NCERT Solutions for Class 9 Science Unit 13
Why Do We Fall Ill Class 9
Unit 13 Why Do We Fall Ill Exercise Solutions
What causes disease- When we think about causes of diseases, we must remember that there are many levels of such causes. Let us look at an example. If there is a baby suffering from loose motions, we can say that the cause of the loose motions is an infection with a virus. So the immediate cause of the disease is a virus.
But the next question is - where did the virus come from? Suppose we find that the virus came through unclean drinking water. But many babies must have had this unclean drinking water. So, why is it that one baby developed loose motions when the other babies did not?