Descibe the structures that form the outside of a prokaryotic cell?

The formed structures outside of the prokaryotic cells are the plasma membranes these are semi-permeable barriers (selective with what passes through and what doesn't). They also have proteins embedded in them for cell signaling and transporting large materials easily inside and outside the cells.
common structures for all prokaryotes are a nucleoid region (the circular DNA), ribosomes, plasma membrane, and a cytoplasm. 
hope that helps!