Question Bank — Microbes in Human Welfare

NCERT Class 12 Biology · Chapter 8 · CBSE Board Pattern

Class 12 Biology Chapter 8 Question Bank CBSE Board Pattern

Section A — MCQs (1 mark each)

  1. Which bacterium is responsible for the large holes in Swiss cheese?
    (a) Lactobacillus (b) Propionibacterium shermanii (c) Streptococcus (d) Acetobacter aceti

  2. The puffed-up appearance of dough used for making dosa and idli is due to:
    (a) Production of lactic acid (b) Production of CO₂ (c) Production of ethanol (d) Production of methane

  3. Cyclosporin A, used as an immunosuppressive agent, is produced by:
    (a) Trichoderma polysporum (b) Monascus purpureus (c) Penicillium notatum (d) Aspergillus niger

  4. Which of the following is a methanogen?
    (a) Methanobacterium (b) Bacillus thuringiensis (c) Rhizobium (d) Saccharomyces cerevisiae

  5. In secondary sewage treatment, the BOD of the effluent:
    (a) Increases (b) Decreases (c) Remains unchanged (d) Becomes zero

  6. Assertion (A): LAB improve the nutritional quality of curd by increasing vitamin B₁₂.
    Reason (R): LAB multiply in milk at suitable temperatures and convert it into curd.
    (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.

  7. Assertion (A): Baculoviruses are considered excellent candidates for species-specific insecticidal applications.
    Reason (R): They have no negative impact on plants, mammals, birds, fish or non-target insects.
    (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.

  8. The fungus used for commercial production of citric acid is:
    (a) Aspergillus niger (b) Trichoderma polysporum (c) Penicillium notatum (d) Glomus

  9. Which of the following is not used as a biofertiliser?
    (a) Rhizobium (b) Azotobacter (c) Anabaena (d) Clostridium butylicum

  10. Streptokinase, used as a clot buster, is produced by:
    (a) Streptococcus (b) Staphylococcus (c) Lactobacillus (d) Propionibacterium

Section B — Very Short Answer (2 marks each)

  1. Name the bacterium used in the production of Swiss cheese and state the reason for the large holes in it.

  2. What is the role of LAB in the human stomach?

  3. Name any two enzymes produced by microbes and mention one industrial use of each.

  4. Differentiate between primary and secondary sewage treatment.

  5. What are methanogens? Give one example and one location where they are commonly found.

  6. Name two free-living nitrogen-fixing bacteria that enrich soil fertility.

Section C — Short Answer (3 marks each)

  1. Explain the role of microbes in the household production of curd and fermented foods like idli and dosa.

  2. Describe how antibiotics are discovered and give two examples of antibiotics along with the microbes that produce them.

  3. What is BOD? Explain its significance in sewage treatment.

  4. How do mycorrhizal fungi act as biofertilisers? Give any two advantages to the host plant.

  5. Explain the use of Bacillus thuringiensis and Trichoderma as biocontrol agents.

Section D — Long Answer (5 marks each)

  1. Describe the process of sewage treatment in detail with emphasis on the role of microbes. (No diagram required)

  2. Explain the production of biogas with the help of a labelled diagram of a biogas plant. Describe the role of methanogens in the process.

  3. Discuss the role of microbes as biocontrol agents. How do they help in reducing the use of chemical pesticides? Give suitable examples.

Section E — Case/Source-Based (4 marks each)

Case 1

A student observed that when a small amount of curd is added to warm milk and kept at suitable temperature, the milk turns into curd within a few hours. The curd also has higher vitamin B₁₂ content. The same student noticed that the dough for idli becomes puffed up due to gas production.

(i) Name the group of bacteria involved in curd formation.
(ii) How does addition of curd act as inoculum?
(iii) Name the gas produced in idli dough and the organism responsible.
(iv) State one beneficial role of these bacteria in the human stomach.

Case 2

In a village, a biogas plant was installed using cattle dung. The plant has a concrete tank where slurry is fed and a floating cover that rises as gas is produced. The gas is supplied to nearby houses for cooking, and the spent slurry is used as fertiliser.

(i) Name the group of bacteria that produce biogas.
(ii) Which gas is produced in maximum amount and what is its use?
(iii) Why is cattle dung considered a good substrate for biogas production?
(iv) Mention one advantage of using biogas plants in rural areas.

▶ Answer Key Attempt all questions first,
then tap to reveal

Section A

  1. (b) 2. (b) 3. (a) 4. (a) 5. (b) 6. (b) 7. (a) 8. (a) 9. (d) 10. (a)

Section B

  1. Propionibacterium shermanii; large amount of CO₂ produced (1+1)
  2. Check growth of disease-causing microbes (2)
  3. Lipases – detergent formulations; Pectinases – clarification of fruit juices (1+1)
  4. Primary: physical removal of particles; Secondary: biological treatment using microbes (1+1)
  5. Bacteria producing methane; Methanobacterium; anaerobic sludge/ruminant stomach (1+1)
  6. Azospirillum, Azotobacter (1+1)

Section C

  1. LAB convert milk to curd, increase vitamin B₁₂; bacteria ferment dough producing CO₂ (definition 1, explanation 1, example 1)
  2. Chance discovery of Penicillin by Fleming; Penicillin – Penicillium notatum; any other antibiotic (1+1+1)
  3. BOD = oxygen consumed by bacteria to oxidise organic matter; high BOD indicates high pollution (definition 1, significance 2)
  4. Glomus forms mycorrhiza, absorbs phosphorus; resistance to pathogens, tolerance to salinity/drought (1+1+1)
  5. Bt toxin kills caterpillars; Trichoderma controls plant pathogens (explanation with examples 3)

Section D

  1. Primary treatment – filtration & sedimentation; Secondary – aeration tanks, flocs, reduction of BOD, activated sludge, anaerobic digesters (points with sequence 5)
  2. Methanogens produce methane from cellulosic waste; labelled diagram of biogas plant showing inlet, digester, gas outlet, slurry outlet (role 2, diagram description 3)
  3. Use of natural predators/parasites instead of chemicals; Ladybird, Bt, Trichoderma, Baculoviruses; reduces environmental pollution (examples + explanation 5)

Section E

Case 1

(i) Lactic acid bacteria (LAB) (1)
(ii) Contains millions of LAB that multiply (1)
(iii) CO₂; bacteria (1)
(iv) Check disease-causing microbes (1)

Case 2

(i) Methanogens (1)
(ii) Methane; cooking/lighting (1)
(iii) Rich in methanogenic bacteria (1)
(iv) Provides clean fuel and manure; reduces pollution (1)

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All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.