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Microbes in Human Welfare: questions with answers

Class 12 Biology, Chapter 8 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.

How to teach this chapter · Common misconceptions & worked visual for this chapter

Microbes in household food production

Question 1

Which statement best explains microbes in household food production?

  1. (a)The process has no biological mechanism and never depends on evidence.
  2. (b)Lactic acid bacteria convert milk sugars into lactic acid during curd formation, while yeasts ferment dough and beverages; microbial metabolism changes texture, flavour and preservation.
  3. (c)Yeast produces oxygen during fermentation
  4. (d)Curd forms without microbial metabolism
Show answer

(b) Lactic acid bacteria convert milk sugars into lactic acid during curd formation, while yeasts ferment dough and beverages; microbial metabolism changes texture, flavour and preservation.

Lactic acid bacteria convert milk sugars into lactic acid during curd formation, while yeasts ferment dough and beverages; microbial metabolism changes texture, flavour and preservation.

Question 2

A learner claims: Curd forms without microbial metabolism. Which correction is best?

  1. (a)Yeast produces oxygen during fermentation
  2. (b)Lactic acid bacteria make milk acidic and coagulate proteins.
  3. (c)The claim is correct because all biological systems behave identically.
  4. (d)Curd forms without microbial metabolism
Show answer

(b) Lactic acid bacteria make milk acidic and coagulate proteins.

Lactic acid bacteria acidify milk and coagulate proteins.

Industrial fermentation products

Question 3

Which statement best explains industrial fermentation products?

  1. (a)Selected microbes are cultured under controlled conditions to produce ethanol, organic acids, enzymes and other metabolites, followed by recovery and purification.
  2. (b)The process has no biological mechanism and never depends on evidence.
  3. (c)Every industrial product is made by the same microbe
  4. (d)Fermentation needs no control of pH or temperature
Show answer

(a) Selected microbes are cultured under controlled conditions to produce ethanol, organic acids, enzymes and other metabolites, followed by recovery and purification.

Selected microbes are cultured under controlled conditions to produce ethanol, organic acids, enzymes and other metabolites, followed by recovery and purification.

Question 4

A learner claims: Every industrial product is made by the same microbe. Which correction is best?

  1. (a)Every industrial product is made by the same microbe
  2. (b)Different organisms and strains are selected for particular products and conditions.
  3. (c)The claim is correct because all biological systems behave identically.
  4. (d)Fermentation needs no control of pH or temperature
Show answer

(b) Different organisms and strains are selected for particular products and conditions.

Different organisms and strains are selected for particular products and conditions.

Antibiotics and responsible use

Question 5

Which statement best explains antibiotics and responsible use?

  1. (a)Stopping antibiotics early prevents resistance
  2. (b)The process has no biological mechanism and never depends on evidence.
  3. (c)Antibiotics are effective against all viruses
  4. (d)Antibiotics are microbial products or derivatives that inhibit susceptible microbes; penicillin came from Penicillium observations. Misuse selects resistant strains and antibiotics do not treat viruses.
Show answer

(d) Antibiotics are microbial products or derivatives that inhibit susceptible microbes; penicillin came from Penicillium observations. Misuse selects resistant strains and antibiotics do not treat viruses.

Antibiotics are microbial products or derivatives that inhibit susceptible microbes; penicillin came from Penicillium observations. Misuse selects resistant strains and antibiotics do not treat viruses.

Question 6

A learner claims: Antibiotics are effective against all viruses. Which correction is best?

  1. (a)Stopping antibiotics early prevents resistance
  2. (b)Antibiotics target susceptible cellular microbes, not viral replication.
  3. (c)Antibiotics are effective against all viruses
  4. (d)The claim is correct because all biological systems behave identically.
Show answer

(b) Antibiotics target susceptible cellular microbes, not viral replication.

Antibiotics target susceptible cellular microbes, not viral replication.

Activated sludge and anaerobic digestion

Question 7

Which statement best explains activated sludge and anaerobic digestion?

  1. (a)Methanogens require abundant oxygen
  2. (b)All activated sludge is discharged untreated
  3. (c)The process has no biological mechanism and never depends on evidence.
  4. (d)Settled microbial flocs form activated sludge; part is recycled as inoculum and the rest enters anaerobic digesters, where methanogens produce biogas and stabilise sludge.
Show answer

(d) Settled microbial flocs form activated sludge; part is recycled as inoculum and the rest enters anaerobic digesters, where methanogens produce biogas and stabilise sludge.

Settled microbial flocs form activated sludge; part is recycled as inoculum and the rest enters anaerobic digesters, where methanogens produce biogas and stabilise sludge.

Question 8

A learner claims: All activated sludge is discharged untreated. Which correction is best?

  1. (a)Methanogens require abundant oxygen
  2. (b)All activated sludge is discharged untreated
  3. (c)A portion is recycled and excess sludge is anaerobically digested.
  4. (d)The claim is correct because all biological systems behave identically.
Show answer

(c) A portion is recycled and excess sludge is anaerobically digested.

A portion is recycled and excess sludge is anaerobically digested.

Methanogens and renewable energy

Question 9

Which statement best explains methanogens and renewable energy?

  1. (a)Biogas is pure methane with no other gases
  2. (b)Methanogenic archaea anaerobically convert organic substrates into methane-rich biogas in digesters and ruminant guts; gas composition and yield depend on feedstock and process conditions.
  3. (c)The process has no biological mechanism and never depends on evidence.
  4. (d)Biogas is produced by aerobic photosynthesis
Show answer

(b) Methanogenic archaea anaerobically convert organic substrates into methane-rich biogas in digesters and ruminant guts; gas composition and yield depend on feedstock and process conditions.

Methanogenic archaea anaerobically convert organic substrates into methane-rich biogas in digesters and ruminant guts; gas composition and yield depend on feedstock and process conditions.

Question 10

A learner claims: Biogas is produced by aerobic photosynthesis. Which correction is best?

  1. (a)Biogas is produced by aerobic photosynthesis
  2. (b)The claim is correct because all biological systems behave identically.
  3. (c)Biogas is pure methane with no other gases
  4. (d)Methanogenesis is an anaerobic microbial process.
Show answer

(d) Methanogenesis is an anaerobic microbial process.

Methanogenesis is an anaerobic microbial process.

Microbial biocontrol

Question 11

Which statement best explains microbial biocontrol?

  1. (a)Biocontrol means applying stronger chemical pesticide
  2. (b)A successful biocontrol agent must eliminate every organism
  3. (c)Biocontrol uses predators, parasites or pathogens such as Bacillus thuringiensis and Trichoderma to suppress pests while reducing broad chemical exposure; it is targeted management, not total eradication.
  4. (d)The process has no biological mechanism and never depends on evidence.
Show answer

(c) Biocontrol uses predators, parasites or pathogens such as Bacillus thuringiensis and Trichoderma to suppress pests while reducing broad chemical exposure; it is targeted management, not total eradication.

Biocontrol uses predators, parasites or pathogens such as Bacillus thuringiensis and Trichoderma to suppress pests while reducing broad chemical exposure; it is targeted management, not total eradication.

Primary and secondary sewage treatment

Question 12

Which statement best explains primary and secondary sewage treatment?

  1. (a)High BOD indicates clean oxygen-rich water
  2. (b)Primary treatment physically removes debris and solids. Secondary treatment uses aerobic microbial flocs to oxidise organic matter, reducing biochemical oxygen demand before discharge.
  3. (c)The process has no biological mechanism and never depends on evidence.
  4. (d)Primary treatment removes dissolved organic load biologically
Show answer

(b) Primary treatment physically removes debris and solids. Secondary treatment uses aerobic microbial flocs to oxidise organic matter, reducing biochemical oxygen demand before discharge.

Primary treatment physically removes debris and solids. Secondary treatment uses aerobic microbial flocs to oxidise organic matter, reducing biochemical oxygen demand before discharge.

Scaling microbial welfare processes

Question 13

Which statement best explains scaling microbial welfare processes?

  1. (a)More microbial growth always means a safer product
  2. (b)Useful microbial processes require matching organism, substrate, environment, containment and downstream handling; household and industrial systems use the same biology at different scales and controls.
  3. (c)A useful microbe performs identically under every condition
  4. (d)The process has no biological mechanism and never depends on evidence.
Show answer

(b) Useful microbial processes require matching organism, substrate, environment, containment and downstream handling; household and industrial systems use the same biology at different scales and controls.

Useful microbial processes require matching organism, substrate, environment, containment and downstream handling; household and industrial systems use the same biology at different scales and controls.

Biofertilisers and nitrogen fixation

Question 14

Which statement best explains biofertilisers and nitrogen fixation?

  1. (a)Rhizobium in legume nodules, free-living bacteria and cyanobacteria increase biologically available nutrients. They supplement soil fertility through living processes rather than directly acting as synthetic fertilisers.
  2. (b)Biofertilisers are concentrated chemical salts
  3. (c)Rhizobium fixes nitrogen equally in every plant without association
  4. (d)The process has no biological mechanism and never depends on evidence.
Show answer

(a) Rhizobium in legume nodules, free-living bacteria and cyanobacteria increase biologically available nutrients. They supplement soil fertility through living processes rather than directly acting as synthetic fertilisers.

Rhizobium in legume nodules, free-living bacteria and cyanobacteria increase biologically available nutrients. They supplement soil fertility through living processes rather than directly acting as synthetic fertilisers.

Mycorrhiza and plant benefit

Question 15

Which statement best explains mycorrhiza and plant benefit?

  1. (a)Mycorrhiza is always a root disease
  2. (b)The process has no biological mechanism and never depends on evidence.
  3. (c)Mycorrhiza is a mutual association between fungi and roots: fungi improve mineral and water uptake, especially phosphorus, while plants supply food made by photosynthesis and may gain stress resistance.
  4. (d)The fungus supplies sugars to the plant without receiving carbon
Show answer

(c) Mycorrhiza is a mutual association between fungi and roots: fungi improve mineral and water uptake, especially phosphorus, while plants supply food made by photosynthesis and may gain stress resistance.

Mycorrhiza is a mutual association between fungi and roots: fungi improve mineral and water uptake, especially phosphorus, while plants supply photosynthate and may gain stress resistance.

Common misconception in Microbes in Human Welfare

Open full misconception guide →

Does fermentation always make the same product?

Wrong

Every microbe that ferments sugar produces alcohol.

Why it feels right. Alcoholic fermentation is the familiar example.

Right

Fermentation products depend on the microbe and pathway.

Worked example

Yeast
Sugar→Ethanol + CO₂
Lactic acid bacteria
Milk sugars→Lactic acid
Different microbes use different pathways and produce different products.
  1. Yeast can turn sugar into ethanol and carbon dioxide.
  2. Lactic acid bacteria in curd formation instead produce lactic acid from milk sugars.