Biology class 9th (Fundamental unit of life) cell part-03

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  BIOLOGY

                 Fundamental unit of life

                             Part - 3


      #   STRUCTURAL ORGANISATION OF A CELL


  • Each living cell has a capacity to perform certain basic functions that are characteristics of all living organisms.


  • The cell possesses special functions such as making new material in the cell, clearing the waste material, protein synthesis, lipid synthesis, RNA synthesis etc.


NOTE : A cell is able to and undertake all its life functions because of its cell organelles.


  • A typical cell contains three parts :


  1. Plasma membrane or cell membrane


  1. Nucleus


  1. Cytoplasm


  • Plasma membrane or cell membrane


  • This is the outermost covering of the cell that separates the contents of the cell from its external environment.


  • Plasma membrane is a living, thin, elastic and relocated outermost covering of the cell.


  • It is 6 - 8 nanometer thick and is made up of phospholipids and proteins.


  • The plasma membrane is also called selectively permeable membrane.


NOTE :  Movement of water molecules through a selectively permeable membrane is called osmosis.


  •  CELL WALL


  •  Cell wall is a supportive, protective and fully permeable covering present outside the plasma membrane.


  • Cell wall is present in only the plant cell.


  • Plant cell wall is made up of cellulose.


  • The Fungi cell wall is made up of chitin (fungal cellulose).


  • Bacteria cell wall is made up of peptidoglycan.


      #.  Functions of Cell Wall 


  1. It provides mechanical strength and support to the cell.


  1. It protects the cell against pathogens and mechanical injury.


  • NUCLEUS


  • It is a dense protoplasmic body which is described as the control room or brain of the cell.


  • It controls all the cellular activities.


  • It was discovered by Robert Brown.


  • The shape and size of the nucleus depends on different types of cell.


  • It may be spherical, rounded, cylindrical, oval etc.


  • The nucleus is covered by two membranes called nuclear membranes, which form the nuclear envelope.





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