Final answer:
Membrane fluidity is influenced by the saturation level of fatty acid tails in phospholipids, temperature, and cholesterol presence. Unsaturated fatty acids increase fluidity, while saturated fatty acids decrease it. Organisms adjust fatty acid content to maintain fluidity in varied temperatures.
Step-by-step explanation:
Several factors influence the fluidity of cell membranes, with fatty acid composition being a major contributor. Membrane fluidity is affected by the level of saturation of fatty acid tails in the phospholipids. Saturated fatty acids have straight tails and no double bonds, leading to denser packing and decreased fluidity. Conversely, unsaturated fatty acids contain double bonds that create kinks and prevent tight packing, thereby increasing fluidity. Additionally, temperatures play a significant role, with higher temperatures increasing fluidity. The presence of cholesterol can also affect fluidity; it fills the gaps between phospholipids, thus reducing membrane fluidity.
Organisms may adapt to varying temperatures by altering the proportion of unsaturated fatty acids in the membrane. In colder environments, increased unsaturated fatty acids with their kinked tails introduce 'elbow room' that prevents the membrane from becoming too rigid. This ability to adjust fatty acid saturation allows organisms to maintain appropriate membrane fluidity across different temperatures, ensuring proper function and integrity of the cell.