Microbes in Human Welfare Class 12 Exemplar Solutions PDF

Correct option: (c) vitamin B12.

Concept used. Curd is formed when lactic acid bacteria (LAB), principally Lactobacillus (and to a lesser extent Lactococcus and Streptococcus), inoculate warm milk and convert milk lactose into lactic acid. The acid lowers the pH below the iso-electric point of casein (∼ 4.6), causing the milk protein to coagulate into the soft semisolid we call curd. Alongside this souring, LAB also synthesize several B-complex vitamins as metabolic by-products, the most prominent of which is cobalamin (vitamin B12).

1. Identify the chemistry: LAB metabolise lactose anaerobically via Lactose ⟶ 2 Lactic acid (catalysed by LAB), which acidifies and coagulates milk into curd.
2. Examine vitamin synthesis: during this fermentation, Lactobacillus also synthesises cobalamin (B12) using cobalt incorporated into a corrin ring. As a result, the curd's B12 content is appreciably higher than the original milk's.
3. Eliminate distractors: (a) vitamin C is not synthesised by LAB and is actually destroyed by heat/acid; (b) vitamin D is fat-soluble and comes only from sunlight or supplementation; (d) vitamin E is plant-oil-derived and not microbially upregulated.

Option (c) vitamin B12.

Correct option: (a) anaerobic digesters.

Concept used. Sewage treatment runs in two main biological steps. Primary treatment removes large solids by sedimentation. Secondary treatment aerates effluent to grow aerobic floc communities that consume biodegradable organic matter (BOD). The biomass that settles afterwards is the activated sludge; the bulk of it is pumped into large, sealed anaerobic digesters where methanogenic bacteria break it down further, producing biogas (a mixture of CH4, CO2 and H2S).

1. Identify what ``sludge'' means: it is the settled microbial-rich biomass left after aerobic floc formation in the secondary settling tank. It is rich in proteins, fats and carbohydrates.
2. Apply the treatment logic: this organic-rich biomass must be stabilised before disposal. The standard route is large heated, oxygen-free anaerobic digesters where methanogens such as Methanobacterium run the reaction: Organic matter -> CH4 + CO2 + H2S + Biomass (by methanogens).
3. Rule out distractors: flocs (b) are the aerobic step, used before sludge forms; chemicals (c) are used in some tertiary polishing but not for primary sludge stabilisation; oxidation ponds (d) treat dilute effluent, not concentrated sludge.

Sludge is treated by anaerobic digesters (option a).

Correct option: (d) activated sludge.

Concept used. Methanogens are strict anaerobic archaea that produce methane (CH4) as an end-product of their energy metabolism. They survive only where oxygen is absent and organic matter is abundant. The four classic habitats are: (i) the rumen of cattle and other ruminants, (ii) the digester of a gobar (cow-dung) biogas plant, (iii) the anoxic mud at the bottom of water-logged paddy fields, and (iv) the anaerobic digester used to treat sludge. Activated sludge itself, however, is the aerated biomass in the secondary aeration tank — full of oxygen — and therefore hostile to methanogens.

1. Test each option against the oxygen criterion:
   • 2pt
   • (a) Rumen: anoxic, methanogens abundant (→ ``cattle burp methane'').
   • (b) Gobar gas plant: sealed digester, anoxic, methanogens drive biogas.
   • (c) Paddy field bottoms: water-logged, anoxic, methanogens make paddies a major methane source.
   • (d) Activated sludge: aerated continuously in the aeration tank. Aerobic flocs of bacteria and protozoa dominate. Methanogens cannot survive.
2. Conclude: the odd one out is (d).

Methanogens are not found in activated sludge (option d).

Correct option: (c) A-iv, B-iii, C-ii, D-i.

Concept used. Each industrial organic acid in this list is associated with a specific microbial workhorse. The four are textbook one-to-one mappings:

• 2pt
• Aspergillus niger — citric acid (used in soft drinks, candies, pharmaceuticals).
• Acetobacter aceti — acetic acid (the souring agent of vinegar).
• Clostridium butylicum (also called C. butyricum) — butyric acid (rancid-butter smell).
• Lactobacillus — lactic acid (curd, yoghurt).

1. Pair A. niger → citric acid (iv). This is a fungus, technically not a bacterium, but NCERT lists it among ``microbes in industrial products''.
2. Pair Acetobacter aceti → acetic acid (iii). The name literally derives from acetum (vinegar).
3. Pair Clostridium butylicum → butyric acid (ii). The Latin butyrum (butter) gives both the genus and the acid names.
4. Pair Lactobacillus → lactic acid (i), the curd workhorse already discussed in Q1.
5. Assembled: A-iv, B-iii, C-ii, D-i — matches option (c).

A-iv, B-iii, C-ii, D-i — option (c).

Correct option: (d) A-iii, B-iv, C-ii, D-i.

Concept used. Four microbial bioactives appear in NCERT, each with a different biomedical or industrial role:

• 2pt
• Statins (from Monascus purpureus) inhibit the enzyme HMG-CoA reductase, the rate-limiting step in cholesterol biosynthesis. They lower blood cholesterol.
• Cyclosporin A (from Trichoderma polysporum) suppresses the T-cell response and is used to prevent rejection in organ transplant patients.
• Streptokinase (from Streptococcus) dissolves fibrin clots; it is used as a clot buster in heart-attack patients.
• Lipase (from many bacteria/fungi) hydrolyses fats and is added to washing detergents to remove oil/grease stains.

1. Statin → lowers blood cholesterol → (iii).
2. Cyclosporin A → immuno-suppressive → (iv).
3. Streptokinase → dissolves clots → (ii).
4. Lipase → removes oil stains → (i).
5. Assemble: A-iii, B-iv, C-ii, D-i = option (d).

A-iii, B-iv, C-ii, D-i — option (d).

Correct option: (b) stable particles.

Concept used. Sewage treatment is staged. The primary treatment is purely physical: it screens out floating debris and lets gravity settle larger, denser, ``stable'' particles in a sedimentation tank. The biological oxidation that removes dissolved organics happens later, in secondary treatment (the aeration tank with its activated sludge flocs). Tertiary treatment polishes the effluent for nitrogen, phosphorus and pathogens.

1. Recall the three stages and their purposes:
   • 2pt
   • Primary → physical: screening + sedimentation → removes stable particles.
   • Secondary → biological: aerobic flocs consume dissolved organics and reduce BOD.
   • Tertiary → chemical/biological polishing: removes dissolved nutrients and pathogens.
2. Map the options: (a) dissolved impurities → secondary, (b) stable particles → primary ⇒ correct, (c) toxic substances → tertiary, (d) harmful bacteria → tertiary (chlorination/UV).

Primary treatment removes stable particles (option b).

Correct option: (d) oxygen consumption.

Concept used. Biochemical Oxygen Demand (BOD) is defined as the amount of dissolved oxygen consumed by aerobic microbes while decomposing the biodegradable organic matter present in a sample of water, over a fixed incubation (usually 5 days at 20). The higher the organic load, the more oxygen the microbes consume, and the higher the BOD. BOD is therefore measured indirectly through O2 depletion, not directly through organic matter.

1. State the operational test: incubate a sealed water sample with bacteria at 20 for 5 days; measure [O2] before and after. BOD₅ = [O2]_initial - [O2]_{after 5 days} (mg/L).
2. Identify what is actually quantified: it is the oxygen consumed, not the organic matter itself. Hence option (d).
3. Rule out distractors: (a) Total organic matter is measured by TOC, not BOD; (b) Biodegradable organic matter is what causes BOD but is not what we read; (c) Oxygen evolution applies to photosynthesis, not respiration.

BOD is measured by oxygen consumption (option d).

Correct option: (a) Wine.

Concept used. Alcoholic drinks split into two categories. Fermented drinks (wine, beer, cider) are made by yeast fermentation of sugar to ethanol; their final alcohol content is limited to about 5–15% ABV because yeast cannot survive higher concentrations. Distilled drinks (whisky, rum, brandy, vodka, gin) are made by distilling a fermented mash — selectively boiling off and condensing ethanol — to reach 40%–50% ABV or more.

1. Categorise each option:
   • 2pt
   • (a) Wine — fermentation of grape juice by Saccharomyces cerevisiae; no distillation. ∼ 12% ABV.
   • (b) Whisky — distilled from fermented grain mash. ∼ 40% ABV.
   • (c) Rum — distilled from fermented molasses. ∼ 40% ABV.
   • (d) Brandy — distilled from fermented fruit juice (often wine). ∼ 40% ABV.
2. Only wine skips the distillation step.

Wine (option a) is produced without distillation.

Correct option: (c) Indian Agricultural Research Institute (IARI) and Khadi & Village Industries Commission (KVIC).

Concept used. ``Gobar gas'' (cow-dung biogas) production was scaled up across rural India by two complementary institutions. IARI contributed the microbiological and engineering R&D, designing efficient digesters and methanogen consortia. KVIC carried out the rural deployment, training farmers and providing subsidies. Together, they pushed biogas from a laboratory novelty to a national programme covering several million plants by the 1980s.

1. Identify the technology owner. The development of fixed-dome and floating-drum biogas plants for cow dung was led in India by IARI's microbiologists.
2. Identify the dissemination partner. KVIC, an autonomous body under the Ministry of MSME, took the lab design to villages with subsidies and training under the National Biogas Programme.
3. Eliminate distractors: GAIL (a), ONGC (b) and IOC (d) are oil-and-gas-sector PSUs concerned with fossil fuels, not rural biogas R&D.

The credit goes to IARI and KVIC (option c).

Correct option: (b) biological control of plant diseases.

Concept used. Trichoderma is a soil-borne, free-living, fast-growing fungus that out-competes plant-pathogenic fungi (such as Pythium, Fusarium, Rhizoctonia) by mycoparasitism, antibiosis and competitive root colonisation. It is one of the most widely used biological control agents against fungal plant diseases. It is not an insecticide (that is the role of Bacillus thuringiensis and ladybirds), nor a primary antibiotic producer (that role belongs to Penicillium, Streptomyces, etc.).

1. Recall Trichoderma's ecological role: a parasitic fungus that attacks other fungi (mycoparasitism) and colonises roots, protecting the plant from soil-borne fungal disease.
2. Map to options: (a) Insects — handled by Bacillus thuringiensis or NPV viruses, not Trichoderma. (b) Plant diseases — yes, Trichoderma controls fungal root rots. (c) Caterpillars — controlled by Bt or NPV, not by a fungus. (d) Antibiotics — produced by Penicillium and Streptomyces; cyclosporin A is the only known Trichoderma drug but is an immuno-suppressant.
3. Confirm option (b).

Trichoderma is used for biological control of plant diseases (option b).

Correct option: (b) The centre of flocs will become anoxic, causing death of bacteria and breakage of flocs.

Concept used. Activated sludge flocs are loose 3D aggregates of aerobic bacteria glued together by extracellular polymeric substances. They function only when dissolved oxygen (DO) can diffuse from the bulk water into the floc centre — typically requiring bulk DO > 2 mg/L. If oxygen supply is reduced, the outer cells consume what little O2 arrives, leaving the central cells with [O2] → 0. These central cells die, the floc weakens and disintegrates, and the whole secondary clarifier stops working.

1. Recall floc architecture: a floc is ∼ 50–500 µm across. Oxygen reaches the centre only by diffusion.
2. Apply Fick's law qualitatively: if bulk O2 drops, the diffusion gradient flattens; central cells see anoxia.
3. Trace the consequence: anoxic core → death of central cells → structural collapse → floc breakage. The biomass disperses, fails to settle, and washes out with the effluent.
4. Compare options: (a) Slower degradation is true but only part of the story; the floc structure also collapses, so (b) is more complete. (c) Anaerobic bacteria do not preferentially colonise aerobic flocs; flocs do not grow under anoxia. (d) Protozoa are aerobic and also die under low DO; they do not bloom.

Reduced O2 ⇒ anoxic floc centres die and flocs break (option b).

Correct option: (d) Increasing its resistance to insects.

Concept used. Mycorrhiza is a symbiotic association between a fungus (typically Glomus, an AM fungus) and the roots of a higher plant. The fungal hyphae extend the effective root surface 100–1000-fold, helping the plant absorb phosphorus (and other immobile nutrients), retain water during drought, and resist soil-borne pathogens. However, insects feed on above-ground plant parts (leaves, stems, fruits) which mycorrhiza does not protect. Hence (d) is the negative match.

1. List the four benefits the question offers and check each against NCERT:
   • 2pt
   • Phosphorus uptake (a) — Yes. AM fungi solubilise and translocate PO4^3-.
   • Drought tolerance (b) — Yes. Hyphae access water films in fine soil pores.
   • Root pathogen resistance (c) — Yes. The mantle and mycorrhizosphere block pathogenic fungi.
   • Insect resistance (d) — No. Insect herbivory targets shoots, which mycorrhiza does not protect.
2. Pick the option that the fungus does NOT help with: (d).

Mycorrhiza does not help with insect resistance (option d).

Correct option: (d) Pseudomonas.

Concept used. Biological nitrogen fixation is carried out by select prokaryotes that express the enzyme nitrogenase, which reduces atmospheric N2 to NH3 via N2 + 8 H+ + 8 e- + 16 ATP -> 2 NH3 + H2 + 16 ADP + 16 Pi. Among the four listed: Anabaena and Nostoc are heterocyst-bearing cyanobacteria (filamentous photosynthetic N-fixers used as biofertilizers in paddies); Azotobacter is a free-living aerobic soil bacterium that fixes N2. Pseudomonas (e.g. P. fluorescens, P. aeruginosa) is famous for denitrification, biocontrol and pollutant degradation but does not fix nitrogen.

1. Mark known N-fixers among the options:
   • 2pt
   • Anabaena — N-fixing cyanobacterium (heterocysts) ⇒ yes.
   • Nostoc — N-fixing cyanobacterium ⇒ yes.
   • Azotobacter — free-living aerobic N-fixer ⇒ yes.
   • Pseudomonas — denitrifier/biocontrol ⇒ NOT a N-fixer.
2. Conclude: (d) is the exception.

Pseudomonas (option d) is not a nitrogen-fixer.

Correct option: (c) a bacterium producing a large amount of carbon dioxide.

Concept used. Swiss cheese (Emmental) gets its characteristic ``eyes'' or holes from Propionibacterium shermanii, a bacterium added during cheese ripening. It ferments lactate to propionic acid, acetic acid and CO2: 3 Lactate -> 2 Propionate + Acetate + CO2 + H2O (P. shermanii). The CO2 cannot escape the firm curd, so it accumulates as bubbles which leave visible holes when the cheese is sliced. The propionic and acetic acids also give Swiss cheese its distinctive nutty, slightly tangy flavour.

1. Identify the bacterium: Propionibacterium shermanii, deliberately inoculated into the curd during ripening.
2. Identify the gas: CO2, not methane. Methane is the by-product of biogas plants, not cheese.
3. Identify the cause of holes: CO2 bubbles trapped in firm curd → persistent voids.
4. Rule out the other options: (a) Machine — wrong; holes are biological. (b) Methane — wrong gas, wrong organism. (d) Fungus — wrong kingdom; in Swiss cheese the eye-maker is a bacterium.

Swiss-cheese holes come from CO2 produced by a bacterium (option c).

Correct option: (c) used as manure.

Concept used. A biogas (gobar gas) plant processes cattle dung in an anaerobic digester. Methanogens convert most of the carbon to CH4 and CO2, leaving a wet, nutrient-rich solid/slurry called digestate or ``spent slurry''. Because methanogenic digestion does not remove nitrogen, phosphorus or potassium, the residue is high in N, P, K and is widely used as an organic manure on farms — closing the nutrient loop in rural mixed-farming systems.

1. Recall what the digester does: it removes mostly C (as CH4 + CO2) but conserves N, P, K and minor minerals in the residue.
2. Identify the nutrient content of the residue: high N (from urea/ureic-acid breakdown), high P (from bone/phytate breakdown), high K.
3. This nutrient profile makes the residue an ideal organic fertilizer. Farmers in rural India apply it directly to fields.
4. Eliminate other options: (a) Burning — wasteful; nutrients lost. (b) Landfill — also wasteful and environmentally poor. (d) Civil construction — residue is wet slurry, not a building material.

Residue is used as manure (option c).

Correct option: (a) oxygen.

Concept used. Methanogens are strict anaerobic archaea that derive energy by reducing one-carbon substrates to methane. Their metabolic outputs are CH4, CO2 and (when sulphur-containing organics are present) H2S. They are obligate anaerobes — exposure to O2 kills them — so they neither use nor produce molecular oxygen. Oxygenic photosynthesis (which produces O2) is the exclusive domain of plants, algae and cyanobacteria, not methanogens.

1. Write the methanogenic reactions: CO2 + 4 H2 -> CH4 + 2 H2O, CH3COOH -> CH4 + CO2. The outputs are CH4 and CO2. From sulphur-bearing inputs (e.g. cysteine) additional H2S is liberated.
2. Note what is missing from the output list: O2. Methanogens have no enzymatic pathway to evolve oxygen — they are not phototrophs.
3. Compare with options: O2 is the one they do NOT make ⇒ (a).

Methanogens do not produce oxygen (option a).

Correct option: (a) be rapidly pumped back from sedimentation tank to aeration tank.

Concept used. The activated sludge process runs as a continuous loop. The aeration tank holds the live floc community; effluent then flows into a secondary sedimentation tank where flocs settle by gravity. Most of the settled sludge is rapidly recycled back into the aeration tank to maintain a high biomass concentration; only a fraction is wasted to the anaerobic digester. For the system to work, the flocs must settle quickly (within 30–60 minutes), so that the return flow is fast enough to keep biomass concentrations in the aeration tank stable.

1. Picture the loop: aeration tank → settling tank → (most sludge) → back to aeration tank.
2. If sludge settles slowly, the return flow stalls, biomass in the aeration tank drops, and BOD removal collapses.
3. Therefore the primary purpose of fast settling is to enable rapid recycle (option a).
4. Eliminate distractors: (b) Pathogen absorption is not the design goal of fast settling. (c) Only a small fraction is wasted; recycle is the main fate. (d) Colloid absorption happens during aeration, not settling.

Fast settling enables rapid recycle back to the aeration tank (option a).

Correct option: (b) A-iii, B-iv, C-ii, D-i.

Concept used. Four standard NCERT pairings, drawn directly from the chapter's biocontrol and biofertilizer sections:

• 2pt
• Lady birds (beetles) feed on aphids — the classic predator–prey biocontrol pair.
• Mycorrhiza is most commonly formed by the AM fungus Glomus (with plant roots).
• Biological control of fungal root rots uses Trichoderma.
• Biogas is produced by methanogens such as Methanobacterium.

1. Match A — Lady bird → Aphids (iii).
2. Match B — Mycorrhiza → Glomus (iv).
3. Match C — Biological control → Trichoderma (ii).
4. Match D — Biogas → Methanobacterium (i).
5. Assemble: A-iii, B-iv, C-ii, D-i ⇒ option (b).

A-iii, B-iv, C-ii, D-i — option (b).

Concept used. Swiss cheese (Emmental) is ripened in the presence of the bacterium Propionibacterium shermanii, which metabolises lactate inside the curd to propionic acid, acetic acid and CO2. The cheese matrix is firm and elastic; the CO2 gas cannot escape and gets trapped as expanding bubbles, which become the visible ``eyes'' or holes when the wheel is sliced.

1. Inoculation: starter cultures of P. shermanii are added to milk along with the usual lactic acid bacteria.
2. Fermentation: 3 Lactate -> 2 Propionate + Acetate + CO2 + H2O. Propionic acid gives Swiss cheese its nutty flavour; the CO2 is the hole-maker.
3. Trapping: the firm curd does not let CO2 diffuse out, so the gas pockets remain as round eyes.

Swiss cheese has big holes because Propionibacterium shermanii releases large amounts of CO2 during ripening, and the gas is trapped in the firm curd.

Concept used. A fermentor (or bioreactor) is a closed industrial-scale vessel (typically 100–10,000 L) in which microbes are grown under tightly controlled conditions (temperature, pH, dissolved O2, agitation, nutrient feed) to produce useful products such as antibiotics, organic acids, enzymes, vitamins or ethanol.

1. Define: large stirred-tank or air-lift vessel designed to support microbial growth at a high cell density.
2. Function: provides controlled pH, temperature, aeration and mixing so that microbes produce the desired metabolite efficiently and reproducibly.
3. Output: harvested broth from which the product is purified.

Fermentors are large stainless-steel bioreactors used to grow microbes under controlled conditions for industrial production of antibiotics, organic acids, enzymes, vitamins and ethanol.

Concept used. Statins are a class of cholesterol-lowering drugs originally isolated from the yeast-like fungus Monascus purpureus. They work by competitively inhibiting the enzyme HMG-CoA reductase, the rate-limiting enzyme in the mevalonate pathway of cholesterol biosynthesis. When this enzyme is blocked, the liver cannot make cholesterol; it compensates by pulling LDL cholesterol out of the bloodstream, lowering circulating LDL.

1. Source microbe: Monascus purpureus (the producer of lovastatin and related statins).
2. Target enzyme: HMG-CoA reductase, which catalyses HMG-CoA + 2 NADPH -> Mevalonate + 2 NADP+ (by HMG-CoA reductase).
3. Mechanism: statin's structure mimics HMG-CoA; it binds the active site and blocks mevalonate formation. The downstream pathway to cholesterol stops.
4. Effect: hepatocytes upregulate LDL receptors to import cholesterol from blood, reducing serum LDL by 30–50%.

Statins are made by Monascus purpureus. They lower blood cholesterol by inhibiting HMG-CoA reductase, the rate-limiting enzyme of cholesterol biosynthesis.

Concept used. Secondary treatment of sewage uses live microbial communities — primarily aerobic bacteria, fungi and protozoa organised into flocs — to break down the dissolved and colloidal organic matter that primary (physical) treatment cannot remove. The biomass actively oxidises BOD-causing organics into CO2, water and new biomass. Because the entire mechanism is driven by living organisms, secondary treatment is also called biological treatment.

1. Step 1: primary treatment removes solids physically; the effluent still contains dissolved organics.
2. Step 2: in the aeration tank, microbial flocs grow on the organics: Organics + O2 -> CO2 + H2O + new cells (by flocs).
3. Conclude: living microbes perform the BOD reduction — hence the name ``biological'' treatment.

Because secondary treatment relies on live microbial flocs (bacteria, protozoa, fungi) to oxidise organic matter, it is called biological treatment.

Concept used. Nucleopolyhedrovirus (NPV) is a genus of baculoviruses that specifically infect and kill insect larvae of certain pest species. Because NPVs are highly host-specific (they will not harm humans, mammals, birds, fish or beneficial insects like honeybees), they are widely used as narrow-spectrum biocontrol agents, especially in Integrated Pest Management (IPM) programmes against caterpillars of moths and butterflies that damage crops.

1. Identify the agent: NPVs are insect-specific viruses, occluded in protein polyhedra that protect them in the soil until ingested by a larva.
2. Mechanism: ingested polyhedra dissolve in the alkaline larval midgut, releasing virions that infect epithelial cells, replicate, and lyse the host larva into a viral-particle-laden ``melted'' body.
3. Application: sprayed on crops as a wettable powder. Pest larvae feed, die, and the virus continues to cycle.

Nucleopolyhedroviruses (NPVs) are used as narrow-spectrum biological pesticides in IPM, mainly to kill caterpillar pests of crops without harming non-target organisms.

Concept used. Antibiotics are antimicrobial chemicals (produced naturally by microbes such as Penicillium, Streptomyces, Bacillus) that selectively kill or inhibit other microbes without harming the human host. Their discovery (penicillin by Fleming in 1928, antibiotic activity established by Chain and Florey in the 1940s) revolutionised medicine by giving humanity, for the first time, a reliable way to cure bacterial infections that had been routinely fatal for thousands of years.

1. Pre-antibiotic era: pneumonia, plague, leprosy, tuberculosis, whooping cough, diphtheria, gonorrhoea and post-surgery infections killed millions every year; surgery itself was extremely dangerous.
2. Post-antibiotic era: most bacterial infections became routinely curable; surgery, transplantation, chemotherapy, ICU care and modern obstetrics all became feasible because secondary bacterial infections could be controlled.
3. Public health impact: life expectancy in many countries jumped by 15–20 years between 1940 and 1970, largely thanks to antibiotics and vaccines.

Antibiotics turned previously fatal bacterial diseases (plague, leprosy, TB, pneumonia, gonorrhoea, post-surgical sepsis) into curable infections, enabling safe surgery, transplantation and a dramatic rise in human life expectancy.

Concept used. Distillation is the physical separation of two liquids of different boiling points by heating and condensing the vapours. Ethanol boils at 78.4 C, water at 100 C — so heating a fermented mash drives off ethanol-enriched vapour, which is condensed to a higher-alcohol distillate. Distillation is required for spirits (whisky, rum, brandy, vodka, gin) because yeast cells die above ∼ 15% ethanol, capping straight fermentation; distillation breaks past that ceiling and concentrates the alcohol to 40%–50% or beyond.

1. Note the yeast tolerance limit: Saccharomyces cells stop fermenting and die at ∼ 15% ethanol.
2. For drinks like wine (12%) and beer (5%) this is enough; no distillation needed.
3. For spirits (whisky, rum, brandy at ∼ 40% ABV), the fermented mash is distilled — vapour from heated mash is condensed to give a far higher-alcohol distillate.

Distillation is required for spirits (whisky, rum, brandy) because yeast cannot survive beyond ∼ 15% ethanol; distillation concentrates the ethanol from ∼ 10% fermented mash to ∼ 40%–50% in the final drink.

Concept used. Aspergillus niger (a fungus), Clostridium butylicum (a bacterium) and Lactobacillus (a bacterium) are taxonomically very different, but they are all industrial producers of organic acids via fermentation. A. niger makes citric acid, C. butylicum makes butyric acid, and Lactobacillus makes lactic acid.

1. List each microbe's signature product:
   • 2pt
   • A. niger → citric acid.
   • C. butylicum → butyric acid.
   • Lactobacillus → lactic acid.
2. Identify the common feature: all three are microbial sources of commercially important organic acids.

All three are microbes used in the industrial production of organic acids: citric (A. niger), butyric (C. butylicum) and lactic (Lactobacillus).

Concept used. The rumen of cattle is a large anaerobic chamber housing methanogens and cellulolytic bacteria that break down cellulose into volatile fatty acids and produce CH4 and CO2. The human intestine is much smaller, oxygen-tolerant on the surface, and has no cellulase-producing bacteria. If we suddenly hosted a rumen-like microbiome, two big changes would follow: (i) we could digest cellulose (eat grass!), and (ii) we would generate large volumes of methane and CO2, leading to severe bloating.

1. Acquire cellulolytic ability: cellulolytic bacteria would secrete cellulase, enabling humans to digest plant cell walls (cellulose, hemicellulose) as cattle do.
2. Co-produce gases: methanogens would release vast quantities of CH4 + CO2, causing severe abdominal distension and flatulence.
3. Net effect: humans could survive on grass and roughage, but the gas load would be uncomfortable and potentially dangerous (eructation in cattle releases ∼ 250 L of methane per day).

We would be able to digest cellulose (grass, leaves) but would also produce huge amounts of methane and CO2, causing severe abdominal bloating.

Concept used. Biotechnology uses microbes as cell factories, restriction-enzyme sources, expression hosts, or recombinant DNA vehicles. Two examples that show up universally are:

• 2pt
• Escherichia coli — the workhorse bacterium used as a host to express recombinant proteins (e.g. human insulin, growth hormone, several vaccines).
• Saccharomyces cerevisiae — baker's/brewer's yeast, used for eukaryotic protein expression, bioethanol production and as a model eukaryote.

1. Name microbe 1: E. coli. Uses: cloning vector host, recombinant protein expression (e.g. rDNA insulin), source of restriction enzyme EcoRI.
2. Name microbe 2: Saccharomyces cerevisiae. Uses: eukaryotic expression host, bioethanol, baking, brewing.

Two microbes useful in biotechnology: Escherichia coli (recombinant protein expression) and Saccharomyces cerevisiae (yeast for ethanol and eukaryotic expression).

Concept used. Restriction endonucleases are bacterial enzymes that cut DNA at specific recognition sequences. Their names follow a convention: Eco-R-I means the enzyme is from Escherichia coli (the first three letters), strain RY13 (the ``R''), and is the first such enzyme isolated from that strain (Roman numeral I). EcoRI recognises the palindrome 5–GAATTC–3 and cuts between G and A leaving sticky ends.

1. Decode the name: Eco = Escherichia coli, R = strain RY13, I = first enzyme.
2. Conclude the source: Escherichia coli (strain RY13).
3. Recognition: cuts 5–G↓AATTC–3 leaving 4-nt 5 overhangs.

EcoRI is isolated from Escherichia coli (strain RY13).

Concept used. A genetically modified (GM) crop is one in which a foreign gene has been introduced through recombinant DNA technology to confer a useful trait (pest resistance, herbicide tolerance, vitamin enrichment, abiotic-stress tolerance). The most famous Indian example is Bt cotton, into which the cry gene from Bacillus thuringiensis has been introduced — the resulting toxin kills bollworm larvae feeding on the plant.

1. Name the crop: Bt cotton (Bollgard).
2. Source of the foreign gene: Bacillus thuringiensis, the cryIAb / cryIAc genes encoding insecticidal crystal proteins.
3. Trait conferred: resistance to bollworm (Helicoverpa armigera) larvae, the most damaging cotton pest.

Bt cotton is a genetically modified crop. Other examples include Bt brinjal, Golden Rice (vitamin A-enriched) and Flavr Savr tomato.

Concept used. Blue-green algae (cyanobacteria) — Anabaena, Nostoc, Oscillatoria — fix atmospheric N2 via heterocysts and so qualify as biofertilizers, particularly in paddy fields. However they are not widely popular commercially because: (i) they grow only in standing water (paddy ecology), not in dryland crops; (ii) they need specific light, pH and temperature conditions; (iii) consortia are fragile and hard to mass-culture compared to Rhizobium; (iv) farmers prefer faster-acting chemical urea.

1. State the agronomic limitation: cyanobacteria thrive only in flooded soils (paddy fields), so their use is restricted geographically.
2. State the production limitation: scaled-up culture is difficult — they are light-dependent and slow-growing; live cultures lose viability during transport.
3. State the economic limitation: chemical fertilizers act faster and are cheaper to apply at scale; cyanobacterial inoculants give only ∼ 25 kg N/ha per season.

Blue-green algae are not popular as biofertilizers because they grow only in standing-water paddy ecologies, are slow-growing, hard to mass-culture, and add nitrogen more slowly than chemical fertilizers.

Concept used. Roquefort cheese is a French blue-veined cheese ripened with the fungus Penicillium roquefortii, whose blue-green spores create the characteristic marbled veins inside the curd. The fungus also secretes proteases and lipases that give Roquefort its distinctive sharp, pungent flavour.

1. Identify the species: Penicillium roquefortii.
2. Function: produces the blue-green veins by sporulation inside the curd, and releases enzymes that ripen the texture and flavour.

Penicillium roquefortii produces Roquefort cheese.

Concept used. The Ganga Action Plan (GAP), launched in 1985 by the Government of India, targets pollution control along the entire Ganga (Ganges) river. The river flows through five Indian states, all of which are covered by GAP: Uttarakhand (origin at Gomukh), Uttar Pradesh, Bihar, Jharkhand and West Bengal (where the Ganga divides into the Hooghly and continues into the Sundarbans).

1. Trace the river: Gomukh (Uttarakhand) → Haridwar → Kanpur, Allahabad, Varanasi (Uttar Pradesh) → Patna (Bihar) → Sahibganj (Jharkhand) → Murshidabad, Kolkata (West Bengal).
2. Listed states: Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, West Bengal.

The Ganga Action Plan covers Uttarakhand, Uttar Pradesh, Bihar, Jharkhand and West Bengal.

Concept used. Microbial industrial enzymes are used in detergents, food processing, leather tanning, paper, pharmaceuticals and bioremediation. Two of the most widely produced are:

• 2pt
• Lipase — hydrolyses fats/triglycerides; added to washing detergents to remove oily/greasy stains.
• Streptokinase — a protease from Streptococcus that dissolves blood clots; used as a clot-buster in myocardial infarction patients.

1. Name enzyme 1: lipase. Use: detergents, food (cheese flavouring), pharmaceuticals.
2. Name enzyme 2: streptokinase. Use: clot-buster in heart-attack therapy.

Lipase (detergents) and streptokinase (clot-buster). Other valid answers: pectinase (juice clarification), protease (detergents), cellulase (textiles, paper).

Concept used. An immunosuppressive agent is a drug that dampens the immune response, used principally to prevent organ-transplant rejection and to treat autoimmune diseases. The classic microbial example is cyclosporin A, produced by the fungus Trichoderma polysporum. It inhibits the calcineurin pathway in T-lymphocytes, blocking T-cell activation.

1. Name: cyclosporin A.
2. Source: Trichoderma polysporum.
3. Mechanism: binds cyclophilin; the complex inhibits calcineurin and blocks IL-2 transcription, suppressing T-cell activation.
4. Use: prevents rejection of transplanted organs (kidney, liver, heart).

Cyclosporin A (from Trichoderma polysporum) is an immunosuppressive agent used in organ-transplant patients.

Concept used. Viruses come in several morphologies — icosahedral (e.g. polio), helical/rod-shaped, complex (e.g. bacteriophages). The textbook example of a rod-shaped virus is the Tobacco Mosaic Virus (TMV), whose helical capsid forms a slender rigid rod about 300 nm long and 18 nm wide enclosing a single-stranded RNA genome.

1. Name: Tobacco Mosaic Virus (TMV).
2. Morphology: rigid rod, ∼ 300 nm long, ∼ 18 nm wide, helical capsid of 2130 identical protein subunits.
3. Genome: single-stranded RNA.
4. Host: tobacco and other Solanaceae; the virus causes mosaic disease.

The Tobacco Mosaic Virus (TMV) is the classic example of a rod-shaped virus.

Concept used. Both the cattle rumen and the anaerobic digester sludge of sewage plants are oxygen-free, organic-rich environments — and both are dominated by methanogens, a group of anaerobic archaea that ferment organic substrates to methane (CH4). Examples include Methanobacterium, Methanococcus, Methanosarcina.

1. Identify the environments: both anaerobic, both organic-rich.
2. Identify the dominant microbial group: methanogens.
3. Confirm by checking outputs: cattle burp CH4 (from rumen methanogens); sludge digesters produce biogas rich in CH4.

Methanogens (e.g. Methanobacterium) are found in both the cattle rumen and sewage digester sludge.

Concept used. Swiss cheese (Emmental) is ripened with the bacterium Propionibacterium shermanii, which ferments lactate to propionic acid, acetic acid and CO2. The acid gives the cheese its nutty flavour, and the CO2 produces the characteristic holes.

1. Microbe: Propionibacterium shermanii.
2. Function: lactate → propionic acid + acetic acid + CO2; the gas forms the eyes.

Propionibacterium shermanii produces Swiss cheese.

Concept used. A floc is a loose, mucus-like aggregate of aerobic bacteria, protozoa and fungi held together by extracellular polymeric substances (EPS). Flocs are the working unit of the secondary (biological) treatment stage of sewage. They serve three roles simultaneously: (i) they offer enormous surface area for aerobic decomposition of organic matter; (ii) their EPS-rich matrix adsorbs colloidal and suspended impurities; and (iii) being heavier than water, they settle out quickly in the secondary clarifier, separating the cleaned water from the active biomass.

1. Composition: bacteria + fungi + protozoa embedded in EPS — a self-organising consortium that does the heavy lifting in the aeration tank.
2. Function 1 (oxidation): with continuous aeration (DO > 2 mg/L), floc microbes oxidise dissolved organics to CO2 + H2O + new biomass, lowering BOD by ∼ 90%.
3. Function 2 (adsorption): the EPS coat traps colloidal particles and even some heavy metals; floc surfaces act as a biofilter.
4. Function 3 (settling): heavier than water, flocs sediment in ∼ 30–60 minutes in the secondary clarifier, separating biomass from cleaned effluent. Most settled sludge is then recycled to the aeration tank.

Flocs are the active biomass of biological sewage treatment: they oxidise organics (lowering BOD), adsorb colloidal impurities, and settle quickly so that biomass and water can be separated.

Concept used. Bacillus thuringiensis (Bt) is a soil-dwelling Gram-positive bacterium that produces insecticidal crystal proteins (Cry proteins) during sporulation. When ingested by a susceptible caterpillar, Cry proteins are solubilised in the alkaline midgut, activated by gut proteases, then bind to specific receptors on the larval gut epithelium and form pores. The gut leaks, the caterpillar stops feeding and dies in 1–2 days. Bt has been deployed in two main ways: (i) as a sprayable biopesticide, and (ii) by transferring the cry gene into crop plants (Bt cotton, Bt brinjal), so that the crop itself produces Cry protein.

1. Source organism: Bacillus thuringiensis, a soil bacterium found globally.
2. Mode of action: caterpillar eats Cry crystal → alkaline midgut dissolves it → proteases activate it → Cry binds midgut receptors → pores form → gut leakage → death within 24–48 hours.
3. Application 1 (biopesticide spray): commercial Bt formulations (e.g. Dipel) are sprayed on crops; the caterpillars eat the toxin while feeding.
4. Application 2 (transgenic Bt crops): the cryIAc / cryIAb gene is inserted into cotton, brinjal, maize. The plant produces Cry protein in its tissues, and any caterpillar feeding on it dies.
5. Selectivity: Bt is highly host-specific — different cry variants target Lepidoptera, Diptera or Coleoptera, but spare mammals, birds, fish and beneficial insects.

Bt produces Cry proteins that selectively kill caterpillars upon ingestion. It is used both as a biopesticide spray and through transgenic Bt crops (cotton, brinjal), reducing chemical pesticide use dramatically.

Concept used. A mycorrhiza is a symbiotic association between a fungus and a plant's roots. The most common form is the arbuscular mycorrhiza (AM), dominated by Glomus. Fungal hyphae extend from the root into the soil up to several centimetres, vastly enlarging the effective absorptive surface. In return for plant-supplied sugars, the fungus delivers four major benefits to the plant.

1. Phosphorus uptake: AM hyphae solubilise and translocate PO4^3- (an immobile ion) from beyond the root's depletion zone. Mycorrhized plants take up 2–3× more phosphorus.
2. Water uptake / drought tolerance: hyphae access fine soil pores below root reach, improving water uptake and helping the plant withstand drought.
3. Nutrient sharing: AM also enhance uptake of N, K, Zn, Cu and other micronutrients.
4. Disease resistance: the mycorrhizosphere out-competes soil-borne fungal pathogens and induces systemic resistance in the host. The plant becomes less susceptible to root pathogens.
5. Stress tolerance: mycorrhized plants tolerate salinity, heavy metals and temperature stresses better than non-mycorrhized ones.

Mycorrhizal fungi help plants by improving phosphorus uptake, water absorption (drought tolerance), micronutrient nutrition, resistance to soil-borne pathogens, and overall stress tolerance.

Concept used. Cyanobacteria (blue-green algae) such as Anabaena, Nostoc and Oscillatoria are photosynthetic prokaryotes that can also fix atmospheric nitrogen via the enzyme nitrogenase housed in specialised cells called heterocysts. Paddy fields are flooded, sun-lit and warm — conditions that perfectly suit cyanobacteria. As they grow in the rice paddy water, they enrich the soil with biologically fixed nitrogen, organic carbon and growth-promoting metabolites, reducing the need for chemical fertilizer.

1. Cyanobacteria photosynthesise in the standing water of paddy fields, producing biomass.
2. In heterocysts, they fix atmospheric N2 to NH3: N2 + 8 H+ + 8 e- + 16 ATP -> 2 NH3 + H2 + 16 ADP + 16 Pi.
3. Upon decomposition, this fixed nitrogen enters the soil as ammonia and nitrate, boosting rice productivity.
4. Additional benefits: they secrete growth promoters (auxin-like compounds), add organic matter, and reduce nitrogen-fertilizer demand by 25–30 kg N/ha/season.
5. Azolla–Anabaena symbiosis (the floating water fern Azolla hosting Anabaena) is exploited as a green-manure crop in paddies.

Cyanobacteria fix atmospheric N2 into bio-available nitrogen in flooded paddy soils, also adding organic matter and growth promoters — saving on chemical fertilizers.

Concept used. Penicillin was discovered in 1928 by Sir Alexander Fleming (St. Mary's Hospital, London) almost by accident. Fleming had left a Petri dish of Staphylococcus aureus cultures uncovered before going on holiday. On his return, he noticed that a stray fungal contaminant (a Penicillium notatum colony) had grown on one plate and around it was a clear zone where the staphylococci had been killed. Fleming inferred that the fungus secreted a diffusible antibacterial substance, which he named penicillin. Its therapeutic potential was demonstrated much later, in the 1940s, by Ernst Chain and Howard Florey, who purified penicillin and used it to cure soldiers wounded in World War II. Fleming, Chain and Florey shared the 1945 Nobel Prize for Medicine.

1. Year 1928: Alexander Fleming observes that a Penicillium notatum contaminant has killed Staphylococcus around it on a plate.
2. Hypothesis: the fungus is secreting an antibacterial diffusible substance.
3. Naming: Fleming names the substance penicillin after the fungus genus.
4. Years 1939–41: Chain and Florey (Oxford) purify penicillin, demonstrate its safety in animals and then in humans.
5. World War II: penicillin is mass-produced and saves countless wounded soldiers.
6. Recognition: 1945 Nobel Prize in Physiology or Medicine to Fleming, Chain and Florey.

Alexander Fleming discovered penicillin in 1928 from a chance Penicillium notatum contamination of a Staphylococcus culture; Chain and Florey later purified it and made it a usable drug. Nobel Prize 1945.

Concept used. Although Alexander Fleming discovered penicillin in 1928, he never managed to purify or test it clinically. The real demonstration of penicillin as a usable antibiotic came in the early 1940s from the Oxford team of Ernst Boris Chain and Howard Walter Florey, who purified the drug, tested it in mice and then in humans. All three — Fleming, Chain and Florey — shared the 1945 Nobel Prize in Physiology or Medicine.

1. Discovery (1928): Sir Alexander Fleming, St Mary's Hospital, London.
2. Purification and therapeutic demonstration (1940–45): Ernst Boris Chain and Howard Walter Florey, University of Oxford.
3. Nobel Prize 1945 (shared, three scientists).

Alexander Fleming, Ernst Chain and Howard Florey are credited; Chain and Florey specifically established penicillin as a clinically usable antibiotic.

Concept used. Fungi are an extraordinarily rich source of bioactive molecules that have transformed medicine. Three NCERT-highlighted examples cover three different therapeutic areas:

• 2pt
• Penicillin (from Penicillium notatum) — the first antibiotic; cured bacterial infections that were previously fatal.
• Cyclosporin A (from Trichoderma polysporum) — an immunosuppressant; prevents organ-transplant rejection.
• Statins (from Monascus purpureus) — lower blood cholesterol; reduce cardiovascular mortality.

1. Antibiotic action — penicillin and related β-lactams from fungi target bacterial cell wall synthesis, curing bacterial diseases.
2. Immunosuppression — cyclosporin A inhibits T-cell activation, enabling organ transplantation; without it, modern transplant medicine would not exist.
3. Cholesterol lowering — statins inhibit HMG-CoA reductase, lowering serum LDL by 30–50%; they have saved millions from cardiovascular deaths.
4. Other examples — griseofulvin (antifungal from Penicillium griseofulvum), ergot alkaloids (Claviceps purpurea), used in obstetrics and migraine.

Fungal bioactives have given humanity three transformative drug classes: antibiotics (penicillin), immunosuppressants (cyclosporin A) and cholesterol-lowering statins — each saving millions of lives.

Concept used. Modern laundry detergents include microbial enzymes that catalyse the breakdown of stubborn stains under mild conditions. The three main enzymes are protease (breaks down protein stains: blood, food, sweat), lipase (breaks down fats and oils: butter, oil, cosmetics), and amylase (breaks down starch stains: pasta, sauces). These enzymes are produced industrially from common, easily-cultured microbes — they are not unique organisms. Detergent enzymes typically come from Bacillus species (e.g. Bacillus subtilis for protease, Bacillus licheniformis for amylase) and fungi like Candida or Aspergillus for lipase.

1. Identify the enzymes added to detergents:
   • 2pt
   • Protease — hydrolyses peptide bonds in protein stains (blood, egg, milk).
   • Lipase — hydrolyses triglycerides in oily/greasy stains.
   • Amylase — hydrolyses starch-based food stains.
   • Cellulase — softens cotton fibres and removes lint.
2. Function in detergent: the enzymes act at moderate temperatures and alkaline pH typical of wash cycles, breaking down stains into smaller soluble pieces that rinse off easily.
3. Source organisms: easily cultured bacteria (Bacillus subtilis, B. licheniformis, B. amyloliquefaciens) and fungi (Aspergillus, Humicola, Candida). These are common, not unique.
4. Industrial production: bulk fermentation in stirred-tank bioreactors → enzyme purification → formulation into liquid or powder detergent.

Detergent enzymes (protease, lipase, amylase, cellulase) break down protein, oily, starchy and cellulosic stains during washing. They are produced by common cultured microbes (Bacillus bacteria, Aspergillus fungi) — not unique organisms.

Concept used. Biogas is a gaseous mixture produced by the anaerobic digestion of organic matter (cow dung, sewage sludge, agricultural residues, food waste) by methanogenic archaea. Its bulk composition is roughly 50–70% methane (CH4), 25–45% carbon dioxide (CO2), with traces of hydrogen sulfide (H2S), water vapour and nitrogen. The methane is what makes biogas a fuel — it burns with a clean blue flame and yields ∼ 4,500–6,000 kcal/m3.

1. State chemical composition:
   • 2pt
   • CH4 : 50–70% (the energy-bearing fuel component)
   • CO2 : 25–45%
   • H2S, H2O, N2 : trace.
2. Name a producer organism: Methanobacterium (or Methanococcus, Methanosarcina). These are strict-anaerobic methanogenic archaea, found in cow rumen and biogas digesters.
3. Note the metabolism: CO2 + 4 H2 -> CH4 + 2 H2O, CH3COOH -> CH4 + CO2.

Biogas is a mixture of methane (∼ 60% CH4), CO2, plus traces of H2S. It is produced by methanogenic archaea such as Methanobacterium.

Concept used. Microbes reduce chemical environmental degradation through two complementary roles: (i) by biodegrading or bioremediating chemicals already released into soil, water and air; and (ii) by serving as biofertilizers, biopesticides and biocontrol agents that replace chemical inputs, thereby preventing further pollution. Both pathways together represent the bio-based alternative to chemical agriculture and chemical waste management.

1. Bioremediation (clean-up role):
   • 2pt
   • Pseudomonas strains degrade oil spills (n-alkanes, polycyclic aromatic hydrocarbons).
   • Phanerochaete chrysosporium (white-rot fungus) degrades lignin, dyes, pesticides.
   • Sewage treatment microbial flocs degrade BOD, lowering organic pollution discharged into rivers.
   • Anaerobic digesters convert organic waste into biogas + manure.
2. Replacement role (prevention):
   • 2pt
   • Rhizobium, Azotobacter, cyanobacteria, mycorrhiza — biofertilizers replacing chemical N, P fertilizers.
   • Bacillus thuringiensis, NPV, Trichoderma, ladybirds — biopesticides replacing chemical insecticides and fungicides.
3. Net effect: less chemical fertilizer + less chemical pesticide + faster biodegradation of waste = drastically reduced environmental load.

Microbes both degrade pollutants already in the environment (bioremediation by Pseudomonas, fungi, sewage flocs, biogas methanogens) and replace chemical fertilizers and pesticides (biofertilizers, biopesticides) — together reducing chemical pollution at source and downstream.

Concept used. A broad-spectrum antibiotic is one that is effective against a wide range of bacterial groups — typically both Gram-positive and Gram-negative bacteria, and sometimes also against atypical organisms like Chlamydia and Rickettsia. This is in contrast to narrow-spectrum antibiotics (e.g. benzylpenicillin), which work against only a limited group (mostly Gram-positives). Classic broad-spectrum antibiotics include tetracycline, chloramphenicol, ampicillin and ciprofloxacin.

1. Define: an antibiotic active against a wide range of bacterial taxa (Gram-positive + Gram-negative).
2. Contrast with narrow-spectrum: e.g. benzylpenicillin works only against Gram-positives.
3. Example: tetracycline (from Streptomyces aureofaciens) acts against a wide range of Gram-positive and Gram-negative bacteria, plus Chlamydia and Rickettsia.
4. Clinical use: empirical therapy when the causative organism is not yet identified.

A broad-spectrum antibiotic is one effective against both Gram-positive and Gram-negative bacteria. Tetracycline is a classic example.

Concept used. Viruses that infect (parasitise) bacteria are called bacteriophages (literally ``bacteria-eaters''). They have a complex morphology: an icosahedral head containing tightly packed double-stranded DNA, a tail sheath that contracts to inject the DNA into the host, a base plate with tail fibres for host recognition. The most-studied example is the T4 bacteriophage that infects Escherichia coli.

1. Name: viruses that infect bacteria are called bacteriophages (``bacteria-eaters''), discovered independently by Twort (1915) and d'Herelle (1917).
2. Structure of T4 phage:
   • 2pt
   • Head: icosahedral protein capsid enclosing dsDNA (the genome).
   • Collar: narrow region linking head and tail.
   • Tail sheath: a contractile cylinder around an inner core; contracts to drive DNA injection.
   • Base plate: hexagonal plate at the tail's distal end.
   • Tail fibres: six slender fibres for attachment to receptors on the bacterial surface.
3. Lifecycle: tail fibres recognise the bacterial cell wall → sheath contracts → inner core pierces the cell envelope → DNA injected → phage replication.

Bacteria-parasitising viruses are called bacteriophages; the T4 phage has a head (with dsDNA), collar, contractile tail sheath, base plate and tail fibres.

Concept used. The bacterium Streptococcus (specifically Streptococcus equisimilis or S. pyogenes) produces an enzyme called streptokinase, which is used clinically as a clot-buster (thrombolytic agent). Streptokinase works by activating the body's own clot-dissolving system: it binds to plasminogen, converting it to plasmin, which then degrades the fibrin meshwork of a clot.

1. Bacterium: Streptococcus (S. equisimilis / S. pyogenes).
2. Product: streptokinase, a protease.
3. Mechanism: streptokinase binds plasminogen (a circulating proenzyme), forming a complex that converts more plasminogen molecules to active plasmin. Plasmin in turn hydrolyses the fibrin meshwork of clots: Plasminogen streptokinase Plasmin Fibrinclot.
4. Clinical use: given by IV infusion within hours of myocardial infarction or pulmonary embolism to dissolve the offending clot and restore blood flow.

Streptococcus produces streptokinase, which activates plasminogen to plasmin; plasmin then dissolves the fibrin clot. Used clinically as a clot-buster after heart attacks.

Concept used. Biofertilisers are living micro-organisms (or carrier-bound preparations of them) that, when applied to seeds, plant surfaces or soil, colonise the rhizosphere or the interior of the plant and promote growth by supplying or making available essential plant nutrients — primarily nitrogen (by N-fixation) and phosphorus (by solubilising soil P). They reduce or replace the need for chemical fertilizers, are environmentally benign, and improve long-term soil health.

1. Define: living microbial preparations that enrich soil with nutrients and promote plant growth.
2. List benefits:
   • 2pt
   • Nitrogen fixation (Rhizobium, Azotobacter, Anabaena).
   • Phosphate solubilisation (Pseudomonas, Glomus mycorrhiza).
   • Production of plant growth promoters (auxins, gibberellins).
   • Disease suppression in the rhizosphere.
3. Examples (any two):
   • 2pt
   • Rhizobium — symbiotic N-fixer in root nodules of legumes.
   • Azotobacter — free-living aerobic N-fixer in soil.
   • Cyanobacteria (Anabaena, Nostoc) — paddy-field biofertilizers.
   • Mycorrhiza (Glomus) — phosphate solubiliser and uptake enhancer.

Biofertilizers are living microbial preparations that enrich soil with nutrients. Two examples: Rhizobium (symbiotic N-fixer) and Azotobacter (free-living N-fixer); other valid pairs include cyanobacteria and mycorrhiza.

Concept used. Sewage treatment must remove organic matter (the BOD load) before discharge to a river. Two metabolic routes are possible:

• 2pt
• Aerobic degradation — bacteria oxidise organics using O2 as final electron acceptor: Organics + O2 -> CO2 + H2O + biomass. This yields ∼ 30 ATP per glucose, is energetically efficient and fast.
• Anaerobic degradation — methanogens reduce organics to CH4 + CO2, yielding only ∼ 2 ATP per glucose, slow but useful for concentrated sludge.

1. Speed of BOD removal. Aerobic oxidation removes ∼ 90% of BOD in 4–8 hours of aeration. Anaerobic digestion takes 15–30 days to achieve comparable removal. For large effluent volumes, only the aerobic route can keep up with the inflow.
2. Energetic efficiency. Aerobic respiration yields ∼ 30 ATP/glucose, so bacteria grow fast, biomass builds up, and BOD falls quickly. Anaerobic methanogens yield only ∼ 2 ATP/glucose; growth is slow.
3. End-products. Aerobic degradation yields CO2 + H2O (innocuous). Anaerobic degradation yields CH4 (a greenhouse gas, also flammable/explosive) and H2S (toxic, smelly). For an open large-volume system, aerobic is far safer.
4. Sludge handling. Anaerobic digestion is reserved for the relatively small volume of concentrated sludge that comes out of the aerobic step. It is uneconomic to digest billions of litres of dilute sewage anaerobically because it would need huge sealed reactors and long retention times.
5. Process robustness. Aerobic systems tolerate shock loads, pH variations and temperature swings better than anaerobic ones. Anaerobic systems crash easily if pH or temperature deviates.
6. Combined strategy. Real sewage plants use BOTH: aerobic for the bulk dilute effluent (secondary treatment), and anaerobic for the resulting concentrated sludge (digester). The two complement each other.

Aerobic degradation is faster (∼ 8 h vs ∼ 20 days), energetically more efficient, produces innocuous CO2 + H2O (vs hazardous CH4 + H2S), tolerates large volumes, and is more robust to shock loads — making it the workhorse for treating bulk dilute wastewater. Anaerobic digestion is reserved for the smaller volume of concentrated sludge.

Concept used. Indian rivers have suffered severe organic, industrial and sewage pollution due to rapid urbanisation. To counter this, the Ministry of Environment, Forests and Climate Change (MoEFCC) has launched several umbrella programmes. The two largest are the Ganga Action Plan (GAP, 1985) and the Yamuna Action Plan (YAP, 1993), later subsumed under the National River Conservation Plan (NRCP) and most recently the Namami Gange mission (2014). In 2008, the Ganga was officially declared the National River, giving it special status in conservation law.

Part (a) — Major programmes initiated by MoEFCC.

1. Ganga Action Plan (GAP), launched 1985: targets pollution along the Ganga across five states (Uttarakhand, UP, Bihar, Jharkhand, West Bengal). Activities: building sewage treatment plants (STPs), interception and diversion of sewage drains, low-cost sanitation, river-front development, electric crematoria.
2. Yamuna Action Plan (YAP), 1993: covers the Yamuna across Delhi, Haryana, UP. Similar STP-building and drain diversion. Multiple phases (YAP I, II, III) with funding from the Japan International Cooperation Agency (JICA).
3. National River Conservation Plan (NRCP): a unified umbrella programme covering 35+ rivers in 16 states (Cauvery, Krishna, Godavari, Mahanadi, Brahmani, Sutlej, Brahmaputra, etc.). Component activities mirror GAP/YAP.
4. Namami Gange (2014): a Rs. 20,000-crore programme integrating sewerage infrastructure, river-front development, surface cleaning, biodiversity conservation, afforestation and public awareness, specifically for the Ganga.
5. Other measures: enforcement of Water (Prevention and Control of Pollution) Act, 1974; CPCB monitoring of water quality at 1,000+ stations; mandatory effluent treatment plants for industries.

Part (b) — Implications of declaring Ganga the National River.

1. Special status: National-River designation makes Ganga conservation a national priority, qualifying it for sustained central funding above and beyond state budgets.
2. Institutional structure: the National Ganga River Basin Authority (NGRBA, 2009) was constituted under the PM with cabinet rank, replaced in 2016 by the National Mission for Clean Ganga (NMCG) under the new Ministry of Jal Shakti.
3. Stricter regulation: industries within the Ganga basin face stricter effluent norms; many polluting tanneries (e.g. Kanpur) have been relocated.
4. Cultural awareness: declaring Ganga ``national'' draws public attention to its religious, cultural and ecological value, raising civic participation in conservation.
5. Catchment-wide approach: instead of piecemeal stretches, the national-river status mandates integrated basin management — sewage, industry, agriculture, deforestation, glacier retreat — all addressed under one umbrella.

MoEFCC's main river conservation programmes are GAP (1985), YAP (1993), NRCP and Namami Gange (2014). Ganga's National-River status (2008) brings sustained central funding, a dedicated mission (NMCG), stricter industrial norms, integrated basin-wide management, and elevated public engagement with its conservation.

Concept used. A typical Indian floating-dome biogas plant (KVIC design) is a brick-and-cement underground tank into which cow dung slurry is fed daily. Methanogens in the sealed digester break down the slurry into biogas (CH4 + CO2) over 30–50 days; the gas is trapped under an inverted metal drum (gas holder) which rises as gas accumulates. The spent slurry (sludge) flows out through an overflow into the sludge chamber and is then used as manure.

1. Dung + water chamber (inlet) (left): cow dung is mixed with an equal volume of water and fed daily into this small inlet tank. Gravity carries the slurry through an inlet pipe to the digester.
2. Digester (centre, underground): the brick-and-cement anaerobic tank in which methanogens (Methanobacterium, Methanococcus) break down organic matter over 30–50 days, producing biogas + sludge.
3. Gas holder (floating dome) (above digester): an inverted metal/concrete drum that floats over the digester; rises as biogas accumulates, falls as gas is drawn off. A pipe taps the gas off the top of the dome and supplies it to the kitchen.
4. Sludge chamber (outlet) (right): the spent slurry, depleted of methane but still nutrient-rich, overflows through an outlet pipe into this chamber and is collected as organic manure.

A floating-dome biogas plant has four labelled parts: dung+water chamber (inlet), digester (anaerobic tank), gas holder (floating dome that traps biogas), and sludge chamber (outlet for spent slurry = manure).

Concept used. Biological control (biocontrol) is the use of living organisms — natural predators, parasites, pathogens or competitors — to keep pest and disease populations below an economically damaging threshold, instead of relying on chemical pesticides. Its core philosophy is to work with ecological balance rather than against it.

1. Use natural enemies. The simplest idea is to introduce or encourage a pest's natural enemy. Classic examples:
   • 2pt
   • Lady bird beetles eat aphids.
   • Dragonflies eat mosquito larvae.
   • Trichoderma fungi parasitise plant-pathogenic fungi (Pythium, Fusarium).
2. Use microbial pathogens of pests. Specific pathogens that kill pests but not non-target organisms:
   • 2pt
   • Bacillus thuringiensis (Bt) produces Cry toxins that kill caterpillars on ingestion.
   • Nucleopolyhedrovirus (NPV) infects and kills specific insect larvae.
   • Entomopathogenic fungi like Beauveria bassiana infect insect cuticles.
3. Species specificity. A central principle: biocontrol agents are typically narrow-spectrum — they target only the pest species, sparing beneficial insects, pollinators, soil microbes and non-target wildlife.
4. Ecological sustainability. Biocontrol agents replicate in the field and persist; one introduction can give multi-season control without continued reapplication. Chemicals must be sprayed repeatedly and pollute the environment.
5. Avoid pest resistance. Because biocontrol agents co-evolve with the pest (especially over generations), pest resistance develops more slowly than to chemical insecticides.
6. Integrated Pest Management (IPM). Modern practice combines biocontrol with crop rotation, resistant varieties, cultural practices and minimal chemical use — a balanced ecosystem approach rather than a single-shot kill.
7. Genetic engineering link. Bt cotton, Bt brinjal etc. take biocontrol a step further: the plant itself produces the Cry toxin, eliminating the need for spraying.

Biological control uses living natural enemies (predators, parasites, pathogens) to suppress pest and disease populations. Its main ideas: species-specific action, ecological sustainability, lower environmental harm, slower resistance evolution, and integration into IPM rather than reliance on chemical pesticides.

Concept used. Untreated sewage carries large amounts of biodegradable organic matter (proteins, fats, sugars), suspended solids, pathogens, nitrogen, phosphorus and chemicals. When discharged into a river, aerobic microbes consume the organics, drawing O2 from the river water at a faster rate than reaeration can replace it; the resulting oxygen sag kills fish and other aerobic life. Anaerobic sludge digestion, by contrast, deliberately uses absence of oxygen to stabilise the concentrated sludge produced during secondary treatment, harvesting biogas in the process.

Part (a) — Consequences of discharging untreated sewage into a river.

1. BOD spike and oxygen depletion. The river's aerobic bacteria consume the organic load, depleting dissolved O2. This is the classic ``oxygen sag'' downstream of a sewage outfall.
2. Fish kills. When DO falls below ∼ 3 mg/L, fish, frogs and aerobic invertebrates die en masse. Anaerobic zones develop and emit H2S.
3. Eutrophication. Sewage delivers large amounts of N and P. These nutrients trigger algal blooms; when algae die, decomposers consume more oxygen, worsening anoxia and creating ``dead zones''.
4. Pathogen spread. Sewage carries E. coli, Vibrio cholerae, Salmonella typhi, hepatitis A virus, polio virus. Drinking water drawn downstream becomes a public-health hazard, causing cholera and typhoid outbreaks.
5. Sediment accumulation and odour. Suspended solids settle and decay anaerobically, releasing CH4 and H2S, producing the characteristic foul smell.
6. Biodiversity loss and economic damage. Loss of fish and clean water harms fisheries, tourism and irrigation; the river becomes effectively ``dead''.

Part (b) — Importance of anaerobic sludge digestion in sewage treatment.

1. Sludge stabilisation. Anaerobic digestion converts unstable, putrescible secondary sludge into a stable, less-odorous, hygienically safer residue.
2. Volume reduction. Up to 50% of the organic matter is broken down to gases, halving the volume of sludge that must be disposed of.
3. Energy recovery. The digester gas (∼ 60% CH4) is a usable fuel — many plants generate electricity by burning it on-site, becoming partly energy self-sufficient.
4. Pathogen reduction. The warm (35 C), prolonged anaerobic environment kills many pathogenic bacteria, helminth eggs and viruses, reducing disease risk from residual sludge.
5. Nutrient recovery. The digested residue (digestate) is rich in N, P, K and is used as organic manure on farms, closing the nutrient loop.
6. Economic and environmental. Anaerobic digestion turns a disposal problem (sludge) into two valuable products (biogas + manure), making sewage treatment more sustainable.

(a) Untreated sewage causes BOD spikes, oxygen sag, fish kills, eutrophication, pathogen-driven outbreaks and biodiversity loss. (b) Anaerobic sludge digestion stabilises sludge, halves its volume, generates biogas (fuel), reduces pathogens, and yields nutrient-rich manure — turning waste into resources.

Concept used. Lactic acid bacteria (LAB) are Gram-positive, microaerophilic bacteria (Lactobacillus, Lactococcus, Streptococcus thermophilus, Leuconostoc) that ferment carbohydrates to lactic acid. Foods that contain LAB include curd/yoghurt, idli/dosa batter, sauerkraut, kimchi, pickles, cheese, fermented milk products like buttermilk, and certain breads (sourdough). Their useful applications span nutrition, food preservation, gut health, and industrial production of lactic acid.

1. Foods containing LAB.
   • 2pt
   • Curd, yoghurt, buttermilk — Lactobacillus acidophilus, L. bulgaricus, Streptococcus thermophilus.
   • Idli and dosa batter — Leuconostoc mesenteroides + Lactobacillus.
   • Cheese — various LAB starters.
   • Sauerkraut, kimchi, pickles — Leuconostoc + Lactobacillus species.
   • Sourdough bread — Lactobacillus sanfranciscensis.
2. Conversion of milk to curd. LAB ferment milk lactose to lactic acid; the acid lowers pH, coagulates casein, and produces curd with characteristic tangy flavour.
3. Vitamin enrichment. LAB synthesise vitamin B12 during fermentation, making curd a key dietary source of B12 for vegetarians.
4. Food preservation. The lactic acid + low pH inhibits spoilage organisms; this is the principle behind pickling, sauerkraut, kimchi and yoghurt — naturally preserved foods that last weeks without refrigeration.
5. Gut-health probiotics. Live LAB taken orally (probiotic curd, probiotic supplements) restore the gut microbiome after antibiotic use, alleviate diarrhoea (especially in children with rotavirus or antibiotic-associated diarrhoea), and improve lactose digestion.
6. Improved digestibility. LAB partly digest milk proteins and lactose, making fermented milk products more tolerable for people with mild lactose intolerance.
7. Idli and dosa fermentation. Leuconostoc mesenteroides produces lactic acid + CO2, leavening the batter, lowering pH, and improving B-complex vitamin content.
8. Industrial production of lactic acid. Lactobacillus is grown on whey or molasses to produce lactic acid for the food, pharmaceutical, plastic (polylactic acid) and textile industries.

Foods containing LAB include curd, yoghurt, buttermilk, idli/dosa batter, cheese, sauerkraut, kimchi, pickles and sourdough. LAB applications: convert milk to curd, enrich foods with vitamin B12, preserve food, serve as probiotics for gut health, improve protein digestibility, leaven idli/dosa batter, and produce industrial lactic acid.