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1 Photosynthesis Chapter 10
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2 Outline Chloroplasts Light-Independent Reactions Absorption Spectra – Pigments Light-Dependent Reactions Photosystems C 3 Photosynthesis C 4 Photosynthesis CAM Photosynthesis
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3 Photosynthesis The energy used by most living cells ultimately comes from the sun, and is captured by plants, algae, or bacteria via photosynthesis. – light dependent reactions capture energy from sunlight use energy to produce ATP and NADPH – Calvin cycle formation of organic molecules
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4 Leaf Structure
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5 Chloroplasts Internal membranes, thylakoids, are organized into grana. – Thylakoid membranes house pigments for capturing light and the machinery to produce ATP. clustered together to form a photosystem acts as an antenna, gathering light energy harvested by multiple pigment molecules
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6 Chloroplasts
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7 Light and Reducing Power Light-dependent reactions of photosynthesis use the energy of light to reduce NADP to NADPH and to manufacture ATP. – Reducing power generated by splitting water is used to convert CO 2 into organic matter during carbon fixation.
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8 Light-Independent Reactions
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9 Energy in Photons Energy content of a photon is inversely proportional to the wavelength of light. – Highest intensity photons, at the short- wavelength end of the electromagnetic spectrum, are gamma rays. – Ultraviolet light possesses considerably more energy than visible light. potent force in disrupting DNA
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10 Electromagnetic Spectrum
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11 Absorption Spectra Photon absorption depends on its wavelength, and the chemical nature of the molecule it hits. – Each molecule has a characteristic absorption spectrum. range and efficiency of photons the molecule is capable of absorbing
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12 Pigments Pigments are molecules that absorb light in the visible range. – green plant photosynthesis carotenoids chlorophyll chlorophyll a - main pigment chlorophyll b - accessory pigment
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13 Absorption Spectra
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14 Chlorophyll Chlorophylls absorb photons by means of an excitation process. – Photons excite electrons in the pigment’s ring structure, and are channeled away through alternating carbon-bond system. Wavelengths absorbed depend on the available energy levels to which excited electrons can be boosted.
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15 Chlorophyll
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16 Light-Dependent Reaction Stages Primary photoevent Charge separation Electron transport Chemiosmosis
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17 Photosystems Photosynthesis output increases linearly at low light intensities but lessens at higher intensities. – saturation point Photosystem - network of pigments that channels excitation energy gathered by any of the molecules to the reaction center – reaction center allows photon excitation to move away from chlorophylls and is the key conversion of light to chemical energy
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18 Light to Chemical Energy
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19 Photosystem Function Bacteria use a single photosystem. – electron is joined with a proton to make hydrogen – electron is recycled to chlorophyll
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21 Photosystem Function Plants use two photosystems – photosystem I and II generate power to reduce NADP + to NADPH with enough left over to make ATP two stage process: photosystem II – I. noncyclic photophosphorylation ejected electrons end up in NADPH
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22 Photosystems I and II
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24 Calvin Cycle Also referred to as C 3 photosynthesis – C 3 plants - ribulose 1,5-bisphosphate is carboxylated to form a three-carbon compound via rubisco activity
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25 Calvin Cycle
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26 Photorespiration In photorespiration, O 2 is incorporated into RuBP, which undergoes additional reactions that release CO 2. – decreased yields of photosynthesis
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27 C 4 Pathway Plants adapted to warmer environments deal with the loss of CO 2 in two ways: – C 4 conducted in mesophyll cells, Calvin cycle in bundle sheath cells creates high local levels of CO 2 to favor carboxylation reaction of rubisco isolates CO 2 production spatially
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28 Crassulacean Acid Metabolism CAM plants open stomata during the night, and close them during the day to cut-down the loss of water vapor. – isolates CO 2 production temporally
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29 Carbon Fixation
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30 Summary Chloroplasts Light-Independent Reactions Absorption Spectra – Pigments Light-Dependent Reactions Photosystems C 3 Photosynthesis C 4 Photosynthesis CAM Photosynthesis
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