What is a key characteristic of the plasma membrane according to the fluid mosaic model?

The fluid mosaic model describes the plasma membrane as a dynamic structure that allows for movement and flexibility of its components. A key characteristic of this model is that the membrane is not static; rather, it consists of a phospholipid bilayer that has various proteins, cholesterol, and carbohydrates embedded within it. These molecules are able to move laterally within the layer, contributing to the fluid nature of the membrane. This dynamic movement is essential for various cellular processes, including cell signaling, transport, and interaction with the environment.

In contrast, a rigid and unchanging membrane would not be able to perform these functions effectively. The notion of a single layer of phospholipids misrepresents the bilayer structure that is fundamental to the plasma membrane's functionality. Furthermore, while the membrane does regulate the passage of substances, describing it as impermeable to all substances overlooks its selective permeability, which is crucial for maintaining homeostasis within the cell. Thus, the characteristic that emphasizes the dynamic movement of components aligns perfectly with the essence of the fluid mosaic model.