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Question #47609
The Question
In a controlled greenhouse experiment, a C3 plant is shifted from standard atmospheric conditions to an environment with elevated temperature and high O2 concentration. Which of the following statements correctly explains the resulting metabolic consequence on the stoichiometry of energy consumption per net CO2 fixed?
Options
- A.
The ATP requirement per net CO2 fixed increases significantly because the photorespiratory salvage pathway consumes extra ATP and releases CO2, disrupting the standard 3:2 ATP:NADPH ratio.
- B.
The ATP to NADPH consumption ratio decreases because the oxygenation of RuBP bypasses the reduction phase of the Calvin cycle, thereby conserving ATP.
- C.
The stoichiometry remains strictly 3 ATP and 2 NADPH per net CO2 fixed, but overall biomass decreases solely due to the competitive binding of O2 at RuBisCO's active site.
- D.
The plant compensates by generating additional ATP in the mitochondria during the conversion of glycine to serine, maintaining the standard energy ratio.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Rubisco|Competitive Enzyme Inhibition Kinetics|C3 Cycle Stoichiometry
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the standard 3 ATP : 2 NADPH ratio for the Calvin cycle but fail to integrate the energetic cost of the photorespiratory salvage pathway.
The trap relies on the misconception that competitive inhibition by O2 merely 'pauses' carbon fixation (Option C), rather than acting as an active metabolic drain that consumes extra ATP and releases previously fixed CO2, fundamentally altering the net stoichiometric efficiency.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | C3 Cycle Stoichiometry |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |