Oxygen is the element essential for respiration in most living organisms. During respiration, cells utilize oxygen to break down glucose and produce energy in the form of adenosine triphosphate (ATP). This process is vital for the survival of aerobic organisms, including humans, animals, and many microorganisms. Without oxygen, these organisms would be unable to efficiently generate the energy required for vital functions, thereby underscoring the importance of this element in biological systems and ecosystems.