Microbes in Household and Industrial Products: ISC Class 12 Biology
Updated 15 October 2026 · Fact-checked
Lactobacillus turns milk into curd, Saccharomyces cerevisiae leavens bread and ferments beverages, and Propionibacterium sharmanii makes the holes in Swiss cheese. In industry, microbes grown in fermentors make antibiotics such as penicillin, organic acids, ethanol, enzymes (lipase, pectinase, protease, streptokinase), cyclosporin A and statins.
Understand Microbes in Household and Industrial Products
Household products.
- Curd: Lactobacillus and other lactic acid bacteria (LAB) grow in milk; the acids they produce coagulate and partially digest milk proteins. A little curd added as inoculum (starter) carries millions of LAB, which multiply at a suitable temperature. Curd is more nutritious than milk because of increased vitamin B₁₂. In the stomach LAB also check disease-causing microbes.
- Idli and dosa dough: fermented by bacteria; the puffed-up look is due to CO₂.
- Bread: dough fermented by baker's yeast, Saccharomyces cerevisiae; CO₂ makes it rise.
- Toddy: traditional drink of parts of southern India, made by fermenting palm sap. Microbes also ferment fish, soyabean and bamboo shoots.
- Cheese: texture, flavour and taste depend on the microbes used. Large holes in Swiss cheese come from much CO₂ produced by the bacterium Propionibacterium sharmanii; Roquefort cheese is ripened by growing a specific fungus on it.
Industrial production needs fermentors: very large vessels in which microbes are grown on an industrial scale.
Fermented beverages. The same yeast, Saccharomyces cerevisiae (here called brewer's yeast), ferments malted cereals and fruit juices to ethanol.
| Without distillation | With distillation of the fermented broth |
|---|---|
| wine, beer | whisky, brandy, rum |
Antibiotics. Chemical substances produced by some microbes that kill or retard the growth of other (disease-causing) microbes. 'Anti' means against and 'bio' life; for humans they are 'pro-life'.
- Penicillin, the first antibiotic, was a chance discovery: Alexander Fleming, working on Staphylococci, saw a mould on an unwashed culture plate around which the bacteria could not grow. He named the chemical penicillin after the mould Penicillium notatum. Ernest Chain and Howard Florey later established its full potential; it was used to treat soldiers wounded in World War II. All three received the Nobel Prize in 1945.
- Antibiotics greatly improved treatment of plague, whooping cough, diphtheria and leprosy.
Organic acids, alcohol and enzymes (source → product → use).
| Microbe | Type | Product |
|---|---|---|
| Aspergillus niger | fungus | citric acid |
| Acetobacter aceti | bacterium | acetic acid |
| Clostridium butylicum | bacterium | butyric acid |
| Lactobacillus | bacterium | lactic acid |
| Saccharomyces cerevisiae | yeast | ethanol (commercial) |
| Enzyme / bioactive molecule | Source | Use |
|---|---|---|
| Lipase | microbes | in detergents; removes oily stains from laundry |
| Pectinase, protease | microbes | clarify bottled fruit juices (home-made juice stays turbid) |
| Streptokinase | bacterium Streptococcus (modified by genetic engineering) | 'clot buster': removes clots from blood vessels of patients after myocardial infarction |
| Cyclosporin A | fungus Trichoderma polysporum | immunosuppressive agent in organ-transplant patients |
| Statins | yeast Monascus purpureus | lower blood cholesterol by competitively inhibiting the enzyme that synthesises cholesterol |
Why fruit juice from the market is clearer. Fruit pulp contains cell-wall material (pectin) and proteins that keep the juice cloudy; pectinases break down pectin of cell walls and proteases break proteins, so the juice clears.
How to remember 'household versus industrial'. Household fermentations are small-scale, use natural or starter cultures and mostly produce CO₂ or lactic acid. Industrial fermentations use selected strains in fermentors to make a single product in bulk.
Flow chart (curd): milk + starter (LAB) → LAB multiply at warm temperature → lactic acid → milk proteins coagulate → curd (more vitamin B₁₂).
Microbes in Household and Industrial Products: key facts
- Three household microbes
Curd Lactobacillus (lactic acid bacteria) Bread Saccharomyces cerevisiae (baker's yeast) Swiss cheese Propionibacterium sharmanii - The ISC syllabus list.
- Beverages
Wine no distillation Beer no distillation Whisky distilled Brandy distilled Rum distilled - All by brewer's yeast.
- Bioactive molecules
Cyclosporin A Trichoderma polysporum (fungus); immunosuppressant Statins Monascus purpureus (yeast); lower blood cholesterol Streptokinase Streptococcus; clot buster - Immunosuppressant; cholesterol lowering; clot buster.
- Organic acids
Citric acid Aspergillus niger Acetic acid Acetobacter aceti Butyric acid Clostridium butylicum Lactic acid Lactobacillus - Match the microbe to the acid.
How to answer Microbes in Household and Industrial Products questions
ISC asks for biological names of microbes for given products, uses of enzymes and bioactive molecules, beverage distillation, the penicillin story, and clue-based reasoning (clear juice, curd, cheese holes).
- 1Give the full binomial name where one exists: Saccharomyces cerevisiae, Trichoderma polysporum, Monascus purpureus.
- 2Spell carefully: link Saccharomyces to 'sugar' (saccharo) and fungus (myces).
- 3For a product clue, name the specific microbe or enzyme, not 'bacteria' or 'enzymes'.
- 4For uses, give one precise use: lipase removes oily stains; streptokinase dissolves clots; cyclosporin A suppresses immunity.
- 5For beverages, say which are distilled and which are not.
- 6For 'processed dairy products', name curd, cheese, yoghurt or butter, not milk.
Microbes in Household and Industrial Products in real life
The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.
Starter culture in curd making
Suppose a family sets curd every night, but in a cold winter week the milk stays liquid till morning, while in summer it sets in a few hours.
Explain the difference and suggest how to set curd in winter.
Try it first, then show the solutionSolution
- Curd forms when lactic acid bacteria from the starter multiply and make lactic acid that coagulates milk proteins.
- LAB multiply fastest at warm temperatures; in cold weather their growth and acid production slow down.
- So set the milk lukewarm, add enough starter, and keep the vessel in a warm place (wrapped, or near a warm spot).
- The curd will also gain vitamin B₁₂ from the bacteria.
Answer: Low temperature slows lactic acid bacteria; warm the milk and keep it warm with an adequate starter.
Memory hook: Warm bugs, firm curd.
Tricks to remember Microbes in Household and Industrial Products
Short memory aids. Say each one aloud once, then use it on a question the same day.
Saccharo = sugar
Saccharomyces is the sugar fungus that eats sugar and makes CO₂ and alcohol.
Use it when: Spelling and role of yeast.
Swiss holes, Propioni gas
Propionibacterium puffs gas into Swiss cheese.
Use it when: Cheese clue.
Tricky transplant, Monascus monitors cholesterol
Trichoderma → transplant drug (cyclosporin A); Monascus → statins for cholesterol.
Use it when: Bioactive molecules.
Microbes in Household and Industrial Products: solved examples
Ordered from board level to HOTS. Try each one before you open the solution.
Example 1: Name the microbe · 2 marks · Short answerBoard level
Give the biological name of the microbe that (i) causes large holes in Swiss cheese, (ii) is used to make bread, (iii) produces citric acid, (iv) produces acetic acid.
Try it first, then show the solutionSolution
- (i) Propionibacterium sharmanii; (ii) Saccharomyces cerevisiae (1 mark).
- (iii) Aspergillus niger; (iv) Acetobacter aceti (1 mark).
Answer: Propionibacterium sharmanii; Saccharomyces cerevisiae; Aspergillus niger; Acetobacter aceti.
Example 2: Curd from milk · 3 marks · Short answerBoard level
How is milk converted into curd? Why is curd considered more nutritious than milk?
Try it first, then show the solutionSolution
- A small amount of curd (starter) adds millions of lactic acid bacteria such as Lactobacillus to fresh milk (1 mark).
- At a suitable temperature they multiply and produce acids that coagulate and partially digest milk proteins (1 mark).
- Curd has more vitamin B₁₂, and LAB in the stomach check disease-causing microbes (1 mark).
Answer: LAB acids coagulate milk proteins; curd has more vitamin B₁₂.
Example 3: Distilled or not · 3 marks · Short answerHarder board level
Which microbe is used in the production of alcoholic beverages? Classify wine, whisky, beer, rum and brandy into those produced with and without distillation, and state what distillation does.
Try it first, then show the solutionSolution
- Brewer's yeast, Saccharomyces cerevisiae, ferments malted cereals and fruit juices to ethanol (1 mark).
- Without distillation: wine, beer; with distillation: whisky, rum, brandy (1 mark).
- Distillation of the fermented broth separates and concentrates the ethanol, giving drinks with a higher alcohol content (1 mark).
Answer: Saccharomyces cerevisiae; wine and beer undistilled; whisky, rum and brandy distilled (concentrated alcohol).
Example 4: Penicillin discovery · 3 marks · Short answerHarder board level
Describe how penicillin was discovered. Who established its potential as an effective antibiotic?
Try it first, then show the solutionSolution
- Alexander Fleming, working on Staphylococci, noticed a mould growing on an unwashed culture plate, around which the bacteria could not grow (1 mark).
- He found that a chemical made by the mould caused this and named it penicillin after Penicillium notatum (1 mark).
- Ernest Chain and Howard Florey established its full potential; the three shared the Nobel Prize in 1945 (1 mark).
Answer: Chance observation by Fleming (Penicillium notatum); potential shown by Chain and Florey.
Example 5: Hospital uses · 3 marks · Short answerHarder board level
A heart-attack patient and a kidney-transplant patient are both given drugs of microbial origin. Name a suitable drug for each, its source and how it helps.
Try it first, then show the solutionSolution
- Heart attack: streptokinase from the bacterium Streptococcus, modified by genetic engineering; a clot buster that dissolves clots in blood vessels (1½ marks).
- Transplant: cyclosporin A from the fungus Trichoderma polysporum; an immunosuppressant that reduces rejection of the new organ (1½ marks).
Answer: Streptokinase (Streptococcus) dissolves clots; cyclosporin A (Trichoderma polysporum) suppresses immunity.
Example 6: A juice factory · 4 marks · Short answerHOTS / competency
Suppose a juice factory finds its apple juice cloudy and its machines' oily residues hard to wash off. (a) Which two microbial enzymes would clear the juice, and how? (b) Which enzyme could be added to the cleaning detergent and why? (c) Why are microbes preferred over plant or animal sources for such enzymes?
Try it first, then show the solutionSolution
- (a) Pectinase and protease: pectinase breaks down pectin from fruit cell walls and protease breaks proteins, which keep the juice turbid (2 marks).
- (b) Lipase, which breaks down fats and oils, removing oily stains (1 mark).
- (c) Microbes multiply quickly in fermentors, give large amounts of enzyme cheaply and can be grown year-round under controlled conditions (1 mark).
Answer: Pectinase and protease clear juice; lipase removes oil; microbes are fast, cheap, controllable sources.
Where students lose marks in Microbes in Household and Industrial Products
The slips examiners see most often, and what to write instead.
Mistake: Misspelt or incomplete binomial names
In 2024 examiners reported binomial nomenclature not followed and Saccharomyces misspelt as Sarcomyces or Sacromyces; Monascus was also misspelt.
Do this: Learn spellings: Saccharomyces cerevisiae, Monascus purpureus, Trichoderma polysporum.
Usually costs: ½ to 1 mark each.
Mistake: Writing 'enzymes' or 'preservatives' for clear juice
Examiners (2024) found chemicals or preservatives named, fermentation confused, or 'enzymes' written without naming pectinase.
Do this: Name pectinase (with protease) and say it breaks down cell-wall pectin.
Usually costs: 1 mark.
Mistake: Giving raw items as processed dairy products
In 2025 examiners noted milk, rice or dal given instead of processed dairy products.
Do this: Give curd, yoghurt, cheese or butter.
Usually costs: 1 mark each.
Mistake: Mixing up cyclosporin A and statins
Swapping the source fungus and use is common.
Do this: Trichoderma → transplant; Monascus → cholesterol.
Usually costs: 1 mark.
Exam tips
- Underline binomial names in handwritten answers.
- Give the use with each product, not only the microbe.
- Remember NCERT calls Monascus purpureus a yeast and Trichoderma polysporum a fungus.
- For penicillin, mention Fleming, Penicillium notatum, Chain and Florey.
- Make one table of microbe, product and use for revision.
Practice questions on Microbes in Household and Industrial Products
Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.
Q1 · 1 mark · MCQBoard level
Statins are produced by:
(a) Trichoderma polysporum (b) Monascus purpureus (c) Aspergillus niger (d) StreptococcusHint
A yeast.
Answer
(b) Monascus purpureus.
Q2 · 2 marks · Short answerBoard level
Name two dairy-based processed products made with the help of microbes, and the microbe for each.
Hint
Not raw milk.
Answer
Curd (or yoghurt) by Lactobacillus (lactic acid bacteria); Swiss cheese by Propionibacterium sharmanii (Roquefort cheese ripened by a fungus).
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The dough for idli and dosa looks puffed up after fermentation.
Reason (R): Microbes fermenting the dough release carbon dioxide.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.Hint
Gas.
Answer
(a).
Q4 · 2 marks · Short answerHarder board level
How do statins lower blood cholesterol?
Hint
Competitive inhibition.
Answer
Statins, from the yeast Monascus purpureus, competitively inhibit the enzyme responsible for cholesterol synthesis, so less cholesterol is made in the body.
Q5 · 2 marks · Short answerHarder board level
Define antibiotic. Name three diseases whose treatment improved greatly because of antibiotics.
Hint
Kill or retard.
Answer
A chemical substance produced by some microbes that kills or retards the growth of other (disease-causing) microbes. Plague, whooping cough, diphtheria, leprosy (any three).
Q6 · 2 marks · Short answerHarder board level
Why is streptokinase called a clot buster? Why is it 'modified by genetic engineering'?
Hint
Myocardial infarction.
Answer
It dissolves blood clots in vessels of patients who have had a myocardial infarction (heart attack). It is produced by Streptococcus and modified by genetic engineering to make it suitable and available for medical use.
Q7 · 3 marks · Short answerHOTS / competency
Suppose a student argues that home-made juice is 'more natural' because no enzymes are added, while bottled juice is 'chemically treated'. Evaluate this argument using what you know about juice clarification.
Hint
Enzymes are biological.
Answer
The bottled juice is clarified with microbial pectinases and proteases, which are biological catalysts, not chemical preservatives; they break down pectin and proteins that cause turbidity. Home-made juice is turbid because these remain. Both are natural in origin; the enzymes simply speed a natural breakdown.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a food-technology student plans a small unit making three items: bread, curd and vinegar (acetic acid) from fruit wine.
(a) Name the microbe for each item. (1½)
(b) Which gas makes bread rise? (½)
(c) Why must the vinegar step be done in air while bread dough needs no aeration for its gas? (1)Hint
Acetobacter is aerobic.
Answer
(a) Bread: Saccharomyces cerevisiae; curd: Lactobacillus; vinegar: Acetobacter aceti. (b) Carbon dioxide. (c) Acetobacter oxidises ethanol to acetic acid, which needs oxygen; yeast releases CO₂ in dough by fermentation, which goes on without aeration.
Test your recall
Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.
1.Which bacterium makes holes in Swiss cheese?Show answer
Propionibacterium sharmanii.
2.Which vitamin increases when milk becomes curd?Show answer
Vitamin B₁₂.
3.Name the source of cyclosporin A.Show answer
Trichoderma polysporum (a fungus).
4.Which enzyme removes oily stains in detergents?Show answer
Lipase.
5.Name two beverages made without distillation.Show answer
Wine and beer.
6.Which mould did Fleming discover penicillin from?Show answer
Penicillium notatum.
Microbes in Household and Industrial Products: frequently asked questions
Which microbes are used in household products?
Lactobacillus (curd), Saccharomyces cerevisiae (bread) and Propionibacterium sharmanii (Swiss cheese); bacteria also ferment idli and dosa batter.
Why is bottled fruit juice clearer than home-made juice?
It is clarified with pectinases and proteases, which break down cell-wall pectin and proteins that cause cloudiness.
What are cyclosporin A and statins used for?
Cyclosporin A is an immunosuppressant for organ-transplant patients; statins lower blood cholesterol.
Which beverages need distillation?
Whisky, brandy and rum; wine and beer are made without distillation.
What is a fermentor?
A very large vessel in which microbes are grown on an industrial scale to make products such as antibiotics, acids and enzymes.