Chapter 8 - Microbes in Human Welfare

Microbes in Human Welfare explains how microorganisms are used in food preparation, industry, medicine, sewage treatment, energy generation, biological pest control and agriculture. NCERT Class 12 Biology Chapter 8 shifts attention from disease-causing microbes to the enormous number of useful microbial activities on which human society depends.

Teachoo’s chapter category organises the examples by application and explains the biological process behind each one. Students can use detailed notes, NCERT solutions, comparison tables, important questions, MCQs and case-based practice for CBSE and NEET.

Microbes in household products

Microorganisms have long been used in food production, often before humans understood their biology.

Lactic acid bacteria convert milk into curd. They produce acids that coagulate milk proteins and improve nutritional qualities. The microbial population in curd also contributes to its characteristic flavour and texture.

Yeast carries out fermentation and is used in preparing bread and traditional fermented foods. Carbon dioxide produced during fermentation causes dough to rise.

Microbes are also involved in products such as cheese, in which specific organisms and ripening conditions generate distinct textures and flavours. NCERT examples should be learned precisely because examinations often ask students to match a product with its microbe.

Microbes in industrial products

Large-scale microbial production takes place in fermenters or bioreactors under controlled conditions. Important products include fermented beverages, antibiotics, organic acids, enzymes and bioactive molecules.

Yeast is used for alcoholic fermentation. Distillation separates and concentrates alcohol in distilled beverages, while other beverages are produced without distillation.

Antibiotics are substances produced by certain microorganisms that suppress or kill other microorganisms. Penicillin is the standard historical example. Students should understand its microbial source and medical significance without confusing antibiotics with disinfectants or antibodies.

Microbial organic-acid examples include:

• Citric acid

• Acetic acid

• Butyric acid

• Lactic acid

Microbial enzymes have industrial uses. Lipases may be used in detergent formulations, pectinases and proteases can help clarify bottled juices, and enzymes can support specialised biochemical processes.

Bioactive molecules include streptokinase, cyclosporin A and statins. Students should match each molecule to its microbial source and application, such as clot dissolution, immune suppression or cholesterol management.

Microbes in sewage treatment

Municipal wastewater contains organic matter and microorganisms and must be treated before release.

Primary treatment mainly uses physical processes such as filtration and sedimentation to remove floating and suspended solids. It produces primary sludge and an effluent.

Secondary treatment uses aerobic microorganisms. Air is pumped into aeration tanks, where microbial flocs consume organic matter. This reduces the biochemical oxygen demand of the effluent.

Part of the activated sludge is returned as inoculum. The remaining sludge enters anaerobic digesters, where methanogenic bacteria break down organic material and produce gases such as methane, carbon dioxide and hydrogen sulphide.

Students must understand why a lower biochemical oxygen demand indicates reduced organic pollution and why untreated sewage depletes dissolved oxygen in receiving water bodies.

Microbes in biogas production

Biogas is a mixture rich in methane produced by anaerobic microbial digestion. Methanogens occur naturally in anaerobic environments and in the rumen of cattle.

In a biogas plant, dung and water form a slurry that enters an anaerobic digester. Microorganisms decompose the organic matter, and the gas collected can be used as fuel. The remaining slurry can serve as manure.

This application combines waste management, renewable energy and nutrient recycling.

Microbes as biocontrol agents

Biological control uses living organisms or their products to manage pests and plant diseases. It can reduce dependence on broad-spectrum chemical pesticides.

Examples include ladybird beetles that consume aphids, dragonflies that feed on mosquitoes, microbial agents such as Bacillus thuringiensis and fungal agents such as Trichoderma.

Baculoviruses can act as species-specific biological control agents and may have limited effects on non-target organisms. Students should understand the ecological advantage of specificity.

Microbes as biofertilisers

Biofertilisers improve nutrient availability through living organisms. Important examples include:

• Rhizobium in legume root nodules

• Free-living nitrogen-fixing bacteria

• Cyanobacteria in agricultural fields

• Azolla–Anabaena association

• Mycorrhizal fungi associated with plant roots

Mycorrhiza can improve phosphorus absorption and provide greater tolerance to selected stresses and pathogens. Biofertilisers support soil fertility and can reduce reliance on synthetic inputs.

Important diagrams and comparisons

• Sewage-treatment flow

• Microbial flocs and activated sludge

• Anaerobic sludge digester

• Biogas plant

• Household versus industrial fermentation

• Biocontrol agents versus chemical pesticides

• Biofertiliser organism–function table

Why is this chapter important for CBSE and NEET?

CBSE often asks process explanations, applications and case-based environmental questions. NEET commonly asks organism–product matches, sewage-treatment stages, BOD, methanogens, biocontrol examples and biofertilisers.

How should students study this chapter?

Create one master table with four columns: microorganism, product or process, use and special fact. Draw sewage treatment as a flowchart and clearly separate physical primary treatment from biological secondary treatment.

Frequently Asked Questions

Are all microorganisms harmful?

No. Many microbes are essential in food production, nutrient cycling, medicine, industry, waste treatment and agriculture.

Why does secondary sewage treatment reduce BOD?

Aerobic microbes consume much of the biodegradable organic matter, reducing the oxygen demand that the effluent would create in natural water.

Which microbes are important in biogas production?

Methanogenic microorganisms carry out anaerobic processes that generate methane-rich biogas.

What is activated sludge?

It is the sediment containing microbial flocs formed after aerated secondary treatment. Some is reused as inoculum and the rest is anaerobically digested.

What is the difference between biocontrol and biofertilisation?

Biocontrol suppresses pests or pathogens. Biofertilisation improves nutrient availability or plant growth through beneficial organisms.

Which NCERT examples are especially important for NEET?

Students should learn product–microbe pairs, streptokinase, cyclosporin A, statins, sewage microbes, methanogens, Bacillus thuringiensis, baculoviruses, Rhizobium and mycorrhiza.