Science — AI-generated practice question

In hemodialysis, the dialysing fluid must be devoid of nitrogenous wastes so that a concentration gradient exists between the blood (which contains urea and other nitrogenous wastes) and the dialysing fluid. This causes the waste products to diffuse out of the blood across the semi-permeable membrane into the fluid, thereby purifying the blood.

The fluid must have the same osmotic pressure as blood to prevent osmosis of water or useful substances (like salts and glucose) from the blood into the dialysing fluid. If osmotic pressure were different, essential components would be lost from the blood, which would be harmful to the patient.

Source: Chapter 5, Section 5.5.1 – Artificial Kidney (Hemodialysis)

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• Examiners expect two distinct, clearly explained reasons — one per condition. Each reason should name the process involved (diffusion / osmosis).
• Key phrase: concentration gradient drives diffusion of wastes outward; equal osmotic pressure prevents unwanted movement of water or useful solutes.
• Don't just state the conditions — explain why each is necessary. That's where marks are awarded.
• The textbook explicitly states: "This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes… waste products pass into dialysing fluid by diffusion." Use this as your basis.