The two phases of aerobic respiration are:
External respiration and Internal respiration.
(i) External respiration: It is simply the intake of oxygen from the surrounding medium (air or water) and giving out of carbon dioxide into that surrounding medium.
(ii) Internal respiration : This involves three steps:
(a) uptake of oxygen by tissue cells,
(b) oxidation of food inside of the cells by oxidising enzymes,
(c) elimination of carbon dioxide from tissues
