http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

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http//www.science.smith.edu/departments/Biology/B
io231/calvin.html
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Alternative mechanismsPhotorespiration

• C3 plants ? rice, wheat, soybeans
• Uses Co2 directly to make PGA
• On hot, dry days they close their stomata
• no CO2 taken in and O2 builds up
• rubisco substitutes O2 for CO2
• Creates a 2 C compound
• 2 C compound gets broken down ? releases CO2
  water
• Called photorespiration
• Uses light, releases CO2 and water
• Doesnt make glucose

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Alternative mechanismsC4 Plants

• Sunny ecosystems
• C is fixed into 4 C molecule
• Carbon fixed outside cells (in bundle sheath
  cells ? very efficient ? requires extra ATP
• Only fixes C, not oxygen
• Donates the carbon to Calvin Cycle
• Balances out photorespiration saves water
• Corn and sugarcane are a C4 plants

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Alternative mechanismsCAM Plants

• Crassulacean acid metabolism ? Hot/dry climates
• Orchids, cacti, pineapple etc.
• Stomates open at night to reduce water loss ?
  evaporation
• CO2 is fixed into a 4 C compound, used later

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