Starch is a polymer. It is made up of many glucose units linked together in long chains. These chains can be either straight (amylose) or branched (amylopectin). The process of linking these glucose monomers through glycosidic bonds results in the formation of a large, complex molecule — a polymer.
In simpler terms, a monomer is a single building block that can join with other monomers to form larger structures. Since starch is composed of numerous glucose monomers joined together, it meets the criteria of a polymer, which is defined as a large molecule made up of repeating subunits. This molecular structure plays a crucial role in its function as an energy storage molecule in plants.