Final answer:
The fatty acid tails of phospholipids and cholesterol in the cell membrane help moderate membrane fluidity.
Step-by-step explanation:
The fatty acid tails of phospholipids in the cell membrane help moderate the fluidity of the membrane. In their saturated form, the fatty acid tails are straight, while unsaturated fatty acids have double bonds that create bends in the carbon chain. These bends increase the space between the tails, making the membrane more fluid and allowing its components to move more freely.
Another factor that helps maintain membrane fluidity is the presence of cholesterol. Cholesterol acts as a buffer against temperature changes, preventing lower temperatures from inhibiting fluidity and higher temperatures from increasing fluidity too much. It extends the range of temperature in which the membrane is appropriately fluid and functional.