Class 9 Science

Why Do We Fall Ill?

Extra Questions & Answers

Question 1: What do you understand by health?

Answer: It is a state of being well enough to properly function physically, mentally and socially. In other words, health is a state of physical, mental and social well being.

Question 2: How does public cleanliness affect our health?

Answer: Public cleanliness is important for our health. If someone is living in a filthy neighborhood, he has a greater risk of being affected by some or the other epidemic.

Question 3: What do you understand by disease?

Answer: A condition in which the affected person is unable to carry out normal activities is termed as disease.

Question 4: What do you understand by symptoms?

Answer: Apparent signs which give a clue about an underlying disease are called symptoms. For example; headache, fever, abdominal cramps, etc.

Question 5: What is an acute disease?

Answer: A disease which appears for a short duration is called acute disease. In most of the cases, an acute disease does not result in debility. Example: cholera, diarrhea, flu, common cold, etc.

Question 6: What do you understand by non-infectious disease?

Answer: When a disease happens because of some malfunctioning in any organ and it is not because of any microorganism, it is called non-infectious disease. A non-infectious disease may happen because of a wrong lifestyle. Some non-infectious diseases may happen because of genetic factor, i.e. they are right from the birth. Example: diabetes, hypertension, heart disease, arthritis, hemophilia, etc.

Question 7: What is a chronic disease?

Answer: A disease which lasts for many years is called chronic disease. Some of the chronic diseases may last for the entire life. A chronic disease often results in debility. Example: arthritis, tuberculosis, diabetes, hypertension, etc.

Question 8: What is an infectious disease?

Answer: When a disease happens because of a microorganism, it is called infectious disease. Bacteria, protozoa, virus and fungi are the causes of diseases in this case. Example: diarrhea, tuberculosis, dengue, malaria, hepatitis, etc.

Question 9: What is an antibiotic?

Answer: A substance which stops the growth of bacteria or kills the bacteria is called antibiotic. Antibiotic is given to treat or prevent bacterial infection.

Question 10: What are vectors for a disease?

Answer: Some animals work as vehicles to transfer infection from one person to another. Such animals are called vectors.

Question 11: Which animal plays the role of vector for malaria?

Answer: Female Anopheles mosquito

Question 12: Which animal plays the role of vector for rabies?

Answer: Dogs, cats, mongoose, monkey

Question 13: What are the limitations of treating an infection?

Answer: Treating an infection has following limitations:

  • An infection hampers the routine activity of a person for a few or many days. This often results in loss of work for that person. This can also result in loss of earning for the person.
  • An infection may result in short term or long term debility.
  • Treating a disease involves many costs; like cost of medicine, fees of doctor, cost of hospital stay, etc.
  • An infected person may become a source of infection for many other persons.

Question 14: How can we prevent air borne diseases?

Answer: Air borne disease can be prevented by some simple measures. If you are suffering from common cold then you should cover your face while sneezing or coughing. In case of a flu scare in the city, you should wear a face mask while going to a public place or traveling by public transport.

Question 15: How can we prevent water borne diseases?

Answer: Water borne disease can be prevented by avoiding the use of contaminated water. You should always carry drinking water from home. If that is not possible then you should buy bottled water for drinking. Never buy food from those vendors who do not keep their food items covered. Don’t eat stale or spoiled food items.

Question 16: Write a short note on vaccination.

Answer: Vaccination is based on the principle that our body learns to fight against a certain microbe when the microbe attacks our body for the first time. Vaccines are made from dead or weak strains of a microbe. Vaccine is inoculated in the body in appropriate dose. After vaccination, the body learns to fight with that microbe. As a result, our body easily wards off any future onslaught of that microbe. Many diseases can be prevented by vaccines.

Matter in Our Surroundings

Anything that has both mass and volume is called matter. You can also say that anything which has mass and which occupies space is called matter.

Is Matter Around Us Pure?

Elements and compounds are pure substances. All other substances are mixtures which means they are not pure substances.

Atoms and Molecules

Read about law of conservation of mass, law of constant proportions and Dalton's atomic theory.

Structure of Atoms

Atom is made of three particles; electron, proton and neutron. These particles are called fundamental particles of an atom or sub atomic particles.

Cell: The Fundamental Unit of Life

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being.


A groups of cells which is meant for a specific task is called tissue. Tissues are the first step towards division of labour in complex organisms.

Diversity in Living Organisms

Without proper classification, it would be impossible to study millions of organisms which exist on this earth.


If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

Force & Laws of Motion

Force has numerous effects. Force can set a stationary body in motion. Force can stop a moving body.


Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitation pull.

Work & Energy

When force is exerted on an object and object is displaced, work is said to be done. It means work is the product of force and displacement.


Sound is a type of energy. Sound travels in the form of wave from one place to another.

Why Do We Fall Ill

Health is a state of physical, mental and social well being. A condition in which the affected person is unable to carry out normal activities is termed as disease.

Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.

Improvement in Food Production

Food security is said to exist when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.