1. Yeast is produced by fermenting yeast species, cultivating a large number of yeast bodies and drying them. Yeast is a commonly used eukaryotic receptor cell in gene cloning experiments, and it is as convenient to culture yeast as Escherichia coli.

2. Yeast is a unicellular fungus, not a unit of phylogenetic classification. A tiny single-celled microorganism invisible to the naked eye can ferment sugar into alcohol and carbon dioxide, which are distributed throughout nature. It is a typical heterotrophic and facultative anaerobic microorganism, which can survive under aerobic and anaerobic conditions and is a natural starter.