Microbes in Human Welfare Mock Test – Class 12 Biology

1. Use the activated-sludge arrangement described below.
After microbial flocs settle, the activated sludge is divided into two branches. Branch P carries a small fraction back to the aeration tank, while Branch Q carries the major fraction to another treatment chamber.
Which combination correctly identifies the purposes of P and Q?

2. Assertion: A decrease in visible suspended solids after primary treatment does not by itself prove that sewage has a low BOD.
Reason: Primary treatment mainly removes materials physically, whereas substantial removal of biodegradable organic matter occurs during secondary microbial treatment.

3. An activated-sludge treatment plant recycles a small fraction of settled sludge but accidentally sends the rest directly into a river instead of to an anaerobic digester. Which useful downstream process is lost?

4. Which option correctly distinguishes traditional household-scale microbial fermentation from industrial microbial production?

5. A chemical produced by one microorganism acts against a disease-causing microorganism. Which description most accurately fits the biological concept of an antibiotic?

6. After aeration and substantial BOD reduction, sewage is accidentally discharged before microbial flocs are allowed to settle. Which treatment step has been omitted?

7. A researcher isolates four useful microorganisms:
P is a yeast used in bread and alcoholic fermentation.
Q is a fungus associated with citric acid production.
R is a bacterium used against caterpillars.
S is a fungus that forms a nutrient-exchange association with plant roots.
Which identification is correct?

8. Three biological-control agents are tested against one target insect pest and several non-target organisms.

If the aim is effective pest control in an ecologically sensitive area while conserving non-target organisms, which agent shows the pattern most characteristic of a suitably specific baculovirus?

9. A batch of milk receives a fresh curd starter containing abundant LAB. The bacteria multiply normally, but acid production is experimentally prevented. Which outcome is most likely?

10. Study the following microbial-product applications.

Which statement is correct?

11. 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?

12. Consider the following events associated with penicillin:
I. A contaminating mould is observed on a Staphylococci culture plate.
II. Bacterial growth is absent around the mould.
III. The mould is identified with Penicillium notatum and the inhibitory substance is associated with penicillin.
IV. Chain and Florey establish the full therapeutic potential of penicillin.
Which sequence best reflects the logical progression from observation to medical development?

13. Which comparison best distinguishes the origin of visible structures in microbial culture and Swiss cheese?

14. The material flow through a simplified biogas plant is represented as follows:
Dung and water -> P -> microbial gas accumulation -> Q
Residual digested material -> R
Which identification of P, Q and R is correct?

15. Two anaerobic microbial systems are described:
System P involves methanogens acting on cellulosic material.
System Q involves anaerobic digestion of activated sludge.
Which gas pattern correctly distinguishes them?

16. A farmer sprays a Bt preparation correctly, but the target caterpillars stop feeding immediately before treatment and do not ingest the sprayed material. What is the most likely result?

17. The usefulness of biogas as a fuel is most directly related to the predominance of

18. A plant associated with mycorrhizal fungi grows better than a non-mycorrhizal plant even though both receive similar nitrogen supply. Which combination of mycorrhizal effects can explain this advantage without invoking nitrogen fixation?

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

20. Which outcome would most strongly indicate that a biological-control programme has become ecologically less selective?

21. Bacillus thuringiensis is ingested normally by susceptible caterpillars, but toxin action in the larval gut is experimentally blocked. What outcome is most likely?

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

23. An organic farmer aims to maintain a biologically diverse field ecosystem rather than eliminate every insect that feeds on crops. Why can this strategy support long-term pest management?

24. A patient with myocardial infarction is accidentally given cyclosporin A instead of streptokinase. What is the key therapeutic mismatch?

25. A biological-control agent is identified as Nucleopolyhedrovirus. Which chain correctly connects its biological identity with its agricultural use?

26. A plate containing a suitable nutritive medium develops visible colonies after inoculation with bacteria. Which change would most directly prevent the visible-colony outcome without proving that the original bacterial cells were absent?

27. A food technologist, a physician and an agricultural scientist each use a different microbial product:
I. The food technologist needs an organism for bread fermentation.
II. The physician needs a molecule that suppresses immune responses after organ transplantation.
III. The agricultural scientist needs a fungus that improves phosphorus acquisition by plant roots.
Which combination correctly satisfies I, II and III respectively?

28. Apart from their role in curd formation, lactic acid bacteria present in fermented milk can also benefit humans by

29. A fermented food shows extensive gas formation but little increase in volume because the gas escapes immediately instead of being retained within the food matrix. Which biological factor most directly explains the reduced physical expansion?

30. Two solid materials are collected from different stages of sewage treatment.
Material P settles during primary sedimentation after filtration.
Material Q consists mainly of microbial flocs that settle after secondary aeration.
Which identification is correct?

31. A list of traditional foods and beverages is being screened for examples of microbial fermentation. Which entry is correctly included in this group?

32. Two fermented foods become visibly expanded:
Product P is dosa batter fermented mainly by bacteria.
Product Q is bread dough fermented by Saccharomyces cerevisiae.
Which statement best explains why similar physical expansion does not imply identical microbiology?

33. A biological-control programme uses ladybird beetles in one field and Bacillus thuringiensis in another. Which comparison is correct?

34. Bacillus thuringiensis and a baculovirus are both effective against insect pests, but their most important distinguishing feature is that

35. Microbial growth is detected near a thermal vent where the temperature approaches . What is the most appropriate conclusion from this observation?

36. Which experimental change would most seriously weaken the inference that Penicillium produced a diffusible substance responsible for Staphylococcal inhibition?

37. Which organism is a standard example of a methanogen?

38. A functioning gobar-gas plant contains fresh dung slurry and has an unobstructed gas outlet, but microbial activity inside the digester becomes severely suppressed. Which change would most directly be expected?

39. The major nutrient-related contribution of nitrogen-fixing cyanobacteria to agricultural soil is that they

40. Which organism-benefit relationship requires a symbiotic association with a plant root rather than free-living growth in soil?

41. Which sequence best represents the biological logic linking untreated sewage with water-borne disease?

42. A leguminous crop fails to develop effective root nodules, but the surrounding soil still contains active Azotobacter. Which conclusion is most reasonable?

43. The cholesterol-lowering effect of statins is explained by their ability to

44. Primary effluent enters an aeration tank containing natural heterotrophic microbes. If the sewage contains almost no biodegradable organic matter, which prediction is most reasonable?

45. Blue-green algae improve agricultural soil not only through nitrogen fixation but also because

46. Primary treatment and secondary treatment differ fundamentally in the major process responsible for purification. Which comparison is correct?

47. Which distinction between primary effluent and final treated effluent is correct?

48. Biological oxygen demand, or BOD, is best defined as

49. Which statement correctly describes the relationship between conventional Bt spray and Bt cotton?

50. A company plans to produce a valuable microbial product on a scale far greater than that used in ordinary household fermentation. Which change most directly represents the transition to industrial microbial production?