The reaction that links monomers to form a polymer is called dehydration synthesis (also known as condensation reaction).

Here's why:

* Dehydration: A molecule of water is removed from the monomers.

* Synthesis: New bonds are formed, creating a larger molecule (the polymer).

This process is essential for building all the macromolecules that make up living organisms, including carbohydrates, lipids, proteins, and nucleic acids.