CBSE Class 12 Biology Study Module (NCERT Based): Microbes in Human Welfare

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit III – Biology and Human Welfare
• Chapter: Chapter 10 – Microbes in Human Welfare
• Prescribed Textbook: NCERT Biology Class XII
• Examination: CBSE Class 12 Board Examination
• Content Type: Study Module with Revision Notes
• Syllabus Alignment: Strictly as per NCERT (CBSE)

CBSE Class 12 Biology Microbes in Human Welfare – NCERT Notes, Concepts & Revision Module

Introduction

Microorganisms, though microscopic, play a massive role in human welfare. From food production and medicine to waste management and sustainable agriculture, microbes are indispensable. The chapter Microbes in Human Welfare highlights the beneficial roles of bacteria, fungi, and other microorganisms in daily life and industrial processes. This chapter is highly scoring and frequently tested in CBSE board exams through MCQs, case-based questions, short notes, and application-based questions.

Understanding this chapter helps students appreciate how biological processes are harnessed for societal benefit while also strengthening concepts related to biotechnology, ecology, and sustainable development.

1. Microbes in Household Products

Microbes have been traditionally used in households for preparing various food products through fermentation.

1.1 Fermented Foods

Fermentation is a microbial process where microorganisms convert sugars into alcohol, acids, or gases.

Examples of Household Products

• Curd:
  • Microbe involved: Lactobacillus
  • Function: Converts milk sugar (lactose) into lactic acid
  • Benefits:
    • Improves digestibility of milk
    • Increases vitamin B12 content
    • Acts as a probiotic
• Idli and Dosa Batter:
  • Microbes involved: Lactic acid bacteria and yeast
  • Function: Fermentation causes batter to rise, improving texture and taste
• Bread:
  • Microbe involved: Yeast (Saccharomyces cerevisiae)
  • Function: Produces carbon dioxide that makes dough fluffy

1.2 Health Benefits of Fermented Foods

• Improve digestion
• Enhance nutritional value
• Suppress harmful pathogens
• Maintain gut health

2. Microbes in Industrial Products

Microbes are widely used in industries to produce valuable products on a large scale using bioreactors.

2.1 Fermented Beverages

• Alcoholic beverages (wine, beer):
  • Produced by fermentation of sugars by yeast
  • Yeast converts sugars into ethanol and carbon dioxide
• Distilled beverages (whisky, rum):
  • Produced by distillation of fermented broth

2.2 Antibiotics

Antibiotics are chemical substances produced by microorganisms that inhibit growth of other microbes.

Examples

• Penicillin – produced by Penicillium
• Streptomycin – produced by Streptomyces

Importance:

• Treatment of bacterial infections
• Revolutionised modern medicine

2.3 Organic Acids

Microbes are used to produce organic acids of commercial importance.

2.4 Enzymes

Microbial enzymes are used in various industries.

• Proteases: Used in detergents to remove protein stains
• Lipases: Used in detergents and dairy industry
• Pectinases & Proteases: Used to clarify fruit juices

2.5 Bioactive Molecules

Some microbes produce compounds that have physiological importance.

• Cyclosporin A:
  • Produced by Trichoderma polysporum
  • Used as an immunosuppressive drug in organ transplantation
• Statins:
  • Produced by Monascus purpureus
  • Lower blood cholesterol levels

3. Microbes in Sewage Treatment

Sewage contains large amounts of organic matter and pathogens. Microbes play a crucial role in sewage treatment plants (STPs).

3.1 Primary Treatment

• Physical removal of large and small particles
• Involves filtration and sedimentation
• Removes floating debris and grit

3.2 Secondary Treatment (Biological Treatment)

This stage uses microbes to degrade organic matter.

Activated Sludge Process

• Sewage is aerated in large tanks
• Aerobic microbes form flocs (masses of bacteria and fungi)
• Microbes consume organic matter, reducing BOD (Biochemical Oxygen Demand)

BOD:

• Measure of organic matter present in water
• Lower BOD indicates cleaner water

3.3 Anaerobic Sludge Digestion

• Sludge is digested by anaerobic bacteria
• Produces biogas (methane, CO₂, H₂S)
• Pathogens are destroyed

3.4 Importance of Sewage Treatment

• Prevents water pollution
• Protects aquatic ecosystems
• Produces reusable water and biogas

4. Microbes in Biogas Production

Biogas is an eco-friendly fuel produced by anaerobic digestion of organic waste.

4.1 Biogas Plant

• Raw materials: Cow dung, agricultural waste, sewage
• Microbes involved: Methanogenic bacteria (e.g., Methanobacterium)

4.2 Steps in Biogas Production

1. Hydrolysis: Complex polymers broken into simpler compounds
2. Acidogenesis: Formation of organic acids
3. Methanogenesis: Methanogens convert acids into methane

4.3 Composition of Biogas

• Methane (50–70%)
• Carbon dioxide
• Hydrogen sulphide

4.4 Advantages of Biogas

• Renewable source of energy
• Reduces pollution
• Produces nutrient-rich slurry used as manure

5. Microbes as Biocontrol Agents

Biocontrol refers to use of biological methods to control pests and pathogens.

5.1 Biological Control of Pests

• Reduces use of chemical pesticides
• Environment-friendly

Examples

• Bacillus thuringiensis (Bt):
  • Produces toxin harmful to insect larvae
  • Used in biopesticides
• Trichoderma species:
  • Fungal biocontrol agents
  • Protect plants from soil-borne pathogens

5.2 Predators and Parasites

• Ladybird beetle → controls aphids
• Dragonflies → control mosquitoes

5.3 Advantages of Biocontrol

• No chemical residue
• Maintains ecological balance
• Target-specific

6. Microbes as Biofertilisers

Biofertilisers are microorganisms that enrich soil nutrients and promote plant growth.

6.1 Nitrogen-Fixing Biofertilisers

• Rhizobium:
  • Symbiotic association with leguminous plants
  • Fixes atmospheric nitrogen
• Azotobacter & Azospirillum:
  • Free-living nitrogen-fixing bacteria

6.2 Cyanobacteria (Blue-Green Algae)

• Examples: Anabaena, Nostoc
• Used in paddy fields
• Improve soil fertility

6.3 Mycorrhiza

• Symbiotic association between fungi and plant roots
• Example: Glomus

Benefits:

• Increased absorption of phosphorus
• Resistance to pathogens
• Enhanced drought tolerance

6.4 Advantages of Biofertilisers

• Eco-friendly
• Improve soil health
• Reduce dependence on chemical fertilisers

CBSE Board Examination Focus

High-Weightage Topics

• Household and industrial uses of microbes
• Antibiotics, enzymes, and bioactive molecules
• Sewage treatment stages and BOD
• Biogas production and methanogens
• Biocontrol agents (Bt, Trichoderma)
• Biofertilisers (Rhizobium, mycorrhiza)

Common Question Patterns

• MCQs on microbes and products
• Case-based questions on sewage treatment
• Short notes on biocontrol and biofertilisers
• Assertion–Reason questions

Quick Revision Notes

• Microbes are useful in food, medicine, agriculture, and waste management
• Fermentation improves food quality and nutrition
• Antibiotics and enzymes are industrial microbial products
• Sewage treatment uses microbes to reduce pollution
• Biogas is produced by methanogens
• Biocontrol reduces chemical pesticide use
• Biofertilisers enhance soil fertility naturally

Conclusion

The chapter Microbes in Human Welfare demonstrates how microorganisms contribute significantly to sustainable living, agriculture, healthcare, and environmental protection. Their controlled use reduces pollution, enhances productivity, and supports eco-friendly development. A thorough understanding of this chapter ensures strong performance in CBSE Class 12 Biology board examinations and builds awareness of real-life biological applications.

✔ Strictly NCERT-Based

✔ CBSE Board Examination Aligned

✔ Ideal for Theory, MCQs & Case-Based Questions