What is the term used to refer to the combination of the cell membrane and the outer membrane?

The term "cell envelope" accurately describes the combination of the cell membrane (also known as the plasma membrane) and the outer membrane, particularly in the context of prokaryotic cells like bacteria. The cell envelope serves as a protective barrier, regulating the movement of substances in and out of the cell and providing structural integrity.

For Gram-negative bacteria, this structure is especially important because it consists of an inner membrane and an outer membrane, with a periplasmic space in between. The outer membrane contains lipopolysaccharides, contributing to the overall architecture and physiology of the bacteria.

Other options, such as "plasma membrane," refer specifically to the innermost lipid bilayer in cells, while "cytosol" refers to the liquid component inside the cell. "Cellular matrix" is a less specific term that might describe the cytoplasm but does not accurately convey the structural elements that make up the cell envelope. Thus, "cell envelope" is indeed the most appropriate term for the combination of the cell membrane and the outer membrane.