Final answer:
Most solute reabsorption in the proximal convoluted tubule (PCT) is primarily via active transport facilitated by energy from mitochondria and increased surface area provided by microvilli.
Step-by-step explanation:
Most solute reabsorption in the proximal convoluted tubule (PCT) involves active transport processes. The PCT cells have a large number of mitochondria to produce ATP, which is necessary for the active transport of ions such as sodium (Na+) and chloride (Cl-) across their membranes. The presence of microvilli on the luminal surface of these cells also helps to maximize absorption by increasing the surface area. Substances like glucose are reabsorbed along with ions. As sodium is reabsorbed, water follows passively due to osmotic gradients, in a process known as obligatory water reabsorption.