How does reabsorption of water occur in the nephrons?

The correct choice highlights that water reabsorption in the nephrons primarily occurs through the process of osmosis. In the nephron, particularly in the renal tubule segments like the proximal convoluted tubule and the loop of Henle, water is reabsorbed from the filtrate back into the bloodstream.

Osmosis is the movement of water molecules across a semipermeable membrane from an area of lower solute concentration to one of higher solute concentration. In the nephron, as solute concentrations increase in the interstitial fluid surrounding the tubules (due to the active transport of solutes like sodium), water moves into the surrounding capillaries to equalize the solute concentrations. This mechanism is essential for the regulation of body fluid balance and maintaining homeostasis.

While other processes such as direct diffusion, active transport, and facilitated diffusion are involved in renal function, they do not primarily account for the reabsorption of water in nephrons. Direct diffusion primarily applies to small nonpolar molecules, active transport involves the energy-dependent movement of substances against a concentration gradient (mainly for solutes), and facilitated diffusion pertains to the movement of specific molecules across cell membranes via transport proteins but does not primarily refer to water movement