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Question #45918
The Question
During a strenuous sprint, white skeletal muscle fibers rapidly fatigue as oxygen becomes limited and fails to act as the terminal electron acceptor in mitochondria. Which of the following best describes the direct molecular mechanism by which this metabolic shift halts the cross-bridge cycle?
Options
- A.
Accumulation of lactic acid lowers sarcoplasmic pH, which decreases the affinity of Troponin for Ca²⁺ ions.
- B.
Exhaustion of ATP directly prevents the formation of the cross-bridge by inhibiting the attachment of the myosin head to F-actin.
- C.
Lactic acid competitively binds to the active sites on F-actin, physically blocking the myosin head from attaching.
- D.
Failure of oxidative phosphorylation stops the active efflux of Ca²⁺ from the sarcoplasmic reticulum into the sarcoplasm.
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
Terminal Electron Acceptor|Red vs. White Muscle Fibers|Cross-bridge Cycling Energy
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the NCERT fact that 'lactic acid accumulation causes muscle fatigue' but fail to bridge the biochemical cause (acidosis/low pH) to the mechanical failure (Troponin-Calcium affinity).
Additionally, Option B exploits a highly common misconception regarding the role of ATP in muscle contraction; students frequently assume ATP is needed to form the cross-bridge, whereas ATP hydrolysis cocks the myosin head, and binding of a new ATP molecule is required to break the cross-bridge.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Respiration in Plants - Class 11 |
| Concept | Terminal Electron Acceptor |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |