Class 12 Biology Chapter 10 Microbes in Human Welfare Notes
Introduction
Microorganisms (microbes) are microscopic living organisms like bacteria, fungi, algae and viruses. Though tiny, they play a huge role in human welfare—from food and medicine to environment and energy.
10.1 Microbes in Household Products
Microbes are widely used in day-to-day food preparations.
Common Examples:
Curd / Yogurt
Made by lactic acid bacteria (LAB)
LAB converts lactose into lactic acid
Improves nutritional quality (Vitamin B₁₂)
Suppresses disease-causing microbes in stomach
Idli, Dosa, Upma
Fermentation of rice and black gram
CO₂ production makes batter fluffy
Swiss Cheese
Large holes due to CO₂ released by Propionibacterium
👉 Gas release during microbial metabolism is clearly seen in fermented dough and cheese.
Sample to Demonstrate Microbes in Lab
Soil sample or water sample
Reason:
Natural habitat of microbes
Rich microbial diversity
Easily observed under microscope
10.2 Microbes in Industrial Products
Microbes are used on a large scale to produce industrial products.
Important Products:
Antibiotics
Penicillin (from Penicillium)
Cephalosporins (from Cephalosporium)
Organic acids
Citric acid
Lactic acid
Enzymes
Used in detergents, food processing
Vaccines
TB, DPT, etc.
👉 Microbes help control diseases caused by harmful bacteria through antibiotics and vaccines.
10.3 Microbes in Sewage Treatment
Sewage:
Wastewater from households and industries.
Harmful Effects of Sewage:
Pollutes water bodies
Spreads pathogenic microbes
Affects aquatic life
Stages of Sewage Treatment:
Primary treatment
Physical process
Removal of large particles
Secondary treatment
Biological process
Microbes degrade organic matter
Tertiary treatment
Chemical process
Removal of nutrients and pathogens
BOD (Biochemical Oxygen Demand)
Indicates organic pollution level
Higher BOD = more polluted water
BOD Values Interpretation:
400 mg/L → Untreated sewage (most polluted)
20 mg/L → Secondary effluent
8 mg/L → River water (cleanest)
10.4 Microbes in Production of Biogas
Anaerobic microbes digest organic waste
Produce biogas (mainly methane)
Importance of Biogas:
Renewable energy source
Reduces waste and pollution
Provides fuel for rural areas
Slurry used as manure
10.5 Microbes as Biocontrol Agents
Microbes are used to control pests and diseases naturally, reducing chemical pesticide use.
Advantages:
Eco-friendly
Target-specific
Safe for humans and environment
10.6 Microbes as Biofertilisers
Biofertilisers are living microorganisms that enhance soil fertility.
How Biofertilisers Improve Soil Fertility:
Fix atmospheric nitrogen
Solubilise phosphorus
Add organic matter (humus)
Improve soil structure
Examples:
Rhizobium with leguminous plants
Cyanobacteria in paddy fields
👉 Biofertilisers reduce dependence on chemical fertilisers and pesticides.
Role of Microbes in Single Cell Protein (SCP)
SCP = microbial biomass rich in protein
Sources: bacteria, algae, yeast
Advantages:
High protein content
Fast growth
Requires less space
Used as food and animal feed
Microbes in Soil
Help in humification
Decompose organic matter
Maintain soil fertility
Act as biofertilisers and biopesticides
Microbes and Important Drugs
Cyclosporin A
Immunosuppressive drug
Used in organ transplantation
Statins
Lower blood cholesterol
Reduce heart disease risk
Importance Ranking for Human Welfare
Most important → Least important
Biogas
Community-level benefits
Renewable energy
Waste management
Penicillin
Life-saving antibiotic
Curd
Nutritional value
Citric acid
Mainly industrial use
How Biofertilisers Enrich Soil Fertility
Replenish nutrients (N, P, Fe, S)
Increase humus content
Improve microbial activity
Enhance crop yield sustainably
10.7 Summary (Exam Ready ✨)
Microbes are essential for human welfare
Used in food, medicine, industry and agriculture
Help in sewage treatment and biogas production
Act as biofertilisers and biocontrol agents
Promote sustainable development
✍️ Top 10 Short Question–Answers
Q1. What are microbes?
Answer: Microbes are microscopic organisms like bacteria, fungi, algae and viruses.
Q2. Which bacteria convert milk into curd?
Answer: Lactic acid bacteria (LAB).
Q3. How does LAB improve nutritional quality of curd?
Answer: By increasing vitamin B₁₂ content.
Q4. Which microbe is responsible for holes in Swiss cheese?
Answer: Propionibacterium.
Q5. Name the antibiotic obtained from Penicillium.
Answer: Penicillin.
Q6. What is sewage?
Answer: Wastewater from households and industries.
Q7. What does BOD indicate?
Answer: Level of organic pollution in water.
Q8. Which gas is mainly produced in biogas plants?
Answer: Methane.
Q9. What are biofertilisers?
Answer: Living microorganisms that enhance soil fertility.
Q10. Name one immunosuppressive drug produced by microbes.
Answer: Cyclosporin A.
📝 Long Answer Questions
Q1. Explain the role of microbes in household products.
Answer:
Microbes are widely used in daily food preparations.
Curd/Yogurt:
Prepared by lactic acid bacteria
Converts lactose into lactic acid
Improves digestibility and nutrition
Idli, dosa, upma:
Fermentation of rice and black gram
CO₂ production makes batter fluffy
Swiss cheese:
Large holes formed due to CO₂ released by Propionibacterium
Thus, microbes enhance taste, texture and nutritional value of food.
Q2. Describe sewage treatment and significance of BOD.
Answer:
Sewage treatment stages:
Primary treatment:
Physical removal of large particles
Secondary treatment:
Biological process
Microbes degrade organic matter
Tertiary treatment:
Chemical removal of nutrients and pathogens
BOD (Biochemical Oxygen Demand):
Indicates organic pollution
Higher BOD = more polluted water
400 mg/L → untreated sewage
8 mg/L → clean river water
Q3. Explain biofertilisers and their importance.
Answer:
Biofertilisers are microorganisms that improve soil fertility.
Functions:
Fix atmospheric nitrogen
Solubilise phosphorus
Increase humus content
Improve soil structure
Examples:
Rhizobium in legumes
Cyanobacteria in paddy fields
They reduce dependence on chemical fertilisers and promote sustainable agriculture.
📝 PYQs (Previous Year Questions)
🔹 1️⃣ Very Short Answer Questions (1 Mark)
What are microbes?
Name the bacteria that convert milk into curd.
Which vitamin content increases in curd due to LAB?
Name the microbe responsible for holes in Swiss cheese.
Name one antibiotic produced by fungi.
What is sewage?
What does BOD stand for?
Which gas is mainly produced in biogas plants?
Name one biofertiliser used in leguminous plants.
Name one immunosuppressive drug obtained from microbes.
🔹 2️⃣ Short Answer Questions (2–3 Marks)
Explain the role of lactic acid bacteria in curd formation.
How do microbes help in preparation of idli or dosa batter?
What are antibiotics? Give one example.
Describe primary and secondary sewage treatment.
What is BOD? What does high BOD indicate?
Write any two advantages of biogas.
What are biofertilisers? How do they improve soil fertility?
Mention two advantages of using microbes as biocontrol agents.
What is single cell protein (SCP)?
Write any two uses of DNA vaccines.
🔹 3️⃣ Long Answer Questions (3–5 Marks)
Describe the role of microbes in household products.
Explain the role of microbes in industrial products.
Describe sewage treatment process with the role of microbes.
Explain biogas production and its importance.
Describe microbes as biofertilisers and biocontrol agents.
Explain single cell protein and its significance.
🔹 4️⃣ Difference-Based PYQs (Very Important)
Primary sewage treatment vs Secondary sewage treatment
Biofertilisers vs Chemical fertilisers
Biocontrol agents vs Chemical pesticides
Antibiotics vs Vaccines
SCP vs Conventional protein sources
🔹 5️⃣ Assertion–Reason / Concept-Based PYQs
LAB improves nutritional quality of curd. Justify.
Secondary sewage treatment is a biological process. Explain.
Biogas plants reduce environmental pollution. Give reason.
Biofertilisers are eco-friendly. Justify.
Microbes play an important role in sustainable development. Explain.
🔹 6️⃣ Diagram / Flowchart Based PYQs
Diagrammatic representation of biogas plant.
Flowchart of sewage treatment.
Labelled diagram of antibody (asked indirectly via vaccines).
❓ FAQs (5)
FAQ 1. Why are microbes important for human welfare?
They are used in food, medicine, industry, agriculture and energy production.
FAQ 2. Why is biogas considered eco-friendly?
It is renewable, reduces pollution and uses waste material.
FAQ 3. How do microbes help in soil fertility?
By decomposing organic matter and acting as biofertilisers.
FAQ 4. What is the role of microbes in SCP?
They provide protein-rich microbial biomass for food and feed.
FAQ 5. Why are biofertilisers preferred over chemical fertilisers?
They are eco-friendly, sustainable and improve long-term soil health.
| Chapter No. | Chapter Name | Visit |
|---|---|---|
| 1 | Reproduction in Organisms | Visit |
| 2 | Sexual Reproduction in Flowering Plants | Visit |
| 3 | Human Reproduction | Visit |
| 4 | Reproductive Health | Visit |
| 5 | Principles of Inheritance and Variation | Visit |
| 6 | Molecular Basis of Inheritance | Visit |
| 7 | Evolution | Visit |
| 8 | Human Health and Disease | Visit |
| 9 | Strategies for Enhancement in Food Production | Visit |
| 10 | Microbes in Human Welfare | Visit |
| 11 | Biotechnology: Principles and Processes | Visit |
| 12 | Biotechnology and its Applications | Visit |
| 13 | Organisms and Populations | Visit |
| 14 | Ecosystem | Visit |
| 15 | Biodiversity and Conservation | Visit |
| 16 | Environmental Issues | Visit |
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