Microbes in Human Welfare (NEET Biology Class 12): Every Microbe and Its Product
Household Products, Beverages & Antibiotics
📌 NEET priority: Important. 2–3 questions a year — and they are almost ALWAYS match the microbe to its product. There is very little concept here and a great deal of exact naming. The five tables below ARE the chapter: learn them and you have the marks.
Microbes include protozoa, bacteria, fungi, microscopic animal and plant viruses, viroids, and prions — which are proteinaceous infectious agents.
Microbes in household products
Product | Microbe | What it does |
Curd | Lactobacillus and other Lactic Acid Bacteria (LAB) | Produce acids that coagulate and partially digest milk proteins. Curd added as INOCULUM/STARTER. Improves nutritional quality by increasing VITAMIN B12. In our stomach, LAB check disease-causing microbes |
Dosa and idli dough | Bacteria | Fermentation — the PUFFED-UP appearance is due to CO₂ production |
Bread dough | Saccharomyces cerevisiae — BAKER'S yeast | Fermentation |
Toddy | (fermentation of sap from palms) | A traditional drink of parts of southern India |
Swiss cheese | Propionibacterium sharmanii | The LARGE HOLES are due to a large amount of CO₂ produced |
Roquefort cheese | A specific fungus grown on it | Ripens the cheese, giving its particular flavour |
Fermented beverages
Saccharomyces cerevisiae — the same yeast used for bread, here called BREWER'S yeast — ferments malted cereals and fruit juices to produce ethanol.
The distinction NEET tests: WINE and BEER are produced WITHOUT distillation; WHISKY, BRANDY and RUM are produced BY distillation of the fermented broth.
Industrial-scale production requires growing microbes in very large vessels called fermentors.
Antibiotics — the Penicillin story
Antibiotic = "anti" (against) + "bio" (life) — chemicals produced by some microbes that kill or retard the growth of other disease-causing microbes.
Penicillin was the FIRST antibiotic discovered, and it was a chance discovery. Alexander Fleming, working on Staphylococci, saw a mould growing in an unwashed culture plate around which Staphylococci could not grow. He named the chemical Penicillin after the mould Penicillium notatum.
Its full potential was established later by Ernest Chain and Howard Florey. It was used extensively on American soldiers wounded in World War II. Fleming, Chain and Florey shared the Nobel Prize in 1945.
Antibiotics transformed treatment of plague, whooping cough, diphtheria and leprosy.
Industrial Products & Sewage Treatment
Chemicals, enzymes and bioactive molecules — the master naming table
Product | Microbe | Type | Use |
Citric acid | Aspergillus niger | Fungus | Organic acid |
Acetic acid | Acetobacter aceti | Bacterium | Organic acid |
Butyric acid | Clostridium butylicum | Bacterium | Organic acid |
Lactic acid | Lactobacillus | Bacterium | Organic acid |
Ethanol | Saccharomyces cerevisiae | Yeast | Commercial alcohol production |
Lipases | (microbial enzyme) | Enzyme | In DETERGENT formulations — remove OILY STAINS from laundry |
Pectinases and proteases | (microbial enzymes) | Enzyme | CLARIFY bottled fruit juices — which is why they are clearer than home-made juice |
Streptokinase | Streptococcus, modified by GENETIC ENGINEERING | Bacterium | A 'CLOT BUSTER' — removes clots from blood vessels of patients after myocardial infarction |
Cyclosporin A | Trichoderma polysporum | Fungus | IMMUNOSUPPRESSIVE agent in organ-transplant patients |
Statins | Monascus purpureus | Yeast | BLOOD-CHOLESTEROL LOWERING agent — works by COMPETITIVELY INHIBITING the enzyme responsible for cholesterol synthesis |
Sewage treatment — the two stages
Stage | What happens | Key terms |
PRIMARY treatment | PHYSICAL removal of particles. Floating debris removed by sequential FILTRATION; grit (soil and small pebbles) removed by SEDIMENTATION | Settled solids = PRIMARY SLUDGE. Supernatant = EFFLUENT, which goes to secondary treatment |
SECONDARY (biological) treatment | Primary effluent enters large AERATION TANKS, constantly agitated with air pumped in. Aerobic microbes grow vigorously into FLOCS — masses of bacteria with fungal filaments in a mesh — and consume the organic matter, significantly REDUCING BOD | FLOCS; BOD reduction |
Settling and sludge | Effluent passes to a settling tank where flocs sediment as ACTIVATED SLUDGE. A SMALL part is pumped BACK to the aeration tank as INOCULUM; the major part goes to ANAEROBIC SLUDGE DIGESTERS | ACTIVATED SLUDGE; anaerobic sludge digesters |
Digestion | Anaerobic bacteria digest the bacteria and fungi in the sludge, producing METHANE, HYDROGEN SULPHIDE and CARBON DIOXIDE — together BIOGAS, which is inflammable and usable as energy | BIOGAS |
BOD (Biochemical Oxygen Demand) is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. It measures the rate of oxygen uptake by microorganisms, and so indirectly measures the organic matter present. The greater the BOD, the greater the polluting potential.
India's Ministry of Environment and Forests initiated the Ganga Action Plan and Yamuna Action Plan to build more sewage treatment plants. NCERT's striking claim: no man-made technology has yet rivalled the microbial treatment of sewage.
Biogas, Biocontrol Agents & Biofertilisers
Biogas
Biogas is a mixture of gases containing predominantly METHANE. Certain bacteria growing anaerobically on cellulosic material produce large amounts of methane along with CO₂ and H₂ — collectively called METHANOGENS. The common example is Methanobacterium.
Methanogens are found in the anaerobic sludge during sewage treatment AND in the RUMEN of cattle, where they break down cellulose and play an important role in cattle nutrition. This is why cattle dung (gobar) is rich in these bacteria — hence gobar gas.
The biogas plant: a concrete tank 10–15 feet deep holding a dung slurry, with a floating cover that rises as gas is produced, an outlet piping biogas to nearby houses, and another outlet for spent slurry — usable as fertiliser. Biogas is used for cooking and lighting.
Developed in India mainly by the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).
Microbes as biocontrol agents
Biocontrol agent | Type | Target | How it works |
Ladybird beetle (red and black markings) | Insect | APHIDS | Natural predation |
Dragonfly | Insect | MOSQUITOES | Natural predation |
Bacillus thuringiensis (Bt) | Bacterium | BUTTERFLY CATERPILLARS | Sold as sachets of DRIED SPORES, mixed with water and sprayed on brassicas and fruit trees. Eaten by insect larvae; the toxin is released IN THE GUT of the larvae, killing them — but leaving OTHER INSECTS UNHARMED. Bt toxin genes have been engineered into plants, e.g. Bt-cotton |
Trichoderma | Free-living fungus, common in ROOT ecosystems | Several plant PATHOGENS | Effective biocontrol of plant disease |
Baculoviruses (genus Nucleopolyhedrovirus) | Virus | Insects and other arthropods | SPECIES-SPECIFIC, narrow spectrum. NO negative impact on plants, mammals, birds, fish or even non-target insects — ideal for integrated pest management (IPM) and ecologically sensitive areas |
Microbes as biofertilisers
Biofertiliser | Type | What it does |
Rhizobium | Bacterium — SYMBIOTIC, in root nodules of leguminous plants | Fixes atmospheric NITROGEN into organic forms usable by the plant |
Azospirillum and Azotobacter | Bacteria — FREE-LIVING in soil | Fix atmospheric nitrogen, enriching soil nitrogen content |
Glomus | Fungus — forms MYCORRHIZA with plant roots | The fungal symbiont absorbs PHOSPHORUS from soil and passes it to the plant. Also gives resistance to root-borne pathogens, tolerance to salinity and drought, and overall growth increase |
Anabaena, Nostoc, Oscillatoria | Cyanobacteria (blue-green algae) | Autotrophic; many fix atmospheric nitrogen. Important biofertiliser in PADDY FIELDS. Also add organic matter to soil, increasing fertility |
Why This Matters for NEET
Why this matters for NEET
High-value one-liners: curd = Lactobacillus/LAB, raises vitamin B12; Swiss cheese holes = Propionibacterium sharmanii; wine and beer are NOT distilled, whisky/brandy/rum ARE; Penicillin = Fleming from Penicillium notatum, Nobel 1945 with Chain and Florey; citric acid = Aspergillus niger; cyclosporin A = Trichoderma polysporum; statins = Monascus purpureus; streptokinase = clot buster; methanogen = Methanobacterium; Bt targets caterpillars.
Trap: higher BOD means MORE pollution, not less — BOD measures the oxygen that would be consumed, so a high value means a lot of organic matter is present. Students often invert this. Also, the same yeast Saccharomyces cerevisiae is baker's yeast, brewer's yeast, and the ethanol producer — three names, one organism.
Second trap: Rhizobium is SYMBIOTIC (lives in root nodules) while Azotobacter and Azospirillum are FREE-LIVING — both fix nitrogen, but the lifestyle distinction is exactly what gets asked. And Glomus supplies PHOSPHORUS, not nitrogen — it's the odd one out among the biofertilisers.
Test Yourself: MCQs, PYQs & Active Recall
Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one.
Practice Questions
Q1. Curd is formed from milk by the action of:
(a) Propionibacterium sharmanii
(b) Saccharomyces cerevisiae
(c) Lactobacillus and other lactic acid bacteria
(d) Aspergillus niger
Show answer
Answer: (c) — LAB produce acids that coagulate and partially digest milk proteins, and also increase vitamin B12 content.
Q2. The large holes in Swiss cheese are due to a large amount of CO2 produced by:
(a) Lactobacillus
(b) Penicillium notatum
(c) Monascus purpureus
(d) Propionibacterium sharmanii
Show answer
Answer: (d) — Propionibacterium sharmanii produces large amounts of CO2, creating the characteristic large holes in Swiss cheese.
Q3. Which alcoholic beverages are produced WITHOUT distillation?
(a) Whisky and brandy
(b) Wine and beer
(c) All are distilled
(d) Rum and whisky
Show answer
Answer: (b) — Wine and beer are produced without distillation; whisky, brandy and rum are produced by distillation of the fermented broth.
Q4. Penicillin was discovered by:
(a) Ernest Chain
(b) Howard Florey
(c) Alexander Fleming
(d) Louis Pasteur
Show answer
Answer: (c) — Fleming observed a mould inhibiting Staphylococci growth and named the chemical Penicillin after the mould Penicillium notatum.
Q5. Fleming, Chain and Florey were awarded the Nobel Prize in the year:
(a) 1935
(b) 1945
(c) 1953
(d) 1928
Show answer
Answer: (b) — They shared the Nobel Prize in 1945 for the discovery and development of Penicillin.
Q6. Citric acid is commercially produced by:
(a) Acetobacter aceti
(b) Lactobacillus
(c) Aspergillus niger
(d) Clostridium butylicum
Show answer
Answer: (c) — Aspergillus niger, a fungus, produces citric acid; Acetobacter aceti produces acetic acid.
Q7. Cyclosporin A, used as an immunosuppressive agent, is produced by:
(a) Monascus purpureus
(b) Streptococcus
(c) Penicillium notatum
(d) Trichoderma polysporum
Show answer
Answer: (d) — The fungus Trichoderma polysporum produces cyclosporin A, used in organ-transplant patients.
Q8. Statins, which lower blood cholesterol, are produced by:
(a) Aspergillus niger
(b) Rhizobium
(c) Monascus purpureus
(d) Trichoderma
Show answer
Answer: (c) — Statins from the yeast Monascus purpureus act by competitively inhibiting the enzyme responsible for cholesterol synthesis.
Q9. Streptokinase, used as a 'clot buster', is produced by:
(a) Lactobacillus
(b) Streptococcus, modified by genetic engineering
(c) Bacillus thuringiensis
(d) Staphylococcus
Show answer
Answer: (b) — Streptokinase from Streptococcus, modified by genetic engineering, removes clots from blood vessels after myocardial infarction.
Q10. Which enzymes are used to clarify bottled fruit juices?
(a) Amylases
(b) Pectinases and proteases
(c) Lipases
(d) Cellulases
Show answer
Answer: (b) — Pectinases and proteases clarify bottled juices; lipases are used in detergents to remove oily stains.
Q11. In secondary sewage treatment, masses of bacteria associated with fungal filaments are called:
(a) Biogas
(b) Flocs
(c) Effluent
(d) Primary sludge
Show answer
Answer: (b) — Aerobic microbes grow into flocs — mesh-like masses of bacteria with fungal filaments — which consume the organic matter.
Q12. BOD is a measure of:
(a) The oxygen produced by algae
(b) The pH of the water
(c) The number of bacteria per litre
(d) The organic matter present in water, measured indirectly
Show answer
Answer: (d) — BOD measures the rate of oxygen uptake by microorganisms and thus indirectly measures the organic matter present.
Q13. A higher BOD value in waste water indicates:
(a) Lower bacterial count
(b) Higher oxygen content
(c) Cleaner water
(d) Greater polluting potential
Show answer
Answer: (d) — The greater the BOD of waste water, the more its polluting potential — because more organic matter is present.
Q14. The sediment of bacterial flocs in the settling tank is called:
(a) Biogas
(b) Effluent
(c) Activated sludge
(d) Primary sludge
Show answer
Answer: (c) — Activated sludge sediments in the settling tank; a small part is pumped back to the aeration tank as inoculum.
Q15. Biogas predominantly contains:
(a) Nitrogen
(b) Methane
(c) Hydrogen sulphide
(d) Carbon dioxide
Show answer
Answer: (b) — Biogas is a mixture of gases containing predominantly methane, produced by methanogens.
Q16. Methanogens such as Methanobacterium are found in:
(a) Aerobic tanks only
(b) Anaerobic sludge AND the rumen of cattle
(c) Only in the rumen
(d) Only in sewage sludge
Show answer
Answer: (b) — Methanogens occur in anaerobic sludge during sewage treatment and in the rumen of cattle, where they break down cellulose.
Q17. Bacillus thuringiensis is used to control:
(a) Mosquitoes
(b) Plant fungal pathogens
(c) Butterfly caterpillars
(d) Aphids
Show answer
Answer: (c) — Bt is sprayed as dried spores; larvae eat it and the toxin is released in their gut, killing them while leaving other insects unharmed.
Q18. Which biocontrol agent is a free-living fungus common in root ecosystems?
(a) Glomus
(b) Trichoderma
(c) Bacillus thuringiensis
(d) Baculovirus
Show answer
Answer: (b) — Trichoderma species are free-living fungi very common in root ecosystems and are effective biocontrol agents of plant pathogens.
Q19. Which biofertiliser supplies PHOSPHORUS rather than nitrogen to the plant?
(a) Anabaena
(b) Glomus (mycorrhiza)
(c) Azotobacter
(d) Rhizobium
Show answer
Answer: (b) — The fungal symbiont Glomus, forming mycorrhiza, absorbs phosphorus from soil and passes it to the plant.
Q20. Azotobacter and Azospirillum differ from Rhizobium in that they are:
(a) Symbiotic nitrogen fixers
(b) Not nitrogen fixers
(c) Free-living nitrogen fixers in the soil
(d) Phosphorus fixers
Show answer
Answer: (c) — Rhizobium is symbiotic in root nodules; Azospirillum and Azotobacter fix atmospheric nitrogen while free-living in the soil.
NEET Previous Year Questions (PYQs)
Real NEET previous-year questions on this chapter, with explanations in our own words.
Q21. The puffed-up appearance of dough used for making dosa and idli is due to: (NEET PYQ)
(a) Production of ethanol
(b) Production of CO2 gas
(c) Water absorption
(d) Protein coagulation
Show answer
Answer: (b) — Bacterial fermentation of the dough produces CO2 gas, causing the puffed-up appearance.
Q22. Which of the following is used in detergent formulations to remove oily stains? (NEET PYQ)
(a) Pectinase
(b) Lipase
(c) Protease
(d) Streptokinase
Show answer
Answer: (b) — Lipases are used in detergent formulations and help remove oily stains from laundry.
Q23. Baculoviruses used as biological control agents belong to the genus: (NEET PYQ)
(a) Bacillus
(b) Nucleopolyhedrovirus
(c) Glomus
(d) Trichoderma
Show answer
Answer: (b) — The majority of baculoviruses used as biocontrol agents are in the genus Nucleopolyhedrovirus — species-specific with no impact on non-target organisms.
Q24. Cyanobacteria used as biofertilisers in paddy fields include: (NEET PYQ)
(a) Anabaena, Nostoc and Oscillatoria
(b) Lactobacillus
(c) Rhizobium and Azotobacter
(d) Glomus and Trichoderma
Show answer
Answer: (a) — Anabaena, Nostoc and Oscillatoria are nitrogen-fixing cyanobacteria that serve as important biofertilisers in paddy fields.
Q25. The biogas technology in India was developed mainly due to the efforts of: (NEET PYQ)
(a) ICAR and CSIR
(b) WHO and FAO
(c) IARI and KVIC
(d) ISRO and DRDO
Show answer
Answer: (c) — The Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC) developed biogas technology in India.
Q26. In the Bt biocontrol method, the toxin is released: (NEET PYQ)
(a) In the gut of the insect larvae
(b) In the soil
(c) In the plant xylem
(d) On the leaf surface
Show answer
Answer: (a) — Larvae eat the sprayed spores; the toxin is released in the gut of the larvae, killing them while other insects remain unharmed.
Q27. Which of these is a proteinaceous infectious agent? (NEET PYQ)
(a) Viroid
(b) Mycoplasma
(c) Bacteriophage
(d) Prion
Show answer
Answer: (d) — Prions are proteinaceous infectious agents, listed by NCERT alongside protozoa, bacteria, fungi, viruses and viroids.
Q28. The same yeast Saccharomyces cerevisiae is known as brewer's yeast when used for: (NEET PYQ)
(a) Producing citric acid
(b) Fermenting malted cereals and fruit juices
(c) Making curd
(d) Making bread
Show answer
Answer: (b) — The same yeast used for bread-making is called brewer's yeast when fermenting malted cereals and fruit juices to produce ethanol.
Q29. Anaerobic sludge digesters produce a mixture of gases including: (NEET PYQ)
(a) Oxygen and nitrogen
(b) Only carbon dioxide
(c) Methane, hydrogen sulphide and carbon dioxide
(d) Ammonia only
Show answer
Answer: (c) — Anaerobic bacteria in sludge digesters produce methane, hydrogen sulphide and carbon dioxide — together forming inflammable biogas.
Q30. Plants having mycorrhizal associations show which additional benefit? (NEET PYQ)
(a) Resistance to root-borne pathogens and tolerance to salinity and drought
(b) Faster flowering only
(c) Nitrogen fixation
(d) Only phosphorus uptake
Show answer
Answer: (a) — Besides phosphorus absorption, mycorrhizal plants show resistance to root-borne pathogens, tolerance to salinity and drought, and overall growth increase.
Active Recall Prompt
Write everything you can recall about Microbes in Human Welfare, naming each microbe and its product: household products (curd, dough, cheeses — and the microbe for each); fermented beverages (which are distilled and which are not); antibiotics (the full Penicillin discovery story with all three names and the year); chemicals, enzymes and bioactive molecules (every acid with its microbe, plus lipase, pectinase, streptokinase, cyclosporin A and statins); sewage treatment (both stages, flocs, activated sludge, and what BOD means); biogas (methanogens, the plant, IARI and KVIC); biocontrol agents; and biofertilisers (symbiotic vs free-living, and which supplies phosphorus). Begin each fact with its topic and end it with a full stop.