Water reabsorption in capillaries via osmosis

Steps:

• Identify water movement from tissue fluid (lower solute concentration) to capillary blood (higher solute concentration due to proteins).
• Recognize capillaries as semi-permeable, allowing passive water flow.
• Recall osmotic pressure gradient drives water back into blood at venous end.
• Conclude process matches osmosis definition.

Why C is correct:

• Osmosis is diffusion of water across a semi-permeable membrane from low to high solute concentration, as per the osmotic pressure law (π = iCRT).

Why the others are wrong:

• A: Active transport uses ATP for solutes against gradients, not passive water movement.
• B: Active pressure is not a biological process; hydrostatic pressure aids filtration, not reabsorption.
• D: Assimilation involves nutrient incorporation into cells, unrelated to fluid exchange.

Final answer: C