Microbes in Human Welfare Class 12 Biology Revision Notes

Class 12 Notes

Please refer to Microbes in Human Welfare Class 12 Biology Revision Notes for Chapter 10 provided below. These concept notes have been prepared based on the latest Class 12 Biology NCERT, CBSE, and KVS books issued for the current academic year. These notes will help you to learn all the important topics given in the chapter and are important to get good marks. We have provided Class 11 Biology Notes for all chapters on our website for download in Pdf.

Class 12 Biology Chapter 10 Microbes in Human Welfare Revision Notes

♦  Lactobacillus or Lactic acid bacteria (LAB):
1. It converts milk to curd by producing acids that coagulate and partially digest the milk proteins.
2. Fresh milk can be converted to curd by adding some curd containing LAB. It also increases vitamin B12 in curd.
3. In stomach, LAB helps to check pathogens.
♦ Bacterial fermentation (anaerobic respiration) In dough is used to make foods such as dosa, idli etc. The puffed-up appearance of dough is due to the production of  CO2 .
♦ Baker’s Yeast (Saccharomyces cerevisiae): It is used to make bread by fermenting dough.
♦ Toddy is made by fermenting sap from palms
♦ Microbes are used to ferment fish, soya bean & bamboo hoots and to produce cheeses.
♦ Swiss cheese has large holes due to production of CO2 by Propionibacterium sharmanii (a bacterium).
Roquefort cheese is ripened by growing a fungus (Penicillium roqueforti) on them

Production of beverages, antibiotics etc. on an industrial scale, requires growing microbes in very large vessels (fermentors).

Fermented beverages 
Saccharomyces cerevisiae (Brewer’s yeast) is used in the production of beverages by fermenting malted cereals and  Butyric acid fruit juices to produce ethanol. 
Wine & Beer are produced without distillation. 
♦ Whisky, Brandy, Rum, Gin, Arrack etc. are produced by distillation of fermented broth.

Chemical substances produced by some microbes and can kill or retard the growth of pathogens. 
They are used to treat plague, whooping cough, diphtheria, leprosy etc. 
Penicillin: First antibiotic discovered by Alexander Fleming. He observed that Staphylococci could not grow around a mould (Penicillium notatum) growing in transplant patients. unwashed culture plates. He extracted penicillin from it. 
Earnest Chain and Howard Florey established its full potential as an effective antibiotic.
♦ Fleming, Chain & Florey were awarded Nobel Prize (1945).

Chemicals, enzymes & other bioactive molecules
1. Organic acids:
Acid producer microbes include 
Aspergillus niger (a fungus)             : Citric acid
Acetobacter aceti (a bacterium)        : Acetic acid
Clostridium butylicum (a bacterium)  :  Butyric acid
Lactobacillus (a bacterium)                : Lactic acid
2. Alcohol: Yeast (S. cerevisiae) is used to produce ethanol.
3. Enzymes:

♦ Lipases: Used in detergent formulations. Help to remove oily stains from the laundry.
♦ Pectinases & Proteases: To clarify bottled juices.
♦ Streptokinase: Produced by Streptococcus. Used as a ‘clot buster’ to remove clots from the blood vessels of  patients who have myocardial infarction.
4. Cyclosporine A:
Produced by Trichoderma polysporum (fungus). Used as an immunosuppressive agent in organ
5. Statins:
Produced by Monascus purpureus (a yeast). Used as blood-cholesterol lowering agents. It inhibits the enzymes responsible for synthesis of cholesterol.

 (municipal waste-water) contains large amount of organic matter and microbes. Sewage is treated in Sewage Treatment Plants (STPs) to make it less polluting. It includes 2 stages.

1. Primary treatment
It is the physical removal of particles. It includes
a. Removal of floating debris by sequential filtration.
b. Removal of the grit (soil & pebbles) by sedimentation.
The settled solids form the primary sludge and the supernatant form the primary effluent.

2. Secondary treatment (Biological treatment)
Primary effluent is passed into large aeration tanks and constantly agitated. This allows vigorous growth of useful aerobic microbes into flocs (bacteria associated with fungal filaments to form mesh-like structures). These microbes consume the organic matter in the effluent. This reduces the BOD (Biochemical Oxygen Demand) of the effluent .

BOD: Amount of O2 consumed by bacteria to oxidize all organic matter in one litre of water. It is a measure of organic matter present in the water. The greater the BOD more is its polluting potential. 
The effluent is then passed into a settling tank where the bacterial ‘flocs’ are sediment. This sediment is called ‘activated sludge’.
A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.
The remaining sludge is pumped into large tanks called anaerobic sludge digesters. Here, some anaerobic bacteria digest the bacteria and fungi in the sludge by producing gases like CH4, H2S and CO2. These gases form the biogas.
The effluent is released into natural water bodies like rivers and streams.
The Ministry of Environment & Forests initiated Ganga Action Plan & Yamuna Action Plan to save from water pollution.

♦ Biogas is a mixture of gases (mainly CH4) produced by the microbial activity. It is used for cooking & lighting.
♦ Methanogens grow anaerobically on cellulosic material and produce CH4. E.g. Methanobacterium.
♦ Methanobacterium is found in the anaerobic sludge and rumen of cattle (for cellulose digestion).
♦ The cattle dung (gobar) is rich in these bacteria. Dung can be used for generation of biogas (Gobar gas).
♦ The Biogas plant consists of
1. A concrete tank (10-15 feet deep) to collect bio-wastes and slurry of dung. A floating cover is placed over the slurry, which keeps on rising as the biogas is produced.
2. An outlet which is connected to a pipe to supply biogas.
3. An outlet to remove spent slurry (used as fertilizer).
Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC): Developed technology of biogas production in India.

Biocontrol is the use of biological methods for controlling plant diseases and pests. E.g. Lady bird (beetle) controls aphids. Dragon flies control mosquitoes.
♦ Chemical pesticides and insecticides kill both useful and harmful organisms and cause pollution. Biocontrol method has no such problems.

Microbial biocontrol agents

Bacillus thuringiensis (Bt): To control butterfly caterpillar. The dried spores of Bt (available in sachets) are mixed with water and sprayed on to vulnerable plants such as brassicas and fruit trees. These are eaten by the caterpillar. In their gut, the toxin is released and the larvae get killed. The scientists have introduced B. thuringiensis toxin genes into plants. E.g. Bt cotton.
Trichoderma sp (fungus): These are free livings present in the root ecosystems. They control several plant pathogens.
Baculoviruses (Especially genus Nucleopolyhedro-virus): Attacks insects and other arthropods. It is suitable for species-specific, narrow spectrum insecticidal applications and desirable in IPM (Integrated Pest Management) program to conserve beneficial insects.

Biofertilisers are organisms that enrich nutrient quality of the soil. E.g. Bacteria, fungi, cyanobacteria etc.
♦ Rhizobium (symbiotic bacteria in root nodules of leguminous plants) fix atmospheric N2.
♦ Free-living bacteria in the soil (E.g. Azospirillum and Azotobacter) enrich the nitrogen content of the soil.
♦ Mycorrhiza: Symbiotic association of fungi (E.g. genus of Glomus) with plants. The fungus gets food from plant. The fungal symbiont performs the following:
1. Absorb phosphorous from soil and passes it to the plant.
2. Give resistance to root-borne pathogens and tolerance tosalinity and draught.
3. Give overall increase in plant growth and development.
♦ Cyanobacteria (Blue green algae): Autotrophic microbes. They fix atmospheric nitrogen. E.g. Anabaena, Nostoc,  Oscillatoria etc. In paddy fields, Cyanobacteria serve as an important biofertilisers. It also adds organic matter to the soil and increases its fertility.

Microbes in Human Welfare Class 12 Biology Revision Notes