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O2 Stroma Photosystem Thylakoid NADP+ ADP + Pi CO2 Sunlight Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cuticle Epidermis Mesophyll Vascular bundle Stoma Vacuole Cell wall 1.58 µm Inner membrane Outer membrane Chloroplast Courtesy Dr. Kenneth Miller, Brown University 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sunlight Photosystem H2O O2 Thylakoid Light-Dependent Reactions NADP+ NADPH ADP + Pi ATP CO2 Calvin Organic Cycle molecules Stroma 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Increasing energy Increasing wavelength 0.001 nm 1 nm 10 nm 1000 nm 0.01 cm 1 cm 1 m 100 m UV Gamma rays X-rays light Infrared Radio waves Visible light 400 nm 430 nm 500 nm 560 nm 600 nm 650 nm 740 nm 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. high carotenoids chlorophyll a chlorophyll b Light Light Absorbtion Absorbtion low 400 450 500 550 600 650 700 Wavelength (nm) 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chlorophyll a: R = CH R 3 H2C CH H Chlorophyll b: R = CHO H C CH CH 3 2 3 Porphyrin N N head Mg H H N N H3C CH3 H H H O CH2 CO2CH3 CH2 O C O CH2 CH CCH3 CH2 CH2 CH2 CHCH3 Hydrocarbon CH2 tail CH2 CH2 CHCH3 CH2 CH2 CH2 CHCH3 CH3 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oak leaf in summer Oak leaf in autumn © Eric Soder 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosystem Electron Photon acceptor e– Electron donor e– Reaction center chlorophyll Chlorophyll molecule Thylakoid membrane 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excited Light chlorophyll molecule Electron Electron donor acceptor e– e– e– e– Chlorophyll Chlorophyll reduced oxidized Donor Acceptor oxidized reduced + – + – e– – e– e e– 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excited reaction center 2. The electrons pass through the b6-f Ferredoxin complex, which uses the energy 2 released to pump protons across e– the thylakoid membrane. The proton gradient is used to produce ATP by Fd Excited reaction center chemiosmosis. NADP reductase 2 Plastoquinone e– + + NADPH – NADP + H PQ 2 e b -f 6 Plastocyanin complex Reaction center e– PC Photon 2 H+ Reaction Proton gradient formed 3. A pair of chlorophylls in the reaction Energy of electrons Energy of center for ATP synthesis center absorb two photons. This excites two electrons that are passed to Photon 2 H O + 2 NADP , reducing it to NADPH. Electron e– transport from photosystem II replaces 2H+ + 1/ O these electrons. 2 2 Photosystem I Photosystem II 1. A pair of chlorophylls in the reaction center absorb two photons of light. This excites two electrons that are transferred to plastoquinone (PQ). Loss of electrons from the reaction center produces an oxidation potential capable of oxidizing water. 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photon Light-Dependent Photon Reactions H+ ATP NADP NADPH ADP + Pi ATP ADP NADPH Antenna + + Calvin H + NADP Cycle Thylakoid complex membrane Fd 2e– PQ 2e– 2e– 2e– Stroma PC H O + 2 H Proton H+ Plastoquinone Plastocyanin Ferredoxin gradient H+ Water-splitting enzyme H+ 1 + Thylakoid /2O2 2H space NADP ATP Photosystem II b6-f complex Photosystem I reductase synthase 3. Photosystem I absorbs 1. Photosystem II 2. The b6-f complex 4. ATP synthase uses absorbs photons, receives electrons photons, exciting the proton gradient exciting electrons from PQ and passes electrons that are to synthesize ATP that are passed to them to plastocyanin passed through a from ADP and Pi plastoquinone (PQ). (PC). This provides carrier to reduce enzyme acts as a NADP+ to NADPH. Electrons lost from energy for the b6-f channel for protons photosystem II are complex to pump These electrons are to diffuse back into replaced by the protons into the replaced by electron the stroma using this oxidation of water, thylakoid. transport from energy to drive the photosystem II. producing O2 synthesis of ATP. 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stroma of chloroplast Light-Dependent 6 molecules of Reactions Carbon + ADP+ Pi NADP NADPH ATP dioxide (CO2) Calvin Cycle 12 molecules of Rubisco 6 molecules of 3-phosphoglycerate (3C) (PGA) Ribulose 1,5-bisphosphate (5C) (RuBP) 12 ATP 12 ADP 6 ADP 12 molecules of Calvin Cycle 1,3-bisphosphoglycerate (3C) 6 ATP 12 NADPH 4 Pi 12 NADP+ 10 molecules of 12 Pi Glyceraldehyde 3-phosphate (3C) 12 molecules of Glyceraldehyde 3-phosphate (3C) (G3P) 2 molecules of Glyceraldehyde 3-phosphate (3C) (G3P) Glucose and other sugars 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Heat Sunlight O Electron Photo- Photo- 2 ATP system system Transport II I System H2O ADP + P i ADP + P ATP NADP NADPH NAD+ NADH i i Calvin Cycle CO2 Krebs Cycle ATP ADP + P Glucose Pyruvate i ATP 12 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Leaf Heat epidermis H O H O 2 2 O2 O2 CO CO Stomata 2 2 Under hot, arid conditions, leaves lose water by The stomata close to conserve water but as a evaporation through openings in the leaves result, O2 builds up inside the leaves, and CO2 called stomata. cannot enter the leaves. 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mesophyll cell Bundle-sheath cell CO 2 Mesophyll cell RuBP Calvin Cycle 3PG (C3) G3P Stoma Vein a. C4 pathway Bundle- CO Mesophyll cell 2 sheath cell Mesophyll cell C 4 Bundle- CO 2 sheath cell Calvin Cycle G3 Stoma Vein b. C4 pathway a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc. 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CO 2 Mesophyll cell Phosphoenolpyruvate Oxaloacetate (PEP) AMP + PPi ATP + P i Pyruvate Malate Pyruvate Malate Bundle-sheath CO2 cell Calvin Cycle Glucose 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. night CO2 C4 day CO2 Calvin Cycle G3P © ClydeH. Smith/Peter Arnold Inc. 17 .
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