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Unformatted text preview: James Chyu Cooper, Spring 05 CHAPTER 8: PHOTOSYNTHESIS: ENERGY FROM SUN Identifying Photosynthetic Reactants and Products- reactants: water, carbon dioxide, light- products: carbohydrates & oxygen gas- 6CO 2 + 12 H 2 O -> C 6 H 12 O 6 + 6 O 2 + 6 H 2 O The Two Pathways of Photosynthesis: An Overview- light reactions: produces ATP & a reduced electron carrier (NADPH + H + )- Calvin-Benson cycle: uses ATP, NADPH + H+, & CO 2-> sugars- both process stop in dark because ATP synthesis and NADP+ reduction require light- two pathways linked by exchange & rate of each reaction depends on rate of other ~ light reactions: thylakoids, Calvin-Benson cycle: stoma of chloroplasts The Interactions of Light and Pigments Light behaves as both a particle and wave- shit bout light characteristics, photons, wavelengths, electromagnetic radiation- for photons to be active in biological process: 1. photons must be absorbed by a receptive molecule 2. photons must have sufficient energy to perform the chemical work required Absorbing a photon puts a pigment in an excited state- when photo meets a molecule 1. photon may bounce off molecule (scattered) 2. photon may pass through molecule (transmitted) 3. photon may be absorbed by molecule (...what are you looking here for...*points left*)- shit explainin how molecules go from ground state -> excited state...whooo-ahhh...psshhh- shit bout the visible spectrum & pigments as if we didn't noe what colors were; but I thought...no- few colors pigment absorbs, rest remaining wavelengths (scattered/transmitted) give color Absorbed wavelengths correlate with biological activity- shit bout absorption and action spectrum...as if the tedious lab didn't engrain it in our memory Photosynthesis uses energy absorbed by several pigments- several pigments absorb different wavelengths for energy used in photosynthesis ex: chlorophylls, carotenoids, phycobilins- chlorophyll a & b main type of chlorophyll 1. complex ring structure (similar to heme group of hemoglobin) 2. center of ring is magnesium atom 3. attached at peripheral location is long hydrocarbon "tail"- allows it to adhere to proteins in hydrophobic portion on thylakoid membrane- accessory pigment...dont look at me, tat's how I felt too, blah blah accessory pigment!...?- carotenoids: absorb blue/green wavelengths, appear deep yellow- phycobilins: absorb yellow/green, orange wavelengths, appear...doesn't say...great Light absorption results in photochemical change- shit bout fluorescence...yay...as if we actually thought things "glow in the dark"...stupid- shit bout fluorescence....
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- Spring '04