Complex sentence: Strictly speaking, there is no periplasmic space in Gram-positive bacteria because there is only one biological membrane, the cytoplasmic membrane, but a region termed inner wall zone (IWZ) has been observed between the cytoplasmic membrane and the mature cell wall.
Split into simpler sentences: Strictly speaking, there is no periplasmic space in Gram-positive bacteria because there is only one biological membrane, the cytoplasmic membrane. A region termed "inner wall zone" (IWZ) has been observed between the cytoplasmic membrane and the mature cell wall.