🌸Chapter 8
Microbes in Human Welfare
(Summary Notes)
🔹 1. Introduction
Microbes (microorganisms) are microscopic living organisms such as bacteria,
fungi, protozoa, algae, and viruses.
They play an essential role in human welfare — in:
- Food and beverage production
- Industrial products (enzymes,
acids, antibiotics)
- Sewage treatment
- Energy production (biogas)
- Agriculture (biofertilizers,
biocontrol)
🔹 2. Microbes in Household
Products
🥛 (A) Lactic Acid Bacteria
(LAB – Lactobacillus)
- Converts milk → curd
(yogurt) by producing lactic acid.
- Lactic acid coagulates milk
protein casein.
- Benefits: Increases nutritional value,
vitamin B12; inhibits harmful microbes in gut.
🍞 (B) Fermentation in Bread
and Beverages
- Yeast (Saccharomyces
cerevisiae)
→ used in:
- Bread-making: CO₂ produced → dough rises.
- Beverages:
- Wine, beer, whisky → fermented
by yeast.
- Fermentation of grains,
fruits → ethanol.
🍶 (C) Traditional Fermented
Foods
- Idli, dosa, dhokla, bhatura: fermented by bacteria
(LAB + yeasts).
- Toddy: fermented sap of palm tree → ethanol.
🔹 3. Microbes in Industrial
Products
Industrial production uses large tanks (fermenters)
for growing microbes.
🧪 Important Microbial
Products:
|
Product |
Microbe |
Function/Use |
|
Lactic acid |
Lactobacillus |
Curd formation, pickles |
|
Acetic acid (vinegar) |
Acetobacter aceti |
Food preservative |
|
Ethanol |
Saccharomyces cerevisiae |
Alcoholic beverages |
|
Citric acid |
Aspergillus niger |
Food industry |
|
Butyric acid |
Clostridium butylicum |
Organic chemical |
|
Gluconic acid |
Aspergillus niger, Penicillium |
Food additive |
|
Antibiotics |
Penicillium notatum (Penicillin) |
Kills/inhibits bacteria |
|
Enzymes |
Aspergillus niger (pectinase, lipase) |
Detergents, juices |
💊 Antibiotics
- Antibiotic: Chemical substance produced by
microbes that kills or inhibits growth of pathogens.
- Discovered by: Alexander Fleming
(1928) — Penicillium notatum.
- Developed commercially by: Ernst Chain and Howard
Florey (WW-II).
- Other examples:
- Streptomycin — Streptomyces griseus
- Tetracycline — Streptomyces
aureofaciens
- Erythromycin — Saccharopolyspora
erythraea
🔹 4. Microbes in Sewage
Treatment
Goal:
Remove organic matter and pathogens before water release.
Stages of Sewage Treatment:
1.
Primary
treatment (physical)
o Removal of large particles (plastic,
soil, oil).
o Sedimentation → primary sludge
(settled solids).
o Supernatant → primary effluent
→ sent for biological treatment.
2.
Secondary
treatment (biological)
o Uses aerobic microbes in aeration
tanks.
o Microbial flocs (bacteria + fungal filaments)
digest organic matter → CO₂ + water.
o Activated sludge formed → some recycled, rest → anaerobic
sludge digester.
3.
Anaerobic
treatment
o Anaerobic bacteria digest sludge → methane,
H₂S, CO₂ (biogas).
4.
Tertiary
treatment (for
advanced purification)
o Chemical disinfection (chlorine, UV)
before releasing effluent into rivers.
🧫 Microbial flocs = masses of bacteria +
fungi forming biofilms.
📘 Important NCERT Keywords
- Primary effluent
- Activated sludge
- Microbial flocs
- Aeration tank
- Anaerobic digester
🔹 5. Microbes in Production
of Biogas
💨 Biogas = Methane-rich fuel
gas produced by anaerobic microbes.
Main microbes:
- Methanogens (e.g.
Methanobacterium)
Biogas composition:
- CH₄ (50–70%), CO₂ (30–40%), H₂, H₂S
(traces)
Raw materials:
- Cattle dung (gobar), agricultural waste, sewage.
Stages in Biogas Plant:
1.
Slurry
preparation
(mix dung + water)
2.
Anaerobic
digestion tank
— Methanobacterium decomposes dung
3.
Biogas
collection chamber
4.
Effluent
outlet (used as
manure)
India’s Biogas Program:
- IARI (Indian Agricultural
Research Institute)
& KVIC (Khadi and Village Industries Commission) — developed
biogas plants.
🪔 Uses: Cooking, lighting, reducing
pollution, producing organic manure.
🔹 6. Microbes as Biocontrol
Agents
Definition: Use of biological methods (natural predators, parasites,
pathogens) to control pests instead of chemicals.
Examples:
|
Biocontrol Agent |
Target Pest |
Mode |
|
Bacillus thuringiensis (Bt) |
Caterpillars of cotton bollworm, cabbage |
Produces Bt toxin → kills larvae |
|
Trichoderma |
Soil-borne fungi |
Antifungal |
|
Ladybird beetle, Dragonfly |
Aphids, mosquitoes |
Predatory insects |
|
Baculoviruses (Nucleopolyhedrovirus) |
Specific insects |
Used in IPM (Integrated Pest Management) |
🌱 Advantages:
- Eco-friendly
- Target-specific
- No pollution or residue
🔹 7. Microbes as
Biofertilizers
Definition: Living organisms that enrich soil nutrients and promote
plant growth.
Types:
|
Type |
Microbe |
Function |
|
Bacteria (free-living) |
Azospirillum, Azotobacter |
Nitrogen fixation |
|
Symbiotic bacteria |
Rhizobium (in root nodules of legumes) |
N₂ fixation |
|
Cyanobacteria (Blue-green algae) |
Anabaena, Nostoc |
N₂ fixation in paddy fields |
|
Fungi |
Mycorrhiza (Glomus) |
Increases phosphorus absorption |
|
Lichens |
Alga + fungus |
Soil binding, N₂ fixation |
🌾 Importance:
- Improve soil fertility &
structure
- Reduce dependence on chemical
fertilizers
- Increase crop yield
🧬 8. Important Diagrams
(from NCERT)
(A) Biogas Plant
[ Mixing tank ] → [ Digester
(anaerobic chamber) ] → [ Gas outlet ]
↓
[ Sludge outlet (manure) ]
(B) Sewage Treatment Plant
Primary treatment → Aeration tank →
Settling tank → Anaerobic digester → Clean water
(C) Rhizobium Root Nodule Diagram
- Shows root nodules on
leguminous roots (peas, beans).
- Site of biological nitrogen
fixation.
🔹 9. Important Definitions
(MUST LEARN for NEET + Boards)
|
Term |
Definition |
|
Fermentation |
Anaerobic breakdown of organic compounds by microbes to
produce alcohol, acids, or gases. |
|
Antibiotic |
Substance produced by microbes that destroys or inhibits
growth of pathogens. |
|
Activated sludge |
Settled sludge containing aerobic bacteria used for
secondary sewage treatment. |
|
Methanogen |
Anaerobic microbe producing methane gas during
decomposition. |
|
Biocontrol |
Use of living organisms to control pests and diseases. |
|
Biofertilizer |
Microorganisms that increase nutrient availability to
plants. |
|
Microbial flocs |
Masses of bacteria and fungi in aeration tank that digest
organic matter. |
💡 10. Quick Revision
Pointers (for NEET/Boards)
✅ Lactobacillus → curd formation
✅ Yeast → alcohol, bread
✅ Penicillium notatum → penicillin (antibiotic)
✅ Acetobacter aceti → acetic acid (vinegar)
✅ Aspergillus niger → citric acid
✅ Methanobacterium → biogas
✅ Bacillus thuringiensis → biopesticide
✅ Rhizobium, Azospirillum, Nostoc → nitrogen fixation
✅ Trichoderma → antifungal
✅ Mycorrhiza → phosphorus uptake
🧭 NCERT Keywords for
Last-Minute Revision
LAB, fermentation, flocs, activated sludge, methanogens, biogas,
biocontrol, biofertilizers, Rhizobium, Trichoderma, Bt toxin, Methanobacterium,
anaerobic digestion, secondary treatment, IARI, KVIC.
🧠 Tips for NEET + CBSE
- NCERT diagrams are directly asked — practice
labeling.
- 1-liners like microbes &
products
are frequent MCQs.
- For NEET, revise biocontrol
& biofertilizer examples.
- For Boards, prepare long
answers on sewage treatment & biogas plant.
