NCERT Solutions for Class 12 Biology Chapter 10 – Microbes in Human Welfare – FREE PDF Download
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Revision Notes Class 12 Biology
NCERT Solutions Class 12 Biology
Answers of Biology NCERT Chapter 10 – Microbes in Human Welfare
Exercise Page No.189-190
Solution:
To demonstrate the presence of microbes with the help of a microscope, Curd is apt. It can be used as a sample as it contains plenty of Lactobacillus or lactic acid bacteria. These are the bacteria that produce acids which coagulate and digest the milk proteins. One drop of bacteria can consists of millions of bacteria. These can be observed easily under a microscope.
Solution:
Microbes release gases during metabolism, some examples are as follows:
- Methano bacterium observed in anaerobic sludge releases methane along with hydrogen gas and carbon dioxide
- The process of fermentation of cheese, dough and production of beverages releases carbon dioxide. The microbes involved in the process are Propionibacterium, lactic acid bacteria and Saccharomyces.
Solution:
We can find lactic acid bacteria in curd. Some of the useful applications of these bacteria are:
- It causes an increase in the Vitamin B12 level of curd, thus increasing the nutritional value of curd
- It can be used to ferment or culture food
- They check the health of the gut
Solution:
Some Indian food made of wheat, rice and Bengal gram are:
- Idli/Dosa traditional south Indian dishes are made from rice and Bengal gram. It is fermented by the action of bacteria
- Vada, an Indian dish is a popular snack or breakfast recipe made of Bengal gram. It is fermented by the action of bacteria
- One of the other food item that is extensively used is bread which is formed by the action of Saccharomyces cerevisiae, Baker’s yeast.
5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Solution:
Microbes play an important role in controlling diseases caused by harmful bacteria, some are:
- Microbes are known to produce antibiotics which can be used to treat harmful diseases such as leprosy, diphtheria etc
- Microbes produce antitoxins or antisera which acts against a specific pathogen. Antisera is known to be widely used against lock jaw tetanus, diphtheria etc
- They produce antibodies which contain antitoxins and opsonins that check the occurrence of diseases namely, cholera, typhoid, small pox etc
- 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 cell lysis is where cells such as blood cells are destructed by bacteria.
- Penicillium notatum, a fungus, produces 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 the antibiotics.
Solution:
Several microbes produce antibiotics,that kills other microbes which cause diseases. These medicines, antibiotics are typically acquired from fungi and bacteria. Two species of fungus that are used in the production of antibiotics are:
- Penicillin, fungal source is Penicillium notatum
- Cephalosporin, fungal source is Cephalosporium acremonium
7. What is sewage? In which way can sewage be harmful to us?
Solution:
The term sewage refers to the municipal waste material which is carried in drains and sewers. Sewage includes both solid and liquid wastes that is rich in microbes and organic matter.
Most of these microbes are pathogenic, i.e., they are capable of causing diseases such as water-borne diseases. This sewage water is one of the major causes to contaminate drinking water. Therefore, it is vital to treat sewage water, by collecting and disposing it.
8. What is the key difference between primary and secondary sewage treatment?
Solution:
The key differences are as follows:
| Primary sewage treatment | Secondary sewage treatment |
| It is the mechanical or physical removal of small and large substances from sewage | It includes the removal of organic matter by microbes |
| The process deployed is through sedimentation and filtration | The process used is Biological digestion of wastes |
| Less complicated and relatively low-priced method of treatment | It is a complicated process and is expensive. |
9. Do you think microbes can also be used as source of energy? If yes, how?
Solution:
Yes, microbes can certainly be a source of energy. Some bacteria such as the Methane bacterium can be used to generate biogas or gobar gas. In a biogas plant, under anaerobic conditions, biogas can be generated. The biogas plant consists of a concrete tank, with a depth of nearly 10-15 feet, comprising of adequate outlets and inlets. The gathered dung is mixed with water for the formation of slurry and flung into the tank. The tank consists of a digester, which is filled with plenty of anaerobic methane-producing bacteria. This produces biogas from the slurry. Biogas can be extracted through a pipe which can be used as a source of energy. The slurry that is used, is removed from the outlet and used as a fertilizer.
10. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Solution:
Organic farming is carried out without the use of any pesticides and chemical fertilizers. Microbes play a major role in organic farming. Bio-fertilizers involves picking advantageous microbes to help improve plant growth, by supplying nutrients as bio-fertilizers are living entities that are known to increase soil fertility. These are introduced into roots, seeds and soil in order to make nutrients available, thus enriching it with organic and soil nutrients. Some species of cyanobacteria and bacteria have the potential to fix the free atmospheric nitrogen.
A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants. Some free living nitrogen-fixing bacteria are Azotobacter and Azospirillium, while Nostoc, Oscillitoria, Anabena are some nitrogen-fixing cyanobacteria. These bio fertilizers are eco-friendly and cost effective.
On the other hand, microbes can also serve as bio-pesticides to check insect pests in plants. The Bacillus thuringiensis, a bio-pesticide, produces a toxin which kills the insect pests.
Withered bacterial spores are mixed with water and sprinkled in fields. These spores enter the gut of the larvae to release toxins, when larvae of various insects feed on the crops. Likewise, a free living fungi, Trichoderma, are found in the roots of higher plants, safeguarding them from pathogens. Another bio-pesticide, Baculovirus, is used as a biological control agent against many arthropods and insects.
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?
Solution:
BOD or the biochemical oxygen demand refers to the amount of oxygen which would be consumed if all the organic matter in one liter of water were to be oxidized by bacteria. This BOD test measures the rate of uptake of oxygen by microbes in a sample of water, hence BOD is said to be a measure of the organic matter found in water. Therefore, greater the BOD of waste water, the greater is the polluting potential.
Sample A with BOD 20mg/L can be assigned as the secondary effluent discharged from a sewage treatment plant.
Sample B with BOD 8mg/L can be assigned as river water
Sample C with BOD 400mg/L can be assigned as untreated sewage water.
This assignment in on the basis that the highest BOD value is the sample carrying the most polluted water.
12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
Solution:
Cyclosporin A, an immunosuppressive drug is obtained from the fungus Trichoderma polysporum. Statins, a blood cholesterol lowering agent, is obtained from 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
Solution:
The role of microbes in the following are as follows:
(a) Single cell protein (SCP)
- It refers to the harmless microbial cells that can be substituted for good proteins.
- 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.
- Methylophilus methylotrophus, Spirulina are cultivated on large scale on materials comprising starch-like waste water from potato processing plants, molasses, straw, animal manure and sewage
(b) Soil
- The role of microbes is crucial in preserving the fertility of soil
- It helps in forming nutrient-rich humus by the phenomena of decomposition
- Several bacteria and cyanobacteria species have the potential to fix atmospheric nitrogen to a form that can be used by plants
- A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants
- Some free living nitrogen-fixing bacteria, Azotobacter and Azospirillium, and some nitrogen-fixing cyanobacteria – Nostoc, Oscillitoria, and Anabena are found here.
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.
Solution:
The following are arranged in decreasing order of importance, the first being most important for welfare of human society.
Penicillin > Biogas > Curd > Citric acid
Reason:
- Penicillin is an antibiotic that kills pathogens which causes harmful diseases and infections hence saving lives. Therefore, it is the most important
- Biogas is the next in line as it serves as a non-polluting clean fuel which is generated as a byproduct of sewage treatment. It can be used to cook food, and as a source of lighting homes in remote areas
- Next is curd. It has a high nutritional value supplying vitamin B12. It helps maintain the health of the gut, and replaces harmful bacteria of the stomach with the beneficial ones.
- The last in order is citric acid. It is used as a food preservative.
15. How do biofertilisers enrich the fertility of the soil?
Solution:
Bio-fertilizers are living entities that are known to increase soil fertility, involving picking advantageous microbes to help improve plant growth, by supplying nutrients. These are introduced into roots, seeds and soil in order to make nutrients available, thus enriching it with organic and soil nutrients. Some species of cyanobacteria and bacteria have the potential to fix the free atmospheric nitrogen. A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants. Some free living nitrogen-fixing bacteria are Azotobacter and Azospirillium, while Nostoc, Oscillitoria, Anabena are some nitrogen-fixing cyanobacteria. These bio fertilizers are eco-friendly and cost effective.
