CHSE Biology Health and Disease Chapter Notes

UNIT-3: Biology and Human Welfare

Chapter-1:- Health & Disease


  • Health is not only absence of disease.
  • WHO has defined health a state of complete physical, mental and social well being.


  • Disease can be defined as, "a Condition of the body or its parts in which the functions are disturbed or deranged."
  • OR
  • When one or more organs are not functioning properly.


  • Pathogen is an organism which is capable of producing a disease
  • OR
  • A pathogen is an infectious agent that causes a disease or illness to its host.
  • Typically, that term pathogen is used to describe, infectious agents such as viruses, bacteria, fungi, prion and parasite of various forms.
  • Major classes of pathogens are described below:-
  • Vruses- Adenovirus, picorna virus, retro virus, papovavirus, polyoma virus etc.
  • Bacteria- Mycobacterium, Streptococcus, Shigella and Salmonella.
  • Fungi- Saprophytic Pathogenic Fungi
  • Prions- Protein pathogens that don't content nucleic acids.
  • Parasites- Protozoon parasites and helminth parasites.
  • Pathogenicity is the disease causing property of pathogens. This property is also known as virulence.


  • An organism that lives on or in organism of another species, known as the host, from the body of which it obtains nutrients.
  • Examples hair and body lice


Disease can be classified into two types

  1. Acquired
  2. Congenital
1) Acquired Diseases:-
  • Acquired diseases occur only after birth.
  • These may be either
  1. Communicable Or
  2. Non-Communicable Disease
a) Communicable Disease:-
  • These are infectious and spread from infected person to healthy person through pathogens.
  • Communicable diseases may be contagious or non-contagious.

Contagious Disease:- Contagious diseases are transmitted through contact example chicken pox, measles, syphilis and leprosy.

Non-contagious Disease:-

  • Non-contagious diseases are transmitted through agencies like water, air, food and vector organisms.

=> Communicable diseases can be categorized into several types:-

  1. Viral diseases
  2. Bacterial diseases
  3. Fungal diseases
  4. Protozoan diseases
  5. Helminths diseases
b) Non-communicable Diseases

It does not spread from person to person.

These are four types:-

Degenerative disease:- These occur due to degenerative changes in some vital organs. example- Brain disease, arthritis.

Deficiency diseases:- These are caused due to deficiencies in food or nutrients. example- kwashiorkor(Protein deficiency), goitre(Iodine deficiency).


  • These are caused by several physical and chemical agents collectively known as cancer causing agents or carcinogens.
  • it occurs due to uncontrolled growth of tissue.

Allergy:- These are caused by several allergens (Foreign substances) Example- asthma, hay fever.

2) Congenital Diseases
  • These are inherited genetic disorders.
  • These diseases are present since birth.
  • Example:- Colour blindness, Down's syndrome and Hemophilia.


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