Prokaryotic and Eukaryotic Cells

          Organisms are classified based on their level of organization. Prokaryotic cells: Are simply cells that lack membranes around its cytoplasm and lack a true nucleus. A typical example is the bacteria cell (singular: bacterium). A prokaryotic cell is bounded by a plasma membrane but has no other membrane bounding other organelles (Note: cytoplasm is the region were all the organelles of the cell are suspended). A bacteria cell which is an example of a prokaryotic cell has a typical structure of 3 layers; The cell wall, the cell membrane and the slime layer. The slime layer otherwise known as the capsule serves as the protective cover for the cell. Once the capsule which can also be seen in an Escherichia coli is affected, the cytoplasmic membrane can be accessed hence causing harm and eventually death to the cell. Organelles not present in prokaryotic cells include;
   * Mitochondria
   * Golgi body
   * Lysosome
   * Endoplasmic reticulum
The cell wall, cytoplasmic membrane and the capsule are collectively called the CELL ENVELOPE. In a prokaryotic cell due to the absence of mitochondria there is an infolding of the cell membrane to form an organelle called mesosome. This organelle serves the function of the mitochondria which is being the site for respiration.
Functions performed by the bacteria cell wall;

   * It is the site of action of some of the most effective antibiotics
   * It determines the gram staining properties of the cell
   * It is composed of sub-units found no were else in nature

Nutrition in prokaryotic cells;
   * Some are saprophytic while others can be photosynthetic
   * Prokaryotic cells lack ingestive mode of nutrition (i.e they cannot digest food.
   * Possess a small membraned line known as Chromatophore that contains a pigment called Bacteriocholophyll.
   * Others feed on organic substances and secret digestive enzymes.
          In prokaryotic cells, the flagella(flagellum - singular) and cilia are structures which are used as adhesives, digestion and responsible for movement.

Eukaryotic cells:
          Eukaryotic cells are distinctive because of their use of membranes. They have membrane - delimited nuclei and membranes play a prominent part in the structure of many other organelles. (Organelles are intracellular structures that perform specific functions in cells similar to the role of organs in the body of multicellular organisms). The Eukaryotic cell is structurally complex. This complexity is chiefly due to the use of internal membranes for several purposes. Unlike the Prokaryotic cell, the Eukaryotic cell possesses a Mitochondria, a smooth and rough endoplasmic reticulum, golgi apparatus, lysosomes etc.
    * The golgi apparatus consist of stakes or stocks of smooth membranes involved in the processing(adding sugar residues) of secretary proteins.
    * The Lysosomes are membrane -bound structures containing a variety of hydrolytic enzymes that take part in the breakdown of complex materials, including the killing of ingested microorganisms.
    * Mitochondria; a double membraned structure that generates ATP, a compound in which energy is stored in the form of high energy phosphate bonds.
    * The smooth and rough endoplasmic reticulum act as site or the bio-synthesis of certain proteins and hormones.
  All these organelles are surrounded by a cellular plasma membrane which acts to contain the intra-cellular organelles within the Eukaryotic cell.