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Question #46960
The Question
In an aquatic ecosystem, a massive bloom of Chrysophytes occurs alongside a high influx of ammonotelic waste. Consequently, the nitrogen-fixing efficiency of symbiotic cyanobacteria (e.g., Anabaena) drops significantly. Which of the following is the most accurate physiological explanation for this decline?
Options
- A.
High ambient ammonia acts as a feedback inhibitor, repressing nitrogenase activity as the microbes preferentially utilize the readily available fixed nitrogen.
- B.
The rapid sequestration of silica by Chrysophytes deprives the cyanobacteria of the essential cofactor required for the Mo-Fe protein complex.
- C.
Ammonotelic waste drastically increases the dissolved oxygen concentration in the water column, which irreversibly inactivates the oxygen-sensitive nitrogenase.
- D.
The accumulation of ammonia degrades the thick glycolipid walls of the heterocysts, allowing oxygen influx that destroys the nitrogenase enzyme.
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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
Chrysophytes Silica Wall|Terminal Electron Acceptor|Respiration in Plants
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often assume that more nutrients (even waste) will stimulate all microbial activity.
The trap lies in failing to recognize the negative feedback loop of nitrogen fixation: organisms will not expend massive amounts of ATP to fix atmospheric nitrogen if a usable nitrogen source (ammonia) is already abundant.
Furthermore, it tests the ability to separate the structural needs of Chrysophytes (silica) from the enzymatic needs of cyanobacteria (Mo-Fe).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biological Classification - Class 11 |
| Concept | Chrysophytes Silica Wall |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |