Yeasts are single-celled, the most commonly used yeast is Saccharomyces cerevisiae, which was domesticated for wine, bread, and beer.
Yeast species can have either obligately aerobic or facultatively anaerobic physiology. There is no known obligately anaerobic yeast. In the absence of oxygen, fermentative yeasts produce their energy by converting sugars into carbon dioxide and ethanol (alcohol). In brewing, the ethanol is bottled, while in baking the carbon dioxide raises the bread, and the ethanol evaporates.
An example with glucose as the substrate is
C6H12O6 (glucose) →2C2H5OH + 2CO2
Yeast can reproduce asexually through budding or sexually through the formation of ascospores. During asexual reproduction, a new bud grows out of the parent yeast when the condition is right, then, after the bud reaches an adult size, it separates from the parent yeast. Under low nutrient conditions yeasts that are capable of sexual reproduction will form ascospores. Yeasts that are not capable of going through the full sexual cycle are classified in the genus Candida.
A common medium used for the cultivation of yeasts is called potato dextrose agar (PDA) or potato dextrose broth. Potato extract is made by autoclaving (i.e. pressure-cooking) cut-up potatoes with water for 5 to 10 minutes and then decanting off the broth. Dextrose (glucose) is then added (10 g/L) and the medium is sterilized by autoclaving.
So, adding o2 and bakingpowder or potato dextrose the yeast will reproduce itself. If you add o2, without any nutrients you will end up with less yeast then to begin with.
*Weee* my first post, I hope my bad English isnt any problem
Greetings from Norway !