Re: What exactly is the purpose of a cell?

Hi Brianna,

This is an excellent question and i'll try to answer as generally as 
possible, you'll undoubtedly come across some exceptions to what I am about 
to describe, but on the whole this is a good place to start.

Cells ... why ?

The purpose of a cell is to carry out a specific function through 
interactions with its environment for the purposes of maintaining the 
organism.  In the case of single celled organisms such as amoebae or 
bacteria, the cell is the organism and as such the cell/organism does all 
the functions required for the life of the organism, e.g. eating, moving, 
reproduction.  
In the case of multicellular organisms, such as human beings, cells are 
often specialized to carry out specific functions, e.g. nerve cells carry 
electrical impulses around the body, muscle cells contract under 
excitation, intestinal cells absorb nutrients from the digestive tract, red 
blood cells carry oxygen to cells throughout the body, etc.  In the case of 
the human being there are thousands of specialized cells (properly called 
differentiated cells) which carry out a function essential to the whole 
organism.  However, each of these cells themselves are also, in some sense, 
an organism, they can be taken out of the body and grown outside the human 
being and studied.  These in vitro cells are often so specialized that they 
carry out their specified function outside the body, but they do retain the 
ability to move, eat and multiply (although in some cells this ability has 
been turned off in the body).  

So cells are biological units that can eat, move and reproduce.  In single 
cell organisms the single cell carries out all the functions requires to 
keep the organism living.  In multicellular organisms, the individual cells 
can eat, move and reproduce, but they have a specialized function important 
for keeping whole organism alive.

Mitosis ... what is it ?

Cells, as I described above, reproduce as a matter of survival, not of the 
organism but of the genes that the organism carries.  Again, in single 
celled organisms, the reproduction gives rise to two new organisms.  In the 
case of the multicellular organism, mitosis gives rise to two new cells, 
each capable of performing a new function within the organism.

Mitosis is carried out in cells which have nuclei (some cells do not have 
nuclei ... another complicated question !!!).  Mitosis follows replication, 
in which the genetic material of the cell is replicated - two copies are 
made, and represents the process in which 1) the copies of the genetic 
material are separated and taken to opposite ends of the cell and 2) the 
cell volume is divided into two new cells such that each contains one copy 
of the genetic material.  This process thereby has created two equal cells, 
each with the same genetic material.

Thus, mitosis is the process by which individual cells divide.  This 
division is important is maintaining the cells in your body since 
sometimes they get old and can no longer perform their specialized 
function.  Sometimes, however, the division can become uncontrolled, 
nobody exactly knows why, but in the body such uncontrolled mitosis is 
called cancer.

Hope that answers your question ... be sure to check out other references 
... hope i've helped !

take care
...Jagesh...