Final answer:
In the described scenario, water molecules will flow from the pure water (hypotonic solution) to the concentrated sucrose solution (hypertonic solution) through osmosis, which is the movement of solvent molecules through a semi-permeable membrane from a region of high concentration to low concentration.
Step-by-step explanation:
In a scenario where a solution of pure water is separated from a concentrated sucrose solution by a partially permeable membrane, the molecules that will flow are water molecules. This is because water moves from an area of higher concentration (the pure water side) to an area of lower concentration (the concentrated sucrose solution side). This process is called osmosis and will continue until the water concentration is equal on both sides of the membrane, reaching a point of equilibrium where the solutions are referred to as isotonic.
In essence, osmosis is a special case of diffusion that specifically involves the movement of the solvent (in this case, water) through a semipermeable membrane. The driving force behind osmosis is the concentration gradient of the solvent across the membrane, leading to a net transfer of solvent molecules from the hypotonic solution (pure water) to the hypertonic solution (concentrated sucrose solution).