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Worksheet Solutions: Microorganisms : Friend or Foe - Notes | Study Science Class 8 - Class 8

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Q.1. What causes malaria?

Malaria is caused by protozoa.


Q.2. What are preservatives?

Chemicals (Salts, edible oils etc.) used to check the growths of microorganisms are called preservatives.


Q.3. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.


Q.4. Give two examples of algae.

Chlamydomonas and Spirogyra


Q.5. How can we prevent the spread of communicable diseases?

We prevent the spread of communicable diseases:

  • By keeping handkerchief on the nose and mouth while sneezing.
  • By keeping distance from infected persons.


Q.6. What are the harmful effects of microorganisms on plants?

Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops.


Q.7. Who discovered penicillin?

In 1929, Alexander Fleming discovered penicillin.


Q.8. How are jams and squashes preserved?

Sodium benzoate and sodium metabisulphite are used in the jams and squashes to check their spoilage.


Q.9. How can food be preserved by adding oil and vinegar?

Use of oil and vinegar prevents spoilage of food because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.


Q.10. What causes foot and mouth disease of cattle?

Foot and mouth disease of cattle is caused by a virus.


Q.11. What diseases are prevented through vaccination?

Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.


Q.12. How does common cold spread?

When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing.


Q.13. How are meat and fish preserved?

Meat and fish are covered with dry salt to check the growth of bacteria.


Q.14. Why dry fruits and even vegetables are sold in sealed air tight packets?

Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.


Q.15. What are biological nitrogen fixers?

Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

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