Breathing, or respiration, is the fundamental physiological process by which organisms obtain oxygen and eliminate carbon dioxide. Mechanically, it involves the rhythmic contraction and relaxation of muscle groups within the chest cavity and diaphragm, creating pressure gradients that draw air into the lungs (inhalation) and expel it (exhalation). At the cellular level, the process continues through gas exchange, where oxygen diffuses from the inhaled air in the alveoli across the capillary membrane into the bloodstream, and carbon dioxide, a metabolic byproduct, diffuses from the blood into the alveoli for expulsion. This entire system is regulated by complex feedback mechanisms that monitor blood acidity and oxygen levels to ensure appropriate gas exchange vital for cellular energy production.