What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Which microorganism is used in the production of curd and how?

Lactobacillus (lactic acid bacteria, LAB) convert lactose in milk to lactic acid, coagulating milk proteins to form curd.

Who discovered penicillin and from which organism?

Alexander Fleming discovered penicillin from the fungus Penicillium notatum.

What is the role of yeast in baking and brewing?

Saccharomyces cerevisiae (baker's yeast) ferments sugars producing carbon dioxide that leavens dough, and produces ethanol in brewing.

Name the bacteria that produce biogas.

Methanogens such as Methanobacterium, which thrive in anaerobic conditions like cattle dung and sludge, produce biogas.

What is the role of Rhizobium as a biofertiliser?

Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into a usable form for the plant.

Give an example of a microbial biocontrol agent for insect pests.

Bacillus thuringiensis (Bt) is sprayed to control butterfly caterpillars; its toxin kills the larvae.

What happens during secondary treatment of sewage?

Microbes form aerobic flocs (activated sludge) that consume organic matter, reducing the BOD of the effluent.

Name an immunosuppressive agent and a cholesterol-lowering agent obtained from microbes.

Cyclosporin A (from Trichoderma polysporum) is an immunosuppressant, and statins (from Monascus purpureus) lower blood cholesterol.

What are mycorrhizae and how do they help plants?

Mycorrhizae are symbiotic associations of fungi with plant roots; the fungus absorbs phosphorus and other nutrients from soil and passes them to the plant.

What is the significance of BOD in sewage treatment?

Biochemical Oxygen Demand measures the amount of oxygen required by microbes to oxidise organic matter; high BOD indicates high pollution, and treatment lowers it.

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Chapter 8: Microbes in Human Welfare — Class 12 Biology

Biology · 13 chapters

Summary, key terms, important questions and a practice quiz with AI diagnosis for each.

Chapter 8: Microbes in Human Welfare

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Curd is formed from milk by the action of:

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.

Microbes in household productsMicrobes in industrial productsMicrobes in sewage treatmentMicrobes in biogas productionMicrobes as biofertilisersMicrobes as biocontrol agents

Key terms

Fermentation

The anaerobic breakdown of sugars by microbes producing products such as alcohol, acids and gases.

Antibiotic

A chemical substance produced by a microbe that kills or inhibits the growth of other microbes, such as penicillin.

Biogas

A mixture of gases (predominantly methane) produced by microbial activity, used as fuel.

Biofertiliser

An organism that enriches the nutrient quality of soil, such as Rhizobium, Azotobacter, cyanobacteria and mycorrhiza.

Biocontrol agent

A biological agent used to control plant pests and pathogens, such as Bacillus thuringiensis and Trichoderma.

Activated sludge

The sediment of microbe-rich flocs in secondary sewage treatment that decomposes organic matter.

Important questions

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Fermentation

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The anaerobic breakdown of sugars by microbes producing products such as alcohol, acids and gases.

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Practice quiz · Microbes in Human Welfare

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Microbes in Human Welfare

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