Why Do We Fall Ill? Class 9 Notes Science

1. Health is a state of physical, mental and social well being and not merely the absence of disease.

2. Health of a person depends upon one's personal habits as well as one's environment.

3. Good economic condition through proper job helps in maintaining health of the individuals due to procurement of proper, healthy and balanced diet.

4. A disease is a condition of the body or a part of it in which functions are disturbed or damaged.

5. Disease causing organisms are called pathogens.

6. Transmission of communicable diseases can be by direct (contact with infected person, soil, animal bite, etc.) or indirect (by vector, air borne, toys, etc.)

7. Disease can be :

Communicable transmitted from infected person to healthy person.

Noncommunicable cannot be transmitted from infected persons.

8. Acute diseases begin abruptly and last only for a short time, whereas chronic diseases develop slowly, last for long periods of time and often cause permanent damage.

9. The various causes of diseases are pathogens, lack of nutritious diet and lack of public health services.

10. The infectious agents are bacteria, viruses, fungi, protozoans and helminths.

11. The infectious agents may attack the same organ where they have entered or they may enter some other organ.

12. There are two main principles of treatmentkilling the microbe and reducing the effect of the disease.

13. We can prevent infection by general practices (like proper habits, nutrition, exercise and relaxation) and by immunisation.

14. Vaccines are available against diphtheria, whooping cough, tuberculosis, polio, typhoid, measles, etc.

15. Jaundice is yellowness of sclera of eyes and skin.

16. Rabies is transmitted by bite of rabid dog or cat. The patient fears from water (hydrophobia).

17. AIDS (Acquired Immuno Deficiency Syndrome) is caused by HIV. This virus weakens the human body's immunity or self defence mechanism. It can be transmitted through transfusion of infected blood, use of infected needle, infected mother to child and through sexual contact with infected person.

18. Diarrhoea is caused by bacteria, protozoa or even virus. In this, patient passes frequent stools with blood and mucus. It results in muscular cramps and dehydration. ORS is useful.

19. Typhoid is caused by Salmonella typhi. TAB vaccine provides immunity.

20. Tuberculosis is caused by Mycobacterium tuberculosis. BCG vaccine provides immunity. This disease mostly affects lungs.21. Malaria is caused by Plasmodium which is transmitted by female Anopheles mosquito.