NCERT Class-9 Science Solutions: Chapter 13-Why Do We Fall Ill Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Long Answer Questions

Question 30:

Explain giving reasons

  1. Balanced diet is necessary for maintaining healthy body.
  2. Health of an organism depends upon the surrounding environmental conditions.
  3. Our surrounding area should be free of stagnant water.
  4. Social harmony and good economic conditions are necessary for good health.


Balanced diet is necessary for maintaining healthy body:

Food is necessary for the growth and development of the body. Balanced diet provides raw materials and energy in appropriate amount needed for the substances likes protein, carbohydrates, fats, minerals etc. which in turn are essential for the proper growth and functioning of the healthy body.

Health of an organism depends upon the surrounding environmental conditions: Health is a state of being well enough to function well physically, mentally and socially and these conditions depend upon the surrounding environmental conditions. e. g. If there is unhygienic conditions in surrounding area, it is likely we might get infected or diseased.

Our surrounding area should be free of stagnant water:

This is so because many water borne diseases and insect vectors flourish in stagnant water, which cause diseases in human beings.

Social harmony and good economic conditions are necessary for good health: Human beings live in societies and different localities like villages or cities, which determines the social and physical environment and hence both are to be kept in harmony. Public cleanliness is important for individual health. For better living conditions lot of money is required. We need good food for healthy body and for this we have to earn more. For the treatment of diseases also, one has to be in good economic condition.

Question 31:

What is a disease? How many types of diseases have you studied? Give examples.


A disease is an illness or sickness. There are two types of disease

1) Chronic disease

2) Acute disease

Examples for chronic diseases are- asthma, diabetes, heart disease, thyroid etc.

Examples for acute diseases are- typhoid, headaches, cold, cough etc.

Image the Chronic Disease and Acute Disease

Question 32:

What do you mean by disease symptoms? Explain giving two examples?


When the functioning or the appearance of one or more systems of the body will change for the worse, it gives certain abnormal signs of the disease. These visual changes in human beings are called symptoms. Symptoms give indication of the presence of a particular disease.


  1. Lesions on the skin are the symptoms of chickenpox.
  2. Cough is the symptom of lung infection.

Question 33:

Why is immune system essential for our health?


The immune system of our body is a kind of defense mechanism to fight against pathogenic microbes. It has cells that are specialized to kill infecting microbes and keep our body healthy.

The immune system is made up of special cells, proteins, tissues, and organs that defends people against germs. The immune system is the body՚s defense against infectious organisms and other invaders. Invades can also be known as pathogen. Pathogen causes infection or disease. The immune system has two lines of defense. The first line of defense is Skin, Mucus, sweat, and body oil. Second line of defense is the stomach and the Phagocytes. Phagocytes are cells, which “eat” foreign germs to destroy them.

Image the Immune System

Question 34:

What precautions will you take to justify “prevention is better than cure” .


Following precautions should be taken for prevention of disease.

  1. Maintaining hygienic conditions.
  2. Awareness about the disease and causal organism.
  3. Balanced diet.
  4. Regular medical checkup.
Image the Prevention is Better Than Cure

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