Diversity in Living World Part 3: MCQs (Q51–Q75)
Part 3 — Questions 51–75 (Microorganisms, useful & harmful organisms, plant/animal examples)
51. Which of these is a helpful bacterium for humans?
A. Bacteria causing cholera.
B. Lactic acid bacteria used in yogurt-making. ← Correct answer: B
C. Bacteria that spoil food only.
D. None of the bacteria are helpful.
Explanations:
A/C/D) Incorrect — some bacteria cause disease or spoilage, but many are beneficial.
B) Correct — lactic acid bacteria ferment milk to produce yogurt and are useful.
52. Which microorganism is used to make bread rise?
A. Lactobacillus.
B. Yeast (a fungus). ← Correct answer: B
C. Amoeba.
D. Algae.
Explanations:
A) Lactic bacteria involved in yogurt/fermentation but bread rising uses yeast.
B) Correct — yeast ferments sugars producing CO₂ that makes dough rise.
C/D) Amoeba and algae are not used for bread leavening.
53. Which disease is caused by a bacterium?
A. Common cold (viral).
B. Tuberculosis. ← Correct answer: B
C. Chickenpox (viral).
D. Influenza (viral).
Explanations:
A/C/D) These are viral diseases.
B) Correct — tuberculosis is caused by Mycobacterium tuberculosis (a bacterium).
54. Which of these organisms are unicellular?
A. Mushroom (multicellular fungus).
B. Amoeba and bacteria (single-celled). ← Correct answer: B
C. Mango tree (multicellular).
D. Earthworm (multicellular).
Explanations:
A/C/D) Incorrect — these are multicellular.
B) Correct — amoeba (protozoan) and bacteria are unicellular.
55. Which statement about viruses is true?
A. Viruses can grow and reproduce by themselves.
B. Viruses need a host cell to replicate (they are parasitic at cellular level). ← Correct answer: B
C. Viruses are plants.
D. Viruses are very large organisms visible to the naked eye.
Explanations:
A/C/D) Incorrect — viruses are not free-living, are not plants, and are microscopic.
B) Correct — viruses replicate inside host cells and are obligate parasites.
56. Yeast helps in making which of these food products?
A. Ice cream.
B. Bread and some alcoholic beverages (fermentation). ← Correct answer: B
C. Raw rice.
D. Salt.
Explanations:
A/C/D) Not produced by yeast.
B) Correct — yeast ferments sugars producing CO₂ and alcohol used in baking and brewing.
57. Which of these is a harmful effect of microbes?
A. Producing yogurt (useful).
B. Causing diseases like typhoid and cholera. ← Correct answer: B
C. Decomposing dead plants and animals (useful).
D. Nitrogen fixation by bacteria (useful).
Explanations:
A/C/D) These are beneficial microbial actions.
B) Correct — microbes can cause disease.
58. Which of the following microorganisms causes malaria?
A. Bacterium.
B. Protozoan (Plasmodium spp.), transmitted by mosquitoes. ← Correct answer: B
C. Fungus.
D. Virus.
Explanations:
A/C/D) Incorrect — malaria is caused by protozoan parasites (not bacteria, fungi, or viruses).
B) Correct.
59. Which of the following processes is carried out by decomposers like bacteria and fungi?
A. Making new food from sunlight.
B. Breaking down dead organic matter to recycle nutrients. ← Correct answer: B
C. Moving clouds.
D. Producing metal ores.
Explanations:
A) That’s photosynthesis (by plants/algae).
B) Correct — decomposers recycle nutrients by decomposition.
C/D) Irrelevant.
60. Which microbe is used in making curd (dahi)?
A. Yeast.
B. Virus.
C. Lactic acid bacteria (Lactobacillus). ← Correct answer: C
D. Protozoa.
Explanations:
A/B/D) Incorrect — curd is made by lactic acid bacteria, not yeast.
C) Correct — Lactobacillus converts milk into curd by fermenting lactose.
61. Which of the following is an example of beneficial fungi?
A. Penicillium (source of antibiotic penicillin).
B. Penicillium — used to make antibiotics; edible mushrooms (food). ← Correct answer: B
C. All fungi are harmful.
D. Fungi are the same as bacteria.
Explanations:
A) Partly correct but B is fuller.
B) Correct — some fungi produce antibiotics and others are edible; they have beneficial uses.
C/D) Incorrect.
62. Which organism causes athlete’s foot disease?
A. Virus.
B. Fungus (dermatophyte). ← Correct answer: B
C. Bacterium.
D. Algae.
Explanations:
A/C/D) Incorrect.
B) Correct — athlete’s foot is a fungal skin infection.
63. Which of these is NOT commonly a mode of asexual reproduction in microorganisms?
A. Binary fission (bacteria).
B. Budding (yeast).
C. Pollination (plants). ← Correct answer: C
D. Spore formation (fungi).
Explanations:
A/B/D) These are common asexual methods in microbes.
C) Correct — pollination is sexual reproduction in flowering plants, not a microbial asexual method.
64. Which microbes help in composting?
A. Only viruses.
B. Bacteria and fungi (decomposers). ← Correct answer: B
C. Fish.
D. Metals.
Explanations:
A/C/D) Incorrect.
B) Correct — bacteria and fungi decompose organic waste to produce compost.
65. Which of these practices helps prevent microbial diseases?
A. Not washing hands.
B. Boiling drinking water and maintaining hygiene. ← Correct answer: B
C. Sharing personal items freely.
D. Eating spoiled food.
Explanations:
A/C/D) Increase disease risk.
B) Correct — boiling water and hygiene reduce infections.
66. Which microorganism is used in biogas production from organic waste?
A. Virus.
B. Fungi only.
C. Anaerobic bacteria (produce methane). ← Correct answer: C
D. Algae only.
Explanations:
A/B/D) Incorrect — specific anaerobic bacteria decompose organic matter producing biogas.
C) Correct.
67. Which of the following is true about beneficial microbes in soil?
A. They reduce soil fertility always.
B. Nitrogen-fixing bacteria increase soil nitrogen available for plants. ← Correct answer: B
C. Microbes have no role in soil.
D. They eat all roots.
Explanations:
A/C/D) Incorrect.
B) Correct — nitrogen-fixing bacteria (e.g., Rhizobium) enrich soil nitrogen.
68. Which food preservation method prevents microbial growth by removing water?
A. Freezing only.
B. Drying (dehydration) and salting. ← Correct answer: B
C. Boiling briefly and leaving.
D. Smelling food.
Explanations:
A) Freezing slows but does not remove water.
B) Correct — drying and salting reduce available water, preventing microbial growth.
C/D) Ineffective for long-term preservation.
69. Which microbe is commonly used in producing antibiotics?
A. Amoeba.
B. Fungi (e.g., Penicillium). ← Correct answer: B
C. Fish.
D. Algae.
Explanations:
A/C/D) Incorrect.
B) Correct — antibiotics such as penicillin are derived from fungal species.
70. Which of the following is a vector that transmits malaria?
A. Housefly.
B. Female Anopheles mosquito. ← Correct answer: B
C. Cockroach.
D. Earthworm.
Explanations:
A/C/D) Incorrect — these do not transmit malaria.
B) Correct — female Anopheles mosquitoes transmit Plasmodium parasites causing malaria.
71. Which microbe is mainly responsible for food spoilage of milk and milk products?
A. Virus.
B. Bacteria (and some fungi). ← Correct answer: B
C. Metal.
D. Plastic.
Explanations:
A/C/D) Incorrect.
B) Correct — bacteria (and yeast/moulds) spoil milk by fermentation and decomposition.
72. Yogurt is produced by the action of:
A. Viruses.
B. Lactic acid bacteria converting lactose into lactic acid. ← Correct answer: B
C. Protozoa.
D. Earthworms.
Explanations:
A/C/D) Incorrect.
B) Correct — lactic acid bacteria ferment milk to form curd/yogurt.
73. Which of the following best describes decomposition?
A. Making new compounds from metals only.
B. Breaking down of dead organic matter into simpler substances by decomposers. ← Correct answer: B
C. Rapid growth of plants without nutrients.
D. Freezing food.
Explanations:
A/C/D) Incorrect.
B) Correct — decomposition recycles nutrients in ecosystems.
74. Which of the following microbes can photosynthesize?
A. Most bacteria (cyanobacteria) and algae.
B. Fungi only.
C. Viruses.
D. None can photosynthesize.
Correct answer: A
Explanations:
A) Correct — cyanobacteria (blue-green bacteria) and algae contain pigments for photosynthesis.
B/C/D) Incorrect — fungi/viruses do not photosynthesize.
75. Which is an example of beneficial microbes in industry?
A. Bacteria used in yogurt production.
B. Microbes used in fermentation (dairy, alcohol, enzymes). ← Correct answer: B
C. Microbes only cause diseases, no use.
D. Microbes produce plastics naturally always.
Explanations:
A) Partly correct but B is broader.
B) Correct — many industries rely on microbes for fermentation and products.
C/D) Incorrect.