Chapter 8 : Microbes in Human Welfare

Class 12 Biology Chapter 8 : Microbes in Human Welfare Exercise Questions and Answers :

1. 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 : You would be surprised to know that we use microbes or products derived from them every day. A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and other lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contains millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin . In our stomach too, LAB play a very beneficial role in checking disease-causing microbes.

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

Answer : Microbes release gases during metabolism in various food production processes. In dosa and idli dough, bacteria perform lactic acid fermentation, generating carbon dioxide () gas, causing the dough to rise. Baker's yeast ferments bread dough, producing that leavens the bread. Toddy is made by fermenting palm sap using microbes, with being a byproduct. Microbes also ferment fish, soybeans, and bamboo shoots, releasing gases. Cheeses like Swiss cheese owe their large holes to production by Propionibacterium sharmanii, while Roquefort cheese derives its unique flavor from specific fungi used during ripening.

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

Answer : Lactic acid bacteria (LAB) are commonly found in milk, and they are used to make curd. During this process, LAB grow in milk and convert it into curd. They produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to fresh milk as an inoculum or starter contains millions of LAB. At suitable temperatures, these LAB multiply, converting milk to curd and improving its nutritional quality by increasing vitamin . In our stomach, LAB also play a beneficial role in checking disease-causing microbes.

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

Answer :

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

Answer : Microbes have played a major role in controlling diseases caused by harmful bacteria through the production of antibiotics, like penicillin, which can kill disease-causing bacteria. Beneficial microbes in our body and the environment compete with harmful bacteria, limiting their growth. Probiotic foods with beneficial bacteria help maintain a healthy balance in the gut, preventing harmful bacteria from taking over. In agriculture, microbes are used to control plant diseases caused by harmful bacteria. Additionally, microbes aid in bioremediation, cleaning up environments polluted by harmful bacteria and their byproducts .

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

Answer : Two species of fungi commonly used in the production of antibiotics are:

Penicillium chrysogenum: Used in the production of penicillin and other beta-lactam antibiotics.

Streptomyces spp.: A group of soil-dwelling bacteria with fungus-like characteristics, used to produce various antibiotics like streptomycin and tetracycline.

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

Answer :  Large quantities of wastewater are generated every day in homes, industries, cities, and towns. A major component of this wastewater is human excreta. This municipal wastewater is also called sewage.

Sewage can be harmful to us in several ways:

(i) Sewage may contain disease-causing pathogens like bacteria and viruses, which can lead to the spread of illnesses if not properly treated.

(ii) It can contaminate natural water bodies like rivers and lakes, harming aquatic life and making water unsafe for drinking or recreation.

(iii) Sewage can lead to the growth of harmful algae and deplete oxygen in water, causing harm to ecosystems.

(iv) It produces unpleasant odors and negatively impacts the aesthetics of an area, affecting the quality of life.

(v) Industrial sewage can contain toxic chemicals, heavy metals, and pollutants harmful to human health and the environment

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

Answer :  The difference between primary and secondary sewage treatment:

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

Answer : Yes, microbes, specifically methanogens, can be used to produce biogas, commonly known as gobar gas when derived from cattle dung. These bacteria thrive in anaerobic conditions and break down organic materials like cellulose found in dung. During this process, they produce methane () along with carbon dioxide () and hydrogen (). This methane can be collected and used as a source of energy for cooking, heating, or electricity generation, making it a sustainable and renewable energy option from organic waste.

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

Answer : Microbes, such as bacteria, fungi, and cyanobacteria, play a crucial role in reducing the need for chemical fertilizers and pesticides through biofertilization. Bacteria like Rhizobium fix atmospheric nitrogen, enriching the soil's nutrient content. Fungi, in symbiotic associations, absorb phosphorus from soil and benefit plant growth while also gaining nutrients. Cyanobacteria, like Anabaena and Nostoc, fix atmospheric nitrogen and enhance soil fertility, especially in paddy fields. Biofertilizers, derived from these microbes, replenish soil nutrients, reduce chemical fertilizer dependence, and promote sustainable and environmentally-friendly farming practices.

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 .

Answer : The BOD values and the likely labels for each water sample, assuming that river water is relatively clean :

So, the most polluted water sample is C, which is likely untreated sewage water, while A is the secondary effluent from the sewage treatment plant, and B is the relatively clean river water

12. 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, an immunosuppressive drug, is produced by the fungus Trichoderma polysporum. Statins, blood cholesterol-lowering agents, are commercialized and derived from the yeast Monascus purpureus. These microbes are the sources of these bioactive molecules used in medical treatments.

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

(a) Single cell protein (SCP)

(b) Soil                 

Answer :  (a) Single Cell Protein (SCP): Microbes, such as bacteria and fungi, are used to produce SCP through fermentation. They convert organic substrates into protein-rich biomass. SCP serves as a valuable protein source for animal feed and human consumption, addressing food security and resource sustainability.

(b) Soil: Microbes in soil play essential roles in nutrient cycling, breaking down organic matter, fixing nitrogen, and improving soil structure. They enhance plant growth, disease suppression, and biodegradation of pollutants, ensuring soil health and fertility, benefiting agriculture and the environment.

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

Answer : The arrangement of these items in decreasing order of importance for the welfare of human society, along with reasons are :

Penicillin: Penicillin is the most crucial because it's a life-saving antibiotic widely used to treat bacterial infections, significantly improving public health and saving lives.

Biogas: Biogas is essential for providing renewable and clean energy, reducing environmental pollution, and addressing energy needs in many parts of the world.

Curd: Curd provides essential nutrition and promotes gut health, contributing to overall well-being and food security.

Citric Acid: While citric acid has various industrial applications, its direct impact on human welfare is less significant compared to the others, as it is primarily used in commercial and industrial processes.

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

Answer : Biofertilizers enrich soil fertility by introducing beneficial microorganisms like bacteria, fungi, and cyanobacteria. These microbes form symbiotic associations with plants or live freely in the soil. For example, nitrogen-fixing bacteria like Rhizobium and Azospirillum convert atmospheric nitrogen into plant-usable forms. Mycorrhizal fungi enhance nutrient uptake, particularly phosphorus. Cyanobacteria, like Anabaena, fix atmospheric nitrogen. They improve soil structure, increase nutrient availability, and reduce the need for chemical fertilizers, promoting sustainable and fertile soils.