Yeast fungus, more commonly known simply as “yeast” is a member of a larger family of eukaryotic organisms that includes microorganisms like molds and mushrooms. Scientifically this type of group of life forms is known as a kingdom. The broad group of the Fungi Kingdom includes multicellular organisms in addition to the simple single-celled yeast organism. Members of this kingdom are neither plant nor animal. They can be distinguished from plants by their inability to create their own food through the photosynthesis process. .
Although some of the more complex members of this kingdom may have a plantlike appearance they lack the green color that identifies true plants and must obtain nutrients by absorbing them from their environment. They can be differentiated from members of the animal kingdom by their cell walls; a trait that they share with plants but that does not occur in the Animal Kingdom. Because they share traits in common with both the Plant Kingdom and the Animal Kingdom many scientists believe they diverged from both of these around a billion years ago. .
Fungi not only possess their own Kingdom they also have their own field of study called Mycology. Mycology is devoted to the broad study of all members of the Fungi Kingdom. The purpose of this paper is to review and summarize the existing information derived from the branch of Mycology that is solely devoted to the study of the yeast fungus. Furthermore, it will more specifically set out the life cycle of yeast.
Yeast is a simple fungus, and the term yeast refers more to the life cycle than it does to a phylogenetic classification. Therefore, to understand what yeast is it is necessary to understand how it lives; and what makes that uniquely distinct from other members of the Fungi Kingdom. Other funguses often have a yeast phase in which they are single cell that reproduces itself until it forms a larger complex structure. . For the purpose of this paper the term yeast will only refer to the simple unicellular organism that never matures past that point to form multi-celled structures the way mushrooms and larger, more complex members of the Fungi Kingdom do.
Yeast appears to be closely related to algae, but it lacks the photosynthetic capability that algae has. Instead of using photo synthesis yeast secretes enzymes that break down complex carbon compounds from plant and animal cells and converts them into sugars. There is a group of yeast strains that can survive and multiply using animals, including humans as hosts. Many of these are benign but some can cause discomfort and lead to complications.
Other strains of yeast are decidedly beneficial as agents used in food preparation. They have been used in brewing and baking for millennia. In addition to providing leavening for bread and producing alcohol in the brewing process they are also a high protein food source in their own right. (Kansas State University, 2013)
Yeast grows naturally in a wide variety of locations but prefer moist, slightly acidic environments. In nature they can be found anywhere from the dry leaves on the forest floor to the body cavities of animals. One of the easiest places to find naturally occurring yeast is on the outside skin of grapes where it appears as a light frost. That yeast is of the same species as is used in the formal brewing of wine and beer. (Kansas State University, 2013).
One of the characteristics of most yeasts is that they reproduce by budding. In this process a small bud forms on the outside of the parent cell. This bud enlarges until it is almost as large as the parent cell itself. When it obtains optimal growth the nucleus of the parent cell divides and one of the resulting nuclei transits over to the bud. After this transference the bud separates from the parent cell. Although this is normally the case, it is not always so. There is one member of the yeast group known as Schizosaccharomyces pombe that grows as a cylindrical cell until it is ready to reproduce. When the time arrives for these cells to reproduce they elongate and split in half by binary fission. This is more similar to a bacteria than to most other strains of yeast.. Yeast can also reproduce using sexual spore production as well as the more common budding. Spores created by this method during a time of environmental stress can then sometimes remain dormant until conditions improve. .
While the majority of the reproductive energy and processes of yeast is devoted by the simple budding activity that is not the only method used by yeast to reproduce. It can also reproduce using sexual reproduction. This is a more frequent method of reproduction in environmentally stressful situations. Sexual reproduction in yeast involves alternation between haploid and diploid phases during which time the cell nucleus divides twice and produces a four haploid nuclei. The resulting haploid then has a new combination of genetic instruction that permits he yeast cell to evolve.
WORKS CITED
Kansas State University. "Baker's Yeast and Its Life Cycle." 2013. Kansas State University. <http://www.phys.ksu.edu/gene/a1.html>.
Medical News Today. "Fungus." 2013. Medical News Today. <http://www.medicalnewstoday.com/articles/158134.php>.
The Gale Encclopedia of Science. "Yeast." 2013. Encyclopedia.Com. <http://science.jrank.org/pages/7438/Yeast-Life-cycle.html>.
