Why Do We Fall ill Chapter 13 Class 9 Science Assignments

Assignments for Class 9

Please refer to Why Do We Fall ill Chapter 13 Class 9 Science Assignments below. We have provided important questions and answers for Why Do We Fall ill which is an important chapter in Class 9 Science. Students should go through the notes and also learn the solved assignment with solved questions provided below. All examination and class tests questions are as per the latest syllabus and books issued by CBSE, NCERT, and KVS. We have also provided Class 9 Science Assignments for all chapters on our website.

Chapter 13 Why Do We Fall ill Class 9 Science Assignments

Question. Name one disease caused when the microbes target-Lungs and liver.


Lungs – Asthma
Liver – Jaundice

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.


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. Name the causal organism of AIDS. Why a person suffering from AIDS cannot fight even very minor infections?


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. How does public cleanliness affect our health?


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?


A condition in which the affected person is unable to carryout normal activities is termed as disease.

Question. What is an antibiotic?


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. Many vaccines form the public health programme of childhood immunisation for preventing infectious disease. Name any two such diseases.


(i) Vaccine against measles.
(ii) BCG vaccine against T.B.

Question. Which animal plays the role of vector for rabies?


Dogs, cats, mongoose, monkey.

Question. What do you understand by symptoms?


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

Question. Why does intake of penicillin not affect human cells?


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. You have suffered from chickenpox, when you were in class three. Why will you not suffer from it again?


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. Penicillin is not effective against common cold. Why?


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?


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. What is disease?


Anything which interferes with the normal functioning of the body and impairs the health.

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


Bacteria and fungi.

Question. What is Incubation Period?


It is the period between the infection and the appearance of the first symptom.

Question. What are the common methods of transmission of disease?


Disease can be spread from infected person to healthy person by means of water, air, food, insect, physical contact.

Question. Which was the first Antibiotic?


Penicillin was the first antibiotic which was invented by Alaxander Flamming in 1928.

Question. Which is the most common type of Plague?


Bubonic Plague is the most common type of Plague.

Question. Which Vaccine was discovered for the first time and who discovered it?


Edward Jenner invented the vaccine for the first time and it was of smallpox.

Question. What are vectors for a disease?


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 malaria?


Female Anopheles mosquito.

Question. What is an acute disease?


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

Question. 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. What are the different types of diseases? Explain them.
Answer. 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. Name the target organs for the following diseases :
(i) Hepatitis targets _____
(ii) Fits or unconsciousness targets _____
(iii) Pneumonia targets _____
(iv) Fungal disease targets _____
(i) liver, (ii) brain, (iii) lungs, (iv) skin.

Question. What is immunization, immune system, immunity?
(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. Which amongst the two diseases : acute or chronic has adverse effect on the health of a person? Explain giving a suitable example.
Answer. 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?
Answer. 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. 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. Our body easily wards off any future onslaught of that microbe. Many diseases can be prevented by vaccines.

Question. What do you mean by active and passive immunisation?
Answer. 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. Give any four factors necessary for a healthy person.
Answer. 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. Differentiate between acute diseases and chronic diseases.

Why Do We Fall ill Chapter 13 Class 9 Science Assignments
Why Do We Fall ill Chapter 13 Class 9 Science Assignments

Question. 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. Define :
(i) Health
(ii) Disease.

(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 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. 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 : Diarrhoea, tuberculosis, dengue, malaria, hepatitis, etc

Question. Why can we not make antiviral drugs?
Answer. 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. State the principle of immunization.
Answer. 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. What are the means of spread of diseases?
Answer. 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. 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?
(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. What are the differences between a virus and a bacteria?

Why Do We Fall ill Chapter 13 Class 9 Science Assignments

Question. What are the different means by which infectious diseases are spread?
Answer. 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 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.