1. 3. The supernatant water is effluent sent

1. Mention the microbes groups and chemical infectious agents that cause diseases to human and other organisms? Ans. Microbes are—protozoa, bacteria, fungi, microscopic plants. Chemical agents (proteins) are—viruses, viroids, prions.

Q.2. Give examples to prove that microbes release gases during metabolism. Ans. (i) Production of C02 gas in dough for making foods such as dosa, idli, bread, swiss cheese etc. (i) Production of CO-, gas methane and hydrogen from the anaerobic sludge, gobar— the gas is also called biogas/gobar gas. Q.3.

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In which food would you find lactic acid bacteria? Mention some of their useful applications? Ans. Milk and curd. They convert the milk into curd. This increases the nutritional quality by increasing the Bp. The LAB also checks the disease causing microbes. Q.

4. Mention a few examples to use of microbes in household products Ans. 1. Lactobacillus in making of curd from milk. 2. Bacteria in making dough or dosa, idli.

3. Microbes in fermentation of palm caps to make toddy. 4.

Microbes-in making cheese. Q. 5.

What is sewage? In which way can sewage be harmful to us? Ans. The municipal waste water is called as sewage. It can cause water-borne diseases if the sewage mixes with water resources such as rivers and streams. Hence, sewage treatment before disposal is essential. Q. 6.

What is the key difference between primary and secondary sewage treatment? Ans. Primary sewage treatment:1. It involves the physical processes filteration and sedimentation. 2. During this small and large floating debris is filtered out followed by the sedimentation process that allows soil and small pebbles settle as bottom. 3. The supernatant water is effluent sent for secondary sewage treatment process.

Secondary sewage treatment: 1. It involves the physical process-aeration of effluent and the biological treatment of effluent with microbes. 2. Sedimentation of bacterial floes is done to aerobic sludge digesters for digestion. 3. The effluent from secondary treatments is released into natural water bodies such as rivers, streams. Q. 7.

What is activated sludge? How it is different from primary sludge? Ans. The sediment obtained from the settling of bacterial floes after reduced BOD of sewage water is called activated sludge. It is formed in secondary treatment process of sewage. It has microbes. Q. 8.

Do you think microbes can also be the source of energy? If yes, how? Ans. Yes. Microbes indeed can also be the source of energy. They can be used extensively to produce biogas/gobar gas from animal dung (gobar) that is used as fuel in rural areas. Q. 9. Microbes can be used to decrease the use of chemical fertilizers and pesticides.

Explain how this can be accomplished. Ans. Chemical fertilizers are the major cause of concern as they cause environmental pollution. The microbes can be of great help in enriching the soil of its nutrients. Such microbes are called biofertilisers. Such as bacteria (Azospirillum, Azotobacter) enrich the soil by adding nitrogen to it. Rhizobium is a symbiotic bacteria that helps the legumes to fix atmospheric nitrogen.

Certain bacteria help is controlling the pests. Such as Bacillus thuringiensis (Bt) when consumed by the butterfly larvae it releases toxins that kills the larvae. Q.

10. How is Bacillus thuringiensis (Bt) helpful to farmers? Ans. This bacteria also called Bt produces toxin in the gut of butterfly larvae. When the larvae feed on the leaves having bacterial spores sprayed by the farmer get infected and later are killed. In brassica and fruit trees, this controls the pest. Bt-cotton has been developed by genetic enginering. It has made the plant resistant to attack by the insect pests. Q.

11. What is mycorrhiza? How it is useful to plants? Ans. The association of fungus with its roots is called mycorrhiza. It helps in absorbtion ofphosphorous from the soil and passes it to plant. In addition to it, plant with this association becomes (a) resistant to root-borne pathogens, (b) tolerant to saline and drought condition. The result to overall increase in plant growth and development. Q.

12. 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 the three samples A, B and C were recovered 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? (NCERT) Ans. River water — 8 mg/L Label — A Secondary effluent — 20mg/L Label — B Untreated sewage water — 400 mg/L Label — C. Q. 13. 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. Ans. 1. Penicillin: It is an antibiotic. That helps to kill many bacteria that cause diseases. It helps to maintain health. 1.

Citric acid: It is a vitamin C. It helps to maintain the health of individual. Such as bleeding gums. 2. Curd: It is also a source of protein and keeps the health of the person. It has more nutritional value than milk. 3.

Biogas: It is the source of energy to rural area. It is obtained from animal dung (gobar). It reduces the environmental pollution.


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