NCERT Microbes In Human Welfare Class 12 Notes And Neet Questions

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NCERT Microbes In Human Welfare Class 12 Notes


Class12th 
Chapter No10
ProvidingQuestions And Answers, Notes & Numericals PDF
Chapter NameMicrobes in Human Welfare
BoardCBSE
Book NCERT
SubjectBiology
Medium English
Study MaterialsFree VVI Study Materials are Available
Download PDF microbes in human welfare pdf

Microbes In Human Welfare Class 12 Notes


1. Microbes are present everywhere in soil, water, air, inside plants and animal bodies including humans.

Microbes In Human Welfare 1

2. Microbes are the most adaptable creatures.

(i) Deep inside the geysers (thermal vents with temperature as high as (100°C).

(ii) Deep in the soil. 

(iii) Under the layers of snow several metres thick.

(iv) In a highly acidic environment. 

3. Microbes are diverse

(i) Protozoa 

(ii) Bacteria

(iii) Fungi

(iv) Microscopic plants viruses

(v) Viroids

(vi) Prions (proteinaceous infectious agents). 

4. Microbes like bacteria and many fungi can be grown on nutritive media to form colonies (Figure), that can be seen with the naked eyes. Such cultures are useful in studies on microorganisms.

5. Some microbes cause infections and diseases in human beings animals and plants. But most of the microbes are useful in many ways. Their biggest contribution is that they can break down all dead and decaying matter and release the nutrients locked up inside so that other organisms can use them.

6. Microbes in Household Products We use microbes or their products daily. Some common examples are as follows: (i) Curd is made by Lactobacillus and others commonly called Lactic Acid Bacteria (LAB) grow in milk and

convert it to curd, during growth. A small amount of curd added to the fresh milk inoculum or starter contains millions of LAB, which at suitable temperatures multiply, producing acids that coagulate and partially digest the milk proteins. It also improves its nutritional quality by increasing vitamin B In our stomach, the LAB play a very beneficial role by replacing harmful microbes.

(ii) The dough, which is used for making foods such as dos and idli or cakes or bread is also fermented by bacteria a yeast (Saccharomyces cerevisiae). 

The puffed-up appearance of dough is due to the production of CO2 gas by these microbes that break down the sugar to make CO₂ that escapes during cooking leaving empty holes that make the bread or cake soft. 

(ii) Cheese is made by using microbes.

Different varieties of cheese have their characteristic texture, flavour and taste, coming from the microbes e.g., the large holes in ‘Swiss cheese’ are due to the production of a large amount of CO2 by a bacterium named Propionibacterium shermanii.

The ‘Roquefort cheese’ are ripened by growing specific fungi on them, which gives them a particular flavour. Microbes are also used to ferment fish, soybean and bamboo shoots to make foods.

7. Microbes in Industrial Products In industry, microbes are used to make a number of products valuable to human beings. Production on an industrial scale requires growing microbes in very large vessels called fermentors.

8. Fermented Beverages Yeasts have been used for the production of beverages like wine, beer, whisky, brandy and rum. Saccharomyces cerevisiae (brewer’s yeast), is used for fermenting malted cereals and fruit juices, to produce ethanol. Depending on the type of raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation. Whisky, brandy and rum are produced by distillation of the fermented broth. 

9. Antibiotics means ‘against life’. Antibiotics are chemical substances, which are produced by some microbes to kill the other microbes competing for their resources. We can make use of these substances to kill or retard the growth of some disease-causing microbes, hence we named them antibiotics. 

Alexander Fleming observed that if a mould Penicillium notatum grows on a nutrient medium, it doesn’t let the bacterium Staphylococcus grow around it. He isolated the growth inhibitory chemical produced by the mould and named it penicillin. This antibiotic was extensively

used to treat American soldiers wounded in world war II. Antibiotics have been used to treat deadly diseases such as plague, whooping cough (Kali khansa), diphtheria (right), leprosy (just rog) and many other common infections.

10. Chemicals, Enzymes and other Bioactive Molecules Microbes are also used for commercial and industrial production of 

(i) Organic acids

(ii) Alcohols

(iii) Enzymes

S.N.MicrobeProduct
1Aspergillus niger (a fungus) Citric acid
2Acetobacter aceti (a bacterium)Acetic acid
3Clostridium butylicum (a bacterium)Butyric acid
4Lactobacillus (a bacterium) Lactic acid
5Yeast (Saccharomyces cerevisiae)Ethanol

Microbes are also used for the production of enzymes.

S.N. EnzymeUSE
1LipasesIn detergent formulations to remove oily stains from laundry
2Pectinases and Proleases To clarify commercial juices.
3StreptokinaseAs a ‘clot buster for removing blood clots
4Cyclosporin AAs an immunosuppressive agent in organ transplant patients
5Statins As blood-cholesterol-lowering agents

11. Microbes in Sewage Treatment In cities and towns, a major component of the wastewater from homes is human excreta. This municipal wastewater is also called sewage. It contains large amounts of organic matter and many pathogenic microbes. That is why before disposal, it needs to be treated in Sewage Treatment Plants (STPs) to make it less polluting. Treatment of waste water is done by the heterotrophic microbes (bacteria, fungi, Protozoa, rotifers, etc.) naturally present in the sewage. This treatment is carried out in two stages

(1) Primary treatment involves physical removal of particles, large and small-from the sewage through filtration and sedimentation. All solids that settle down, form the primary sludge and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

(ii) Secondary treatment or Biological treatment The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it.

This allows vigorous growth of naturally present useful aerobic microbes into flocs (big clumps of bacteria associated with fungal filaments to form mesh-like structures).

While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (Biochemical Oxygen Demand) of the effluent (BOD refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria).

The BOD test measures the rate of uptake of oxygen by microorganisms in a sample of water. BOD is a measure of the organic matter present in the water. The greater the BOD of wastewater, more is its polluting potential. The sewage water is treated till the BOD is reduced significantly.

The effluent is then passed into a settling tank where the bacterial flocs sediment. This sediment is called activated sludge as it contains active microbes. From here

(a) A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. 

(b) The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

(c) The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, lack of oxygen kills the aerobic bacteria and they are digested along with the other biomass by anaerobic bacteria and fungi.

During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas which is inflammable and therefore can be used as fuel.

12. River Pollution with Sewage Water Untreated sewage is often discharged directly into rivers leading to their pollution and an increase in water-borne diseases. The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan to save these major

rivers of our country from pollution. Under these plans, it is proposed to build a large number of sewage treatment plants so that only treated sewage may be discharged into the rivers.

13. Microbes in the Production of Biogas Biogas which may be used as fuel, is a mixture of gases (mainly CH, CO2, H₂) produced by microbial activity.

Microbes produce different types of gaseous end-products during growth and metabolism. The type of gas produced depends upon the microbes and the organic substrates they utilise. Bacteria that grow anaerobically on cellulosic material, produce large amounts of methane along with CO, and H.

These bacteria are collectively called methanogens and are found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of the stomach) of cattle, helping in the breakdown of cellulose so that the animal can further break it down for release From the rumen, some of the methanogens pass into the energy

BAL excreta (dung) of cattle, commonly called gobar. Dung can be used for the generation of biogas, commonly called gobar gas.

The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed in. A floating cover is placed over the slurry. The biogas plant has an outlet, which is connected to a pipe to

supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertiliser.

The biogas is used for cooking and lighting in houses in the rural area. Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC) developed this technology.

14. Microbes as Biocontrol Agents Biocontrol refers to the use of biological methods for controlling plant diseases and pests. For a long time chemical insecticides, pesticides and weedicides have been used.

Now, it has been realised that these chemicals are toxic and extremely harmful, to human beings, and animals and also pollute the environment (soil, groundwater) and even fruits, vegetables and crop plants.

Biological control of pests and diseases Pests can be controlled by making use of natural predation rather than chemicals. Instead of complete eradication, insect pests can be kept at

manageable levels by using various means. The organic farmers believe that eradication of the creatures would disturb the delicate balance of the ecosystem as without these insects, the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive.

Jo Thus, the use of biocontrol measures has become preferable since it will greatly reduce our dependence on toxic chemicals and would also maintain the natural balance of the ecosystem by not eliminating harmless insects but keeping harmful pests in control. Examples of biocontrol agents

6) The beetle with red and black markings, the ladybird, is useful to get rid of aphids.

(ii) Dragonflies are able to hold the mosquito population in check. 

(ii) Trichoderma, a free-living fungi found in root ecosystems, control many plant pathogens.

(iv) Baculoviruses are used for specific pest control. 

(v) Butterfly caterpillar can be killed by using the bacteria

Bacillus thuringiensis (often written as Bt). It is available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae.

In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars but leave other insects unharmed.

Using genetic engineering techniques scientists have introduced B. thuringiensis toxin genes into cotton plants. Such Bt-cotton plants are resistant to attack by insect pests. 

15. Microbes as Biofertilisers Chemical fertilisers are used to increase agricultural production but it has significant environmental pollution. To cut down on further pollution, it is important to switch to

Organic farming, using biofertilizers. Biofertilizers are organisms, e.g., bacteria, fungi and cyanobacteria, that enrich the nutrient quality of the soil. Soil enrichment is done by following organisms Rhizobium bacteria that live in root nodules of

leguminous plants, fix atmospheric nitrogen into organic forms, which is used by the plant as a nutrient.

Azospirillum and Azotobacter can fix atmospheric nitrogen while living freely in the soil, thus enriching the nitrogen content of the soil.

Anabaena, Nostoc, and Oscillatoriaia (cyanobacteria) all fix nitrogen in aquatic and terrestrial environments. Blue-green algae also add organic matter to the soil and increase its fertility.

Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza, absorb phosphorus from soil and pass it to the plant.

Plants having such associations also show resistance tolerance to salinity and drought and an overall increase in plant growth and development. root-borne pathogens, Currently, in India a number of biofertilisers are available commercially in the market and are used regularly in the fields to replenish soil nutrients and to reduce pendency o chemical fertilisers.


microbes in human welfare neet questions


Question 1. Bacteria cannot be seen with the naked eye, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes under a microscope, which sample would you carry and why?

Answer A sample of pond water would be opt for demonstrating the presence of microbes under a microscope as it would contain a multitude of microorganisms of all shapes and sizes.

Question 2. Give examples to prove that microbes release during metabolism.

Answer Examples to prove that microbes release gases during The puffed-up appearance of dough of dosa and idli is because of the CO, metabolism released by bacteria during fermentation of the dough. During the digestion of sludge during wastewater treatment, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide.

Question 3. In which food would you find lactic acid bacteria Mention some of their useful applications.

Answer Generally, Lactic Acid Bacteria (LAB), are found in milk and products. Lactic Acid Bacteria (LAB), are a group of related bacteria that produce lactic acid from carbohydrate fermentation. They are generally used in making fermented milk products.

(1) They can grow in milk, break down the lactose sugar in the milk and produce acids that coagulate and partially digest the milk proteins. They also add vitamin B, in milk thereby increasing its nutritional quality 

(i) In our stomach too, the LAB play a very beneficial role in checking

Question 4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) that involve the use of microbes. 

Answer For making dosa and idli rice powder is fermented by bacteria and for making bread (from wheat), yeast (Saccharomyces cerevisiae) is used.

Gutta (made from black gram) also uses bacteria. Microbes are also used to ferment fish, soybean and bamboo shoots to make foods.

Question 5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

Answer Microbes produce certain chemical substances, called antibiotics that can be used to kill or retard the growth of other disease-causing microbes.

Antibiotics have been used to treat deadly diseases such as plague, whooping cough (kali khans), diphtheria (galghotu) and leprosy (just rog) and many other common infections.

Question 6. Name any two species of fungus, which are used in the production of antibiotics.

Answer Penicillium notatum and Streptomyces are two fungus, which are used in the production of antibiotics. species of

Question 7. What is sewage? In which way can sewage be harmful to us?

Answer Sewage is the municipal wastewater collected from city or townhomes, that contains toilet, bathroom and kitchen waste. It contains large amounts of organic matter and many pathogenic microbes which are harmful to humans as they can cause many diseases like cholera, typhoid, and polio. 

Question 8. What is the key difference between primary and secondary sewage treatment?

Answer Primary treatment involves the physical removal of large and small particles from the sewage through filtration and sedimentation. Whereas, secondary sewage treatment involves biological digestion of organic matter by microbes.

Question 9. Do you think microbes can also be used as a source of energy? If yes, How? 

Answer Microbes produce different types of gaseous end-products during growth and metabolism. A mixture of gases called biogas produced by microbial activity can be used as fuel. Another end product alcohol can also be mixed with other fuels and used

as a source of energy. Question 10. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished. Answer Microbes can be used as biofertilisers, organisms that enrich the nutrient quality of the soil.

The main sources of bio-fertilisers are bacteria, fungi and cyanobacteria.

They help in increasing the fertility of the soil in many ways (1) Rhizobium that forms nodules on the roots of leguminous plants (a symbiotic association) and fixes atmospheric nitrogen into organic forms, which is used by the plant as a nutrient. 

(i) Azospirillum and Azotobacter fix atmospheric nitrogen while living freely and enriching the nitrogen content of the soil.

() Many members of the genus Glomus (fungi) form symbiotic associations with plants known as mycorrhiza that

(a) absorb phosphorus from soil and pass it to the plant 

(b) help the plants to develop resistance to root-borne pathogens 

(c) increase their tolerance to salinity and drought and thus, help in the overall increase in plant growth and development.

(iv) Cyanobacteria autotrophic microbes, e.g., Anabaena, Nostoc, and Oscillatoria can fix atmospheric nitrogen, in the aquatic and terrestrial environments and also add organic matter to the soil and increase its fertility.

Question 11. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/L and 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Answer Sample A (BOD 20mg/L) is secondary effluent discharged from an 8mg/L) is a river a sewage treatment plant.

Sample B (BOD water. Sample C (BOD 400mg/L) is untreated sewage water. As BOD is the direct measure of the organic matter present in water, the higher the BOD, the more polluted the water.

Question 12. Find out the name of the microbes from which Cyclosporin-A (an immunosuppressive drug) and statins (blood cholesterol lowering agents) are obtained. 

Answer

(1) Cyclosporin-A is obtained from the fungus Trichoderma polysporum. (i) Statins is obtained from Monascus purpureus. nA following and

Question 13. Find out the role of microbes in discussing it with your teacher.

(a) Single Cell Protein (SCP)

(b) Soil

Answer

(a) Single Cell Protein (SCP) refers to harmless microbial cells that can be used as an alternate source of good protein.

Just like mushrooms (a fungus) is eaten by many people and yeast is used by athletes as a protein source; similarly, other forms of microbial cells can also be used as food rich in protein, minerals, fats, carbohydrates and vitamins.

cl din beru Microbes like Spirulina and Methylophilus methylotrophs are being grown on an industrial scale on materials containing starch like wastewater from potato processing plants, straw, molasses, animal manure and even sewage. These single-cell microbes can be used as sources of proteins. dans! (b) Role of microbes in the soil. Refer to Ans. 10

Question 14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid. Penicillin, Card. Penicillin is an antibiotic that helps kill pathogens that cause

Answer

infections and diseases and thus, saves lives. Biogas is a non-polluting clean fuel that is produced as a byproduct of sewage treatment. It is used for cooking and lighting up homes in rural areas.

Curd has good nutrient value, provides vitamin B,2 and replaces harmful bacteria in the stomach with helpful ones. Citric acid is used as a preservative in food. Question 5. How do biofilters enrich the fertility of the out Answer Refer to Ans. 10.


microbes in human welfare ncert Questions Answer


Question 1. Why does ‘Swiss cheese’ have big holes?

Answer The large holes in ‘Swiss cheese’ are due to the production of a large amount of CO₂ by a bacterium named Propionibacterium Sharman.

Question 2. What are fermentors? 

Answer Fermentors are large vessels used on an industrial scale in which microbes are grown for synthesising a number of products like antibiotics and beverages, through a process of fermentation.

Question 3. Why do we prefer to call secondary treatment biological treatment?

Answer Secondary wastewater treatment is called biological treatment because microorganisms are involved in the breakdown of organic matter

in this phase of wastewater treatment. The primary effluent is passed into large aeration tanks where the organic matter in it is consumed by aerobic microbes which are later themselves

digested by anaerobic bacteria and fungi in anaerobic sludge digesters. Question 4. Write the most important characteristic the

Aspergillus niger, Clostridium butylicum and Lactobacillus share. Answer Their common characteristic is that they produce organic acids as part of their metabolism and are, therefore, used for commercial and industrial production of the same.

(i) Aspergillus niger (a fungus) for citric acid 

(i) Clostridium bretylium (a bacterium) for butyric acid

(I) Lactobacillus (a bacterium) for lactic acid.

Question 5. What would happen if our intestine harbours microbial flora exactly similar to that found in the rumen of cattle? 

Answer If our intestine harbours microbial flora exactly similar to that found in the rumen of cattle, we would be able to digest the cellulose present in our foods because the microbes present in the rumen (a part of the stomach) of cattle collectively called methanogens, are capable of digesting cellulose.

Question 6. Give any two microbes that are useful in biotechnology.

Answer Two microbes that are useful in biotechnology

(1) Bacillus thuringiensis a gene isolated from this bacterium, is introduced in plants to make them able to kill butterfly caterpillars. 

(i) Escherichia coli is a bacterium that is used in many biotechnology procedures.

Question 7. What is the source organism for Eco RI, restriction endonuclease?

Answer Escherichia coli strain RY 13 is the source organism.

Question 8. Name any genetically modified crop. 

Answer Bt cotton is a genetically modified plant that has been modified to resist attack by insect pests by the introduction of Bacillus thuringiensis.

Question 9. Which species of Penicillium produces Roquefort cheese?

Answer: Penicillium roqueforti produces roquefort cheese.

Question 10. Name any two industrially important enzymes.

Answer

(1) Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry. 

(ii) Pectinases and proteases that are used as clarifying agents in making commercial juices.

Question 11. Name an immune immunosuppressive agent. 

Answer Cyclosporin-A (produced by the fungus Trichoderma polysporum) is used as an immunosuppressive agent.

Question 12. Give an example of a rod-shaped virus. 

Answer:- Tobacco mosaic virus is a rod-shaped virus.


microbes in Human welfare ncert solutions


Question 1. Why are flocs important in the biological treatment of wastewater?

Answer Flocs refers to masses of bacteria associated with fungal filaments that form mesh-like structures. These help digest the organic matter, remove pathogens and release nutrients in the sewage effluent.

2. Why are cyanobacteria considered useful in paddy Question fields?

Ans:- Cyanobacteria like Anabaena, Nostoc, Oscillatoria serve as important biofertilizers in paddy fields as they fix atmospheric nitrogen and add organic matter to the soil and increase its fertility.

Question 3. What roles do enzymes play in detergents that we use for washing clothes? Are these enzymes produced from some unique microorganisms?

Answer Enzymes like Lipases are used in detergent formulations, which cause the breakdown of oils and thus help in removing oily stains from the which laundry.

These are obtained from Candida lipolytic and Geotrichum candidum.

Question 4. Which bacterium has been used as a clot buster? What is its mode of action?

Answer The bacterium Streptococcus which produces streptokinase is used as a ‘clot buster’.

This enzyme has a fibrinolytic action that breaks down the clots formed in the blood vessels of patients who have undergone myocardial infarction This prevents heart attack in these patients that can otherwise occur because of occlusion by the clots.

Question 5. What are biofertilizers? Give two examples.

Answer Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

Example

(1) Azospirillum and Azotobacter can fix atmospheric nitrogen in the soil Blue-green algae add organic matter to the soil to increase its fertility


microbes in human welfare important questions


Question 1. Why is aerobic degradation more important than anaerobic degradation for the treatment of large volumes of wastewater rich in organic matter? Discuss.

Answer Aerobic degradation is more important as naturally occurring aerobic and facultative microbes (bacteria, fungi, Protozoa and others) in the wastewater can rapidly oxidize soluble organic and nitrogenous compounds. Mechanical addition of oxygen makes the process faster and most of the

pathogenic content of the effluent is removed. Anaerobic degradation majorly removes these aerobes from the water before it can be released into the rivers, etc.

Question 2. (a) What would happen if a large volume of untreated sewage is discharged into a river?

(b) In what way anaerobic sludge digestion is important in sewage treatments?

Answer

(a) If untreated sewage is discharged directly into rivers it will lead to serious pollution of the waters with organic matter and pathogenic bacteria and Protozoa.

This water, if used, will cause outbreaks of waterborne diseases. 

(b) In anaerobic sludge digestion, anaerobic bacteria digest the aerobic bacteria and the fungi in the sludge and the remaining organic matter.

During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases (biogas) can be used as a source of energy as it is inflammable. 


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