Why do sharks have high urea concentrations?

Biology 20 question: A Dialyzing Machine Has A Membrane...?

• Hello, I am a biology student and am having trouble with this question if anyone could help me out: "A dialyzing machine has a membrane that is permeable to water, urea, uric acid, ammonia, salts, and glucose. The membrane is impermeable to protein molecules. In relation to the blood flowing through the dialysis machine, the dialyzing solution must have A. Lower concentration of glucose and protein B. Lower concentration of urea, uric acid, and ammonia, and higher or equal concentration of glucose C. The same concentrations of urea and salts D. Higher concentration of urea, uric acid, and ammonia, and lower or equal concentrations of glucose" If you can help me out it would be absolutely fantastic! Thanks :)

• Answer:

  Lower concentration of urea, uric acid, and ammonia, and higher or equal concentration of glucose. The dialyzing fluid has to receive the excess of these metabolites so they mist be in a lower concentration (gradient) so they will pass through.