Read the following passage carefully and answer the given questions.
We use microbes and microbially derived products almost every day. Bacteria called lactic acid bacteria (LAB) grow in milk to convert it into curd. The dough, which is used to make bread, is fermented by yeast called Saccharomyces cerevisiae. Microbes are used to produce industrial products like lactic acid, acetic acid and alcohol, which are used in a variety of processes in the industry. However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with \( CO_2 \) and \( H_2 \). These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. Examples of acid producers are Aspergillus niger (a fungus) of citric acid. You are familiar with the commonly used antibiotic Penicillin. Do you know that Penicillin was the first antibiotic to be discovered, and it was a chance discovery? Statins produced by the yeast Monascus purpureus have been commercialised as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.
Which of the following statements is not true with respect to microbes?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The puffed up appearance of dough is due to the production of CO gas by bacteria.
Option (1) Wine is produced by fermentation without distillation. — A true statement. Wine and beer are made without distillation. Whisky, brandy and rum are made by distilling the fermented broth.
Option (2) Microbes can also be used to kill harmful pests, a process called as biocontrol. — A true statement. Biocontrol uses living things, such as Bacillus thuringiensis against caterpillars, in place of chemical pesticides.
Option (3) The puffed up appearance of dough is due to the production of CO gas by bacteria. — Not a true statement. Dough puffs up because of carbon dioxide (CO2), not carbon monoxide (CO). The bacteria that ferment idli and dosa dough, and the yeast in bread dough, give out CO2. One missing ‘2’ turns a true line into a false one. Check every symbol, not just the words.
Option (4) Methanogens are anaerobic bacteria. — A true statement. Methanogens such as Methanobacterium grow without oxygen on cellulose and give out methane.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Microbes in Household Products – “… The dough, which is used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas.”
Fermented Beverages – “… Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth.”
Microbes as Biocontrol Agents – “Biocontrol refers to the use of biological methods for controlling plant diseases and pests.”
Microbes in Production of Biogas – “… However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium.”