Class 8 – Microorganisms: Friend and Foe – Question Paper (100 Marks)

Chapter: Microorganisms: Friend and Foe

Time: 3 Hours | Max Marks: 100

General Instructions:

1. All questions are compulsory.

2. Section A: Q1–Q10 are 1-mark MCQs.

3. Section B: Q11–Q20 are 2-mark short-answer questions.

4. Section C: Q21–Q30 are 3-mark questions.

5. Section D: Q31–Q35 are 5-mark long-answer questions.

6. Diagrams should be labeled properly wherever required.

SECTION A (1 × 10 = 10 Marks)

Choose the correct option:

1. Which microorganism is used to make bread soft and fluffy?
   a) Lactobacillus
   b) Yeast
   c) Rhizobium
   d) Penicillium

2. The process of conversion of sugar into alcohol is called:
   a) Fermentation
   b) Pasteurization
   c) Nitrogen fixation
   d) Vaccination

3. Which disease is transmitted by the female Aedes mosquito?
   a) Malaria
   b) Dengue
   c) Tuberculosis
   d) Cholera

4. Curd formation is due to the action of:
   a) Virus
   b) Bacteria
   c) Protozoa
   d) Algae

5. Which of these is NOT a communicable disease?
   a) Chickenpox
   b) Diabetes
   c) Cholera
   d) Tuberculosis

6. The microorganism that fixes atmospheric nitrogen in soil is:
   a) Lactobacillus
   b) Rhizobium
   c) Yeast
   d) E. coli

7. Which preservative is used in jams and pickles?
   a) Sodium chloride
   b) Sodium benzoate
   c) Calcium carbonate
   d) Magnesium hydroxide

8. Alexander Fleming discovered:
   a) Vaccine
   b) Penicillin
   c) Nitrogen cycle
   d) Fermentation

9. Viruses reproduce only:
   a) In air
   b) Inside host cells
   c) In soil
   d) In water

10. The method used to preserve milk is:
    a) Fermentation
    b) Pasteurization
    c) Vaccination
    d) Dehydration

SECTION B (2 × 10 = 20 Marks)

11. Why are viruses considered non-living outside a host cell?

12. Name two diseases caused by bacteria.

13. How does sugar act as a food preservative?

14. What is the role of yeast in baking industries?

15. Why should we complete the full course of antibiotics?

16. Give two examples of fungi used in food production.

17. How do vaccines provide immunity?

18. Why do we add vinegar to pickles for preservation?

19. Differentiate between bacteria and fungi.

20. Name two diseases spread by houseflies and mosquitoes.

SECTION C (3 × 10 = 30 Marks)

21. Explain how microorganisms help in increasing soil fertility.

22. Describe the steps involved in the production of alcohol using microbes.

23. How do microorganisms decompose organic waste?

24. Why are some microbes called “friends” while others are “foes”? Give examples.

25. Explain the process of curd formation using Lactobacillus.

26. What are antibiotics? Name two antibiotics and their sources.

27. How can we prevent water-borne diseases?

28. Differentiate between bacteria and viruses with examples.

29. Why is it advised to boil drinking water during floods?

30. Describe Edward Jenner’s contribution to microbiology.

SECTION D (5 × 5 = 25 Marks)

31. Explain the commercial uses of microorganisms in food and medicine production.

32. Describe the harmful effects of microorganisms on humans, animals, and plants with examples.

33. Explain any five methods of food preservation with examples.

34. Draw a labeled diagram of the nitrogen cycle and explain its significance.

35. Design an experiment to show the action of yeast in sugar solution. Include observations.

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