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Fig. 10-2 (a) Plants (c) Unicellular protist 10 µm (e) Purple sulfur bacteria (b) Multicellular alga (d) Cyanobacteria 40 µm 1.5 µm Fig. 10-3a Leaf cross section Vein Mesophyll Stomata Chloroplast CO2 O2 Mesophyll cell 5 µm Fig. 10-3b Chloroplast Outer membrane Thylakoid Stroma Granum Thylakoid space Intermembrane space Inner membrane 1 µm Fig. 10-4 Reactants: Products: 6 CO2 C6H12O6 12 H2O 6 H2 O 6 O2 Fig. 10-7 Light Reflected light Chloroplast Absorbed light Granum Transmitted light Fig. 10-6 10–5 nm 10–3 nm 103 nm 1 nm Gamma X-rays rays UV 106 nm Infrared 1m (109 nm) Microwaves 103 m Radio waves Visible light 380 450 500 Shorter wavelength Higher energy 550 600 650 700 750 nm Longer wavelength Lower energy Fig. 10-9 RESULTS Chlorophyll a Chlorophyll b Carotenoids (a) Absorption spectra 400 500 600 700 Wavelength of light (nm) (b) Action spectrum Aerobic bacteria Filament of alga (c) Engelmann’s experiment 400 500 600 700 Fig. 10-5-4 CO2 H2O Light NADP+ ADP + P i Light Reactions Calvin Cycle ATP NADPH Chloroplast O2 [CH2O] (sugar) Fig. 10-11 Energy of electron e– Excited state Heat Photon (fluorescence) Photon Chlorophyll molecule Ground state (a) Excitation of isolated chlorophyll molecule (b) Fluorescence Fig. 10-12 Photosystem STROMA Light-harvesting Reaction-center complex complexes Primary electron acceptor Thylakoid membrane Photon e– Transfer of energy Special pair of chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Fig. 10-13-4 4 Primary acceptor 1/ 2 H+ 2 + O2 H2O e– 2 Primary acceptor e– Pq Cytochrome complex 3 Pc e– e– P700 5 P680 Light 1 Light 6 ATP Pigment molecules Photosystem II (PS II) Photosystem I (PS I) Fig. 10-13-5 4 Primary acceptor 2 H+ + 1/ O 2 2 H2O e– 2 Primary acceptor e– Pq Cytochrome complex 7 Fd e– e– 8 NADP+ reductase 3 NADPH Pc e– e– P700 5 P680 Light 1 Light 6 ATP Pigment molecules Photosystem II (PS II) NADP+ + H+ Photosystem I (PS I) Fig. 10-14 e– ATP e– e– NADPH e– e– e– Mill makes ATP e– Photosystem II Photosystem I Fig. 10-16 Mitochondrion Chloroplast MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE H+ Intermembrane space Inner membrane Diffusion Electron transport chain Thylakoid space Thylakoid membrane ATP synthase Stroma Matrix Key ADP + P i [H+] Higher Lower [H+] H+ ATP Fig. 10-17 STROMA (low H+ concentration) Cytochrome Photosystem I complex Light Photosystem II 4 H+ Light Fd NADP+ reductase NADP+ + H+ NADPH Pq H2O THYLAKOID SPACE (high H+ concentration) e– 1 e– 1/ Pc 2 2 3 O2 +2 H+ 4 H+ To Calvin Cycle Thylakoid membrane STROMA (low H+ concentration) ATP synthase ADP + Pi ATP H+ Fig. 10-18-3 Input 3 (Entering one at a time) CO2 Phase 1: Carbon fixation Rubisco 3 P Short-lived intermediate P 6 P 3-Phosphoglycerate 3P P Ribulose bisphosphate (RuBP) 6 ATP 6 ADP 3 ADP 3 Calvin Cycle 6 P P 1,3-Bisphosphoglycerate ATP 6 NADPH Phase 3: Regeneration of the CO2 acceptor (RuBP) 6 NADP+ 6 Pi P 5 G3P 6 P Glyceraldehyde-3-phosphate (G3P) 1 Output P G3P (a sugar) Glucose and other organic compounds Phase 2: Reduction 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 instead of CO2 in the Calvin cycle • Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 • Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings C4 Plants • C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells • This step requires the enzyme PEP carboxylase • PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low • These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 10-19 The C4 pathway C4 leaf anatomy Mesophyll cell Mesophyll cell CO2 PEP carboxylase Photosynthetic cells of C4 Bundleplant leaf sheath cell Oxaloacetate (4C) Vein (vascular tissue) PEP (3C) ADP Malate (4C) Stoma Bundlesheath cell ATP Pyruvate (3C) CO2 Calvin Cycle Sugar Vascular tissue CAM Plants • Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 10-20 Sugarcane Pineapple C4 CAM CO2 Mesophyll cell Organic acid Bundlesheath cell CO2 1 CO2 incorporated into four-carbon Organic acid organic acids (carbon fixation) CO2 Calvin Cycle CO2 2 Organic acids release CO2 to Calvin cycle Night Day Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps 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 • Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits • In addition to food production, photosynthesis produces the O2 in our atmosphere Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 10-21 H2O CO2 Light NADP+ ADP + P i Light Reactions: Photosystem II Electron transport chain Photosystem I Electron transport chain RuBP ATP NADPH 3-Phosphoglycerate Calvin Cycle G3P Starch (storage) Chloroplast O2 Sucrose (export) Fig. 10-UN1 H2O CO2 Primary acceptor Primary acceptor H2O O2 Fd Pq NADP+ reductase Cytochrome complex Pc ATP Photosystem II O2 Photosystem I NADP+ + H+ NADPH Drought? …. Abscisic acid •In preparation for winter, ABA is produced in terminal buds, this slows plant growth. •ABA also inhibits the division of cells adjusting to cold conditions in the winter by suspending primary and secondary growth. •ABA then translocates to the leaves, where it rapidly alters the osmotic potential of stomatal guard cells, causing them to shrink and stomata to close. •Reduces transpiration Indian Pipe