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Sylvia S. Mader Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor BIOLOGY 10th Edition Insert figure 7.4 here 1 Photosynthesis Chapter 7: pp. 117-132 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. thylakoid membrane NADP + NADP ATP Calvin Cycle reactions Light reactions Solar energy H2OH2O CO 2 CH 2 O O2O2 stroma thylakoid membrane NADP + ADP + P
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What is photosynthesis? Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water Carbon dioxide WaterGlucoseOxygen gas PHOTOSYNTHESIS
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4 Photosynthesis Reaction 6 CO 2 + 6 H 2 O + Light energy → C 6 H 12 O 6 + 6 O 2
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5 Structure of the Chloroplast lThylakoid – Saclike photosynthetic membranes Light-dependent reactions occur here lGranum – Stack of thylakoids lStroma – Region outside the thylakoid membrane Reactions of the Calvin Cycle occur here
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11 Photosynthetic Reactions: Two Sets of Reaction Light Reaction – takes place only in the presence of light They are the energy ‑ capturing reactions Chlorophyll absorbs solar energy This energizes electrons Electrons move down electron transport chain Pumps H + into thylakoids Used to make ATP out of ADP and NADPH out of NADP Calvin Cycle Reaction takes place in stroma CO 2 is reduced to a carbohydrate Use ATP and NADPH produced carbohydrate They are synthetic reactions
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7 Photosynthetic Pigments Pigments: Chemicals that absorb some colors in rainbow more than others Colors least absorbed reflected/transmitted most Absorption Spectra Pigments found in chlorophyll absorb various portions of visible light Graph showing relative absorption of the various colors of the rainbow Chlorophyll is green because it absorbs much of the reds and blues of white light
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.6B Light Chloroplast Reflected light Absorbed light Transmitted light The chlorophyll absorbs the sunlight.
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Chlorophyll Chlorophyll a Chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center in chlorophyll a CH 3 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown CHO in chlorophyll b
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The Nature of Sunlight Light is a form of electromagnetic energy The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see Wavelength is the distance between crests of waves Wavelength determines the type of electromagnetic energy
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9 Photosynthetic Pigments Wavelengths (nm) Increasing wavelength a. The electromagnetic spectrum includes visible light.b. Absorption spectrum of photosynthetic pigments. Increasing energy Gamma rays X raysUVInfrared Micro- waves Radio waves visible light 500600750 Wavelengths (nm) 380500600750 chlorophyll a chlorophyll b carotenoids Relative Absorption Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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12 Photosynthesis Overview Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. thylakoid membrane ADP + P NADP + NADP ATP Calvin Cycle reactions Light reactions Solar energy H2OH2O CO 2 CH 2 O O2O2 stroma
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13 Photosynthetic Reactions: The Light Reactions Light reactions consist of two alternate electron pathways: Noncyclic electron pathway Cyclic electron pathway Capture light energy with photosystems Pigment complex helps collect solar energy like an antenna Occur in the thylakoid membranes Both pathways produce ATP The noncyclic pathway also produces NADPH
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14 Light Reactions: The Noncyclic Electron Pathway Takes place in thylakoid membrane Uses two photosystems, PS-I and PS-II PS II captures light energy Causes an electron to be ejected from the reaction center (chlorophyll a) Electron travels down electron transport chain to PS-I Replaced with an electron from water Which causes H + to concentrate in thylakoid chambers Which causes ATP production PS-I captures light energy and ejects an electron Transferred permanently to a molecule of NADP + Causes NADPH production
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15 Light Reactions: Noncyclic Electron Pathway NADPH 2H + H2OH2O electron acceptor NADP + H + pigment complex pigment complex reaction center sun electron transport chain (ETC) Photosystem II Photosystem I NADPH thylakoid membrane solar energy Calvin cycle ATP Calvin cycle reactions energy level CO 2 CH 2 O Light reactions O2O2 1 2 ADP+P NADP + e-e- e-e- e e e e-e- e-e- electron acceptor CH 2 O H2OH2O CO 2 O2O2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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18 Light Reactions: The Cyclic Electron Pathway Uses only photosystem I (PS-I) Begins when PS I complex absorbs solar energy Electron ejected from reaction center Travels down electron transport chain Causes H + to concentrate in thylakoid chambers Which causes ATP production Electron returns to PS-I (cyclic) Pathway only results in ATP production
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19 Organization of the Thylakoid Membrane PS II: Consists of a pigment complex and electron-acceptors Adjacent to an enzyme that oxidizes water Oxygen is released as a gas Electron transport chain: Consists of cytochrome complexes Carries electrons between PS II and PS I Also pump H + from the stroma into thylakoid space PS I: Has a pigment complex and electron acceptors Adjacent to enzyme that reduces NADP + to NADPH ATP synthase complex: Has a channel for H + flow Which drives ATP synthase to join ADP and P i
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20 Organization of a Thylakoid stroma P NADPH Calvin cycle reactions ATP thylakoid photosystem II Stroma NADP reductase NADP + H+H+ H + Pq H+H+ H+H+ ATP synthase chemiosmosis electron transport chain photosystem I granum thylakoid membrane thylakoid space stroma ATP NADPH +ADPP O2O2 2 + 2 1 Thylakoid space e-e- H2OH2OCO 2 O2O2 CH 2 O solar energy thylakoid membrane Light reactions ADP + NADP + e-e- e-e- H+H+ H+H+ H+H+ H+H+ H+H+ e-e- H2OH2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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22 ATP Production Thylakoid space acts as a reservoir for hydrogen ions (H + ) Each time water is oxidized, two H + remain in the thylakoid space Electrons yield energy Used to pump H + across thylakoid membrane Move from stroma into the thylakoid space Flow of H + back across thylakoid membrane Energizes ATP synthase Enzymatically produces ATP from ADP + P i This method of producing ATP is called chemiosmosis
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14 Light Dependent Reactions 14
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The production of ATP by chemiosmosis in photosynthesis = photophosphorylation Figure 7.9 Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE
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BASIC DIAGRAM of LIGHT DEPENDENT REACTION
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Reverse Process of Each Other Both create H+ gradient, allowing H+ to diffuse through ATP synthase and ATP production Oxidative phosphorylation O2 reduced to H2O using electrons donated by NADH or FADH2 (Respiration) Photophosphorylation just the reverse, H2O oxidized to O2 with electrons accepted (Photosynthesis)
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25 Calvin Cycle Reactions: Overview of C3 Photosynthesis A cyclical series of reactions where ATP and NADPH generated in light reactions used to fuel the reactions which take CO 2 and break it apart, then reassemble the carbons into glucose Utilizes atmospheric carbon dioxide to produce carbohydrates Known as C3 photosynthesis Involves three stages: Carbon dioxide fixation Carbon dioxide reduction RuBP regeneration
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (Entering one at a time) CO 2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 P P P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P 6 P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP + 6 P i P 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 6 ATP 3 ATP 3 ADP CALVIN CYCLE P 5 Phase 3: Regeneration of the CO 2 acceptor (RuBP) P 1 G3P (a sugar) Output Glucose and other organic compounds G3P 6 ADP Light H2OH2O CO 2 LIGHT REACTIONS NADPH NADP + [CH 2 O] (sugar) CALVIN CYCLE Input ATP ADP O2O2 6 The Calvin Cycle
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26 Calvin Cycle Reactions: Carbon Dioxide Fixation CO 2 is attached to 5-carbon RuBP molecule Result in a 6-carbon molecule This splits into two 3-carbon molecules (3PG) Reaction accelerated by RuBP Carboxylase (Rubisco) CO 2 now “fixed” because it is part of a carbohydrate
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Calvin cycle: Carbon Fixation Light H2OH2O CO 2 LIGHT REACTIONS ATP NADPH NADP + [CH 2 O] (sugar) CALVIN CYCLE ADP (Entering one at a time) CO 2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 PP P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate 6 ATP 6 ADP Input CALVIN CYCLE O2O2 6
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28 Calvin Cycle Reactions: Carbon Dioxide Reduction 3PG reduced to BPG BPG then reduced to G3P Utilizes NADPH and some ATP produced in light reactions
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.18 The Calvin cycle (Entering one at a time) CO 2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 PP P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P6 P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP + 6 P i P 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 6 ATP CALVIN CYCLE P 1 G3P (a sugar) Output Glucose and other organic compounds 6 ADP Input Light H2OH2O CO 2 LIGHT REACTIONS ATP NADP + [CH 2 O] (sugar) CALVIN CYCLE NADPH ADP O2O2 6
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29 The Calvin Cycle: Reduction of CO 2 NADPHNADP + ATP 3PG G3P BPG ADP + P As 3PG becomes G3P, ATP becomes ADP +and NADPH becomes NADP + P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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30 Calvin Cycle Reactions: Regeneration of RuBP RuBP used in CO 2 fixation must be replaced Every three turns of Calvin Cycle, Five G3P (a 3-carbon molecule) used To remake three RuBP (a 5-carbon molecule) 5 X 3 = 3 X 5
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (Entering one at a time) CO 2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 P P P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P 6 P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP + 6 P i P 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 6 ATP 3 ATP 3 ADP CALVIN CYCLE P 5 Phase 3: Regeneration of the CO 2 acceptor (RuBP) P 1 G3P (a sugar) Output Glucose and other organic compounds G3P 6 ADP Light H2OH2O CO 2 LIGHT REACTIONS NADPH NADP + [CH 2 O] (sugar) CALVIN CYCLE Input ATP ADP O2O2 6 The Calvin Cycle: Regeneration of RuBP
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31 The Calvin Cycle: Regeneration of RuBP As five molecules of G3P become three molecules of RuBP, three molecules of ATP become three molecules of ADP +. 3 ATP 5 G3P3 RuBP 3 ADP +P P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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32 Importance of Calvin Cycle G3P (glyceraldehyde-3-phosphate) can be converted to many other molecules The hydrocarbon skeleton of G3P can form Fatty acids and glycerol to make plant oils Glucose phosphate (simple sugar) Fructose (which with glucose = sucrose) Starch and cellulose Amino acids
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Light Fig. 10-5-1 H2OH2O Chloroplast Light Reactions NADP + P ADP i +
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Light Fig. 10-5-2 H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2
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Light Fig. 10-5-3 H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2
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Light Fig. 10-5-4 H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)
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The Two Stages of Photosynthesis A Review The light reactions (in the thylakoids): – Split H 2 O – Release O 2 – Reduce NADP + to NADPH – Generate ATP from ADP by photophosphorylation The Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
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36 C 4 Photosynthesis In hot, dry climates Stomata must close to avoid wilting CO 2 decreases and O 2 increases O 2 starts combining with RuBP instead of CO 2 Photorespiration, a problem solve in C 4 plants In C 4 plants Fix CO 2 to PEP a C 3 molecule The result is oxaloacetate, a C 4 molecule In hot & dry climates Avoid photorespiration Net productivity about 2-3 times C 3 plants In cool, moist, can’t compete with C 3
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38 CO 2 Fixation in C 4 vs. C 3 Plants Calvin cycle CO 2 G3P 3PG RuBP mesophyll cell CO 2 C4C4 G3 bundle sheath cell mesophyll cell a. CO 2 fixation in a C 3 plant, blue columbine, Aquilegia caerulea b. CO 2 fixation in a C 4 plant, corn, Zea mays Calvin cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b: © Nigel Cattlin/Photo Researchers, Inc.
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some plants have special adaptations that enable them to save water CALVIN CYCLE 4-C compound Figure 7.12B –Special cells in C 4 plants—corn and sugarcane—incorporate CO 2 into a four-carbon molecule –PEP carboxylase –This molecule can then donate CO 2 to the Calvin cycle 3-C sugar
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39 CAM Photosynthesis Crassulacean-Acid Metabolism CAM plants partition carbon fixation by time During the night CAM plants fix CO 2 Forms C 4 molecules, Stored in large vacuoles During daylight NADPH and ATP are available Stomata closed for water conservation C 4 molecules release CO 2 to Calvin cycle
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism CALVIN CYCLE 4-C compound Figure 7.12C –They open their stomata at night and make a four-carbon compound 3-C sugar Night Day
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40 CO 2 Fixation in a CAM Plant Calvin cycle CO 2 C4C4 G3P CO 2 fixation in a CAM plant, pineapple, Ananas comosus night day Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © S. Alden/PhotoLink/Getty Images.
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42 Climatic Adaptation: Photosynthesis Each method of photosynthesis has Advantages and disadvantages Depends on the climate C 4 plants most adapted to: High light intensities High temperatures Limited rainfall C 3 plants better adapted to Cold (below 25°C) High moisture CAM plants better adapted to extreme aridity CAM occurs in 23 families of flowering plants Also found among nonflowering plants
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