🌸Chapter 8
Microbes in Human Welfare
(5 Marks)
Q1. Explain the role of microbes in
household products with suitable examples.
Answer:
Microbes play an important role in the preparation of household products:
1.
Curd
Formation – Lactobacillus
converts lactose into lactic acid, coagulating milk proteins.
2.
Dosa
& Idli Batter
– Fermentation by Leuconostoc and Streptococcus species causes
puffing due to CO₂ release.
3.
Bread
Making – Saccharomyces
cerevisiae (yeast) ferments sugar, producing CO₂ that makes bread rise.
4.
Cheese
Production –
Different microbes (like Penicillium roqueforti) give flavor and texture
to cheese.
5.
Beverages – Fermentation by yeast produces
ethanol used in wine, beer, whisky, etc.
Q2. Describe the role of
microorganisms in industrial production.
Answer:
Industrial microbiology uses microbes to produce various products at a large
scale:
1.
Beverages – Saccharomyces cerevisiae
produces alcohols like beer, wine.
2.
Antibiotics – Penicillium notatum
produces penicillin; Streptomyces produces streptomycin, tetracycline.
3.
Organic
Acids – Aspergillus
niger (citric acid), Acetobacter aceti (acetic acid), Clostridium
butylicum (butyric acid).
4.
Enzymes – Aspergillus produces
pectinases, proteases; Streptococcus produces streptokinase.
5.
Bioactive
Molecules –
Cyclosporin A (immunosuppressant from Trichoderma polysporum), Statins
from Monascus purpureus.
Q3. What is an antibiotic? Describe
the discovery and uses of Penicillin.
Answer:
- Antibiotic: A chemical substance produced
by microbes that kills or inhibits the growth of other microbes.
- Discovery: Alexander Fleming (1928)
observed Penicillium notatum inhibited Staphylococcus
bacteria growth.
- Further Development: Ernst Chain & Howard
Florey developed it for medical use during WWII.
- Uses:
- Treat bacterial infections
like pneumonia, gonorrhea, and syphilis.
- It prevents bacterial cell
wall synthesis without affecting human cells.
Q4. Explain the role of microbes in
sewage treatment.
Answer:
Sewage treatment removes organic waste using microbes:
1.
Primary
Treatment: Physical
removal of floating and suspended solids by sedimentation.
2.
Secondary
(Biological) Treatment:
o Aeration tanks with aerobic
microbes oxidize organic matter into CO₂ and water.
o Activated sludge forms; part is recycled, rest used
as manure.
3.
Anaerobic
Sludge Digestion:
Methanogens (e.g., Methanobacterium) decompose organic matter producing
biogas.
4.
Outcome: Treated water is released into
rivers; reduces BOD (Biochemical Oxygen Demand).
Q5. What is Biogas? Explain its
production process.
Answer:
Biogas is a mixture of methane, CO₂, and hydrogen, produced by anaerobic
digestion of biomass.
Production Process:
1.
Input: Cow dung, sewage, and plant waste.
2.
Anaerobic
Digestion:
o Hydrolytic and fermentative bacteria → convert complex organics to
acids.
o Acetogenic bacteria → convert acids into acetate.
o Methanogens (Methanobacterium) → produce methane and CO₂.
3.
Output: Biogas used for cooking and
lighting.
4.
Byproduct: Slurry used as nutrient-rich
manure.
Q6. Describe the stages in the
biogas plant developed by Indian Agricultural Research Institute (IARI).
Answer:
Structure and Process:
1.
Inlet
Chamber: Cow dung
and water mixture added.
2.
Digester: Anaerobic tank where microbes act
on slurry for 50–60 days.
3.
Methanogenic
Activity: Methanobacterium
decomposes matter to methane, CO₂, H₂.
4.
Gas
Outlet: Biogas
collected and used.
5.
Sludge
Outlet: Residual
slurry removed and used as manure.
Importance: Provides renewable energy and reduces pollution.
Q7. What are methanogens? Describe
their role in sewage treatment and biogas production.
Answer:
- Methanogens: Anaerobic archaebacteria
producing methane.
- Examples: Methanobacterium,
Methanococcus.
- Role in Sewage Treatment:
- Decompose organic matter in
anaerobic sludge digesters.
- Reduce BOD and generate
methane.
- Role in Biogas Plants:
- Convert acetic acid and CO₂ +
H₂ into CH₄ (methane).
- Provide renewable fuel and
reduce waste.
Q8. Discuss the role of microbes as
biofertilizers.
Answer:
Biofertilizers are microorganisms that enrich soil fertility:
1.
Rhizobium: Nitrogen fixation in legume root
nodules.
2.
Azospirillum,
Azotobacter:
Free-living nitrogen fixers.
3.
Cyanobacteria: Anabaena, Nostoc fix
atmospheric nitrogen in paddy fields.
4.
Mycorrhiza: Symbiosis of fungi with roots;
absorb phosphorus, provide drought resistance.
5.
Benefits: Eco-friendly, sustainable, improves
soil fertility.
Q9. Describe the role of microbes in
the production of bioactive molecules.
Answer:
Microbes produce several bioactive compounds:
1.
Cyclosporin
A – from Trichoderma polysporum;
immunosuppressant for organ transplantation.
2.
Statins – from Monascus purpureus;
lower blood cholesterol by inhibiting HMG-CoA reductase.
3.
Streptokinase – from Streptococcus;
dissolves blood clots in myocardial infarction.
Importance: Used in medicine for therapeutic purposes.
Q10. Explain how microbes are used
in wastewater treatment plants.
Answer:
1.
Aeration
Tanks: Aerobic
microbes oxidize organic waste → CO₂ + H₂O.
2.
Formation
of Activated Sludge:
Settles as flocculent mass of microbes.
3.
Part
Recycled: To seed
new sewage.
4.
Remaining
Sludge: Sent to
anaerobic digesters → Methanogens release biogas.
5.
Effluent
Released: After
reducing BOD, water released into rivers.
Q11. What is Biological Oxygen Demand
(BOD)? How is it related to pollution?
Answer:
- Definition: Amount of oxygen required by
microorganisms to oxidize organic matter in 1 liter of water.
- High BOD: Indicates high organic
pollution → more microbial activity.
- Low BOD: Indicates cleaner water.
- In Sewage Treatment: BOD decreases as microbes
decompose organic matter, indicating purification.
Q12. How do microbes help in the
dairy industry?
Answer:
1.
Curd
Formation: Lactobacillus
converts milk to curd, improving digestibility.
2.
Flavor
and Texture:
Lactic acid gives curd sour taste.
3.
Probiotic
Effect: Enhances
immunity and gut health.
4.
Cheese
Production:
Streptococcus lactis and Penicillium roqueforti impart unique
texture and flavor.
Q13. Discuss the role of microbes in
the production of antibiotics other than penicillin.
Answer:
1.
Streptomycin – from Streptomyces griseus;
effective against tuberculosis.
2.
Tetracycline – from Streptomyces aureofaciens.
3.
Chloramphenicol – from Streptomyces venezuelae;
effective against typhoid.
4.
Erythromycin – from Saccharopolyspora
erythraea; used in respiratory infections.
These antibiotics inhibit bacterial growth, saving lives.
Q14. What are fermented beverages?
Name microbes involved and steps of production.
Answer:
- Fermented Beverages: Alcoholic drinks produced by
fermentation of sugars using yeast.
Examples: - Saccharomyces cerevisiae ferments malted grains → Beer.
- Fermentation of grapes → Wine.
Steps:
1.
Sugary
substrate (grains/fruits) → Fermentation by yeast.
2.
Ethanol
and CO₂ released.
3.
Distillation
→ Whisky, Rum.
Uses: Alcoholic drinks, fuel alcohol.
Q15. Differentiate between primary
and secondary sewage treatment.
|
Feature |
Primary Treatment |
Secondary Treatment |
|
Type |
Physical |
Biological |
|
Method |
Sedimentation, filtration |
Aerobic microbial oxidation |
|
Removes |
Suspended solids |
Dissolved organic matter |
|
End Product |
Primary sludge |
Activated sludge |
|
Microbes Used |
None |
Aerobic bacteria, fungi, protozoa |
Q16. How are microbes used in
biocontrol of pests and diseases?
Answer:
1.
Bacillus
thuringiensis (Bt):
Produces toxin (Bt toxin) that kills larvae of lepidopteran insects.
2.
Trichoderma: Fungal bioagent against other soil
pathogens.
3.
Baculoviruses
(Nucleopolyhedrovirus):
Targets specific insects, safe for other species.
4.
Advantages: Eco-friendly, target-specific,
biodegradable, no resistance.
Q17. What is mycorrhiza? Explain its
benefits.
Answer:
- Mycorrhiza: Symbiotic association between
fungus and plant roots (e.g., Glomus).
Benefits:
1.
Increase
phosphorus absorption.
2.
Provide
drought and disease resistance.
3.
Enhance
plant growth.
4.
Reduce
dependence on chemical fertilizers.
Q18. Describe the microbial
processes in biogas generation from cattle dung.
Answer:
1.
Slurry
Preparation:
Cow dung + water mixture.
2.
Anaerobic
Fermentation:
o Hydrolytic bacteria → Fatty acids.
o Acetogenic bacteria → Acetate, CO₂, H₂.
o Methanogens → Convert to CH₄ + CO₂.
3.
Collection: Gas rises and stored in dome
chamber.
4.
Residue: Used as manure.
Q19. Explain how Bacillus
thuringiensis helps in pest control.
Answer:
- Bt produces crystal (Cry) proteins
toxic to insect larvae.
- When ingested by larvae, Cry
protein dissolves → releases toxin → creates pores in gut → kills larvae.
- Used in Bt cotton, Bt
corn to control bollworms and caterpillars.
Q20. Write notes on the use of
cyanobacteria as biofertilizers.
Answer:
- Anabaena, Nostoc, Oscillatoria
fix atmospheric nitrogen.
- Found in paddy fields,
forming symbiosis with Azolla fern.
- Increase soil nitrogen, reduce
chemical fertilizer need.
- Environmentally safe and
cost-effective.
Would you like me to continue with Q21–50 (remaining
5-mark answers)?
These will include detailed questions on biocontrol, biofertilizers,
industrial enzymes, antibiotics, and sewage treatment applications —
perfect for NEET + CBSE Board prep.
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continue
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Perfect 👍 Let’s continue with the remaining
5-mark questions (Q21–50) from Chapter: Microbes in Human Welfare
(Class 12, NCERT-based, ideal for CBSE Boards + NEET prep).
🌿 Microbes in Human Welfare
— 5 Marks Questions (Q21–50)
Q21. Describe the role of microbes
in organic acid production.
Answer:
Microbes are used in industrial fermentation to produce organic acids:
1.
Citric
Acid: Produced
by Aspergillus niger from molasses. Used in food, beverages,
pharmaceuticals.
2.
Acetic
Acid: Produced
by Acetobacter aceti from ethanol. Used in vinegar production.
3.
Butyric
Acid: Produced
by Clostridium butylicum. Used in plastics, perfumes.
4.
Lactic
Acid: Produced
by Lactobacillus; used in food and pharmaceutical industries.
These acids have wide industrial applications and are produced in large
fermenters.
Q22. Explain the process of
wastewater treatment and its significance.
Answer:
1.
Primary
Treatment: Physical
removal of solids by sedimentation and filtration.
2.
Secondary
Treatment:
Biological degradation by aerobic microbes in aeration tanks.
o Forms activated sludge
containing microbes.
o Reduces BOD.
3.
Anaerobic
Digestion:
Methanogens act on remaining sludge → Biogas + manure.
4.
Significance:
o Prevents water pollution.
o Reduces organic waste.
o Produces renewable biogas.
o Maintains ecological balance.
Q23. Discuss the working and
importance of the activated sludge process.
Answer:
1.
Sewage
+ Air → Aeration Tanks.
2.
Microbes
form Flocs:
Masses of bacteria + fungi + organic matter.
3.
Decomposition: Microbes oxidize organic matter →
CO₂ + H₂O.
4.
Sedimentation: Flocs settle → Activated Sludge.
5.
Part
Recycled: For next
treatment cycle; rest sent to anaerobic digester.
Importance: Reduces BOD, purifies sewage, and produces biogas.
Q24. What are biofertilizers?
Explain different types with examples.
Answer:
Biofertilizers are microorganisms that enhance nutrient availability to plants.
Types:
1.
Nitrogen-Fixing:
o Rhizobium (symbiotic in legumes)
o Azospirillum, Azotobacter (free-living)
2.
Phosphate-Solubilizing
Bacteria (PSB):
Convert insoluble phosphates → soluble form.
3.
Cyanobacteria: Nostoc, Anabaena, Oscillatoria
fix nitrogen in paddy fields.
4.
Mycorrhiza: Glomus species help absorb
phosphorus and water.
Benefits: Reduce chemical fertilizer use, eco-friendly, improve soil
fertility.
Q25. What are biocontrol agents?
Explain with examples.
Answer:
Biocontrol agents are natural organisms used to control pests and diseases.
Examples:
1.
Bacillus
thuringiensis (Bt)
– kills insect larvae (used in Bt cotton).
2.
Trichoderma – fungal bioagent against soil
pathogens.
3.
Ladybird
beetles – feed on
aphids.
4.
Dragonflies – control mosquito population.
5.
Baculoviruses
(Nucleopolyhedrovirus)
– specific insect pathogens, safe for non-target species.
Advantages: Environment-friendly, pest-specific, prevent resistance.
Q26. How are microbes used in the
production of industrial enzymes?
Answer:
Microbes produce useful enzymes at industrial scale:
1.
Pectinases – Aspergillus niger, used in
fruit juice clarification.
2.
Proteases – Bacillus subtilis, used in
detergents and leather industries.
3.
Amylases – Used in starch and textile
industries.
4.
Streptokinase – From Streptococcus,
dissolves blood clots.
5.
Lipases – Used in dairy and detergent
industries.
Importance: Cost-effective, biodegradable, and efficient catalysts.
Q27. Discuss the steps involved in
sewage treatment and disposal.
Answer:
1.
Screening: Removes floating solids.
2.
Sedimentation: Removes heavier particles → Primary
sludge.
3.
Aeration: Aerobic microbes oxidize organic
matter → Activated sludge.
4.
Settling: Activated sludge separated; part
recycled.
5.
Anaerobic
Digestion:
Methanogens act on sludge → Biogas.
6.
Disposal: Treated effluent released into
rivers.
Significance: Reduces pollution and recycles nutrients.
Q28. Explain the microbial activity
in a biogas plant.
Answer:
Three stages of microbial activity:
1.
Hydrolytic
Stage: Organic
polymers → Sugars, fatty acids by hydrolytic bacteria.
2.
Acidogenic
Stage: Sugars →
Organic acids, CO₂, H₂ by acid-forming bacteria.
3.
Methanogenic
Stage: Methanobacterium
converts acids → CH₄ + CO₂.
End Products: Biogas (methane, CO₂, H₂), and digested slurry
(fertilizer).
Q29. What are the advantages of
biogas plants in rural areas?
Answer:
1.
Provides
clean, renewable energy (methane).
2.
Reduces
dependence on firewood → prevents deforestation.
3.
Manure
(slurry) improves soil fertility.
4.
Controls
waste and pollution.
5.
Improves
sanitation and rural health.
6.
Provides
income and employment opportunities.
Q30. Describe the structure and
function of a biogas plant.
Answer:
Parts:
1.
Mixing
Tank: Cow dung
+ water → slurry.
2.
Inlet
Pipe: Slurry
enters digester.
3.
Digester: Anaerobic tank where methanogens
act.
4.
Gas
Chamber: Collects
biogas.
5.
Outlet: Spent slurry removed.
Functions: Converts organic waste to CH₄-rich fuel, reduces waste,
provides manure.
Q31. What is the importance of
microbes in food and beverage industries?
Answer:
1.
Fermented
Foods: Bread,
curd, idli, dosa – improved flavor and digestibility.
2.
Alcoholic
Beverages: Yeast
fermentation produces wine, beer, rum.
3.
Dairy
Products: Lactobacillus
gives curd and cheese.
4.
Pickles
and Sauerkraut:
Preserved using lactic acid bacteria.
Advantages: Enhance taste, nutrition, shelf-life, and digestibility.
Q32. Explain how microbes contribute
to environmental management.
Answer:
1.
Sewage
Treatment:
Decomposes organic waste.
2.
Biogas
Production:
Converts waste → renewable energy.
3.
Bioremediation: Degrades pollutants like oil
spills.
4.
Biofertilizers: Improve soil fertility.
5.
Biocontrol
Agents: Control
pests naturally.
Impact: Reduces pollution and maintains ecological balance.
Q33. Explain the significance of
Cyanobacteria in agriculture.
Answer:
1.
Fix
atmospheric nitrogen (heterocysts).
2.
Enrich
soil fertility, especially in paddy fields.
3.
Symbiotic
with Azolla (used as green manure).
4.
Eco-friendly
and self-sustaining biofertilizer.
5.
Reduces
need for chemical fertilizers.
Q34. What are single-cell proteins
(SCP)? Mention their advantages.
Answer:
- Definition: Protein-rich food obtained
from microbial biomass (e.g., Spirulina, Chlorella).
Advantages:
1.
High
protein (up to 60–70%).
2.
Grows
on waste materials.
3.
Reduces
pollution.
4.
Rich
in vitamins, minerals.
5.
Provides
cheap food source to fight malnutrition.
Q35. Explain the role of microbes in
the medicine industry.
Answer:
1.
Antibiotics: Penicillin, streptomycin.
2.
Vaccines: Produced using microbial cultures.
3.
Bioactive
Molecules:
Cyclosporin A (immunosuppressant), Statins (cholesterol control).
4.
Enzymes: Streptokinase for clot dissolution.
Conclusion: Microbes revolutionized modern medicine and human health.
Q36. What are bioactive molecules?
Explain their industrial importance.
Answer:
Definition: Microbial products with biological activity in humans.
Examples:
1.
Cyclosporin
A: Trichoderma polysporum, used
in organ transplant.
2.
Statins: Monascus purpureus, lower
cholesterol.
3.
Streptokinase: Streptococcus, dissolves
blood clots.
Importance: Used in pharmaceuticals for therapeutic applications.
Q37. Discuss how microbes help in
recycling of nutrients.
Answer:
1.
Decomposition: Bacteria and fungi degrade dead
matter → CO₂, NH₃.
2.
Nitrogen
Fixation: Converts
N₂ → ammonia/nitrates.
3.
Methanogens: Convert waste to methane.
4.
Phosphate
Solubilizers:
Make phosphorus available to plants.
Result: Maintain nutrient cycles and ecosystem stability.
Q38. What are the different
applications of yeast in industries?
Answer:
1.
Alcoholic
Beverages: Ferments
sugar → ethanol.
2.
Bread
Making: Produces
CO₂ → makes dough rise.
3.
Bioethanol
Production:
Used as fuel.
4.
Single
Cell Protein:
High nutritional value.
Microbe: Saccharomyces cerevisiae (Baker’s yeast) is most widely
used.
Q39. What are the advantages of
microbial products over chemical products?
Answer:
1.
Environmentally
safe and biodegradable.
2.
Cost-effective
and renewable.
3.
Target-specific
(no side effects).
4.
Produced
under mild conditions.
5.
Sustainable
for long-term use.
Q40. How are microbes used in the
leather and detergent industries?
Answer:
1.
Leather
Industry:
o Bacillus subtilis produces proteases → removes hair
and proteins from hides.
2.
Detergent
Industry:
o Lipases and proteases remove stains.
o Enzymes remain active in alkaline
conditions.
Benefits: Eco-friendly, efficient, and non-toxic cleaning agents.
Q41. How do microbes help in pest
control without harming non-target organisms?
Answer:
- Baculoviruses: Infect only specific insect
species.
- Bt Toxin: Acts only on larval midgut
cells.
- Trichoderma: Attacks only plant pathogens.
Result: Natural pest control with no harm to humans, animals, or beneficial insects.
Q42. Explain the significance of Trichoderma
and Bacillus thuringiensis in agriculture.
Answer:
- Trichoderma: Fungal bioagent controlling
soil pathogens.
- Bt: Bacterium producing Cry toxin
→ kills insect larvae.
Significance:
1.
Reduces
pesticide use.
2.
Increases
yield.
3.
Safe
and eco-friendly.
Q43. What are Baculoviruses? Mention
their role as biocontrol agents.
Answer:
- Definition: Insect-specific viruses
(family Baculoviridae).
- Example: Nucleopolyhedrovirus.
- Mode: Infect insect larvae → kill
them → safe for others.
- Advantages:
1.
Target-specific.
2.
Biodegradable.
3.
Maintain
natural balance.
Q44. Discuss the environmental
benefits of using biofertilizers and biocontrol agents.
Answer:
1.
Reduce
chemical fertilizer/pesticide use.
2.
Prevent
soil and water pollution.
3.
Enhance
soil fertility and biodiversity.
4.
Maintain
ecological balance.
5.
Sustainable
and renewable approach.
Q45. How is Rhizobium
associated with nitrogen fixation?
Answer:
1.
Lives
symbiotically in legume root nodules.
2.
Converts
atmospheric N₂ → ammonia using nitrogenase enzyme.
3.
Ammonia
→ amino acids → plant growth.
4.
Increases
soil nitrogen for next crops.
Q46. Explain the working and
benefits of mycorrhizal associations.
Answer:
1.
Fungal
hyphae penetrate plant roots (Glomus).
2.
Increase
surface area for absorption.
3.
Absorb
phosphorus and micronutrients.
4.
Provide
drought and disease resistance.
5.
Improve
plant growth and yield.
Q47. What is the significance of
microbial activity in ecosystems?
Answer:
1.
Decomposition
→ nutrient recycling.
2.
Nitrogen
fixation → soil fertility.
3.
Methanogenesis
→ renewable energy.
4.
Bioremediation
→ pollution control.
5.
Symbiosis
→ ecosystem stability.
Q48. Describe the process of
formation of curd and its benefits.
Answer:
- Lactobacillus converts lactose → lactic
acid.
- Milk proteins coagulate → curd.
Benefits:
1.
Improves
digestibility.
2.
Increases
vitamin B₁₂.
3.
Inhibits
harmful bacteria.
4.
Acts
as probiotic improving gut health.
Q49. What is the role of Aspergillus
niger in industry?
Answer:
1.
Produces
citric acid (used in food & pharma).
2.
Produces
enzymes – pectinase, amylase.
3.
Used
in juice clarification.
4.
Involved
in biotransformation of organic compounds.
Q50. “Microbes are indispensable for
human welfare.” Justify this statement.
Answer:
Microbes contribute to:
1.
Food
Industry –
fermentation, flavor, preservation.
2.
Medicine – antibiotics, vaccines, enzymes.
3.
Environment – waste treatment, biogas,
recycling.
4.
Agriculture – biofertilizers, biocontrol.
5.
Industry – organic acids, enzymes, SCP.
➡️ Conclusion: Microbes
sustain life, improve health, enhance food, and protect the environment —
making them essential for human welfare.
