Autotrophic organisms: organisms that can make their own organic food, such as green plants, can make organic matter through photosynthesis, and some bacteria that synthesize organic matter by light energy-nitrifying bacteria.

Heterotrophs: Organisms that can't make their own organic nutrients but live on ready-made organic nutrients, such as all animals and microorganisms that live saprophytically and parasitically.

The fundamental difference between autotrophs and heterotrophs lies in whether inorganic substances can synthesize organic heterotrophs by themselves. Most microorganisms, most animals and other heterotrophs can act as decomposers and consumers in the ecosystem.