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Question #47613
The Question
During a laboratory experiment, isolated intact chloroplasts of a typical plant are subjected to extreme heat stress (). Despite maintaining an optimal stromal concentration of , ATP, and NADPH, the synthesis of 3-phosphoglycerate (3-PGA) completely ceases. What is the primary physiological reason for this observation?
Options
- A.
The affinity of RuBisCO for significantly exceeds that for at this temperature, leading to exclusive photorespiration.
- B.
The thermal disruption of non-covalent bonds in RuBisCO alters its tertiary structure, abolishing its catalytic active site.
- C.
The high temperature uncouples the proton gradient across the thylakoid membrane, preventing the utilization of the proton motive force.
- D.
The accumulation of NADPH causes severe allosteric feedback inhibition of the reduction phase enzymes in the Calvin cycle.
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
C3 Cycle Stoichiometry|Protein Denaturation Specificity|Rubisco
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between a kinetic shift in enzyme affinity (oxygenase vs. carboxylase activity) and the absolute structural collapse of the enzyme (denaturation).
Students reflexively associate 'high temperature in C3 plants' solely with 'increased photorespiration' (Option A).
They fail to realize that photorespiration still yields 3-PGA, and that extreme heat causes actual protein denaturation, breaking the stoichiometry of the Reductive Pentose Phosphate Cycle entirely.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | C3 Cycle Stoichiometry |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |