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Question #47625
The Question
A C4 grass species naturally thriving in an open tropical savanna is experimentally transplanted into a shaded forest ecotone. Despite possessing a near-zero CO2 compensation point, the C4 plant exhibits stunted growth and is rapidly outcompeted by native C3 species. Which of the following best explains the metabolic burden experienced by the C4 plant in this shaded habitat?
Options
- A.
The carbon-concentrating mechanism requires 5 ATP per CO2 fixed, a bioenergetic demand that cannot be sustained under light-limiting conditions.
- B.
Low light intensity triggers the oxygenase activity of RuBisCO within the bundle sheath cells, leading to high rates of photorespiration.
- C.
PEP carboxylase loses its high affinity for CO2 in shaded environments, raising the CO2 compensation point above that of C3 plants.
- D.
The spatial separation of carbon fixation and the Calvin cycle breaks down, causing pyruvate to accumulate toxically in the mesophyll cells.
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
C4_Pathway|Compensation_Point|Ecotone_Dynamics
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'C4 plants are always more efficient than C3 plants' due to the absence of photorespiration and a lower CO2 compensation point.
The trap is failing to account for the bioenergetic cost of this efficiency.
The extra ATP required for PEP regeneration makes the C4 pathway a metabolic burden in environments where light (and thus photophosphorylation) is a limiting factor.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | C4 Pathway Efficiency |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |