What is the definition of a molecule in biological terms?

In biological terms, a molecule is defined as two or more atoms that are chemically bonded together. This definition encompasses a wide variety of structures, ranging from simple molecules like oxygen (O₂) to complex organic compounds such as proteins and nucleic acids, which are fundamental to life. The arrangement and types of atoms within a molecule determine its properties and functions within biological systems.

Understanding this definition is crucial because molecules serve as the building blocks of cells and tissues, playing vital roles in energy storage, structural integrity, and biological reactions. For example, water (H₂O) is a simple molecule essential for all forms of life, while macromolecules like carbohydrates, lipids, proteins, and nucleic acids are composed of multiple atoms bonded in specific ways to perform distinct and critical functions within an organism.

The other options do not accurately capture this definition; a single atom refers to the most basic unit of matter, leading to a misunderstanding of molecular structure. A collection of cells pertains to an entirely different organizational level of biological life, and while living organisms do contain DNA, this statement does not pertain to the definition of a molecule itself.