A student is experimenting with a substance that moves into the cell via facilitated diffusion. The student notes that as the concentration of the substance outside of the cell increases, the rate of movement of the substance into the cell increase and then plateaus. What explains the phenomenon seen by the student?

The phenomenon seen by the students is Osmosis.

Explanation:

Osmosis is the movement of molecules from higher concentration to lower concentration through a semi-permeable membrane. This type of movement of molecules occurs in the body cells. When the concentration of molecules is higher outside the cell than the inside, the molecules goes inside the cell through semi-permeable membrane.