Microbes in Human Welfare – Daily Practice Problem (DPP)

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🎯 NEET 2026 Daily Practice Problem (DPP)

Class 12 | Unit 3: Biology in Human Welfare | Topic: Microbes in Human Welfare

Q1. The large holes in ‘Swiss Cheese’ are due to the production of a large amount of CO2 by:

  1. Propionibacterium shermanii
  2. Saccharomyces cerevisiae
  3. Lactobacillus
  4. Penicillium roqueforti
✅ View Answer & Explanation

Correct Answer: (1) Propionibacterium shermanii
Explanation: This bacterium consumes the lactic acid produced during cheese ripening and releases carbon dioxide gas, which forms the characteristic large holes.

Q2. Which bioactive molecule is used as an immunosuppressive agent in organ-transplant patients?

  1. Streptokinase
  2. Statins
  3. Cyclosporin A
  4. Lipase
✅ View Answer & Explanation

Correct Answer: (3) Cyclosporin A
Explanation: Cyclosporin A is produced by the fungus Trichoderma polysporum and suppresses the immune system to prevent organ rejection.

Q3. Statins, used as blood cholesterol-lowering agents, act by:

  1. Competitively inhibiting the enzyme responsible for cholesterol synthesis
  2. Breaking down cholesterol in the blood
  3. Preventing absorption of cholesterol from the intestine
  4. Enhancing the excretion of cholesterol
✅ View Answer & Explanation

Correct Answer: (1) Competitively inhibiting the enzyme responsible for cholesterol synthesis
Explanation: Produced by the yeast Monascus purpureus, statins resemble mevalonate and inhibit HMG-CoA reductase.

Q4. The ‘Clot Buster’ enzyme streptokinase is produced by:

  1. Staphylococcus
  2. Streptococcus
  3. Aspergillus
  4. Trichoderma
✅ View Answer & Explanation

Correct Answer: (2) Streptococcus
Explanation: Genetically modified Streptococcus bacteria produce Streptokinase, which removes clots from the blood vessels of patients who have undergone myocardial infarction.

Q5. Citric acid is industrially produced by:

  1. Clostridium butylicum
  2. Aspergillus niger
  3. Lactobacillus
  4. Acetobacter aceti
✅ View Answer & Explanation

Correct Answer: (2) Aspergillus niger
Explanation: Aspergillus niger (a fungus) produces Citric acid. Clostridium produces Butyric acid, and Acetobacter produces Acetic acid.

Q6. During sewage treatment, the primary treatment involves:

  1. Biological breakdown of organic matter
  2. Physical removal of particles through filtration and sedimentation
  3. Chemical treatment with chlorine
  4. Digestion by anaerobic bacteria
✅ View Answer & Explanation

Correct Answer: (2) Physical removal of particles through filtration and sedimentation
Explanation: Primary treatment is a physical process involving the removal of large and small particles (floating debris and grit).

[Image of sewage treatment plant diagram]

Q7. BOD refers to:

  1. Biochemical Oxygen Demand
  2. Biological Ozone Depletion
  3. Bacterial Oxygen Demand
  4. Biosynthetic Oxygen Demand
✅ View Answer & Explanation

Correct Answer: (1) Biochemical Oxygen Demand
Explanation: BOD is the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.

Q8. Methanogens are found in:

  1. Aerobic sludge
  2. Activated sludge
  3. Anaerobic sludge digesters
  4. Aeration tanks
✅ View Answer & Explanation

Correct Answer: (3) Anaerobic sludge digesters
Explanation: Methanogens are anaerobic bacteria (e.g., Methanobacterium) that grow in anaerobic sludge digesters and produce biogas.

Q9. The major component of Biogas is:

  1. Carbon dioxide
  2. Hydrogen sulfide
  3. Methane
  4. Hydrogen
✅ View Answer & Explanation

Correct Answer: (3) Methane
Explanation: Biogas typically contains 50-70% Methane ($CH_4$), along with $CO_2$ and trace amounts of $H_2S$ and $H_2$.

Q10. A biocontrol agent used to control butterfly caterpillars is:

  1. Trichoderma
  2. Bacillus thuringiensis (Bt)
  3. Nosema
  4. Nucleopolyhedrovirus
✅ View Answer & Explanation

Correct Answer: (2) Bacillus thuringiensis (Bt)
Explanation: Spores of Bt are mixed with water and sprayed on plants like brassicas. When eaten by the caterpillar, the toxin is released in the gut, killing the larvae.

Q11. Baculoviruses belong to the genus:

  1. Retrovirus
  2. Nucleopolyhedrovirus
  3. Adenovirus
  4. Rhinovirus
✅ View Answer & Explanation

Correct Answer: (2) Nucleopolyhedrovirus
Explanation: These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications.

Q12. The symbiotic association between fungi and roots of higher plants is called:

  1. Lichen
  2. Mycorrhiza
  3. Coralloid root
  4. Root nodule
✅ View Answer & Explanation

Correct Answer: (2) Mycorrhiza
Explanation: Fungi (e.g., genus Glomus) form mycorrhiza, helping the plant absorb phosphorus from the soil.

Q13. Which of the following is a free-living nitrogen-fixing bacterium?

  1. Rhizobium
  2. Azospirillum
  3. Glomus
  4. Frankia
✅ View Answer & Explanation

Correct Answer: (2) Azospirillum
Explanation: Azospirillum and Azotobacter are free-living nitrogen fixers. Rhizobium is symbiotic.

Q14. The secondary sewage treatment is mainly a:

  1. Mechanical process
  2. Biological process
  3. Chemical process
  4. Physical process
✅ View Answer & Explanation

Correct Answer: (2) Biological process
Explanation: It involves the action of heterotrophic microbes (flocs) to consume organic matter.

Q15. Ladybird and Dragonflies are used to get rid of:

  1. Aphids and Mosquitoes
  2. Mosquitoes and Fruit flies
  3. Butterflies and Moths
  4. Aphids and Caterpillars
✅ View Answer & Explanation

Correct Answer: (1) Aphids and Mosquitoes
Explanation: Ladybird (beetle) controls Aphids, and Dragonflies control Mosquitoes.

Q16. During which stage of sewage treatment are ‘flocs’ formed?

  1. Primary treatment
  2. Secondary treatment
  3. Tertiary treatment
  4. Anaerobic digestion
✅ View Answer & Explanation

Correct Answer: (2) Secondary treatment
Explanation: Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures in the aeration tank.

Q17. Which of the following is NOT a biofertilizer?

  1. Rhizobium
  2. Mycorrhiza
  3. Agrobacterium
  4. Nostoc
✅ View Answer & Explanation

Correct Answer: (3) Agrobacterium
Explanation: Agrobacterium tumefaciens is a pathogen (natural genetic engineer) used as a vector, not a biofertilizer. Nostoc is a nitrogen-fixing cyanobacterium.

Q18. The vitamin content increased by LAB (Lactic Acid Bacteria) in curd is:

  1. Vitamin C
  2. Vitamin B12
  3. Vitamin A
  4. Vitamin D
✅ View Answer & Explanation

Correct Answer: (2) Vitamin B12
Explanation: LAB improves the nutritional quality of curd by increasing Vitamin B12 content.

Q19. Activated sludge is:

  1. The sediment from primary settling tank
  2. The sediment from secondary settling tank
  3. The supernatant from primary settling tank
  4. The floating debris
✅ View Answer & Explanation

Correct Answer: (2) The sediment from secondary settling tank
Explanation: The bacterial flocs that settle down after secondary treatment are called activated sludge.

Q20. Trichoderma species are potentially useful as:

  1. Antibiotics
  2. Biofertilizers
  3. Biocontrol agents
  4. Source of food
✅ View Answer & Explanation

Correct Answer: (3) Biocontrol agents
Explanation: Trichoderma species are free-living fungi common in root ecosystems that are effective biocontrol agents against several plant pathogens.

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