Heterotrophic type: People and animals can't do photosynthesis like green plants, nor can they do chemical synthesis like nitrifying bacteria. They can only rely on the ready-made organic matter in the external environment to maintain their own life activities. This metabolic type belongs to heterotrophic type. In addition, the metabolic types of fungi and most saprophytic or parasitic bacteria are also heterotrophic. In a word, in the process of assimilation, organisms convert ready-made organic matter absorbed from the external environment into their own components and store energy. This metabolic type is called heterotrophy.

Parastisu: that is, two creatures live together, one benefits and the other suffers, and the latter provides nutrients and shelter for the former. This relationship between organisms is called parasitism.