Final answer:
The nephron loop's structure and function results in higher solute concentration at the bottom of the loop of Henle as compared to the top, mainly due to water being drawn out in the descending limb and ions being transported out in the ascending limb.
Step-by-step explanation:
The question concerns the comparison of solute concentration in the filtrate at different sections of the nephron loop, specifically the loop of Henle. The loop acts as a countercurrent multiplier to create concentration gradients. While the descending limb of the loop of Henle is water permeable, causing water to flow from the filtrate to the interstitial fluid and thereby increasing osmolality inside the limb, the ascending limb features the transport of Na+ and Cl- ions out of the filtrate. Initially, ions exit through ion channels, then further up, Na+ is actively transported out, with Cl- following.
At the bottom of the loop of Henle, the filtrate has the highest concentration of solute due to water leaving the filtrate in the descending limb. Therefore, the concentration of solute is greater at the bottom of the nephron loop than at the top, where active and passive ion transport reduces the filtrate's osmolality.