Article- cell organelles- 2. Plasma membrane

     Plasma membrane is otherwise called as cell membrane. It is the outer most covering of animal cell, human cell ..etc. In plants inside the cell wall this membrane is present. It gives shape and protection to the animal cell. It surrounds the cytoplasm of animal and plant cells. It is 7 to 9 nanometers thick.

Structure and functions of Plasma membrane:

                                                                                                       
                                                           

        According to the Fluid mosaic model plasma membrane is made up of proteins and lipids. The lipids are arranged in two layers. One layer is called as polar head region, facing outwards.

     These region  is  attractive towards water and containing phosphate. second one is non polar tail region is non attractive towards water and contains fatty acids are facing each other in the middle of the bilayer. This bilayer contains carbon and hydrogen.

Integral proteins:

      Usually they draw out and twist into threads from one side of the phospholipid bilayer. They are involved in transport of substances .


Peripheral proteins:


      They are arranged in the peripheral way these can move smoothly on a surface. They contain glycoproteins and cholestral . Glycoproteins sit on the one of the surfaces and collide with each other. Cholestral binds together in the plasma membrane reducing its fluidity.

Functions of plasma membrane:

     It gives shape to the cell and it has some functions.

A.Diffusion: 

   In this picture some particles are accumulated in the one corner of the bottle. By the process of diffusion the accumulated particles randomly move around the water, and uniformly organized. In this way transport of small molecules of water, corbon-di-oxide and oxygen can move across the plasma membrane by diffusion.

         B. Osmosis:

              Osmosis is a process in which movement of solvent from the less concentrated to the low concentrated solution through a semi permeable membrane and balance the two unequal concentrated solutions. Plasma membrane is semi-permeable in nature . Generally it is impermeable to large and polar molecules , ions , proteins, polysaccrides and permeable to non polar molecules like lipids , molecules like oxygen corbon- di- oxide and nitrogen.

        C..Endocytosis

                                      

               
        In  this process cells absorb molecules by engulfing them. It is used by all the cells for the transport of water , large objects.

There are three types of endocytosis.

1.Phagocytosis for the transport of actual particles.

2. Pinocytosis for the transport of water with molecules and

3.Receptor mediated endocytosis for importing molecules at low concentration.

         D. Exocytosis

                                  

         This process occurs to remove undigested substances from the cell organelles. In this process the undigested wastes containing food vacuoles is removed from the interior of the cell to the surface. The bilipid layers of plasma membrane rearrange themselves leave a passage and the food vacuoles are discharged its contents outside the cell.