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Microbes in Human Welfare — NEET Biology MCQs

30 questions written by hand against the NCERT chapter. Every wrong option is explained, not just the right one.

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Sample questions from this chapter

Warm milk inoculated with a spoonful of curd thickens and gains vitamin B₁₂. Which microbial activity caused this?
  1. Lactic acid bacteria produced acid that coagulated and partly digested milk proteins ✓
  2. Methanogens converted milk to methane
  3. Viruses lysed casein into ethanol
  4. Rhizobium fixed nitrogen in the milk
Answer: A. Starter curd supplies millions of LAB that multiply at suitable temperature and acidify milk. The acid changes protein texture while the culture improves nutritional quality.
Why not B: Methanogens act anaerobically on cellulosic wastes and do not make curd.
Why not C: Curd formation is bacterial acid fermentation, not viral lysis or alcoholic fermentation.
Why not D: Rhizobium associates with legume roots and is not a dairy starter.
Why is air pumped into secondary-treatment tanks?
  1. To float primary sludge for collection
  2. To suppress useful bacteria
  3. To support vigorous aerobic flocs that consume organic matter ✓
  4. To make methanogens produce oxygen
Answer: C. Mechanical agitation and aeration expand bacterial-fungal flocs, accelerating oxidation of organic load and lowering BOD. Oxygen is the resource for this biological stage.
Why not A: Primary solids are removed earlier by settling.
Why not B: Aeration promotes rather than suppresses the useful aerobic community.
Why not D: Methanogens are anaerobic and produce methane, not oxygen.
Samples A, B and C have BOD values of 400, 20 and 8 mg/L respectively. They represent one untreated sewage inflow, one relatively clean river and one secondary-treatment discharge. Which assignment is most reasonable?
  1. A is raw municipal inflow; B is the river; C is processed discharge ✓
  2. The treatment-plant discharge is A, with raw sewage at B and river water at C
  3. River = A; secondary effluent = B; untreated inflow = C
  4. The measurement cannot rank biodegradable organic pollution
Answer: A. Untreated sewage has extreme demand; biological treatment lowers it substantially. Given the stated relatively clean river, 20 versus 8 depends local context, but the exercise's intended ordering assigns the lowest to treated discharge.
Why not B: Treatment should reduce rather than leave the maximum oxygen demand.
Why not C: Untreated sewage has the greatest organic load, not the lowest.
Why not D: BOD is specifically an indirect measure of biodegradable organic matter.

These are 3 of the 30 questions in the test. Take the full chapter test →

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Every NCERT question in this chapter is solved, free: NCERT solutions — Microbes in Human Welfare →

Other NEET Biology chapters

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Questions

How many NEET questions are there on Microbes in Human Welfare?

This chapter test has 30 questions — 10 easy, 14 medium and 6 hard — all written against the NCERT Class 12 chapter.

Is this NEET Biology chapter test free?

Yes. Every chapter test is free with no login. The only paid thing on the site is the full-length 90-question Biology mock and its all-India rank.

Do the questions explain the wrong options?

Yes — every distractor carries its own explanation naming the specific misconception that makes a student pick it. That is the part most question banks skip, and it is the part that changes your next attempt.