Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Worksheet – FULL Answers (Step-by-Step)

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Section A – Fill in the Blanks (Answers)

1. Microorganisms that fix nitrogen in soil are called Rhizobium.
2. The process of heating milk to kill germs is called pasteurisation.
3. Yeast is used in the production of bread and alcohol.
4. Cholera is caused by bacteria.
5. Vaccines help our body to develop immunity against diseases.

Section B – True or False (Answers)

1. All microorganisms are harmful – False
2. Viruses can reproduce only inside a living cell – True
3. Antibiotics are effective against viral diseases – False
4. Microorganisms help in making curd – True
5. Food preservation prevents the growth of microorganisms – True

Section C – Very Short Answer (Answers)

1. Typhoid is a disease caused by bacteria.
2. Yeast is used in bread making.
3. Vaccination is the process of giving vaccines to protect the body from diseases.
4. Rhizobium is a nitrogen-fixing bacterium.

Section D – Short Answer (Answers)

1. Uses of microorganisms:
   • Help in making curd, bread and alcohol.
   • Used in medicines like antibiotics.
2. Antibiotics should not be taken without a doctor’s advice because improper use can make bacteria resistant and reduce the medicine’s effectiveness.
3. Microorganisms spoil food by growing on it and releasing harmful substances, causing bad smell, taste and food poisoning.

Section E – Long Answer (Answers)

1. Role of microorganisms in agriculture:
   • Fix nitrogen in soil and increase fertility.
   • Used to make biofertilisers.
   • Help in decomposition of organic matter.
2. Methods of food preservation:
   • Refrigeration
   • Drying
   • Salting and sugaring
   • Pasteurisation
   • Use of preservatives

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