Final answer:
Hemodialysis uses negative pressure to pull the blood from the access and remove waste molecules through a semipermeable membrane.
Step-by-step explanation:
In hemodialysis, the blood is pulled from the access using negative pressure. The patient's blood is passed through a semipermeable membrane in the dialyzer, where waste molecules and excess water are removed through diffusion. Red and white blood cells remain in the blood as they are too large to pass through the membrane. After being cleansed, the blood is returned to the body. This process relies on osmotic pressure and the semipermeable nature of the membrane to selectively remove waste molecules from the blood.