Microbes in Human Welfare Class 12 Biology NCERT Chapter 10

Key Features of NCERT Material for Class 12 Biology Chapter 10 –  Microbes in Human Welfare

In the previous chapter 9, we studied how animal husbandry is used as a method of food production due to the growing demand for food. Have you asked why food is ruined whenever left unrefrigerated for quite a long time? Or then again how you get cheddar from milk? These are for the most part because of the activity of living beings that are not noticeable to the unaided eye, called microbes or microorganisms. These microbes likewise have some significant applications in our lives. Alongside plants and creatures, microorganisms likewise structure a significant piece of the biological framework on earth. We should find out about them in chapter 10 of class 12  biology: Microbes in Human Welfare. 

Quick revision notes

Microbes cause numerous illnesses in individuals, plants and creatures. A few microorganisms are valuable to a man in various manners.


Microbes exist all over the place – in soil, air, water and furthermore in the human body and the groups of plants and different creatures! They additionally exist in places where no other living thing exists, for example, somewhere down in the fountains where the temperature is incredibly high! Bacteria, fungi, protozoa, viroids are microorganisms. Albeit microscopic, they can develop on nutritive media and form colonies that can be seen by naked-eye. This permits us to learn about them better. 

Uses of microbes 

Up until now, we have discovered that microorganisms cause illnesses in people, plants and creatures. In any case, they can likewise be valuable to a man in different ways. Let’s study the various manners by which they are helpful to us. 

Bacteria and fungi can be developed on nutritive media to form colonies, which can be seen by eyes and valuable in the study of microorganisms. 

Microbes in household product

  1. Microorganisms like Lactobacillus and other normally called lactic acid bacteria (LAB) develop in milk and convert it to curd. The LAB produces acids that coagulate and in part digests the milk proteins. It likewise improves its healthful quality by boosting nutrient B12. In our stomach as well, the LAB plays an advantageous role in checking illness-causing microbes.
  2. The batter is utilized for making food items, for example, dosa and idli are fermented by bacteria. The puffed-up appearance of the mixture is because of the creation of CO2 gas. The mixture utilized for making bread is fermented utilizing baker’s yeast (Saccharomyces cerevisiae). 
  3. Cheddar is one of the earliest food things in which microbes were utilized. The large gaps in ‘Swiss cheddar’ are because of the creation of a lot of CO2 by a bacterium named Propionibacterium sharmanii. The ‘Roquefort cheddar’ is developed by growing a particular fungus on them for a specific flavour. 

Microbes in industrial production

Various items like refreshments and antibiotics include the utilization of microbes. Large scaled production requires developing microbes in huge vessels called fermenters. 

Microbes in Human Welfare Class 12 Biology

  1. Fermented Beverages-Saccharomyces cerevisiae utilized for bread-production and generally called brewer’s yeast, is utilized for fermenting malted grains and fruit juices, to deliver refreshments like wine, beer, whisky and rum. Wine and beer are created without distillation though whisky, liquor and rum are delivered by the distillation of the fertilised broth. 
  2. Anti-microbials they are chemical substances delivered by certain microbes and can kill or prevent the development of different microbes. The first antibiotic to be found was Penicillin. Antibiotics have incredibly improved our ability to treat serious diseases, for example, plague, leprosy, diphtheria and whooping cough. 
  3. Organic acids, chemicals, Enzymes and other Bioactive Molecules are industrially and commercially created by microbes. 


  • Aspergillus niger (fungus): Citric acid 
  • Acetobacter aceti (bacterium):  Acetic acid 
  • Clostridium butylicum (bacterium):  Butyric acid 
  • Lactobacillus (bacterium): Lactic acid 
  • Saccharomyces cerevisiae: Ethanol 


  • Lipase: utilized in clothing cleansers 
  • Pectinase and protease: utilized in packaged juices 
  • Streptokinase (Streptococcus bacterium):  utilized as clot buster (to expel clots) 

Bioactive molecules: 

  • Cyclosporin A (Trichoderma polysporum fungi) – utilized as immunosuppressive specialist (for organ relocated patients). 
  • Statins (Monascus purpureus yeast) – utilized as blood cholesterol bringing down agents. 

Microbes in Sewage Treatment 

Municipal wastewater (sewage) contains a huge measure of organic matter and microbes which are pathogenic and can’t be released into regular water bodies like waterways and streams. 

Sewage is treated in the sewage treatment plant to make it less polluting by utilizing heterotrophic microbes normally present in sewage. Sewage treatment is done in two phases 

Microbes in Sewage Treatment 

In the primary treatment, floating debris is drained by sequential filtration. Grift (soil and little rocks) are ousted by sedimentation. 

Secondary treatment or biological treatment includes moving of primary effluents in an enormous air circulation tank to help the development of aerobic microbes into flocs (masses of bacteria related to fungal filaments to devise mesh-like structures). These microbes increment the utilization of organic wastes and decline the BOD (biological oxygen demand)of the effluents. 

Bod is the measure of oxygen that would be utilised if all the organic matter in one litre of water were oxidized by bacteria. It quantifies the measure of organic matter present in the water. Higher the BOD of water more it is polluted. 

When the BOD of sewage or wastewater is diminished, the effluents are then moved into a settling tank where the bacterial ‘flocs’ are permitted to sediment. This sediment is described as activated sludge. 

Sludge is passed into huge tanks called anaerobic sludge digesters in which anaerobic bacteria digest the bacteria and fungi in the sludge and produce a blend of gas called biogas, which is a blend of methane, hydrogen sulfide and carbon dioxide. 

The effluents from the secondary treatment plant are discharged into water bodies. 

Microbes in Production of Biogas 

Biogas is a blend of gases created by the microbial movement that can be utilized as fuel. Certain bacteria that develop anaerobically on cellulosic material produce a huge measure of methane alongside CO2and H2. These bacteria are called methanogens (Methanobacterium). 

Microbes in Production of Biogas 

Biogas Plant – the excreta of cattle (gobar) is prosperous in methanogens bacteria and is utilized for the generation of biogas likewise called gobar gas. 

  • The innovation of biogas production was found in India basically because of the endeavours of the Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC). 

Biogas plant comprises of a concrete tank where bio-waste are gathered and a slurry of waste is fed. 

A floating cover is set over digester that moves upward when gas is created. The gas created is evacuated and provided through an outlet pipe for utilization. 

The spent slurry is discharged through another outlet and utilized as manures. A biogas plant is mostly built in rural zones as a huge measure of cattle dug is accessible without any problem. 

Microbes as Biocontrol operator 

Biocontrol implies the utilization of biochemical strategy for controlling plant sickness and irritations. The chemical utilized as pesticides and bug sprays is destructive to people and creatures. 

Biological control of irritations and sickness is a strategy for controlling pests on natural forecast instead of chemical substances. The organic farmer makes a framework where the pests are not destroyed however kept at a sensible level by a complex arrangement of check and balance inside the living and dynamic biological system. For instance, the Ladybird and Dragonflies are utilized to dispose of aphids and mosquitoes separately. On brassicas and fruit trees, to control butterfly caterpillars bacteria Bacillus thuringiensis is utilized. 

Biological control created for use in the treatment of plant infection is the fungus Trichoderma. Trichoderma is a free-living fungus that is common in the root frameworks that control a few plant microbes. 

  • Baculoviruses are pathogens that strike insects and different arthropods. Most of the baculoviruses utilized as biological control operators are in the variety Nucleopolyhedrovirus. These viruses are an excellent contender for species-explicit, narrow spectrum insecticidal applications.

Microbes as Bio composts 

Biofertilizers are living beings that advance the nutrient quality of the soil. The principle sources incorporate bacteria, fungi and cyanobacteria. 

The root nodule framed by Rhizobium bacteria on the foundation of leguminous plants increments the nitrogen level of soil, essential for different metabolic procedures. Azotobacter and Azospirillum are free-living bacteria that live in soil and fix air nitrogen into organic forms. 

Symbiotic association of fungi with angiosperm plants (mycorrhiza) likewise increment the richness of the soil. Glomus structure mycorrhiza that retains phosphorus from the soil and passes it to the plant. These microbes likewise give benefits like protection from root-borne microorganisms, tolerance to saltiness and drought. 

Cyanobacteria (Nostoc, Anabaena), an autotrophic microbes found in aquatic and terrestrial condition fix climatic nitrogen. In the paddy field, this is a significant bio-fertilizer. Blue-green algae likewise add an organic matter to the soil and increment its fertility.


Which of these biological oxygen demand levels show the most pollution? 

  1. 400mg/L 
  2. 8mg/L 
  3. 100mg/L 
  4. 20mg/L 

Answer: Answer is ‘A’’. Higher BOD level means increasingly polluted water.

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