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

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

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

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

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 ?

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.

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

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

78. How do biofertilizers enrich the soil ?

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.

80. What advantages fungus and plants derives from symbiotic association called mycorrhiza ?