CBSE Class 12 Biology Microbes In Human Welfare Worksheet Set C

Very Short Answer Questions

Question:  What are biofertilisers? Give two examples. 
Answer. Biofertilisers are organisms that enrich the nutrients in the soil. e.g. Rhizobium, Azotobacter.

Question: What causes doughing of wheat flour?
Answer. Production of CO₂ gas during yeast fermentation of bacteria.

Question: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Answer. The major role of microbes in controlling the diseases is the ‘antibiotic production’. Antibiotics have been used against pathogenic bacteria, e.g., penicillin from Penicillium notatum, streptomycin from Streptomyces griseus, etc.

Question: How is the presence of cyanobacteria in the paddy fields beneficial to rice crop?
Answer. Cyanobacteria can fix atmospheric nitrogen. In paddy fields, the cyanobacteria act as an important biofertiliser. They also add organic matter to soil and increase its fertility.

Question: What for Nucleopolyhedroviruses are being used nowadays? 
Answer. Nucleopolyhedroviruses are used for the biological control of insect pests.

Question: Why are drinks like Whisky and Rum more intoxicating than wine?
Answer. This is because wine is produced without distillation whereas whisky and rum are produced by distillation of the fermented broth.

Short Answer Questions

Question: 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. (i) Penicillin: It is an antibiotic used in curing numerous bacterial diseases.
(ii) Biogas: It is a source of energy in rural areas, produced by anaerobic degradation of organic matter.
(iii) Curd: It is vitamin-rich milk preparation which is easily digested.
(iv) Citric acid: It is an organic acid used as preservative in juices, jams and jellies, etc.

Question: To reduce the percentage of population suffering from hunger and malnutrition, microbes are grown on a large scale to act as food supplements. Mention any two microbes used as food supplement and suggest their role. 
Answer. Spirulina and Methylophilus methylotrophus are used as food supplements.
Spirulina produces large quantities of food rich in protein, minerals, fats, carbohydrates and vitamins.
250 gm of Methylophilus methylotrophus produces 25 tonnes of protein per day.

Question: Name the blank spaces a, b, c and d given in the following table:

Answer. (a) Streptococcus
(b) Fungus
(c) Cyclosporin A
(d) Clostridium butylicum

Question: Write the binomials of two fungi and mention the products/bioactive molecules they help to produce.
Answer. 

Question: What is the key difference between primary and secondary sewage treatment?
Answer. The key difference between primary and secondary treatment of sewage is that primary treatment is the physical process of removing grit and floating debris while secondary treatment is a biological process that involves digestion of organic matter by microbes.

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

Question: Why are some molecules called bioactive molecules? Give two examples of such molecules.
Answer. Some molecules are called bioactive molecules, because microbes like bacteria or fungi are used in their production.
e.g., Citric acid produced by Aspergillus niger Butyric acid produced by Clostridium butylicum Ethanol produced by Saccharomyces cerevisiae Streptokinase produced by Streptococcus (Any two)

Question: (a) Patients who have undergone myocardial infarction are given clot buster. Mention the clot buster administered and its microbial source.
(b) A person recuperating from illness is advised to have curd regularly. Why?
Answer. (a) Streptokinase is the clot buster and its microbial source is Streptococcus.
(b) Curd contains Lactic Acid Bacteria, which play beneficial role in checking disease-causing microbes. It is also a source of vitamin B12.

Question: Give the binomials of two types of yeast and the commercial bioactive products they help to produce. 
Answer.

Question: Name the source of statin and state its action on the human body. 
OR
Name a microbe used for statin production. How do statin lower blood cholesterol level?
Answer. Statin is produced by the yeast Monascus purpureus. It acts as a blood-cholesterol lowering agent,by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

Question: Mention the importance of Lactic acid bacteria to humans other than setting milk into curd.
Answer. Lactic acid bacteria increase vitamin B12 absorption and also checks disease-causing microbes.

Question: 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 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.
Ladybirds used to control aphids and dragonflies used to control mosquitoes.

Long Answer Questions

Question: (i) List the components of biogas.
(ii) What makes methanogens suitable for biogas production?
Answer. (i) Biogas is a mixture of inflammable gases like methane, carbon dioxide and hydrogen.
(ii) Methanogens grow anaerobically and help in breakdown of cellulosic material to produce large amount of methane, carbon dioxide and hydrogen and so it is suitable for biogas production.

Question: Explain the function of “anaerobic sludge digester” in a sewage treatment plant.
Answer. Anaerobic sludge digester has anaerobic bacteria that digests the aerobic bacteria and fungi present in the sludge. During the digestion these bacteria produce mixture of gases such as methane, H₂S and CO₂ (biogas).

Question: How can sewage be used to generate biogas? Explain.
Answer. When biochemical oxygen demand (BOD) of sewage is reduced, effluent is passed into a settling tank for bacterial flocs to settle down. The sediment is called activated sludge. Activated sludge is pumped into anaerobic sludge digesters. In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in the sludge producing a mixture of gases which form the biogas.

Question: (a) Why are the fruit juices bought from market clearer as compared to those made at home?
(b) Name the bioactive molecules produced by Trichoderma polysporum and Monascus purpureus. 
Answer. (a) The fruit juices bought from market are clearer because they have been clarified by pectinases and proteases.
(b) Trichoderma polysporum: Cyclosporin A Monascus purpureus: Statins

Question: Explain the different steps involved during primary treatment phase of sewage. 
Answer. Primary treatment or physical treatment
- It is the physical removal of large and small particles from sewage.
- First, the floating debris is removed by sequential filtration by passing through wire mesh screens.
- Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant is the effluent.
- The effluent is taken for secondary treatment.

Question: (a) Name the category of microbes occurring naturally in sewage and making it less polluted during the treatment.
(b) Explain the different steps involved in the secondary treatment of sewage. 
Answer. (a) Aerobic microbes
(b) Secondary treatment or biological treatment
- Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.
- Useful aerobic microbes grow rapidly and form flocs.
- Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.
- The growing microbes consume organic matter and thus reduce the biochemical oxygen demand (BOD).
- When BOD of sewage has reduced, the effluent is passed into settling tank.
- Here, the bacterial flocs settle and the sediment is called activated sludge.
- A small part of the sludge is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digesters.
- In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in sludge producing mixture of gases such as methane, hydrogen sulphide (H₂S) and CO₂, which form the biogas.
- Effluent is now released into rivers and streams.