Biology Support & Movement ETEA 2023
PMDC Verified Question 39 of 75
According to sliding filament hypothesis, the release of ____ ions from the sarcoplasmic reticulum causes the reorientation of certain components in thin filament, permitting them to bind with extensions from the thick myosin filaments:
A
Sodium
B
Calcium
C
Magnesium
D
Potassium
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Calcium
Concept:

Excitation-contraction chemical triggers.

Formula:

N/A (Conceptual)

Solution:

  • The sarcoplasmic reticulum is a specialized organelle designed to aggressively pump and store large quantities of Calcium ions (Ca\(^{2+}\)).


  • When an action potential arrives, gated channels open, flooding the sarcoplasm with Calcium.


  • This Calcium physically binds to troponin, causing a massive structural shift that moves tropomyosin out of the way, exposing actin to myosin.


Why other options are incorrect:

Sodium and Potassium are strictly responsible for conducting the electrical action potential along the membrane, but they do not interact directly with the internal contractile proteins.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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