Answer the following question given this paragraph: 

Cell transport refers to the movement of substances across the cell membrane. Probably the most important feature of a cell’s phospholipid membranes is that they are selectively permeable. A membrane that is selectively permeable , or semipermeable, has control over what molecules or ions can enter or leave the cell, as shown in Figure below . This feature allows a cell to control the transport of materials, as dictated by the cell's function. The permeability of a membrane is dependent on the organization and characteristics of the membrane lipids and proteins. In this way, cell membranes help maintain a state of homeostasis within cells (and tissues, organs, and organ systems) so that an organism can stay alive and healthy.


Q: Cell transport refers to the movement of substances across what structure?


A:
cell membrane