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Question #45707
The Question
A dense population of the cephalochordate Amphioxus is maintained in a closed, un-aerated aquatic mesocosm. Despite adequate algal photosynthesis, the Biochemical Oxygen Demand (BOD) of the water spikes rapidly over a few days, leading to a severe drop in Dissolved Oxygen (DO). Which of the following best explains the physiological and ecological basis of this event?
Options
- A.
Protonephridia actively secrete large amounts of urea, which acts as an organic substrate for aerobic heterotrophic decomposers, increasing BOD.
- B.
The organisms are ammonotelic, and the continuous diffusion of ammonia into the water fuels high oxygen consumption by chemoautotrophic nitrifying bacteria.
- C.
The protonephridial network requires excessive ATP to actively transport ammonia against a concentration gradient, directly depleting dissolved oxygen.
- D.
High concentrations of excreted uric acid precipitate in the closed system, blocking light penetration and indirectly lowering DO by halting photosynthesis.
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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
Ammonotelism|BOD|Microbial decomposition
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often compartmentalize Human Physiology (Excretion) and Ecology (Environmental Issues).
They fail to connect that inorganic nitrogenous waste (ammonia) acts as a substrate for chemoautotrophs, driving up BOD just like organic waste does for heterotrophs.
Furthermore, a common misconception is that protonephridia actively excrete nitrogenous waste, whereas NCERT explicitly states their primary role is osmoregulation, with ammonia escaping via simple diffusion.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Excretory Products and Their Elimination - Class 11 |
| Concept | Protonephridia vs Metanephridia |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |