# Microbes in Human Welfare (NEET Biology Class 12): Every Microbe and Its Product Source: https://tracknation.in/story/microbes-in-human-welfare-neet-biology-class-12-every-microbe-and-its-product (TrackNation — free UPSC notes with PYQs) > NEET Class 12 Microbes in Human Welfare, mined from NCERT and built as five dense reference tables — because this chapter is almost entirely match-the-microbe-to-its-product: household products (curd, cheeses, dough), fermented beverages (which are distilled and which are not), the full Penicillin discovery story, a 10-row industrial chemicals/enzymes/bioactive molecules table (citric acid, streptokinase, cyclosporin A, statins), sewage treatment stage by stage with BOD explained, biogas and met ## 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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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 **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.