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Unformatted text preview: Photosynthesis Photosynthesis In simple terms: photosynthesis uses light energy (photons) to make organic compounds (sugars) 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 It is the most important set of chemical reactions in the biosphere Revisit some basic chemistry: o Loss and gain of electrons -> Redox Reactions (revisited) Oxidation: the loss of electrons o In biological systems: often dehydrogenation) Reduction: the gain of electrons Usually coupled so: thus called a redox reaction The same molecule can be: o Oxidized by one molecule o Reduced by different molecule Affinity for electrons controls direction of electron flow Electron Carriers Electron carriers : molecules that can be reversibly oxidized and reduced o Can accept and donate electrons Vary in their affinity for electrons o Arrange by increasing affinity for electrons: electron transport chain o Gradual release of energy that can be captured Allows maximal synthesis of ATP What does this have to do with Photosynthesis? We are going to oxidize H 2 O to O 2 and H + during part of photosynthesis o Endergonic energy input required We are going to reduce CO 2 to glucose during part of photosynthesis o Also endergonic 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 Site of Photosynthesis Occurs within cells, usually in the leaf Organelle involved is the chloroplast Structure of chloroplast is important o Thylakoid membranes: Create enclosed compartment within disks o Must be intact for photosynthesis to occur Must maintain H + concentration gradient (form of potential energy) o Stroma: Compartment where soluble reactions occur Figure 8.1 Two Parts to Photosynthesis: the light reactions Light reactions (occur in thylakoid) o Requires light as energy source...
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