Which substance must be further digested before it can be absorbed by specific carriers in intestinal cells?

The substance that must be further digested before it can be absorbed by specific carriers in intestinal cells is sucrose. Sucrose is a disaccharide composed of glucose and fructose linked together. In order to be absorbed through the intestinal lining, sucrose must first be broken down into its constituent monosaccharides. This digestion occurs via the action of the enzyme sucrase, which hydrolyzes sucrose into glucose and fructose. Only the monosaccharides, glucose and fructose, can then be absorbed by specific transporters located in the intestinal epithelial cells.

In contrast, lactose is also a disaccharide that requires digestion, primarily by lactase, into glucose and galactose for absorption. However, it is not the primary focus in this context. Fructose and glucose, on the other hand, are monosaccharides and do not require further enzymatic breakdown; they can be readily absorbed by the transport mechanisms present in the intestinal cells without the need for additional digestion. Therefore, sucrose uniquely requires prior digestion to be absorbed effectively.