Why Do We Fall - Revision Notes

 CBSE Class 9 Science

Revision Notes
Why do we fall ill?

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 Disease

Chronic Disease

They are short duration disease

They are long lasting disease

Patient recovers completely after the cure

Patient does not recover completely

There is no loss of weight or feeling of tiredness afterward

There is often loss of weight of feeling of tiredness

There is short duration loss of work and efficiency

There 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.


Type of Disease



Air born Diseases

Pneumonia, common cold, Tuberculosis;


Water born diseases

Cholera, hepatitis


Sexual Diseases

HIV, Syphilis


Animal born Disease

- Rabbis.

*(Vector- the animal carrying infectious agent from a sick personto another potential host without getting affected Ex. Mosquitocarrying Malaria Parasite)

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.