October 26, 2011 Biology 311C Lecture 26 • Photorespiration occurs when higher than normal levels of oxygen are present in the leaf. • When you close the stomata, the oxygen levels go up and it occurs photorespiration. • C 4 is named for the 4-carbon molecule present in the first product of carbon fixation in these plants. • Both C 4 and CAM store carbon dioxide. C 4 stores it as a 4 carbon organic acid. • CAM photosynthesis is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. • The stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2). • The CO2 is stored as the four-carbon acid malate, and then used during photosynthesis during the day. • The pre-collected CO2 is concentrated around the enzyme RuBisCo, increasing photosynthetic efficiency. • PEP carboxylase is better than RuBisCo because it has a high affinity for carbon dioxide.
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