What does osmosis specifically refer to?

Osmosis specifically refers to the diffusion of water across a selectively permeable membrane. This process is vital for maintaining the balance of fluids in biological systems. In osmosis, water molecules move from an area of lower solute concentration (where there are fewer solute particles) to an area of higher solute concentration (where there are more solute particles). This movement continues until there is an equal concentration of solutes on both sides of the membrane or until other physical pressures prevent further movement.

This process is crucial in cells, as it affects how cells regulate their internal environments, ensuring that they maintain proper hydration and cellular function. Water is essential for countless biochemical reactions and is a key factor in cell volume and pressure.

The other options describe different processes that do not specifically pertain to osmosis. The movement of solutes across a membrane involves different mechanisms such as diffusion or active transport, which pertain to solute molecules rather than water. Active transport of nutrients requires energy input to move substances against their concentration gradients, which is not a characteristic of osmosis. The formation of protein channels refers to the structural components that aid in various types of transport across membranes but does not define osmosis itself.