The membrane surrounding the cytoplasm of the cell is known as “Plasma membrane or Plasmalemma” .It is the outermost layer of animal cell while cell wall is present outside of plasmalemma in plant cell. Plsmalemma is a unit membrane and differentially permeable(permeable for some substances).
Structure - The structure of plasma membrane can be understood by “Fluid-mosaic model” given by S.J.Singer & G.Nicolson in1972. According to this model in the middle of membrane bimolecular lipid layer is present.
Peripheral proteins are present on outer surface of lipid layer while Intrinsic proteins are embedded in lipid layers. Peripheral proteins can be separated easily while intrinsic proteins cannot be separated easily. Peripheral proteins are glycoproteins and some glycolipids are also present with them. Glycoproteins and glycolipids are specific with cells. Cells can recognize cell with same glycoproteins and glycolipid. This specification plays important role in immune response, blood transfusion or organ transplantation.
Functions of Plasmamembrane-
• Plasma membrane maintains the shape of cell and protect it from exterior shocks.
• It prevents the outflow of cytoplasm.
• The membrane of cell organelles like mitochondria ,plastids etc are like PM and performs many functions.
• The plasma membrane performs the functions of diffusion, osmosis and helps the exchange of substances between cell and outer environment.
• It helps in feeding of unicellular protozoans like Amoeba by the process of phagocytosis (cell eating) and pinocytosis (cell –drinking).
