The process in which small molecules (monomers) combine to form large molecules (polymers) with the release of water is known as condensation.

The main chemical structure of the cells is large molecules called macromolecules or polymers. The joining of these unit which are called monomers results in macromolecules. Two monomers join together when a hydroxyl group (OH) is removed from one monomer and hydrogen (H) is removed from another. This is called condensation rection.

     This reaction is also known as dehydration reaction.

The process in which large molecules (polymers or macromolecules) are broken down into monomers by addition of water is known as hydrolysis.

Hydrolysis is a reverse of condensation. In this process hydroxyl group from water attaches to one monomer and hudrogen attaches to the other. This is a hydrolysis reaction because water (hydro) is used to break (lyse) a bond.

This reaction is also known is hydration reaction.