Which factors are known to increase membrane fluidity?

The correct choice highlights how cis-unsaturated fatty acids and high temperatures contribute to increased membrane fluidity.

Cis-unsaturated fatty acids possess one or more double bonds in their hydrocarbon chains that introduce kinks. These kinks prevent the fatty acid molecules from packing tightly together, resulting in a less ordered and more fluid membrane structure. When temperatures rise, the kinetic energy of the fatty acid chains increases, further enhancing the fluidity of the membrane. Higher temperatures promote movement within the lipid bilayer, allowing for more dynamic interactions that contribute to the overall fluid nature of the membrane.

In contrast, other options include factors that do not facilitate increased fluidity in membranes. For example, saturated fatty acids have straight chains that allow for tight packing, which decreases fluidity. Low temperatures typically solidify membranes, reducing fluidity further. Cholesterol, while it can stabilize membranes, tends to reduce fluidity at high temperatures while preventing solidification at low temperatures. Trans fatty acids, which are often structurally similar to saturated fats, also lead to decreased fluidity due to their straight-chain configuration that encourages tight packing. Elevated pH does not directly affect membrane fluidity in the same manner.

Understanding the relationship between lipid types and temperature is essential for grasping