Notes Microbes in Human Welfare Class 12 Biology

Notes Class 12

Please refer to the Microbes in Human Welfare heritance and Variation Notes Class 12 Biology given below. These revision notes have been designed as per the latest NCERT, CBSE, and KVS books issued for the current academic year. Students will be able to understand the entire chapter in your class 12th Biology book. We have provided chapter-wise Notes for Class 12 Biology as per the latest examination pattern.

Revision Notes Chapter 10 Microbes in Human Welfare Class 12 Biology

Students of Class 12 Biology will be able to revise the entire chapter and also learn all important concepts based on the topic-wise notes given below. Our best teachers for Grade 12 have prepared these to help you get better marks in upcoming examinations. These revision notes cover all important topics given in this chapter.

  • Those organisms which are not visible with naked eyes and viewed under the microscope are called microorganisms or microbes. These include bacteria, protozoans, yeasts, viruses etc. 
  • The microbes are almost omnipresent (i.e., found every where). They are found in snow, inside thermal vents (or inside geysers, high acidic habitats etc.) Some remain viable when cooled upto – 190°C.
  • Microbes are both useful and harmful for humans. They cause several diseases, can spoil food and  used in many economical products. Here, we are concerned mainly with beneficial effects of microbes.

A variety of microbes or products obtained from them are used in our daily life. 

Dairy Products

  • Lactic acid bacteria convert lactose sugar of milk into lactic acid.
  • Lactic acid causes coagulation of milk protein casein. Milk is changed into curd, yoghurt and cheese.
  • Curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at temperature of about 40°C.
  • Yoghurt is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus.
  • Butter milk is acidulated product which is formed by inoculating skimmed milk with starter culture of Streptococcus cremoris, S. lactis, Lactobacillus acidophilus, Leuconostoc species at 22°C for 18 hours.
  • Cheese is the partially degraded concentrate of milk fat and casein manufactured by microorganisms. Swiss cheese is characterised by the characteristic flavour and large holes. The large holes are formed due to amount of CO2 released by a thermophilic bacteria (Propionibacterium sharmanii). Roquefort cheese is characterised by greenish blue mottling. It is ripened by Penicillium roquefortii. It is probably the best known cheese made from sheep’s milk. Camembert cheese employs Penicillium camemberti for ripening. 

Dough for Making Food Items

  • Numerous food items such as ‘dosa’, ‘idli’, ‘jalebi’ and ‘bread’ are prepared by fermentation process in which one or more kinds of microbes are used.
  • The ‘dough’ which is used for making dosa and idli is allowed to ferment overnight for 10 to 12 hours. The bacteria, which come from atmosphere (particularly Leuconostoc  mesenteroides, Streptococcus faecalis) cause fermentation so that the dough increases in volume and gets sour. Increase in the volume of dough is due to carbon dioxide gas (CO2 ) that is released as a result of fermentation
  • Bread is made from flour obtained by grinding cereal grain usually wheat. Selected strains of Saccharomyces cerevisiae grown on molasses are used as baker’s yeast. A small quantity of yeast is added to wheat flour and kneaded. The kneaded flour is kept at warm temperature for a few hours. It swells up. The phenomenon is called leavening.

Other Household Products

  • Toddy, a traditional drink of South India is made by fermenting latex obtained from toddy palm and coconut water. It undergoes fermentation with the help of naturally occurring yeast. It is a refreshing drink which can be heated to produce palm sugar (Jaggery).
  • Other foods like tempeh (Indonesia), tofu (Japanese) and sufu (Chinese) are fermented foods  obtained from soyabean.
  • Soy sauce is brown flavoured salty sauce fermented from soyabean and wheat.
  • Several types of sausages are prepared by fermentation and curing of fish and meat is also done with the help of microbes.

A variety of products in enormous amounts are produced by microbes such as – beverages (alcoholic and non alcoholic ),antibiotics, organic acids, enzymes, vitamins, hormones, amino acids, vaccines and steroids.

Alcoholic fermentation

  • Yeast species used in alcoholic fermentation are Saccharomyces cerevisiae, S. ellipsoideus, S. sake, etc.
  • Fermented nutrient medium used differs based on products.
  • The yeasts which are used in the brewing industry for the preparation of alcoholic drinks are collectively called brewer’s yeast.
  • different types of alcoholic beverages are produced by using different brewer’s yeast.
Products (Source)MethodBrewer’s yeast
Beer (Grain)Non distillationSaccharomyces cerevisiae and S. carisbergensis
Wine (Fruit juice)Non distillationS. ellipsoideus
  • Whisky, rum, gin, brandy, vodka and fenny are distilled beverages, so called hard liquors (Higher % of alcohol). 
  • By products of alcoholic fermentation are CO2 and ethanol.


  • Antibiotics are the chemical substances produced by microorganisms that in low concentration inhibits the growth or kill the pathogenic organisms without harming the host. The term “antibiotic“ (means against life) was coined by Waksman (1942).
  • Alexander Fleming (1928) discovered first antibiotic penicillin from Penicillium notatum in 1928.
  • It was commercially extracted by efforts of Chain and Florey.
  • This antibiotic was extensively used in treating wounded American soldiers in world war II.
  • Fleming, Chain and Florey were awarded with Nobel prize in 1945.
  • Over 7000 antibiotics are known. Streptomyces griseus produces more than 41 antibiotics while Bacillus subtilis can give about 60 antibiotics. 
  • Antibiotics are obtained from lichens, eubacteria, fungi and actinomycetes.
ChloramphenicolS. venezuelaeTyphoid, whooping cough (Kali Khansi)
ErythromycinS. erythreusDiphtheria (gal ghotu)
ChloromycetinS. lavendulaePneumonia
StreptomycinS. griseusMeningitis, Pneumonia, TB
BacitracinBacillus licheniformisSyphilis
  • Antibiotics are medicines used for treatment of a number of pathogenic or infectious diseases.

Single Cell Protein

  • Single cell protein (SCP) is the production of microbial biomass for consumption as human food or animal feed. The common SCP are Spirulina, yeast and Fusarium graminearum.
  • SCP is rich in high quality proteins but poor in fat.
  • SCP is useful in reducing environmental pollution by managing industrial and agricultural wastes.

Chemicals, Enzymes and other Bioactive Molecules

  • A number of organic acids are manufactured with the help of microbes e.g., acetic acid, citric acid, lactic acid, gluconic acid, cyclosporin A, statins.
  • Acetic acid is produced from fermented alcohol with the help of bacteria, Acetobacter aceti.
  • Citric acid is obtained through the fermentation carried out by Aspergillus niger and Mucor species on sugary syrup.
  • Gluconic acid is prepared by the activity of Aspergillus niger and Penicillium species.
  • Cyclosporin A is an important bioactive chemical produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ transplantation.
  • Statins are produced by yeast Monascus purpureus. It acts as competitive inhibitor of enzyme for cholesterol synthesis. So, it is used as blood cholesterol lowering agent.
  • Enzymes are proteinaceous substances of biological origin which are capable of catalysing biochemical reactions without themselves undergoing any change. 
  • Pectinases are enzymes obtained commercially from Byssochlamys fulva. Alongwith proteases they are used in clearing of fruit juices and also in retting of fibres and preparation of green coffee.
  • Lipases are lipid dissolving enzymes that are obtained from Candida lipolytica and Geotrichum candidum. Lipases are added in detergents for removing oily stains from laundry and also used in flavouring cheese.
  • Streptokinase (Tissue Plasminogen Activator or TPA) is an enzyme obtained from the cultures of some haemolytic streptococci. It has fibrinolytic effect, therefore it helps in clearing blood clots inside the blood vessels.
  • Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.

Sewage or municipal waste contains human excreta and other organic wastes. It also contains a number of pathogenic microbes, so should not be passed into rivers, streams and other water bodies. It is made less polluting by passing it through sewage treatment plants (STPs)  

Notes Microbes in Human Welfare Class 12 Biology


  • Biogas is a methane rich fuel gas produced by anaerobic breakdown or digestion of biomass with the help of methanogenic bacteria. 
  • It is an ideal gas made up of 50 – 70% methane (CH4), 30 – 40% CO2 , 1 – 5% H2, traces of O2 and N2 and H2S.
  • The most important microbes involved in production of biogas are – methanogenic archaebacteria and Bacillus etc. The energy released from biogas depends upon the proportion of methane present in it.
  • Biogas is commercially produced inside the biogas plants. Each biogas plant consists of a deep (10 – 15 ft) concrete tank covered by floating lid. It is fed with a mixture of dung (commonly called gobar) and water (1: 1).
Notes Microbes in Human Welfare Class 12 Biology
  • Cattle dung is a rich source of cellulosic material from plants. After filling the slurry of the dung, the biogas tank is covered by a floating lid which keeps on raising as the gas is produced from the slurry. The microbial activity in the slurry of dung results in the release of biogas.
  • Biogas is allowed to pass through an outlet pipe which is connected with the supply line. The leftover slurry is removed through another outlet, that can be used as fertiliser.
  • Biogas is used as fuel for heating, cooking and lighting. It is considered ecofriendly and pollution free source of energy.


  • Biocontrol agents refer to the use of biological methods for controlling plant diseases and pests.
  • Biopesticides are pesticides derived from natural or biological agents like animals, plants, bacteria, viruses, fungi etc. to destroy or control weeds, insects and pathogens.
  • According to the nature of organism – biopesticides are of different types as microbial pesticides, plant pesticides and biochemical pesticides.
  • Microbial pesticides consist of a microorganism (e.g., a bacterium, fungus, virus, or protozoan) as the active ingredient. The most widely used microbial pesticides are subspecies and strains of Bacillus thuringiensis (Bt).
  • Biochemical pesticides are naturally occurring substances that control pests by nontoxic mechanisms. For example, Lady bird beetle (beetle with red and black markings) feeds on aphids while dragonflies prey upon mosquitoes. Free living fungus Trichoderma exerts biocontrol over several plant pathogens.
  • Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are of the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. They have been shown to have  no negative impacts on plants, mammals, birds, fish or even on non-target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.


  • Biofertilisers are widely used in organic farming. Organic farming is the technique of raising crops through the use of manures, fertilisers and pesticides of biological origin, resistant varieties, crop rotation, intercropping etc.
  • Biofertilisers are organisms which bring about nutrient enrichment of the soil by enhancing the availability of nutrients like nitrogen and phosphorus to the crops.
  • Biofertilisers increase the yield of plants by 15- 35% 
Notes Microbes in Human Welfare Class 12 Biology
Notes Microbes in Human Welfare Class 12 Biology