The element essential for respiratory function in humans is oxygen. Oxygen is vital for cellular respiration, a process in which cells convert glucose and oxygen into energy, producing carbon dioxide and water as byproducts. Humans and most living organisms require oxygen to sustain life, as it is crucial for energy production within cells. Oxygen is obtained through the respiratory system when we inhale air, which contains approximately 21% oxygen. The oxygen is then transported by red blood cells throughout the body, supplying tissues and organs. Without oxygen, human cells would not be able to function efficiently, leading to severe health complications.