NCERT Class 12 Biology Solutions: Chapter 10 - Microbes in Human Welfare

May 10, 2019
NEET

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?

Solution: Curd can be used as a sample for the study of microbes. Curd contains numerous lactic acid bacteria (LAB) or Lactobacillus. A small drop of curd contains millions of bacteria, which can be easily observed under a microscope.

Give examples to prove that microbes release gases during metabolism.

Solution: The examples of bacteria that release gases during metabolism are:

  • Bacteria and fungi carry out the process of fermentation and during this process, they release carbon dioxide. Fermentation of sugar produces alcohol with the release of carbon dioxide and very little energy.
  • The dough used for making idli and dosa gives a puffed appearance. This is because of the action of bacteria which releases carbon dioxide.

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

Solution: Lactic acid bacteria can be found in curd. It is this bacterium that promotes the formation of milk into curd. Conversion of milk into curd increases the vitamin  content in curd. Lactic acid bacteria are also found in our stomach where it keeps a check on the disease-causing micro-organisms.

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

Solution:

Wheat:

Product: Bread, cake, etc.

Rice:  

Product: Idli, dosa

Bengal gram:

Product: Dhokla, Khandvi, Kadhi

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

Solution:

  • Antibiotics are medicines produced by certain micro-organisms to kill other disease-causing micro-organisms. These medicines either kill or stop the growth of disease-causing micro-organisms. Streptomycin, tetracycline, and penicillin are common antibiotics.
  • Example - Penicillium notatum produces chemical penicillin, which checks the growth of Staphylococcus bacteria in the body. Antibiotics are designed to destroy bacteria by weakening their cell walls. Which ultimately leads to lysis of cell wall and hence destruction of the pathogen.

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

Solution:

The species of fungus used in the production of antibiotics are:

Antibiotic

  • Penicillin
  • Cephalosporin

Fungus source

  • Penicillin notatum
  • Cephalosporium acremonium

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

Solution: Sewage is the municipal waste that is carried away in sewers and drains. It includes both liquid and solid wastes. It is rich in organic matter and microbes. Many of these microbes are pathogenic and can cause several water- borne diseases. Sewage water is a major cause of pollution of drinking water. Hence, it is essential that sewage water is properly collected, treated, and disposed.

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

Solution:

Primary sewage treatment

  • It is a mechanical process involving the removal of coarse solid materials
  • It is inexpensive and relatively less complicated

Secondary sewage treatment

  • It is biological process involving the action of microbes
  • It is very expensive and complicated process  

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

Solution: Yes, microbes can be used as a source of energy.

For example

Bacteria such as Methane bacterium is used for the generation of gobar gas or biogas. The generation of biogas is an anaerobic process in a biogas plant, which consists of a concrete tank (10−15 feet deep) with sufficient outlets and inlets. The dung is mixed with water to form the slurry and thrown into the tank. The digester of the tank is filled with numerous anaerobic methane producing bacteria, which produce biogas from the slurry. Biogas can be removed through the pipe which is then used as a source of energy, while the spent slurry is removed from the outlet and is used as a fertilizer.

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

Solution: Microbes play an important role in organic farming, which is done without the use of chemical fertilizers and pesticides. Bio-fertilizers are living organisms which help increase the fertility of soil. Biofertilizers are introduced in seeds, roots, or soil to mobilize the availability of nutrients. 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 ecofriendly.

Microbes can also act as bio-pesticides to control insect pests in plants. An example of bio-pesticides is Bacillus thuringiensis, which produces a toxin that kills the insect pests.

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: Biological oxygen demand (BOD) is the method of determining the amount of oxygen required by micro-organisms to decompose the waste present in the water supply. If the water sample is more polluted, then it will have a higher BOD value. Out of the above three samples, sample C is the most polluted since it has the maximum BOD value of 400 mg/L. After untreated sewage water, secondary effluent discharge from a sewage treatment plant is most polluted. Thus, sample A is secondary effluent discharge from a sewage treatment plant and has the BOD value of 20 mg/L, while sample B is river water and has the BOD value of 8 mg/L.

Hence, the correct label for each sample is:

Label: A, BOD Value: 20 mg/L, Sample: Secondary effluent discharge from a sewage treatment plant

Label: B, BOD Value: 8 mg/L, Sample: River water

Label: C, BOD Value: 400 mg/L, Sample: Untreated sewage water

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

Solution:

Drug: Cyclosporine – A, Function: Immune suppressive drug, Microbe: Trichoderma polysporum

Drug: Statin, Function: Blood cholesterol lowering agent, Microbe: Monascus purpureus

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): A single cell protein is a protein obtained from certain microbes, which forms an alternate source of proteins in animal feeds. The microbes involved can be algae, yeast, or bacteria. These microbes are grown on an industrial scale to obtain the desired protein. For example, Spirulina can be grown on waste materials obtained from molasses, sewage, and animal manures. It serves as a rich supplement of dietary nutrients such as proteins, carbohydrate, fats, minerals, and vitamins.

(b) Soil: Microbes play an important role in maintaining soil fertility. They also help in the formation of nutrient-rich humus by the process of decomposition. Many species of bacteria and cyanobacteria have the ability to fix atmospheric nitrogen into usable form. 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.

Related: NCERT Class 12 Biology solutions - Chapter 9 - Strategies for Enhancement in Food Production

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 order of arrangement of products according to their decreasing importance is:   Penicillin- Biogas − Citric acid − Curd

Penicillin is the most important product for the welfare of human society. It is an antibiotic, which is used for controlling various bacterial diseases. The second most important product is biogas. It is an eco-friendly source of energy. The next important product is citric acid, which is used as a food preservative. The least important product is curd, a food item obtained by the action of lactobacillus bacteria on milk  

How do biofertilizers enrich the fertility of the soil?

Solution: Bio-fertilizers are living organisms which help in increasing the fertility of the 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.

Example: Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants.          

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