Polymers are molecules made from a large number of monomers joined together.

Welcome to this A-Level AQA Biology breakdown on monomers and polymers. A polymer is a large molecule made from many monomers joined together in a chain. The joins are made by condensation reactions, with one chemical bond formed and one water molecule released per join. In this video we will connect the monomer, the bond and the chain arrangement, then apply that to exam figures involving polysaccharides, polypeptides and polynucleotides. Think of polymer structure as a concept map. At the centre are monomers—many small units. They join by condensation to form a polymer chain. The guide gives three named families: starch, glycogen and cellulose are polymers of glucose; polypeptides are polymers of amino acids; DNA and RNA are polynucleotides. But the monomer alone does not determine properties. Chain arrangement matters too: straight versus branched, 1,4 backbone linkages, 1,6 branch points, and alternate beta monomers flipped through 180 degrees. Core notes: always state that a polymer is many monomers joined together, formed by condensation, with one water molecule released per bond formed. Name the bond in a named example—glycosidic bonds in a polysaccharide, or peptide bonds in a polypeptide. Describe the chain as straight, linear or unbranched where the diagram shows it, and identify 1,4 linkages in the backbone. Cellulose and chitin chains are straight and unbranched because alternate beta monomers are flipped through 180 degrees, so their hydroxyl groups line up and hydrogen bonds form between neighbouring chains. Now follow the assembly process. Monomers are brought together, and a condensation reaction joins them into a chain, releasing one water molecule for each bond formed. The resulting backbone may show 1,4 linkages. If alternate beta monomers are rotated or inverted through 180 degrees, their hydroxyl groups can line up, letting hydrogen bonds form between neighbouring straight chains—as in cellulose and chitin. Branching is different: amylopectin and glycogen carry 1,6 branch points, while amylose coils into a helix. Branching produces a more compact molecule with more free ends for rapid hydrolysis. Let’s work through an exam-style figure question. The question says: use Figure 1 to describe the structure of the polymer shown. Step one: read the monomer directly from the figure. Step two: identify the bond—glycosidic if it is a polysaccharide, peptide if it is a polypeptide. Step three: describe the chain shape as straight, linear or unbranched if that is what the drawing shows, and identify 1,4 linkages in the backbone. Step four: check for flipped monomers—alternate beta monomers rotated 180 degrees—and for hydrogen bonds between neighbouring chains. Step five: mention 1,6 linkages only if branch points are visible. A strong answer uses the figure, not a memorised example. Watch for common pitfalls. Do not offer that both polymers contain carbon, hydrogen and oxygen as a structural similarity—structure means monomer, bond, chain shape and chain interactions. Do not state that a straight, unbranched polymer such as cellulose or chitin contains 1,6 bonds; 1,6 bonds occur only at branch points. Do not say both molecules are polysaccharides when the question has already told you that. Do not call a triglyceride a polymer of fatty acids—triglycerides are not polymers because no repeating chain is formed. And never describe a polymer as 'lots of molecules stuck together' without naming the bond or the condensation reaction. When a question says use Figure 1, every point must be visible in the figure. To recap: a polymer is many monomers joined by condensation, with one water molecule released per bond. Name the bond—glycosidic in a polysaccharide, peptide in a polypeptide. Describe the chain as straight, linear or unbranched where shown, and identify 1,4 linkages in the backbone. Note alternate monomers flipped 180 degrees in cellulose and chitin, allowing hydrogen bonds between chains. Mention 1,6 linkages only where branching is shown; branching makes a more compact molecule with more free ends for rapid hydrolysis. And when you meet an unfamiliar polymer diagram, read the monomer, the bond and the chain shape directly from the figure.