Microbes in Human Welfare — Class 12 MCQs with Answers
Class 12 CBSE Biology · Chapter 8
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 12 CBSE Biology questions from Chapter 8, "Microbes in Human Welfare". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG apart.
To score well in "Microbes in Human Welfare", focus on diagrams, key terms and knowing NCERT line by line. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Microbes in Human Welfare, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 12 Biology mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Microbes in Human Welfare (Class 12 Biology)
Microbes in human welfare: microbes in household products (curd, cheese, dough); industrial products — fermented beverages, antibiotics, organic acids, enzymes and bioactive molecules; sewage treatment and its BOD; microbes in biogas production; and biofertilisers and biocontrol agents for sustainable agriculture.
- Household microbes
- Lactic acid bacteria (Lactobacillus) curdle milk and add vitamin B₁₂; yeast (Saccharomyces) leavens dough and idli/dosa batter by releasing CO₂.
- Cheese
- Made by microbial fermentation; Swiss cheese's holes and flavour come from Propionibacterium (CO₂), and Roquefort is ripened by Penicillium roqueforti.
- Fermented beverages
- Saccharomyces cerevisiae (brewer's yeast) ferments sugars to ethanol; wine and beer are undistilled, whisky and rum are distilled for higher alcohol.
- Antibiotics
- Chemicals from microbes that kill or inhibit other microbes; penicillin, from Penicillium notatum, was discovered by Alexander Fleming.
Microbes in Human Welfare — important questions & MCQs with answers (Class 12 Biology)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
Curd from milk is produced by:
A.E. coliB.Lactobacillus✓ CorrectC.YeastD.Bacillus subtilisAnswer: B. Lactobacillus
Explanation: Lactobacillus (LAB) ferments lactose to lactic acid, lowering pH so milk casein coagulates into curd. Yeast instead ferments sugars to CO₂/ethanol, not lactic acid — a common mix-up.
- Q2Easy
The first antibiotic, penicillin, was discovered by:
A.Robert KochB.Louis PasteurC.Alexander Fleming✓ CorrectD.Edward JennerAnswer: C. Alexander Fleming
Explanation: Alexander Fleming discovered penicillin in 1928 when a stray Penicillium mould killed Staphylococcus on his culture plate; Chain and Florey later mass-produced it as a drug.
- Q3Easy
Bread is leavened by:
A.E. coliB.LactobacillusC.Yeast (Saccharomyces)✓ CorrectD.BacillusAnswer: C. Yeast (Saccharomyces)
Explanation: Saccharomyces cerevisiae respires sugars in the dough to release CO₂, trapped by gluten to leaven bread. Lactobacillus instead makes lactic acid, souring rather than raising dough.
- Q4Easy
Penicillin is produced by the fungus:
A.Penicillium notatum / chrysogenum✓ CorrectB.Aspergillus nigerC.SaccharomycesD.StreptococcusAnswer: A. Penicillium notatum / chrysogenum
Explanation: Penicillin is synthesised by Penicillium notatum (and the higher-yield P. chrysogenum), fungal moulds — Aspergillus niger instead makes citric acid, a common source of confusion.
- Q5Easy
Curd is formed from milk by the action of:
A.VirusB.YeastC.PenicilliumD.Lactic acid bacteria (LAB)✓ CorrectAnswer: D. Lactic acid bacteria (LAB)
Explanation: Lactic acid bacteria (Lactobacillus) convert milk's lactose to lactic acid, curdling its casein protein. Yeast and Penicillium instead drive alcoholic fermentation and cheese-ripening, not curd.
- Q6Easy
Ethanol for alcoholic beverages is produced by fermentation using:
A.LactobacillusB.Saccharomyces cerevisiae (brewer's yeast)✓ CorrectC.PenicilliumD.AspergillusAnswer: B. Saccharomyces cerevisiae (brewer's yeast)
Explanation: Brewer's yeast (Saccharomyces cerevisiae) anaerobically ferments sugars to ethanol and CO₂, the basis of alcoholic beverages — Lactobacillus produces lactic acid, not ethanol.
- Q7Medium
Adding a small amount of curd to warm milk as a starter introduces:
A.AntibioticsB.YeastC.Millions of LAB that multiply and curdle the milk✓ CorrectD.MethanogensAnswer: C. Millions of LAB that multiply and curdle the milk
Explanation: A spoonful of curd added to warm milk acts as an inoculum, seeding it with millions of live LAB that multiply rapidly and ferment the lactose, curdling the fresh milk.
- Q8Medium
Penicillin was discovered by:
A.Alexander Fleming✓ CorrectB.PasteurC.KochD.WatsonAnswer: A. Alexander Fleming
Explanation: Alexander Fleming noticed in 1928 that Penicillium notatum mould killed nearby Staphylococcus colonies, discovering penicillin — Chain and Florey later purified it into a usable drug.
- Q9Medium
The role of microbes in fermentation was first scientifically established by:
A.Robert HookeB.Alexander FlemingC.Louis Pasteur✓ CorrectD.Charles DarwinAnswer: C. Louis Pasteur
Explanation: Louis Pasteur experimentally established that fermentation is driven by living microorganisms, laying the foundation for microbiology and industrial fermentation.
- Q10Medium
Activated sludge in sewage treatment is rich in:
A.AlgaeB.Anaerobes onlyC.VirusesD.Aerobic bacteria✓ CorrectAnswer: D. Aerobic bacteria
Explanation: Activated sludge is a floc of aerobic heterotrophic bacteria (with fungal filaments) that oxidise dissolved organic matter during forced aeration, sharply cutting the effluent's BOD.
- Q11Medium
In dough fermentation, yeast produces CO₂ AND a small amount of:
A.Lactic acid onlyB.MethaneC.Ethanol✓ CorrectD.Acetic acidAnswer: C. Ethanol
Explanation: Yeast's alcoholic fermentation of dough sugars yields both CO₂, which raises the dough, and a small amount of ethanol, which evaporates during baking.
- Q12Hard
Which product–process match is INCORRECT?
A.Wine — alcoholic fermentationB.Curd — lactic acid fermentationC.Bread — lactic acid fermentation✓ CorrectD.Vinegar — oxidation of ethanolAnswer: C. Bread — lactic acid fermentation
Explanation: Bread rises via yeast's alcoholic (CO₂-producing) fermentation, not lactic acid fermentation — lactic acid fermentation is what curdles milk into curd via Lactobacillus.
- Q13Hard
Biogas (gobar gas) is mainly:
A.EthaneB.Methane✓ CorrectC.PropaneD.ButaneAnswer: B. Methane
Explanation: Methanogenic archaebacteria digest cattle-dung slurry anaerobically, releasing methane (CH₄) as the main combustible gas — the same organisms also live in the cattle rumen.
- Q14Hard
Which is NOT a benefit of LAB in the human gut/curd?
A.They produce penicillin✓ CorrectB.They increase vitamin B₁₂C.They check disease-causing microbesD.They curdle milkAnswer: A. They produce penicillin
Explanation: LAB (Lactobacillus) curdle milk, raise Vitamin B₁₂ and suppress pathogenic gut microbes — they do not make penicillin, which comes from the unrelated fungus Penicillium.
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Start this chapter free →Microbes in Human Welfare — FAQs
What are the key concepts in Class 12 Biology Microbes in Human Welfare?+
Microbes in human welfare: microbes in household products (curd, cheese, dough); industrial products — fermented beverages, antibiotics, organic acids, enzymes and bioactive molecules; sewage treatment and its BOD; microbes in biogas production; and biofertilisers and biocontrol agents for sustainable agriculture. Key ideas include Household microbes, Cheese, Fermented beverages, Antibiotics.
What does Class 12 Biology Chapter 8 (Microbes in Human Welfare) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Microbes in Human Welfare": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG.
Are these "Microbes in Human Welfare" questions free to practise?+
Yes. Sign in with Google to practise "Microbes in Human Welfare" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Microbes in Human Welfare" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Microbes in Human Welfare" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Microbes in Human Welfare" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Microbes in Human Welfare (Class 12 Biology)?+
The questions that matter most test Household microbes, Cheese, Fermented beverages, Antibiotics. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Microbes in Human Welfare?+
Yes — Class 12 Biology Microbes in Human Welfare has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.