Important Questions Class 9 Science Chapter 13 Why do we fall ill

Notes for Class 9

Please refer to Why do we fall ill Class 9 Science Notes and important questions below. The Class 9 Science Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 9 Science examination questions given below to obtain better marks in exams

Why do we fall ill Class 9 Science Notes and Questions

The below Class 9 Why do we fall ill notes have been designed by expert Science teachers. These will help you a lot to understand all the important topics given in your NCERT Class 9 Science textbook.

Refer to Chapter 13 Why do we fall ill Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.

1.”Health” is a state of being well enough to function well physically, mentally, and socially.

2.”Disease”( disturbed ease) means being uncomfortable. One or more systems of the body will change, give rise to “Symptoms” ( Cough, loose motions, pus formation, headache, fever, breathlessness, vomiting, fits, unconsciousness, inflammation , swelling and general effects – a Doctor look for the basis of symptoms). Diseases are basically two types- Acute Disease & Chronic Disease.

3.Acute Disease: The disease which lasts for only a short period of time is called Acute Disease Ex. Common Cold.

4.Chronic Disease: The disease which lasts for long period of time is called Chronic Disease Ex. Tuberculosis.

Acute DiseaseChronic Disease
They are short duration diseaseThey are long lasting disease
Patient recovers completely after the curePatient does not recover completely
There is no loss of weight or feeling of tiredness afterwardThere is often loss of weight of feeling of tiredness
There is short duration loss of work and efficiencyThere is a prolonged loss of work and efficiency

5. Causes of Diseases : Most of the diseases have many causes, rather than one single cause, like unclean water, nourishment, genetic differences, genetic abnormalities e.g. Based on the causes diseases are of two types: Non-Infectious Diseases and Infectious Diseases.

6. Non-Infectious Diseases: Not caused by infectious agents, mostly internal and non- infectious cause. Ex. Cancer

7. Infectious Diseases: Caused by infectious agents.

Type Of Disease

  • Bacterial diseases – Typhoid, Cholera, Tuberculosis, Acne, Anthrax,
  • Viral diseases – Common Cold, Influenza, Dengue fever, AIDS, Japanese encephalitis or brain fever
  • Fungal diseases: Skin diseases
  • Protozoan diseases -Malaria ( Plasmodium), Kalaazar (Leishmania), Sleeping sickness( Trypanosomes)
  • Worm diseases – Ascariosis ( Round worm), Elephantiasis(Wuchereria )

8. The infectious diseases spread by agents are called as Communicable Diseases.

Important Questions Class 9 Science Chapter 13 Why do we fall ill?

9. Principles of Treatment

  1. Antibiotics– many bacteria make a cell wall to protect themselves, the antibiotic (Penicillin) blocks the bacterial process that builds cell wall and blocks the biochemical pathways. Antibiotics do not work against viral infections. Antiviral medicine is harder than making Antibacterial medicine because Virus has only few biochemical mechanisms of their own. Other medicines bring down fever, reduce pain or loose motions. We can take bed rest to conserve energy.

10 Principles of Prevention :Following three limitation are normally confronted while treating an infectious disease:

  • Once someone has disease, their body functions are damaged and may never recover completely.
  • Treatment will take time, which means that someone suffering from a disease is likely to be bedridden for some time even if we can give proper treatment.
  • The person suffering from an infectious disease can serve as the source from where the infection may spread to other people.

General ways of preventing infectious disease

  • Air-borne – We can prevent exposure by providing living condition that are not over crowded.
  • Water-borne – prevent by providing safe drinking water. This is done by treating the water to kill any microbial contamination.
  • Vector-borne – We can provide clean environment, which would not allow mosquito breeding.

Proper nutrition is essential to maintain body immunity. There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many other diseases.

12. Prevention of disease is better than cure. Hygiene is the basic key to maintain good health.

Vaccination is another way to prevent the disease in which killed microbes are introduced into the body to develop antibodies and can preveent occurence of disease during actual entry of disease causing microbes.

Questions for Class 9 Science Chapter 13 Why do we fall ill

Question. What causes Japanese encephalitis? How it can be prevented?
Ans :(i) Japanese encephalitis is caused by virus which enters into human body through mosquito bite.
(ii) By keeping the surrounding clean and taking proper measures against mosquito bite, it can be prevented.

Question. Write the expanded form of AIDS.
Ans : Acquired Immuno Deficiency Syndrome.

Question. Why is immune system essential for our health?
Ans : The immune system of our body is a type of defence mechanism to fight against pathogenic microbes. It has cells that are specialized to kill infecting microbes and keep our body healthy.

Question. Give difference between Congenital Diseases and Acquired Diseases.
Ans : Congenital :
(i) These occur since from birth.
(ii) Inherited from the parents to the offspring. Acquired : (i) It occurs during the lifetime of the person and not from the birth. (ii) It does not get inherited. It occurs due to pathogens or due to deficiency of nutrients, hormonal imbalance or due to degeneration of the tissues.

Question. Name any two groups of microorganisms from which antibiotics could be extracted.
Ans : Bacteria and fungi.

Question. A child is suffering from fever but the doctor cannot immediately pinpoint the ailment on the basis of this one symptom. Explain, why? Also mention another two such general symptoms.
Ans : Only one symptom cannot tell the name of disease. For example : a headache may just be due to an examination stress or due to meningitis or one of a dozen different diseases. Similarly, fever may be due to different reasons.

Question. Which animal plays the role of vector for malaria?
Ans : Female Anopheles mosquito.

Question. Why is AIDS a fatal disease?
Ans : In AIDS, immune system of the body is highly weakened and body suffers from severe infections which lead to death of the individual. Hence, it is a fatal disease.

Question. Which is the most common type of Plague?
Ans : Bubonic Plague is the most common type of Plague.

Question. What are non-communicable diseases? Give examples.
Ans : Those diseases which cannot be spread from person to person, e.g., Diabetes, Cancer, etc.

Question. What are the causes of diseases?
Ans : Causes of diseases are : (a) Infection by microorganisms – bacteria, virus, fungi, protozoa and worms cause communicable diseases.
(b) Malfunctioning of body org
(c) Deficiency of one or more nutrients.
(d) Genetic factors.
(e) Polluted environment.

Question. Name five diseases against which immunization vaccine are available.
Ans : Five diseases against which immunization vaccines are available :
(i) Tetanus
(ii) Diphtheria
(iii) Whooping cough
(iv) Polio
(v) Measles

Question. (i) List any three reasons why you would think that you are sick and ought to see a doctor.
(ii) If only one of these symptoms were present, would you still go to the doctor? Why or why not?
Ans : (i) When there is a disease, body will change for the worse. This gives rise to symptoms and signs of disease. Symptoms of disease indicate that a person is not well. These symptoms can be in the form of headache, cough and loose motions. These symptoms indicate the presence of disease but never mention the name of disease.
(ii) It is advisable to go to the doctor, even if you have any of these symptoms, because only doctor can diagnose about any signs of a disease on the basis of these symptoms. But if there is only one symptom of headache, then there is no need of visiting a doctor because it could be due to tiredness or stress.

Question. Write a short note on vaccination.
Ans : 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 the body fight back strongly to prevent disease.

Question. Define : (i) Health (ii) Disease.
Ans : (i) Health : It is defined as a state of complete physical, mental and social well being and not merely the absence of disease or infirmity. (ii) Disease : A disease in the malfunctioning of body organs due to one reason or the other.

Question. What is an infectious disease?
Ans : 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 : Diarrhoea, tuberculosis, dengue, malaria, hepatitis, etc. 

Question. What do you mean by immune response?
Ans : Immune response is the reaction of the body’s immune system to foreign cells or substances that cause disease or may even be potentially dangerous. This response involves the production of cells (lymphocytes) and chemicals (antibodies) designed to defend the body against the pathogen.

Question. What is an acute disease?
Ans : 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. Why does intake of penicillin not affect human cells?
Ans : It is because penicillin blocks cell wall and formation of biochemical pathways in bacteria. Human cells do not have cell wall, thus remain unaffected.

Question. (a) What is immunisation?
(b) Define immunity and vaccination.
(c) What type of diseases can be prevented through vaccination?
Ans : (a) A process of injecting of vaccine into a healthy person in order to develop immunity against the disease is called immunisation.
(b) An ability of a body to diagnose, destroy and diminish external disease-causing agents is called immunity. This immunisation can be done by giving vaccine and thus, it is also known as vaccination.
(c) Smallpox, rabies, polio, diphtheria, chickenpox and hepatitis can be prevented through vaccination. It has been possible to cure smallpox by vaccination programmes.

Question. Name the organs which are targeted by specific diseases.
Ans : (i) Hepatitis : Liver
(ii) Fungal diseases : Skin
(iii) Pneumonia : Lungs
(iv) TB : lungs
(v) Diarrhoea : Intestines.

Question. What are the limitations of treating an infection?
Ans : 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. Which Vaccine was discovered for the first time and who discovered it?
Ans : Edward Jenner invented the vaccine for the first time and it was of smallpox.

Question. Why is making of anti-viral drugs more difficult than making anti-bacterial medicines?
Ans : Because viruses have very few biochemical mechanism of their own.

Question. State the principle of immunization.
Ans : Immune system responds against infectious microbes after detecting it first time. If this microbe again enter in body, immune system respond vigorously. This eliminate the infection more quickly than the first time. This is the principle of immunization.

Question. Many vaccines form the public health programme of childhood immunisation for preventing infectious disease. Name any two such diseases.
Ans : (i) Vaccine against measles. (ii) BCG vaccine against T.B.

Question. What is an epidemic disease? Which organ is affected if a person is suffering from jaundice?
Ans : An epidemic is the rapid and extensive spread of disease that affects many individuals simultaneously in a particular area. It is generally an infectious disease. Liver is affected if the person is suffering from jaundice.

Question. State two principles of treatment of a disease. Name the approaches generally adopted to treat infectious diseases.
Ans : There are two ways to treat an infectious disease :
(i) Reducing the effect of the disease.
(ii) Killing the microorganisms that act as infectious agents. There is two approaches to treat the infectious diseases. These are : (a) To reduce the effects of the disease. (b) To eliminate or kill the cause of the disease.

Question. What is inflammation? What are the symptoms and sign of inflammation?
Ans : It is the recruitment process by immune system in which immune system recruits many cells to the affected tissue to kill the disease causing germs. During this process, certain local effects such as swelling and pain and general effects such as fever may develop.

Question. Name the pathogens which can cause acne and sleeping sickness.
Ans : Acne – Staphylococci. Sleeping sickness – Trypanosoma.

Question. Name any four diseases transmitted through vectors.
Ans : Malaria, Dengue, Kala-azar and Plague.

Question. State giving reasons whether the following statements are correct or not :
(i) Our surrounding area should be free from stagnant water.
(ii) Staying clean is not necessary as long as you eat a balanced diet.
(iii) Social equality and harmony are necessary for good health.
Ans : (i) Yes, because stagnant water is the breeding place of mosquitoes which causes diseases like malaria, dengue, etc.
(ii) No, as balance diet is essential for a good health but hygiene is also important to remain disease free.
(iii) Yes, because health refers to a state of physical, mental and social well-being. Our social environment plays an important role in our individual health.

Question. How does public cleanliness affect our health?
Ans : Public cleanliness is important for our health. If someone is living in a filthy neighbourhood, he has a greater risk of being affected by some or the other epidemic.

Question. What do you understand by disease?
Ans : A condition in which the affected person is unable to carryout normal activities is termed as disease.

Question. What is the various dimensions of health?
Ans : Various dimensions of health is :
(i) Physical dimensions : Physical health implies perfect functioning of all the organs and systems of the body.
(ii) Mental dimensions : Mental health implies a state of balance and harmony between the individual and surrounding world.
(iii) Social dimensions : A person is socially healthy if he has a good job, a good house, a happy family, good neighbours and understanding friends.

Question. Name the target organs for the following diseases :
(i) Hepatitis targets _____
(ii) Fits or unconsciousness targets _____
(iii) Pneumonia targets _____
(iv) Fungal disease targets _____
Ans : (i) liver, (ii) brain, (iii) lungs, (iv) skin.

Question. Penicillin is not effective against common cold. Why?
Ans : Penicillin is an antibiotic which blocks the formation of biochemical pathways. Common cold is caused by virus which does not have any cell wall. Hence, penicillin is not effective against it.

Question. Why making anti-viral medicines is harder than making anti-bacterial medicines?
Ans : Antibiotics block the biochemical pathways important for bacteria which inhibit growth of bacteria or kill them. However, viruses do not use biochemical pathways like bacteria. Hence, these remain unaffected by antibiotics.

Question. Which amongst the two diseases : acute or chronic has adverse effect on the health of a person? Explain giving a suitable example.
Ans : Chronic disease lasts for long time so it is more harmful than acute disease. For example : Cough and cold, viral fever are acute diseases which do not affect our health badly and we become well within a week or so while tuberculosis (TB) which is a chronic disease affects health drastically and has a long time effect on our body.

Question. What do signs and symptoms indicate if a person is suffering from any disease?
Ans : Signs and symptoms indicate presence of a particular disease. Because when there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse.

Question. What do you mean by active and passive immunisation?
Ans : Active immunisation : It promotes the production of circulating antibodies against foreign antigens by injecting a small quantity of modified antigen into the bloodstream.
Passive immunisation : It is the application of antibodies from an immune individual to non-immune patient. This treatment is used when an individual has been or probably will be, exposed to an infectious disease and there is insufficient time for active immunisation.

Question. What are limitations for the approach to deal with infectious diseases?
Ans : Three limitations are :
(i) If someone is suffering from disease, his body function will disturb.
(ii) Treatment will take time.
(iii) Infectious person can be a source of spreading infection.

Question. What do you understand by non-infectious disease?
Ans : 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. What is a chronic disease?
Ans : 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. What are the different means by which infectious diseases are spread?
Ans : Means of spread of diseases is called Epidemiology. Air-borne diseases
(i) These diseases spread through air.
(ii) While sneezing or coughing, the droplets released in the air is inhaled by healthy person and the infection spreads.
(iii) E.g. TB, Common cold, Pneumonia, etc. Water-borne diseases These diseases spread through contaminated water. Sexually transmitted/physical contact diseases (STDs)
(i) These diseases spread by sexual contact from infected partner to the healthy.
(ii) E.g. AIDS, Syphilis, Gonorrhea, etc. Vector-borne diseases
(i) Vectors are intermediate carriers of infections.
(ii) E.g. Female Anopheles mosquito is a vector for malaria parasite, plasmodium.

Question. What are the conditions favouring air-bone diseases?
Ans : Conditions favouring air-borne infections :
(a) Close proximity to the infected person.
(b) Over-crowding
(c) Poor-ventilation

Question. Explain the following statements :
(a) Being disease free, is not the same as being healthy.
(b) Community health is essential for good individual health.
(c) Villagers suffer with cholera more than urban people.
Ans : (a) Being disease free is not the same as being healthy because health means a state of physical, mental and social well-being. One should also be mentally and socially well to have a good health.
(b) Health of all organisms depend on their environment. So public cleanliness and good social environment are necessary for good individual health.
(c) Cholera is a water-borne disease, i.e., it spreads by contaminated water. Villagers suffer with cholera more than the urban people in the absence of pure drinking water.

Question. Give any four factors necessary for a healthy person.
Ans : For a healthy person it is necessary that :
(i) Clean surrounding.
(ii) Personal hygiene prevents infectious diseases.
(iii) Sufficient and nourishing food.
(iv) Immunisation against severe diseases.

Question. What are the means of spread of diseases?
Ans : Diseases spread through :
(i) Air : When an infected person sneezes or coughs or spits, a healthy person standing nearby can inhale these droplets, causing infection in that person.
(ii) By water : Some diseases can spread from one person to another when a sick person’s stools gets into water. The people drinking the infected water thus get the disease.
(iii) By physical contact : Some of the diseases like AIDS, syphilis and gonorrhea spread by sexual contact. These diseases are not transmitted by casual physical contact like handshakes, hugs, sports like wrestling and other ways in which we touch other socially. 

Question. What are the common methods of transmission of disease?
Ans : Disease can be spread from infected person to healthy person by means of water, air, food, insect, physical contact.

Question. Name one disease caused when the microbes target- Lungs and liver.
Ans : Lungs – Asthma Liver – Jaundice

Question. 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 will help to find out sickness?
Ans : (a) The following symptoms will help us to find out that the baby is sick :
(i) Repeated crying
(ii) High body temperature
(iii) Loose motions
(iv) flagging of eyes
(v) Redness of eyes
(b) The following signs will help us to find out what is the sickness :
(i) Yellowing of eyes, pale skin and passing of yellow urine indicate that baby is suffering from jaundice.
(ii) Redness in the eye and persistent rubbing of eyes indicate about eye-flu.
(iii) Gripping pain in the stomach, loose skin and repeated loose motions indicates about diarrhoea.
(iv) High fever, headache, nausea, muscular pains and feeling very cold and shivering indicate about malaria.
(v) If only fever is there with no other visible symptoms then laboratory tests are to be done which will reveal about the signs of any disease

Question. Why do female anopheles mosquito feed on human blood?
Ans : They need nutritious food in the form of blood in order to be able to lay mature eggs.

Question. Why are we normally advised, to take bland and nourishing food when we are sick?
Ans : Normal body functions get disturbed during disease. In such a case, nutritious and easily digestible food is good for fast recovery. Thus, bland and nourishing food is required during sickness.

Question. What is the work of vaccination?
Ans : Vaccination is to grow the production of specific antibodies to confer immunity against subsequent infection.

Question. Name the microorganism causing elephantiasis.
Ans : Worms. 

Question. Name any two diseases which are caused due to unprotected sexual intercourse.
Ans : (i) AIDS, (ii) Syphilis.

Question. Give any four essential factors that must be taken care of by an individual for keeping good health.
Ans : (i) Balanced diet.
(ii) Healthy environment.
(iii) Personal hygiene.
(iv) Mental and social stability.

Question. Give four modes of transmission of AIDS.
Ans : (i) Transfusion of blood.
(ii) From an infected mother to her unborn baby during pregnancy.
(iii) At the time of breast feeding.
(iv) Sexual contact.

Question. How can we prevent water borne and vector borne infections?
Ans : (i) Water borne infections can be prevented by providing safe drinking water.
(ii) Vector borne infections can be prevented by providing clean environment.

Question. State conditions essential for good health.
Ans :Health is a state of being well enough to function well physically, mentally and socially. The health of any individual depends upon :
(i) Better social environment.
(ii) Better public cleanliness
(iii) Good economic conditions.
(iv) Social equality and harmony.

Question. What are the symptoms shown by a person if :
(i) Lungs get infected
(ii) Stomach is infected
Ans : (i) Cough and breathlessness.
(ii) Stomach ache, loose motion, vomiting.

Question. Name the causal organism of AIDS. Why a person suffering from AIDS cannot fight even very minor infections?
Ans : HIV is the causal organism of AIDS. This virus goes to the human immune system, thus can damage the bodily function. So, the body can no longer fight off even very minor infections.

Question. What is an antibiotic?
Ans : 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. How do we know that someone is suffering from disease?
Ans : Signs and symptoms indicate presence of a particular disease. Because when there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse.

Question. What are vectors for a disease?
Ans : Some animals work as vehicles to transfer infection from one person to another. Such animals are called vectors.

Question. Which animal plays the role of vector for rabies?
Ans : Dogs, cats, mongoose, monkey.

Question. What do you understand by symptoms?
Ans : Apparent signs which give a clue about an underlying disease are called symptoms. For example : Headache, fever, abdominal cramps, etc.

Question. You have suffered from chickenpox, when you were in class three. Why will you not suffer from it again?
Ans : As I suffered from chickenpox, when I were in class three. I got well by cure. Now, my immune system has developed antibodies against it.

Question. Common cold spreads faster and is difficult to control. Give reason.
Ans : Common cold is a communicable and air borne disease, i.e., the microbes spread through the air. Thus, common cold spreads faster and is difficult to control.

Question. What is disease?
Ans : Anything which interferes with the normal functioning of the body and impairs the health. 38. What is Incubation Period? Ans : It is the period between the infection and the appearance of the first symptom.

Question. Which was the first Antibiotic?
Ans : Penicillin was the first antibiotic which was invented by Alaxander Flamming in 1928.

Question. A child goes to a party and come back with cough, running nose, headache and fever. What could be the possible disease? Name the pathogen causing it.
Ans : It could be influenza caused by the virus.
Question. Why is Vaccination of children necessary?
Ans : Children are more vulnerable and susceptible to diseases and are hence given vaccines so they are able to develop immunity against diseases.

Question. (i) Why a person suffering from AIDS cannot fight even small infections?
(ii) In a slum area, many people are suffering from malaria. Mention any two unhygienic conditions that must be prevailing in that locality.
(iii) Why female Anopheles mosquito feeds on human blood?
Ans : (i) AIDS is caused by HIV which damages the immune system of the person suffering from it. Thus, the person cannot fight even small infections.
(ii) Stagnant water in the surroundings and accumulation of garbage.
(iii) Because Female Anopheles mosquitoes require large amount of proteins to lay their eggs.

Question. Why can we not make antiviral drugs?
Ans : The viruses lie on the border of living and non-living organism. The virus needs a host body to live and multiply. They cannot be grown and their biological pathways cannot be affected. Hence, the anti-viral drugs is difficult to make. 

Question. Name the diseases which’ are caused by :
Ans : Bacteria : TB, Typhoid, Anthrax and Tetanus. Viruses : Common Cold, AIDS, Dengue fever and Mumps. Fungi : Ring worm, Skin infections and Athlete’s foot. Protozoa : Malaria, Kala-Azar, Sleeping Sickness and Amoebiasis.

Question. Define carriers. Give two examples.
Ans : Carriers are the organisms which harbor diseasecausing germs without showing away sign of disease themselves, but have the ability to infect other healthy individuals. For example : Housefly, female insect Anopheles.

Question. The body of a patient has lost its power of fighting against infections. Which disease may the patient be suffering from? Name the pathogen and describe any two modes of its transmission from the patient to other person.
Ans : Patient is suffering from AIDS. HIV (Human Immuno deficiency Virus) can be transmitted by : (1) sexual contact with infected person. (2) the use infected syringe.

Question. What are the different types of diseases? Explain them.
Ans : Diseases are broadly grouped into two types : Communicable or infectious disease : Those diseases which are passed on from one person to another in various ways through air, water, food, physical contact and insects.
Non-communicable diseases : Those diseases which cannot be spread from person to person. For example : Arthritis, marasmus, etc.

Question. What is immunization, immune system, immunity?
Ans : (i) Immunization is a specific method of preventing diseases by inoculating vaccines in the human body.
(ii) Immune system : It is a system which protect our body against infection.
(iii) Immunity : The body’s power to resist and overcome infection is called immunity.

Question. Give four modes of transmission of AIDS.
Ans : (i) Blood to blood contact (transfusion).
(ii) From an infected mother to her unborn baby during pregnancy, labour or delivery.
(iii) Through breast feeding.

Question. How can we prevent air borne diseases?
Ans : 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. Our body easily wards off any future onslaught of that microbe. Many diseases can be prevented by vaccines.

Question. How can we prevent water borne diseases?
Ans : 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. What precautions can you take in your school to reduce the incidence of infectious diseases?
Ans : The following precautions can be taken in my school to reduce the incidence of infectious diseases :
(i) Isolation of infected students to prevent the spreading of air borne diseases. (ii) Availability of clean drinking water.
(iii) Clean surroundings to stop the growth and multiplication of vectors. (iv) Starting public health programme of childhood immunisation.
(v) Spreading awareness through lectures and seminars about prevention and health concept.

Question. “On exposure with an infectious microbe does not necessarily mean developing noticeable disease.” Do you agree? Explain with reason. If yes, how severe infections occur in our body?
Ans : Yes. I agree with the statement. The severity of disease manifestations depends on the number of microbes in the body. If the number of microbes is very small, the disease manifestations may be minor or unnoticed. But if the number of the microbes is large, the disease can be severe enough to be life-threatening. The immune system is also a major factor that determines the number of microbes surviving in the body. The cells of immune system go into action each time infecting microbes enter the body. If they are successful, we do not actually come down with any disease and the manifestation of the disease will be minor. However, if the immune system fails, severe infections occur in the body.

Why do we fall ill Class 9 Science Notes