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Question #47650
The Question
According to NCERT, the respiratory pathway is classically described as an 'amphibolic pathway' because it facilitates both catabolism and anabolism, providing carbon skeletons for biosynthesis. If a culture of yeast (Saccharomyces cerevisiae) is shifted from aerobic respiration to strictly anaerobic alcoholic fermentation, the amphibolic utility of its respiratory pathway is severely compromised. Which of the following is the primary biochemical reason for this?
Options
- A.
The accumulation of cytosolic NADH directly inhibits the beta-oxidation of fatty acids, preventing their entry into the pathway as Acetyl CoA.
- B.
Pyruvate is diverted to form ethanol and CO2, halting the TCA cycle and preventing the withdrawal of intermediates like alpha-ketoglutarate for amino acid synthesis.
- C.
The lack of oxygen forces the TCA cycle to operate in reverse, consuming fatty acids and amino acids to generate ATP.
- D.
Fermentation enzymes competitively inhibit the withdrawal of Acetyl CoA, forcing it to be exclusively used for ATP generation rather than fatty acid synthesis.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Acetyl_CoA|Ethanol|Alcoholic_Beverage_Fermentation_Source
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize 'respiration is an amphibolic pathway' as a static, absolute fact.
The trap lies in failing to recognize that this amphibolic nature is highly dependent on aerobic conditions and an active TCA cycle.
By shifting to fermentation, the pathway becomes almost exclusively catabolic (glycolysis) to survive, starving the mitochondrial matrix of Acetyl CoA and halting the supply of biosynthetic precursors.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Respiration in Plants - Class 11 |
| Concept | Amphibolic Pathway |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |