Class Nine Science Chapter 13 NCERT Solution

Chapter 13: Why do we fall ill?


Q. 1. State any two conditions essential for good health. Ans. Conditions essential for good health are :

(i) State of physical, mental and social well-being.

(ii) Better surroundings or environment.

Q. 2. State any two conditions essential for being free of disease.

Ans. The two conditions essential for being free of disease.

(i) Personal and domestic hygiene.

(ii) Clean environment and surroundings.

Q. 3. Are the answers to the above questions necessarily the same or different? Why?

Ans. The answers are not always the same. It varies from man to man. For example, “good health” for a dancer may mean being able to stretch his/her body into difficult but graceful positions. On the other hand, good health for a musician may mean having enough breathing capacity in his/her lungs.


Q. 1. List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?

Ans. The three reasons why one would think that he is sick are :

(1) headache (2) cold and cough

(3) loose-motions.

If only one of the above three symptoms were present, I still would have gone to consult a doctor. It is so because all the three symptoms made me uncomfortable and bedridden for some time due to the attack of some disease.

Q. 2. In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?

• If you get jaundice,

• If you get lice,

• If you get acne.


Ans. The louse is an ectoparasite. It can easily be removed from the body. Acne is also curable. Both of these, generally have no long term effects. On the other hand, jaundice has long term effect on the liver. Jaundice is often accompanied by vomiting and in acute cases. It affects the liver severely. Therefore, it may be concluded that long term-effect of jaundice is most serious.


Q. 1. Why are we normally advised to take bland and nourishing food when we are sick?

Ans. (i) Nourishing food is good for health and simple food is easy to digest.

(ii) Such a diet contains adequate nutrients for a speedy recovery.

Q. 2. What are the different means by which infectious diseases are spread?

Ans. The different means by which infectious diseases spread are :

(i) Through air: They are also called air-borne diseases. The air carries bacteria, virus and the diseases that can be caused are a common cold, influenza, tuberculosis, etc.

(ii) Through food and water: When one eats/drinks contaminated food/water that contains bacteria, virus, worm etc., it can cause diseases like cholera, typhoid, hepatitis.

(iii) Through contact: Many diseases spread by contact of an infected person with a healthy person. Example: fungal infections, skin diseases, scabies etc.

(iv) By sexual contact: Many diseases can be transmitted. Example Syphilis, AIDS.

(v) Body fluids: Fluids like blood, mother’s milk when infected, can also cause diseases. Example: AIDS.

Q. 3. What precautions can you take in your school to reduce the incidence of infectious diseases?

Ans. Following precautions can be taken in the school to reduce the incidence of infectious diseases :

(i) providing clean drinking water.

(ii) educating students about the causes of infectious diseases.

(iii) vaccination of students against common infectious diseases from time to time.

(iv) proper sanitation or the clean environment in school and its surroundings to eradicate vectors of infectious diseases, and (v) by not allowing the affected students to attend the classes till they recover from infectious diseases.

Q. 4. What is immunisation?

Ans. It is the process of developing disease resistance, called immunity, which may be achieved by vaccination or providing proper nutrient and sufficient food.

Q. 5. What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?

Ans. The immunisation programmes available at the nearest health centre in my locality is :

For a pregnant woman — TT and Hepatitis B

For infants — DPT




For children — Typhoid