logging in or signing up PHOTOSYNTHESIS EDLEON1369 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 3744 Category: Education License: All Rights Reserved Like it (6) Dislike it (0) Added: October 08, 2008 This Presentation is Public Favorites: 2 Presentation Description No description available. Comments Posting comment... By: janithbandara (17 month(s) ago) Please be kind enough to grant me permission download this presentation to use it in our government school. iasjayantha@sltnet.lk I.A.S jayantha Saving..... Post Reply Close Saving..... Edit Comment Close By: ashraf4ever_3 (23 month(s) ago) It's really a very wonderful presentation. Saving..... Post Reply Close Saving..... Edit Comment Close By: achira (28 month(s) ago) i request you to share this ppt with me. It is very simple and informative. Saving..... Post Reply Close Saving..... Edit Comment Close By: hanif21 (28 month(s) ago) hey this is good, i need it so much thanks Saving..... Post Reply Close Saving..... Edit Comment Close By: brandon27 (29 month(s) ago) I like your presentation, pls allow me to download it...thanks. Saving..... Post Reply Close Saving..... Edit Comment Close loading.... See all Premium member Presentation Transcript Chapter 10 : Chapter 10 Photosynthesis Overview: The Process That Feeds the Biosphere : Overview: The Process That Feeds the Biosphere Photosynthesis is the process that converts solar energy into chemical energy Directly or indirectly, photosynthesis nourishes almost the entire living world Slide 3: Autotrophs sustain themselves without eating anything derived from other organisms Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from water and carbon dioxide Slide 5: Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes These organisms feed not only themselves but also the entire living world LE 10-2 : LE 10-2 Plants Unicellular protist Multicellular algae Cyanobacteria Purple sulfur bacteria 10 µm 1.5 µm 40 µm Slide 7: Heterotrophs obtain their organic material from other organisms Heterotrophs are the consumers of the biosphere Almost all heterotrophs, including humans, depend on photoautotrophs for food and oxygen Concept 10.1: Photosynthesis converts light energy to the chemical energy of food : Concept 10.1: Photosynthesis converts light energy to the chemical energy of food Chloroplasts are organelles that are responsible for feeding the vast majority of organisms Chloroplasts are present in a variety of photosynthesizing organisms Chloroplasts: The Sites of Photosynthesis in Plants : Chloroplasts: The Sites of Photosynthesis in Plants Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast Through microscopic pores called stomata, CO2 enters the leaf and O2 exits Slide 10: Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf A typical mesophyll cell has 30-40 chloroplasts The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana Chloroplasts also contain stroma, a dense fluid LE 10-3 : LE 10-3 Leaf cross section Vein Mesophyll Stomata CO2 O2 Mesophyll cell Chloroplast 5 µm Outer membrane Intermembrane space Innermembrane Thylakoid space Thylakoid Granum Stroma 1 µm Tracking Atoms Through Photosynthesis: Scientific Inquiry : Tracking Atoms Through Photosynthesis: Scientific Inquiry Photosynthesis can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O The Splitting of Water : The Splitting of Water Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules LE 10-4 : LE 10-4 Reactants: Products: 6 CO2 12 H2O C6H12O6 6 H2O 6 O2 Photosynthesis as a Redox Process : Photosynthesis as a Redox Process Photosynthesis is a redox process in which water is oxidized and carbon dioxide is reduced The Two Stages of Photosynthesis: A Preview : The Two Stages of Photosynthesis: A Preview Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part) The light reactions (in the thylakoids) split water, release O2, produce ATP, and form NADPH The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules LE 10-5_1 : LE 10-5_1 H2O LIGHT REACTIONS Chloroplast Light LE 10-5_2 : LE 10-5_2 H2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2 LE 10-5_3 : LE 10-5_3 H2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2 NADP+ CO2 ADP P + i CALVIN CYCLE [CH2O] (sugar) Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH : Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH Chloroplasts are solar-powered chemical factories Their thylakoids transform light energy into the chemical energy of ATP and NADPH The Nature of Sunlight : The Nature of Sunlight Light is a form of electromagnetic energy, also called electromagnetic radiation Like other electromagnetic energy, light travels in rhythmic waves Wavelength = distance between crests of waves Wavelength determines the type of electromagnetic energy Light also behaves as though it consists of discrete particles, called photons Slide 22: The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation Visible light consists of colors we can see, including wavelengths that drive photosynthesis LE 10-6 : LE 10-6 Visible light Gamma rays X-rays UV Infrared Micro- waves Radio waves 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m (109 nm) 103 m 380 450 500 550 600 650 700 750 nm Longer wavelength Lower energy Shorter wavelength Higher energy Photosynthetic Pigments: The Light Receptors : Photosynthetic Pigments: The Light Receptors Pigments are substances that absorb visible light Different pigments absorb different wavelengths Wavelengths that are not absorbed are reflected or transmitted Leaves appear green because chlorophyll reflects and transmits green light Animation: Light and Pigments LE 10-7 : LE 10-7 Chloroplast Light Reflected light Absorbed light Transmitted light Granum Slide 26: A spectrophotometer measures a pigment’s ability to absorb various wavelengths This machine sends light through pigments and measures the fraction of light transmitted at each wavelength LE 10-8a : LE 10-8a White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. Green light Slit moves to pass light of selected wavelength 0 100 LE 10-8b : LE 10-8b White light Refracting prism Chlorophyll solution Photoelectric tube The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. Blue light Slit moves to pass light of selected wavelength 0 100 Slide 29: An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process LE 10-9a : LE 10-9a Chlorophyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption spectra Absorption of light by chloroplast pigments 400 500 600 700 Slide 31: The action spectrum of photosynthesis was first demonstrated in 1883 by Thomas Engelmann In his experiment, he exposed different segments of a filamentous alga to different wavelengths Areas receiving wavelengths favorable to photosynthesis produced excess O2 He used aerobic bacteria clustered along the alga as a measure of O2 production LE 10-9c : LE 10-9c Engelmann’s experiment 400 500 600 700 Aerobic bacteria Filament of algae Slide 33: Chlorophyll a is the main photosynthetic pigment Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll Excitation of Chlorophyll by Light : Excitation of Chlorophyll by Light When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat LE 10-11 : LE 10-11 Excited state Heat Photon (fluorescence) Ground state Chlorophyll molecule Photon Excitation of isolated chlorophyll molecule Fluorescence Energy of electron e– A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes : A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes A photosystem consists of a reaction center surrounded by light-harvesting complexes The light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center Slide 37: A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll a Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions LE 10-12 : LE 10-12 Thylakoid Photon Light-harvesting complexes Photosystem Reaction center STROMA Primary electron acceptor e– Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Thylakoid membrane Slide 39: There are two types of photosystems in the thylakoid membrane Photosystem II functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm Photosystem I is best at absorbing a wavelength of 700 nm The two photosystems work together to use light energy to generate ATP and NADPH Noncyclic Electron Flow : Noncyclic Electron Flow During the light reactions, there are two possible routes for electron flow: cyclic and noncyclic Noncyclic electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH LE 10-13_1 : LE 10-13_1 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 LE 10-13_2 : LE 10-13_2 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 LE 10-13_3 : LE 10-13_3 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP LE 10-13_4 : LE 10-13_4 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e– Primary acceptor Photosystem I (PS I) Light LE 10-13_5 : LE 10-13_5 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e– Primary acceptor Photosystem I (PS I) e– e– Electron Transport chain NADP+ reductase Fd NADP+ NADPH + H+ + 2 H+ Light LE 10-14 : LE 10-14 ATP Photosystem II e– e– e– e– Mill makes ATP e– e– e– Photon Photosystem I Photon NADPH Cyclic Electron Flow : Cyclic Electron Flow Cyclic electron flow uses only photosystem I and produces only ATP Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle LE 10-15 : LE 10-15 Photosystem I Photosystem II ATP Pc Fd Cytochrome complex Pq Primary acceptor Fd NADP+ reductase NADP+ NADPH Primary acceptor A Comparison of Chemiosmosis in Chloroplasts and Mitochondria : A Comparison of Chemiosmosis in Chloroplasts and Mitochondria Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP The spatial organization of chemiosmosis differs in chloroplasts and mitochondria LE 10-16 : LE 10-16 MITOCHONDRION STRUCTURE Intermembrane space Membrane Electron transport chain Mitochondrion Chloroplast CHLOROPLAST STRUCTURE Thylakoid space Stroma ATP Matrix ATP synthase Key H+ Diffusion ADP + P H+ i Higher [H+] Lower [H+] Slide 51: The current model for the thylakoid membrane is based on studies in several laboratories Water is split by photosystem II on the side of the membrane facing the thylakoid space The diffusion of H+ from the thylakoid space back to the stroma powers ATP synthase ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place Animation: Calvin Cycle LE 10-17 : LE 10-17 STROMA (Low H+ concentration) Light Photosystem II Cytochrome complex 2 H+ Light Photosystem I NADP+ reductase Fd Pc Pq H2O O2 +2 H+ 1/2 2 H+ NADP+ + 2H+ + H+ NADPH To Calvin cycle THYLAKOID SPACE (High H+ concentration) STROMA (Low H+ concentration) Thylakoid membrane ATP synthase ATP ADP + P H+ i [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar : Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2 Slide 54: The Calvin cycle has three phases: Carbon fixation (catalyzed by rubisco) Reduction Regeneration of the CO2 acceptor (RuBP) Play LE 10-18_1 : LE 10-18_1 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input 3 CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) LE 10-18_2 : LE 10-18_2 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) 3 6 NADP+ 6 6 NADPH P i 6 P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P 1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds LE 10-18_3 : LE 10-18_3 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) 3 6 NADP+ 6 6 NADPH P i 6 P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P 1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds 3 3 ADP ATP Phase 3: Regeneration of the CO2 acceptor (RuBP) P 5 G3P Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates : Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates Dehydration is a problem for plants, sometimes requiring tradeoffs with other metabolic processes, especially photosynthesis On hot, dry days, plants close stomata, which conserves water but also limits photosynthesis The closing of stomata reduces access to CO2 and causes O2 to build up These conditions favor a seemingly wasteful process called photorespiration Photorespiration: An Evolutionary Relic? : Photorespiration: An Evolutionary Relic? In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound In photorespiration, rubisco adds O2 to the Calvin cycle instead of CO2 Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar Slide 60: Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle C4 Plants : C4 Plants C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle LE 10-19 : LE 10-19 Photosynthetic cells of C4 plant leaf Mesophyll cell Bundle- sheath cell Vein (vascular tissue) C4 leaf anatomy Stoma Bundle-sheath cell Pyruvate (3 C) CO2 Sugar Vascular tissue CALVIN CYCLE PEP (3 C) ATP ADP Malate (4 C) Oxaloacetate (4 C) The C4 pathway CO2 PEP carboxylase Mesophyll cell CAM Plants : CAM Plants CAM plants open their stomata at night, incorporating CO2 into organic acids Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle LE 10-20 : LE 10-20 Bundle- sheath cell Mesophyll cell Organic acid C4 CO2 CO2 CALVIN CYCLE Sugarcane Pineapple Organic acids release CO2 to Calvin cycle CO2 incorporated into four-carbon organic acids (carbon fixation) Organic acid CAM CO2 CO2 CALVIN CYCLE Sugar Spatial separation of steps Temporal separation of steps Sugar Day Night The Importance of Photosynthesis: A Review : The Importance of Photosynthesis: A Review The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells In addition to food production, photosynthesis produces the oxygen in our atmosphere LE 10-21 : LE 10-21 Light CO2 H2O Light reactions Calvin cycle NADP+ RuBP G3P ATP Photosystem II Electron transport chain Photosystem I O2 Chloroplast NADPH ADP + P i 3-Phosphoglycerate Starch (storage) Amino acids Fatty acids Sucrose (export) You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
PHOTOSYNTHESIS EDLEON1369 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 3744 Category: Education License: All Rights Reserved Like it (6) Dislike it (0) Added: October 08, 2008 This Presentation is Public Favorites: 2 Presentation Description No description available. Comments Posting comment... By: janithbandara (17 month(s) ago) Please be kind enough to grant me permission download this presentation to use it in our government school. iasjayantha@sltnet.lk I.A.S jayantha Saving..... Post Reply Close Saving..... Edit Comment Close By: ashraf4ever_3 (23 month(s) ago) It's really a very wonderful presentation. Saving..... Post Reply Close Saving..... Edit Comment Close By: achira (28 month(s) ago) i request you to share this ppt with me. It is very simple and informative. Saving..... Post Reply Close Saving..... Edit Comment Close By: hanif21 (28 month(s) ago) hey this is good, i need it so much thanks Saving..... Post Reply Close Saving..... Edit Comment Close By: brandon27 (29 month(s) ago) I like your presentation, pls allow me to download it...thanks. Saving..... Post Reply Close Saving..... Edit Comment Close loading.... See all Premium member Presentation Transcript Chapter 10 : Chapter 10 Photosynthesis Overview: The Process That Feeds the Biosphere : Overview: The Process That Feeds the Biosphere Photosynthesis is the process that converts solar energy into chemical energy Directly or indirectly, photosynthesis nourishes almost the entire living world Slide 3: Autotrophs sustain themselves without eating anything derived from other organisms Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from water and carbon dioxide Slide 5: Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes These organisms feed not only themselves but also the entire living world LE 10-2 : LE 10-2 Plants Unicellular protist Multicellular algae Cyanobacteria Purple sulfur bacteria 10 µm 1.5 µm 40 µm Slide 7: Heterotrophs obtain their organic material from other organisms Heterotrophs are the consumers of the biosphere Almost all heterotrophs, including humans, depend on photoautotrophs for food and oxygen Concept 10.1: Photosynthesis converts light energy to the chemical energy of food : Concept 10.1: Photosynthesis converts light energy to the chemical energy of food Chloroplasts are organelles that are responsible for feeding the vast majority of organisms Chloroplasts are present in a variety of photosynthesizing organisms Chloroplasts: The Sites of Photosynthesis in Plants : Chloroplasts: The Sites of Photosynthesis in Plants Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast Through microscopic pores called stomata, CO2 enters the leaf and O2 exits Slide 10: Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf A typical mesophyll cell has 30-40 chloroplasts The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana Chloroplasts also contain stroma, a dense fluid LE 10-3 : LE 10-3 Leaf cross section Vein Mesophyll Stomata CO2 O2 Mesophyll cell Chloroplast 5 µm Outer membrane Intermembrane space Innermembrane Thylakoid space Thylakoid Granum Stroma 1 µm Tracking Atoms Through Photosynthesis: Scientific Inquiry : Tracking Atoms Through Photosynthesis: Scientific Inquiry Photosynthesis can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O The Splitting of Water : The Splitting of Water Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules LE 10-4 : LE 10-4 Reactants: Products: 6 CO2 12 H2O C6H12O6 6 H2O 6 O2 Photosynthesis as a Redox Process : Photosynthesis as a Redox Process Photosynthesis is a redox process in which water is oxidized and carbon dioxide is reduced The Two Stages of Photosynthesis: A Preview : The Two Stages of Photosynthesis: A Preview Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part) The light reactions (in the thylakoids) split water, release O2, produce ATP, and form NADPH The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules LE 10-5_1 : LE 10-5_1 H2O LIGHT REACTIONS Chloroplast Light LE 10-5_2 : LE 10-5_2 H2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2 LE 10-5_3 : LE 10-5_3 H2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2 NADP+ CO2 ADP P + i CALVIN CYCLE [CH2O] (sugar) Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH : Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH Chloroplasts are solar-powered chemical factories Their thylakoids transform light energy into the chemical energy of ATP and NADPH The Nature of Sunlight : The Nature of Sunlight Light is a form of electromagnetic energy, also called electromagnetic radiation Like other electromagnetic energy, light travels in rhythmic waves Wavelength = distance between crests of waves Wavelength determines the type of electromagnetic energy Light also behaves as though it consists of discrete particles, called photons Slide 22: The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation Visible light consists of colors we can see, including wavelengths that drive photosynthesis LE 10-6 : LE 10-6 Visible light Gamma rays X-rays UV Infrared Micro- waves Radio waves 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m (109 nm) 103 m 380 450 500 550 600 650 700 750 nm Longer wavelength Lower energy Shorter wavelength Higher energy Photosynthetic Pigments: The Light Receptors : Photosynthetic Pigments: The Light Receptors Pigments are substances that absorb visible light Different pigments absorb different wavelengths Wavelengths that are not absorbed are reflected or transmitted Leaves appear green because chlorophyll reflects and transmits green light Animation: Light and Pigments LE 10-7 : LE 10-7 Chloroplast Light Reflected light Absorbed light Transmitted light Granum Slide 26: A spectrophotometer measures a pigment’s ability to absorb various wavelengths This machine sends light through pigments and measures the fraction of light transmitted at each wavelength LE 10-8a : LE 10-8a White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. Green light Slit moves to pass light of selected wavelength 0 100 LE 10-8b : LE 10-8b White light Refracting prism Chlorophyll solution Photoelectric tube The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. Blue light Slit moves to pass light of selected wavelength 0 100 Slide 29: An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process LE 10-9a : LE 10-9a Chlorophyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption spectra Absorption of light by chloroplast pigments 400 500 600 700 Slide 31: The action spectrum of photosynthesis was first demonstrated in 1883 by Thomas Engelmann In his experiment, he exposed different segments of a filamentous alga to different wavelengths Areas receiving wavelengths favorable to photosynthesis produced excess O2 He used aerobic bacteria clustered along the alga as a measure of O2 production LE 10-9c : LE 10-9c Engelmann’s experiment 400 500 600 700 Aerobic bacteria Filament of algae Slide 33: Chlorophyll a is the main photosynthetic pigment Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll Excitation of Chlorophyll by Light : Excitation of Chlorophyll by Light When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat LE 10-11 : LE 10-11 Excited state Heat Photon (fluorescence) Ground state Chlorophyll molecule Photon Excitation of isolated chlorophyll molecule Fluorescence Energy of electron e– A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes : A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes A photosystem consists of a reaction center surrounded by light-harvesting complexes The light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center Slide 37: A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll a Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions LE 10-12 : LE 10-12 Thylakoid Photon Light-harvesting complexes Photosystem Reaction center STROMA Primary electron acceptor e– Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Thylakoid membrane Slide 39: There are two types of photosystems in the thylakoid membrane Photosystem II functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm Photosystem I is best at absorbing a wavelength of 700 nm The two photosystems work together to use light energy to generate ATP and NADPH Noncyclic Electron Flow : Noncyclic Electron Flow During the light reactions, there are two possible routes for electron flow: cyclic and noncyclic Noncyclic electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH LE 10-13_1 : LE 10-13_1 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 LE 10-13_2 : LE 10-13_2 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 LE 10-13_3 : LE 10-13_3 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP LE 10-13_4 : LE 10-13_4 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e– Primary acceptor Photosystem I (PS I) Light LE 10-13_5 : LE 10-13_5 Light P680 e– Photosystem II (PS II) Primary acceptor [CH2O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP+ Light H2O CO2 Energy of electrons O2 e– e– + 2 H+ H2O O2 1/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e– Primary acceptor Photosystem I (PS I) e– e– Electron Transport chain NADP+ reductase Fd NADP+ NADPH + H+ + 2 H+ Light LE 10-14 : LE 10-14 ATP Photosystem II e– e– e– e– Mill makes ATP e– e– e– Photon Photosystem I Photon NADPH Cyclic Electron Flow : Cyclic Electron Flow Cyclic electron flow uses only photosystem I and produces only ATP Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle LE 10-15 : LE 10-15 Photosystem I Photosystem II ATP Pc Fd Cytochrome complex Pq Primary acceptor Fd NADP+ reductase NADP+ NADPH Primary acceptor A Comparison of Chemiosmosis in Chloroplasts and Mitochondria : A Comparison of Chemiosmosis in Chloroplasts and Mitochondria Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP The spatial organization of chemiosmosis differs in chloroplasts and mitochondria LE 10-16 : LE 10-16 MITOCHONDRION STRUCTURE Intermembrane space Membrane Electron transport chain Mitochondrion Chloroplast CHLOROPLAST STRUCTURE Thylakoid space Stroma ATP Matrix ATP synthase Key H+ Diffusion ADP + P H+ i Higher [H+] Lower [H+] Slide 51: The current model for the thylakoid membrane is based on studies in several laboratories Water is split by photosystem II on the side of the membrane facing the thylakoid space The diffusion of H+ from the thylakoid space back to the stroma powers ATP synthase ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place Animation: Calvin Cycle LE 10-17 : LE 10-17 STROMA (Low H+ concentration) Light Photosystem II Cytochrome complex 2 H+ Light Photosystem I NADP+ reductase Fd Pc Pq H2O O2 +2 H+ 1/2 2 H+ NADP+ + 2H+ + H+ NADPH To Calvin cycle THYLAKOID SPACE (High H+ concentration) STROMA (Low H+ concentration) Thylakoid membrane ATP synthase ATP ADP + P H+ i [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar : Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2 Slide 54: The Calvin cycle has three phases: Carbon fixation (catalyzed by rubisco) Reduction Regeneration of the CO2 acceptor (RuBP) Play LE 10-18_1 : LE 10-18_1 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input 3 CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) LE 10-18_2 : LE 10-18_2 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) 3 6 NADP+ 6 6 NADPH P i 6 P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P 1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds LE 10-18_3 : LE 10-18_3 [CH2O] (sugar) O2 NADPH ATP ADP NADP+ CO2 H2O LIGHT REACTIONS CALVIN CYCLE Light Input CO2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP) 3 6 NADP+ 6 6 NADPH P i 6 P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P 1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds 3 3 ADP ATP Phase 3: Regeneration of the CO2 acceptor (RuBP) P 5 G3P Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates : Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates Dehydration is a problem for plants, sometimes requiring tradeoffs with other metabolic processes, especially photosynthesis On hot, dry days, plants close stomata, which conserves water but also limits photosynthesis The closing of stomata reduces access to CO2 and causes O2 to build up These conditions favor a seemingly wasteful process called photorespiration Photorespiration: An Evolutionary Relic? : Photorespiration: An Evolutionary Relic? In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound In photorespiration, rubisco adds O2 to the Calvin cycle instead of CO2 Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar Slide 60: Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle C4 Plants : C4 Plants C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle LE 10-19 : LE 10-19 Photosynthetic cells of C4 plant leaf Mesophyll cell Bundle- sheath cell Vein (vascular tissue) C4 leaf anatomy Stoma Bundle-sheath cell Pyruvate (3 C) CO2 Sugar Vascular tissue CALVIN CYCLE PEP (3 C) ATP ADP Malate (4 C) Oxaloacetate (4 C) The C4 pathway CO2 PEP carboxylase Mesophyll cell CAM Plants : CAM Plants CAM plants open their stomata at night, incorporating CO2 into organic acids Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle LE 10-20 : LE 10-20 Bundle- sheath cell Mesophyll cell Organic acid C4 CO2 CO2 CALVIN CYCLE Sugarcane Pineapple Organic acids release CO2 to Calvin cycle CO2 incorporated into four-carbon organic acids (carbon fixation) Organic acid CAM CO2 CO2 CALVIN CYCLE Sugar Spatial separation of steps Temporal separation of steps Sugar Day Night The Importance of Photosynthesis: A Review : The Importance of Photosynthesis: A Review The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells In addition to food production, photosynthesis produces the oxygen in our atmosphere LE 10-21 : LE 10-21 Light CO2 H2O Light reactions Calvin cycle NADP+ RuBP G3P ATP Photosystem II Electron transport chain Photosystem I O2 Chloroplast NADPH ADP + P i 3-Phosphoglycerate Starch (storage) Amino acids Fatty acids Sucrose (export)