CBSE Class 9 Answered

It is a model proposed by S.J. Singer and Garth Nicolson in 1972 to describe the structural features of biological membranes.

According to the model, the plasma membrane is a lipid bilayer, interspersed with proteins. It is so because of its phospholipid component that can fold in itself creating a double layer - or bilayer - when placed in a polar surrounding, like water. This structural feature of the membrane is essential to its functions, such as cellular transport and cell recognition

The plasma membrane is described to be fluid because of its hydrophobic integral components such as lipids and membrane proteins that move laterally or sideways throughout the membrane. 

The membrane is depicted as mosaic because like a mosaic that is made up of many different parts, the plasma membrane is composed of different kinds of macromolecules, such as integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol and lipoproteins.