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Science Animation:  Cell Membrane

This cell membrane animation shows the function of a cell membrane (selective cell membrane permeation is shown). The cell membrane is a biological membrane separating the cell's interior from the outside environment. The cell membrane is selectively permeable to ions and organic molecules. It controls the movement of substances into and out of cells. Small polar molecules, such as water and ethanol, can pass through the cell membrane. Cell membranes may also restrict diffusion of highly charged molecules, such as ions, and large molecules such as sugars and amino acids.