What is CelI. Its Structure and Functions

What is celI. its structure and functions

The structural and functional unit of all the organisms or living beings
is called cell and the shape and size of the cell are different. The shape and
size of the cells are not only different for various organisms but the cells are
also different in the same organism of the different organs. Also unicellular
organisms have different shape and size of their cells. The shape and size of
the cells completely depend on the metabolic activities while their numbers
depend on the size of organs and the body of the organism. Thus smaller
organism has limited cells, while larger organism like elephant, whale, jack
tree etc. have unlimited (uncounted) cells. Usually in human body nearly
104 cells exist.
The cell was firstly invented by an English Scientist Robert Hook in
1665 and he asserted that cell has been made from a life saving substance.


Leter in 1939 j.e.  Purkinje pointed out that this life saving substance is
protoplasm which is the physical base of the life and in protoplasm nearly
807 water is to be found. Further protoplasm is also of two types
Cytoplasm and Nucleoplasm. In the cell cytoplasm is confined between
the nucleus and cell membrane, while Nucleoplasm is confined inside the
Nucleoplasm.

Cell theory : The cell theory was jointly propounded by a botanist
Schleden and a Zoologist Schwann in 1818-1839. The main points regarding
the cell theory were:-
1. Every organism originates from a cell.
2.The body of every organism is made from one or more cells.
3. The cell is a self independent unit, although it takes part in the
metabolic activities and with other cells form an organism.
4.The process through which thecellisformed hasa complex mechanism
but the core of the cell is nucleus.

Cell structure: The cells have varioustypes of structures like cylindrical,
elliptical, spherical, transverse ete.
Almostall cells have three maincomponents-Cell membrane, Nucleus
and Nucleoplasm.

Cellular Components
Cell membrane: The cell membrane of the cell is a outer layer of the cell
and it is basically a semipermeable membrane. The main function (work)
of the cell membrane is to control the molecular activities between the cell
and its outer medium which interacts with the cell.

Cell wall : The cell wall is only found in the plant cells, The cell wall
is made from a non-living substance and in various plant communities
the composition of the cell walls are different. The cell wall of algaes and
developed green plants are made from the cellulose, while the cell walls of
bacteria and fungi are made from the carbohydrate. The main function of
the cell wall is to protect nucleoplasm and cell membrane from the external
invasion (attack).

Nucleus: The nucleus of the cell was invented by Robert Brown in 1831
and it is spherical orelliptical. Thenucleus is confined near the cellular centre
of the cell. This is the controlling centre of almost all activities taking place
inside the cell.
There are various components of the nucleus of the cell like nuclear
membrane, nucleoplasm, nucleolus, nuclear network etc.

Nuclear membrane: The nuclear membrane is made from the two
yer's membrane through which nucleus of the cell is surrounded. The
leyer's membrane is made of protein and fat. In every nuclear membrane
co holes exist through which cytoplasm and nucleoplasm exchange in
e cell, The outer layer of the nuclear membrane is connected through the
endoplasmic reticulum of the cell.

Nucleoplasm: The nucleoplasm is the protoplasm of the inside nucleus
e cellThe nucleoplasm is basically made from protein, phosphorous
and nucleic acids which are abundantly found in it.

Nucleolus: There is one or more spherical structures inside the nuclens
of the cell is called nucleolus.
The main funstions of the nusleolus are-