Natural or synthetic

Remember the polymers studied above. All of them were synthesised artificially. Have you heard of natural polymers?

Think back to the biological molecules you learned about in grade 10. Molecules such as proteins, starch, cellulose and DNA are polymers; they belong to the natural polymers. So by origin, polymers can be divided into two groups: natural and synthetic. Rubber, used widely in industry, is also a natural polymer.

Why living things build polymers

A cell cannot store energy or build a body from single glucose molecules or single amino acids: they dissolve and wash about. Linking them into long chains gives molecules too big to escape, with new properties. Plants join glucose into starch to store food and into cellulose to build strong cell walls; our cells join amino acids into proteins, and nucleotides into DNA to store genetic information. The monomers differ, but the idea is the same as polythene: small units joined over and over into a very large molecule.