oxygen is not necessary for anaerobic respiration to take place. In micro-organisms such as yeast, a uni-cellular (or single cell) fungi, the process of anaerobic respiration is called fermentation.

Respiration is the cellular process of releasing energy from food. Aerobic respiration releases fifteen times more energy than fermentation.

This process requires specialized organs such as the lungs or gills. This oxygen is used for cellular respiration and metabolism, a byproduct of which is carbon dioxide.