Which of the following is not classified as a polysaccharide?

The correct answer highlights that sterols in cell membranes are not classified as polysaccharides. Polysaccharides are long chains of monosaccharide units linked together through glycosidic bonds. They are characterized by their carbohydrate nature and include substances such as starch, cellulose, and agar, which are made from sugar monomers.

Cellulose, agar, and dextran all fall under the category of polysaccharides. Cellulose is a structural component of plant cell walls, agar is a gelatinous substance extracted from algae that is used as a solidifying agent in microbiological media, and dextran is a polysaccharide produced by certain bacteria and fungi, often used in medical applications for its properties.

In contrast, sterols are a class of lipids and are not comprised of sugar units; they have a characteristic structure that includes multiple fused carbon rings and are an essential component of cell membranes in eukaryotic organisms, contributing to membrane fluidity and integrity. This distinction is critical for understanding the differences between various biological macromolecules and their functions.