One substance has no membrane transporters to move it but can diffuse freely through open leak channels if there is a concentration gradient.Initially,this substance's concentrations in the filtrate and extracellular fluid are equal.Later,however,the active transport of Na⁺ and other solutes creates a gradient by removing water from the lumen of the tubule where it is located.What substance is this? A) glucose B) calcium C) urea D) glucose and calcium E) glucose, calcium, and urea

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Urea is the only substance mentioned that has no membrane transporters and can freely diffuse through leak channels. The active transport of Na+, ^+,, and removal of water from the lumen of the tubule will create a concentration gradient for other solutes, including urea. Glucose and calcium are not capable of freely diffusing through leak channels and require membrane transporters.

One Substance Has No Membrane Transporters to Move It but Can