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Microbes in Human Welfare

Q1. Write the role of microbes in household food products.


  • Lactobacillus and lactic acid bacteria (LAB) help in the conversion of milk into curd.

  • Saccharomyces cerevisiae (yeast) is helps in the fermentation of dough which is used to make bread.

  • Toddy is made by fermentation of sap from palm trees by bacteria.

  • Cheese is formed by partial degradation of milk by different microorganisms such as Propionibaclerium sharmanii, Penicillium roqueforti.

Q2. Discuss the role of microbes as biofertilizers.


  • Rhizobium is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into organic compounds.

  • Azospirillum and Azotobacter are free-living bacteria which absorb free nitrogen from soil, air and convert it into salts of nitrogen.

  • Fungi form symbiotic association with the roots of higher plants called mycorrhiza, e.g., Glomus. Helps in the absorption of phosphorous and other nutrients.

  • Mycorrhiza provides resistance against root-borne pathogens. and tolerance against salinity and drought.

  • Cyanobacteria fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity, e.g., Nostoc, Anabaena, Oscillatoria, etc.

  • Blue-green algae increase the soil fertility by adding organic matter to the soil.

Q3. Mention the source and function each of the following;
  1. Penicillin

  2. Streptokinase

  3. Cyclosporin A

  4. Statins

  5. Lactic acid


  1. Penicillin- Penicillin is extracted from the penicillium notatum and used as an antibiotic.

  2. Streptokinase- Obtained from Streptococcus and used as 'clot-buster' for removing clots from blood vessels of patients.

  3. Cyclosporin A- It is obtained from Trichoderma polysporum and used as immunosuppressive agent in organ transplant patients.

  4. Statins- It is obtained from Moascus purpureus and used as 'blood-cholesterol lowering agent'.

  5. Lactic acid- Obtained from Lactobacillus sps. helps in the conversion of milk into curd.

Q4. How anaerobic bacteria are beneficial in secondary sewage treatment.


Anaerobic bacteria such as methanogens which grow anaerobically, digest bacteria and fungi in sludge. During this digestion, bacteria produce mixture of gases such as methane, hydrogen sulphide and C02 which form the biogas.

Q5. Define biocontrol. Explain by giving any three examples.

Ans: Biocontrol is defined as controlling plant diseases and pests using biological methods.


  • Ladybirds and Dragonflies are used to get rid of aphids and mosquitoes.

  • The bacteria Bacillus thuringiensis (Bt) are used to control butterfly caterpillars.

  • Trichoderma sps., free-living fungi, are present in root ecosystems where they act against several plant pathogens

  • Baculoviruses are pathogens that attack insects and other arthropods.

Q6. List some organic acids obtained from microbes.


  1. Citric acid - Aspergillus niger

  2. Acetic acid - Acetobacter aceti

  3. Butyric acid - Clostridium butylicum

  4. Lactic acid - Lactobacillus sps.

Q7. Explain the role of microbes in Secondary treatment or biological treatment of sewage.


  • Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.

  • Useful aerobic microbes grow rapidly and form flocs.

  • Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.

  • The growing microbes consume organic matter and thus reduce the biochemical oxygen demand (BOD).

  • When BOD of sewage has reduced, the effluent is passed into settling tank.

Q8. Explain the role of microbes in production of any five industrial products.


  1. Antibiotics: like penicillin extracted from Penicillium notatum.

  2. Fermented beverages: Wine, beer, whisky, brandy are obtained from yeast.

  3. Enzymes: lipases used in laundry, pectinases are used to purify the bottled fruit juices.

  4. Chemicals: organic acids like Acetic acid (Acetobacter aceti), butyric acid (Clostridium butylicum), lactic acid (Lactobacillus sp.)

  5. Bioactive molecules: Cyclosporine A (Trichoderma polysporum), Statin (Monascus purpureus).

Q9. Describe the role of microbes in biogas production with a neat labeled diagram.


  • Biogas is a mixture of inflammable gases (methane, SO2, CO2, etc.,) produced by microbial activity that can be used as fuel.

  • Methanogens, particularly Methanobacterium, anaerobically breaks down cellulosic material to produce large amount of methane along with CO2 and H2.

  • These bacteria are commonly found in the anaerobic sludge in sewage treatment plants. And in rumen (a part of stomach) of cattle, thus providing nutrition to cattle.

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