AP Bio Ch. 10 C3 c4 and cam plants


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AP Bio Ch. 10 C3 c4 and cam plants

  1. 1. Photosynthesis Alternative methods of carbon fixation in hot, arid climates
  2. 2. You may want to set up your notes like this C3 Plants C4 Plants CAM Plants
  3. 3. Plant evolutionary history  Life began in water  The first plants were aquatic  Since plants evolved to living out of water, they have had a hard time dealing with dehydration
  4. 4. Plant adaptations Most adaptations involve some sort of trade off For plants, the trade off with photosynthesis is that they lose water to the environment through transpiration
  5. 5. A little plant anatomy  The 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 hot days, but CO2 intake is cut off
  6. 6. C3 plants “3” comes from the 3-carbon molecule produ ced after CO 2 is fixed Most plants Fix carbon by attaching CO2 to RuBP
  7. 7. C3 Plants On hot days, they close their stomata part way Produce little sugar then
  8. 8. C3 plants As the CO2 that the plant does have gets used up, rubisco will fix O2 and send it into the Calvin cycle instead of CO2
  9. 9. Peroxisomes & mitochondria split the new compound and release CO2 This is called photorespiration Occurs in the light Consumes oxygen and releases CO2
  10. 10. Photorespiration uses ATP but makes no ATP Photorespiration makes no sugars Photorespiration decreases photosynthesis output
  11. 11. So why would any plant do this… Photorespiration may be an evolutionary leftover 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
  12. 12. C3 Crop plants Rice, wheat, soybeans May lose as much as 50% of the Carbon fixed in the Calvin Cycle to photorespiration
  13. 13. 3 Things What are 3 things you know for sure about C3 plants?
  14. 14. C4 plants C4 plants have adaptations that allow them to minimize the effects of photorespiration Many are tropical grasses
  15. 15. C4 plants “4” comes fro m the 4-carb on compound th at is formed when CO is fixed in C 2 4 plants Have an alternate means of fixing carbon C4 plants fix carbon out in the cytoplasm before it enters the Calvin Cycle
  16. 16. C4 plant adaptations  1st step 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
  17. 17.  2. The 4-carbon compound enters photosynthetic 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
  18. 18. C4 plants thrive in hot climates where stomata will be closed often Some important C4 plants are sugarcane, corn, tropical grasses
  19. 19. 3 Things What are 3 things you know for sure about C4 plants?
  20. 20. CAM plants Another alternate method of carbon fixation Common in succulents like cacti
  21. 21. CAM plants CAM plants keep stomata closed during the day to minimize water loss Only open stomata at night
  22. 22. Closed stomata during the day means no CO2 entering the plant during the day
  23. 23. CAM plants  When stomata are open at night, CAM plants take in CO2 and fix it by incorporating it into organic molecules  This is called Cr a crassulacean acid namssulaceae is the e of the family of metabolism plants that inc lud succulents e
  24. 24. CAM plants  Cells of CAM 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
  25. 25. CAM plants Important CAM plants include pineapple and agave
  26. 26. 3 Things What are 3 things you know for sure about CAM plants?
  27. 27. Comparison of C3, C4, and CAM plants C3 plants Most plants C4 plants Tropical grasses like corn, sugarcane CAM plants Succulents, pineapple, agave Fix carbon in Calvin Fix carbon in cycle - attach CO2 cytoplasm - attach CO2 to PEP to RuBP 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