Microbes in Human Welfare Class 12 Important Questions and Answers Biology Chapter 10

Class 12 Biology Chapter 10 Important Questions Microbes in Human Welfare

Question 1.
What are ‘floes’, formed during secondary treatment of sewage ? (Delhi 2019)
Answer:
Floes are masses of bacteria held together by slime and fungal filaments to form mesh-like structures. They are used during the secondary sewage treatment in the aeration tank to increase the rate of decomposition.

Question 2.
Why do we add an inoculum of curd to milk for curdling it? (Delhi 2015C)
Or
Why is ‘starter’ added to set the milk into curd? Explain. (All India 2014C)
Or
Name the nutrient that gets enhanced while curdling of milk by Lactobacillus? (All India 2014C)
Answer:
When a small amount of curd as starter or inoculum is added to fresh milk, millions of Lactic Acid Bacteria (LAB) present in the starter grow in milk and convert it into curd. During this process, acids are produced by LAB that coagulate and partially digest the milk proteins (casein). LAB increase vitamin-B12 content along with other vitamins in the curd.

Question 3.
How is lactic acid bacteria beneficial to us other than helping in curdling the milk? (All India 2015C)
Answer:
Two benefits of LAB are given below

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

Question 4.
Give the scientific name of the source organisms from which the first antibiotic was produced. (Foreign 2014)
Answer:
The scientific name of the source organism, i.e. mould from which first antibiotic was produced is Penicillium notatum.

Question 5.
Name the gas released and the process responsible for puffing up of the bread dough when Saccharomyces cerevisiae is added to it. (All India 2013c)
Answer:
Saccharomyces cerevisiae (baker’s yeast) when added to dough causes its fermentation and releases CO2 gas which is responsible for the puffed appearance of dough.

Question 6.
Which of the following is the baker’s yeast used in fermentation ? Saccharum barberi, Saccharomyces cerevisiae and Sonalika. (All India 2012,2011,2009)
Answer:
Saccharomyces cerevisiae is the baker’s yeast used in fermentation.

Question 7.
Write the scientific name of the microbe used for fermenting malted cereals and fruit juices. (Delhi 2011)
Answer:
Saccharomyces cerevisiae also called brewer’s yeast, is the microbe used for fermenting malted cereals and fruit juices.

Question 8.
Mention the information that the health workers derive by measuring BOD of a water body. (All India 2010)
Answer:
Biological Oxygen Demand or BOD value indicates the quantity of organic matter present in the water. Higher the BOD of water body, more is its polluting potential and vice-versa.

Question 9.
Why is sewage water treated until the BOD is reduced? Give a reason. (Delhi 2010C)
Answer:
The higher the BOD of sewage water, more is its polluting potential. So, the sewage water is treated, till its BOD-is reduced which further indicates the reduction in the organic matter present in it.

Question 10.
Distinguish between the roles of flocks and anaerobic sludge digesters in sewage treatments. (Delhi 2016)
Answer:
In sewage treatment, floes consume major part of the organic matter, converting it into microbial biomass and releasing lot of minerals.
It reduces the BOD of sewage, while in anaerobic sludge digesters, many anaerobic bacteria are present, which digest the organic mass. During this digestion, methane, CO2 etc. are produced.

Question 11.
List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. (Delhi 2016)
Answer:
To reduce the BOD of primary effluent during sewage treatment, it is passed into large aeration tanks with constant mechanical agitation and air supply. This allows vigorous growth of aerobic microbes into floes which consume major part of organic matter in the effluent. Hence, BOD of effluent is reduced.

Question 12.
Explain the different steps involved during primary treatment phase of sewage. (All India 2015)
Answer:
Primary treatment of sewage involves the physical removal of large and small particles from sewage through filtration and sedimentation.
The steps involved in this process are

Floating debris is removed by sequential filtration by passing through wire mesh screens.
After this, the grit (soil and small pebbles) is removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant forms the primary effluent.
The effluent is then taken for the secondary treatment.

Question 13.
Mention a product of human welfare obtained with the help of each one of the following microbes.
(i) LAB
(ii) Saccharomyces cerevisiae
(iii) Propionibacterium shermanii
(iv) Aspergillus niger (Delhi 2015)
Answer:

Microbe	Product of human welfare
(i) LAB	Curd
(ii) Saccharomyces cerevisiae	Bread and cakes
(iii) Propionibacterium shermanii	Swiss cheese
(iv) Aspergillus niger	Citric acid

Question 14.
Bottled fruit juices are clearer as compared to those made at home. Explain. (Foreign 2015)
Answer:
Bottled fruit juices are clearer as compared to those made at home because, in these juices pectinase enzyme is added, which digests the pectin and other fibres present in juices.

Question 15.
Name two groups of organisms which constitute ‘floes’. Write their influence on the level of BOD during biological treatment of sewage. (All India 2014C)
Answer:
The groups of organisms that constitute mesh-like structures called ‘floes’ are bacteria and fungi.
These bacterial masses associated with fungal filaments called floes, consume the major part of organic matter present in effluent, thereby reducing the BOD of the waste significantly during biological or secondary treatment of sewage.

Question 16.
Name the bacterium responsible for the large holes seen in Swiss cheese. What are these holes due to? (All India 2013)
Answer:
Swiss cheese is produced by the bacterium Propionibacterium shermanii. The large holes in Swiss cheese are due to the large amount of CO2 production.

Question 17.
Name source of streptokinase. How does this bioactive molecule function in our body? (Delhi 2012)
Or
Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences. (All India 2011)
Answer:
Streptokinase enzyme is produced by the bacterium Streptococcus. It is modified by genetic engineering and is used as a clot buster for removing clots from the blood vessels of patients who have suffered from myocardial infarction.

Question 18.
Mention the importance of lactic acid bacteria to humans other than setting milk into curd. (Delhi 2012)
Answer:

Lactic Acid Bacteria (LAB) are used to produce an acid called lactic acid that is an important industrial product. It is also used in beverages, meat products, confectionary, dairy products, etc.
It checks the disease causing microbes in the stomach.

Question 19.
Name the source of cyclosporin-A. How does this bioactive molecule function in our body? (All India 2012.)
Or
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. (Foreign 2011)
Answer:
Cyclosporin-A is produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ-transplant patients as it suppresses the activation of T-cells in body.

Question 20.
Name the source of statin and state its action on the human body. (Foreign 2012)
Answer:
Statin is produced by yeast Monascus purpureus. It is used as blood cholesterol lowering agent.
It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.

Question 21.
Why are some molecules called bioactive molecules? Give two examples of such molecules. (All India 2011)
Answer:
Bioactive molecules are produced from microbes that are useful to other living organisms in modifying their metabolism, e.g. streptokinase, cyclosporin-A, statins, etc.

Question 22.
How does addition of a small amount of curd to fresh milk help formation of curd? Mention a nutritional quality that gets added to the curd. (Delhi 2010)
Or
During the production of curd, a small amount of curd is added as a starter to the fresh milk at a suitable temperature. Explain the changes the milk undergoes when it sets into curd. (Delhi 2o11c)
Answer:
Refer to Answer No. 2.

Question 23.
State the medicinal value and the bioactive molecules produced by Penicillium notatum, Monascus perpureus and Trichoderma polysporum. (All India 2019,2015)
Answer:

Microbe	Bioactive molecule	Medicinal value
Penicillium	Penicillin	Used as antibiotic against many fungal and bacterial diseases in humans and animals.
Monascus purpureus	Statins	Used as blood cholesterol lowering agent. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.
Trichoderma polysporum	Cyclosporin-A	Used as immuno suppressive agent in organ transplant patients.

Question 24.
The three microbes are listed below. Name the product produced by each one of them and mention their use. (2018C)
(i) Aspergillus niger
(ii) Trichoderma polysporum
(iii) Monascus purpureus
Answer:
(i) Citric acid
(ii) Cyclosporin-A
(iii) Statins.

Question 25.
Secondary treatment of the sewage is also called biological treatment. Justify this statement and explain the process. (All India 2017)
Answer:
The secondary treatment of sewage is also called biological treatment because in this treatment, sewage is subjected to biodegradation. It means that it involves the participation of microorganisms. The process of secondary treatment involves following steps

Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply. This allows vigorous growth of useful aerobic microbes into floes (masses of bacteria and fungi filaments).
These microbes consume major part of organic matter in the effluent, while growing. This reduces the BOD of the effluent.
When BOD of sewage gets reduced, it is passed into settling tank. The bacterial floes settle in tank and the sediment is called activated sludge. A, small amount of activated sludge is pumped back into the aeration tank to serve as inoculum.
The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters, where other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.

During this process, bacteria produce a mixture of gases, such as methane, hydrogen sulphide and the carbon dioxide, which form biogas. The effluent from secondary treatment is generally released into natural water bodies. It helps to reduce water pollution and water borne diseases.

Question 26.
Describe how do ‘floes’ and ‘activated sludge’ help in sewage treatment. (Delhi 2017)
Answer:
Roles of ‘floes’ and ‘activated sludge’ in sewage treatment are as follows

Floes These are masses of bacteria held together by slime and fungal filaments to form mesh-like structures. These are used during the secondary sewage treatment in the aeration tank to increase the rate of decomposition.
The microbes digest a lot of organic matter, converting it into microbial biomass and releasing a lot of minerals. As a result, BOD of the sewage reduces. As the BOD of waste is reduced to 10-15% of raw sewage, it is passed into settling tank. In these tanks, floes are allowed to undergo sedimentation.
Activated sludge The sediment of settling tank is called’activated sludge. A part of it is used as inoculum in aeration tanks.
The remaining part is passed into a large tank called anaerobic sludge digester. In these tanks, anaerobic microbes are present that digest the organic mass as well as aerobic microbes of activated sludge. The remaining sludge is used as manure or compost.

Question 27.
Make a list of three household products along with the names of the microorganisms producing them. (All India 2016)
Answer:

Curd : Lactobacillus
Bread : Saccharomyces cerevisiae
Swiss cheese : Propionibacterium shermanii.

Question 28.
Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body. Explain. (Delhi 2015)
Answer:
BOD is the amount of dissolved oxygen required for the microbial breakdown of biodegradable organic matter. Aerobic organisms use a lot of oxygen and as a result, there is a sharp decline in Dissolved Oxygen (DO) in the water body. This can cause death of fishes and other aquatic species.

Determination of BOD is thus, an important parameter in determining the quality of a water body. The presence of more organic waste increases the microbial activity thus, decreasing the DO. BOD is higher in polluted water and lesser in clean water.

Question 29.
How can sewage be used to generate biogas? Explain. (Foreign 2015)
Or
Describe how biogas is obtained from the activated sludge. (Foreign 2010)
Answer:
Refer to Answer No. 25 (iii) and (iv).

Question 30.
Identify A, B, C, D, E and F in the table given below (Foreign 2014)

Scientific name of the organism	Product produced	Use in human welfare
Streptococcus	Streptokinase modified	A
B	Cyclosporin-A	C
Monascus purpureus	D	E
Lactobacillus	F	Sets milk into curd

Answer:
The codes are identified as
A- Clot buster in patients who underwent myocardial infarction.
B- Trichoderma polysporum
C- Immunosuppressive agent in organ transplantation D-Statins
E – Blood cholesterol lowering agents
F – Lactic acid

Question 31.
Explain the different steps involved in sewage treatment before it can be released into natural water bodies. (Foreign 2011)
Answer:
Sewage treatment includes following steps
(i) Primary Treatment
Refer to Answer No. 12.

(ii) Secondary Treatment
Refer to Answer No. 25.

Question 32.
Identify A, B, C, D, E and F in the table given below (Delhi 2010C)

Organism	Bioactive molecule	Use
Monascus purpureus (yeast)	A	B
C	D	Antibiotic
E	Cyclosporin-A	F

Answer:
A-Statins
B-They are used as blood cholesterol lowering agents,
C-Penicillium notatum
D-Penicillin
E-Trichoderma polysporum
F-Uscd as an immunosuppressive agent in organ transplant patients.

Question 33.
Mention the product and its use, produced by each of the microbes listed below
(i) Streptococcus
(ii) Lactobacillus
(iii) Saccharomyces cerevisiae (All India 2010)
Answer:
(i) Streptococcus Product is streptokinase. It is used as a clot buster for removing the clots from the blood vessels of patients suffering from myocardial infarction.
(ii) Lactobacillus Product is lactic acid. It is used to convert milk into curd and improves nutrient quality of curd by enriching it with vitamin-B12
(iii) Saccharomyces cerevisiae Product is ethanol and it is used in making bread and beverages.

Question 34.
List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. (Delhi 2016)
Answer:
For floes and activated sludge, Refer to Answer No. 26.

Question 35.
List the events that lead to biogas production from waste water whose BOD has been reduced significantly. (Delhi 2016)
Or
Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of Biological Oxygen Demand (BOD) in it. (All India 2015)
Or
Explain, the process of sewage water treatment before it can be discharged into natural water bodies. Why is this treatment essential? (All india 2014)
Answer:
For biogas production, Refer to Answer No. 12 and 25.
The gases from biogas are used as a source of energy because it is inflammable.

Question 36.
(i) Name the category of microbes naturally occurring in sewage and making it less polluted during the treatment.
(ii) Explain the different steps involved in the secondary treatment of sewage. (Foreign 2014)
Answer:
(i) The category of microbes naturally occurring in sewage and making it less polluted are bacteria and fungi, wherein masses of bacteria get associated with filaments of fungi to form mesh-like structure called floes.
(ii) For different steps involved in secondary or biological treatment of sewage,
Refer to Answer No. 25.

Question 37.
Write any two places yhere methanogens can be found. (Delhi 2019)
Answer:

Rice fields
Ruminants alimentary canal.

Question 38.
Name the type of association that the genus Glomus exhibits with higher plants. (All India 2014)
Answer:
The genus-Glomus exhibits symbiotic association with higher plants called mycorrhiza.

Question 39.
State one reason for adding blue-green algae to the agricultural soil. (Delhi 2014c)
Answer:
Blue-green algae are added to agricultural soil because they add organic matter to the soil and also increase its fertility.

Question 40.
What makes the Nucleopolyhedrovirus a desirable biological control agent? (All India 2013C; 2012C)
Or
What is the significance of Nucleopolyhedrovirus in pest management?
Answer:
Nucleopolyhedrovirus, a genus of baculoviruses is useful in controlling many insects and other arthropods. They are species specific narrow spectrum bioinsecticide with no side effects on plants, mammals, birds, fish and non-target insects. Therefore, they serve as an important component of integrated pest management programme in dealing with ecological sensitive areas. These properties are useful in organic farming.

Question 41.
Mention the role of cyanobacteria as biofertilisers. (All India 2012)
Answer:
Role of cyanobacteria as biofertilisers: Cyanobacteria fix atmospheric nitrogen and increase the organic matter of the soil through their photosynthetic activity.

Question 42.
Mention two advantages of adding blue-green algae to paddy fields. (All India 2011)
Answer:
In the paddy fields, cyanobacteria such as blue-green algae fix atmospheric nitrogen to enrich the nitrogen content of soil. Therefore, the entire need of nitrogen to rice crop can be supplied by blue-green algae, leading to increase in yield.

Question 43.
Name any one symbiont, which serves as biofertiliser. Mention it’s specific role. (All India 2010C)
Answer:
Rhizobium is a symbiotic bacteria that serves as biofertiliser.
The bacteria fix the atmospheric nitrogen into organic forms, which is used by the plants as nutrients.

Question 44.
Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
(i) Recommend two microbes that can enrich the soil with nitrogen.
(ii) Why do leguminous crops require such enrichment of the soil ? (2018)
Answer:
(i) Azospirillum
Azotobacter

(ii) 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 nutrient. Therefore, they do not require enrichment of the soil.

Question 45.
How does the application of the fungal genus, Glomus, to the agricultural farm increase the farm output? (Delhi 2017)
Answer:
The application of Glomus to agricultural field increases the farm output by increasing the nutrient availability to the crops. Glomus develops symbiotic association with the roots of plants, called mycorrhiza. It absorbs phosphorus from the soil and passes it to the plant it is associated with.
In return, it derives sugars from the host plant cells for its survival.
Thus, it acts as a biofertiliser. This association has other advantages also, like

Resistance to root borne pathogens
Tolerance to salinity and drought
Increase in plant growth and development.

Question 46.
How does the application of cyanobacteria help to improve agricultural output? (Delhi 2017)
Answer:
Role of cyanobacteria in improving agricultural output Cyanobacteria are autotrophic microbes found in aquatic and terrestrial environments. Most of these fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.
In paddy fields, cyanobacteria serve as an important biofertiliser as they enrich the nitrogen content in the soil. They also add organic matter to the soil, thus increasing the fertility. Thus, application of cyanobacteria helps in improving agricultural output.

Question 47.
Name a genus of baculovirus. Why are they considered good biocontrol agents? (All India 2016)
Answer:
A genus of baculoviruses is Nucleopolyhedrovirus.
Refer to Answer No. 4 for their role as an biocontrol agents.

Question 48.
What are methanogens? Name the animals in which methanogens occur and the role they play there. (Delhi 2014)
Answer:
Methanogens are the groups of anaerobic bacteria, that produce large amount of methane.
Methanogens are found in the rumen of cattle and intestine of humans.
The methanogens present in the intestine of animals and humans act on cellulosic part of food and digest them, thereby releasing methane along with CO2 and H2.

Question 49.
Draw a labelled sketch of a typical biogas plant. (Delhi 2014C)
Answer:
Refer figure 10.1 on page no. 266.

Question 50.
Explain the significant role of the genus Nucleopolyhedrovirus in an ecological sensitive area. (All India 2014)
Answer:
For Nucleopolyhedrovirus, Refer to Answer No. 4.

Question 51.
How do mycorrhizae act as biofertilisers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants. (Delhi 2012)
Or
How do plants benefit from having mycorrhizal symbiotic association? (Foreign 2010)
Answer:
Fungi form symbiotic association with plants, which is called mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant.

It also provides resistance to root borne pathogens and increases plant growth. Thus, it acts as a biofertiliser. The fungi belonging to the genus -Glomus form mycorrhizal associations with plants.

Question 52.
How do methanogens help in producing biogas? (Delhi 2012)
Answer:
Methanogens grow anaerobically on cellulosi material and produce large amount of methane along with CO2 and H2. Since, biogas is a mixture of methane and CO2, methanogens help in its production.

Question 53.
Why is Rhizobium categorised as a symbiotic bacterium? How does it act as biofertilisers? (Deihi 2012)
Answer:
The nodules on the roots of leguminous plants are formed by Rhizobium bacteria for their survival. These bacteria fix atmospheric nitrogen into organic form, which is used by the plant as nutrients.

Since, Rhizobium forms symbiotic association with leguminous plants, these are considered as symbiotic bacteria.
Rhizobiiim fixes the atmospheric nitrogen into organic form, i.e. nitrates which can be utilised by the plant as nutrient. So, it is used as biofertilisers.

Question 54.
Name a free-living and a symbiotic bacterium that serves as biofertiliser. Why are they called so? (All India 2010C)
Answer:
Azotobacter is a free-living bacteria serving as a biofertiliser. These bacteria absorb free-nitrogen from the soil, air and convert it into salts of -nitrogen compounds and enrich the soil nutrients.
Rhizobium is a symbiotic bacteria that lives in the root nodules of legumes and fixes atmospheric nitrogen info organic compounds and enrich the soil nutrients.

Question 55.
How does the activity of each one of the following help in organic farming? (Delhi 2019)
(i) Mycorrhiza
(ii) Cyanobacteria
(iii) Rhizobium
Answer:
Refer to text on page no. 267 and 268.

Question 56.
Name the genus to which baculoviruses belong. Describe their role in the integrated pest management programmes. (All India 2019)
Or
Baculoviruses are good example of biocontrol agents. Justify giving three reasons. (2018C)
Answer:
Refer to text on page no. 267.

Question 57.
(i) Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify.
(ii) Give an example of a bacterium, a fungus and an insect that are used as biocontrol agents.
Answer:
(i) Organic farmers do not use any chemical for raising crops. They simply depend on biological control methods to control insects and pests. This way they avoid deleterious effects of chemicals on food products as well as on the environment. These chemicals get accumulated in food chain and ecosystem whereas biological control methods are safe as they do not harm any form of life.

(ii) Examples of biological control agents are as follows

Bacterium Bacillus thuringiensis for the control of cotton bollworm.
Fungus Trichoderma species for controlling fungal soil borne diseases like damping off of vegetables.
Insects Ladybird beetle for the control of aphids.

Question 58.
What are methanogens? How do they help to generate biogas? (All India 2015)
Answer:
For methanogens and biogas, Refer to Answer No. 12 and 16.

Question 59.
How are baculoviruses and Bacillus thuringiensis used as biocontrol agents? Why are they preferred over readily available chemical pesticides? (All India 2014C)
Answer:
Bacillus thuringiensis as Biocontrol Agent:

Through genetic engineering, the gene coding for the toxic protein is introduced into crop plants, which makes them resistant to insect pests.
When they are eaten by the larvae, the toxin becomes active in the gut of larvae and kills the larvae.
They are available in sachets as dried spores, which have to be mixed with water and sprayed onto vulnerable plants.

Baculoviruses uses (Nucleopolyhedrovirus) as biocontrol agents Refer to Answer No. 4.

Biological control of pests and pathogens must be preferred over conventional use of chemical pesticides because:

the chemicals cause pollution to soil, ground water and agricultural products.
the chemicals are toxic and harmful to both human beings and animals.
overuse of chemical fertilisers makes soil infertile.
chemicals kill harmful as well as useful organisms indiscriminately.

Question 60.
How is the Bt cotton plant created as a GM plant? How is it protected against bollworm infestation? (Delhi 2013C)
Answer:
Bt cotton is created by using some strains of a bacterium known as Bacillus thuringiensis. This bacterium produces protein that kills certain insects such as Lepidopterans, Coleopterans and Dipterans. Bt gene is cloned from this bacteria and had been expressed in cotton plant to provide resistance to the insects without the need for insecticides.

It is protected against corn borer disease by encoding Cry protein with the gene cry IAb. These genes produce Bt toxins which are released in the gut of insects, who feed upon them, thus killing them and protecting the plant from the pests.

Question 61.

The diagram above is that of a typical biogas plant. Explain the sequence of events occurring in a biogas plant.
Identify A, B and C. (Delhi 2011)
Answer:
The sequence of events occurring in a biogas plant are as follows:

The biogas plant tank is fed with a slurry of dung.
A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity.
Methanogens like Methanobacterium grows anaerobically on cellulosic plant material in cow dung to produce large amount of methane, CO2 and H2.
The plant has an outlet, which is connected by a pipe to supply biogas in nearby houses.
The spent slurry is removed through another outlet and used as biofertilisers.
A-Sludge tank
B-Gas holder
C-Dung water

Question 62.
(i) Why do farmers prefer biofertilisers to chemical fertilisers these days? Explain.
(ii) How do Anabaena and mycorrhiza act as biofertilisers? (Delhi 2011)
Answer:
(i) A farmer relies on biofertilisers then chemical fertilisers because

Chemical fertilisers significantly increase the soil pollution and reduce quality of soil, cause water pollution, when it drains into nearby water bodies, after rain.
Overuse of chemical fertiliser makes the soil unfit for raising any crop.

(ii) Anabaena fixes atmospheric nitrogen, thus enriching the nitrogen content of the soil, as well as the organic matter.

In mycorrhiza, the fungal symbiont absorbs phosphorus from the soil and passes it to the plant and provides resistance to root borne diseases. Since, they fulfil the nitrogen and phosphorus requirement, they act as biofertilisers.

Question 63.
Name the genus to which baculoviruses belong. Describe their role in the. Integrated Pest Management (IPM) programme. (Delhi 2011; Foreign 2011)
Answer:
Baculoviruses belong to the genus-Nucleopolyhedrovirus.
Their role in IPM is as follows

Baculoviruses are pathogens that attack insects and other arthropods.
The majority of baculoviruses act as biocontrol agents.
These viruses are excellent for species-specific, narrow spectrum insecticidal applications.
They do not show negative impacts on plants, mammals, bird, fish or even non-target insects. Therefore, they play an important role as biocontrol agent.

Question 64.
An organic farmer relies on natural predation for controlling pests and diseases. Justify by giving reasons, why this is considered to be a holistic approach? (Foreign 2010)
Answer:
Organic farming is a holistic approach that seeks to develop an understanding of the webs of interaction among the myriads of organisms that form the flora and fauna of the field.

An organic farmer works to create a system, where the insects are not eradicated, but kept at manageable level by a complex system of checks and balance within a living and vibrant ecosystem.
Organic farming states that the eradication of pests is not only possible, but also undesirable, because many beneficial predatory and parasitic insects cannot survive without them.
This use of biocontrol methods reduces the use of chemical pesticides and thereby pollution.

Question 65.
What are biofertilisers? Describe their role in agriculture. Why are they preferred to chemical fertilisers? (Foreign 2015)
Answer:
Biofertilisers are the living organisms that promote the growth of plants by replenishing the nutrients in the soil. These include bacteria, fungi and cyanobacteria.

Role of Biofertlisers in Agriculture Some biofertilisers such as Rhizobium bacteria live in symbiotic association with plants. They live within the root nodules of leguminous plants. These bacteria fix atmospheric nitrogen and enrich the nitrogen content of soil.

Fungi such as Glomus forms symbiotic association with plants (mycorrhiza) by absorbing phosphorus and passing it to plants. Cyanobacteria such as Nostoc and Anabaena fix atmospheric nitrogen and act as biofertilisers especially in paddy fields.

Biofertilisers are preferred over chemical fertilisers. Refer to Answer No. 26 (i).

Question 66.
Name the microbes that help in the production of the following products commercially.
(i) Statin
(ii) Citric acid
(iii) Penicillin
(iv) Butyric acid
Answer:
(i) Statin – Monascus purpureus
(ii) Citric acid – Aspergillus niger
(iii) Penicillin – Penicillium notatum
(iv) Butyric acid – Clostridium butylicum

Question 67.
Choose any four microbes, from the following which are suited for organic farming which is in great demand these days for various reasons. Mention one application of each one chosen.
Mycorrhiza, Monascus, Anabaena, Rhizobium, Methanobacterium, Trichoderma.
Answer:
The four microbes that can be chosen for organic farming are

Rhizobium The nodules on the roots of leguminous plants are formed by the symbiotic association of Rhizobium bacteria.
These bacteria fix atmospheric nitrogen into its organic form, which is used by the plants as nutrient.
Mycorrhiza (Glomus) Many members of genus-Glomus form symbiotic association with plants called mycorrhiza. The fungal symbiont absorbs phosphorus from soil and passes it to the plant. Mycorrhiza shows resistance to root-borne pathogens, tolerance to salinity and drought and helps in overall increase in plant growth and development.
Anabaena It is a cyanobacteria that is used as a biofertiliser. It fixes atmospheric nitrogen.
Trichoderma It is a free-living fungi that is very common in the root ecosystems. It is a very effective biocontrol agent of several plant pathogens.

Question 68.
(i) How do organic farmers control pests? Give two examples.
(ii) State the difference in their approach from that of conventional pest control methods.
Answer:
(i) The organic farmers control pests by the use of insect pests resistant varieties. The two examples are

The Pusa Gaurav variety of Brassica is resistant to aphids.
Pusa Sawani variety of okra is resistant to shoot and fruit borer.

(ii) The use of resistant variety is safer to control the pests as it does not involve chemical pesticides which are used in conventional method of controlling pests. Thus, it is environmental friendly method and reduces soil pollution.