• The plasma membrane is the outermost, extremely delicate and elastic membranous that covers the cell and separates the contents of the cell from its external environment is called the plasma membrane. The plasma membrane selectively permeable because it allows the entry of certain substances, the exit of some substances while preventing passage to remaining substances. The plasma membrane is a living flexible membrane.


  1. SHAPE:  The plasma membrane provides a definite shape to the semi fluids contents of the cell.
  2. MECHANICAL BARRIER: The plasma membrane functions as a mechanical barrier that protects the internal contents of the cell.
  3. ENDOCYTOSIS: Endocytosis is a special function of this cell membrane by which it will engulf either foreign particles or food particles. For example, Amoeba is a single cell organism and it has only one cell so that the cell is covered with cell membranes and other substances from its external environment by endocytosis. Amoeba acquires its food by this process.
  4. SELECTIVE PERMEABILITY: The membrane determines what substances are to be allowed entry or exit from the cell.
  5. CELL CONTINUITY: Cell membrane join together and form plasmodesmata and also form cell junction that unites with other cells they join with other cells to form a continuous network or group of cells. In the case of tissues, the cells are not individual and it is dependent they are joined to the adjacent cells and connected by the plasmodesmata.
  6. RECOGNITION: The plasma membrane has substances over its surface which function as recognition centers and points of attachment. They help in tissue formation, a distinction of foreign substances and defense against microbes.
  7. SPECIALIZATION: Plasma membrane gets modified to perform functions, e.g., absorption in microvilli
  8. OSMOSIS: Osmosis occurs due to the presence of tiny water channels in the plasma membrane.


  • The nature of the plasma membrane is
  1. The plasma membrane allows it to pass through it.
  2. It allows certain materials dissolved in water to pass through it.
  3. The plasma membrane will not allow certain materials to pass through it.

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