Final answer:
Option d)Enhanced membrane rigidity would most likely be observed if lower phospholipid levels are due to the inhibition of fatty acid synthesis, as this would decrease the number of unsaturated fatty acids that increase membrane fluidity.
Step-by-step explanation:
If lower phospholipid levels are due to inhibition of fatty acid synthesis, then researchers would most likely observe d) enhanced membrane rigidity.
This outcome is due to the relationship between the fatty acid composition of phospholipids and membrane properties. Membrane fluidity is increased when there are more unsaturated fatty acids with kinks in the phospholipid tails, which tend to push apart the phospholipid tails, creating more space and thus more fluidity. On the other hand, saturated fatty acids have straight tails that pack closely together, making the membrane denser and more rigid. As fatty acid synthesis is inhibited, the relative number of unsaturated fatty acids in the membrane would decrease, resulting in a more rigid membrane.