biology : class12 Biogas Generation : Food Processing, Industrial Production, Sewage Treatment, Energy Production : Microbes in Human Welfare MCQ Questions and Answers
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Biogas Generation
MCQ questions and answers.
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MCQ Questions
1. Which microbial group is primarily responsible for the final conversion of organic acids and hydrogen into methane during biogas generation?
A.
Lactic acid bacteria
B.
Methanogenic archaea
C.
Nitrifying bacteria
D.
Sulphur-oxidising bacteria
Correct Answer:
Methanogenic archaea
Explanation:
Methanogens are anaerobic microorganisms that produce methane by acting on substrates such as hydrogen, carbon dioxide, and organic acids during the final stage of biogas formation.
2. Why must the digester of a biogas plant remain substantially anaerobic for efficient gas production?
A.
Methanogens require oxygen to oxidise methane
B.
Oxygen inhibits or kills the anaerobic methanogens responsible for methane formation
C.
Oxygen converts all organic matter directly into nitrogen gas
D.
Oxygen prevents the formation of carbon dioxide by fermentative microbes
Correct Answer:
Oxygen inhibits or kills the anaerobic methanogens responsible for methane formation
Explanation:
Biogas generation depends on methanogens, which are anaerobic organisms. The presence of oxygen disrupts their activity and therefore reduces methane production.
3. In a conventional rural biogas plant, which sequence most accurately represents the biological processing of cattle dung?
A.
Methane oxidation, nitrification, and oxygenation
B.
Hydrolysis and fermentation, followed by conversion of products into methane
C.
Photosynthesis, carbon fixation, and aerobic respiration
D.
Sulphur reduction, nitrogen fixation, and methane oxidation
Correct Answer:
Hydrolysis and fermentation, followed by conversion of products into methane
Explanation:
Complex organic matter in dung is first broken down and fermented by anaerobic microbes. Methanogens then convert suitable products, including organic acids and hydrogen with carbon dioxide, into methane-rich biogas.
4. Which property of the residual slurry from a biogas plant makes it useful as manure?
A.
It is enriched with stabilized, mineralisable nutrients after anaerobic digestion
B.
It contains only methane-producing archaea and no nutrients
C.
It consists entirely of undecomposed cellulose and lignin
D.
It has been sterilized and therefore cannot undergo nutrient cycling
Correct Answer:
It is enriched with stabilized, mineralisable nutrients after anaerobic digestion
Explanation:
The digested slurry retains nutrients in forms useful for agriculture and can be applied as manure, while much of the readily decomposable organic matter has already been processed.
5. A sudden fall in methane output occurs after acidic organic waste is added rapidly to a digester. Which explanation is most appropriate?
A.
The acidic load suppresses methanogenic activity and disturbs the digester balance
B.
The acid immediately converts methane into oxygen
C.
The acid stimulates aerobic microbes to produce more methane
D.
The acid removes all carbon dioxide required by fermentative bacteria
Correct Answer:
The acidic load suppresses methanogenic activity and disturbs the digester balance
Explanation:
Methanogens are sensitive to unsuitable pH conditions. Excessive acid formation can lower the digester pH and inhibit methane-producing activity.
6. Which combination best identifies the major combustible constituent and the principal non-combustible diluent of biogas?
A.
Methane and carbon dioxide
B.
Oxygen and nitrogen
C.
Hydrogen and oxygen
D.
Nitrogen and hydrogen sulphide
Correct Answer:
Methane and carbon dioxide
Explanation:
Biogas is primarily a mixture of methane and carbon dioxide. Methane is the major combustible gas responsible for the fuel value of biogas.
7. Why is cattle dung particularly suitable as a feedstock for rural biogas production?
A.
It supplies biodegradable organic matter and naturally associated anaerobic microbes
B.
It contains large quantities of oxygen that support methanogens
C.
It is composed only of inorganic salts that release methane spontaneously
D.
It prevents all fermentation and directly releases pure methane
Correct Answer:
It supplies biodegradable organic matter and naturally associated anaerobic microbes
Explanation:
Cattle dung provides both organic substrates for microbial degradation and microorganisms that participate in anaerobic digestion, making it a practical feedstock for gobar-gas plants.
8. If methanogens are selectively inhibited in an operating digester while fermentative bacteria remain active, which immediate change is most likely?
A.
Methane production decreases while acidic intermediates accumulate
B.
Methane production increases because fermentation becomes aerobic
C.
Oxygen production replaces methane production
D.
All organic matter is converted directly into nitrate
Correct Answer:
Methane production decreases while acidic intermediates accumulate
Explanation:
Fermentative microbes can continue producing organic acids and other intermediates, but inhibition of methanogens prevents their efficient conversion into methane.
9. Which operational condition would most directly favour sustained methane generation in a biogas digester?
A.
Continuous exposure to atmospheric oxygen
B.
Stable anaerobic conditions with a suitable temperature and pH
C.
Repeated removal of all microbial biomass after feeding
D.
Strongly acidic conditions maintained throughout digestion
Correct Answer:
Stable anaerobic conditions with a suitable temperature and pH
Explanation:
Methanogens function efficiently when oxygen is excluded and the digester maintains conditions, especially temperature and pH, that support anaerobic microbial activity.
10. A biogas plant produces less fuel when its feedstock contains a high proportion of material that is difficult for anaerobic microbes to degrade. What is the most direct reason?
A.
Less biodegradable substrate is available for conversion into methane
B.
Refractory material supplies excess oxygen to methanogens
C.
Undegradable material converts methane into nitrogen
D.
Refractory material causes photosynthesis inside the digester
Correct Answer:
Less biodegradable substrate is available for conversion into methane
Explanation:
Methane production depends on the microbial conversion of biodegradable organic matter. Material that resists anaerobic degradation contributes little to the formation of methane.
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