NCERT Exemplar Class 9 Science Chapter 13 Why do We Fall ill Solutions

NCERT Exemplar Solutions for Class 9 Science Chapter 13 Why do We Fall ill covers all the important questions and answers as well as advanced level questions. It helps in learning about the human body and its capabilities, health, disease, nutritious diet, types of diseases, acute disease, chronic diseases, antibiotics, viral infections and means of spread of infectious diseases.

The NCERT Exemplar solutions for class 9 science is very important in the examination. NCERT Exemplar Solutions for Class 9 Science Chapter 13 Why do We Fall ill is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like principles of treatment, symptoms, microbes causing diseases, Principles of Prevention, physical surroundings, Public Health hygiene, General and specific ways of prevention.

Chapter Name

Chapter 13 Why do We Fall ill

Book Title

NCERT Exemplar for Class 9 Science

Related Study

  • NCERT Solutions for Class 9 Science Chapter 13 Why do We Fall ill
  • Revision Notes for Class 9 Science Chapter 13 Why do We Fall ill
  • MCQ for Class 9 Science Chapter 13 Why do We Fall ill
  • Important Questions for Class 9 Science Chapter 13 Why do We Fall ill

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 13 Why do We Fall ill Class 9 Science

Multiple Choice Questions

1. Which one of the following is not a viral disease?
(a) Dengue
(b) AIDS
(c) Typhoid
(d) Influenza


(c) Typhoid
Typhoid is caused by a bacterium called Salmonella typh.

2. Which one of the following is not a bacterial disease?
(a) Cholera
(b) Tuberculosis
(c) Anthrax
(d) Influenza


(d) Influenza
Cholera is caused by Vibrio cholera. Tuberculosis is caused by Mycobacterium tuberculosis. Anthrax is caused by Bacillus anthracis. Influenza is caused by Influenza virus.

3. Which one of the following disease is not transmitted by mosquito?
(a) Brain fever
(b) Malaria
(c) Typhoid
(d) Dengue


(c) Typhoid
Typhoid is transmitted through contaminated food and water.

4. Which one of the following disease is caused by bacteria?
(a) Typhoid
(b) Anthrax
(c) Tuberculosis
(d) Malaria


(d) Malaria
Malaria is caused by protozoan called Plasmodium vivax.

5. Which one of the following diseases is caused by protozoans?
(a) Malaria
(b) Influenza
(c) AIDS
(d) Cholera


    (a) Malaria
    Malaria is caused by protozoan Plasmodium vivax.

    6. Which one of the following has a long term effect on the health of an individual?
    (a) Common cold
    (b) Chickenpox
    (c) Chewing tobacco
    (d) Stress


    (c) Chewing tobacco
    Common cold and chicken pox are acute disease and they do not produce any long term effects. Stress is manageable and does not have long term effect. Chewing tobacco is dangerous as it produces a long term effect.

    7. Which of the following can make you ill if you come in contact with an infected person?
    (a) High blood pressure
    (b) Genetic abnormalities
    (c) Sneezing
    (d) Blood cancer


    (c) Sneezing
    Sneezing is a symptom of common and other respiratory diseases. These diseases are transmitted through inhalation of contaminated air. Other diseases in the question are not infectious disease.

    8. AIDS cannot be transmitted by :
    (a) Sexual contact
    (b) Hugs
    (c) Breast feeding
    (d) Blood transfusion


    (b) Hugs
    AIDS is transmitted by exchange of body fluids. There is no exchange of body fluids when we hug each other.

    9. Making anti-viral drugs is more difficult than making anti-bacterial medicines because :
    (a) Viruses make use of host machinery
    (b) Viruses are on the border line of living and non- living
    (c) Viruses have very few biochemical mechanisms of their own
    (d) Viruses have a protein coat


      (c) Viruses have very few biochemical mechanisms of their own
      Antibacterial drugs stop certain biochemical reaction in the bacteria. This kills the bacteria. In viruses there are a few biochemical processes which are difficult to target, this makes anti-viral drugs difficult to make.

      10. Which one of the following causes kala-azar?
      (a) Ascaris
      (b) Trypanosoma
      (c) Leishmania
      (d) Bacteria


      (c) Leishmania

      11. If you live in a overcrowded and poorly ventilated house, it is possible that you may suffer from which of the following diseases?
      (a) Cancer
      (b) AIDS
      (c) Air borne diseases
      (d) Cholera


      (c) Air borne diseases

      12. Which disease is not transmitted by mosquitoes?
      (a) Dengue
      (b) Malaria
      (c) Brain fever or encephalitis
      (d) Pneumonia


      (d) Pneumonia
      Pneumonia is transmitted through air and not mosquitos.

      13. Which one of the following is not important for individual health?
      (a) Living in clean space
      (b) Good economic condition
      (c) Social equality and harmony
      (d) Living in a large and well furnished house


      (d) Living in a large and well furnished house

      14. Choose the wrong statement :
      (a) High blood pressure is caused by excessive weight and lack of exercise
      (b) Cancers can be caused by genetic abnormalities
      (c) Peptic ulcers are caused by eating acidic food
      (d) Acne is not caused by staphylococci


      (c) Peptic ulcers are caused by eating acidic food
      Peptic ulcers are caused by a bacterium called Helicobacter pylori.

      15. We should not allow mosquitoes to breed in our surroundings because they :
      (a) multiply very fast and cause pollution
      (b) are vectors for many diseases
      (c) bite and cause skin diseases
      (d) are not important insects


      (b) are vectors for many diseases
      Mosquitos are dangerous as they spread disease like Malaria, Dengue, Japanese encephalitis etc.

      16. You are aware of Polio Eradication Programme in your city. Children are vaccinated because vaccination :
      (a) kills the polio causing microorganisms
      (b) prevents the entry of polio causing organism
      (c) creates immunity in the body
      (d) all of the above


      (c) creates immunity in the body
      Vaccines create immunity against the pathogens against which it is designed.

      17. Viruses, which cause hepatitis, are transmitted through :
      (a) air
      (b) water
      (c) food
      (d) personal contact


        (b) water

        18. Vectors can be defined as :
        (a) Animals carry the infecting agents from sick person to another healthy person
        (b) Microorganisms which cause many diseases
        (c) Infected person
        (d) Diseased plants


          (a) Animals carry the infecting agents from sick person to another healthy person

          Short Answer Questions

          19. Give two examples for each of the following :
          (i) Acute diseases
          (ii) Chronic diseases
          (iii) Infectious diseases
          (iv) Non-infectious diseases


          (i) Viral fever and Typhoid
          (ii) Diabetes, Cancer and Tuberculosis
          (iii) Smallpox and Chickenpox
          (iv) Cancer, Epilepsy and Goiter

          20. Name two diseases caused by Protozoa. What are their causal organisms?


          1. Malaria is caused by Plasmodium
          2. Kala-azar is caused by Leishmania

          21. Which bacterium causes peptic ulcers? Who discovered the peptic ulcer’s pathogen for the first time?


          Peptic ulcers are caused by bacterium Helicobacter pylori. This pathogen was first discovered by Barry J. Marshal and Robin Warren.

            22. What is an antibiotic? Give two examples.


            Antibiotic is a chemical agent that kills the bacteria or fungi by blocking their biochemical pathway.
            Example: Penicillin, Azithromycin and Streptomycin.

            23. Fill in the blanks :
            (a) Pneumonia is an example of _____ disease.
            (b) Many skin diseases are caused by _____
            (c) Antibiotics commonly block biochemical pathways important for the growth of _____
            (d) Living organisms carrying the infecting agents from one person to another are called _____


            (a) Communicable
            (b) Fungi
            (c) Bacteria
            (d) Vectors

            24. Name the target organs for the following diseases :
            (a) Hepatitis targets
            (b) Fits or unconsciousness targets
            (c) Pneumonia targets
            (d) Fungal disease targets


            (a) Hepatitis targets liver.

            (b) Fits or unconsciousness targets brain.

            (c) Pneumonia targets lungs.

            (d) Fungal disease targets skin.

            25. Who discovered ‘vaccine’ for the first time? Name two diseases which can be prevented by using vaccines.


            Edward Jenner discovered vaccine. Polio and Diptheria are two diseases which can be prevented by using vaccines.

            26. Fill in the blanks :
            (a) _____ disease continues for many days and _____causes on body.
            (b) _____disease continues for a few days and causes no long term effect on body.
            (c) _____is defined as physical, mental and social well-being and comfort.
            (d) Common cold is_____ disease.
            (e) Many skin diseases are caused by_____


            (a) Chronic, long term effect
            (b) Acute
            (c) Health
            (d) communicable (infectious)
            (e) fungi

            27. Classify the following diseases as infectious or non- infectious.
            (a) AIDS
            (b) Tuberculosis
            (c) Cholera
            (d) High blood pressure
            (e) Heart disease
            (f) Pneumonia
            (g) Cancer


            (a) AIDS: Infectious disease

            (b) Tuberculosis: Infectious disease

            (c) Cholera: Infectious disease

            (d) High blood pressure: non-Infectious disease

            (e) Heart disease non: Infectious disease

            (f) Pneumonia: Infectious disease

            (g) Cancer: non-Infectious disease

            28. Name any two groups of microorganisms from which antibiotics could be extracted.


            Two groups of microorganisms from which antibiotics could be extracted are:

            1. Bacteria
            2. Fungi

            29. Name any three diseases transmitted through vectors.


            Three diseases transmitted through vectors are:

            1. Malaria
            2. Typhoid
            3. Dengue

            Long Answer Questions

            30. Explain giving reasons :
            (i) Balanced diet is necessary for maintaining healthy body.
            (ii) Health of an organism depends upon the surrounding environmental conditions.
            (iii) Our surrounding area should be free of stagnant water.
            (iv) Social harmony and good economic conditions are necessary for good health.


            (i) Our body is made up of tiny cells which are made up of variety of organic and inorganic substances. A balanced diet is the one which consists of all the essential nutrients in an appropriate quantity. It gives our body proper nutrition required to function properly. It provides all the necessary raw materials such as carbohydrates, proteins, fats, minerals, and vitamins which are essential for proper functioning of all the body system.

            (ii) Health is defined as physical, mental and social well-being and comfort. Health is always dependent on our surroundings. Good environmental conditions help us to prevent diseases, increase the life span and improve health standards. Therefore, surrounding environmental conditions is also a necessary factor for a healthy individual. Following points should be maintained to keep the surrounding healthy :

            1. Proper removal and disposal of garbage.
            2. Proper disposal of sewage.
            3. Drinking water should be pure.
            4. Timely pest control to control communicable diseases.

            (iii) Stagnant water is not flowing and often foul-smelling water. It can become a breeding ground for the mosquitoes. Mosquitoes transmit various infectious water borne diseases like Malaria, Dengue, Elephantiasis, chikungunya etc. So, it is required to keep our surrounding area free from stagnant water to stop the spread of diseases.

            (iv) Human beings are social organisms. Social harmony and good economic conditions are also the necessary elements for good health. Proper earning helps in providing adequate and complete balanced diet, clean clothes and hygienic conditions. When we get caught by diseases, we need money and our economic status in order to get proper treatment.
            Good social environment is important factor in maintaining good health. If people mistreat each other, they could be mentally ill and they cannot lead a healthy life.

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


            The literal meaning of the term ‘disease’ is disturbed ease or being uncomfortable. Hence, disease is a condition when functioning of the body changes or gets disrupted due to the discomfort or impairment.

            Type of diseases:

            1. Acute diseases: Diseases that last for only very short periods of time.
              Example: Typhoid, flu.
            2. Chronic diseases: Diseases that last for a long time even for lifetime.
              Example: Asthma, elephantiasis.
            3. Congenital diseases: Physiological abnormalities by birth.
              Example: Colour blindness.
            4. Acquired diseases: Disease that is not present at the time of birth but developed after birth.
              Example: AIDS
            5. Infectious diseases: Diseases which are caused by microorganisms. These diseases can spread from one person to another by vectors or by other means such as air, food and water.
              Example: Tuberculosis, chickenpox, smallpox.
            6. Non-infectious diseases: Non-communicable diseases can be genetic or due to malfunctioning of internal body organ without any infection. Their causes vary, but they are not external causes like microbes that can spread in the community.
              Example: Cancer, diabetes.

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


            When our body encounters a disease, it results in the abnormal functioning of the body. These abnormal functions are known as symptoms.

            The most common symptoms observed in various diseases are :

            1. Fever
            2. Diarrhoea
            3. Fatigue
            4. Body ache
            5. Severe headache/nausea
            6. Cold and cough

            Few examples are as follows :

            • A malaria patient would have symptoms such as high fever with shaking chills, headache, vomiting, nausea, abdominal pain diarrhoea, etc.
            • Lesions on the skin can be seen when an individual is infected with chickenpox.
            • Swelling of liver and yellowing of eyes can be observed in jaundice.

            33. Why is immune system essential for our health?


            The defense mechanism present in our body which is responsible for fighting and destroying infecting microbes is known as immune system. It comprises of different kinds of cells which kill the infecting microorganism. When a pathogen enters our body, antibodies are released in response to the pathogen. These antibodies kill the pathogens and prevent us from falling ill.


            Immune system is essential for our health because:

            1. Immune system is a defense mechanism which fight against pathogenic microbes.
            2. This system plays the main role in distinguishing the acquired and inborn diseases of a body.
            3. Having specialized cell to kill infecting microbes and keep our body healthy.
            4. Vaccine also helps in acquiring immunity.
            5. Instant actions against highly active molecules like sneezing (dust particle), coughing (presence of smoke) are some common reactions observed in our daily life.

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


              Prevention is better than cure can have the following precious precautionary steps :

              1. Maintenance of proper sanitation.
              2. Maintaining personal as well as public hygiene
              3. Removal of pathogenic vectors.
              4. Consumption of proper balanced diet.
              5. Using clean water and avoid storage of water to avoid the growth of mosquitos.
              6. Educating about the various diseases, cause, symptoms and prevention.
              7. Sharing of knowledge of proper medication, suitable tests, and treatment standard.
              8. Vaccination for proper immunization.

              35. Why do some children fall ill more frequently than others living in the same locality?


                Some children fall ill more frequently than others living in the same locality due to poor immune system. Possible reasons for poor immune system :

                1. Lack of balanced diet leading to malnutrition
                2. Unhygienic conditions at home
                3. Improper sanitation
                4. Weak immunity
                5. Lack of clean drinking water and hygienic food
                6. Using contaminated water
                7. Missing vaccinations

                36. Why are antibiotics not effective for viral disease?


                Antibiotics act on bacteria and fungi as they block certain biochemical activities necessary for their survival. Viruses have property to use host cell for their own life processes as they can operate only few biochemical cycles by themselves whereas bacteria are capable of performing all the different life processes without the help of host cell. This is the reason why antiviral drugs work differently than the antibiotics.

                37. Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. Explain.


                Our immune system of the body fights disease-causing pathogens and clears them by killing through various immune cells, during this infection. Immune system sends active cells that kill and clear the pathogen. Such cells might be capable of completely diminishing the pathogens from the body or could also be incompetent further developing into a disease. Therefore, the development of a disease in individuals varies in reference to even same pathogenic exposure.

                38. Give any four factors necessary for a healthy person.


                The essential factors which are necessary for a healthy individual are :
                (a) Healthy environment:

                1. Good drainage and sanitation system
                2. Clean drinking water
                3. Clean surrounding
                4. Vendor free environment.

                (b) Healthy economic conditions :

                1. Balanced diet
                2. Proper medical facility
                3. Timely vaccination

                (c) Healthy social harmony :

                1. Awareness in society
                2. Healthy social environment
                3. Green society clean society

                (d) Immunisation against such diseases.

                39. Why is AIDS considered to be a ‘Syndrome’ and not a disease?


                HIV AIDS is caused by HIV Virus which enters our body through body fluids such as blood and breast milk or by sexual means. HIV virus spreads to the lymph nodes and blocks our immune system. This creates a condition where the body cannot fight minor diseases like common cold.

                A person with HIV can get pneumonia from common cold, minor gut infection may turn into severe diarrhoea. In HIV a person will not have specific symptoms rather he will have a series of infections. Hence HIV is called a syndrome, not a disease.

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