Nutrition involves acquiring energy and materials, carbon being the most fundamental material required by living organisms. On the basic of energy source organisms are classified as photosynthetic (phototrophic), and chemosynthetic (chemotrophic).hemosynthetic requires chemical energy, while photosynthetic requires light energy. On the basis of carbon source, organisms are classified as autotrophic or heterotrophic. Autotrophs depend on inorganic source of carbon (and may be chemo autotrophic or photo autotrophic), While heterotrophs depend on organic source of carbon (as in parasitism, saprophytism etc.).