Sample 1Easy
Consider the following statements: I. Lactic acid bacteria convert milk into curd. II. The large holes in Swiss cheese are due to a large amount of CO2 produced by Propionibacterium sharmanii. III. Cyclosporin A, used as an immunosuppressive agent, is produced by Monascus purpureus. Which of the statements above are correct?
- A
I and II only
- B
I and III only
- C
II and III only
- D
I, II and III
Show the answer
The answer is A.Lactobacillus and other lactic acid bacteria convert milk to curd, and Propionibacterium sharmanii produces the CO2 that forms the large holes in Swiss cheese. Cyclosporin A is produced by the fungus Trichoderma polysporum; Monascus purpureus produces statins.
- B.
Statement III is wrong: cyclosporin A comes from Trichoderma polysporum, and statement II is correct.
- C.
Statement III is wrong, and statement I is correct.
- D.
Statement III is wrong: Monascus purpureus produces statins, not cyclosporin A.
NCERT: Class 12 Biology, Chapter 8 (Microbes in Human Welfare), Microbes in Household Products and Microbes in Industrial Products
Sample 2Medium
A flow chart of sewage treatment shows: stage 1, filtration and sedimentation remove floating debris and grit; the supernatant goes to stage 2, aeration tanks with constant agitation and air pumped in, where aerobic microbes grow into flocs; the flocs then settle in a tank as X; a small part of X is pumped back into the aeration tank, and the rest goes to large tanks Y where anaerobic bacteria digest it. What are X and Y?
- A
X is primary sludge; Y are aeration tanks
- B
X is activated sludge; Y are anaerobic sludge digesters that produce biogas
- C
X is activated sludge; Y are aerobic digesters that release oxygen
- D
X is the primary effluent; Y are tanks in which the BOD rises
Show the answer
The answer is B.In secondary treatment the flocs sediment as activated sludge; a small part is returned to the aeration tank as inoculum. The rest goes to anaerobic sludge digesters, where bacteria produce methane, hydrogen sulphide and CO2, which form biogas.
- A.
Primary sludge forms in stage 1; the floc sediment after aeration is activated sludge.
- C.
The digesters are anaerobic and release methane, hydrogen sulphide and CO2.
- D.
The primary effluent is the stage 1 supernatant, and treatment lowers BOD.
NCERT: Class 12 Biology, Chapter 8, 8.3
Sample 3NEET level
Assertion (A): The BOD of sewage is significantly reduced during secondary treatment. Reason (R): The aerobic microbes in the flocs consume the major part of the organic matter in the effluent.
- A
Both A and R are true and R is the correct explanation of A
- B
Both A and R are true but R is not the correct explanation of A
- C
A is true but R is false
- D
A is false but R is true
Show the answer
The answer is A.In secondary (biological) treatment the primary effluent is agitated in aeration tanks, where aerobic bacteria and fungal filaments form flocs. These microbes consume most of the organic matter, which is what significantly reduces the BOD, so R explains A.
- B.
R is the very cause of the fall in BOD: it measures organic matter that microbes would oxidise.
- C.
R is true: floc-forming aerobic microbes consume most of the organic matter.
- D.
A is true: secondary treatment lowers BOD significantly.
NCERT: Class 12 Biology, Chapter 8 (Microbes in Human Welfare), Microbes in sewage treatment