Respiration is one of the requirements for living things because it is the process where organisms exchange oxygen and carbon dioxide. This is related yet different from cellular respiration, which is the process where individual cells convert oxygen into carbon dioxide while converting food to energy.
All mammals and most living organisms require oxygen for common biological processes. They must continually breathe in air to sustain life. The amount of air that is needed and the amount of air that can be taken in depends on the size and structure of an organism. Most mammals that dwell in water can hold their breathe many times longer than a human.