Which term is used for small carbohydrate molecules often composing larger structures in biological systems?

The term used for small carbohydrate molecules that often compose larger structures in biological systems is "simple sugars." Simple sugars, also known as monosaccharides, are the most basic form of carbohydrates, composed of single sugar molecules such as glucose and fructose. They serve as the building blocks for larger carbohydrates, such as disaccharides (which consist of two simple sugars) and polysaccharides (which are long chains of simple sugars).

These small molecules play critical roles in metabolism and energy production, making them fundamental to various biological processes. For instance, when simple sugars are linked together, they can form more complex structures like starch and glycogen, which are essential for energy storage in organisms.

In contrast, the other options refer to different types of biological molecules. Complex carbohydrates are composed of many simple sugars linked together, polypeptides are chains of amino acids that make up proteins, and monoglycerides are a type of lipid consisting of glycerol and one fatty acid. Thus, "simple sugars" accurately describes the small carbohydrate molecules that form larger biochemical structures.