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Question #47622
The Question
In a transgenic sugarcane plant, a targeted mutation severely impairs the function of the enzyme Pyruvate phosphate dikinase (PPDK). Under conditions of high light intensity and high temperature, which of the following physiological consequences will be most immediately observed?
Options
- A.
The bundle sheath cells will exhibit a significant increase in photorespiratory loss due to the breakdown of the CO2-concentrating mechanism.
- B.
The plant will seamlessly transition to a standard C3 pathway, synthesizing one glucose molecule using exactly 18 ATP and 12 NADPH.
- C.
Pyruvate will accumulate in the bundle sheath chloroplasts because its transport back to the mesophyll is actively driven by PPDK.
- D.
Primary CO2 fixation will be taken over by RuBisCO in the mesophyll cytoplasm to maintain the photosynthetic rate.
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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
ATP_Synthesis|PEP_Carboxylase|NADPH_Requirement
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the stoichiometric difference between C3 (18 ATP) and C4 (30 ATP) plants.
A common misconception is that knocking out the C4 pathway (saving the extra 12 ATP used by PPDK) makes the plant more energy-efficient.
This question tests the understanding that the extra ATP is a mandatory 'thermodynamic cost' to suppress photorespiration.
Without PPDK, the plant does not become an efficient C3 plant; instead, it suffers massive photorespiratory loss due to the failure of the spatial CO2 pump.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Kranz Anatomy Adaptations |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |