Lec19.photosyn.slide - I. Significance II. Pigments A....

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Unformatted text preview: I. Significance II. Pigments A. Chlorophyll B. Accessory Pigments III. Light Reactions IV. Dark Reactions (Calvin Cycle C 3 ) Photosynthesis light 6CO 2 + 6H 2 O ----> C 6 H 12 O 6 + 6O 2 Global Significance: plants are the ultimate source of: 1. nearly all biologically useful energy 2. all O 2 permitting oxidative phosphorylation 3. all O 3 (ozone) protecting (terrestrial) life from harmful UV Plants also lower atmospheric CO 2 Nearly all land plants are PHOTOAUTOTROPHIC - utilize solar energy to create complex organic compounds from simple inorganic ones Significance 3 4 Stroma Thylakoids Thylakoid Chloroplast Light reactions Dark reactions: CO 2 fixation Light (photon) Chlorophyll 1. Light energy is captured by pigments to create energy-rich mobile currency : ATP Rapidly cycles between ADP and ATP (or GDP + GTP) via PHOTOPHOSPHORYLATION (ADP + P i ) ATP easily releases energy when converted back to ADP 2. Light energy also used to place electrons on e- donors: NAD (nicotinamide-adenine dinucleotide) NADP +--> NADPH + H + T They provide reducing power/capability 3. ATP and NADPH are used to convert CO 2 into sucrose Core Process of Photosyntheis Light Reactions: Physics & Chemistry Capture and conversion of light energy into chemical energy Frequencies of light must meet two criteria Must have enough energy to drive the reactions which produce ATP and NADPH Must not have so much energy that chemical bonds are broken in biologically important compounds Just so happens that the visible spectrum is the correct energy Remember: light comes in quanta Discrete packages of a particular frequency/wavelength Energy of a quantum is a function of its frequency (E = h ) Features : 1. need light 2. produce ATP and NADPH 3. evolve molecular oxygen (O 2 ) 4. occur on the thylakoid membranes of chloroplasts4....
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Lec19.photosyn.slide - I. Significance II. Pigments A....

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