Microbes in Human Welfare

33 solved questions from Class 12 Biology, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the primary topic or theoretical principle explored in 'Microbes in Human Welfare' (Class 12 BIOLOGY)? medium MCQ Chapter Core Principle
• 2 Which key mechanism or analytical rule is highlighted in 'Microbes in Human Welfare'? medium MCQ Key Analytical Mechanism
• 3 What is the primary topic or principle explained in 'Microbes in Human Welfare' (Class 12 Biology)? medium MCQ Chapter Core Concept
• 4 Which key observation or fact is central to understanding 'Microbes in Human Welfare'? medium MCQ Key Fact & Mechanism
• 5 Why is the study of 'Microbes in Human Welfare' important for students of Class 12? medium MCQ Learning Significance
• 6 What is a common application or real-world example related to 'Microbes in Human Welfare'? medium MCQ Real World Application
• 7 What key takeaway should students retain after completing 'Microbes in Human Welfare'? medium MCQ Chapter Summary & Takeaway
• 8 Penicillin, a widely used antibiotic, is obtained from which of the following microbes? easy MCQ 1 mark Antibiotic production source
• 9 A 5 L biogas digester containing cow dung produces biogas at a constant rate of 0.3 L per hour. If the digester operates continuously for 30 days, calculate (a) the total volume of biogas produced in cubic metres, and (b) the volume of methane produced, given that methane makes up 60 % of the biogas. hard 3 marks Biogas volume calculation
• 10 Describe the role of Rhizobium in biological nitrogen fixation and explain how this symbiosis benefits leguminous crops, including the steps of nodule formation. hard 4 marks Biological nitrogen fixation by Rhizobium
• 11 Explain how yeast is employed in the industrial production of ethanol for bio‑fuel, specifying the biochemical pathway involved. medium 2 marks Alcoholic fermentation by yeast
• 12 In a dairy industry, probiotic strains *Lactobacillus rhamnosus* and *Bifidobacterium lactis* are used as starter cultures. Which of the following statements about their role is NOT true? medium MCQ 3 marks Role of probiotic starters in dairy
• 13 A hospital reports that 18% of the 200 Enterococcus faecalis isolates from wound infections are resistant to vancomycin. After introducing a new antibiotic stewardship program, the resistance percentage drops to 9%. Calculate the number of resistant isolates before and after the program. medium 4 marks Calculating antibiotic resistance frequencies
• 14 Pseudomonas putida is employed for the bioremediation of petroleum‑contaminated soil. Describe, in detail, (i) the metabolic pathway it uses to degrade alkanes, (ii) the enzymes involved, and (iii) the environmental factors that influence the efficiency of this biodegradation. hard 5 marks Bioremediation of hydrocarbons by Pseudomonas
• 15 A 200 ml batch of curd is prepared using a starter culture containing Lactobacillus delbrueckii subsp. bulgaricus. The culture ferments lactose at a rate of 0.02 g per litre per hour. If the fermentation lasts 6 hours, how much lactose is converted to lactic acid in grams? easy 1 mark Fermentation rate of lactobacilli
• 16 Which microorganism is responsible for the fermentation of soybeans to produce the traditional Indonesian food "tempeh"? hard MCQ 4 marks Microbes in food fermentation
• 17 Explain how probiotics help in preventing antibiotic‑associated diarrhoea. Include the mechanisms involved. medium 3 marks Probiotics and gut health
• 18 A 3 L biogas digester receives cow dung and produces biogas at a constant rate of 0.25 L per hour. If the digester operates continuously for 15 days, calculate: (a) the total volume of biogas produced in cubic metres, (b) the volume of methane produced, given methane is 55% of the biogas. easy 2 marks Biogas production and unit conversion
• 19 Bacillus subtilis is employed to remediate soils contaminated with lead (Pb^2+). Describe in detail (i) the biochemical pathway it uses to detoxify lead, (ii) the enzymes involved, and (iii) the environmental factors affecting the efficiency of this bioremediation. hard 5 marks Microbial lead bioremediation
• 20 Describe the mechanism by which Rhizobium species fix atmospheric nitrogen in leguminous root nodules, including the symbiotic signaling pathway, the role of nodule organogenesis, and the energy cost for the plant. hard 4 marks Symbiotic nitrogen fixation
• 21 A 250 ml (0.25 L) batch of curd is prepared using a starter culture containing Lactobacillus delbrueckii subsp. bulgaricus. The culture ferments lactose at a rate of 0.015 g per litre per hour. If the fermentation lasts 5 hours, how much lactose is converted to lactic acid in grams? medium 2 marks Rate calculation in microbial fermentation
• 22 Briefly explain how probiotic Lactobacillus rhamnosus colonizes the human gut and its impact on the host's immune response. hard 3 marks Probiotic colonization and immune modulation
• 23 Which microorganism is primarily used as a starter culture in the Indian fermented drink ‘lassi’? easy MCQ 1 mark Starter cultures in fermented dairy foods
• 24 A 500 ml batch of curd is prepared using a starter containing Lactobacillus delbrueckii subsp. bulgaricus. The culture ferments lactose at a rate of 0.018 g per litre per hour. If fermentation proceeds for 4 hours, how many grams of lactose are converted to lactic acid? medium 2 marks Quantitative calculation of lactose fermentation
• 25 Penicillin, a widely used β‑lactam antibiotic, is obtained from which of the following microorganisms? easy MCQ 1 mark Microbial source of antibiotics
• 26 Briefly explain how *Bacillus subtilis* detoxifies lead in contaminated soil, mentioning the key enzymes involved and the environmental factors that affect its efficiency. medium 2 marks Microbial bioremediation of heavy metals
• 27 A 1 L batch of fermented milk uses a starter culture containing Lactobacillus bulgaricus that ferments lactose at a rate of 0.02 g per litre per hour. If fermentation is carried out for 8 hours, how many grams of lactose are converted to lactic acid? medium 2 marks Rate of lactose fermentation
• 28 Which of the following microorganisms is primarily responsible for the production of the antibiotic streptomycin? medium MCQ 2 marks Source of streptomycin antibiotic
• 29 A 10 L biogas digester receives cow dung and produces biogas at a constant rate of 0.4 L per hour. The digester runs continuously for 20 days. (a) What is the total volume of biogas produced in cubic metres? (b) If biogas contains 60 % methane, how many cubic metres of methane are produced? (c) Given the calorific value of methane is 55.5 kJ per litre, estimate the total energy produced in megajoules. hard 4 marks Biogas production and energy estimation
• 30 Explain how lactic acid bacteria contribute to the texture of Indian yogurt and name one bacterial species commonly used. easy 1 mark Role of lactic acid bacteria in yogurt texture
• 31 In the NCERT chapter, two types of nitrogen-fixing biofertilizers are discussed for rice and paddy cultivation: *Azotobacter* (a free-living soil bacterium) and *Anabaena* / *Nostoc* (filamentous cyanobacteria). Both fix atmospheric N₂. State **one key difference** between how *Anabaena* (a cyanobacterium) and *Rhizobium* (a soil bacterium) obtain the energy needed to power the nitrogenase enzyme during nitrogen fixation, and name the specialised cell in *Anabaena* where nitrogenase is located. easy 2 marks Cyanobacteria as biofertilizers
• 32 Answer the following three parts concisely (about 2–3 lines each): medium 4 marks Bioactive molecules from microbes
• 33 Which microorganism is traditionally used for the industrial production of penicillin? easy MCQ 1 mark Antibiotic production