A polymer is a large molecule made up of many identical monomers. Polymers are made when monomers are combined by condensation.
Condensation involves molecules joining together with the release of water.
Polymers can be broken down into monomers by hydrolysis. This occurs when molecules of water are added to the polymer causing the bonds between the monomers to break up. Important biological polymers include polysaccharides, proteins and nucleic acids. These polymers may also be described as macromolecules - a word that simply means large molecules. So all polymers are macromolecules but not all macromolecules are polymers.