- Carbon (C)

- Hydrogen (H)

- Oxygen (O)

- Nitrogen (N)

These elements make up the vast majority of the mass of living things and are essential for their structure and function. Carbon is the backbone of all organic molecules and is found in proteins, carbohydrates, lipids, and nucleic acids. Hydrogen is the lightest and most abundant element in the universe and is found in water, proteins, carbohydrates, and lipids. Oxygen is the third most abundant element in the universe and is found in water, proteins, carbohydrates, and nucleic acids. Nitrogen is the fourth most abundant element in the universe and is found in proteins, nucleic acids, and some lipids.