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

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

Case Study

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Case Set 1

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Priya, a student of Class 12, noticed that the dosa batter left overnight had risen considerably. Her mother explained that microbes present in the environment had caused fermentation. Priya became curious and read about lactic acid bacteria (LAB) and their role in food. She found that LAB such as Lactobacillus grow in milk, producing acids that coagulate and partially digest milk proteins, converting it to curd. LAB also multiply at suitable temperatures and improve nutritional quality. She also discovered that the same process of microbial fermentation is responsible for making idli, dosa, cheese, and various traditional drinks. Priya then investigated how a small amount of old curd can act as an inoculum to prepare fresh curd, and why homemade curd tastes different from commercially prepared curd.

Question 1: Name the microorganism responsible for converting milk to curd and mention one nutritional benefit of this conversion.

Lactic acid bacteria (LAB) such as Lactobacillus are responsible for converting milk to curd.
The conversion increases the vitamin B12 content of curd, improving its nutritional quality.

Question 2: Why does the dosa batter rise overnight, and what metabolic pathway is responsible for this?

The dosa batter rises due to the production of CO2 gas by fermenting bacteria.
The metabolic pathway responsible is anaerobic fermentation (glycolysis leading to fermentation), in which bacteria break down carbohydrates and release CO2 as a by-product.

Question 3: Explain why a small amount of old curd can be used as an inoculum to prepare fresh curd. Also mention the role of LAB in the stomach.

Old curd contains millions of live LAB cells. When added to fresh warm milk, these bacteria multiply rapidly at suitable temperature.
They produce lactic acid, which coagulates milk proteins and converts the milk into curd.
In the stomach, LAB check the growth of harmful disease-causing microbes, thus playing a beneficial role in gut health.

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Case Set 2

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A cheese manufacturer wants to introduce a new variety of cheese in the market. He studies how different microbes impart specific characteristics to cheese. He learns that the bacterium Propionibacterium sharmanii is responsible for the large holes seen in Swiss cheese due to massive CO2 production. He also finds that Roquefort cheese gets its unique flavour because specific fungi are grown on it during ripening. His team experiments with different microbial cultures to develop varied textures, flavours, and tastes. The manufacturer realizes that the diversity in cheese varieties is entirely due to the specific microbes used in their preparation. He also notes that cheese is one of the oldest foods where microbes were deliberately used.

Question 1: Which microorganism is responsible for the large holes in Swiss cheese, and what causes them?

The bacterium Propionibacterium sharmanii is responsible for the large holes in Swiss cheese.
It produces a large amount of CO2 during metabolism, which forms the characteristic holes.

Question 2: How is Roquefort cheese different from Swiss cheese in terms of the microorganisms used?

Roquefort cheese is ripened by growing specific fungi on it, which gives it a particular flavour.
Swiss cheese, on the other hand, involves the bacterium Propionibacterium sharmanii which produces CO2 giving the cheese its characteristic holes.

Question 3: Explain the role of microorganisms in determining the characteristics of different varieties of cheese. Why is cheese considered one of the oldest examples of microbial use?

Different microbes impart specific texture, flavour, and taste to cheese, making each variety unique.
For example, CO2-producing bacteria create holes in some cheeses, while fungi provide distinct flavours in others.
Cheese is one of the oldest food items in which microbes were deliberately used by humans, demonstrating early, albeit unintentional, knowledge of microbial applications in food processing.

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Case Set 3

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During World War II, wounded American soldiers were successfully treated with a drug that stopped many fatal bacterial infections. This drug was the first antibiotic ever discovered. Alexander Fleming had accidentally found it while working on Staphylococci bacteria; he noticed that a mould contaminating one of his culture plates prevented bacterial growth nearby. He named the substance Penicillin after the mould Penicillium notatum. However, the full therapeutic potential was established by Ernest Chain and Howard Florey. Fleming, Chain and Florey were awarded the Nobel Prize in 1945 for this discovery. Following this, many more antibiotics were isolated from various microbes and have since helped control diseases like plague, whooping cough, diphtheria, and leprosy.

Question 1: How was Penicillin discovered, and who discovered it?

Penicillin was discovered by Alexander Fleming through a chance observation.
He noticed that a mould (Penicillium notatum) growing on his unwashed Staphylococci culture plate produced a substance that inhibited bacterial growth around it.

Question 2: What is the literal meaning of the word 'antibiotic', and why is this term considered context-dependent?

'Anti' means against and 'bio' means life; together 'antibiotic' means 'against life' in the context of disease-causing organisms.
However, with reference to human beings, antibiotics are 'pro life' since they kill harmful microbes and protect human health.

Question 3: Describe the contributions of Fleming, Chain, and Florey to the development of Penicillin and explain the significance of antibiotics in modern medicine.

Fleming discovered Penicillin by noticing that Penicillium notatum inhibited Staphylococci growth.
Chain and Howard Florey established its full potential as an effective antibiotic and helped develop it as a therapeutic agent.
Antibiotics have greatly improved the capacity to treat deadly diseases like plague, whooping cough, diphtheria and leprosy, which previously killed millions worldwide.

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Case Set 4

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A biotechnology company is exploring the use of microbes for the production of useful chemicals and enzymes. Their research involves Aspergillus niger for citric acid production, Acetobacter aceti for acetic acid, Clostridium butylicum for butyric acid, and Lactobacillus for lactic acid. They are also interested in enzymes like lipases for detergent formulations and pectinases for clarifying fruit juices. Additionally, a modified version of Streptokinase derived from Streptococcus is being explored as a clot buster. The company also investigates cyclosporin A from Trichoderma polysporum as an immunosuppressive agent and statins from Monascus purpureus as cholesterol-lowering agents.

Question 1: Name the microorganism and the chemical produced by it which is used as a clot buster in heart attack patients.

Streptokinase is produced by the bacterium Streptococcus (modified by genetic engineering).
It is used as a 'clot buster' to remove clots from blood vessels in patients who have undergone myocardial infarction (heart attack).

Question 2: Why are bottled fruit juices clearer than freshly made home juices? Which enzymes are responsible?

Bottled fruit juices are clarified by the use of pectinases and proteases.
These enzymes break down pectin and proteins that cause cloudiness, resulting in clearer juice compared to homemade ones.

Question 3: Explain the roles of cyclosporin A and statins as bioactive molecules. Name the microorganisms that produce them and state their mechanisms of action.

Cyclosporin A is produced by the fungus Trichoderma polysporum and is used as an immunosuppressive agent in organ-transplant patients to prevent rejection.
Statins are produced by the yeast Monascus purpureus and have been commercialised as blood-cholesterol-lowering agents.
Statins act by competitively inhibiting the enzyme responsible for synthesis of cholesterol, thereby reducing blood cholesterol levels.

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Case Set 5

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A municipal corporation is planning to set up a sewage treatment plant (STP) for a growing city. The engineers study the standard two-stage treatment process. In primary treatment, physical methods like filtration and sedimentation are used to remove large particles and grit. The resulting effluent undergoes secondary (biological) treatment in aeration tanks where aerobic microbes form flocs and reduce the Biochemical Oxygen Demand (BOD) of the water. The activated sludge produced settles in settling tanks. Part of it is recycled as inoculum, and the remainder is digested anaerobically. The engineers note that BOD is a critical parameter for assessing water pollution levels and that reducing it is the main goal of secondary treatment.

Question 1: What is BOD and what does a high BOD value indicate?

BOD (Biochemical Oxygen Demand) refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria.
A high BOD value indicates greater organic pollution and higher polluting potential of the water.

Question 2: What are flocs and what role do they play in secondary sewage treatment?

Flocs are masses of bacteria associated with fungal filaments that form mesh-like structures in the aeration tank.
They consume the major part of organic matter in the effluent during their vigorous aerobic growth, significantly reducing the BOD of the waste water.

Question 3: Describe the complete secondary treatment of sewage, including the fate of activated sludge and the gases produced during anaerobic digestion.

Primary effluent enters large aeration tanks where it is agitated and aerated, promoting vigorous growth of aerobic microbes that form flocs and reduce BOD.
The effluent then passes to a settling tank where flocs sediment as activated sludge; a small part is recycled as inoculum into the aeration tank.
The remaining sludge is pumped into anaerobic sludge digesters where anaerobic bacteria digest the organic matter, producing biogas (a mixture of methane, hydrogen sulphide, and CO2) that can be used as fuel.

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Chapter sections

Chapter 8: Microbes in Human Welfare | Case Study Questions

Passage

Question 1: Name the microorganism responsible for converting milk to curd and mention one nutritional benefit of this conversion.

Question 2: Why does the dosa batter rise overnight, and what metabolic pathway is responsible for this?

Question 3: Explain why a small amount of old curd can be used as an inoculum to prepare fresh curd. Also mention the role of LAB in the stomach.

Passage

Question 1: Which microorganism is responsible for the large holes in Swiss cheese, and what causes them?

Question 2: How is Roquefort cheese different from Swiss cheese in terms of the microorganisms used?

Question 3: Explain the role of microorganisms in determining the characteristics of different varieties of cheese. Why is cheese considered one of the oldest examples of microbial use?

Passage

Question 1: How was Penicillin discovered, and who discovered it?

Question 2: What is the literal meaning of the word 'antibiotic', and why is this term considered context-dependent?

Question 3: Describe the contributions of Fleming, Chain, and Florey to the development of Penicillin and explain the significance of antibiotics in modern medicine.

Passage

Question 1: Name the microorganism and the chemical produced by it which is used as a clot buster in heart attack patients.

Question 2: Why are bottled fruit juices clearer than freshly made home juices? Which enzymes are responsible?

Question 3: Explain the roles of cyclosporin A and statins as bioactive molecules. Name the microorganisms that produce them and state their mechanisms of action.

Passage

Question 1: What is BOD and what does a high BOD value indicate?

Question 2: What are flocs and what role do they play in secondary sewage treatment?

Question 3: Describe the complete secondary treatment of sewage, including the fate of activated sludge and the gases produced during anaerobic digestion.

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