Osmosis of water primarily occurs via simple diffusion. It is the process by which water molecules move from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane.
Here’s how it works: Water is a small, polar molecule that can pass through the lipid bilayer of cellular membranes, although this process is generally slow. However, in biological systems, water often moves more efficiently through specialized channels known as aquaporins, which facilitate the flow of water. This process is distinct from facilitated diffusion as it specifically refers to the passive movement of water molecules without energy expenditure, relying on concentration gradients.
Active transport, on the other hand, involves the movement of substances against their concentration gradient and requires energy, typically in the form of ATP. Secondary active transport utilizes the energy from the electrochemical gradient created by primary active transport to move other molecules, not applicable to water’s osmosis. Therefore, while there are several mechanisms of transport in cells, osmosis is best described as a type of simple diffusion, often facilitated by specific proteins like aquaporins to enhance the process.