Why is life based upon the cell?

More or less, why are cells necessary for life?

Is there a limit to how large a cell can be?

** If anyone can help or just give me an idea to go on for this it would be helpful! Even a good site to start research!

THANKS!

There may be life elsewhere that is not cellular. On earth it appears to be the only system (other than viruses) Cells are mostly small because they have a large surface area in relation to volume. This allows for sufficient diffusion. Please see:

http://www.tiem.utk.edu/~gross/bioed/bealsmodules/area_volume.html

http://en.wikipedia.org/wiki/Cell_(biology)#Origins_of_cells