Chapter 8 — Microbes in Human Welfare

NCERT Class 12 Biology Chapter 8 covers the beneficial roles of microbes in human welfare, including their use in household food products, industrial production of antibiotics and chemicals, sewage treatment, biogas generation, biocontrol of pests, and as biofertilisers.

Microbes in Human Welfare (Class 12 Biology Chapter 8) explains how microbes — bacteria, fungi, and cyanobacteria — benefit humanity beyond causing disease. Lactic acid bacteria convert milk to curd and improve its vitamin B12 content. Yeasts like Saccharomyces cerevisiae ferment dough and produce beverages such as wine, beer, whisky, and rum. Industrially, microbes produce antibiotics (Penicillin from Penicillium notatum), organic acids, enzymes (lipases, pectinases), and bioactive molecules like cyclosporin A and statins. Sewage treatment plants use heterotrophic microbes to reduce BOD and generate biogas. Methanogens produce methane-rich biogas used as rural fuel. Biocontrol agents like Bacillus thuringiensis (Bt) and Trichoderma combat pests naturally, while biofertilisers such as Rhizobium, Azotobacter, and cyanobacteria enrich soil nitrogen and reduce chemical fertiliser use.

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.