Which of the following is NOT a macromolecule?

The correct answer is water, as it is not classified as a macromolecule. Macromolecules are large, complex molecules that are essential for various biological functions and include carbohydrates, lipids, proteins, and nucleic acids. They are typically made up of smaller subunits called monomers, which are linked together to form polymers.

Water, on the other hand, is a simple molecule comprised of two hydrogen atoms bonded to one oxygen atom (H2O). It serves as a solvent and is crucial for many biochemical reactions but does not fit the criteria of a macromolecule due to its small size and lack of complex structure. Understanding the distinction between macromolecules and smaller molecules like water is fundamental in biochemistry and biology, as it helps clarify the roles different substances play within living organisms.