]6. which neurotransmitter stimulates the beginning of muscle contraction and movement?
a. acetylcholine
b. dopamine
c. epinephrine
d. serotonin

The correct answer option is A. Acetylcholine.

Explanation:

Acetylcholine is that neurotransmitter which stimulates the beginning of the muscle contraction and movement its movement.

The muscle tissues are composed of cells known as the muscle fibers. The nerve terminals present at the neuro muscular points releases a chemical message which is actually released by the motor neuron.

This  neurotransmitter called acetylcholine binds itself to receptors on the outside of the muscle fiber which then causes muscle contraction and movement.

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.