In addition to the plasma membrane at its outer surface, a eukaryotic
cell has extensive and elaborately arranged internal
membranes that divide the cell into compartments the organelles
mentioned earlier. The cell s compartments provide
different local environments that facilitate speci c metabolic
functions, so incompatible processes can go on simultaneously
inside a single cell. The plasma membrane and organelle
membranes also participate directly in the cell s metabolism,
because many enzymes are built right into the membranes.