Heterotrophs cannot themselves synthesize the whole set of organic substances they need for life. Therefore, they absorb the compounds they need from the environment. Then they build their own proteins, lipids, carbohydrates from the obtained organic substances. Heterotrophs include animals, fungi, and many bacteria. In addition, plant cells incapable of photosynthesis (for example, root cells) also feed heterotrophically, as they receive organic matter from other organs of the green plant.
There are also organisms that can use both methods of nutrition. This, for example, is green euglena, which botanists attribute to unicellular green algae, and zoologists to flagellate protozoa. Both of them are right, because in the light this organism is a phototroph, and in the dark – a heterotroph. Some plants, such as the venus flytrap or sundew, are able to replenish the lack of nitrogen by catching and digesting insects, other plants have partially switched to a parasitic lifestyle and, in addition to photosynthesis, can receive organic substances from the host through special modifications of the roots (mistletoe, Peter cross, dodger )
Organic substances obtained by auto- or heterotrophic methods cannot directly provide energy to the processes occurring in the cell. Due to the energy of the chemical bonds of these substances, the universal source of energy, universal for all living beings, is necessarily synthesized first – ATP