The Cell Membrane is found in both plant and animal cells. The function of the Cell Membrane is to hold the cytoplasm inside the cell and to also control the movement inside and outside of the cell. The cell membrane is on the outside of an animal cell since it has to hold everything in, but in a plant cell it is almost on the outside and is placed right before the cell wall. Without a Cell Membrane all of the cytoplasm would just fall out of the cell and there would be no more cell.