Diffusion of small waste molecules in dialysis

Steps:

• Dialysis mimics kidney function by filtering blood across a semi-permeable membrane.
• Small molecules diffuse from high concentration in blood to low in dialysis fluid.
• Urea, a waste product, is small and excess in blood, so it diffuses out.
• Salts (ions) are also small and balanced by diffusion to match fluid levels.

Why C is correct:

• In dialysis, the membrane allows small solutes like urea (waste) and salts (electrolytes) to pass via diffusion, removing toxins while retaining larger components.

Why the others are wrong:

• A: Proteins are large molecules blocked by the membrane.
• B: Platelets are cells too large to pass; proteins are retained.
• D: Platelets are cellular components that do not diffuse across the membrane.

Final answer: C