Microbes in Human Welfare — Class 12 Biology NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Biology chapter "Microbes in Human Welfare" — 8 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 12 Biology chapter "Microbes in Human Welfare" — 8 important questions with detailed answers for CBSE boar…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

Define microbes.
What is fermentation? Give two examples of fermentation products.
What is the role of Lactobacillus in human welfare? Name any two products.
Explain the process of sewage treatment and the role of microbes in secondary…
What are probiotics? How do they benefit human health?
What is biogas? Write the microbial process of its production.
+ 2 more questions in the full chapter

Solutions Summary:

Question	Status
Define microbes.	✓ Solved
What is fermentation? Give two examples of fermentation p…	✓ Solved
What is the role of Lactobacillus in human welfare? Name …	✓ Solved
Explain the process of sewage treatment and the role of m…	✓ Solved
What are probiotics? How do they benefit human health?	✓ Solved
What is biogas? Write the microbial process of its produc…	✓ Solved

Showing 6 of 8 questions

Q1: Define microbes.

Microbes are microscopic organisms that are not visible to the naked eye and require a microscope for observation. They include bacteria, fungi, protozoa, algae, and viruses. These organisms are found everywhere in nature - in soil, water, air, and even inside the human body.

Q2: What is fermentation? Give two examples of fermentation products.

Fermentation is an anaerobic process by which microorganisms break down organic compounds in the absence of oxygen, releasing energy and producing byproducts like ethanol and CO2. Examples: - Lactobacillus ferments milk to produce yogurt and cheese - Saccharomyces cerevisiae (yeast) ferments glucose to produce ethanol and CO2 in beer and wine production

Q3: What is the role of Lactobacillus in human welfare? Name any two products.

Lactobacillus is a beneficial bacterium that plays a crucial role in human nutrition and health: 1. Produces lactic acid through fermentation which preserves food and prevents pathogenic growth 2. Aids in digestion and nutrient absorption in the human gut 3. Produces essential vitamins like B12 and K 4. Acts as a probiotic to maintain healthy gut microbiota Products: - Yogurt (fermented milk with L. bulgaricus and L. thermophilus) - Cheese (various types using different Lactobacillus strains) ...

Q4: Explain the process of sewage treatment and the role of microbes in secondary treatment.

Sewage treatment occurs in three stages: PRIMARY TREATMENT: - Physical removal of large particles, grit, and sand through screening and sedimentation - No microbial action SECONDARY TREATMENT (BIOLOGICAL): - Microbes play the main role in decomposing organic matter - Heterotrophic bacteria oxidize organic compounds to CO2 and H2O - Nitrifying bacteria convert ammonia to nitrate - Fungal degradation of complex compounds - Takes 5-7 days - Reduces BOD (Biochemical Oxygen Demand) by 80-90% TERTI...

Q5: What are probiotics? How do they benefit human health?

Probiotics are live beneficial microorganisms that confer health benefits when administered in adequate amounts. They are mainly lactic acid bacteria and bifidobacteria. BENEFITS: 1. Improve digestion and lactose tolerance by producing lactase enzyme 2. Enhance nutrient absorption and vitamin synthesis (B vitamins, K) 3. Strengthen intestinal barrier function and prevent pathogen colonization 4. Modulate immune system by promoting beneficial immune responses 5. Produce antimicrobial compounds (...

Q6: What is biogas? Write the microbial process of its production.

Biogas is a mixture of methane (50-70%), carbon dioxide (30-40%), and traces of H2S and N2. It is a renewable energy source produced through anaerobic digestion of organic matter. MICROBIAL PROCESS (ANAEROBIC DIGESTION): STAGE 1 - HYDROLYSIS: - Hydrolytic bacteria break down complex polymers (cellulose, proteins, lipids) into simple monomers - Produces glucose, amino acids, fatty acids STAGE 2 - ACIDOGENESIS: - Acidogenic bacteria ferment monomers into volatile fatty acids, alcohols, CO2, and...

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