Hello!
We know that the movement of molecules from an area of low concentration to high concentration. This movement is against the concentration gradient and thus requires the use of adenosine triphosphate (ATP) to successfully move. This process is the opposite of diffusion, which requires the use of no energy because it moves materials DOWN the concentration gradient.
I hope I helped! Feel free to leave a comment down below if you need any more assistance, even if it is not with this question. :)
