Scale bar represents 10µm
The plasma membrane consists of a lipid bilayer which encloses the cell and protects it from its surroundings. It enables the selective transport of molecules in and out of the cell, either through passive diffusion or through active transport. Additionally, it takes part in many other cellular processes including signal conduction through receptors embedded in the membrane.
Immunofluorescent staining of the plasma membrane can appear differently. Sometimes the staining appears as a clear rim around the cell and sometimes membrane protrusions extending from the plasma membrane are clearly visible. In other cases the staining can be uniform and flat across the entire cell (since the plasma membrane beneath the cell is stained). For those cases it can be difficult to distinguish between a staining of the plasma membrane and a cytoplasmic staining.
Read more about the proteome of the plasma membrane.