Plants are autotrophs and use light energy. Carbon dioxide and water photosynthesize under light to produce organic sugar and oxygen. In plants, sugar is glycolytic to form intermediate products, and then oil is synthesized. Oil is an efficient energy storage substance, which is usually contained in seeds and used for seed germination.

For cattle, sheep and other animals, animals can only make use of the ready-made organic matter in heterotrophs. The grass eaten by cattle and sheep is mainly cellulose, which is a high polysaccharide. In herbivores, it is decomposed by bacteria to produce absorbable sugars, which are converted into intermediate products through glycolysis and then synthesized into oil. Oils in animals are mainly used for energy storage and cold resistance.