Microorganisms or microbes are tiny living organisms that cannot be seen with the naked eye. They include bacteria, fungi, protozoa, viruses, algae, and archaea. Although some microbes are harmful and cause diseases, most of them play a beneficial role in human welfare.
They are essential in food processing, medicine production, sewage treatment, agriculture, and various industrial processes. Understanding the positive contributions of microbes helps us appreciate their importance in everyday life and in sustaining ecosystems.
This chapter from Class 12 Biology emphasizes the applications of microbes in human welfare, highlighting their in
dustrial, agricultural, and medical uses.
Class 12 Biology Chapter – Microbes in Human Welfare | Notes, MCQs, Q&A
Microbes in Household Products
Fermented Beverages
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Yeast (Saccharomyces cerevisiae) is used in the production of beverages like wine, beer, whisky, rum, and brandy.
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Fermentation of malted cereals and fruit juices by yeast produces ethanol (alcohol).
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The type of beverage depends on the raw material and fermentation process.
Curd and Cheese
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Lactic acid bacteria (LAB), such as Lactobacillus, are used for curdling milk.
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LAB increases the nutritional quality of curd by enhancing vitamin B12 content.
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Cheese is produced by partial degradation of milk by microbes like Propionibacterium sharmanii, which also give cheese its characteristic flavor.
Bread Making
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Baker’s yeast (Saccharomyces cerevisiae) is used in baking bread, cakes, and pastries.
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It produces carbon dioxide during fermentation, which makes the dough rise and softens it.
Traditional Foods
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Many fermented foods in Asian countries use microbes, e.g.:
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Idli, dosa batter → fermented by Leuconostoc and Streptococcus.
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Soy sauce → produced using fungi like Aspergillus oryzae.
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Microbes in Industrial Products
Industrial production of many compounds such as alcohols, organic acids, enzymes, and antibiotics depends on microbes.
Fermenters
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Large vessels called fermenters or bioreactors are used for growing microbes on an industrial scale.
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These provide controlled conditions (temperature, pH, oxygen supply) to maximize production.
Antibiotics
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Antibiotics are chemical substances produced by microbes to kill or inhibit the growth of other microbes.
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Examples:
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Penicillin – discovered by Alexander Fleming in 1928 from Penicillium notatum.
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Streptomycin – from Streptomyces griseus.
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Tetracycline – from Streptomyces aureofaciens.
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Erythromycin – from Saccharopolyspora erythraea.
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Antibiotics have revolutionized medicine by controlling bacterial infections.
Alcoholic Drinks
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Different alcoholic drinks are produced by fermentation using yeast.
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Examples:
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Beer, wine → low alcohol content.
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Whisky, brandy, rum → produced by distillation, higher alcohol concentration.
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Organic Acids
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Microbes are widely used to produce organic acids:
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Acetic acid → Acetobacter aceti.
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Citric acid → Aspergillus niger.
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Lactic acid → Lactobacillus.
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Butyric acid → Clostridium butylicum.
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Enzymes
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Many industrial enzymes come from microbes:
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Lipase – used in detergents.
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Pectinase, Protease, Cellulase – used in fruit juice clarification and textile industries.
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Streptokinase – from Streptococcus, used to dissolve blood clots in patients with myocardial infarction.
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Bioactive Molecules
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Microbes also produce bioactive substances with therapeutic applications:
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Cyclosporin A – from Trichoderma polysporum, used as an immunosuppressive drug during organ transplantation.
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Statins – from Monascus purpureus, used to lower blood cholesterol by inhibiting cholesterol synthesis.
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Microbes in Sewage Treatment
Importance
Wastewater or sewage contains organic matter and harmful microbes. If untreated, it pollutes water bodies and spreads diseases. Microbes play a vital role in biological sewage treatment.
Sewage Treatment Steps
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Primary Treatment – Physical removal of large particles through filtration and sedimentation.
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Secondary Treatment (Biological Treatment) –
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Uses aerobic microbes in aeration tanks to decompose organic matter.
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The microbes grow in masses called activated sludge.
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The effluent is treated further, while sludge is used for biogas production.
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Tertiary Treatment – Advanced methods like chemical disinfection, chlorination, and UV treatment.
Activated Sludge
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Contains aerobic bacteria and fungi that digest organic matter.
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Reduces BOD (Biochemical Oxygen Demand) of wastewater, making water safer to release into rivers.
Microbes in Production of Biogas
Biogas
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Biogas is a mixture of methane (CH4), carbon dioxide (CO2), and hydrogen (H2).
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Produced by anaerobic digestion of biomass (animal waste, plant residue) by methanogenic bacteria.
Microbes Involved
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Methanogens (Methanobacterium): anaerobic archaebacteria that produce methane.
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They are present in the rumen (stomach) of cattle and help digest cellulose.
Biogas Plants
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Slurry of cattle dung (gobar gas) is fed into biogas plants.
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Methanogens decompose organic waste to release biogas.
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Biogas is used as a clean and renewable source of energy.
Microbes as Bio-control Agents
Chemical pesticides harm the environment and human health. Microbes provide an eco-friendly alternative called biocontrol agents.
Examples
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Bacillus thuringiensis (Bt):
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Produces Bt toxin that kills insects like caterpillars and larvae.
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Used as a biopesticide spray and in genetically modified Bt crops (e.g., Bt cotton).
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Trichoderma:
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A fungus that acts against plant pathogens.
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Baculoviruses (Nucleopolyhedrovirus):
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Biological control of insects, highly host-specific.
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Safe for beneficial insects and pollinators.
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Microbes as Biofertilizers
Biofertilizers are living microorganisms that increase soil fertility and promote plant growth. They are alternatives to chemical fertilizers.
Examples
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Rhizobium: Nitrogen-fixing bacteria in root nodules of legumes.
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Azospirillum, Azotobacter: Free-living nitrogen fixers.
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Cyanobacteria (Blue-green algae): Anabaena, Nostoc fix nitrogen in paddy fields.
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Mycorrhiza (Glomus species): Fungal symbionts that enhance nutrient and water absorption.
Advantages of Biofertilizers
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Environmentally friendly.
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Improve soil structure and fertility.
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Reduce dependence on chemical fertilizers.
Microbes in Medicine
Apart from antibiotics, microbes play a crucial role in producing vaccines, hormones, and therapeutic agents.
Examples
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Recombinant DNA technology uses microbes to produce human insulin.
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Vaccines like BCG, hepatitis-B, and polio vaccines involve microbial use.
Multiple Choice Questions- Microbes in Human welfare
Q1. Which microorganism is used in the production of curd?
a) Saccharomyces
b) Lactobacillus
c) Penicillium
d) Aspergillus
Answer: The correct answer is Lactobacillus.
Q2. Which antibiotic was first discovered by Alexander Fleming?
a) Streptomycin
b) Penicillin
c) Tetracycline
d) Erythromycin
Answer: The correct answer is Penicillin.
Q3. Which microbe is used in the production of citric acid?
a) Aspergillus niger
b) Acetobacter aceti
c) Lactobacillus
d) Saccharomyces cerevisiae
Answer: The correct answer is Aspergillus niger.
Q4. Which bacterium is present in the rumen of cattle and produces methane?
a) Azotobacter
b) Methanobacterium
c) Rhizobium
d) Clostridium
Answer: The correct answer is Methanobacterium.
Q5. Which organism is commonly called Baker’s yeast?
a) Saccharomyces cerevisiae
b) Candida albicans
c) Penicillium notatum
d) Lactobacillus bulgaricus
Answer: The correct answer is Saccharomyces cerevisiae.
Q6. Which acid is produced by Acetobacter aceti?
a) Citric acid
b) Acetic acid
c) Lactic acid
d) Butyric acid
Answer: The correct answer is Acetic acid.
Q7. The immunosuppressive drug Cyclosporin A is obtained from:
a) Aspergillus niger
b) Trichoderma polysporum
c) Streptomyces griseus
d) Monascus purpureus
Answer: The correct answer is Trichoderma polysporum.
Q8. Bt cotton has resistance against:
a) Bacterial diseases
b) Insect pests
c) Viral diseases
d) Fungal infections
Answer: The correct answer is Insect pests.
Q9. Which fungus is used in ripening of Swiss cheese?
a) Saccharomyces cerevisiae
b) Propionibacterium sharmanii
c) Aspergillus oryzae
d) Clostridium butylicum
Answer: The correct answer is Propionibacterium sharmanii.
Q10. Which enzyme is used to dissolve blood clots?
a) Lipase
b) Streptokinase
c) Pectinase
d) Amylase
Answer: The correct answer is Streptokinase.
Q11. Biofertilizer Rhizobium is associated with which plants?
a) Wheat
b) Rice
c) Legumes
d) Maize
Answer: The correct answer is Legumes.
Q12. Monascus purpureus produces which cholesterol-lowering drug?
a) Tetracycline
b) Statins
c) Erythromycin
d) Penicillin
Answer: The correct answer is Statins.
Q13. In sewage treatment, flocs are:
a) Masses of fungi only
b) Bacteria and fungal filaments
c) Pure algal cells
d) Only viruses
Answer: The correct answer is Bacteria and fungal filaments.
Q14. Biogas mainly contains:
a) Oxygen
b) Methane
c) Nitrogen
d) Ozone
Answer: The correct answer is Methane.
Q15. Which cyanobacterium is used as a biofertilizer in paddy fields?
a) Oscillatoria
b) Anabaena
c) Nostoc
d) Both b and c
Answer: The correct answer is Both b and c.
Q16. Which bio-control agent is used against insect larvae?
a) Rhizobium
b) Bacillus thuringiensis
c) Azotobacter
d) Nostoc
Answer: The correct answer is Bacillus thuringiensis.
Q17. Mycorrhiza is a symbiotic association between:
a) Bacteria and algae
b) Fungi and roots of plants
c) Algae and fungi
d) Virus and bacteria
Answer: The correct answer is Fungi and roots of plants.
Q18. Which method is used in secondary treatment of sewage?
a) Chemical oxidation
b) UV radiation
c) Aeration tanks with microbes
d) Sand filtration
Answer: The correct answer is Aeration tanks with microbes.
Q19. Which of the following is a biopesticide?
a) Bt toxin
b) Urea
c) DDT
d) Ammonium sulfate
Answer: The correct answer is Bt toxin.
Q20. Which of the following is not an organic acid produced by microbes?
a) Citric acid
b) Acetic acid
c) Hydrochloric acid
d) Lactic acid
Answer: The correct answer is Hydrochloric acid.
Short Answer Questions- Microbes in Human welfare
Q1. Name any two antibiotics and the microbes that produce them.
Answer: Penicillin (Penicillium notatum), Streptomycin (Streptomyces griseus).
Q2. What is the role of Lactobacillus in food production?
Answer: Lactobacillus ferments milk into curd, enhances vitamin B12, and improves digestibility.
Q3. Define biofertilizers with one example.
Answer: Biofertilizers are living microbes that enhance soil fertility, e.g., Rhizobium in leguminous plants.
Q4. What are methanogens?
Answer: Methanogens are anaerobic archaebacteria (e.g., Methanobacterium) that produce methane in biogas plants and rumen of cattle.
Q5. Name one industrial product of fungi used in medicine.
Answer: Cyclosporin A from Trichoderma polysporum.
Long Answer Questions- Microbes in Human welfare
Q1. Explain the role of microbes in sewage treatment.
Answer: Sewage treatment involves primary, secondary, and tertiary processes. In secondary treatment, aerobic microbes form flocs in aeration tanks and digest organic matter, reducing BOD. Activated sludge is used for biogas production. This ensures safe disposal of wastewater and prevents water pollution.
Q2. Describe the role of microbes in the production of industrial products.
Answer: Microbes produce antibiotics (Penicillin, Streptomycin), organic acids (Citric acid, Acetic acid), enzymes (Streptokinase, Pectinase), bioactive molecules (Cyclosporin A, Statins), and alcoholic beverages. Large-scale production takes place in bioreactors under controlled conditions.
Q3. What is biogas? Explain the role of microbes in its production.
Answer: Biogas is a renewable fuel mainly composed of methane, produced by methanogenic bacteria like Methanobacterium. In biogas plants, cattle dung is decomposed anaerobically to release methane, which is used for cooking and lighting. Methanogens also help cattle digest cellulose.
Q4. Discuss the role of microbes as biocontrol agents and biofertilizers.
Answer:
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Biocontrol agents: Bt toxin (Bacillus thuringiensis), Trichoderma (fungus against pathogens), Baculoviruses (control insect pests).
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Biofertilizers: Nitrogen-fixing bacteria (Rhizobium, Azotobacter), cyanobacteria (Anabaena, Nostoc), and mycorrhizae improve soil fertility, enhance nutrient absorption, and promote sustainable farming.
Conclusion
Microbes are indispensable allies of humans. From food production to medicine, agriculture to energy, and environment to industry, microbes contribute significantly to human welfare.
Understanding their role helps us use them wisely for sustainable development while minimizing harmful effects. This chapter in Class 12 Biology gives us a holistic view of the positive contributions of microorganisms in our lives.
We are you Completed Microbes in Human Welfare Notes.