* * * Life is a phenomenon in which two creatures or one of them can't live independently but live together, or one lives in the other, and each can gain certain benefits. It is a concept of mutual benefit between two creatures, and strangeness refers to the nutritional model of one creature. For example, termites and flagellates are mutually beneficial, but termites are xenobiotics. The relationship between people and Escherichia coli in the stomach is * * *, and people are obviously stunted. Autogenesis refers to a way of life that does not depend on entering other organisms, as opposed to mutual growth. Autotrophic means that only one person can synthesize nutrients. Example: Compared with * * * nitrogen-fixing bacteria, autotrophic nitrogen-fixing bacteria refer to nitrogen-fixing bacteria that do not need to enter organisms for nitrogen fixation. In middle school, except cyanobacteria, all nitrogen-fixing bacteria are heterotrophic, so autotrophic nitrogen-fixing bacteria are heterotrophic, and autotrophic does not mean autotrophic.