Final answer:
Diffusion is the most important process in the function of an artificial kidney, facilitating the removal of waste such as urea from the blood through a semipermeable membrane in a dialysis machine.
Step-by-step explanation:
The process most important to the function of an artificial kidney is A) Diffusion. In an artificial kidney, or a dialysis machine, diffusion is used to remove harmful substances like urea from the blood.
This is accomplished by passing the patient's blood through a semipermeable membrane, where waste molecules and excess water move from a higher concentration in the blood to a lower concentration in the dialysate. Osmosis, a specific type of diffusion for water, also plays a critical role in dialysis, as it helps equilibrate solute concentrations on both sides of the membrane.