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Question #46947
The Question
A researcher isolates a mutant strain of the filamentous cyanobacterium Anabaena in which the genetic silencing of Photosystem II (PSII) during heterocyst differentiation fails to occur. If this mutant is grown in a nitrogen-deficient, illuminated environment, which of the following represents the most immediate physiological consequence?
Options
- A.
Irreversible inactivation of the nitrogenase enzyme complex due to internal oxygen evolution, leading to nitrogen starvation.
- B.
Increased rate of nitrogen fixation due to the supplementary ATP provided by non-cyclic photophosphorylation.
- C.
Accumulation of toxic reactive oxygen species (ROS) leading to the immediate degradation of Photosystem I (PSI) in the heterocyst.
- D.
A shift from nitrogen fixation to active carbon dioxide assimilation within the heterocyst due to restored non-cyclic electron transport.
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
Nitrogenase|Heterocyst|Photosystem_II
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that nitrogen fixation is a highly energy-demanding process requiring massive amounts of ATP.
The trap (Option B) exploits the misconception that adding PSII would benefit the cell by providing more ATP via non-cyclic photophosphorylation.
The critical pivot is recognizing the functional trade-off: PSII's byproduct () is lethally toxic to nitrogenase, which is the exact evolutionary reason PSII is naturally absent in heterocysts.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biological Classification - Class 11 |
| Concept | Cyanobacteria Heterocyst Function |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |