The given blank can be filled with the Fluid mosaic model.
The fluid mosaic model illustrates different observations considering the composition of the functional cell membranes. It describes the membrane of the cell as a two-dimensional liquid, which limits the lateral diffusion of the components of the membrane.
The model illustrates the composition of the plasma membrane as a mosaic of constituents comprising the cholesterol, phospholipids, carbohydrates, and proteins, which gives the membrane a fluid characteristic. This model illustrates that the constituents of the cell membrane shifts spontaneously.