Heterotrophy
Heterotrophic organisms are contrasted with autotrophic life forms in that their carbon needs derive from organic nutrients which they take up from the growth environment.  These organic nutrients are also used as the source of reducing equivalents for reductive biosyntheses and, in addition, their oxidation provides the free energy needed to support a chemiosmotic mechanism which powers ATP synthesis.  Animals are heterotrophs, and most microorganisms are hetertrophs.