Final answer:
The correct statement regarding solute reabsorption in the nephron is that Na+ is reabsorbed from all parts of the nephron, which is key for fluid and electrolyte balance in the body, significantly affecting the osmolarity of the filtrate.
Step-by-step explanation:
The correct statement about solute reabsorption is b) Na+ is reabsorbed from all parts of the nephron. In the kidneys, sodium (Na+) plays a pivotal role in regulating the fluid and electrolyte balance. During the filtration process within the nephron, Na+ is actively and passively reabsorbed at various segments, including the proximal convoluted tubule (PCT), ascending limb of the loop of Henle, distal convoluted tubule (DCT), and collecting ducts.
As the filtrate moves through the PCT, water, and sodium are reabsorbed mainly through active transport. The osmolarity of the filtrate is affected by the reabsorption process, where osmolality increases as water leaves in the descending limb due to the presence of aquaporins. In the ascending limb of the loop of Henle, Na+, and Cl- are removed through ion channels, and higher up, sodium is actively extruded. This active transport of ions has a critical impact on the osmolarity of the filtrate, which is central to kidney function in maintaining body fluid homeostasis.