What is a sarcomere?

The functional unit of the contractile system in the striped muscle is

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:

Which mineral element is essential for muscle contraction?

Identify the muscle which represents the following characteristics and choose the correct option accordingly.
$I.$ Transportation of food through the digestive tract.
$II.$ Transportation of gametes through the genital tract.

Latissimus dorsi muscles are