The structures that present interior to the cell wall include cell membrane, mesosomes, cytoplasm, nuclear material, cytoplasmic inclusions and vacuoles.
i) Cell membrane (or) cytoplasmic membrane:
Immediately beneath the cell wall there is a thin membrane around the cytoplasm. This membrane is called the cytoplasmic membrane or plasma membrane. It contains phospholipids, proteins and polysaccharides. The cell membrane is a vital structure and critical barrier that seperates the inside of the cell from the outer environment. The most widely accepted current model for cell membrane structure is the fluid mosaic proposed by Singer and Nicholson.