Cellularrespiration refers to the process of breakdown of food in the cell with the release of energy. This cellular respiration can take place in either aerobic respiration or anaerobic respiration.
While breathing we breathe in Oxygen breathe out carbon-dioxide.
The breathed in oxygen is transported to the entire body parts and to each cell. This oxygen is required by the cells for breakdown of food in order to derive energy to perform necessary functions for survival.