Microbes in Human WelfareNEET MCQs with solutions
Microbes in Human Welfare covers the beneficial roles of microorganisms in household products, industrial processes, sewage treatment, biogas production, biocontrol and biofertilisers. NEET questions are highly factual — which microbe does what. A clear table of organisms and their applications is the fastest way to score.
- Class
- 12 Biology
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- 24 questions
- In the RankUp app
- 524 questions
- ELITE questions
- 282
- NCERT topics
- 9
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Important PYQ Mixed Concepts
Which of the following correctly identifies the microorganism used for commercial production of ethanol and the major product formed during its fermentation?
Not quite — the answer is B.
Yeast Saccharomyces cerevisiae carries out alcoholic fermentation and produces ethanol along with carbon dioxide. Lactobacillus is associated with lactic acid fermentation, not ethanol. The trap is confusing yeast with lactic acid bacteria.
Q2Important PYQ Mixed Concepts
The dough for idli and dosa becomes soft and puffed mainly because of the combined activity of which microorganisms?
Not quite — the answer is A.
Traditional fermented foods such as idli and dosa involve combined microbial fermentation by both bacteria and yeast. Selecting only yeast is the classic trap, as NCERT specifically describes combined microbial activity in dough fermentation.
Q3Microbes as Biocontrol Agents
What is the primary purpose of using biocontrol agents in agriculture?
Not quite — the answer is A.
Biocontrol is defined as the use of living organisms — microbes, predators, or parasites — to suppress pest populations below economically damaging levels, without synthetic chemicals. The other options describe unrelated agricultural or industrial processes.
Q4Microbes as Biocontrol Agents
Which bacterium is most widely used as a microbial biocontrol agent against insect pests in crops?
Not quite — the answer is A.
Bacillus thuringiensis (Bt) produces crystalline Cry proteins toxic to specific insect larvae and is the most extensively used bacterial biopesticide globally. Rhizobium fixes nitrogen; Lactobacillus is a probiotic; Nitrosomonas is a nitrifying bacterium — none produce insecticidal toxins.
Q5Microbes in Sewage Treatment
Which of the following correctly describes the primary goal of sewage treatment before effluent is discharged into natural water bodies?
Not quite — the answer is C.
NCERT states treated sewage is released into water bodies only after BOD is sufficiently reduced; high BOD in receiving water causes oxygen depletion, killing aquatic life. Drinking water production and methane generation are secondary outcomes, not the primary objective of sewage treatment.
Q6Microbes in Sewage Treatment
Which step of sewage treatment primarily removes large floating solids and suspended particles through physical processes?
Not quite — the answer is A.
Primary treatment uses sequential filtration (removal of large debris) followed by sedimentation in settling tanks to remove suspended particles — no biological agents are involved. Secondary treatment uses microbes; tertiary treatment targets dissolved chemicals; anaerobic digestion treats sludge.
Q7Microbes in Household Products
Which microorganism mentioned in NCERT converts milk into curd?
Not quite — the answer is A.
Lactobacillus (LAB) ferments lactose in milk, producing lactic acid that lowers pH and causes coagulation. Saccharomyces is a yeast involved in bread/alcohol fermentation, not curd. Methanobacterium and Azotobacter have no role in curd formation.
Q8Microbes in Household Products
Which milk sugar is fermented by lactic acid bacteria during curd formation?
Not quite — the answer is B.
Lactobacillus specifically targets lactose, the disaccharide unique to milk, fermenting it into lactic acid. Glucose, sucrose, and maltose are not the primary substrate in milk fermentation.
Q9Grand Test
Which of the following correctly explains why beer is classified as a non-distilled alcoholic beverage?
Not quite — the answer is B.
Beer and wine are produced by fermentation alone, without any subsequent distillation step. Whisky, brandy and rum involve distillation of fermented broth. The trap is conflating fermentation with distillation, which are distinct processing steps described in NCERT.
Q10Grand Test
Which microorganism-product pair is correctly matched?
Not quite — the answer is D.
Aspergillus niger is used commercially for large-scale citric acid production. Acetobacter aceti produces acetic acid for vinegar, not penicillin. Monascus purpureus produces statins and Trichoderma polysporum produces cyclosporin A. This is a high-frequency NCERT product-source discrimination question.
Q11Mixed Revision
Which of the following correctly distinguishes a biofertilizer from a biocontrol agent?
Not quite — the answer is C.
Rhizobium forms symbiotic associations with legume roots and fixes atmospheric nitrogen, making it a biofertilizer. Trichoderma is used as a biological control agent against plant pathogens. The trap is swapping the agricultural roles of the two organisms or assigning antibiotic roles to both.
Q12Mixed Revision
A microorganism converts alcohol into acetic acid during vinegar production. Which organism is responsible?
Not quite — the answer is D.
Acetobacter aceti oxidises ethanol to acetic acid and is the organism responsible for vinegar production. Saccharomyces cerevisiae produces ethanol during fermentation, Clostridium butylicum produces butyric acid and Monascus purpureus produces statins. Each option is a genuine product-source pair to increase discrimination difficulty.
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Get RankUp on Google PlayQ13Microbes in Production of Biogas
Which group of microorganisms is primarily responsible for biogas production from organic waste?
Not quite — the answer is A.
Methanogens anaerobically convert organic substrates — especially cellulosic material in cow dung — into methane, the primary component of biogas. Nitrifying bacteria oxidise ammonia to nitrate and play no role in methanogenesis. Lactic acid bacteria and cyanobacteria are aerobic/facultative and do not produce methane.
Q14Microbes in Production of Biogas
Which environmental condition is essential for methanogens to carry out biogas production?
Not quite — the answer is B.
Methanogens are strict anaerobes — even trace oxygen is toxic to them, halting methanogenesis completely. Aerobic conditions (Option A) support decomposition but not methane generation. Alkalinity and light are irrelevant to methanogen activity.
Q15Microbes as Biofertilisers
Which microorganisms are primarily used as biofertilisers to enhance soil nitrogen availability?
Not quite — the answer is A.
Biofertilisers are microorganisms (bacteria, cyanobacteria, fungi) that fix atmospheric N₂ or solubilise nutrients. Nitrifying bacteria like Nitrosomonas oxidise ammonia but do not fix N₂ — a common trap. Photosynthetic algae alone are not classified as biofertilisers unless they also fix nitrogen.
Q16Microbes as Biofertilisers
Which bacterium forms symbiotic nitrogen-fixing nodules in leguminous plant roots?
Not quite — the answer is B.
Rhizobium enters root hairs of legumes and forms nodules where it fixes atmospheric N₂ into ammonia. Azotobacter is free-living, not symbiotic. Azospirillum associates with cereal roots but does not form nodules — a key distinction tested in NEET.
Q17Microbes in Industrial Products
Which antibiotic was the first to be discovered from a microorganism, and who discovered it?
Not quite — the answer is C.
Penicillin was discovered by Alexander Fleming in 1928 when he observed that Penicillium notatum inhibited bacterial growth on a culture plate. Streptomycin was discovered by Waksman; tetracycline and erythromycin were discovered later by others.
Q18Microbes in Industrial Products
Which microorganism produces the antibiotic penicillin?
Not quite — the answer is D.
Penicillium notatum (fungus) produces penicillin, which inhibits bacterial cell wall synthesis. Aspergillus niger produces citric acid; Rhizobium is a nitrogen fixer; Lactobacillus produces lactic acid — none produce penicillin.
Q19Microbes in Household Products
What is the main organic acid produced during conversion of milk to curd?
Not quite — the answer is C.
Lactic acid accumulation lowers milk pH and causes coagulation of proteins forming curd. Acetic acid is produced in vinegar fermentation; propionic acid is produced by Propionibacterium in Swiss cheese; citric acid is produced by Aspergillus niger.
Q20Microbes in Household Products
Which milk protein coagulates during curd formation due to lactic acid production?
Not quite — the answer is D.
Lactic acid lowers pH to the isoelectric point of casein (~4.6), causing it to precipitate and form curd. Lactalbumin and lactoglobulin are whey proteins that remain in solution and do not coagulate under these conditions.
Q21Microbes in Household Products
Which practice accelerates curd formation in household preparation?
Not quite — the answer is A.
Previous curd acts as a starter inoculum, introducing active Lactobacillus cells that rapidly initiate fermentation. Refrigeration inhibits LAB growth; boiling kills bacteria; NaCl has no role in accelerating fermentation.
Q22Microbes in Household Products
Which additional nutritional benefit does NCERT specifically mention for curd compared to milk?
Not quite — the answer is B.
NCERT explicitly states that LAB increase vitamin B12 content during fermentation of milk to curd. Fat and calcium content are not significantly altered; lactose is consumed, not increased, during fermentation.
Q23Microbes in Household Products
A student adds previous curd to warm milk and observes curd formation within hours. Which property of the added curd is directly responsible for initiating this process?
Not quite — the answer is A.
The starter curd introduces viable Lactobacillus cells (LAB) that proliferate and ferment lactose. The acidity of previous curd, casein aggregates, and vitamin B12 do not independently initiate fermentation in fresh milk.
Q24Microbes in Household Products
Which environmental condition most favors rapid curd formation?
Not quite — the answer is D.
Lactobacillus grows optimally between 30–40°C, accelerating fermentation. Low temperature inhibits growth; alkaline pH is unfavorable for LAB; LAB are aerotolerant anaerobes but do not require a vacuum.
ELITE question · AIR under 50 level
This chapter has 282 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Microbes & Applications
Quick revision: most questions in this chapter test these facts.
| Application | Key Microbe |
|---|---|
| Curd (yoghurt) | Lactobacillus — converts lactose to lactic acid |
| Bread / Ethanol | Saccharomyces cerevisiae (yeast) — fermentation |
| Antibiotics | Penicillium notatum (penicillin); Streptomyces (streptomycin) |
| Sewage treatment | Flocs of aerobic bacteria + fungi in aeration tank; methanogens in anaerobic sludge digester |
| Biogas | Methanogens (Methanobacterium) in biogas plant — produce CH₄, CO₂, H₂ |
| Biofertilisers | Rhizobium (N₂ fixation in legumes), Azospirillum (free-living), mycorrhiza (phosphorus) |
What the app covers in this chapter
524 questions in total, each with a detailed explanation.
| Important PYQ Mixed Concepts | 100 |
| Microbes as Biocontrol Agents | 81 |
| Microbes in Sewage Treatment | 62 |
| Microbes in Household Products | 60 |
| Grand Test | 60 |
| Mixed Revision | 59 |
| Microbes in Production of Biogas | 41 |
| Microbes as Biofertilisers | 41 |
| Microbes in Industrial Products | 20 |
Questions students ask
Is Microbes in Human Welfare important for NEET?
Yes — it is short and purely factual. Questions on which microbe is used for which application (curd, bread, antibiotics, sewage, biogas, biofertilisers) are common and easy marks.
Which topics should I revise first?
Revise the specific microorganisms for household products, industrial products (antibiotics, enzymes), the two stages of sewage treatment, biogas plant organisms, and biofertilisers (Rhizobium, mycorrhiza).
How many questions from this chapter are on RankUp?
The RankUp app has 524 questions on Microbes in Human Welfare, including 282 ELITE questions written for students aiming at AIR under 50. Every question has a detailed explanation.
