. . . "When H+ enter across membrane in direction of lower concentration-actually it crosses through ATP synthase in memebrane , ATP synthase gets energy for making ATP from ADP and Pi.Substrate level production of ATP is a process in which ATP is produced by enzyme that transfers directly a phosphate group from substrate to ADP.Like in glycolysis from 1,3-biphosphoglycerate to 3-phosphoglycerate.Zami'87" .