NCERT Class VIII Science Solutions: Chapter 2-Microorganisms: Friend and Foe Part 4

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Question 21:

  1. Name two diseases that are caused by virus.

  2. Write one important characteristic of virus.


  1. Polio/Chicken Pox/Influenza

  2. Virus can reproduce only inside the cells of host.


Question 22:

Observe the Fig and answer the questions that follows.

Result for plant


  1. Write the name of the disease.

  2. Name the causative agent of this disease?

  3. How does the disease spread from one plant to another?

  4. Name any two plant diseases and the microbes that cause them.


  1. Yellow vein mosaic of lady’s finger/okra

  2. Bhindi yellow vein mosaic virus.

  3. The disease spreads from one plant to another through insects.

  1. Citrus canker caused by bacteria

  2. Rust of wheat caused by fungus or any other disease

Question 23:

How do vaccines work?


Vaccines contain dead or weakened microbes of a particular disease. When a vaccine is introduced into a healthy body, the body fights and kills them by producing suitable antibodies. These antibodies remain in the body and protect it when the microbe enters the body again.

Question 24:

Observe the set up given in Fig and answer the following questions.

  1. What happens to the sugar solution in A?

  2. Which gas is released in A?

  3. What changes will you observe in B when the released gas passes through it?

Result for Observe the set up given in Fig

Observe the Set up Given in Fig


  1. Yeast causes fermentation converting sugar into alcohol and carbon dioxide

  2. Carbon dioxide

  3. Lime water turns milky

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