Microbes in Human Welfare Chapter Chapter 8: NCERT Solutions for Class 12

Our Subject experts at SimplyAcad have provided the best solutions for Microbes in Human Welfare Class 12 to help students get their basics strong. It will benefit students in various ways as students can use them to learn how to approach the questions correctly, followed by a better understanding of the core concepts discussed in the chapter and many more. This compiled set of solutions also helps in strengthening the thinking ability of students and expects them to write more creative answers. Scroll below to access the entire solutions of the chapter.

Microbes in Human Welfare Class 12 Biology Class 8 Questions 1 to 5

Question 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 with the help of a microscope, which sample would you carry and why?

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. A small drop of curd consists of millions of bacteria. These can be observed easily under a microscope.

---

Question 2

Give examples to prove that microbes release gases during metabolism.

Solution:

Microbes release gases during metabolism; some examples are as follows:

(i) Methanobacterium observed in anaerobic sludge releases large amounts of methane along with hydrogen gas and carbon dioxide.

(ii) The process of fermentation of cheese, dough, and the production of beverages releases carbon dioxide. The microbes involved in the process are Propionibacterium shermanii, lactic acid bacteria, and Saccharomyces cerevisiae.

---

Question 3

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

Solution:

We can find lactic acid bacteria in curd. 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 improve the health of the gut.

---

Question 4

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

Solution:

Some Indian food made of wheat, rice, and Bengal gram are:

(i) Wheat: Bread, Bhatura, and Cake.

(ii) Rice: Idli, Dosa, and Uttapam.

(iii) Bengal gram: Dhokla and Khandvi.

---

Question 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 given below:

(i) Microbes are known to produce antibiotics which 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 widely used against lockjaw 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.

Microbes in Human Welfare Class 12 Biology Class 8 Questions 6 to 10

Question 6

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

Solution:

Several microbes produce antibiotics that kill other microbes which cause diseases. These antibiotics are typically acquired from fungi and bacteria. Two species of fungus that are used in the production of antibiotics are:

(i) Penicillin – the fungal source is Penicillium notatum.

(ii) Cephalosporin – the fungal source is Cephalosporium acremonium.

---

Question 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 away in drains and sewers. Sewage includes both solid and liquid wastes that are 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 of contaminating drinking water. Therefore, it is vital to treat sewage water by collecting and disposing of it properly.

---

Question 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 involves sedimentation and filtration.	The process used is the biological digestion of wastes.
Less complicated and relatively low-priced method of treatment.	It is a complicated process and is expensive.

---

Question 9

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

Solution:

Yes, microbes can certainly be a source of energy. Some bacteria, such as the Methanobacterium, 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 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 and used as a source of energy. The slurry that is used is removed from the outlet and used as fertilizer.

---

Question 10

Microbes can be used to decrease the use of chemical fertilizers 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 involve selecting advantageous microbes to help improve plant growth by supplying nutrients. 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 the soil with organic nutrients. Many species of cyanobacteria and bacteria have the potential to fix free atmospheric nitrogen.

A symbiotic bacterium, Rhizobium, is found in the root nodules of leguminous plants. Some free-living nitrogen-fixing bacteria are Azotobacter and Azospirillum, while Nostoc, Oscillatoria, and Anabaena are examples of nitrogen-fixing cyanobacteria. These biofertilizers are eco-friendly and cost-effective.

On the other hand, microbes can also serve as bio-pesticides to control insect pests in plants. Bacillus thuringiensis, a bio-pesticide, produces a toxin that kills 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, the 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 other arthropods and insects.

Microbes in Human Welfare Class 12 Biology Class 8 Questions 11 to 15

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 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 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 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, the greater the BOD of wastewater, the greater 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 is based on the principle that the highest BOD value corresponds to the most polluted water sample.

---

Question 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, are obtained from the yeast Monascus purpureus.

---

Question 13

Find out the role of microbes in the following and discuss it with your teacher.

(a) Single-cell protein (SCP)
(b) Soil

Solution:

(a) Single-cell protein (SCP)

(i) SCP refers to the harmless microbial cells that can be used as a protein substitute.

(ii) Some forms of microbial cells can be consumed as food enriched in minerals, proteins, fats, vitamins, and carbohydrates, such as mushrooms and yeast.

(iii) Methylophilus methylotrophus and Spirulina are cultivated on a large scale on materials like wastewater from potato processing plants, molasses, straw, animal manure, and sewage.

(b) Soil

(i) Microbes play a crucial role in preserving soil fertility.

(ii) They help form nutrient-rich humus through decomposition.

(iii) Several bacteria and cyanobacteria species can fix atmospheric nitrogen into a form usable by plants.

(iv) Symbiotic bacteria like Rhizobium are found in the root nodules of leguminous plants.

(v) Free-living nitrogen-fixing bacteria such as Azotobacter and Azospirillum and nitrogen-fixing cyanobacteria like Nostoc, Oscillatoria, and Anabaena are present in the soil.

---

Question 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.

Solution:

The following are arranged in decreasing order of importance, the first being the most important for the welfare of human society:

Penicillin > Biogas > Curd > Citric acid

Reason:

(i) Penicillin is an antibiotic that kills pathogens responsible for harmful diseases and infections, hence saving lives. Therefore, it is the most important.

(ii) Biogas is next as it serves as a non-polluting, clean fuel generated as a byproduct of sewage treatment. It can be used to cook food and as a source of energy in remote areas.

(iii) Curd has a high nutritional value, supplying vitamin B12. It helps maintain gut health by replacing harmful bacteria in the stomach with beneficial ones.

(iv) Citric acid is used as a food preservative, making it the last in order of importance.

---

Question 15

How do biofertilizers enrich the fertility of the soil?

Solution:

Biofertilizers involve selecting advantageous microbes that help in improving plant growth by supplying nutrients. Biofertilizers are living entities that are known to increase soil fertility. These are introduced into roots, seeds, and soil to make nutrients available, thus enriching the soil with organic nutrients. Many species of cyanobacteria and bacteria can fix free atmospheric nitrogen. Symbiotic bacteria like Rhizobium are found in the root nodules of leguminous plants. Free-living nitrogen-fixing bacteria like Azotobacter and Azospirillum and nitrogen-fixing cyanobacteria like Nostoc, Oscillatoria, and Anabaena are examples. These biofertilizers are eco-friendly and cost-effective.