Plasma Membrane or Cell Membrane


 
 
Concept Explanation
 

Plasma Membrane or Cell Membrane

It is the outer covering of a cell. It separates the cell from its environment. It is a bilipid layer composed of proteins and carbohydrates. Such membranes are also called as the unit membrane.  It is a porous membrane through which selected substances can enter or leave the cell. The cell membrane is also called plasma membrane. The thickness of a unit membrane is about 75 A°.

Functions of Plasma Membrane :-

  • It gives shape to the cell and protect the cell from external injury.
  • Plasma membrane is porous and allows entry and exit  of only selected substances. It also prevents the movement of some other substances across it. Thus, it is called selectively permeable membrane.
  • It provides an outer boundary to the cell and separates cell from one another and also from the surrounding medium. It also protects the cell from injury.
  • In addition, the plant cell and bacterial cell have an outer wall surrounding the cell membrane. This wall is called cell wall. The cell wall in plant cells provides protection against temperature variations, high wind speed and atmospheric moisture.
  • Movement of Carbon Dioxide and Oxygen: 

    ]Movement of carbon dioxide or oxygen across the cell membrane occurs by a process called diffusion. Diffusion is the process of movement of molecules from one region with higher concentration to a region of lower concentration.

                                    

     

    Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    Which of the following membrane is selectively permeable and flexible ?

    Right Option : A
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    Explanation
    Question : 2

    The structure of plasma membrane is consist of ____________________.

    Right Option : C
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    Explanation
    Question : 3

    Unit cell membrane is having average thickness of ____________

    Right Option : C
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    Explanation
     
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