Correct Option
The correct option is (c) 1 and 3 only.
Explanation
Yeast, specifically Saccharomyces cerevisiae (also known as brewer's yeast or baker's yeast), is a unicellular fungus widely utilized in biotechnology. Its primary industrial application relies on its ability to perform anaerobic respiration (fermentation), converting sugars into metabolic byproducts.
Statement-wise Analysis
- Statement 1 is Correct: In the baking industry, yeast is used as a leavening agent. During respiration (specifically alcoholic fermentation), yeast breaks down carbohydrates to produce carbon dioxide ($CO_2$) and ethanol. The carbon dioxide gas gets trapped in the dough, causing it to rise and creating a soft, porous texture in bread and pastries.
- Statement 2 is Incorrect: Yeast is not used to prevent fermentation; rather, it is the active agent used to facilitate fermentation. It is deliberately added to substrates like malted cereals and fruit juices to initiate the breakdown of sugars.
- Statement 3 is Correct: Yeast acts on natural sugars present in grains (such as barley, wheat, or rice) and fruit juices. Through metabolic action, it converts these sugars into ethanol (alcohol) and carbon dioxide. This process is the foundation of the brewing (beer) and wine-making industries.
Key Takeaway: Yeast is utilized in the industry for fermentation, a process that yields carbon dioxide (essential for the rising of dough in baking) and ethanol (essential for the production of alcoholic beverages).