Before You Begin
Question #46309
The Question
A freshwater lake experiences a massive influx of untreated sewage, leading to a sharp spike in Biochemical Oxygen Demand (BOD). Shortly after, a massive fish kill is observed. Which of the following best explains the molecular and physiological mechanism that accelerates the asphyxiation of these fish?
Options
- A.
The high BOD depletes dissolved oxygen, drastically reducing the pO2 gradient at the gills. The resulting tissue hypoxia induces lactic acidosis, causing a rightward shift of the O2-Hb dissociation curve (Bohr effect) and further impairing oxygen loading at the gills.
- B.
The high BOD increases the dissolved CO2 in the water, which diffuses into the fish and causes a leftward shift of the O2-Hb dissociation curve, preventing oxygen unloading at the systemic tissues.
- C.
The microbial activity responsible for high BOD releases excess H+ ions into the water, which actively transport into the fish's blood, causing a leftward shift of the dissociation curve and inhibiting the Bohr effect.
- D.
The severe hypoxia causes the fish to hyperventilate, leading to respiratory alkalosis. This decreases the blood H+ concentration, causing a rightward shift of the O2-Hb curve and failing to oxygenate the tissues.
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
Hemoglobin|CO2_partial_pressure|BOD_Biochemical_Oxygen_Demand
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the Bohr effect (right shift = good for tissue unloading) without realizing its detrimental impact at the respiratory surface (gills/lungs) when environmental pO2 is severely compromised.
The trap lies in bridging an ecological concept (BOD/Eutrophication) with a molecular physiology concept (Oxy-Hb curve shifts) and recognizing that a right shift during severe environmental hypoxia is a fatal positive feedback loop.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Breathing and Exchange of Gases - Class 11 |
| Concept | Oxygen-Hemoglobin Dissociation Curve |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |