Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Worksheet – FULL ANSWERS

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✍️ Section A: Fill in the Blanks – Answers

1. Microorganisms that can be seen only with a microscope are called microbes.
2. Yeast is used in making bread and cakes.
3. Malaria is caused by a protozoan (Plasmodium).
4. The process of heating milk to kill harmful germs is called pasteurization.
5. Rhizobium bacteria help in fixing nitrogen in soil.

📝 Section B: True or False – Answers

1. All microorganisms are harmful. (False)
2. Viruses can reproduce only inside a host. (True)
3. Salt is used as a food preservative. (True)
4. Cholera is caused by a virus. (False – it is caused by bacteria)
5. Algae can prepare their own food. (True)

❓ Section C: Very Short Answer – Answers

1. One disease caused by bacteria: Cholera / Tuberculosis.
2. Microorganism used to make curd: Lactobacillus.
3. One food preservation method: Salting / Drying / Refrigeration.
4. Microorganism causing malaria: Plasmodium.

📘 Section D: Short Answer – Answers

1. Usefulness of microorganisms:
   Microorganisms help in making food like curd and bread, producing medicines like antibiotics, improving soil fertility, and decomposing waste.
2. Pasteurization:
   Pasteurization is the process of heating milk to a high temperature and then cooling it quickly to kill harmful microorganisms.
3. Two ways diseases spread:
   Diseases spread through air, water, food, direct contact, and insects like mosquitoes.
4. Food spoilage:
   Microorganisms spoil food by growing in it and producing harmful substances, causing bad smell, taste, and texture.

🧠 Section E: Long Answer – Answers

1. Methods of food preservation:
   Food can be preserved by drying, salting, sugaring, refrigeration, canning, pickling, and using preservatives to prevent the growth of microorganisms.
2. Harmful effects of microorganisms:
   Some microorganisms cause diseases in humans, animals, and plants. They spoil food and damage crops, leading to loss of food and health problems.

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📌 Next: Chapter 2 – Important Exam Questions (VSA / SA / LA)