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

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

Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 1

Applied Concept

A farmer notices that his legume crop (groundnut) grows well even without applying nitrogen fertiliser, while his neighbouring wheat crop requires frequent nitrogen application. With reference to nitrogen-fixing microbes, explain the reason for this difference.

Leguminous plants like groundnut harbour Rhizobium bacteria in specialised root nodules formed by a symbiotic association; these bacteria fix atmospheric nitrogen (N2) into organic nitrogen compounds that the plant uses directly, eliminating the need for external nitrogen fertiliser.
Wheat is a non-leguminous crop and does not form symbiotic associations with Rhizobium; it cannot fix atmospheric nitrogen on its own and therefore depends entirely on soil nitrogen (which gets depleted) and externally applied nitrogen fertilisers for its nitrogen needs.
The farmer can reduce nitrogen fertiliser use for wheat by applying free-living nitrogen-fixing biofertilisers such as Azotobacter or Azospirillum to the wheat fields; these bacteria enrich soil nitrogen without requiring a symbiotic relationship with the host plant.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 2

Applied Concept

Three water samples labelled A, B, and C were tested for BOD. Sample A showed BOD of 400 mg/L, Sample B showed 20 mg/L, and Sample C showed 8 mg/L. Identify which sample is untreated sewage, which is river water, and which is secondary effluent from a sewage treatment plant. Justify your answer.

Sample A (BOD 400 mg/L) is untreated sewage water: raw sewage contains the highest concentration of organic matter and pathogenic microbes, resulting in the maximum oxygen consumption during bacterial oxidation and thus the highest BOD value.
Sample B (BOD 20 mg/L) is river water: although relatively clean, river water contains natural organic matter from decaying plant material and animal waste, giving it a moderate BOD — higher than treated effluent but far lower than raw sewage.
Sample C (BOD 8 mg/L) is secondary effluent from a sewage treatment plant: biological treatment by aerobic microbe flocs removes most organic matter, drastically reducing BOD to near-clean-water levels before the effluent is discharged into natural water bodies.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 3

Applied Concept

A patient who suffered a severe heart attack was administered a drug to dissolve the clot in his coronary artery. The doctor mentioned it was derived from a bacterium and modified using genetic engineering. Name the drug and bacterium, and explain how the drug works.

The drug is Streptokinase, a microbial enzyme originally produced by the bacterium Streptococcus; it has been modified by genetic engineering to enhance its safety and effectiveness as a therapeutic agent for human use.
Streptokinase functions as a 'clot buster' — it activates plasminogen (a naturally occurring blood protein) to form plasmin, which in turn breaks down fibrin, the protein mesh that forms blood clots in coronary arteries.
By dissolving the clot blocking the coronary artery, Streptokinase restores blood flow to the heart muscle, preventing further cardiac tissue death; it is administered as an emergency treatment shortly after a myocardial infarction to minimise permanent heart damage.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 4

Applied Concept

A villager in rural Rajasthan uses cattle dung and kitchen waste to run a biogas plant that provides fuel for cooking and whose spent material is used in the fields. Explain the microbiology behind this process and its dual benefit to the household.

The biogas plant works because cattle dung is naturally rich in methanogenic bacteria (e.g., Methanobacterium) that grow anaerobically; these bacteria break down cellulose and other organic matter in the dung and kitchen waste, releasing methane, CO2, and H2 as metabolic by-products.
The methane produced is piped to the household as biogas (gobar gas) — a cheap, renewable, and clean-burning fuel that replaces firewood or LPG for cooking and lighting, reducing energy expenditure and indoor air pollution from traditional chulhas.
After gas extraction, the spent slurry retains essential nutrients (nitrogen, phosphorus, potassium) in a form accessible to plants; it serves as a rich organic fertiliser for the fields, improving soil fertility and reducing the need for expensive chemical fertilisers — a complete nutrient and energy cycle.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 5

Applied Concept

An organic farmer decides not to use any chemical pesticides on his brassica crop infested with butterfly caterpillars. He instead purchases sachets of a bacterial product from an agricultural store. Identify the product, describe its action, and explain why it is preferred over chemical pesticides.

The product is dried spores of Bacillus thuringiensis (Bt); the farmer mixes the spores with water and sprays the suspension on the brassica plants, where caterpillars will consume them while feeding on the leaves.
In the alkaline environment of the caterpillar's gut, the Bt spores release a proteinaceous insecticidal toxin that disrupts the gut lining, killing the larvae; the bacterial disease affects only the caterpillars, leaving other insects, birds, and mammals completely unharmed.
Bt is preferred over chemical pesticides because it is species-specific (kills only the target caterpillars), biodegradable, non-toxic to humans and beneficial insects like bees and natural predators, and does not accumulate in the food chain or pollute soil and water.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 6

Applied Concept

A kidney transplant patient is prescribed a drug derived from a fungus to prevent organ rejection. Name the drug and the fungus, and explain why this drug is necessary after organ transplantation.

The drug is Cyclosporin A, produced by the fungus Trichoderma polysporum; it belongs to the class of immunosuppressive agents and is one of the most widely used drugs in organ transplant medicine.
After transplantation, the recipient's immune system recognises the donor organ as 'foreign' due to differences in cell surface antigens; it mounts an immune response to destroy the transplanted organ, a process called organ rejection.
Cyclosporin A suppresses this immune response by inhibiting the activation of T-lymphocytes (key immune cells involved in organ rejection); by preventing the immune system from attacking the donor organ, it allows the transplanted kidney to function normally, making Cyclosporin A essential for long-term graft survival.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 7

Applied Concept

A housewife notices that the bottled fruit juice she bought from a supermarket is much clearer than the juice she extracts at home. With reference to microbially produced enzymes, explain the reason for this difference.

Freshly extracted fruit juice contains pectin (a structural polysaccharide from cell walls) and proteins that remain suspended in the juice, causing it to appear cloudy or turbid.
Commercial bottled fruit juice manufacturers treat their juices with microbially produced enzymes — pectinases (which break down pectin) and proteases (which break down proteins) — causing these molecules to be degraded and removed from the juice.
The breakdown and removal of pectin and proteins results in a significantly clearer, more transparent juice; home-made juices lack this enzymatic treatment, which is why they appear cloudier — the commercial process exploits microbially produced enzymes to achieve superior clarity and shelf stability.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 8

Applied Concept

A person with high blood cholesterol levels is advised by his doctor to take a drug derived from a yeast. Name the drug and yeast, and explain the mechanism by which it reduces cholesterol levels.

The drug is a Statin (e.g., lovastatin), produced commercially by the yeast Monascus purpureus; Statins have been widely commercialised as blood-cholesterol lowering agents prescribed for patients with hypercholesterolaemia.
Statins work by competitively inhibiting HMG-CoA reductase, the key enzyme in the mevalonate pathway responsible for the biosynthesis of cholesterol in the liver; by blocking this enzyme, less cholesterol is synthesised.
The reduced intracellular cholesterol level in liver cells signals them to increase production of LDL receptors on their surface, leading to increased uptake and clearance of LDL cholesterol (bad cholesterol) from the blood, thereby lowering total blood cholesterol levels and reducing cardiovascular disease risk.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 9

Applied Concept

In a biology laboratory, a student observes that the mould growing on an agar plate has cleared the bacterial growth around it. Relate this observation to a landmark event in the history of medicine.

This observation directly parallels Alexander Fleming's accidental discovery of Penicillin in 1928: he noticed that a mould (Penicillium notatum) contaminating his Staphylococci culture plate had created a clear zone of inhibited bacterial growth around it.
Fleming correctly deduced that the mould was producing a diffusible chemical substance that killed or inhibited the surrounding bacteria; he named this substance Penicillin after the mould, marking the discovery of the world's first antibiotic.
This observation led to the development of Penicillin as the first therapeutic antibiotic (with Chain and Florey establishing its medical use), for which Fleming, Chain, and Florey received the Nobel Prize in 1945; the student's observation on the agar plate is therefore a direct visual demonstration of the principle behind antibiotic activity.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 10

Applied Concept

A municipal corporation wants to reduce water pollution in a river near a growing city. The environmental officer suggests building more Sewage Treatment Plants rather than just increasing fines for industrial discharge. With reference to microbial sewage treatment, justify this recommendation.

The largest and most consistent source of organic pollution in urban rivers is untreated municipal sewage — domestic wastewater containing human excreta, food waste, and detergents; STPs specifically address this using heterotrophic microbes naturally present in the sewage to biodegrade organic matter.
In STPs, aerobic bacteria form flocs in aeration tanks that consume organic matter and reduce BOD, followed by anaerobic digestion of sludge that produces biogas; the final effluent released into the river has a much lower organic load and pathogen count than raw sewage.
This methodology, practiced for over a century worldwide, has no man-made technological rival in treating millions of gallons of wastewater efficiently and cost-effectively; building more STPs as recommended under the Ganga and Yamuna Action Plans addresses the source and volume of organic pollution directly, making it a more effective long-term solution than purely punitive industrial measures.

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Chapter 8: Microbes in Human Welfare | Application Questions

A farmer notices that his legume crop (groundnut) grows well even without applying nitrogen fertiliser, while his neighbouring wheat crop requires frequent nitrogen application. With reference to nitrogen-fixing microbes, explain the reason for this difference.

Three water samples labelled A, B, and C were tested for BOD. Sample A showed BOD of 400 mg/L, Sample B showed 20 mg/L, and Sample C showed 8 mg/L. Identify which sample is untreated sewage, which is river water, and which is secondary effluent from a sewage treatment plant. Justify your answer.

A patient who suffered a severe heart attack was administered a drug to dissolve the clot in his coronary artery. The doctor mentioned it was derived from a bacterium and modified using genetic engineering. Name the drug and bacterium, and explain how the drug works.

A villager in rural Rajasthan uses cattle dung and kitchen waste to run a biogas plant that provides fuel for cooking and whose spent material is used in the fields. Explain the microbiology behind this process and its dual benefit to the household.

An organic farmer decides not to use any chemical pesticides on his brassica crop infested with butterfly caterpillars. He instead purchases sachets of a bacterial product from an agricultural store. Identify the product, describe its action, and explain why it is preferred over chemical pesticides.

A kidney transplant patient is prescribed a drug derived from a fungus to prevent organ rejection. Name the drug and the fungus, and explain why this drug is necessary after organ transplantation.

A housewife notices that the bottled fruit juice she bought from a supermarket is much clearer than the juice she extracts at home. With reference to microbially produced enzymes, explain the reason for this difference.

A person with high blood cholesterol levels is advised by his doctor to take a drug derived from a yeast. Name the drug and yeast, and explain the mechanism by which it reduces cholesterol levels.

In a biology laboratory, a student observes that the mould growing on an agar plate has cleared the bacterial growth around it. Relate this observation to a landmark event in the history of medicine.

A municipal corporation wants to reduce water pollution in a river near a growing city. The environmental officer suggests building more Sewage Treatment Plants rather than just increasing fines for industrial discharge. With reference to microbial sewage treatment, justify this recommendation.

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