Light. When an electron falls to a lower orbit it gives off energy as a photon. Spectral lines give evidence of electrons moving from one energy level to another within the atom.
Same genus is more closely related. The farther down the list Phylum-Class-Order-Family-Genus-Species you go, the more closely related are the species in that taxon.
Fat is used as a form of energy when the body really needs it. where as an enzyme is used to speed up a reaction in the body or might be needed to start a reaction in a body.
