ENVS 3010 Lecture Notes - Lecture 5: C4 Carbon Fixation, Stoma, Phloem
21 Jul 2016
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5. 1: different types of photosynthesis: co2 + h2o + light -> (ch2o) + o2. Energy from sunlight transfers water into oxygen and releases atp (energy required for light-independent reaction) Co2 with the help of atp undergoes the calvin cycle producing sugars. Rubisco is main enzyme in calvin cycle: co2 binds with rubisco, rubisco can also bind to oxygen undergoing photorespiration. Photorespiration is likely an evolutionary artifact that is of no big use to the plants because rubisco evolved when o2 levels were very low. Oxygenase activity: co2/o2 = specificity factor. Evolved during a time of low co2 concentrations. A new mechanism needed to be implemented to contain rubisco within the plant. Calvin cycle happens within the bundle sheath cells where the rubisco is not exposed to atmospheric air. This way rubisco does not have to compete with o2. Has a co2 concentration mechanism in mesophylls.
