Microbes in Human Welfare

NCERT Line-by-Line Breakdown for NEET 2026

Unit 3: Biology in Human Welfare

Microbes are not always harmful “germs”. They are a major component of biological systems on Earth. From making curd to treating sewage, microbes play a vital role in human welfare. This chapter explores their utility in household, industrial, and agricultural sectors.

1. Microbes in Household Products

Product	Microbe	Key Action / Note
Curd	Lactobacillus (LAB)	Converts milk sugar to Lactic acid (coagulates milk proteins). Increases Vitamin B12. Checks disease-causing microbes in stomach.
Bread	Saccharomyces cerevisiae (Baker’s Yeast)	Fermentation releases CO₂ causing dough to rise (puffing up).
Swiss Cheese	Propionibacterium sharmanii	Large holes due to production of large amount of CO₂.
Roquefort Cheese	Fungi (Penicillium roqueforti)	Ripened by fungi for specific flavor.
Toddy	Natural Microbes	Traditional drink of South India (Fermented sap of palms).

2. Microbes in Industrial Products

Production on an industrial scale requires large vessels called Fermentors.

A. Fermented Beverages

Brewer’s Yeast (Saccharomyces cerevisiae) ferments malted cereals/fruit juices to Ethanol.

Without Distillation: Wine, Beer (Low alcohol).
With Distillation: Whisky, Brandy, Rum (High alcohol).

B. Antibiotics

Chemical substances produced by some microbes to kill other disease-causing microbes.

First antibiotic: Penicillin (from Penicillium notatum) by Alexander Fleming.
Full potential established by: Chain and Florey (Nobel Prize 1945).

C. Chemicals, Enzymes & Bioactive Molecules (NEET Favorites)

Product	Microbial Source	Application
Citric Acid	Aspergillus niger (Fungus)	Preservative, Flavoring.
Acetic Acid	Acetobacter aceti (Bacteria)	Vinegar.
Butyric Acid	Clostridium butylicum (Bacteria)	Rancid butter smell.
Lactic Acid	Lactobacillus (Bacteria)	Curd.
Streptokinase	Streptococcus (Bacteria)	“Clot Buster” (Myocardial infarction).
Cyclosporin A	Trichoderma polysporum (Fungus)	Immunosuppressive Agent (Organ transplant).
Statins	Monascus purpureus (Yeast)	Blood Cholesterol Lowering Agent (Inhibits cholesterol synthesis enzyme).

3. Microbes in Sewage Treatment

Treatment is done in two stages:

A. Primary Treatment (Physical)

Removal of particles (large and small) by filtration and sedimentation.

Floating debris removed by filtration.
Grit (soil/pebbles) removed by sedimentation.
Solids settle as Primary Sludge; Supernatant is Effluent.

B. Secondary Treatment (Biological)

Effluent passed to Aeration Tanks. Mechanically agitated, air pumped in.
Vigorous growth of useful aerobic microbes into Flocs (bacteria associated with fungal filaments).
Microbes consume organic matter → Reduces BOD (Biochemical Oxygen Demand).
Once BOD reduced, effluent passed to Settling Tank. Bacterial flocs settle as Activated Sludge.
Activated sludge pumped into Anaerobic Sludge Digesters. Anaerobic bacteria digest bacteria/fungi producing Biogas (Methane, H₂S, CO₂).

[Image of sewage treatment plant flow chart]

4. Biogas & Biocontrol Agents

A. Biogas Production

Methanogens (e.g., Methanobacterium) grow anaerobically on cellulosic material producing Methane (CH₄).
Found in Rumen of cattle (break down cellulose) and Anaerobic sludge.

[Image of biogas plant diagram]

B. Biocontrol Agents (Natural Pest Control)

Ladybird (Beetle): Controls Aphids.
Dragonfly: Controls Mosquitoes.
Bacillus thuringiensis (Bt): Controls Butterfly caterpillars (available as sachets of dried spores).
Trichoderma (Fungus): Free-living in root ecosystem. Controls several plant pathogens.
Baculoviruses (Nucleopolyhedrovirus): Attack insects/arthropods. Species-specific, narrow spectrum (No harm to plants/mammals). Important in IPM (Integrated Pest Management).

5. Biofertilizers

Organisms that enrich the nutrient quality of the soil.

Type	Examples	Role
Bacteria	Rhizobium (Symbiotic), Azospirillum, Azotobacter (Free-living).	Fix atmospheric Nitrogen.
Fungi (Mycorrhiza)	Genus Glomus.	Absorbs Phosphorus from soil. Provides resistance to root-borne pathogens, salinity, and drought.
Cyanobacteria	Anabaena, Nostoc, Oscillatoria.	Nitrogen fixation (Heterocysts). Adds organic matter to soil. Important in Paddy fields.

📝 Rapid Fire MCQs

Q1. A patient brought to a hospital with myocardial infarction is normally immediately given:

A) Penicillin
B) Streptokinase
C) Cyclosporin A
D) Statins

Click to check Answer

Answer: B) Streptokinase (Clot buster).

Q2. Which of the following is mainly produced by the activity of anaerobic bacteria on sewage?

A) Laughing gas
B) Propane
C) Mustard gas
D) Marsh gas