Each myofibril of a muscle contains:

Which part of a muscle cell is the storehouse of calcium ions?

In a $A$ state,the edge of thin filaments on either side of thick filaments $B$ overlap the free ends of $C$ filaments leaving the central part of thick filaments. This central part of thick filament,not overlapped by thin filaments is called $D$ zone.
Choose the correct options to fill the gaps $A, B, C$ and $D$,so as to complete the given $NCERT$ statement.

Muscle contains a red-coloured oxygen-containing pigment called

Discuss the role of $Ca^{2+}$ ions in muscle contraction. Draw neat sketches to illustrate your answer.

Define the following terms:
$(1)$ Sarcomere
$(2)$ Acromion process