Before You Begin
Question #46306
The Question
In an experiment, C3 plants are grown under elevated atmospheric CO2 concentrations (e.g., 800 μL L^-1). Initially, there is a marked increase in net photosynthetic rate due to the suppression of photorespiration. However, the long-term biomass yield often plateaus and fails to match the theoretical predictions of the 'CO2 fertilization effect'. Which of the following is the most accurate physiological explanation for this discrepancy?
Options
- A.
Elevated CO2 induces permanent stomatal closure, completely blocking O2 efflux and causing severe photo-oxidative damage.
- B.
The initial thermodynamic advantage is bottlenecked by soil nitrogen limitation, restricting the de novo synthesis of RuBisCO and sink tissues.
- C.
The plants acclimate by converting their mesophyll anatomy to Kranz anatomy, which is highly ATP-dependent and reduces net yield.
- D.
High internal CO2 partial pressure enhances the oxygenase activity of RuBisCO, leading to the accumulation of toxic phosphoglycolate.
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
Rubisco Dual Functionality|Partial Pressure Gradient Logic|C4 Pathway Efficiency
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Blackman's Law of Limiting Factors with Mineral Nutrition.
Students often assume that optimizing the gaseous exchange gradient (high CO2) guarantees indefinite yield increases.
The misconception lies in ignoring the biochemical 'sink' requirements—specifically, that sustained carbon fixation demands massive amounts of Nitrogen to build the RuBisCO enzyme.
When Nitrogen becomes the new limiting factor, the thermodynamic advantage of reduced photorespiration is nullified.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Breathing and Exchange of Gases - Class 11 |
| Concept | Partial Pressure Gradient Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |