Chapter 13 Why Do We Fall ill? Class 9 Notes | EduRev

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Class 9 : Chapter 13 Why Do We Fall ill? Class 9 Notes | EduRev

 Page 1


Chapter 13 Why Do We fall Ill 
 
Health – The state of physical, social and mental well-being is called heath 
Disease – A condition that causes discomfort to the body 
Health and disease free – Health include social, physical and mental well-being while disease free means a 
person is not suffering from any particular disease  
E.g. Good health for a singer may be a clear throat and for a dancer it could be enough energy for the dance 
whereas disease free will mean they are not suffering from a terrible disease such as cough, cold, diarrhea etc. 
Types of Diseases 
Based on time period: 
1. Acute disease  
Disease that last for a very short period of time  
The effects are short term and can be recovered with proper diet. 
E.g. Common cold, fever etc. 
 
2. Chronic disease 
Disease that last for a very long time some of them for entire life 
Have drastic long term effects on a person’s health 
E.g. Diabetes, cancer, AIDS etc. 
 
Based on causes: 
 
1. Infectious disease 
Caused by microorganisms 
 
 Some common infectious disease: 
 Disease   Causative organism  Type of organism Transmission  
a. Kala azar    Leismania donowani   Protozoa Sand fly 
b. Sleeping Sickness  Trypanosoma    Protozoa Tsetse fly 
c. Malaria   Plasmodium vivax   Protozoa Female Anopheles 
d. Amoebiasis   Entamoeba histolytica   Protozoa Food, water 
e. Cholera   Vibrio cholerae   Bacteria Food, water 
f. Anthrax   Bacillus anthracis   Bacteria Infected animal 
g. Botulinum   Clostridium botulinum  Bacteria Food and Water 
h. Diphtheria   Corynebacterium diphtheria  Bacteria Physical contact 
i. Pneumonia   Streptococcus pneumonia  Bacteria Physical contact 
j. Typhoid   Salmonella typhii   Bacteria Food and Water 
k.  Tetanus   Clostridium tetani    Bacteria Injured surface 
l. Tuberculosis   Mycobacterium tuberculosis  Bacteria Infected person 
Page 2


Chapter 13 Why Do We fall Ill 
 
Health – The state of physical, social and mental well-being is called heath 
Disease – A condition that causes discomfort to the body 
Health and disease free – Health include social, physical and mental well-being while disease free means a 
person is not suffering from any particular disease  
E.g. Good health for a singer may be a clear throat and for a dancer it could be enough energy for the dance 
whereas disease free will mean they are not suffering from a terrible disease such as cough, cold, diarrhea etc. 
Types of Diseases 
Based on time period: 
1. Acute disease  
Disease that last for a very short period of time  
The effects are short term and can be recovered with proper diet. 
E.g. Common cold, fever etc. 
 
2. Chronic disease 
Disease that last for a very long time some of them for entire life 
Have drastic long term effects on a person’s health 
E.g. Diabetes, cancer, AIDS etc. 
 
Based on causes: 
 
1. Infectious disease 
Caused by microorganisms 
 
 Some common infectious disease: 
 Disease   Causative organism  Type of organism Transmission  
a. Kala azar    Leismania donowani   Protozoa Sand fly 
b. Sleeping Sickness  Trypanosoma    Protozoa Tsetse fly 
c. Malaria   Plasmodium vivax   Protozoa Female Anopheles 
d. Amoebiasis   Entamoeba histolytica   Protozoa Food, water 
e. Cholera   Vibrio cholerae   Bacteria Food, water 
f. Anthrax   Bacillus anthracis   Bacteria Infected animal 
g. Botulinum   Clostridium botulinum  Bacteria Food and Water 
h. Diphtheria   Corynebacterium diphtheria  Bacteria Physical contact 
i. Pneumonia   Streptococcus pneumonia  Bacteria Physical contact 
j. Typhoid   Salmonella typhii   Bacteria Food and Water 
k.  Tetanus   Clostridium tetani    Bacteria Injured surface 
l. Tuberculosis   Mycobacterium tuberculosis  Bacteria Infected person 
m. AIDS    HIV (Human Immuno Virus)  Virus  Sexual contact 
n. Dengue   Dengue virus    Virus  Aedes mosquito 
o. Rabies    Rabies virus    Virus  Infected animal 
p. Chicken pox   Varicella zoter virus   Virus  Physical contact 
q. Measles   Measles virus    Virus  Air 
r. Hepatitis   Hepatitis virus    Virus  Blood transfusion 
s. Filariasis   Wuchreria bancrofti   Round worm Mosquito 
 
2. Non-infectious disease 
Causes other than microorganisms such has deficiency of a mineral, lack of exercise, fat etc. 
 
Some non-infectious disease: 
 
Disease     Deficiency 
a. Night blindness    Vitamin A 
b. Beri-Beri     Vitamin B1 
c. Scurvy      Vitamin C 
d. Rickets     Vitamin D 
e. Goitre      Iodine 
f. Anaemia     Iron 
 
Based on transmission 
 
1. Communicable Disease 
Disease that can spread from an infected to a healthy person by air, water, food or physical contact is 
known as communicable disease.  
E.g. Common cold, tuberculosis, AIDS, Whooping cough, chicken pox 
 
2. Non-Communicable Disease 
Disease that cannot spread from an infected person to a healthy person through air, water food or 
physical contact. 
E.g. Night blindness, scurvy, goiter, malaria, sleeping sickness etc. 
 
Organ or tissue specific diseases: 
 
1. AIDS – infects the immune system and make body vulnerable to other diseases. 
2. Jaundice – liver 
3. Disease that targets brain – Causes brain fever 
 
Treatment 
 
1. Targeting the symptoms 
Medicines that reduces symptoms such as fever, inflammation, reduce pain or running nose etc. 
Page 3


Chapter 13 Why Do We fall Ill 
 
Health – The state of physical, social and mental well-being is called heath 
Disease – A condition that causes discomfort to the body 
Health and disease free – Health include social, physical and mental well-being while disease free means a 
person is not suffering from any particular disease  
E.g. Good health for a singer may be a clear throat and for a dancer it could be enough energy for the dance 
whereas disease free will mean they are not suffering from a terrible disease such as cough, cold, diarrhea etc. 
Types of Diseases 
Based on time period: 
1. Acute disease  
Disease that last for a very short period of time  
The effects are short term and can be recovered with proper diet. 
E.g. Common cold, fever etc. 
 
2. Chronic disease 
Disease that last for a very long time some of them for entire life 
Have drastic long term effects on a person’s health 
E.g. Diabetes, cancer, AIDS etc. 
 
Based on causes: 
 
1. Infectious disease 
Caused by microorganisms 
 
 Some common infectious disease: 
 Disease   Causative organism  Type of organism Transmission  
a. Kala azar    Leismania donowani   Protozoa Sand fly 
b. Sleeping Sickness  Trypanosoma    Protozoa Tsetse fly 
c. Malaria   Plasmodium vivax   Protozoa Female Anopheles 
d. Amoebiasis   Entamoeba histolytica   Protozoa Food, water 
e. Cholera   Vibrio cholerae   Bacteria Food, water 
f. Anthrax   Bacillus anthracis   Bacteria Infected animal 
g. Botulinum   Clostridium botulinum  Bacteria Food and Water 
h. Diphtheria   Corynebacterium diphtheria  Bacteria Physical contact 
i. Pneumonia   Streptococcus pneumonia  Bacteria Physical contact 
j. Typhoid   Salmonella typhii   Bacteria Food and Water 
k.  Tetanus   Clostridium tetani    Bacteria Injured surface 
l. Tuberculosis   Mycobacterium tuberculosis  Bacteria Infected person 
m. AIDS    HIV (Human Immuno Virus)  Virus  Sexual contact 
n. Dengue   Dengue virus    Virus  Aedes mosquito 
o. Rabies    Rabies virus    Virus  Infected animal 
p. Chicken pox   Varicella zoter virus   Virus  Physical contact 
q. Measles   Measles virus    Virus  Air 
r. Hepatitis   Hepatitis virus    Virus  Blood transfusion 
s. Filariasis   Wuchreria bancrofti   Round worm Mosquito 
 
2. Non-infectious disease 
Causes other than microorganisms such has deficiency of a mineral, lack of exercise, fat etc. 
 
Some non-infectious disease: 
 
Disease     Deficiency 
a. Night blindness    Vitamin A 
b. Beri-Beri     Vitamin B1 
c. Scurvy      Vitamin C 
d. Rickets     Vitamin D 
e. Goitre      Iodine 
f. Anaemia     Iron 
 
Based on transmission 
 
1. Communicable Disease 
Disease that can spread from an infected to a healthy person by air, water, food or physical contact is 
known as communicable disease.  
E.g. Common cold, tuberculosis, AIDS, Whooping cough, chicken pox 
 
2. Non-Communicable Disease 
Disease that cannot spread from an infected person to a healthy person through air, water food or 
physical contact. 
E.g. Night blindness, scurvy, goiter, malaria, sleeping sickness etc. 
 
Organ or tissue specific diseases: 
 
1. AIDS – infects the immune system and make body vulnerable to other diseases. 
2. Jaundice – liver 
3. Disease that targets brain – Causes brain fever 
 
Treatment 
 
1. Targeting the symptoms 
Medicines that reduces symptoms such as fever, inflammation, reduce pain or running nose etc. 
 
2. Kill microorganisms 
Using antibiotics to kill bacteria that has caused the disease 
Medicines that kill microbe target a biochemical pathway in the microbe that is specific to the microbe 
only so that it does not kill human cells. 
It is difficult to create medicines that kill viruses because they do not have their own machinery and use the 
machinery of the host cells. 
 
Prevention 
 
1. Using clean drinking water, preparing food in clean environment, washing fruits and vegetable before 
eating can prevent several food and water born disease. 
2. Maintaining distance from patients suffering from communicable disease can prevent the spread of those 
diseases. 
3. Eating a balanced diet can prevent various deficiency disease 
4. Proper nourishment also strengthens our immune system that can prevent a number of disease. 
5. Keeping the surroundings clean can help the prevention of disease that are spread by mosquitoes 
6. Animals can be regularly injected with anti-rabies drugs to prevent rabies. 
7. Vaccination  
The weakened or dead microorganisms given to a healthy person to prevent the occurrence of disease in 
the future is called vaccination. This process is also called immunization 
E.g. Polio vaccine, Hepatitis vaccine 
The body prepare antibodies against the microbe and store them. When the live microbe infects the 
person these antibodies kill the microbe before it can spread throughout the body. 
 
Immunity – The ability of the body to fight against the disease of foreign microbes that cause diseases 
Immune cells – Cells that fight against these microbes or disease. E.g. White blood cells 
 
 
 
 
 
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