Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Worksheet – FULL Answers (Step-by-Step)
A. Very Short Answer – Answers
- Microorganisms are very tiny living organisms that cannot be seen with naked eyes.
- Lactobacillus is a useful microorganism.
- Lactobacillus bacteria helps in making curd.
- Cholera is caused by bacteria.
- Pasteurization is the process of heating milk to kill harmful germs.
B. Short Answer – Step-by-Step
- Microorganisms are called friends because they help us in making food and medicines. They are called foes because some cause diseases.
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Microorganisms help in food production by:
- Making curd (bacteria)
- Making bread (yeast)
- Producing alcohol and vinegar
- Antibiotics are medicines that kill disease-causing bacteria. They should be used carefully because overuse makes bacteria resistant.
- Rhizobium bacteria live in root nodules of leguminous plants and fix nitrogen in soil, increasing soil fertility.
- Food gets spoiled due to growth of microorganisms like bacteria and fungi, especially in warm and moist conditions.
C. Fill in the Blanks – Answers
- Curd is formed by the action of Lactobacillus.
- Malaria is caused by Plasmodium.
- Heating milk to kill germs is called pasteurization.
- Rhizobium bacteria fix nitrogen in soil.
- Vaccines protect us from infectious diseases.
D. True or False – Answers
- All microorganisms are harmful – False
- Viruses reproduce only inside a host – True
- Antibiotics work against viral diseases – False
- Yeast is used in baking bread – True
- Preservation prevents food spoilage – True
E. Long Answer – Step-by-Step
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Methods of Food Preservation:
- Salting
- Sugaring
- Refrigeration
- Canning
- Pasteurization
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Harmful Effects of Microorganisms:
- Cause diseases like cholera, tuberculosis, malaria
- Spoil food
- Cause plant diseases
- Vaccines help the body develop immunity by producing antibodies, which protect us from future infections.
✅ NCERT Step-by-Step Answers | Exam Ready
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