Biomolecules are organic compounds that play a crucial role in the structure and function of living organisms. Defined by the presence of carbon and hydrogen atoms linked together through covalent bonds, these molecules are essential for life, as indicated by the prefix "bio," which means life. There are four primary classes of biomolecules: carbohydrates, proteins, nucleic acids, and lipids.

Carbohydrates serve as a primary energy source and are composed of sugar molecules. They can be simple sugars, like glucose, or complex carbohydrates, such as starch and cellulose. Proteins are made up of amino acids and are vital for numerous biological functions, including catalyzing reactions as enzymes, providing structural support, and facilitating communication within and between cells.

Nucleic acids, which include DNA and RNA, are responsible for storing and transmitting genetic information. They are composed of nucleotide units that encode the instructions for building proteins. Lastly, lipids are hydrophobic molecules that include fats, oils, and phospholipids, playing key roles in energy storage, cellular structure, and signaling.

Understanding these four classes of biomolecules is fundamental to studying biology, as they are integral to the processes that sustain life. Each class has unique properties and functions that contribute to the complexity of living organisms.