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

Question 1:

State any two conditions essential for good health.


Two conditions essential for good health are proper nutrition or balanced diet and proper sanitation or clean surroundings.

Question 2:

State any two conditions essential for being free of disease.


Two conditions essential for being free of diseases are maintaining personal and community hygiene; and getting vaccinated against common infectious diseases.

Question 3:

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


Answers to the above questions are different because being disease free does not mean being healthy. It is possible to be in poor health without actually suffering from a particular disease. This is particularly true in terms of social and mental health. Being healthy includes being socially and mentally healthy and not just being disease free. However, being disease free is a part of being healthy.

Question 4:

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?


Three reasons why one would think that he/she is sick and ought to see a doctor are:
(a) Symptoms such as cough, cold, fever, vomiting or loose motions
(b) Pain, inflammation, acute itching, etc. anywhere in the body
(c) Impairment of any of the organs

Question 5:

In which case would the long-term effects on your health be most unpleasant? (i) If you get jaundice (ii) If you get lice (iii) If you get acne. Why?


Jaundice will have the most unpleasant and long-term effect on a person’s health. Jaundice involves a vital organ, i.e., liver and jaundice is a chronic disease. Lice infestation or acne are acute diseases.

Question 6:

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


Bland and nourishing food is easy to digest and provides energy to fight infections. It helps in strengthening the immune system and provides nutrition to the body, thus enabling quick healing and recovery.

Question 7:

What are the different means by which infectious diseases are spread?


Infectious diseases are spread by pathogens or disease causing organisms. The agents through which pathogens spread are air, water, food, sexual and casual physical contacts and vectors.

Question 8:

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


Following precautions can be taken to reduce the incidence of infectious diseases in the school:
(a) Maintaining proper sanitation and hygienic environment
(b) Using clean drinking water
(c) Educating student about the importance of sanitary practices
(d) Vaccinating against common infectious diseases
(e) Prohibiting sick students (suffering from an infectious disease) from attending classes

Question 9:

What is immunisation?


The process of developing resistance towards a disease by vaccination is called immunisation. In this process people are given a particular vaccine so that they develop immunity against a particular infectious disease.

Question 10:

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


Main immunisation programmes available in most health centres include vaccines to prevent disease like measles, mumps, rubella, polio, tuberculosis, tetanus, etc. They form the public health programme of childhood immunisation. Diphtheria, whooping cough and tuberculosis are major health problems in our area.

Question 11:

How many times did you fall ill in the last one year? What were the illnesses?
(a) Think of one change you could make in your habits in order to avoid any or/most of the above illnesses.
(b) Think of one change you would wish for in your surroundings in order to avoid any or/most of the above illnesses.


In the last one year, I fell ill thrice due to common cold (viral infection) and once due to malaria. (This answer will vary from person to person).
(a) Common cold infection is unavoidable. However, taking balanced diet and maintaining personal hygiene, i.e., washing hands, covering mouth while sneezing and staying away from people suffering from common cold can help. For avoiding getting malaria, one should use a mosquito repellent or sleep under a mosquito net.
(b) Maintaining cleanliness in the surroundings, not having stagnant water in pots or pans and spraying open drains with kerosene oil can help.

Question 12:

A doctor/nurse/health-worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/himself.


(a) Doctors, nurses or health-workers use gloves to protect themselves from air-borne diseases.
(b) They get themselves vaccinated against diseases like hepatitis, typhoid, rabies, tuberculosis, etc.
(c) Proper washing of exposed parts after coming in contact with infected persons.

Question 13:

Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.


The three most common diseases in the neighbourhood are cholera, typhoid and malaria. Suggested measures to be taken by the authorities are:
(a) Spraying of insecticides to kill the vectors of malaria (mosquitoes)
(b) Providing safe and germfree drinking water to avoid spreading of cholera and typhoid
(c) People should be made aware about the preventive measures through health education programmes

Question 14:

A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out:
(a) that the baby is sick? (b) what is the sickness?


(a) Symptoms like continuous crying, restlessness, fever, loose motions, improper or no food intake, etc., can help us find if a baby is sick.
(b) Kind of sickness can be known by certain organ-specific and tissue-specific symptoms. For example, yellowness of skin and eyes indicate jaundice and hepatitis.

Question 15:

Under which of the following conditions is a person most likely to fall sick?
(a) When she is recovering from malaria.
(b) When she has recovered from malaria and is taking care of someone suffering from chicken pox.
(c) When she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chicken pox. Why?


A person is most likely to fall sick in condition (c) because a malaria attack causes large scale destruction of blood cells making a person weak and anaemic. Being on four-day fast further decreases the functioning of the immune system as the person is not getting proper and sufficient food. Lastly chickenpox is a communicable and contagious disease.

Question 16:

Under which of the following conditions are you most likely to fall sick?
(a) When you are taking examinations.
(b) When you have travelled by bus and train for two days.
(c) When your friend is suffering from measles. Why?


I will be most likely to fall sick when my friend is suffering from measles because it is an infectious and contagious disease. It is a droplet infection disease.