Chapter 10 — Microbes in Human Welfare — covers the beneficial uses of microorganisms in food, medicine, agriculture, and waste management. Carries 4-6 marks. Learn the microbe-product-process connections.
Key Concepts
Microbes in Food Production
| Product | Microbe | Process |
|---|---|---|
| Curd/Yogurt | Lactobacillus | Lactic acid fermentation of milk |
| Bread | Saccharomyces cerevisiae (yeast) | CO₂ production → makes dough rise |
| Cheese (Swiss) | Propionibacterium shermanii | Large holes due to CO₂ |
| Cheese (Roquefort) | Penicillium roqueforti | Ripening, specific flavour |
| Toddy (palm wine) | Yeast (natural) | Fermentation of palm sap |
| Idli/Dosa | Leuconostoc mesenteroides | Fermentation of rice-dal batter |
Microbes in Industrial Products
| Product | Microbe | Use |
|---|---|---|
| Ethanol | Saccharomyces cerevisiae | Beverages, fuel, solvent |
| Citric acid | Aspergillus niger | Food preservative, flavouring |
| Acetic acid | Acetobacter aceti | Vinegar production |
| Butyric acid | Clostridium butylicum | Industrial chemical |
| Lactic acid | Lactobacillus | Food industry |
| Streptokinase | Streptococcus | Clot buster (removes blood clots) |
| Cyclosporin A | Trichoderma polysporum | Immunosuppressant (organ transplant) |
| Statins | Monascus purpureus | Lowers blood cholesterol |
Antibiotics
Penicillin — discovered by Alexander Fleming (1928) from Penicillium notatum
First antibiotic; revolutionised medicine; full-scale production by Ernst Chain and Howard Florey
First antibiotic; revolutionised medicine; full-scale production by Ernst Chain and Howard Florey
Microbes in Sewage Treatment
Primary treatment: Physical — filtration, sedimentation → primary sludge + effluent
Secondary treatment (Biological): Effluent + aerobic microbes in aeration tank → BOD decreases
→ Settling tank → activated sludge (some recycled) + effluent
Anaerobic sludge digester: Anaerobic bacteria → biogas (CH₄ + CO₂ + H₂S)
BOD (Biochemical Oxygen Demand): Amount of O₂ needed by microbes to decompose organic matter. High BOD = more pollution.
Secondary treatment (Biological): Effluent + aerobic microbes in aeration tank → BOD decreases
→ Settling tank → activated sludge (some recycled) + effluent
Anaerobic sludge digester: Anaerobic bacteria → biogas (CH₄ + CO₂ + H₂S)
BOD (Biochemical Oxygen Demand): Amount of O₂ needed by microbes to decompose organic matter. High BOD = more pollution.
Microbes in Biogas Production
- Methanogens (e.g., Methanobacterium) produce methane anaerobically
- Found in cattle dung (gobar gas plant) and sewage digesters
- Biogas = CH₄ + CO₂ + H₂ — used as fuel in rural India
- IARI and KVIC developed biogas technology in India
Microbes as Biocontrol Agents
| Agent | Target |
|---|---|
| Bacillus thuringiensis (Bt) | Insect pests (produces Bt toxin — also basis for Bt crops) |
| Trichoderma | Plant pathogens (fungi) |
| Baculoviruses (NPV) | Insects (narrow host range — species-specific) |
| Ladybird beetle (Coccinella) | Aphids |
Microbes as Biofertilisers
| Organism | Function |
|---|---|
| Rhizobium | Nitrogen fixation (symbiotic, in root nodules of legumes) |
| Azospirillum, Azotobacter | Free-living N₂ fixers |
| Anabaena, Nostoc | Cyanobacteria — N₂ fixation in paddy fields |
| Mycorrhiza (Glomus) | Fungi — help absorb phosphorus from soil |
Quick Revision Points
- Curd: Lactobacillus; Bread: yeast; Swiss cheese: Propionibacterium
- Penicillin: Penicillium notatum (Fleming); Cyclosporin: Trichoderma; Statins: Monascus
- Sewage: primary (physical) → secondary (biological, reduces BOD) → anaerobic digestion → biogas
- BOD: higher = more pollution
- Biogas: methanogens (Methanobacterium); cattle dung; KVIC/IARI
- Biocontrol: Bt, Trichoderma, Baculovirus, ladybird beetle
- Biofertilisers: Rhizobium (legume N₂-fixation), Mycorrhiza (phosphorus absorption)
Chapter Navigation
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Related Chapters in Class 12 Biology
- Strategies for Enhancement in Food Production Class 12 Notes
- Biotechnology Principles and Processes Class 12 Notes
- Human Health and Disease Class 12 Notes
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