Concept 30 - Concept 10.4 Alternative mechanisms of carbon...

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Concept 10.4 Alternative mechanisms of carbon fixation have evolved in hot, arid climates One of the major problems facing terrestrial plants is dehydration. At times, solutions to this problem require tradeoffs with other metabolic processes,  especially photosynthesis. The stomata are not only the major route for gas exchange (CO 2  in and O 2  out), but also for  the evaporative loss of water. On hot, dry days, plants close their stomata to conserve water. This causes problems for  photosynthesis. In most plants  (C 3 plants),  initial fixation of CO 2  occurs via rubisco, forming a three- carbon compound, 3-phosphoglycerate. C 3  plants include rice, wheat, and soybeans. When their stomata partially close on a hot, dry day, CO 2  levels drop as CO 2  is consumed in  the Calvin cycle. At the same time, O 2  levels rise as the light reaction converts light to chemical energy. While rubisco normally accepts CO 2 , when the O 2 :CO 2  ratio increases (on a hot, dry day  with closed stomata), rubisco can add O 2  to RuBP. When rubisco adds O
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.

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Concept 30 - Concept 10.4 Alternative mechanisms of carbon...

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