occurs in the mesophyll.Oxaloacetate enters the bundle sheath cells where the Calvin Cycle takes placeOccurs in warm dry climatesPartition PSS in spaceSee Figure 10.14
50The C4 pathway Mesophyll cell CO2 PEP carboxylase Oxaloacetate (4C) Fig bThe C4pathwayMesophyllcellCO2PEP carboxylaseOxaloacetate (4C)PEP (3C)ADPMalate (4C)ATPPyruvate (3C)Bundle-sheathcellCO2CalvinCycleFigure C4 leaf anatomy and the C4 pathwaySugarVasculartissue
51CAM plant PathwayA C4 compound is produced similar to the C-4 pathway.That compound is produced during the night, and stored in the vacuole until day.Occurs in the mesophyllOccurs in hot, dry and stressful environmentsAllows Stomates to open at night when it is cooler and less water is lost to evaporation.
52(a) Spatial separation of steps (b) Temporal separation of steps FigSugarcanePineappleC4CAMCO2CO2Mesophyllcell1CO2 incorporatedinto four-carbonorganic acids(carbon fixation)NightOrganic acidOrganic acidFigure C4 and CAM photosynthesis comparedBundle-sheathcellCO2CO2Day2Organic acidsrelease CO2 toCalvin cycleCalvinCycleCalvinCycleSugarSugar(a) Spatial separation of steps(b) Temporal separation of steps
53The Importance of Photosynthesis: A Review The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compoundsSugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cellsPlants store excess sugar as starch in structures such as roots, tubers, seeds, and fruitsIn addition to food production, photosynthesis produces the O2 in our atmosphere