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Microbes in Human Welfare

Short Answer Type

71. Find out the role of microbes in the following and discuss it with your teacher.

(a) Single cell protein (SCP) (b) Soil.

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72. List three examples of antibiotics that are industrially viable. Give their source.

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

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74. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg / L, 8 mg / L, and 400 mg / 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 ?

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75. 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.

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Long Answer Type

76. Describe primary and secondary treatment of domestic sewage before it is released for reuse.

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77. Explain any one biological control of pests with examples.

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Short Answer Type

78. How do biofertilizers enrich the soil ?

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Long Answer Type

79.
You have been deputed by your school principal to train local villagers in the use of biogas plant. With the help of a labelled sketch explain the various parts of the biogas plant.

Biogas plant.

1. The plant consists of well-like underground tank made of bricks. This tank is called digester.

2. The roof of the digester is dome-shaped made of cement and bricks. The dome of the digester tank acts as a gas holder (or storage tank for biogas). Thus, the gas holder in this type of gas-plant is fixed.

3. There is a gas outlet at the top of dome for the supply of biogas.

4. On the one side of digester tank, there is a slopping inlet tank and on the other side there is a rectangular outlet tank, or overflow tank. Both these tanks are made of cement and bricks.

5. Mixing tank is connected with slopping inlet chamber (or tank) while outflow tank is connected with rectangular outlet chamber (or tank).

6. The inlet-chamber is for introducing fresh dung slurry into the main digester tank whereas the outlet chamber is for taking out spent dung slurry after extraction of biogas.

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