Saccharomyces cerevisiae, the budding yeast, is the common yeast used in baking ("baker's yeast") and brewing ("brewer's yeast"). (It is only distantly related to another unicellular fungus, Schizosaccharomyces pombe, the fission yeast.)
It is a popular "model" organism in the laboratory because it is a unicellular eukaryote whose cellular activities are much more like ours than those of a bacterium like E. coli. But like E. coli,