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Two Stages of Photosynthesis

Two Stages of Photosynthesis. Light Reaction aka light dependent rxn. Calvin Cycle aka light independent reaction. Transforming light photons into ATP and the electron carrier NADPH. Use ATP/NADPH to make glucose. The Calvin Cycle : C 3 carbon fixation . In stroma of chloroplast.

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Two Stages of Photosynthesis

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  1. Two Stages of Photosynthesis Light Reaction aka light dependent rxn Calvin Cycle aka light independent reaction Transforming light photons into ATP and the electron carrier NADPH Use ATP/NADPH to make glucose

  2. The Calvin Cycle : C3 carbon fixation In stroma of chloroplast Inputs CO2 ATP NADPH from air from light rxn e Output G3P: a 3C organic molecule used to make glucose, fructose, starch, cellulose…

  3. The Calvin Cycle : C3 carbon fixation 3 turns of the cycle Rubisco enzyme RuBP ATP ATP Energy input Most G3P used to regenerate RuBP e- G3P one ‘extra’ G3P Energy stored

  4. Calvin Cycle Accounting Per turn 3 turn 6 turns Consume CO2 1 3 6 Consume ATP 3 9 18 Consume NADPH 2 6 12 Produces G3P 1 2 Produces Glucose 1

  5. http://www.science.smith.edu/departments/Biology/Bio231/calvin.htmlhttp://www.science.smith.edu/departments/Biology/Bio231/calvin.html http://faculty.nl.edu/jste/calvin_cycle.htm http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html http://www.blinkx.com/watch-video/photosynthesis-bioflix-animation/zWVQ8TsGQEG7FGsd2MWPTw http://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.htm

  6. This version of photosynthesis is used by 85% of plants - the C3 plantsC3 plants include grains, soy, legumes, cotton, most trees, and more Selection produces functional adaptations, but not necessarily at optimal efficiency What about the other 15%? i.e. the C4 and CAM plants

  7. In hot, dry conditions, plant will undergo Photorespiration • to conserve water, leaf stomata close, preventing CO2 intake and O2 release. • as CO2 concentration in the chloroplasts drops, Rubisco fixes oxygeninstead of CO2. • Photorespiration wastes radiant energy no glucose is made, no ATP is made What’s a plant to do?

  8. C4 Plantsseparate C-fixation and the Calvin cycle into different cells CO2 uptake in mesophyll cells Light reaction occurs O2 produced stays here 4C molecule – PEP - made PEP shuttles CO2 to bundle-sheath cells 4C 3C + CO2 used in Calvin cycle Therefore can keep stomata closed

  9. C4 Plantscorn, sugarcane In mesophyll: H20 input light rxn O2 , PEP fixes C PEP yields CO2 In bundle-sheath cells: Calvin cycle G3P sugar

  10. CAM Plants C-fixation and Calvin at different times of the day Avoiding evaporative loss • Stomates open at night • CO2 is converted to an acid and stored hottest, driest conditions • During the day, the acid is broken down • CO2 released to RUBISCO for photosynthesis CAM plants can ‘idle’ a while

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