Science · Class 12
Microbes in Human Welfare
Learn Microbes in Human Welfare with notes, examples, and practice questions.
5 sections15–25 min read8 MCQs · 3 examples
Chapter Overview
Not all microbes are germs. Lactobacillus turns milk into curd; Rhizobium feeds plants nitrogen.
Microbes — bacteria, fungi, protozoans, viruses, and microalgae — are indispensable. They ferment food, treat sewage, produce antibiotics, and fix nitrogen in soil.
Microbes in Household & Industry
- Curd: Lactobacillus acidophilus converts lactose to lactic acid
- Bread: Saccharomyces cerevisiae — CO₂ makes dough rise
- Alcoholic drinks: yeast fermentation; toddy from palm sap
- Swiss cheese: Propionibacterium sharmanii — large holes from CO₂
Antibiotics & Chemicals
- Penicillin: Alexander Fleming; from Penicillium notatum
- Streptomycin: Streptomyces griseus — first effective against TB
- Statins: Monascus purpureus — cholesterol lowering
- Cyclosporin A: Trichoderma polysporum — immunosuppressant for transplants
Sewage & Biogas
- Primary treatment: physical removal of debris
- Secondary: aerobic microbes reduce BOD of effluent
- Anaerobic sludge digesters: biogas (methane) + manure
- Gobar gas plants in rural India
Biocontrol & Biofertilisers
- Rhizobium: root nodules fix N₂ on legumes
- Azospirillum, Azotobacter: free-living nitrogen fixers
- Mycorrhiza: fungi + roots — phosphorus uptake
- Bt and Trichoderma: biocontrol agents vs pests
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Example 1: Curd Formation
How does Lactobacillus make curd?
- 1Bacteria ferment lactose to lactic acid.
- 2Acid denatures milk proteins → coagulation → curd.
Answer
Lactic acid fermentation of lactose
Example 2: Biogas
Main combustible component of biogas?
- 1Anaerobic methanogens digest sludge
- 2Produce CH₄ (methane)
Answer
Methane (CH₄)
Example 3: Biofertiliser
Role of Rhizobium in legume roots.
- 1Forms root nodules
- 2Contains nitrogenase — fixes atmospheric N₂ to ammonia
Answer
Biological nitrogen fixation
Key Points to Remember
- ✓ BOD: biochemical oxygen demand — water pollution indicator
- ✓ Antibiotics vs antibodies — don't confuse
- ✓ Single Cell Protein (Spirulina): food supplement
- ✓ Know scientific names of useful microbes
Exam Tips
- • Match microbe to product in table format
- • Explain secondary sewage treatment steps
- • Differentiate biofertiliser vs chemical fertiliser
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Formula Cheat Sheet
Quick reference — NCERT board exam formulas
Microbes in Food & Medicine
- Curd:Lactobacillus — lactose → lactic acid → protein coagulation
- Bread / alcohol:Saccharomyces cerevisiae — fermentation produces CO₂ / ethanol
- Penicillin:Penicillium notatum (fungus) — Alexander Fleming
- Streptomycin:Streptomyces griseus — first effective anti-TB antibiotic
- Statins:Monascus purpureus — cholesterol-lowering
- Cyclosporin A:Trichoderma polysporum — immunosuppressant for transplants
Sewage, Biogas & Biofertilisers
- BOD:Biochemical oxygen demand — indicator of organic water pollution
- Biogas:Anaerobic digestion → mainly CH₄ (methane) + manure
- Rhizobium:Root nodules on legumes — nitrogenase fixes N₂ → NH₃
- Azospirillum / Azotobacter:Free-living nitrogen-fixing bacteria in soil
- Mycorrhiza:Fungus + root symbiosis — improves phosphorus uptake
- Secondary sewage treatment: aerobic microbes reduce BOD of effluent
Practice MCQs — Microbes in Human Welfare
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 8Score: 0/0
Curd is made using: