Microbes in Human Welfare notes

Microbes are microscopic organisms such as bacteria, fungi, protozoa, algae and viruses. Although many microbes cause diseases, NCERT emphasizes that a very large number are beneficial and are used in food preparation, industry, sewage treatment, biogas production, pest control and soil fertility improvement. They ferment milk into curd, raise bread dough, produce antibiotics, organic acids, enzymes, alcohol, biogas and biofertilisers. They also help clean sewage by decomposing organic matter and lowering biological oxygen demand. In agriculture, microbes reduce chemical pesticide and fertiliser dependence through biocontrol agents and nitrogen-fixing organisms. For NEET, this chapter is fact-rich: organism-product pairs, process sequences and NCERT examples are repeatedly asked.

Household microbial products show how simple fermentation improves taste, texture, preservation and nutrition. Lactic acid bacteria, commonly called LAB, grow in milk and convert lactose into lactic acid. This acid coagulates milk proteins and forms curd while increasing vitamin B12 content and checking disease-causing microbes in the stomach. Yeast, especially Saccharomyces cerevisiae, ferments sugars in dough and releases carbon dioxide, making bread soft and porous. Microbes are also used in traditional fermented foods such as dosa, idli, cheese and beverages like toddy. For NEET, focus on the exact roles of LAB, baker’s yeast, curd formation, fermented food examples and the difference between lactic acid fermentation and alcoholic fermentation.

Industrial microbiology uses selected microbial strains in large fermenters to produce valuable compounds under controlled conditions. These products include antibiotics such as penicillin, organic acids such as citric acid, acetic acid, butyric acid and lactic acid, enzymes such as lipase, pectinase, protease and streptokinase, alcoholic beverages and bioactive molecules such as cyclosporin A and statins. Industrial fermentation requires sterile nutrient medium, inoculum, aeration or anaerobic conditions depending on the product, temperature control, pH control and downstream processing. NEET questions frequently ask exact organism-product pairs: Aspergillus niger produces citric acid, Acetobacter aceti produces acetic acid, Clostridium butylicum produces butyric acid and Monascus purpureus produces statins.

Sewage is municipal wastewater containing organic matter, suspended solids and microbes. It cannot be released directly into rivers because decomposition consumes dissolved oxygen and harms aquatic life. Sewage treatment has primary and secondary stages. Primary treatment is physical removal of large and small particles by filtration and sedimentation, producing primary sludge and effluent. Secondary treatment is biological: aerobic microbes form flocs in aeration tanks and degrade organic matter, reducing BOD. The microbial flocs settle as activated sludge; part is recycled as inoculum and the rest enters anaerobic sludge digesters. Anaerobic microbes digest sludge and release biogas. NEET focuses on BOD, activated sludge, flocs, aeration and sludge digestion sequence.

Biogas is a renewable fuel produced by anaerobic decomposition of organic waste such as cattle dung, sewage sludge and plant residues. It mainly contains methane, along with carbon dioxide and hydrogen sulphide. The key microbes are methanogens, especially Methanobacterium, which occur in anaerobic sludge and in the rumen of cattle where they help digest cellulose. A gobar gas plant has a concrete digester, inlet for dung slurry, gas holder or gas outlet and outlet for spent slurry. In the digester, anaerobic microbes break complex organic matter into simpler compounds and finally methane. Biogas is useful for cooking, lighting and rural energy, while the spent slurry serves as manure.

Biocontrol means using living organisms or their products to control pests, weeds and plant diseases instead of depending only on chemical pesticides. It is a key part of Integrated Pest Management, which aims to manage pests economically and ecologically while protecting beneficial organisms. Bacillus thuringiensis, or Bt, produces protein toxins that kill insect larvae when ingested. Trichoderma species are free-living fungi found in root ecosystems and are effective against several plant pathogens. Baculoviruses are pathogens that attack insects and other arthropods; the genus Nucleopolyhedrovirus is highly specific and safe for non-target organisms. NEET focuses on specificity, Bt toxin, Trichoderma, baculoviruses and the ecological advantage of biocontrol.

Biofertilisers are organisms that enrich nutrient quality of soil and reduce dependence on chemical fertilisers. Major biofertilisers include bacteria, cyanobacteria and fungi. Rhizobium forms root nodules in leguminous plants and fixes atmospheric nitrogen symbiotically. Azospirillum and Azotobacter are free-living bacteria that fix nitrogen in the soil. Cyanobacteria such as Anabaena, Nostoc and Oscillatoria fix atmospheric nitrogen and are especially important in paddy fields; some form symbiosis with aquatic fern Azolla. Mycorrhiza is a symbiotic association between fungi and plant roots; Glomus helps absorb phosphorus, improves resistance to root-borne pathogens and increases tolerance to salinity and drought. NEET often asks symbiotic vs free-living examples.