Microbes in Human Welfare is an important and high-scoring chapter in Class 12 Biology that explains how microorganisms are beneficial to humans in daily life and industry. This chapter covers the role of microbes in food production, industrial products, sewage treatment, biogas production, and biological pest control, making it highly relevant for CBSE board exams and NEET.
NCERT Solutions for Class 12 Biology Chapter 8 – Microbes in Human Welfare are prepared strictly according to the latest CBSE syllabus and exam pattern. The answers are written in simple, clear language with step-by-step explanations and examples, helping students understand applications of microbiology easily and score well in board examinations and competitive exams.
NCERT Solutions for Class 12 Biology Chapter 8 – Microbes in Human Welfare
Q.
What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Q.
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 under a microscope, which sample would you carry and why?
Q.
Give examples to prove that microbes release gases during metabolism.
Q.
In which food would you find lactic acid bacteria? Mention some of their useful applications.
Q.
Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Q.
In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Q.
Name any two species of fungus, which are used in the production of the antibiotics.
Q.
What is sewage? In which way can sewage be harmful to us?
Q.
What is the key difference between primary and secondary sewage treatment?
Q.
Do you think microbes can also be used as source of energy? If yes how?
Q.
Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Q.
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 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 20 mg/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?
Q.
Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
Q.
Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil
Q.
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
Q.
How do biofertilisers enrich the fertility of the soil?
NCERT Solutions for Class 12 Biology Chapter 8 – Microbes in Human Welfare
Q.1) What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Ans: Domestic sewage consists of waste from kitchens, bathrooms, toilets and laundry. Its main constituents are:
- Suspended solids such as sand, silt and clay
- Colloidal matter like faecal matter, bacteria, cloth and paper
- Dissolved substances such as nitrates, phosphates, ammonia, soaps, detergents and pesticides
Effects on rivers:
- Microbes consume dissolved oxygen, increasing BOD and causing death of aquatic organisms
- Excess nutrients lead to algal blooms, reducing water quality
- Increased turbidity reduces light penetration affecting plants
- Toxic chemicals and pathogens cause long-term ecological damage
Q.2) Which sample would you carry to show microbes under a microscope and why?
Ans: Fresh homemade curd would be ideal because it contains lactic acid bacteria (Lactobacillus), which are present in large numbers and can be easily observed under a microscope after staining.
Q.3) Give examples to prove that microbes release gases during metabolism.
Ans:
- Microbes in idli and dosa batter release carbon dioxide during fermentation, making the batter fluffy.
- Methanogens present in cattle dung produce methane, carbon dioxide and hydrogen during anaerobic digestion, used in biogas production.
Q.4) In which food are lactic acid bacteria found? Mention their uses.
Ans: Lactic acid bacteria are found in curd. They convert milk into curd and are also used for commercial production of lactic acid.
Q.5) Name traditional Indian foods made using microbes.
Ans:
- Wheat: Bread, kulcha, bhatura
- Rice: Idli, dosa
- Bengal gram: Dhokla, khandvi
Q.6) How have microbes helped in controlling diseases?
Ans: Microbes produce antibiotics such as penicillin and streptomycin that kill or inhibit harmful bacteria, helping control infectious diseases.
Q.7) Name two fungi used in antibiotic production.
Ans:
- Penicillium notatum: Penicillin
- Streptomyces griseus: Streptomycin
Q.8) What is sewage and why can it be harmful?
Ans: Sewage is municipal wastewater containing human excreta and household waste. It is harmful because it contains organic matter and pathogens that pollute water and spread diseases.
Q.9) Differentiate between primary and secondary sewage treatment.
Ans:
- Primary treatment: Physical removal of debris by filtration and sedimentation
- Secondary treatment: Biological treatment using microbes to reduce organic matter and BOD
Q.10) Can microbes be used as a source of energy?
Ans: Yes. Methanogenic bacteria produce biogas from cattle dung and organic waste, which is used as a clean source of energy.
Q.11) How can microbes reduce the use of chemical fertilisers and pesticides?
Ans: Microbes act as biofertilisers and biopesticides. They fix nitrogen, solubilise phosphorus and control pests naturally, reducing chemical use.
Q.12) Which water sample is most polluted based on BOD values?
Ans: The sample with the highest BOD value (400 mg/L) is untreated sewage water and is the most polluted.
Q.13) Name the microbes producing Cyclosporin A and Statins.
Ans:
- Cyclosporin A: Tolypocladium inflatum
- Statins: Monascus purpureus and Aspergillus terreus
Q.14) Explain the role of microbes in:
(a) Single Cell Protein (SCP): Microbial biomass used as protein-rich food or feed supplement.
(b) Soil: Microbes improve soil fertility through nutrient cycling and nitrogen fixation.
Q.15) Arrange the following in decreasing importance: Biogas, Citric acid, Penicillin, Curd.
Ans: Penicillin > Biogas > Citric Acid > Curd
Q.16) How do biofertilisers enrich soil fertility?
Ans: Biofertilisers fix atmospheric nitrogen, solubilise phosphorus and improve nutrient availability, enhancing soil fertility naturally.
FAQs: Class 12 Biology Chapter 8 – Microbes in Human Welfare
Q1. Why is Microbes in Human Welfare important for exams?
It is a frequently asked and scoring chapter for CBSE and NEET.
Q2. Which topics are most important in this chapter?
Microbes in food production, antibiotics, sewage treatment, and biogas.
Q3. Are application-based questions asked from this chapter?
Yes, short and long application-based questions are common.
Q4. How do NCERT Solutions help students?
They provide NCERT-aligned, exam-ready explanations with clear examples.
Q5. Is this chapter useful for NEET preparation?
Yes, it is an important NEET Biology chapter with repeated PYQs.