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Question #45937

Difficulty: 8/10 | 🟢 Free

The Question

During strenuous exercise, skeletal muscles rely on anaerobic glycolysis, leading to muscular fatigue. Beyond the mere depletion of ATP, what is the precise molecular mechanism by which the primary byproduct of this metabolic pathway impairs the cross-bridge cycle at the sarcomere level?

Options

A.
Lactic acid lowers sarcoplasmic pH, which reduces the affinity of Troponin-C for $Ca^{2+}$ , thereby hindering the unmasking of active sites on F-actin.
B.
Pyruvic acid accumulation increases intracellular osmolarity, causing the sarcoplasmic reticulum to irreversibly sequester $Ca^{2+}$ ions.
C.
Lactic acid competitively binds to the ATPase site on the heavy meromyosin (HMM) head, preventing the hydrolysis of ATP required for the power stroke.
D.
The drop in pH denatures the voltage-gated $Ca^{2+}$ channels in the T-tubules, preventing the propagation of the motor end-plate potential.

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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

Lactic_Acid|pH_Fluctuations|Sarcoplasmic_Reticulum

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often rote-memorize the NCERT line 'accumulation of lactic acid causes fatigue' without understanding the underlying intracellular homeostasis and calcium dynamics.

This question bridges 'Respiration' and 'Locomotion and Movement' by testing the exact molecular bottleneck (Troponin-C affinity) caused by the pH drop, distinguishing it from ATP depletion or action potential failure.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Respiration in Plants - Class 11
Concept	Fermentation Limitations
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free