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Factors Affecting Photosynthesis 1. light intensity, [CO2] and temperature 2. C3 plant limitations 3. C4 plants 4. CAM plants 1. increased [CO2] = increased photosynthesis - up to a certain point until enzyme active sites are filled (photosynthetic rate will plateau) - due to increase in # of reactant molecules in Calvin Cycle 2. increased temperature = increased photosynthesis - up to a certain point until enzymes start to denature causing the photosynthetic rate to decrease - due to movement of reactant molecules within the Calvin Cycle 3. increased light intensity = increased photosynthesis only to a certain plateau after which an increase in light intensity results in no increase in the rate of photosynthesis This is because the Calvin cycle cannot keep up with the light reactions Photosynthesis Rate CO2 + H2O light C6H12O6 + O2 The overall rate of carbon fixation varies with temperature, not with the intensity of light Light reactions are affected by changes in light intensity, not by significant changes in temperature. C3 plants undergo photosynthesis as described stomata are open during the day / closed at night What happens to stomata in hot, arid conditions? In hot, arid conditions, plants close the stomata to prevent water loss increasing [O2] within the cells At high [O2], rubisco binds to O2 rather than CO2 in the process of photorespiration causes the plant to skip the Calvin cycle. Glucose is not produced. adaptation to hot, arid environments e.g. corn, sugarcane, grasses C4 plants have a special mesophyll cell & bundlesheath cell structure. 1. Mesophyll cells create 4-carbon molecules using PEP carboxylase and release CO2 into the bundle-sheath cells. Bundle-sheath cells only perform the Calvin cycle. In hot, arid conditions, C4 cells provide enough CO2 to ensure rubisco does not bind to O2 molecules. 2. adaptation to hot, arid environments e.g. cactus, pineapples (water storing plants) Stomata are closed in the day and open at night. Pineapple Sugarcane C4 Mesophyll Cell Organic acid Bundlesheath cell (a) Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in different types of cells. CALVIN CYCLE Sugar CAM CO2 1 CO2 incorporated into four-carbon organic acids (carbon fixation) 2 Organic acids release CO2 to Calvin cycle CO2 Organic acid Night Day CALVIN CYCLE Sugar (b) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times. 1. NIGHT: CO2 collected & incorporated into organic molecules 2. DAY: CO2 released from the organic molecules where ATP & NADPH is produced to allow the Calvin cycle to proceed http://www.youtube.com/watch?v=Dq38MpYOb8w HOMEWORK: - Pg. 166 #9-12 - Pg. 172 #3, 4, 6 - Pg. 178 #1, 2, 6, 8 (a,b)