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Class 12 Biology CH 10 Microbes in Human Welfare

NCERT Solutions For Class 12 Biology CH-10 Microbes in Human Welfare

1. Bacteria cannot be seen with the naked eye, 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:  Do it yourself

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

Ans: Examples that prove that microbes release gases during metabolism are as follows :

  • In swiss cheese formed due to the amount of CO2 released by the bacterium Propionibacterium sharmanii.
  • Dough, which is used for making dosa and idli is fermented by bacteria. The puffy appearance of dough is due to the production of CO2 by the fermentation process.

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

Ans: We can find lactic acid bacteria in curd, cheese, Paneer, etc. Some of the useful applications of these bacteria are:

(i) It causes an increase in the Vitamin B12 level of curd, thus increasing the nutritional value of curd

(ii) It can be used to ferment or culture food

(iii) They check the health of the gut

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

Ans: We can prepare many dishes through the fermentation process by using microbes. Some Indian food made of wheat, rice, and Bengal gram are:

(i) Wheat: Bread, Bhatura, and Cake are made of Wheat

(ii) Rice: Idli, Dosa, and Uttapam are made of Rice

(iii) Bengal gram: Dhokla and Khandvi are made of Bengal gram

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

Ans: Microbes play an important role in controlling diseases caused by harmful bacteria, some are:

(i) Microbes are known to produce antibiotics that can be used to treat harmful diseases such as leprosy, diphtheria, etc

(ii) Microbes produce antitoxins or antisera which act against a specific pathogen. Antisera is known to be widely used against lock jaw tetanus, diphtheria, etc

(iii) They produce antibodies that contain antitoxins and opsonins that check the occurrence of diseases namely, cholera, typhoid, smallpox etc

(iv) The design of antibiotics is such that they destroy bacteria by weakening their cell walls. This in turn weakens several immune cells (white blood cells) that enter the bacterial cell causing cell lysis. The process of destructing cells such as blood cells by bacteria is known as cell lysis.

(v) Penicillium notatum, a fungus, produces the chemical penicillin. It inhibits the growth of bacteria named Staphylococci in the body

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

Ans: Penicillium chrysogenum, P. notatum, produce penicillin and Cephalosporium produces cephalosporins.

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

Ans: Sewage is waste water release from household and industrial applications. It is harmful as
(i) it decreases flora mid fauna of H2O.
(ii) contamination of H2O/food/soil.
(iii) dissemination of pathogenic bacteria.

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


Primary sewage treatmentSecondary sewage treatment
It is the mechanical or physical removal of small and large substances from sewageIt includes the removal of organic matter by microbes
The process deployed is through sedimentation and filtrationThe process used is the Biological digestion of wastes
Less complicated and relatively low-priced method of treatmentIt is a complicated process and is expensive.

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

Ans: Yes, the microbes present in activated sludge are digested anaerobically to generate biogas i.e. by the release of inflammable biogas in the biogas plants, which is a source of energy.
Use of microbial culture for SCP (single cell protein).

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

Ans: Microbes can be used to decrease the use of chemical fertilizers and pesticides. This can be accomplished by the use of biofertilizers. The main source of biofertilizers are bacteria, fungi, and cyanobacteria. They can provide plant nutrients at a cheaper cost when compared with chemical fertilizers. e.g.
(i) Use of leguminous plant with Rhizobium.
(ii) Use of sulfur-fixing bacteria.
(iii) Use of hydrogen-fixing bacterium.

11. Three water samples namely river water, untreated sewage water, and secondary effluent discharged from a sewage treatment plant were subjected to the BOD test. The samples were labeled 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, and 8 mg/Land 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?

Ans: The sample with a BOD value of 400 mg/h is the most polluted and should be leveled as B —> untreated sewage river H2O will be —> less BOD —> 8 mg/L – sample A.
Untreated water —> 2° effluent BOD —>River water 400 —> 20 —> 8 and so should be labeled as sample C.

12. Find out the name of the microbes from which cyclosporin A (an immunosuppressive drug) and statins (blood cholesterol lowering agents) are obtained.

Ans: Cyclosporin A, an immunosuppressive drug is obtained from the fungus Trichoderma polysporum. Statins, a blood cholesterol-lowering agent, is obtained from the yeast Monascus purpureus.

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

The role of microbes in the following are as follows:

(a) Single-cell protein (SCP)

(i) It refers to harmless microbial cells that can be substituted for good proteins.

(ii) Some forms of microbial cells can be consumed as food enriched in minerals, proteins, fats, vitamins, and carbohydrates like how mushrooms are consumed and yeast is eaten by athletes as a source of protein.

(iii) Methylophilus methylotrophs and Spirulina are cultivated on large scale on materials comprising starch-like wastewater from potato processing plants, molasses, straw, animal manure, and sewage

(b) Soil

(i) The role of microbes is crucial in preserving the fertility of the soil

(ii) It helps in forming nutrient-rich humus by the phenomena of decomposition

(iii) Several bacteria and cyanobacteria species have the potential to fix atmospheric nitrogen to a form that can be used by plants

(iv) A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants

(v) Some free-living nitrogen-fixing bacteria, Azotobacter and Azospirillum, and some nitrogen-fixing cyanobacteria – Nostoc, Oscillitoria, and Anabaena are found here.

14. Arrange the following in 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: Curd: Less important for society – as it depends on individual use and has only nutritions value.
Citric acid: Industrial use, not for dissipation in the community.
Penicillin: Medicinal use of microbes, good for the health of society, commercially more usable.
Biogas: Most important for community welfare as
(i) it reduces excreta, waste from the community.
(ii) it produces inflammable gases, and can be used as an energy source.
(iii) it is a renewable source.
(iv) it has multidimensional utility.
(v) it is easily maintained and dissipated for the community purpose.
So,Penicillin > Biogas > Curd > Citric acid.

15. How do biofertilizers enrich the fertility of the soil?

Ans: Biofertilizers enrich the fertility of the soil by:
(i) replenishment of lost nutrients like N2, phosphorus, iron, and sulfur.
(ii) addition of required micronutrients and macronutrients.
(iii) making humus acid compost.
(iv) acting as scavengers.

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