Final answer:
The fatty acid content of a lipid bilayer affects its fluidity. Saturated fatty acids make the bilayer rigid, while unsaturated fatty acids increase fluidity by creating more space between lipid molecules.
Step-by-step explanation:
The fatty acid content of a lipid bilayer affects its fluidity by influencing the packing and interactions between the lipid molecules. Saturated fatty acids with straight tails pack tightly together, making the bilayer more rigid. On the other hand, unsaturated fatty acids with kinks in their tails create more space between lipid molecules, resulting in a more fluid bilayer. The presence of unsaturated fatty acids weakens the interactions between lipid molecules, allowing them to move more freely.