Chapter 8 — Microbes in Human Welfare

Chapter 8 of the Class 12 Biology NCERT textbook, "Microbes in Human Welfare", covers the beneficial roles of microbes — in household food products, industrial production of antibiotics and chemicals, sewage treatment, biogas generation, biocontrol of pests, and as biofertilisers.

• Microbes in food and beverages — Household microbes such as lactic acid bacteria turn milk into curd and yeasts ferment dough and produce beverages, showing that many microbes are useful partners in food production rather than agents of disease.
• Industrial and medicinal products — On an industrial scale microbes yield antibiotics like penicillin, organic acids, enzymes, and bioactive molecules such as statins, making them central to pharmaceutical and chemical manufacturing.
• Waste treatment and clean energy — Heterotrophic microbes break down sewage to reduce pollution load, and methanogens convert cattle dung into methane-rich biogas, turning waste into treated water and a renewable rural fuel.
• Biocontrol agents and biofertilisers — Microbes like Bacillus thuringiensis and Trichoderma control pests and pathogens naturally, while Rhizobium, Azotobacter, mycorrhiza, and cyanobacteria enrich soil, reducing reliance on chemical pesticides and fertilisers.

1. 01Lactic acid bacteria (LAB) convert milk to curd by producing acids that coagulate milk proteins and increase vitamin B12; small amount of curd acts as inoculum for the next batch.
2. 02Penicillin, the first antibiotic, was discovered by Alexander Fleming from the mould Penicillium notatum; Fleming, Chain, and Florey received the Nobel Prize in 1945 for this discovery.
3. 03Sewage treatment involves primary (physical removal of solids) and secondary (biological reduction of BOD using aerobic microbes forming flocs) stages; anaerobic digestion of sludge produces biogas.
4. 04Methanogens such as Methanobacterium break down cellulosic material to produce methane, CO2, and H2; cattle dung (gobar) is the key input for rural biogas plants developed by IARI and KVIC.
5. 05Bacillus thuringiensis (Bt) spores are used as biopesticides to kill insect larvae without harming other insects; Trichoderma fungi control plant pathogens as biocontrol agents.
6. 06Biofertilisers — Rhizobium (legume root nodules), Azotobacter/Azospirillum (free-living nitrogen fixers), Glomus fungi (mycorrhiza absorbing phosphorus), and cyanobacteria (Anabaena, Nostoc) — enrich soil and reduce dependence on chemical fertilisers.