Final answer:
Osmosis is the process by which water flows across a membrane down its concentration gradient, from an area of higher water concentration to an area of lower water concentration.
Step-by-step explanation:
The flow of water across a membrane down its concentration gradient is called osmosis. This process allows water to pass from an area where it is more concentrated, or where there are fewer solutes, to an area where it is less concentrated, or where there are more solutes.
During osmosis, water moves through a semipermeable membrane, which allows the passage of water molecules but not solutes. Osmosis is an example of passive transport and is vital for maintaining cellular integrity and adapting to changes in the extracellular environment.
This natural process relies on aquaporins for the facilitated transport of water and happens without the expenditure of energy by the cell. The diffusion of water continues until there is an equilibrium of solute concentration on both sides of the membrane or until osmotic pressure and hydrostatic pressure balance each other.