The definition of saprophytic bacteria (a way of life that absorbs nutrients from dead animals, plants or other organic substances to maintain their normal life. Many bacteria and fungi fall into this category. Microorganisms living in saprophytic way belong to chemotactic heterotrophic microorganisms if they are divided according to their required nitrogen and carbon sources. The definition of parasitism is that two creatures live together, one benefits and the other suffers, and the latter provides nutrients and living places for the former. The relationship between these creatures is called parasitism. The definition of heterotrophy is that inorganic substances cannot be directly synthesized into organic substances, but ready-made organic substances must be absorbed to maintain a nutritious lifestyle, which is called heterotrophy. Heterotrophication includes predation, parasitism and saprophy. Note that saprophytic bacteria are mainly a way of life of bacteria and fungi, absorbing nutrients from dead animals and plants. Parasitism means that two creatures live together and the host is alive. From the definition of heterotrophy, we can know that heterotrophy includes parasitism and saprophy, saprophy and parasitism are heterotrophy, but heterotrophy is not saprophy and parasitism.