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Question #47628
The Question
In the C4 pathway, the regeneration of Phosphoenolpyruvate (PEP) from pyruvate is catalyzed by Pyruvate phosphate dikinase in the mesophyll cells, normally consuming 2 ATP equivalents per CO2 fixed. If a mutation alters the enzyme's kinetics, increasing this cost to 3 ATP equivalents per CO2, how will it directly affect the bioenergetics of synthesizing one glucose molecule and the plant's ecosystem productivity?
Options
- A.
The total ATP requirement per glucose molecule increases from 30 to 36; Net Primary Productivity (NPP) decreases due to increased metabolic energy losses (R).
- B.
The total ATP requirement per glucose molecule increases from 18 to 24; Gross Primary Productivity (GPP) decreases due to reduced RuBisCO efficiency.
- C.
The total ATP requirement per glucose molecule increases from 30 to 36; Net Primary Productivity (NPP) increases because the plant fixes more CO2 to compensate.
- D.
The total ATP requirement per glucose molecule remains 30, but the NADPH requirement increases from 12 to 18; NPP decreases due to induced photorespiration.
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
Productivity_Ratios|PEP_Regeneration_Energy_Cost|Gross_Primary_Productivity
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize '30 ATP for C4' without understanding that the extra 12 ATP (compared to C3's 18 ATP) are specifically spent on PEP regeneration.
This question forces the synthesis of molecular bioenergetics (ATP counting) with ecosystem ecology (NPP = GPP - R), testing if the student understands that increased metabolic inefficiency directly inflates 'R', thereby reducing 'NPP'.
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 |