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Question #46002
The Question
A C_3 plant is exposed to a prolonged, artificially high O_2/CO_2 ratio in a controlled greenhouse. Researchers observe rapid premature leaf senescence, yet the actual physical separation of these leaves (abscission) is significantly delayed. Which of the following metabolic cascades best explains this physiological paradox?
Options
- A.
Photorespiration generates excess hydrogen peroxide in peroxisomes, which destroys chlorophyll to induce senescence, while simultaneously inhibiting ethylene synthesis to delay abscission.
- B.
RuBisCO acts as an oxygenase, causing a futile cycle that drains ATP and fixed carbon. This metabolic starvation accelerates senescence, but the severe ATP deficit impairs the energy-dependent synthesis of pectinases needed for abscission layer separation.
- C.
The high O_2 concentration competitively inhibits PEP carboxylase, leading to rapid senescence, while the lack of malate accumulation prevents the osmotic changes required for leaf drop.
- D.
Photorespiratory loss of CO_2 in mitochondria directly triggers the premature upregulation of abscission zone proteins, but the lack of NADH production from the Calvin cycle halts the process.
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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
Rubisco Dual Functionality|Senescence vs Abscission|Oxygenase Activity
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize photorespiration as a 'wasteful process' but fail to apply its specific metabolic costs (ATP and carbon drain) to downstream physiological events.
The trap lies in assuming that because senescence and abscission are temporally linked, a stressor that accelerates senescence will automatically accelerate abscission.
This question tests the NCERT-Plus understanding that abscission is an active, ATP-dependent process (requiring enzyme synthesis) that can be stalled if the plant's energy reserves are depleted by the photorespiratory futile cycle.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Senescence vs Abscission |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |