Final answer:
Enzymes that transfer phospholipids across a lipid bilayer are known as flippases, which contribute to membrane fluidity and function as described by the fluid mosaic model.
Step-by-step explanation:
The type of enzyme that moves randomly selected phospholipids from one monolayer of a lipid bilayer to the other is called a flippase. These enzymes are critical for maintaining the appropriate distribution of phospholipids between the two layers of a cell membrane's lipid bilayer. Moreover, the fluid mosaic model of cell membranes depicts a dynamic and diverse environment where proteins and lipids can move laterally within the layer, and flippases contribute to this fluidity by relocating phospholipids to maintain the bilayer's stability and function. In addition to flippases, the membrane contains integral proteins and peripheral proteins, which have various roles, including substance transportation and cell signaling.