Define internal respiration and external respiration

External respiration: occurs in the lungs where oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar air. 

Internal respiration: occurs in the metabolizing tissues, where oxygen diffuses out of the blood and carbon dioxide diffuses out of the cells.

Internal respiration refers to a metabolic process in which oxygen is released to tissues or living cells and carbon dioxide is absorbed by the blood.

External respiration is the transfer of gas between respiratory organs such as lungs and the outer environment.