Microbes in Human Welfare Mock Test – Class 12 Biology

1. If aeration in secondary sewage treatment is intensified but the wastewater entering the tank contains very little biodegradable organic matter, which observation is most reasonable?

2. Which sequence best links cattle nutrition with rural energy production?

3. Which set correctly separates major cellular microbial groups from other microscopic biological entities?

4. A treatment plant reduces BOD successfully during aeration, but the settled activated sludge is not divided correctly afterward. Why is the division of activated sludge biologically important?

5. Consider two samples collected from the same sewage treatment plant.

What best explains the change from P to Q?

6. Use the biogas-plant arrangement described below.
Slurry enters an underground concrete tank. Gas accumulates beneath a movable cover. One outlet carries gas away, while another removes digested residue.
Which relationship among the components is correct?

7. Which relationship between BOD and the polluting potential of wastewater is correct?

8. Study the following microbial products.

Which option correctly identifies the row whose function depends specifically on competitive inhibition of an enzyme involved in a human biosynthetic pathway?

9. An industrial unit wants to increase microbial production from a small laboratory culture to a commercial scale while maintaining a large actively growing microbial population in a controlled vessel. Which change is most directly required for industrial-scale microbial production?

10. Untreated sewage is discharged directly into a river. Why is this biologically and environmentally undesirable?

11. A crop has adequate nitrogen but remains weak because the soil is phosphorus-poor, moderately saline and prone to root-borne pathogens. Which microbial intervention is most likely to address several of these problems simultaneously?

12. Two genetically similar plants are grown under increasing salinity and periodic water shortage. One plant has a well-developed mycorrhizal association, while the other does not. Based on the known effects of mycorrhiza, the mycorrhizal plant would be expected to

13. Which gas-related comparison is completely correct?

14. A curd culture performs three measurable functions:
I. It acidifies milk.
II. It increases vitamin content.
III. It helps check disease-causing microbes in the stomach.
Which interpretation is most accurate?

15. A field has large mosquito populations around standing water but very few dragonflies. If dragonflies are successfully re-established, which outcome is most consistent with biological control?

16. A farmer wants one microbial treatment to improve nitrogen availability and another to increase phosphorus acquisition. Which pair best satisfies these two goals respectively?

17. Which integrated pair shares the same broad purpose but relies on fundamentally different biological mechanisms?

18. Raw sewage contains large amounts of biodegradable organic matter and numerous microbes. Which combination best explains why direct discharge into a river is undesirable?

19. A fermentation company produces two ethanol-containing broths using Saccharomyces cerevisiae. Broth P is bottled after fermentation, whereas Broth Q is distilled. Which conclusion is biologically and technologically sound?

20. In a typical biogas plant, the floating cover over the digester gradually rises during active microbial digestion. What most directly causes this movement?

21. A student observes visible growth on a nutritive-medium plate after inoculation with microorganisms that were individually too small to see clearly with the unaided eye. Which interpretation is most appropriate?

22. Equal water samples P and Q contain the same biodegradable organic matter. In P, bacteria remain metabolically active during a BOD measurement, whereas in Q bacterial oxidation of organic matter is strongly inhibited. Which result is most likely?

23. Saccharomyces cerevisiae has several human-welfare applications. Which combination correctly integrates its major roles?

24. A student concludes that microbes should be eliminated wherever possible because some microbes cause disease. The main biological error in this conclusion is that

25. Three viral biocontrol candidates show the following host ranges:
Virus P infects one major pest species and leaves most other insects unaffected.
Virus Q infects many pest and beneficial insect species.
Virus R infects birds, fish and several insects.
Which virus has the ecological profile most desirable for a baculovirus-based integrated pest-management programme?

26. Why is the immunosuppressive property of cyclosporin A particularly valuable in organ-transplant patients?

27. A treatment plant removes most settleable solids successfully, yet the receiving water would still face strong oxygen depletion if the effluent were discharged immediately. What is the most likely explanation?

28. Fresh milk is inoculated with a small quantity of curd and maintained under suitable conditions. The microorganisms primarily responsible for converting the milk into curd are

29. The primary objective of a sewage treatment plant is to

30. When Saccharomyces cerevisiae ferments suitable substrates during the production of alcoholic beverages, the principal product emphasised is

31. A plant root is intimately associated with fungal hyphae, and both partners benefit from the relationship. This association is called

32. Which row contains four fungal examples correctly matched with four different human-welfare roles?

33. The mould associated with Fleming's penicillin discovery was identified as

34. A farming programme progressively replaces part of its chemical fertiliser input with effective commercial biofertilisers. Which long-term objective is most consistent with this strategy?

35. A farmer claims, "Mycorrhizal fungi improve crop growth mainly because they fix atmospheric nitrogen in exactly the same way as Rhizobium." Which evaluation is most accurate?

36. Which option correctly identifies the rows in which the organism, product and microbial group are correctly matched?

37. Three industrial acids are accidentally relabelled. Laboratory records show:
Sample P came from Aspergillus niger.
Sample Q came from Acetobacter aceti.
Sample R came from Clostridium butylicum.
Which relabelling restores the correct identities?

38. A farming programme introduces Rhizobium, free-living nitrogen-fixing bacteria, mycorrhizal fungi and cyanobacteria into suitable crops and soils. What is the most reasonable long-term objective of this programme?

39. A crop receives two microbial treatments. Treatment P produces a fungal-root association that increases phosphorus uptake and improves drought tolerance. Treatment Q introduces a bacterium that fixes atmospheric nitrogen in legume root nodules. Which identification is correct?

40. Suppose fermentation of dosa batter proceeds poorly and microbial production is greatly reduced. The most immediate visible change expected in the batter is

41. Which comparison between toddy and industrial alcoholic beverages is most accurate?

42. An unknown fungal culture produces a substance that inhibits Staphylococcal growth, and the mould is identified as Penicillium notatum. Which organism-product-action chain is correct?

43. A scientist compares three nitrogen-fixing systems:
System P: bacteria inside legume root nodules.
System Q: free-living bacteria in soil.
System R: autotrophic microorganisms growing abundantly in a paddy field.
Which identification is correct?

44. Cattle dung is particularly suitable for use in a gobar-gas plant because

45. Which management decision would be most inconsistent with the ecological philosophy of biocontrol?

46. A fermented alcoholic product is subjected to an additional distillation step after microbial fermentation. Which conclusion is most appropriate?

47. During curd formation, multiplication of LAB is followed by acid production. The acid is important because it

48. A farmer observes that a biogas plant receives normal dung slurry but produces little gas even though the gas outlet and floating holder are functioning mechanically. Which explanation is most consistent with the biological process?

49. Saccharomyces cerevisiae is used in bread making, alcoholic beverage production and commercial ethanol manufacture. Which statement best explains why these are considered different applications of the same microorganism?

50. Equal amounts of the same starter curd are added to two milk samples. One is maintained at a suitable temperature for LAB growth, whereas the other is kept under conditions unfavourable for their multiplication. The second sample would most likely show slower curd formation because