Aspirin must enter cells to alleviate pain. given that the active form of this drug is polar, how does it cross the phospholipid bilayer membrane?

The cell membrane is made of two layer of phospholipid called phospholipid bilayer. Phospholipid has a hydrophilic head and hydrophobic tail. The hydrophilic head stick out on the membrane, pushing polar substance that go inside. Hydrophobic substance would be easily pass through the membrane while the hydrophilic doesn't.

If the active form of this drug is polar, then the substance would be hydrophilic. The drug should pass the membrane through active transport like carrier mediated transport or endocytosis.

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.