2. Metabolic types: Most acetic acid bacteria belong to facultative anaerobic; Mucor belongs to aerobic; Lactic acid bacteria are facultative anaerobic or anaerobic, and yeast is facultative anaerobic. All of them. They are heterotrophic microorganisms.

Prokaryote: A unicellular (or multicellular, such as Nostoc commune) organism that does not form nuclei or mitochondria. According to the data of molecular biology in 1970s, the nucleotide sequences of 16S rRNA of methanogenic bacteria, halophilic bacteria, acid-resistant and heat-resistant eumycetes and thermophilic plastids are different from those of common bacteria and eukaryotes.

In addition, the cell membrane structure, cell wall structure, coenzyme, metabolic pathway, translation mechanism of tRNA and rRNA of these organisms are different from those of ordinary bacteria.

Therefore, some people advocate that the above-mentioned organisms should be classified as "the third biological world" or archaea other than prokaryotes and eukaryotes.