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.

This ICSE Class 12 Biology practice quiz has 54 multiple-choice questions on Microbes in Human Welfare – Antibiotics, Fermentation, Waste Treatment, Biofertilizers, Biocontrol, and 54 of them come with an explanation. Try the 5 sample questions below (tap an option to check yourself), then play the full quiz 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.

More questions in this quiz

Answers and explanations are in the full quiz.

1. In the context of industrial fermentation for producing lactic acid, which organism is most commonly employed, and what is the key metabolic pathway utilized for its production?
2. Trickling filters are a type of secondary wastewater treatment process that utilizes aerobic microorganisms. What is the primary mechanism by which these microorganisms remove organic pollutants from the wastewater?
3. Mycorrhizae are symbiotic associations between fungi and plant roots that significantly enhance nutrient uptake for the plant. Which essential micronutrient's availability is most dramatically improved by the presence of endomycorrhizal fungi (arbuscular mycorrhizae)?
4. The biocontrol agent *Bacillus thuringiensis* (Bt) is widely used in agriculture. What is the mechanism by which Bt toxins are lethal to specific insect pests?
5. Consider the production of penicillin. The mold *Penicillium chrysogenum* is cultured under specific conditions to maximize antibiotic yield. Which of the following is a crucial factor that influences the production of penicillin by this organism?
6. In the context of antibiotics, the mechanism of action of chloramphenicol is to inhibit bacterial protein synthesis. At which specific site on the bacterial ribosome does chloramphenicol exert its inhibitory effect?
7. Activated sludge process is a common method for biological wastewater treatment. In this process, what is the primary role of the activated sludge itself?
8. Rhizobium bacteria are well-known for their symbiotic relationship with leguminous plants, contributing to nitrogen fixation. Which of the following is a key characteristic of the process of symbiotic nitrogen fixation involving Rhizobium?
9. Trichoderma species are increasingly used as biocontrol agents against plant pathogens. What is the primary mode of action through which Trichoderma controls fungal diseases?
10. In the industrial production of citric acid using *Aspergillus niger*, the fermentation process is typically carried out under submerged conditions. What is a critical factor in optimizing citric acid yield by this fungus?
11. Anaerobic digestion is a biological process used for treating organic waste and producing biogas. During the anaerobic digestion of wastewater sludge, which group of microorganisms is primarily responsible for the initial breakdown of complex organic polymers into simpler molecules?
12. Azotobacter species are free-living nitrogen-fixing bacteria found in soil. What is the primary mechanism by which they contribute to soil fertility as biofertilizers?
13. The biocontrol bacterium *Bacillus subtilis* is effective against various plant diseases. Which of the following is a key mechanism of action attributed to *Bacillus subtilis* in plant disease control?
14. Vancomycin is an antibiotic used to treat serious infections caused by Gram-positive bacteria, particularly resistant strains like MRSA. What is the specific molecular target of vancomycin in bacterial cell wall synthesis?
15. The production of wine involves the fermentation of grape sugars by yeast. What is the primary role of *Saccharomyces cerevisiae* in this process, and what are the main end products relevant to wine characteristics?
16. In the context of municipal wastewater treatment, the primary goal of the secondary treatment stage is to remove dissolved and colloidal organic matter. Which of the following technologies relies on the biological degradation of these pollutants by a mixed microbial community?
17. Cyanobacteria, such as *Nostoc* and *Anabaena*, are photosynthetic prokaryotes that can also fix atmospheric nitrogen. How do these organisms, when used as biofertilizers, enhance soil fertility?
18. The bacterium *Bacillus thuringiensis* (Bt) is a potent biopesticide. Its effectiveness relies on the production of specific insecticidal proteins. What are these proteins, and in what form are they initially produced and stored by the bacterium?
19. Aminoglycoside antibiotics, such as gentamicin, are bactericidal and inhibit protein synthesis. What is the primary mechanism of action for aminoglycosides?
20. In the context of anaerobic digestion of organic matter, the process is often divided into several stages. The stage where volatile fatty acids, ammonia, hydrogen, and carbon dioxide are produced from the breakdown of intermediate products is known as:
21. Plant growth-promoting rhizobacteria (PGPR) contribute to plant health and growth through various mechanisms. Which of the following is a direct benefit provided by PGPR that enhances nutrient availability to plants?
22. Beauveria bassiana is a naturally occurring fungus widely used as a biological control agent against a broad spectrum of insect pests. What is its primary mode of action against insects?
23. Tetracycline antibiotics exert their action by inhibiting bacterial protein synthesis. Specifically, they bind to the bacterial ribosome and interfere with the process of elongation. Which ribosomal subunit is the primary target for tetracyclines?
24. The production of baker's yeast (*Saccharomyces cerevisiae*) for commercial purposes is a large-scale fermentation process. Which of the following conditions are typically optimized to maximize yeast biomass yield?
25. Trickling filters are a type of biological wastewater treatment. The microorganisms involved in the purification process primarily exist as:
26. Azotobacter and *Rhizobium* are both nitrogen-fixing microbes used as biofertilizers. A key difference in their mode of action is that *Rhizobium* fixes nitrogen symbiotically within root nodules of legumes, whereas Azotobacter:
27. The entomopathogenic fungus *Metarhizium anisopliae* is a significant biological control agent. Its infectivity against insects is primarily due to its ability to:
28. Streptomycin, an aminoglycoside antibiotic, is effective against a range of bacteria. Its mechanism of action involves interfering with protein synthesis. Specifically, how does streptomycin achieve this inhibition?
29. The symbiotic relationship between *Rhizobium* bacteria and leguminous plants is a prime example of biofertilization. Which of the following is essential for the nitrogenase enzyme, responsible for nitrogen fixation, to function within the *Rhizobium*-legume symbiosis?
30. Which of the following is a primary role of microorganisms in secondary wastewater treatment processes like the activated sludge process?
31. The antibiotic group known as beta-lactams, which includes penicillin, primarily inhibits bacterial cell wall synthesis. What specific step in peptidoglycan synthesis do beta-lactams target?
32. In the industrial production of antibiotics like streptomycin, the fermentation process involves the cultivation of *Streptomyces griseus*. Which of the following is a critical factor for optimizing streptomycin yield?
33. The activated sludge process in wastewater treatment relies on a complex ecosystem of microorganisms. The flocs formed in activated sludge are primarily composed of:
34. Which of the following microorganisms is widely used as a biofertilizer, known for its ability to fix atmospheric nitrogen and form associations with the roots of many non-leguminous plants, particularly grasses and cereals?
35. The bacterium *Bacillus thuringiensis* (Bt) produces insecticidal toxins. These toxins are proteinaceous and are toxic to certain insect larvae. What is the primary target site of these toxins once ingested by a susceptible insect?
36. Doxycycline is a broad-spectrum tetracycline antibiotic. Its mechanism of action involves inhibiting bacterial protein synthesis by targeting which part of the ribosome?
37. The production of cheese, like cheddar, relies on microbial fermentation. Which two types of bacteria are primarily responsible for the initial fermentation of lactose and the subsequent development of flavor and texture in cheddar cheese?
38. In a conventional activated sludge system, the primary objective of the aeration tank is to provide aerobic conditions for the microbial community. What is the main process occurring here?
39. Mycorrhizal fungi are beneficial symbionts for plants. Arbuscular mycorrhizal fungi (AMF) are particularly widespread. What is the primary mechanism by which AMF enhance nutrient uptake for their host plants?
40. Gentamicin is an aminoglycoside antibiotic commonly used to treat bacterial infections. It targets bacterial protein synthesis. At what specific ribosomal site does gentamicin bind, and what is the functional consequence of this binding?
41. The production of lactic acid in industrial fermentation, often using *Lactobacillus* species, is a key process for various food and chemical industries. What is the primary biochemical pathway employed by these bacteria for converting glucose to lactic acid?
42. In the design of activated sludge wastewater treatment plants, the Mixed Liquor Suspended Solids (MLSS) concentration is a critical operational parameter. What does MLSS primarily represent?
43. Which of the following biofertilizers is a free-living nitrogen-fixing bacterium that promotes plant growth by producing plant growth-promoting substances (like IAA and gibberellins) and enhancing nutrient availability in addition to fixing atmospheric nitrogen?
44. The entomopathogenic bacterium *Bacillus thuringiensis* (Bt) is widely used as a biological pesticide. Its toxicity to specific insect pests is due to the production of crystal proteins. What is the characteristic feature of these crystal proteins (Cry proteins) that enables their insecticidal activity?
45. The antibiotic rifampicin (or rifampin) is used to treat infections caused by bacteria, including tuberculosis. It inhibits bacterial RNA synthesis. What is the specific molecular target of rifampicin?
46. In the process of making bread, yeast (*Saccharomyces cerevisiae*) plays a crucial role. What is the primary metabolic activity of yeast in dough that leads to the rising of bread?
47. Anaerobic digesters are used to treat organic waste. During the methanogenesis stage, which group of microorganisms is primarily responsible for converting acetate and hydrogen into methane and carbon dioxide?
48. Phosphate solubilizing bacteria (PSB) are important biofertilizers. Which mechanism do they primarily employ to make insoluble soil phosphates available to plants?
49. The biocontrol agent *Bacillus subtilis* is known for its ability to suppress plant pathogens. Which of the following is a key antagonistic mechanism employed by *B. subtilis*?

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