A. Standard / Conceptual MCQs – Microbes in Human Welfare (50 MCQs)

1. Microbes in Food Production

Q1. Lactic acid bacteria are used in the production of:
A. Yogurt
B. Beer
C. Wine
D. Antibiotics

Q2. Cheese is produced using:
A. Lactobacillus and rennet
B. Streptococcus pneumoniae
C. Saccharomyces cerevisiae
D. Bacillus subtilis

Q3. Alcoholic fermentation in brewing uses:
A. Yeast (Saccharomyces cerevisiae)
B. Lactobacillus
C. E. coli
D. Penicillium

Q4. Vinegar production involves:
A. Acetobacter
B. Bacillus
C. Clostridium
D. Lactobacillus

Q5. Single-cell protein (SCP) is produced using:
A. Microbes like Spirulina
B. Yeast in bread
C. Penicillium for antibiotics
D. E. coli in sewage

Q6. Microbes used in idli/dosa fermentation:
A. Lactobacillus and Leuconostoc
B. Saccharomyces cerevisiae only
C. Acetobacter
D. Clostridium

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2. Microbes in Industrial Products

Q7. Penicillin is produced by:
A. Penicillium notatum
B. Streptomyces
C. Bacillus subtilis
D. Saccharomyces cerevisiae

Q8. Antibiotic streptomycin is obtained from:
A. Streptomyces griseus
B. Penicillium
C. Lactobacillus
D. Clostridium

Q9. Industrial production of citric acid uses:
A. Aspergillus niger
B. Penicillium
C. Saccharomyces
D. Bacillus

Q10. Microbial enzymes like amylase are produced by:
A. Aspergillus and Bacillus
B. Saccharomyces only
C. Lactobacillus only
D. Clostridium only

Q11. Vitamins produced by microbes include:
A. B12 by Propionibacterium
B. Vitamin C by yeast
C. Vitamin D by bacteria
D. Vitamin K by fungi

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3. Microbes in Agriculture

Q12. Biofertilizers contain:
A. Nitrogen-fixing bacteria like Rhizobium, Azotobacter
B. Bacillus for antibiotics
C. Lactobacillus for food
D. Yeast for alcohol

Q13. Azotobacter is:
A. Free-living nitrogen-fixing bacterium
B. Symbiotic nitrogen-fixer
C. Phosphate-solubilizing bacterium
D. Biopesticide

Q14. Rhizobium forms nodules in:
A. Leguminous plants
B. Cereals
C. Fungi
D. Non-legumes

Q15. Mycorrhizal fungi help in:
A. Mineral absorption
B. Nitrogen fixation
C. Pesticide degradation
D. Antibiotic production

Q16. Biopesticides like Bacillus thuringiensis control:
A. Insect pests
B. Fungal infection
C. Bacterial infection
D. Viral infection

Q17. Phosphate-solubilizing bacteria (PSB) enhance:
A. Soil phosphate availability
B. Nitrogen fixation
C. Pathogen resistance
D. Antibiotic production

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4. Microbes in Sewage Treatment

Q18. Primary treatment of sewage involves:
A. Settling of solids
B. Bacterial degradation
C. Chemical treatment
D. UV treatment

Q19. Secondary treatment of sewage uses:
A. Microbes to degrade organic matter
B. Sedimentation only
C. Filtration
D. Chlorination

Q20. Activated sludge in sewage treatment contains:
A. Bacteria and protozoa
B. Viruses only
C. Yeast only
D. Fungi only

Q21. Anaerobic treatment of sludge produces:
A. Biogas (methane)
B. Alcohol
C. Vinegar
D. Antibiotics

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5. Microbes in Biodegradation & Bioremediation

Q22. Oil spills can be treated using:
A. Hydrocarbon-degrading bacteria
B. Yeast
C. Penicillium
D. Rhizobium

Q23. Biodegradable plastics can be decomposed by:
A. Microbial action
B. Sunlight only
C. Heat only
D. Inert chemicals

Q24. Sewage and industrial effluents can be detoxified using:
A. Microbes capable of bioremediation
B. Yeast fermentation
C. Antibiotics
D. Algae only

Q25. Microbes like Pseudomonas degrade:
A. Hydrocarbons and pesticides
B. Proteins
C. Lactose
D. Cellulose only

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6. Microbes as Pathogens (contextual)

Q26. E. coli contamination in water can cause:
A. Gastroenteritis
B. Malaria
C. TB
D. Influenza

Q27. Saccharomyces cerevisiae is generally:
A. Non-pathogenic and useful in food industry
B. Pathogenic
C. Soil bacterium
D. Biopesticide

Q28. Some fungi like Aspergillus flavus produce:
A. Aflatoxins
B. Antibiotics
C. Vitamins
D. Biofertilizers

Q29. Lactic acid bacteria are:
A. Beneficial in food fermentation
B. Pathogenic
C. Soil nitrogen fixers
D. Vector-borne pathogens

Q30. Industrial microbes are selected based on:
A. High yield, non-pathogenic, safe
B. Pathogenicity
C. Rapid spoilage
D. Antibiotic resistance only

B. Assertion–Reason MCQs – Microbes in Human Welfare (15 MCQs)

Q31.
Assertion: Lactobacillus is used in yogurt and cheese production.
Reason: It ferments lactose to lactic acid, which coagulates milk proteins.

Q32.
Assertion: Saccharomyces cerevisiae is used in alcohol fermentation.
Reason: It converts sugars into ethanol and carbon dioxide under anaerobic conditions.

Q33.
Assertion: Penicillium produces penicillin.
Reason: Penicillin inhibits bacterial cell wall synthesis.

Q34.
Assertion: Rhizobium forms nodules in leguminous plants.
Reason: It fixes atmospheric nitrogen symbiotically.

Q35.
Assertion: Bacillus thuringiensis is used as a biopesticide.
Reason: It produces toxins that kill insect larvae.

Q36.
Assertion: Microbes like Pseudomonas can degrade hydrocarbons.
Reason: Certain bacteria have enzymes that metabolize pollutants.

Q37.
Assertion: Aspergillus niger is used in citric acid production.
Reason: It secretes enzymes that convert sugars into citric acid.

Q38.
Assertion: Biofertilizers increase soil fertility.
Reason: They add nitrogen and other nutrients through microbial activity.

Q39.
Assertion: Activated sludge contains bacteria and protozoa.
Reason: They degrade organic matter during sewage treatment.

Q40.
Assertion: Microbes can be used in bioremediation of oil spills.
Reason: Hydrocarbon-degrading bacteria break down toxic compounds.

Q41.
Assertion: Single-cell protein (SCP) provides a source of protein.
Reason: Microbial biomass contains high-quality protein suitable for humans and animals.

Q42.
Assertion: Lactic acid bacteria prevent spoilage of milk.
Reason: Lactic acid lowers pH, inhibiting growth of pathogenic microbes.

Q43.
Assertion: E. coli contamination in water causes gastroenteritis.
Reason: Certain strains of E. coli produce toxins affecting the intestinal lining.

Q44.
Assertion: Microbes are essential in the production of antibiotics.
Reason: They produce secondary metabolites with antimicrobial properties.

Q45.
Assertion: Yeast fermentation is used in bread-making.
Reason: Carbon dioxide produced by yeast makes the dough rise.

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C. Difficult / Case / Diagram-Based MCQs – Microbes in Human Welfare (15 MCQs)

Q46. A factory produces citric acid using a fungus. Which fungus is used?
A. Aspergillus niger
B. Penicillium notatum
C. Saccharomyces cerevisiae
D. Rhizobium

Q47. A farmer applies Rhizobium biofertilizer to legume fields. The expected outcome is:
A. Increased nitrogen availability
B. Pest control
C. Antibiotic production
D. Alcohol production

Q48. A sewage treatment plant shows foam in aeration tanks. This is due to:
A. Microbial activity degrading organic matter
B. Chemical contamination
C. Air pollution
D. Heavy metals

Q49. A bioremediation project uses Pseudomonas to clean oil-contaminated soil. This works because:
A. Bacteria metabolize hydrocarbons
B. Bacteria produce ethanol
C. Bacteria fix nitrogen
D. Bacteria ferment milk

Q50. Industrial production of SCP involves:
A. Cultivation of microbes under controlled conditions for protein-rich biomass
B. Fermentation of milk
C. Alcohol production
D. Citric acid production

Q51. Bacillus thuringiensis is applied to crops. Its effect is:
A. Killing insect larvae
B. Killing fungal pathogens
C. Increasing soil nitrogen
D. Producing alcohol

Q52. Yogurt production involves lactic acid fermentation. The main product that coagulates milk is:
A. Lactic acid
B. Ethanol
C. Carbon dioxide
D. Acetone

Q53. A lab diagram shows microbe degrading organic matter in sludge. This represents:
A. Secondary sewage treatment
B. Primary treatment
C. Tertiary chemical treatment
D. Chlorination

Q54. A fungal culture produces enzymes converting starch to sugar. This enzyme is:
A. Amylase
B. Protease
C. Lipase
D. Cellulase

Q55. Spirulina is used as a single-cell protein source because:
A. It has high protein content and is edible
B. It ferments milk
C. It produces citric acid
D. It fixes nitrogen

Q56. Vinegar is produced using:
A. Acetobacter oxidizing ethanol to acetic acid
B. Saccharomyces producing alcohol
C. Lactobacillus producing lactic acid
D. Bacillus producing toxins

Q57. A diagram shows Rhizobium inside root nodules. The function is:
A. Nitrogen fixation
B. Phosphate solubilization
C. Biopesticide production
D. Biogas production

Q58. A contaminated water sample contains pathogenic E. coli. The likely health impact is:
A. Diarrhea and gastroenteritis
B. Malaria
C. Influenza
D. Tuberculosis

Q59. In cheese-making, microbial fermentation produces lactic acid. Its role is:
A. Coagulating milk proteins
B. Killing yeast
C. Producing ethanol
D. Producing acetic acid

Q60. Industrial microbes are selected for safety because:
A. Non-pathogenic strains ensure no risk to humans or environment
B. They grow rapidly only
C. They produce toxins
D. They are resistant to all antibiotics

A. Standard / Conceptual MCQs – Answers + Explanations (Q1–Q30)

Q.No	Answer	Explanation
1	A	Lactobacillus ferments lactose to lactic acid, used in yogurt.
2	A	Cheese is produced by lactic acid bacteria and rennet coagulating milk proteins.
3	A	Saccharomyces cerevisiae ferments sugars to ethanol and CO₂ in brewing.
4	A	Acetobacter oxidizes ethanol to acetic acid in vinegar production.
5	A	SCP uses microbial biomass (e.g., Spirulina) as protein source.
6	A	Idli/dosa fermentation involves Lactobacillus and Leuconostoc.
7	A	Penicillin is produced by Penicillium notatum, acting against bacteria.
8	A	Streptomycin is obtained from Streptomyces griseus.
9	A	Citric acid is industrially produced using Aspergillus niger.
10	A	Enzymes like amylase are produced by Aspergillus and Bacillus.
11	A	Vitamin B12 is produced by Propionibacterium.
12	A	Biofertilizers contain nitrogen-fixing bacteria like Rhizobium.
13	A	Azotobacter is a free-living nitrogen-fixing bacterium.
14	A	Rhizobium forms root nodules in leguminous plants.
15	A	Mycorrhizal fungi enhance mineral absorption for plants.
16	A	Bacillus thuringiensis produces insecticidal toxins.
17	A	Phosphate-solubilizing bacteria increase soil phosphate availability.
18	A	Primary sewage treatment involves settling solids.
19	A	Secondary treatment uses microbes to degrade organic matter.
20	A	Activated sludge contains bacteria and protozoa degrading waste.
21	A	Anaerobic digestion of sludge produces biogas (methane).
22	A	Hydrocarbon-degrading bacteria clean oil spills via metabolism.
23	A	Biodegradable plastics are decomposed by microbial activity.
24	A	Bioremediation uses microbes to detoxify sewage and industrial waste.
25	A	Pseudomonas degrade hydrocarbons and pesticides in the environment.
26	A	E. coli contamination causes gastroenteritis in humans.
27	A	Saccharomyces cerevisiae is non-pathogenic and used in food industry.
28	A	Aspergillus flavus produces aflatoxins, which are toxic.
29	A	Lactic acid bacteria are beneficial for fermentation.
30	A	Industrial microbes are selected for high yield, safety, and non-pathogenicity.

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B. Assertion–Reason MCQs – Answers + Explanations (Q31–Q45)

Q.No	Answer	Explanation
31	A	Lactobacillus ferments lactose → lactic acid → coagulates milk.
32	A	Saccharomyces cerevisiae converts sugar → ethanol + CO₂ anaerobically.
33	A	Penicillin inhibits bacterial cell wall synthesis.
34	A	Rhizobium fixes atmospheric nitrogen symbiotically in legume nodules.
35	A	Bt produces crystal proteins toxic to insect larvae.
36	A	Hydrocarbon-degrading bacteria metabolize oil pollutants.
37	A	Aspergillus niger secretes enzymes converting sugar → citric acid.
38	A	Biofertilizers enrich soil nutrients via microbial activity.
39	A	Activated sludge microbes degrade organic matter in secondary treatment.
40	A	Bioremediation uses bacteria to break down toxic compounds.
41	A	SCP microbial biomass provides high-quality protein.
42	A	Lactic acid lowers pH, inhibiting pathogenic microbes.
43	A	Certain E. coli strains produce enterotoxins causing gastroenteritis.
44	A	Microbes produce secondary metabolites like antibiotics.
45	A	Yeast fermentation produces CO₂, making bread dough rise.

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C. Difficult / Case / Diagram-Based MCQs – Answers + Explanations (Q46–Q60)

Q.No	Answer	Explanation
46	A	Citric acid is produced industrially by Aspergillus niger.
47	A	Rhizobium fixes nitrogen, increasing soil nitrogen content.
48	A	Foam in aeration tanks is due to microbial degradation of organic matter.
49	A	Pseudomonas metabolizes hydrocarbons for bioremediation.
50	A	SCP production involves cultivation of protein-rich microbes.
51	A	Bt toxins kill insect larvae, acting as biopesticide.
52	A	Lactic acid coagulates milk proteins in yogurt production.
53	A	Microbial degradation in sludge is secondary sewage treatment.
54	A	Amylase converts starch to sugar in industrial processes.
55	A	Spirulina biomass is rich in protein, suitable for human and animal consumption.
56	A	Acetobacter oxidizes ethanol → acetic acid to produce vinegar.
57	A	Rhizobium nodules fix atmospheric nitrogen for plants.
58	A	Pathogenic E. coli produces toxins causing diarrhea.
59	A	Lactic acid lowers pH → milk protein coagulation in cheese-making.
60	A	Non-pathogenic microbes ensure industrial safety for humans and environment.