What is a macromolecule formed when monomers join together?

Answer

Well, monomers of what? If it is monomers of a sugar than it would be a monosaccharide, and when joined a disaccharide. If it is just a monomer in the general term, it when joined it would be a dimer. You see mono in the beginning of the word means 1, while di means 2. If even more monomers were joined it would be tri and tetra and on and on. However anything more than two can be called a polymer, poly meaning many.

Other monomers of macromolecules include nucleotides, and amino acids.