Question

Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein, which helps the process along, is called ________.

Answer 1

I believe the answer is facilitated diffusion. :)
The binding of the substance selectively to a membrane-spanning protein changes the 3D conformation and charge of the protein, such that the protein projects the substances towards the other side of the membrane down a concentration gradient.

Hope this helps! :)