If Rubisco adds O2 to RuBP instead of CO2, what is the consequence for carbon fixation?

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Multiple Choice

If Rubisco adds O2 to RuBP instead of CO2, what is the consequence for carbon fixation?

Explanation:
Rubisco can catalyze two competing reactions: carboxylation with CO2 and oxygenation with O2. When O2 is added to RuBP, the reaction splits RuBP into 3-phosphoglycerate and 2-phosphoglycolate. The latter is processed through photorespiration, a pathway that ultimately releases CO2 and uses energy, so there is no net gain of fixed carbon. In effect, carbon that could have been turned into sugars is lost as CO2, lowering the overall efficiency of carbon fixation, especially under conditions of high O2 or low CO2.

Rubisco can catalyze two competing reactions: carboxylation with CO2 and oxygenation with O2. When O2 is added to RuBP, the reaction splits RuBP into 3-phosphoglycerate and 2-phosphoglycolate. The latter is processed through photorespiration, a pathway that ultimately releases CO2 and uses energy, so there is no net gain of fixed carbon. In effect, carbon that could have been turned into sugars is lost as CO2, lowering the overall efficiency of carbon fixation, especially under conditions of high O2 or low CO2.

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