Microbes in Human Welfare – Antibiotics, Fermentation, Waste Treatment, Biofertilizers, Biocontrol Quiz - ICSE Class 12 Biology

Free practice quiz: Microbes in Human Welfare – Antibiotics, Fermentation, Waste Treatment, Biofertilizers, Biocontrol (ICSE Class 12 Biology). 54 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. Which of the following antibiotics is produced from a species of *Streptomyces* and is effective against a broad spectrum of bacteria, including Gram-positive and Gram-negative types, by inhibiting protein synthesis through binding to the 30S ribosomal subunit?

   1. Penicillin
   2. Tetracycline
   3. Erythromycin
   4. Streptomycin
   Show answer

   Answer: B. Tetracycline

   Tetracyclines are a class of antibiotics produced by *Streptomyces* species. They function by inhibiting bacterial protein synthesis by binding to the 30S ribosomal subunit. Penicillin targets cell wall synthesis, Erythromycin targets the 50S ribosomal subunit, and Streptomycin also targets the 30S subunit but has a more specific mechanism and spectrum compared to the broad-spectrum nature often associated with tetracyclines.

2. Erythromycin, a macrolide antibiotic, inhibits bacterial protein synthesis by binding to a specific site on the ribosome. Which ribosomal subunit does erythromycin primarily interact with, and what is the consequence of this binding?

   1. 30S subunit; prevents the binding of aminoacyl-tRNAs.
   2. 50S subunit; blocks the translocation of the ribosome along mRNA.
   3. 30S subunit; interferes with the initiation complex formation.
   4. 50S subunit; inhibits the peptidyl transferase activity.
   Show answer

   Answer: B. 50S subunit; blocks the translocation of the ribosome along mRNA.

   Erythromycin is a macrolide antibiotic that binds to the 50S ribosomal subunit of bacteria. This binding interferes with the translocation step of protein synthesis, where the ribosome moves along the mRNA. By blocking translocation, erythromycin prevents the movement of the peptidyl-tRNA from the A-site to the P-site, thereby halting polypeptide chain elongation.

3. Which of the following microorganisms is commonly used in the production of yogurt and plays a crucial role in its characteristic texture and flavor development through lactic acid fermentation?

   1. *Aspergillus oryzae*
   2. *Saccharomyces cerevisiae*
   3. *Streptococcus thermophilus* and *Lactobacillus bulgaricus*
   4. *Penicillium roqueforti*
   Show answer

   Answer: C. *Streptococcus thermophilus* and *Lactobacillus bulgaricus*

   Yogurt production relies on the symbiotic fermentation carried out by *Streptococcus thermophilus* and *Lactobacillus bulgaricus*. These bacteria ferment lactose in milk into lactic acid, which lowers the pH and causes the milk proteins (casein) to coagulate, creating the characteristic texture of yogurt. They also contribute to flavor development through the production of various byproducts.

4. In the context of industrial fermentation for producing ethanol from biomass, which organism is most commonly utilized, and what is the primary metabolic pathway it employs under anaerobic conditions?

   1. *Aspergillus niger* (Citric acid cycle)
   2. *Lactobacillus* species (Lactic acid fermentation)
   3. *Saccharomyces cerevisiae* (Alcoholic fermentation)
   4. *Bacillus subtilis* (Propionic acid fermentation)
   Show answer

   Answer: C. *Saccharomyces cerevisiae* (Alcoholic fermentation)

   Baker's yeast, *Saccharomyces cerevisiae*, is the primary organism used for industrial ethanol production from sugars derived from biomass. Under anaerobic conditions, it carries out alcoholic fermentation, converting pyruvate (derived from glucose glycolysis) into ethanol and carbon dioxide. This is a highly efficient process for generating ATP for the yeast in the absence of oxygen.

5. The fungus *Trichoderma harzianum* is recognized as an important biological control agent for plant diseases. Which of the following is a key mechanism by which *T. harzianum* antagonizes fungal pathogens?

   1. Production of systemic acquired resistance (SAR) inducers.
   2. Direct parasitism (mycoparasitism) of the pathogen.
   3. Secretion of volatile organic compounds that disrupt pathogen cell membranes.
   4. Production of phytotoxins that are lethal to pathogens.
   Show answer

   Answer: B. Direct parasitism (mycoparasitism) of the pathogen.

   *Trichoderma* species are aggressive mycoparasites. They can directly attack pathogenic fungi by attaching to them, secreting cell-wall degrading enzymes (like chitinases and glucanases) to penetrate the pathogen's hyphae, and then absorbing nutrients from the pathogen. Other mechanisms include competition for nutrients and space, and production of antibiotics.

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