Question

when a myosin head engages with the active site on the actin, this is known as a -
sarcomere
cross-bridge
z-line
m-line
what provides the energy for the myosin head to move?
atp
calcium
myosin
sarcomeres
when your muscles are worked strenuously and the oxygen supply is exhausted, the muscle cells will begin to use the process of -
aerobic respiration
anaerobic respiration

Explanation:

First Question (When a myosin head engages...):

To solve this, we recall muscle contraction terminology:

• Sarcomere: Basic contractile unit of muscle, not the engagement.
• Cross - bridge: Defined as the myosin head binding to actin's active site.
• Z - line: Defines sarcomere boundaries, not related to myosin - actin binding.
• M - line: In the middle of sarcomere, for myosin filament attachment, not binding.

So the correct option is the one related to myosin - actin binding.

For muscle contraction energy:

• ATP: Hydrolysis of ATP provides energy for myosin head movement.
• Calcium: Triggers contraction by exposing actin sites, not energy source.
• Myosin: A protein, not an energy source.
• Sarcomeres: Contractile units, not energy providers.

So the energy source for myosin head movement is ATP.

For muscle respiration types:

• Aerobic respiration: Requires oxygen. When oxygen is exhausted, muscles switch.
• Anaerobic respiration: Occurs without oxygen, used when oxygen is low (strenuous exercise, oxygen exhausted).

So when oxygen is exhausted, muscle cells use anaerobic respiration.

Answer:

B. cross - bridge

Second Question (What provides the energy...):