Question

explain what a concentration gradient is and what it means for a molecule to diffuse down its concentration gradient

Answer 1

A concentration gradient is the difference in concentration of a substance from one location to another. A molecule diffuses down its concentration gradient by moving from one region of higher concentration to a region of lower concentration. Both are proteins and may work with only specific molecules. is this your anwser? if not ill paraphase 

Answer 2

How spaced out all the molecules are. To diffuse down a concentration gradient is to reduce a number of molecules in an area