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Question #47627
The Question
Under high-temperature stress (>35°C), C4 plants maintain high photosynthetic productivity while C3 plants suffer significant carbon loss due to photorespiration. However, the C4 mechanism's avoidance of photorespiration comes with a specific metabolic trade-off. Which of the following accurately identifies this energetic trade-off and its exact cellular location?
Options
- A.
An expenditure of 12 extra ATP per glucose molecule synthesized, utilized during the conversion of pyruvate to phosphoenolpyruvate (PEP) in the mesophyll cells.
- B.
An expenditure of 12 extra ATP per glucose molecule synthesized, utilized during the decarboxylation of malic acid in the bundle sheath cells.
- C.
An expenditure of 2 extra ATP per glucose molecule synthesized, utilized directly by PEP carboxylase during primary CO2 fixation in the mesophyll cells.
- D.
An expenditure of 18 extra ATP per glucose molecule synthesized, utilized to actively pump CO2 into the bundle sheath cells against a concentration gradient.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
PEP_Regeneration_Energy_Cost|RuBisCO|PEP_Carboxylase
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that C4 plants are 'more efficient' and mistakenly assume this means they use less energy.
In reality, C4 plants use MORE ATP (30 vs 18 per glucose) to power the CO2 concentrating mechanism.
The efficiency arises because this 12 ATP 'investment' prevents the massive carbon and energy drain of photorespiration at high temperatures.
The question also tests the Location Trap, ensuring students know PEP regeneration occurs in the mesophyll, not the bundle sheath.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | PEP Regeneration Energy Cost |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |