Biology 12 Microbes In human Welfare Chapter 10 – Exercise

Q 1. Bacteria can’t 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?
Ans 1. The common household product that shows the presence of bacteria is curd. Milk is converted to curd by lactic acid bacteria (LAB).
Q 2. Give examples to prove that microbes release gases during metabolism.
Ans 2. The best examples that microbes release gases during metabolism are the pffed up appearance of dough used for making ‘dosa’ idli and bread.
Q 3. In which food would you find lactic acid bacteria? Mention same of their useful applications.
Ans 3. Lactic acid bacteria occur in curd. These bacteria convert lactose sugar into lactic acid. They also improve the nutritional quality of curd by increasing vitamin B12. Lactic acid bacteria are also found in our stomach where they check disease-causing microbes.
Q 4.name some traditional Indian food made of wheat, rice and Bengal gram (or their products) which involve using microbes.
Ans 4. Dosa and Idli.
Q 5. In which way microbes have played major role in controlling diseases caused by harmful bacteria?
Ans 5. Microbes are the major source of antibiotic production. The antibiotics are used in controlling diseases caused by harmful bacteria.
Q 6. Name any two species of fungus, which are used in the production of antibiotics.
Ans 6. Penicillium notatum and Aspergillus fumigatus.
Q 7. What is sewage? In which way can this be harmful for us?
Ans 7. Sewage is municipal waste water (both liquid and solid wastes) which is carried off in sewages.
Proper sewage disposal is of prime importance nowadays because untreated sewage if disposed in river and other water bodies leads to following-
i. It results in dissemination of water-borne diseases caused by microorganisms.
ii. It may cause depletion of dissolved oxygen in water. Reduction in oxygen availability may kill aerobic aquatic organisms.
iii. Untreated sewage produces offensive odour.
Q 8. What is the difference between primary and secondary sewage treatment?
Ans 8.
Primary sewage treatment
Secondary sewage treatment
1. It is a physical method of treatment
2. It involves in removal of large particles and floating materials such as leaves, papers, rags, solids such as sand, grit and oily substances
3. It makes the used of sedimentation and filtration process
4. It is relatively simple and less time consuming process
1. It is a biological method of treatment
2. It involves the removal of fine suspended and dissolved organic matter.
3. It makes the use of aerobic or anaerobic biological units
4. It is relatively complex and takes a long time for its completion.
Q 9. Do you think microbes can also be used as source of energy? If yes, how?
Ans 9. Yes, the microbes present in activated sludge are digested anaerobically to generate an inflammable biogas which is used as source of energy.
Q 10. Microbes can be used to lessen the burden of use of chemical and pesticides. Explain how this can be accomplished.
Ans 10. Fertility of soul is very important from view point of an agriculturist. The fertility of soil depends not only on its chemical composition but also on the quality and quantity of useful microbes present in it. Moreover, if the composition of the soil is not upto the mark and poor in fertility, materials of biological origin are added into it to improve and maintain its fertility. These biological organisms are microbes which act as bio fertilizers and lessen the burden of use of chemicals. There are microbes which act as bio pesticides. If these bio-pesticides are applied in agricultural fields, they can reduce the burden of chemical pesticides.
Q 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 20 mg/l, 8mg/l, and 400 mg/l respectively. Which sample of water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
Ans 11. Sample A, having BOD 20mg/l, is secondary effluent discharged from a sewage treatment plant.
Sample B, having BOD 8mg/l, is river water.
Sample C, having BOD 400mg/l, is untreated sewage water.
Q 12. Name the microbes from which cyclosporine A (an immunosuppressive drug) and statins (blood cholesterol lowering agents) are obtained.
Ans 12.
1. Cyclosporin A is obtained from the fungus – Trichoderma Polysporum.
2. Statins are produced by yeast Monascus purpureus.

Q 13. Find out the role of microbes in the following and discuss it with your teacher.
i. Single cell protein
ii. Soil
Ans 13.
i. Single cell protein (SCP): The fact that protein deficiency is becoming alarming as a large number as a large number of human population is suffering from hunger and malnutrition and the protein and vitamins can be obtained from moulds (e.g., mushrooms, yeasts etc.), led to the idea to produce edible proteins in a large scale from micro-organisms. Productions of edible proteins on a large scale by means of microorganisms for animal and human nutrition is called single cell protein.
ii. Soil: the most favorable habitat of microorganisms is soil where they occur in abundance. Their greatest amount (1000000 per cu cm) is found generally in the top layer of the soil up to a depth of 5 to 15 cm. the microorganisms present in soil increase the fertility of soil by decomposing organic matter. They also fix atmospheric N2 into usable forms.
Q 14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answers.
Biogas, Citric acid, Penicillin and Curd.
Ans 14.
1. Penicillin – it is used to obtain antibiotic which a used to cure many bacterial diseases.
2. Biogas – it is an ecofriendly source of energy particularly in rural areas.
3. Citric acid – it is used mainly as preservative of many food items.
4. Curd – it is easily digestible food.
Q 15. How do bio-fertilizers enrich the fertility of the soil?
Ans 15. Bio-fertilizers are living organisms which help in increasing the fertility of soil. It involves the selection of beneficial micro-organisms that help in improving plant growth through the supply of plant nutrients. These are introduced to seeds, roots, or soil to mobilize the availability of nutrients by their biological activity. Thus, they are extremely beneficial in enriching the soil with organic nutrients. Many species of bacteria and cyanobacteria have the ability to fix free atmospheric nitrogen. Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effective and eco-friendly.

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