concentration gradient concentration gradient /ˌkɒnˌsɛntrəˈʃən ɡrædɪənt/

noun

1. A gradient in concentration of a solute as a function of distance through a solution  ( concentration gradient )
   a gradient in concentration of a solute as a function of distance through a solution
    The movement of a solute down its concentration gradient is called diffusion
   the movement of a solute down its concentration gradient is called diffusion