NCERT Exemplar Solutions Class 9 Science Solutions for Why Do We Fall ill ? - Exercise in Chapter 13 - Why Do We Fall ill ?

Question 31 Why Do We Fall ill ? - Exercise

What is a disease? How many types of diseases have you studied? Give examples.


Each organ of an organ system has specific functions to do. When this functioning change or disrupt it leads to a condition called disease. These changes result in some adverse effects on the body’s normal functioning and the changes observed are called signs and symptoms of the disease.

Types of Diseases


Diseases that last for only very short periods of time are called acute diseases. Ex: common cold


Diseases that last for a long time, even as much as a lifetime are called chronic diseases. Ex: elephantiasis.


Diseases that are caused by microorganisms are called infectious diseases. These diseases can spread from one person to another by vectors or by other means such as air, food, and water. Ex: Typhoid

Non- Infectious

Diseases that are not caused by infectious agents. Their causes vary, but they are not external causes like microbes that can spread in the community. Instead, these are mostly internal, non-infectious causes. Example: High blood pressure.

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