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Microbes in Human Welfare

NCERT Class 12 Biology Chapter 8

Microbes in Human Welfare for Class 12 Biology and NEET: microbes in food, industry, sewage treatment, biogas, biocontrol and biofertilisers.

6 topics Updated 8 Nov 2026

For: Class 12 and NEET

In the syllabus: NEET Class 12 syllabus

With your textbook

NCERT Biology (Class 12), Chapter 8 “Microbes in Human Welfare”, reprint 2026-27.

Open the official NCERT chapter (PDF, 12.9 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Microbes in household products

    Microbes in household products for Class 12 Biology and NEET: lactic acid bacteria and curd, idli, dosa and bread dough, toddy, cheese and curd vs yoghurt.

    NCERT Section 8.1 9 min read 3 solved examples 8 practice questions

  2. Microbes in industrial products

    Microbes in industrial products for Class 12 Biology and NEET: beverages, penicillin and how it works, organic acids, enzymes, streptokinase and statins.

    NCERT Section 8.2 9 min read 3 solved examples 8 practice questions

  3. Microbes in sewage treatment

    Microbes in sewage treatment for Class 12 Biology and NEET: primary and secondary treatment, BOD and COD, activated sludge, biogas and a flow diagram.

    NCERT Section 8.3 11 min read 3 solved examples 8 practice questions

  4. Microbes in biogas production

    Microbes in biogas production for Class 12 Biology and NEET: methanogens, biogas composition, gobar gas from cattle dung and a biogas plant diagram.

    NCERT Section 8.4 9 min read 3 solved examples 8 practice questions

  5. Microbes as biocontrol agents

    Microbes as biocontrol agents for Class 12 Biology and NEET: organic farming, ladybirds, dragonflies, Bt and its toxin, fungi, baculoviruses and IPM.

    NCERT Section 8.5 10 min read 3 solved examples 8 practice questions

  6. Microbes as biofertilisers

    Microbes as biofertilisers for Class 12 Biology and NEET: nitrogen fixers, mycorrhiza and its types, cyanobacteria, and biofertilisers vs biopesticides.

    NCERT Section 8.6 7 min read 3 solved examples 8 practice questions

Key formulas in this chapter

Microbes in household products

  • milk → curd: lactic acid bacteria (LAB)
  • LAB acids coagulate milk proteins; curd has more vitamin B
  • idli, dosa dough: bacteria; bread dough: yeast
  • dough puffs up: CO from fermentation
  • toddy: fermented palm sap
  • Swiss cheese holes: CO from a bacterium
  • Roquefort cheese: ripened by a fungus

Microbes in industrial products

  • antibiotic: kills or retards disease-causing microbes
  • penicillin: the first antibiotic, from a mould
  • wine, beer: no distillation
  • whisky, brandy, rum: distilled
  • lipases: detergents; pectinases, proteases: juices
  • streptokinase: clot buster
  • cyclosporin A: immunosuppressant
  • statins: lower blood cholesterol

Microbes in sewage treatment

  • primary treatment: filtration, sedimentation
  • secondary treatment: aerobic microbes in flocs
  • higher BOD → more organic matter
  • activated sludge: part back as inoculum
  • digester: anaerobic bacteria → biogas
  • biogas: methane, HS, CO

Microbes in biogas production

  • biogas: mostly methane, from microbes
  • methanogens: anaerobic; methane + CO + H
  • methanogens: rumen, dung, anaerobic sludge
  • gobar gas: biogas from cattle dung
  • floating cover rises as gas forms
  • spent slurry: fertiliser

Microbes as biocontrol agents

  • ladybird: aphids; dragonfly: mosquitoes
  • Bt: kills butterfly caterpillars
  • Bt toxin: released in the larval gut
  • fungal biocontrol: plant pathogens
  • baculoviruses: species-specific insecticides
  • IPM: integrated pest management

Microbes as biofertilisers

  • biofertilisers: bacteria, fungi, cyanobacteria
  • legume root nodules: symbiotic N fixation
  • free-living N fixers in the soil
  • mycorrhiza: phosphorus to the plant
  • cyanobacteria: N fixation in paddy fields

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