Yeast are simple fungi. Yeast refers to the unicellular phase of the life cycles of many different fungi, but it is used more commonly as a generic term for fungi that have only a unicellular phase. Yeast have simple nutritional needs. Unable to carry out photosynthesis, they require a reduced carbon source which can be as simple a compound as acetate. In addition, they also require a nitrogen source such as ammonium sulfate.
Yeasts can use a variety of organic nitrogen compounds, including urea and various amino acids.
The only other complex compound that they require is the vitamin, biotin. Of course, they also require a variety of salts and trace elements. A small bud emerges from the surface of the parent cell and enlarges until it is almost the size of the parent. While this is happening the chromosomes of the parent replicate. At mitosis, when the nucleus divides, one of the nuclei is transferred to the bud, and then the two cells separate.