MCQs on Microbes in Human Welfare – Class 12 Biology (NCERT Based)

Course: CBSE Class 12 Biology
Unit III: Biology and Human Welfare
Topic: Microbes in Human Welfare
Strictly as per NCERT | CBSE Board Exam Oriented | Concept-Clearing Explanations

Section A: Microbes in Household Products (Q1–Q15)

Q1. Microbes are useful to humans mainly because they

A. cause diseases
B. increase pollution
C. help in production of useful products
D. reduce biodiversity

Correct Answer: C
Explanation: Microbes play an important role in producing food, medicines, and industrial products beneficial to humans.

Q2. The microorganism used in bread making is

A. Lactobacillus
B. Rhizobium
C. Saccharomyces cerevisiae
D. Aspergillus

Correct Answer: C
Explanation: Baker’s yeast (Saccharomyces cerevisiae) ferments sugars producing CO₂, which makes bread soft and spongy.

Q3. Curd formation from milk is carried out by

A. yeast
B. Lactobacillus
C. virus
D. protozoa

Correct Answer: B
Explanation: Lactobacillus converts lactose into lactic acid, coagulating milk proteins to form curd.

Q4. Which acid is responsible for sour taste of curd?

A. Acetic acid
B. Citric acid
C. Lactic acid
D. Formic acid

Correct Answer: C
Explanation: Lactic acid produced during fermentation gives curd its sour taste.

Q5. Which beverage is produced by fermentation of malted barley?

A. Wine
B. Beer
C. Vinegar
D. Toddy

Correct Answer: B
Explanation: Beer is produced by fermentation of malted barley using yeast.

Q6. Toddy is obtained from

A. fruits
B. flowers
C. palm sap
D. grains

Correct Answer: C
Explanation: Toddy is fermented sap of palms like coconut and date palm.

Q7. Which microbe is used in production of vinegar?

A. Yeast
B. Lactobacillus
C. Acetobacter
D. Rhizobium

Correct Answer: C
Explanation: Acetobacter converts alcohol into acetic acid to form vinegar.

Q8. Cheese production involves

A. only bacteria
B. only fungi
C. bacteria and fungi
D. viruses

Correct Answer: C
Explanation: Bacteria and fungi are used in cheese ripening and flavor development.

Q9. Swiss cheese contains large holes due to

A. oxygen bubbles
B. CO₂ released by Propionibacterium
C. nitrogen gas
D. lactic acid

Correct Answer: B
Explanation: CO₂ produced by Propionibacterium shermanii forms holes.

Q10. Which fungus is used in production of Roquefort cheese?

A. Aspergillus
B. Penicillium roqueforti
C. Rhizopus
D. Saccharomyces

Correct Answer: B
Explanation: Penicillium roqueforti gives characteristic flavor to Roquefort cheese.

Q11. Microbes increase nutritional value of curd by increasing

A. fats
B. vitamins B₁₂ and B-complex
C. carbohydrates
D. proteins

Correct Answer: B
Explanation: Lactic acid bacteria enhance vitamin content in curd.

Q12. Which of the following is NOT a fermented product?

A. Curd
B. Bread
C. Cheese
D. Butter

Correct Answer: D
Explanation: Butter is produced by churning, not fermentation.

Q13. Fermentation is an example of

A. aerobic respiration
B. anaerobic respiration
C. photosynthesis
D. oxidation

Correct Answer: B
Explanation: Fermentation occurs in absence of oxygen.

Q14. The alcohol content in toddy is low because

A. fermentation is incomplete
B. yeast is absent
C. sugar content is low
D. it is distilled

Correct Answer: A
Explanation: Toddy undergoes mild and natural fermentation.

Q15. Microbial activity in food products mainly helps in

A. spoilage only
B. improving taste and digestibility
C. causing infection
D. reducing nutrition

Correct Answer: B
Explanation: Fermentation improves flavor, digestibility, and nutritional value.

Section B: Microbes in Industrial Products (Q16–Q30)

Q16. Industrial production of alcohol uses

A. bacteria
B. algae
C. yeast
D. virus

Correct Answer: C
Explanation: Yeast ferments sugars into alcohol on a large scale.

Q17. Which organic acid is produced by Aspergillus niger?

A. Lactic acid
B. Acetic acid
C. Citric acid
D. Formic acid

Correct Answer: C
Explanation: Aspergillus niger is used for commercial citric acid production.

Q18. Lactic acid is produced by

A. Yeast
B. Lactobacillus
C. Penicillium
D. Rhizobium

Correct Answer: B
Explanation: Lactobacillus produces lactic acid through fermentation.

Q19. Which antibiotic was the first to be discovered?

A. Streptomycin
B. Tetracycline
C. Penicillin
D. Chloramphenicol

Correct Answer: C
Explanation: Penicillin was discovered by Alexander Fleming.

Q20. Penicillin is produced by

A. Penicillium notatum
B. Aspergillus
C. Rhizopus
D. Lactobacillus

Correct Answer: A
Explanation: Penicillium notatum produces penicillin.

Q21. Antibiotics are effective against

A. viruses
B. bacteria
C. protozoa only
D. all pathogens

Correct Answer: B
Explanation: Antibiotics target bacterial infections, not viral ones.

Q22. Statins are used to

A. kill bacteria
B. lower blood cholesterol
C. cure viral diseases
D. improve digestion

Correct Answer: B
Explanation: Statins reduce cholesterol levels by inhibiting its synthesis.

Q23. Statins are produced by

A. Yeast
B. Monascus purpureus
C. Lactobacillus
D. Penicillium

Correct Answer: B
Explanation: Monascus purpureus produces statins.

Q24. Single Cell Protein (SCP) refers to

A. plant protein
B. animal protein
C. microbial protein
D. synthetic protein

Correct Answer: C
Explanation: SCP is protein derived from microbial biomass.

Q25. SCP helps in

A. reducing pollution
B. solving protein deficiency
C. increasing soil fertility
D. causing disease

Correct Answer: B
Explanation: SCP is a cheap and rich protein source.

Q26. Which organism is used for SCP production?

A. Chlorella
B. Wheat
C. Rice
D. Fish

Correct Answer: A
Explanation: Chlorella is an alga rich in protein.

Q27. Fermenters are used in industries to

A. grow plants
B. culture microbes under controlled conditions
C. store food
D. dry products

Correct Answer: B
Explanation: Fermenters provide optimum conditions for microbial growth.

Q28. Which gas is produced during alcoholic fermentation?

A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen

Correct Answer: C
Explanation: CO₂ is released during fermentation by yeast.

Q29. Industrial enzymes are produced using

A. plants
B. animals
C. microbes
D. minerals

Correct Answer: C
Explanation: Microbes are efficient enzyme producers.

Q30. Which enzyme is used in detergent industry?

A. Amylase
B. Protease
C. Lipase
D. All of the above

Correct Answer: D
Explanation: Detergents contain enzymes to break stains.

Section C: Microbes in Sewage Treatment, Biogas and Biocontrol (Q31–Q50)

Q31. Sewage treatment helps to

A. increase pollution
B. remove organic matter
C. spread diseases
D. kill all microbes

Correct Answer: B
Explanation: Treatment reduces organic load and pathogens.

Q32. Primary sewage treatment is mainly

A. biological
B. chemical
C. physical
D. genetic

Correct Answer: C
Explanation: It involves physical removal of solids.

Q33. Secondary sewage treatment is also called

A. mechanical treatment
B. chemical treatment
C. biological treatment
D. thermal treatment

Correct Answer: C
Explanation: Microbes degrade organic matter biologically.

Q34. Activated sludge consists of

A. algae only
B. bacteria and fungi
C. viruses
D. protozoa only

Correct Answer: B
Explanation: It contains microbial flocs that digest organic matter.

Q35. BOD stands for

A. Biological Oxygen Demand
B. Basic Oxygen Deficit
C. Biochemical Organic Demand
D. Bacterial Oxygen Demand

Correct Answer: A
Explanation: BOD measures organic pollution level.

Q36. High BOD indicates

A. clean water
B. polluted water
C. distilled water
D. saline water

Correct Answer: B
Explanation: More oxygen is required to decompose organic matter.

Q37. Biogas is produced by

A. aerobic bacteria
B. methanogenic bacteria
C. fungi
D. algae

Correct Answer: B
Explanation: Methanogens produce methane gas anaerobically.

Q38. The main component of biogas is

A. carbon dioxide
B. methane
C. oxygen
D. nitrogen

Correct Answer: B
Explanation: Methane is the major combustible gas.

Q39. Slurry left after biogas production is used as

A. fuel
B. pesticide
C. manure
D. insecticide

Correct Answer: C
Explanation: Slurry is rich in nutrients and used as fertilizer.

Q40. Biocontrol agents are used to

A. kill crops
B. control pests naturally
C. increase pollution
D. destroy soil microbes

Correct Answer: B
Explanation: Biocontrol uses natural predators or pathogens.

Q41. Which bacterium is used as a biocontrol agent?

A. Lactobacillus
B. Bacillus thuringiensis
C. Rhizobium
D. Azotobacter

Correct Answer: B
Explanation: Bacillus thuringiensis produces toxins harmful to insects.

Q42. Bt cotton is resistant to

A. viruses
B. bacteria
C. insect pests
D. fungi

Correct Answer: C
Explanation: Bt toxin kills specific insect larvae.

Q43. Trichoderma is used as

A. fertilizer
B. biocontrol agent
C. pollutant
D. antibiotic

Correct Answer: B
Explanation: Trichoderma suppresses plant pathogens.

Q44. Which microbe is used as biofertilizer?

A. Rhizobium
B. Virus
C. Protozoa
D. Yeast

Correct Answer: A
Explanation: Rhizobium fixes atmospheric nitrogen.

Q45. Blue-green algae act as

A. pathogens
B. biofertilizers
C. decomposers
D. parasites

Correct Answer: B
Explanation: Cyanobacteria fix nitrogen in paddy fields.

Q46. Mycorrhizae help plants in absorption of

A. nitrogen
B. phosphorus
C. potassium
D. calcium

Correct Answer: B
Explanation: Mycorrhizal fungi enhance phosphorus uptake.

Q47. Which is NOT a benefit of microbes?

A. Food production
B. Disease cure
C. Pollution reduction
D. Ozone depletion

Correct Answer: D
Explanation: Microbes do not cause ozone depletion.

Q48. Microbes in human welfare mainly promote

A. environmental degradation
B. sustainable development
C. extinction
D. toxicity

Correct Answer: B
Explanation: Microbes support eco-friendly and sustainable practices.

Q49. Biofertilizers reduce dependence on

A. organic manure
B. irrigation
C. chemical fertilizers
D. crop rotation

Correct Answer: C
Explanation: Biofertilizers naturally improve soil nutrients.

Q50. Microbes are called backbone of biotechnology because they

A. cause mutations
B. are easy to culture and manipulate
C. are harmful
D. reduce productivity

Correct Answer: B
Explanation: Microbes are versatile tools in biotechnology applications.

✅ End of MCQs – Microbes in Human Welfare (Class 12 Biology, NCERT)