Final answer:
In hemodialysis, the dialysate should have a lower solute concentration than the blood to facilitate the diffusion of urea from the blood to the dialysate.
Step-by-step explanation:
Patients with kidney illnesses use dialysis machines to remove harmful urea from their blood. The blood is separated from a solution, called the dialysate, that is designed to remove wastes by diffusion through a semipermeable membrane. In the process of hemodialysis, the dialysate should have a lower solute concentration than the blood. This difference in solute concentration allows urea to move from the blood, where it is at a higher concentration, to the dialysate, where its concentration is lower. This movement down the concentration gradient occurs according to the principles of diffusion, not active transport or facilitated diffusion.