We need to breathe in order to carry out various processes of the body the animals need energy to be used by the body cells. This energy is liberated by burning the food, i.e., oxidize food with oxygen through the process of cellular respiration. It was Antoine Lavoisier (1743-1794) who reported that animals obtain oxygen from environment and use it for cellular respiration to synthesize ATP and produce carbon dioxide and water that are eventually liberated into the environment.