Chapter 8: Microbes in Human Welfare Long Questions | biology Class 12 CBSE

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Chapter 8: Microbes in Human Welfare Long Questions | biology Class 12 CBSE | ByteNotes.in

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Question 1

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Explain how microbes have been used in household food preparations. Give at least four distinct examples with the specific microorganism involved in each.

Lactic acid bacteria (LAB), particularly Lactobacillus, convert milk into curd by producing lactic acid that coagulates proteins; a small amount of curd serves as inoculum for fresh milk.
Idli and dosa dough is fermented by bacteria that produce CO2, causing the dough to puff up and giving these foods their spongy texture; fermentation also adds nutritional value.
Bread dough is fermented by baker's yeast Saccharomyces cerevisiae, which produces CO2 (causing dough to rise) and ethanol during anaerobic respiration.
Cheese varieties are made using specific microbes — Swiss cheese by Propionibacterium sharmanii (large CO2-produced holes) and Roquefort cheese ripened by specific fungi for unique flavour.
Toddy, a traditional drink from southern India, is made by fermenting palm sap using microbes; fermentation is also used to make foods from fish, soyabean, and bamboo-shoots.

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Question 2

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Describe the two stages of sewage treatment and explain how each stage reduces the polluting nature of sewage.

Primary treatment is physical: floating debris is removed by sequential filtration and grit (soil, pebbles) is removed by sedimentation; primary sludge settles at the bottom while the clearer supernatant (primary effluent) proceeds to secondary treatment.
Secondary (biological) treatment passes primary effluent into large aeration tanks; mechanical agitation and air pumping encourage vigorous growth of aerobic microbes that form flocs which consume most organic matter.
As microbes in flocs break down organic matter aerobically, the BOD of the effluent is significantly reduced; once BOD drops sufficiently, the effluent is passed into a settling tank.
In the settling tank, bacterial flocs sediment to form activated sludge; a small portion is recycled as inoculum into the aeration tank, and the bulk is sent to anaerobic sludge digesters.
Anaerobic bacteria in the digesters produce biogas (methane, H2S, CO2) while decomposing the sludge; the treated effluent from secondary treatment is released into rivers, making it far less polluting than raw sewage.

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Question 3

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Analyse the significance of antibiotics in the history of medicine. Trace the discovery of Penicillin and explain how it transformed the treatment of infectious diseases.

Antibiotics are chemical substances produced by some microbes that can kill or retard the growth of disease-causing microbes; they are regarded as one of the most significant discoveries of the twentieth century.
Penicillin was discovered accidentally by Alexander Fleming when he observed that the mould Penicillium notatum contaminating a Staphylococci culture plate inhibited bacterial growth around it; he identified and named the active substance.
Ernest Chain and Howard Florey later established the full therapeutic potential of Penicillin; it was used extensively to treat American soldiers wounded in World War II, saving countless lives.
Fleming, Chain and Florey were awarded the Nobel Prize in 1945 for this discovery, which opened the entire field of antibiotic research and led to the development of numerous other antibiotics.
Antibiotics transformed medicine by enabling effective treatment of previously deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu), and leprosy (kusht rog), dramatically reducing mortality from bacterial infections worldwide.

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Question 4

Long Form

Compare and contrast the roles of bacteria, fungi, and cyanobacteria as biofertilisers, with suitable examples for each group.

Bacteria act as biofertilisers by fixing atmospheric nitrogen: Rhizobium forms symbiotic nodules on legume roots fixing nitrogen into organic form, while free-living bacteria like Azospirillum and Azotobacter fix nitrogen directly in soil.
Fungi contribute as biofertilisers through mycorrhizal associations — Glomus species colonise plant roots and absorb phosphorus from soil, transferring it to the plant in exchange for photosynthetically produced carbohydrates.
Cyanobacteria (blue-green algae) are autotrophic nitrogen-fixers; Anabaena, Nostoc, and Oscillatoria fix atmospheric nitrogen and also add organic matter to soil, making them especially valuable in flooded paddy fields.
A key contrast: bacterial (Rhizobium) nitrogen fixation is symbiotic and root-associated, fungal contribution is primarily phosphorus mobilisation (not nitrogen), while cyanobacterial contribution is non-symbiotic and also includes organic matter enrichment.
All three groups reduce dependence on chemical fertilisers, improve soil fertility sustainably, and are available as commercial biofertiliser products that farmers use to replenish soil nutrients.

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Question 5

Long Form

Evaluate the role of microbes in the production of industrially and medically important bioactive molecules with examples of at least four distinct molecules.

Streptokinase, produced by Streptococcus and modified by genetic engineering, is used as a 'clot buster' to dissolve blood clots in arteries of myocardial infarction patients, restoring cardiac blood flow.
Cyclosporin A, produced by the fungus Trichoderma polysporum, acts as an immunosuppressive agent prescribed to organ-transplant patients to prevent immune rejection of the donor organ.
Statins, produced by the yeast Monascus purpureus, lower blood cholesterol by competitively inhibiting the enzyme responsible for cholesterol synthesis, reducing risk of cardiovascular disease.
Lipases produced by microbes are incorporated in detergent formulations to digest oily stains, while pectinases and proteases are used in the fruit juice industry to clarify juices.
These microbial products demonstrate how microbes serve as biological factories for diverse industrial and pharmaceutical applications, often providing more specific, efficient, and eco-friendly solutions than chemical synthesis.

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Question 6

Long Form

Discuss the philosophy and methods of biological control of pests. How does this approach promote sustainability in agriculture?

Biocontrol is based on the principle that biodiversity sustains ecosystem health; organic farmers believe pests should be kept at manageable levels by natural checks and balances rather than eradicated chemically.
Natural predators like Ladybirds (eliminate aphids) and Dragonflies (eliminate mosquitoes) are examples of biocontrol using beneficial insects that keep pest populations in check within the agro-ecosystem.
Bacillus thuringiensis (Bt) spores are sprayed on plants; when consumed by insect larvae, the bacterium produces a gut-specific toxin killing the larvae without harming other organisms; Bt genes have also been incorporated into crops like Bt-cotton.
Trichoderma fungi are used as free-living biocontrol agents against plant pathogens in root ecosystems, while Baculoviruses (Nucleopolyhedrovirus) provide species-specific insect control with no impact on non-target organisms.
This approach promotes sustainability by avoiding toxic chemical pollution of soil and ground water, preserving beneficial insects, reducing health hazards for humans and animals, and maintaining long-term ecosystem balance.

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Question 7

Long Form

Describe the role of microbes in biogas production. Explain how the biogas plant functions and discuss its socioeconomic importance in rural India.

Methanogens (e.g., Methanobacterium) are anaerobic bacteria that break down cellulosic and organic material in the absence of oxygen, producing methane, CO2, and H2; methane (biogas) is the primary usable energy output.
A biogas plant is a 10–15 feet deep concrete tank into which bio-wastes and cattle dung slurry are fed; a floating cover rises as methane accumulates from the microbial digestion below the surface.
The gas is channelled through pipes to supply fuel for cooking and lighting to nearby homes; the spent slurry left after gas extraction is removed and used as an organic fertiliser, adding further value.
Cattle dung (gobar) is rich in methanogens due to the rumen of cattle; rural areas with large cattle populations have abundant, low-cost feedstock for biogas plants, making them an ideal rural energy solution.
Developed by IARI and KVIC, biogas plants provide rural communities with a cheap, renewable, and clean energy source, reduce dependence on firewood (preventing deforestation), and generate organic fertiliser — combining energy security with improved agricultural productivity.

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Question 8

Long Form

Explain how microbes can be used to produce fermented beverages. Describe the role of yeast in fermentation and distinguish between beverages produced with and without distillation.

Yeasts, particularly Saccharomyces cerevisiae (brewer's yeast), are used to ferment sugars in malted cereals and fruit juices into ethanol through anaerobic respiration (glycolysis followed by alcoholic fermentation).
The same yeast used for bread-making (S. cerevisiae) is used for beverage production; it converts glucose into ethanol and CO2; ethanol is the intoxicating component of alcoholic beverages.
Wine and beer are produced without distillation — the fermented broth (relatively low ethanol concentration) is used directly as the final product after filtration or clarification.
Whisky, brandy, and rum are produced by distillation of the fermented broth; distillation concentrates the ethanol to achieve higher alcohol content and develops characteristic flavours and aromas.
Industrial-scale production of beverages requires large fermentors; the type of raw material (fruit juice for wine, malted barley for beer/whisky) and processing method together determine the specific beverage produced.

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Question 9

Long Form

Analyse how microbes contribute to maintaining soil fertility through nitrogen fixation. Describe the different types of nitrogen-fixing microbes and explain why nitrogen fixation is critical for agriculture.

Nitrogen (N2) makes up 78% of the atmosphere but cannot be used directly by most organisms; nitrogen-fixing microbes convert atmospheric N2 into usable organic nitrogenous compounds through the process of biological nitrogen fixation.
Symbiotic nitrogen fixation occurs when Rhizobium bacteria form nodules in the roots of leguminous plants; they fix N2 and supply it to the plant, which in return provides carbohydrates to the bacteria.
Free-living nitrogen-fixing bacteria such as Azospirillum and Azotobacter fix N2 independently in the soil, enriching soil nitrogen without requiring a plant host, making them useful for non-leguminous crop fields.
Cyanobacteria (Anabaena, Nostoc, Oscillatoria) are autotrophic nitrogen-fixers that also add organic matter to the soil; they are particularly important in paddy (rice) cultivation in flooded fields.
Biological nitrogen fixation reduces dependence on costly and environmentally harmful synthetic nitrogen fertilisers, maintains long-term soil health, and is a cornerstone of sustainable and organic agriculture.

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Question 10

Long Form

Examine the environmental and public health significance of sewage treatment plants (STPs). Discuss the consequences of discharging untreated sewage into rivers.

Sewage contains high concentrations of organic matter and pathogenic microbes; untreated discharge into rivers introduces disease-causing organisms, leading to outbreaks of water-borne diseases such as typhoid, cholera, and hepatitis.
The high organic content of untreated sewage drastically increases the BOD of receiving water bodies, depleting dissolved oxygen levels and causing death of aquatic organisms including fish and other life.
STPs reduce BOD through biological treatment by aerobic microbe flocs; treated effluent is far less polluting and safe for river discharge, enabling natural water bodies to sustain aquatic ecosystems.
Increasing urbanisation has created more sewage than existing STPs can treat; untreated sewage is often discharged into major rivers like the Ganga and Yamuna, severely degrading their water quality.
The government has initiated the Ganga Action Plan and Yamuna Action Plan to construct more STPs and ensure only treated sewage reaches these rivers; the microbial sewage treatment methodology has been successfully practiced worldwide for over a century.

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Chapter 8: Microbes in Human Welfare | Long Questions

Explain how microbes have been used in household food preparations. Give at least four distinct examples with the specific microorganism involved in each.

Describe the two stages of sewage treatment and explain how each stage reduces the polluting nature of sewage.

Analyse the significance of antibiotics in the history of medicine. Trace the discovery of Penicillin and explain how it transformed the treatment of infectious diseases.

Compare and contrast the roles of bacteria, fungi, and cyanobacteria as biofertilisers, with suitable examples for each group.

Evaluate the role of microbes in the production of industrially and medically important bioactive molecules with examples of at least four distinct molecules.

Discuss the philosophy and methods of biological control of pests. How does this approach promote sustainability in agriculture?

Describe the role of microbes in biogas production. Explain how the biogas plant functions and discuss its socioeconomic importance in rural India.

Explain how microbes can be used to produce fermented beverages. Describe the role of yeast in fermentation and distinguish between beverages produced with and without distillation.

Analyse how microbes contribute to maintaining soil fertility through nitrogen fixation. Describe the different types of nitrogen-fixing microbes and explain why nitrogen fixation is critical for agriculture.

Examine the environmental and public health significance of sewage treatment plants (STPs). Discuss the consequences of discharging untreated sewage into rivers.

Unlock all Long Questions