Which of the following factors affects membrane fluidity?

Membrane fluidity is influenced primarily by the composition and structure of the lipids that make up the membrane, and the correct choice highlights the key factors that play a crucial role in this property.

Temperature directly affects the kinetic energy of the molecules within the membrane. As temperature increases, the movement of lipid molecules becomes more vigorous, leading to a more fluid membrane. In contrast, lower temperatures can result in a more rigid membrane as the lipid molecules slow down and pack more closely together.

The presence of cholesterol within the membrane also significantly impacts fluidity. Cholesterol acts as a fluidity buffer; at high temperatures, it helps stabilize the membrane and decrease fluidity, while at lower temperatures, it prevents the fatty acid chains from packing too tightly, thereby maintaining a degree of fluidity.

The types of fatty acids present in the membrane also contribute to fluidity. Saturated fatty acids tend to pack tightly, making the membrane less fluid. Conversely, unsaturated fatty acids, which contain one or more double bonds, introduce kinks in the fatty acid chains. These kinks disrupt the packing of the lipids, resulting in increased fluidity.

Together, these three factors—temperature, the presence of cholesterol, and the types of fatty acids—interact