Read the Passage carefully and answer the questions.
Microbes in human welfare
Microbes are a very important component of life on earth. We use microbes and microbially derived products almost every day, like LAB to make curd, yeast to make bread, adding flavor and texture to cheese, producing antibiotics etc. The addition of LAB, improves the milk quality by increasing vit. B12. Cheese is one of the oldest food items in which microbes are used. For example, large holes in Swiss cheese are due to CO2 produced by the bacterium Propionibacterium sharmanii. The BOD test measures the rate of uptake of oxygen by microorganisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, the more is its polluting potential. In anaerobic sludge digesters, bacteria produce a mixture of gases like methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as a source of energy. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. You have studied about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as a nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter).
Which statement is true about LAB?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Addition of LAB in milk improves the nutritional quality by increasing vitamin B12.
Option (1) Inoculum containing LAB produces bases which coagulate and convert milk into curd. — Incorrect. LAB stands for lactic acid bacteria, and the name tells what they make. They produce acids, not bases. The acids coagulate and partly digest the milk proteins, and the milk sets into curd.
Option (2) Addition of LAB in milk improves the nutritional quality by increasing vitamin B12. — Correct. A little curd added to milk as a starter carries millions of LAB. They multiply and turn the milk into curd. While doing so they raise its vitamin B12, so curd is more nutritious than milk.
Option (3) Addition of LAB in milk improves the nutritional quality by increasing vitamin D. — Incorrect. The vitamin is wrong. LAB increase vitamin B12, not vitamin D. Our skin makes vitamin D in sunlight.
Option (4) LAB cause diseases and are very harmful to human. — Incorrect. LAB are useful microbes. In our stomach they even check the growth of disease-causing microbes.
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.