Final answer:
Fructose crosses the apical border of intestinal cells through facilitated diffusion using specific carrier proteins, without the need for ATP.
Step-by-step explanation:
Fructose is transported across the apical border using a carrier protein called Na+/glucose symport protein. This symport protein assists in the movement of both Na+ and glucose into the cell from the tubular lumen. The transport of fructose is considered facilitated transport, as it does not require energy (ATP).
The transporter that fructose uses to cross the apical border of intestinal cells is known as a facilitated transport system. Unlike glucose, which can be transported by SGLT proteins (sodium-glucose transport proteins) that function as part of secondary active transport systems, fructose enters cells via a different mechanism. Fructose is moved across cell membranes through facilitated diffusion, which is a form of passive transport that does not require energy in the form of ATP. Instead, fructose uses specific carrier proteins that allow it to cross the cell membrane due to the concentration gradient, moving from an area of high concentration to one of lower concentration.