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Photosynthesis Part 5

Photosynthesis Part 5. Page 118. Plants must prevent H 2 O loss. 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

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Photosynthesis Part 5

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  1. Photosynthesis Part 5 Page 118

  2. Plants must prevent H2O loss • 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

  3. Adaptations to save H2O • 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

  4. Adaptations to save H2O • 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

  5. Adaptations to save H2O • 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

  6. Fig. 10-20 Pineapple Sugarcane C4 CAM CO2 CO2 Mesophyll cell Night CO2 incorporated into four-carbon organic acids (carbon fixation) 1 Organic acid Organic acid Day Bundle- sheath cell CO2 CO2 Organic acids release CO2 to Calvin cycle 2 Calvin Cycle Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps

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