NEET 2025 MCQ with Answer Explanation : Microbes in Human Walefare.

31. The role of bacteria in the nitrogen cycle is:
    A. Production of oxygen
    B. Fixation of nitrogen
    C. Decomposition of dead organic matter
    D. Photosynthesis

Answer: B. Fixation of nitrogen

Explanation:
Nitrogen-fixing bacteria, such as Rhizobium and Azotobacter, convert atmospheric nitrogen into forms usable by plants, an essential step in the nitrogen cycle.

32. Which of the following microorganisms is used in the production of ethanol from starch?
    A. Lactobacillus
    B. Streptococcus
    C. Saccharomyces cerevisiae
    D. Clostridium

Answer: C. Saccharomyces cerevisiae

Explanation:
Saccharomyces cerevisiae (yeast) is employed in fermenting starch-derived sugars to produce ethanol, particularly in biofuel and beverage industries.

33. Which of the following biofertilizers is commonly used for improving soil fertility in legume crops?
    A. Rhizobium
    B. Penicillium
    C. Lactobacillus
    D. Aspergillus

Answer: A. Rhizobium

Explanation:
Rhizobium forms a symbiotic relationship with legumes, fixing atmospheric nitrogen and converting it into a form that plants can absorb.

34. The bacterium responsible for the production of the vitamin B12 in fermentation processes is:
    A. Pseudomonas
    B. Streptococcus
    C. Propionibacterium shermanii
    D. Escherichia coli

Answer: C. Propionibacterium shermanii

Explanation:
Propionibacterium shermanii is used in the fermentation process for the industrial production of vitamin B12, a crucial vitamin for human health.

35. Which microbe is used for the production of citric acid on an industrial scale?
    A. Rhizobium
    B. Aspergillus niger
    C. Clostridium
    D. Azotobacter

Answer: B. Aspergillus niger

Explanation:
Aspergillus niger is extensively used for large-scale industrial production of citric acid, which is used in food, beverages, and as an industrial additive.

36. In which of the following processes are microbes not involved?
    A. Alcohol production
    B. Antibiotic production
    C. Photosynthesis in plants
    D. Biogas production

Answer: C. Photosynthesis in plants

Explanation:
Photosynthesis in plants is carried out by plant chloroplasts (not microbes), whereas microbes are involved in processes like alcohol production, antibiotic production, and biogas formation.

37. Which bacteria is involved in the formation of curd?
    A. Lactobacillus bulgaricus
    B. Clostridium butylicum
    C. Pseudomonas syringae
    D. Streptomyces griseus

Answer: A. Lactobacillus bulgaricus

Explanation:
Lactobacillus bulgaricus is commonly used in the fermentation of milk to form curd, by converting lactose into lactic acid.

38. The use of which bacterium in agriculture results in nitrogen fixation in non-leguminous plants?
    A. Rhizobium
    B. Azospirillum
    C. Aspergillus
    D. Clostridium

Answer: B. Azospirillum

Explanation:
Azospirillum is a free-living nitrogen-fixing bacterium that enhances nitrogen availability in non-leguminous plants, often used in biofertilizers.

39. Which microorganism is used in the production of single-cell protein (SCP)?
    A. Streptococcus lactis
    B. Methylophilus methylotrophus
    C. Penicillium notatum
    D. Azotobacter

Answer: B. Methylophilus methylotrophus

Explanation:
Methylophilus methylotrophus is used to produce single-cell proteins (SCP) due to its rapid growth rate and high protein content, which can serve as a protein-rich food supplement.

40. Which organism is used to produce the antibiotic tetracycline?
    A. Streptomyces aureofaciens
    B. Penicillium notatum
    C. Saccharomyces cerevisiae
    D. Lactobacillus acidophilus

Answer: A. Streptomyces aureofaciens

Explanation:
Tetracycline is produced by Streptomyces aureofaciens, a bacterium, and is widely used as an antibiotic to treat bacterial infections.