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[A] : Upon stimulation of a muscle cell...

[A] : Upon stimulation of a muscle cell, cal- cium ions `(Ca^(++))` are released from the sar- coplasmic reticulum.
[R]: In reacting with a protein complex, `Ca^(++)` unmasks myosin binding sites on the ac-tin filaments.

A

If both A and R are true and R is the correct explanation of A

B

If both A and R are true but R is not the correct explanation of A

C

If A is true and R is false

D

If both A and R are false

Text Solution

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The correct Answer is:
B
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Assertion: on stimulation, a muscle cell releases calcium ions (Ca^(2+)) from sarcoplasmic reticulum. Reason: By reacting with a protien complex, Ca^(2+) uncover active sites on the actin filaments.

Muscle protein __binds Ca^(2+) that is released from the sarcoptasmic reticulum.

Go through the following statements During muscle contraction, the width of A-band remains constant while I-band shortens. During muscle contraction, the Ca^(2+) released from the SR bind to the troponin component of thin filament The process of muscle contraction is faster in smooth muscle as they have a well developed sarcoplasmic reticulum. The red muscle fibres have abundant mitochondria, low glycogen and poorly formed sarcoplasmic reticulum.

Read the following statements (i) In cardiac muscle fibres sacroplasmic reticulum is poorly formed (ii)B Blood supply is scanty in case of smooth muscle fibres (iii) Tropomyosin occurs in actin filaments in the form of complexes which are arranged over actin fibres and represent sites where myosin binds to actin. (iv) Salts of citrate and oxalates act as anticoagulants as they precipitate Ca^(2+) Select the correct statements

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