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

Q1. 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 with the help of a microscope, which sample would you carry and why?

Answer:

To demonstrate the presence of microbes with the help of a microscope, the best sample we can carry is curd. Curd contains lactic acid bacteria(LAB), such as Lactobacillus and is safe. A small portion of curd contains millions of bacteria, which can easily be observed under the microscope.

Q2. Give examples to prove that microbes release gases during metabolism.

Answer:

There are many examples where we find that microbes release gases during metabolism:

• The dough that is used for making foods such as dosa and idli is fermented by bacteria. The puffed appearance of dough is due to the production of CO2 gas.

• The dough that is used for making bread, is fermented by using baker’s yeast(Saccharomyces cerevisiae).

Q3. In which food would you find lactic acid bacteria? Mention some of their useful applications.

Answer:

• Lactic acid bacteria grow in milk and convert it to curd. Besides this, there are other applications of lactic acid bacteria given below:

• It improves the nutritional quality of curd by increasing the amount of vitamin B12.

• In our stomachs, too, the LAB plays a very beneficial role in checking disease-causing microbes.

Q4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve the use of microbes.

Answer:

Traditional Indian foods made of wheat, rice, and Bengal gram are:-

• Wheat- Bread, Bathura, and cake are prepared from wheat

• Rice - Dosa and idli involve the use of microbes.

• Bengal gram- Dhokla and khandvi are made from the Bengal gram

Q5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

Answer:

Microorganisms have several characteristics that make them ideal organisms for the production of various products ,including medicines, vaccines, and antibiotics that help in controlling diseases caused by harmful bacteria, which are given below:

• Many medicines like Ergot, Cyclosporin A, and Statins are produced from the fungus and bacteria which are used to induce uterine contractions, immunosuppressive agents, and blood cholesterol lowering agents respectively.

• Penicillin, Cephalosporins, Streptomycin, Erythromycin etc. Antibiotics are prepared from microbes for the treatment of diseases like pneumonia, cough, diphtheria, leprosy, etc.

• Inactivated strains of microbes are used for producing vaccines.

Answer:

Microorganisms possess several characteristics and are used in various fields, one of which is the important field where microbes are used in the production of antibiotics. Two species of fungus which are used in the production of antibiotics are:-

1) Penicillin - It's the first antibiotic to be discovered from the fungus Penicillium notatum.

Q7. What is sewage? In which way can sewage be harmful to us?

Answer:

Large quantities of wastewater are generated every day in cities. A major component of this wastewater is human excreta. This municipal wastewater is called sewage. It contains a large amount of organic matter and microbes.

Hence, proper sewage disposal is of prime importance; otherwise, untreated sewage, if disposed of in water bodies results in waterborne diseases such as malaria and dengue and also causes depletion of dissolved oxygen in the water.

Q8. What is the key difference between primary and secondary sewage treatment?

Answer:

The differences between the primary and secondary treatment of sewage are as follows:

Answer:

Several microbes have been found helpful in the solution of energy crises. Synthetic fuels produced by the activity of microbes, including ethanol, methane, hydrogen, and hydrocarbons

Gasohol- Gasohol is a mixture of 90% gasoline and 10% alcohol and is used in several countries to combat the energy shortage.

Production of Biogas- Biogas is a mixture of gases containing mainly methane produced by microbial activity. Livestock waste is used for the generation of biogas through microbial fermentation.

Answer:

Chemical fertilizers and pesticides are made up of a few minerals, thus making the soil toxic and also exploiting its nutrients. To overcome these problems, the use of biofertilizers is being encouraged. Biofertilizers are organisms that enrich the nutrient quality of the soil. They promote growth by increasing the supply or availability of primary nutrients to the plant. They mostly include nitrogen-fixing microorganisms. Some of them are given below:

Legume-Rhizobium symbiosis- Certain nitrogen-fixing bacteria example rhizobium live in symbiosis where the legume provides carbohydrates to the bacteria. rhizobium not only increases the production of crops but also leaves a fair amount of nitrogen in the soil, which benefits the crop.

Another example of this type of symbiosis is the Azolla-Anabaena symbiosis. Apart from them Azotobacter and Azospirillum are free-living bacteria that fix nitrogen and make it available for crop plants.

Answer:

Biological oxygen demand(BOD) is a measure of the organic matter present in the water. The greater the BOD of wastewater, the more its polluting potential.

• So, according to this, Sample C, having BOD 400mg/,L is the most polluted, and it's the untreated sewage water.

• Secondary discharge from a sewage treatment plant can be labeled as Sample B, which is less polluted than Sample C

• River water is relatively clean, so it can be labeled as Sample B, as sample B has the minimum amount of BOD.

Q12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.

Answer:

Cyclosporin A is produced by the fungus Trichoderma polysporum which is an immunosuppressive drug and statins from the yeast, Monascus purpureus which are blood cholesterol-lowering agents.

Q13. Find out the role of microbes in the following

(a) Single cell protein (SCP)

Answer:

1. Single-cell protein

• SCP is a microbial biomass that can be used as a food additive. Microbes used for the production of SCP include algae, bacteria, yeasts, and fungi.

• Because of their rapid growth and high protein content.

• The production of SCP does not depend upon climatic factors and the cost is also very low.

Q13. Find out the role of microbes in the following

(b) Soil

Answer:

Soil

• The microbes present in the soil increase the fertility of the soil by decomposing organic matter.

• The bacteria Rhizobium lives symbiotically in the nodules of the roots of leguminous plants fixing atmospheric nitrogen into organic forms, which is used by the plant as a nutrient.

• Similarly, some free-living bacteria in the soil like Azospirillum and Azotobacter) fix atmospheric nitrogen, thus enriching the nitrogen content of the soil.

Q14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare ofhuman society. Give reasons for your answer.

Biogas, Citric acid, Penicillin and Curd

Answer:

• Penicillin: Penicillin is the first antibiotic to be discovered, an effective antibiotic to treat deadly diseases

• Biogas: a mixture of gases (majorly containing methane) produced by the microbial activity on excreta (dung) of cattle, an eco-friendly source of energy particularly in rural areas.

• Curd: a portion of nutritious and easily digestible food for all age groups obtained from milk by the action of lactic acid bacteria (LAB).

• Citric acid: synthetically produced by microbial transformations and used mainly as a preservative of food items.

Q15. How do biofertilisers enrich the fertility of the soil?

Answer:

• Biofertilizers are organisms that enhance the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.

• Rhizobia bacteria live in a symbiotic association on the roots of leguminous plants. These bacteria fix atmospheric nitrogen into organic forms, which are used by the plant as a nutrient.

• Other bacteria like Azospirillum and Azotobacter can also fix atmospheric nitrogen while free-living in the soil, thus enriching the nitrogen content of the soil and improving its quality.

• Cyanobacteria (e.g., Anabaena, Nostoc, etc.) can also fix atmospheric nitrogen. In paddy fields, cyanobacteria add organic matter to the soil and increase its fertility.