What Is External Respiration?


External respiration is part of a three-part process that includes external respiration, internal respiration and cellular respiration, which together constitute how we exchange gases with our environment and how our cells convert food energy into chemical energy.

Oxygen and Carbon Dioxide

  • Oxygen is a very electronegative atom, which means that it has a strong desire to pull electrons from other atoms towards it. Carbon dioxide is a gas that's toxic in large quantities because it makes our blood too acidic and reduces blood oxygen levels.

External Respiration

  • When we breathe, we're bringing gases from our external environment into our internal environments, or inside our bodies. We're also moving gases out of our bodies when we exhale.

Internal Respiration

  • The air moving into our bodies interacts with our respiratory surfaces, namely the lungs. We absorb oxygen from the air we inhale into our cells, and at the same time, we release and exhale carbon dioxide out of our bodies. This process of gas exchange across a respiratory surface is known as internal respiration.

Cellular Respiration

  • The oxygen we take in during external respiration uses its strong electronegativity to power the conversion of sugar molecules into adenosine triphosphate (ATP), a form of chemical energy. Carbon dioxide is a byproduct of this reaction and is exhaled during external respiration.


  • Our cells can't function without ATP. ATP molecules allow cells to do work, including fight infection, replenish tissues and move our muscles.


  • Photo Credit Image by Flickr.com, courtesy of Andrew Mason
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