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Question #45983
The Question
A rosette-habit Long Day Plant (LDP) is cultivated under continuous short-day conditions. Upon exogenous application of a specific Plant Growth Regulator (PGR), the plant exhibits bolting followed by flowering. Which of the following statements correctly identifies the PGR and evaluates the systemic consequence of this hormonal override?
Options
- A.
Gibberellin; it bypasses the phytochrome-mediated photoperiodic threshold, leading to precocious flowering but a reduced overall reproductive yield due to insufficient vegetative biomass.
- B.
Cytokinin; it substitutes for the long-day requirement by synthesizing florigen directly in the shoot apical meristem, maximizing both vegetative and reproductive biomass.
- C.
Gibberellin; it lowers the critical photoperiod required for Pr to Pfr conversion, ensuring an extended vegetative phase and enhanced seed set.
- D.
Auxin; it induces apical dominance and internode elongation, substituting for the cold treatment requirement (vernalization) to produce robust floral appendages.
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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
Photoperiodism Thresholds|Gibberellin Bolting Logic|Phototropin
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the isolated NCERT fact that 'GA causes bolting and flowering in LDPs' but fail to integrate the physiological cost of this hormonal override.
The common misconception is assuming that exogenous growth promoters always lead to 'enhanced' agricultural outcomes.
This question tests the understanding of source-sink relationships—specifically, that bypassing the vegetative phase compromises the biomass required for optimal reproductive yield.
It also tests the precise mechanism of action: GA bypasses the phytochrome system rather than altering its photochemical conversion.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Photoperiodism Thresholds |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |