Answer:
Hybrids are the offspring of two species. A mule is the hybrid offspring of a female horse and male donkey. Because mules are sterile, they are not classified as a distinct species. The biological species concept connects the idea of a species to the process of evolution.
<span>Norepinephrine uses the Second
Messenger System, which means, cells signal to each other what molecules have
been released that will trigger a physiological reaction. </span>
<span>
This phenomenon is activated after the ligand (ion or molecule) is bonded to its receptor
(protein molecule), creating a variation that causes a chain-reaction, that will
finally activate the Second Messenger. The latter will activate intercellular
molecules that will be able to control the cell’s activity. </span>
