Types of cells - Prokaryotes and Eukaryotes

 

 A cell is the basic functional unit of living things. Based on the cellular structures and arrangements, Living things can be classified into;

                                         

                                          ➧ Prokaryotes

                                          ➧ Eukaryotes

 

PROKARYOTES :          

  

• These are the single cell (unicellular) organisms. 
• Prokaryotic cells are very small, simple cells without a nucleus. "kary" means 'nucleus' and "pro" means 'before' thus, the name means "before nucleus". 
• Size is about 0.1-5µm in diameter.
• They also lack membrane-bound organelles and possess cell wall mostly made of complex polysaccharides.
• A Plasma membrane surrounds the cytoplasm. Ribosomes are scattered throughout the cytoplasm.
• They may possess one or more flagella for locomotion. 
• In prokaryotes, DNA or the genetic material is wound together in the nucleoid region of the cytoplasm.

  

                                          

                                Diagramatic representation of Prokaryotic cell

  

Examples : Bacteria and archaea.

 

EUKARYOTES :                     

 

• Eukaryotes are either unicellular or multi-cellular organisms.
• These are large and complex cells.
• They measures about 100µm. Eukaryotic cells have many membrane-bound organelles surrounded by a plasma membrane.
• "Eu" means 'true' and "kary" means 'nucleus' thus, the word Eukaryote means 'true nucleus'.
• Hence they possess a membrane-bound nucleus which contain the DNA or the genetic material. 
• Scientists believes that the Eukaryotes are evolved from prokaryotes before 2.7 billion years ago.

                       
                                                                                                  Diagramatic representation of labelled Eukaryotic cell

                         

Examples : Fungi, animals, plants, protozans.

Eukaryotic cells has number of cell organelles which is essential for the cell functions. They are listed below,

 ORGANELLES AND ITS FUNCTIONS   :

    CELL MEMBRANE : it's the outer boundary which surrounds the cell and its components.

   

     PLASMA MEMBRANE : it's a phospholipid bilayer which surrounds the cell organelles.

    

    CYTOPLASM : or cytosol is the component of the cell which covers the region between the nucleus and cell membrane.

    

    MITOCHONDRIA : power house of the cell. Helps in the formation of ATP (energy-rich molecule).

    

    RIBOSOME : helps in protein synthesis.

   

    GOLGI APPARATUS : they synthesize and packs cell products for cells' own use and for export.

   

    LYSOSOME : it contains degradative enzymes which helps in the digestion of macro-molecules, proteins, etc. Also helps in the removal of phagocytized foreign materials.

    

   ENDOPLASMIC RETICULUM : has two types- rough (RER) and smooth (SER) endoplasmic reticulum which helps in protein maturation.

   

   VESICLES AND VACOULES : empty sacs used for transportation and storage of molecules.

   

   CENTRIOLES : important during cell division.

   

   NUCLEAR ENVELOPE : an envelope which encloses the whole nucleus.

   

   NUCLEUS : it contains DNA, the genetic information necessary for cell activities.

    

   NUCLEOLUS  : normal resting nuclei, present as small round or oval structures.

 

 SIMILARITIES BETWEEN PROKARTYOTIC AND EUKARYOTIC CELLS

   Both the cells have the following features;

• DNA
• ribosomes
• cytoplasm
• plasma membrane