Final answer:
The synthesis of unsaturated fatty acids increases membrane fluidity due to the kinks in their hydrocarbon tails that create more space within the membrane for movement.
Step-by-step explanation:
The enhanced rate of synthesis of unsaturated fatty acids is likely to increase membrane fluidity. Unsaturated fatty acids have kinks or bends in their hydrocarbon tails due to the presence of double bonds, which push apart the phospholipid tails. This additional space allows for more movement within the membrane, making it more fluid. In contrast, cholesterol serves to stiffen membranes by filling in gaps between phospholipids, which decreases fluidity. Additionally, organisms in cold environments may adapt by increasing the unsaturated fatty acid content in their cell membranes to maintain fluidity, despite compressive forces that make membranes less fluid and more rigid.