When in solution, a molecule that moves slowly across an artificial membrane moves rapidly across a plasma membrane. this molecule rapidly enters the cell regardless of whether its concentration is higher inside or outside the cell. using this information, which transport mechanism is most likely to be responsible for the movement of the molecule across a plasma membrane?

Active transport.

Explanation:

Since the transport across the plasma happens regardless of the concentration gradient, the transport must me active.

Passive transport only happens from a high concentration to a low concentration environment.

In addition, the molecule moves fast across the plasma membrane and slow across the artificial membrane. This means that the molecule require something from the cell membrane to be transported.