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AP Biology Photosynthesis: Life from Light
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AP Biology How are they connected? glucose + oxygen carbon + water + energy dioxide C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP +++ Heterotrophs and Autotrophs + water + energy glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy +++ Autotrophs making energy & organic molecules from light energy making energy & organic molecules from ingesting organic molecules Where ’ s the ATP? exergonic endergonic
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AP Biology 2005-2006 Plant structure Obtaining raw materials sunlight leaves = solar collectors CO 2 stomates = gas exchange Found under leaves H 2 O uptake from roots Nutrients N, P, K, S, Mg, Fe… uptake from roots
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AP Biology Chloroplasts double membrane stroma thylakoid sacs grana stacks Chlorophyll & ETC in thylakoid membrane H + gradient built up within thylakoid sac Plant structure H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+
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AP Biology 2005-2006 Pigments of photosynthesis chlorophyll & accessory pigments “photosystem” embedded in thylakoid membrane structure function Why does this structure make sense?
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AP Biology Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a (dominant pigment) absorbs best in red & blue wavelengths & least in green other pigments with different structures absorb light of different wavelengths Why are plants green?
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AP Biology Photosynthesis Light reactions light-dependent reactions energy production reactions convert solar energy to chemical energy ATP & NADPH Calvin cycle light-independent reactions sugar production reactions uses chemical energy (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6 It ’ s the Dark Reactions!
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AP Biology 2005-2006 Light reactions Electron Transport Chain (like cell respiration!) membrane-bound proteins in organelle electron acceptor NADPH proton (H + ) gradient across inner membrane ATP synthase enzyme
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AP Biology Photosystems 2 photosystems in thylakoid membrane act as light-gathering “antenna complex” Photosystem II chlorophyll a P 680 = absorbs 680nm wavelength red light Photosystem I chlorophyll b P 700 = absorbs 700nm wavelength red light reaction center
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AP Biology ETC of Photosynthesis ETC produces from light energy ATP & NADPH NADPH (stored energy) goes to Calvin cycle PS II absorbs light excited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER. splits H 2 O (Photolysis!!) O 2 released to atmosphere ATP is produced for later use
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AP Biology ETC of Photosynthesis Photosystem IIPhotosystem I
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AP Biology 2005-2006 Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH
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AP Biology 2005-2006 Cyclic photophosphorylation If PS I can’t pass electron to NADP, it cycles back to PS II & makes more ATP, but no NADPH coordinates light reactions to Calvin cycle Calvin cycle uses more ATP than NADPH X
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AP Biology 2005-2006 From Light reactions to Calvin cycle Calvin cycle Chloroplast stroma Need products of light reactions to drive synthesis reactions ATP NADPH What is there left to do? Make sugar!
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AP Biology From CO 2 C 6 H 12 O 6 CO 2 has very little chemical energy fully oxidized C 6 H 12 O 6 contains a lot of chemical energy reduced endergonic Reduction of CO 2 C 6 H 12 O 6 proceeds in many small uphill steps each catalyzed by specific enzyme using energy stored in ATP & NADPH
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AP Biology PGAL to make glucose 6C 1C CO 2 Calvin cycle 5C RuBP 3C 2x PGA 6 ADP 6 ATP 3C 2x 3C x2 PGAL 6 NADP 6 NADPH 3 ADP 3 ATP Rubisco 1. Carbon fixation 2. Reduction 3. Regeneration of RuBP ribulose bisphosphate -enzyme that Binds CO 2 to RuBP sucrose cellulose etc.
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AP Biology Calvin cycle PGAL important intermediate Six turns of Calvin Cycle = 1 glucose PGAL glucose carbohydrates lipids amino acids nucleic acids
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AP Biology Summary Light reactions produced ATP produced NADPH consumed H 2 O produced O 2 as by product Calvin cycle consumed CO 2 produced PGAL regenerated ADP regenerated NADP ADPNADP
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AP Biology Factors that affect Photosynthesis Enzymes are responsible for several photosynthetic processes, therefore, temperature and pH can affect the rate of photosynthesis. The amount and type of light can affect the rate. A shortage of any of the reactants,CO 2 and/or H 2 O, can affect the rate.
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AP Biology Supporting a biosphere On global scale, photosynthesis is the most important process for the continuation of life on Earth each year photosynthesis synthesizes 160 billion tons of carbohydrate heterotrophs are dependent on plants as food source for fuel & raw materials
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AP Biology Energy cycle Photosynthesis Cellular Respiration glucoseO2O2 H2OH2OCO 2 ATP sun The Great Circle of Life! Where ’ s Mufasa?
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AP Biology 2005-2006 Summary of photosynthesis Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the H 2 O go? Where did the energy come from? What’s the energy used for? What will the C 6 H 12 O 6 be used for? Where did the O 2 come from? Where will the O 2 go? What else is involved that is not listed in this equation? 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy +++
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