Photorespiration is a process that occurs when the concentration of carbon dioxide is low and the concentration of oxygen is high. It is a result of Rubisco utilizing oxygen as substrate instead of carbon dioxide. This means that when stomata partially close on a hot day, the levels of carbon dioxide come down as this carbon dioxide is consumed in the Calvin cycle. Simultaneously, oxygen levels rise as the light is converted to chemical energy in light reaction. Thus, photorespiration in plants consumes oxygen and releases carbon dioxide without producing ATP or sugar.
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