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NCERT Solutions for Class 9 Science Chapter 13 : Why Do We Fall Ill

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Chapter 13 : Why Do We Fall Ill

When we do this exercise, we realise that health and disease in human communities are very complex issues, with many interconnected causes. We also realise that the ideas of what ‘health’ and ‘disease’ mean are themselves very complicated. When we ask what causes diseases and how we prevent them, we have to begin by asking what these notions mean.

13.1 Health And Its Failure

13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite frequently all around us. We use it ourselves as well, when we say things like ‘my grandmother’s health is not good’. Our teachers use it when they scold us saying ‘this is not a healthy attitude’. What does the word ‘health’ mean?

13.2 Disease And Its Causes

13.2.1 WHAT DOES DISEASE LOOK LIKE?
Let us now think a little more about diseases. In the first place, how do we know that there is a disease? In other words, how do we know that there is something wrong with the body? There are many tissues in the body, as we have seen in Chapter 6. These tissues make up physiological systems or organ systems that carry out body functions. Each of the organ systems has specific organs as its parts, and it has particular functions. So, the digestive system has the stomach and intestines, and it helps to digest food taken in from outside the body. The musculoskeletal system, which is made up of bones and muscles, holds the body parts together and helps the body move.

13.3 Infectious Diseases

13.3.1 INFECTIOUS AGENTS
We have seen that the entire diversity seen in the living world can be classified into a few groups. This classification is based on common characteristics between different organisms. Organisms that can cause disease are found in a wide range of such categories of classification. Some of them are viruses, some are bacteria, some are fungi, some are single-celled animals or protozoans. Some diseases are also caused by multicellular organisms, such as worms of different kinds.


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