QUESTION 1
According to the sliding-filament model of contraction, how does muscle contraction occur?
The myosin heads propel the actin myofilaments toward the center of the sarcomere; this pulls the Z disks closer tog
sarcomere and the entire muscle.
The actin heads propel the myosin filaments toward the center of the sarcomere; this pulls the Z disks closer together
sarcomere and the entire muscle.
The myosin heads propel the actin myofilaments toward the center of the sarcomere. This causes the myofilaments to
disks closer together to shorten the sarcomere and the entire muscle.
Both the actin and myosin myofilaments shorten, which shrinks the sarcomere and pulls the Z disks closer together. A
together, the muscle contracts.

According to the sliding-filament model of contraction, the muscle contraction occur due to the myosin heads propel the actin myofilaments toward the center of the sarcomere. This pulls the Z disks closer together, shortening  sarcomere and the entire muscle

Explanation:

In the muscle fiber there are two proteins that facilitate the process of contraction, myosin and actin. Myosin is thicker and more abundant than actin, and its interaction is responsible for the process of muscle contraction.

Both molecules, myosin and actin, form bonds -called cross bridges- where the myosin heads produce the mobilization of actin towards the center of the sarcomere. Z discs are associated with actin myofibrils, so they come close, and promote the shortening of the sarcomere.

This process requires the action of calcium ions, which depolarize the muscle cell and consume energy in the form of ATP.

It should be noted that the myosin and actin molecules do not change their length, but their action causes the muscle fibers to shorten during contraction.

Learn more:

Types of muscle contraction link

the endomembrane system i think