What type of movement allows water to cross a membrane through a semi-permeable barrier?

The correct answer is that osmosis is the type of movement that allows water to cross a membrane through a semi-permeable barrier. Osmosis specifically refers to the passive movement of water molecules from an area of lower solute concentration to an area of higher solute concentration, allowing for the equalization of solute levels on both sides of the membrane.

In the case of a semi-permeable membrane, which allows only certain substances to pass through while blocking others, water is able to move freely while larger solutes remain on one side. This process is essential in maintaining cellular homeostasis and regulating fluid balance within biological systems.

Other processes like diffusion and facilitated diffusion involve the movement of solutes and substances other than water, but they do not specifically pertain to water's unique movement. Active transport, on the other hand, requires energy input to move molecules against their concentration gradient, which is not how water movement through osmosis functions. Thus, understanding the unique nature of osmosis is crucial in the context of fluid dynamics in biological systems.