Final answer:
Glucose and galactose use active transport with secondary active co-transport with sodium ions, and facilitated diffusion to move across the basolateral side of enterocytes. Fructose is absorbed only through facilitated diffusion, as it moves down its concentration gradient.
Step-by-step explanation:
Glucose (Glu), galactose (Gal), and fructose are monosaccharides that move across the basolateral side of enterocytes by different mechanisms during the process of carbohydrate absorption. Glucose and galactose are absorbed into the bloodstream through active transport and facilitated diffusion, whereas fructose is absorbed only by facilitated diffusion.
For Glu and Gal, the initial step involves the monosaccharides being transported into the epithelial cells of the small intestine by a common carrier protein through a form of active transport known as secondary active transport. This co-transport with sodium ions allows the sugars to move against their concentration gradient. After entering the cell, Glu and Gal diffuse to the basolateral side where they are then transported into the bloodstream.
On the other hand, fructose enters the enterocytes via facilitated diffusion, a process that does not require energy, since it transports the sugars down their concentration gradient by attaching to another type of carrier protein.