Provide the full names for the following abbreviations:
$(1)$ $HMM$
$(2)$ $ATP$

Which one of the following pairs of chemical substances is correctly categorized?

Striated muscles contract by

During muscle contraction,$(P)$ get reduced whereas $(Q)$ retain the length. Here $P$ and $Q$ are $-$

Select the correct statement with reference to muscle structure.
$I.$ Each myosin is a polymerized protein.
$II.$ Many meromyosin constitute one thick filament (myosin).
$III.$ Each meromyosin's tail is called heavy meromyosin $(HMM)$ and head is called light meromyosin $(LMM)$.
$IV.$ The globular head is an active $ATPase$ enzyme and has binding sites for $ATP$ and active sites for actin.
Choose the option with correct statements.

$A$ sarcomere consists of