Read the given passage and answer the following question :
Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel. Microbes produce different types of gaseous end-products during growth and metabolism. The type of the gas produced depends upon the microbes and the organic substrates they utilise. In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO2. 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. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas. The technology of biogas production was developed in India mainly due to the efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).
What role do methanogenic bacteria play in the rumen of cattle?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → They help in the breakdown of cellulose.
The passage states that “In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.”
Cattle eat grass and fodder that are rich in cellulose. The rumen, a part of the stomach of cattle, has no oxygen, and methanogens grow there on this cellulosic material. By breaking down cellulose, they help the animal get food value from it. This is also why cattle dung is rich in methanogens and is used to make biogas.
Option (1) They produce oxygen. — Incorrect. Methanogens grow without oxygen and give off methane, carbon dioxide and hydrogen. They do not produce oxygen.
Option (2) They help in the breakdown of cellulose. — Correct. Their role in the rumen is the breakdown of cellulose, which supports the nutrition of cattle.
Option (3) They increase the pH of the rumen. — Incorrect. The passage gives no role for them in changing the pH of the rumen. Their role is the breakdown of cellulose.
Option (4) They produce enzymes for protein digestion. — Incorrect. Cellulose is a carbohydrate, not a protein. The passage links methanogens with cellulose, not with protein digestion.