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Question #47582
The Question
A researcher cultivates a plant in a controlled phytotron illuminated by a custom light spectrum that completely lacks the 660 nm wavelength but contains adequate blue (450 nm) and far-red (730 nm) light. Which of the following represents the most accurate physiological consequence for this plant?
Options
- A.
The rate of photosynthesis drops to zero because the action spectrum of Chlorophyll a is entirely dependent on the 660 nm wavelength for the excitation of Photosystem II.
- B.
Photosynthesis continues via blue light absorption, but the plant fails to initiate red-light-dependent morphogenetic responses due to the inability to form the physiologically active Pfr.
- C.
The plant exhibits normal photomorphogenesis because far-red light directly converts Pfr to Pr, which acts as the active promoter for flowering and seed germination.
- D.
Both energy metabolism and developmental signaling cease to function, as the absorption spectrum of accessory pigments cannot compensate for the lack of red light in the photosynthetically active radiation (PAR).
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
Action Spectrum|Absorption Spectrum|Phytochrome Interconversion
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Decoupling of the Action Spectrum of Photosynthesis from the Absorption Spectrum of Phytochrome.
Students often conflate 'light required for plant survival' (photosynthesis via blue/red) with 'light required for plant development' (photomorphogenesis via red/far-red).
The primary trap is assuming that if a plant can photosynthesize efficiently, it can also complete its life cycle, failing to recognize that the Pr to Pfr conversion strictly requires the red wavelength to initiate developmental signaling.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Photosynthesis in Higher Plants - Class 11 |
| Concept | Action Spectrum vs Absorption Spectrum |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |