Macromolecules

A macromolecule is a molecule large enough that its size, not its functional groups, dominates its behaviour, and the usual way to build one is to join many small units. The repeating unit is the monomer and the large molecule is the polymer, so a polymer is a monomer written many times over. Ethene polymerises to polythene, written with the repeating unit in brackets and $n$ monomers consumed:

$$n\text{CH}_2=\text{CH}_2 \xrightarrow{100\ \text{atm},\ 400^\circ\text{C}} [\text{CH}_2-\text{CH}_2]_n$$

The idea reaches past plastics. Starch is a polymer of $\alpha$-D-glucose, a protein is a polymer of amino acids joined by peptide bonds, and chlorophyll, the pigment of photosynthesis, is a naturally occurring macromolecule built round a single $\text{Mg}^{2+}$ ion. The distinction that matters is origin and route: some macromolecules are natural and some synthetic, and the synthetic ones are the ones whose monomers you are expected to name.