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Chapter 10 Photosynthesis PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and Jane Reece Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.1 Sunlight consists of a spectrum of colors, visible here in a rainbow Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2 Photoautotrophs These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical globules) (c, d, e: LMs). (a) Plants (c) Unicellular protist 10 m (d) Pruple sulfur bacteria (b) Multicellular algae Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (c) Cyanobacteria 40 m 1.5 m Figure 10.3 Focusing in on the location of photosynthesis in a plant Leaf cross section Vein Mesophyll CO2 O2 Mesophyll cell Stomata Chloroplast 5 µm Outer membrane Granum Storma Thylakoid Thylakoid Space Intermembrane space Inner membrane 1 µm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.4 Tracking atoms through photosynthesis Reactants: Products: 12 H2O 6 CO2 C6H12O6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6 H2O 6 O2 Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O Light LIGHT REACTIONS Chloroplast Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O Light LIGHT REACTIONS ATP NADPH Chloroplast O2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O CO2 Light NADP ADP + Pi CALVIN CYCLE LIGHT REACTIONS ATP NADPH Chloroplast O2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings [CH2O] (sugar) Figure 10.6 The electromagnetic spectrum 10–5 nm 10–3 Gamma rays 103 1 nm nm X-rays UV 106 nm Infrared 1m 106 nm nm Microwaves 103 m Radio waves Visible light 380 450 500 550 Shorter wavelength Higher energy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 600 650 700 750 nm Longer wavelength Lower energy Figure 10.7 Why leaves are green: interaction of light with chloroplasts Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.8 Research Method Determining an Absorption Spectrum APPLICATION An absorption spectrum is a visual representation of how well a particular pigment absorbs different wavelengths of visible light. Absorption spectra of various chloroplast pigments help scientists decipher each pigment’s role in a plant. TECNIQUE A spectrophotometer measures the relative amounts of light of different wavelengths absorbed and transmitted by a pigment solution. 1 White light is separated into colors (wavelengths) by a prism. 2 One by one, the different colors of light are passed through the sample (chlorophyll in this example). Green light and blue light are shown here. 3 The transmitted light strikes a photoelectric tube, which converts the light energy to electricity. 4 The electrical current is measured by a galvanometer. The meter indicates the fraction of light transmitted through the sample, from which we can determine the amount of light absorbed. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Refracting Chlorophyll solution prism White light Photoelectric tube Galvanometer 2 1 3 4 Slit moves to pass light of selected wavelength Green light 0 The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. 0 Blue light Result 100 100 The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. See Figure 10.9a for absorption spectra of three types of chloroplast pigments. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.9 Inquiry Which wavelengths of light are most effective in driving photosynthesis? EXPERIMENT Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. RESULTS Chlorophyll a Absorption of light by chloroplast pigments Chlorophyll b Carotenoids 400 500 600 700 Wavelength of light (nm) (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rate of photosynthesis (measured by O2 release) (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Aerobic bacteria Filament of alga 400 500 600 700 (c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b. Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis. CONCLUSION Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.10 Structure of chlorophyll molecules in chloroplasts of plants CH3 in chlorophyll a CHO in chlorophyll b CH2 CH C H3C C C C H C C N C C C CH2 H H C O C H C CH3 Porphyrin ring: Light-absorbing “head” of molecule; note magnesium atom at center C O O C CH3 C C CH2 CH2 C N C C C N Mg C H C N C H3C CH3 H O O CH3 CH2 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.11 Excitation of isolated chlorophyll by light e– Excited state Heat Photon (fluorescence) Photon Chlorophyll molecule Ground state (a) Excitation of isolated chlorophyll molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Fluorescence Figure 10.21 A review of photosynthesis Light reactions Calvin cycle H2O CO2 Light NADP+ ADP +P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP NADPH G3P Starch (storage) Amino acids Fatty acids Chloroplast O2 Light reactions: • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sucrose (export) Calvin cycle reactions: • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions Figure 10.12 How a photosystem harvests light Thylakoid Photosystem Photon Reaction Primary election center acceptor Light-harvesting complexes Thylakoid membrane STROMA e– Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Energy of electrons e Light 1 2 P680 Photosystem II (PS II) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Energy of electrons 2 H+ H2O e 2 + 1⁄ 2 Light O2 3 e e P680 1 Photosystem II (PS II) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Energy of electrons 2 1⁄ Light 1 2 H+ + O2 H2O e 2 4 Pq Cytochrome complex 3 e e 5 P680 ATP Photosystem II (PS II) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pc Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH [CH2O] (sugar) O2 Primary acceptor Primary acceptor 4 e Energy of electrons Pq 2 H+ + 1⁄ O2 2 Light H2O 3 e 2 Cytochrome complex Pc e e 5 P700 P680 Light 1 6 ATP Photosystem II (PS II) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosystem I (PS I) Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH [CH2O] (sugar) O2 Primary acceptor Primary acceptor 4 e Energy of electrons Pq 1⁄ Light 2 H+ + O2 2 H2O e 2 7 Fd e 8 e Cytochrome complex NADP+ NADP+ + 2 H+ reductase NADPH 3 e e 5 Pc + H+ P700 P680 Light 1 1 6 6 ATP Photosystem II (PS II) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosystem I (PS I) Figure 10.14 A mechanical analogy for the light reactions e– ATP e– e– NADPH e– e– e– Mill makes ATP e– Photosystem II Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosystem I Figure 10.15 Cyclic electron flow Primary acceptor Primary acceptor Fd Fd NADP+ Pq NADP+ reductase Cytochrome complex NADPH Pc Photosystem II (PS II) ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosystem I (PS I) Figure 10.16 Comparison of chemiosmosis in mitochondria and chloroplasts Key Higher [H+] Lower [H+] Chloroplast Mitochondrion CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE H+ Diffusion Thylakoid space Intermembrance space Membrance Electron transport chain ATP Synthase Matrix Stroma ADP+ P H+ Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Figure 10.17 The light reactions and chemiosmosis: the organization of the thylakoid membrane H2O CO2 LIGHT NADP+ ADP CALVIN CYCLE LIGHT REACTOR ATP NADPH STROMA (Low H+ concentration) O2 [CH2O] (sugar) Photosystem II Cytochrome complex Photosystem I NADP+ reductase Light 2 H+ 3 NADP+ + 2H+ Fd NADPH + H+ Pq Pc 2 H2O THYLAKOID SPACE (High H+ concentration) 1⁄ 2 1 O2 +2 H+ 2 H+ To Calvin cycle STROMA (Low H+ concentration) Thylakoid membrane ATP synthase ADP ATP P Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H+ Figure 10.18 The Calvin cycle H2 O CO2 Input 3 (Entering one CO2 at a time) Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate 3 P 6 P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate 6 6 ADP CALVIN CYCLE Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Figure 10.18 The Calvin cycle H2 O CO2 Light Input 3 (Entering one CO2 at a time) NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP Phase 1: Carbon fixation NADPH O2 Rubisco [CH2O] (sugar) 3 P P Short-lived intermediate 3 P P Ribulose bisphosphate (RuBP) P 6 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P 6 P Glyceraldehyde-3-phosphate (G3P) P 1 G3P (a sugar) Output Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings i Glucose and other organic compounds Phase 2: Reduction Figure 10.18 The Calvin cycle CO2 H2 O Input 3 (Entering one CO2 at a time) Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 ADP 3 6 P ATP P 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of the CO2 acceptor (RuBP) 6 NADP+ 6 P 5 i P G3P 6 P Glyceraldehyde-3-phosphate (G3P) 1 P G3P (a sugar) Output Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glucose and other organic compounds Phase 2: Reduction Figure 10.19 C4 leaf anatomy and the C4 pathway Mesophyll cell Mesophyll cell Photosynthetic cells of C4 plant leaf CO CO 2 2 PEP carboxylase Bundlesheath cell PEP (3 C) ADP Oxaloacetate (4 C) Vein (vascular tissue) Malate (4 C) ATP C4 leaf anatomy BundleSheath cell Pyruate (3 C) CO2 Stoma CALVIN CYCLE Sugar Vascular tissue Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.20 C4 and CAM photosynthesis compared Pineapple Sugarcane C4 Mesophyll Cell Organic acid Bundlesheath cell (a) Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in different types of cells. CAM CO2 CO2 CALVIN CYCLE CO2 1 CO2 incorporated Organic acid into four-carbon organic acids (carbon fixation) 2 Organic acids release CO2 to Calvin cycle Sugar Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CALVIN CYCLE Sugar Night Day (b) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times. Figure 10.21 A review of photosynthesis Light reactions Calvin cycle H2O CO2 Light NADP+ ADP +P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP NADPH G3P Starch (storage) Amino acids Fatty acids Chloroplast O2 Light reactions: • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sucrose (export) Calvin cycle reactions: • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions