What is Respiration:

The process of releasing energy from food is known as respiration. 

  • It is achieved by oxidising simple food molecules like glucose.
  • This process requires oxygen .
  • The exchange of gases in our body is brought about by the process of breathing.
  • Respiration takes place in the mitochondria of cells.



  • The mechanism by which organisms obtain oxygen from the air and release carbon dioxide is called breathing .  
  • Breathing is a physical process whereas respiration is a biochemical process .
  • The process of breathing takes place with the lungs of the organism.

Inhalation and Exhalation:

  • In breathing, we take in oxygen and give out carbon dioxide. 
  • The taking in of oxygen rich air is called inhalation and expelling air rich in carbon dioxide is called exhalation
  • Both inhalation and exhalation take place regularly during breathing.


One breath = 1 inhalation + 1 exhalation

Inhalation and Exhalation of air in lungs - Teachoo.jpg

Parts of Human Respiratory System:

The Respiratory System - Teachoo.jpg


  • The air enters the body through the nostrils present in the nose. This air then moves into the nasal passage.


Nasal Passage (Nasal Cavity):

  • The nasal passage has fine hair and mucus
  • Mucus is secreted by the mucosal glands
  • Air is filtered with the help of hair and mucus thereby ensuring that only clean air enters the lungs.


  • The part of the throat between the nasal passage and the windpipe is known as pharynx.
  • The wind passes from the nasal passage to the trachea through the pharynx. 


  • It is also known as the windpipe .
  • The air from the nasal passage enters the trachea.
  • Trachea is a tube supported by rings of soft bones called cartilage. This is why the trachea does not collapse when there is no air in it. 
  • The upper end of the trachea has a voice box called larynx .



  • The trachea runs down the neck and divides into two smaller tubes called bronchi (singular: bronchus ) at its lower end. 
  • The two bronchi are connected to the two lungs .



  • The lungs are present in the chest cavity .
  • These lungs are enclosed in the rib cage .
  • Each bronchus divides to form a large number of still smaller tubes called bronchioles. 
  • Bronchioles have millions of pouch-like air sacs at their end called alveoli which are present inside the lung.


  • The gaseous exchange takes place in alveoli.
  • The walls of alveoli are very thin and have thin blood capillaries
  • They are very small, high in number they provide a large surface area which maximizes the exchange of gases .
  • When we breathe in, the alveoli get filled with air containing oxygen . The blood capillaries surrounding the alveoli diffuse the oxygen from inside the alveoli into the blood
  • This oxygen is then carried by the blood to all parts of the body.
  • The carbon dioxide gas is produced as waste during respiration in the cells of the body tissues. This gas diffuses into the blood which is carried back to the lungs where it diffuses into the alveoli. 

Exchange of gases at alveoli - Teachoo.jpg


  • It is a muscular partition which separates the chest cavity from the abdominal cavity.
  • When we breathe in, the diaphragm contracts due to which the chest cavity expands and oxygen is inhaled.
  • When we breathe out, the diaphragm relaxes due to which the chest cavity contracts and CO2 is released out into the air.


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Maninder Singh's photo - Co-founder, Teachoo

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo