301. Which conclusion is most strongly supported by comparing fermented dosa batter, Swiss cheese and a biogas plant?
ⓐ. Any microbial process producing gas must be classified as methanogenesis
ⓑ. \(CO_2\) and methane are interchangeable indicators of the same microbial process
ⓒ. Gas identity must be interpreted with the organism, substrate and biological setting
ⓓ. Gas identity alone is sufficient to identify the microbial process, regardless of the organism or substrate involved
Correct Answer: Gas identity must be interpreted with the organism, substrate and biological setting
Explanation: Fermented dosa or idli batter becomes puffed because microbial fermentation produces \(CO_2\). Swiss-cheese holes also result from \(CO_2\), but the microorganism and food system are different, with Propionibacterium sharmanii playing the characteristic role. In a biogas plant, the most important useful gas is methane produced under anaerobic conditions by methanogens. Therefore, gas production alone is not sufficient to identify a microbial process. Correct interpretation requires connecting the gas with the responsible microorganism, substrate, environmental condition and biological outcome.
302. A patient receives a microbial product that reduces blood cholesterol, while another patient receives a microbial product following organ transplantation. Which pair of mechanism-function relations is correct?
ⓐ. Statins -> competitive inhibition of a cholesterol-synthesis enzyme; cyclosporin A -> immunosuppression
ⓑ. Streptokinase -> cholesterol synthesis inhibition; penicillin -> immunosuppression
ⓒ. Statins -> competitive inhibition of a cholesterol-synthesis enzyme; streptokinase clot-buster -> immunosuppression
ⓓ. Penicillin -> phosphorus uptake; streptokinase -> nitrogen fixation
Correct Answer: Statins -> competitive inhibition of a cholesterol-synthesis enzyme; cyclosporin A -> immunosuppression
Explanation: Statins produced by Monascus purpureus lower blood cholesterol by competitively inhibiting an enzyme involved in cholesterol synthesis. Cyclosporin A, produced by Trichoderma polysporum, suppresses immune responses and is useful in organ transplantation. These microbial products are both medically important, but they act through different biological mechanisms. Recognising the source-product-function relation is essential because medical usefulness alone does not imply a common mode of action.
303. A microbial preparation reduces caterpillar damage only when larvae feed on treated plant surfaces. Another preparation kills a specific insect pest while leaving most beneficial insects unaffected. Which interpretation is correct?
ⓐ. Feeding-dependent action indicates baculovirus; narrow specificity indicates Bt
ⓑ. Feeding-dependent action indicates Bt; narrow specificity indicates baculovirus
ⓒ. The first represents mycorrhiza, whereas the second represents LAB
ⓓ. Both preparations act mainly by increasing soil nitrogen
Correct Answer: Feeding-dependent action indicates Bt; narrow specificity indicates baculovirus
Explanation: Bacillus thuringiensis preparations must be ingested by susceptible caterpillar larvae for toxin action to occur in the larval gut. Therefore, feeding on treated surfaces is essential for effective control. Baculoviruses, in contrast, are valued for their narrow host range and species specificity. A viral agent that efficiently kills the target pest while sparing beneficial insects demonstrates the ecological selectivity desired in integrated pest management.
304. Study the following organism-process-effect relationships.
| Organism | Process | Effect |
|---|
| P. Rhizobium | Symbiotic nitrogen fixation | Improved nitrogen nutrition of legumes |
| Q. Glomus | Mycorrhizal association | Improved phosphorus acquisition |
| R. Bacillus thuringiensis | Larval ingestion of microbial preparation | Caterpillar mortality |
| S. Monascus purpureus | Statin production | Reduction in blood cholesterol |
Which evaluation is correct?
ⓐ. Only P and Q are correct
ⓑ. Only R and S are correct
ⓒ. P, Q, R and S are correct
ⓓ. Only P, Q and R are correct
Correct Answer: P, Q, R and S are correct
Explanation: Each row correctly integrates a microorganism, a biological process and its practical outcome. Rhizobium fixes atmospheric nitrogen in symbiosis with legumes. Glomus forms mycorrhiza that enhances phosphorus acquisition. Bacillus thuringiensis controls susceptible caterpillars when they ingest the preparation, and Monascus purpureus produces statins that reduce blood cholesterol. The table demonstrates the central biological theme that microbial usefulness spans agriculture, pest management and medicine through different biological mechanisms.
305. A sewage-treatment plant shows a strong decrease in BOD but almost no methane production from its sludge digester. Which combined interpretation is most reasonable?
ⓐ. BOD reduction proves that methane production must also be high
ⓑ. Secondary aerobic treatment is impaired; anaerobic sludge digestion is functioning normally
ⓒ. Secondary aerobic treatment is working; anaerobic sludge digestion is impaired
ⓓ. The sludge digester has become a mycorrhizal system
Correct Answer: Secondary aerobic treatment is working; anaerobic sludge digestion is impaired
Explanation: A substantial fall in BOD indicates that aerobic microbial flocs in secondary treatment are successfully consuming biodegradable organic matter. Methane production, however, belongs to the later anaerobic digestion stage. If methane production is unusually low while BOD reduction remains strong, the most logical interpretation is that the aerobic stage is functioning normally but the anaerobic microbial process has been disrupted. The two stages are biologically linked within the treatment plant but depend on different microbial communities and oxygen conditions.
306. A farmer wants one microbial treatment to improve nitrogen availability and another to increase phosphorus acquisition. Which pair best satisfies these two goals respectively?
ⓐ. Penicillium notatum and Streptococcus
ⓑ. Trichoderma and baculovirus
ⓒ. Saccharomyces cerevisiae and Methanobacterium
ⓓ. Rhizobium and mycorrhizal Glomus
Correct Answer: Rhizobium and mycorrhizal Glomus
Explanation: Rhizobium contributes to nitrogen nutrition by fixing atmospheric nitrogen in symbiotic association with legume root nodules. Glomus forms mycorrhiza with plant roots and improves phosphorus absorption and transfer from soil to the plant. The two microorganisms therefore represent different nutrient-related biofertiliser strategies. Nitrogen enrichment and phosphorus acquisition should not be treated as the same microbial function simply because both improve plant growth.
307. Which sequence correctly traces the biological logic of a successful dung-based biogas system?
ⓐ. Dung -> primary sedimentation -> curd formation -> distilled beverage
ⓑ. Dung -> aerobic flocs -> BOD increase -> gas holder collapse -> ethanol production
ⓒ. Dung -> Rhizobium nodules -> phosphorus uptake -> methane loss
ⓓ. Dung -> anaerobic digestion -> biogas -> gas-holder rise -> cooking or lighting
Correct Answer: Dung -> anaerobic digestion -> biogas -> gas-holder rise -> cooking or lighting
Explanation: Cattle dung contains methanogenic microorganisms originating from the rumen microbial community. In the anaerobic digester of a biogas plant, these microorganisms contribute to methane-rich gas production. As gas accumulates, the floating gas holder rises, providing a visible indication of gas formation. The gas can then be directed through an outlet for practical uses such as cooking and lighting. The sequence connects microbial origin, anaerobic metabolism, plant structure and human use.
308. Which observation most clearly distinguishes a microbial biofertiliser effect from a microbial biocontrol effect?
ⓐ. Increased root phosphorus uptake without reduced pest abundance
ⓑ. Reduced caterpillar survival after Bt treatment
ⓒ. Reduced plant-pathogen damage after Trichoderma application
ⓓ. Selective mortality of an insect pest following baculovirus exposure
Correct Answer: Increased root phosphorus uptake without reduced pest abundance
Explanation: Biofertilisers improve nutrient availability or soil fertility rather than directly suppressing pests or pathogens. Increased phosphorus acquisition is a characteristic effect of mycorrhizal fungi such as Glomus. In contrast, Bt, Trichoderma and baculoviruses are used for biological control because they suppress insects or plant pathogens. The functional outcome therefore provides the clearest boundary between biofertilisation and biocontrol.
309. Assertion: A baculovirus that kills many beneficial insect species would be less suitable for use in an ecologically sensitive area.
Reason: The major advantage of many baculoviruses is their narrow host range and minimal effect on non-target organisms.
ⓐ. Assertion is false, but Reason is true
ⓑ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓒ. Assertion is true, but Reason is false
ⓓ. Both Assertion and Reason are true, and Reason correctly explains Assertion
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion
Explanation: Both statements are correct and causally linked. Baculoviruses are useful in integrated pest management partly because many of them show high species specificity and a narrow host range. This allows effective suppression of target insect or arthropod pests while conserving beneficial insects and avoiding adverse effects on plants and vertebrates. A virus that also kills many beneficial insects would lose this ecological advantage and therefore be less suitable in sensitive ecosystems.
310. A batch of milk receives a fresh curd starter containing abundant LAB. The bacteria multiply normally, but acid production is experimentally prevented. Which outcome is most likely?
ⓐ. Swiss-cheese holes will develop through Propionibacterium activity
ⓑ. Curd formation will improve because acid is unnecessary
ⓒ. Methane-rich biogas will form in the milk
ⓓ. Poor curd formation despite normal LAB growth
Correct Answer: Poor curd formation despite normal LAB growth
Explanation: LAB do more than simply multiply in milk. Their growth is useful because they produce acids, and these acids bring about coagulation and partial digestion of milk proteins, producing the characteristic curd structure. If bacterial multiplication occurs but acid formation is blocked, the crucial biochemical cause of milk-protein transformation is missing. Thus, microbial presence alone is insufficient; the metabolic product responsible for the visible food change must also be produced.
311. Which comparison best distinguishes the origin of visible structures in microbial culture and Swiss cheese?
ⓐ. Both structures form because individual microbes become macroscopic
ⓑ. A microbial colony becomes visible because many microscopic cells accumulate, whereas Swiss-cheese holes form because microbial \(CO_2\) accumulates within the cheese
ⓒ. A microbial colony becomes visible because many microscopic cells accumulate, whereas Swiss-cheese holes form because microbial methane-rich gas accumulates within the cheese
ⓓ. Colonies and cheese holes are both caused by methane
Correct Answer: A microbial colony becomes visible because many microscopic cells accumulate, whereas Swiss-cheese holes form because microbial \(CO_2\) accumulates within the cheese
Explanation: A visible microbial colony represents a large aggregate of cells produced by repeated growth on a suitable nutritive medium. The individual cells may remain microscopic even though the population becomes visible. Swiss-cheese holes arise through a completely different mechanism: Propionibacterium sharmanii produces large amounts of \(CO_2\), and gas accumulation creates cavities in the cheese. The two visible outcomes therefore reflect microbial multiplication in one case and microbial gas production in the other.
312. A food product develops normally even though no distillation occurs after fermentation. Which conclusion is most consistent with the alcoholic-beverage examples?
ⓐ. Wine or beer rather than whisky or rum
ⓑ. Fermentation must have failed
ⓒ. Saccharomyces cerevisiae cannot be involved
ⓓ. The product must be methane-rich biogas
Correct Answer: Wine or beer rather than whisky or rum
Explanation: Distillation is not required for all alcoholic beverages. Wine and beer are produced through fermentation without the additional distillation step, whereas whisky, brandy and rum undergo distillation after fermentation. Therefore, a successfully fermented alcoholic product that is not distilled can still be a normal beverage. The distinction depends on processing after microbial fermentation rather than on whether ethanol was produced.
313. Four industrial microbial products are shown below.
| Product | Source organism | Use |
|---|
| P. Citric acid | Aspergillus niger | Industrial organic acid |
| Q. Streptokinase | Streptococcus | Clot-busting application |
| R. Cyclosporin A | Trichoderma polysporum | Immunosuppression |
| S. Statins | Monascus purpureus | Reduction of blood cholesterol |
Which conclusion best follows?
ⓐ. All four products have the same biochemical function
ⓑ. Microorganisms can generate chemically and functionally diverse products for industrial and medical use
ⓒ. Microorganisms cannot generate chemically and functionally diverse products for industrial and medical use
ⓓ. All four are produced by bacteria
Correct Answer: Microorganisms can generate chemically and functionally diverse products for industrial and medical use
Explanation: The four microbial products serve very different purposes. Citric acid is an industrial organic acid, streptokinase functions as a clot buster, cyclosporin A suppresses immune responses, and statins reduce blood cholesterol. Their microbial sources also differ, including bacteria and fungi. The table therefore illustrates the broad biochemical and practical diversity of microbial products rather than a single common function.
314. If aeration in secondary sewage treatment is intensified but the wastewater entering the tank contains very little biodegradable organic matter, which observation is most reasonable?
ⓐ. Strong aeration does not by itself create a high BOD
ⓑ. BOD must rise because more air always means more pollution
ⓒ. Methane production must increase immediately
ⓓ. Primary sludge must become activated sludge before flocs form
Correct Answer: Strong aeration does not by itself create a high BOD
Explanation: BOD reflects the amount of biodegradable organic matter whose microbial oxidation would require oxygen. Aeration supports aerobic microbial activity, but it does not itself create biodegradable organic matter. Therefore, if the incoming wastewater already contains little biodegradable material, strong aeration does not automatically produce a high BOD. This distinction prevents confusion between oxygen availability during treatment and the oxygen demand used as an indicator of organic pollution.
315. A paddy field contains abundant cyanobacteria but receives little chemical nitrogen fertiliser. Crop performance remains satisfactory and soil organic matter gradually increases. Which interpretation best fits the biological evidence?
ⓐ. Nitrogen-fixing cyanobacteria can contribute both biologically available nitrogen and microbial biomass to soil fertility
ⓑ. Cyanobacteria act mainly by producing statins
ⓒ. Nitrogen-fixing cyanobacteria cannot contribute both biologically available nitrogen and microbial biomass to soil fertility
ⓓ. Crop performance is explained by baculovirus activity
Correct Answer: Nitrogen-fixing cyanobacteria can contribute both biologically available nitrogen and microbial biomass to soil fertility
Explanation: Cyanobacteria such as Anabaena, Nostoc and Oscillatoria are important agricultural biofertilisers, particularly in paddy fields. They can fix atmospheric nitrogen and thereby enrich the nitrogen status of the agricultural system. Their biomass also contributes organic matter to the soil. These two effects together help explain why cyanobacterial growth can support soil fertility and reduce dependence on chemical fertilisers.
316. Which of the following represents a correct progression from microbial ecological relationship to human-welfare benefit?
ⓐ. Rumen methanogens -> \(CO_2\)-dominated dung-derived biogas -> household energy
ⓑ. Mycorrhiza -> insect-pathogen infection -> clot dissolution
ⓒ. Rhizobium -> \(CO_2\) production in cheese -> food texture
ⓓ. Rumen methanogens -> methane-rich dung-derived biogas -> household energy
Correct Answer: Rumen methanogens -> methane-rich dung-derived biogas -> household energy
Explanation: Methanogens occur in the anaerobic rumen of cattle and are also present in dung. When dung is used in a biogas plant, these microorganisms contribute to methane-rich gas production under anaerobic conditions. The resulting gas can be used for cooking and lighting. This chain therefore connects microbial ecology in cattle, dung composition, anaerobic metabolism and practical household energy generation.
317. Which pair of statements is logically consistent?
I. Primary sewage treatment may remove visible solids without producing a large fall in BOD.
II. Secondary treatment can produce a large fall in BOD even though its main action is microbial rather than simple physical removal.
ⓐ. I false; II true
ⓑ. I true; II false
ⓒ. I true; II true
ⓓ. I false; II false
Correct Answer: I true; II true
Explanation: Primary treatment relies mainly on physical processes such as filtration and sedimentation. These remove floating debris, grit and settleable solids, but much biodegradable organic matter can remain dissolved or suspended in the primary effluent. Secondary treatment is biological: aerobic microbial flocs consume that organic material, producing a substantial reduction in BOD. Therefore, physical removal and biological BOD reduction are distinct but sequential components of sewage treatment.
318. A single agricultural field receives three microbial interventions:
Treatment P enhances phosphorus uptake and drought tolerance.
Treatment Q selectively kills a target insect while sparing most non-target organisms.
Treatment R enriches nitrogen through a legume root-nodule association.
Which sequence identifies P, Q and R respectively?
ⓐ. Rhizobium, Lactobacillus, Methanobacterium
ⓑ. Glomus mycorrhiza, a baculovirus, and Rhizobium
ⓒ. Bacillus thuringiensis, Glomus, Azotobacter
ⓓ. Saccharomyces cerevisiae, Trichoderma polysporum, Nostoc
Correct Answer: Glomus mycorrhiza, a baculovirus, and Rhizobium
Explanation: Glomus forms mycorrhiza with plant roots and improves phosphorus acquisition while also increasing tolerance to stresses such as drought. Baculoviruses are narrow-spectrum viral biological-control agents useful for selectively suppressing particular insect pests while conserving many non-target organisms. Rhizobium forms symbiotic root nodules on legumes and fixes atmospheric nitrogen. The three treatments therefore represent distinct agricultural functions: mineral acquisition and stress support, selective pest control and nitrogen biofertilisation.
319. A city produces a large volume of sewage, but its sewage-treatment capacity increases much more slowly than the sewage load. Which consequence is most biologically consistent?
ⓐ. Primary sludge will be converted directly into drinking water
ⓑ. BOD of untreated sewage must automatically become zero
ⓒ. More untreated sewage may enter rivers, increasing pollution and disease risk
ⓓ. River microorganisms will necessarily eliminate all pathogens before human exposure
Correct Answer: More untreated sewage may enter rivers, increasing pollution and disease risk
Explanation: Rapid urbanisation can produce more sewage than available sewage-treatment plants can process effectively. If untreated or inadequately treated sewage enters rivers, it introduces biodegradable organic matter and potentially pathogenic microorganisms. The organic load increases pollution, while disease-causing microbes can contribute to water-borne diseases. Thus, insufficient treatment capacity is not merely an engineering limitation; it has direct environmental and public-health consequences.
320. The Ganga Action Plan and Yamuna Action Plan are most directly connected with which biological problem?
ⓐ. Excessive fermentation of milk by LAB
ⓑ. River pollution from untreated sewage
ⓒ. Decline of methanogens in cattle rumen
ⓓ. Lack of fungal ripening in cheese
Correct Answer: River pollution from untreated sewage
Explanation: The Ganga Action Plan and Yamuna Action Plan are associated with reducing river pollution, particularly by improving sewage treatment before wastewater enters natural water bodies. Urban centres can generate quantities of sewage that exceed available treatment capacity, allowing untreated sewage to contaminate rivers. Expanding sewage-treatment facilities is therefore an important part of controlling organic pollution and reducing exposure to disease-causing microorganisms.
