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AP Biology Photosynthesis C3 C4 and CAM plants
C3, C4, and CAM plants have evolved different carbon fixation pathways to adapt to hot, arid environments. C3 plants fix carbon directly in the Calvin cycle but lose efficiency through photorespiration. C4 plants fix carbon in the cytoplasm first before the Calvin cycle to concentrate CO2. CAM plants fix carbon at night and store it to use during the day to minimize water loss through closed stomata.
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AP Biology Photosynthesis C3 C4 and CAM plants
- 1. Photosynthesis Alternative methods ofcarbon fixation in hot, arid climates
- 2. Your goals ◊ Explainhow C4 and CAM plants have adapted to live in hot, windy climates
- 3. You may wantto set up your notes like this C3 Plants C4 Plants CAM Plants
- 4. Plant evolutionary history Lifebegan in water The first plants were aquatic Since plants evolved to living out of water, they have had a hard time dealing with dehydration
- 5. Plant adaptations Most adaptationsinvolve some sort of trade off For plants, the trade off with photosynthesis is that they lose water to the environment through transpiration
- 6. A little plantanatomy The openings on leaves are called stomataThe openings on leaves are called stomata This is where CO2 and O2 can enter and exit the plant Water is also lost through the stomata Plants often close the stomata on very hotPlants often close the stomata on very hot days, but COdays, but CO22 intake is cut offintake is cut off
- 7. C3 plants Most plants Fixcarbon byFix carbon by attaching COattaching CO22 to RuBPto RuBP “3” comes from the 3-carbonmolecule produced after CO2is fixed
- 8. C3 Plants On hotdays, they close their stomata part way Produce little sugar then
- 9. C3 plants As theCOAs the CO22 that the plant does havethat the plant does have gets used up, rubisco will fix Ogets used up, rubisco will fix O22 insteadinstead and send it into the Calvin cycle instead of CO2
- 10. Peroxisomes & mitochondriasplit the new compound and release CO2 This is called photorespiration Occurs in the light Consumes oxygen and releases CO2
- 11. Photorespiration uses ATP but makesno ATP Photorespiration makes no sugars PhotorespirationPhotorespiration decreasesdecreases photosynthesisphotosynthesis outputoutput
- 12. So why wouldany plant do this… Photorespiration mayPhotorespiration may be an evolutionarybe an evolutionary leftoverleftover In early atmosphere, with little O2, it didn’t matter if Rubisco had an affinity for O2 Today, with so much O2 in the atmosphere, it is inevitable that some O2 will be fixed instead of
- 13. C3 Crop plants Rice,wheat, soybeansRice, wheat, soybeans May lose as much as 50% of the Carbon fixed in the Calvin Cycle to photorespiration
- 14. 3 Things What are3 things you know for sure about C3 plants?
- 15. C4 plants C4 plantshave adaptations that allow them to minimize the effects of photorespiration Many are tropical grasses
- 16. C4 plants Have analternate means of fixing carbon C4 plants fix carbon out in the cytoplasm before it enters the Calvin Cycle “4” comes from the 4-carboncompound that is formed when CO2 is fixed in C4 plants
- 17. C4 plant adaptations 1ststep is binding CO2 to PEP (phosphoenolpyruvate) by the enzyme PEP carboxylase to make a 4-C compound: oxaloacetate PEP has a high affinity for CO2 and none for O2
- 18. 2. The 4-carboncompound enters photosynthetic cellsphotosynthetic cells CO2 is released from PEP and the Calvin cycle continues as normal This adaptation allows C4 plants to keep a high concentration of CO2 in the photosynthetic cells, preventing Rubisco from binding to O2 instead of CO2
- 19. C4 plants thrivein hot climates where stomata will be closed often Some important C4 plants are sugarcane, corn, tropical grasses
- 20. 3 Things What are3 things you know for sure about C4 plants?
- 21. CAM plants Another alternatemethod of carbon fixation Common in succulents like cacti
- 22. CAM plants CAM plantskeep stomata closed during the day to minimize water loss Only open stomata at night
- 23. Closed stomata duringthe day means no CO2 entering the plant during the day
- 24. CAM plants When stomataare open at night, CAM plants take in CO2 and fix it to PEP This is called crassulacean acid metabolism Crassulaceae is the name of the family ofplants that include succulents
- 25. CAM plants Cells ofCAM plants store the organic molecules that CO2 was fixed to in their vacuoles until morning Light reactions then produce ATP and NADPH to drive the Calvin Cycle The CO2 in the organic molecules is released for use in the Calvin Cycle
- 26. CAM plants Important CAMplants include pineapple and agave
- 27. 3 Things What are3 things you know for sure about CAM plants?
- 29. Comparison of C3,C4, and CAM plants C3 plants C4 plants CAM plants Most plants Tropical grasses like corn, sugarcane Succulents, pineapple, agave Fix carbon in Calvin cycle - attach CO2 to RuBP Fix carbon in cytoplasm - attach CO2 to PEP Fix carbon at night only, fix it to organic molecules Enzyme - Rubisco Enzyme – PEP-ase Enzyme – PEP-ase Most energy efficient method 1/2 way between these two Best water conservation Loses water through photorespiration Loses less water Loses least water