Biology Report: Plants:
By Sterling Haws
1. What Is Yeast?
Yeast is simple fungus. The term "yeast" refers more to a life-style than to a phylogenetic classification. 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. The organisms most often called "yeast" such as common baking or brewing yeast are strains of the species Saccharomyces cerevisiae. As fungi, they are classified as ascomycetes, a group which also includes a number of other popular genetic organisms, such as Neurospora and Sordaria. Except when we refer to other species of yeast by name, we will use the term "yeast" to refer to Saccharomyces cerevisiae.
Yeast has 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.
Ascomycetes, such as baker's yeast, are popular for genetics research because the ascospores they produce in each ascus are the products of meiosis. When yeast is nutritionally stressed, for example by deprivation of either a carbon source or a nitrogen source, diploid yeast will sporulate. The diploid nucleus goes through meiosis, producing four haploid nuclei, which are then incorporated into four stress-resistant ascospores, encapsulated in the ascus. This packaging of the four meiotic products makes genetic analysis particularly simple.
2. What Are Yeast Good For?
People have used yeast, undoubtedly one of the earliest domesticated organisms, for...