Final answer:
Monosaccharides are transported across the basolateral border primarily by GLUT proteins through facilitated diffusion and SGLT proteins through secondary active transport.
Step-by-step explanation:
Monosaccharides use a variety of transporters to cross the basolateral border of intestinal epithelial cells. The primary transporters involved in this process are the GLUT proteins, specifically for glucose, and the SGLT proteins for both glucose and sodium ions. These transporters facilitate the absorption of dietary glucose from the small intestine into the bloodstream. GLUT proteins are responsible for the facilitated diffusion of monosaccharides, allowing them to move down their concentration gradient. On the other hand, the SGLT proteins engage in secondary active transport, using the energy derived from the transport of sodium ions to move glucose against its concentration gradient. After crossing the epithelial cells, monosaccharides like glucose and galactose enter the capillaries through intercellular clefts. Fructose, on the other hand, is transported predominantly by facilitated diffusion without the co-transport of sodium ions.