NCERT Solutions for Class 12 Biology Chapter 8 - Microbes in Human Welfare
NCERT Solutions for Class 12 Chapter 8 are available for free download on Vedantu. All the concepts covered in the chapter are well-explained in these NCERT Solutions. You can download and refer to the NCERT Solutions for Class 12, Chapter 8 - Microbes in Human Welfare PDF from Vedantu for free. Everything you read in your high school serves as the foundation for your college education, and thus, your career afterward. Therefore, an accurate NCERT Solutions bank is an essential tool for performance-oriented study sessions.
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It serves as an easy tool to ensure your grasp on various topics, and remove any lingering doubts about the concepts. Since entrance exams start right after Class 12, preparation is the key to acing the exams with ease.
Microbes in Human Welfare Chapter at a Glance - Class 12 NCERT Solutions
Microbes in Human Welfare
- Microbes or microorganisms are small which are not visible to the naked eye because they have a size of 0.1 mm or less. They can therefore be seen only under the microscope.
Microbes are seen everywhere inside the soil, in all types of waters, in air, on dust particles, inside and outside our body as well as in plants and animals. They even occur in inhospitable environments where no other life form exists like in snow. In thermal vents or inside geysers (at temperature of 100° C), deep inside soil, highly acidic soil.
Microbes belong to a diverse group of organisms like bacteria, protozoa, fungi and microscopic plants. Most of these microbes can grow in nutritive media where they form colonies- bacteria and fungi. The colonies can be seen with the naked eye. They are useful in the study of various aspects of microorganisms.
Some other types of microorganisms are viruses, viroids and prions.
FAQs on NCERT Solutions for Class 12 Biology Chapter 8 Microbes In Human Welfare
1. According to the NCERT exercise for Chapter 8, what sample from home is ideal for demonstrating microbes under a microscope, and why?
The ideal sample to carry from home is curd. A single drop of curd contains millions of Lactic Acid Bacteria (LAB), such as Lactobacillus. These bacteria are easily visible under a microscope, making curd an excellent and readily available sample to demonstrate the presence of microorganisms as per the CBSE Class 12 Biology syllabus.
2. How can you prove that microbes release gases during metabolism, based on the examples in the NCERT solutions?
The release of gases by microbes can be demonstrated with these examples:
- Dough Fermentation: The puffed-up appearance of dough used for making dosa, idli, or bread is due to the production of carbon dioxide (CO₂) gas by bacteria or yeast during fermentation.
- Sewage Treatment: During the anaerobic digestion of sludge in a sewage treatment plant, microbes produce a mixture of gases, including methane (CH₄), hydrogen sulphide (H₂S), and CO₂, which collectively form biogas.
3. In which food product are Lactic Acid Bacteria (LAB) found, and what are their useful applications?
Lactic Acid Bacteria (LAB) are primarily found in curd. Their useful applications include:
- They convert milk sugar (lactose) into lactic acid, which helps in the coagulation and partial digestion of milk proteins to form curd.
- They improve the nutritional quality by increasing the Vitamin B12 content.
- In the human stomach, they help check the growth of disease-causing microbes.
4. What is the key difference between primary and secondary sewage treatment as per the NCERT methodology?
The key difference lies in the method of waste removal:
- Primary treatment is a physical process. It involves the removal of large and small solid particles from sewage through sequential filtration and sedimentation.
- Secondary treatment is a biological process. The primary effluent is treated with aerobic microbes, which consume the organic matter, thereby significantly reducing the Biochemical Oxygen Demand (BOD) of the water.
5. How do microbes play a major role in controlling diseases caused by harmful bacteria?
Microbes are the source of antibiotics, which are chemical substances that can kill or inhibit the growth of other disease-causing microbes. For example, the antibiotic Penicillin, obtained from the fungus Penicillium notatum, is used to treat numerous bacterial infections. These antibiotics often work by disrupting essential bacterial processes, such as the formation of the cell wall.
6. Which two species of fungus are used in the production of antibiotics?
As per the NCERT solutions for Class 12 Biology, two important species of fungus used to produce antibiotics are:
- Penicillium notatum (or P. chrysogenum), which produces the antibiotic Penicillin.
- Aspergillus species, from which other antibiotics have been derived.
7. What are statins and cyclosporin A, and which microbes are used to produce them?
The correct solution identifies the following:
- Statins are blood cholesterol-lowering agents. They are produced by the yeast Monascus purpureus.
- Cyclosporin A is an immunosuppressive agent, widely used in organ transplant patients. It is obtained from the fungus Trichoderma polysporum.
8. How do microbes function as a source of energy?
Microbes can be used to generate energy in the form of biogas. In a biogas plant, anaerobic bacteria called methanogens digest organic waste (like cow dung) in an oxygen-free environment. This process releases a mixture of gases, primarily methane (CH₄), which is a combustible fuel that can be used for cooking and lighting.
9. Explain how microbes help reduce the use of chemical fertilisers and pesticides.
Microbes can act as biofertilisers and biocontrol agents.
- As Biofertilisers: Bacteria like Rhizobium (in root nodules) and free-living bacteria like Azotobacter fix atmospheric nitrogen into the soil. Fungi like Glomus form mycorrhiza to help plants absorb phosphorus.
- As Biocontrol Agents: The bacterium Bacillus thuringiensis (Bt) is used to control butterfly caterpillars, and the fungus Trichoderma is effective against several plant pathogens, thus reducing the need for chemical pesticides.
10. A lab test on three water samples (A, B, C) recorded BOD values of 20 mg/L, 8 mg/L, and 400 mg/L. If the samples were from a river, secondary effluent, and untreated sewage, which label corresponds to which sample?
Biochemical Oxygen Demand (BOD) indicates the level of organic pollution. A higher BOD means more pollution. Based on the NCERT solution logic:
- Sample C (BOD 400 mg/L) is the most polluted and corresponds to untreated sewage water.
- Sample A (BOD 20 mg/L) is less polluted than sewage and corresponds to secondary effluent from a treatment plant.
- Sample B (BOD 8 mg/L) is the least polluted and corresponds to the relatively clean river water.
11. Why must a biogas plant operate as an anaerobic system?
A biogas plant must be anaerobic because the production of methane is carried out by methanogens, a group of strictly anaerobic bacteria. These microbes can only break down organic matter and produce methane in the complete absence of oxygen. If oxygen were present, aerobic microbes would thrive instead, producing carbon dioxide and water, and the methane generation process would stop.
12. How do microbial antibiotics like Penicillin specifically target bacteria without harming human cells?
Antibiotics like Penicillin exhibit selective toxicity by targeting structures unique to bacteria. Penicillin works by inhibiting the enzymes responsible for building the bacterial cell wall (made of peptidoglycan). This weakens the wall, causing the bacterium to lyse (burst) due to osmotic pressure. Since human cells lack a cell wall, Penicillin does not affect them, making it a safe and effective treatment for bacterial infections.
13. How do biofertilisers like Rhizobium and Mycorrhiza enrich soil fertility differently?
Both enrich soil fertility but through different mechanisms:
- Rhizobium is a bacterium that forms a symbiotic relationship with the roots of leguminous plants. It performs nitrogen fixation, converting atmospheric nitrogen (N₂) into ammonia (NH₃), a form the plant can directly use as a nutrient.
- Mycorrhiza is a symbiotic association between a fungus (like Glomus) and plant roots. The fungus does not fix nitrogen but extends its network of hyphae into the soil, vastly increasing the root's surface area for absorbing essential minerals, especially phosphorus.
14. According to the NCERT problem, why is Penicillin ranked as most important for human welfare, followed by Biogas, Curd, and Citric Acid?
The ranking is based on the scale and criticality of impact:
- Penicillin: As a life-saving antibiotic, it has revolutionised medicine and saved millions of lives from deadly bacterial diseases.
- Biogas: It provides a sustainable, non-polluting source of energy and helps in waste management.
- Curd: It is a highly nutritious food item with probiotic benefits.
- Citric Acid: While useful as a food preservative, its impact is less critical compared to the others.
15. What are the main topics covered in the NCERT solutions for Class 12 Biology, Chapter 8?
The NCERT solutions for this chapter provide step-by-step answers for problems related to key topics, including:
- Microbes in household products (curd, dough).
- Microbes in industrial products (antibiotics, beverages, enzymes).
- The process of sewage treatment (primary and secondary).
- Microbes in the production of biogas.
- The role of microbes as biocontrol agents and biofertilisers.
