The passage of fluid to an organ or tissue is called?

• A. Diffusion
• B. Filtration
• C. Osmosis
• D. Perfusion

Answer: (D)

The main idea being tested is how fluid reaches tissues, which is described by perfusion. Perfusion refers to the flow of blood through the vessels to an organ or tissue, delivering oxygen and nutrients and carrying away wastes. This is the whole-tissue delivery concept, not just movement of water or solutes at the cellular level.

Diffusion is the spread of molecules from high to low concentration, usually within a space or across membranes, and Osmosis is the movement of water across a semipermeable membrane due to solute differences. Filtration involves fluid and solutes moving across a barrier due to pressure differences, such as in capillary exchange. While these are important processes, they describe mechanisms of movement at smaller scales or under specific conditions, rather than the overall delivery of fluid to tissue, which is perfusion.