The structural unit of a carbohydrate is a monosaccharide, which is a simple sugar molecule. Common examples include glucose and fructose. Monosaccharides can combine through glycosidic bonds to form larger carbohydrate molecules such as disaccharides (e.g., sucrose) or polysaccharides (e.g., starch, cellulose). These compounds serve various roles in biological systems, including energy storage and structural support in plants. Understanding monosaccharides is fundamental in biochemistry, nutrition, and understanding metabolic pathways involving carbohydrates, which are crucial for life.