Cell the unit of life

about the fundamental unit of life which a cell , without a cell there's no existence of being living. It's a defining feature of every living organism. Virus are not considered in this category because they are just Protein crystals outside the cell they also need a host machinery or more appropriately a cell machinery for it's functioning.

Cell are of two types 

Prokaryotic ones which do not have well defined nucleus no membrane bound organelles 

So basically primitive cells are prokaryotes which lack advance organelles and membrane bound systems such as bacteria.

The second type of cell is Eukaryotic cells which are advanced type of cells contains membrane bound nucleus and organelles.

There are two type of organisms first one unicellular means they only have is a single cell which performs all essential functions of a living.

Second one multicellular means there are a group of cells in which each set of group perform specific function.