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

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

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Question 1

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What is the role of Lactobacillus in curd formation?

Lactobacillus is a lactic acid bacterium (LAB) that grows in milk at suitable temperatures, multiplying rapidly when a small amount of curd is added as inoculum.
During growth, LAB produce lactic acid, which coagulates milk proteins (casein) and partially digests them, converting milk into curd.
Curd formation also increases the nutritional quality of milk by enhancing vitamin B12 content, and LAB in the gut help check the growth of harmful microbes.

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Question 2

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Why does idli and dosa dough appear puffed after fermentation?

The dough used for making idli and dosa is fermented by bacteria present in the environment or the raw ingredients.
During bacterial fermentation of the carbohydrates in the dough, CO2 gas is produced as a metabolic by-product of anaerobic respiration.
The CO2 gas gets trapped within the dough, causing it to rise and appear puffed, giving idli and dosa their characteristic light and spongy texture.

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Question 3

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What makes Swiss cheese distinctively different in texture from other varieties?

Swiss cheese has characteristically large holes throughout its body, which distinguishes it texturally from other cheese varieties.
These holes are formed due to the production of a large amount of CO2 gas by a specific bacterium named Propionibacterium sharmanii during the ripening process.
The CO2 gets trapped within the solid cheese matrix during formation, creating the distinctive large holes as the gas accumulates and the cheese solidifies around it.

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Question 4

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Distinguish between the production of wine and whisky in terms of the process used.

Both wine and whisky are produced by the fermentation of sugars (from fruit juices or malted cereals) by the yeast Saccharomyces cerevisiae, which converts sugars to ethanol.
Wine is produced without distillation — the fermented broth is directly used as the beverage after fermentation.
Whisky, on the other hand, is produced by distillation of the fermented broth, concentrating the ethanol to achieve higher alcohol content and a distinct flavour profile.

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Question 5

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How was Penicillin discovered, and why is this discovery considered significant?

Alexander Fleming discovered Penicillin accidentally while working with Staphylococci bacteria; he observed a mould (Penicillium notatum) growing on an unwashed culture plate around which bacterial growth was inhibited.
He identified that the mould produced a chemical substance responsible for this inhibition and named it Penicillin; its full therapeutic potential was later established by Ernest Chain and Howard Florey.
The discovery is significant because Penicillin was the first antibiotic ever identified; it saved millions of lives (including wounded soldiers in World War II) and paved the way for the development of other antibiotics to treat deadly infectious diseases.

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Question 6

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Name the microorganism and acid produced in each case: (i) citric acid (ii) acetic acid (iii) butyric acid.

Citric acid is produced by the fungus Aspergillus niger; it is used widely in food and pharmaceutical industries.
Acetic acid is produced by the bacterium Acetobacter aceti; acetic acid is the main component of vinegar used in food preservation.
Butyric acid is produced by the bacterium Clostridium butylicum; it has applications in the production of certain flavouring agents and plastics.

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Question 7

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What is Streptokinase and how is it used medically?

Streptokinase is an enzyme produced by the bacterium Streptococcus and further modified by genetic engineering to enhance its therapeutic properties.
It is used as a 'clot buster' drug — it dissolves blood clots that form in the coronary arteries of patients who have undergone myocardial infarction (heart attack).
By breaking down fibrin clots in blood vessels, Streptokinase restores blood flow to the heart muscle, significantly reducing damage and improving survival outcomes in cardiac patients.

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Question 8

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What is Cyclosporin A, and from which microorganism is it obtained?

Cyclosporin A is a bioactive molecule classified as an immunosuppressive agent, meaning it suppresses or reduces the activity of the immune system.
It is produced by the fungus Trichoderma polysporum and has been commercialised for therapeutic use.
Cyclosporin A is used in patients who have undergone organ transplants to prevent the immune system from rejecting the transplanted organ, which it would otherwise recognise as foreign.

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Question 9

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Explain the role of Statins in human health and name the microorganism that produces them.

Statins are blood-cholesterol lowering agents produced by the yeast Monascus purpureus and have been commercialised as drugs to manage high cholesterol levels.
They act by competitively inhibiting the enzyme responsible for the synthesis of cholesterol in the body, thereby reducing its production.
By lowering cholesterol levels in the blood, Statins reduce the risk of cardiovascular diseases such as atherosclerosis, coronary artery disease, and heart attacks.

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Question 10

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What is sewage and why can it not be directly discharged into natural water bodies?

Sewage is municipal waste water generated in cities and towns; it contains large amounts of organic matter, including human excreta, and a high number of microbes, many of which are pathogenic.
Discharging untreated sewage directly into rivers or streams would introduce vast quantities of disease-causing microbes and organic pollutants into these water bodies, making the water unsafe for drinking and other uses.
The high organic content of sewage increases the BOD of the receiving water body, depleting dissolved oxygen and killing aquatic life; hence sewage must be treated in Sewage Treatment Plants (STPs) before release.

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Question 11

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Define BOD. What does a high BOD value indicate about a water sample?

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; it is a measure of organic pollution.
The BOD test measures the rate of oxygen uptake by micro-organisms in a water sample, and thus indirectly indicates the amount of organic matter present.
A high BOD value indicates that the water sample contains a large amount of organic matter and is therefore highly polluted with greater polluting potential; it may also mean more pathogenic organisms are present.

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Question 12

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What is activated sludge? Describe its fate after formation in the secondary treatment process.

Activated sludge is the sediment formed in the settling tank during secondary sewage treatment; it consists mainly of bacterial flocs (masses of aerobic bacteria with fungal filaments) that have been separated from the treated effluent.
A small portion of the activated sludge is pumped back into the aeration tank to serve as inoculum, seeding the incoming primary effluent with the active microbial community needed to continue treatment.
The remaining and larger portion of the activated sludge is pumped into large anaerobic sludge digesters, where anaerobic bacteria digest the organic matter in the sludge and produce biogas (methane, H2S, CO2) as a usable energy by-product.

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Question 13

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What are methanogens? Mention two habitats where they are naturally found.

Methanogens are anaerobic bacteria that grow on cellulosic material and produce large amounts of methane (CH4) along with CO2 and H2 as by-products of their metabolism; a common example is Methanobacterium.
They are naturally found in the rumen of cattle, where they help break down cellulose present in the cattle's food, playing an important role in cattle nutrition.
Methanogens are also present in the anaerobic sludge formed during sewage treatment; since cattle dung is rich in these bacteria, gobar (dung) is used as the primary feedstock for biogas plants.

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Chapter 8: Microbes in Human Welfare | Short Questions

What is the role of Lactobacillus in curd formation?

Why does idli and dosa dough appear puffed after fermentation?

What makes Swiss cheese distinctively different in texture from other varieties?

Distinguish between the production of wine and whisky in terms of the process used.

How was Penicillin discovered, and why is this discovery considered significant?

Name the microorganism and acid produced in each case: (i) citric acid (ii) acetic acid (iii) butyric acid.

What is Streptokinase and how is it used medically?

What is Cyclosporin A, and from which microorganism is it obtained?

Explain the role of Statins in human health and name the microorganism that produces them.

What is sewage and why can it not be directly discharged into natural water bodies?

Define BOD. What does a high BOD value indicate about a water sample?

What is activated sludge? Describe its fate after formation in the secondary treatment process.

What are methanogens? Mention two habitats where they are naturally found.

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