The major chemical compound that is a component of all living organisms is water (H₂O). Water is essential for various biological processes, including metabolism, nutrient transport, and thermoregulation. It acts as a solvent, enabling chemical reactions to occur in cells. Approximately 60-70% of the human body is composed of water, highlighting its importance in maintaining homeostasis. The unique properties of water, such as its high heat capacity and polarity, make it vital for sustaining life on Earth.