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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

Jump to the 6 solved questions

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 top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG get right.

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 helps you stay accurate when time is short, just 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. Try the 6 sample questions below: tap an option to see the answer and a worked explanation. Sign in free to start practising.

Microbes in Human Welfare — important questions & MCQs with answers (Class 12 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

  1. Q1 of 6Easy

    Curd from milk is produced by:

    Show answer

    Answer: 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.

  2. Q2 of 6Easy

    The first antibiotic, penicillin, was discovered by:

    Show answer

    Answer: 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.

  3. Q3 of 6Medium

    Adding a small amount of curd to warm milk as a starter introduces:

    Show answer

    Answer: 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.

  4. Q4 of 6Medium

    Penicillin was discovered by:

    Show answer

    Answer: 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.

  5. Q5 of 6Hard

    Which product–process match is INCORRECT?

    Show answer

    Answer: 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.

  6. Q6 of 6Hard

    Biogas (gobar gas) is mainly:

    Show answer

    Answer: 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.

Microbes in Human Welfare notes: key concepts (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.
Organic acids and enzymes
Aspergillus niger → citric acid; Acetobacter aceti → acetic acid; lipases in detergents; pectinases/proteases clarify juices; streptokinase is a clot-buster.
Bioactive molecules
Cyclosporin A (from Trichoderma) is an immunosuppressant used in transplants; statins (from Monascus) lower cholesterol by inhibiting HMG-CoA reductase.
Sewage treatment
Primary treatment physically removes solids; secondary (biological) treatment uses aerobic microbes forming flocs that lower the BOD of the effluent.
A flow chart of sewage treatment. Raw sewage goes through primary treatment, filtration and sedimentation, which removes solids as primary sludge. Secondary, biological treatment follows: in the aeration tank aerobic microbes form flocs that consume organic matter, lowering the BOD; in the settling tank the flocs settle as activated sludge. Part of it is pumped back into the aeration tank; the rest goes to anaerobic sludge digesters, which release biogas. The treated effluent goes to a river.
BOD
Biochemical Oxygen Demand — oxygen microbes need to break down organic matter in water; high BOD indicates heavy organic pollution.
Activated sludge
Sediment of aerobic microbe flocs in secondary treatment; part is recycled as inoculum, the rest digested anaerobically to release biogas.
Biogas
A mixture chiefly of methane (CH₄) produced by anaerobic methanogens (e.g., Methanobacterium) in cattle dung and sludge; used as a clean fuel.
A biogas plant. A pit below ground, the digester, holds a slurry of cattle dung and water. On the left, dung and water are poured into the slurry inlet tank, and a pipe carries the slurry to the bottom of the digester. There anaerobic methanogens break it down to biogas, mainly methane, which collects under a floating cover, the gas holder; a gas outlet pipe from its top supplies the gas. On the right, a pipe from the digester's bottom carries spent slurry out as sludge to a tank at ground level.
Biofertilisers
Organisms enriching soil nutrients — Rhizobium (root nodules) and Azotobacter fix nitrogen; mycorrhiza (Glomus) aids phosphorus uptake; cyanobacteria in paddy.
Biocontrol agents
Biological pest/disease control — Bacillus thuringiensis kills insect larvae, Trichoderma controls plant pathogens, Baculovirus is a narrow-spectrum insecticide.
Predatory biocontrol
Ladybird beetles control aphids and dragonflies control mosquitoes — natural predators used to cut chemical pesticide use in IPM.
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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, Organic acids and enzymes, Bioactive molecules.

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 ₹1,999/year. One year from the day you pay. Class 12 is your last school year, so your class stays as it is. 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. 6 sample questions are on this page with answers: tap an option, or "Show answer", to see the correct option and a step-by-step 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, Organic acids and enzymes, Bioactive molecules. This page shows 6 solved important MCQs with answers and explanations. Sign in to practise all 90 questions on the chapter as timed quizzes.

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.

Are there question answers and extra questions for Microbes in Human Welfare (Class 12 Biology)?+

Yes. This page has 6 solved questions on Microbes in Human Welfare, each with the correct answer and a short explanation. Sign in to practise all 90 questions on the chapter as timed quizzes.

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