How is a molecule defined in biology?

In biology, a molecule is defined as the union of two or more atoms, which can be of the same element or different elements. This definition is critical because molecules are the fundamental building blocks of biological compounds, including proteins, lipids, carbohydrates, and nucleic acids. These molecules define the chemical properties and functions of biological systems.

For instance, water is a molecule consisting of two hydrogen atoms and one oxygen atom, while glucose is made up of carbon, hydrogen, and oxygen atoms. The interactions and arrangements of these atoms within a molecule dictate its behavior in biological processes, such as metabolism, genetics, and cellular structure.

Understanding this definition helps students grasp the molecular composition of living organisms and the biochemical reactions that support life. In contrast, a single atom describes an individual unit of an element, while a structure made up of cells pertains to larger biological entities, such as tissues and organs, and the smallest unit of a compound may not encapsulate the broader union of different atomic structures that define molecules.