🌸Chapter 8
Microbes in Human Welfare
(MCQs)
1. Which microorganism is used to
ferment milk to produce curd?
A. Rhizobium
B. Lactobacillus
C. Aspergillus
D. Penicillium
✅ Answer: B
Explanation: Lactobacillus converts lactose (milk sugar) to
lactic acid, coagulating milk proteins to form curd.
2. Which acid is produced during
curd formation?
A. Acetic acid
B. Lactic acid
C. Citric acid
D. Butyric acid
✅ Answer: B
Explanation: Lactobacillus produces lactic acid during
fermentation of milk.
3. The process by which yeast
converts sugar into alcohol is known as—
A. Distillation
B. Fermentation
C. Respiration
D. Filtration
✅ Answer: B
Explanation: Fermentation is an anaerobic process converting sugar to
ethanol and CO₂.
4. Which of the following organisms
is used in bread making?
A. Aspergillus niger
B. Saccharomyces cerevisiae
C. Rhizopus
D. Clostridium
✅ Answer: B
Explanation: Saccharomyces cerevisiae (baker’s yeast) produces
CO₂, making dough rise.
5. The holes in Swiss cheese are due
to—
A. Lactobacillus
B. Aspergillus
C. Propionibacterium shermanii
D. Penicillium roqueforti
✅ Answer: C
Explanation: Propionibacterium shermanii releases CO₂ during
fermentation, forming holes.
6. Penicillium notatum
produces—
A. Citric acid
B. Acetic acid
C. Penicillin
D. Butyric acid
✅ Answer: C
Explanation: Penicillium notatum is the source of the antibiotic
penicillin.
7. Who discovered penicillin?
A. Louis Pasteur
B. Alexander Fleming
C. Robert Koch
D. Edward Jenner
✅ Answer: B
Explanation: Fleming discovered penicillin in 1928 from Penicillium
notatum.
8. Which scientists developed
penicillin for large-scale use?
A. Jenner and Koch
B. Florey and Chain
C. Watson and Crick
D. Pasteur and Koch
✅ Answer: B
Explanation: Florey and Chain mass-produced penicillin during World War
II.
9. Which is not an antibiotic?
A. Streptomycin
B. Tetracycline
C. Erythromycin
D. Statin
✅ Answer: D
Explanation: Statins are cholesterol-lowering agents, not antibiotics.
10. Aspergillus niger is used
for industrial production of—
A. Acetic acid
B. Citric acid
C. Butyric acid
D. Lactic acid
✅ Answer: B
Explanation: Aspergillus niger produces citric acid on large
scale.
11. Acetobacter aceti
produces—
A. Acetic acid
B. Citric acid
C. Butyric acid
D. Lactic acid
✅ Answer: A
Explanation: Acetobacter aceti oxidizes ethanol to acetic acid
(vinegar).
12. Clostridium butylicum
produces—
A. Lactic acid
B. Butyric acid
C. Citric acid
D. Acetic acid
✅ Answer: B
Explanation: Clostridium butylicum is used for butyric acid
production.
13. Which fungus is used in the
production of cyclosporin A?
A. Penicillium
B. Trichoderma polysporum
C. Monascus purpureus
D. Aspergillus niger
✅ Answer: B
Explanation: Trichoderma polysporum produces cyclosporin A, an
immunosuppressant drug.
14. Statins are produced by—
A. Penicillium
B. Trichoderma
C. Monascus purpureus
D. Aspergillus
✅ Answer: C
Explanation: Monascus purpureus produces statins, which lower
blood cholesterol.
15. Statins act by—
A. Increasing cholesterol
B. Inhibiting cholesterol synthesis
C. Enhancing blood sugar
D. Killing bacteria
✅ Answer: B
Explanation: Statins inhibit enzyme HMG-CoA reductase responsible for
cholesterol synthesis.
16. Cyclosporin A is used as—
A. Antibiotic
B. Immunosuppressive drug
C. Anti-cholesterol agent
D. Antifungal
✅ Answer: B
Explanation: It suppresses immune response during organ transplantation.
17. Which of the following is used
in organic acid production?
A. Trichoderma
B. Aspergillus niger
C. Monascus purpureus
D. Penicillium notatum
✅ Answer: B
Explanation: Aspergillus niger produces citric acid.
18. Biogas mainly contains—
A. Carbon dioxide
B. Methane
C. Hydrogen
D. Oxygen
✅ Answer: B
Explanation: Methane (CH₄) is the major component of biogas.
19. Which microorganism produces
biogas from cow dung?
A. Rhizobium
B. Methanobacterium
C. Azotobacter
D. Nitrosomonas
✅ Answer: B
Explanation: Methanobacterium (a methanogen) generates methane
under anaerobic conditions.
20. Methanogens belong to which
group?
A. Eubacteria
B. Archaebacteria
C. Cyanobacteria
D. Fungi
✅ Answer: B
Explanation: Methanogens are Archaebacteria that produce methane gas.
21. The substrate used in biogas
production is—
A. Cow dung
B. Compost
C. Sewage sludge
D. All of these
✅ Answer: D
Explanation: Any organic waste (cow dung, sludge, or agricultural
residue) can be used.
22. Which organization developed the
biogas plant in India?
A. ISRO
B. KVIC and IARI
C. CSIR
D. ICAR
✅ Answer: B
Explanation: Khadi and Village Industries Commission (KVIC) and IARI
developed it.
23. In sewage treatment, primary
treatment removes—
A. Organic matter
B. Pathogens
C. Suspended solids
D. All microbes
✅ Answer: C
Explanation: Primary treatment involves physical removal of suspended
solids.
24. The biological treatment of
sewage is also known as—
A. Tertiary treatment
B. Aerobic treatment
C. Secondary treatment
D. Primary treatment
✅ Answer: C
Explanation: Secondary treatment uses aerobic microbes to oxidize
organic matter.
25. The microbial flocs consist of—
A. Only bacteria
B. Fungi only
C. Bacteria and fungal filaments
D. Algae only
✅ Answer: C
Explanation: Flocs are masses of bacteria held together by fungal
filaments.
26. Activated sludge is—
A. Sludge from primary treatment
B. Aerated microbial flocs
C. Sludge with sand and stones
D. Dead organic matter
✅ Answer: B
Explanation: Activated sludge contains aerobic microbes used as
inoculum.
27. The gas produced in anaerobic
sludge digestion is—
A. Methane
B. Oxygen
C. Carbon monoxide
D. Sulphur dioxide
✅ Answer: A
Explanation: Methane is formed by methanogenic archaebacteria.
28. Biogas can be used for—
A. Cooking
B. Lighting
C. Running engines
D. All of these
✅ Answer: D
Explanation: Biogas is a multipurpose fuel.
29. In biogas plant, the digestion
of waste occurs in—
A. Aerobic condition
B. Anaerobic condition
C. Sunlight
D. High temperature only
✅ Answer: B
Explanation: Methanogens act only in absence of oxygen.
30. Which of the following is a
biocontrol agent?
A. Rhizobium
B. Trichoderma
C. Aspergillus
D. Penicillium
✅ Answer: B
Explanation: Trichoderma is a free-living fungus controlling soil
pathogens.
31. Bacillus thuringiensis is
used as—
A. Biofertiliser
B. Biopesticide
C. Antibiotic producer
D. Fungicide
✅ Answer: B
Explanation: Bt produces a toxin lethal to insect larvae.
32. Bt cotton has—
A. Bt insect
B. Bt bacterium
C. Bt toxin gene
D. Bt virus
✅ Answer: C
Explanation: Bt cotton is genetically modified to carry Bt toxin gene
from B. thuringiensis.
33. Bt toxin acts on—
A. Aphids
B. Bollworm larvae
C. Termites
D. Mosquitoes
✅ Answer: B
Explanation: Bt toxin kills larvae of cotton bollworm.
34. Mechanism of Bt toxin:
A. Destroys plant cell wall
B. Forms pores in insect gut
C. Blocks enzyme activity
D. Inhibits DNA replication
✅ Answer: B
Explanation: Bt toxin creates pores in midgut epithelium of insects
causing death.
35. Trichoderma species
control pathogens by—
A. Releasing antibiotics
B. Competing for nutrients
C. Mycoparasitism
D. All of these
✅ Answer: D
Explanation: They employ all mechanisms to suppress pathogens.
36. Example of free-living nitrogen
fixer—
A. Rhizobium
B. Azospirillum
C. Anabaena
D. Nostoc
✅ Answer: B
Explanation: Azospirillum and Azotobacter are free-living
bacteria.
37. Rhizobium lives
symbiotically with—
A. Rice roots
B. Legume roots
C. Wheat roots
D. Maize roots
✅ Answer: B
Explanation: Rhizobium forms root nodules in legumes for nitrogen
fixation.
38. Cyanobacteria act as
biofertiliser by—
A. Fixing carbon
B. Fixing nitrogen
C. Producing oxygen
D. Releasing hormones
✅ Answer: B
Explanation: Anabaena, Nostoc fix atmospheric N₂ in paddy
fields.
39. Example of cyanobacterial
biofertiliser—
A. Rhizobium
B. Anabaena
C. Trichoderma
D. Monascus
✅ Answer: B
Explanation: Anabaena (blue-green algae) enriches nitrogen in
soil.
40. Mycorrhiza is association
between—
A. Algae and fungi
B. Bacteria and fungi
C. Fungi and roots of plants
D. Two fungi
✅ Answer: C
Explanation: Mycorrhiza = fungus + plant root symbiosis.
41. The fungal partner of mycorrhiza
helps the plant by—
A. Providing nitrogen
B. Increasing phosphate absorption
C. Forming nodules
D. Fixing CO₂
✅ Answer: B
Explanation: Mycorrhizal fungi (e.g., Glomus) enhance phosphorus
and water absorption from soil.
42. Which of the following is a
phosphate-absorbing fungus?
A. Rhizobium
B. Glomus
C. Anabaena
D. Aspergillus
✅ Answer: B
Explanation: Glomus forms mycorrhiza with roots and aids
phosphate uptake.
43. Biofertilizers are—
A. Chemical fertilizers
B. Synthetic hormones
C. Living microorganisms increasing soil fertility
D. Artificial pesticides
✅ Answer: C
Explanation: Biofertilizers are microbes that enrich soil with nutrients
naturally.
44. Example of symbiotic nitrogen
fixer—
A. Azotobacter
B. Rhizobium
C. Azospirillum
D. Nostoc
✅ Answer: B
Explanation: Rhizobium forms nodules in legumes and fixes
atmospheric nitrogen.
45. Anabaena is found in
association with—
A. Fern roots
B. Water hyacinth
C. Azolla
D. Glomus
✅ Answer: C
Explanation: Anabaena lives symbiotically inside Azolla
leaves (paddy fields biofertiliser).
46. Paddy fields commonly use which
biofertilizer?
A. Rhizobium
B. Anabaena
C. Trichoderma
D. Penicillium
✅ Answer: B
Explanation: Anabaena fixes nitrogen in waterlogged paddy fields.
47. Which process converts milk into
curd?
A. Aerobic respiration
B. Alcoholic fermentation
C. Lactic acid fermentation
D. Anaerobic respiration
✅ Answer: C
Explanation: Lactic acid bacteria ferment lactose into lactic acid.
48. Which vitamin increases during
curd formation?
A. Vitamin A
B. Vitamin B12
C. Vitamin C
D. Vitamin D
✅ Answer: B
Explanation: LAB enhances vitamin B12 content in curd.
49. Which of these is a fungal
biocontrol agent?
A. Trichoderma harzianum
B. Rhizobium leguminosarum
C. Methanobacterium
D. Azospirillum
✅ Answer: A
Explanation: Trichoderma harzianum suppresses soil-borne
pathogens.
50. Biocontrol means—
A. Use of chemicals to control pests
B. Use of living organisms to control pests
C. Mechanical pest removal
D. Sterilization of soil
✅ Answer: B
Explanation: Biological control uses natural organisms instead of toxic
chemicals.
51. Bt toxin is active in—
A. Acidic medium
B. Alkaline medium
C. Neutral medium
D. None
✅ Answer: B
Explanation: Bt toxin activates in the alkaline gut of insects.
52. Bt toxin affects—
A. Human cells
B. Plant cells
C. Insect midgut cells
D. Fungal cells
✅ Answer: C
Explanation: It creates pores in insect midgut cells causing death.
53. Ladybird beetle is used to
control—
A. Aphids
B. Mosquitoes
C. Bollworms
D. Termites
✅ Answer: A
Explanation: Ladybird beetles eat aphids and act as biological pest
controllers.
54. Dragonflies are useful because
they eat—
A. Caterpillars
B. Mosquito larvae
C. Beetles
D. Butterflies
✅ Answer: B
Explanation: Dragonflies feed on mosquito larvae, controlling their
population.
55. Which of the following is not
a biofertilizer?
A. Rhizobium
B. Azotobacter
C. Anabaena
D. Penicillium
✅ Answer: D
Explanation: Penicillium produces antibiotics, not biofertilizer.
56. Activated sludge is mainly used
for—
A. Primary treatment
B. Secondary treatment
C. Tertiary treatment
D. Chlorination
✅ Answer: B
Explanation: It is used in secondary (biological) treatment for sewage.
57. The effluent from primary
treatment is rich in—
A. Organic matter
B. Heavy metals
C. Sand and gravel
D. None
✅ Answer: A
Explanation: It still contains dissolved organic matter for biological
treatment.
58. The process used to remove
biological matter from sewage is—
A. Chlorination
B. Aeration
C. Flocculation
D. Oxidation
✅ Answer: B
Explanation: Aeration provides oxygen for aerobic microbes to oxidize
organic waste.
59. The microbial digestion in a
biogas plant produces—
A. Carbon monoxide
B. Methane
C. Ethanol
D. Lactic acid
✅ Answer: B
Explanation: Methanogenic bacteria convert waste into methane gas.
60. Methane is produced during—
A. Aerobic respiration
B. Anaerobic digestion
C. Photosynthesis
D. Nitrification
✅ Answer: B
Explanation: Methanogens act under anaerobic conditions.
61. What is the function of
methanogens in sewage treatment?
A. Produce methane
B. Oxidize ammonia
C. Decompose plastics
D. Kill pathogens
✅ Answer: A
Explanation: Methanogens digest sludge anaerobically, releasing methane.
62. Biogas is a—
A. Fossil fuel
B. Renewable source of energy
C. Non-renewable fuel
D. Mineral fuel
✅ Answer: B
Explanation: It’s renewable because it’s produced from organic waste.
63. Which of the following microbes
is used in producing acetic acid?
A. Acetobacter aceti
B. Lactobacillus
C. Clostridium
D. Monascus
✅ Answer: A
Explanation: Acetobacter aceti oxidizes ethanol to acetic acid
(vinegar).
64. The first antibiotic discovered
was—
A. Streptomycin
B. Penicillin
C. Chloramphenicol
D. Erythromycin
✅ Answer: B
Explanation: Penicillin was the first antibiotic discovered by Fleming.
65. Microbes used in cheese
production include—
A. Lactobacillus bulgaricus
B. Penicillium roqueforti
C. Saccharomyces
D. Rhizopus
✅ Answer: B
Explanation: Penicillium roqueforti ripens cheese and gives it
flavor.
66. Swiss cheese is made by—
A. Rhizopus
B. Propionibacterium shermanii
C. Penicillium
D. Aspergillus
✅ Answer: B
Explanation: CO₂ from Propionibacterium forms holes in Swiss
cheese.
67. Yeast used in brewing industry—
A. Saccharomyces cerevisiae
B. Penicillium chrysogenum
C. Rhizopus stolonifer
D. Clostridium butylicum
✅ Answer: A
Explanation: S. cerevisiae ferments sugars into ethanol and CO₂.
68. Ethanol is produced from
molasses by—
A. Aspergillus
B. Saccharomyces cerevisiae
C. Acetobacter
D. Rhizopus
✅ Answer: B
Explanation: Yeast converts sugars in molasses to alcohol (ethanol).
69. Antibiotic “Streptomycin” is
produced by—
A. Streptomyces griseus
B. Aspergillus niger
C. Clostridium
D. Monascus
✅ Answer: A
Explanation: Streptomyces griseus produces Streptomycin
antibiotic.
70. The process of increasing BOD
(Biochemical Oxygen Demand) occurs during—
A. Primary treatment
B. Aeration of sewage
C. Decomposition of organic matter
D. Anaerobic digestion
✅ Answer: C
Explanation: BOD increases when microbes consume organic matter.
71. High BOD indicates—
A. Clean water
B. Polluted water
C. Sterile water
D. Mineral water
✅ Answer: B
Explanation: High BOD = high organic load = polluted water.
72. Methanogens are found in—
A. Cow dung
B. Rumen of cattle
C. Sewage sludge
D. All of these
✅ Answer: D
Explanation: Methanogens live in anaerobic environments rich in organic
matter.
73. Which bacteria is used in the
dairy industry?
A. Rhizobium
B. Lactobacillus
C. Streptomyces
D. Azotobacter
✅ Answer: B
Explanation: Lactobacillus ferments milk into curd and yogurt.
74. LAB stands for—
A. Lactic Acid Bacteria
B. Lactose Active Bacteria
C. Lactic Acid Base
D. Lactose Alkaline Bacteria
✅ Answer: A
Explanation: LAB are bacteria producing lactic acid.
75. Which of the following is not
used in industrial fermentation?
A. Yeast
B. Rhizobium
C. Clostridium
D. Aspergillus
✅ Answer: B
Explanation: Rhizobium is used in nitrogen fixation, not
industrial fermentation.
76. What is common among Rhizobium,
Azospirillum, and Anabaena?
A. Nitrogen fixation
B. Antibiotic production
C. Fermentation
D. Acid formation
✅ Answer: A
Explanation: All fix atmospheric nitrogen.
77. Microbial enzymes are used in—
A. Textile industry
B. Detergent industry
C. Food industry
D. All of these
✅ Answer: D
Explanation: Microbial enzymes are used widely in multiple industries.
78. The main gas in biogas
responsible for energy—
A. CO₂
B. CH₄
C. H₂
D. CO
✅ Answer: B
Explanation: Methane is the combustible gas in biogas.
79. Which one is an example of
Archaebacteria?
A. Nitrosomonas
B. Methanobacterium
C. Streptomyces
D. Rhizobium
✅ Answer: B
Explanation: Methanobacterium is an Archaebacterium producing
methane.
80. Trichoderma lives—
A. In roots of legumes
B. Freely in soil and rhizosphere
C. In animal gut
D. In stagnant water
✅ Answer: B
Explanation: Trichoderma species are free-living fungi in root
region.
Q81. Which of the following microbes is used in the production of Swiss cheese?
A. Lactobacillus bulgaricus
B. Propionibacterium shermanii
C. Penicillium notatum
D. Aspergillus niger
✅ Answer: B
Explanation: Propionibacterium shermanii produces large amounts
of CO₂, which creates the characteristic holes in Swiss cheese.
Q82. The bacterium Lactobacillus
is commonly used in the:
A. Production of wine
B. Production of curd from milk
C. Production of vinegar
D. Ripening of cheese
✅ Answer: B
Explanation: Lactobacillus converts milk lactose into lactic
acid, causing milk to coagulate and form curd.
Q83. Which of the following pairs is
correctly matched?
A. Penicillium notatum – Antibiotic
B. Rhizobium – Alcohol production
C. Streptococcus – Vinegar production
D. Aspergillus niger – Bread making
✅ Answer: A
Explanation: Penicillium notatum produces the antibiotic
penicillin.
Q84. Which of the following
statements about antibiotics is incorrect?
A. They are used to kill or inhibit the growth of harmful
microorganisms.
B. They are used in viral infections.
C. They can be produced by certain fungi and bacteria.
D. Penicillin is one example.
✅ Answer: B
Explanation: Antibiotics are effective against bacteria, not viruses.
Q85. Streptococcus and Lactobacillus
are involved in:
A. Cheese making
B. Curd formation
C. Sewage treatment
D. Antibiotic production
✅ Answer: B
Explanation: Both bacteria help in converting milk into curd by
producing lactic acid.
Q86. Which of the following is NOT
an example of a microbial product used in industries?
A. Lactic acid
B. Acetic acid
C. Chloroform
D. Citric acid
✅ Answer: C
Explanation: Chloroform is not produced by microbes; it’s a chemical
compound made industrially.
Q87. Which of the following microbes
is used to produce cyclosporin A, an immunosuppressive drug?
A. Clostridium butylicum
B. Trichoderma polysporum
C. Monascus purpureus
D. Streptomyces
✅ Answer: B
Explanation: Trichoderma polysporum is a fungus that produces
cyclosporin A, which suppresses the immune response in organ transplant
patients.
Q88. Monascus purpureus is
used commercially for the production of:
A. Citric acid
B. Statins
C. Alcohol
D. Lactic acid
✅ Answer: B
Explanation: Monascus purpureus produces statins, which reduce
blood cholesterol levels.
Q89. The bioactive molecule statin
is used for:
A. Controlling blood pressure
B. Lowering blood cholesterol
C. Acting as a painkiller
D. Curing fungal infections
✅ Answer: B
Explanation: Statins inhibit cholesterol synthesis in the liver, thus
reducing blood cholesterol.
Q90. Which of the following is not
used in sewage treatment?
A. Aerobic bacteria
B. Fungi
C. Protozoa
D. Viruses
✅ Answer: D
Explanation: Viruses do not play a role in sewage treatment; mainly
aerobic bacteria, fungi, and protozoa do.
Q91. The primary treatment of sewage
involves:
A. Physical removal of large and small particles
B. Biological degradation
C. Chemical treatment
D. Chlorination
✅ Answer: A
Explanation: Primary treatment removes large and small suspended solids
through sedimentation and filtration.
Q92. The secondary treatment of
sewage is also known as:
A. Chemical treatment
B. Biological treatment
C. Physical treatment
D. Tertiary treatment
✅ Answer: B
Explanation: It uses aerobic microbes to degrade organic matter
biologically.
Q93. Activated sludge is:
A. Aerated sewage water containing microbial flocs
B. Raw sewage water
C. Dried sludge used as manure
D. Chemical solution for sewage purification
✅ Answer: A
Explanation: Activated sludge is rich in microbial flocs (bacteria +
fungi), used in secondary treatment.
Q94. Biogas mainly contains:
A. CO₂ and O₂
B. CO₂ and CH₄
C. CH₄ and N₂
D. CO₂ and NH₃
✅ Answer: B
Explanation: Biogas primarily contains methane (CH₄) and carbon dioxide
(CO₂).
Q95. Which of the following is the
chief producer of biogas in the rumen of cattle?
A. Methanobacterium
B. Rhizobium
C. Azotobacter
D. Clostridium
✅ Answer: A
Explanation: Methanobacterium, an anaerobic archaeon, produces
methane in the rumen of cattle.
Q96. In biogas plants, the slurry
left after gas production is used as:
A. Fuel
B. Fertilizer
C. Pesticide
D. Food for animals
✅ Answer: B
Explanation: The residual slurry is rich in nitrogen and phosphorus,
making it a good manure.
Q97. The BOD (Biochemical Oxygen
Demand) test measures:
A. The amount of oxygen required by microorganisms to
decompose organic matter
B. The total oxygen content in water
C. The amount of nitrogen in water
D. The pH of water
✅ Answer: A
Explanation: BOD indicates organic pollution; higher BOD means more
organic matter.
Q98. A high value of BOD indicates:
A. Water is pure
B. Water is highly polluted
C. Less microbial activity
D. Low organic matter
✅ Answer: B
Explanation: High BOD means more organic waste, leading to greater
microbial activity and pollution.
Q99. The first antibiotic discovered
by Alexander Fleming was:
A. Streptomycin
B. Penicillin
C. Tetracycline
D. Chloramphenicol
✅ Answer: B
Explanation: Penicillin was discovered accidentally by Fleming
from Penicillium notatum in 1928.
Q100. The use of microbes for the
welfare of humans is called:
A. Microbial genetics
B. Microbial biotechnology
C. Microbiology
D. Microbial ecology
✅ Answer: B
Explanation: Using microbes for human benefit in fields like industry,
medicine, and environment is called microbial biotechnology or applied
microbiology.
