NCERT Exemplar Problems Class 12 Biology Chapter 10 Microbes in Human Welfare
Multiple Choice Questions
Single Correct Answer Type
1. The vitamin whose content increases following the conversion of milk into curd by lactic acid bacteria is
(a) Vitamin C (b) Vitamin D
(c) Vitamin B12 (d) Vitamin E
Answer. (c) The vitamin B12 content increases following the conversion of milk into curd by lactic acid bacteria (LAB).
2. Wastewater treatment generates a large quantity of sludge, which can be treated by
(a) Anaerobic digesters (b) Floe
(c) Chemicals (d) Oxidation pond
Answer. (a) Wastewater treatment generates a large quantity of sludge, which can be treated by anaerobic sludge digesters.
3. Methanogenic bacteria are not found in
(a) Rumen of cattle (b) Gobar gas plant
(c) Bottom of water-logged paddy fields (d) Activated sludge
Answer. (d) Methanogenic bacteria are found in rumen of cattle, gobar gas plant and bottom of,water-logged paddy fields.
4. Match the following list of bacteria and their commercially important products.
Choose the correct match:
(a) i—B, ii—C, iii—D, iv—A (b) i—B, ii—D, iii—C, iv—A
(c) i—D, ii—C, iii—B, iv—A (d) i—D, ii—A, iii—C, iv—B
5. Match the following list of bio active substances and their roles:
Choose the correct match:
(a) i—B, ii—C, iii—A, iv—D (b) i—D, ii—B, iii—A, iv—C
(c) i—D, ii—A, iii—B, iv—C (d) i—C, ii—D, iii—B, iv—A
6. The primary treatment of waste water involves the removal of
(a) Dissolved impurities (b) Stable particles
(c) Toxic substances (d) Harmful bacteria
Answer. (b) 10 treatment basically involves physical removal of particles from sewage through: (i) Filtration and (ii) Sedimentation
These are removed in stages:
(i) Initially floating debris is removed by sequential filtration.
(ii) Then the grit (soil and pebbles) are removed by sedimentation
7. BOD of waste water is estimated by measuring the amount of
(a) Total organic matter (b) Biodegradable organic matter
(c) Oxygen evolution (d) Oxygen consumption
Answer. (d) BOD of waste water is estimated by measuring the amount of oxygen consumption.
8. Which one of the following alcoholic drinks is produced without distillation?
(a) Wine (b) Whisky
(c) Rum (d) Brandy
Answer. (a) Wine and beer are produced, withont distillation. Whisky, brandy and rum are produced by distillation.
9. The technology of biogas production from cow dung was developed in India largely due to the efforts of
(a) Gas Authority of India
(b) Oil and Natural Gas Commission
(c) Indian Agricultural Research Institute and Khadi and Village Industries Commission
(d) Indian Oil Corporation
Answer. (c) The technology of biogas production from cow dung was developed in India largely due to the efforts of Indian Agricultural Research Institute and Khadi and Village Industries Commission.
10. The free-living fungus Trichoderma can be used for
(a) Killing insects
(b) Biological control_of plant diseases
(c) Controlling butterfly caterpillars
(d) Producing antibiotics
Answer. (b) The free-living fungus Trichoderma can be used for biological control of plant diseases.
11. What would happen if oxygen availability to activated sludge floes is reduced?
(a) It will slow down the rate of degradation of organic matter.
(b) The center of floes will become anoxic, which would cause death of bacteria and eventually breakage of floes.
(c) Floes would increase in size as anaerobic bacteria would grow around floes.
(d) Protozoa would grow in large numbers.
Answer. (b) If oxygen availability to activated sludge floes is reduced the center of floes will become anoxic, which would cause death of bacteria and eventually breakage of floes.
12. Mycorrhiza does not help the host plant in
(a) Enhancing its phosphorus uptake capacity
(b) Increasing its tolerance to drought
(c) Enhancing its resistance to root pathogens
(d) Increasing its resistance to insects
Answer. (d) Mycorrhiza help the host plant in enhancing its phosphorus uptake capacity, increasing its tolerance to drought and enhancing its resistance to root pathogens.
13. Which one of the following is not a nitrogen-fixing organism?
(a) Anabaena (b) Nostoc
(c) Azdtobacter (d) Pseudomonas
Answer. (d) Anabaena, Nostoc and Azotobacter are the cyanobacteria. All are nitrogen-fixing organism.
14. Big holes in Swiss cheese are made by a
(b) bacterium that produces methane gas
(c) bacterium producing a large amount of carbon dioxide
(d) fungus that releases a lot of gases during its metabolic activities.
Answer. (c) Large holes in Swiss cheese are due to production of large amount of C02
by a bacterium named Proponibacterium sharmanii.
15. The residue left after methane production from cattle dung is
(a) Burnt (b) Buried in landfills
(c) Used as manure (d) Used in civil construction
- Thus gobar (excreta/dung) of cattle is rich in these bacteria. Dung can be used for generation of biogas, commonly called gobar gas.
- The residue left after methane production from cattle dung is used as manure.
16. Methanogens do not produce
(a) Oxygen (b) Methane
(c) Hydrogen sulfide (d) Carbon dioxide
Answer. (a) Methanogens are obligate anaerobes, which produce methane, hydrogen sulfide and carbon dioxide but do not produce oxygen.
17. Activated sludge should have the ability to settle quickly so that it can
(a) Be rapidly pumped back from sedimentation tank to aeration tank
(b) Absorb pathogenic bacteria present in waste water while sinking to the bottom of the settling tank
(c) Be discarded and anaerobically digested
(d) Absorb colloidal organic matter
Answer. (a) Activated sludge should have the ability to settle quickly so that it can be rapidly pumped back from sedimentation tank to aeration tank.
18. Match the items in Column ‘A’ and Column ‘B’ and choose the correct answer.
The correct answer is
(a) i—B, ii—D, iii—C, iv—A (b) i—C, ii—D, iii—B, iv—A
(c) i—D, ii—A, iii—B, iv—C (d) i—C, ii—B, iii—A, iv—D
Very Short Answer Type Questions
1.Why does ‘Swiss cheese’ have big holes?
Answer. The large holes in ‘Swiss cheese’ are due to the production of a large amount of C02 by a bacterium named Propionibacterium sharmanii.
2.What are fermentors?
Answer. Even in industry, microbes are used to synthesise a number of products valuable to human beings. Beverages and antibiotics are some of the examples. Production on an industrial scale, requires growing microbes in very large vessels called fermentors.
3.Name a microbe used for statin production. How do statins lower blood cholesterol level?
Answer. Monascus purpureus statins lower blood cholesterol level by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.
4. Why do we prefer to call secondary waste water treatment as biological treatment? .
Answer. The secondary treatment is also called biological treatment because in secondary treatment living organisms like bacteria and fungi are used.
5. What for Nucleopolyhydro viruses are being used now-a-days?
Answer. Necleopolyhydroviruses are used for the biological control of insect pesto.
6. How has the discovery of antibiotics helped mankind in the field of medicine?
Answer. If antibiotics were not discovered bacterial and fungal diseases would not have been controllable.
7. Why is distillation required for producing certain alcoholic drinks?
Answer. Distillation increases the alcohol content in alcoholic drinks.
8. Write the most important characteristic that Aspergillus niger, Clostridium butylicum and Lactobacillus share.
Answer. These all are acid producers. Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.
9. What would happen if our intestine harbours microbial flora exactly similar to that found in the rumen of cattle?
Answer. If our intestine harbours microbial flora exactly similar to that found in the rumen of cattle then we would be able to digest the cellulose present in our food.
10. Give any two microbes that are useful in biotechnology.
Answer. E.coli and Saccharomyces cerevisae
11. What is the source organism for EcoRI, restriction endonuclease?
Answer. Escherichia coli RY 13.
12. Name any genetically modified crop.
Answer. Bt cotton.
13. Why are blue green algae not popular as biofertilisers?
Answer. Blue green algae are not popular as biofertilisers because they causes algal bloom in polluted water bodies.
14. Which species of Penicillium produces Roquefort cheese?
Answer. Roquefort cheese produced by Penicillium roqueforti.
15. Name the states involved in Ganga action plan.
Answer. Uttarakhand, Uttar Pradesh, Bihar, West Bengal and Jharkhand.
16. Name any two industrially important enzymes.
Answer. Lipase, Amylase.
17. Name an immune immunosuppressive agent.
Answer. Cyclosporin A
18. Give an example of a rod shaped virus.
Answer. Tobacco mosaic virus (TMV).
19. What is the group of bacteria found in both the rumen of cattle and sludge of sewage treatment?
20. Name a microbe used for the production of Swiss cheese.
Answer. Propionibacterium shaynanii.
Short Answer Type Questions
1. Why are floes important in biological treatment of waste water?
Answer. Secondary treatment or Biological treatment: The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into floes (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.
2. How has the bacterium Bacillus thuringiensis helped us in controlling caterpillars of insect pests?
Answer. Bacillus thuringiensis products are endotoxin which when ingested and released in the gut of the larvae of insect pest disrupts the insect gut lining thereby killing them.
3. How do mycorrhizal fungi help the plants harbouring them?
Answer. The mycorrhizal fungi absorb phosphorus from the soil and transfer them to the host cells. They also’impart resistance to host plants against root pathogens. They also help plant tolerate salinity and draught.
4. Why are cyanobacteria considered useful in paddy fields?
Answer. Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.
5. How was penicillin discovered?
Answer. Penicillin was an accidental discovery. Sir Alexander Fleming observed that in unwashed culture plates of Staphylococcus, a mould Penicillium was growing. This mould inhibited the-growth of Staphylococcus. Later the antibiotic Penicillin was isolated from this fungus.
6. Name the scientists who were credited for showing the role of Penicillin as an antibiotic.
Answer. Its full potential as an effective antibiotic was established much later by Ernest Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.
7. How do bioactive molecules of fungal origin help in restoring good health of humans?
Answer. A bioactive molecule, cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polysporum. Statins produced by the yeast Monascus purpureus have been commercialised as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.
8. What roles do enzymes play in detergents that we use for washing clothes? Are these enzymes produced from some unique microorganisms?
Answer. Microbes are also used for production of enzymes. Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry. Lipases are produced by Candida lipolytica (fungus).
9. What is the chemical nature of biogas? Name an organism which is involved in biogas production.
Answer. The chemical nature of Biogas is methane, CO2 and H2. Methanobacterium, a type of methanogen is employed for biogas productioh.
10. How do microbes reduce the environmental degradation caused by chemicals?
Answer. Chakravarthy Bug is a super bug of Pseudomonas with multiple plasmid.
They are helpful in removing oil spills.
11. What is a broad spectrum antibiotic? Name one such antibiotic.
Answer. A broad spectrum antibiotic is one which can inhibit the growth of both G +ve and G -ve bacteria.
12. What are viruses parasitising bacteria called? Draw a well labelled diagram of the same.
Answer. Viruses parasitising bacteria are called bacteriophages.
13. Which bacterium has been used as a clot buster? What is its mode of action?
Answer. Streptokinase produced by the bacterium Streptococcus and modified by
genetic engineering is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack.
14. What are biofertilisers? Give two examples.
Answer. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.
Long Answer Questions
1. Why is aerobic degradation more important than anaerobic degradation for the treatment of large volumes of waste waters rich in organic matter? Discuss.
Answer. Secondary treatment or Biological treatment: The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into floes (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. BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. The sewage water is treated till the BOD is reduced. The BOD test measures the rate of uptake of oxygen by micro¬organisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.
Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘floes’ 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.
2. (a) Discuss about the major programs that the Ministry of Environment and Forests, Government of India, has initiated for saving major Indian rivers from pollution.
(b) Ganga has recently been declared the national river. Discuss the implication with respect to pollution of this river.
Answer. (a) The untreated sewage is often discharged directly into rivers leading to their pollution and increase in water-borne diseases. The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan to save these major rivers of our country from pollution. Under these plans, it is proposed to build a large number of sewage treatment plants so that only treated sewage may be discharged in the rivers.
(b) The Ganga is the largest river in India with an extraordinary religious ‘ importance for Hindus. Situated along its banks are some of the world’s oldest inhabited cities like Varanasi and Patna. It provides water to about 40% of India’s population across 11 states, serving an estimated population of 500 million people or more, which is larger than any other river in the world.
A number of initiatives have been undertaken to clean the river but failed to deliver desired results. After getting elected, India’s Prime minister Narendra Modi affirmed to work for cleaning the river and controlling pollution. Subsequently, Namami Ganga project was announced by the Government in July 2014 budget. An estimated Rs 2,958 crores have been spent till July 2016 in various efforts to clean up the river.
3. Draw a diagrammatic sketch of biogas plant and label its various components given below: Gas Holder, Sludge Chamber, Digester, Dung+water chamber
4. Describe the main ideas behind the biological control of pests and diseases.
Answer. Biological control means life against life. It is a natural and ecofriendly
concept. It employs the natural organisms to control the population of pathogens and pests in an ecosystem. Classical examples are Trichoderma which is antagonist against many soil borne plant pathogens. Similarly, Penicillium inhibits the growth of Staphylococcus and therefore has been successfully used in the production of Penicillin antibiotic to control many human bacterial pathogens.
5. (a) What would happen if a large volume of untreated sewage is discharged into a river?
(b) In what way anaerobic sludge digestion is important in sewage treatments?
Answer. (a) Due to increasing urbanisation, sewage is being produced in much larger quantities than ever before. However the number of sewage treatment plants has not increased enough to treat such large quantities. So the untreated sewage is often discharged directly into rivers leading to their pollution and increase in water-borne diseases.
(b) Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘floes’ 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 a source of energy as it is inflammable.
6. Which type of food would have lactic acid bacteria? Discuss their useful application.
Answer. Curd. Micro organisms such as lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk into curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking disease causing microbes.