Useful and Harmful Microorganisms MCQs
CBSE Class 8 Science – MCQs with Answers & Explanations
Section 2: Microorganisms – Friend and Foe
Topic: Useful and Harmful Microorganisms MCQs
Based on NCERT | CBSE Board Examinations
These Multiple Choice Questions (MCQs) are designed strictly as per the NCERT syllabus, making them ideal for CBSE Class 8 Science examination preparation.
1. Which microorganism is used in baking bread?
Answer: B. Yeast
Explanation: Yeast ferments sugar to produce carbon dioxide, which makes the dough rise, giving bread its soft texture.
Explanation: Yeast ferments sugar to produce carbon dioxide, which makes the dough rise, giving bread its soft texture.
2. Lactobacillus helps in the formation of:
Answer: B. Curd
Explanation: Lactobacillus converts lactose into lactic acid, which thickens milk and forms curd.
Explanation: Lactobacillus converts lactose into lactic acid, which thickens milk and forms curd.
3. Microorganisms useful in agriculture are called:
Answer: C. Biofertilizers
Explanation: Microbes like Rhizobium fix nitrogen and increase soil fertility, acting as natural fertilizers.
Explanation: Microbes like Rhizobium fix nitrogen and increase soil fertility, acting as natural fertilizers.
4. Penicillin is obtained from:
Answer: C. Fungus
Explanation: Penicillin is produced from the fungus Penicillium and is used to kill harmful bacteria.
Explanation: Penicillin is produced from the fungus Penicillium and is used to kill harmful bacteria.
5. Which microorganism causes malaria?
Answer: B. Protozoa
Explanation: Malaria is caused by Plasmodium, a protozoan transmitted by female Anopheles mosquitoes.
Explanation: Malaria is caused by Plasmodium, a protozoan transmitted by female Anopheles mosquitoes.
6. Cholera spreads through:
Answer: B
Explanation: Cholera bacteria spread through unsafe drinking water and poor sanitation.
Explanation: Cholera bacteria spread through unsafe drinking water and poor sanitation.
7. Nitrogen fixation is done by:
Answer: B
Explanation: Rhizobium converts atmospheric nitrogen into usable compounds for plants.
Explanation: Rhizobium converts atmospheric nitrogen into usable compounds for plants.
8. Food poisoning is caused by:
Answer: B
Explanation: Harmful bacteria release toxins in spoiled food, causing illness.
Explanation: Harmful bacteria release toxins in spoiled food, causing illness.
9. Vinegar is produced using:
Answer: B
Explanation: Acetobacter bacteria convert alcohol into acetic acid (vinegar).
Explanation: Acetobacter bacteria convert alcohol into acetic acid (vinegar).
10. Tuberculosis is caused by:
Answer: B
Explanation: TB is caused by Mycobacterium tuberculosis affecting lungs.
Explanation: TB is caused by Mycobacterium tuberculosis affecting lungs.
11. Which helps in making antibiotics?
Answer: A
Explanation: Many antibiotics are derived from fungi.
Explanation: Many antibiotics are derived from fungi.
12. Harmful microbes that cause disease are:
Answer: B
Explanation: Pathogens infect humans, animals, and plants.
Explanation: Pathogens infect humans, animals, and plants.
13. Which is a useful fungus?
Answer: A
Explanation: Yeast is widely used in baking and brewing.
Explanation: Yeast is widely used in baking and brewing.
14. Preservation by cooling is:
Answer: A
Explanation: Low temperature slows microbial growth.
Explanation: Low temperature slows microbial growth.
15. Citrus canker affects:
Answer: B
Explanation: It is a bacterial plant disease.
Explanation: It is a bacterial plant disease.
16. Vaccination protects by:
Answer: B
Explanation: Vaccines stimulate antibody production.
Explanation: Vaccines stimulate antibody production.
17. Decomposers help by:
Answer: B
Explanation: They break down dead matter into simpler substances.
Explanation: They break down dead matter into simpler substances.
18. Which spreads dengue?
Answer: B
Explanation: Aedes mosquitoes transmit dengue virus.
Explanation: Aedes mosquitoes transmit dengue virus.
19. Blue‑green algae improve soil by:
Answer: B
Explanation: They add nitrogen to soil naturally.
Explanation: They add nitrogen to soil naturally.
20. The major harmful effect of microbes is:
Answer: B
Explanation: Many microbes act as pathogens causing illnesses.
Explanation: Many microbes act as pathogens causing illnesses.
