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To prevent water loss C3 plants close stomata which results in photorespiration Photorespiration – plants fix O2 instead of CO2 – producing a 2C compound instead of G3P Photorespiration = use of ATP from light reactions but with no sugar production C4 Plants › Corn, Sugar Cane › Plant prefaces the Calvin Cycle w/ reactions that incorporate CO2 into 4C compounds › 4C transported from mesophyll to bundle sheath cells to supplies CO2 to Calvin Cycle C4 Plants › PEP carboxylase is highly efficient at fixing CO2 › Fix CO2 rapidly to keep high concentration gradient that favors movement into stoma › Fix large amount of CO2 rapidly so stoma can be closed most of the time CAM Plants › Crassulacean Acid Metabolism › Plants in arid conditions (eg. pineapples) › Close stomata during the day – open stomata at night › Fix carbon in a 4C compound (like C4 plants) at night › 4C releases CO2 for Calvin Cycle during the day Fig. 10-20 Sugarcane C4 Pineapple CO2 Mesophyll cell Organic acid Bundlesheath cell CO2 1 CO2 incorporated into four-carbon Organic acid organic acids (carbon fixation) CO2 Calvin Cycle CAM CO2 2 Organic acids release CO2 to Calvin cycle Night Day Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps