Which element is most abundant in living beings?

The most abundant element in living organisms is oxygen (O). It constitutes about 65% of human body mass and is a primary component of water, which dominates all biological systems. Oxygen is also found in organic molecules such as carbohydrates, proteins, nucleic acids, and lipids. It plays a central role in cellular respiration, where it acts as the final electron acceptor in the electron transport chain, allowing cells to generate ATP, the body’s energy currency. 

In addition to oxygen, other key elements include carbon, hydrogen, and nitrogen, forming the “CHON” group that makes up over 96% of living matter. Oxygen’s high electronegativity makes it vital for forming hydrogen bonds, maintaining structure in proteins and DNA, and stabilizing water molecules. It’s also essential for combustion and oxidation reactions within the body. In short, oxygen fuels energy production, shapes molecular structures, and supports life by enabling efficient metabolism and water chemistry.