MICROBES IN HUMAN WELFARE

NCERT EXERCISES

Question 1: Bacteria cannot be seen with the 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 under a microscope, which sample would you carry and why?

Answer: I will carry curd because it is full of bacteria. Moreover, curd is much safer, does not produce obnoxious smell and does not cause a disease.

Question 2: Give examples to prove that microbes release gases during metabolism.

Answer: Bread becomes fluffy due to carbon dioxide gas produced in the dough. One can get obnoxious smell from any big open drain. This smell comes because of formation of biogas.These examples show that microbes release gases during metabolism.


Question 3: In which food would you find lactic acid bacteria? Mention some of their useful applications.

Answer: Lactic acid bacteria are found in curd. By converting milk into curd, these bacteria make the milk healthier. It helps in increasing vitamin B12 in the stomach. It helps in countering many disease-causing microbes in stomach. It helps in balancing the gut flora.

Question 4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.

Answer: Nan, bhature (made from wheat flour), idli, dosa (made from rice flour) and pakoda (made from Bengal gram flour).

Question 5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

Answer: Many antibiotics are made from microbes. For example; Penicillin is made from a fungus called Penicillium notatum.. Antibiotics have immensely helped in fighting many diseases which were considered incurable around half a century back. Tuberculosis; which was once a dreaded disease is now completely curable; because of antibiotics.

Question 6: Name any two species of fungus, which are used in the production of the antibiotics.

Answer: Penicillium notatum and Streptomyces

Question 7: What is sewage? In which way can sewage be harmful to us?

Answer: Wastewater coming from households and offices is called sewage. It contains harmful microbes, and has the potential for spreading epidemics. It can end up polluting water bodies. It can also pollute the groundwater. Thus, sewage is highly harmful for us.


Question 8: What is the key difference between primary and secondary sewage treatment?

Answer: Primary treatment involves physical methods of separation of impurities from sewage. Secondary treatment involves biological methods of removal of impurities from sewage.

Question 9: Do you think microbes can also be used as source of energy? If yes, how?

Answer: We know that some microbes produce methane during metabolism and growth. Methane is highly inflammable gas and is a good fuel. Hence, microbes can also be used as source of energy. This can be done by making Biogas Plant, in which biological waste can be treated by microbes to produce biogas.

Question 10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

Answer: We know that chemical fertilizers and pesticides have many harmful effects. They end up polluting the soil and groundwater. Some harmful chemicals in them cause bioaccumulation at the top of the food chain. Hence, we need to find alternate means to control insect pests and to improve soil fertility. There are many microbes which help in nitrogen fixation in soil, i.e. Rhizobium and Cyanobacteria. There are microbes which help in fighting insect pests, e.g. Bacillus thuringiensis. These examples show that microbes can be used to decrease the use of chemical fertilizers and pesticides.

Question 11: 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 20mg/L, 8mg/L and 400mg/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: Sample C is most polluted. Label C is untreated sewage water, label A is secondary effluent and label B is river water.


Question 12: Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.

Answer: Cyclosporin is produced from Trichoderma polysporum (a fungus), and statins are produced from Monascus purpures (a fungus).

Question 13: Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP) (b) Soil.

Answer: (a) Spirullina, (b) Rhizobium

Question 14: 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: Biogas < Penicillin < Curd < Citric acid

Biogas can immensely help in reducing our dependency on fossil fuels. It will transform the economy if used in proper way.

Penicillin has helped and is helping in treating many difficult diseases, and has thus helped the mankind.

Curd is an important food and has been in use since time immemorial. It has many health benefits.

Question 15: How do biofertilisers enrich the fertility of the soil?

Answer: Organisms that enrich the nutrient quality of the soil are called biofertilisers. Bacteria, fungi and cyanobacteria are the main sources of biofertilisers. Some examples of biofertilisers are as follows:

Rhizobium bacteria live in symbiotic association with leguminous plants. These bacteria help in nitrogen fixation in soil. Azospirillum and Azotobacter are the free-living soil bacteria which help in nitrogen fixation.

Many members of the genus Glomus (fungi) form mycorrhiza, i.e. symbiotic association with plants. These fungi help the plant in absorption of phosphorus from soil.

Cyanobacteria serve as an important biofertiliser in paddy fields. Blue green algae also add organic matter to the soil and thus increase its fertility. Many biofertilisers are commercially available.


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