Difference between Internal and External Respiration
By Theydiffer - December 29, 2016

Adults breathe at a rate of 12 to 20 times a minute. Children one to five years of age breathe faster, at 24 to 30 times a minute. Now, breathing in and out is one thing. What the body does to the air it takes in is another. These interrelated, yet very different processes are called external and internal respiration, respectively. How are they different from each other? Let’s find out!


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Internal respiration is the process of breaking down food with the help of oxygen. It is a metabolic process that takes place at cellular level. Here, glucose found in food interacts with oxygen to produce adenosine triphosphate, or ATP. This biochemical energy is essential in carrying out biological processes, including cognitive processes such as thinking and dreaming.

Internal respiration is also critical in the production of fatty acids and amino acids which are essential nutrients used in respiration. Carbon dioxide, water, and ammonia are produced as waste products of internal respiration. In general, carbon dioxide and water are expelled from the body through breathing, while ammonia is excreted through urine.


External respiration involves the essential mechanics of breathing. It is basically an exchange of gases to and from the body. The process of breathing ensures that oxygen is adequately supplied and diffused into the blood. It is also through breathing that carbon dioxide is removed as a waste product of internal respiration. Moreover, external respiration ensures the removal of excess body water through exhalation.

Breathing is divided into two stages: ventilation and gas exchange. The movement of air to and from the lungs is called ventilation. Gas exchange occurs when oxygen is diffused into the blood and carbon dioxide is expelled from the lungs.

Internal vs External Respiration

So what’s the difference between internal and external respiration? Internal respiration is a chemical process in which glucose from food interacts with oxygen at a cellular level. This results in the production of energy needed by the body to carry out the majority of its biological functions. External respiration, on the other hand, is the mechanical process of breathing. This process involves the transfer of oxygen into the lungs and of carbon dioxide out of the body. Internal respiration is considered an active process as it needs a constant supply of energy for it to produce energy itself.

External respiration is a both an active and passive process. This is because breathing in (inhalation) is an active process, while breathing out (exhalation) is considered a passive process. Internal respiration, being a chemical process, is an involuntary event, while external respiration is voluntary (holding one’s breath) and involuntary as it is controlled by the brain.

Comparison Chart

Internal RespirationExternal Respiration
Oxygen and glucose interact to produce energyExchange of gases to and from the body
A chemical processA mechanical process
An active body functionComposed of active and passive body functions
An involuntary actionBoth voluntary and involuntary
Occurs at a cellular levelOccurs between the body and the outside world.