External Respiration Definition

External respiration is the process of exchanging oxygen, carbon dioxide, and other blood solutes with the external environment. Respiration in whole is the process of delivering oxygen to the cells to extract the energy from sugars in oxidative phosphorylation in the mitochondria. This process uses oxygen, and produces carbon dioxide, as well as a number of other waste metabolites during the normal function of cells. Aquatic animals tend to exchange these waste products through the gills during external respiration with the water in their environment. Terrestrial animals may rid the body of gaseous metabolites such as carbon dioxide and nitrogen through the lungs, but many others must be filtered out in the kidney and condensed into urine.

  • Cellular Respiration – Otherwise known as oxidative phosphorylation, or using oxygen to eventually add phosphate groups to energy holding molecules.
  • Internal Respiration – The exchange of ions and gases between the blood and the fluid in the tissues, separating cells.
  • Breathing – In humans, the expansion and constriction of the diaphragm and rib muscles to increase and decrease the volume of the lungs, exchanging the air inside.
  • Respiration – The entire process of bringing air into the lungs, and transferring the oxygen to the cells for use.


1. Which of the following organisms does not show external respiration?
A. A lancelet is a small invertebrate resembling a fish, and diffuses oxygen directly from the environment.
B. A large water buffalo exchanges oxygen and carbon dioxide in the lungs.
C. A spider passes air over an organ called a book lung, which cycles oxygen with the blood.

Answer to Question #1
A is correct. The lancelet does not have any special tissues that exchange blood with the environment. In a way, the oxygen is exchanged directly through the skin into the interstitial fluid, making it a form of internal respiration. The other two animals have obvious organs dedicated to the exchange of gases to and from the blood with the external environment, which is external respiration.