Which statement best describes the fluid mosaic model of membrane structure and how cholesterol content affects membrane fluidity across temperatures?

• A. The membrane is a rigid, static bilayer with fixed proteins.
• B. The membrane is a dynamic phospholipid bilayer with embedded and associated proteins forming a mosaic; fluidity increases with temperature, but cholesterol has no effect on fluidity.
• C. The membrane is a dynamic phospholipid bilayer with embedded and associated proteins forming a mosaic; fluidity increases with higher temperature and decreases with lower temperature. Cholesterol modulates fluidity by restricting movement at high temperatures and preventing tight packing at low temperatures, stabilizing the membrane across temperatures.
• D. Cholesterol has no effect on membrane fluidity.

Answer: (C)

The fluid mosaic model describes a dynamic phospholipid bilayer with proteins embedded or attached, forming a mosaic that can move laterally. The membrane’s fluidity rises with temperature because warmer conditions increase molecular motion, while cooler conditions slow movement and can make the membrane more rigid. Cholesterol acts as a regulator: at higher temperatures it dampens excessive movement of phospholipid tails, reducing fluidity; at lower temperatures it prevents tight packing of the tails, helping maintain a more fluid, permeable membrane. This dual effect keeps membrane structure and function more stable across temperature changes. So the statement that the membrane is a dynamic bilayer with embedded and associated proteins forming a mosaic, with fluidity increasing with higher temperature and decreasing with lower temperature, and cholesterol modulating fluidity by restricting movement at high temperatures and preventing tight packing at low temperatures, best captures the concept.