Photorespiration

<h1>Text Preview</h1> <p>In the presence of light, plants consume carbon dioxide and release molecular oxygen. At the same time, plants consume molecular oxygen and release carbon dioxide. Both of these reactions are catalyzed by rubisco, the enzyme that catalyzes the fixation of carbon in the first stage of the Calvin-Benson cycle. </p> <p>When rubisco binds with molecular oxygen instead of carbon dioxide, it catalyzes the conversion of ribulose 1,5-bisphosphate to one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate. 2-Phosphoglycolate then undergoes several reactions to yield carbon dioxide, which undoes some of the work of photosynthesis. Photorespiration also wastes chemical energy when 2-phosphoglycolate is converted into 3-phosphoglycerate. </p> <p>Why, then, does such an unproductive metabolic process take place in plants?</p> <p>Scientists believe that rubisco first evolved when oxygen levels in the atmosphere were so low that its reaction with oxygen had little effect. However, now that atmospheric oxygen levels are 1000 times higher than carbon dioxide levels, photorespiration has a significant impact on a plant’s energy efficiency.</p> <p>Photorespiration is observed in all photosynthetic organisms. It’s possible that photorespiration offers some selective advantage, such as protecting an organism from damage when carbon dioxide is unavailable. In the absence of carbon dioxide and photorespiration, a plant would have no way of releasing the light energy it absorbs.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>