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

Question

Quizplus · Accepted Answer

Urea is the only option that fits the given description: it has no membrane transporters but can diffuse through leak channels, and its concentration gradient is created by the active transport of other solutes. Glucose and calcium both have membrane transporters, and therefore would not rely solely on diffusion through leak channels.

One Substance Has No Membrane Transporters to Move It but Can