Microbes in Human Welfare Questions Class 12 Biology

ICSE Class 12 Biology

Microbes-in Household Products, Industrial Products and in Sewage Treatment and Biogas

Very Short Answer Type Questions

Question. How is lactic acid bacteria beneficial to us other than helping in curdling the milk ?
Name the nutrient that gets enhanced while curdling of milk by Lactobacillus.
Answer : 
Lactic acid bacteria improves the nutritional quality by increasing Vitamin B12.
Vitamin B12

Question. Name the metabolic pathway associated with the rising of dough in making bread. What makes the dough rise ?
Answer : 
Metabolic pathway : Alcoholic fermentation by yeast. CO2 produced in this process is responsible for rising of dough.

Question. Why do we add an inoculum of curd to milk for curdling it ?
Answer : 
Inoculum contains Lactobacilli which curdles milk into curd with lactic acid. Lactobacillus converts lactose sugar of milk into lactic acid which causes coagulation and partial digestion of milk protein casein. As a result, milk gets changed into curd.
Commonly Made Error

Question. Give the scientific name of the source organism from which the first antibiotic was produced.
Answer :
 Penicillium notatum. 

Question. Write the scientific name of the microbe used for fermenting malted cereals and fruit juices.
Answer :
 Saccharomyces cerevisiae. 

Question. Name the gas released and the process responsible for puffing up of the bread dough when Saccharomyces cerevisiae is added to it.
Answer : 
Gas – Carbon dioxide
Process – Fermentation 

Question. Which of the following in the baker’s yeast is used in fermentation : Saccharam barberi, Saccharomyces cerevisiae 
Answer : 
Saccharomyces cerevisiae.

Question. Name the group of organisms and the substrate that act to produce biogas.
Answer : 
Name of the group of organisms-Methanogens Substrate-Cellulosic material, cow dung and agricultural waste. 

Question. Milk start to coagulate when lactic acid bacteria are added to warm milk as a starter. Mention any other two benefits LAB provide.
Answer : 
Besides curdling of milk the lactic acid bacteria are beneficial to us in following ways :
(i) They improve the nutritional quality of curd by producing Vitamin B12.
(ii) They help in inhibiting the development of disease causing microorganism in the gut.

Question. Bottled fruit juices are clearer as compared to those made at home. Explain
Answer :
 Bottled fruit juices are clearer as compared to those prepared at home because they are treated with enzyme pectinase and protease. This enzymes acts
on juices and make them clearer.

Short Answer Type Questions – l

Question. List the events that lead to biogas production from waste water whose BOD has been reduced significantly.
Answer : Sedimentation of flocs to form activated sludge, sludge pumped to anaerobic sludge digester, growth of anaerobic bacteria, digestion of sludge by bacteria to release biogas.

Question. List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment.
Answer : Effluent from the primary settling tank passed into aeration tank, agitated mechanically and air is pumped into it, vigorous growth of aerobic microbes into flocs, microbes consume major part of the organic matter in effluent.

Question. 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.
Answer : Supernatant from the primary treatment is passed into large aeration tanks during secondary treatment. In these tanks, the effluent is agitated mechanically and air is pumped into it. This causes vigorous growth of bacteria that lead to the formation of floc, which consists of bacteria and
fungal filaments in a mesh like structure. While growing, these microbes consume the major part of organic matter in the effluent, it decreases the biological oxygen demand (BOD). After a significant drop in BOD is observed, effluent is passed into the settling tank. 

Question. Explain the different steps involved during primary treatment phase of sewage.
Answer : Physical removal of particles (large and small), by filtration and sedimentation, forming primary sludge / sedimented solids, forming effluent (supernatant) for secondary treatment.

Question. Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatments.
Answer :

Question. 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
Answer : (i) Milk to curd
(ii) Bread / ethanol / alcoholic drinks / whiskey / brandy / beer/ rum
(iii) Swiss cheese
(iv) Citric acid 

Question. Name two groups of organisms which constitute ‘flocs’. Write their influence on the level of BOD during biological treatment of sewage.
Answer : The bacteria and fungal mycelium constitute flocs. These microorganisms bring about the decomposition aerobically of the major part of organic matter in primary effluent and thus helps in lowering the BOD (Biological Oxygen Demand) of the effluent.

Question. State the use of :
(i) Trichoderma with respect to organ transplant and
(ii) Nucleopolyhedrovirus with respect to pest management.
Answer : (i) Trichoderma : It produces a bioactive molecule called cyclosporin A, which is used as an immunosuppressive agent in organ transplant.
(ii) Nucleopolyhedrovirus : Belongs to the family baculoviruses which are used as biocontrol agents.
These viruses attack insects and they are excellent for species-specific, narrow-spectrum insecticidal applications. They are quite specific and therefore do not have any negative impact on non target organisms, thus making them useful in overall integrated pest management programme.

Question. Explain the function of ‘‘anaerobic sludge digester’’ in a sewage treatment plant.
Answer : In anaerobic sludge digester, the anaerobic bacteriathe methanogen digest the flocs of bacteria and fungi in activated sludge and produce methane along with H2S and CO2 i.e. biogas which is a source of energy as it is inflammable. 

Question. Name the source of cyclosporin-A. How does this bioactive molecules function in our body ?
Answer : Cyclosporin-A is produced by the fungus Trichoderma polysporum. Cyclosporin-A is antifungal, antiinflamatory and used as an immunosuppressant.
It is able to suppress the immune system enough so that organs and tissues, not original to the body, can be transplanted.

Question. Name the bacterium responsible for the large holes seen in ‘Swiss cheese ‘. What are these holes due to ?
Answer : The large holes in ‘Swiss cheese’ are due to the production of a large amount of CO2 by a bacterium named Propionibacterium shermanii.

Question. Mention the importance of lactic acid bacteria to humans other than setting milk into curd.
Answer : (i) While converting milk into curd, lactic acid bacteria (LAB) improve its nutritional quality by increasing vitamin B12.
(ii) In our stomach, LAB play beneficial role in preventing growth of disease-causing microbes.

Question. Why are some molecules called bioactive molecules ? Give two examples of such molecules.
Give the scientific name of microbes from which cyclosporin-A and statin are obtained. Write one medical use of each one of these drugs.
Answer : Some molecules are produced by certain living organism and have ability to perform functions and modify metabolism in body of other living organims are known as bioactive molecule.
Examples of bioactive molecules are :
(i) Cyclosporin-A : It is used as an immunosuppressive agent in organ-transplant patients. It is produced by Trichoderma polysporum.
(ii) Statins : Statins are produced by the yeast Monascus purpureus and have been commercialized as cholesterol-lowering agents.

Question. Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences.
Answer : Streptokinase.
It is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack. It helps in clearing blood clots inside the blood vessels through dissolution of intravascular fibrin.

Question. 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.
Why is ‘starter’ added to set the milk into curd ?
Answer : When a small amount of curd is added as a starter to the fresh milk at a suitable temperature, amicroorganism Lactobacillus and lactic acid bacteria grows in milk in millions. These bacteria convert the lactose sugar of milk into lactic acid which coagulates and partially digests milk protein casein. This causes curdling of milk and converts milk into curd.

Question. Name the first antibiotic discovered and by whom.
Answer : Penicillin, Alexander Fleming.

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

Question. Name a bioactive molecule, its source organism and the purpose for which it is given to organ transplant patients. 
Answer : Cyclosporin A.
Source – Trichoderma polysporum.
Purpose – Immuno suppressive agent.

Question. (i) A patient who had an organ transplant was given cyclosporin – A. Mention the microbial source and state the reason for administration of this bioactive molecule.
(ii) Bottled fruit juices bought from the market are clearer as compared to those made at home. Give reason.

Answer : (i) Source – Trichoderma polysporum.
Reason – Immuno suppressive agent.
(ii) They are clarified by pectinases and proteases.

Question. Name the source of statin and state its action on human body.
Answer : Statin is produced by a yeast called Monascus purpureus. It’s use lowers the blood cholesterol level in the body. It acts by inhibiting the activity of the enzyme which brings about the synthesis of cholesterol.

Short Answer Type Questions – ll

Question. Cow dung and water is mixed and this slurry is fed into the biogas plant for digestion by microbes. The person performing the process shares that there is no need to provide inoculum for it, why?
What is the role of microbes at the source? Under which condition will they be most active and effective ?
Answer : Methanogens are present in cow dung.
Breakdown of cellulose.
Anaerobic condition. 

Question. Explain the changes that can be observed in the characteristics of river water when sewage is discharged into it and a few weeks after the discharge with respect to :
(i) level of dissolved oxygen
(ii) population of fresh water organisms.
Answer :

Question. State the medicinal value and the bioactive molecules produced by Streptococcus, Monascus and Trichoderma.
Answer : Streptococcus : It produces Streptokinase enzyme that is used to dissolve clots formed in the blood vessels.
Monascus (Yeast) : It produces statins that help in lowering blood cholesterol levels.
Trichoderma (Fungus) : It produces cyclosporin A that is used as an immunosuppressant agent in organ transplantation. It inhibits activation of T-cells and thus prevents rejection of transplants.

Question. Given below is a figure of a biogas plant.
(i) Identify A and justify its floating nature.
(ii) Identify the products B and C and discuss their

Answer : (i) A is the floating cover which is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity.
(ii) B is the biogas which is a mixture of gases consisting of methane, hydrogen sulphide and carbon dioxide. It can be used as a source of energy to nearby houses as it is inflammable.
C is the spent slurry or sludge which is removed through another outlet and may be used as fertiliser.

Question. Identify a, b, c, d, e and f in the table given below :

Answer : (a) Clot buster for removing clots from blood vessels.
(b) Trichoderma polysporum.
(c) Antifungal, anti-inflammatory and immunosuppressive agent in organ transplant, prevents reactions in organ transplantation.
(d) Statins.
(e) Blood cholesterol lowering agent.
(f) Lactic acid.

Question. What are methanogens ? How do they help to generate biogas.
Answer : Micro-organisms that produce methane along with CO2 and H2 gases under anaerobic conditions are called methanogens Example, Methanobacterium.
These are the bacteria found in cattle dung (gobar) and in anaerobic sludge during sewage treatment,
They grow anaerobically on cellulosic material and produce a large amount of methane (main constituent of biogas) along with CO2 and H2. Thus, methanogens are used in biogas production.

Question. What are Methanogens ? Name the animals they are present in and the role they play there.
Answer : Methanogens are the bacteria which grow anaerobically on cellulosic material and produce large amount of methane along with CO2 and H2S.
(i) Present in cattle (rumen) a part of stomach.
(ii) They help in
(a) Breaking down of cellulose present in food of cattle.
(b) Nutrition of animal for digestion of cellulose.
The excreta of cattle is rich in these bacteria (methanogens) and therefore can be used for generation of biogas.

Question “Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body.” Explain.
Answer : High BOD in a water body indicates more number of micro-organisms in water, resulting in bad quality of water / death of aquatic creatures, more polluting potential.
Lower BOD of water body indicates less number of micro-organisms in water, good quality of water / aquatic life flourishes / less polluting potential

Question. Explain the different steps involved in the secondary treatment of sewage.
Answer :
(a) Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply. Useful aerobic microbes grow rapidly and form flocs.
(b) Flocs while growing consume organic matter and thus reduce the biochemical oxygen demand (BOD), the effluent is passed into settling tank.
(c) The bacterial flocs settle at the bottom of the tank and it forms activated sludge, a small part this is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digesters.

Question. Describe how do ‘flocs‘ and ‘activated sludge‘ help in Sewage Treatment.
Answer : Flocs : Aerobic microbes consume the major part of the organic matter in the effluent, significantly reduces BOD.
Activated sludge : Small part of activated sludge is used as inoculum and pumped back to aeration tank / pumped into anaerobic sludge digesters where microbes or bacteria grow anaerobically to produce CH4 or H2S or CO2 or biogas. 

Question. Describe how biogas is generated from activated sludge. List the components of biogas.
Answer : After the significant decline of BOD of the sewage, the effluent is passed into the settling tank. In these tanks, the bacterial flocs sediment forming the activated sludge. A small part of activated sludge is pumped back into aeration tanks to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Other kinds of bacteria, that grow anaerobically, digest the bacteria and fungi in the sludge. During this digestion, bacteria produce a mixture of gases called biogas.
The components of biogas are :
(i) Methane (CH4)
(ii) Hydrogen sulphide (H2S)
(iii) Carbon dioxide (CO2)

Question. Identify a, b, c, d, e and f in the following table :

Answer : (i) (a) Streptokinase.
(b) ‘Clot buster‘ for removing clots from the blood vessels (of patients who have undergone myocardial infarction leading to heart attack) / clot buster enzyme.
(ii) (c) Cyclosporin.
(d) Trichoderma polysporum.
(iii) (e) Monascus purpureus (yeast).
(f) Blood cholesterol lowering agent.

Question. The three microbes are listed below. Name the product produced by each one of them and mention their use.
(a) Aspergillus niger
(b) Trichoderma polysporum
(c) Monascus purpureus
Answer : (a) Aspergillus niger – Citric Acid, natural preservative / flavouring agent.
(b) Trichoderma polysporum – Cyclosporin A , immunosuppressive agent.
(c) Monascus purpureus – Statin, blood cholesterol lowering agent.

Question. (i) Why are the fruit juices bought from market clearer as compared to those made at home ?
(ii) Name the bioactive molecules produced by Trichoderma polysporum and Monascus purpureus.
Answer : (i) The fruit juices prepared at home are turbid due to the presence of fibers and pectin in it whereas those purchased from the market are clearer because of the use of enzymes like proteases and pectinases which remove turbidity.

Question. Microbes play a dual role when used for sewage treatment as they not only help to retrieve usable water but also generate fuel. Write how this happens ?
Answer : Heterotrophic microbes naturally present in sewage are used. Vigorous growth of aerobic microbes as flocs uses organic matter in effluent and reduce BOD of waste water. Other kinds of bacteria grow in it anaerobically and digest the bacteria and fungi called flocs (masses of bacteria associated with fungal filaments). As they digest flocs, a mixture of CH4, H2S, and CO2 or biogas is evolved, which can be used as a fuel.

Question. (i) How is activated sludge formed during sewage treatment ?
(ii) This sludge can be used as an inoculum or as a source of biogas. Explain. 
Answer : (i) When the BOD of sewage or waste is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.
(ii) A small part of the activated sludge is pumped back into aeration tanks to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as a source of energy as it is inflammable.

Question. Make a list of three household products along with the names of the micro-organism producing them.
Answer : Lactic acid bacteria ; curd
Saccharomyces cerevisiae ; bread
Propionibacterium shermanii ; swiss cheese

Question. Name the two different categories of aerobic microbes naturally occurring in sewage water.
Explain their role in cleaning sewage water into usable water.
Answer : The two different categories of aerobic microbes naturally occurring in sewage water are bacteria and fungi. The two together forms flocs a mesh like structure.
The following three treatments are carried out for purifying sewage water:
(i) Primary treatment :
(a) Separation of large debris.
(b) Sedimentation in tanks.
(ii) Secondary treatment :
(a) Waste water is pumped in shallow stabilization or oxidation ponds, where microbes oxidize its organic matter.
(b) The process results in release of CO2 and formation of sludge.
(c) Sludge is continuously aerated further for its oxidation.
(iii) Tertiary treatment :
(a) Removal of turbidity in waste water caused by the presence of nutrients (N2, P, etc.) in dissolved organic matter, metals or pathogens.
(b) It involves chemical oxidation by strong oxidising agents such as chlorine gas, perchlorate salts, ozone gas, UV radiations.

Question. Identify a, b, c, d, e and f in the table given below :

Answer : a – Statins.
b – Blood cholesterol lowering agent.
c – Penicillium notatum.
d – Penicillin.
e – Trichoderma polysporum.
f – Immuno-suppressive agent in organ transplant patients.

Question. Mention the product and its use produced by each of the microbes listed below :
(i) Streptococcus
(ii) Lactobacillus
(iii) Saccharomyces cerevisiae
Answer :
 (i) Streptokinase, clot buster / dissolves clot from blood vessels.
(ii) Lactic acid, coagulates milk / partial digestion of milk proteins casein.
(iii) Ethyl alcohol + CO2, ferments dough to make bread / idli. 


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.
Answer : Bio wastes are collected and a slurry of dung is fed. A floating cover having gas outlet is placed over slurry which keeps on rising as the gas is produced in the tank, the spent slurry is removed through another outlet and may be used as fertilizer.
(a) sludge loader.
(b) gas holder / CH4 and CO2.
(c) dung and water.

Long Answer Type Questions

Q. 1. Describe the process of waste-water treatment under the following heads :
(i) Primary treatment.
(ii) Secondary treatment.
Explain the process of sewage water treatment before it can be discharged into natural water bodies. Why is this treatment essential ?
Answer : (i) Primary treatment
(a) Physical removal of particles like debris, soil, sand or silt through filtration, sedimentation in stages. 
(b) Solids settle to form primary sludge, the supernatants form the primary effluent.
(ii) Secondary Treatment : It is the biological treatment.
(a) Effluent passed into aeration tanks.
(b) Vigorous growth of useful aerobic microbes into flocs.
(c) Significant reduction of BOD due to use of organic matter by microorganisms.
(d) After fall in the level of BOD, the effluent is passed on to settling tanks where bacterial flocs settle to form activated sludge. ½
(e) Activated sludge is passed on to anaerobic sludge digester, where bacteria and fungi are anaerobically digested.

Q. 3. (i) Name the category of microbes occurring naturally in sewage and making it less polluted during the treatment.
(ii) Explain the different steps involved in the secondary treatment of sewage.
Answer : (i) Aerobic microbes.
(ii) 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 useful aerobic microbes into flocs (masses 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. The sewage water is treated till the BOD is reduced. Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

Microbes as Biocontrol Agents and Bio-fertilisers

Question. Name the types of association that the genus Glomus exhibits with higher plants.
Answer :
 Symbiosis / Mycorrhiza / Mutualism.

Question. Write the significance of nucleopolyhedrovirus in pest management.
Answer :
 Nucleopolyhedroviruses are the effective biocontrol agent. They are species specific and have narrow spectrum insecticidal application having no negative impact on non target beneficial organisms.
They play significant role in pest management.

Question. Name any one symbiont which serves as a biofertilizer. Mention its specific role.
Answer :
 Rhizobium, a root nodule bacterium of legumes is a symbiont. It fixes nitrogen symbiotically and thus help the plants in obtaining their nitrogen nutrition and therefore serve as a biofertilizer.

Question. State one reason for adding blue-green algae to agricultural soil.
Mention the role of cyanobacteria as a biofertilizer.
Answer : 
Blue-green algae are cyanobacteria. They fix atmospheric free nitrogen. Therefore, they increase soil fertility and also add the organic matter to the soil.

Question. Mention two advantages of adding blue-green algae to paddy fields.
Answer : 
In paddy fields, cyanobacteria (blue-green algae) add organic matter to the soil and increases its fertility.

Question. Name any two free living nitrogen fixing bacteria.
Answer :
 Azotobacter and Azospirillum.

Question. What makes Nucleopolyhedrovirus a desirable biological control agent ?
Answer :
 Nucleopolyhedrovirus is the genus of baculoviruses. 
They are quite effective biocontrol agent. Its specificity makes it a desirable biocontrol agent.
They selectively attack insect and other arthropods.
They are suitable for species specific, narrow spectrum insecticidal application. They do not harm non-target organisms. They are also desirable in IPM programme to conserve beneficial insects.

Question. Which of the following is a cyanobacterium that can fix atmospheric nitrogen. Azospirillum, Oscillatoria, Spirulina.
Answer :

Short Answer Type Questions – l

Question. How does the application of the fungal genus, Glomus, to the agricultural farm increase the farm output ?
Answer : Glomus forms mycorrhizal association, absorbs phosphorus, provide resistance to root borne pathogens, enhanced to tolerate salinity / drought.

Question. Explain the significant role of the genus Nucleopolyhedrovirus in an ecological sensitive area.
Answer : The genus Nucleopolyhedrovirus include baculoviruses which are insecticidal and therefore used as biocontrol agents. They have narrow spectrum, insecticidal application (IPM). They have no negative impact on plants / mammals / birds / fish / even non target insects. They are desirable in integrated pest management programme.

Question. 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/ Azotobacter/ Anabaena/ Nostoc / Oscillatoria /Frankia (Any two correct names of microbes).
(If cyanobacteria mentioned=½, but if along with cyanobacteria-Anabaena / Nostoc / Oscillatoria mentioned then No mark on cyanobacteria).
(b) They can fix atmospheric nitrogen, due to presence of Rhizobium/N2 fixing bacteria in their root nodules.

Question. What is the pathogenic property of baculovirus, used as a biological agents ? Name the genus of these organisms.
Answer : Attacks insect and other arthropods.

Question. Name a free-living symbiotic bacterium that serve as bio-fertilizer. Why are they so called?
Answer : Azospirillum/Azotobacter, Rhizobium.
They enrich soil nutrient/nitrogen fixation.
(Any other correct example)

Question. Why is Rhizobium categorized as a ‘symbiotic bacterium’ ? How does it act as a biofertiliser ?
Answer : Rhizobium is a symbiotic bacterium living in the root nodule of leguminous plants, it fixes atmospheric nitrogen into organic forms to be used by plants as nutrient and in turn bacteria get carbohydrate food and shelter from the plant. It is a biofertiliser as it is a living organism that enriches nutrient content of the plant / soil.

Question. How do mycorrhizae help the plants to grow better?
How do mycorrhiza act as biofertilizers ? Explain. Name a genus of fungi that forms a mycorrhizal association with plants.
Answer : Mycorrhiza refers to symbiotic association between the fungus and the root of higher plants. These fungi in these associations absorb water, phosphorus, nitrogen, potassium, calcium from soil and pass it to the plant. The fungus brings about the solubilization of organic matter of soil humus, release of inorganic nutrients absorption and their transfer to roots. The genus Glomus forms a mycorrhizal association with plants.

Short Answer Type Questions – ll

Question. Given below is a list of six micro-organisms. State their usefulness to humAnswer :
(i) Nucleopolyhedroviruses
(ii) Saccharomyces cerevisiae
(iii) Monascus purpureus
(iv) Trichoderma polysporum
(v) Penicillium notatum
(vi) Propionibacterium sharmanii
Answer : (i) Nucleopolyhedrovirus : It is a biological control agent and is a species-specific insecticide.
(ii) Saccharomyces cerevisiae : It is used to ferment bread dough and used in the preparation of ethanol.
(iii) Monascus purpureus : It is commercialised as blood cholesterol lowering agent.
(iv) Trichoderma polysporum : It produces cyclosporin A, which act as an immunosuppressive agent in organ transplant patients.
(v) Penicillium notatum : It is a source of penicillin, an antibiotic.
(vi) Propionibacterium shermanii : It is used in the preparation of cheese for texture, flavour and taste. 

Question. (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) Natural predation / biological control. 
Examples – lady bird used to kill aphids / dragon flies used to kill mosquitoes / Bacillus thuringiensis used to kill cotton bollworm / caterpillar / butterfly caterpillar.

Question. Explain the role of Baculoviruses as biological control agents. Mention their importance in organic farming.
Explain the significant role of the genus Nucleopolyhedrovirus in an ecological sensitive area.
Answer : The role of Baculoviruses :
Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent species-specific, biocontrol agents have narrow spectrum insecticidal applications. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects.
Importance in organic farming :
(i) Baculoviruses are known to control pests like potato beetles, aphids and corn borers.
(ii) Entomopox virus is another baculovirus which adversely affects the rate of development of grasshopper and the amount of food it eats.

Question. Choose any three 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 : Mycorrhiza : Fungal symbiont of the association. absorb phosphorus from soil.
Anabaena : Fix atmospheric nitrogen / Adds organic matter to the soil.
Rhizobium : It is a symbiotic root nodule bacterium which fixes atmospheric nitrogen (in leguminous plants) in organic form which is used by plant as nutrient.
Methanobacterium : They digest cellulosic material and the product / spent slurry can be used as fertilizer.
Trichoderma : Biocontrol agent for several plant pathogens.

Question. Some microbes act as biofertilisers. Explain with the help of three suitable examples.
Answer : (i) Rhizobium : Symbiotically fix atmospheric nitrogen into organic forms which can be used by the plant as nutrients.
(ii) Azospirullum / Azotobacter : Free living bacteria fix atmospheric nitrogen.
(iii) Glomus / Fungi : Symbiotic with plants absorbs phosphorus from soil and passes it to plant.
(iv) Cyanobacteria / Anabaena / Nostoc / Oscillatoria: Fix atmospheric nitrogen in aquatic and terrestrial environment.
(v) Blue green algae : Add organic matter to soil and increase soil fertility.

Question. (i) Why do farmers prefer biofertilizers to chemical fertilizers these days ? Explain.
(ii) How do Anabaena and Mycorrhiza act as biofertilisers ?
Answer : (i) Farmers prefer biofertilisers to chemical fertilizers because :
(a) They help to get high yield of crops by making the soil rich with nutrients and useful microorganisms necessary for the growth of the plants.
(b) Chemical fertilizers make the environment polluted by releasing harmful chemicals and show biological magnification.
(c) Biofertilisers destroy only those harmful components from the soil that cause diseases in the plants.
(d) Biofertilisers are environment friendly and protect the environment against pollutants.
(ii) Fungi are known to form symbiotic association with plants called mycorrhiza. Many members of the genus Glomus forms mycorrhiza. The
fungal symbiont in this association absorbs phosphorus from soil. Arbuscular mycorrhizal fungi play a vital role as a phosphatic biofertilizer.
Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments, many of which can fix atmospheric nitrogen e.g. Anabaena, Nostoc, Oscillatoria etc.

Question. How are Baculoviruses and Bacillus thuringiensis used as bio-control agents? Why are they preferred over readily available chemical pesticides.
Answer : Baculoviruses belong to Nucleopolyhedroviruses.
They are used as biocontrol agents and preferred over readily available chemical pesticides because they are species specific and have narrow spectrum insecticidal application. They do not harm the non target organisms.
Bacillus thuringiensis is a bacterium and is a biocontrol agent against cotton bollworm insects.
They produce a toxin that specifically kill the insect larvae when the toxin is released in their gut. It is also preferred over chemical pesticides because it is
specific and does not have any negative role over non target organisms. Moreover, the biopesticides are inexpensive and do not cause environmental pollution.

Question. (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) (i) Reduces dependence on toxic chemicals.
(ii) Protects our ecosystem or environment.
(iii) Protects and conserves non-target organisms / they are species – specific.
(iv) These chemicals being non-biodegradable may pollute the environment permanently.
(v) These chemicals being non-biodegradable may cause biomagnification.
(b) Bacteria : Bacillus thuringiensis. ½
Fungus : Trichoderma.
Insect : Ladybird / Dragonfly / Moth or any other correct example.

Question. What are biopesticides ? Give the scientific name and use of the first commercially used biopesticide in the world.
Answer : The biological agent which are used to control weeds, insects and pathogen are called biopesticides.
The micro-organisms that are used as biopesticides are some viruses, bacteria, fungi and their products.
The bacterium Bacillus thuringiensis was the first biopesticide to be used on commercial scale.

Question. Baculoviruses are good example of biocontrol agents. Justify giving three reasons.
Answer : i. Species specific / narrow spectrum insecticidal application.
ii. They have no negative impact on plants / mammals / birds / fish / non target insects.
iii. They are beneficial for IPM (Integrated Pest Management ) / Pest Management Programme.

Question. An organic farmer relies on natural predation for controlling plant pests and diseases. Justify giving reasons why this is considered to be holistic approach.
Answer : Organic farming is holistic approach for controlling plant pest because it seeks to develop an understanding of the interactions amongst the organisms in the ecosystem.
Organic farmers do not try to completely eradicate the pest but keep them at manageable levels. A complete eradication of the pest is not beneficial and also not desirable because many beneficial predatory and parasitic insects can not survive without them.

Question. Microbes can be used to decrease the use of chemical fertilizers. Explain how this can be accomplished.
Answer : (a) Rhizobium bacteria present in the root nodules of leguminous plants forms a symbiotic association and fixes atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
(b) Free-living bacteria in the soil Azospirillum and Azotobacter can fix atmospheric nitrogen, thus enriching the nitrogen content of the soil.
(c) Many members of the genus Glomus (Fungi) form mycorrhizal symbiotic associations with higher plants, in these the fungal symbiont absorbs phosphorus from soil and passes it to the plant.
(d) Cyanobacteria like Anabaena, Nostoc, Oscillatoria are autotrophic microbes widely distributed in aquatic and terrestrial environments, which can fix atmospheric nitrogen, also add organic matter to the soil and increase its fertility.

Long Answer Type Questions

Question. (i) How does Bacillus thuringiensis act as a biocontrol agent for protecting Brassica and fruit trees ? Explain.
(ii) (a) List the components of biogas.
(b) What makes methanogens a suitable source for biogas production ?
Answer :
(i) Bacterium Bacillus thuringiensis (Bt) are available in sachets as dried spores, mixed with water and sprayed onto vulnerable plants, these are eaten up by the insect larvae, the toxins are released in the gut and larva gets killed.
(ii) Methane, H2S, CO2, H2
(iii) Methanogens grow anaerobically on cellulosic material, produce large amount of methane, alongwith CO2 & H2.