Chapter 10: Microbes in Human Welfare – Long Answer Type Questions

CBSE Class 12 Biology Long Answer Questions (NCERT): Microbes in Human Welfare

Course & Examination Details

Course: CBSE Class 12 Biology
Unit: Unit III – Biology and Human Welfare
Chapter: Chapter 10 – Microbes in Human Welfare
Prescribed Textbook: NCERT Biology Class XII
Examination: CBSE Class 12 Board Examination
Question Type: Long Answer Type
Answer Length: 120–150 words
Syllabus Alignment: Strictly as per NCERT

Section A: Microbes in Household Products

Q1. Explain the role of microbes in the preparation of household food products.

Answer:
Microbes play a crucial role in the preparation of several traditional household food products through fermentation. Lactobacillus converts lactose in milk into lactic acid, leading to curd formation. This process improves digestibility, enhances flavour, increases vitamin B12 content, and inhibits harmful microbes. In idli and dosa batter, lactic acid bacteria and yeast ferment carbohydrates, releasing carbon dioxide that makes the batter light and fluffy. Yeast (Saccharomyces cerevisiae) is used in bread making, where it produces carbon dioxide causing dough to rise. Fermented foods are nutritious, easy to digest, and beneficial for gut health, making microbes essential for household food processing.

Q2. Why are fermented foods considered beneficial for human health?

Answer:
Fermented foods are considered beneficial because they contain useful microbes that improve digestion and nutritional value. During fermentation, microbes break down complex substances into simpler forms, making food easier to digest. They enhance the availability of vitamins, especially B-complex vitamins, and improve flavour and texture. Fermented foods like curd also contain probiotics, which maintain gut health by suppressing harmful microorganisms. Additionally, fermentation increases shelf life and prevents food spoilage. Thus, fermented foods contribute significantly to better digestion, improved immunity, and overall health.

Section B: Microbes in Industrial Products

Q3. Describe the role of microbes in the production of antibiotics.

Answer:
Antibiotics are chemical substances produced by certain microorganisms that inhibit or kill disease-causing microbes. Microbes such as fungi and bacteria are cultured on a large scale in bioreactors under controlled conditions. Penicillin, produced by Penicillium, was the first discovered antibiotic and revolutionised medical treatment of bacterial infections. Other antibiotics like streptomycin are produced by Streptomyces. Antibiotics are purified and used to treat diseases such as pneumonia, tuberculosis, and typhoid. The use of microbes in antibiotic production has greatly reduced mortality and improved healthcare standards worldwide.

Q4. Explain how microbes are used in the production of alcoholic beverages.

Answer:
Alcoholic beverages are produced using the process of fermentation carried out by yeast, mainly Saccharomyces cerevisiae. Yeast converts sugars present in fruits or grains into ethanol and carbon dioxide under anaerobic conditions. Beverages like wine and beer are produced directly by fermentation, while spirits such as whisky and rum are obtained by distillation of fermented products. The type of raw material and fermentation conditions determine the quality and alcohol content of the beverage. Microbial fermentation has been used for centuries and remains a major industrial application of microbes.

Q5. Discuss the industrial importance of enzymes produced by microbes.

Answer:
Microbial enzymes are widely used in industries because they are efficient, specific, and eco-friendly. Proteases, lipases, and amylases are used in detergents to remove protein, fat, and starch stains. Pectinases and proteases are used to clarify fruit juices. Lipases are also used in the dairy industry for cheese production. Enzymes produced by microbes work under mild conditions and are biodegradable, making them environmentally safe. Their use reduces energy consumption and chemical pollution, highlighting the industrial importance of microbial enzymes.

Q6. Explain the significance of bioactive molecules produced by microbes.

Answer:
Bioactive molecules are compounds produced by microbes that have important physiological effects on humans. Cyclosporin A, produced by Trichoderma polysporum, is used as an immunosuppressive drug in organ transplantation to prevent rejection. Statins, produced by Monascus purpureus, lower blood cholesterol levels by inhibiting cholesterol synthesis. These molecules play a vital role in modern medicine by preventing diseases and improving quality of life. Thus, microbes contribute significantly to healthcare through production of bioactive compounds.

Section C: Microbes in Sewage Treatment

Q7. Describe the primary and secondary treatment of sewage.

Answer:
Primary sewage treatment involves physical removal of large and small particles through filtration and sedimentation. This reduces suspended solids but does not remove dissolved organic matter. Secondary treatment, also called biological treatment, uses aerobic microorganisms to degrade organic matter. Sewage is aerated in large tanks, allowing microbes to form flocs that consume organic waste, significantly reducing BOD. The treated water is then released into natural water bodies. These treatments help reduce pollution and protect the environment.

Q8. Explain the activated sludge process in sewage treatment.

Answer:
In the activated sludge process, sewage after primary treatment is aerated in tanks where aerobic microbes form flocs. These flocs digest organic matter, reducing BOD. The mixture is then passed to settling tanks where flocs settle as activated sludge. A portion is recycled to maintain microbial population, while the rest is sent for anaerobic digestion. This process effectively cleans sewage and produces biogas, making it environmentally beneficial.

Q9. What is BOD and why is it an important parameter in sewage treatment?

Answer:
Biochemical Oxygen Demand (BOD) is the amount of oxygen required by microorganisms to oxidise organic matter in water. High BOD indicates high organic pollution, while low BOD signifies cleaner water. Measuring BOD helps assess the effectiveness of sewage treatment. Reduction in BOD after treatment confirms successful removal of organic waste, making water safe for discharge.

Section D: Microbes in Biogas Production

Q10. Explain the process of biogas production.

Answer:
Biogas is produced by anaerobic digestion of organic waste such as cow dung and sewage. The process occurs in stages: hydrolysis breaks down complex compounds, acidogenesis produces organic acids, and methanogenesis converts acids into methane by methanogenic bacteria like Methanobacterium. Biogas mainly contains methane, carbon dioxide, and traces of hydrogen sulphide. It is a renewable, eco-friendly fuel and the leftover slurry is used as manure.

Q11. State the advantages of biogas production.

Answer:
Biogas production provides renewable energy, reduces dependence on fossil fuels, and helps in waste management. It reduces environmental pollution and produces nutrient-rich manure. Biogas plants are especially useful in rural areas, providing clean energy for cooking and lighting while improving soil fertility.

Section E: Microbes as Biocontrol Agents

Q12. What is biological control? Explain with examples.

Answer:
Biological control is the use of living organisms to control pests and pathogens. Bacillus thuringiensis produces toxins that kill insect larvae and is used as a biopesticide. Trichoderma species suppress soil-borne plant pathogens. Predators like ladybird beetles control aphids. Biocontrol is eco-friendly and reduces chemical pesticide use.

Q13. Discuss the advantages of using biocontrol agents.

Answer:
Biocontrol agents are target-specific, biodegradable, and do not harm non-target organisms. They reduce chemical pollution, maintain ecological balance, and promote sustainable agriculture. Their use ensures long-term pest control without environmental damage.

Section F: Microbes as Biofertilisers

**Q14. Explain the role of Rhizobium as a biofertiliser.**

Answer:
Rhizobium forms a symbiotic association with leguminous plants, fixing atmospheric nitrogen into usable forms. This improves soil fertility and reduces dependence on chemical fertilisers. It plays a key role in sustainable agriculture.

Q15. Describe the role of mycorrhiza in plant nutrition.

Answer:
Mycorrhiza is a symbiotic association between fungi and plant roots. It increases absorption of phosphorus and water, enhances drought tolerance, and protects plants from pathogens. It improves overall plant growth and soil health.

Q16. Explain the importance of cyanobacteria as biofertilisers.

Answer:
Cyanobacteria like Anabaena and Nostoc fix atmospheric nitrogen in paddy fields, enriching soil fertility. They reduce the need for chemical fertilisers and promote sustainable agriculture.

Section G: Integrated & Application-Based

Q17. How do microbes contribute to sustainable agriculture?

Answer:
Microbes act as biofertilisers and biocontrol agents, improving soil fertility and reducing chemical inputs. They promote eco-friendly farming and long-term sustainability.

Q18. Explain the role of microbes in environmental protection.

Answer:
Microbes reduce pollution through sewage treatment, waste decomposition, and biogas production. They help maintain ecological balance and environmental health.

Q19. Discuss the importance of probiotics.

Answer:
Probiotics are beneficial microbes that improve gut health, digestion, and immunity. They suppress harmful bacteria and enhance nutrient absorption.

Q20. Why is sewage treatment essential for public health?

Answer:
Sewage treatment removes pathogens and organic pollutants, preventing waterborne diseases and protecting public health.

Q21. How do microbes help in waste management?

Answer:
Microbes decompose organic waste through sewage treatment and biogas production, reducing pollution and generating useful products.

Q22. Why are microbes called “friends of humans”?

Answer:
They provide food, medicine, energy, and environmental protection, supporting human welfare in multiple ways.

Q23. Explain the economic importance of industrial microbes.

Answer:
Industrial microbes produce antibiotics, enzymes, and acids, contributing significantly to the economy and healthcare.

Q24. How does Chapter 10 relate to real-life applications?

Answer:
It highlights practical uses of microbes in food, medicine, agriculture, and waste management.

Q25. Why is Chapter 10 important for CBSE board exams?

Answer:
The chapter is application-based, frequently tested, and essential for understanding biotechnology and sustainable development.