8.8 Exercise Problems

Q1. Bacteria cannot be seen with naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?

Answer: If I have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a micro cope, then in order to demonstrate the presence of microbes, we can take curd from our homes as curd contains millions of bacteria.

Q2. Give examples to prove that microbes release gases during metabolism.

Answer: When any bacteria grow on any material, it uses that material as the substratum to acquire food and starts metabolizing that material to release some products. For example, the puffed appearance of dough of dosa is due to the release of gases like CO 2 by the bacteria growing on them. Large holes on Swiss cheeses are also due to the release of gases produced by bacteria growing on them.

Q3. In which food would you find lactic acid bacteria? Mention some of their useful applications.

Answer: Lactic acid bacteria ( LAB ) is found in curd. The useful applications of LAB are as follows:
1. These bacteria can convert milk into curd.
2. LAB is also found in our stomach to check the growth of harmful bacteria in the stomach.
3. LAB increases the amount of vitamin B12 in curd. Thus, it makes curd nutritious.

Q4. Name some traditional Indian foods made of wheat, rice, and Bengal gram (or their products) that involve the use of microbes.

Answer: Indian food made of Wheat- Bread, bhatura, cake Indian food made of rice- Idli, hdoa, uttapam-Indian food made of Bengal gram- Dhokla, Khandvi.

Q5. In which way do microbes play a major role in controlling diseases caused by harmful bacteria?

Answer: Role of microbes in controlling diseases caused by harmful bacteria:
Microbes are used to produce antibiotics. Antibiotics are chemical substances that are obtained from microorganisms and that kill other microorganisms like bacteria. The first antibiotic was penicillin and it was obtained from the fungus Penicillium notatum. Penicillin acts by degrading the cell wall of bacteria.

Q6. Name any two species of fungus, which are used in the production of antibiotics.

Answer: Penicillium notatum and Penicillium chrysogenum are used for preparing Penicillin.

Q7. What is sewage? In which way can sewage be harmful to us?

Answer: The municipal wastewater that is drained into sewers and drains is known as sewage. It contains a large amount of organic matter, microbes, human excreta, etc. When sewage is not treated properly, it degrades the quality of water and acts as a breeding site for mosquitoes. This may lead to diseases like dengue, malaria, etc in nearby communities. Thus sewage can be harmful to us.

Q8. What is the key difference between primary and secondary sewage treatment?

Answer: Sewage is treated in a sewage treatment plant so that it can be free from pollution. This treatment is completed in two stages. The differences between the primary and secondary treatment of sewage are as follows:

• 1. Primary treatment – In primary treatment, mainly large and small particles are separated by physical processes such as sedimentation, filtration, flotation etc. First of all, floating garbage is removed by filtration. After this, grit soil and small particles are separated by sedimentation. The fine particles settle down as primary sludge and supernatant effluent is formed. The effluent is taken from the primary treatment tank for secondary treatment.
• 2. Secondary treatment – Microorganisms are used in secondary treatment. For example, an oxidation pool is a shallow reservoir collecting sewage. Due to the high amount of organic matter in it, algae and bacteria start growing well.
  The bacteria decompose and the algae use the carbon dioxide they produce in photosynthesis. The oxygen released in photosynthesis protects the water from getting contaminated. Thus, an oxidation pool is an example of symbiosis between algae and bacteria. Infectious bacteria are destroyed by the processes taking place in the oxygen pool and only harmless substances remain after the decomposition of organic matter. After secondary treatment, the effluent from the plant is usually released into natural sources of water such as rivers, springs etc. or for tertiary treatment, after separating nitrogen and phosphorus salts from it through chemical processes, the effluent is released into reservoirs.

Q9. Do you think microbes can also be used as a source of energy? If yes, how?

Answer: Yes, microbes can be used as sources of energy. For example, we know that various microbes produce different types of gases as their end products. One such gas is biogas. It is a mixture of gases produced by microbes and is used as a fuel. Similarly, some anaerobic bacteria which grow on cellulosic materials produce gases like methane, hydrogen gas, and CO 2 . Thus, we can say that microbes can be used as a source of energy.

Q10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.

Answer: Generally, farmers use chemical fertilizers and pesticides in their fields. However, these chemic 1-b sed fertilizers and pesticides have deleterious effects on us. They tend to pollute the environment including soil and nearby water bodies. The fruits, vegetables, and grains are grown in fields in chemical fertilizers and pesticides, the chemicals get incorporated in them and they become toxic for animals and humans. Thus, farmers need to find more environmentally friendly methods to control pests and fertilize the soil.

Microbes as biocontrol agents: These are microbes or other biological organisms that can be used to control pests and parasite populations in fields. For example, the Bt toxins of Bacillus thuringiensis are used to control lepidopteran insects. Trichoderma is free-living fungi that are very common in the root systems and control several plant pathogens. Baculoviruses are also 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 candidates for species-specific, narrow spectrum insecticidal applications.

Microbes as biofertilizers: Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources include bacteria, fungi, and cyanobacteria. The root nodule formed by Rhizobium bacteria on the root of leguminous plants increases the nitrogen level of soil, necessary for various metabolic processes. Azotobacter and Azospirillum are free-living bacteria that live in soil and fix atmospheric nitrogen into organic forms. Cyanobacteria such as Nostoc, Anabaena are autotrophic microbes found in aquatic and terrestrial environments that fix atmospheric nitrogen.

Q11. Three water samples namely river water, untreated sewage water, and secondary effluent discharged from a sewage treatment plant were subjected to a BOD test. The samples were labeled \(A, B\), and \(C\); but the laboratory attendant did not note which was which. The BOD values of the three samples \(\mathrm{A}, \mathrm{B}\), and C were recorded as \(20 \mathrm{mg} / \mathrm{L}, 8 \mathrm{mg} / \mathrm{L}\), and \(400 \mathrm{mg} / \mathrm{L}\), respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Answer: BOD means biochemical oxygen demand. It refers to the amount of oxygen consumed if all organic matter in 1 ltr of water is oxidized by bacteria. BOD tests measure the rate of update of oxygen by microorganisms in the water sample. The greater the value of BOD more is the polluting potential. Out of the three samples mentioned above, secondary effluent has the highest BOD value, so it is the most polluted. So, the correct labeling will be:
a. Secondary effluent
b. River water
c. Untreated sewage water.

Q12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterollowering agents) are obtained.

Answer: Cyclosporin A – Trichoderma polysporum (fungus) and Statins – Monascus purpureus (yeast)

Q13. Find out the role of microbes in the following
(a) Single-cell protein (SCP) (b) Soil

Answer: (a) Microorganisms like bacteria, yeast, etc. can be cultured on a large scale in the fermenters. They can be treated in many ways, dried, and used as a food source or animal feed. These microorganisms that can be used as potential sources of proteins for animals and humans are called single-cell proteins. SCP is rich in proteins and can be produced in laboratories.
The major advantage of SCP is as follows:
1. The production of SCP does not depend upon climatic factors.
2. The microorganism grows at a very fast rate and requires very little space.
3. The cost of production of SCP is very low.
4. Microorganisms used as substrates are otherwise pollutants so it also reduces pollution.

(b) Microbes decompose complex organic debris into a dark amorphous substance called humus and degradation products can be used as manure to increase the fertility of the soil. The manure can loosen the soil and increase aeration in soil. It contains many organic substances which are easily assimilated by plants. Some microbes are used for enriching soil fertility. Microorganisms like Azotobacter and Rhizobium can be used as nitrogen fertilizers. Thus, it can be said that microbes play an important role in improving the quality of the soil.

Q14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd.

Answer: These can be arranged as Penicillin – Biogas- Curd- Citric acid. Penicillin is an antibiotic that is used to cure many diseases like pneumonia. Thus it should be the most important. Biogas serves as a source of clean fuel, so it is the second most important. Curd comes next which is a nutritious milk product. Citric acid is used in the food processing industry. Thus, it is last on the list.

Q15. How do biofertilizers enrich the fertility of the soil?

Answer: The term biofertilizer is used for microorganisms that bring nutrient enrichment and minimize the environmental hazards of chemical fertilizers. These fertilizers increase the physical and chemical structure of soil like buffer capacity and water holding capacity of the soil. Biofertilizers can be introduced into seeds, roots, or soil in order to mobilize the desired nutrient. Rhizobium is a biofertilizer that is introduced in roots and fixes nitrogen for the plants. Similarly, Cyanobacteria like Nostoc, Anabaena are also used for fixing nitrogen.

Exemplar Section

VERY SHORT ANSWER TYPE QUESTIONS

Q1. Why does ‘Swiss cheese’ have big holes?

Answer: The large holes in ‘Swiss cheese’ are due to the production of a large amount of \(CO_2\) by a bacterium named Propionibacterium sharmanii.

Q2. 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.

Q3. 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.

Q4. 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.

Q5. What for Nucleopolyhydro viruses are being used now a days?

Answer: Necleopolyhydroviruses are used for the biological control of insect pesto.

Q6. 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.

Q7. Why is distillation required for producing certain alcoholic drinks?

Answer: Distillation increases the alcohol content in alcoholic drinks.

Q8. 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.

Q9. 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.

Q10. Give any two microbes that are useful in biotechnology.

Answer: E.coli and Saccharomyces cerevisae.

Q11. What is the source organism for ECORI, restriction endonuclease?

Answer: Escherichia coli RY 13

Q12. Name any genetically modified crop.

Answer: Bt Cotton.

Q13. 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.

Q14. Which species of Penicillium produces Roquefort cheese?

Answer: Roquefort cheese produced by Penicillium roqueforti.

Q15. Name the states involved in Ganga action plan.

Answer: Uttarakhand, Uttar Pradesh, Bihar, West Bengal and Jharkhand.

Q16. Name any two industrially important enzymes.

Answer: Lipase, Amylase.

Q17. Name an immune immunosupressive agent?

Answer: Cyclosporin A

Q18. Give an example of a rod shaped virus.

Answer: Tobacco mosaic virus (TMV).

Q19. What is the group of bacteria found in both the rumen of cattle and sludge of sewage treatment?

Answer: Methanogens

Q20. Name a microbe used for the production of Swiss cheese.

Answer: Propionibacterium shaynanii.

SHORT ANSWER TYPE QUESTIONS

Q1. Why are flocs 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.

Q2. 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.

Q3. 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.

Q4. 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.

Q5. 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.

Q6. 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.

Q7. 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.

Q8. 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).

Q9. What is the chemical nature of biogas. Name an organism which is involved in biogas production? 

Answer: The chemical nature of Biogas is methane, \(\mathrm{CO}_2\) and \(\mathrm{H}_2\). Methanobacterium, a type of methanogen is employed for biogas production.

Q10. 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.

Q11. 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.

Q12. What are viruses parasitising bacteria called? Draw a well labelled diagram of the same.

Answer: Viruses parasitising bacteria are called bacteriophages.

Q13. 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.

Q14. 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

Q1. 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 microorganisms 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.

Q2. (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.

Q3. Draw a diagrammatic sketch of biogas plant, and label its various components given below: Gas Holder, Sludge Chamber, Digester, Dung + water chamber.

Answer: 

Q4. 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.

Q5.  (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.

Q6. 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 \(\mathrm{B}_{12}\). In our stomach too, the LAB play very beneficial role in checking disease causing microbes.