5. Cell Structure And Organization - part 03 - Cell wall

 


5. Cell Structure And Organization - part 03 - Cell wall


Eukaryotic Cells :

  • Cells in which the nucleus has a definite nuclear membrane are known as Eukaryotic cells. 
  • These cells exhibit presence of membrane bound cell organelles. 
  • e.g. Cells of Protists, Plants, Animals and Fungi.
  • The eukaryotic cells have different shape, size and physiology but all the cells are typically composed of-  
  1. plasma membrane
  2. cytoplasm and its organelles viz. Mitochondria
  3. Endoplasmic Reticulum
  4. Ribosomes
  5. Golgi complex, etc. and 
  6. a true nucleus.

Components of Eukaryotic cell :

1. Cell wall: 

  • It is rigid, supportive and protective outer covering of plasma membrane of plant cells, fungi and some protists. 
  • Algae show presence of cellulose, galactans, mannans and minerals like calcium carbonate in cell wall. 
  • In other plants, it is made up of hemicelluloses, pectin, lipids and protein.
  • Microfibrils of plant cell wall show presence of cellulose which is responsible for rigidity. 
  • Some of the depositions of cell wall are -
  1. silica (grass stem)
  2. cutin (epidermal walls of land plants)
  3. suberin (endodermal cells of root)
  4. wax
  5. lignin.
  • It gives shape to the cell and protects from mechanical injury and infections.
  • In plants, cell wall shows - 
  1. middle lamella
  2. primary wall and 
  3. secondary wall.

Middle lamella : 

  • It is thin and lies between two adjacent cells. 
  • It is the first structure formed from cell plate during cytokinesis. 
  • It is mainly made up of -
  1. pectin
  2. calcium and 
  3. magnesium pectate. 
  • Softening of ripe fruit is due to solubilization of pectin.

Primary wall : 

  • In young plant cell, it is capable of growth. 
  • It is laid inside to middle lamella.
  • It is the only wall seen in -  
  1. meristematic tissue
  2. mesophyll
  3. pith, etc.

Secondary wall : 


  • It is present inner to primary wall. 
  • Once the growth of primary wall stopps, secondary wall is laid. 
  • At some places thickening is absent which leads to formation of pits.
  • Plasmodesmata are cytoplasmic bridges between neighbouring cells. 
  • It shows pores between cell wall and middle lamella.

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