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NCERT Solutions for Class 12 Biology Chapter 10 - Strategies for Enhancement in Food Reproduction

Aakash NCERT Solutions for Chapter 10 of Class 12 Biology talks about Microbes which are also referred to as micro-organisms or microscopic organisms as they can only be seen under a microscope. Being tiny living creatures, they are invisible to the naked eye and are present all around us, in air, water, soil, and so on.

Q1. Bacteria cannot be seen with 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: If I have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a micro cope, then in order to demonstrate the presence of microbes, we can take curd from our homes as curd contains millions of bacteria.

Q2. Give examples to prove that microbes release gases during metabolism.
Answer: When any bacteria grow on any material, it uses that material as the substratum to acquire food and starts metabolizing that material to release some products. For example, the puffed appearance of dough of dosa is due to the release of gases like CO2 by the bacteria growing on them. Large holes on Swiss cheeses are also due to the release of gases produced by bacteria growing on them.

Q3. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Answer: Lactic acid bacteria (LAB) is found in curd. The useful applications of LAB are as follows:
1. These bacteria can convert milk into curd.
2. LAB is also found in our stomach to check the growth of harmful bacteria in the stomach.
3. LAB increases the amount of vitamin B12 in curd. Thus, it makes curd nutritious.

Q4. Name some traditional Indian foods made of wheat, rice, and Bengal gram (or their products) that involve the use of microbes.
Answer: Indian food made of Wheat- Bread, bhatura, cake Indian food made of rice- Idli, hdoa, uttapam Indian food made of Bengal gram- Dhokla, Khandvi.

Q5. In which way do microbes play a major role in controlling diseases caused by harmful bacteria?
Answer: Role of microbes in controlling diseases caused by harmful bacteria:
Microbes are used to produce antibiotics. Antibiotics are chemical substances that are obtained from microorganisms and that kill other microorganisms like bacteria. The first antibiotic was penicillin and it was obtained from the fungus Penicillium notatum. Penicillin acts by degrading the cell wall of bacteria.

Q6. Name any two species of fungus, which are used in the production of antibiotics.
Answer: Penicillium notatum and Penicillium chrysogenum are used for preparing Penicillin.

Q7. What is sewage? In which way can sewage be harmful to us?
Answer: The municipal wastewater that is drained into sewers and drains is known as sewage. It contains a large amount of organic matter, microbes, human excreta, etc. When sewage is not treated properly, it degrades the quality of water and acts as a breeding site for mosquitoes. This may lead to diseases like dengue, malaria, etc in nearby communities. Thus sewage can be harmful to us.

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:

Primary sewage treatment

Secondary sewage treatment

Primary sewage treatment is a mechanical process that removes solid waste materials.

Secondary sewage treatment is a biological process in which waste materials are enzymatically treated by bacteria and other microbes.

It is a less expensive and simple process.

It is an expensive and complicated process.

Q9. Do you think microbes can also be used as a source of energy? If yes, how?
Answer: Yes, microbes can be used as sources of energy. For example, we know that various microbes produce different types of gases as their end products. One such gas is biogas. It is a mixture of gases produced by microbes and is used as a fuel. Similarly, some anaerobic bacteria which grow on cellulosic materials produce gases like methane, hydrogen gas, and CO 2 . Thus, we can say that microbes can be used as a source of energy.

Q10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Answer: Generally, farmers use chemical fertilizers and pesticides in their fields. However, these chemic l-b sed fertilizers and pesticides have deleterious effects on us. They tend to pollute the environment including soil and nearby water bodies. The fruits, vegetables, and grains are grown in fields in chemical fertilizers and pesticides, the chemicals get incorporated in them and they become toxic for animals and humans. Thus, farmers need to find more environmentally friendly methods to control pests and fertilize the soil.
Microbes as biocontrol agents: These are microbes or other biological organisms that can be used to control pests and
parasite populations in fields. For example, the Bt toxins of Bacillus thuringiensis are used to control lepidopteran insects. Trichoderma is free-living fungi that are very common in the root systems and control several plant pathogens. Baculoviruses are also pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications.
Microbes as biofertilizers: Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources include bacteria, fungi, and cyanobacteria. The root nodule formed by Rhizobium bacteria on the root of leguminous plants increases the nitrogen level of soil, necessary for various metabolic processes. Azotobacter and Azospirillum are free-living bacteria that live in soil and fix atmospheric nitrogen into organic forms. Cyanobacteria such as Nostoc, Anabaena are autotrophic microbes found in aquatic and terrestrial environments that fix atmospheric nitrogen.

Q11. Three water samples namely river water, untreated sewage water, and secondary effluent discharged from a sewage treatment plant were subjected to a 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, 8 mg/L, and 400 mg/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: BOD means biochemical oxygen demand. It refers to the amount of oxygen consumed if all organic matter in 1 ltr of water is oxidized by bacteria. BOD tests measure the rate of update of oxygen by microorganisms in the water sample. The greater the value of BOD more is the polluting potential. Out of the three samples mentioned above, secondary effluent has the highest BOD value, so it is the most polluted. So, the correct labeling will be:
a. Secondary effluent
b. River water
c. Untreated sewage water.

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 – Trichoderma polysporum (fungus) and Statins – Monascus purpureus (yeast)

Q13. Find out the role of microbes in the following
(a) Single-cell protein (SCP)
Answer: Microorganisms like bacteria, yeast, etc can be cultured on a large scale in the fermenters. They can be treated in many ways, dried, and used as a food source or animal feed. These microorganisms that can be used as potential sources of proteins for animals and humans are called single-cell proteins. SCP is rich in proteins and can be produced in laboratories.
The major advantage of SCP is as follows:
1. The production of SCP does not depend upon climatic factors.
2. The microorganism grows at a very fast rate and requires very little space.
3. The cost of production of SCP is very low.
4. Microorganisms used as substrates are otherwise pollutants so it also reduces pollution.
(b) Soil
Answer: Microbes decompose complex organic debris into a dark amorphous substance called humus and degradation products can be used as manure to increase the fertility of the soil. The manure can loosen the soil and increase aeration in soil. It contains many organic substances which are easily assimilated by plants. Some microbes are used for enriching soil fertility. Microorganisms like Azotobacter and Rhizobium can be used as nitrogen fertilizers. Thus, it can be said that microbes play an important role in improving the quality of the soil.

Q14. 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: These can be arranged as Penicillin - Biogas- Curd- Citric acid. Penicillin is an antibiotic that is used to cure many diseases like pneumonia. Thus it should be the most important. Biogas serves as a source of clean fuel, so it is the second most important. Curd comes next which is a nutritious milk product. Citric acid is used in the food processing industry. Thus, it is last on the list.

Q15. How do biofertilizers enrich the fertility of the soil?
Answer: The term biofertilizer is used for microorganisms that bring nutrient enrichment and minimize the environmental hazards of chemical fertilizers. These fertilizers increase the physical and chemical structure of soil like buffer capacity and water holding capacity of the soil. Biofertilizers can be introduced into seeds, roots, or soil in order to mobilize the desired nutrient. Rhizobium is a biofertilizer that is introduced in roots and fixes nitrogen for the plants. Similarly, Cyanobacteria like Nostoc, Anabaena are also used for fixing nitrogen.

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