The cell membrane is a slim semi-permeable membrane which surroundings the cytoplasm of a cell. Membrane function is to defend the integrity of the interior of the cell by allowing assured substances into the cell, though keeping other substances out. It also gives as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane also serves to help support the cell and help preserve its shape. Plant cells, prokaryotic cells, fungal cells and Animal cells which have cell membranes.