What occurs during photorespiration that prevents the Calvin cycle from proceeding?

• A. Glucose is directly synthesized, bypassing the need for the Calvin cycle.
• B. ATP is produced instead of consumed, disrupting the energy balance of the cycle.
• C. Rubisco incorporates O\(_2\) instead of CO\(_2\), leading to the production of 2-phosphoglycolate.
• D. Chlorophyll absorbs less light, reducing the availability of NADPH.

Answer: (C)

Verified step by step guidance

1. Understand the role of Rubisco in the Calvin cycle: Rubisco is an enzyme that normally catalyzes the fixation of CO\(_2\) into ribulose-1,5-bisphosphate (RuBP), forming two molecules of 3-phosphoglycerate, which are essential for the Calvin cycle to proceed.
2. Recognize the conditions that lead to photorespiration: Photorespiration occurs when oxygen (O\(_2\)) competes with carbon dioxide (CO\(_2\)) for binding to Rubisco, typically under conditions of high temperature, low CO\(_2\) concentration, or high O\(_2\) concentration.
3. Analyze the consequences of Rubisco incorporating O\(_2\): When Rubisco incorporates O\(_2\) instead of CO\(_2\), it produces one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate. The latter cannot directly enter the Calvin cycle and must be processed through a costly salvage pathway.
4. Understand the impact on the Calvin cycle: The production of 2-phosphoglycolate disrupts the Calvin cycle because it reduces the efficiency of carbon fixation and consumes energy and resources to recycle 2-phosphoglycolate back into usable intermediates.
5. Connect the disruption to the overall process: Photorespiration reduces the availability of intermediates for glucose synthesis, decreases the efficiency of photosynthesis, and prevents the Calvin cycle from proceeding effectively under certain environmental conditions.