1) Elements are substances that cannot be broken down further, while compounds are made of two or more elements chemically bonded together. Air contains elemental gases like nitrogen and oxygen as well as compound gases like carbon dioxide. 2) Water and organic compounds like carbohydrates, lipids, proteins, and nucleic acids are essential compounds found in living things. Water dissolves nutrients and helps regulate cell functions and temperature. 3) Proteins are compounds made of amino acids that form structures and carry out functions within cells. Nucleic acids like DNA and RNA contain the genetic instructions for cells and play important roles in protein production.