Chapter 10: Microbes in Human Welfare – MCQs
🟢 Part 1: Microbes in Human Welfare (Q1–Q25)
Q1. Curd formation from milk is mainly carried out by
a) Saccharomyces cerevisiae
b) Lactobacillus
c) Penicillium
d) Rhizobium
Answer: b) Lactobacillus
Explanation: Lactic acid bacteria (LAB) ferment lactose to lactic acid, coagulating milk proteins to form curd.
Q2. The microorganism used in baking industry for leavening is
a) Aspergillus niger
b) Saccharomyces cerevisiae
c) Penicillium notatum
d) Lactobacillus bulgaricus
Answer: b) Saccharomyces cerevisiae
Explanation: Baker’s yeast releases CO₂ during fermentation, making dough rise.
Q3. Swiss cheese has characteristic holes due to CO₂ produced by
a) Penicillium roqueforti
b) Propionibacterium shermanii
c) Lactobacillus acidophilus
d) Aspergillus oryzae
Answer: b) Propionibacterium shermanii
Explanation: Propionic acid fermentation liberates CO₂ that forms the “eyes” in Swiss cheese.
Q4. The antibiotic penicillin was discovered by
a) Louis Pasteur
b) Alexander Fleming
c) Robert Koch
d) Edward Jenner
Answer: b) Alexander Fleming
Explanation: Fleming observed lysis of bacteria around Penicillium; later Chain & Florey mass-produced it.
Q5. Which microbe is the source of the immunosuppressant Cyclosporin A?
a) Trichoderma polysporum
b) Monascus purpureus
c) Streptomyces griseus
d) Penicillium chrysogenum
Answer: a) Trichoderma polysporum
Explanation: Cyclosporin A suppresses T-cell activation; key drug in organ transplantation.
Q6. Statins that lower blood cholesterol are produced by
a) Aspergillus niger
b) Monascus purpureus
c) Rhizobium
d) Candida albicans
Answer: b) Monascus purpureus
Explanation: Statins inhibit HMG-CoA reductase, reducing endogenous cholesterol synthesis.
Q7. The fibrinolytic enzyme used as a clot buster is
a) Streptokinase
b) Lysozyme
c) DNA polymerase
d) Trypsin
Answer: a) Streptokinase
Explanation: Streptokinase from Streptococcus dissolves clots by activating plasminogen.
Q8. BOD (Biochemical Oxygen Demand) is a measure of
a) Toxic chemicals in water
b) Organic matter biodegradable by microbes
c) Dissolved oxygen saturation
d) Nitrate concentration
Answer: b) Organic matter biodegradable by microbes
Explanation: Higher BOD indicates more organic pollution; used to assess sewage strength.
Q9. Flocs in secondary sewage treatment are
a) Pure bacterial pellets
b) Aggregates of bacteria with fungal filaments
c) Sand–silt particles
d) Algal colonies only
Answer: b) Aggregates of bacteria with fungal filaments
Explanation: Flocs actively oxidize organic matter in aeration tanks, lowering BOD.
Q10. In an anaerobic sludge digester, the key gas-forming microbes are
a) Nitrifying bacteria
b) Methanogens
c) Sulfur-oxidizers
d) Cyanobacteria
Answer: b) Methanogens
Explanation: Methanogenic archaea convert acetate/H₂ + CO₂ into biogas (mainly CH₄).
Q11. A typical methanogen used in biogas plants is
a) Methanobacterium
b) Azotobacter
c) Nitrosomonas
d) Pseudomonas
Answer: a) Methanobacterium
Explanation: Common in cattle rumen and sludge digesters; essential for biogas production.
Q12. The Indian biogas plant model widely used in rural areas is
a) UASB
b) Trickling filter
c) KVIC model
d) ASP model
Answer: c) KVIC model
Explanation: Khadi and Village Industries Commission design for household/community biogas.
Q13. Biofertilizer for paddy fields fixing nitrogen symbiotically with Azolla is
a) Frankia
b) Rhizobium
c) Anabaena azollae
d) Azotobacter
Answer: c) Anabaena azollae
Explanation: Cyanobacterium living in Azolla leaf cavities adds N to rice paddies.
Q14. Free-living nitrogen fixer used as a biofertilizer in cereals is
a) Rhizobium
b) Azotobacter
c) Mycorrhiza
d) Nitrobacter
Answer: b) Azotobacter
Explanation: Fixes atmospheric N₂ in rhizosphere, improving soil fertility.
Q15. Blue-green algae used as biofertilizers include
a) Spirogyra
b) Anabaena and Nostoc
c) Euglena and Volvox
d) Ulothrix and Chlorella
Answer: b) Anabaena and Nostoc
Explanation: Cyanobacteria fix nitrogen via heterocysts; useful in rice cultivation.
Q16. Mycorrhiza enhances plant growth mainly by
a) Fixing atmospheric nitrogen
b) Increasing water and phosphate uptake
c) Producing auxins only
d) Killing root pathogens directly
Answer: b) Increasing water and phosphate uptake
Explanation: Fungal hyphae extend root absorption; some also provide disease protection.
Q17. SCP (Single Cell Protein) refers to
a) Edible protein from animal cells
b) Protein-rich biomass from microbes
c) Protein from transgenic plants
d) Enzyme supplements
Answer: b) Protein-rich biomass from microbes
Explanation: Yeast (Candida), algae (Spirulina), and bacteria provide high-protein feed/food.
Q18. The microbe used to produce citric acid industrially is
a) Aspergillus niger
b) Rhizopus stolonifer
c) Penicillium camemberti
d) Acetobacter aceti
Answer: a) Aspergillus niger
Explanation: A. niger ferments sugars to citric acid at scale.
Q19. Vinegar production from ethanol uses
a) Lactobacillus
b) Acetobacter aceti
c) Saccharomyces cerevisiae
d) Clostridium acetobutylicum
Answer: b) Acetobacter aceti
Explanation: Acetic acid bacteria oxidize ethanol to acetic acid (vinegar).
Q20. Roquefort cheese is ripened with
a) Penicillium roqueforti
b) Penicillium camemberti
c) Aspergillus oryzae
d) Mucor spp.
Answer: a) Penicillium roqueforti
Explanation: Gives blue-green veins and characteristic aroma/flavor.
Q21. Which step is NOT part of primary sewage treatment?
a) Screening and grit removal
b) Sedimentation to form primary sludge
c) Aeration with activated sludge
d) Removal of floating scum
Answer: c) Aeration with activated sludge
Explanation: Aeration with flocs is secondary treatment; primary is physical separation.
Q22. During secondary sewage treatment, most BOD is removed by
a) Chlorination
b) Aerobic microbial oxidation
c) Filtration through sand
d) Chemical coagulation
Answer: b) Aerobic microbial oxidation
Explanation: Aeration allows bacteria/fungi to oxidize organics, reducing BOD drastically.
Q23. “Activated sludge” refers to
a) Untreated sewage
b) Primary sludge rich in sand
c) Aerated microbial flocs sediment
d) Pure fungal pellets
Answer: c) Aerated microbial flocs sediment
Explanation: Portion is recycled as inoculum; rest sent to anaerobic digester.
Q24. Bt in “Bt cotton” stands for a bacterium that produces
a) Antifungal antibiotics
b) Endotoxin against insect larvae
c) Growth hormones
d) Nitrogenase enzyme
Answer: b) Endotoxin against insect larvae
Explanation: Bacillus thuringiensis Cry proteins are toxic to specific insect pests (biopesticide concept).
Q25. A common probiotic added to foods for gut health is
a) Clostridium botulinum
b) Vibrio cholerae
c) Lactobacillus/Bifidobacterium
d) Salmonella typhi
Answer: c) Lactobacillus/Bifidobacterium
Explanation: Beneficial bacteria that improve gut microbiota and immunity.
🟢 Part 2: Microbes in Human Welfare (Q26–Q50)
Q26. The primary function of lactic acid bacteria (LAB) in curd is
a) Production of vitamins only
b) Lowering milk pH by lactic acid production
c) Killing all bacteria in milk
d) Enhancing fat content
Answer: b) Lowering milk pH by lactic acid production
Explanation: LAB ferment lactose into lactic acid, lowering pH and coagulating casein.
Q27. Ethanol production from molasses requires
a) Lactobacillus
b) Saccharomyces cerevisiae
c) Aspergillus niger
d) Penicillium roqueforti
Answer: b) Saccharomyces cerevisiae
Explanation: Yeast ferments sugars in molasses to ethanol and CO₂ (alcoholic fermentation).
Q28. The major product of anaerobic digestion of sewage by methanogens is
a) Carbon dioxide
b) Methane
c) Hydrogen
d) Ammonia
Answer: b) Methane
Explanation: Biogas is ~60–70% methane, produced by methanogenic archaea.
Q29. Which microbe is used in commercial production of butanol and acetone?
a) Clostridium acetobutylicum
b) Saccharomyces cerevisiae
c) Lactobacillus acidophilus
d) Aspergillus oryzae
Answer: a) Clostridium acetobutylicum
Explanation: Performs ABE fermentation (Acetone-Butanol-Ethanol).
Q30. The antibiotic streptomycin is produced by
a) Streptomyces griseus
b) Penicillium notatum
c) Monascus purpureus
d) Aspergillus niger
Answer: a) Streptomyces griseus
Explanation: Many antibiotics (streptomycin, tetracycline, erythromycin) are derived from Streptomyces.
Q31. Microbes used as biocontrol agents against plant pests include
a) Trichoderma
b) Bacillus thuringiensis
c) Nucleopolyhedrovirus
d) All of these
Answer: d) All of these
Explanation: Trichoderma (fungus) suppresses pathogens, Bt kills insects, NPV viruses control pests.
Q32. Cyanobacteria like Nostoc and Anabaena are useful in agriculture as
a) Bio-pesticides
b) Biofertilizers
c) Antibiotic producers
d) Food additives
Answer: b) Biofertilizers
Explanation: Fix atmospheric nitrogen in paddy fields, improving fertility.
Q33. Mycorrhizae are associations between
a) Bacteria and fungi
b) Fungi and algae
c) Fungi and plant roots
d) Plant roots and cyanobacteria
Answer: c) Fungi and plant roots
Explanation: Symbiotic fungi enhance water/nutrient absorption and protect roots.
Q34. Rhizobium forms symbiotic association with
a) Rice
b) Maize
c) Leguminous plants
d) Wheat
Answer: c) Leguminous plants
Explanation: Rhizobium fixes nitrogen in root nodules of legumes like peas and beans.
Q35. Biofortified crop “Quality Protein Maize (QPM)” is enriched with
a) Lysine and tryptophan
b) Vitamin A
c) Iron
d) Iodine
Answer: a) Lysine and tryptophan
Explanation: QPM contains higher essential amino acids than normal maize.
Q36. Blue-green algae in paddy fields contribute mainly by
a) Releasing antibiotics
b) Adding nitrogen to soil
c) Increasing water level
d) Removing pesticides
Answer: b) Adding nitrogen to soil
Explanation: BGA fix atmospheric nitrogen, improving rice field productivity.
Q37. Biofertilizer containing phosphate-solubilizing microbes increases
a) Protein content
b) Availability of phosphorus to plants
c) Root growth only
d) Oil content
Answer: b) Availability of phosphorus to plants
Explanation: Solubilizers like Pseudomonas and Bacillus convert insoluble phosphates into usable forms.
Q38. Antibiotic chloramphenicol is obtained from
a) Streptomyces venezuelae
b) Penicillium
c) Aspergillus
d) Trichoderma
Answer: a) Streptomyces venezuelae
Explanation: Produces broad-spectrum antibiotic chloramphenicol, effective against typhoid.
Q39. The edible unicellular protein-rich alga commonly used as SCP is
a) Chlorella
b) Spirogyra
c) Ulothrix
d) Volvox
Answer: a) Chlorella
Explanation: Chlorella and Spirulina are protein-rich edible algae used as SCP.
Q40. The nitrogen-fixing bacterium associated with sugarcane is
a) Azotobacter
b) Azospirillum
c) Rhizobium
d) Clostridium
Answer: b) Azospirillum
Explanation: Endophytic Azospirillum associates with sugarcane roots, fixing nitrogen.
Q41. Biogas mainly consists of
a) CH₄, CO₂, and H₂S
b) O₂, CO₂, and N₂
c) NH₃, O₂, and H₂
d) H₂, CO₂, and N₂
Answer: a) CH₄, CO₂, and H₂S
Explanation: Biogas has ~60–70% methane, ~30% CO₂, and traces of H₂S.
Q42. Methanogens are found in
a) Aerated soils
b) Hot springs
c) Rumen of cattle
d) Salty lagoons
Answer: c) Rumen of cattle
Explanation: Archaebacteria in cattle gut ferment cellulose anaerobically, producing biogas.
Q43. Which fungus is commonly used as a biocontrol agent against plant pathogens?
a) Trichoderma harzianum
b) Saccharomyces cerevisiae
c) Aspergillus niger
d) Penicillium notatum
Answer: a) Trichoderma harzianum
Explanation: It is free-living in soil, suppressing soil-borne plant pathogens.
Q44. Nucleopolyhedrovirus (NPV) belongs to which group?
a) Fungi
b) Bacteria
c) Viruses (baculoviruses)
d) Cyanobacteria
Answer: c) Viruses (baculoviruses)
Explanation: NPV is used in integrated pest management, highly species-specific biocontrol.
Q45. Biofertilizers reduce the need for
a) Antibiotics
b) Pesticides
c) Chemical fertilizers
d) Irrigation
Answer: c) Chemical fertilizers
Explanation: Biofertilizers supply nutrients naturally, reducing chemical input.
Q46. Edible fungus used in SCP production is
a) Agaricus bisporus
b) Fusarium venenatum
c) Penicillium roqueforti
d) Mucor mucedo
Answer: b) Fusarium venenatum
Explanation: Produces “mycoprotein,” a commercial SCP product used as meat substitute.
Q47. Which microbe produces vitamin B12 industrially?
a) Pseudomonas denitrificans
b) Lactobacillus
c) Azotobacter
d) Rhizobium
Answer: a) Pseudomonas denitrificans
Explanation: Widely used for commercial production of vitamin B12.
Q48. The main advantage of using microbes in sewage treatment is
a) Low cost and eco-friendly
b) Quick disinfection
c) High oxygen supply
d) No sludge formation
Answer: a) Low cost and eco-friendly
Explanation: Microbes degrade organic matter naturally, without harmful chemicals.
Q49. Cheese with characteristic flavor due to microbial activity is
a) Mozzarella
b) Camembert
c) Swiss
d) All of these
Answer: d) All of these
Explanation: Each cheese has specific microbial flora imparting distinct flavor.
Q50. Spirulina is considered a “superfood” because it is rich in
a) Protein, vitamins, minerals
b) Lipids only
c) Carbohydrates only
d) Fiber only
Answer: a) Protein, vitamins, minerals
Explanation: Spirulina (cyanobacterium) is ~60% protein and contains vitamins A, B12, and iron.
🟢 Part 3: Microbes in Human Welfare (Q51–Q75)
Q51. The antibiotic erythromycin is obtained from
a) Streptomyces griseus
b) Streptomyces erythraeus
c) Penicillium chrysogenum
d) Monascus purpureus
Answer: b) Streptomyces erythraeus
Explanation: Produces erythromycin, a broad-spectrum antibiotic effective against Gram-positive bacteria.
Q52. The sour taste of vinegar is due to
a) Lactic acid
b) Citric acid
c) Acetic acid
d) Propionic acid
Answer: c) Acetic acid
Explanation: Acetobacter aceti oxidizes ethanol to acetic acid (vinegar).
Q53. Which microorganism is used to produce the antibiotic tetracycline?
a) Penicillium
b) Streptomyces aureofaciens
c) Trichoderma
d) Aspergillus
Answer: b) Streptomyces aureofaciens
Explanation: Several Streptomyces species produce tetracyclines widely used in medicine.
Q54. Which of the following is NOT an industrial product of microbes?
a) Citric acid
b) Ethanol
c) Penicillin
d) Insulin
Answer: d) Insulin
Explanation: Human insulin is produced by recombinant DNA technology, not directly by natural microbes.
Q55. Which bacteria convert milk into yoghurt?
a) Streptococcus thermophilus and Lactobacillus bulgaricus
b) Saccharomyces cerevisiae
c) Pseudomonas spp.
d) Rhizobium spp.
Answer: a) Streptococcus thermophilus and Lactobacillus bulgaricus
Explanation: These bacteria ferment lactose into lactic acid to form yoghurt.
Q56. Biogas production is most efficient when using
a) Plant residues
b) Animal dung
c) Kitchen waste
d) Petroleum waste
Answer: b) Animal dung
Explanation: Cow dung (gobar) contains methanogens, making it the best substrate for biogas plants.
Q57. Single Cell Protein (SCP) production is useful because
a) It needs less land and water
b) It is protein-rich
c) It grows rapidly
d) All of these
Answer: d) All of these
Explanation: SCP provides protein cheaply and sustainably using microbes like Spirulina.
Q58. Which of the following antibiotics is produced by fungi?
a) Streptomycin
b) Erythromycin
c) Penicillin
d) Tetracycline
Answer: c) Penicillin
Explanation: Penicillin was the first true antibiotic discovered, produced by Penicillium notatum.
Q59. Blue-green algae fix nitrogen through
a) Pyrenoids
b) Heterocysts
c) Conidia
d) Zoospores
Answer: b) Heterocysts
Explanation: Specialized thick-walled heterocysts provide anaerobic environment for nitrogenase activity.
Q60. Which is used as a biocontrol agent against root-knot nematodes?
a) Bacillus thuringiensis
b) Trichoderma
c) Paecilomyces lilacinus
d) Azotobacter
Answer: c) Paecilomyces lilacinus
Explanation: A fungus that parasitizes nematode eggs and controls root-knot nematodes.
Q61. The antibiotic griseofulvin is obtained from
a) Penicillium griseofulvum
b) Streptomyces spp.
c) Monascus
d) Rhizopus
Answer: a) Penicillium griseofulvum
Explanation: Griseofulvin is an antifungal antibiotic derived from Penicillium.
Q62. The microbe used to ferment soybeans into soy sauce is
a) Saccharomyces cerevisiae
b) Aspergillus oryzae
c) Lactobacillus
d) Trichoderma
Answer: b) Aspergillus oryzae
Explanation: A. oryzae ferments soybeans, imparting flavor to soy sauce.
Q63. Antibiotic bacitracin is produced by
a) Bacillus subtilis
b) Clostridium tetani
c) Pseudomonas aeruginosa
d) Azotobacter
Answer: a) Bacillus subtilis
Explanation: Bacitracin is a polypeptide antibiotic produced by Bacillus.
Q64. Which microbe is used in bioremediation of oil spills?
a) Pseudomonas putida
b) Azotobacter
c) Trichoderma
d) Rhizobium
Answer: a) Pseudomonas putida
Explanation: Engineered Pseudomonas strains degrade hydrocarbons in oil spills.
Q65. Yeast used in brewing industry tolerates
a) High ethanol concentration
b) Low temperature only
c) High salt concentration
d) Antibiotics
Answer: a) High ethanol concentration
Explanation: Brewer’s yeast (S. cerevisiae) tolerates ethanol, enabling alcohol fermentation.
Q66. Which antibiotic is effective against tuberculosis?
a) Streptomycin
b) Penicillin
c) Erythromycin
d) Rifampicin
Answer: d) Rifampicin
Explanation: Rifampicin is a key anti-TB drug derived from Streptomyces.
Q67. Which organism is commonly used for citric acid production?
a) Saccharomyces cerevisiae
b) Aspergillus niger
c) Penicillium notatum
d) Candida albicans
Answer: b) Aspergillus niger
Explanation: Industrial-scale citric acid is produced using this fungus.
Q68. Microbial flocs in sewage treatment consist of
a) Algae only
b) Bacteria and fungi
c) Viruses
d) Protozoans only
Answer: b) Bacteria and fungi
Explanation: Flocs are aggregates of bacteria with fungal filaments that oxidize organic matter.
Q69. Production of biogas from biomass is a type of
a) Aerobic fermentation
b) Anaerobic digestion
c) Photosynthesis
d) Aeration
Answer: b) Anaerobic digestion
Explanation: Methanogens work anaerobically in digesters to produce methane-rich biogas.
Q70. The microbe used in the ripening of Camembert cheese is
a) Penicillium camemberti
b) Aspergillus niger
c) Rhizopus stolonifer
d) Saccharomyces cerevisiae
Answer: a) Penicillium camemberti
Explanation: This fungus imparts flavor and aroma to Camembert cheese.
Q71. Which bacteria are used in the nitrification step of nitrogen cycle?
a) Nitrosomonas and Nitrobacter
b) Rhizobium
c) Azotobacter
d) Clostridium
Answer: a) Nitrosomonas and Nitrobacter
Explanation: Convert ammonia → nitrite (Nitrosomonas) → nitrate (Nitrobacter).
Q72. Probiotics are beneficial because they
a) Kill gut microbes
b) Improve gut health and immunity
c) Cause diarrhea
d) Increase pathogen growth
Answer: b) Improve gut health and immunity
Explanation: Probiotics (Lactobacillus, Bifidobacterium) restore gut flora and enhance immunity.
Q73. Which bacterium produces the antibiotic polymyxin?
a) Streptomyces rimosus
b) Bacillus polymyxa
c) Penicillium
d) Trichoderma
Answer: b) Bacillus polymyxa
Explanation: Polymyxin is a polypeptide antibiotic effective against Gram-negative bacteria.
Q74. The bacterium used for commercial production of lactic acid is
a) Lactobacillus delbrueckii
b) Saccharomyces cerevisiae
c) Aspergillus niger
d) Clostridium acetobutylicum
Answer: a) Lactobacillus delbrueckii
Explanation: Widely used in industries for lactic acid fermentation.
Q75. A microbe commonly used for vitamin C production is
a) Acetobacter suboxydans
b) Rhizobium
c) Trichoderma
d) Aspergillus oryzae
Answer: a) Acetobacter suboxydans
Explanation: Used in the production of ascorbic acid (vitamin C) from sorbitol.
🟢 Part 4: Microbes in Human Welfare (Q76–Q100)
Q76. Which microbe is used in the production of beer and wine?
a) Lactobacillus
b) Saccharomyces cerevisiae
c) Aspergillus niger
d) Penicillium notatum
Answer: b) Saccharomyces cerevisiae
Explanation: Brewer’s yeast ferments sugars into ethanol, used in beer and wine production.
Q77. Which fungus is used in the production of citric acid?
a) Rhizopus stolonifer
b) Aspergillus niger
c) Penicillium chrysogenum
d) Mucor mucedo
Answer: b) Aspergillus niger
Explanation: Industrial citric acid is produced at large scale using A. niger.
Q78. Which of the following is NOT an example of SCP (Single Cell Protein)?
a) Spirulina
b) Chlorella
c) Rhizobium
d) Fusarium venenatum
Answer: c) Rhizobium
Explanation: SCP includes edible microbes like Spirulina, Chlorella, and Fusarium; Rhizobium is a biofertilizer.
Q79. In sewage treatment, activated sludge is rich in
a) Sand particles
b) Fungal spores
c) Microbial flocs
d) Oil droplets
Answer: c) Microbial flocs
Explanation: Activated sludge consists of bacteria and fungi aggregated into flocs that degrade organic matter.
Q80. Methanogens produce methane by
a) Oxidizing ethanol
b) Reducing CO₂ with H₂
c) Fermenting glucose aerobically
d) Breaking proteins
Answer: b) Reducing CO₂ with H₂
Explanation: Methanogens convert CO₂ + H₂ or acetate into methane under anaerobic conditions.
Q81. Vinegar is produced by two-step fermentation involving
a) Saccharomyces and Acetobacter
b) Rhizopus and Trichoderma
c) Lactobacillus and Bacillus
d) Aspergillus and Clostridium
Answer: a) Saccharomyces and Acetobacter
Explanation: Yeast ferments sugar to ethanol, then Acetobacter oxidizes it to acetic acid.
Q82. Antibiotic vancomycin is obtained from
a) Streptomyces orientalis
b) Penicillium notatum
c) Trichoderma polysporum
d) Monascus purpureus
Answer: a) Streptomyces orientalis
Explanation: Vancomycin is a glycopeptide antibiotic effective against Gram-positive bacteria.
Q83. In rural biogas plants, the common raw material is
a) Sawdust
b) Cow dung (gobar)
c) Plastic waste
d) Coal
Answer: b) Cow dung (gobar)
Explanation: Gobar is rich in methanogens, making it ideal for anaerobic digestion.
Q84. In SCP production, Spirulina is grown in
a) Wastewater tanks
b) Open ponds and tanks
c) Soil pits
d) Animal intestines
Answer: b) Open ponds and tanks
Explanation: Spirulina cultivation in open tanks provides cheap, protein-rich biomass.
Q85. Cheese maturation and flavor development are due to
a) Microbial enzymes
b) Genetic engineering
c) High salt alone
d) High pressure
Answer: a) Microbial enzymes
Explanation: Bacteria and fungi release enzymes that generate flavor compounds in cheese.
Q86. Flocs formation in sewage treatment indicates
a) Nutrient deficiency
b) Active microbial growth
c) Chemical contamination
d) Oxygen depletion
Answer: b) Active microbial growth
Explanation: Bacteria aggregate with fungal filaments, forming flocs that degrade organics.
Q87. Which microbe is used in bio-control of butterfly caterpillars?
a) Trichoderma
b) Bacillus thuringiensis
c) Pseudomonas putida
d) Aspergillus oryzae
Answer: b) Bacillus thuringiensis
Explanation: Bt Cry toxin kills caterpillars of butterflies and moths (biopesticide).
Q88. In secondary sewage treatment, most microbes function under
a) Aerobic conditions
b) Anaerobic conditions
c) Facultative conditions
d) Alkaline conditions
Answer: a) Aerobic conditions
Explanation: Secondary treatment uses aerobic bacteria in aeration tanks to reduce BOD.
Q89. Which antibiotic is produced by Streptomyces venezuelae?
a) Chloramphenicol
b) Streptomycin
c) Erythromycin
d) Rifampicin
Answer: a) Chloramphenicol
Explanation: Produced by S. venezuelae, used against typhoid fever.
Q90. Microbial biomass used directly as food is called
a) Probiotic
b) Single Cell Protein
c) Enzyme supplement
d) Prebiotic
Answer: b) Single Cell Protein
Explanation: SCP is protein-rich microbial biomass used as food or feed.
Q91. Which step is last in sewage treatment?
a) Primary sedimentation
b) Aeration
c) Sludge digestion
d) Chlorination
Answer: d) Chlorination
Explanation: Final disinfection (often chlorination) ensures pathogen-free water before release.
Q92. Which fungus produces immunosuppressant cyclosporin A?
a) Penicillium notatum
b) Trichoderma polysporum
c) Aspergillus niger
d) Monascus purpureus
Answer: b) Trichoderma polysporum
Explanation: Produces cyclosporin A, crucial for preventing organ transplant rejection.
Q93. Which microbe is used in the production of vitamin B12?
a) Pseudomonas denitrificans
b) Rhizobium
c) Azotobacter
d) Clostridium
Answer: a) Pseudomonas denitrificans
Explanation: Industrial production of vitamin B12 relies on fermentation by this bacterium.
Q94. The gas mainly responsible for the odor in sewage treatment plants is
a) Ammonia
b) Hydrogen sulfide
c) Methane
d) Carbon dioxide
Answer: b) Hydrogen sulfide
Explanation: Produced by anaerobic sulfate-reducing bacteria during sludge digestion.
Q95. Microbial source of bioinsecticide used in Bt cotton is
a) Trichoderma viride
b) Bacillus thuringiensis
c) Monascus purpureus
d) Streptomyces griseus
Answer: b) Bacillus thuringiensis
Explanation: Bt toxin genes are inserted into cotton plants for pest resistance.
Q96. Nucleopolyhedroviruses (NPVs) are particularly useful because
a) They are broad-spectrum pesticides
b) They are species-specific and safe for other organisms
c) They kill weeds
d) They fix nitrogen
Answer: b) They are species-specific and safe for other organisms
Explanation: NPVs target only insect pests, minimizing environmental damage.
Q97. Which is an example of microbe used in organic acid production?
a) Aspergillus niger – citric acid
b) Clostridium butylicum – butyric acid
c) Lactobacillus – lactic acid
d) All of these
Answer: d) All of these
Explanation: Many microbes produce organic acids industrially.
Q98. Which edible fungus is used in SCP production as mycoprotein?
a) Fusarium venenatum
b) Penicillium roqueforti
c) Agaricus bisporus
d) Rhizopus stolonifer
Answer: a) Fusarium venenatum
Explanation: Provides mycoprotein (Quorn), a high-protein meat substitute.
Q99. Which microorganism is used in cleaning up oil spills?
a) Trichoderma
b) Pseudomonas putida
c) Lactobacillus
d) Rhizobium
Answer: b) Pseudomonas putida
Explanation: Engineered strains degrade hydrocarbons, useful in bioremediation.
Q100. The main advantage of using microbes in industries is
a) Low cost and eco-friendly processes
b) Very slow reactions
c) High pollution generation
d) Limited scalability
Answer: a) Low cost and eco-friendly processes
Explanation: Microbial biotechnology provides sustainable, large-scale industrial production.
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