The fluid-mosaic model, proposed by S.J. Singer and Garth L. Nicolson in 1972, is a widely accepted model that describes the structure and function of the cell membrane. The model explains that the cell membrane is composed of a fluid phospholipid bilayer with various proteins embedded or associated with it. The key features of the fluid-mosaic model are as follows:1. Fluidity: The phospholipid bilayer is not a rigid structure but rather a fluid matrix. The phospholipids are not covalently bonded to each other, allowing them to move laterally within the bilayer. This fluidity is essential for the proper functioning of the cell membrane, as it allows for membrane flexibility, self-healing, and the movement of proteins within the membrane.2. Mosaic of proteins: The cell membrane contains a diverse array of proteins that are either embedded within the phospholipid bilayer integral proteins or loosely associated with its surface peripheral proteins . These proteins serve various functions, such as transport, signal transduction, cell adhesion, and enzymatic activity. The mosaic nature of the proteins allows for a high degree of functional diversity within the cell membrane.3. Asymmetry: The two layers of the phospholipid bilayer are not identical. The composition of lipids and proteins can vary between the inner and outer leaflets of the bilayer. This asymmetry is important for maintaining the proper orientation of membrane proteins and for the selective transport of molecules across the membrane.4. Selective permeability: The phospholipid bilayer acts as a barrier to the free passage of most polar and charged molecules, while allowing the passive diffusion of small, nonpolar molecules such as oxygen and carbon dioxide. The embedded proteins, particularly the transport proteins, facilitate the selective transport of specific ions and polar molecules across the membrane, maintaining the appropriate balance of substances within the cell.5. Dynamic nature: The cell membrane is constantly undergoing changes in its composition and organization. Proteins and lipids can be added or removed, and their positions within the membrane can change. This dynamic nature allows the cell membrane to adapt to changes in the cell's environment and to perform its various functions efficiently.In summary, the fluid-mosaic model explains the structure and function of the cell membrane by describing it as a fluid phospholipid bilayer with a diverse array of proteins embedded or associated with it. This model accounts for the membrane's flexibility, selective permeability, and ability to adapt to changes in the cell's environment.