Striated muscle fibers are found in......

Which of the following statements about the molecular arrangement of actin and myosin are correct?
$I.$ Each actin (thin filament) is made up of $2$ $F$ (filamentous) actins.
$II.$ $F$-actin is the polymer of $G$ (globular) actin.
$III.$ $2$ $F$-actins are twisted into a helix.
$IV.$ Two strands of tropomyosin (protein) lie in the grooves of $F$-actin.
The correct option is:

Who put forward the sliding filament theory?

Muscles are attached to bones by which of the following?

Where are calcium ions stored in muscle cells?

Draw the diagram of a sarcomere of skeletal muscle showing different regions.