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Question #45989
The Question
A mutant angiosperm possesses a targeted deletion in the Light Responsive Elements (LREs) within the promoter regions of its genome. If this plant is cultivated under continuous high-intensity red light, which of the following represents the most likely phenotypic outcome and its correct physiological basis?
Options
- A.
Normal photomorphogenesis; Pfr acts as a kinase in the cytoplasm to directly synthesize chlorophyll, bypassing the need for nuclear transcription.
- B.
Etiolated growth (skotomorphogenesis); although Pr converts to Pfr, the absence of LREs prevents the transcriptional shift required for light-induced gene expression.
- C.
Normal photomorphogenesis; the accumulation of Pfr constitutively degrades Phytochrome Interacting Factors (PIFs), which alone is sufficient to trigger greening.
- D.
Etiolated growth (skotomorphogenesis); the mutation in LREs directly alters the phytochrome chromophore structure, preventing the conversion of Pr to Pfr.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
PIF_Proteins|Promoter_Binding|Transcription_Factors
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Decoupling light perception from transcriptional response.
Students often fall into the trap of assuming that if the active receptor (Pfr) is present, the physiological phenotype automatically follows.
This question tests the understanding that signal transduction is a multi-step pathway; a functional photoreceptor is useless if the ultimate genomic target (LRE) is mutated, leaving the plant locked in its default etiolated state.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Plant Growth and Development - Class 11 |
| Concept | Phytochrome Interconversion |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |