What are molecules composed of?

Molecules are made up of two or more combined atoms. This fundamental concept in chemistry underscores how atoms, which are the smallest units of an element, can bond together in various configurations to form molecules. For instance, a molecule of water consists of two hydrogen atoms bonded to one oxygen atom. This combination and interaction of atoms result in the formation of distinct substances with unique properties.

The other options refer to different structures and levels of organization in biology. A single atom does not qualify as a molecule, as molecules require the bonding of two or more atoms. Additionally, cells are larger organizational units made up of multiple molecules, meaning they represent a higher level of biological structure. Complex carbohydrates also fall into the category of macromolecules, but they themselves consist of multiple smaller molecules (like monosaccharides) linked together, making them more a specific example rather than a definition of what constitutes a molecule.