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CBSE Class 9 Biology Notes for Chapter 4  Why do we fall ill?

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                       CHAPTER 4 WHY DO WE FALL ILL?
 

  • Health is a state of physical, mental and social well-being.

 

  • The health of an individual depends on his/her surroundings.

 

  • Diseases are classified as acute or chronic depending on the duration for which they last.

 

  • Diseases that last for a very short time are called acute. The diseases that last for a very long time are called chronic.

 

  • Diseases may be due to infectious or non-infectious causes.

 

  • Infectious agents belong to different categories or organisms. These may be unicellular or multicellular.

 

  • The treatment for a disease depends on the type of the disease causing organism.

 

  • Infectious agents spread through air, water and even physical contact. It is better to stay away from contaminated air and water.

 

  • Preventing a disease is more important and necessary. Prevention is better than cure.

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