In which of the following,growth is possible through increase in volume?

Which of the following statements is correct regarding muscle contraction?

Select the correct option for the following statements:
$(i)$ The most important respiratory organ in frogs is the skin / lungs.
(ii) Skeletal muscle / Cardiac muscle exhibits rhythmic contraction.

$A : Ca^{2+}$ plays an important role in muscle contraction.
$R : Ca^{2+}$ combines with the troponin chain,displacing tropomyosin and allowing the myosin head to combine with actin to form an actomyosin complex.

The membrane sarcolemma is found over

Which one of the following takes place in a myofibril when skeletal muscle contracts?
$A$-band (Dark band) | $I$-band (Light band) | $H$-zone