🦠 Microorganisms: Friend and Foe – MCQs for Class 8 Science

Part 1: Q1 – Q25

Q1. Which of the following is NOT a microorganism?

A) Bacteria
B) Fungi
C) Amoeba
D) Mango tree

✅ Correct Answer: D) Mango tree

Explanation:

• A) Bacteria – Microorganism (unicellular).
• B) Fungi – Microorganism (some unicellular like yeast).
• C) Amoeba – Unicellular protozoa, microscopic.
• D) Mango tree – ✔ A large multicellular plant, not a microorganism.

Q2. Which microorganism is used in the production of alcohol?

A) Lactobacillus
B) Yeast
C) Rhizobium
D) Penicillium

✅ Correct Answer: B) Yeast

Explanation:

• A) Lactobacillus – Converts milk into curd.
• B) Yeast – ✔ Ferments sugar → alcohol and CO₂.
• C) Rhizobium – Nitrogen-fixing bacteria.
• D) Penicillium – Produces antibiotic (penicillin).

Q3. The microorganism used in the production of antibiotics is:

A) Yeast
B) Penicillium
C) Lactobacillus
D) Algae

✅ Correct Answer: B) Penicillium

Explanation:

• A) Yeast – Alcohol production.
• B) Penicillium – ✔ Source of penicillin antibiotic.
• C) Lactobacillus – Curd formation.
• D) Algae – Photosynthetic organisms, not antibiotics.

Q4. Which microorganism causes tuberculosis (TB)?

A) Salmonella typhi
B) Mycobacterium tuberculosis
C) Plasmodium vivax
D) Rhizobium

✅ Correct Answer: B) Mycobacterium tuberculosis

Explanation:

• A) Salmonella typhi – Causes typhoid.
• B) Mycobacterium tuberculosis – ✔ Bacteria causing TB.
• C) Plasmodium vivax – Causes malaria.
• D) Rhizobium – Nitrogen fixer, not disease-causing.

Q5. Which disease is caused by protozoa?

A) Tuberculosis
B) Typhoid
C) Malaria
D) Cholera

✅ Correct Answer: C) Malaria

Explanation:

• A) Tuberculosis – Caused by bacteria.
• B) Typhoid – Caused by bacteria.
• C) Malaria – ✔ Protozoan disease (Plasmodium).
• D) Cholera – Caused by bacteria (Vibrio cholerae).

Q6. Which microorganism converts milk into curd?

A) Yeast
B) Penicillium
C) Lactobacillus
D) Rhizobium

✅ Correct Answer: C) Lactobacillus

Explanation:

• A) Yeast – Used in fermentation.
• B) Penicillium – Antibiotic.
• C) Lactobacillus – ✔ Converts lactose sugar into lactic acid.
• D) Rhizobium – Fixes nitrogen in soil.

Q7. The disease cholera is caused by:

A) Virus
B) Bacteria
C) Fungus
D) Protozoa

✅ Correct Answer: B) Bacteria

Explanation:

• A) Virus – Not for cholera.
• B) Bacteria – ✔ Vibrio cholerae causes cholera.
• C) Fungus – Wrong.
• D) Protozoa – Causes malaria, not cholera.

Q8. Which microorganism is used in baking industry?

A) Lactobacillus
B) Rhizobium
C) Yeast
D) Penicillium

✅ Correct Answer: C) Yeast

Explanation:

• A) Lactobacillus – Curd.
• B) Rhizobium – Nitrogen fixation.
• C) Yeast – ✔ Produces CO₂ → dough rises.
• D) Penicillium – Antibiotic production.

Q9. The microorganism that lives in the root nodules of legumes is:

A) Yeast
B) Rhizobium
C) Penicillium
D) Plasmodium

✅ Correct Answer: B) Rhizobium

Explanation:

• A) Yeast – Fermentation.
• B) Rhizobium – ✔ Nitrogen-fixing bacteria in legume roots.
• C) Penicillium – Antibiotic.
• D) Plasmodium – Protozoa causing malaria.

Q10. The process of preserving food by adding salt is called:

A) Pasteurization
B) Fermentation
C) Salting
D) Pickling

✅ Correct Answer: C) Salting

Explanation:

• A) Pasteurization – Heating milk to kill microbes.
• B) Fermentation – Microbial conversion of sugar.
• C) Salting – ✔ Removes moisture, prevents microbial growth.
• D) Pickling – Uses salt + oil + vinegar.

Q11. Which disease is caused by a virus?

A) Typhoid
B) Polio
C) Cholera
D) Tuberculosis

✅ Correct Answer: B) Polio

Explanation:

• A) Typhoid – Bacteria.
• B) Polio – ✔ Virus.
• C) Cholera – Bacteria.
• D) Tuberculosis – Bacteria.

Q12. The first antibiotic discovered was:

A) Streptomycin
B) Penicillin
C) Tetracycline
D) Erythromycin

✅ Correct Answer: B) Penicillin

Explanation:

• A) Streptomycin – Later discovery.
• B) Penicillin – ✔ Discovered by Alexander Fleming.
• C) Tetracycline – Later.
• D) Erythromycin – Later.

Q13. The microorganism used in sewage treatment is:

A) Viruses
B) Bacteria
C) Algae
D) Protozoa

✅ Correct Answer: B) Bacteria

Explanation:

• A) Viruses – Cause diseases.
• B) Bacteria – ✔ Decompose organic matter.
• C) Algae – Produce oxygen, not sewage treatment.
• D) Protozoa – Not mainly used in sewage treatment.

Q14. The disease Anthrax is caused by:

A) Virus
B) Bacteria
C) Protozoa
D) Fungus

✅ Correct Answer: B) Bacteria

Explanation:

• A) Virus – Not anthrax.
• B) Bacteria – ✔ Bacillus anthracis causes anthrax.
• C) Protozoa – Malaria, not anthrax.
• D) Fungus – Ringworm, not anthrax.

Q15. Which microorganism causes dengue fever?

A) Plasmodium
B) Dengue virus
C) Salmonella
D) Rhizobium

✅ Correct Answer: B) Dengue virus

Explanation:

• A) Plasmodium – Malaria.
• B) Dengue virus – ✔ Causes dengue.
• C) Salmonella – Typhoid.
• D) Rhizobium – Nitrogen fixer.

Q16. Which microorganism is used in making antibiotics?

A) Bacteria and fungi
B) Algae and protozoa
C) Yeast and bacteria
D) Only viruses

✅ Correct Answer: A) Bacteria and fungi

Explanation:

• A) Bacteria and fungi – ✔ Major antibiotic sources.
• B) Algae/protozoa – Not antibiotic producers.
• C) Yeast – Fermentation, not antibiotics.
• D) Viruses – Cause disease.

Q17. Which one is NOT a viral disease?

A) Common cold
B) AIDS
C) Polio
D) Tuberculosis

✅ Correct Answer: D) Tuberculosis

Explanation:

• A) Common cold – Virus.
• B) AIDS – Virus (HIV).
• C) Polio – Virus.
• D) Tuberculosis – ✔ Bacterial disease.

Q18. The method of preserving milk by heating and cooling quickly is:

A) Salting
B) Pasteurization
C) Pickling
D) Canning

✅ Correct Answer: B) Pasteurization

Explanation:

• A) Salting – For meat/fish.
• B) Pasteurization – ✔ Developed by Pasteur, kills harmful microbes in milk.
• C) Pickling – Preserves vegetables.
• D) Canning – Preservation, not for milk.

Q19. The microorganism that causes malaria is:

A) Plasmodium
B) Dengue virus
C) Salmonella
D) Vibrio cholerae

✅ Correct Answer: A) Plasmodium

Explanation:

• A) Plasmodium – ✔ Protozoan parasite.
• B) Dengue virus – Dengue.
• C) Salmonella – Typhoid.
• D) Vibrio cholerae – Cholera.

Q20. Which is NOT a method of food preservation?

A) Refrigeration
B) Salting
C) Fermentation
D) Infection

✅ Correct Answer: D) Infection

Explanation:

• A) Refrigeration – Preservation.
• B) Salting – Preservation.
• C) Fermentation – Preservation.
• D) Infection – ✔ Causes spoilage.

Q21. Which of these diseases is spread by female Anopheles mosquito?

A) Malaria
B) Cholera
C) Tuberculosis
D) Dengue

✅ Correct Answer: A) Malaria

Explanation:

• A) Malaria – ✔ Spread by female Anopheles.
• B) Cholera – Water-borne.
• C) Tuberculosis – Air-borne.
• D) Dengue – Spread by Aedes mosquito.

Q22. The first scientist to discover microorganisms was:

A) Pasteur
B) Fleming
C) Leeuwenhoek
D) Koch

✅ Correct Answer: C) Leeuwenhoek

Explanation:

• A) Pasteur – Fermentation and pasteurization.
• B) Fleming – Penicillin.
• C) Leeuwenhoek – ✔ First to see microbes under microscope.
• D) Koch – Discovered anthrax bacteria.

Q23. Which microorganism is used in making bread fluffy?

A) Yeast
B) Rhizobium
C) Penicillium
D) Amoeba

✅ Correct Answer: A) Yeast

Explanation:

• A) Yeast – ✔ Releases CO₂ → dough rises.
• B) Rhizobium – Nitrogen fixation.
• C) Penicillium – Antibiotic.
• D) Amoeba – Protozoan.

Q24. The disease AIDS is caused by:

A) Fungus
B) Virus
C) Bacteria
D) Protozoa

✅ Correct Answer: B) Virus

Explanation:

• A) Fungus – Wrong.
• B) Virus – ✔ HIV virus.
• C) Bacteria – Not correct.
• D) Protozoa – Not correct.

Q25. Which microorganism is used in the production of vaccines?

A) Live/weakened microbes
B) Antibiotics
C) Fertilizers
D) Pesticides

✅ Correct Answer: A) Live/weakened microbes

Explanation:

• A) Live/weakened microbes – ✔ Used in vaccines.
• B) Antibiotics – Kill microbes, not vaccines.
• C) Fertilizers – Not related.
• D) Pesticides – Not related.

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