110. The oxidative photosynthetic carbon cycle salvages:
(1) C3 carbon
(2) C4 carbon
(3)CO2
(4) C2 carbon
Detailed Explanation:
Question:
The oxidative photosynthetic carbon cycle salvages:
✅ Correct Answer: (4) C2 carbon
What Is the Oxidative Photosynthetic Carbon Cycle?
The oxidative photosynthetic carbon cycle, more commonly known as photorespiration, is a process in C3 plants that occurs when ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) fixes oxygen instead of carbon dioxide.
This results in the production of 2-phosphoglycolate, a two-carbon (C2) compound, which is toxic and needs to be salvaged by the plant to prevent loss of carbon and energy.
Why C2 Carbon?
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During photorespiration, RuBisCO adds O₂ to RuBP, forming:
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One molecule of 3-phosphoglycerate (3-PGA) – usable in the Calvin cycle.
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One molecule of 2-phosphoglycolate – a C2 compound that cannot be used directly.
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The oxidative photosynthetic carbon cycle salvages this C2 compound through a complex series of reactions involving chloroplasts, peroxisomes, and mitochondria.
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Ultimately, C2 carbon is recycled back into the Calvin cycle, minimizing carbon and nitrogen loss.
Why Not the Other Options?
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(1) C3 carbon: C3 compounds like 3-PGA are part of the Calvin cycle, not photorespiration salvage.
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(2) C4 carbon: Involved in C4 photosynthesis, which avoids photorespiration.
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(3) CO₂: Although CO₂ is a byproduct of photorespiration, it’s not what is salvaged—it is actually lost in the process.
Biological Importance
While photorespiration is often seen as inefficient due to CO₂ loss, it plays several crucial roles:
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Prevents photoinhibition by consuming excess ATP and NADPH.
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Salvages carbon and nitrogen that would otherwise be lost.
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Important in stress responses, especially under high oxygen or low CO₂ conditions.
Conclusion
The oxidative photosynthetic carbon cycle is essential for salvaging C2 carbon generated from the oxygenation activity of RuBisCO. Despite its energy cost, this cycle is critical for maintaining plant metabolism and preventing the accumulation of toxic intermediates.
✅ Correct Answer: (4) C2 carbon
