1. Carbon (C): The backbone of all organic molecules, forming the foundation of carbohydrates, lipids, proteins, and nucleic acids.

2. Hydrogen (H): A crucial component of water, which makes up a large percentage of living organisms, and also found in various organic molecules.

3. Oxygen (O): Essential for respiration and found in water, carbohydrates, lipids, proteins, and nucleic acids.

4. Nitrogen (N): A key component of proteins and nucleic acids (DNA and RNA).

5. Phosphorus (P): Forms part of the backbone of DNA and RNA, as well as being essential for energy transfer (ATP).

6. Sulfur (S): Found in some amino acids and proteins, playing a role in protein structure and function.

These six elements, also known as the "CHNOPS" elements, make up the vast majority of the mass of living organisms.