Microbes in Human Welfare Class 12 | Biology in Human Welfare |


Microbes in Human Welfare Class 12, Biology in Human Welfare

What are Microbes?

Microbes are diverse protozoans bacteria fungi and microscopic plants and viruses viroid and also prions that are proteinaceous infectious agents.

Microbes in Household Products


  • Microorganisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it into curd.
  • During growth LAB produce acids that coagulate and partially digest milk proteins.
  • LAB also improves the nutritional quality by increasing vitamin B12.
  • LAB also plays beneficial role in checking disease causing microbes in stomach.


  • Different varieties of cheese are known by their characteristics, texture, flavour and taste .
    The large holes in swiss cheese are due to production of co2 by bacterium named Propionibacterium Sharmanii.
  • The Roquefort Cheese are ripened by growing on specific fungi on them , which give particular flavour.
  • Toddy– a traditional drink of some southern parts of india made by fermenting sap from palms.
  • Baker’S Yeast– Saccharomyces cerevisiae

Microbes in Industrial Products

  • Microbes specially yeast have been used from the time immemorial for the production of beverages like wine, beer, whisky , brandy, rum.
  • Saccharomyces cerevisiae used for bread making is also used for fermenting malted cereals and fruit juices to produce ethanol and also known as BREWER’S YEAST.
  • Wine and beer are produced without distillation.
  • Whisky, brandy & rum are produced by distillation.


  • The term was coined by SELMAN WAKSMAN in 1942.
  • Antibiotics produced by microbes are regarded as one of the most significant discoveries of the twentieth century and have great contributed towards the welfare of human society.
  • Anti is a Greek word that means “against life” (In the contest of disease causing organisms whereas in reference to human they are “pro life” and not against.
  • PENCILLLIN was first antibiotic discovered by Alexander Fleming.
  • He observed it while working on Staphylococci bacteria.
  • The full potential of antibiotic was established much later by ERNEST CHAIN and HOWARD FLOREY.
  • This antibiotic was extensively used to treat American soldiers wounded in world war 2
    Fleming, Chain, Florey were awarded with Nobel prize in 1945.

Microbes in Sewage Treatment

Sewage- The municipal waste water is called sewage.

Primary Wastewater Treatment

Primary treatment of wastewater involves sedimentation of solid waste within the water. This is done after filtering out larger contaminants within the water. Wastewater is passed through several tanks and filters that separate water from contaminants. The resulting “sludge” is then fed into a digester, in which further processing takes place. This primary batch of sludge contains nearly 50% of suspended solids within wastewater.

Secondary Wastewater Treatment

Secondary treatment is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option.


The ministry of Environment and forests has initiated this plan to save the major rivers of our country from pollution.

Microbes in Production of Biogas

  • Biogas is the mixture of gases produced by the microorganisms. It is a renewable source of energy. Methane is the predominant gas present in the biogas mixture.
  • Certain bacteria grow under anaerobic conditions and produce a large amount of methane along with carbon dioxide and hydrogen. The bacteria which produce the gaseous mixture are collectively known as methanogens. Methanobacterium is one such methanogen.
  • Methanobacterium is present inside the rumen of the cattle and the sludge produced during sewage treatment. The Methanobacterium present in the food of the cattle digests the cellulose present. The dung then produced by the cattle contains these methanogens which can be used for the production of biogas also known as the Gobar Gas.

  • The technology of biogas production was developed by Indian Agricultural Research Institute (IARI) and Khadi And Village Industries Commission (KVIC).

Microbes as Biocontrol Agents

  • Biocontrol refers to the use of biological methods for controlling plant diseases and pests.
  • Chemicals, insecticides and pesticides are extremely harmful to human beings and also these pollute our environment.
  • The use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides.

Biocontrol agents are which are useful in controlling plant diseases and pests are;

  • The ladybird, a beetle with red and black markings and dragon flies are useful to get rid of aphids and mosquitoes respectively.

  • Bacteria Bacillus thuringiensis (Bt) is used to get rid of butterfly caterpillars where dried spores of Bacillus thuringiensis are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees and these are eaten by the insect larvae and in the gut of the larvae, the toxin is released and the larvae get killed.

Fig. Bacillus thuringiensis

  • Trichoderma species are free-living fungi found in the root ecosystem these are effective as biocontrol agents of several plant pathogens.
  • Baculoviruses are pathogens that attack insects and other arthropods and the majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus.

Microbes as Biofertilisers

Biofertilisers are formulation of living microorganisms that enrich the nutrient quality of the soil.

The main sources of biofertilisers are bacteria, fungi and cyanobacteria. Rhizobium is a classical example for symbiotic nitrogen fixing bacteria. This bacterium infects the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms. Azospirillum and Azotobacter are free living bacteria that fix atmospheric nitrogen and enrich the nitrogen content of soil.


A symbiotic association between a fungus and the roots of the plants is called mycorrhiza. The fungal symbiont in these associations absorbs the phosphorus from soil and transfers to the plant.


Cyanobacteria (or) blue green algae (BGA) are prokaryotic free-living organisms which can fix nitrogen. Oscillatoria, Nostoc, Anabaena, Tolypothrix are well known nitrogen fixing cyanobacteria. Their importance is realized in the water logged paddy fields where Cyanobacteria multiply and fix molecular nitrogen.


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