Cells are of two basic types. There are cells without a nucleus, these are the most primitive type of cell and are called prokaryotes. Cell with a nucleus, the cells of plant and animals, are called eukaryotes. [See the section cells in http://www.panspermia.org/whatis2.htm.] Common to both types of cell are:
The aqueous interior of a cell indicates that cell evolved in an aqueous environment.
The mechanism whereby the cell wall evolved is an important step in the emergence of living organisms (see http://cmex-www.arc.nasa.gov/VikingCD/Puzzle/Early.htm).
One model is that small bubbles of iron sulphide material, were the precursors to biological cells.
An alternative explanation is that there is an interstellar origin for organic molecules and cell like shapes. (See http://www.seti.org/science/clues_origin_life.html.)