[Biology Class Notes] on Yeast Fungus Pdf for Exam

Yeasts are single-celled organisms of the kingdom, Fungi. Yeasts constitute about 1% of the fungi species and currently, around 1500 species of yeasts are known. Yeast fungus is eukaryotic in nature which means they have a nucleus enclosed within a nuclear membrane. The most common question asked about yeasts is, is yeast a fungus? The answer is yes. Yeasts are a type of fungi.

Yeast is a very useful microorganism and is used to cause fermentation. Yeast grows by fermentation, feeding upon sugars. During fermentation, yeast converts glucose into ethanol and carbon dioxide and is therefore used in beer and wine manufacturing, and baking. In beer and wine manufacturing, ethanol is the desired product and carbon dioxide is useful in baking. 

 

What Type of Organism is Yeast?

Yeasts are single-celled organisms that evolved from multicellular organisms. The size of yeast mainly depends upon its environment. Typically yeasts are 3-4min in diameter but can grow up to 40m.

As the cell organization in yeast resembles that of higher organisms. Due to a high degree of similarity between yeast and human genes, yeast has become a popular model system for the study of human diseases. Yeast is increasingly becoming the organism of choice in the study of drug targeting and mode of action. 

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Yeast Reproduction

Yeast fungus can reproduce both sexually and asexually. The most common form of yeast reproduction is by the method of budding. It is an asexual reproduction process in which a small bud is formed on the parent cell. This bud is called a bleb or a daughter cell. Further, the nucleus of the parent cell splits into two and migrates towards the daughter cell. The growth of the bud continues and then is separated from its parent cell forming a new cell. Yeasts can also reproduce by the method of fission in which two identical daughter cells are formed. 

Under conditions such as nutrient starvation, the haploid cells can’t survive. Under these high-stress conditions, the diploid cells undergo sporulation and perform meiosis, which is a mode of sexual reproduction to produce haploid cells. The haploid cells then can further conjugate to form diploid cells. However, this mode of yeast reproduction occurs only when the nutrients are limited as in a nutrient abundance situation, yeast cells reproduce using asexual modes of reproduction.

 

Characteristics of Yeast

The various characteristics of Yeast are as follows:

Yeasts are single-celled microorganisms and are members of the Kingdom Fungi. Yeasts are then further classified based on the characteristics of their cell, ascospore and cellular physiology.

Even though yeasts are single-celled, their cellular organization resembles that of higher organisms including humans. Their genetic content is contained within their nucleus and are therefore considered eukaryotic in nature. 

The natural habitat of yeast is widely dispersed in nature. Yeasts are commonly found on plant leaves, flowers, fruits and soil. They are also present on the skin surface and in the intestinal tract of warm-blooded animals. The common yeast infection such as vaginal yeast infections, diaper rash, and thrush of the mouth and throat are caused by Candida albicans.

Yeast grows by fermentation by converting glucose into carbon dioxide and ethanol. Fermentation is an anaerobic process as it generally occurs in the absence of oxygen. Yeast cells prefer to grow by fermentation when they are grown in rich carbon sources and even in the presence of oxygen due to the crabtree effect. 

Yeasts normally reproduce through asexual modes of reproduction such as budding and fission. But under nutrient starvation, can undergo sexual mode of reproduction as well.

Yeasts are used to ferment glucose into ethanol and carbon dioxide and find their use in the production of alcoholic beverages, bread, lubricants, detergents, food additives, enzymes, chemicals etc.

 

Conclusion

Yeasts are single-celled microorganisms that are commonly used for a variety of purposes. Yeasts are a type of fungus and belong to the kingdom fungi. The most common use of yeast is for the fermentation of sugars in the production of alcoholic beverages and bread. Also, yeasts are being used in the study of human diseases and drugs research.