Dark Reaction The Calvin Cycle. 6CO 2 +6H 2 O C 6 H 12 O 6 +6O 2 The dark reactions use the energy stored in ATP and NADPH the light reactions. The dark.

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    28-Dec-2015

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<ul><li><p>Dark ReactionThe Calvin Cycle</p></li><li><p>6CO2 +6H2O C6H12O6 +6O2</p><p>The dark reactions use the energy stored in ATP and NADPH the light reactions.Carbon atoms from CO2 are bonded, or fixed, into organic compounds = carbon fixation. THIS OCCURS IN THE STROMA</p></li><li><p>STEP 1An enzyme (rubisco), combines CO2 with a 5-carbon sugar RuBPThe product, 6-C sugar, immediately splits into 2, -3C molecules (PGA)</p><p>PGA Phosphoglyceric Acid</p></li><li><p>Step 2PGA is converted to another 3- Carbon molecule PGAL in a 2 part process:Each PGA receives a P group from ATPThe resulting compound receives a proton from NADPH and releases the P, producing PGAL( ADP &amp; NADP+ return to light rxn., to make ATP and NADPH)</p></li><li><p>Step 3Most of the PGAL is converted back to RuBPRequires a P from another ATP</p><p>Some PGAL leave and used by plants create organic compounds</p></li><li><p>Balance Sheet for PhotosynthesisHow much ATP &amp; NADH are required to make 1 molecule of PGA from carbon dioxide?Each turn fixes one CO2PGAL is a 3-C molecule (takes 3 turns to make each molecule)Each turn of the cycle:3 ATP ( 2 in step 2 &amp; 1 in step 3)2 NADPH (step 3)</p></li><li><p>About 50% made to fuel cell Respiration</p><p>Some of the PGAL is used to make amino acids, lipids, carbohydrates like glucose and fructose, glycogen, starch, and cellulose.</p></li><li><p>Alternative PathwaysPlants that fix carbon exclusively through the Calvin Cycle- C3 PlantsBecause of the 3-C compound PGA, that is initially formed.Example: Rice, wheat, oats, and soybeans</p></li><li><p>Alternative PathwaysPlants in hot, dry climates use alternative pathwaysPlant lose H2O to the air-through small pores called stomata (underside of leaf)Can be partially closed to prevent water lossStomata are the major passageways through which CO2 enters and O2 leaves(when stomata are closed CO2 levels decrease and O2 levels increase)</p></li><li><p>Transpiration-Evaporation of water from leaves</p><p>Rate of transpiration related to the degree of stomata opening and evaporation demand of environment</p></li><li><p>C4 PlantsFix CO4 into 4-C compoundsPartially close stomata during hottest part of the dayEnzymes fix CO2 into 4-C compounds and transport them to cells where CO2 is released and enters calvin cycle ( lose as much H2O as C3)ExamplesCorn, sugar cane, crabgrass</p></li><li><p>CAM PathwaysOpen stomata at night; close during the day</p><p>Take in CO2 at night and fix into compounds</p><p>Release O2 during the day and enter the Calvin cycle</p><p>Example: cacti, pineapples</p></li><li><p>Rate of PhotosynthesisLight Intensity:Increase rate of photosynthesis, then levels off ( max. rate of photosynthesis)Higher intensity, excites more electrons in cholorphyll @ same intensity, all available electrons are excited</p></li><li><p>Amount CO2Amount of CO2:Increases rate of photosynthesis to a point, then levels off</p></li><li><p>TemperatureHigher temperature accelerates the chemical rxns. Peaks @ certain temp. because the enzymes becomes ineffective and unstableStomata closes-limiting H2O loss and CO2 entry into the leaves</p></li><li><p>Concentration of O2Higher O2 will decrease the rate of photosynthesis and increase the rate of photorespirationRubisco will bind with oxygenWill send PGA into respiration, instead of finishing photosynthesis Decreasing amount of organic compound produced</p></li></ul>

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