ROUTERA


Chapter 10 Microbes in human welfare

Class 12th Biology Chapter MCQs


1. Which of the following is an example of a mutualistic relationship between microbes and humans?

  • A) Pathogenic bacteria causing disease
  • B) Lactic acid bacteria in the human intestine
  • C) Yeast causing infections
  • D) Protozoa causing malaria

Answer: B
Explanation: Lactic acid bacteria in the human intestine help in digestion and produce essential vitamins. This is an example of a mutualistic relationship.


2. Which microbe is used for the production of insulin?

  • A) Escherichia coli
  • B) Bacillus thuringiensis
  • C) Saccharomyces cerevisiae
  • D) Lactobacillus acidophilus

Answer: A
Explanation: Escherichia coli is genetically modified to produce insulin used in treating diabetes.


3. Which of the following microbes is used in the fermentation of milk to make curd?

  • A) Aspergillus niger
  • B) Streptococcus thermophilus
  • C) Saccharomyces cerevisiae
  • D) Bacillus subtilis

Answer: B
Explanation: Streptococcus thermophilus is used in the fermentation of milk to make curd by producing lactic acid.


4. Which of the following is used in the production of alcohol during fermentation?

  • A) Lactobacillus
  • B) Saccharomyces cerevisiae
  • C) Aspergillus
  • D) Penicillium

Answer: B
Explanation: Saccharomyces cerevisiae (baker's yeast) is used in the fermentation of sugars to produce alcohol.


5. Which of the following microorganisms is used in the production of antibiotics?

  • A) Saccharomyces cerevisiae
  • B) Penicillium notatum
  • C) Rhizobium
  • D) Escherichia coli

Answer: B
Explanation: Penicillium notatum is the source of the antibiotic penicillin.


6. Which of the following microorganisms is involved in nitrogen fixation in soil?

  • A) Rhizobium
  • B) Saccharomyces
  • C) Aspergillus
  • D) Streptococcus

Answer: A
Explanation: Rhizobium bacteria fix atmospheric nitrogen into a form that plants can use, enriching the soil with nitrogen.


7. Which microbe is used in the production of vinegar?

  • A) Saccharomyces cerevisiae
  • B) Acetobacter
  • C) Bacillus thuringiensis
  • D) Aspergillus niger

Answer: B
Explanation: Acetobacter is used in the production of vinegar through the fermentation of ethanol.


8. Which of the following microbes is used for the bioremediation of oil spills?

  • A) Pseudomonas
  • B) Saccharomyces cerevisiae
  • C) Bacillus subtilis
  • D) Rhizobium

Answer: A
Explanation: Pseudomonas species are used for the bioremediation of oil spills by degrading hydrocarbons in the oil.


9. Which of the following microorganisms is responsible for the production of natural gas (biogas)?

  • A) Methanogens
  • B) Rhizobium
  • C) E. coli
  • D) Aspergillus

Answer: A
Explanation: Methanogens are archaea that produce methane (biogas) by breaking down organic matter in anaerobic conditions.


10. Which of the following microbes is used in the production of bread?

  • A) Saccharomyces cerevisiae
  • B) Rhizobium
  • C) Streptococcus thermophilus
  • D) Escherichia coli

Answer: A
Explanation: Saccharomyces cerevisiae (yeast) is used in the production of bread by fermenting sugars to produce carbon dioxide, which causes the dough to rise.


11. Which of the following processes is carried out by the microbe, Rhizobium?

  • A) Nitrogen fixation
  • B) Fermentation
  • C) Nitrogen denitrification
  • D) Decomposition

Answer: A
Explanation: Rhizobium is responsible for nitrogen fixation in legumes by converting atmospheric nitrogen into ammonia.


12. Which of the following is a biotechnological application of yeast?

  • A) Production of yogurt
  • B) Production of ethanol
  • C) Production of antibiotics
  • D) Production of citric acid

Answer: B
Explanation: Yeast (Saccharomyces cerevisiae) is used in the production of ethanol through fermentation.


13. Which of the following microorganisms is used to produce the enzyme rennin used in cheese-making?

  • A) Saccharomyces cerevisiae
  • B) Rhizobium
  • C) Mucor
  • D) Aspergillus

Answer: C
Explanation: Mucor is used in the production of rennin, an enzyme used in cheese-making.


14. What is the function of nitrogen-fixing bacteria in the soil?

  • A) To decompose organic matter
  • B) To convert nitrogen into a form usable by plants
  • C) To break down pesticides
  • D) To increase the acidity of the soil

Answer: B
Explanation: Nitrogen-fixing bacteria, like Rhizobium, convert atmospheric nitrogen into forms like ammonia that plants can absorb and use.


15. Which microbe is involved in the production of antibiotics like streptomycin?

  • A) Bacillus
  • B) Penicillium
  • C) Streptomyces
  • D) Escherichia coli

Answer: C
Explanation: Streptomyces is a genus of bacteria used to produce several antibiotics, including streptomycin.


16. Which of the following is used to produce biofertilizers?

  • A) E. coli
  • B) Rhizobium
  • C) Aspergillus
  • D) Bacillus subtilis

Answer: B
Explanation: Rhizobium is used as a biofertilizer because it fixes nitrogen in the soil, which is beneficial for plants.


17. Which of the following microbes is used in the production of vitamin B12?

  • A) Saccharomyces cerevisiae
  • B) Lactobacillus acidophilus
  • C) Propionibacterium
  • D) Rhizobium

Answer: C
Explanation: Propionibacterium is used in the production of vitamin B12, particularly in the fermentation process.


18. Which of the following microbes is used for the commercial production of citric acid?

  • A) Aspergillus niger
  • B) Saccharomyces cerevisiae
  • C) Lactobacillus acidophilus
  • D) Bacillus subtilis

Answer: A
Explanation: Aspergillus niger is used for the industrial production of citric acid through fermentation of sugars.


19. Which of the following is used as a biocontrol agent?

  • A) Bacillus thuringiensis
  • B) Saccharomyces cerevisiae
  • C) Aspergillus niger
  • D) Lactobacillus acidophilus

Answer: A
Explanation: Bacillus thuringiensis is a bacterium used as a biocontrol agent to control pests by producing toxins harmful to insects.


20. Which of the following organisms is involved in the production of the alcoholic beverage, beer?

  • A) Escherichia coli
  • B) Saccharomyces cerevisiae
  • C) Lactobacillus
  • D) Bacillus subtilis

Answer: B
Explanation: Saccharomyces cerevisiae (baker's yeast) is used in beer fermentation to convert sugars into ethanol.


21. Which of the following microbes is responsible for the decomposition of dead organic matter?

  • A) E. coli
  • B) Rhizobium
  • C) Fungi and bacteria
  • D) Yeast

Answer: C
Explanation: Fungi and bacteria are primarily responsible for the decomposition of organic matter, recycling nutrients back into the ecosystem.


22. Which of the following is an example of a biofertilizer used to enhance soil fertility?

  • A) Rhizobium
  • B) Saccharomyces cerevisiae
  • C) Streptomyces
  • D) Bacillus thuringiensis

Answer: A
Explanation: Rhizobium is a type of biofertilizer that fixes nitrogen in leguminous plants, improving soil fertility.


23. Which microorganism is used in the production of the antibiotic penicillin?

  • A) Streptomyces
  • B) Penicillium
  • C) Saccharomyces
  • D) Escherichia coli

Answer: B
Explanation: The fungus Penicillium notatum is used to produce the antibiotic penicillin.


24. Which of the following microorganisms is used in the production of lactic acid?

  • A) Streptococcus thermophilus
  • B) Bacillus subtilis
  • C) Rhizobium
  • D) Saccharomyces cerevisiae

Answer: A
Explanation: Streptococcus thermophilus is used in the fermentation of milk to produce lactic acid, which is key in the formation of curd.


25. Which of the following is an example of a beneficial effect of microorganisms in human welfare?

  • A) Antibiotic production
  • B) Food spoilage
  • C) Pathogenic infections
  • D) Air pollution

Answer: A
Explanation: Microorganisms are used in the production of antibiotics such as penicillin, which are beneficial for human health.


26. Which microbe is used in the production of biogas?

  • A) Saccharomyces cerevisiae
  • B) Methanogens
  • C) Rhizobium
  • D) Bacillus thuringiensis

Answer: B
Explanation: Methanogens are archaea that produce methane (biogas) by degrading organic matter in anaerobic conditions, such as in sewage treatment plants.


27. Which of the following is used as a biocontrol agent for controlling caterpillar pests?

  • A) Bacillus thuringiensis
  • B) Saccharomyces cerevisiae
  • C) Lactobacillus
  • D) Rhizobium

Answer: A
Explanation: Bacillus thuringiensis produces toxins that specifically kill caterpillar pests, making it a natural biocontrol agent.


28. Which microbe is used for the production of rennet used in cheese-making?

  • A) Rhizobium
  • B) Saccharomyces cerevisiae
  • C) Mucor
  • D) Aspergillus

Answer: C
Explanation: Mucor is used for the production of rennet, an enzyme used in the curdling of milk to make cheese.


29. Which of the following bacteria is involved in the nitrogen cycle by converting ammonia into nitrates?

  • A) Nitrosomonas
  • B) Rhizobium
  • C) Pseudomonas
  • D) Escherichia coli

Answer: A
Explanation: Nitrosomonas is involved in the nitrification process, where it converts ammonia into nitrates, making nitrogen available to plants.


30. Which of the following is the first step in the nitrogen cycle carried out by microbes?

  • A) Nitrogen fixation
  • B) Denitrification
  • C) Nitrification
  • D) Ammonification

Answer: A
Explanation: The first step in the nitrogen cycle is nitrogen fixation, where nitrogen-fixing bacteria like Rhizobium convert atmospheric nitrogen into ammonia.


31. Which of the following microbes is used in the process of bioremediation to clean oil spills?

  • A) Pseudomonas
  • B) Saccharomyces cerevisiae
  • C) Rhizobium
  • D) Streptococcus thermophilus

Answer: A
Explanation: Pseudomonas species are used in bioremediation to break down hydrocarbons in oil spills, making the process of cleaning up oil contamination more efficient.


32. Which of the following microorganisms is used in the production of lactic acid in the fermentation process?

  • A) Bacillus subtilis
  • B) Lactobacillus
  • C) Rhizobium
  • D) Saccharomyces cerevisiae

Answer: B
Explanation: Lactobacillus is used in the fermentation of sugars to produce lactic acid, which is used in food processing (like yogurt production).


33. Which of the following is used in the production of citric acid?

  • A) Aspergillus niger
  • B) Penicillium
  • C) Bacillus subtilis
  • D) Saccharomyces cerevisiae

Answer: A
Explanation: Aspergillus niger is used in the industrial production of citric acid, which is widely used in food processing.


34. Which of the following organisms is most commonly used for the production of alcoholic beverages?

  • A) Aspergillus
  • B) Saccharomyces cerevisiae
  • C) Rhizobium
  • D) Bacillus thuringiensis

Answer: B
Explanation: Saccharomyces cerevisiae (baker’s yeast) is commonly used in the fermentation process to produce alcoholic beverages like beer and wine.


35. Which microorganism is used in the process of brewing?

  • A) Saccharomyces cerevisiae
  • B) Rhizobium
  • C) Lactobacillus
  • D) Penicillium

Answer: A
Explanation: Saccharomyces cerevisiae (baker’s yeast) is used in brewing to ferment sugars into alcohol and carbon dioxide.


36. Which of the following microbes is responsible for the decomposition of plant material in composting?

  • A) Rhizobium
  • B) Pseudomonas
  • C) Actinomycetes
  • D) Saccharomyces cerevisiae

Answer: C
Explanation: Actinomycetes are microorganisms involved in the decomposition of plant material, breaking down complex organic substances into simpler compounds in composting.


37. Which of the following microbes is used to produce the antibiotic tetracycline?

  • A) Penicillium
  • B) Streptomyces
  • C) Rhizobium
  • D) Saccharomyces cerevisiae

Answer: B
Explanation: Streptomyces is the bacterium used for producing several antibiotics, including tetracycline.


38. Which of the following is a biocontrol method of managing agricultural pests?

  • A) Bacillus thuringiensis
  • B) Streptomyces
  • C) Rhizobium
  • D) Aspergillus niger

Answer: A
Explanation: Bacillus thuringiensis is used in biocontrol to manage pests by producing a toxin harmful to insects.


39. Which of the following is the main source of biofuels?

  • A) Methanogens
  • B) Rhizobium
  • C) E. coli
  • D) Saccharomyces cerevisiae

Answer: A
Explanation: Methanogens are used in the production of biogas (a form of biofuel) from organic waste.


40. Which of the following microbes is responsible for the formation of nitrogen compounds like ammonia in the soil?

  • A) Nitrosomonas
  • B) Rhizobium
  • C) Azotobacter
  • D) Both B and C

Answer: D
Explanation: Rhizobium and Azotobacter are bacteria that fix nitrogen, converting atmospheric nitrogen into ammonia, a form that plants can absorb and use.


41. Which of the following bacteria is used to degrade synthetic pollutants in bioremediation?

  • A) Pseudomonas
  • B) Rhizobium
  • C) Escherichia coli
  • D) Bacillus

Answer: A
Explanation: Pseudomonas species are used in bioremediation to degrade synthetic pollutants, including hydrocarbons and other organic contaminants.


42. Which microorganism is used to produce insulin for the treatment of diabetes?

  • A) Bacillus thuringiensis
  • B) Saccharomyces cerevisiae
  • C) Escherichia coli
  • D) Rhizobium

Answer: C
Explanation: Escherichia coli has been genetically engineered to produce insulin for the treatment of diabetes.


43. Which of the following microorganisms is used in the commercial production of antibiotics?

  • A) Streptomyces
  • B) Lactobacillus
  • C) Saccharomyces cerevisiae
  • D) Rhizobium

Answer: A
Explanation: Streptomyces is a genus of bacteria that produces several antibiotics like streptomycin, tetracycline, and others.


44. Which of the following is used to degrade cellulose in the rumen of ruminants?

  • A) Methanogens
  • B) Saccharomyces cerevisiae
  • C) Ruminococcus
  • D) Rhizobium

Answer: C
Explanation: Ruminococcus is a bacterium that helps degrade cellulose in the rumen of ruminants, enabling them to digest plant material.


45. Which of the following microorganisms is used in the production of antibiotics from fungi?

  • A) Penicillium notatum
  • B) Aspergillus
  • C) Saccharomyces cerevisiae
  • D) Rhizobium

Answer: A
Explanation: Penicillium notatum is a fungus that produces penicillin, one of the most famous antibiotics.


46. Which of the following microbes is used to produce the beverage vinegar?

  • A) Saccharomyces cerevisiae
  • B) Acetobacter
  • C) Lactobacillus
  • D) Aspergillus niger

Answer: B
Explanation: Acetobacter is used to convert alcohol into acetic acid, which is used in the production of vinegar.


47. Which microbe is used in the production of the biofertilizer known as azolla?

  • A) Azotobacter
  • B) Rhizobium
  • C) Anabaena
  • D) Pseudomonas

Answer: C
Explanation: Anabaena, a cyanobacterium, is used in the production of azolla, which is a biofertilizer for rice paddies.


48. Which of the following microorganisms is used in the production of biofuels?

  • A) Saccharomyces cerevisiae
  • B) Pseudomonas
  • C) Rhizobium
  • D) Escherichia coli

Answer: A
Explanation: Saccharomyces cerevisiae is used in the production of bioethanol, a type of biofuel, through fermentation.


49. Which of the following is used to break down organic matter in sewage treatment?

  • A) Methanogens
  • B) Pseudomonas
  • C) Actinomycetes
  • D) Saccharomyces cerevisiae

Answer: A
Explanation: Methanogens are used in sewage treatment processes to break down organic matter and produce biogas.


50. Which of the following is an example of a microorganism used in the preparation of the dairy product curd?

  • A) Lactobacillus
  • B) Streptococcus thermophilus
  • C) Rhizobium
  • D) Bacillus thuringiensis

Answer: A
Explanation: Lactobacillus is used to ferment milk and produce lactic acid, which helps form curd.