The Cell Membrane: Structure and Function

The cell surface membrane (also called the plasma membrane) is a fundamental structure in all living cells. Understanding its structure and function is central to Edexcel A-Level Biology (9BI0) Topic 2. The fluid mosaic model proposed by Singer and Nicolson (1972) is the accepted model of membrane structure and is a key concept you must be able to describe and explain.

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The Fluid Mosaic Model

The fluid mosaic model describes the cell membrane as a dynamic structure consisting of a phospholipid bilayer with various proteins embedded in it or attached to its surface.

The name "fluid mosaic" reflects two key properties:

• Fluid — the individual phospholipid molecules and proteins are not fixed in place; they can move laterally within the plane of the membrane (lateral diffusion)
• Mosaic — the membrane contains a diverse array of proteins scattered throughout, creating a mosaic-like pattern when viewed from above

Components of the Cell Membrane