RBSE Class 12 Biology Important Questions Chapter 10 Microbes in Human Welfare

Rajasthan Board RBSE Class 12 Biology Important Questions Chapter 10 Microbes in Human Welfare Important Questions and Answers.

RBSE Class 12 Biology Chapter 10 Important Question Microbes in Human Welfare

Multiple Choice Questions

Question 1.    
Biogas mainly contains:
(a) carbon dioxide    
(b) oxygen
(c) methane    
(d) liquid nitrogen
Answer:
(c) methane

Question 2.    
Methanogens are found in:
(a) rumen of cattle    
(b) cattle dung
(c) domestic sewage 
(d) all of these
Answer:
(d) all of these

Question 3.    
The scientist to discover penicillin was:
(a) Flemming    
(b) Burkholder
(c) Waksman    
(d) Pasteur
Answer:
(a) Flemming

Question 4.    
A treated sewage water has:
(a) maximum BOD    
(b) moderat BOD
(c) low BOD    
(d) least BOD
Answer:
(d) least BOD

Question 5.    
Mycorrhizae are symbiotic association of:
(a) algae and fungus
(b) algae and bryophytes
(c) algae and roots of gymnosperms
(d) fungal hyphae and roots of higher plants
Answer:
(d) fungal hyphae and roots of higher plants

Question 6.    
Yeast is employed for the production of:
(a) curd    
(b) cheese
(c) acetic acid    
(d) ethyl alcohol
Answer:
(d) ethyl alcohol

Question 7.    
Most common nitrogen - fixing cyanobacterium of paddy fields is:
(a) Oscillatoria    
(b) Nostoc
(c) Aulosira    
(d) Rhodospirillum
Answer:
(c) Aulosira

Question 8.    
“Tody” is prepared by the yeast fermentation of:
(a) wheat flour    
(b) coconut water
(c) grapes juice    
(d) sugarcane juice
Answer:
(b) coconut water

Question 9.    
Bt gene occurs in:
(a) Bacillus thuringiensis
(b) Escherichia coli
(c) Agrobacterium tumifaciens
(d) Rhizobium leguminosarum
Answer:
(a) Bacillus thuringiensis

Question 10.    
Streptomycin is produced by:
(a) Streptomyces scoleus 
(b) S. fradiae 
(c) S. venzueleae    
(d) S. giseus
Answer:
(d) S. giseus

Question 11.    
Milk is fermented or curdled by:
(a) Rhizobium    
(b) Lactobacillus
(c) Azotobacter    
(d) Clostridium
Answer:
(b) Lactobacillus

Question 12.    
Bt cotton is resistant to:
(a) insects    
(b) herbicides
(c) salt    
(d) drought
Answer:
(a) insects

Question 13.    
Baker’s yeast is:
(a) Saccharomyces cerevisae
(b) Saccharomyces ludwingii
(c) Saccharomyces octospours
(d) Schizosaccharomyces
Answer:
(a) Saccharomyces cerevisae

Question 14.    
Which of the following is not a biofertilizers?
(a) Agrobacterium    
(b) Rhizobium
(c) Nostoc    
(d) Mycorrhiza
Answer:
(a) Agrobacterium

Question 15.    
Antibiotic, terramycin is obtained by:
(a) Streptomyces rimosus 
(b) S. fradiae 
(c) S. nivens    
(d) S. erythraeus
Answer:
(a) Streptomyces rimosus

Question 16.    
Alcoholic fermentation is performed by:
(a) Chlorella    
(b) Yeast
(c) Agaricus    
(d) Puccinia
Answser:
(b) Yeast

Question 17.    
Cyclosporin - A is used to:
(a) regulate blood pressure
(b) dissolve the blood clot
(c) treat respiratory disorders 
(d) inhibit the rejection of transplanted organ
Answer:
(b) dissolve the blood clot

Question 18.    
Anabaena azollae found in leaves of a/an:
(a) angiospermic plant    
(b) fern
(c) gymnosperm    
(d) moss    
Answer:
(b) fern

Question 19.    
The microbes commonly used in kitchens are:
(a) Lactobacillus and yeast
(b) Penicillium and yeast
(c) Microspora and E. coli
(d) Rhizopus and Lactobacillus
Answer:
(a) Lactobacillus and yeast

Very Short Answer Type Questions

Question 1. 
Mention the functions of Lactic acetic acid bacteria (LAB) that are useful to man.
Answer:

• Lactic acid bacteria convert milk into curd and are employed in dairy industries.
• LAB in human intestine synthesizing vitamin B₁₂. 

Question 2. 
What is the role of baker’s yeast in the production of bread?
Answer:
Saccharomyces cerevisae (Baker’s yeast) cause the alcoholic fermentation of sugars in wheat flour and produce ethanol and CO₂. CO₂ raises the bread when baked and makes it soft.

Question 3. 
How is ‘tody’ prepared?
Answer:
Tody is traditional drink of sduthern India which is prepared by the yeast fermentation of coconut water. 

Question 4. 
Name the two vitamins produced by microbial fermentation.
Answer:

• Vitamin B₁₂ (Cobalamine).
• Vitamin B₂ (Riboflavin).

Question 5. 
Which microbes are used to prepare swiss cheese and Roquefort cheese.
Answer:
Swiss cheese: bacterium, propionibacterium shrmanii.
Roquefort cheese: Fungus, Pmicillium roqueforti.

Question 6. 
Who discover the first antibiotic and who gave the term antibiotic?
Answer:
Alexander Fleming discovered the first antibiotic named penicillin and Seltnan Waksman gave the term antibiotic.

Question 7. 
What are floes? Formed during secondary treatment of sewage?
Answer:
Floes are masses of bacteria, associated with fungal hyphae, which form mesh- like structures, during secondary treatment of water.

Question 8. 
What are vaculoviruses?
Answer:
Viruses used in biological control of insects, pests and other arthropods named as vaculoviruses.

Question 9. 
Name the group of organisms and the substrate they act on to produce biogas.
Answer:
Name of the group of organisms: Methanogens. 
Substrate: Cellulosic material / cow dung / agriculture waste.

Question 10. 
Name two alcoholic drink prepared in each of the following ways:
(i) with distillation.
(ii) without distillation.
Answer:
(i) With distillation: Brandy, Whisky, Rum.
(ii) Without distillation: Wine and Beer.

Question 11. 
Name the bacterium responsible for the large holes seen in “Swiss Cheese”. What are these holes due to?
Answer:
Propionibacterium sharmanii: The holes are because of production of large amount of C02.

Question 12. 
What is the chemical nature of biogas? Name an organism which is known to be employed in biogas.
Answer:
The biogas contains methane, CO₂ and H₂. Methanobacterium, a type of methanogen is employed for biogas production.

Question 13. 
Give the fullform of:
(a) SCP    
(b) BOD.
Answer:
(a) SCP: Single Cell Protein.
(b) BOD: Biochemical Oxygen Demand.

Question 14. 
What does it mean if water sample has more BOD?
Answert:
More value of BOD means the water sample is polluted by organic matter.

Question 15. 
Define sewage.
Answer:
Sewage is the municipal wastewater produced in cities and towns that contains human and animal exreta and other organic wastes.

Question 16. 
Why does a farmer and Azotobacter culture to the soil before sowing maize?
Answer:
Azotobacter is a free living nitrogen fixing bacterium which fixes the atmospheric nitrogen into the soil and makes it available to the maize crop, resulting in increased yield of crop.

Questin 17. 
What are fermentors?
Answer:
Fermentors are very large-sized vessels where microbes are grown for the synthesizing products valuable to human beings on industrial scale.

Question 18. 
What for Nucleopolyhydro viruses are being used now a days?
Answer:
Nucleopolyhydro viruses are used for biological control of insect pests.

Question 19. 
What are mycorrhizae?
Answer:
They associations of fungi with roots of higher plants are symbiotic called mycorrhizae.

Question 20. 
What are biofertilizers? Give two examples. 
Answer:
Some microorganisms have the capability to enrich soil nutrients, they are called biofertilizers.
Example: Azotobacter, Nostoc.

Question 21. 
Penicillin is obtained from which fungus?
Answer:
Penicillin is obtained from fungi. Penicillium notatum and P. chrysogenum.

Question 22. 
Give the name of that bacterial product which is used as a “clot burster”.
Answer:
Streptokinase, (Tissue plasminogen activator) produced by bacterium Streptococcus.

Question 23. 
How is lactic acid bacteria beneficial to us other than helping in curdling the milk? 
Or 
Write down the two beneficial roles of bacteria converting milk into curd.
Answer:
Two benefits of lactic acid bacteria are given below:

• They improve the nutrient quantity of curd by increasing the vitamin B₁₂ content.
• LAB also check the growth of disease causing microbes in the stomach.

Question 24. 
Define Antibiotics.
Answer:
Antibiotics are the organic substances obtained from microorganisms and used to kill other harmful microorganisms.

Question 25. 
The Bt toxin produced by Bt does not kill Bacillus but kills insect. Why?
Answer:
Bt toxin does not kill Bacillus but kill the insect that ingests it because the endotoxin that accumulates in the bacterium is an inactive precursor. It gets activated only in the alkaline gut of insect.

Question 26. 
Write any two places where methanogens can be found.
Answer:
(i) Rice field.
(ii) Ruminants alimentary canal.

Short Answer Type Questions - I

Question 1. 
Why does bread have soft and spongy texture?
Answer:
Bakers yeast, specially Sacsharomyces cerevisiae, is used for making bread, where it converts the fermentable sugars present in the dough into CO₂. This causes the dough to expand or rise as the CO₂ forms bubbles. When the dough is baked it ‘sets’ and the pockets / bubbles remain, giving the baked product a soft and spongy texture.

Question 2. 
Give two examples of biofertilizers.
Answer:

1. Rhizobium is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into nitrogenous compounds.
2. Azospirillum and Azotobacter are free living bacteria which absorb free nitrogen from soil, air and convert it into salts of nitrogen like amino acids and enrich soil nutrients.

Question 3. 
Why are some molecules called bioactive molecules? Give two examples of such molecules?
Answer:
This is because microbes like bacteria or fungi are used in their production.
Examples: Citric acid : Acetic acid.
Butyric acid : Lactic acid.

Question 4. 
Give the scientific name of the microbes from which cyclosporin A and statin are Obtained. Write one medical use of each one of these drugs. 
Answer:
Cyclosporin A that is used as an immuno - suppressive agent during organ transplantation in patients is produced by the fungus Trichodermapolysporum. Statin produced by yeast Monascus purpureus have been commercialised as blood cholestrol lowering agents.

Question 5. 
How was penicillin discovered?
Answer:
Penicillin was an accidental discovery. Sir Alexander Flaming observed that in unwanted culture plates of Staphylococcus a mould of Penicillium was growing. This mould inhibited the growth of Staphylococcus around it. Later the antibiotic penicillin was isolated from this fungus.

Question 6. 
What are biopesticides? Give the scientific name and use of first commercially used biopesticides in the world.
Answer:
Biopesticides are living organisms which are able to kill or repel specific pests. Now a days biopesticides are used in place of chemical fertilizers. Bacillus thuringionsis (Bt) is the first bacterial biopesticide to be used on commercial scale.

Question 7. 
Write four harmful effects of chemical pesticides.
Answer:
The harmful effects of chemical pesticides:

• They pollute the soil and water.
• They kill many useful organisms in the soil.
• They effects the salinity of the soil.
• They enter the food chain and cause disease at various trophic levels.

Question 8. 
Name the genus to which baculaviruses belong. Describe their role in the integrated pest management programmes
Answer:
Baculoviruses belong to the genus Nucleopolyhedrovirus. They control only species - specific pest, do not affect non - target organisms and benificial insects are conserved, they aid in IPM problems and there is no negative impact on plants or other animals. 

Question 9. 
(a) Why do farmers prefer biofertilizers to chemical fertilizers these days? Explain.
(b) How do Anabaena and mycorrhiza act as biofertilizers?
Answer:
(a) Chemical fertilizers have significantly increased the soil pollution, reducing its quality. Therefore, farmers use biofertilizers which enrich the quality of the soil.
(b) Anabaena fix atmospheric nitrogen, thus enriching the nitrogen content of the soil. In mycorrhiza, the fungal, symbiont absorbs phosphorus from soil and passes it other plant.

Quesiton 10. 
Name the organism which produce the following products:
(i) Ethanol 
(ii) Citric acid 
(iii) Cyclosporin A 
(iv) Acetic acid.
Answer:
(i) Saccharomyces cerevisiae
(ii) Aspergillus niger
(iii) Trichoderma polysporum
(iv) Acetobacter aceti

Question 11. 
What will be the effect on treatment of sewage of microbes are removed from it? Clarify.
Answer:
If the microbes are removed from the sewage treatment, there will be no breakdown of the wastes. The wastes will be present in the treatment plant and the BOD will not reduce.

Question 12. 
Bottled fruit juices are clearer as compared to those made at home. Explain.
Answer:
Bottled fruit juices are clearer as compared to those made at home because, in these juices pectinase enzyme is added, which digest the pectin and other fibres present in juices.

Question 13. 
Write down the application of biofertilizers. Explain the role of cyanobacteria as biofertilizers.
Answer:
Biofertilizers enrich the nutrient (nitrogen, phosphorus, etc.) quality of the soil. 
Cyanobacteria are autotrophic microbes and many of them can fix atmospheric nitrogen. e.g., Nostoc, Anabaena etc.

Question 14. 
Name a genus of baculovirus. Why are they considered good biocontrol agents? 
Answer:
A genus of baculovirus is Nucleopolyhedrovirus. It is useful in controlling many insects and other arthopods. They are species - specific narrow spectrum bioinsecticide with no side effect on plants, and other organisms. They serves as an important component of integrated pest management programme in dealing with ecological sensitive areas. These properties are useful in organic farming.

Question 15. 
Name a freeliving and symbiotic bacterium that serve as biofertilizer. Why are they so called?
Answer:
Free living bacterium: Azospirillum.
Symbiotic bacterium: Rhizobium.
They fix atmospheric nitrogen into nitrogenous compound and enrich the nutrient quality of the soil. Hence, are called biofertilizers.

Question 16. 
What suggestion will you give a farmer to increase the productivity of is field? Explain.
Answer:
Suggestion for a farmer to increase the productivity of his field:

• He should be use biopesticides to protect his crops.
• He should be use biofertilizers to enrich soil fertility.    

Question 17. 
With reference to fermented beverages explain the role of microbes in industrial products.
Answer:
Many beverages on industrial scale produced by several microorganisms. Beverages are formed by fermenting malted cereals and fruit juice with Saccharomyces cerevisiae or brewer’s yeast to produce ethanol.
E.g., Beer, wine, whisky, rum etc.

Question 18. 
Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non - leguminous terrestrial crop.
(a) Recommend two microbes that can enrich the soil with nitrogen.
(b) Why do leguminous crops not require such enrichment of the soil?
Answer:
(a) Azospirillum and Azotobacter.
(b) The leguminous plants have nodules in their roots. These root nodules are formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen and convert it into organic form. This organic form of nitrogen is used later on by the plants nutrients. Therefore, they do not, require enrichment of the soil.

Short Answer Type Questions - II

Question 1. 
What are antibiotics? Name the classes of organisms that produce antibiotics.
Answer:
Antibiotics are chemical substances primarily produced by some microorganisms which in low concentration can kill or retard the growth of other disease causing microorganisms. Antibiotics are mainly produced from three groups of microorganisms:

• Eubacteria (True bacteria).
• Actinomycetes (Ramified bacteria).
• Fungi.

Question 2.
(a) What are the properties of an antibiotic? 
(b) Give two examples of antibiotics.
Answer:
(a) Properties of antibiotics:

• It should have quick action and should be broad spectrum i.e., must have the ability to act on various pathogenic microorganisms which differ from each other.
• The action of antibiotics must be specific on the pathogen only.
• It should not cause side effect in the host.
• It should not kill useful microorganisms found in alimentary canal of man.

(b) Examples: 

• Novomycin
• Streptomycin.

Question 3. 
How curd is prepared? Name the inoculum used to curd formation.
Answer:

Curd: Indian curd is prepared by inoculating skimmed milk or cream milk with lactic acid bacteria (LAB). To preparation of curd milk is boild and then cooled to a temperature of below than 40°C. It is inoculated with a small amount of inoculum or curd. The curd or inoculum contains lactic acid bacteria (Lactobacillus acidophilus). In milk, the bacterium produces lactose which converts milk sugar lactose into lactic acid. It also partially digests milk protein and casien. Lactic acid coagulates milk protein to form curd. Curd is more nutritious then milk as it contains vitamin B₁₂ and other vitamins and organic acids. Lactic acid bacteria (LAB) in curd also checks growth of disease causing microbe^. Curd is eaten as such salted or sweetened. It is also used to obtain butter, butter milk, mattha or chhach.

Question 4. 
Name three chemicals and microorganisms which are used to prepare these chemicals.
Answer:

• Lactic acid: Streptococcus lacti.
• Acetic acid: Acetobacter aceti.
• Citric acid: Aspergillus niger.

Question 4. 
Explain the role of baculoviruses as biological control agents. Mention their importance in organic farming.
Answer:
A large number of toxic chemical substances are used to kill the pests. These chemicals are called pesticides and are of different types such as herbicides (used against herbs), fungicides (used against fungi), bactericides (used against bacteria), insecticides (used against insects), nematicides (used against nematodes) rotendicides (used against rotifers) etc. These chemicals are very toxic and extremely harmful to human beings and animals alike. Moreover, they have been polluting our environment (soil and groundwater), fruits, vegetables and crop plants.

Our soil also getting polluted and loosing its texture by the use of weedicides to remove weeds. Therefore, our scientists are searching for novel approaches to control insects and pests. A remarkable progress has been made to control various type of pests by the use of biopesticides. Thus, biopesticides are the pesticides of biological origin which are used to eradicate the pests and weeds. The natural method of pest and pathogen control involving use of viruses, bacteria, fungi and other insects is called biocontrol. 

Question 5. 
What are the advantages of using biofertilizers in agriculture?
Answer:
Following are the advantages of using biofertilizers in agriculture:    

• They are cheap and economical.
• They improve soil structure and function.
• They dp not cause any pollution.
• Some of them act as biopesticides also.
• In ill - irrigated conditions few biofertilizers can enhance the crop yield.
• They make available vitamins and other growth promoting biochemicals.

Question 6. 
(a) How do organic farmers control pests? Give two examples.
(b) State the difference in their approach from that of conventional pest control methods.
Answer:
(a) Organic farmers do not use any chemical for raising crops. They simply depend on biological control methods of control insects and pests. This way they avoid deleterious effects of chemicals on food products as well as on the environment. These chemical get accumulated in food chain and ecosystem whereas  biological control methods are safe as they do not harm any form of life.
Examples: Bacterium Bacillus thuringiensis for cotton ball worm. Fungus Trichoderma for fungal soil born diseases.

(b) Conventional pest control methods are hazard to many useful organisms. These methods cause pollution and degrade food chain.

Question 7. 
(a) Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify.
(b) Give an example of a bacterium, a fungus and an insect that are used as biocontrol agents.
Answer:
(a) Organic farmers do not use any chemical for raising crops. They simply depend on biological control methods of control insects and pests. This way they avoid deleterious effects of chemicals on food products as well as on the environment. These chemical get accumulated in food chain and ecosystem whereas  biological control methods are safe as they do not harm any form of life.
Examples: Bacterium Bacillus thuringiensis for cotton ball worm. Fungus Trichoderma for fungal soil born diseases.

(b) Examples of biological control agents are as follows:

• Bacterium Bacillus thuringiensis for the control of cotton ball worm.
• Fungus Trichoderma for controlling fungal soil born diseases like damping off of vegetables.
• Insects, Ladybird beetle for the control of aphids.

Question 8. 
Explain the changes that milk undergoes when suitable starter/inoculum is added to it. How does the end product formed prove to the beneficial for human health?
Answer:
Curd: Indian curd is prepared by inoculating skimmed milk or cream milk with lactic acid bacteria (LAB). To preparation of curd milk is boild and then cooled to a temperature of below than 40°C. It is inoculated with a small amount of inoculum or curd. The curd or inoculum contains lactic acid bacteria (Lactobacillus acidophilus). In milk, the bacterium produces lactose which converts milk sugar lactose into lactic acid. It also partially digests milk protein and casien. Lactic acid coagulates milk protein to form curd. Curd is more nutritious then milk as it contains vitamin B12 and other vitamins and organic acids. Lactic acid bacteria (LAB) in curd also checks growth of disease causing microbes. Curd is eaten as such salted or sweetened. It is also used to obtain butter, butter milk, mattha or chhach.

Question 9. 
Explain three enzymes which are prepared biologically.
Answer:
Enzynies are proteinaceous substances which are capable of catalysing biochemical reactions without undergoing any change in themselves. Therefore, they are called biocatalysts. The term ‘enzym’ was coined by William Kuhne (1867). Out of over 22000 enzymes known, only 1 - 1.5 percent are used in industries. Some of the enzymes in industries are:

(a) Proteases (Proteolytic Enzymes): These enzymes are used in leather industry in bating of hide, in textile industry for removing proteinaceous stains, in silk industry to liberate the silk fibres, in dry - cleaning industry for removing food spots etc. These enzymes are obtained by the actions of Bacillus sp. and Aspergillus sp.

(b) Amylase: They are starch digesting enzymes. They are obtained from Aspergillus oryzae, A. niger, Mucor sp. and Bacillus subtilis. These enzymes are used in softening and sweetening of bread desizing fibres, flavouring of soft drinks and cleaning starchy stains from utensils and cloths.

(c) Amylase, glucoamylase and glucoisomerases: They are employed in the conversion of com starch into fructose - rich corn syrup. Since fructose is the sweetest of all the sugar, corn syrup is sweeter than sucrose solution. It is used in sweetening and flavouring soft drinks, cakes, biscuits etc.

Question 10. 
What is river action plan? Explain.
Answer:
Due to increasing urbanisation and rapid industrialisation. Sewage is being produced in substantially larger quantities than ever before. Prear to 1985, orily few cities and towns had sewage treatment plants. Most of the sewage water of urban as well as rural areas was discharged directly into rivers resulting in their pollution. Realising the importance of microbes in pollution control, the ministry of environment and forests has initiated development of sewage treatment plants under the national rivers conservation authority i. e., Yamuna Action Plan and Ganga Action Plan and others to save these major rivers of our country from pollution.

Yamuna Action Plan: On december 10, 1997, the Central Pollution Control Board (CPCB) submitted as Rs. 480 crore, Yamuna Action Plan to Delhi high court to cleanse the polluted water. This plan was likely to be completed by 31 March, 1999. It involves the following measures:

• Fourteen sewage treatment plants are being constructed in various parts of Delhi.
• Arrangements would be made for proper treatment of Panipat.
• To ensure that no effluents from NFL, Panipat flow into the river.
• To ensure that the forthcoming Panipat refinery treats its effluents to desired level and uses the same for irrigation.

Ganga Action Plan: To control the pollution of Ganga water, there is a full - fledged Ganga Project Directorate in the Ministry of Environmental and Forests. As Rs. 550 crore ambitious Ganga Action Plan (GAP) was started in 1985. Under the GAP - II programme, which started in 1993, the Pollution Control Research Institute (PCRI) of Bharat Heavy Electrical Ltd. (BHEL) at Haridwar, has been conducting monthly to analyse the quality of Ganga river water.

Long Answer Type Questions

Question 1. 
How microbes are useful in preparation of household products. Give any two examples.
Answer:
A close relationship of man and microbes is as old as human civilization and date back into antiquity. An oldest microbial process, the fermentation is discovered by people by prolonged steeping of grains before cooking or by storing juice of fruits or palms. Fermented honey (or mead) may have provided one of the earliest alcoholic beverage fermentation for human beings. Other early fermentation processes practiced’by man including leavening of bread, ratting of flax, production of alcoholic beverages, production of vinegar, production of curd etc.

Some of the household products, produced by microbial activities are as follows:
1. Curd: Indian curd is prepared by inoculating skimmed milk or cream milk with lactic acid bacteria (LAB). To preparation of curd milk is boild and then cooled to a temperature of below than 40°C. It is inoculated with a small amount of inoculum or curd. The curd or inoculum contains lactic acid bacteria (Lactobacillus acidophilus). In milk, the bacterium produces lactose which converts milk sugar lactose into lactic acid. It also partially digests milk protein and casien. Lactic acid coagulates milk protein to form curd. Curd is more nutritious then milk as it contains vitamin B12 and other vitamins and organic acids. Lactic acid bacteria (LAB) in curd also checks growth of disease causing microbes. Curd is eaten as such salted or sweetened. It is also used to obtain butter, butter milk, mattha or chhach.

2. Yoghurt (Yogurt): Curd or dahi is a dairy product which is made by curdiling milk with edible acidic substance like lemon juice and curd itself. Youghurt on the other hand, is prepared by bacterial fermentation of milk. To make yoghurt, yogurt culture consisting Lactobacillus bulgaricus and Streptococcus thermophilus is used. Milk is heated to 80° - 90°C for half an hour, then cooled to 44°C to mix it with inoculum. Yoghurt is often sweetened and flavoured with fruits. Yoghurt mqre advantageous than milk because of the presence of additional vitamins produced by bacteria and absence of lactose, to which some persons are allergic. The unique flavour of yogurt and other fermented milk is of acetaldehyde.

Question 2. 
How cheese are prepared by microbial activities? Give examples of different types of cheese and microbes used for their preparation.
Answer:
Cheese: Cheese is a protein - rich nutritive milk - product, prepared by curdling and ripening of milk. It consists of milk curd separated from whey or liquid part. The method of preparing cheese with the help of microbes has been known in Asia and Europe for a long time. Now a day it is prepared and eaten all over the globe. There are several hundred varieties of cheese which are prepared by selected types of microorganisms. Curdling is done with the help of lactic acid bacteria and enzyme rennin, rennet from calfs stomach or fruit extract of Withania coagulans.

Cheese is of mainly three types: soft (with 50 - 80% water), semihard (about 45% water) and hard (less than 40% water). The quality and characteristic taste of cheese are determined by the biochemical activities of specific microbes.
1. Cottage Cheese: It is prepared by using the inoculum of Streptococcus lactis and Lactobacillus to allow the milk to curdle. The curd is then separated from the whey, some salt is added and then bells or cakes are prepared. The liquid left in cheese is drained by hanging it in cloth. The cheese is now ready for consumption.

2. Swiss Cheese: It is characterised by having the characteristic flavour and large holes. The number of holes, their size and whether or not the inside the shiny is determined by the gas produced by thermophilic bacteria. The big holes are formed due to the amount of CO2 released by a bacterium, named Propionibacterium sharmanii.

3. Roquefort Cheese : It shows a characteristic greenis blue mottling due to presence of specific fungi, Penicillium roquefortii. It is probably the best known cheese made from sheep’s milk. For camembert cheese, Penicillium camemberti is use for ripening.

Question 3. 
How fermentation takes place in industrial scale for preparation of fermented beverages? 
Answer:
Several industrial products are prepared by the activity of micro-organisms. Some of such industrial products are alcoholic beverages, industrial alcohols, antibiotics, enzymes etc. Production on an industrial scale requires growing microbes in very large vessels called fermentors.

Fermented Beverages:
Since time immemorial, yeast have been used for the production of beverages like beer, wine, whisky, brandy or rum. For this purpose the same yeast, Saccharomyces cerevisiae is used for bread making and commodity called brewer’s yeast, is used for fermented cereals and fruit juices. Fruit juices are used for preparing wine and brandy. Barley malt is used for preparing beer. Cereals are used for production of whisky. Molasses are used for preparation of rum. Likewise, rice is used for making sake, potato for vodka and cashew apple for fenny. Besides Saccharomyces cerevisae (Brewer’s yeast) other yeasts are also used such as S. ellipsoidens (wine yeast), S. pyriformis (ginger and ale yeast), S. sake (sake yeast). Generally, one percent malt or Rhizopus is added to nutrient medium having starch (potato, cereal etc.), because yeast producess a small amount of amylase. Hydrolysis is carried out in separate tanks at a moderate temperature (55°C) for 30 minutes. The crushed food mixed with hot water for obtaining malt is called mash. The sweetened nutrient medium prior to alcoholic fermentation is called wort.
Procedure:
1. Fermentation tank or fermentars or bioreactor is steam sterilised under pressure. The liquid medium or wort is added into the tank and sterilised. Now it is allow to cool.
2. When the liquid medium cools down, it is inoculated with a suitable strain of yeast. Fermentation occurs in three ways.
(a) Batch Process: In this type of fermentation, a large volume of nutrient medium (with volume as large as 2,25,000 litres) is inoculated and allowed to proceed until maximum yield have been obtained. At this point, the fermentation process is stopped, the product is recovered the fermentation tank cleaned, resterilized and fresh batch is started. 


(b) Continuous Process: In this process, half a portion of the medium with fermented product is removed at intervals and same quantity of fresh medium is added every time.

(c) Immobilised Fermentation Process: In this method, yeast cells are immobilised in calcium alginate beads and kept into two columns in the fermentation tank. This technique is 20 times more efficient.

Question 4. 
(a) Draw a well labeled diagram of gobar gas plant.
(b) Give the microbial activities in biogas production.
Answer:
(a) 

(b) Some special type of bacteria, called methanogens, play an important role in the biogas production. They are obligate anaerobes and produce biogas by decomposition of cellulosic materials present abundantly in the dung of cattle. As cattle available in plenty in rural areas so the gobar gas plants are more common in that areas. The methanogens are also present in the ruman of compound stomach of cud-chewing mammals and activated sludge of sewage treatment plant. Apart from methane bacteria other bacteria such as Clostridium, Bacillus, Ruminococcus, Cellulomonas are also involved in degradation process. Most common methanogens are Methanobacterium and Methanococcus.

Biogas Plant:
The animal excreta and plant debrises are easily degraded by anaerobic microorganisms in the presence of water.  Biogas plant is a 10 feet deep, rotunda, concrete tank called digester. It has a charge pit for passage of slurry into digester, a floating gas holder or metal with an outlet which is connected to a pipe to supply biogas to nearby houses, and a pit for removal of sludge to be used a manure or deshi fertilizer. Raw materials used in biogas plants are cattle dung, night soil, farm refuse and other organic wastes. The biogas thus produced is used for cooking and lighting.

The biogas production technology was developed in India mainly due to the efforts to Indian Agricultural Research Institute (LARI) and Khadi and Village Industries Commission (KVIC). Already thousands of familysized biogas plants and several hundred community gas plants are in operation in India.


Production of biogas is a three staged anaerobic digestion of cattle dung, night soil and other organic waste materials. In the first step, fucultative anaerobic decomposer microbes bring about enzymatic breakdown of complex organic compounds into simple and soluble compounds. The enzymes involved in decomposition are cellulases, proteases and lipases. They are secreted by anaerobic microbes.


In the second stage, soluble compounds (i. e., monomers) are acted upon by microbes which convertes them into organic acids. In the third stage, organic acids are acted upon by methanogenic bacteria to produce biogas. Produced biogas collects in floating gasholder which keeps rising. The gas holder is connected through gas pipes to houses where gas is used as a fuel and lighting. The gas may also be used in running tube cells and production of electricity. Five cattle produce enough dung cooking gas for a family of 4 - 5 members.

Question 5. 
Write short notes on the following:
(a) Bioherbicides 
(b) Bioinsecticides.
Answer:
(a) Bioherbicides: They are those organisms, which control the growth of weeds.

1. The first effective bioherbicide was a mycoherbicide (a fungus which destroys weeds) developed in 1981. The mycoherbicide is Phytophthora palmivora which control the growth of milk weed vines in citrus orchards.
2. Cochineal insect (cactoblastis cactarum) is used to reduce the overgrowth of cacti.
3. Some fungal mycoherbicides are commercially available in the form of fungal spores by the trade name ‘Devine’ and ‘Collego’. These are the fungal spores which have long viability and resistant to adverse conditions. These fungal spores are commercially available for controlling weeds in India.
4. Certain crop plants (called smoother crops) do not allow the weeds to grow nearby, e.g., Alfalfa, Soyabean, Sunflower, Sweet clover etc. These crops, having seeds with good germination rate, give a vigorous first and compete with weeds.
5. Latest technique in controlling weeds is to produce transgenic crop plants like tomato, tobacco etc., by genetic engineering. It involves introduction of genes for herbicidal resistance into crop plants that are able to tolerate a hetbicide.

(b) Bioinsecticides: They are those living organisms which help in biological control of insect pests.
1. Bacillus thuringiensis (A bacterium, often written Bt) produces a protenaceous toxin, called thurioside. When this substance is ingested by larvae of insects, then it blocks the ion transpart in mid-gut and kill them. Spores of this bacterium produce a insecticidal cry protein and are able to kill larvae of some insects. In this way larvae of the insects are killed but other insects remain unaffectated. Spores of this bacteria are available in sachets as dried spores.

2. The free living fungi, Trichoderma are very common in the root ecosystems. They are very effective in biocontrol of several plant pathogens.

3. Entomopox virus adversely affects the rate of development of grass hopper and the amount of food it eats.

4. Scientists have been able to introduce Bt toxin genes into the plants by gene transfer techniques of genetic engineering. Such plants are resistant to attack by insect pests. Bt cotton is one such genetically modified (GM) crop which contains Bt toxin gene.

5. Baculovirus are the pathogenic viruses which infect and kill many insect pests and other arthropod pests. Nucleopolyhedrovirus is the most important baculovirus involved in biological control. Baculo - viruses are species - specific and have a narrow spectrum insecticidal effect, so they do not have any negative effect on other organisms. They are known to control pests like potal beetles aphids and corn borers.

6. Fungi - based Bioinsecticides: Fungi as Beauveria bassiana and some other fungi have been found useful in controlling the insect population specially.

7. Insect Resistance Plants: Insects resistance in transgenic plants has been made through the transfer of insect toxic gene of Bacillus thuringiensis in plants by genetic engineering. Most strains of this toxic gene are toxic to lepidopteron larvae. The toxicity is due to toxin gene. This gene has been successfully introduced in cotton and tobacco.

Question 6. 
How bacteria are useful as biofertilizers? Explain in detail.
Answer:
Several bacteria improve the soil fertility by adding nutrients due to their biological activity. They enrich the soil by fixing free nitrogen into nitrogen compounds and thereby minimise the dependence on chemical fertilizers. There are different kinds of bacteria, i.e., symbiotic or free - living (non - symbiotic) or occuring in loose association with the roots of higher plants. They increase soil fertility as follows:

(a) Symbiotic Nitrogen - Fixing Bacteria or Legume - Rhizobium Symbiosis or Rhizobial Biofertilizers:
Rhizobium are symbiotic bacteria which are found in root nodules of leguminous plants. Root nodules are formed by Rhizobium themselves. They fix atmospheric nitrogen to nitrogenous compounds. Within the root nodules in the presence of a redish pigment called leghaemoglobin. The enzyme nitrogenase catalyses the process nitrogen fixation under anaerobic condition. Leghaemoglobin combines with oxygen and protects nitroginase. Culture of Rhizobium are raised in the lavoratory'for inoculating the seeds of legumes before sowing. Sometimes the soil is also inoculated with the cultures of Rhizobium. This ensures development of root nodules in the seedling at an early stage, thus providing better nitrogen fixation and higher yields. Phosphorus is also supplemented at optimal levels for better nitrogen fixation. Therefore, to an increased yield of crop a combination of phosphatic fertilizers with Rhizobium culture is recommended.

After harvesting the crop, roots of legume plants are allowed to decay in the soil. This enriches the soil with nitrogenous compounds. This ensures the good availability of nitrogenous compound to succeeding crop. Thus, legume crops are used in crop rotation and green manuring. Frankia, a nitrogen fixing mycelial bacterium, lives in symbiotic association with the root nodules of several non - legume plants like Alnus, Rubus, Casuarina, Myrica etc. Mycobacterium and Xanthomonas are also form symbiotic association with leaves of few plants like Ardisia. They lives in special internal cavities of leaf and provide nitrogenous compound to leaf. Such leaves are a constant source of nitrogen fertilizer to the soil.

(b) Free - living or Non - symbiotic Bacteria: Azotolacter and Bacillus polymyxa are free - living bacteria which fix atmospheric free nitrogen. This nitrogen is utilized by the crops such as creals, millets, n ait and vegetable crops. With cotton, rice, maize and jawar crops, Azotobacter results in increased yield and there is a saving of nitrogenous fertilizers up to 10 - 25 kg per hectare.

(c) Loose Association of Nitrogen Fixing Bacteria: Scientists at the IARI, New Delhi have isolated Azospirillum from the roots of rice, sorghum, maize etc. Simple seed inoculation with this bacterium increases the dry weight of cereals. When mixed with a chemical fertilizer, it gives high yields.

Question 7. 
Describe the process of secondary treatment given to municipal waste water (sewage) before it can be released into fresh waterbodies. Mention another benefit provided by this process. 
Answer:
It involves biological process of microbial degradation of organic substances. There are several methods of secondary treatment, like oxidation tanks, trickling filter and activated sludge methods.

 In activated sludge method, the primary effluent is passed into large tank (aeration tanks), here it is constantly agitated mechanically and air is pumped into efflusent. Some activated sludge of the previous process is inoculated to allow quick growth of aerobic microbes. Numerous aerobic microorganisms grow in the aeration tank. These are some algae, filamentous fungi, protozoa and bacteria. These organisms form floes, which are the masses of bacteria, micro - algae and micro - fungi. These microbes consume the major part of organic matter in the effluent. This considerably reduces the biochemical oxygen demand (BOD) of the effluent. Now effluent is passed through a sedimentation tank, where microbial floes are allowed to settle down.

The settled material is called activated sludge. A small part of the activated sluge is pumped back into the areation tank to serve as the inoculum. The major part of the activated sludge is pumped into a large anaerobic sludge digester (a large tank). In this tank anaerobic microbes start digesting the bacteria and fungi come with effluent. During the anaerobic digestion, bacteria produce a mixer of gases i. e., methan, CO2 and hydrogen sulphide. This gas is highly inflammable and can be used as biogas, a source of energy. Finally, the spent sludge can be used as manure or a part of compost. The effluent left from the secondary treatment plant is released into natural waterbodies as rivers and streams.