BASIC STRUCTURE OF A CELL

 BASIC STRUCTURE OF A CELL

    Though the cell very greatly in their size and shape, but all of these have a similar basic structure and perform similar basic functions like respiration, etc. in a similar manner.

        So cell is rightly called the fundamental, structural and functional unit of life.

THREE FUNCTIONAL REGIONS OF A CELL 

1) Plasma Membrane

2 2) Cytoplasm

   3) Nucleus

        Cytoplasm and nucleus collectively from the protoplasm. In plant cells, cell membrane is externally covered by a cell wall.

 

1 1) PLASMA MEMBRANE (CELL MEMBRANE)

Position :-

        Outermost, thin, transparent, elastic, porous, regenerative and electron microscopic covering of cell.

Structure :-

        Lipoproteinous (Lipid and Proteins) and trilaminar (3-layered).

Function :-

         ·Acts as semipermeable membrane and regulates exchange of materials between cytoplasm and extra cellular medium.

        ·Protects various cytoplasmic structures.

        ·Provide definite shape.

 

22) CYTOPLASM

Position :-

        A colloidal and viscous ground substance present between the plasma membrane and nucleus.

Structure and Function:-

Ground substance is called matrix which has a number of living structure, called cell organelles, each for specific function.

 

        I.            Cell Organelles (Living Structure)

a.       Mitochondria

·Act as “Power houses” of cell and seat of cell respiration and energy (ATP) formation.

b.      Ribosomes

·Sites of protein synthesis so called protein factories. 

c.       Endoplasmic Reticulum

·Storage and Intracellular transport  of materials.

d.      Golgi Body

·Synthesis and secretion.

e.      Lysosomes

·Intracellular digestion  of  food , germs, etc.

·Autodigestion  after  cellular  death, so  called  suicidal bags.

f.        Centrioles (Only in animal cells)

·Spindle  formation  and  cell  division.

g.       Cilia and Flagella (Generally in animal cells)

·Movement  and  locomotion

h.      Chloroplasts (Only in plant cells)

·Act  as  “kitchens”  of the cell as are sites  of photosynthesis.

      II.            Cell  inclusions  (Non-living  structures)

a.          Starch grains and Glycogen grain

·Starch is stored food of plants.

·Glycogen is stored food of animals.

b.         Vacuoles  (Generaly in Plant cell)

·Store the cell sap.

c.          Urea, Uric  acid  etc.

·Metabolic  wastes

 

3 3)  NUCLEUS

Position :-

    It is found in the centre of a cell.

Structure and Function:-

    Generally there is single, centric, spherical or oval-shaped nucleus.

a.       Nuclear membrane (2-layered porous envelope)

·Regulates  exchange of materials between cytoplasm and nucleoplasm .

b.      Nucleoplasm  (Transparent and colloidal ground substance)

·Seat of RNA and DNA synthesis;  help  in cell division.

c.       Nucleolus

·Formation of ribosomal-RNA

d.      Nuclear Chromatin  (A network of dark coloured chromatin fibres which condense and form chromosome during cell division)

·Carry genes which help in transmission of characters (heredity).