Read the passage and answer the following questions:
Yeasts, such as Saccharomyces cerevisiae, have been used for centuries to produce alcoholic beverages like wine, beer, whisky, brandy, and rum. These beverages are made through the fermentation of malted cereals and fruit juices by yeast, specifically brewer's yeast. During fermentation, yeast undergoes metabolic reactions that result in the production of ethanol, the primary alcohol in alcoholic beverages. Different types of alcoholic drinks are obtained based on the raw materials used and the processing methods employed. Wine and beer are produced without distillation, while whisky, brandy, and rum are produced by distilling the fermented mixture. On the other hand, antibiotics, which are chemical substances produced by certain microbes, are considered one of the significant discoveries of the twentieth century. They have greatly contributed to the well-being of human society. Antibiotics are capable of killing or inhibiting the growth of disease-causing microbes, thereby having a positive impact on human health.
Given below are two statements:
Statement I: The yeast Saccharomyces cerevisiae used for bread-making is the same yeast that is used to ferment malted cereals and fruit juices.
Statement II: Saccharomyces cerevisiae is used for the commercial production of acetic acid.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is true but Statement II is false
The yeast Saccharomyces cerevisiae has many uses. It ferments bread dough (baker’s yeast), it ferments malted cereals and fruit juices to make drinks (brewer’s yeast), and it is used to produce ethanol on a commercial scale. Organic acids such as acetic acid come from other microbes.
Statement I: The yeast Saccharomyces cerevisiae used for bread-making is the same yeast that is used to ferment malted cereals and fruit juices. — True. NCERT says that the same yeast used for bread-making, called brewer’s yeast here, ferments malted cereals and fruit juices to produce ethanol.
Statement II: Saccharomyces cerevisiae is used for the commercial production of acetic acid. — False. Yeast is used for the commercial production of ethanol. Acetic acid is produced by the bacterium Acetobacter aceti.
NCERT Extract:
Fermented Beverages – “Microbes especially yeasts have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum. For this purpose the same yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol.”
Chemicals, Enzymes and other Bioactive Molecules – “… Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid. Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.”