Chapter 8: Microbes in Human WelfareClass 12 Biology — summary, notes, extra questions & MCQ quiz

Summary

This chapter highlights the beneficial roles of microbes in human life across food, industry, agriculture and the environment. In household products, microbes such as Lactobacillus convert milk to curd, yeast (Saccharomyces cerevisiae) leavens dough and ferments to produce bread, and microbes are used in making cheese, idli, dosa and toddy. In industry, microbes produce fermented beverages (wine, beer, whisky), antibiotics (penicillin from Penicillium notatum, discovered by Alexander Fleming), organic acids (citric acid, acetic acid, butyric acid), enzymes (lipases, pectinases, streptokinase, cyclosporin A, statins) and other bioactive molecules. In sewage treatment, microbes act in primary and secondary (biological) treatment, with activated sludge and anaerobic sludge digesters producing biogas (methane). Microbes are used in biogas production (methanogens like Methanobacterium in gobar gas plants) and as biofertilisers (Rhizobium, Azospirillum, Azotobacter, mycorrhiza like Glomus, and cyanobacteria like Anabaena and Nostoc) that enrich soil nutrients. They also serve as biocontrol agents (Bacillus thuringiensis, Trichoderma, baculoviruses, ladybird and dragonfly) to manage pests and pathogens, reducing reliance on chemical pesticides. The chapter emphasises sustainable and eco-friendly applications of microbes for human welfare.

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