Answer: Serotonin
Explanation:
Serotonin is an hormone, derived from the amino acid, tryptothan. It is involved in vasodilation, sleep regulation, mood changes, capillary permeability, and causes contraction of smooth muscles like that of the stomach to signal hunger.
The correct answers are:
Tissue level- similar cells work together to accomplish a goal.
Examples of tissue are muscles, skin, bone, and brain (nervous tissue).
A sponge is an example of an organism that is only organized to the cellular level.
